Reproductive mechanisms of plains silver sagebrush Artemisia cana cana in southeastern Montana
by Todd Patrick Walton
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Range Science
Montana State University
© Copyright by Todd Patrick Walton (1984)
Abstract:
A study was conducted during the years of 1982 and 1983 to investigate reproductive characteristics
and mechanisms important in plains silver sagebrush (Artemisia cana Pursh ssp. cana). The study was
conducted on the Fort Keogh Livestock and Range Research Laboratory at Miles City, Montana. In
particular, studies examined: (1) seed dispersal from individual plants and among sites, (2) factors
affecting germination, (3) emergence, growth and survival of seedlings under controlled and field
conditions, and (4) whether the primary origin of individual plants was from seed or vegetative
propagation.
Dispersal patterns were examined for a one-month period in the fall of 1982. Wind dispersal appeared
to be the most influential factor in the dispersal of achenes from plains silver sagebrush for the area
studied. A definite three-directional distribution of dispersed seed was found. Most seed was dispersed
close to, or under, the shrub, but this depended on date and direction. No major differences in dispersal
patterns were found among the three study sites. Plains silver sagebrush can germinate under a variety
of environmental conditions, but certain situations did favor higher germination percentages.
Stratification had no effect on germination success. Date of seed collection, light and dark regimes,
temperature and water stress had important influences on germination success. Higher temperatures
that had adverse effects on germination were favored in seedling growth. Seedling response was
enhanced by addition of supplementary water and burial at 5 mm. Mortality was lowest from seedlings
emerging from 15 and 25 mm. Despite large numbers of seeds that were planted, very few seedlings
emerged in the field (1.2%), and of these only 11 percent survived the summer. The degree to which
plains silver sagebrush relies on vegetative reproduction was established by root excavations. Plains
silver sagebrush in almost all cases showed some degree of rhizomatous growth, even among small
seedlings. Most excavated individuals turned out to be sprouts from an already established plant. No
differences could be found among sites or between disturbed or undisturbed sites in terms of numbers
of sprouts or seedlings. Drought was likely the most important influence on growth habits. REPRODUCTIVE MECHANISMS OF PLAINS SILVER SAGEBRUSH
ARTEMISIA CANA CANA IN SOUTHEASTERN MONTANA
by
. Todd P a tr ic k W alton
A t h e s i s su b m itted i n p a r t i a l f u lf illm e n t
of th e re q u ire m e n ts f o r th e degree
M aster o f S cien ce
in
Range S cien ce
MONTANA STATE UNIVERSITY
Bozeman, Montana
August 1984
APPROVAL
o f a th e s i s su b m itted by
Todd P a tric k W alton
T his t h e s i s has been read by each member o f th e t h e s i s com m ittee
and h a s been fo u n d to be s a t i s f a c t o r y r e g a r d i n g c o n t e n t , E n g lis h
usage, fo rm a t, c i t a t i o n s , b ib lio g r a p h ic s t y l e , and c o n s is te n c y , and i s
ready f o r su bm ission to th e C ollege o f G raduate S tu d ie s .
Co-chairm an, G raduate Committee
Co-chairm an, G raduate Committee
Approved f o r th e Major Department
Date
Head, Major Department
Approved f o r the C ollege o f G raduate S tu d ie s
D a te
G r a d u a te D ean
i
iii
■ STATEMENT OF PERMISSION TO USE
In
p re s e n tin g
th is
th e s is
in
p a rtia l
f u l f i l l m e n t o f th e
r e q u i r e m e n t s f o r a m a s t e r ’s d e g re e a t M ontana S t a t e U n i v e r s i t y ,
I
a g r e e t h a t th e L i b r a r y s h a l l make i t a v a i l a b l e to b o r r o w e r s u n d e r
r u l e s o f th e L ib ra ry . B r ie f q u o ta tio n s from t h i s t h e s i s a re a llo w a b le
w ith o u t s p e c ia l p e rm issio n , p ro v id ed t h a t a c c u ra te acknowledgement o f
so u rce i s made.
P e rm issio n f o r e x te n s iv e q u o ta tio n from or re p ro d u c tio n o f t h i s
t h e s i s may be g ra n te d by my' m ajor p ro f e s s o r (s ),
by th e D i r e c t o r o f L i b r a r i e s w hen,
o r i n ' t h e i r absence,
i n th e o p in io n o f e i t h e r ,
th e
proposed use o f th e m a te r ia l i s f o r s c h o la r ly purpose's. Any copying or
u se o f th e m a t e r i a l i n t h i s t h e s i s f o r f i n a n c i a l g a in s h a l l n o t be
allow ed w ith o u t ny w r i t t e n perm ission.,
S ig n a tn n o -.
../&$%/ /7 )
3, / M t -
iv
ACKNOWLEDGEMENT
I w is h to e x te n d my d eep a p p r e c i a t i o n t o Dr. R. S. W h ite and Dr.
C. L. Wa m b o lt, f o r t h e i r g u id a n c e , e n c o u ra g e m e n t and p a t i e n c e t h a t
made p o s s ib le th e c o m p le tio n o f t h i s t h e s i s ;
S p e c ia l th an k s go to Dr.
W h ite and th e s t a f f a t th e F o r t Keogh L i v e s to c k and Range R e s e a rc h
L a b ra to ry f o r th e e x c e lle n t le a r n in g environm ent th ey p ro v id e d .
A p p r e c i a t i o n a l s o i s e x te n d e d to th e f o l l o w i n g : C h e ry l M urphy,
M ile s C ity , f o r h e r tim e and e n e rg y s p e n t on many a s p e c t s o f t h i s
s tu d y ; Tom H ilk e n , Deb M urphy, C orey Sw enson, Todd Z e c h i a l , V a l e r i e
D yer, and L i s a S ta n d s f o r t h e i r a s s i s t a n c e i n t h e f i e l d w o rk ; B rad
Knapp f o r h i s a s s is ta n c e i n th e s t a t i s t i c a l d e sig n and a n a ly s is o f th e
d a ta produced; and th e Range S cience s t a f f a t Montana S ta te U n iv e rs ity
f o r t h e i r in p u t and encouragem ent th ro u g h o u t the co u rse o f th e stu d y .
I w is h a l s o to th a n k Dr. R. S. W h ite , Dr. C. L. Wa m b o lt, Dr. C.
B. M arlow and Dr. J. E. Rum ely f o r
t h e i r c r i t i c a l re v ie w
o f th e
m a n u sc rip t.
F i n a l l y , my d e e p e s t g r a t i t u d e to my w if e L in d a f o r h e r s u p p o r t
and p a tie n c e .
T h is s tu d y
w as a c o o p e r a t i v e
p ro g ram
b e tw e e n t h e USDA-
A g r ic u ltu r a l R esearch S e rv ic e and th e Montana A g r ic u ltu r a l E xperim ent
S ta tio n . F in a n c ia l su p p o rt f o r t h i s p r o je c t was p ro v id ed by th e F o rt
Keogh L iv e sto c k and R esearch L ab o ra to ry a t M iles C ity , Montana.
V
TABLE OF CONTENTS
PAGE
ACKNOWLEDGEMENT.
.
.
........................................................................ ......
TABLE OF CONTENTS.............................................. ......
LIST OF TABLES
.
iv
. • ................................. v
...............................................................................v i i
LIST OF FIGURES......................................................................................................... v i i i
ABSTRACT.............................................. ....................................................J
.
.
x ii
INTRODUCTION............................................................................................................... I
LITERATURE REVIEW................................. ......
' ..............................................
.,
4
In tr o d u c tio n to A rte m isia Taxonomy ........................................
C h a r a c te r is tic s and Taxonomy o f S ag eb ru sh ......................... 4
S ilv e r Sagebrush Taxonomy .....................................................
D is tr ib u tio n o f S ilv e r Sagebrush . . . . . . .
Ecology and C h a r a c te r is tic s o f Sagebrush . . . . .
C o n tro l Methods and R e s u lts
. . . . . . . .
Forage C o n sid e ra tio n s
...........................................................
Sagebrush C hem istry ................................. . . . . .
E c o lo g ic a l A spects o f Sagebrush ........................................
R eproductive C h a r a c te r is tic s .....................................................
Seed D i s p e r s a l ................................
G erm ination F a c to rs ..................................................................
E a rly S e e d lin g Growth............................................................... 28
V e g e ta tiv e R eprodu ctio n ...........................................................
4
1 METHODS AND SITE DESCRIPTIONS...................................
5
7
8
9
12
14
16
18
18
21
29
35
I n tr o d u c tio n ........................................................................
35
Seed D i s p e r s a l .......................................
36
G e r m i n a t i o n ...................................................................................41
E a rly S e e d lin g G r o w t h ............................................................... 44
S p ro u tin g and S e e d lin g E sta b lish m e n t
................................ 50
RESULTS AND DISCUSSION
...............................................................................
.5 6
Seed D is p e rs a l
....................................................
56
G erm ination
...........................................................................................75
E a rly S e e d lin g Growth . .. . . . . . . . . . 101
S p ro u tin g and S e e d lin g E sta b lish m e n t
................................ 122
vi
PAGE
SUMMARY............................................................................................................................
LITERATURE C IT E D .............................................
APPENDICES
.
.
.
.
.
.
.
.142
.................................................................152
Appendix A - P r e c i p i t a t i o n and te m p e ra tu re Data f o r
th e y e a rs 1981 , 1982 and 1983 .............................................
154
Appendix B
- D is p e rs a l A n a ly sis o f V ariance Table .
.
157
Appendix C
- G erm ination A n a ly sis o f V arian ce Table
.
159
Appendix D
- C o n stru c tio n o f D is p e rs a l F ig u re s . .
.
161
v ii
L IS T OF TABLES
TABLE
1
PAGE
G erm ination means from in d iv id u a l main e f f e c t s and
s e p a ra te com binations o f two-way in te r a c t i o n s .
76
2
G erm ination means from th ree-w ay i n t e r a c t i o n s .
.77
3
Boot to sh o o t r a t i o s f o r s e e d lin g growth under two
te m p e ra tu re regim es
..................................................................
105
Age r e l a t i o n s h i p s o f above and belowground p a r t s
o f p la in s s i l v e r sag eb ru sh .....................................................
127
Growth r e l a t i o n s h i p s o f above and belowground p a r ts
o f p la in s s i l v e r sag eb ru sh .....................................................
127
Frequency o f occurance f o r d is ta n c e s en co u n tered
from p a re n t p la n ts or rhizom es to d a u g h ter p la n ts
o f p la in s s i l v e r sagebrush .....................................................
129
4
5
6
7
P la n t e x c a v a tio n r e s u l t s . Sum m arization o f numbers
o f in d iv id u a l p la n ts i n each stu d y s i t e f a l l i n g i n
one o f two c a te g o r ie s : rh izo m ato u s c o n n e c tio n s or n o t. 129
8
P r e c i p i t a t i o n and te m p e ra tu re av erag es by month
f o r th e y e a r s 1981 , 1982 and 1983 a t M iles C ity
9
.
.
154
Maximum te m p e ra tu re s and days above 90 F (5 0 .4 C)
d u rin g Ju n e, J u ly and August o f 1982 and 1983 a t
M iles C ity
.....................................................................................
155
10
Sum m arization o f d is p e r s a l a n a ly s is o f v a ria n c e
157
11
Sum m arization o f g e rm in a tio n a n a ly s is o f v a ria n c e
159
\
v iii
L IS T OF FIGURES
FIGURE
I
2
PAGE
D is tr ib u tio n o f th e th re e s u b sp e c ie s o f s i l v e r
sagebrush i n w e ste rn N orth America ........................................
D is p e rs a l stu d y la y o u t w ith s ix t r a n s e c ts a t e q u al
angles: (60 d e g re e s) su rro u n d in g th e c e n tr a l shrub .
6
39
3
P e rs p e c tiv e view o f f i e l d see d in g r e p l i c a t i o n
4
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
p er p la te i n a l l d ir e c tio n s a t each stu d y s i t e and
a t each o f f i v e d a te s
,
58
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
p er p la te i n a l l d ir e c tio n s from a p a re n t p la n t. A ll
p la n ts summarized a t each o f f iv e d a te s
. . . .
.
61
Mean numbers o f p la in s s i l v e r sag eb ru sh seed d is p e rs e d
per p la te i n a l l d ir e c tio n s from a p a re n t p la n t over
a l l d a te s a t fo u r d is ta n c e s
. . ...
. . . .
62
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
p e r p la te i n a l l d ir e c tio n s from a p a re n t p la n t.
D is ta n c e s and d a te s s e p a ra te d .....................................................
64
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
per p la te i n s ix d ir e c tio n s
.....................................................
65
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
per p l a t e from a p a re n t p la n t i n s ix d ir e c tio n s a t fo u r
d is ta n c e s
. . . .
..................................................................
67
Mean numbers of p la in s s i l v e r sagebrush seed d is p e rs e d
p e r p la te from a p a re n t p la n t i n s ix d ir e c tio n s a t fo u r
d is ta n c e s on November 1-5 ...........................................................
68
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
p er p l a t e from a p a re n t p la n t i n s ix d ir e c tio n s a t fo u r
d is ta n c e s on November 6 - 9 .............................................. .
69
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
p e r p la te from a p a re n t p la n t i n s i x d i r e c t i o n s a t fo u r
d is ta n c e s on November 1 0 - 1 2 ........................................'
•70
5
6
7
8
9
IO
11
12
.
.
.
48
ix
FIGURE
13
PAGE
Mean numbers o f p la in s s i l v e r sagebrush seed d is p e rs e d
per p la te from a p a re n t p la n t i n s ix d i r e c t i o n s a t fo u r
d is ta n c e s on November 1 3 - 1 6 ....................................... ......
.
71
14
Mean numbers of p la in s s i l v e r sagebrush seed d is p e rs e d
p e r p la te from a p a re n t p la n t i n s ix d ir e c tio n s a t fo u r
d is ta n c e s on November 17-19
. .............................................. 72
15
Osmotic p o t e n t i a l e f f e c t s on t o t a l g e rm in a tio n
p e rc e n ta g e s and r a t e s o f g e rm in a tio n
. . . .
.
.
80
16
Tem perature e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s
and r a t e s o f g e r m i n a t i o n ........................................................... 83
17
L ig h t/d a rk e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s
and r a t e s o f g e r m i n a t i o n ........................................................... 85
18
L ig h t/d a rk com parisons among th r e e te m p e ra tu re s and
t h e i r e f f e c t on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . F i r s t c o lle c tio n d a te . . . .
88
L ig h t/d a rk com parisons among th r e e te m p e ra tu re s and
t h e i r e f f e c t on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . Second c o lle c tio n d a te . . . .
89
19
20
21
22
23
24
L ig h t/d a rk com parisons among th r e e te m p e ra tu re s and
t h e i r e f f e c t on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . T hird c o lle c tio n d a te . . .
.
.
90
Osmotic p o te n tia l com parisons betw een l i g h t and dark
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s of g e rm in a tio n . F i r s t c o lle c tio n d a te . . . .
92
Osmotic p o t e n t i a l com parisons between l i g h t and d ark
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . Second c o lle c tio n d a te . . . .
93
Osmotic p o te n tia l com parisons between l i g h t and dark
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . T hird c o lle c tio n , d a te . . . .
94
Osmotic p o t e n t i a l com parisons among th r e e te m p e ra tu re s
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . F i r s t c o l le c tio n d a te . . . .
96
X
FIGURE
25
26
PAGE
Osmotic p o te n tia l com parisons among th re e te m p e ra tu re s
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . Second c o lle c tio n d a te
. . .
97
Osmotic p o t e n t i a l com parisons among th r e e te m p e ra tu re s
and t h e i r e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e rm in a tio n . T hird c o lle c tio n d a te . . . .
98
27
Tem perature e f f e c t s on s e e d lin g grow th: h e ig h t, number
o f le a v e s , and two h o r iz o n ta l cover m easurem ents
. .102
28
Tem perature e f f e c t s on s e e d lin g grow th: r o o t and sh o o t
grow th, and l e a f a r e a ................................. ;
. . . . 104
29
Emergence and s u r v iv a l o f greenhouse s e e d lin g s a t th re e
d e p th s o f b u r ia l . ................................. ...... . . . . . 1 0 7
30
Growth p a ra m ete rs i n th e greenhouse a s a f f e c te d by d ep th
o f seed b u r i a l . H eight and number of le a v e s . . . . 1 0 9
31
Growth p a ra m ete rs i n th e greenhouse a s a f f e c te d by d ep th
o f seed b u r i a l . Length and w i d t h ........................................I l l
32
S e e d lin g numbers p re s e n t th ro u g h o u t summer o f 1983
a f t e r em erging from fo u r p la n tin g d e p th s i n th e f i e l d . 112
33
S e e d lin g numbers p re s e n t th ro u g h o u t summer o f 1983
a f t e r r e c e iv in g w a te r or no t .
114
34
Growth p a ra m ete rs i n th e f i e l d a s a f f e c te d by. w a te r
tre a tm e n t. H eig h t, number o f le a v e s , and length)
and w id th
•............................................................................................... Hg
35
Growth p a ra m e te rs i n th e f i e l d a s a f f e c te d by d ep th
o f b u r i a l . H eig h t, number o f le a v e s , and le n g th
and w i d t h ............................................................................................... 117
36
Growth p a ra m e te rs i n th e f i e l d a s a ffe c te d by e x tr a
w a ter and depth of b u r i a l . H eig h t, number o f le a v e s ,
h o r iz o n ta l le n g th
and w i d t h .........................................
.1 1 8
Growth p a ra m e te rs i n th e f i e l d a s a f f e c te d by no
e x tr a w a te r and depth of b u r i a l . H eig h t, number o f
le a v e s , h o r iz o n ta l le n g th and w id th ........................... .
.119
37
38
G raphic example o f an e x cav ated s e e d lin g
.
.
.
.
124
. xi
FIGURE
39
. PAGE
G raphic example o f excav ated s p ro u t connected to o ld e r
m a te ria l i n s e r i e s o f s p r o u t s .......................... ......
125
G raphic example o f excav ated s p ro u t connected to a
p a re n t p la n t (rhizom e)
...........................................................
126
41
Map o f f i r s t l a r g e , i s o l a t e d p la n t e x c a v a tio n . . .
134
42
Map o f second la r g e , i s o l a t e d p la n t e x c a v a tio n
.
135
43
Map o f s e p a ra te rhizom e system s in c lu d e d i n second
m ajor p la n t e x c a v a tio n
...........................................................
136
D is p e rs a l f ig u r e showing c o n s tr u c tio n methods .
161
40
44
.
.
.
x ii
ABSTRACT
A s tu d y w as c o n d u c te d d u r in g t h e y e a r s o f 1982 and 1983 to
i n v e s t i g a t e re p ro d u c tiv e c h a r a c t e r i s t i c s and m echanism s im p o rta n t i n
p l a i n s s i l v e r s a g e b r u s h ( A r t e m i s i a c a n a P u rsh s s p . c a n a ). The s tu d y
w as c o n d u c te d on th e F o r t Keogh L i v e s to c k and Range R e s e a rc h
L a b o r a to r y a t M ile s C ity , M ontana. I n p a r t i c u l a r , s t u d i e s e x a m in e d :
(I ) seed d is p e r s a l from in d iv id u a l p la n ts and among s i t e s , (2) f a c to r s
a f f e c t i n g g e rm in a tio n , (3) em ergence, grow th and s u r v iv a l o f s e e d lin g s
u n d e r c o n t r o l l e d and f i e l d c o n d i t i o n s , and (4) w h e th e r th e p r im a ry
o r i g i n o f in d iv id u a l p la n ts was from seed o r v e g e ta tiv e p ro p a g a tio n .
D is p e rs a l p a tte r n s w ere exam ined f o r a one-m onth p e rio d i n th e
f a l l o f 1982. Wind d i s p e r s a l a p p e a re d t o be th e m o st i n f l u e n t i a l
f a c t o r i n th e d i s p e r s a l o f a c h e n e s fro m p l a i n s s i l v e r s a g e b r u s h f o r
th e a r e a s t u d i e d . A d e f i n i t e t h r e e - d i r e c t i o n a l d i s t r i b u t i o n o f
d is p e rs e d seed was found. Most seed was d is p e rs e d c lo s e to , or under,
t h e s h ru b , b u t t h i s d ep en d ed on d a t e and d i r e c t i o n . No m a jo r
d i f f e r e n c e s i n d i s p e r s a l p a t t e r n s w e re fo u n d among th e t h r e e s tu d y
s i t e s . P l a i n s s i l v e r s a g e b ru s h can g e r m in a te u n d e r a v a r i e t y o f
e n v ir o n m e n ta l c o n d i t i o n s , b u t c e r t a i n s i t u a t i o n s d id f a v o r h ig h e r
g e rm in a tio n p e rc e n ta g e s. S t r a t i f i c a t i o n had no e f f e c t on g e rm in a tio n
su c c e ss. Date o f seed c o lle c tio n , l i g h t and dark re g im e s, te m p e ra tu re
and w a te r s t r e s s h ad i m p o r t a n t i n f l u e n c e s on g e r m i n a t i o n s u c c e s s .
H ig h e r t e m p e r a t u r e s t h a t had a d v e r s e e f f e c t s on g e r m i n a t i o n w e re
fa v o re d i n s e e d lin g grow th. S e e d lin g re sp o n se was enhanced by a d d itio n
o f su p p lem en tary w a te r and b u r ia l a t 5 mm. M o rta lity w as lo w e s t from
s e e d lin g s em erging from 15 and 25 mm. D e sp ite la r g e numbers o f seeds
th a t w ere p la n te d , v e ry few s e e d lin g s emerged i n th e f i e l d ( 1.2%), and
o f th e s e o n ly 11 p e r c e n t s u r v iv e d t h e sum m er. The d e g r e e to w h ic h
p l a i n s s i l v e r s a g e b r u s h r e l i e s on v e g e t a t i v e r e p r o d u c t i o n w as
e s ta b lis h e d by r o o t e x c a v a tio n s. P la in s s i l v e r sag eb ru sh i n a lm o st a l l
c a s e s show ed some d e g r e e o f r h iz o m a to u s g ro w th , e v e n among s m a ll
s e e d lin g s . Most e x cav ated in d iv id u a ls tu rn e d o u t to be s p ro u ts from an
a lre a d y e s ta b lis h e d p la n t. No d if f e r e n c e s could be found among s i t e s
o r b e tw e e n d i s t u r b e d o r u n d i s t u r b e d s i t e s i n te r m s o f n u m b ers o f
s p ro u ts or s e e d lin g s . D rought was l i k e l y th e m ost im p o rta n t in flu e n c e
on growth h a b its .
I
INTRODUCTION
An a d e q u a te u n d e r s ta n d in g o f how i n d i v i d u a l s p e c i e s i n f l u e n c e
p la n t—community dynam ics i s fu n d am en tal to s u c c e s s fu l management o f
r a n g e la n d s . M em bers o f th e s a g e b r u s h g e n u s ( A r t e m i s i a L.) h av e lo n g
b een r e g a r d e d a s h a v in g a n i m p o r t a n t r o l e i n r a n g e la n d s o f N o rth
America. In th e p a s t, sagebrush s p e c ie s have g e n e r a lly been c o n sid e re d
u n d e s i r a b l e i n r a n g e la n d o p e r a t i o n s due to t h e i r a d v e r s e im p a c t pn
p r e f e r r e d f o r a g e s p e c i e s and l i v e s t o c k o p e r a t i o n s .
C o n s e q u e n tly ,
c o n t r o l m e a s u re s w e re o f t e n recom m ended w ith h ig h b r u s h d e n s i t i e s .
R e c e n tly , w ith e x p a n d in g k n o w le d g e , th e s a g e b ru s h c o m p le x h a s b e en
r e g a r d e d a s o f t e n p r o v id i n g v a l u a b l e f o r a g e and c o v e r f o r e i t h e r
l i v e s t o c k a n d / o r w i l d l i f e . As s u c h , i t s e r v e s a n i m p o r t a n t r o l e i n
w e ste rn ecosystem s. However, th e econom ic and management im p o rtan ce of
sag eb ru sh depends upon th e s p e c i f i c taxon p re s e n t (B e e tle 1977).
S il v e r sag eb ru sh (A rte m is ia cana P u rsh 1) o c c u p ie s an e s tim a te d 13
m i l l i o n h e c t a r e s (h a ) i n th e 11 w e s t e r n U n ite d S t a t e s ( B e e tl e I9 6 0 ).
I t r a n k s s e c o n d t o b ig s a g e b r u s h ( A r t e m i s i a t r i d e n t a t a N u tt.) w ith
r e s p e c t to a re a occupied. In Montana th e re a re ab o u t 7.8 m illio n ha o f
b ig sag eb ru sh and 5.2 m illio n ha o f s i l v e r sag eb ru sh , w h ile i n Wyoming
th e re
a r e 9.1
m i l l i o n h a and 2.85
m illio n
ha r e s p e c tiv e ly .
g e o g r a p h ic ra n g e and e c o l o g i c a l d o m in a n c e o f t h i s
in te n s iv e re se a rc h
o ccu rred .
a tte n tio n .
H ow ever,
The
s h ru b m e r i t s
t h i s h as n o t p re v io u s ly
W hile b ig sagebrush, h a s been s tu d ie d e x te n s iv e ly i n re c e n t
1 S c i e n t i f i c n o m e n clatu re i n t h i s t h e s i s fo llo w s B e e tle I960, B e e tle
and Young 1965, S h e tle r and Skog 1978.
2
y e a r s , b i o l o g i c a l i n f o r m a t i o n d e a l i n g w ith s i l v e r sag eb ru sh i s v ery
lim ite d . S ta te s such a s Montana and Wyoming r e ly h e a v ily on range and
p a s tu r e fo ra g e f o r t h e i r liv e s to c k in d u s try .
T h e re fo re ,
a p p re c ia tio n
of s i l v e r sagebrush com m unities and t h e i r im p lic a tio n s f o r management
i s im p o rta n t.
P l a i n s s i l v e r s a g e b r u s h ( A r t e m i s i a P u rsh c a n a asp. c a n a l i s an
im p o r t a n t s h ru b i n th e N o r th e r n G re a t P l a i n s . I t i s fo u n d on d e e p ,
lo w land s o i l s o f f lo o d p la in s and i s g e n e r a lly c o n sid e re d to in c re a s e
i n r e s p o n s e to c a t t l e g r a z in g . T h is s a g e b r u s h i s a n e r e c t , f r e e l y
b ra n c h in g s h ru b o f up t o 1.5 m e te r s o f t e n fo u n d i n d e n se s ta n d s . I t
s p ro u ts v ig o ro u s ly a f t e r d is tu rb a n c e s such as burning.
It
is
im p o rta n t
to
u n d e rs ta n d
fa c to rs
c o n trib u tin g
to
re p ro d u c tiv e su c c e ss o r f a i l u r e i n o rd e r to g a in a b e t t e r a p p r e c ia tio n
o f p l a n t p o p u l a t i o n d y n a m ic s. T h is i s p ro b a b ly b e s t a c c o m p lis h e d i n
c o n ju n c t io n w ith a u t e c o l o g i c a l s t u d i e s o f p r i n c i p a l s p e c i e s t h a t
i n c l u d e r e s e a r c h on p h e n o lo g y and p r o d u c tio n o f f i e l d p o p u l a t i o n s
(M o tt I 979). Due to p l a i n s i l v e r sa g e b r u s h ’ s e x t e n s i v e o c c u r e n c e i n
many N orthern G reat P la in s p la n t com m unities,
a stu d y was u n d ertak en
to ex am in e some o f th e v a r i a b l e s in v o lv e d i n i t s s u c c e s s . The s tu d y
was conducted over a two y e a r p e rio d a t th e F o rt Keogh L iv e sto c k and
Range R esearch L ab o rato ry a t M iles C ity ,
Montana. I t was desig n ed to
ex am in e
and m e c h a n ism s w h ich
re p ro d u c tiv e
c h a ra c te ris tic s
a re
im p o rta n t i n the su c c e ss and m aintenance o f p la in s s i l v e r sagebrush.
Two study g o a ls w ere ad d re ssed i n th e course o f ,my re s e a rc h . They
w ere: ( I ) to e s t a b l i s h b a s e lin e in fo rm a tio n on p la in s s i l v e r sagebrush
re p ro d u c tio n ,
-K .
and
( 2 ) to
c o n s id e r
sex u al
and a s e x u a l
m eans o f
3
r e p r o d u c t i o n w ith r e g a r d to th e r e l a t i v e im p o r ta n c e o f e a c h . More
s p e c i f i c o b je c tiv e s w ere e s ta b lis h e d w ith in t h i s c o n te x t and examined
i n in d iv id u a l s tu d ie s .
T his re s e a rc h work was d esig n ed to re a ch fo u r
o b je c tiv e s . These w ere:
(I) to exam ine seed d is p e r s a l c h a r a c t e r i s t i c s
fro m i n d i v i d u a l p l a n t s ,
g e rm in a tio n ,
s e e d lin g s ,
(2 ) to i n v e s t i g a t e f a c t o r s a f f e c t i n g seed
(3) to e v a lu a te em ergence, e a r ly grow th and s u rv iv a l o f
and
(4) t o
d e te r m in e
w h e th e r
th e
p r im a r y
in d iv id u a l p la n ts was from seed o r v e g e ta tiv e p ro p a g a tio n .
o rig in
of
4
LITERATURE REVIEW
I n tr o d u c tio n to A rte m isia Taxonomy
A New World group o f c lo s e ly r e l a t e d sag eb ru sh s p e c ie s com prise a
N orth A m erican endem ic S e c tio n o f th e w o rld -w id e Genus A rte m is ia L.
(300 s p e c i e s ) and o c c u r i n v a r y in g a m o u n ts o v e r a b o u t 109 m illi o n ,
h e c t a r e s (h a ) i n th e 11 w e s t e r n U n ite d S t a t e s ( B e e t l e I9 6 0 ). T h is
S e c tio n ,
d e s i g n a t e d T r i d e n t a t a e , l i k e l y e v o lv e d i n N o rth A m erica
d u rin g th e l a t e T e r tia r y or e a r ly Q u atern ary tim e s from an a n c e s tr a l
s p e c ie s o f A rte m is ia o r ig i n a tin g i n A sia.
D i f f e r e n t i a t i o n th ro u g h o u t
th e C enozoic, e ra p ro b ab ly o c cu rred under th e s tim u lu s o f a r id c y cle s.
T rid e n ta ta e i s o f m ountain o r ig i n and G reat B asin a d a p ta tio n (B e etle
I960, Johnson 1978, McArthur and Plummer 1978). Members o f T rid e n ta ta e
a r e d i s t i n g u i s h e d fro m Old W orld c o u n t e r p a r t s by woody s te m s and a
l a c k o f ra y f l o r e t s . I n a d d i t i o n th e y s h a r e common c h a r a c t e r i s t i c s
w ith in th e S e c tio n , in c lu d in g : (I) d e n ta te le a v e s , i n g e n e r a l, covered
w ith c h a r a c t e r i s t i c s e ric e o u s or c a n e sce n t pubescence, (2.) an a ro m a tic
o d o r c a u s e d by a v a r i e t y
of te rp e n e s ,
and ( 3 ) c a m p a n u la te h e a d s
arra n g ed i n m o d ified p a n ic le s (B e e tle 1977, McArthur and Plummer 1978,
T isd a le and H ironaka 1981).
C h a r a c te r is tic s and Taxonomy o f Sagebrush
S e v e ra l a d a p tiv e f e a tu r e s have been a s s o c ia te d w ith th e S e c tio n
T r i d e n t a t a e and h a v e r e s u l t e d i n i t s
e x t e n s i v e d i s t r i b u t i o n and
p e r s i s t e n c e o f many s p e c i e s i n a v a r i e t y o f h a b i t a t s . P h y s i o l o g i c a l
5
fe a tu re s
such
as
a b ility
to
c a rry
on p h o t o s y n t h e s i s a t lo w
te m p e ra tu re s , a b i l i t y to g e rm in a te o v er a w ide range o f te m p e ra tu re s ,
e x te n s iv e r o o t system , and p rom in en t secondary' m e ta b o lic compounds may
c o n f e r a c o m p e t i t i v e a d v a n ta g e f o r s a g e b r u s h (D e P u it and C a ld w e ll
1973, C aldw ell 1978).
Evidence in d ic a te s t h a t a l l s p e c ie s and su b sp e c ie s o f T rid e n ta ta e
can be g iv e n th e s t a t u s o f a t l e a s t to p o g r a p h ic and e d a p h ic c lim a x
dom inants. As such, each d e fin e s i n i t s own way a d i f f e r e n t e c o lo g ic a l
a re a . Many o f th e f a c t o r s which in f lu e n c e th e d i s t r i b u t i o n a l p a tte r n s
i n sag eb ru sh a re r e f l e c t e d i n s o i l developm ent combined w ith c lim a tic
o r en v iro n m e n ta l c h a r a c t e r i s t i c s ( H a z l e t t and H offm an 1975, W inw ard
1980,
F ro e m in g 1981).
S e v e ra l s p e c ie s such a s s i l v e r
s a g e b ru s h
(A rte m is ia cana Pursh) and b ig sag e b ru sh (A rte m is ia t r i d e n t a t a N utt.)
h av e a c h ie v e d
s u ffic ie n tly
w id e d i s t r i b u t i o n
t o h a v e d e v e lo p e d
s u b s p e c ie s . B oth h a v e t h r e e s u b s p e c i e s . B ig s a g e b r u s h i s th e m o st
w id e s p r e a d and h a s r e c e i v e d t h e m o st r e s e a r c h a t t e n t i o n .
S ilv e r
sageb ru sh i s second i n d i s t r i b u t i o n and i s n o t w e ll re s e a rc h e d .
Two g e n e ti c a lly d i f f e r e n t i a t e d g roups i n th e T r id e n ta ta e S e c tio n
a re re c o g n ize d .
One group r e s p r o u ts a f t e r d is tu rb a n c e QL t r i p a r t i t a
Rydb., A.c a n a and A. r i s i d a ( N u tt.) G ra y ), w h ile th e o t h e r g ro u p d o e s
n o t QL t r i d e n t a t a . A. a r b u s c u l a N u t t ., JL l o n g i l o b a ( O s te r h o u t)
B e e tle , JL nova N elson, JL b i g l o v i i Gray and JL PVgmeae Gray).
S ilv e r Sagebrush Taxonomy
The s i l v e r sageb ru sh complex i s composed o f th re e s u b sp e c ie s w ith
a llo p a tric d is trib u tio n
( F ig u r e I ) and c h a r a c t e r i s t i c e c o l o g i c a l
6
distribution
of
Artemisia
c a na
cana
distribution
of
Artemisia
cana
bolanderi
----- d i s t r i b u t i o n
of
Artemisia
cana
viscidula
★
location of Fort Keogh Livestock and Range Research Lab
F ig u re I. D is tr ib u tio n o f th e th r e e su b sp e c ie s o f s i l v e r sagebrush in
w e ste rn N orth America (H arvey 1981).
7
n ic h e s (B e e tle 1977). S u b sp ecies a r e s e p a ra te d m o rp h o lo g ic a lly on th e
b a s i s o f l e a f w id th , s e s q u i t e r p e n e c o n t e n t and g e o g ra p h y ( M o rris e t
a l . 1976).
M o u n ta in s i l v e r s a g e b ru s h ( A. c a n a s s p . v i s c i d u l a ( O s te r h o u t)
B e e tle ) i s t y p i f i e d by i t s g r e e n i s h , l i n e a r l e a v e s , and i t o c c u r s on
stream banks, meadows and d e p re s s io n s g e n e r a lly a t h ig h e r e le v a tio n s .
I t i s o f te n i n c lo s e a s s o c ia ti o n w ith c o n if e r s i n th e Rocky M ountain
re g io n o f th e w e s te rn s t a t e s .
B olander s i l v e r sag eb ru sh (At. cana ssp.
b o la n d e ri (Gray) Ward), i n c o n tr a s t,
g r o w s on p o o r l y
h as l i n e a r ,
d ra in e d s o i l s in
c e n tra l
c a n e sc e n t le a v e s and
O re g o n a n d e a s t e r n
C a l i f o r n i a . P l a i n s s i l v e r s a g e b r u s h ( A. c a n a P u rsh s s p . c a n a ) i s an
e r e c t , c a n e s c e n t, f r e e l y b r a n c h in g s h ru b o f up t o 1.5 m w ith l a r g e
l i n e a r le a v e s . T his taxon i s found grow ing on w e ll w a te re d , deep s o i l s
th ro u g h o u t th e N o rth e rn G reat P la in s ,
e p p a c ia lly alo n g stre am b o tto m s
and d rain ag ew ay s, i n s p a rs e to dense sta n d s . Wyoming b ig sag eb ru sh (A.
t r i d e n t a t a ssp. wjyomingensis B e e tle and Young) i s th e o n ly o th e r m ajor
shrubby sageb ru sh i n th e N o rth ern G reat P la in s (B e e tle 1977,
1978,
Johnson
T isd a le and H ironaka 1981).
D is tr ib u tio n o f P la in s S ilv e r Sagebrush
P l a i n s s i l v e r s a g e b r u s h o c c u r s e a s t o f th e c o n t i n e n t a l d iv id e
(ex cep t f o r th e Yampa R iv er V a lley , Colorado) i n Wyoming and Montana
n o rth to so u th e rn A lb e rta and Saskatchew an and e a s t to c e n tr a l North
and South Dakota and n o rth w e s t N ebraska. S everal, d is ju n c t p o p u la tio n s
occur i n th e e a s te r n D akotas (Harvey 1981).
8
S i l v e r s a g e b r u s h w as f i r s t c o l l e c t e d by L e w is and C la rk on th e
b l u f f s o f th e M is s o u r i R iv e r ( N u t t a l l 1841) and t y p i c a l h a b i t a t s
i n c l u d e loam y to s a n d y , w e ll d r a in e d s o i l s o f u p la n d s , and a l l u v i a l
f l a t s and t e r r a c e s o f v a lle y bottom s. I t i s f u r t h e r d is tin g u is h e d a s
g ro w in g i n d e n se o r open s t a n d s a lo n g s tr e a m s and v a l l e y s t h a t a r e
s u b je c t to e ro s io n , flo o d in g and d e p o s itio n . Hence, s t r a t i f i c a t i o n and
h e te r o g e n e ity a re conspicuous i n th e a l l u v i a l p r o f i l e s (T h atch er 1959,
H a z l e t t and H offm an I 975, J o h n s o n 1978). T h a tc h e r (1 959) n o te d t h a t
o n ly one o f th e f o u r s a g e b ru s h s p e c i e s h e s t u d i e d ,
p la in s s ilv e r
s a g e b r u s h , grew on s o i l s i n f l u e n c e d by h ig h w a te r t a b l e s . Jo h n so n
( 1978) r e p o r t e d t h a t o n ly s i l v e r s a g e b r u s h and w e s t e r n wh e a t g r a s s
(Agropyron s m i t h i i Rydb.) th riv e d i n a re a s o f fre q u e n t flo o d in g .
Ecology and C h a r a c te r is tic s o f Sagebrush
Winward (1980) n o te s t h a t q u e s tio n s c o n tin u a lly a r i s e a s to (I)
how much sagebrush i s r e q u ire d f o r w i l d l i f e , (2) th e e c o lo g ic a l s ta t u s
o f th e p l a n t , and (3) w h e th e r c o n t r o l i s d e s i r a b l e . E ach s a g e b ru s h
ta x o n h a s u n iq u e b i o l o g i c a l
f e a tu r e s th a t in flu e n c e
m anagem ent
d e c is io n s . M oreover, m ost o f th e re g io n dom inated by sag eb ru sh i n th e
w e s te rn s t a t e s i s
s ta b le ,
m e an in g t h a t s p e c i e s p r e s e n c e h a s n o t
changed a p p re c ia b ly s in c e th e tim e o f s e ttle m e n t. However,
some a re a s
h a v e show n a s u b s t a n t i a l i n c r e a s e i n s a g e b r u s h d e n s i t y due to h eav y
liv e s to c k
g ra z in g
(T is d a le
and
H iro n a k a
1 9 8 1 ).
U nder
th e s e
c irc u m sta n c e s , im p le m e n ta tio n o f c o n tr o l p r a c tic e s may be d e s ir a b le .
9
C o n tro l Methods and R e s u lts
M ethods o f c o n t r o l t h a t h a v e b e en u se d on s a g e b r u s h in c lu d e
h e r b ic id a l, m e ch a n ic al, b i o l o g i c a l o r b u r n in g t r e a t m e n t s . A l t e r n a t e
p o s s ib ilitie s
fe rtiliz e r
of
a lte rin g
tre a tm e n ts
and
sag e b ru sh
g e n e tic
c o m m u n itie s
s e le c tio n
of
have
in c lu d e d
im p ro v e d
p la n t
m a t e r i a l s . H ow ever, w h a t c o n t r o l w ork on s i l v e r s a g e b r u s h t h a t h a s
been d one, i n s o u t h e a s t e r n M ontana, i s r e p o r t e d i n W h ite and C u r r ie
(1983).
S p e c ie s o f s a g e b r u s h w h ic h do n o t l a y e r o r s p r o u t i n n a t u r e a r e
r e l a t i v e l y e a s y to c o n t r o l by v a r i o u s m e th o d s. Heavy k i l l h a s b een
r e p o r t e d w ith 2 ,4 -D on b ig s a g e b r u s h ( B l a i s d e l l and M u eg g le r 1956,
C o rn e liu s and Graham 1958). M echanical and b u rn in g tr e a tm e n ts a re a ls o
e f f e c t i v e i n re d u c in g b ig sag eb ru sh (Johnson and Payne 1968).
W right
'et a l . (1979) h av e n o te d t h a t f i r e h a s p ro b a b ly p la y e d an h i s t o r i c
r o l e i n keep in g brush d e n s ity low i n s a g e b ru s h /g ra s s com m unities. I t
w as e s t i m a t e d t h a t f i r e s
o ccu red
e v ery
32-70
y e ars
in
th e s e
com m unities.
W h ite ( p e r s o n a l comm.) h a s s t u d i e d h e r b i c i d a l , m e c h a n ic a l and
bu rn in g tr e a tm e n ts on p la in s s i l v e r sag eb ru sh i n s o u th e a s te r n Montana
and h a s fo u n d t h a t f a l l b u r n in g c a n l e a d to good c o n t r o l (W h ite and
C u r r ie 1983). B l a i s d e l l and M u e g g le r (1956) i n d i c a t e d t h a t s i l v e r
sa g e b ru sh
s h o w s m uch g r e a t e r r e s i s t a n c e
sa g e b ru sh e s.
th re e tip
The s p r o u t i n g
sa g e b ru sh
( A.
n a tu re
t o 2 ,4 - D
th a n o th e r
o f s h ru b s su c h a s s i l v e r
t r i p a r t i t a ) m akes
c o n tro l
e ffo rts
and
m ore
d i f f i c u l t . I t has a ls o c o n trib u te d to h ig h e r p la n t d e n s ity when anim al
use i s
h ig h a n d /o r f i r e
f r e q u e n c y h a s b een r e d u c e d .
In t h r e e t i p
10
s a g e b r u s h p o p u l a t i o n s i n O regon, W inw ard (1980) b e l i e v e d c o n t r o l
e f f o r t s may be th e o n ly way to k e ep s h ru b d e n s i t i e s low enough to
a llo w fo r h e a lth y s ta n d s o f . herbaceous s p e c ie s . He r e p o r te d t h a t l i g h t
g r a z in g and e v en n o n u se w i l l f a i l
to r e s t o r e
s t a b l e h e rb a c e o u s
co m p o sitio n . M ountain s i l v e r sag eb ru sh d e n s ity in c re a s e d l e s s r a p id ly
i n re s p o n se
to m a in te n a n c e o f a good h e rb a c e o u s c o v e r th a n d id
t h r e e t i p sagebrush.
D e f o l i a t i o n o f b ro w se s p e c i e s a p p e a re d t o r e d u c e c a r b o h y d r a te
re s e rv e s to ab o u t th e same e x te n t r e g a r d le s s o f c o n tro l tre a tm e n t d a te
(D o n a rt and Cook I 970). S tu r g e s (1 9 7 7 a ) r e p o r t e d t h a t f a l l m o is tu r e
was reduced by 19 p e rc e n t i n a b ig sag eb ru sh stan d w ith g a in s noted a t
91-183 cm depth.
However,
m o is tu re d e p le tio n was g r e a te r on sprayed
s i t e s i n th e top 61 cm because g ra s s d e n s ity in c re a s e d when sagebrush
w as
c o n tro lle d .
T h is r e s p o n s e
w a s o b s e r v e d w h e re s o i l s w e re
s u f f i c i e n t l y deep so th a t g ra s s r o o ts w ere above sag e b ru sh ro o ts .
B io lo g ic a l c o n tro l has gain ed r e c e n t a t t e n t i o n and G ates (1964)
h as in d ic a te d t h a t a l e a f - d e f o l i a t i n g moth ( Aroea w e b s te r ii) has been
one o f th e m ost p ro m isin g i n t h i s re g a rd because i t p r e f e r s sagebrush
s p e c ie s . B esid e s t h i s moth,
d e s tr u c ti v e to sagebrush.
some o th e r i n s e c t s have been re p o rte d a s
These in c lu d e T rirh a b d a p ilo s a and v a rio u s
s p e c i e s o f g r a s s h o p p e r s (H arv ey 1981, T i s d a le and H iro n a k a 1981).
V oles (M icro tu s sp p ,),
a ro d e n t on ra n g e la n d s ,
have caused e x te n s iv e
damage on b ig and s i l v e r sagebru sh p o p u la tio n s a s w e ll a s o th e r p la n t
s p e c i e s (M u e g g le r 1 966, T i s d a le and H iro n a k a 19 8 1 ). In s o u t h e a s t
Montana, they w ere p re s e n t i n s u f f i c i e n t numbers i n 1983 to g ir d l e and
t o p k i l l many s h r u b s on b o th my s tu d y a r e a and i n n e a rb y p a s t u r e s .
11
Rodents do n o t seem to ta k e th e seed a s food how ever, p o s s ib ly due to
te rp e n o id s p re s e n t (E v e re tt, Meeuwig and S tev en s 1978).
Sagebrush p la n ts t h a t s u rv iv e c o n tro l tre a tm e n ts have been found
to be th e m ost im p o rta n t f a c t o r i n sh ru b re in v a s io n (Johnson and Payne
1968). G e n era lly , r e e s ta b lis h m e n t o c c u rre d d u rin g th e f i r s t few y e a rs
a f t e r tre a tm e n t and u ltim a te ly was a ls o due to p la n ts grow ing to seed
b e a rin g s i z e (B artolom e and Heady 1978). C ontrol tr e a tm e n ts m ight a ls o
a llo w
o t h e r s p e c i e s su ch a s g r e e n
ra b b itb ru s h
( C h r v s o th a m n u s
v i s c i d i f l o r u s (Hook.) N u tt.) to e x p l o i t new s i t e s w h e re c o m p e t i t i o n
has been e lim in a te d (Young and Evans 1972).
C ontrol o f p la in s s i l v e r
sagebrush was s i g n i f i c a n t i n re d u c in g sh ru b c o m p e titio n and in c r e a s in g
d e s i r a b l e f o r a g e . When m e c h a n ic a l t r e a t m e n t s w e re e x a m in e d i n t h i s
c o n te x t,
c u ttin g
d a t e and o r i g i n a l
p l a n t s i z e w e re fo u n d t o be
i m p o r t a n t i n d e te r m in in g , s u b s e q u e n t s p r o u t i n g and r e g r o w th (W h ite
p e rso n a l com m unication). Phenology and m o is tu re s t r e s s a ls o a f f e c te d
m o r ta lity .
Many s h r u b s ,
in c lu d in g
s ilv e r
sa g e b ru sh ,
a re
d e s ira b le
in
re c la m a tio n o f d is tu rb e d la n d s f o r c a tc h in g snow and f u r n is h in g fo rag e
or
cover fo r liv e s to c k
and w i l d l i f e .
H ow ever,
s ilv e r
s a g e b ru s h
c o n s i s t e n t l y had th e l e a s t g ro w th o f f i v e s h r u b s t r a n s p l a n t e d a s
s e e d lin g s on to p s o il and overburden i n Wyoming (Howard e t a l.
1977).
To im p ro v e on t h e s e c h a r a c t e r i s t i c s , W elch and M cA rth u r (1979) h av e
s u g g e s te d t h a t s a g e b r u s h can p r o b a b ly be g e n e t i c a l l y im p ro v ed to
becom e a m ore v a l u a b l e f o r a g e r e s o u r c e . T h is i s b e c a u s e o f a r i c h l y
v a r ia b le germ plasm .
12
Forage C o n sid e ra tio n s
A ll sag eb ru sh es have some im p o rtan c e a s fo ra g e (B e e tle I960), but
i t h a s b e en e s t a b l i s h e d t h a t t h e r e a r e s i g n i f i c a n t d i f f e r e n c e s i n
anim al p re fe re n c e among ta x a .
Most re s e a rc h on t h i s s u b je c t h as been
concerned w ith b ig sag eb ru sh ,
low sag eb ru sh (Ae. a rb u s c u la I and b la ck
sag eb ru sh (Ae, ,nova). L im ite d s tu d ie s w ith s i l v e r sag eb ru sh have been
done. G e n e tic v a r i a t i o n b e tw e e n s a g e b r u s h s p e c i e s and s u b s p e c ie s
in flu e n c e d anim al p re fe re n c e more th a n e n v iro n m e n ta l v a r i a t i o n w ith in
th e taxon (Sheehy and Winward 1981). S tu d ie s r e l a t i n g to g ra z in g use
of p la in s
s ilv e r
sag e b ru sh
h a v e show n t h a t i t
is
a re la tiv e ly
im p o r t a n t p l a n t f o r w i n t e r u se by som e w i l d l i f e s p e c i e s su ch a s e l k
( C erv u s .c an a .d e n s i s ) , m ule d e e r ( O d o c o ile u s h e m io n u s ) and a n te l o p e
(A nt.ilocapra am ericaqa) (D ietz e t a l . 1962,
Mackie 1970, K ufeld 1973,
D usek 1975, B e e tle 1977, S c h o ll e t a l . 1977, W ilso n 1977, Sheehy and
W inw ard 1981). I t w i l l be u sed by l i v e s t o c k o n ly i f t h e r e i s l i t t l e
e l s e a v a i l a b l e (M ack ie 1970, K u fe ld 1973, D usek 1975, B ran so n and
M ille r 1981, Sheehy and Winward 1981, Roath and K rueger 1982).
W ild lif e Forage C o n sid e ra tio n s
B e e t l e (1977) r e p o r t e d t h a t p l a i n s s i l v e r s a g e b r u s h w as l e s s
p a la ta b le th an Wyoming b ig sag eb ru sh ,
but s ta te d t h a t i t was r e a d ily
ta k e n by e lk and d e er i n w in te r. Sheehy and Winward (1981) showed t h a t
B olander s i l v e r sag eb ru sh was h ig h ly p r e f e r r e d by mule d e er. S c h o ll e t
a l . ( 1977) r e p o r t e d t h a t m o u n ta in s i l v e r s a g e b ru s h w as m o d e r a te ly
p a la ta b le to mule d eer. Two s tu d ie s i n th e M isso u ri B reaks o f Montana
d e m o n strated t h a t use o f p la in s s i l v e r sagebrush by mule d e e r and e lk
13
was e x te n s iv e (Mackie 1970, K ufeld 1973). H eav iest use was observed on
b o tto m la n d s ,
b u t m o d e ra te u s e w as o b s e r v e d
th r o u g h o u t th e a r e a
s tu d ie d . M ackie based h i s c o n c lu sio n s on o b s e rv a tio n s o f freq u en cy of
shrub use and rumen c o n te n t from dead a n im a ls. P la in s s i l v e r sagebrush
w as fo u n d i n 50 p e r c e n t o f th e c o l l e c t e d m u le d e e r ru m e n s and i n 22
p e r c e n t o f th e e l k ru m e n s. A lth o u g h th e s e n u m b ers d i f f e r , e lk w e re
o b s e r v e d to u se th e s h ru b a s f r e q u e n t l y a s t h e d e e r . A n te lo p e i n
Wyoming used s i l v e r sagebrush p re d o m in a n tly d u rin g l a t e f a l l ,
w in te r
and e a r l y s p r i n g (W ils o n 1977). D ie tz e t a l . (1962) r e p o r t e d t h a t use
o f sag eb ru sh was dependent on w hat o th e r p la n t s p e c ie s w ere a v a ila b le .
S a g e b ru s h w as r e g a r d e d a s m ore p a l a t a b l e when o t h e r p l a n t s w e re
a v a ila b le . Mule d e e r i n low c o n d itio n re fu s e d to e a t sagebrush alone.
Deer w ere seldom observed i n a s i l v e r sag eb ru sh type d u rin g w in te r i n
c e n tr a l Montana, and d i e t s c o n ta in e d l e s s th a n 10 p e rc e n t of th e .s h ru b
i n a l l s e a s o n s (D usek 1975). T h is w as n o te d e v en th o u g h u se o f t h i s
ty p e
d o u b le d
fro m
e a rly
to l a t e
sum m er i n
a s s o c ia tio n
w ith
a
c o r r e s p o n d in g d e c r e a s e i n u se o f th e b ig s a g e b r u s h a r e a s . W hite
(p e rso n a l comm.)
c o n s id e rs
s i l v e r sagebrush o f l i m i t e d fo ra g e v alu e.
He h a s o b s e r v e d u se by r a b b i t s and v o l e s , b u t o n ly o c c a s i o n a l u se by
mule d eer. More fre q u e n t use by d e er seemed to be r e s t r i c t e d to w in te r
p e rio d s when d eer p o p u la tio n s w ere high.
L iv e sto c k Forage C o n sid e ra tio n s
R eported liv e s to c k use o f s i l v e r sag eb ru sh p re s e n ts a c o n f lic tin g
and u n c le a r p i c t u r e . M ackie (1 9 7 0 ) and K u fe ld (1 9 7 3 ) r e p o r t e d no u se
by c a t t l e on p la in s s i l v e r sagebrush i n th e M isso u ri B reaks. Although
•14 '
D usek (1 975) r e p o r t e d t h a t c a t t l e s p e n t 64 p e r c e n t o f t h e i r tim e i n
s i l v e r s a g e b r u s h c o m m u n itie s fro m J u n e t o S e p te m b e r, no u se o f th e
p la n t
w as o b s e r v e d .
S e a so n
u t i l i z a t i o n w e re r e l a t e d
of
to
c a ttle
u se
p a la ta b ility
and
an d
d e g re e
of
s h ru b
a v a ila b ility
of
h e rb a c e o u s v e g e t a t i o n . H ow ever, s h ru b u t i l i z a t i o n was n o t e x c e s siv e
and had no lo n g term e f f e c t s on abundance o r v ig o r i n Oregon. The only
s h r u b s w h ic h w e re
o b v io u s ly
a v o id e d
by l i v e s t o c k
w e re sh ru b b y
c i n q u e f o i l ( P o t e n t i l l a f r u t i c o s a L.) and m o u n ta in s i l v e r s a g e b r u s h
( Roath and K rueger 1982). Sheehy and Winward (1981) showed some sheep
u t i l i z a t i o n o f B olander s i l v e r sag eb ru sh i n Oregon, but p re fe re n c e was
low . In n o r th e a s te r n Montana, Branson and M ille r (1981) re p o rte d t h a t
p la in s s i l v e r sag eb ru sh ,
in p a rtic u la r,
in c re a s e d g r e a tly i n d e n s ity
w hen r e s t e d fro m c a t t l e . T h is w as a t t r i b u t e d t o tw o f a c t o r s . F i r s t ,
p l a i n s s i l v e r s a g e b r u s h w as m ore p a l a t a b l e th a n m o st s h r u b s i n th e
a re a and showed ra p id re c o v e ry from reduced g ra z in g . Secondly, s i l v e r
sag eb ru sh was lo c a te d on l e v e l flo o d p la in s , a d ja c e n t to stre a m s w here
i t was r e a d ily a c c e s s a b le to liv e s to c k and v u ln e ra b le to heavy use.
Sagebrush C hem istry
I n t e r e s t i n th e chem ical p r o p e r tie s o f sagebrush i n r e l a t i o n to
ta x o n o m ic r e f i n e m e n t i n t o
s p e c ie s
and s u b s p e c ie s
h as le d
to
s p e c u la tio n s a s to why c e r t a i n ta x a a re p r e f e r r e d by a n im a ls. M ineral
and n u t r i e n t
c o n te n t c an be show n to
c o in c i d e w i t h
th e
u se o f
sag eb ru sh by season. T his may be p r im a r ily due to a v a i l a b i l i t y and n o t
i l l u s t r a t e a c a u s e and e f f e c t r e l a t i o n s h i p . Gough and Erdman (1 9 8 0 )
'f o u n d s i g n i f i c a n t d i f f e r e n c e s i n c o n c e n t r a t i o n s o f 30 e le m e n ts i n
15
Wyoming b ig s a g e b r u s h by s e a s o n . The h i g h e s t c o n c e n t r a t i o n s o f th e
m a jo r e le m e n ts (Ca, Cu, Mg, P, K, S) w e re i n J u n e and J u l y and th e
lo w e s t w e re i n t h e w i n t e r . The i n v e r s e w as fo u n d w ith tw o g ro u p s o f
m in o r e le m e n ts (A l, Cr, An, Ar, Ba, Cd, Fe, Pb, Na, Co, Mn ). In
g e n e ra l, h igh crude p r o te in and low crude f i b e r c o n te n ts a r e found i n
w in te r and o f te n r e l a t e d to in c re a s e d p re fe re n c e d u rin g t h a t season.
The v a r i a t i o n i n secondary m e ta b o lic compounds among th e ta x a may
s tro n g ly in flu e n c e p a l s t a b i l i t y . Secondary c h em ica ls may be m o d ifie rs
o f fo ra g in g b eh av io r and a re l i k e l y in f lu e n c e s on s e l e c t i v i t y .
Black
s a g e b r u s h h a s b e en fo u n d to p r e c o n d i t i o n s h e e p f o r th e a c t i o n o f
T e tr a d y m ia t o x i n s i n p h o t o s e n s i t i s m (J o h n so n 1982). The s a g e b ru s h
genus
has
p h en o li c s ,
th re e
g ro u p s
of
s e c o n d a ry
com pounds.
T h ese
in c lu d e
v o l a t i l e o i l s and s e s q u ite rp e n e la c to n e s . The f i r s t group,
w h ic h i n c l u d e s f l a v e n o i d s and c o u m e r in s , a r e f l o u r e s c e n t u n d e r UV
l i g h t and w e re f i r s t u s e d t o s e p a r a t e s u b s p e c ie s o f c e r t a i n ta x a
(W inw ard and T i s d a l e 1969). C o lo r e x t r a c t s h av e b e e n l i n k e d w ith
p a l a t a b i l i t y to m u le d e e r ( S te v e n s and M cA rthur I 9 7 4 ), w ith s i l v e r
sag eb ru sh being f a i r l y p a la ta b le and i n th e same c a te g o ry a s Wyoming
b ig s a g e b r u s h .
The l i g h t b lu e c o l o r fo u n d i n e x t r a c t s o f s i l v e r
s a g e b r u s h d e n o te s a medium p r e f e r e n c e w h e re a s th e d a r k e r b lu e o f
m o u n ta in b ig s a g e b r u s h e x t r a c t s ( A r te m is ia t r i d e n t a t a ssp . vasevana
(R ydb.) B e e t l e ) i n d i c a t e s h ig h e r a n im a l p r e f e r e n c e . The p r e s e n c e o f
c o u m e rin d e r i v a t i v e s and t h e i r g l y c o s i d e s a r e a l s o c o r r e l a t e d w ith
t h i s d a rk e r b lue (S h afized eh and M eln ik o ff 1970). This co n cep t has n o t
been c o n s is te n tly v e r i f i e d under w ide ra n g in g c irc u m sta n c e s .
16
S e s q u ite r p e n e l a c t o n e s a r e a l s o
b e in g s t u d i e d a s ta x o n o m ic
m arkers and may be r e l a t e d to p re fe re n c e . S p e c ific compounds i n t h i s
g ro u p h a v e b e e n i d e n t i f i e d ( B hadane and S h a f iz e d e h I 9 7 5 ), b u t i t i s
n o t known w h ic h h av e a r o l e to p r e f e r e n c e . P l a i n s s i l v e r s a g e b ru s h
c h ro m o t o g r a p h i c
s u b s p e c ie s ,
p a tte rn s
a re
v e ry
c lo s e t o th e n o n ~ p re f e r r e d
b a s in b ig s a g e b r u s h ( A r t e m i s i a t r i d e n t a t a N u tt.
t r i d e n t a t a ) (K elsey e t a l.
ssp .
1976).
E c o lo g ic a l A spects o f Sagebrush
G razing Im pacts
Shrub com m unities may be e x c e p tio n a lly s ta b l e i n th e absence o f
e x te r n a l p e r tu r b a tio n (H arper 1977). T h e re fo re ,
community c o m p o sitio n
may depend more upon th e n a tu re o f p re v io u s d is tu rb a n c e s and th e f l o r a
t h a t d e v e lo p e d im m e d ia te ly t h e r e a f t e r
th a n
upon s u c c e s s io n a l
developm ent.
In one
b ig s a g e b r u s h / g r a s s co m m u n ity i n Id a h o ,
s h ru b s and
p e r e n n i a l g r a s s e s d o u b le d a f t e r 25 y e a r s o f no l i v e s t o c k g r a z in g
(A nderson and H o lte 1981). S e l e c t i v e g r a z in g by c a t t l e i n s p r i n g
e n c o u ra g e d g ro w th o f s a g e b r u s h , b u t sh e e p g r a z in g i n l a t e autum n on
com m unities w ith low shrub d e n s i t i e s p re v e n te d an in c r e a s e i n d e n s ity
o f b ig sagebrush. At h ig h e r shru b d e n s i t i e s , th e sheep l o s t w eig h t and
f a i l e d t o c o n t r o l s a g e b r u s h . A f te r s i x y e a r s s a g e b r u s h i n c r e a s e d i n
both s iz e and p o te n tia l seed p ro d u c tio n i n t h i s s i t u a t i o n (F risc h n e c h t
and H a rris 1973).
17
S o il R e la tio n s h ip s
S o il c h a r a c t e r i s t i c s have been.exam ined to e v a lu a te r e l a t i o n s h i p s
w ith sag eb ru sh d i s t r i b u t i o n . S i l v e r s a g e b r u s h p r e f e r s w e l l 'd r a in e d ,
a llu v ia l,
c o a r s e r t e x t u r e d s o i l s i n b o tto m la n d s. More d e ta i le d s o i l
and v e g e ta tio n r e l a t i o n s h i p s i n s i l v e r sag eb ru sh com m unities have been
re p o rte d . Lower l e v e l s o f P, K, N, o rg a n ic m a tte r and c a tio n exchange
c a p a c i t y w e re r e p o r t e d i n s i l v e r s a g e b r u s h s o i l s th a n a d j a c e n t b ig
sag eb ru sh s o i l s (H a z Ie tt and Hoffman 1975).
m ore m a tu re
s o il
d e v e lo p m e n t i n
th e
T his was p ro b ab ly due to
b ig
sag e b ru sh
co m m u n ity .
Cunningham (1971) r e p o rte d t h a t m o derate to h ig h l e v e l s o f e x tr a c ta b le
m agnesium i n th e 12-24 i n c h l a y e r , w as i m p o r t a n t to th e -p re se n c e and
su c c e ss o f s i l v e r sagebrush.
T his was a s s o c ia te d w ith im p e rfe c t s o i l
d r a in a g e and a s h a llo w r o o t s y s te m i n th e p l a n t . Optimum h a b i t a t
seemed to in c lu d e a m o ist upper s ix in c h e s o f s o i l a lo n g w ith co arse
m a te r ia ls i n th e s o i l p r o f i l e .
S tu rg e s (1977b) s t a t e s t h a t w a te r-u se
z o n e s s h i f t o u tw a rd and dow nw ard i n t h e s o i l fro m th e b ig s a g e b ru s h
p l a n t s a s th e g ro w in g s e a s o n a d v a n c e s . S tu r g e s (1 9 7 7 b ) and C a ld w e ll
( 1978) both c h a r a c te r iz e b ig sag eb ru sh a s h av in g a p ro m in en t ta p ro o t
w ith s u f f i c i e n t l a t e r a l s p r e a d and r o o t d e n s i t y to c a p t u r e summer
p r e c i p i t a t i o n . D eeper r o o t s a r e p r e s e n t w h ic h a llo w u t i l i z a t i o n o f
d eep er w a te r r e s e r v e s and m o is tu re re c h a rg e . S im ila r r e s e a r c h has n o t
been done w ith s i l v e r sagebrush.
A lle lo p a th y
A l l e lo p a th y
lite ra tu re
is
o n e ■a r e a
th a t i s e x te n s iv e ly
c o v e re d i n t h e
on A rte m isia . T his w e a lth o f in fo rm a tio n i s pro b ab ly due,
18
i n p a r t , to i n t e r e s t i n why t h i s g e n u s i s so s u c c e s s f u l . A l le lo p a th y
i s a p r o m in e n t f e a t u r e fo u n d i n A r te m is ia th r o u g h o u t th e w o r ld , and
much o f th e fo r e ig n r e s e a r c h fo c u s e s on i t ,
A lle lo p a th ic s u b s ta n c e s from A rte m is ia rh izo m es and le a v e s have
u n i v e r s a l l y d e c r e a s e d r e s p i r a t i o n o r in h i b i t e d g e rm in a tio n o f g ra s s
s e e d s ( C h irc a and F a b ia n 1973» F rie d m a n e t a l . 1977, H offm an and
H a z l e t t 1 977, W eaver and K lb v ic h 1977, G roves and A n d erso n 1981,
H ussain and Khanum 1982). In In d ia ,
th e
a lle lo p a th ic p o te n tia l
h y d ro p h ilic m e ta b o lite s .
b io lo g ic a lly
M elkania e t a l.
(1982) a t t r i b u t e d
o f A r t e m i s i a v u l g a r i s L.
In Japan,
N um ata e t a l .
to
c e rta in
(1 9 7 5 ) fo u n d a
a c t i v e a g e n t ( c a f f e i c a c i d ) i n t h e r o o t s o f m ugw ort
(A rte m is ia p rin c e o s Pampan.). I n h ib i tio n o f g ra s s g e rm in a to n has been
th e most commonly re p o rte d re sp o n se , but i n some c a se s s tim u la tio n o f
g ro w th h a s b e e n r e c o r d e d by H offm an and H a z l e t t (1 9 7 7 ), W eaver and
K lo v ic h ( 1977) and C h ir c a and F a b ia n (1 9 7 3 ). H ale ( 1982) n o te d t h a t
l e a c h a t e s fro m A. v u l g a r i s L. a l s o i n c r e a s e d g ro w th o f t h e fu n g u s
Pvthium m vriotvlum . Harvey (1981) o b serv ed au to p ath y i n some sagebrush
s p e c ie s i n Montana, p la in s s i l v e r sag eb ru sh in c lu d e d .
R eproductiv e C h a r a c te r is tic s
Seed D is p e rs a l
One o f th e prim ary f e a tu r e s o f any re p ro d u c tiv e s tr a te g y i s th e
number o f p ro p a g u le s t h a t a re produced and d is p e rse d . In t h i s r e s p e c t,
e f f i c i e n c y o f s e e d d i s p e r s a l by w ind an d r e p r o d u c t i v e c a p a c i t y a r e
a s s o c ia te d .
S a g e b ru s h s p e c i e s
a re
g e n e ra lly
lo w
in
d is p e rs a l
e f f i c i e n c y and s e e d p r o d u c tio n c a p a c i t y i s h ig h ( B o sto c k and B en to n
19
1979). Seed d is p e r s a l i s one o f th e m ost im p o rta n t f a c t o r s prom oting
g e n e flo w i n p l a n t p o p u l a t i o n s . I n m o st p l a n t s p e c i e s , i n c l u d i n g
sag eb ru sh , d is p e r s a l seem s to be i n c id e n ta l, e s p e c ia lly d u rin g sto rm s,
and i s not based on any s p e c ia l m o rp h o lo g ica l s tr u c tu r e . D is p e rs a l i s
one way t h a t p la n ts can keep t h e i r d e sc e n d en ts s e p a ra te d i n sp ace, and
i t p r o v id e s e a c h new p l a n t w ith i t s own s i t e w h e re i t h a s g r e a t e r
p o te n tia l to compete w ith o th e r p la n ts (van d er F i j i 1982). D is p e rsa l
s tr a te g y i s complex and r e p r e s e n ts a compromise betw een c o n f lic tin g
dem ands,
su c h
as avenues o f
e n e rg y
e x p e n d it u r e .
C o n s e q u e n tly ,
e s ta b lis h m e n t m ight be more im p o rta n t i n some s p e c ie s th a n d is p e r s a l
f o r a c h ie v in g r e p ro d u c tiv e su ccess.
D i s p e r s a l can p la y a c r i t i c a l r o l e i n d e t e r m in in g p o p u la tio n
s iz e . Because seed s o f m ost p la n ts a re d is p e rs e d c lo s e to th e p a re n t,
seed d e n s ity f a l l s o f f s te e p ly a s d is ta n c e from th e p a re n t in c r e a s e s
(H a rp e r 1977, Cook 1980). T h is i s th e c a s e w ith s a g e b r u s h ( B e e tle
I9 6 0 , F rie d m a n and O rsh an 1975, H arvey 1981, T i s d a l e and H iro n a k a
1981). Seed d is p e r s a l i n a r id com m unities i s d e sc rib e d a s f a l l i n g i n t o
two c la s s e s (M ott 1979). They a re :
(I) w id esp read d is p e r s a l,
o fte n of
la r g e numbers of seed s, e n a b lin g e x p l o i t a t i o n o f a number o f p o te n tia l
s ite s ,
and ( 2 ) u t i l i z a t i o n o f a f a v o r a b l e h a b i t a t f a c i l i t a t e d
m in im a l m ovem ent o f s e e d fro m
c o n d itio n s ,
th e
p a re n t
p la n t.
by
U nder d e s e r t
t h i s second s tr a te g y i s th o u g h t to im prove th e chances o f
s e e d lin g e s ta b lis h m e n t s in c e a d ja c e n t s i t e s have a lre a d y proved to be
s u i t a b l e f o r g ro w th and d e v e lo p m e n t o f p a r e n t p l a n t s (F rie d m a n and
O rsh an 1975). The p a t t e r n s o f a c h e n e d i s p e r s a l , s e e d l i n g e m e rg e n c e ,
appearence o f c o ty le d o n s and s e e d lin g m o r t a lit y o f Aa, h e r bar a lb a Asso
20
w ere r e l a t e d to d is ta n c e from th e p a re n t p la n t. E ighty f i v e p e rc e n t o f
th e a c h e n e s o f t h i s s p e c i e s f e l l u n d e r th e e x i s t i n g s h ru b canopy.
A lth o u g h d i s p e r s a l i s i m p o r t a n t , o n ly a few d i s p e r s a l p a t t e r n s a r e
noted by Cook (1980) a s b ein g p u b lish e d .
D is p e rs a l can be by wind, w a te r or a n im a ls i n sag eb ru sh (T isd a le
and H ironaka 1981) w ith v a ry in g im p o rtan c e g iv e n to each by d i f f e r e n t
a u th o rs .
H arvey (19 8 1 ) s t a t e s lo n g d i s t a n c e d i s p e r s a l by s i l v e r
sag eb ru sh i s probably due to m u c ila g in o u s seed s a tta c h in g to an im als.
B e e t l e (I9 6 0 ) d e c l a r e s t h a t w a te r i s u n d o u b te d ly a m ore im p o r t a n t
d is p e rs a l
agent
th a n
w in d .
A n e m o c h o ry
(w in d
d is p e rs a l)
is
r e p r e s e n ta tiv e o f A steraceae (C om positae) and seem s to be o f g r e a te s t
im p o r ta n c e (H a rp e r 1977, B o s to c k and B e n t o n .1979» E vans and Young
1 982). S e e d lin g s o f b a s i n b ig s a g e b r u s h h av e b een fo u n d up t o 33
m e te rs away from th e n e a r e s t p o s s ib le so u rce p la n t.
S in ce sag eb ru sh
s e e d s h a v e l i m i t e d m o r p h o lo g ic a l m echanism s f o r d i s t a n t w ind-borne
d is p e r s a l,
th e range o f th e p la n t i s p ro b ab ly ex ten d ed i n co n tig u o u s
b ands a ro u n d t h e p e r i p h e r y o f e s t a b l i s h e d s t a n d s (D a u b en m ire 1975).
A lth o u g h r o d e n t s p la y an a c t i v e r o l e i n
se e d d i s p e r s a l
o f many
h e rb a c e o u s s p e c i e s , no s a g e b ru s h s e e d w as r e p o r t e d l y d i s p e r s e d by
ro d e n ts (L aT o u rette e t a l.
1971).
Achenes o f c e r t a i n sag eb ru sh s p e c ie s , in c lu d in g s i l v e r sagebrush,
develop a tr a n s p a r e n t g e la tin o u s envelope around the seed upon c o n ta c t
w ith w a te r
( C lo r e t a l . I 974, H arvey 1981, van d e r P i j l I 9 82). T h is
seem s an i m p o r t a n t m ethod f o r a t t a c h i n g to s o i l p a r t i c l e s , w h ich
th e r e b y e n h a n c e s g e r m i n a t i o n c o n d i t i o n s by p r o t e c t i n g t h e d e l i c a t e
embryo from d e s s ic a ti o n and m echanical in j u r y (Clo r e t a l .
1974, van
21
d e r F i j i 1982). The m u cilag in o u s seed c o a t h a s a ls o been re g a rd e d a s a
d i s p e r s a l a g e n t (H a rv e y I 981, v an d e r F i j i I 982), and i n g e n e r a l th e
d r i e r th e c lim a te th e more myxospermy (m u cilag in o u s c o a tin g ) p re s e n t.
P h en o lo g ical developm ent i n sagebrush r e s u l t s i n most seed being
shed d u rin g l a t e f a l l and w in te r , alth o u g h a few rem ain th ro u g h o u t th e
w i n t e r ( B e e t l e I9 6 0 , H a rv ey 1981, T i s d a l e and H ir o n a k a 1981). Most
v i a b l e seed i s d is p e r s e d d u rin g t h e f i r s t seven days, alth o u g h a b o rte d
f lo w e r s and h a l f - f i l l e d seed s a re commonly d is p e r s e d over the next two
to f o u r weeks (Goodwin 1956). T is d a le and Hironaka (1981) have s t a t e d
t h a t up to 300,000 achenes p er p la n t can be produced i n b ig sagebrush,
b u t H arvey (1981) r e p o r t e d
a maximum p r o d u c t i o n o f o n ly 54,000
achenes i n s i l v e r sagebrush.
G erm ination F a c to rs
I n t e r e s t i n g e rm in a tio n c h a r a c t e r i s t i c s o f sagebrush i s two fo ld .
F irst,
e f f o r t s to use sa g e b ru sh
to p ro v id e fo ra g e
or cover fo r
l i v e s t o c k , w i l d l i f e and e r o s i o n c o n t r o l depend upon t h i s knowledge.
S e c o n d ly , t h e r e i s o f t e n a d e s i r e t o r e d u c e s t a n d d e n s i t y i n a r e a s
w h e re p l a n t s become to o a b u n d a n t and c o m p e te w i t h f o r a g e p l a n t s
( Pechanec e t a l . 1965, McArthur e t a l . 1974, Harvey 1981).
The c o m b i n a t i o n
of h a b ita t
c o n d itio n s
th a t favor
e s ta b lis h m e n t has been r e f e r r e d to a s a s a f e s i t e (Cook 1980).
se e d lin g
In t h i s
environm ent, th e w a te r and n u t r i e n t r e s o u r c e s and s t i m u l i im m ed iately
s u rro u n d in g a seed d e te r m in e s w h eth er i t w i l l g erm in a te (H arper 1977).
G e r m i n a t i o n on a s p e c i f i c s e e d b e d i s a l s o c o n t r o l l e d by i n h e r e n t
c h a r a c t e r i s t i c s o f s e e d s , o r i n some c a s e s , t h r o u g h m o d i f i c a t i o n o f
22
t h e p h y s i c a l e n v ir o n m e n t by t h e s e e d i t s e l f (E vans a n d Young 1982).
H e t e r o g e n e i t y i n t h e m i c r o e n v i r o n m e n t and t h e e x t r e m e s u b t l e t y o f
g e r m i n a t i o n r e q u i r e m e n t s can d e t e r m i n e t h e num ber and v a r i e t y o f
se e d lin g s th a t a re r e c r u ite d in to
t h e p l a n t p o p u l a t i o n fro m t h e
s e e d b a n k . High d e n s i t y s t r e s s can a d v e r s e ly a f f e c t s e e d lin g su ccess.
Another im p o r ta n t e lem en t, h e rb iv o ry ,
te n d s to d i v e r s i f y range p la n t
communities. Herbivory in f l u e n c e s l o c a l l y d i f f e r e n t m icro en v iro n m en ts
f o r s e e d l i n g e s t a b l i s h m e n t and s u b s e q u e n t g ro w th o f p l a n t s ,
and
t h e r e f o r e i n i t i a t e s r e g e n e r a t i o n c y c le s on a s m a ll s c a l e w i t h i n t h e
community.
One a s p e c t o f sagebrush com m unities i s t h a t v ery few
sagebrush
seeds g e rm in a te (E v e rn a ri e t a l . 1971, H a z l e t t and Hoffman 1975, Cook
1980, Harvey 1981). T h is o c c u r s d e s p i t e t h e g r e a t s e e d p r o d u c t i o n
t y p i c a l o f s a g e b r u s h p l a n t s . S e v e r a l f a c t o r s can c o n t r i b u t e to t h i s
phenomenon in c lu d in g : s o i l m e tr ic p o t e n t i a l w ith i t s e f f e c t on w e tte d
c o n ta c t between seed and s o i l (C o llis-G e o rg e and H ecto r 1966),
d e ath o f s e e d lin g s (Eddleman 1979),
p la n t
ag e
(N osova
1973,
e a r ly
s e a s o n a l c l i m a t i c c o n d itio n s and
Evans and
Young
1982),
so il
m o istu re
A c h e n e s o f s a g e b r u s h i n g e n e r a l do n o t e x h i b i t
sp e c ific
r e l a t i o n s h i p s and l i t t e r (B e e tle I960).
g e rm in a tio n re q u ire m e n ts . T h erefo re, they a re u s u a ll y c o n sid e re d nondormant (McDonough and H a rn is s 1975, C ald w ell 1978) and do no t p e r s i s t
f o r lo n g p e r i o d s i n t h e s o i l (Young and Evans 1975). However, i f seeds
a r e s u b j e c t e d t o i d e a l l a b o r a t o r y c o n d i t i o n s , g e r m i n a t i o n can be a s
h ig h as 90 p e rc e n t (Harvey 1981). Im p o rta n t f a c t o r s t o examine,
w ith .
23
resp ect
to
g e rm in a tio n
re q u ire m e n ts,
in c lu d e co ld tr e a t m e n t s
( s t r a t i f i c a t i o n ) , te m p e ra tu re , l i g h t , w a te r s t r e s s and m a t u r i t y of the
-
;
seed .
S tra tific a tio n
S t r a t i f i c a t i o n h a s been d e fin e d a s a cold tr e a tm e n t which breaks
s e e d d o rm ancy. I t i s i m p o r t a n t i n many s p e c i e s . B ew ley and B la c k
(1982) s t a t e t h a t i t i s m#§t ^ g n e f i c i a l if- n e e d s a r e h y d r a t e d . The
amount o f p r e c h i l l i n g t h a t i s needed t o enhance g e r m in a tio n i s q u i t e
v a r i a b l e among s p g g ie s and can range from a few days t o s e v e r a l months
(Young and E vans 1979,
B ew ley and B la c k
1982).
It
can a ls o
be
u n n e c e s s a r y . S tid h a m efc §1. (1980) s t a t e t h a t m o st s h r u b s r e q u i r e a
p r e c h i l l t o a c h i e v e maximum g e r m i n a t i o n , and t h e y i d e n t i f i e d b ig
sagebrush i n t h i s c a te g o ry w ith o u t r e g a r d t o s u b sp e c ies.
S h a n e r (1982) r e p o r t e d
p ro stra te
sp u rg e
Krueger and
( E u p h o r b ia s u o i n a
R af.)
i n c r e a s e d i t s g e r m i n a t i o n by 70=80 p e rc e n t w ith s t r a t i f i c a t i o n , but
K rasikova (1978) showed seeds of annual co m p o sites (A rte m is ia v u l g a r i s
L. i n c l u d e d ) w e re n o t a f f e c t e d by s t r a t i f i c a t i o n . B ec a u se s e e d s o f
s a g e b r u s h s p e c i e s h av e b e en c l a s s i f i e d a s n o n d o rm a n t, i t m ig h t be
h y p o th e siz e d t h a t such seeds would n o t b e n e f i t from p r e c h i l l i n g .
The
o n ly e x c e p t i o n to t h i s s p e c u l a t i o n h a s b e e n m o u n ta in b i g s a g e b r u s h
(McDonough and H a rn iss 1974, 1975, C aldw ell 1978). S t r a t i f i c a t i o n can
a ls o a f f e c t g e rm in a tio n re s p o n se s to e n v iro n m e n ta l v a r ia b le s .
a rro w le a f
b a lsa m ro o t
(B a lsa m o rh iz a
s a e itta ta
In
(P u rsh ) N u tt.),
s t r a t i f i c a t i o n lo w e re d the optimum te m p e ra tu re f o r g e rm in a tio n (Young
and E vans 1 9 7 9 ), and i n a s i m i l a r f a s h i o n , p r e c h i l l s i g n i f i c a n t l y
24
l e s s e n e d t h e e f f e c t o f w a t e r s t r e s s on g e r m i n a t i o n o f m o u n ta in b i g
sagebrush seeds (McDonough and H a rn is s 1975).
Temperature E f f e c t s
The e f f e c t s o f te m p e ra tu re on seed g e rm in a tio n have been s tu d ie d
e x t e n s i v e l y i n many s p e c i e s .
T e m p eratu re re g im e s a r e f r e q u e n tly
i n v o l v e d i n s e a s o n a l c o n t r o l o f d o rm ancy e s p e c i a l l y i n r e s p o n s e t o
i n t e r a c t i o n s w ith l i g h t . An optimum te m p e ra tu re becomes a p p a re n t when
seeds g e rm in a te over a wide range. In a d d itio n ,
most seeds g erm in a te
b e t t e r under c o n s ta n t r a t h e r th a n f l u c t u a t i n g te m p e ra tu re re g im e s
(Bewle y and Black 1982, Evans and Young 1982). Bewley and Black (1982)
a l s o n o te t h a t r a t e o f g e rm in a tio n i s of g r e a t v a lu e i n c h a r a c t e r i z i n g
s e e d r e s p o n s e s t o t e m p e r a t u r e , a l t h o u g h th e r e i s o f t e n c o n s id e ra b le
v a r i a b i l i t y due to g e n e t i c d i f f e r e n c e s .
This g e n e ti c h e te r o g e n e ity i s
d e m o n strated through su b p o p u la tio n s o f seed from a p la n t p o p u la tio n .
These su b p o p u la tio n s g e rm in a te under d i f f e r e n t te m p e ra tu re re g im e s and
r a t e s change w ith th e se te m p e ra tu re s . All s u b sp e c ie s o f b ig sagebrush
a r e n o te d to s p e e d up g e r m i n a t i o n fr o m 18 t o 2 d a y s a s a f u n c t i o n o f
i n c r e a s i n g te m p e ra tu re s (McDonough and H a rn iss 1975). Sagebrush seeds
g e rm in a te over a wide range of te m p e ra tu re s , but optimum te m p e ra tu re s
a re u su a lly
w e l l - d e f i n e d (Weldon e t a l„
1959,
C lo r e t a l .
1974,
C a l d w e l l 1978, K r a s i k o v a 1978, Sabo e t a l . 1979, W ils o n 1982). I n
s i l v e r sag eb ru sh , th e optimum seems t o be about 14 C (Harvey 1981).
L ig h t and Dark E f f e c t s
The l i g h t re q u ire m e n t o f seeds h a s a l s o been s tu d ie d w id e ly . To a
l a r g e e x t e n t , l i g h t se e m s t o p l a y a n i n t e r a c t i v e r o l e w i t h o t h e r
25
en v iro n m en tal f a c t o r s .
Seed dormancy i s te r m in a te d i n a l a r g e number
o f s p e c i e s when h y d r a t e d s e e d i s i l l u m i n a t e d . L i g h t is , t h e r e f o r e o f
g r e a t e c o lo g i c a l im p o rtan ce (Cook 1980). L ig h t can d e te rm in e w hether
g e r m i n a t i o n o c c u r s i n o r on th e s o i l ; i t c o n t r o l s g e r m i n a t i o n u n d e r
v e g e t a t i o n a l c an o p ies; and i t i n t e r a c t s w ith te m p e ra tu re to d eterm in e
t h e l e n g t h o f s e a s o n a l d o rm ancy. An i n c r e a s e i n t e m p e r a t u r e may
d e c r e a s e t h e e f f e c t s o f l i g h t so much t h a t g e r m i n a t i o n i n t h e d a r k
becom es g r e a t e r . The o p p o s i t e c an o c c u r w h e reb y some g e r m i n a t i o n
occurs a t
lo w e r
te m p e ra tu re s,
but l i g h t
a lo n g w ith
in c re a sin g
te m p e ra tu re s w i l l i n c r e a s e g e rm in a tio n (Bewley and Black 1982). Some
s p e c i e s t h a t h a v e n e v e r b e e n d o rm a n t r e a d i l y g e r m i n a t e i n d a r k n e s s
when im bibed w i t h w a te r. Other s p e c ie s , i n c o n t r a s t ,
seem i n s e n s i t i v e
to l i g h t u n le s s exposed t o o sm o tic s t r e s s .
I n some s p e c i e s l i g h t i n h i b i t s
seed g e r m in a tio n a t c e r t a i n
te m p e ra tu re s due to changes i n t h e makeup o f th e c e l l membrane. This
i n h i b i t i o n see m s t o o c c u r d u r i n g t h e l a t e r s t a g e s o f th e g e r m i n a t o n
p ro cess.
T h e re
can a l s o
be a l i g h t r e q u i r e m e n t a t
th e tim e of
d i s p e r s a l w h ic h i s n e g a t e d a f t e r b u r i a l and p a s s a g e o f t i m e (Bew ley
and B la c k I 982). I n c o n t r a s t , Cook ( I 980) r e p o r t s t h a t some s p e c i e s
w i l l d is p la y no l i g h t re q u ire m e n t a s f r e s h seed, but they w i l l have a
l i g h t re q u ire m e n t a f t e r b u r ia l.
L ig h t-s tim u la te d g e rm in a tio n of
s e e d lin g s in v o lv e s a complex i n t e r a c t i o n o f t h e p h y to c h ro m e s y s te m .
However, th e p r e c is e mechanism of m a in ta in in g dormancy i n seeds t h a t
r e q u i r e l i g h t i s unknown a l t h o u g h i t
seem s c l e a r t h a t t h e r e a r e
c o m p le x i n t e r a c t i o n s w i t h t e m p e r a t u r e and h o rm o n e s (A l-A n i e t a l .
1972, Wooley and S t o l l e r 19,78).
26
L ig h t
e x e rts
a v a ria b le
in flu e n c e
on s e e d
g e rm in a tio n
of
s a g e b r u s h d e p e n d in g on t h e s p e c i e s and a s s o c i a t e d e n v i r o n m e n t a l
f a c t o r s . F r i n g e d s a g e w o r t ( A r t e m i s i a f r i a i d a W i l l c . ) show ed a l i g h t
r e q u i r e m e n t , b u t t h i s c o u ld be c i r c u m v e n t e d by t r e a t i n g s e e d w i t h
g i b b e r i l l i c a c i d (W ils o n I 982). Sabo e t a l . (1979) a s s e r t t h a t l i g h t
has no e f f e c t on g e rm in a tio n o f seed i n e i t h e r f r in g e d sag ew o rt or b ig
s a g e b r u s h . H owever, e v i d e n c e t o t h e c o n t r a r y h a s b e en p r e s e n t e d by
s e v e ra l re s e a rc h e r s th a t s t a t e th a t l i g h t s i g n i f i c a n t l y in c re a s e d
g e rm in a tio n by a s much as t h r e e tim e s i n b ig sagebrush (Weldon e t a l .
1959, B e e tle I960, C ald w ell 1978).
The g e rm in a tio n re sp o n se t h a t h a s been observed i n o th e r s p e c ie s
c l e a r l y d e m o n stra te s t h a t l i g h t can p lay a v a r i a b l e r o l e . I n Ira q , AlAni e t a l . (1972) r e p o r t e d a v a r i e t y o f r e a c t i o n s among 10 s p e c i e s
w i t h r e s p e c t to g e r m i n a t i o n r e q u i r e m e n t f o r l i g h t .
Two s p e c i e s
r e q u i r e d l i g h t , w h i l e s i x show ed no r e s p o n s e and tw o h a d t h e i r b e s t
g e r m in a tio n i n dark. L e ttu c e ,
a l i g h t s e n s i t i v e seed, d id n o t r e q u i r e
l i g h t a t t e m p e r a t u r e s below 20 C (W o o lle y and S t o l l e r 1978). Most
o th e r s t u d i e s of v a r io u s s p e c ie s show a re q u ire m e n t f o r l i g h t (W aller
e t a l . 1980, Mayeux and L e o tta 1981, Krueger and Shaner 1982).
Osmotic P o t e n t i a l
T h e re a r e a t l e a s t t h r e e s t a g e s o f t h e g e r m i n a t i o n p r o c e s s i n
w hich w a te r r e l a t i o n s h i p s a r e im p o r ta n t: (I) i m b i b i t i o n , (2) enzym atic
t r a n s f o r m a t i o n and m e r i s t e m a t i c a c t i v i t i e s , and (3) s t a r t o f growth
through e lo n g a t io n and emergence of th e r a d i c l e through th e seed coat.
A ll o f t h e s e a r e r e g u l a t e d by w a t e r u p t a k e fro m t h e s o i l o r s o i l
27
s o l u t i o n . W ater s t r e s s i s a n i m p o r t a n t v a r i a b l e t h a t c a n i n f l u e n c e
g e rm in a tio n resp o n se. Because of t h e d i f f i c u l t y i n m e a s u r i n g m a t r i c
p o te n tia l,
o s m o t i c p o t e n t i a l h a s u s u a l l y b een u s e d i n s o i l - w a t e r
s t u d i e s (E vans and Young 1982). H ow ever, m a t r i c p o t e n t i a l h a s b e en
found to be an im p o r ta n t f a c t o r i n seed g e rm in a tio n (C o llis-G e o rg e and
H ector 1966).
G erm ination r a t e s and t o t a l s c o n s i s t e n t l y d e c re a se w ith a d e c lin e
i n e x te r n a l w a te r p o t e n tia l.
Under t h e s e
c o n d itio n s,
e x c e ssiv e
t e m p e r a t u r e s and m o i s t u r e s t r e s s a r e u s u a ll y a d d i t i v e i n d e c re a s in g
g e rm in a tio n . Seeds, i n a w a te r s t r e s s s i t u a t i o n , a re p la c e d under
re la tiv e ly
m o re
stre ss
in
e x tre m e ly
warm o r c o o l i n c u b a t i o n
te m p e ra tu re s (Bewley and Black 1982, Evans and Young 1982).
In c re a se d w a te r
stre ss
e ith e r
d e la y s th e
c o m p le tio n of
g e rm in a tio n or red u ces g e rm in a tio n . This a ls o depends on th e v ig o r of
t h e s e e d . An a b i l i t y
t o g e r m i n a t e u n d e r s t r e s s may c o n f e r c e r t a i n
e c o lo g i c a l adv an tag es (Bewley and Black 1982). Parmar and Moore (1966)
showed t h a t re s p o n se s t o m o is tu r e s t r e s s d i f f e r e d between see d s o f low
and h i g h v i g o r , and t h e y s u g g e s t e d t h a t i n c r e a s e d o s m o t i c p o t e n t i a l
d e crea se d w a te r a b s o r p tio n , d is tu r b e d n u t r i e n t uptake, caused abnormal
m etabolism and u l t i m a t e l y reduced growth.
Big sag eb ru sh responded to more n e g a tiv e
l e s s t o t a l g e rm in a tio n ,
o sm otic p o t e n t i a l w ith
bu t t h i s c o n d itio n was a m e lio ra te d by l i g h t
(W eldon e t a l . I 959). I n c o n t r a s t , Sabo e t a l . (1979) r e p o r t e d l i t t l e
e f f e c t of o s m o tic p o t e n t i a l u n t i l 10 atm was reached. F rin g ed sagew ort
was much m ore s e n s i t i v e
re s p o n se s a t 2 atm.
th a n b ig sag e b ru sh
and show ed i n i t i a l
28
M atu rity of Seed
M a tu rity o f seed a l s o te n d s to have an e f f e c t on g e r m in a tio n w ith
h i g h e r v a l u e s b e i n g o b s e r v e d i n l a t e r s e e d c o l l e c t i o n s . Cl o r e t a l .
(1974) r e p o r te d t h a t A r te m is ia h e r b a - a l b a Asso r e a c t e d t h i s way,
and
b o th p r o s t r a t e s p u r g e and p r o s t r a t e k o c h i a ( K o o h ia n r o s t r a t a (L.)
Schrad.) showed h ig h e r g e rm in a tio n p e rc e n ta g e s when seed was c o l l e c t e d
l a t e r (W aller e t a l . 1980, Krueger and Shaner 1982).
E a rlv S e e d lin g Growth
Growth
c h a ra c te ris tic s
of
sagebrush
see d lin g s
seem, to
be
p r i m a r i l y s u b j e c t to g e n e ti c c o n tr o l alth o u g h en v iro n m e n ta l in f l u e n c e s
a ls o c o n t r i b u t e to s e e d lin g resp o n se (McArthur and Welch 1982). Among
b i g s a g e b r u s h a c c e s s i o n s and s u b s p e c i e s , g ro w th p a r a m e t e r s showed
s i g n i f i c a n t d i f f e r e n c e s i n e a c h m e a s u r e . H e ig h t, c ro w n , l e n g t h o f
l e a d e r s and a n n u a l y i e l d w e re among p a r a m e t e r s d i f f e r i n g b e tw e e n
a c c e s s io n s and s u b sp e c ie s .
Although seed p ro d u c tio n i s h ig h i n sagebrush, very few s e e d lin g s
em erg e and s u r v i v e . T h is can be a t t r i b u t e d t o am ount o f v e g e t a t i o n
p re se n t (c o m p e titio n ), l i t t e r ,
w a te r
stre ss
and d e p t h
of
a d v e r s e e n v i r o n m e n t a l f a c t o r s (eg.
b u ria l),
and a l l e l o p a t h y
(au to p a th y )
( J o h n s o n and Payne 1968, E v e r n a r i e t a l . 1971, F r ie d m a n and O rshan
1975, H a r n i s s and McDonough 1975, E d d lem a n 1979, Cook 1980, H arvey
1981, Evans and Young 1982, Wilson 1982). The maximum dep th from which
s a g e b r u s h s e e d w i l l e m erg e h a s b e e n e s t i m a t e d a t 5 mm by Harvey
(1 9 8 1 ). B u r i a l a t 2 mm w as c o n s i d e r e d an optim um d e p t h f o r p l a i n s
s i l v e r sagebrush.
Y e a rs t h a t a r e f a v o r a b l e f o r n a t u r a l
se e d lin g
29
e s ta b lis h m e n t can occur a t i r r e g u l a r i n t e r v a l s w ith th e p rim ary f a c t o r
b eing s o i l m o is tu re (Johnson and Payne 1968, Gordon and W right 1981).
However,
e s ta b lis h m e n t can be o f l i t t l e e c o lo g ic a l im p o rtan ce u n le s s
i t o c c u rs on h ig h ly d is tu r b e d a r e a s a c c o rd in g to Harvey (1981).
'
V e g e ta tiv e (A sexual) R eproduction
V e g e t a t i v e r e p r o d u c t i o n i n A r t e m i s i a has been examined s e v e r a l
tim e s ,
b u t few i n - d e p t h s t u d i e s h ave b een c o m p le te d . B o s to c k and
Benton (1979) s t u d ie d f i v e p e r e n n ia l co m p o sites w ith v a ry in g d eg rees
o f l a t e r a l , e x t e n s i o n and g ro w th . They s u b s e q u e n t l y r e l a t e d s e e d and
v e g e t a t i v e r e p r o d u c tiv e s t r a t e g i e s . Seed was g e n e r a lly more im p o r ta n t
th a n v e g e t a t i v e c a p a c ity . H ow ever, A r t e m i s i a v u l g a r i s L= p e r e n n a t e s
only by v e g e t a t i v e l y produced p ro p a g u le s,
and i t had rhizom e growth
measured a t 30 cm p e r y ear.
Went (1979) c o n t e n d s t h a t s u r v i v a l i n p e r e n n i a l d e s e r t p l a n t s
d e p e n d s m a i n l y upon a v e g e t a t i v e s t r a t e g y ,
and s e e d s a r e o n ly a
secondary method o f re p ro d u c tio n t h a t becomes im p o r ta n t when summer
r a i n s a l l o w a b u n d a n t g e r m i n a t i o n . C o n t r a d i c t o r y e v i d e n c e h a s b een
p r e s e n t e d i n a s t u d y by Young and E vans (1 9 7 2 ). They e x a m in e d g r e e n
r a b b i t b r u s h which was lo n g th o u g h t t o invade s i t e s by r o o t s p ro u tin g .
They d is c o v e re d t h a t i t r e l i e d h e a v il y on s e e d lin g s t o e s t a b l i s h new
p la n ts . T h erefo re, e i t h e r mechanism can be s u c c e s s f u l.
There a r e s p e c i a l problem s t h a t v e g e t a t i v e r e p r o d u c tio n p r e s e n ts
f o r t h e f i e l d and e x p e r i m e n t a l e c o l o g i s t . A braham son (1980) s t a t e s
th a t v e g e ta tiv e re p ro d u c tio n i s
m ore s i m i l a r t o g r o w th t h a n t o
r e p r o d u c tio n w ith co n fu sio n coming from u s in g a n im a ls a s models,
He
30
s t a t e s f u r t h e r t h a t v e g e t a t i v e r e p r o d u c t i o n i s a d i s t i n c t and w e l l d e fin e d phenomenon.
V e g e ta tiv e re p ro d u c tio n i s
common i n f o r e s t h e r b s ,
a q u a tic
p l a n t s , and a t h i g h e r l a t i t u d e s and a l t i t u d e s w h e re e c o s y s t e m s a r e
more i n f l u e n c e d by f i r e ,
c l i m a t i c and o t h e r d is tu r b a n c e s (Abrahamson
1980, Legere and P a y e tte 1981). A c lo n e i s d e fin e d a s th e a g g re g a te of
i n d iv id u a l o rganism s descended by a sex u al r e p ro d u c tio n from a s i n g l e
s e x u a l l y p ro d u c e d i n d i v i d u a l ( B a r n e s 1966).
Many p l a n t s i n su ch
d iv e r s e g e n era a s Oohioglossum. P te r id iu m , Populus, E quisetum * Carey,
Rhus. C o rn u s . P ru n u s and A r t e m i s i a fo rm c l o n e s by i n i t i a t i n g s h o o t s
from underground p a r t s . I t i s common f o r c lo n a l growth to be much more
p r e v a le n t th an sexual r e p r o d u c tio n i n s p i t e of th e f a c t t h a t t h e r e may
be a l a r g e and v i a b l e s e e d b a n k i n t h e s o i l ( E v e r n a r i e t a l . 1971»
H a z l e t t and Hoffman 1975,
Cook 1980, Harvey 1981, L o y e tt-D o u st 1981).
The d e g r e e t o w h ic h c l o n i n g p l a y s a r o l e i n some e c o s y s t e m s can be
q u i t e la r g e . I n F in la n d , 80 p e r c e n t of the an g io sperm v e g e t a t i o n i n a
l o c a l f l o r a had t h e c a p a c i t y t o c l o n e (A braham son 1 9 8 0 ), w h i l e i n
G reat B r i t a i n ,
t w o - t h i r d s of the common p e r e n n ia l s p e c ie s a re c lo n a l
(Cook 1983). Moreover,
th e most p e r n ic io u s weeds u s u a ll y become more
s e r io u s economic p e s t s p r e c i s e l y because they grow from underground
r o o t s , rhizom es and buds.
T m p n rta n ce
o f V e g e ta tiv e R eproduction
S ev eral
reasons
can re a s o n a b ly
e x p la in
why
v e g e ta tiv e
r e p r o d u c tio n i s of such im p o rta n c e . V e g e ta tiv e r e p r o d u c tio n a llo w s
s u r v i v a l of p e r e n n ia l p o ly p lo id s i n s p i t e o f t h e i r t y p i c a l l y i n f e r i o r
31
seed b eing l e s s a b le to s u c c e s s f u l l y e s t a b l i s h or m a in ta in v ig o r. In
a d d itio n ,
re p ro d u c tio n
te m p e ra tu re s
by s e e d :
th a n th o se
fo r
(I)
g e n e ra lly
v e g e ta tiv e
g r o w th ,
re q u ire s
h ig h e r
(2) s e e m s a t
d isa d v a n ta g e w ith r e s p e c t to e f f e c t i v e n e s s o f gene tr a n s m is s io n ,
a
and
(3) i s u s u a l l y i n c o m p e t i t i o n w i t h v e g e t a t i v e r e p r o d u c t i o n f o r t h e
sam e l i m i t e d r e s o u r c e s (A braham son 1980). When b o th m e th o d s o c c u r
s im u lta n e o u s ly , v e g e t a t i v e o f f s p r i n g w i l l commonly develop im m e d ia te ly
and q u ic k ly become a d u lt. This i s a p p a r e n tly accom plished w i t h l a r g e r
c a r b o h y d r a t e r e s e r v e s t h a n t h o s e i n d i v i d u a l s d e v e l o p i n g fro m s e e d .
Cloning seems to be a low r i s k mechanism f o r i n c r e a s i n g lo n g e v ity and
p e r e n n a t i o n o f t h e g e n e t . The g e n e t i s d e f i n e d a s a l l g e n e t i c a l l y
i d e n t i c a l members of a clone d e riv e d from a s i n g l e zygote (Cook 1983).
A braham son (1980) a l s o p r e d i c t s t h a t when p o p u la tio n d e n s i t y i s low
and c lo n a l e x p r e s s io n i s p o s s i b l e , v e g e t a t i v e r e p r o d u c t i o n w ould be
more advantageous because i t f a c i l i t a t e s l o c a l sp read and o c cu p a tio n
by th e g e n e t . H ow ever, when p l a n t d e n s i t y i s h i g h ,
b e tte r.
s e e d s w ould be
Seed s f a c i l i t a t e d i s p e r s a l t o new s i t e s t h a t may be l e s s
d en sely p o p u lated and t h e r e f o r e m ore f a v o r a b l e f o r s e e d l i n g g ro w th .
L i f e e x p e c t a n c y o f p l a n t s r e g e n e r a t i n g from seed i s f r e q u e n t l y l e s s
t h a n t h a t o f v e g e t a t i v e l y p ro d u c e d p l a n t s (A braham son 1980,
Cook
1979). This h a s been a t t r i b u t e d t o more in t e n s e c o m p e titiv e s t r e s s f o r
l i g h t and o t h e r re s o u rc e s .
Cook (1983) r e i t e r a t e s t h e b e l i e f t h a t n o th in g i n b io lo g r makes
sense e x c e p t i n l i g h t of e v o lu tio n . He f u r t h e r s t a t e s t h a t b e n e f i t s of
c lo n a l r e p ro d u c tio n i n c lu d e :
(I) an enhanced a b i l i t y to u t i l i z e sc a rc e
r e s o u r c e s , (2) g r e a t e r c o m p e titiv e a b i l i t y both to in v ad e o t h e r c lo n e s
32
and t o r e s i s t i n v a s i o n o f s e e d l i n g s , and (3) r e d u c e d p r o b a b i l i t y o f
g en et e x t i n c t i o n by s p re a d in g r i s k among a number o f i n d i v i d u a l s .
C h a r a c t e r i s t i c s o f V e g e ta tiv e R eproduction
P o p u la tio n s of i n d i v i d u a l g e n e ts can ex ten d over a l a r g e a r e a and
can a t t a i n s u b s t a n t i a l ages. Shrubs pose s p e c i a l demographic problem s
i n t h a t age s t r u c t u r e of aboveground s h o o ts may d iv e rg e s h a rp ly from
t h a t o f belowground p a r t s (Fernandez and C aldw ell 1975,
N oble
et
a l.
1979).
Demography o f
c lo n a l
Harper 1977,
sh ru b s i s •u l t i m a t e l y
d e t e r m i n e d by t h e m o rp h o lo g y o f t h e g r o w th s y s te m and w i l l h av e a
c o m p le x ag e s t r u c t u r e .
Thus,
rh iz o m e a g e s w i l l u s u a l l y be q u i t e
d i f f e r e n t t h a n t h a t o f a e r i a l s h o o t s , and t h e a g e s o f buds w i l l be
d i f f e r e n t fro m t h a t o f e i t h e r r h i z o m e s o r s h o o t s . H a rb e r d (1967)
r e p o r te d on one l a r g e p o p u la tio n o f Holous m o l l i s L. t h a t c o n s is te d o f
only f o u r genotypes. One of th e genotypes was 1/2 m ile (0.8 km) wide.
Comparable a n a l y s i s o f sh ee p 's fe s c u e (F estu c a ov in a L.) r e v e a le d one
genotype t h a t was c o n sid e re d to be over 1000 y e a r s old (Harberd 1962).
A spens (P o o u lu s t r e m u l o i d e s M ich x .) h av e b e e n r e c o g n i z e d f o r t h e i r
c lo n a l
n a tu re
a n d c a n c o v e r 43 h e c t a r e s
w ith
4 7 ,0 0 0
ra m e ts
( in d i v id u a ls ) (Kemperman and Barnes 1976). They f r e q u e n tly a t t a i n very
g r e a t ag e (>10000 y e a r s ) . C r e o s o t e b u sh ( L a r r e a t r i d e n t a t a (S es. &
Hoc.
Exdc.) Cov.) i n t h e M ojave D e s e r t c lo n e by i r r e g u l a r r a d i a l
g r o w th on o u t e r e d g e s o f stem s e g m e n ts (V asek 1980). They h av e b een
e s t i m a t e d t o r e a c h a g e s o f a l m o s t 12000 y e a r s .
L o n g e v ity o f t h e
rh iz o m e s y s te m can be a s l o n g a s t h e l i f e o f th e g e n e t , a s i n san d
sedge
(C a re x a r e i i a r i a
L.) (N oble e t
a l.
1 9 7 9 ),
or rh iz o m e s
can
r
33
d i s i n t e g r a t e a f t e r e s ta b lis h m e n t o f d a u g h ter p l a n t s w ith independent
r o o t s y s t e m s ( L o v e t t - D o u s t 1981).
The m ere p r e s e n c e o f p h y s i c a l
c o n n e c tio n s
o ffsp rin g i s in s u ffic ie n t for
b e tw e e n v e g e t a t i v e
d e m o n s tra tin g p h y s io lo g ic a l in te rd e p e n d e n c e (Ashmun e t a l . 1982).
The o c c u p a t i o n o f h o r i z o n t a l s p a c e , c h a r a c t e r i s t i c o f c l o n a l
grow th ( I t o e t a l . 1976, Noble e t a l . 1979, Cook 1983), may be g r e a t l y
a f f e c t e d by p h y s i c a l f e a t u r e s o f t h e h a b i t a t . The s u c c e s s o f o f t h e
clo n e i s
g re a tly
g ra d a tio n s,
(2)
in c re a s e d
by:
in itia tio n
e s ta b lis h m e n t of new sh o o ts.
(I)
of
c a p a c ity
to
a d v e n titio u s
d e te c t
ro o ts,
n u trie n t
and
(3)
This c lo n a l c a p a c ity seems to overcome
l i m i t i n g a s p e c t s o f th e s o i l and c o m p e t itiv e i n f l u e n c e s (Noble e t a l .
1979,
Cook 1983). S to rag e o f c a rb o h y d ra te s i n a p e r e n n ia l rhizome h a s
been noted a s advantageous to r a p i d development and s u r v i v a l o f c lo n es
(Ashmun e t a l . 1982). Rhizome f o r m a tio n o f mugwort was observed from
A p ril to May i n Jap an w ith l a t e r a l e x te n s io n b eing 5.4 m e te rs ( I to e t
a l . 1976). Endogenous hormones have been r e l a t e d to s t o l o n development
w i t h g i b b e r i l l i c a c i d s t i m u l a t i n g s t o l o n e l o n g a t i o n and c y t o k i n i n
i n i t i a t i n g l e a f y s h o o t d e v e lo p m e n t fro m s t o l o n s (Kumar and W a re in g
1972). S i l v e r sagebrush p u t t i n g s r o o t e a s i l y w i t h i n e i g h t weeks when
c o l l e c t e d a t th e l e a f grow th p h o n o lo g ic a l s ta g e ( E v e r e tt,
Meeuwig and
R obertson 1978).
F a c to rs th a t s tim u la te v e g e ta tiv e re p ro d u c tio n a re general in
n a t u r e (A braham son I 980). S o i l m o i s t u r e can p ro m o te e i t h e r m eans o f
re p ro d u c tio n .
In creased
s o il
m o i s t u r e w as show n t o
favor
seed
r e p r o d u c t i o n i n w i l d g a r l i c ( A lli u m c a r i n a t u m L.) ( S a l i s b u r y 1942).
L i t t l e s e e d w as s e t i n a w e t summer by tw o o t h e r s p e c i e s , y e llo w
34
d e a d n e t t l e Cfialeobdolon JLuteum Hudson) and blue gromwell (Lithosnermum
-RUiJ.Rureor-coeraleum L.), each o f w h ic h w as r e p r o d u c i n g v i g o r o u s l y by
v e g e t a t i v e m eans. S o i l t e x t u r e i n f l u e n c e s w hat s t r a t e g y i s fav o re d ,
w ith c la y c o n te n t u s u a lly f a v o r in g v e g e t a t i v e r e p ro d u c tio n (Abrahamson
1980). I n c r e a s i n g l i t t e r d e c r e a s e d t h e s u c c e s s o f c l o n i n g , w h i l e
in c r e a s e d e n v iro n m e n ta l s e v e r i t y a c c e n tu a te d v e g e t a t i v e re p ro d u c tio n .
Methods w ere designed to examine c e r t a i n r e p r o d u c tiv e s t r a t e g i e s
in
p la in s
silv e r
sagebrush
w ith
re s u lts
fro m
th is
lite ra tu re
e x am in atio n i n mind. S p e c i f i c a l l y , e x p erim en ts d e a li n g w ith d i s p e r s a l ,
g e r m in a tio n f a c t o r s , e a r l y s e e d lin g grow th and v e g e t a t i v e r e p ro d u c tio n
were implemented.
35
METHODS AND SITE DESCRIPTIONS ■
I n tr o d u c ti o n
This p r o j e c t was conducted a t th e F o r t Keogh L iv e s to c k and Range
Research L a b o ra to ry n ear M iles C i t y i n s o u t h e a s t M ontana. F i e l d w o r k
w as i n i t i a t e d i n J u n e o f 1982 and c o m p l e t e d i n O c to b e r 1983. The
s t a t i o n h as a v a r i e t y o f range s i t e s and topography r e p r e s e n t a t i v e of
much o f t h e N o r t h e r n G r e a t P l a i n s (J o h n s o n I 978). T o pography r a n g e s
from rough b re a k s to a l l u v i a l f l o o d p l a i n s and t e r r a c e s . Land form s a re
i n t e r s e c t e d by numerous i n t e r m i t t e n t stre am ch an n e ls where s u b s t a n t i a l
p o p u la tio n s o f p l a i n s s i l v e r sagebrush e x i s t .
The c l i m a t e i s f a i r l y t y p i c a l o f th e N o rth ern G re at P la in s w ith
d r o u g h t p l a y i n g a s u b s t a n t i a l r o l e ( J o h n s o n 1978). A v erag e a n n u a l
p r e c i p i t a t i o n a t M iles C ity f o r th e p e rio d 1878-1981 h as been 34.29 cm
(13.5 in ). D e v ia tio n s from t h i s average can be extrem e a s evidenced by
h i s t o r i c maximums and minimums: 57.9 cm (22.8 in ) i n 1879 and 14.0 cm.
(5.5 i n ) i n
1934,
re sp e c tiv e ly .
P re c ip ita tio n
w as
below
n o rm a l
p r e c e d i n g t h i s s t u d y w i t h 1979, 1980 and 1981 r e c e i v i n g 22.1 cm (8.7
in ),
26.7 cm (10.5 i n )
p re c ip ita tio n
and 26.9 cm (10.6 i n ) ,
and t e m p e r a t u r e d a t a f o r
1981 ,
re sp e c tiv e ly .
The
1982 and 1983 a r e
summarized by month i n Appendix A. Data f o r 1981 was in c lu d e d because
O lso n (1982) fo u n d t h a t p r e c i p i t a t i o n fr o m t h e p r e v i o u s y e a r w as
im p o rta n t i n d e te rm in in g su b seq u en t v e g e t a t i o n re s p o n se .
F o u r d i s t i n c t a s p e c t s o f s a g e b r u s h r e p r o d u c t i o n w e r e e x am in ed
d u r i n g t h e c o u r s e o f my r e s e a r c h . They i n c l u d e d : s e e d d i s p e r s a l ,
36
g e rm in a tio n ,
s e e d lin g development and a se x u a l re p ro d u c tio n . D is p e r s a l
c h a r a c t e r i s t i c s w e re m e a s u re d i n f i e l d
p o p u la tio n s.
G erm in a tio n
f a c t o r s w e re o b s e r v e d i n g r o w th c h a m b e rs . E m erg en ce, g r o w th and
s u r v i v a l p a ra m e te rs were d i f f e r e n t i a t e d i n f i e l d ,
g reenhouse s tu d ie s . • F i n a l l y ,
grow th chamber and
f i e l d e x c a v a t i o n s w e r e c o n d u c te d t o
e v a lu a te th e r e l a t i v e im portance o f v e g e t a t i v e r e p r o d u c tio n .
Seed D is p e r s a l
T h ree s t u d y s i t e s w e re s e l e c t e d i n t h e f a l l o f I 982 t o e v a l u a t e
seed d i s p e r s a l i n p l a i n s s i l v e r sagebrush. These s i t e s w ere t y p i c a l of
p l a i n s s i l v e r sa g e b ru sh c o m m u n ities th ro u g h o u t th e N o rth e rn G reat
P l a i n s . They w e re l o c a t e d so a s t o a l l o w e a s y a c c e s s d u r i n g t h e l a t e
f a l l and e a r l y w in te r . These th r e e p a s t u r e s a r e r e f e r r e d t o l o c a l l y a s
Paddy Faye, Lower Flood and Lower Black S p rin g s.
S i t e D e s c r ip tio n s
P ad d y
Faye
is
an
a llu v ia l
b o tto m la n d
th a t
is
lo c a te d
a p p ro x im a te ly 11 km s o u th e a s t of s t a t i o n h e a d q u a rte rs and a d ja c e n t to
t h e Tongue R i v e r . The p a s t u r e i s i n t e r s e c t e d
by an i n t e r m i t t e n t
d r a i n a g e , Paddy Faye C reek. P l a i n s s i l v e r s a g e b r u s h i s a p r o m i n e n t
v e g e t a t i v e c h a r a c t e r i s t i c o f Paddy Faye, but p la n t d e n s i t y ran g es from
s p a r s e to dense.
U nderstory v e g e t a t i o n c o n s i s t s o f g re e n n e e d le g ra s s
(J S tip a V i r i d u l a T r i n . ) ,
b u f f a l o g r a s s (B u c h lo e d a c t v l o i d e s ( N u tt.)
E n g e lm .),
( B o u te lo u a
b lu e
gram a
g ra c ilis
(H.B.K.)
L a g .)
and
c o n s i d e r a b l e w e s t e r n w h e a t g r a s s (Agroovron s m i t h i i Rydb). In tro d u ce d
37
sp e c ie s
in c lu d e
Japanese
b ro m e
( B r o mus
i a p o n i c u s Thunb.) and
c h e a tg r a s s (Bromus te cto ru m L„).
■ S o ils i n Paddy Faye a r e p r e d o m i n a n t l y Kobar s i l t y c l a y lo a m s.
Kobar s i l t y
c l a y lo a m s a r e c l a s s i f i e d a s f i n e ,
m o n tm o rillo n itic
B o r o l l i c Camborthids. They a r e deep, w e ll- d r a in e d , n e a r ly l e v e l s o i l s
th a t
are
fo r m e d
in
allu v iu m .
The
so ils
have
m o d e ra te ly
slow
T-
p e rm e a b ility
and h i g h a v a i l a b l e w a t e r c a p a c i t y .
A v a ila b le w a te r
c a p a c i t y i s t h e am ount o f w a t e r c a p a b l e o f b e in g s t o r e d i n th e s o i l
p r o f i l e . The range s i t e i s c l a s s i f i e d a s clay ey and i s l o c a t e d i n th e
25 to 36 cm (10-14 in ) p r e c i p i t a t i o n zone. Paddy Faye h a s a h ig h w a te r
t a b l e u n d e rly in g much o f th e p a s tu re .
Paddy F ay e h a s had a l o n g h i s t o r y o f h eavy g r a z i n g u s e . D u rin g
e a r l y s e t t l e m e n t i t w as s i t u a t e d a l o n g t h e Tongue R i v e r T r a i l . As
such,
i t r e c e iv e d co n tin u o u s,
s e a s o n -lo n g g ra z in g by la r g e l i v e s t o c k
h erds. More r e c e n t l y t h i s p a s tu r e has been used d u rin g th e summer a s a
b re e d in g p a s tu r e .
B ecau se o f d r o u g h t c o n d i t i o n s and a "change i n
g r a z i n g m an ag em en t, t h e s t u d y s i t e had n o t been g r a z e d f o r t h e p a s t
f i v e y e a r s p r i o r to t h i s s tu d y .
Lower F lo o d P a s t u r e i s an a l l u v i a l f l o o d p l a i n a d j a c e n t t o t h e
Tongue R iv e r and l o c a t e d 7 -9 km s o u t h e a s t o f s t a t i o n h e a d q u a r t e r s .
V e g e ta tio n i s s i m i l a r to t h a t o f Paddy Faye. P la in s s i l v e r sagebrush
i s the dominant shrub s p e c ie s p re s e n t.
stan d s w ith w e ste rn w h e a tg ra ss,
I t i s found i n s p a r s e to dense
g r e e n n e e d l e g r a s s , . b l u e g ram a,
b u f f a lo g r a s s , Jap an ese brome and c h e a tg r a s s c o n s t i t u t i n g most of the
u n d e rsto ry .
The p r i n c i p l e s o i l s fo u n d i n Low er F lo o d a r e H arlem
V a r i a n t s i l t y c l a y s . They a r e c l a s s i f i e d a s f i n e , m o n t m o r i l l o n i t i c
38
B o r o l l i c C a m b o rth id s . P e r m e a b i l i t y i s slo w w h i l e a v a i l a b l e w a t e r
c a p a c i t y i s h ig h . These d e e p , w e l l - d r a i n e d , a l l u v i a l s o i l s a r e b e s t
d e s c rib e d a s clay ey range s i t e s .
Grazing i n Lower Flood h a s t r a d i t i o n a l l y been imposed during- th e
s p r in g and e a r l y summer. Grazing b e g in s every y e a r a t c a lv in g (e a r ly
A p r i l ) and c o n t i n u e s th r o u g h t h e e a r l y
season w ith i n t e r m i t t e n t
g ra z in g d u rin g the summer.
The Lower Black S p rin g s stu d y s i t e i s r e p r e s e n te d by a sm a ll a re a
on a t e r r a c e o f t h e Y e l l o w s t o n e R iv e r a p p r o x i m a t e l y 6.5 km w e s t o f
s t a t i o n h e a d q u a r t e r s . A lth o u g h h e r b a c e o u s v e g e t a t i o n f o r t h i s s i t e
w o u ld n o r m a l l y be w e s t e r n w h e a t g r a s s and a s s o c i a t e d s p e c i e s , i t i s
c u r r e n t l y occupied by c r e s t e d w h e a tg ra s s (Agroovron c r i s t a t u m (L.) P.
G a ertn.) t h a t was seeded s e v e r a l y e a r s ago.
of p la in s
silv e r
s a g e b r u s h d o m i n a t e s t h i s a r e a w i t h g re a s e w o o d
CS a r c o b a t u s v e r m i c u l a t u s
in te rsp erse d .
A m o d e ra tely dense stan d
(H o o k .)
J.
T o rr.)
b e in g o c c a s io n a ll y
C rested w h e a tg ra s s i s th e m ajor u n d e rs to ry c o n s t i t u e n t .
H a v re-V arian t loam s a r e th e common s o i l found i n Lower B lack Springs.
It
is
a deep,
w e ll-d ra in e d
s o il
fo rm e d i n
allu v iu m .
M o d e ra te
p e rm e a b lity and high a v a i l a b l e w a t e r c a p a c i t y a r e c h a r a c t e r i s t i c o f
t h i s fin e -lo a m ,
m ixed ( c a l c a r e o u s ) f r i g i d U s t i c T o r r i f l u v e n t . The
range s i t e i s c o n sid e re d a s s i l t y . Use by g ra z in g c a t t l e t r a d i t i o n a l l y
h as been a s a b re e d in g p a s t u r e i n th e summer.
Experim ental Methods
F iv e p l a n t s w e re s e l e c t e d i n e a c h o f t h e t h r e e s t u d y s i t e s and
marked f o r seed d i s p e r s a l measurements.
The sh ru b s were s e l e c t e d to
39
ty p ify
th e
c o m m u n ity .
average
a d u lt
In a d d itio n ,
(seed
care
b e a rin g )
w as t a k e n
siz e
to
stru c tu re
se le c t
of
p la n ts
th e
w ith
s u f f i c i e n t a r e a a ro u n d them t o a c c o m o d a te s i x u n o b s t r u c t e d l i n e
t r a n s e c t s f o r m o n ito rin g d i s p e r s a l .
All seedheads were removed from
a d ja c e n t sagebrush p l a n t s w i t h i n a 10 m r a d iu s o f th e marked sh ru b s to
e l i m i n a t e t h e i r in f l u e n c e on th e d i s p e r s a l measurements. Six permanent
l i n e t r a n s e c t s w e re t h e n e s t a b l i s h e d i n a r a d i a l f a s h i o n fro m t h e
c e n te r of each marked shrub. T ra n s e c ts were o r ie n te d so t h a t one l i n e
la y alo n g th e p r e v a i l i n g wind d i r e c t i o n . The o th e r f i v e t r a n s e c t s were
e q u a lly spaced a t 60 degree a n g le s from one a n o th e r around the c e n t r a l
s h r u b . Aluminum s h e e t - m e t a l p l a t e s (36x36 cm) w ere a n c h o r e d t o t h e
g ro u n d a t one m e t e r i n t e r v a l s ( 0 , 1 , 2 , 3 and 4 m) a l o n g e a c h t r a n s e c t
( F i g u r e 2 ).
F i g u r e 2. D i s p e r s a l s tu d y l a y o u t w i t h s i x t r a n s e c t s a t e q u a l a n g l e s
(60 d e g r e e s ) s u r r o u n d i n g th e c e n t r a l s h r u b . F iv e s p a c e d
( a t 0 , 1 , 2 , 3 m) p l a t e s w e re f o r c o l l e c t i o n o f d i s p e r s e d
seed i n each t r a n s e c t .
40
Each p l a t e ( F i g u r e 2) was c o a t e d w i t h an a d h e s i v e ( p e t r o l e u m
j e l l y ) i n o r d e r to c a t c h i n d i v i d u a l s e e d s a s th e y f e l l . T h is s p a t i a l
arrangem ent a llo w e d f o r an i n v e s t i g a t i o n o f wind e f f e c t .
Seeds t h a t
dropped on the p l a t e s were c o l l e c t e d and counted through th e November
d i s p e r s a l p e rio d . Sample c o l l e c t i o n s w ere r e p e a te d ev ery 3 or 4 days.
An o n g o in g r e c o r d w a s m a i n t a i n e d on n u m b e rs and t i m i n g o f s e e d
d i s p e r s a l i n r e l a t i o n to d is ta n c e and d i r e c t i o n from th e p a re n t plant".
New a d h e s i v e w a s r e a p p l i e d a s n e ed e d a f t e r e a c h c o l l e c t i o n .
A p p lic a tio n was accom plished by h e a ti n g t h e p etroleum j e l l y u n t i l i t
m e l t e d i n a 0.47 l i t e r m e t a l p a i n t can. A p o r t a b l e , w h i t e - g a s camp
s to v e was used f o r t h i s purpose i n th e f i e l d . L iq u id p e tro le u m j e l l y
was th e n e i t h e r r o l l e d or brushed onto th e aluminum p l a t e s depending
on a i r
te m p e ra tu re .
Use o f t h e r o l l e r w as m o st e f f e c t i v e i f a i r
te m p e ra tu re s w ere below 10 C, and th e b ru sh was most e f f e c t i v e above
t h i s te m p e ra tu re .
This method was used s u c c e s s iv e ly a t te m p e ra tu re s
r a n g i n g fro m - 1 8 t o 25 C. P r e c i p i t a t i o n o ecu r i n g d u r i n g t h e s tu d y
p e rio d had no ad v erse e f f e c t .
Counting was han d led i n two ways. I f th e number of. seeds was low
and c o u ld be c o u n te d q u i c k l y ,
th e y w e r e t a l l i e d i n t h e f i e l d and
d is c a rd e d . However, i f seeds w ere to o numerous t o be r e a d i l y counted,
t h e y w e re c o l l e c t e d f o r l a t e r
e n u m eratio n .
A p a in t
e m p lo y e d t o c o l l e c t t h e m i x t u r e o f p e t r o l e u m j e l l y ,
s c r a p e r w as
s e e d s and any
a d d i t i o n a l m a t e r i a l such a s le a v e s . This m ix tu re was th en p laced i n a
sh allo w -sid e d ,
d isp o sa b le
s e p a r a t i o n i n th e l a b o r a t o r y .
a lu m in u m
pan (22x15x3 cm)
fo r
la te r
41
Seeds w ere s e p a ra te d from th e p etro leu m j e l l y ■by f i r s t - p la c in g
th e s o l i d i f i e d
m i x t u r e on f o u r l a y e r s
of c h ee sec lo th
t h a t w e re
s t r e t c h e d and s t a p l e d over th e aluminum pans. Pans w ere th e n placed i n
a 100 degree oven u n t i l the p etro leu m j e l l y m elted.
This r e s u l t e d i n
l a t e r a l s p r e a d i n g o f t h e m i x t u r e , l e a v i n g s e e d s s p r e a d o u t on t h e
c h e e s e c lo th and the p e tro le u m j e l l y i n the pan below. Seeds could then
be e a s i l y counted and re c o rd e d .
I
S t a t i s t i c a l A n aly sis
Seed d i s p e r s a l was analy zed w ith a s p l i t - s p l i t p l o t d e sig n w ith
d a te b eing a c o v a r ia n t (see Appendix B). Because seed c o u n ts on p l o t s
a t t h e 4 m d i s t a n c e c o n t a i n e d many z e r o v a l u e s , t h i s d i s t a n c e was
d is re g a r d e d i n the a n a ly s is . Mean s e p a r a t i o n t e s t s f o r a l l f a c t o r s and
c o m b in atio n s w ere e v a lu a te d w ith S tu d en t t - s t a t i s t i c s .
'
Germination
G erm ination s u c c e ss o f p l a i n s s i l v e r sagebrush was examined i n
r e l a t i o n to f i v e d i f f e r e n t f a c t o r s t h a t have been w id e ly r e p o r te d to
a f f e c t seed g e rm in a tio n . The f i v e f a c t o r s w ere s tu d ie d c o n c u r re n tly so
t h a t the e f f e c t s of an i n d i v i d u a l f a c t o r could be examined along w ith
a s s o c i a t e d i n t e r a c t i o n s . A lth o u g h one o r two f a c t o r s a r e commonly
e v a lu a te d i n g e rm in a tio n re s e a r c h , s t u d i e s o f t h i s m agnitude (ie . f i v e
f a c t o r s ) a r e seld o m r e p o r t e d i n t h e l i t e r a t u r e . None h a v e i n v o l v e d
p l a i n s s i l v e r sag eb ru sh .
42
Methods
The f i v e f a c t o r s ( tr e a tm e n ts ) c o n sid e re d i n t h i s stu d y were:
d a te
of
seed
te m p e ra tu re ,
c o lle c tio n ,
(2)
(4) l i g h t / d a r k ,
stra tific a tio n
(p re c h illin g ),
and (5) o s m o t i c p o t e n t i a l .
(I)
(3)
Seed w as
g a t h e r e d fro m t h e Low er B la c k S p r i n g s s t u d y s i t e on t h r e e o c c a s i o n s
d u r i n g t h e d i s p e r s a l p e r i o d . The f i r s t s e e d c o l l e c t i o n w as made i n
l a t e O ctober j u s t a f t e r d i s p e r s a l s t a r t e d .
The second c o l l e c t i o n was
made i n l a t e November, and t h e f i n a l one took p la c e i n e a r l y January.
The m eth o d t h a t w as u s e d to c o l l e c t
seeds in v o lv e d s t r i k i n g
th e
i n f l o r e s c e n c e b ran ch es so t h a t seeds would f a l l i n t o a paper sack t h a t
was h e ld a lo n g sid e . This te c h n iq u e r e s u l t e d i n a l a r g e p r o p o r tio n of
m ature seeds.
A t o t a l of 15 to 25 p l a n t s w ere c o l l e c t e d
from i n t h i s
f a s h io n a t each c o l l e c t i o n d a te . Seeds were pooled to e n su re adequate
numbers o f f i l l e d se e d s ,
to p ro v id e a r e p r e s e n t a t i v e sam ple of seeds
from th e p la n t p o p u la tio n ,
and to re d u c e th e e f f e c t s o f s e m i - s t e r i l e
in d iv id u als.
A fte r each c o l l e c t i o n ,
f i l l e d seed s w ere h a n d -s e p a ra te d
from le a v e s ,
f l o r a l b r a c t s and u n f i l l e d seed.
Seeds from each c o l l e c t i o n were su b d iv id ed i n t o groups o f 50 so
t h a t i n d i v i d u a l tr e a tm e n t c o m b in atio n s could be imposed and e v alu a te d .
Each g ro u p o f s e e d s w as t h e n e x p o s e d t o d i f f e r e n t c o m b i n a t i o n s o f
s tra tific a tio n ,
lig h t,
te m p e ra tu re or o sm o tic p o t e n t i a l f o r each
c o l l e c t i o n d a te . All t r e a t m e n t s w ere r e p l i c a t e d t h r e e tim e s . Seed was
c o n sid e re d g erm in ated when r a d i c l e s had emerged and ach ie v e d a le n g th
o f a t l e a s t 3 mm.
A f t e r h a l f t h e g r o u p s o f s e e d s h ad u n d e rg o n e a s t r a t i f i c a t i o n
tr e a tm e n t, a l l groups were p laced i n p e t r i d is h e s h av in g two p ie c e s of
43
No. 3 Whatman f i l t e r paper. The paper was m o isten ed w ith one of f o u r
o s m o t i c s o l u t i o n s (0 ,2 .5 ,5 .0 ,7 * 5 b a r s ) . Each p e t r i d i s h w a s e i t h e r
op en t o ' l i g h t o r w ra p p e d i n alu m in u m f o i l f o r a d a r k t r e a t m e n t and
th e n p la ce d i n one of th re e grow th chambers s e t a t i n d i v i d u a l c o n s ta n t
te m p e ra tu re s (1 0 ,2 0 ,3 0 C).
G erm ination co u n ts w ere made f o r 21 days on seeds i n every p e t r i
d i s h f o r each seed c o l l e c t i o n , A fte r 21 days, c o u n ts were d is c o n tin u e d
on th o se p e t r i d is h e s i n which no new g e rm in a tio n had occured d u rin g
th e
p re v io u s
seven days.
When d i s h e s
c o n ta in e d
seeds
th a t
had
g e rm in a te d w i t h i n t h e p re v io u s seven days, co u n ts w ere c o n tin u ed u n t i l
a p e r i o d o f s e v e n c o n s e c u t i v e d a y s o f no g e r m i n a t i o n o c c u r e d . A few
i n d i v i d u a l s e e d s g e r m i n a t e d up t o 45 d a y s a f t e r i n c e p t i o n o f t h e
g e rm in a tio n t r i a l s .
S t r a t i f i c a t i o n w a s a c h i e v e d by p l a c i n g h a l f o f t h e g r o u p s o f
s e e d s i n c o l d s t o r a g e o f - 2 3 C f o r 30 d a y s. The n o n - s t r a t i f i e d s e e d s
w ere kep t a t room te m p e ra tu re of 18 to 21 C (65 to 75 F). The 50 seeds
i n e ac h g ro u p w e re t h e n p l a c e d i n th e p e t r i d i s h e s h a v i n g m o i s t e n e d
f i l t e r paper w ith th e f o u r osm otic s o l u t i o n s .
The f o u r c o n c e n tr a tio n s (0,2.5,5.0,7.5 b a rs) of o sm o tic s o l u t i o n s
w ere achieved
by u s in g p o ly e th y le n e g ly c o l (PEG-6000) a s a s o lu te i n
d i s t i l l e d w a te r. PEG-6000 s o l u t i o n s have been w id e ly used to provide
a c c u r a te o sm o tic c o n c e n t r a t i o n s ; and because o f chem ical i n e r t n e s s , i t
may be s u p e r i o r to o t h e r commonly u s e d s o l u t e s s u c h a s d - m a n n i t o l
(W eldon e t a l . 1957, P a rm a r and Moore 1966, Sabo e t a l . 1979, B e r k a t
and B r i s k e
1981, W ils o n 1982).. The am ount o f PEG-6000 n e ed ed to
s i m u l a t e d i f f e r e n t o s m o t i c p o t e n t i a l s w e re a d j u s t e d f o r t h e t h r e e
d iffe re n t
te m p e ra tu re s u sin g th e s ta n d a rd fo rm u la p re se n te d
by
H elm rick and P f e i f e r (1954). ■
T h ree g r o w th c h a m b e rs w e re u s e d t o
c o n tro l
th e f a c t o r s of
t e m p e r a t u r e and l i g h t . Each g r o w th c h a m b e r was s e t a t one o f t h r e e
c o n s ta n t te m p e r a tu r e s : 10, 20, and 30 C. The p e t r i d is h e s w ere placed
i n th e c h a m b e rs w i t h h a l f o f them e x p o s e d to b o th i n c a n d e s c e n t and
flu o resc en t lig h t.
The o th e r h a l f w ere wrapped i n aluminum f o i l f o r a
com plete dark regim e. The seed s i n the d ark regim e were counted under
u l t r a v i o l e t (UV) l i g h t .
S t a t i s t i c a l A n a ly sis
Two g e r m i n a t i o n r e s p o n s e s ( t o t a l and r a t e ) w e re a n a l y z e d t o
d e te rm in e th e r e l a t i v e im p o rtan ce o f i n d i v i d u a l f a c t o r s . A f i v e f a c t o r
(3x2x2x3x4) f a c t o r i a l d e sig n w ith t h r e e r e p l i c a t i o n s was employed to
a n aly ze t o t a l g e rm in a tio n p e rc e n ta g e s. A n a ly sis of v a r ia n c e was ru n to
d e t e r m i n e t h e s i g n i f i c a n c e o f m a in e f f e c t s and i n t e r a c t i o n s ( s e e
A pp en d ix C).
When s i g n i f i c a n t F v a l u e s w e re o b t a i n e d ,
D u n can 's
m u l t i p l e r a n g e t e s t w as u s e d t o s e p a r a t e m eans and d e t e r m i n e w h e re
d i f f e r e n c e s i n means occured. R ates o f g e rm in a tio n w ere e v a lu a te d by
g ra p h ic methods.
G erm ination p e rc e n ta g e s from i n d i v i d u a l days d u rin g
th e g e r m in a tio n t r i a l s w ere p l o t t e d a g a i n s t s i n g l e f a c t o r s ,
te m p e ra tu re ,
such as
and c o m b in atio n s o f f a c t o r s found to be s i g n i f i c a n t i n
t h e f a c t o r i a l a n a l y s i s . S t u d e n t t - s t a t i s t i c s w e re r u n t o e v a l u a t e
s i g n i f i c a n c e on i n d i v i d u a l days.
45
E a rly S e e d lin g Growhh
S e e d l i n g e m e rg e n c e , g r o w th and s u r v i v a l w e re i n v e s t i g a t e d i n
th r e e d i f f e r e n t s tu d ie s .
g r o w th
c h a m b e rs
to
One study u t i l i z e d t r a n s p l a n t e d s e e d lin g s i n
d e lin ia te
th e
e ffe cts
of
d iffe re n t
d iu rn a l
t e m p e r a t u r e s on g ro w th . A se c o n d s t u d y i n v o l v e d f a l l s e e d i n g i n t h e
f i e l d w ith subsequent m easurements on emergence, grow th and s u r v iv a l
d u r i n g t h e f o l l o w i n g g r o w in g s e a s o n . The t h i r d s t u d y c o n s i s t e d o f
greenhouse work i n which emergence, grow th and s u r v i v a l w ere observed
under more c o n t r o l l e d c irc u m stan c es th a n th e f i e l d stu d y would be.
The f i r s t study was i n i t i a t e d to e v a lu a te th e e f f e c t o f d i f f e r e n t
t e m p e r a t u r e r e g i m e s on e a r l y g r o w th o f s e e d l i n g s u n d e r c o n t r o l l e d
c o n d i t i o n s . The se c o n d s t u d y w as t o a s c e r t a i n e m e r g e n c e , g r o w th and
su rv iv a l
of
s e e d lin g s
in
th e
fie ld
p la n te d
at
fo u r
d e p th s.
( 0 ,0 .5 * 1.5 ,2 .5 cm) and u n d e r d i f f e r e n t m o i s t u r e r e g i m e s . The f i n a l
s tu d y was to d e term in e s e e d lin g emergence from th e same f o u r depths
( 0 , 0 . 5 , 1.5 ,2 .5 cm) and s u b s e q u e n t g r o w th and s u r v i v a l
u n d e r more
c o n to lle d c irc u m sta n c e s.
Methods
T ra n s p la n te d S e e d lin g s
In June
ap p ro x im a te ly
of
1982,
th e
sam e
100 p l a i n s
h e ig h t
s ilv e r
(28
mm)
sagebrush
and
g r o w th
se e d lin g s of
sta g e
w e re
t r a n s p l a n t e d i n d i v i d u a l l y fro m t h e f i e l d i n t o 10x10x12 cm p l a s t i c
pots. The p o ts w ere f i l l e d w i t h 2 cm o f sand i n the bottom and n a tiv e
t o p s o i l to w i t h i n 2 cm o f th e top. S e e d lin g s were i n i t i a l l y placed i n
46
t h e g r e e n h o u s e f o r one m onth t o r e c o v e r fro m any t r a n s p l a n t sh o ck .
E i g h t y p l a n t s w e re t h e n s e l e c t e d b a s e d on s i m i l a r i t y t o one a n o t h e r
and p la ce d i n growth chambers s e t a t one o f two d i u r n a l l y f l u c t u a t i n g
te m p e ra tu re reg im es.
These re g im e s were choosen to ro u g h ly s im u la te
cool and warm c o n d itio n s found i n d i f f e r e n t seasons. Regimes c o n s is te d
o f a 12 h o u r p h o t o p e r i o d w i t h d a y / n i g h t t e m p e r a t u r e s b e i n g s e t a t
e i t h e r 9 0 /7 0 F (32/21 C) o r 7 0 /5 0 F ( 2 1 /1 0 C). F o r t y s e e d l i n g s w e re
p la ce d i n t o each chamber. P r e lim in a r y m easurements of p l a n t h e ig h t and
number of le a v e s w ere o b ta in e d a t th e tim e s e e d lin g s w ere put i n t o th e
growth chambers.
G row th m e a s u r e m e n ts w e re made on s e e d l i n g s e v e r y f i v e w eeks.
T h ese i n c l u d e d h e i g h t ,
(le n g th ,
num ber o f l e a v e s , and tw o h o r i z o n t a l a x e s
w id th ). In a d d itio n ,
e ig h t s e e d lin g s w ere randomly s e l e c t e d
a t e a c h r e c o r d i n g p e r i o d f o r d e s t r u c t i v e s a m p l in g . M e a s u re m e n ts on
th e se p l a n t s in c lu d e d l e a f a re a , r o o t and s h o o t w e ig h ts. Leaf a re a was
d eterm in ed by the l i g h t a t t e n u a t i o n method and employed a L ic o r model
LI-3000 a r e a m eter. Leaf a re a of each sample was measured t h r e e tim e s
and th e r e s u l t s averaged. Shoot w e ig h ts in c lu d e d t o t a l w e ig h ts of both
stem and l e a f t i s s u e cu t a t ground l e v e l . Root w e ig h t was d eterm in ed
a f t e r a l l s o i l was th ro u g h ly washed away. Both shoot and r o o t m a te r ia l
was oven d r ie d and weighed. This study was completed i n December 1982;
Greenhouse Seeding
The e f f e c t s o f s e e d i n g d e p t h oh s e e d l i n g e m e r g e n c e , g r o w th and
s u r v i v a l w as e x a m in e d i n t h e g r e e n h o u s e . Ten p o t s w e re f i l l e d w i t h
w i t h s i f t e d n a t i v e s o i l fro m Paddy Faye and s e e d e d a t one o f f o u r
47
.
d e p t h s ( 0 , 0 . 5 , 1.5 ,2 .5 dm). Ten s e e d s w e re p l a n t e d i n e a c h p l o t i n a
d e f i n i t e , mapped p a t t e r n . As e a c h s e e d em erg ed i t w as r e c o r d e d and
mapped a s t o l o c a t i o n so t h a t l a t e r growth measurements could be made
i n r e l a t i o n to emergence d a te .
Once s e e d l i n g s p a s s e d t h e c o t y l e d o n s t a g e and e n t e r e d t h e tw o l e a f s ta g e o f phenology, m easurements on h e ig h t, number o f le a v e s and
th e two h o r i z o n t a l axes w ere re c o rd e d weekly f o r e ig h t weeks. The p o ts
were w a tered so a s to keep s o i l n ear f i e l d c a p a c ity ,
and te m p e ra tu re s
were m a in ta in e d a t about 21 C (70 F) th ro u g h o u t th e t r i a l .
F i e l d Seeding
S eed s w e re c o l l e c t e d d u r i n g t h e f a l l o f 1982 and p l a n t e d i n t o
n a tiv e
so il
in
th e
Paddy Faye p a s t u r e
d e s c r i p t i o n ) on November 3,
( s e e Seed D i s p e r s a l
s ite
1982. Three r e p l i c a t i o n s w ere e s t a b l i s h e d
so t h a t a s s o c i a t e d w a t e r t r e a t m e n t s and p l a n t i n g d e p t h s c o u ld be
e v a lu a te d f o r e f f e c t s on s e e d lin g emergence, growth and s u r v iv a l.
The th r e e r e p l i c a t i o n s w ere l o c a t e d on l e v e l ,
open ground w i t h i n
a p l a i n s s i l v e r sagebrush community. P lo t s were mowed t o ground l e v e l
t o f a c i l i t a t e p l a n t i n g . E i g h t s e v e n m e t e r l i n e s w e re s t a k e d o u t f o r
s ee d in g and randomly s e l e c t e d t o r e c e i v e one of fo u r depth tr e a tm e n ts
(s e e F i g u r e 3). A w e ig h e d s a m p le o f m a tu r e s e e d s , u n f i l l e d s e e d s and
f l o r a l b r a c t s w as p l a c e d i n a h a n d —o p e r a t e d , s i n g l e row cone s e e d e r
and
p la n te d
at
th e
d e sire d
d e p th
( 0 , 0 . 5 , 1.5 ,2 .5
cm).
D epth was
c o n t r o l l e d by a d j u s t i n g p e n e t r a t i o n o f double d is k openers.
Seeds i n
te n sam ples of t h i s weighed amount of seed m a t e r i a l were counted to
d e te rm in e
how many f i l l e d
s e e d s w e re a c t u a l l y
p la n te d .
It
w as
F ig u re
3.
P e r s p e c t i v e view o f f i e l d p l a n t i n g r e p l i c a t i o n g i v i n g d i m e n s i o n s and a s a m p le of
randomized a rra y of p la n t i n g d ep th s. O ne-half of each row was g iv en a w a te r tre a tm e n t.
R a b b it-p ro o f fence and barbed w ire surrounded e n t i r e p lo t.
49
d e t e r m i n e d t h a t e a c h s a m p le c o n t a i n e d an a v e r a g e o f 706+43 s e e d s .
T h erefo re,
each o f th e l i n e s
t h a t w e re p l a n t e d
c o n ta in e d
101+6
seeds/m.
Each r e p l i c a t i o n was e n c lo se d i n a r a b b i t - p r o o f fe n c e c o n s tr u c te d
w ith r a ilr o a d t i e s as co rn er p o sts,
two t h i c k n e s s e s o f .61 m h ig h
c h i c k e n w i r e , and tw o s t r a n d s o f b a rb e d w i r e above t h e c h i c k e n w i r e
(F ig u re 3). Seeded p l o t s passed through th e w i n t e r i n a dormant s t a t e
and s e e d lin g s began t o emerge th e f o llo w in g sp rin g .
I
W a t e r i n g t r e a t m e n t s s t a r t e d May 15, I 983, and m e a s u r e m e n ts o f
s e e d l i n g e m e rg e n c e and s u r v i v a l b egan on J u n e 15. T h is s c h e d u l e was
based upon p re v io u s work which r e p o r te d t h a t sagebrush s e e d lin g s w i l l
em erge
from
C o n s e q u e n tly ,
A p ril
th ro u g h J u ly
(B e e tle
t h e r e w as an i n i t i a l
I9 6 0 .,
H arvey
1 9 81).
p e r i o d d u r i n g w h ic h n a t u r a l
g e r m i n a t i o n and e m e r g e n c e c o u ld o c c u r w i t h o u t b e i n g s u b j e c t e d t o
s t r e s s f u l c o n d itio n s t h a t might cause m o r t a l i t y . Each emerged s e e d lin g
was marked w ith a l a r g e w asher on June 15. Subsequent s e e d lin g s were
marked w ith f la g s . Supplem entary w a te r was a p p lie d as needed once each
w eek t o p r o v i d e s e e d e d a r e a s w i t h a minimum o f 2.5 cm (1 i n c h / p e r
week). A djustm ents w ere made f o r any p r e c i p i t a t i o n t h a t occured d u rin g
th e p re c ed in g week. D i s t i l l e d w a te r was t r a n s p o r t e d i n t o th e f i e l d and
a p p lie d i n 30.5 cm s t r i p s a d ja c e n t to seeded l i n e s .
This a p p l i c a t i o n
w as im p o s e d upon h a l f o f e a c h row by u s i n g I g a l l o n hand g a r d e n
s p r i n k l e r s . P r e c i p i t a t i o n was m onitored by f o u r wedge ty p e r a i n gauges
l o c a t e d w i t h i n 50 m of th e study p lo ts .
50
S e e d lin g h e ig h t,
number o f l e a v e s and tw o h o r i z o n t a l
axes
(le n g th , w id th ) measurements w ere re c o rd e d each week i n June and J u ly .
During August, th e se same measurements w ere ta k e n .e v e ry o th e r week.
S o il m o is tu r e l e v e l s and te m p e ra tu re s w ere re c o rd ed by burying
c a l i b r a t e d f i b e r g l a s s w a f e r s a t d e p t h s o f 7.5 and 15 cm w i t h i n e ac h
r e p l i c a t i o n . Four w a fe r s were p la ce d i n each r e p l i c a t i o n so t h a t two
d e p t h s w e re m e a s u re d i n b o th w a t e r e d and u n w a t e r e d s e c t i o n s o f t h e
p lo t. T h e rm isto rs measured r e s i s t a n c e f o r s o i l te m p e ra tu re s w h ile s o i l
m o istu re
w as g a u g ed
p e rio d ic a lly
by c a p a c i t a n c e .
C o re s a m p l e s w e re t a k e n
to c h e c k g r a v i m e t r i c d e t e r m i n a t i o n s w i t h
th e s o i l
m o is tu re w a fe rs.
S t a t i s t i c a l A n aly sis
D a ta e v a l u a t i o n w as a c c o m p l i s h e d by c h i - s q u a r e a n a l y s i s f o r
emergence and s u r v i v a l re sp o n se s. Growth c u rv e s were c o n s tr u c te d from
d a t a m eans and t e s t e d w i t h S t u d e n t t - s t a t i s t i c s . G r a p h s .w e r e a l s o
c o n s tr u c te d t o h e lp i n t e r p r e t r e s u l t s .
S p ro u tin g and S e e d lin g E sta b lish m en t
The s p r o u tin g n a tu re o f p l a i n s s i l v e r sagebrush was e v alu a te d by
two s e p a r a te s tu d ie s .
th e
shrub r e l i e s
These w ere i n i t i a t e d to q u a n tif y to what degree
on e i t h e r v e g e t a t i v e
re p ro d u c tio n
or
se e d lin g
e s ta b lis h m e n t to r e c r u i t new members i n t o a community. The f i r s t phase
o f t h i s work in v o lv e d e x am in atio n of i n d i v i d u a l p l a n t s from s e v e ra l
r e p r e s e n t a t i v e c o m m u n itie s . I n d i v i d u a l p l a n t s o f a u n if o r m h e i g h t
c l a s s (16 to 40 cm) were s e l e c t e d a lo n g l i n e t r a n s e c t s and excavated
51
to d e te rm in e w hether t h a t p la n t o r i g i n a t e d in d e p e n d e n tly from seed or
was a s p ro u t from an a lre a d y e s t a b l i s h e d shrub. The second phase was
c o m p r is e d o f e x c a v a t i n g a r e a s a ro u n d tw o , l a r g e ,
f a ir ly iso la te d
p l a n t s t h a t were surrounded by numerous s m a ll p la n ts . The e n t i r e a re a,
i n c l u d i n g t h e m a in s h r u b , was e x c a v a t e d i n o r d e r t o d e t e r m i n e : (I )
w h e t h e r p l a n t s w e re o f c l o n a l o r s e e d o r i g i n ,
p la n ts
had f o r v e g e t a t i v e . s p r e a d
(2) w h a t p o t e n t i a l
b a s e d on n u m b e r o f s p r o u t s
s u r r o u n d i n g a p l a n t , and (3) th e d e g r e e t o w h ic h a d v e n t i t i o u s buds
w ere p r e s e n t bn e s t a b l i s h e d rhizom es.
T ra n se c t E x cav atio n s
S ix s e p a r a t e s i t e s w e re s e l e c t e d a s r e p r e s e n t a t i v e o f p l a i n s '
s i l v e r sagebrush com m unities i n th e N o rth e rn G reat P la in s . Three s i t e s
had been s u b j e c t t o some fo rm o f r e c e n t d i s t u r b a n c e s u c h a s f i r e o r
i c e s c r a p i n g . These s i t e s a r e r e f e r r e d t o a s t h e Y e l l o w s t o n e R iv e r,
Lower B la c k S p r i n g s and Lower F lo o d p a s t u r e s . The o t h e r t h r e e s i t e s
were no t s u b je c te d to r e c e n t d is tu r b a n c e e x c e p t f o r p e r i o d i c g ra z in g
by c a t t l e .
These a r e a s w ere L i g n i t e Creek,
Paddy Faye and Moon Creek
p a s tu r e s . For s i t e d e s c r i p t i o n s on Paddy Faye, Lower Flood and Lower
Black S p rin g s see Seed D is p e r s a l s i t e d e s c r i p t i o n s .
S i t e D e s c r ip tio n s
The Y e l l o w s t o n e R iv e r p a s t u r e i s l o c a t e d on t e r r a c e s on t h e
n o rth e rn
sid e
of
th e
Y ellow s t o n e
R iv e r
near a r a ilr o a d
b rid g e
a p p r o x i m a t e l y 5 km n o r t h w e s t o f s t a t i o n h e a d q u a rte rs . P la in s s i l v e r
sagebrush i s
sta n d s..
th e d o m in a n t s h r u b and i s fo u n d i n s p a r s e t o d e n se
The u n d e r s t o r y
is
d o m in a te d
by w e s t e r n w h e a t g r a s s ,
52
n e e d l e a n d t h r e a d and a n n u a l b ro m es. Two b a s i c s o i l t y p e s a r e p r e s e n t
depending on p ro x im ity to th e r i v e r . S o i l s a re dominated by deep, w e ll
d r a i n e d f i n e san d y lo a m s and lo a m s n e a r t h e r i v e r . Such s o i l s h ave
m oderate to m o d e ra tely r a p i d p e r m e a b i l i t y and m o d e r a t e l y a v a i l a b l e
w a te r c a p a c ity from 15 to 25 cm. These s o i l s a r e c l a s s i f i e d a s sandy
ra n g e s i t e s . As d i s t a n c e fro m t h e r i v e r i n c r e a s e s , t h e s o i l s g r a d e
i n t o deep,
w e ll- d r a in e d loam s o f m oderate and slow p e r m e a b il ity and
high a v a i l a b l e w a te r c a p a c ity . The s o i l s th roughout the study s i t e are
d o m in a te ly f r i g i d , U s tic T o r r i f l uvents.
L i g n ite Creek i s an i n t e r m i t t e n t stream d i s s e c t i n g much of th e
s o u th e rn p o r tio n of th e s t a t i o n f o r s e v e r a l k ilo m e te r s i n a n o rth so u th
d ire c tio n .
The s t u d y
a r e a w as
10 km d i r e c t l y
w est
of
h e a d q u a r te r s c lo se to where t h i s d ra in a g e j o i n s th e Y ellow stone River.
I t w a s l o c a t e d on a l l u v i a l d e p o s i t s t h a t w e re c l o s e t o th e s t r e a m
ch an n el.
The s i t e
h ad m o d e r a t e l y d e n s e
stan d s o f p la in s
s ilv e r
sag e b ru sh w i t h w e s te r n w h e a t g r a s s and a n n u a l brom es d o m i n a t i n g t h e
u n d e r s t o r y v e g e t a t i o n . S o i l s w e re i n t h e C a m b o r t h i d - T o r r i f l u v e n t
c o m p le x and w e re
c h a ra c te riz e d
by n o t h a v in g
a
ty p ie
p ro file .
P e r m e a b i l i t y c an be slo w t o m o d e r a t e l y r a p i d w i t h low t o m o d e r a te
a v a i l a b l e w a t e r c a p a c i t y fro m 8 t o 28 cm. The s o i l s r a n g e fro m f i n e
sandy loams t o s i l t y c la y loams w ith s t r a t a o f sand and g r a v e l common
i n some a re a s . Range s i t e s a re s i l t y and overflow .
Moon Creek i s an i n t e r m i t t e n t stre am on th e w e s te r n b o rd er of th e
s t a t i o n . Minor d ra in a g e s d i s s e c t th e Moon Creek flo o d p l a i n r e g u l a r l y .
P l a i n s s i l v e r s a g e b r u s h i s t h e d o m in a n t s p e c i e s t h r o u g h o u t t h i s
d r a i n a g e w i t h s m a l l g r o v e s o f p l a i n s c o tto n w o o d ( P o p u lu s d e l t o i d e s
53
B a r tr .) s c a t t e r e d a lo n g th e creek. The dominant u n d e rs to ry v e g e ta tio n
i s w e s t e r n w h e a t g r a s s , o f t e n i n d e n s e s t a n d s . G reen n e e d l e g r a s s i s
a l s o common.
Some o f t h e d r i e r a r e a s o f t h e t e r r a c e s h a v e l a r g e
p r o p o r t i o n s o f J a p a n e s e brom e, c h e a t g r a s s and b lu e gram a. D om inant
s o i l s i n Moon C reek a r e i n t h e G e r d r u m - C reed c o m p le x w i t h some
s c a tte re d T o rriflu v e n ts.
This study a r e a i s c l a s s i f i e d a s a c lay pan
range s i t e and t h e s o i l s belong t o th e f i n e , m o n t m o r i l l o n i t i c B o r o l l i c
N a t r i a r g id s. S o i l s a re about evenly d iv id e d between Gerdrum s i l t y c lay
lo a m s and C reed lo a m s w i t h s m a l l a r e a s o f s l i c k s p o t s . A p r e v a i l i n g
in flu e n c e
in
th e se
P e rm e a b ility i s
so ils
is
th e ir
sa lt
and
s o d iu m
c o n te n t.
slo w and t h e i r h i g h a v a i l a b l e w a t e r c a p a c i t y i s
d e crea se d to 15 to 20 cm due to s a l t c o n te n t.
Methods
A fte r
stu d y
areas
w ere
se le c te d ,
fo u r
25
m tra n se c ts
w e re e s t a b l i s h e d and u s e d to s a m p le i n d i v i d u a l s fro m p l a i n s s i l v e r
s a g e b r u s h p o p u l a t i o n s . S a m p lin g p r o c e e d e d so t h a t th e n e a r e s t p la n t
w i t h i n a p a r t i c u l a r h e i g h t c a t e g o r y (16 t o 40 cm) w a s f l a g g e d a t
in te rv a ls
of fiv e
m e te rs.
T h is
siz e
c ate g o ry
was c h o s e n a f t e r
p r e l i m i n a r y e x c a v a t i o n s and a g i n g had e s t a b l i s h e d t h a t su ch p l a n t s
re p re se n te d
s te m
m a te ria l
b e tw e e n one and f o u r y e a r s o ld .
The
p r e lim in a r y study a l s o e s t a b l i s h e d t h a t u n d e rg ro u n d m a t e r i a l v a r i e d
c o n s i d e r a b l y a c c o r d i n g t o w h e t h e r t h e p l a n t o r i g i n a t e d fro m p a r e n t
rhizom es, p l a n t s or s e e d lin g s .
R o o ts o f f l a g g e d p l a n t s w e re e x c a v a t e d w i t h g r e a t c a r e so t h a t
fra g ile
rh iz o m e
c o n n e c tio n s re m a in e d i n t a c t .
The p l a n t
was
54
su ffic ie n tly
e x c a v a t e d t o d e t e r m i n e i f i t w as c o n n e c t e d t o a n o t h e r
p l a n t o r w as an i n d e p e n d e n t i n d i v i d u a l . A f t e r t h i s d e t e r m i n a t i o n ,
m e a s u r e m e n ts w e re r e c o r d e d on p l a n t h e i g h t ,
l e n g t h o f r h iz o m e s
( r o o ts ) , and stem and rhizome (r o o t) d ia m e te r s . Root d i s t r i b u t i o n from
each in d i v i d u a l e x c a v a tio n was mapped, and l i n e s k e tc h e s o f each p la n t
w e re d ra w n f o r a p i c t o r i a l r e c o r d . S a m p le s w e re t a k e n fro m m a jo r
s e c t i o n s o f each ex cavated p la n t.
These in c lu d e d stem ,
r o o t,
rhizome
and c o n n e c t i n g rh iz o m e s e c t i o n s . They w e re p l a c e d i n s e a l e d p l a s t i c
bags i n
th e f i e l d
and t r a n s p o r t e d
to
th e la b o r a to r y
f o r age
d e te r m in a tio n . Aging o f sag eb ru sh was f e a s i b l e i n s p i t e o f common stem
s p l i t t i n g and l a y e r i n g (Ferguson 1964).
I s o l a t e d P la n t E x cav atio n s
Two l a r g e p l a n t s w ere s e l e c t e d i n Lower Flood t o be i n d i v i d u a l l y
e x cav ated f o r a study on a s e x u a l ( v e g e ta ti v e ) re p r o d u c tiv e p o t e n t i a l .
Only two p l a n t s w ere s e l e c t e d due to h ig h la b o r r e q u ire m e n ts involved.
The p l a n t s w e re s u b j e c t i v e l y s e l e c t e d by two c r i t e r i a .
The f i r s t
c r i t e r i a was t h a t th e p la n t should be r e l a t i v e l y i s o l a t e d from o th e r
l a r g e p l a i n s s i l v e r sagebrush p l a n t s so t h a t c o m p e t i t i v e i n f l u e n c e s
fro m o t h e r i n d i v i d u a l s w e re m in im i z e d .
p o te n tia l
c o u ld be f r e e l y
ex p ressed .
In. t h i s w ay,
v e g e ta tiv e
The sec o n d c r i t e r i a was a
p r e d o m in a n c e o f s m a l l e r " i n d i v i d u a l s " su rro u n d in g t h i s l a r g e r p la n t
w h ic h w as I m o r g r e a t e r i n h e i g h t . A re a s a ro u n d t h e l a r g e p l a n t s
( a p p r o x i m a t e l y 4 to 5 m r a d i u s ) w e re e x c a v a t e d so t h a t r o o t s and
rhizom es of a l l th e s m a l l e r p l a n t s w ere exposed and r e l a t i o n s h i p s to
th e l a r g e r p l a n t s determ in ed .
Root d i s t r i b u t i o n from th e e x c a v a tio n s
55
w ere
mapped so t h a t s e e d lin g s and s p r o u ts could be d i f f e r e n t i a t e d and
s i z e c a te g o ry reco rd ed .
S ta tistic a l
A n a lv siR
C h i-sq u are a n a l y s i s was perform ed on t r a n s e c t d a ta to d eterm in e
w h e th er m ajor d is tu r b a n c e s had an e f f e c t on th e r a t i o o f s e e d lin g s to
s p r o u ts and i f t h e r e w ere d i f f e r e n c e s among in d i v i d u a l s i t e s . Student
t - s t a t i s t i c s w ere r u n to d e te rm in e o v e r a l l s i g n i f i c a n c e o f th e r a t i o
o f s e e d l i n g s and s p r o u t s . The i s o l a t e d p l a n t e x c a v a t i o n s w e re n o t
d e s i g n e d to be a n a l y z e d ,
r a t h e r t h i s e x p e r i m e n t w as d e s i g n e d to
p ro v id e a d d i t i o n a l i n s i g h t i n t o a se x u a l r e p r o d u c tiv e p o t e n t i a l .
56
RESULTS AND DISCUSSION
Seed D is p e r s a l
One o f
th e
p rim ary
fe a tu re s
to
in v e stig a te
in
reg ard s
to
r e p ro d u c tiv e s t r a t e g i e s i s the number of p ro p a g u le s t h a t a re produced
and
d isp e rse d .
Seed
d isp e rsa l
in
p la in s
i n v e s t i g a t e d i n re g a r d s to s i t e com parisons,
d ista n c e
th a t
seed
fe ll
fro m
parent
silv e r
sagebrush
was
d i r e c t i o n of seed f a l l ,
p la n ts,
and d a t e
of
seed
d i s p e r s a l . S t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s were n o t found among
th e
th re e
stu d y
s ite s
d i r e c t i o n of seed f a l l
in
te rm s of
n u m b ers o f s e e d s d i s p e r s e d ,
and d i s t a n c e r e l a t i o n s h i p s
of seed f a l l .
H owever, h i g h l y s i g n i f i c a n t i n t e r a c t i o n s (p< 0.01) e x i s t e d b e tw e e n
stu d y s i t e s
and t i m e o f
seed d i s p e r s a l .
Numbers o f
seeds
th a t
d is p e r s e d a ls o changed s i g n i f i c a n t l y from th e f i r s t r e c o r d in g d a te to
f o l l o w i n g d a t e s . The s e e d d i s p e r s a l d i s t a n c e fro m t h e p a r e n t p l a n t
f o l l o w e d a d e f i n i t e p a t t e r n . D i r e c t i o n o f d is s e m in a tio n d is p la y e d a
th r e e - lo b e d s t e l l a t e type d i s t r i b u t i o n . Wind played th e m ajor r o l e i n
d e t e r m i n i n g s e e d d i s p e r s a l i n p l a i n s s i l v e r s a g e b r u s h a t t h e s tu d y
s ite s.
The m a jo r ity of seed d is p e r s e d th ro u g h o u t th e study p e rio d was i n
t h e sam e t h r e e
p rin c ip le
d ire c tio n s.
H ow ever,
d a te p la y e d a
s i g n i f i c a n t r o l e because i t d eterm in ed th e t o t a l number of seeds t h a t
fe ll,
and t h i s i n d i r e c t l y a f f e c t e d t h e number o f s e e d s t h a t w e re
d is p e r s e d a t v a ry in g d i s t a n c e s on th e d i f f e r e n t t r a n s e c t s .
57
A lth o u g h d i s p e r s a l o f s a g e b r u s h s e e d s h a s b e en a t t r i b u t e d t o
w in d , w a t e r and a n i m a l s , w ind (a n e m o ch o ry ) see m s t o be o f m a jo r
im p o rtan ce (B e etle I960, Harper 1977, Bostock and Benton 1979, T isd a le
and H ironaka 1981, Evans and Young 1982). My study confirm ed t h a t wind
d i s p e r s a l w as an i m p o r t a n t f a c t o r i n t h e d i s p e r s a l o f p l a i n s s i l v e r
sag eb ru sh
seed.
H ow ever,
th e s tu d y d e s ig n d id n o t a llo w
fo r
c a t e r g o r i z i n g w a te r or anim al in f l u e n c e s a s l e s s e r f a c t o r s . The s i t e s
on
w h ic h
th is
stu d y
was
c o n d u c te d
and
th e
m o rp h o lo g ic a l
c h a r a c t e r i s t i c s o f th e seed seemed to p o in t t o a l e s s e r c o n t r i b u t i o n
by th e s e f a c t o r s .
A lth o u g h
k ilo m e te r s ,
th e
th re e
stu d y
areas
wjere s e p a r a t e d
by s e v e r a l
no n o ta b le d i f f e r e n c e s i n d i s p e r s a l c h a r a c t e r i s t i c s could
be d e te c te d . The same en v iro n m en tal in f l u e n c e s , e s p e c i a l l y p r e v a i l i n g
and s to r m w in d s ,
seem ed t o e x e r t s i m i l a r i n f l u e n c e s on d i s p e r s a l
th r o u g h o u t t h e s t u d y a r e a v i c i n i t y .
P r e v a i l i n g w in d s a s w e l l a s
c y c lo n ic w inds from a tm o sp h eric d i s tu r b a n c e s would not o r d i n a r i l y be
e x p e c t e d t o ch an g e w i t h i n t h e g e o g r a p h i c a l ra n g e o f t h e p r o j e c t .
T herefore,
t h i s r e s u l t e d i n w in d d i r e c t i o n s t h a t w e r e r e l a t i v e l y
c o n s i s t e n t f o r a l l th r e e study s i t e s .
The p a t t e r n s o f seed d i s p e r s a l
t h a t were observed were c h a r a c t e r i s t i c o f each i n d i v i d u a l p l a n t ,
and
\
.
f o r t h i s re a s o n th ey should not v ary r e g a r d l e s s o f where a p o p u la tio n
was lo c a te d .
Timing o f d i s p e r s a l v a r ie d between s i t e s (F igure 4).
Paddy Faye
showed a s i g n i f i c a n t l y l a r g e r num ber o f s e e d s f a l l i n g on t h e f i r s t
m e a s u re m e n t d a t e (7.1 s e e d s p e r p l a t e ) w i t h a s e c o n d p e a k on t h e
f o u r t h m e a s u re m e n t d a t e (3.5 s e e d s p e r p l a t e ) . A g r a d u a l d e c r e a s e i n
Dates
8-
November 1-5
November 6 -9
m m
« Si
w ro
m a. 6—
a
.22 E
■a o
CO
■a
4)
0)
CO
November 10-12
m m
November 13-16
m m
m m
November 17- 19
CO
CO
x
— CO
O CO
Ul
« <D
X) a
E
z —
OO
2
-
Paddy
Faye
11!
Lower
Flood
Date of Dispersal by Site
Black
Springs
F ig u re 4. Mean numbers o f p l a i n s s i l v e r sagebrush seed d is p e r s e d p er p l a t e i n a l l d i r e c t i o n s from a
p a re n t p la n t. D is p e rsa l from f i v e p l a n t s i n each study a re a i s summarized. D iff e re n c e s i n
each study s i t e a re summarized by d a te a t which d i s p e r s a l was ach eiv ed .
59
seed numbers was observed on Lower Flood a f t e r th e i n i t i a l high v alu e
(fro m 3.1 t o 1.1 s e e d s p e r p l a t e ) . The d e c l i n e i n s e e d n u m b e rs and
d i f f e r e n c e s among d a t e s w e re l e s s p ro n o u n c e d . Lower B la c k S p r i n g s
showed a f a i r l y u n if o r m d i s t r i b u t i o n o f d i s p e r s e d s e e d s among a l l
d a te s , and th u s no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s i n numbers o f
s e e d s d i s p e r s e d w e re d e t e c t e d . D i f f e r e n c e s among s i t e s can b e s t be
e x p l a i n e d by d i s s i m i l a r p h e n o l o g i c a l m a t u r a t i o n o f p l a n t s a t e a c h
s i t e . I n d i v i d u a l p l a n t s w e re s e l e c t e d f o r m e a s u re m e n t b e f o r e s e e d
d i s p e r s a l w as i n i t i a t e d .
C o n s e q u e n tly ,
p l a n t s t h a t w e re s am p led
r e p r e s e n t e d a h e t e r o g e n e o u s m i x t u r e w i t h r e s p e c t t o rhow r a p i d l y
p h o n o lo g ical development occured. As th e season p ro g resse d , th e r e were
more i n d i v i d u a l s re a c h in g seed m a tu r ity e a r l y on th e f i r s t two s i t e s .
The t h i r d s i t e had a b o u t e q u a l n u m b e rs o f p l a n t s a t t a i n i n g s e e d
m a tu r ity th ro u g h o u t th e study p e rio d .
due to two in f l u e n c e s ,
These d i f f e r e n c e s a re p o s s ib ly
namely m icroenvironm ent and s o i l s .
Paddy Faye
and Low er F lo o d a r e c h a r a c t e r i z e d by s i m i l a r v e g e t a t i o n and s o i l
components. Both study s i t e s have a r e l a t i v e l y s h o r t v e g e t a t i o n cover
and s o i l s w i t h a d o m in a n t c l a y f r a c t i o n . Low er B la c k S p r i n g s , i n
c o n t r a s t , has a dominant cover of c r e s t e d w h e a tg ra s s and more s i l t y to
san d y s o i l s . The m i c r o e n v i r o n m e n t and, s o i l m o i s t u r e r e l a t i o n s h i p s
w o u ld m o st l i k e l y be d i f f e r e n t b e tw e e n Lower B la c k S p r i n g s and t h e
first
two s i t e s .
T h erefo re,
t h i s w o u ld
in flu e n c e
th e d i f f e r i n g
p h e n o lo ic a l development f,br p l a i n s s i l v e r sagebrush between th e f i r s t ,
two s i t e s and Lower Black Springs.
P h e n o ld g ical development i n most sagebrush s p e c ie s i s such t h a t
t h e m a j o r i t y o f s e e d s a r e sh ed i n l a t e f a i l and w i n t e r . Most o f th e
60
v i a b l e seed i s dropped d u rin g th e f i r s t seven days a f t e r d i s p e r s a l i s
in itia te d
(Goodwin 1956,
B e e tle
1960,
H arvey 1981,
T i s d a l e and
Hironaka 1981). Over th e f o ll o w i n g two to fo u r weeks o f th e se s t u d i e s
d i s p e r s a l w as o b s e r v e d t o c o n s i s t p r i m a r i l y o f a b o r t e d f l o w e r s and
h a l f - f i l l e d s e e d s . I n my s t u d y , h o w e v e r, v a r i a b i l i t y i n m a t u r i t y o f
i n d i v i d u a l p l a n t s r e s u l t e d i n a n e x t e n d e d d i s p e r s a l p e r i o d when
c o n s i d e r e d on a p o p u l a t i o n b a s i s .
D i s p e r s a l w as p r o p o r t i o n a t e l y
g r e a t e s t i n t h e f i r s t week (4.2 s e e d s p e r p l a t e ) ( F i g u r e 5). T h is
w ould
be c o n s i s t e n t w i t h p r e v i o u s l y
re p o rte d r e s u l t s .
However,
p h e n o lo g ie s! d i f f e r e n c e s i n the p la n t p o p u la tio n in f lu e n c e d the number
of
v ia b le
seeds
th a t
fa ll
in
subsequent
d isp e rsa l
p e rio d s.
No
s t a t i s t i c a l d i f f e r e n c e s e x i s t e d among t h e s e c o n d , t h i r d o r f o u r t h
sam p lin g p e r io d s
(1 .9 7 ,
2 .2 ,
2.4 s e e d s p e r p l a t e ,
re sp e c tiv e ly ),
a l t h o u g h s i g n i f i c a n t l y l e s s s e e d f e l l i n t h e l a s t p e r i o d (1.4 s e e d s
per p la te ).
R e s u l t s i n d i c a t e d t h e r e w as a s h a r p d e c r e a s e i n t h e number o f
p l a i n s s i l v e r s a g e b r u s h s e e d s (f ro m 5.4 t o 1.4 s e e d s p e r p l a t e ) t h a t
w e re d i s p e r s e d b e tw e e n t h e z e r o and one m e t e r a r e a a d j a c e n t t o t h e
p a r e n t p l a n t ( F i g u r e 6). No s t a t i s t i c a l d i f f e r e n c e c o u ld be fo u n d
among m easurements f o r th e next th r e e m e te rs. T h erefo re, th e se r e s u l t s
a re c o n s i s t e n t w ith p re v io u s r e s e a r c h which r e p o r te d t h a t most seeds
w e re d i s p e r s e d n e a r t h e p a r e n t p l a n t w i t h s e e d d e n s i t y d e c l i n i n g
s h a rp ly as d i s t a n c e i n c r e a s e s (Harper 1977, Cook 1980). This d i s p e r s a l
p a t t e r n h a s b een shown t o e x i s t i n A r t e m i s i a s p e c i e s ( B e e t l e I9 6 0 ,
Friedm an and Orshan 1975, Harvey 1981, T is d a le and H ironaka 1981).
Number of seeds dispersed
(x per 36 x 36 cm. plate)
61
I-
1 -5
6 -9
10-12
13-16
NOVEMBER
Date of Dispersal
17-19
F i g u r e 5. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d is p e r s e d i n a l l d i r e c t i o n s from a p a re n t p la n t. D is p e rsa l
from a t o t a l of 15 p l a n t s i s summarized. D iff e re n c e s a r e
summarized f o r each d a te a t which d i s p e r s a l was achieved.
62
w co
a) a
a
Is
S *
—
CD
O CO
0
)
jd
E
0
)
a
Z —
'I ' ..
Om
1m
Distance
2 m
Seed Dispersed
(meters)
3 m
F i g u r e 6. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d i n a l l d i r e c t i o n s fro m a p a r e n t p l a n t o v e r
e n t i r e s tu d y p e r i o d . D i s p e r s a l from a t o t a l o f 15 p l a n t s
i s s u m m a riz e d . D i f f e r e n c e s a r e s u m m a riz e d f o r each
d is ta n c e a t which d i s p e r s a l was achieved.
63
Measurement d a te had a c o n s id e ra b le e f f e c t on th e number of seeds
t h a t w e re d i s p e r s e d a t i n c r e a s i n g d i s t a n c e s from t h e p a r e n t p l a n t
( F i g u r e 7)« I n t h r e e o f t h e f i v e d i s p e r s a l p e r i o d s i n v e s t i g a t e d , th e
m a jo r ity of seed s f e l l under the p a re n t p l a n t w ith s u b s t a n t i a l l y l e s s
being found a t d is t a n c e s o f one or more m e te rs. However, i n two case s,
th e se c o n d and f i f t h
sa m p lin g
d is trib u te d across a ll
p e rio d s,
fo u r d is ta n c e s .
i n t e r v a l (November 17-19),
d isp e rsa l
w as
e v e n ly
On a t l e a s t one s a m p l in g
d i s p e r s a l was s i g n i f i c a n t l y h ig h e r a t two
m e te rs (2.3 see d s p e r p l a t e ) th a n a t th e one m eter d i s t a n c e (0.6 seeds
per p la te )
fro m
(November 13-16),
h ig h e r th a n a t
th e p a r e n t p l a n t .
On a n o t h e r s a m p l i n g i n t e r v a l
d i s p e r s a l a t th r e e m e te rs (1.8 seeds p e r p l a t e ) was
e ith e r
one (1.1
s e e d s ) o r two (0.9 s e e d s ) m e t e r s
d i s t a n c e fro m t h e p a r e n t p l a n t . S t r o n g c y c l o n i c w in d s on t h e s e two
sam pling i n t e r v a l s b e s t e x p la i n the a p p a re n t d e v i a t i o n from what would
be ex p ected i n d i s p e r s a l p a t t e r n s .
w in d s w ould
d isp e rse
seeds
to
The g u sty winds in h e r e n t i n th e se
a g re a te r
d ista n c e
th a n
n o rm a l
c o n d itio n s might.
D i s p e r s a l p a t t e r n s showed t h r e e p r i n c i p l e r e g i o n s w h e re s e e d s
w e re u s u a l l y
downwind fro m
c o n c e n tra te d .
The m a j o r i t y
of seeds f e l l
t h e p r e v a i l i n g n o r t h w e s t w in d s .
d ire c tly
In a d d itio n ,
two
s e c o n d a r y r e g i o n s o f s e e d c o n c e n t r a t i o n w e re l o c a t e d a t 120 d e g r e e
a n g le s on e i t h e r s id e o f th e p rim ary d i s p e r s a l reg io n .
S ig n ific a n tly
h i g h e r q u a n t i t i e s (2 t o 9 t i m e s ) o f s e e d w e re fo u n d i n t h e s e t h r e e
a re a s th a n th e re m a in in g a re a s .
T h is r e s u l t e d
in a th re e -lo b e d
s t e l l a t e f i g u r e when s e e d n u m b e rs w e re p l o t t e d a s a f u n c t i o n o f
d i s p e r s a l d i r e c t i o n (F ig u re 8). V a r i a t i o n between t h e t h r e e prom inent
12-
D ates
No v em b er 1 - 5
N o vem ber 6 - 9
No v em b er 1 0 - 1 2
Novem ber 1 3 - 1 6
No v em b er 17 - 19
(7\
-fcr
F ig u re 7. Mean numbers o f p l a i n s s i l v e r sagebrush seed d is p e r s e d p e r p l a t e i n a l l d i r e c t i o n s from a
p a ren t p la n t.
a c h e iv e d .
D i f f e r e n c e s a r e s u m m a r iz e d f o r
each
d is ta n c e
by d a t e
d is p e r s a l
w as
65
prevailing
NW wind
5
J-6
TRANSECT
A
F i g u r e 8. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d is p e r s e d from a p a re n t p l a n t i n s i x d i r e c t i o n s . Numbers
on axes r e p r e s e n t mean numbers o f seeds d is p e r s e d . Shaded
a r e a r e p r e s e n t s a g e n e r a liz e d seed d i s p e r s a l p a tte r n . See
Appendix D f o r example of how t h i s graph was c o n stru c te d .
66
lo b e s o f th e f i g u r e o c cu rred a s d is ta n c e was co n sid e re d . The p rim ary
d i s p e r s a l r e g i o n ( t r a n s e c t A) r e c e i v e d t h e g r e a t e s t am ount o f s e e d
w ith th e m a jo r ity f a l l i n g d i r e c t l y under th e p a re n t p l a n t (0 m eters)
(F ig u re 9). A second peak of seed s f e l l a t two m e te rs. Although few er
seeds f e l l
in
th e
n o rth e rly
l o b e a l o n g t r a n s e c t E,
th e seed
d i s t r i b u t i o n p a t t e r n w as t h e same a s i n t r a n s e c t A. W ith r e s p e c t to
d i s p e r s a l d i s t a n c e , t h e s o u t h w e s t l o b e ( t r a n s e c t C) d e m o n s t r a t e d a
s t a t i s t i c a l l y d i f f e r e n t d i s p e r s a l p a t t e r n w ith seeds f a l l i n g m ainly a t
th e one and t h r e e m e te rs d is t a n c e s from th e p a re n t p la n t. In th e f i r s t
tra n se c t,
a m ean o f 1 3 .8 ,
1 .1 , 3 .5 ,
a n d 0 .3 s e e d s f e l l
a t th e
r e s p e c t i v e d is t a n c e s o f 0, I , 2, and 3 m eters. In c o n t r a s t , t r a n s e c t C
e x h ib ite d
a mean o f 1 .3 ,
5 .7 ,
0.3; and 6.7 s e e d s f a l l i n g
at
th e
r e s p e c t i v e d i s t a n c e s o f 0, I , 2 and 3 m eters. This g e n e r a l p a t t e r n o f
seed d i s p e r s a l was observed on p l a i n s s i l v e r sagebrush th roughout th e
study p e rio d a lth o u g h some v a r i a t i o n s w ere encountered among sam pling
i n t e r v a l s (F ig u re s 10 to 14). E s s e n t i a l l y the same type of th r e e lobed
g e o m e tric shape was found f o r a l l f i v e sampling, p e rio d s . However, the
p r i n c i p l e r e g io n s of seed d i s p e r s a l d id change a c c o rd in g to c o l l e c t i o n
d a t e . F o r e x a m p le , on t h e se c o n d ( F i g u r e 11) and t h i r d ( F i g u r e 12)
sam p lin g p e rio d ,
th e l a r g e s t p r o p o r tio n o f seeds f e l l i n t r a n s e c t s C
and E, r e s p e c t i v e l y .
O b serv atio n s on wind d i r e c t i o n and speed d u rin g
t h e s e tw o p e r i o d s showed a d i f f e r i n g p a t t e r n fro m
t h e d o m in a n t
p r e v a i l i n g winds and speeds t h a t would e x p la i n th e s e d i p a r i t i e s .
The
o th e r th r e e p e rio d s e x h i b i t e d a s i m i l a r p a t t e r n to t h a t d e s c rib e d f o r
F i g u r e 9,
th a t is ,
d is p e r s e d s e e d s .
tr a n s e c t A re c e iv e d th e l a r g e s t p ro p o rtio n of
-
67
prevailing
NW wind
I
10
TRANSECT
A
F i g u r e 9. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d fro m a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0, 1 , 2 , 3 m). Numbers on a x e s r e p r e s e n t mean
n u m b ers o f s e e d s d i s p e r s e d . Shaded a r e a r e p r e s e n t s a
g e n e r a l i z e d s e e d d i s p e r s a l p a t t e r n . See A ppendix D f o r
example of how t h i s graph was c o n stru c te d .
68
D
-20
prevailing
NW wind
-50
TRANSECT A
F ig u re 10.
Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d fro m a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0, 1 , 2, 3 m). D ate o f d i s p e r s a l w as from
November 1 -5 . Numbers on a x e s r e p r e s e n t mean s e e d s
d is p e rse d . Areas a r e a g e n e r a liz e d seed d i s p e r s a l p a t t e r n
a t e ach s u c c e s s i v e d i s t a n c e . See A ppendix D f o r e x am p le
o f how t h i s graph was c o n s tr u c te d .
69
prevailing
NW wind
Area
of
disp ersal
and 3 m, respectively
TRANSECT
F i g u r e 11. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d from a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0, 1 , 2 , 3 m). D ate o f d i s p e r s a l was from
November 6 - 9 . Numbers on a x e s r e p r e s e n t mean s e e d s
d is p e rse d . Areas a r e a g e n e r a liz e d seed d i s p e r s a l p a t t e r n
a t each s u c c e s s i v e d i s t a n c e . See A ppendix D f o r ex am p le
o f how t h i s graph was c o n s tru c te d .
70
prevailing
NW
wind
TRANSECT A
F i g u r e 12. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d fro m a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0 , I , 2 , 3 m). D ate o f d i s p e r s a l w as from
November 1 0-12. Numbers on a x e s r e p r e s e n t mean s e e d s
d is p e rse d . Areas a r e a g e n e r a liz e d seed d i s p e r s a l p a t t e r n
a t e ach s u c c e s s i v e d i s t a n c e . See A ppendix D f o r e x a m p le
o f how t h i s graph was c o n s tru c te d .
71
prevailing
NW
F i g u r e 13« Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d fro m a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0, I , 2, 3 m). D ate o f d i s p e r s a l w as from
November 13-16. Numbers on a x e s r e p r e s e n t mean s e e d s
d is p e rse d . Areas a r e a g e n e r a liz e d seed d i s p e r s a l p a t t e r n
a t each s u c c e s s i v e d i s t a n c e . See A ppendix D f o r e x a m p le
of how t h i s graph was c o n s tru c te d .
72
prevailing
wind
NW
Area of dispersal
1 and 3 m, respectively
TRANSECT
A
F i g u r e 14. Mean n u m b e rs o f p l a i n s s i l v e r s a g e b r u s h s e e d p e r p l a t e
d i s p e r s e d fro m a p a r e n t p l a n t i n s i x d i r e c t i o n s a t f o u r
d i s t a n c e s (0 , I , 2 , 3 m). D ate o f d i s p e r s a l was from
November 17-19. Numbers on a x e s r e p r e s e n t mean s e e d s
d is p e rse d . Areas a r e a g e n e r a liz e d seed d i s p e r s a l p a t t e r n
a t each s u c c e s s i v e d i s t a n c e . See A ppendix D f o r e x am p le
o f how t h i s graph was c o n s tr u c te d .
73
Q u a l i t a t i v e o b s e r v a tio n s on wind d i r e c t i o n and speed w ere made
d u rin g each d i s p e r s a l p e rio d . The r e s u l t i n g changes i n wind d i r e c t i o n
seemed to c o r r e l a t e w e ll w ith d i s p e r s a l p a t t e r n s t h a t w ere observed..
Although the p r e v a i l i n g wind was from the n o rth w e s t, changes .did occu r
a c c o rd in g t o w e ath e r v a r i a t i o n and to p o g ra p h ic a l in f lu e n c e s . All th re e
study s i t e s w ere l o c a t e d i n b o tto m lan d s t h a t are d i s s e c t e d to v a ry in g
deg rees.
Local
e sta b lish e d
in
w in d p a t t e r n s
th ese
situ a tio n s
a n d f l u c t u a t i o n s w e re n a t u r a l l y
th a t
c o n trib u te d
to
d isp e rsa l
d i f f e r e n c e s between d a te s . These l o c a l winds would a l s o te n d to be i n
c o n s i s t e n t p a t t e r n s , a l t h o u g h i n v a r y i n g d e g r e e s o f i n t e n s i t y , and
th ey t h e r e f o r e in f l u e n c e th e seed d i s p e r s a l p a t t e r n s i n t o a t h r e e lobed s t e l l a t e g e o m e tric d i s t r i b u t i o n . While the p r e v a i l i n g winds were
g e n e r a lly c o n s i s t e n t and o f low speed, th e changes due to w eath er and
t o p o g r a p h y te n d e d t o be i n t h e fo rm o f g u s t s and w i t h i n c r e a s e d
v e l o c i t y . Thus th e d i s p e r s a l p a t t e r n s observed i n t h i s stu d y were not
uniform on each d a te. The t r a n s e c t (A) under th e most d i r e c t in f l u e n c e
o f th e p r e v a i l i n g wind d is p la y e d th e c h a r a c t e r i s t i c p a t t e r n o f having
t h e l a r g e s t n u m b e rs o f s e e d s n e x t t o t h e p a r e n t p l a n t and s m a l l e r
a m o u n ts a t g r e a t e r d i s t a n c e s . The o t h e r tw o m a jo r r e g i o n s o f s e e d
d i s p e r s a l w e re t h e r e s u l t o f w h a t te n d e d t o be r a t h e r c o n s i s t e n t
w e a t h e r and t o p o g r a p h i c i n f l u e n c e s t h a t w e re r e p e a t e d i n v a r y i n g
d e g re es of i n t e n s i t y d u rin g each sam pling i n t e r v a l .
T h i s ty p e o f d i s t r i b u t i o n a l p a t t e r n o f d i s p e r s e d s e e d h a s n o t
b een d e s c r i b e d i n t h e l i t e r a t u r e on s a g e b r u s h and p r o b a b l y i s th e
74
r e s u l t o f th e sam pling te ch n iq u e. Most o f th e r e s e a r c h on d i s p e r s a l of
sagebrush i s o b s e r v a tio n a l i n n a tu re o r was s tu d ie d i n l e s s d e t a i l and
w ith s m a l le r numbers and p e rio d s th a n t h i s study provided.
75
Germination Responses
Response to I n d iv i d u a l F a c to rs
All main f a c t o r s ,
except s t r a t i f i c a t i o n ,
had h ig h ly s i g n i f i c a n t
(p< .01) e f f e c t s on g e rm in a tio n re sp o n se . These in c lu d e d : d a te of seed
c o lle c tio n ,
l i g h t and dark,
te m p e ra tu re ,
and o sm o tic p o t e n t i a l .
Most
i n t e r a c t i o n s t h a t d id n o t in c lu d e s t r a t i f i c a t i o n a s a f a c t o r w ere a ls o
h i g h l y s i g n i f i c a n t (p< .0 1 ). These i n c l u d e d : ( I ) l i g h t / d a r k and d a t e
o f s e e d c o l l e c t i o n , (2) t e m p e r a t u r e and d a t e o f s e e d c o l l e c t i o n , (3)
l i g h t / d a r k and te m p e ra tu re , (4) te m p e ra tu re and o sm o tic p o t e n t i a l ,
(5)
l i g h t / d a r k and o s m o t i c p o t e n t i a l , (6) l i g h t / d a r k , t e m p e r a t u r e , and
d a t e o f s e e d c o l l e c t i o n , (7) l i g h t / d a r k ,
p o te n tia l,
(8) t e m p e r a t u r e ,
c o lle c tio n ,
p o te n tia l,
ranked
and f i n a l l y
o sm o tic p o t e n t i a l ,
(9 )
lig h t/d a rk ,
and d a t e o f s e e d c o l l e c t i o n .
by r e l a t i v e
t e m p e r a t u r e , and o s m o t i c
im p o rta n c e
in
and d a t e o f s e e d
te m p e ra tu re ,
o sm o tic
Means w e re s e p a r a t e d and
reg ard s
to
th e se
sig n ific a n t
re sp o n se s. R e s u lta n t p e rc e n ta g e s f o r i n d i v i d u a l main e f f e c t s and twoway i n t e r a c t i o n s a r e summarized i n Table I. For th e t h r e e way (Table
2) and f o u r - w a y i n t e r a c t i o n s , , n o r a n k i n g s w e re p o s s i b l e and o n ly
g e n e r a l p a t t e r n s could be observed.
D ate o f s e e d c o l l e c t i o n a f f e c t e d g e r m i n a t i o n p e r c e n t a g e s . The
seed t h a t was c o l l e c t e d i n th e w i n t e r had h ig h e r g e r m in a tio n t o t a l s
(35%) th a n t h a t o b ta in e d from seeds c o l l e c t e d i n l a t e f a l l (24%). Dark
g e r m in a tio n was g e n e r a lly p r e f e r r e d over l i g h t i n th e f i r s t and t h i r d
c o lle c tio n d a tes,
b u t no s i g n i f i c a n t d i f f e r e n c e w a s shown on t h e
second c o l l e c t i o n . However, g e r m in a tio n i n l i g h t or d ark was h ig h e r i n
T ab le I . M eans1 from in d iv id u a l main e f f e c t s and s e p a r a te c o m b in a tio n s o f two-way i n t e r a c t i o n s where
s i g n i f i c a n c e (p .0 1 ) was fou n d . For f a c t o r i a l ANOV s e e A ppendix C. L e t t e r s o n ly a p p ly in
in d i v id u a l b lo c k s o f m eans.
____________ ______________ _____________________________________ _________________________________
Main F a c to r
2
Date
O sm otic P o t e n t ia l( b a r s )
T
em
perature(C
)
L ig h t
I n t e r a c t io n
I
2
3
5 .0
2 .5
0
7 .5
10
20
30
T reatm en t( s )
L
D
F a c to r (s )
27b 32*
•None
L ig h t/d a r k
L
D
Tem perature
10
20
30
O sm otic
^
P o te n tia l
29b
36*
23C
34b
24d
29°
43*
18®
28c
57*
57b
64*
50°
40b
17*
35d
44*
8f
26*
41d
48*
30*
16f
25f
10
24* 29b 35*
4d
2 2 d 29* 35b
26* 29* 39*
X
a !
2
’
'
“
25
d
5 Ib
0
2 .5
5 .0
7 .5
___C
33f
26*
39*
-d
22
39*
40*
__cd
25
5S 6S
3 9 - 47
I i
2fs
1 Numbers a r e mean t o t a l g e r m in a tio n p e r c e n t a g e s . Means fo llo w e d by d i f f e r e n t l e t t e r s d e n o te s i g n i f i c a n t
d i f f e r e n c e s (p .0 1 ) from D u ncan's m u lt ip le ran ge t e s t .
2 D a te s a r e a s f o llo w s :
seed c o lle c t io n .
3 No s i g n i f i c a n c e (p
( I ) l a t e O cto b e r , (2 ) l a t e November, and (3 ) e a r ly J an u ary. T hese a r e d a te s o f
.0 1 ) c o u ld be d i f f e r e n t i a t e d betw een d a te s in r e g a rd s to o sm o tic p o t e n t i a l s .
T ab le 2 . Means from th r ee -w a y i n t e r a c t i o n s o f main e f f e c t c o m b in a tio n s where s i g n i f i c a n c e (p
.0 1 )
__________ was fo u n d . For f a c t o r i a l ANOV s e e A ppendix C.______________________________
Main F a c t o r ( s )
O sm otic P o t e n t i a l ( b a r s )
D ate
Temperature & Osm. P o t e n t i a l
(C)
(b a r s)
I n t e r a c t io n
10
20
30
F a cto r(s)
T reatm en t(s) I
5 .0
0
2 .5
7 .5
I
2
3
0 2 .5 5 7 .5 0 2 .5 5 7 .5 0 2 .5 5 7 .5
D ate
I
2
3
L ig h t/d a r k &
Osm. P o t e n t i a l
L-O
D-O
L -2 .5
D -2 .5
L -5 .0
D -5 .0
L -7 .5
D -7 .5
L ig h t/d a r k &
.Tem perature
L-10
D-IO
L-20
D-20
L -30
D-30
50 27 - 5 .2
53 41 10 3
67 57 37 5
58
45
28
38
2
22
.1
I
71
42
69
60
54
46
48
34
40
55
16
43
17
15
6
44
I
19
2
3
I
15
0
4
24
17
25
38
20
25
69
47
34
43
9
21
2
5
37
16
33
44
16
27
59 40 22 2
73 49 26 7
63 54 27 14
67
57
43
51
13
34
.3
15
42
38
32
48
18
32
Numbers are mean t o t a l g e r m in a tio n p e r c e n t a g e s .
D a tes a r e as f o llo w s :
( I ) l a t e O cto b er, (2 ) l a t e November, and (3 ) e a r ly January.
48 32 10
49 27 9
54 30 10
0
2
4
78
seed from th e l a s t c o l l e c t i o n th a n e i t h e r of th e two o th e r c o l l e c t i o n
d a te s.
C o lle c tio n d a te
changed th e e f f e c t of te m p e ra tu re
on
g e r m i n a t i o n t o t a l s ( T a b le I ) . A lth o u g h 20 C w as p r e f e r r e d o v e r a l l
(36%) and 30 C was th e l e a s t p r e f e r r e d (23%), g e rm in a tio n of seeds a t
10 C in c r e a s e d s u b s t a n t i a l l y as d a te became l a t e r . Seeds o f th e f i r s t
c o l l e c t i o n a t 10 C w ere th e lo w e s t g e rm in a tin g (22%) compared to seeds
a t 20 C (33%). By t h e t h i r d d a t e o f c o l l e c t i o n t h e i m p o r t a n c e o f 10 C
w as su ch t h a t s e e d s i n t h i s t e m p e r a t u r e r e g i m e w e re g e r m i n a t i n g a t
a b o u t t h e same l e v e l a s t h o s e i n t h e 20 C r e g i m e (40%). T h e re w e re no
s i g n i f i c a n t i n t e r a c t i o n s b e tw e e n w a t e r p o t e n t i a l and d a t e o f s e e d
c o lle c tio n .
G erm ination i n t h e d ark was h ig h e r (32%) th a n i n t h e l i g h t (27%)
(Table 1). H ighest g e r m in a tio n was observed w ith seed s exposed- to dark
c o n d i t i o n s a t 20 C (43%) when l i g h t and t e m p e r a t u r e w a s a n a ly z e d .
S e e d s u n d e r g o i n g a t r e a t m e n t o f 30 C i n t h e l i g h t h a d t h e l o w e s t
g e r m i n a t i o n (18%).
P r o g r e s s i v e l y d e c r e a s i n g o s m o t i c p o t e n t i a l s caused s i g n i f i c a n t
d e c r e a s e s i n g e rm in a tio n p e rc e n ta g e s (57 t o 4%) (Table I). I n t e r a c t i o n
e f f e c t s o f o sm otic p o t e n t i a l and l i g h t and dark r e s u l t e d i n response
r e v e r s a l a s w a t e r s t r e s s i n c r e a s e d beyond 0 b a r s . Under no w a t e r
stre ss,
seeds had h ig h e r g e rm in a tio n t o t a l s i n th e l i g h t (65%) th a n i n
th e dark. (49%). H ow ever, t h i s r e l a t i o n s h i p r e v e r s e d a t 2.5 b a r s so
t h a t g e r m i n a t i o n i n t h e d a r k (44%) was g r e a t e r t h a n i n t h e l i g h t
(35%). This re sp o n se co n tin u e d a s o sm o tic p o t e n t i a l s reach ed 5 and 7.5
b a rs.
G erm ination p e rc e n ta g e s d e crea se d a s o sm o tic s t r e s s in c re a s e d ,
b u t th e d e c r e a s e w as l e s s p r e c i p i t o u s f o r s e e d s m a i n t a i n e d i n t h e
79
d a r k . G e r m i n a t i o n r e a c t i o n s t o t e m p e r a t u r e and o s m o t i c p o t e n t i a l
c o m b in atio n s fo llo w e d a p r e d i c t a b l e p a t t e r n . R eg a rd le ss of the o sm o tic
p o te n tia l,
g e r m in a tio n was h ig h e s t i n th e 20 C reg im e fo llo w e d by th e
10 and 30 C re g im e s, r e s p e c t i v e l y .
S tra tific a tio n
h a d no s t a t i s t i c a l
e f f e c t on g e r m i n a t i o n .
Sagebrush seed s a re g e n e r a lly c o n sid e re d to be hondormant (McDonough
and H a rn iss 1975,
C aldw ell 1978). Since s t r a t i f i c a t i o n i s no rm ally a
dormancy b r e a k e r , i t might be e x p ected t h a t p l a i n s s i l v e r sagebrush
w o u ld n o t r e s p o n d t o a c o l d t r e a t m e n t . S a g e b ru s h s e e d s r i p e n and
d i s p e r s e l a t e i n t h e f a l l and e a r l y w i n t e r . Cold t e m p e r a t u r e s a r e
common a t t h i s t i m e i n t h e N o r t h e r n G r e a t P l a i n s and m i g h t a l r e a d y
r e s u l t i n a f i e l d i n d u c e d s t r a t i f i c a t i o n . T h is t y p e o f r e s p o n s e i s
s u g g e s t e d by t h e f a c t t h a t a s s e e d c o l l e c t i o n d a t e becam e l a t e r ,
g e rm in a tio n p e rc e n ta g e s in c re a s e d .
G e r m i n a t i o n o c c u r r e d u n d e r a v a r i e t y o f c o n d i t i o n s , and t h i s
r e s p o n s e c o n f i r m e d t h a t s a g e b r u s h s e e d s do n o t e x h i b i t s p e c i f i c
g e r m i n a t i o n r e q u i r e m e n t s . More optim um c o n d i t i o n s a r e f a v o r e d by
seeds, bu t th e se c o n d itio n s a re n o t r e s t r i c t e d to narrow re q u ire m e n ts.
Rate Response to I n d iv i d u a l F a c to rs
A ll t h r e e s e e d c o l l e c t i o n s e x h i b i t e d s i m i l a r r a t e re s p o n se s to
i n c r e a s i n g w a t e r s t r e s s ( F i g u r e 15). How ever, h i g h e r g e r m i n a t i o n
p e r c e n t a g e s w e re o b s e r v e d a s d a t e o f c o l l e c t i o n a d v a n c e d . The l e s s
n e g a tiv e o s m o tic p o t e n t i a l s had f a s t e r r a t e s of g e rm in a tio n a s w e ll as
h ig h e r g e rm in a tio n p e rc e n ta g e s. R ates o f g e rm in a tio n w ere d eterm in ed
by b o th t h e
s p e e d a t w h ic h s e e d s r e a c h e d
t h e maximum l e v e l
of
80
70
COLLECTION
TREATMENT
■ 0.0 BARS
60 -
•
2.5 BARS
•
•
6.0 BARS
7.6 BARS
I
70
TREATMENT
• 0.0 BARS
60 /3 9 DAYS
—i 5 1.4 %
60 -
•
2.5 BARS
•
•
5.0 BARS
7 JS BARS
COLLECTION
2
/ 3 7 DAYS
68.2
%
50 -
40 -
4 0 DAYS
_ / 38.7 %
304 4 DAYS^
33.0%
E
20
-
20
X 3 3 DAYS
" 12.4 %
100
- -
0
rT ! ■ I I l I M t y r T T
15
20
-
»4 DAYS
16.1 %
10-
, 26 DAYS
____ / 0 -8 %
0
25
30
„z
- -
0
35
......................
+4
10
OBSERVATION TIME (DAYS)
70
-.2 1 DAYS
3.6%
* ' ' ' ' I ' ' ’ ' I ' ' ’ ' I ' ' ' ' I ' ' 1I I ' • ' ' I
15
20
25
30
35
40
45
OBSERVATION TIME (DAYS)
COLLECTION
y 34 DAYS
„ ^ Z61.6X
60 -
0 BARS
50 -
I
.W
2 .5 BARS
40 -
30 -
E
■«
20
-
10-
/ 3 8 DAYS
23.2 X
5 .0 BARS
DAYS
X
BARS
I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' '
0
5
10
15
20
25
30
35
' ' I '
40
' '
I
45
OBSERVATION "HME (DAYS)
F ig u re 15. Osmotic p o t e n t i a l e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s
and r a t e s of g e rm in a tio n . Numbers a re mean v a lu e s f o r a l l
s e e d s u n d e r t h e f o u r p o t e n t i a l s (0, 2 .5 , 5, 7.5 b a r s ) .
Three seed c o l l e c t i o n s a re p re se n te d ( l a t e October, l a t e
November, and e a r l y J a n u a r y ) .
81
g e r m in a tio n (th e s te e p n e s s o f s lo p e s i n t h e f o ll o w i n g g rap h s) and days
a f t e r i n i t i a t i o n of g e rm in a tio n , As w a te r s t r e s s i n c r e a s e d ,
th e r e was
a d e c r e a s e i n b o th am ount o f s e e d g e r m i n a t i n g and r a t e ( s l o p e ) o f
g e rm in a tio n . These f i n d i n g s a re c o n s i s t e n t w ith th e f i n d i n g s o f Bewley
and B la c k (1982) and E vans and Young (1 9 8 2 ). P l a i n s s i l v e r s a g e b r u s h
seems to be v e ry s e n s i t i v e t o in c r e a s e d w a te r s t r e s s and w i l l d e c re a se
g e r m i n a t i o n by a s much a s 1 /3 b e tw e e n 0 and 2.5 b a r s , and by a s much
a s 100 t i m e s b e tw e e n 0 and 7.5 b a r s d e p e n d in g on d a t e o f c o l l e c t i o n
( F i g u r e 15). T h is i s c o m p a r a b le t o t h e r e s p o n s e fo u n d w i t h f r i n g e d
sag ew o rt a s i n c r e a s i n g l y n e g a tiv e o sm o tic p o t e n t i a l s w ere encountered
(Sabo e t a l . 1979).
At l e a s t
th re e a s p e c ts of th e seed g e rm in a tio n p ro c e ss a re
a f f e c t e d by w a t e r u p t a k e fro m t h e s o i l s o l u t i o n (E v an s and Young
1982). They a r e : ( I ) i m b i b i t i o n ,
(2) e n z y m a t i c t r a n s f o r m a t i o n and
m e riste .m atic a c t i v i t i e s , and (3) s t a r t o f growth. As o s m o tic p o t e n t i a l
becomes more n e g a tiv e , i t becomes h a rd e r f o r th e seed t o ta k e up w a te r
to meet th e needs of th e s e th r e e s ta g e s . I n the p r e lim in a r y i m b i b i t i o n
sta g e ,
w a t e r u p ta k e i s c r i t i c a l b e c a u s e i t i n i t i a l i z e s e n z y m a t i c
t r a n s f o r m a t i o n , m e r i s t e m a t i c a c t i v i t i e s and f i n a l l y t h e s t a r t o f
e lo n g a tio n and emergence of th e r a d i c l e .
In g e n e ra l,
in c r e a s e d w a ter
s t r e s s d e la y s c o m p letio n of and red u ces g e rm in a tio n . T his i s caused by
decreased w a te r a b so rp tio n ,
d is tu r b e d n u t r i e n t u p ta k e ,
a b n o rm a l
m etabolism and reduced grow th (Parmar and Moore 1966). F a c to r s such as
th e se undoubtedly c o n tr ib u te d t o th e r e d u c t i o n i n g e rm in a tio n t h a t was
o b s e r v e d . i n t h i s study under i n c r e a s e d m o is tu re s t r e s s .
82
Seed c o l l e c t i o n d a t e a f f e c t e d t h e r e s p o n s e t o a l l f a c t o r s and
i n t e r a c t i o n s o f f a c t o r s . As seed was c o l l e c t e d l a t e r ,
enhanced r e g a r d l e s s o f o th e r c o n d itio n s .
g e rm in a tio n was
A lth o u g h m o st s e e d i s
d is p e r s e d i n th e f i r s t . f e w weeks a f t e r r ip e n in g , seed re m a in in g on the
p l a n t pro b ab ly a t t a i n s g r e a t e r m a tu r ity .
Research on e f f e c t s o f seed
r ip e n in g o r m a tu r ity have i n d i c a t e d t h a t l a t e r seed c o l l e c t i o n s showed
h ig h e r g e r m in a tio n p e rc e n ta g e s (Clor e t a l .
1974, W aller e t a l .
1980,
Krueger and Shaner 1982).
When a l l
f a c t o r s w e re c o n s i d e r e d t o g e t h e r ,
h i g h e s t a t 20 C a n d l o w e s t a t 30 C. H o w e v e r ,
g e r m i n a t i o n was
th e
e ffe c ts
of
t e m p e r a t u r e on g e r m i n a t i o n ch an g ed w i t h r e s p e c t t o s e e d c o l l e c t i o n
p e rio d (F ig u re 16). Changes w ere i n r e s p e c t t o im p o rtan ce of the 10 C
regim e.
As c o l l e c t i o n d a te advanced,
h ig h e s t g e r m in a tio n was s t i l l
o b s e r v e d u n d e r t h e 20 C r e g im e . I n c o n t r a s t , t h e l o w e s t t e m p e r a t u r e
re g im e
(10
C) becam e
m ore i m p o r t a n t
in
stim u la tin g
g e r m i n a t i o n . Under t h i s t e m p e r a t u r e r e g i m e ,
in c re a se d
t w i c e a s many s e e d s
g e r m i n a t e d fro m t h e t h i r d c o l l e c t i o n d a t e (40%) a s fr o m t h e f i r s t
c o lle c tio n
d a te
(22%).
The f a s t e s t
g e rm in a tio n r a t e s
w e re
a lso
r e c o r d e d i n t h e 20 C r e g i m e . Seed s a t 10 C had t h e s l o w e s t s t a r t i n g
and th e l o n g e s t g e rm in a tio n p e r i o d s r e c o r d e d . When t h i s g e r m i n a t i o n
p e rio d i s c o n sid e re d ,
th e l a s t c o l l e c t i o n o f seed had no s i g n i f i c a n t
d i f f e r e n c e b e tw e e n t h e 10 and 20 C t e m p e r a t u r e r e g i m e s .
of
v a lu e
in
c h a ra c te riz in g
seed
R a te s o f
g e rm in a tio n
are
resp o n ses
to
te m p e ra tu re ,
alth o u g h th e r e i s o f te n c o n s id e r a b le v a r i a b i l i t y due to
g e n e t i c d i f f e r e n c e s ( Bewl e y and B la c k 1982). G enetic su b p o p u la tio n s
w i l l g e r m i n a t e u n d e r d i f f e r e n t t e m p e r a t u r e r e g i m e s and r a t e s w i l l
83
70
7 0 -I
COLLECTION
COLLECTION
TREATMENT
50 -
I
♦
o
10*C
20* C
*
30* C
♦
"
•
50 -
10* C
20* C
30* C
40 °
3 0 DAYS
33.1 %
30 -
I
8
23 DAYS
24.5 %
E
20
30-
-
, 4 0 DAYS
» 26.4 %
20
-
2 3 DAYS
21.6 %
44 DAYS^
21.7%
10-
0-)-,-f l f |
0
, 3 0 DAYS
38.7 %
E
10-
2
TREATMENT
60 -
5
I 1 1 * ' I ' 1 ' ' I ' ' ' ' I ' ' ' ... .. .. .. .. .. .. .. .
10
15
20
25
30
0
35
40
45
- -
0
5
I
1 ' ' ' ' I 111' I ' ‘
10
15
OBSERVATION TIME (DAYS)
20
25
' I 1 ' ' ' I '
1I ■ ■ ' • I
30
40
35
45
OBSERVATION TIME (DAYS)
70
COLLECTION
3
60 -
50 -
I
38 DAYS
V r 40.3 %
23 DAYS
» - « / 39.5 %
40-
I ■
8
E
30-
-
/
21 DAYS
24.9 %
♦IOC
o 20 C
* 30 C
100
0
5
10
15
20
25
30
35
40
45
OBSERVATION TIME (DAYS)
F i g u r e 16. T e m p e r a tu r e e f f e c t s on t o t a l g e rm in a tio n p e rc e n ta g e s and
r a t e s o f g e r m i n a t i o n . N umbers a r e mean v a l u e s f o r a l l
s e e d s u n d e r t h e t h r e e t e m p e r a t u r e s (1 0 , 2 0 , and 30 C).
Three seed c o l l e c t i o n s a re p re s e n te d ( l a t e October, l a t e
November, and e a r l y J a n u a r y ) .
84
change w ith th e se te m p e ra tu re s . McDonough and H a rn iss (1975) n o te t h a t
g e r m i n a t i o n t i m e i n b i g s a g e b r u s h d e c r e a s e d fr o m 18 t o 2 d a y s w i t h
in c re a s in g , te m p e ra tu re s .
One a p p a r e n t
sag eb ru sh
is
re p ro d u c tiv e
th a t
seed
c h a ra c te ristic
can g e r m in a te
over
in
p la in s
a w id e
s ilv e r
ran g e
t e m p e r a t u r e s . T h is i s a l s o c h a r a c t e r i s t i c o f b i g s a g e b r u s h .
of
T h is
c h a r a c t e r i s t i c a s w e ll a s the changing r e l a t i o n s h i p o f te m p e ra tu re and
s e e d c o l l e c t i o n d a t e s u g g e s t a d a p t i v e f e a t u r e s f o r h e te r o g e n e ity of
seed p o p u la tio n s .
a b ility
to
C ald w ell (1978) r e g a r d s sag e b ru s h e s ’ (most sp e c ie s)
g e rm in a te
over
a w id e
range
of
te m p e ra tu re s
as
a
c o m p e titiv e advantage over o th e r a s s o c i a t e d s p e c ie s . A s u b s t a n t i a t i o n
o f McDonough and H a r n i s s ’ (1975) i m p l i c a t i o n t h a t t h e r e a r e g e n e t i c
s u b p o p u la tio n s of sag e b ru sh w ith c h a r a c t e r i s t i c te m p e ra tu re o p tim a f o r
g e rm in a tio n i s a p p a re n t i n th e a b i l i t y o f p l a i n s s i l v e r sagebrush seed
to g e rm in a te over a wide range of te m p e ra tu re s . This h e te r o g e n e ity of
g e rm in a tio n re q u ire m e n ts a llo w seeds t o g e rm in a te under a v a r i e t y of
e n v iro n m e n ta l c o n d itio n s t h a t th e seed w i l l e n c o u n te r i n th e e a r ly
g ro w in g s e a s o n .
T h is i s m a n i f e s t e d b o th i n t h e n u m b e rs o f s e e d s
g e rm in a tin g and r a t e s of g e rm in a tio n i n r e l a t i o n to te m p e ra tu re .
G e r m i n a t i o n r e s p o n s e s u n d e r l i g h t o r dark c o n d itio n s in d ic a te d
t h a t g e r m i n a t i o n w as s l i g h t l y f a v o r e d by a d a rk e n v i r o n m e n t i n a l l
c o l l e c t i o n d a te s (F ig u re 17). Rates w ere n o t d i f f e r e n t betw een th e two
tr e a tm e n ts , a lth o u g h g e rm in a tio n p e rio d s w ere g e n e r a lly lo n g e r i n the
dark. In l i g h t , t h i s p e rio d was from 24 to 43 days w h ile i n dark seeds
g erm in ated from 38 to 44 days. D if f e r e n c e s among and w i t h i n in d i v i d u a l
c o l l e c t i o n d a te s w ere s m a ll even though g e rm in a tio n t o t a l s w ere h ig h e r
85
70
70
COLLECTION
60 -
COLLECTION
2
TREATMENT
TREATMENT
50 -
•
UGHT
•
DARK
40 -
44 DAYS
26.7% \
30 -
-
10
—
0
UGHT
DARK
40 -
g
20
•
•
4 3 DAYS ^
24.0 %
I
S 30O
B
J
24 DAYS
28.7%
40 DAYS
/ 2 9 .1 %
10-
•
I
I
10
15
' 1' I ' 1■ ' I ' ' ' ' I ' ' ' 1I ■ ■ ' • I ' ' ' ' I
20
25
30
35
40
' 1 ' ' ' ' 1' ' "' • ' ' 11I 1 111 I 11I I I i
15
20
25
30
35
40
45
OBSERVATION TIME (DAYS)
OBSERVATION TIME (DAYS)
70
COLLECTION
3
50 -
I
40 -------------- x 25 DAYS
0 30.6 %
O 30 B
20
y 38 DAYS
39.2 %
-
• LIGHT
• DARK
100
10
I ' ' ' ' I ' ' ' ' I
15
20
25
' I ' ' ' ' I ' ' ' ' I ' 1 1 1I
30
35
40
45
OBSERVATION TIME (DAYS)
F ig u r e 17. L i g h t / d a r k e f f e c t s on t o t a l g e r m in a tio n and r a t e s o f
g e rm in a tio n . Numbers a re mean v a lu e s f o r a l l seeds under
t h e tw o t r e a t m e n t s ( l i g h t an d d a r k ) . T h r e e s e e d
c o lle c tio n s a re p re se n te d ( l a t e O c to b e r, l a t e N ovem ber,
and e a r l y Jan u ary ).
86
i n s e e d s fro m th e t h i r d c o l l e c t i o n d a te . On t h e f i r s t c o l l e c t i o n ,
g e r m i n a t i o n w as 27 and 24% f o r d a r k and l i g h t , r e s p e c t i v e l y . On th e
th ird
c o lle c tio n ,
s e e d s i n d a rk had 39% g e r m i n a t i o n w h ile l i g h t
tr e a te d seed s w ere a t 31%.
The e f f e c t s o f l i g h t on seed g e rm in a tio n i s v a r ia b le depending on
s p e c ie s in v o lv e d and complex i n t e r a c t i o n s w ith en v iro n m e n ta l f a c to r s
su ch a s t e m p e r a t u r e , w a te r r e l a t i o n s and tim e (A l-.Ani e t a l . 1972,
W o o lley and S t o l l e r 1978, Cook 1980, B ew ley and B la c k 1982). L ig h t
seems to be more im p o rta n t i n seed s r e q u ir in g a dorm ant p e rio d and a
dorm ancy b r e a k in g m ech an ism . B e c a u se m o st s a g e b ru s h s p e c i e s a r e
re g a rd ed a s nondorm a n t,
e v id e n c e f o r
l i g h t may n o t be o f c r i t i c a l im p o rtan ce. The
g e rm in a tio n
re sp o n se s
in
o th e r
A r te m is ia
s p e c ie s
i n d i c a t e s a v a r i a b l e i n f l u e n c e . S t u d i e s on f r i n g e d s a g e w o r t and b ig
s a g e b ru s h d e m o n s tr a te d s i g n i f i c a n t l y m ore g e r m i n a t i o n w i t h l i g h t
(W eldon e t a l . 1 957, B e e tle 1960, C a ld w e ll 1978, W ilso n 1 9 8 2 ), b u t
o t h e r s h av e show n th e o p p o s i t e r e s p o n s e (S abo e t a l .
1979).
Seed
b u r ia l and i t s r e l a t i o n s h i p to l i g h t c o n d itio n s seem s to be o f m ajor
im p o rtan ce i n f i e l d em ergence and s u r v iv a l o f p la in s s i l v e r sagebrush
(d is c u ss e d on pp.
107-124).
T h ere w e re s e v e r a l i m p o r ta n t e n v ir o n m e n ta l i n t e r a c t i o n s t h a t
a ffe c te d
g e rm in a tio n
re sp o n se
to
in d iv id u a l
fa c to rs .
T hese
i n t e r a c t i o n s w e re m o st e a s i l y i n t e r p r e t e d by e v a lu a tin g g e rm in a tio n
r e s p o n s e to any tw o f a c t o r s ta k e n t o g e t h e r . F o r e x a m p le , l i g h t and
d a rk t r e a t m e n t s w e re i n v e s t i g a t e d i n c o n ju n c t io n w ith th e t h r e e
t e m p e r a t u r e r e g im e s . By u s in g t h i s a p p ro a c h , th e e f f e c t s o f s i n g l e
fa c to rs
c o u ld
be
put
in
b e tte r
p e rs p e c tiv e
because
th e y
w ere
87
superim posed upon a second v a r ia b le .
M oreover,
in d iv id u a l c o lle c tio n
d a te s could a ls o be e v a lu a te d i n more d e p th w ith in t h i s c o n te x t. Thus
i t becam e c l e a r t h a t c o l l e c t i o n d a t e ch an g ed t h e r e l a t i o n s h i p s o f
l i g h t and d a rk w i t h i n th e d i f f e r e n t t e m p e r a t u r e s r e g im e s . T h is i s
i l l u s t r a t e d by F ig u re s 18, 19» and 20 in which l i g h t and d ark re g im e s
a r e co m p ared a t th e t h r e e t e m p e r a t u r e s and f o r th e t h r e e c o l l e c t i o n
d a te s .
1!
In g e n e ra l, d ark c o n d itio n s r e s u l t e d i n h ig h e r g e rm in a tio n i n a l l
t h r e e c o l l e c t i o n s . When s e e d s fro m th e f i r s t c o l l e c t i o n d a te w e re
g erm in ated under l i g h t ,
e s s e n t i a l l y no d if f e r e n c e s could be d e te c te d
w ith r e s p e c t to te m p e ra tu re regim e (F ig u re 18). However, as c o lle c tio n
d a te advanced te m p e ra tu re e x e rte d more o f an in flu e n c e on g e rm in a tio n
( F ig u r e s 19» 20). By th e t h i r d d a t e , . l i g h t co m b in ed w i t h th e 10 C
te m p e ra tu re showed s i g n i f i c a n t l y h ig h e r g e rm in a tio n (42%) th a n e i t h e r
th e 20 o r 30 C r e g im e s (32 and 18% r e s p e c t i v e l y ) .
te m p e ra tu re
The h ig h 30 C
r e s u l t e d i n lo w e s t g e rm in a tio n from a l l th r e e d a te s when
l i g h t w as p r e s e n t . I n c o n t r a s t , d a rk t r e a t e d s e e d s 'g e n e r a l l y show ed
b e s t g e r m i n a t i o n u n d e r th e 20 C r e g im e and l e a s t a t 1 0 C . Under d a rk
c o n d itio n s , d if f e r e n c e s among te m p e ra tu re re g im e s w ere commonly 10% -or
m ore d e p e n d in g upon c o l l e c t i o n d a te . G e rm in a tio n r e s p o n s e s d id n o t
v ary t h i s much i n th e l i g h t . In d ark c o n d itio n s , g e rm in a tio n r a t e s (o r
slo p e s ) were slo w er and s t a r t o f g e rm in a tio n was u s u a lly delayed by
th re e to s ix days. The t o t a l p e rio d o f g e rm in a tio n was a ls o prolonged,
e s p e c ia lly
f o r th o s e s e e d s i n t h e 10 C t e m p e r a t u r e re g im e w h e re
g e r m in a tio n o c c u r r e d a t 38 t o 44 d a y s . On th e t h i r d c o l l e c t i o n , th e
e x te n d e d g e r m i n a t i o n .p e r i o d r e s u l t e d i n s e e d r e s p o n s e a t 10 C b e in g
88
70
—,
TREATMENT
♦ 10‘ C
LIGHT
» 20* C
60 -
* 30* C
(%) GERMINATION
50 -
40 -
30 —
„=o=oD;:s e e *
20
2 4 DAYS
25.0 %
-
*
‘ °
10
/
4 3 D A Y S/
24.1 %
2 1 DAYS^
22.2
*
%
-
o **
0
♦
- T t M I
T
0
T-llllI
10
15
5
20
25
' ! ' ' ' ' I 1111I
30
35
40
45
OBSERVATION TIME (DAYS)
70
TREATMENT
♦
10*0
DARK
» 20° C
60 -
* 30° C
:%) GERMINATION
50 / 3 0 DAYS
40 -
°
40.2 %
30 —
D
20
-
/ 2 3 DAYS
26.1 %
. . . .
.
A
0AA
44 D A Y S/
1 7 .0 %
10 .............•
................................................
5
10
15
20
25
30
I
35
' '
I ' ' ' ‘ I
40
45
OBSERVATION TIME (DAYS)
Figure
18.
L i g h t / d a r k c o m p a r is o n s among t h r e e t e m p e r a t u r e s and t h e i r
e f f e c t on t o t a l g e r m i n a t i o n p e r c e n t a g e s and r a t e s o f
g e rm in a tio n . F i r s t seed c o l l e c t i o n ( l a t e O ctober) d a ta i s
p r e s e n te d . N um bers a r e mean v a lu e s f o r a l l s e e d s i n t h i s
c o lle c tio n period.
89
70
TREATMENT
♦ 10*C
LIGHT
» 20* C
60 -
» 30* C
60 -
I
40 ++ + +_ + /
H 0 C 0 = - O
23 DAYS
37.1 %
^ 2 4
DAYS
30 33.3 %
?
20
-
* .
' IA
*
**
> -2 1 DAYS
15.8 %
10 S ♦
-f-H-
1I
' 1 • ■I
40
45
OBSERVATION TIME (DAYS)
70
TREATMENT
♦ 10°C
DARK
o 20°C
60 -
* 30* C
50 -
I
S
a
OO
40 -
CO = =------------------- »
30-
*
1
* *
20
/ 3 0 DAYS
44.0 %
*-23 DAYS
27.3 %
-
A O
10 -
4 0 DAYS
15.8%
It
Pt
. ♦ ♦ ♦
1 I r
r I r
10
15
1T r
20
25
tT
30
35
I ' ' ' ‘ I
40
45
OBSERVATION TIME (DAYS)
Figure
19.
L i g h t / d a r k c o m p a r is o n s among t h r e e t e m p e r a t u r e s and t h e i r
e f f e c t s on t o t a l g e r m i n a t i o n p e r c e n t a g e s and r a t e s o f
g e r m i n a t i o n . S e c o n d s e e d c o l l e c t i o n ( l a t e November) d a t a
i s p r e s e n te d . N um bers a r e m ean v a lu e s f o r a l l se e d s i n
th is c o lle c tio n period.
90
70
LIGHT
60 -
(%) GERMINATION
50 x 24 DAYS
42.3%
40 -
DAYS
30 -
20
-
♦ I o'C
" 20'C
1 30'C
> 2 1 DAYS
*
10 -
♦
♦
' I ' ' ' ' I '
10
15
20
' I ' ' ' ' I ' ' ' ' I
25
30
' I • ■• 1I
40
45
35
OBSERVATION TIME (DAYS)
70
DARK
(%) GERMINATION
50 -
, 2 3 DAYS
O o O O O—O 47.5%
O
d
0 0 0
d
40 -
,3 8 DAYS
/ 3 8 .3 %
v21 DAYS
***^31.8%,
30 -
♦♦
20
-
♦
A°
10 0
♦
♦ 1 0 'C
" 20 C
♦
» 30 C
- -
0
' I 1 ' ' ' I
30
35
' I ' ' ' ' I
40
45
OBSERVATION TIME (DAYS)
Figure
20.
L i g h t / d a r k c o m p a r i s o n s among t h r e e t e m p e r a t u r e s and t h e i r
e f f e c t s on t o t a l g e r m i n a t i o n p e r c e n t a g e s and r a t e s o f
g e rm in a tio n . Third seed c o l l e c t i o n (e a rly Jan u ary ) d a ta i s
p r e s e n te d . N um bers a r e mean v a lu e s f o r a l l s e e d s i n t h i s
c o lle c tio n period.
91
s l i g h t l y h ig h e r th an t h a t o f th e 30 C reg im e but s t i l l lo w e r th a n seed
r e s p o n s e a t 20 C.
My r e s u l t s h a v e d e m o n s tr a te d t h a t p la in s s i l v e r sag eb ru sh seed
can g e r m in a te u n d e r b o th l i g h t and d a r k c o n d i t i o n s . H ow ever, l i g h t
see m s
to
be l e s s
e ffe c tiv e
in
i n d u c in g
g e rm in a tio n
th a n
d a rk
c o n d i t i o n s . B e c a u se t e m p e r a t u r e r e l a t i o n s h i p s ch an g e a c c o r d in g to
l i g h t o r d a rk t r e a t m e n t , i t seem s a p p a r e n t t h a t th e i n t e r a c t i o n s o f
l i g h t and te m p e r a tu r e
can e ith e r
s tim u la te
or in h ib it
seed
g e rm in a tio n . This could be o f c o n s id e ra b le im p o rtan ce w ith re g a rd s to
se e d b e in g b u r ie d o r on th e s o i l s u r f a c e . D u rin g th e g ro w in g s e a s o n ,
t e m p e r a t u r e s a r e n o r m a lly h ig h e r and f l u c t u a t e m ore on t h e s o i l
s u r f a c e . T h is m eans t h a t s u r f a c e c o n d i t i o n s e x i s t t h a t w i l l p r o v id e
lim ite d
g e r m i n a t i o n o f th o s e
te m p e r a t u r e and l i g h t r e g im e s .
seed s a b le
to re s p o n d t o v a r i a b l e
H ow ever,
c o o l e r and m ore s t a b l e
t e m p e r a t u r e s e x i s t b e n e a th th e s o i l s u r f a c e . S in c e d a r k c o n d i t i o n s
a ls o p r e v a il,
t h i s p ro v id e s a more fa v o ra b le env iro n m en t f o r seed s to
g e r m in a te . The h e t e r o g e n e i t y a s s o c ia te d w ith in d iv id u a l g e rm in a tio n
re q u ire m e n ts or s i t e s c r e a te s a w ide range o f en v iro n m e n ta l c o n d itio n s
to which p la in s s i l v e r sagebrush seem s w e ll adapted.
The e f f e c t s o f o s m o tic p o t e n t i a l on see d g e r m i n a t i o n ch an g e
a c c o r d in g
to
w h e th e r l i g h t o r d a rk c o n d i t i o n s p r e v a i l
21 , 2 2 , 23). No s i g n i f i c a n t d i f f e r e n c e s , i n r e g a r d s to
( F ig u r e s
t h e s e two
f a c t o r s , w e re o b s e rv e d a s s e e d c o l l e c t i o n d a te a d v a n c e d . At o s m o tic
p o t e n t i a l s o f 0 b a r s , g e r m i n a t i o n w as h i g h e r i n th e l i g h t re g im e .
G erm ination t o t a l s w ere from 10 to 22 p e rc e n t h ig h e r i n l i g h t th an i n
dark a t t h i s o sm o tic p o te n tia l, In t h i s reg im e, t o t a l s ranged from 58
0 .0
BAR
60 °
2 .5
x 24 DAYS
58.0 %
60 -
50-
8
.39 DAYS
/ 4 4 .9 %
50-
j
44 DAYS
38.2 % \
40 -
4 3 DAYS
27 .8 % X
O30g
30-
20-
20-
TREATMENT
100
- -
I ' ' 11I ‘ *
10
15
0
o
UGHT
•
DARK
TREATMENT
LIGHT
DARK
io -
' I ' ' ' ' I ' ' 1‘ I 1 ' ' ' I ' ' ‘ ' I ' ' ' ' I
20
25
30
35
40
45
0-| I
0
I ' ' ' ' I ' ' ‘ ‘ I ' ' ' ’ I ' ' ' r I ' ' ' ' I 1 ' ' ' I ' ' ' ' I ' ' 1 ' I
5
10
OBSERVATION TIME (DAYS)
15
20
25
30
35
40
45
OBSERVATION TIME (DAYS)
7 0 -.
70 i
5 .0
7 .5
BAR
•
UGHT
•
DARK
BAR
NO
rv>
60 -
TREATMENT
I
BAR
50 -
40 -
B
20
-
10
-
^ 3 3 DAYS
2 2.3%
20
-
TREATMENT
LIGHT
10.
. „ O e e • • o Oe e o e O O e e ---------------------- -
0
- -
0
f I ' ' ' ' I ' ' ' ' I ' ' ' ' I 1 ' ' ' I ' ' ' ‘ I ' ' ' ' I ' ' ' 1 T
5
10
15
20
25
30
OBSERVATION TIME (DAYS)
F igure
21.
DARK
31 DAYS
2.4%
35
40
' ' ' I
45
0
...........................1 1
- -
0
5
10
15
20
25
30
35
1I ‘
40
' I
45
OBSERVATION TIME (DAYS)
O sm o tic p o t e n t i a l c o m p a r is o n s b e tw e e n l i g h t and d a rk and t h e i r e f f e c t s on t o t a l
g e r m in a tio n p e r c e n ta g e s and r a t e s o f g e rm in a tio n . F i r s t seed c o l l e c t i o n ( l a t e O ctober)
d a t a i s p r e s e n t e d . Numbers a r e mean v a l u e s f o r a l l s e e d s i n t h i s c o l l e c t i o n p e r i o d .
0 .0
BAR
70
2 .5
70
BAR
X 24 DAYS
69.4 %
50 -
50 -
40 DAYS
|
"i ' V .
3 7 DAYS
4 6 .9 %
40 -
30 -
DAYS
3 4 .3 %
I
20
-
TREATMENT
100
- -
0
^T
5
I ' ‘
10
•
UGHT
•
DARK
20 -
TREATMENT
io _
' I ' ' ' ' I ' ' ' ' I ' ' ‘ 1I' ' ‘ ' I ' ' ' 1I ' ' ' ' I
15
20
25
30
35
40
45
I *' ' ' I ' ' ' 1I ' 1' ' I 1
15
20
25
30
10
OBSERVATION TIME (DAYS)
UGHT
DARK
' I ■’ • ' I ' ’ ' ' I
35
40
45
OBSERVATION TIME (DAYS)
70
5 .0
•
•
7 .5
BAR
60 -
60 -
50 -
50 -
BAR
VO
LU
I
40 -
30 -
I
B
20
100
21.2 %
•
-
- -
0
22.
UGHT
•
DARK
TREATMENT
10-
'
________
I‘ 1’ ‘ I
r I ‘ ‘ ' 1 I 11‘ 1 I 1’ 1 ‘ I ’ 1 ' 1 I 1‘ 11I 1 1’ 1 I 11
5
10
15
20
25
-
21 DAYS
e
30
OBSERVATION TIME (DAYS)
F igure
•
•
20
TREATMENT
^ 2 1 DAYS
8 .9 %
;.°
30-
B
x 2 4 DAYS
35
40
45
0
_ 50%\
0
5
10
15
20
UGHT
•
DARK
21 DAYS
2.2
- -
•
%
' I ' ' ' ' I'
25
30
' I‘
35
' I ‘ 1‘ ' I
40
45
OBSERVATION TIME (DAYS)
O sm o tic p o t e n t i a l c o m p a r is o n s b e tw e e n l i g h t and d a r k and t h e i r e f f e c t s on t o t a l
g e rm in a tio n p e r c e n ta g e s and r a t e s of g e rm in a tio n . Second seed c o l l e c t i o n ( l a t e
November) d a t a i s p r e s e n t e d . Numbers a r e mean v a l u e s f o r a l l s e e d s i n t h i s c o l l e c t i o n
period.
0 .0
BAR
2 .5
BAR
/ 2 2 DAYS
, • • • eZ 6 6 .7 %
/ 3 4 DAYS
,./5 6 .7 %
.35 DAYS
,/5 1 .0 %
I
/ 2 3 DAYS
—» 4 2 . 8 %
4 0 -
• LIGHT
• LIGHT
• DARK
• DARK
O --M -
' I '
20
"n
25
45
' 1
10
' ' ' " I ' ' " I ' ' ' ' I ' ' ' ' I ' ' ' ' I'
15
20
25
30
35
40
OBSERVATION TIME (DAYS)
OBSERVATION VUE (DAYS)
5 .0
BAR
7 .5
BAR
VO
• LIGHT
• DARK
y 3 8 DAYS
______ X 3 3 8%
9
10
/ 2 5 DAYS
12 .7 %
* LIGHT
' DARK
—
^ 3 0 DAYS
15 J %
' I '
20
OBSERVATION TIME (DAYS)
OBSERVATION TIME (DAYS)
F igure
23.
O sm otic p o t e n t i a l c o m p a ris o n s b etw een l i g h t and d a rk and t h e i r e f f e c t s on t o t a l
g e rm in a tio n p e rc e n ta g e s and r a t e s of g e rm in a tio n . T hird seed c o l l e c t i o n (e a rly
J a n u a r y ) d a t a i s p r e s e n t e d . Numbers a r e mean v a l u e s f o r a l l s e e d s i n t h i s c o l l e c t i o n
P G x 1I O Q •
95
to 6 9% i n t h e l i g h t and 45 to 57% i n t h e d a rk d e p e n d in g on d a te o f
c o lle c tio n . When seed s a r e lo c a te d on th e s o i l s u rfa c e w here l i g h t i s
g e n e r a lly a. c o n s ta n t f a c t o r ,
g e rm in a tio n would be fa v o re d o n ly when
w a te r i s f r e e l y a v a ila b le . This r e l a t i o n s h i p was re v e rs e d a t 2.5 b a rs
so t h a t d a rk c o n d i t i o n s w e re s l i g h t l y fav o red , a lth o u g h g e rm in a tio n
p e rio d s w ere le n g th e n e d . D iffe re n c e s o f around 10% w ere n o ted h e re i n
a l l c o l l e c t i o n d a t e s b e tw e e n s e e d s i n d a rk and th o s e i n t h e l i g h t .
Response d if f e r e n c e s to l i g h t and d ark re g im e s became g r e a te r a s w a te r
s t r e s s i n c r e a s e d fro m 2.5 b a r s t o 5 and 7.5 b a r s . D ark c o n d i t i o n s
seem ed to a m e l i o r a t e th e e f f e c t o f i n c r e a s e d w a te r s t r e s s on s e e d s .
G e r m in a tio n u n d e r d a rk c o n d i t i o n s a t t h e s e m ore n e g a t i v e o s m o tic
p o t e n t i a l s w as 2 to 30 tim e s g r e a t e r th a n t h a t o f l i g h t c o n d i t i o n s .
T h e r e f o r e , g e r m i n a t i o n i n l a t e r s t a g e s o f th e g ro w in g s e a s o n , when
m o is tu r e c o n d i t i o n s a r e g e n e r a l l y m ore s e v e r e , w o u ld be f a v o r e d i n
d a rk e n v ir o n m e n ts su c h a s b u r i a l i n t h e s o i l . G e rm in a tio n r a t e s o r
tim e to re a c h maximum g e rm in a tio n w ere n o t s u b s t a n t i a l l y d i f f e r e n t i n
any o f th e reg im es.
The g e rm in a tio n re sp o n se t h a t was ob serv ed when o sm o tic p o te n tia l
was c o n sid e re d alo n g w ith te m p e ra tu re re g im e s showed t h a t th e re w ere
d iffe re n c e s in
g e r m in a tio n t o t a l s
among c o l l e c t i o n
d a t e s and a
changing im p o rtan ce o f th e 10 C te m p e ra tu re regim e a s c o lle c tio n d a te
a d v a n c e d ( F ig u r e s 2 4 , 2 5 , 2 6 ). G e rm in a tio n t o t a l s i n c r e a s e d i n a l l
p o t e n t i a l s a s d a te a d v a n c e d and t h i s i s e s p e c i a l l y t r u e f o r s e e d s
g e rm in a tin g a t 10 C. At 0 b a rs , g e rm in a tio n i n t h i s te m p e ra tu re regim e
in c r e a s e s from 50% on th e f i r s t d a te to 67% on th e th ir d . G erm in atio n
o .o
BAR
/ S i DAYS
585%
3 9 DAYS
../I50.2%
♦ 10* C
e 20* C
• 3 < fC
15
20
25
30
35
OBSERVATION TIME (DAYS)
VO
OV
OBSERVATION TIME (DAYS)
F ig u r e 24
O sm o tic p o t e n t i a l c o m p a r is o n s am ong t h r e e t e m p e r a t u r e s and t h e i r e f f e c t s on t o t a l
g e r m in a tio n p e r c e n ta g e s and r a t e s o f g e r m in a tio n . F i r s t seed c o l l e c t i o n ( l a t e O ctober)
d a t a i s p r e s e n t e d . Numbers a r e mean v a l u e s f o r a l l s e e d s i n t h i s c o l l e c t i o n p e r i o d
0 .0
. . "O"
.
. . . . .
'
BAR
2 .5
. ' { T ---------------> 2 2 DAYS
. . .
BAR
3 0 DAYS
7 3.3%
-------------------
3 7 DAYS
523%
"
* 3 0 DAYS
48.7 %
.**
'
" \
4 0 DAYS
4 0 .8 %
*
TREATMENT
.
' ^ I 1 1 11I ' ' '
S
10
15
1 I '
1' ‘ I 1
20
25
30
35
.
10‘ C
«
20* C
*
30* C
> 2 3 DAYS
•
10*0
20*0
.
30*0
♦
' ■■I '
40
' ' .................................................. I 1
1' ' ' ' *I ’■'1I1'1'I 1' 1' 1I ' 11' I 111' I 1111I ''
10
OBSERVATION TIME (DAYS)
5 .0
TREATMENT
15
20
25
30
35
40
OBSERVATION TIME (DAYS)
BAR
7.5
BAR
TREATMENT
„
21 DAYS
93 % \
;::****«»— *
: .
1f i|t;
10*0
20*0
„ 2 4 DAYS
%
♦ 10*0
• 2(fC
30*0
9.7
I' ' ' ' I' ' ' ' I' ' ' ' I' ' ' ' I' ' ' ' I' ' ' ' I' ' ' ' I
10
15
20
25
30
OBSERVATION TIME (DAYS)
35
40
45
I,
^ 2 1 DAYS
. . . . . . . . . . .
2 , DAYS
I l t t m t t I > ^ -21 DAYS
25
8.5 %
2 .7 %
1.7%
*
30*0
' I '
30
OBSERVATION TIME (DAYS)
F ig u r e 25. O sm o tic p o t e n t i a l c o m p a ris o n s among t h r e e t e m p e r a t u r e s and t h e i r e f f e c t s on t o t a l
0 .0
70I
BAR
21 DAYS
I 6 3 .0 %
21 DAYS
5 4.8 %
50-
35 DAYS
56.5 %
50 -
I
£
30 -
B
-
♦
-
e
20* C
30* C
> ' 2 1 DAYS
302 %
30-
TREATMENT
20
IOeC
*
40 -
B
TREATMENT
10
2 3 DAYS
5 4 .0 % __
/
40 -
20
BAR
60 -
60 -
I
2 .5
70
34 DAYS
67.0 %
*
-
10-
♦
10*C
■
20* C
«
30*0
A°
0 —{ t f I + f I . . . I . . . . j . . . t p
0
5
10
15
■. ■I ■. I i I I i ■• I • • >I I - • • • I
20
25
30
35
40
0
-
-
0
45
' I ' ‘
15
OBSERVATION TIME (DAYS)
‘ I ' ’ ' ' I' ‘
20
25
JI ■1■' I '
30
35
OBSERVATION TIME (DAYS)
70
70
5 .0
BAR
7.5
VO
OO
BAR
Z 3 8 DAYS
’*
3 2 .7 %
2 6.7 % ,
TREATMENT
♦
‘
^ 2 1 DAYS
10.3 %
TREATMENT
10*C
•
20* C
*
30* C
.......................
i*
15
20
25
30
OBSERVATION TIME (DAYS)
: %%
„"°
•
....
F ig u re 26.
1I 1’ ’ ’ I
40
45
21 daysV -3 *
“
*“
30* C
to d a ys
; ; * -------------------*
4 .a %
...................................................................
5
10
15
20
25
30
35
40
OBSERVATION TIME (DAYS)
O sm otic p o t e n t i a l c o m p a riso n s among t h r e e te m p e r a tu r e s and t h e i r e f f e c t s on t o t a l
g e r m in a tio n p e r c e n ta g e s and r a t e s o f g e rm in a tio n . T hird seed c o l l e c t i o n (e a rly
J a n u a r y ) d a t a i s p r e s e n t e d . Numbers a r e mean v a l u e s f o r a l l s e e d s i n t h i s c o l l e c t i o n
99
a t 10 C w as s e c o n d o r t h i r d i n im p o r ta n c e on t h e f i r s t and sec o n d
d a te s i n a l l p o t e n tia ls . However, th e th i r d c o lle c tio n showed seed s a t
10 C had s l i g h t l y h ig h e r g e r m i n a t i o n p e r c e n ta g e s th a n e i t h e r 20 o r
30. C, e x c e p t a t 7.5 b a r s w h e re i t w as th e sec o n d h i g h e s t . A lth o u g h
g e r m i n a t i o n t o t a l s d id i n c r e a s e w ith an advance i n c o l l e c t i o n d a te ,
th e s e in c r e a s e s w ere m a g n ifie d a s p o te n tia l became more n e g a tiv e . At 0
b a rs ,
th e in c r e a s e from th e f i r s t to l a s t c o lle c tio n was o n ly on th e
o r d e r o f 1 /15 t o I / 1 0 th . At 7;5 b a r s , t h i s i n c r e a s e w as 7 t o 14 tim e s
th e g e rm in a tio n on th e t h i r d c o l l e c t i o n a s i n th e f i r s t . Although th e
im p o r ta n c e o f g e r m in a tio n i n th e 10 C re g im e i n c r e a s e d w ith th e
a d v an ce o f c o l l e c t i o n d a t e , r a t e s h ad m ore g r a d u a l s l o p e s w h e re th e
g e rm in a tio n p o te n tia l was reach ed a t a slo w er pace th a n i n 20 o r 30 C.
P e rio d s o f g e rm in a tio n was a ls o ex ten d ed f o r seeds a t 10 C by 9 to 17
d ay s.
There i s a s i g n i f i c a n t r e l a t i o n s h i p betw een le n g th of tim e seeds
rem ain on th e p a re n t p la n t and th e optimum g e rm in a tio n te m p e ra tu re . As
le n g th o f tim e (or m a tu rity ) becomes g r e a te r , g e rm in a tio n i s enhanced,
e s p e c i a l l y a t lo w e r t e m p e r a t u r e s su c h a s
10 C.
T h is i s
e v id e n t
r e g a r d le s s o f w a te r s t r e s s .
I t i s a p p a r e n t t h a t p l a i n s s i l v e r s a g e b ru s h h a s a n a b i l i t y to
g e r m in a te u n d e r a v a r i e t y
o f e n v ir o n m e n ta l c o n d i t i o n s . H ow ever,
i n d i v i d u a l f a c t o r s and i n t e r a c t i o n s o f c o m b in a tio n s o f f a c t o r s do
s ig n ific a n tly
in h ib it
or
s tim u la te
g e r m in a tio n .
P la in s
s ilv e r
s a g e b r u s h see m s t o be m o st s e n s i t i v e to o s m o tic p o t e n t i a l and to a
le s s e r
d e g re e
te m p e r a t u r e ,
lig h t
c o n d itio n s
and
d a te
of
se e d
c o l l e c t i o n (o r d i s p e r s a l ) . S t r a t i f i c a t i o n c o u ld n o t be d e t e c t e d a s
100
h a v in g any i n f l u e n c e on g e r m i n a t i o n r e s p o n s e s . S eed s u n d e r no w a te r
s t r e s s g erm in ated b e s t,
e s p e c ia lly i n c o n d itio n s o f l i g h t .
The seed s
u n d e r no w a te r s t r e s s w e re a l s o f a v o r e d i n t e m p e r a t u r e s o f 10 and
20 C. G erm in atio n te m p e ra tu re s o f 20 C w ere m ost fa v o re d o v e r a ll,
but
s e e d s a t 10 C show ed c o m p a ra b le r e s u l t s w hen c o l l e c t e d t h e l a t e r i n
th e s e a s o n . As w a te r s t r e s s i n c r e a s e d , d a rk c o n d i t i o n s w e re a m ore
im p o rta n t s tim u la n t to
g e r m in a tio n .
D a te o f s e e d c o l l e c t i o n o r
d i s p e r s a l fro m a p a r e n t p l a n t w as i m p o r t a n t i n t h a t i t s t i m u l a t e d
g e rm in a tio n .
101
E a rly S e e d lin g Growth
S t u d i e s on p l a i n s s i l v e r s a g e b r u s h i n g ro w th c h a m b e rs ,
greenhouse and under f i e l d
th e
c o n d itio n s co nfirm ed t h a t th e environm ent
f a c t o r s t h a t a f f e c t e d g e r m in a tio n a l s o p la y an i m p o r t a n t r o l e i n
d e te rm in in g how many s e e d lin g s w i l l em erge, su rv iv e and grow. W ater
a v a ila b ility ,
te m p e ra tu re and p la n tin g d ep th a l l a f f e c te d th e degree
o f s e e d lin g s u c c e ss. Depth from w hich a s e e d lin g em erges i s a ffe c te d ,
by l i g h t and m o is tu re c o n d itio n s . H e te ro g e n e ity i n th e seed pool a lso
e x p re sse d i t s e l f i n t h i s work on s e e d lin g developm ent.
Temperatu re E f f e c ts on T ran sp la n ted S e e d lin g s
Growth chamber s tu d ie s on th e e f f e c t o f two d iu r n a l te m p e ra tu re s
on s e e d l i n g g ro w th i n d i c a t e d t h a t th e h ig h e r t e m p e r a t u r e re g im e
r e s u l t e d i n g r e a t l y e n h an c e d g ro w th . Those s e e d l i n g s i n th e 3 2 /2 1 C
tre a tm e n t had s i g n i f i c a n t l y more grow th i n te rm s o f h e ig h t, number of
le a v e s , and cover ex p re ssed by two h o r iz o n ta l axes (F ig u re 27). H eight
i n th e warm regim e (32/21 C) responded im m e d ia te ly and s u s ta in e d ra p id
grow th f o r more th an th r e e months. In c o n tr a s t, s e e d lin g h e ig h t i n th e
c o o l re g im e (2 1 /1 0 C) d id n o t m a rk e d ly change f o r tw o m o n th s. "As a
c o n s e q u e n c e , h e i g h t i n th e warm re g im e (80 mm) w as m ore th a n tw ic e
t h a t o f t h a t o f th e c o o l re g im e (38 mm) a t th e end o f th e s tu d y .
N um bers o f l e a v e s i n c r e a s e d (b o th r e g im e s fro m a ro u n d 12 l e a v e s ) i n
th e warm regim e a t a g r e a te r r a t e th a n th o se i n th e c o o le r regim e so
t h a t a t th e end o f th e s tu d y , th o s e s e e d l i n g s i n th e 3 2 /2 1 C re g im e
had about th r e e tim e s a s many le a v e s (180 and 70 le a v e s ). Although th e
102
I
7 /6
8 /1 2
9/14
1C/21
11/22
12/27
7 /6
8 /1 2
DATE (MOZDAY)
7 /6
8 /1 2
9/14
1C/21
DATE (MO/DAY)
F ig u r e 27.
1 1/22
9/14
I C/21
11/22
12/27
DATE (MO/DAY)
12/27
7 /6
8/12
9/14
1C/21
11/22
12/27
DATE (MOZDAY)
T e m p e ra tu re e f f e c t s on s e e d l i n g g ro w th . F o u r g ro w th
p a ra m e te rs a re p re s e n te d : h e ig h t, number o f le a v e s , and
two h o r iz o n ta l cover e s tim a te s .
103
h o r iz o n ta l axes d em o n strated th e same re sp o n se o f g r e a te r grow th i n
th e warmer reg im e,
th e d if f e r e n c e s w ere n o t a s g r e a t a s th e p re v io u s
tw o p a r a m e te r s . F o r t h r e e m o n th s , th e i n c r e a s e s w e re s te a d y , b u t
a f te r w a r d s .th e r e was a
d e crea se i n both h o r iz o n ta l axes.
R e s u lts f o r grow th i n te rm s o f l e a f a re a and r o o t/s h o o t biom ass
re fle c te d
th e
sam e t r e n d ,
d iffe re n t c h a ra c te ris tic s
but d iffe re n c e s
b e tw e e n r e g im e s h ad
( F ig u r e 2 8 ). L e a f a r e a g ro w th i n
re g im e s in c re a s e d s u b s t a n t i a l l y ,
b o th
bu t two c h a r a c t e r i s t i c s w ere r e a d ily
a p p a re n t. F i r s t , l e a f a re a in c re a s e d i n th e c o o le r reg im e (21/10 C) a t
th e same r a t e a s t h a t o f l e a f a re a i n th e warm regim e. However, grow th
w as d e la y e d by a m onth i n th e c o o l e r re g im e and p e ak e d a t a b o u t th e
same l e v e l as t h a t i n th e 32/21 C reg im e. S e e d lin g l e a f a re a d e c lin e d
a f t e r th re e o r f o u r m onths w ith t h a t o f th e c o o le r reg im e a t a s te e p e r
r a t e th an i n th e warmer regim e. Leaf a re a was s i g n i f i c a n t l y h ig h e r i n
th e w a rm e r r e g im e i n e v e ry s a m p lin g p e r io d e x c e p t th e n e x t t o l a s t
one.
Root b io m a s s i n b o th t r e a t m e n t s w as s i g n i f i c a n t l y h ig h e r th a n
shoot biom ass i n th e r e s p e c tiv e te m p e ra tu re reg im es (F ig u re 28). Root
and s h o o t b io m a s s i n t h e 32/21 C r e g im e i n c r e a s e d th r o u g h o u t th e
e x p e r im e n t, w h e re a s r o o t and s h o o t b io m a s s i n th e c o o l e r re g im e
in c re a s e d s t e a d i l y u n t i l th e l a s t d a te when a p r e c ip ito u s d e crea se was
o b s e r v e d . O v e r a l l, th e t i s s u e w e ig h t i n th e w arm er r e g im e f o r b o th
r o o ts and s h o o ts was g r e a te r th an r e s p e c tiv e r o o t and sh o o t biom ass a t
the c o o le r regim e. No s t a t i s t i c a l d if f e r e n c e s w ere found among r o o t
biom ass i n both reg im es ex cep t a t th e end o f th e stu d y a t w hich tim e
s e e d lin g s a t 32/21 C showed ab o u t 30% more r o o t biom ass due to a s te e p
TREATMENT
TREATMENT
-----' 3 0 / 2 1 SHOOT
• — • 30 / 21
'— -2 1 / 10 SHOOT
50 -
'— * 30 / 21 ROOT
21 / 10 ROOT
W 0.4 -
30 -
20
IrOl
LEAF AREA (cm'
—
*"....♦ 21 / 10
-
10-
DATE (MO/DAY)
F ig u re 28. T em perature e f f e c t s on s e e d lin g grow th,
shoot grow th, and l e a f a re a .
8/12
9/14
10/21
11/22
12/27
DATE (MO/DAY)
Two grow th p a ra m e te rs a re p re se n te d : ro o t and
105
d e c lin e i n biom ass a t 21/10 C. M easurem ents o f sh o o t biom ass showed a
s i g n i f i c a n t d if f e r e n c e on a l l sam p lin g p e rio d s e x c e p t f o r th e n ex t to
l a s t one. At t h i s tim e sh o o t biom ass a t 21/10 C responded s i m i l a r l y to
t h a t o f r o o t b io m a s s i n t h i s re g im e . T h e re w as a s t e e p d e c l i n e i n
biom ass on th e l a s t d a te . At th e end o f th e stu d y sh o o t biom ass i n th e
w arm er reg im e was tw ic e t h a t o f sh o o t biom ass i n th e c o o le r regim e.
Root to s h o o t r a t i o s i n c r e a s e d th r o u g h o u t t h e e x p e r im e n t (T a b le 3 ),
w ith g r e a te r sh o o t grow th a p p a re n t th e f i r s t two re c o rd in g p e rio d s f o r
s e e d lin g s i n th e warm regim e. R o o t/sh o o t r a t i o s changed from 0.94 fo r
th e warm re g im e and 1.8 f o r
th e
c o o l e r re g im e t o
1.49 and 2 .4 ,
r e s p e c tiv e ly . R a tio s o f ro o t biom ass to sh o o t biom ass w ere h ig h e r f o r
s e e d lin g s i n th e c o o le r re g im e , w ith th e d if f e r e n c e betw een tre a tm e n t
r a t i o s a p p a r e n t l y b e in g due t o th e g r e a t e r i n i t i a l s h o o t g ro w th f o r
s e e d lin g s i n th e warmer regim e.
T able
3•
Root to sh o o t r a t i o s f o r s e e d lin g grow th under two
te m p e ra tu re re g im e s. R a tio s a re p re se n te d by te m p eratu re
regim e and sam pling d a te .
R o o t/sh o o t r a
Tem perature
regim e^
Sampling d a te
-———-------------------------------:---------8/12
9/14
10/21
t i o
s
' .
11/22
12/22
32/21 C
.94
.72
1,13
1.33
1.49
21/10 C
1.80
2.25
2 .14
1.50
2.43
4
Root and sh o o t r a t i o s were determ ined by oven dry t i s s u e w eig h ts
from fo u r s e e d lin g s ta k e n from each te m p e ratu re regim e a t each
sam pling p e rio d .
Tem perature regim es w ere re g u la te d f o r a 12 hour p e rio d a t each
te m p e ra tu re i n growth cham bers.
106
Most grow th p a ra m e te rs e x h ib ite d a p o s itiv e grow th r e la tio n s h ip
i n i t i a l l y t h a t becam e n e g a ti v e to w a r d s th e end o f th e f i v e and one
h a l f month stu d y (F ig u re s 27» 28). The only e x c e p tio n s w ere th e number
o f le a v e s a t 32/21 C and r o o t and sh o o t biom ass a t th e 32/21 C regim e.
In g e n e ra l,
te m p e ra tu re s
g ro w th c u r v e s s t a r t e d d e c l i n i n g e a r l i e r i n t h e lo w e r
th a n f o r
th e h ig h e r
t e m p e r a t u r e r e g im e .
The o n ly
e x c e p tio n was f o r l e a f a re a w here th e s e e d lin g s i n th e c o o le r regim e
peaked l a t e r and th en d e c lin e d sh a rp ly . The m echanics f o r th e n e g a tiv e
grow th was m ost l i k e l y th e l o s s o f l a r g e r ,
e a r l i e r grow th le a v e s and
re p la ce m e n t by s m a lle r le a v e s .
G ro w th
of s e e d lin g s
w as s t r o n g l y
in flu e n c e d
by a m b ie n t
te m p e ra tu re s . However, optimum g e r m i n a t i o n t e m p e r a t u r e s w e re lo w e r
th a n th o s e fo u n d t o be t h e m o st f a v o r a b l e f o r s e e d l i n g g ro w th . T h is
seems to co rresp o n d w e ll w ith en v iro n m e n ta l te m p e ra tu re s l i k e l y to be
e n c o u n te r e d d u r in g t h e c o u rs e o f th e g ro w in g s e a s o n . As p r e v i o u s l y
d i s c u s s e d , g e r m i n a t i o n w as m o st s u c c e s s f u l a t 10 o r 20 C (s e e p a g e s
8 4 -8 6 ) , w h ile g ro w th o f s e e d l i n g s w as m ore s u c c e s s f u l a t d a y tim e
t e m p e r a t u r e s o f 32 C ( n i g h t t i m e 21 C). S eed s g e r m in a te and em erge
e a r l y i n th e g ro w in g s e a s o n when a m b ie n t t e m p e r a t u r e s a r e n o rm a lly
lo w e r th a n th o se i n th e summer grow ing months.
Greenhouse Seeding
S e e d lin g e m e rg e n c e o c c u re d a t d e p th s o f 0 , 0.5 and 1.5 cm, b u t
none w as o b s e r v e d a t th e d e e p e s t d e p th o f 2.5 cm ( F ig u r e 2 9 ). The
g re a te s t
e m e rg e n c e to o k p la c e
s e e d l i n g s n e v e r m ak in g i t
at
th e
s o i l s u r f a c e w ith s e v e r a l
p a s t th e c o ty le d o n s t a g e .
F o r th e tw o
O cm
0 .5 cm
1 .5 cm
10 29
F ig u re 29. Emergence and s u r v iv a l o f greenhouse s e e d lin g s a t th re e d ep th s o f b u r ia l.
108
s h a llo w e r d e p th s o f b u r ia l (0 and 0.5 cm), s u rv iv a l was v ery s im ila r
in
te r m s o f h a v in g , a n i n i t i a l
p e ak o f e m e rg e n c e ,
a d ie -o ff
of
s e e d lin g s and th e n a s ta b l e number s u rv iv in g th e stu d y . A la r g e f lu s h
o f seeds g e rm in a te d and emerged i n th e f i r s t th re e w eeks. The g r e a t e s t
num ber o f e m erg ed s e e d l i n g s a t any one tim e w as 33 a t th e s o i l
s u rfa c e , a lth o u g h a t o t a l o f 37 (o f 100) emerged over th e e n t i r e stu d y
p e rio d . This same p a tte r n was ob serv ed a t 0.5 cm, but w ith lo w er t o t a l
numbers. The h ig h e s t number o f emerged s e e d lin g s a t t h i s d ep th was 20,
a lth o u g h 22 em erg ed o v e r th e e n t i r e s tu d y p e r io d . Only one s e e d l i n g
emerged from th e 1.5 cm depth.
Those s e e d lin g s th a t d id n o t e s t a b l i s h
an a d e q u a te r o o t s y s te m d ie d s h o r t l y a f t e r e m e rg in g . T h is l e f t a
r a th e r s ta b le number w hich su rv iv e d th ro u g h o u t th e r e s t o f th e t r i a l .
T h is p e r io d b e tw e e n g e r m in a tio n and s t a b i l i z a t i o n i n t h e g ro w th
environm ent i s p ro b ab ly th e m ost c r i t i c a l i n th e l i f e o f th e p la n t and
i s th e p e rio d w here m ost m o r t a lit y has been observed (Eddleman 1,979,
Evans and Young 1982).
W ater r e l a t i o n s h i p s p r o b a b ly b e s t e x p l a i n t h e h ig h num ber o f
g e rm in a tin g seqds and e s ta b lis h in g s e e d lin g s on th e s o i l s u rfa c e .
In
t h i s s tu d y w a te r s t r e s s w as m in im iz e d so t h a t l i g h t p r e s e n te d a
fa v o ra b le environm ent i n which to g erm in ate (see page 9 2 ).
G row th m e a s u re m e n ts e s t a b l i s h e d t h a t th o se s e e d lin g s s u rv iv in g
in itia l
e m e rg e n c e fro m
mm g r e a t e r ) and
th e 0.5 cm d e p th
h ad m ore l e a v e s
(11
to
grew
h ig h e r
(19 t o
22
14 g r e a t e r ) th a n th o s e
s u r v i v i n g s e e d l i n g s fro m th e 0 and 1.5 cm d e p th s ( F ig u r e 30). The
s e e d l i n g fro m 1.5 cm show ed t h e l e a s t g ro w th i n t h e s e tw o g ro w th
p a r a m e te r s . S e e d lin g s e m e rg in g fro m 0.5 cm e x h i b i t e d m ore l a t e r a l
TREATMENT
TREATMENT
*-— •
O mm
5
0 mm
5 mm
15 mm
9 /9
9 /1 6
15 mm
9 /2 3
9 /3 0
1 0 /8
DATE (MO/DAY)
1 0 /1 4
1 0 /2 0
1 0 /2 8
9/9
9/16
9/23
9/30 10/8 1o)l4 IO^O 10:28
DATE (MO/DAY)
F ig u r e 30. G row th p a r a m e te r s i n th e g re e n h o u s e a s a f f e c t e d
uy uepcn ot se e d b u r i a l . Number o f
le a v e s and h e ig h t o f s e e d lin g s a re p re s e n te d .
110
g ro w th th a n s e e d l i n g s fro m th e o t h e r tw o d e p th s ( F ig u r e 3 1 ). The
l o w e s t am ount o f g ro w th i n t h e s e tw o m e a s u re m e n ts w e re fo u n d i n
s e e d lin g s
t h a t w e re i n i t i a l l y
on t h e
s o il
su rfa ce
a lth o u g h th e
s e e d lin g from th e 1.5 cm depth s t a r t e d w ith th e l e a s t . In g e n e ra l, th e
one
s e e d lin g
th a t
e m erg ed
fro m
1.5
cm h a d
s im ila r
g r o w th
c h a r a c t e r i s t i c s a s s e e d l i n g s fro m a t th e s o i l s u r f a c e . The e n h an c e d
s e e d l i n g g ro w th t h a t w as m e a su re d fro m s e e d s b u r ie d 0.5 cm d eep w as
p ro b a b ly due to m ore f a v o r a b l e g e r m in a tio n c o n d i t i o n s a s w e l l a s
b e t t e r r o o t g ro w in g c o n d i t i o n s . S eeds g e rm in a tin g below th e su rfa c e
a re surrounded by th e s o i l m a trix and th e r e f o r e have a c o n sta n t s o i l
c o n ta c t. T his r e s u l t s i n more fa v o ra b le m o is tu re and a g r e a te r i n i t i a l
n u tr i e n t base from w hich to draw. Those s e e d lin g s th a t can e s ta b lis h a
w o rk in g r o o t s y s te m by th e tim e th e c o ty le d o n s a r e a b o v e th e s o i l
s u r f a c e a l r e a d y h a v e a s u b s t a n t i a l a d v a n ta g e f o r c o n tin u e d g ro w th .
T h is i s i l l u s t r a t e d
by th e g r e a t e r g ro w th e x h i b i t e d by s e e d l i n g s
e s ta b lis h in g from 0.5 cm.
F ie ld Seeding
Emergence o f p la in s s i l v e r sag eb ru sh i n th e f i e l d to t a l e d about
1.2 p e r c e n t o f th e s e e d s p la n te d . Of th o s e s e e d l i n g s t h a t em erg ed ,
only about 11% s u rv iv e d th e summer. S e e d lin g s w ere m ost abundant from
th e 0.5 cm d e p th th a n fro m th e o t h e r p l a n t i n g d e p th s ( F ig u r e 32). At
th e h ig h e s t l e v e l o f em ergence,
th e r e w ere 85 s e e d lin g s from th e 0.5
cm depth and 59» 52 and 17 s e e d lin g s r e s p e c tiv e ly from th e 0, 1.5 and
2.5 cm d e p th s. Those g e rm in a tin g on th e s u rfa c e and em erging from 1.5
cm w e re n e a r l y e q u a l i n num ber. T h is r e l a t i o n s h i p w as m a in ta in e d
TREATMENT
TREATMENT
Omm
* -—
■*
5
5 mm
X 30-
9 /9
9 /1 6
9 /2 3
9 /3 0
1 0 /8
DATE (MO/DAY)
1 0 /1 4
1 0 /2 0
1 0 /2 8
9 /9
9 /1 6
9 /2 3
9 /3 0
1 0 /8
1 0 /1 4
1 0 /2 0
1 0 /2 8
DATE (MO/DAY)
F i g u r e 3 1 . G r o w th p a r a m e t e r s i n t h e e g r e e n h o u s e a s a f f e c t e d by d e p t h o f s e e d b u r i a l
g r o w t h o f s e e d l i n g s by l e n g t h a n d w i d t h a r e p r e s e n t e d .
. H o r iz o n ta l
112
TREATMENT (DEPTH)
0 mm
B
E3
5 mm
15 mm
B
25 mm
SEEDUNG
no.
■
I
7 /5
F ig u re 32.
I
7/11
7 /1 8
8/1
DATE (MO/DAY)
8 /1 5
8/29
S e e d lin g numbers p re s e n t th ro u g h o u t summer o f 1983 a f t e r
e m e rg in g fro m f o u r p l a n t i n g d e p th s (0 , 5 , 15, 25 mm).
1 13
th r o u g h o u t t h e s tu d y p e r io d e x c e p t on t h e l a s t tw o r e c o r d i n g d a t e s .
The num ber o f s e e d l i n g s t h a t s u r v iv e d fro m 1.5 cm w as s i g n i f i c a n t l y
h ig h e r (60% g r e a te r ) th a n th o se s u rv iv in g from th e s o i l s u rfa c e on th e
l a s t d a te . E m ergence fro m 2.5 cm w as n o te d , b u t w as s i g n i f i c a n t l y
lo w e r th a n any o f th e o th e r d ep th s. Emergence from t h i s depth was 12
t o 20% o f th e e m e rg e n c e fro m th e o t h e r d e p th s . A f te r th e f i r s t o f
J u l y , s e e d l i n g m o r t a l i t y w as c o n s id e r a b le . In a d d itio n , s i g n i f i c a n t
d iffe re n c e s in m o rta lity
r a t e s w e re o b s e r v e d among t h e v a r i o u s
t r e a t m e n t d e p th s . In g e n e r a l , g r e a t e r m o r t a l i t y was o b s e r v e d w h ere
t h e r e w as th e l a r g e s t num ber o f s e e d l i n g s . The g r e a t e s t s e e d l i n g
m o r t a l i t y o c c u r r e d w ith p l a n t s t h a t em erg ed fro m 0.5 cm, and th e
second h ig h e s t m o r t a lit y was observ ed on p la n ts t h a t w ere seeded on
th e s u r f a c e . S e e d lin g s t h a t em erg ed fro m th e tw o d e e p e s t d e p th s had
lo w e r m o r t a lit y r a te s .
D is tin c t d if f e r e n c e s i n s e e d lin g grow th w ere m easured i n resp o n se
to see d in g d ep th ,
so h ig h
but the c a lc u la te d v a ria n c e among o b s e rv a tio n s was
th a t s t a t i s t i c a l
s ig n ific a n c e
c o u ld n o t be e s t a b l i s h e d .
However, i d e n t i f i a b l e re s p o n se p a t t e r n s c o u ld be d i s c e r n e d . G row th,
except f o r h e ig h t, responded more under a w a te rin g tre a tm e n t. P la n tin g
depth a ls o p lay ed a r o l e i n grow th p a tte r n s w ith b u r ia l b ein g s l i g h t l y
fav o red . These r e l a t i o n s h i p s w ere s t i l l ap p aren t when d ep th and w a ter
tre a tm e n ts were analyzed to g e th e r.
Weekly w a te r a p p lic a tio n s s i g n i f i c a n t l y in flu e n c e d both emergence
and s u r v i v a l o f s e e d l i n g s ( F ig u r e 33). E m ergence w as a p p r o x im a te ly
tw ic e as g r e a t i n th e w a te re d s e c tio n s a s i n th e nonwa te r e d s e c tio n s .
S u rv iv a l was a ls o enhanced under th e w a te r tre a tm e n t. W hereas o n ly 2.6
114
O
Z
W
6 /2 0
6 /2 7
7 /5
7/11
7 /1 8
8/1
8 /1 5
8 /29
DATE (MO/DAY)
F ig u re 33. Numbers o f s e e d lin g s p re s e n t th ro u g h o u t th e summer of 1983
a f t e r r e c e i v i n g o n e i n c h o f w a t e r p e r w e e k o r no
a d d itio n a l w a te r.
115
p e rc en t o f
th e s e e d l i n g s
s u r v iv e d t h e summer i n t h e n o n w a te red
tr e a tm e n t, U.6% made i t through th e seaso n w ith a d d itio n a l w a ter.
Supplem entary w a ter a f f e c te d grow th c h a r a c t e r i s t i c s o f s e e d lin g s
i n t h a t w a te r e d •p la n ts became somewhat l a r g e r th an th o se grown under
am bient c o n d itio n s (F ig u re 34). However, d if f e r e n c e s w ere sm a ll and no
s ta tis tic a lly
s i g n i f i c a n t r e l a t i o n s h i p s w ere found w ith in any of th e
g ro w th p a r a m e te r s t h a t w e re m e a s u re d . E x c e p t f o r s e e d l i n g h e i g h t ,
w a te r e d p l a n t s w e re a lw a y s l a r g e r
a d d i t i o n a l w a te r .
th a n
th o s e
t h a t re c e iv e d
no
The h e i g h t o f n o n w a te re d p l a n t s w as l e s s th a n
w a te r e d p l a n t s f o r th e f i r s t f o u r w e ek s a lth o u g h t h i s r e l a t i o n s h i p
re v e rse d i t s e l f l a t e r .
Numbers o f le a v e s and th e two h o r iz o n ta l axes
were g r e a te r on a l l d a te s f o r w atered p la n ts .
A n a ly s is o f r e s u l t s o f p l a n t i n g d e p th t r e a t m e n t s show ed t h a t
t h e r e w as g e n e r a l l y m ore g ro w th i n s e e d l i n g s t h a t grew fro m b u r ie d
v
seed th a n from seed p la n te d on th e s o i l s u rfa c e (F ig u re 35). However,
only lim it e d grow th was observed i n any tre a tm e n t over th e summer. The
g r e a te s t s e e d lin g growth occured a t p la n tin g d e p th s o f 0 .5 and 2.5 cm.
No s i g n i f i c a n t d if f e r e n c e s i n s e e d lin g grow th w ere d e te c te d when
w a te r and d e p th t r e a t m e n t s w e re e v a l u a t e d c o n c o m i ta n tl y . H ow ever,
t h e s e f i n d i n g s w e re c o m p lic a te d by t o t a l m o r t a l i t y f o r 0 and 2.5 cm
s e e d l i n g s t h a t w e re n o t w a te r e d . I n g e n e r a l , th o s e s e e d l i n g s t h a t
o r i g i n a t e d fro m th e 0.5 and 2.5 cm p l a n t i n g d e p th s h ad th e h i g h e s t
r e l a t i v e grow th and s e e d lin g s t h a t o r ig in a te d a t th e s u rfa c e had th e
lo w e s t (F ig u re s 36, 37). Here to o , only lim it e d grow th w as o bserved i n
HEIGHT (mm)
Ll 4 ■
TREATMENT
WATERED
TREATMENT
»... -» NON-WATERED
WATERED
AXIS I (mm)
DATE (MO/DAY)
DATE (MO/DAY)
CM 4 .
TREATMENT
WATERED
* NON-WATERED
DATE (MO/DAY)
F i g u r e 34.
» ... -* NON-WATERED
TREATMENT
WATERED
NON-WATERED
DATE (MO/DAY)
Four grow th p a ram eters o f s e e d lin g s under f i e l d co n d itio n s.
o f s e e d l i n g s r e c e i v i n g one i n c h o f w a t e r p e r week o r n o t .
Graphs p r e s e n t r e l a t i o n s h i p s
HEIGHT (mm)
TREATMENT
O mm
15 mm
* .... -» 5 mm
•— e 2 5 mm
0 mm
* ....+
TREATMENT
15 mm
5 mm
DATE (MO/DAY)
• — • 2 5 mm
AXIS 1 (mm)
DATE (MO/DAY)
TREATMENT
0 mm
15 mm
• — -e 2 5 mm
0 mm
*—•
DATE (MO/DAY)
F ig u r e 35. F o u r g ro w th p a r a m e te r s o f s e e d lin g s u n d e r f i e l d
o f s e e d lin g s p la n te d a t fo u r d e p th s .
TREATMENT
5 mm
• — • 15 mm
• — -e 2 5 mm
DATE (MO/DAY)
c o n d itio n s ,
G ra p h s p r e s e n t r e l a t i o n s h i p s
K 15
u. 6 •
TREATMENT
•— • O mm Z W
» —« .5 mm Z W
( DEPTH Z WATER )
•— • 1.5 mm Z W
•— • 2.5 mm Z W
DATE (MOZDAY)
TREATMENT
• — • 5 mm Z W
( DEPTH Z WATER )
•— • 15 mm Z W
• — • 25 mm Z W
DATE (MOZDAY)
TREATMENT
•— • O mm Z W
» ... • 5 mm Z W
( DEPTH Z WATER )
•— • 15 mm Z W
•— • 25 mm Z W
DATE (MOZDAY)
TREATMENT
• — • 0 mm Z W
* —+ 5 mm Z W
( DEPTH Z WATER )
•— • 15 mm Z W
•— » 25 mm Z W
DATE (MOZDAY)
F ig u r e 36. F o u r g ro w th p a r a m e te r s o f s e e d l i n g s u n d e r f i e l d c o n d itio n s . G ra p h s p r e s e n t r e l a t i o n s h i p s
o f s e e d lin g s p la n te d a t f o u r d e p th s and r e c e iv in g o n e in c h o f w a te r p e r w eek.
TREATMENT (DEPTH / WATER)
* 0 mm /NW • — # 15 mm / mvv
• 25 mm /NW
8 - »••■••5 mm /NW
* FULL
MORTALITY
d 61
Li.
<
y 4
64o64?74 7/11 74'18
84
84s
DATE (MO/DAY)
TREATMENT (DEPTH / WATER)
•—« 0 mm /NW • — e 1 5 mm /NW
•■ • 5 mm /NW
* FULL
y
• 25 mm /NW
MORTALITY
TREATMENT (DEPTH / WATER)
*— 0 mm /NW e— « 1 5 mm /NW
•" " •5 mm /NW • — e 2 5 mm / NW
* FULL
MORTALITY
/
DATE (MO/DAY)
DATE (MO/DAY)
F ig u re 37. F o u r g r o w t h p a r a m e t e r s o f s e e d l i n g s u n d e r f i e l d c o n d i t i o n s . G r a p h s p r e s e n t
re la tio n s h ip s
o f s e e d lin g s
p la n te d a t f o u r d e p th s and r e c e iv in g no ad d ed w a te r .
120
any t r e a t m e n t . o v e r th e sum m er.
M e a su re m e n ts f o r th e n o n w a te re d
s e e d lin g s tended to be more w id e ly spaced th a n th o se f o r th e w atered
s e e d lin g s .
The environm ent im m e d ia te ly su rro u n d in g a seed d e te rm in e s w hether
it
re c e iv e s
th e
c o n d itio n s ,
g e rm in a tio n (H arper 1977).
re so u rc e s
and
s tim u li
n eed ed
fo r
This environm ent a ls o p la y s a key r o le i n
d e te rm in in g i f th e s e e d lin g w i l l s u rv iv e and p ro sp e r. In t h i s stu d y , a
m ore f a v o r a b l e
fie ld
e n v iro n m e n t
w as p r e s e n t f o r
b u r ie d
seed.
A d d itio n a l w a te r should have im proved th e environm ent f o r emergence
and s u r v iv a l.- H o w e v e r , th e e f f e c t o f b u r i a l and a d d i t i o n a l w a te r on
grow th p a ra m e te rs was n o t alw ays e a s i l y d eterm in ed . T his can perhaps
be a t t r i b u t e d t o a m o d e ra te d ro u g h t t h a t o c c u re d d u r in g t h e s tu d y
p e rio d . Below average p r e c i p i t a t i o n and ab n o rm ally h ig h te m p e ra tu re s
w ere c h a r a c t e r i s t i c o f th e 1983 grow ing seaso n (see Appendix A), and
t h i s a p p a re n tly r e s u l t e d i n an i n h i b i t i o n o f grow th i n a l l s e e d lin g s .
As a c o n s e q u e n c e ,
s e e d l i n g r e s p o n s e s i n t h e g ro w th c h a m b e rs and
greenhouse phases of t h i s study could n o t be d i r e c t l y r e l a t e d to f i e l d
r e s p o n s e s . High m o r t a l i t y o f f i e l d s e e d l i n g s a l s o made a n a l y s i s o f
growth c h a r a c t e r i s t i c s d i f f i c u l t .
When s e e d fro m
th e p a r e n t p l a n t i s b u r ie d ,
i t i s i n a m ore
a d v a n ta g e o u s e n v iro n m e n t u n le s s b u r ie d to o d eep . The s m a l l s i z e o f
p l a i n s s i l v e r s a g e b r u s h s e e d l i m i t s t h e d e p th to w h ic h i t can be
b u r ie d . I t w as l i k e l y t h a t th o s e s e e d s e m e rg in g fro m 2.5 cm w e re
s l i g h t l y l a r g e r and t h e r e f o r e had s u f f i c i e n t fo o d r e s e r v e s t o r e a c h
th e s u rfa c e , w h ile s m a lle r ones w ere in c a p a b le of t h i s resp o n se.
The
same p r o p e r tie s w ere undoubtedly p re s e n t i n th o se s e e d lin g s em erging
121
from th e 1.5 cm depth.
The s e e d lin g s t h a t emerged from th e se g r e a te r
d e p th s had much lo w e r m o r t a l i t y r a t e s . T h is may i n d i c a t e t h a t th e s e
p la n ts e s ta b lis h e d deep er and more e x te n s iv e r o o t sy ste m s t h a t w ere
a b le to ta k e advantage o f fa v o ra b le m o is tu re c o n d itio n s .
Although s e e d lin g s a t th e s u rfa c e and a t shallow d e p th s w ere a b le
to tak e advantage of e a r l i e r , more o p p o rtu n e m o istu re c o n d itio n s , they
soon l o s t t h i s a d v a n ta g e a s d r o u g h t c o n d i t i o n s w e re e n c o u n te r e d . As
th e season p ro g re s se d , t h e i r s h a llo w e r and l e s s developed r o o t system s
w ould be m ore s u s c e p t a b l e to d ro u g h t th a n th o s e o f d e e p e r r o o te d
s e e d l i n g s . T h is w as e v id e n c e d by b o th th e h i g h e r m o r t a l i t y r a t e s i n
s e e d lin g s from th e two s h a llo w e r d e p th s and th e e f f e c t o f added w a ter
on emergence and s u r v iv a l (F ig u re s 32, 3 3 ).
S a g e b ru sh . com m unities t y p i c a l l y have v e ry few seed s g e rm in a tin g
i n th e f i e l d d e s p i t e a l a r g e se e d p r o d u c t i o n e a c h y e a r ( E v e r n a r i e t
a l.
1971» H a z l e t t a n d H o ffm a n 1 9 7 5 , Cook 1 9 8 0 , H a rv e y 1 9 8 1 ).
C o n trib u tin g f a c t o r s to t h i s phenomena in c lu d e : s o i l m a tr ic p o te n tia l
and i t s e f f e c t on w e tte d c o n ta c t betw een seed and s o i l ( C o l l i s - George
196 6 ), e a r l y d e a th o f s e e d l i n g s (E d d lem an 1979), s e a s o n a l c l i m a t i c
c o n d i t i o n s and p l a n t a g e (N osova 1973, Evans and Young 19 8 2 ), s o i l
m o i s t u r e r e l a t i o n s h i p s and l i t t e r ( B e e t l e 1960), A ll t h e s e f a c t o r s
a f f e c te d outcom es i n t h i s ex p erim en t. However, m o istu re c o n d itio n s , as
m a n ife ste d by c lim a tic c o n d itio n s ( e s p e c ia lly d ro u g h t),
th e m ajor in flu e n c e on s e e d lin g su c c e ss.
seemed to be
122
S p ro u tin g and S e e d lin g E sta b lish m en t
Two s t u d i e s .w e r e c o n d u c te d t o e v a l u a t e th e s p r o u t i n g n a t u r e o f
p la in s s i l v e r sagebrush. The deg ree to w hich th e shrub r e l i e s more on
v e g e t a t i v e r e p r o d u c t i o n th a n s e e d l i n g e s ta b lis h m e n t was e v id e n t i n
both th e tr a n s e c t stu d y and th e i s o l a t e d p la n t e x c a v a tio n s.
T ra n se c t E x cavations
D i f f e r e n c e s b e tw e e n n u m b ers o f s p r o u ts and in d iv id u a ls a r i s i n g
fro m s e e d l i n g s w e re e v i d e n t i n a l l s i x s tu d y a r e a s and th e f i v e
t r a n s e c t s w i t h i n e a c h s i t e . M e a su re m e n ts o f ab o v e and b e lo w g ro u n d
v e g e ta tiv e p a r t s re v e a le d d if f e r e n c e s i n a g es, biom ass and h o r iz o n ta l
space occupied. I t was a p p a re n t t h a t an e la b o r a te su b su rfa c e rhizom e
sy ste m , e x i s t s t h a t i s com m only o l d e r th a n a b o v e g ro u n d s h o o ts and
s te m s . P l a n t s t h a t o r i g i n a t e d fro m v e g e t a t i v e s p r o u t s o u tn u m b e re d
in d iv id u a ls o r ig i n a tin g from seed. D is tin c tio n s could n o t be made f o r
s i t e or d is tu rb a n c e in flu e n c e on r a t i o s . o f s p ro u ts to s e e d lin g s w ith in
com m unities.
P la n ts
w e re
s e p a ra te d
in to
tw o
c a te g o rie s
b ased
on
a
d e te rm in a tio n a s to w h e th er the p la n t o r ig in a te d from a seed o r was a
s p r o u t o r i g i n a t i n g fro m an e s t a b l i s h e d p l a n t . P l a n t s fo u n d w ith o u t
c o n n e c tio n s to a n o th e r p l a n t w e re c o n s id e r e d a s o r i g i n a t i n g fro m a
seed. T his f i r s t group in c lu d e d some p la n ts w ith aboveground m a te r ia l
t h a t had o r i g i n a t e d fro m o l d e r p l a n t s t h a t had b e e n t o p k i l l e d . The
second c a te g o ry in c lu d e d two d i s t i n c t groups based on morphology of
th e rh iz o m e s y s te m . T h is c a te g o r y i n c l u d e d th o s e p l a n t s t h a t w e re a
123
s e r i e s o f s p ro u ts a lo n g a s in g le rhizom e t h a t u s u a lly te rm in a te d w ith
a stum p t h a t was dead o r
d ecad en t. The second group in c lu d e d
th o se
p l a n t s t h a t had a d e f i n i t e rh iz o m e c o n n e c tio n t o a h e a l t h y p a r e n t
p la n t. In m ost c a s e s a s e r i e s o f s p ro u ts o r a s in g le p la n t was u s u a lly
•
"c o n n e c te d by a rh iz o m e to a n o th e r l a t e r a l rh iz o m e fro m a l a r g e ,
e s ta b lis h e d
p a re n t p la n t.
G ra p h ic e x a m p le s
of
th e
th re e
cases
d e s c r i b e d ab o v e a r e d is p l a y e d i n F ig u r e s 3 8 , 39 and ifO. F ig u r e 38
d e m o n s t r a t e s how a s e e d l i n g g e n e r a l l y a p p e a re d . F ig u r e 39 show s an
e x a m p le o f a s e r i e s o f s p r o u t s o r i g i n a t i n g fro m an o l d e r stu m p o r
p la n t. F in a lly ,
F ig u r e 40 e x h i b i t s how a s i n g l e
s p r o u t c o u ld be
a tta c h e d to a l a t e r a l rhizom e from a p a re n t p la n t.
There w ere s i g n i f i c a n t (p< .05) age d if f e r e n c e s betw een above and
b e lo w g ro u n d v e g e t a t i v e o rg a n s . Ages o f p l a n t s t e m s , . t a p r o o t s and
rh iz o m e s a r e su m m a riz e d i n T a b le 4. A boveground s te m s w e re 3 to 5
y e a r s younger th a n ta p r o o ts and a s s o c ia te d rh izo m es.
P a re n t rh izo m es
w ith d i r e c t l y c o n n e c te d s p r o u t s w e re c l e a r l y th e o l d e s t . H ow ever,
ta p r o o ts and rh izo m es w ith o u t d i r e c t l y c o n n ec tin g rh izo m es to a p a re n t
p la n t w ere n o t s i g n i f i c a n t l y d i f f e r e n t from one a n o th er.
L a te r a l e x te n s io n o f rhizo m es and rhizom e sy stem s was g r e a t i n
com parison to aboveground h e ig h ts (T able 5). Aboveground s iz e and age
c o r r e la te d w e ll and t h i s r e l a t i o n s h i p was an a p p ro p ria te c r i t e r i a f o r
s e l e c t i n g p l a n t s f o r t h i s s tu d y . D e v ia ti o n fro m th e g e n e r a l p a t t e r n
was due to in c lu s io n o f a l l stem s a lo n g th e rhizom e sy stem , n o t j u s t
th e in d iv id u a l p la n ts th a t'w e r e marked f o r study. Rhizome le n g th was
about 2 1/2 tim e s t h a t o f p la n t h e ig h t when s p ro u ts w ere connected to
p a re n t p la n ts . L a te r a l spread of th e rhizom e system was a p p ro x im a te ly
124
:A d V B n tltio u i
buds'
-Q f Q u n r i
ARTEMISIA
CANA CANA
F ig u re 38. G raphic exam ple o f an e x cav ated se e d lin g . D em o n stratio n o f
common appearance of a s e e d lin g .
125
Ground
Iltlous Buds
Subsurface Connecting Rhlzoi
16cm
ARTEMISIA
CANA CANA
F ig u re 39. G raphic
p la n t.
system
o ld e s t
exam ple of ex cav ated s p ro u t connected to a p a re n t
D e m o n s tr a tio n o f common a p p e a ra n c e o f a rh iz o m e
w ith a s s o c ia te d s p ro u ts i n a s e r ie s . O rig in a l or
m a te r ia l i s on f a r r ig h t .
126
Ground
Rhizome
from
mother
plant
F ig u r e 40. G ra p h ic e x a m p le o f an e x c a v a te d s p r o u t c o n n e c te d to a
p a r e n t p l a n t . D e m o n s tr a tio n o f common a p p e a ra n c e o f a
s p r o u t c o n n e c te d to a p a r e n t p l a n t by way o f a rh iz o m e
from th a t p la n t.
127
T a b le 4 . Age r e l a t i o n s h i p s o f ab o v e and below g ro u n d p a r t s o f p l a i n s
s i l v e r s a g e b ru s h . S iz e s o f s te m s and rh iz o m e s a r e
sum m arized i n T able 5.
P la n t p a r t
measured
Average
a g e (y e a rs )
S tan d ard
d e v ia tio n
Number o f
sam ples2
Stems
3 .4 ^
1.97
T aproots
6 .9 b
3.1
28
P a re n t rhizom e
or stump^
Rhizome system 2*
8 .8 °
3.7
68
6 . Ob
2.5
128
204
S ig n if ic a n t mean d if f e r e n c e s a r e denoted when fo llo w e d by d i f f e r e n t
l e t t e r s (p < .0 5 ).
S am ple n u m b ers v a r i e d due to a v a r i e t y o f s i t u a t i o n s p r e s e n t i n
in d iv id u a l e x c a v a tio n s .
^ Rhizom e o r i g i n a t i n g fro m a p a r e n t p l a n t (o r d ead stu m p ) t o w h ic h
s p ro u t was d i r e c t l y connected .
^ Rhizome s e c tio n s o th e r th an th o se d e fin e d i n 3 above.
'
Table 5. Growth r e l a t i o n s h i p s of above and belowground p a r t s o f p la in s
s i l v e r sag eb ru sh .
Measurement
d e s c r ip tio n
P la n t (s p ro u t)
h e ig h t
L a te r a l d is ta n c e to
p a re n t conn ectio n ^
L a te r a l sp re ad o f
rhizom e system 2*
Number o f
sam ples2
Mean (cm)
Range (cm)
32al
11-59
155
78b
14-277
61
105°
11-369
90
1 S ig n i f ic a n t mean d if f e r e n c e s a re d enoted when fo llo w e d by d i f f e r e n t
l e t t e r s (p < .0 5 ).
2 S am ple n u m b ers v a r i e d due to a v a r i e t y o f s i t u a t i o n s p r e s e n t i n
in d iv id u a l e x c a v a tio n s .
3 L a te ra l d is ta n c e from p a re n t p la n t o r rhizom e to n e a r e s t sp ro u t on
rh iz o m e s y ste m e x p r e s s e d a s a mean o f a l l p l a n t s w ith t h i s g ro w th
h a b it.
" T o ta l' l a t e r a l e x te n t o f a l l rhizom es i n an e x c a v a tio n ex p re ssed a s a
mean o f a l l p la n ts w ith rhizom e sy stem s.
128
3 1 /2 tim e s t h a t o f p l a n t h e i g h t . C o n s id e r a b le v a r i a t i o n e x i s t e d i n
b oth m easurem ents. The maximum m easurem ents f o r both in s ta n c e s w ere
277 cm and 369 cm, r e s p e c tiv e ly . The minimum m easurem ents w ere U cm
and 11 cm, r e s p e c t i v e l y . T o ta l l a t e r a l s p r e a d o f rh iz o m e s u s u a l l y
exceeded th e d is ta n c e of a sp ro u t to a c o n n ec tin g rhizom e. However, in
some c a s e s t h i s d i s t a n c e w as
g e n e ra l,
lo c a te d
s im ila r.
c o n s id e ra b le
D a u g h te r p l a n t s w e re ,
d is ta n c e s
fro m
p a re n t
p la n ts
in
or
rhizom es.
The r e l a t i v e fre q u e n c ie s o f occurance f o r d is ta n c e s en co u n tered
from p a re n t p la n ts or rh izo m es to d a u g h te r p la n ts a re sum m arized i n
T a b le 6 .
The l a r g e s t
p ro p o rtio n
(5 9 p e r c e n t ) o f r h i z o m a t o u s
c o n n ec tio n s betw een p a re n t and d au g h ter p la n ts w ere from 50 to 100 cm
i n d is ta n c e .
The second h ig h e s t p ro p o rtio n (20 p e rc e n t) was i n th o se
rhizom e c o n n ec tio n s betw een 0 and 50 cm, w ith th e 100-150 cm c ateg o ry
being c lo se to t h i s w ith 15 p e rc e n t.
P la n ts a r i s i n g from rhizom es w ere more abundant th a n th o se t h a t
grew fro m
s e e d lin g s
(T a b le 7).
A p p ro x im a te ly 63 p e r c e n t o f th e
ex cav ated p la n ts w ere connected by rh izo m es to an e s ta b lis h e d p la n t or
rhizom e system . About 37 p e rc e n t w ere in d iv id u a ls w ith no c o n n ectio n s
to any o t h e r p l a n t o r rh iz o m e . S t a t i s t i c a l a n a l y s i s c o n firm e d t h a t
t h i s d i f f e r e n c e w as s i g n i f i c a n t (p< .0 2 5 ). H ow ever, one o f th e s i x
s ite s ,
L ig n ite
C reek ,
show ed an o p p o s i t e tr e n d .
The p r e s e n c e o f
e x tre m e ly clay ey and e x te n s iv e g r a v e lly s o i l s i n th e stu d y a re a m ight
e x p la in
th e
p re p o n d e ra n c e
o f n o n c o n n e c te d i n d i v i d u a l s .
W ater
r e l a t i o n s h i p s w ou ld be m ore u n f a v o r a b le i n b o th s o i l c o n d i t i o n s .
T h e re fo re ,
ta p rq o tin g
p la n ts
m ig h t h a v e an a d v a n ta g e
in
th e se
129
Table 6. Frequency o f occurance f o r d is ta n c e s e n co u n tered from p a re n t
p l a n t s o r rh iz o m e s to d a u g h te r p l a n t s o f p l a i n s s i l v e r
sag eb ru sh .
D istan c e to
p a re n t (cm)
0-50
50-100
100-150
150-200
200+
I
2
—
2
3
I
7
«
Study s i t e s
4
3
5
4
8
2
I
2
2
7
I
3
4
3,.
I
61
I
7
2
ee
T o tal c a te g o ry
numbers
12
36
9
3
I
T o ta ls
9
6 15 11 10 10
TT2
:
“
1
S i t e n u m b ers c o r r e s p o n d to nam es a s f o l l o w s : I-L o w e r F lo o d ,
^- L ig h ite Creek, 3-Paddy Faye, 4-Low er B lack S p rin g s, 5-Moon Creek,
2 6-Y ellow stone R iver p a s tu r e s .
T h is num ber d o e s n o t in c l u d e p l a n t s w ith rh iz o m e s y s te m s t h a t
o r ig in a te d from a dead stump and was in c lu d e d i n a s e r i e s o f s p ro u ts
and rhizom es.
T a b le 7» P la n t e x c a v a tio n r e s u l t s . S u m m a riz a tio n o f n u m b ers o f
in d iv id u a l p la n ts i n each stu d y s i t e f a l l i n g i n one of two
c a te g o r ie s : h av in g rh izo m ato u s co n n ec tio n s o r n o t \
C ategory
I
Rhizomatous^
7
Nonrhizomatous
13
1I O-.
2
Study S it e ii
4
3
5
6
C ategory
to ta ls
15
13
13
14
13
75 a
5
7
7
6
7
45b
__
t - t e s t s . A ll s i t e s showed s i g n i f i c a n t d if f e r e n c e s .
Study s i t e s correspond to names a s f o llo w s : I- L ig n ite Creek, 2-Lower
F lo o d , 3 - Paddy F a y e , 4 -L o w er B la c k S p r in g s , 5-M oon C reek ,
6-Y ellow stone R iver p a s tu re s . Lower Flood, Lower B lack S p rin g s and
the Y ellow stone R iver p a s tu r e s w ere co n sid e re d d is tu rb e d . The o th e rs
were n o t.
Rhizomatous p la n ts in c lu d e d a l l in d iv id u a ls h aving rh izo m e system s
e i t h e r from h e a lth y p a re n ts o r w e ll-d e fin e d rh izo m es and th o se th a t
w ere members o f a s e r i e s o f s p ro u ts u s u a lly o r ig i n a tin g from dead
stum ps.
130
c irc u m sta n c e s i n re a c h in g d e ep e r, more fa v o ra b le c o n d itio n s , over more
s h a ll o w , r h iz o m a to u s i n d i v i d u a l s . S i g n i f i c a n t d i f f e r e n c e s (p< .0 5 )
w e re n o t fo u n d among s i t e s a c c o r d in g t o C h i- s q u a r e a n a l y s i s . A ll
s i t e s , e x c e p t L ig n ite Creek, had ab o u t eq u al p ro p o rtio n s o f connected
s p r o u t s and s e p a r a t e p l a n t s . The L i g n i t e C reek d a t a a c c o u n te d f o r
n in e ty p e rc e n t o f th e v a r i a b i l i t y among s i t e s . Comparison o f th e th re e
d is tu rb e d
s ite s
w ith
th e
th re e
u n d is tu r b e d
s ite s
re v e a le d
no
s i g n i f i c a n t d i f f e r e n c e s (p< .0 5 ).
S e v e r a l f a c t o r s m ig h t e x p l a i n why v e g e t a t i v e r e p r o d u c t i o n w as
common i n th e se s i l v e r sageb ru sh com m unities.
E v o lu tio n p la y s a key
r o l e i n u n d e rsta n d in g why a p a r t i c u l a r p la n t o r community r e a c ts to
e x t e r n a l f o r c e s a s th e y do (Cook
re p ro d u c tio n in c lu d e :
1983).
B e n e fits
( I ) an e n h a n c e d a b i l i t y
o f v e g e ta tiv e
to u t i l i z e unevenly-
d i s t r i b u t e d r e s o u r c e s , and (2 ) an i n c r e a s e d c o m p e t i t i v e a b i l i t y to
in v a d e o t h e r a r e a s . I n a d d i t i o n , s p r o u t s a r e b e t t e r a b l e to r e s i s t
in v a s io n of o th e r s e e d lin g s w h ile r e d u c in g th e p r o b a b i l i t y o f g e n e t
e x t i n c t i o n . T h is i s a c c o m p lis h e d by s p r e a d in g t h e r i s k among many
g e n e ti c a lly i d e n t i c a l i n d i v i d u a l s . An e v o l u t i o n a r y s t r a t e g y su ch a s
t h i s i s th e r e f o r e c o n s is te n t w ith th e fin d in g s o f Abrahamson (1980),
who re p o rte d t h a t in c re a s e d en v iro n m e n ta l s e v e r ity g e n e r a lly s h if te d
em phasis to v e g e ta tiv e re p ro d u c tio n .
The s p ro u tin g n a tu re o f s i l v e r sag eb ru sh may be i n d i c a t i v e o f th e
h a b i t a t i n w h ic h i t i s e n c o u n te r e d . B e in g l o c a t e d p r e d o m in a n tly on
f l o o d p l a i n s and b o tto m la n d s ,
in flu e n c e
ic e
th e p l a n t i s c o n t i n u a l l y u n d e r th e
o f d i s t u r b a n c e s su c h a s ( d e p o s itio n fro m
s c ra p in g i n w in te r.
flo o d in g
and
F i r e may a l s o h a v e p la y e d a r o l e i n t h e
131
e v o lu tio n o f th e taxon’s r e s p r o u tin g c h a r a c t e r i s t i c s . P la n t p ro d u c tio n
i s g e n e r a lly h ig h e r i n the b o tto m lan d s,
both i n h erb aceo u s and woody
grow th, and t h i s would presum ably c p n tr ib u te to h ig h e r f u e l lo a d s f o r
n a t u r a l and m a n -in d u c e d f i r e s .
C o n s e q u e n tly ,
f i r e w o u ld be m ore
in te n s e and more prone to c a rry i n such ecosystem s. S ilv e r sagebrush
i s a v ig o r o u s s p r o u t e r and t h i s i s m o st l i k e l y
th e r e s u l t o f th e
e v o lu tio n a ry in flu e n c e s o f r e c u r r in g c y c li c o r p e r io d ic d is tu rb a n c e s .
U t i l i z a t i o n o f l i m i t e d r e s o u r c e s th ro u g h l a t e r a l e x t e n s i o n o f
rhizom es would a p p ea r to be a c o m p e titiv e advantage over e sta b lis h m e n t
by s e e d s .
M ore a b u n d a n t h e r b a c e o u s v e g e t a t i o n
in
th e
m e sic
enviro n m en ts o f f lo o d p la in s produces g r e a te r c o m p e titio n f o r sagebrush
s e e d lin g s . V e g e ta tiv e s p ro u ts may com pensate f o r t h i s d isad v a n ta g e by
more ra p id m o rp h o lo g ical developm ent.
la rg e r,
m ore a v a i l a b l e
S p ro u ts a re a s s o c ia te d w ith a
n u t r i e n t and c a r b o h y d r a te r e s e r v e s fro m
e s ta b lis h e d r o o ts and s h o o ts ,
th u s in c r e a s in g l i f e expectancy o f th e
g en et (Abrahamson 1980). Although n o t r a r e i n th e com m unities s tu d ie d ,
s e e d lin g e s ta b lis h m e n t was found i n o n ly one t h i r d o f th e p la n ts t h a t
w ere ex cav ated . This r e l a t i v e l y low o ccu ran ce i s p erh ap s a t t r i b u t a b l e
to d is a d v a n t a g e s a s s o c i a t e d w ith g e rm in a tio n re q u ire m e n ts , s e e d lin g
emergence and s u r v iv a l, and su b se q u e n t c o m p e t i t i o n fro m e s t a b l i s h e d
p la n ts .
Whereas s e e d lin g s m ust draw upon t h e i r own re s o u rc e s , s p ro u ts
p r o l i f e r a t e by u t i l i z i n g e s ta b lis h e d sh o o t and r o o t re s o u r c e s .
E n v iro n m e n ta l f a c t o r s , e s p e c i a l l y d r o u g h t, m ig h t b e s t e x p l a i n
d i f f e r e n c e s i n r a t i o s o f s p r o u t s and s e e d l i n g s . E a s t e r n M ontana i s
u n d e r th e c o n s t a n t e m b ra ce o f d r o u g h t c y c le s . F o r e x a m p le , a t h r e e
y e a r drought e x te n d in g from 1979 th ro u g h 1981 preceded th e w et y e a r o f
132
1982. This l a t e s t drought c o in cid ed w ith th e ages o f th e m a jo rity o f
th e p l a n t s p ic k e d f o r t h i s s tu d y (m ean o f 3.4 y e a r s ) . The r e l a t i v e l y
m o is t y e a r p r e c e d i n g 't h i s d ro u g h t o f 1979-1981 and t h e w e t y e a r o f
1982 w as a p p a r e n t l y
th e
so u rc e f o r
m ost o f
th e
n o n c o n n e c te d
in d iv id u a ls . S p ro u ts w ere, i n g e n e ra l, on e i t h e r s id e of th e spectrum ,
e s p e c ia lly th e o ld e r in d iv id u a ls . T his p a r t i c u l a r d ro u g h t was p ro b ab ly
th e g r e a t e s t in flu e n c e on w heth er a s p ro u t o r s e e d lin g was observed.
There does seem to be a s t r a t i f i c a t i o n i n s i l v e r sagebrush com m unities
and i s i n r e l a t i o n t o o c c u r a n c e o f w e t y e a r s and d ry y e a r s , w ith
s e e d lin g s b ein g fa v o re d i n w et y e a rs.
The r e l a t i v e l y
cool grow ing sea so n o f 1982 was a s s o c ia te d w ith
r e l a t i v e l y h igh p r e c i p i t a t i o n . N um erous s e e d l i n g s and a few s p r o u t s
w e re p ro d u c e d i n t h i s y e a r . The d r y , warm g ro w in g s e a s o n o f 1983
p ro d u c e d few s e e d l i n g s and a n a b u n d a n c e o f s p r o u t s . I t w as o b s e rv e d
t h a t few s e e d l i n g s fro m 1982 s u r v iv e d t h e sec o n d s e a s o n . I t w ould
th e re fo re ap p ear t h a t th e mode a s w e ll a s the su c c e ss o f re p ro d u c tio n
i s s t r o n g l y r e l a t e d t o c l i m a t i c re g im e . These g e n e ra l o b s e rv a tio n s ,
com bined w ith t h i s s h r u b 's a b i l i t y to s p r o u t u n d e r s t r e s s , s u g g e s t
t h a t d ro u g h t c o n d i t i o n s . m ig h t p ro d u c e s u f f i c i e n t s t r e s s to f a v o r
v e g e ta tiv e re p ro d u c tio n . This o v e rrid in g im p o rtan ce o f d ro u g h t s t r e s s
on re p ro d u c tiv e s tr a te g y m ight a ls o e x p la in why d if f e r e n c e s could n o t
be found betw een and w ith in d is tu rb e d and u n d istu rb e d stu d y s i t e s .
I s o la te d P la n t E x cavations
The e x t e n s i v e s p r o u t i n g n a t u r e o f p l a i n s s i l v e r s a g e b r u s h w as
r e a d ily a p p a re n t a f t e r com plete e x c a v a tio n s had been com pleted on th e
133
a re a s su rro u n d in g two la r g e ,
i s o l a t e d p la n ts . In a d d itio n ,
c le a r t h a t m ost r o o ts c o n s is te d o f a s h a llo w ,
i t became
underground netw ork of
r h iz o m e s . Maps o f th e e x c a v a tio n s e s t a b l i s h e d t h a t p l a i n s s i l v e r
sagebrush p o s se ss e s a h ig h ly complex r o o t system (F ig u re s 41, 42) t h a t
may in c lu d e s e v e ra l s m a lle r , in d ep en d en t sy stem s (F ig u re 43).
R oot e x c a v a t i o n s r e v e a l e d t h a t o l d e r w e l l - e s t a b l i s h e d p l a n t s
c o n s is te d o f n o t one,
but an a g g re g a te o f s e v e ra l in d iv id u a l system s
or p la n ts (F ig u re s 41, 42). There was c o n sid e ra b le d i v e r s i t y i n degree
o f rh iz o m e s y s te m c o m p le x ity . I n d i v i d u a l c lo n e s had a s many a s 52
s p r o u t s and a s few a s one ( F ig u r e 4 3 ). No e v id e n c e w as fo u n d to
in d ic a te t h a t a l l in d iv id u a l c lo n es w ere o f th e same g e n et. That i s ,
no common r o o t c o n n e c tio n s c o u ld be t r a c e d . H ow ever, t h i s d o es n o t
ex clu d e th e p o s s i b i l i t y t h a t they m ight have been co nnected and l a t e r
s e p a ra te d a f t e r d e a th o f c o n n e c tiv e rh izo m es.
E x c a v a tio n s e s t a b l i s h e d t h a t r h iz o m e s can ex ten d and s p ro u t a t
l e a s t t h r e e m e te r s away fro m th e p a r e n t p l a n t . T h e r e f o r e , a l a r g e
number o f progeny can p o t e n t i a l l y a r i s e from one g e n e tic in d iv id u a l. A
d e n d r i t i c p a t t e r n w as c h a r a c t e r i s t i c
rhizom e expansion,
o f t h i s ty p e o f h o r i z o n t a l
w ith s iz e c la s s e s d e c re a s in g i n g e n e ra l c o n c e n tric
c i r c l e s away from th e m ain canopy. That i s ,
s p ro u ts d e c re a se d i n s iz e
a s d is ta n c e from th e p la n t in c re a s e d .
One o f th e f a c t o r s t h a t m ight h e lp e x p la in d i s t r i b u t i o n p a tte r n s
in
fie ld
p o p u la tio n s
of p la in s
s ilv e r
s a g e b r u s h w o u ld
in v o lv e
u t i l i z a t i o n o f s o i l m o is tu r e and n u t r i e n t s . A lle lo p a th y m ig h t a l s o
p la y a r o l e . A s p a t i a l r e l a t i o n s h i p i s f r e q u e n t l y i d e n t i f i a b l e i n
w hich rh izo m es w i l l grow in to a re a s t h a t a r e no t a lre a d y occupied by
3
HEIGHT
NUMBERS IN
CATEGORY
S 4 5 + cm
4 3 5 —4 5 cm
3 2 5 —3 5 cm
2
1 5 —2 5 cm
I
0 —1 5 cm
-----rhizome
Q aboveground shoots
Th canopy cover of main plant
F ig u r e 41. Map o f f i r s t l a r g e , i s o l a t e d p l a n t e x c a v a tio n . A ll a b o v eg ro u n d s h o o ts a r e shown
i n d i v i d u a l l y and num bered a c c o r d in g to s t a t u r e . R hizom es a r e shown a s l i n e s w ith
th ic k n e s s r e l a t i v e to s iz e .
2
HEIGHT
5
4 5 + cm
4
3 5 —4 5 cm
3
2 5 —3 5 c m
2
1 5 —2 5 cm
I
0 — 15 cm
NUMBERS IN
CATEGORY
'— rhizome
O aboveground shoots
canopy cover of main plant
F ig u r e 42. Map o f se c o n d l a r g e , i s o l a t e d p l a n t e x c a v a tio n . A ll a b o v eg ro u n d s h o o ts a r e shown
i n d i v i d u a l l y and num bered a c c o r d in g to s t a t u r e . R hizom es a r e shown a s l i n e s w ith
th ic k n e s s r e l a t i v e to s iz e .
O plant or sh oot la rger than 15 cm
- plant or sh oot smaller than 15 cm
rhizome ______
.
0
.5
Im
F ig u re 43.
a
137
o t h e r s a g e b r u s h p l a n t s . L im ite d n u t r i e n t s and s o i l m o is tu r e e x e r t a
dom inant im pact on a p la n ts a b i l i t y to s u rv iv e and p ro sp e r. Abrahamson
(1980) p r e d i c t s t h a t w hen
p o p u l a t i o n d e n s i t y i s low i n c l o n a l ty p e
p la n ts , v e g e ta tiv e re p ro d u c tio n w o u ld be m ore a d v a n ta g e o u s , th e r e b y
enhancing g e n et spread and o ccu p a tio n . Such a s i t u a t i o n e x i s t s i n many
p la in s s i l v e r sagebrush com m unities where s p a rse p la n t p o p u la tio n s a re
common.
C o m p e titio n f o r
a v a i l a b l e r e s o u r c e s seem s t o
be th e m a jo r
in flu e n c e on d e te rm in in g w here a p la n t can become e s ta b lis h e d (Noble
et
a l.
1 979»
Cook 198 3 ).
In
c o m m u n itie s w h e re c o m p e t i t i o n f o r
re s o u rc e s i s g r e a t, c lo n a l e s ta b lis h m e n t m ight be a t an ad vantage when
expanding a p la n t's a re a of e s ta b lis h m e n t.
This i s la r g e ly due to th e
a b i l i t y to draw upon n u t r i e n t s and r e s e r v e s from e s ta b lis h e d r o o ts and
s h o o ts . S p a t i a l a r r a n g e m e n ts i n p l a i n s s i l v e r sag eb ru sh co m m unities
can be m o stly e x p la in e d by c o m p e titiv e s t r e s s th a t l i m i t s d e n s i t i e s i n
any one a re a and in flu e n c e w here a rhizom e can grow.
A l l e lo p a th y i s a f e a t u r e i n s a g e b r u s h c o m m u n itie s t h a t c o u ld
p e rh a p s p la y a r o l e i n d e t e r m in in g s p a t i a l p a t t e r n s . L e a c h a te s fro m
l e a f m a te r ia l would p robably n o t a f f e c t rhizom e fo rm a tio n and grow th,
because rh izo m es a re g e n e r a lly lo c a te d i n th e 8 to 30 cm zone. S tu d ie s
have shown th a t c e r t a i n h y d ro p h ilic m e ta b o lite s exuded from rhizom es
can p e rm e a te th e im m e d ia te ly s u r r o u n d in g s o i l ( N um ata e t a l . 1 975,
Hale 1982, M elkania e t a l . 1982), th u s in f lu e n c in g nearby developm ent
e ith e r
by s e e d l i n g s o r r h iz o m e s .
re p o rte d f o r p la in s s i l v e r sag eb ru sh .
H ow ever,
no su ch f i n d i n g s a r e
138
SUMMARY
T h is s tu d y was d e s ig n e d t o g a in a b e t t e r a p p r e c i a t i o n o f p l a n t
p o p u l a t i o n d y n a m ic s.
S p e c ific a lly ,
it
in v e s tig a te d re p ro d u c tiv e
c h a r a c t e r i s t i c s and m echanism s im p o rta n t i n p la in s s i l v e r sagebrush.
I n p a r t i c u l a r , s t u d i e s e x a m in e d : ( I ) se e d d i s p e r s a l fro m i n d i v i d u a l
p la n ts
and among s i t e s ,
(2) f a c t o r s a f f e c t i n g
g e r m in a tio n ,
(3)
em ergence, grow th and s u r v iv a l o f s e e d lin g s under c o n tr o lle d and f i e l d
c o n d i t i o n s , and (4) w h e th e r th e p r im a r y o r i g i n o f i n d i v i d u a l p l a n t s
was from seed o r v e g e ta tiv e s p ro u ts .
Wind a p p e a rs to be th e most i n f l u e n t i a l f a c to r i n th e d is p e r s a l
o f a c h e n e s fro m p l a i n s s i l v e r s a g e b r u s h p l a n t s . A d e f i n i t e t h r e e d i r e c t i o n a l d i s t r i b u t i o n o f d i s p e r s e d s e e d w as fo u n d . The l a r g e s t
p ro p o rtio n o f seed was d is p e rs e d i n l i n e w ith the p r e v a ilin g n o rth w e st
w in d , b u t s e c o n d a ry a r e a s o f s e e d d e p o s i t i o n w e re a l s o fo u n d a t 120
d e g re es on e i t h e r s id e o f th e prim ary one. The mechanism f o r t h i s type
o f d i s t r i b u t i o n i s b a s ic a lly u n ex p lain ed . D is p e rsa l i n th e s e secondary
d i r e c t i o n s w a s,
a t tim e s ,
m ore p r e v a l e n t d e p e n d in g on d a te and
a s s o c i a t e d w in d s (o r s to r m s ) . M ost s e e d w as d i s p e r s e d c l o s e t o , o r
under, th e shrub. However, i n a t l e a s t one case th e l a r g e s t p ro p o rtio n
o f s e e d w as d i s p e r s e d a t t h r e e m e te r s . I n t h i s i n s t a n c e , se e d w as
evenly d is p e rs e d from th e p la n t o u t to th r e e m e te rs, and th e r e was no
ste a d y d e c re a se o f d is p e rs e d seed, u n t i l th e th re e m e te rs d is ta n c e was
reach ed . Seed numbers th en dropped o f f s h a rp ly .
There w ere no m ajor d if f e r e n c e s i n d is p e r s a l p a tte r n s among th e
th re e stu d y s i t e s ,
but p la n t phenology seemed to be v a r ia b le so th a t
139
th e m a jo rity o f seed f e l l a t d i f f e r e n t tim e s depending on s i t e . At one
s i t e , d is p e r s a l was evenly d i s t r i b u t e d th ro u g h o u t th e stu d y p e rio d due
to d if f e r e n c e s i n p henolo g ic a l developm ent.
P l a i n s s i l v e r s a g e b r u s h see d can g e r m in a te u n d e r a v a r i e t y o f
e n v ir o n m e n ta l c o n d i t i o n s , b u t c e r t a i n s i t u a t i o n s d id f a v o r h ig h e r
g e rm in a tio n p e rc e n ta g e s.
S t r a t i f i c a t i o n had no e f f e c t on g e rm in a tio n
s u c c e s s , p ro b a b ly due to s e e d n o t b e in g d o rm a n t and t h e r e f o r e n o t
re q u irin g
th e
dorm ancy
b r e a k in g
c o ld
tre a tm e n t.
P o s s ib ly
some
s t r a t i f i c a t i o n w as i n h e r e n t l y p r e s e n t b e c a u se o f co ld te m p e ra tu re s
d u rin g th e l a t e f a l l and e a r ly w in te r when seed s w ere c o lle c te d from
th e f i e l d . Date of seed c o lle c tio n , l i g h t and dark reg im e, te m p e ra tu re
and w a te r s t r e s s had im p o rta n t in f lu e n c e s on g e rm in a tio n s u c c e ss ,
sa g e b ru sh
seeds
w e re
n o t n o te d
to
have
but
s p e c i f i c g e r m in a tio n
re q u ire m e n ts.
H ig h e r g e r m i n a t i o n p e r c e n ta g e s w e re o b s e rv e d i n l a t e r se e d
c o lle c tio n p e rio d s . Seeds i n com plete dark g erm in ated b e t t e r th an in
l i g h t e x c e p t w hen th e y w e re u n d e r no w a t e r s t r e s s . T e m p e ra tu re s o f
20 C w e re g e n e r a l l y m o st f a v o r a b l e f o r g e r m in a tio n . H ow ever, on th e
l a s t seed c o lle c tio n ,
at
seed g e rm in a tio n a t 10 C was n o t d i f f e r e n t th a n
20 C. R a te s o f g e r m i n a t i o n i n c r e a s e d w ith h ig h e r t e m p e r a t u r e s .
G e rm in a tio n p e r c e n ta g e s and r a t e s d ro p p e d o f f s t e e p l y u n d e r th e
in flu e n c e o f more n e g a tiv e o sm o tic p o te n tia ls . L ig h t- a f f e c te d seeds i n
th e 10 C te m p e ra tu re reg im e showed fa v o ra b le g e rm in a tio n ,
but under
d ark c o n d itio n s , 20 C became more im p o rta n t w ith slo w e r r a t e s th an i n
l i g h t . H e te r o g e n ie ty i n t h e s e e d p o p u l a t i o n w as p r o b a b ly th e m ost
im p o rta n t v a r ia b le
e x p la in in g
th e r e s u l t s
of
th is
s tu d y
on
g e rm in a tio n ,
As co m b in atio n s o f f a c t o r s such as te m p e ra tu re ,
p o te n tia l o r l i g h t changed,
osm otic
t h i s h e t e r o g e n i e t y a llo w e d s e e d s to
g e rm in a te .
A fte r seeds have g e rm in a te d , th e environm ent t h a t th e s e e d lin g i s
s u b je c te d to d e te rm in e s s e e d lin g su c c e ss. Tem perature was fo u n d .to be
i m p o r t a n t i n t h e g ro w th o f s e e d l i n g s . H ig h e r t e m p e r a t u r e s t h a t had
a d v e rse e f f e c t s on g e rm in a tio n w ere fa v o re d i n s e e d lin g grow th.
This
m ight be ex p ected because h ig h e r te m p e ra tu re s a re n o rm ally p re s e n t i n
th e l a t e r s ta g e s of th e s e e d lin g grow ing season. S e e d lin g re sp o n se was
e n h a n c e d by th e a d d i t i o n o f s u p p le m e n ta r y w a te r .
More s e e d l i n g s
. em erged, and su rv iv e d through the summer. Seeds th a t had been p la n te d
a t 5 mm produced th e m ost s e e d lin g s i n th e f i e l d (85), w h ile th o se a t
th e s u r f a c e and a t 15 mm p ro d u c e d a b o u t th e same n u m b ers (59 and 52
r e s p e c tiv e ly ) . M o rta lity was g r e a te s t among s e e d lin g s em erging from 5
mm and th e l e a s t f o r th o se em erging from 15 and 25 mm.
S e e d lin g g ro w th w as r e l a t i v e l y u n a ffe c te d by a d d itio n a l w a ter,
b u t p a t t e r n s c o u ld be d is c e r n e d . W a te re d s e e d l i n g s show ed som ew hat
g r e a t e r g ro w th ,
e s p e c i a l l y from th e 5 and 25 mm p l a n t i n g d e p th s .
B u ria l p la c e s t h e . th e seed s i n a l e s s sev e re environm ent i n te rm s o f
te m p e ra tu re s and w a te r s t r e s s . D e sp ite th e la r g e numbers o f seed s t h a t
w ere p la n te d , v ery few s e e d lin g s emerged i n th e f i e l d (1.2
%) ,
and of
th e se only 11 p e rc e n t su rv iv e d th e summer.
The d eg ree to which p la in s s i l v e r sag eb ru sh r e l i e s on v e g e ta tiv e
r e p r o d u c t i o n w as e s t a b l i s h e d
by r o o t e x c a v a tio n s .
P la in s s ilv e r
sag eb ru sh i n a lm o st a l l c a s e s showed some d egree o f rh izo m ato u s grow th
even among s m a ll s e e d lin g s . However, most ex cav ated in d iv id u a ls tu rn e d
141
out
to
be s p r o u t s
fro m
an a l r e a d y
e s ta b lis h e d
p la n t.
a b o v e g ro u n d s h o o ts w e re y o u n g e r th a n any b e lo w g ro u n d
Ages o f
ro o ts
or
r h iz o m e s , w h ile t h e o l d e s t p l a n t s e g m e n ts w e re p a r e n t rh iz o m e s to
w hich in d iv id u a l p la n ts w ere connected. Most grow th was below ground
and was re p re s e n te d by su b su rfa c e l a t e r a l e x te n s io n o f rh izo m es and
rhizom e system s. On av erag e, t h i s l a t e r a l sp read was 3 1/2 tim e s th a t
o f th e shoot h e ig h t. The l a r g e s t p ro p o rtio n o f rh izo m ato u s co n n ectio n s
to p a r e n t p l a n t s o r rh iz o m e s w e re fro m 50 to 100 cm i n d i s t a n c e . No
d iffe re n c e s
c o u ld be fo u n d among s i t e s
o r b e tw e e n d i s t u r b e d o r
u n d is tu r b e d s i t e s . T h is w as m o st l i k e l y due to d r o u g h t c o n d i t i o n s
o v e rrid in g any e f f e c t o f d is tu rb a n c e a s f a r a s an in flu e n c e on grow th
h a b its .
I n e x c a v a tio n s o f l a r g e ,
i s o l a t e d p l a n t s t h e l a r g e d e g re e to
w h ic h s p r o u t s a r i s e fro m rh iz o m e s w as e v i d e n t . T hese " i n d i v i d u a l "
p l a n t s w e re com posed n o t o f on e, b u t a n a g g r e g a te o f c l o n a l s y s te m s
in d i c a t i n g a g r e a t p o te n tia l f o r v e g e ta tiv e re p ro d u c tio n .
LITERATURE CITED
143
LITERATURE CITED
Abraham son, W. G. 1980. Demography and v e g e ta tiv e re p ro d u c tio n . I n :
Demography and e v o lu tio n i n P la n t P o p u la tio n s, ed. 0. T. Sol b rig ,
pp. '8 9 -1 0 6 . Oxford: B la ck w e ll S c i e n t i f i c P u b lic a tio n s .
A l- A n i, T.A., M.M. A l-M u f t i , an d F.M.R. A l- C h er c h a f e h y . 1 972.
G e r m i n a b i l i t y o f some n a t i v e ra n g e s p e c i e s o f I r a q . J ji: F i r s t
S c i e n t i f i c C onference, S c i e n t i f i c R e s e a rc h F o u n d a tio n , G e n e ra l
and A g r ic u ltu r a l S cien ces. Baghdad, pp.234-242.
A n d erso n , J .E ., and K.E. H o lte . 1981. V e g e ta tio n d e v e lo p m e n t o v e r 25
y e a r s w ith o u t g r a z i n g on s a g e b r u s h - d o m in a te d r a n g e la n d s i n
s o u th e a s te rn Idaho. J. Range M anage. 34( I ):2 5 -2 9 .
Ashmun, J.W., R.J. Thom as, and L.F. P i t e l k a . 1982. T r a n s l o c a t i o n o f
p h o to a s s im ila te s betw een s i s t e r ra m e ts i n two rh iz o m a to u s f o r e s t
h e r b s . Ann, B ot. 4 9 :4 0 3 -4 1 5 .
B arnes, B.V. 1966. The c lo n a l growth- h a b it o f American asp en s. Ecology
47:439-447.
B a r to lome, J.W., and H.F. Heady. 1978. Ages o f b ig sag eb ru sh fo llo w in g
brush c o n tro l. J. Range M anage. 31 (6 ):4 0 3 -4 0 6 .
B e e t l e , A.A. I9 6 0 . A s tu d y o f s a g e b r u s h - s e c t i o n .T r i d e n t a t a e o f
A r t e m i s i a . Wyo. A gri Exp. S ta . B u l l . 36 8 , 83p. .
B e e t l e , A.A. 1 965. A t h i r d s u b s p e c ie s i n t h e A r t e m i s i a t r i d e n t a t a
complex. Rhodora 67:405-406.
B e e tle , A.A. 1977. R eco g n itio n o f A rte m is ia su b sp e c ie s - a n e c e s s ity ,
.la : P roceedings 6 th an n u al Wyoming Shrub Ecology Workshop, pp.3542.
B e r k a t, 0., and D.D. B r is k e . 1981. A w a t e r p o t e n t i a l c o m p a ris o n o f
t h r e e g e r m i n a t i o n te c h n i q u e s u t i l i z i n g p o l y e th y le n e g ly c o l
20000. S o c ie ty o f Range Management, 34th annual m eeting, T ulsa,
Okla. A b s t r a c t .
Bewle y , J.D., and M. Black. 1982. Physiology and b io c h e m istry o f seeds
i n r e l a t i o n to g e r m in a tio n . V o l.2 . S p r i n g e r - V e r l a g , B e r l i n
H eid elb e rg New York. 375 p.
B hadane, N.R., and F. S h a fiz a d e h . 1 975. S e s q u ite r p e n e l a c t o n e s o f
sag eb ru sh : th e s t r u c t u r e o f a r t e c a n i n . P h y to c h e m is tr y 1 4 :2 6 5 1 2653.
il
1#
B l a i s d a l e , J .P ., and W.F. M ueggle r . 1956. E f f e c t o f 2 ,4 -D on f o r b s and
sh ru b s a s s o c ia te d w ith b ig sagebrush. J. Range Manage. 9:38-40.
B o s to c k , S .J . , and R.A. B enton. 1 979. The r e p r o d u c t i v e s t r a t e g i e s o f
f iv e p e re n n ia l Composita e . J. E col. 67:91-107.
B r a n s o n , F .A ., an d R.F. M i l l e r . I 981 . E f f e c t s o f i n c r e a s e d
p r e c i p i t a t i o n and g r a z i n g m an ag em en t on N o r t h e a s t e r n M ontana
r a n g e la n d s . J . Range Manage. 34(1):3-10.
C a ld w e ll, M.M. 1978. P h y s io lo g y o f s a g e b r u s h . %&: The S a g e b ru s h
Ecosystem : a symposium. Utah S ta te Univ. Logan, pp. 74-85.
C h ir c a , E., and A. F a b ia n , 1973. Some a l l e l o p a t h i c e f f e c t s c a u se d by
A jltem isja .absinthium L. C o n tr ib u tii B o tan ica U n iv e r s ita te a BabesB olyai d in C luj. p. 267-276.
Cl o r, M.A., T.A. A l-A n i, and F. C h a rc h a f chy. 1974. Range r e s o u r c e s o f
I r a q . 15. G e r m in a tio n , s t o r a g e c o n d i t i o n s and a f t e r r i p e n i n g o f
th e s e e d s o f A r t e m i s i a h e r b a - a l b a . I n s t i t u t e f o r App. Res. on
N at. R e s o u rc e s , I r a q . Tech. B u ll. No.76. 19p.
C o ll is - G e o r g e , N., and J.B . H e c to r. 1 966. G e rm in a tio n o f s e e d s a s
i n f l u e n c e d by m e t r i c p o t e n t i a l and by a r e a o f c o n t a c t b e tw e e n
■s e e d and s o i l w a te r . A ust. J . S o il Res. 4 :1 4 5 -1 6 4 .
Cook, R.E. 1979. A se x u a l r e p r o d u c t i o n : a f u r t h e r c o n s i d e r a t i o n . Am.
N at. 113:769-772.
Cook, R.E. I 980. The b io lo g y o f s e e d s i n s o i l . J j i i O.T. S o l b r i g (e d .),
D em ography and th e D ynam ics o f P l a n t P o p u la tio n s . O x fo rd :
B lack w ell S c i e n t i f i c P u b lic a tio n s , pp. 107-127.
Cook, R.E. I 983. C lo n a l p l a n t p o p u l a t i o n s . Amer. S c i e n t i s t 7 1 (3 ):2 4 4 253.
C o r n e liu s , D.R., and C.A. Graham. I 958. S a g e b ru s h c o n t r o l w ith 2,4-D .
J.' Range Manage. 11 :1 2 2 -1 2 5 .
Cunningham, H. 1971. S o il v e g e ta tio n r e l a t i o n s h i p s o f a b itte r b r u s h sage brush a s s o c ia tio n i n N o rth e a ste rn Colorado. M.S1T h esis. Colo.
S t a t e U niv. 83p.
Daubenm ire, R. 1975. Ecology of A rte m is ia t r i d e n t a t a subsp. t r i d e n t a t a
i n th e s t a t e o f W ashington. N o rth w est S c i. 49:24-35.
D e p u it, E .J ., and M.M. C a ld w e ll. 1973. S e a s o n a l p a t t e r n o f n e t
p h o to s y n th e s is o f A rte m is ia t r i d e n t a t a , Amer. J. B ot. 60(5):426435.
145
D i e t z , D.R., R.H. U d a ll, and L.E. Y e a g e r.1962. C h em ica l c o m p o s itio n
and d i g e s t i b i l i t y by mule d e er o f s e le c te d fo ra g e s p e c ie s , Cache
, l a P o u d re R ange, C o lo ra d o . C olo. Game and F is h Dep. Tech. Pub.
14. 89p.
D o n a rt, G.B., and C.W.Cook. 1970. C a rb o h y d ra te r e s e r v e c o n te n t o f
m o u n ta in ra n g e p l a n t s f o l l o w i n g d e f o l i a t i o n and r e g r o w th . J.
Range Manage. 23:15-19.
D usek, G.L. 1 975. Range r e l a t i o n s o f m u le d e e r and c a t t l e i n p r a i r i e
h a b ita t. J. W ildl. Manage. 3 9 (3 ):6 0 5 -6 16.
Eddleman, L.E. 1979. R eg en eratio n s t r a t e g i e s o f m ix e d - p r a ir ie p la n ts .
In.: (J.R . G oodin and D.K. N o r th in g to n , e d .) A rid l a n d s p l a n t
re s o u rc e s : p ro c e ed in g s o f th e I n te r n a tio n a l Arid Lands Conference
on P la n t R esources, Texas Tech Univ.
E v an s, R.A., and J.A. Young. I 982. M i c r o h a b i t a t v a r i a t i o n i n r e l a t i o n
t o w e ed s e e d g e r m i n a t i o n a n d s e e d l i n g e m e r g e n c e . I n :
B io m e te r o lo g y i n i n t e g r a t e d p e s t m an ag em en t. A cadem ic P r e s s .
PP. 421-448.
E v e n a r i , M .L., L. S h a n a n , an d N. T a d m o r. 1 9 7 1 . The N e g e v : t h e
c h a ll e n g e o f th e d e s e r t . H a rv a rd U n i v e r s i t y P r e s s , C am b rid g e,
Mass.
E v e r e t t , R .L ., R.O. M e e u w ig , an d R. S t e v e n s . 1 9 7 8 . D e e r m ouse
p re fe re n c e f o r seed o f commonly p la n te d s p e c ie s , in d ig e n o u s weed
s e e d , and s a c r i f i c e fo o d s . J. Range Manage. 31(1):70-73.
E v e r e t t , R.L., R.O. M eeuw ig, and J.H. R o b e r ts o n . 1978. P r o p a g a tio n o f
Nevada shrubs by stem c u ttin g s . J. Range Manage. 31(6):426-429.
F e rg u s o n , C.W. 1964. A nnual R in g s i n B ig S a g e b ru s h . U niv. o f A riz o n a
P r e s s , T ucson. 95p.
F e rn a n d e z , O.A., and M.M. C a lw e ll. 1 975. P h e n o lo g y and d y n a m ic s o f
r o o t g ro w th o f t h r e e c o o l s e m i - d e s e r t s h r u b s u n d e r f i e l d
c o n d itio n s . J. Ecol. 63:703-714.
F rie d m a n , J ., and G. O rsh an . 1975. The d i s t r i b u t i o n , em erg en c e and
s u r v iv a l o f s e e d lin g s o f A rte m is ia h e rb a -a lb a Asso i n th e Negev
D e s e r t o f I s r a e l i n r e l a t i o n to d i s t a n c e fro m th e a d u l t p l a n t s .
J . E c o l. 6 3 (2 ):6 2 7 -6 3 2 .
F rie d m a n , J ., G. O rsh an , and Y. Z i g e r - C f i r . 1977. S u p p r e s s io n o f
an n u als by A rte m is ia h e rb a -a lb a i n th e Negev D e se rt o f I s r a e l . J.
E c o l. 6 5 ( 2 ) : 4 l 3-426.
F r i sch k n e c h t, N.C., and L.E. H a rris . 1973. Sheep can c o n tro l sagebrush
on s e e d e d ra n g e i f ... U tah S c i. 34( I ):2 7 -3 0 .
146
F ro e m in g , D.K. 1981. I n f l u e n c e s o f s o i l and c l i m a t e on t h e c lim a x
d i s t r i b u t i o n o f s e l e c t e d A r te m is ia s p e c i e s . %&: Soc. o f Range
Manage., 34 th annual m eeting, T ulsa, Okla. A b stra c t.
G a te s , D.H. 1964. S a g e b ru s h i n f e s t e d
Range M anage.17 :2 0 9 -2 1 0 .
by l e a f d e f o l i a t i n g m oth. J.
G oodw in, D.L. 1 956. A u te c o lo g i c a l s t u d i e s o f A r t e m i s i a t r i d e n t a t a
N u tt. Ph.D. d i s s . W a sh in g to n S t a t e U n iv ., P u llm a n . 79p.
G ordon, R.A., and H.A. W rig h t. 1981. E c o lo g ic a l f a c t o r s i n f l u e n c i n g
common broomweed emergence arid s u r v iv a l. Soc. o f Range Manage.,
34th annual m eeting, T ulsa, Okla. A b stra c t.
Gough, L .P ., and J.A. Erdm an. 1980. S e a s o n a l d i f f e r e n c e s i n th e
e le m e n t c o n te n t o f Wyoming b ig s a g e b r u s h . J . Range Manage.
3 3 (5 ):3 7 4 -3 7 8 .
G ro v es, C.R., and J.E . A nderso n . 1981. A l l e l o p a t h i c e f f e c t s o f
A r t e m i s i a t r i d e n t a t a l e a v e s on g e r m i n a t i o n and g ro w th o f tw o
g ra s s s p e c ie s . Amer. Mid. Nat. 106( 1):73-79.
H ale, M. 1982. A lle lo p a th ic p o te n tia l o f A rte m is ia v u lg a r is rhizom es.
P la n t P h y s io l. 69(4):23.
H a rb e rd , D.J. 1 962. Some o b s e r v a t i o n s on n a t u r a l c lo n e s o f F e s tu c a
o v in a L. New Phyt o l . 61:85-100.
H arberd, D.J. 1967. O b serv atio n s on n a tu r a l c lo n es o f . H olcus m o llis .
New P h y to l..6 6 :4 0 1 -4 0 8 .
H a r n is s , R.O., and W.T. McDonough. I 975. S e e d lin g g ro w th o f t h r e e b ig
sagebrush s u b sp e c ie s u n d e r c o n t r o l l e d te m p e r a t u r e re g im e n s . J.
Range M anage. 28(3):243-244.
H a rp e r, J.L . 1 977. P o p u la tio n B io lo g y o f P l a n t s . A cadem ic P r e s s ,
London New Y ork' San F ra n c isc o . 892p.
H arvey, S .J. 1981. L i f e h i s t o r y and r e p r o d u c t i v e
A rte m isia . M.S. T hesis. Montana S ta te Univ. 132p.
s tra te g ie s
in
H a z l e t t , D.L., and G.R. H offm an. 1975. P l a n t s p e c i e s d i s t r i b u t i o n a l
p a tte r n s i n A rte m is ia t r i d e n t a t a - and A r te m is ia c a n a - d o m in a te d
v e g e ta tio n i n w e s te rn N orth Dakota. Bot. Gaz. 136(1):72-77.
H e lm ric k , R.H., and R. P. P f e i f e r . 1 9 5 4 . D i f f e r e n t i a l v a r i e t a l
r e s p o n s e s o f w i n t e r w h e a t g e r m in a tio n and e a r l y g ro w th to
c o n tr o lle d li m i t e d m o is tu re c o n d itio n s . Agroru J o u r. 46:560-562.
>
Hoffman* G.R»* and D.L« H a z l e t t . I 977• E f f e c t s o f a q u eo u s A r t e m i s i a
e x t r a c t s and v o l a t i l e s u b s t a n c e s on g e r m in a tio n o f s e l e c t e d
s p e c i e s . J . Range Manage. 30(2): 134-137.
H ow ard, G.S., G.E. Schum an, and F. R auzi . 1977. G row th o f s e l e c t e d
p l a n t s on Wyoming s u r f a c e - m i n e d s o i l s and f l y a sh . J . Range
Manage. 3 0 (4 ):3 0 6 -3 1 0 .
H ussain, F., and H. Khanum. 1982. Phytoto x ic p o t e n t i a l i t y o f A rte m isia
m a ritim e. P a k is ta n J. Hot. 14:18-19.
I t o , K., K. I d e , and J .I n o u y e . 1976. E c o lo g ic a l s t u d i e s and c o n t r o l o f
mugwort. l a : P roceedings o f 5 th A s ia n -P a c ific Weed S cien ce Soc.
Con., Tokyo, Ja p a n , pp. 6 6 -6 9.
J o h n so n , A.E. I 982. T o x i c o lo g ic a l a s p e c t s o f p h o to s e n s i t i z a t i o n i n
liv e s to c k . M Nat. Cancer I n s t i t u t e . 69:253-258.
J o h n so n , K.L. 1 97 8. B a s ic sy n e c o l o g i c a l r e l a t i o n s h i p s o f th e b ig
s a g e b r u s h ty p e s on th e h ig h p l a i n s o f M ontana, Wyoming and th e
D akotas. J jn The Sagebrush Ecosystem : A symposium, p. 42-49.
J o h n s o n , J.R ., and G.F. P ayne. I 968. S a g e b ru s h r e i n v a s i o n a s a f f e c t e d
by some en v iro n m e n ta l in flu e n c e s . J. Range Manage. 21:209-213.
K e ls e y , R.G., M.S. M o r r is , and F. S h a f iz a d e h . 1976. The u se o f
s e s q u i t e r p e n e l a c t o n e s a s ta x o n o m ic m a rk e rs i n t h e s h ru b b y
s p e c ie s o f A rte m isia ( s e c tio n T r id e n ta ta e ) i n Montana. J. Range
M anage. 29(6):502-505.
Kemperman, J.A., and B.V. Barnes. 1976. Clone s iz e i n American aspens.
Can. J . B o t. 5 4 :2 6 0 3 -2 6 0 7 .
K ra s ik o v a , N.S. 1978. B y u l l e t e n 1 V sesoyuznogo N a u c h n o -I s s le d o v a t el*
skogo I n s t i t u t a R a ste n ie v o d stv a im en i N i V a silo v a No. 81:67-82.
K rueger, R.R., and D.L. Shaner. 1982. G erm ination and e s ta b lis h m e n t o f .
p r o s t r a t e spurge (,Euphorbia su o in a). Weed S c i. 30:286-290.
Kuf e ld , R.C. 1973. Foods e a te n by Rocky M ountain Elk. J. Range Manage.
2 6 (2 ):1 0 6 -1 1 3 .
i
Kumar, D., and P.F, W areing . 1972. F a c t o r s c o n t r o l l i n g
developm ent i n th e p o ta to p la n t. New Phyto l . 71:639-648.
s to lo n
La T o u r e t t e , J.E ., J.A, Young, and R.A. E vans. 1971. Seed d i s p e r s a l i n
r e l a t i o n to ro d e n t a c t i v i t i e s i n s e r a i b ig sag eb ru sh com m unities.
J . Range Manage. 24:118-120.
148
a a ^ y u sa ) c lo n a l
M S : ' Bepx
0i i r o i! T 3 ? 3 h 2 6 ,nf 2 ? r t i a l deveiopaent- ^
“ d
LoveU-DousI;, L. 1981. P o p u la tio n dynam ics and lo c a l s p e c i a l i z a t i o n i n
a c lo n a l p e re n n ia l (Rgyiuneulus Zepes a ). L The dynam ics o f ram ets
i n c o n tr a s tin g h a b i t a t s . J. Ecol. 69:743-755.
MaCkiat ^ filjL J1970.6 Rf n e e e c o l o Sy and r e l a t i o n s h i p s o f m ule d e e r , e l k
and c a t t l e i n t h e M is s o u r i B re a k s , M ontana. W ild l. Monogr. No.
^u* f 9p« •
Mayeux, H.S., and L. L e o tta . 1981. G e rm in a tio n o f broom sn ak ew eed
( G-U t i e r r e ^ ^ a s a r p t .h r ^ e ) a n d t h r e a d l e a f s n a k e w e e d (G.
m .ozocephalum ) seed. Weed S ci. 24:530-534.
M cA rth u r, E.D., B.C. G iu n ta , and A.P. Plum m er. 1974. S h ru b s f o r
r e s t o r a t i o n o f d e p le t e d r a n g e s and d i s t u r b e d a r e a s . U tah S c i.
3 5 :28-33.
cA rth u r, E.D., and A.P. Plummer. 1978. Biogeography and management o f
n a t i v e w e s t e r n s h r u b s : A c a s e s tu d y , s e c t i o n T r i d e n t a t a e o f
A r t e m i s i a . J s : G re a t B a s in M em o irs, No. 2 . I n t e r m o u n t a i n
B iogeography: a symposium. BYU.
M cA rthur, E.D., and B.L. W elch. I 982. G row th r a t e d i f f e r e n c e s among
b ig sag eb ru sh (Ag te jn js ia t rAd.e n t ^ t a ) a c c e s s i o n s and s u b s p e c ie s ?
J . Range Manage. 35(3 ):3 9 6 -4 0 0 .
McDonough, W.T., and R. 0. H a r n is s . 1974. Seed dorm ancy i n A r te m is i a
t r i d e n t a t a N u tt, s u b s p e c ie s Jg asev an a Rydb. N o rth w e s t S c i.
4 8 (1 ):1 7 -2 0 .
McDonough, W.T., and R.0. H a r n is s . 1975. Know -your s a g e b r u s h - and
b e t t e r y our range. Utah S c i. 3 6 (3 ):9 9 -l0 3 .
M e lk a n ia , N.P., J.S . S in g h , and K.K.S. B is h t . 1982. A l l e p a t h i c
p o t e n t i a l o f A z te m js ja m l f t a r l g L. and P in u s r o x h i n r i i , a
b i © assay s tu d y . J s : P r o c e e d in g s o f th e I n d ia n N a tio n a l S c ie n c e
Academy. 4 8 ( 5 ) :6 8 5 -6 8 8 .
M o r r is , M.S., R.G. K e ls e y , and D. G rig g s . 1 976. The g e o g r a p h ic and
e c o l o g i c a l d i s t r i b u t i o n o f b ig s a g e b ru s h and o t h e r woody
i Z.t .e m js ia ys i n Montana. Jns P roceedings' o f th e Montana Academy of
S c ie n ce s 36: 56-79.
M ott, J .J . I 979. F lo w e r in g , s e e d f o r m a t i o n and d i s p e r s a l . J s : A r id la n d e co sy stem s: s tr u c tu r e , fu n c tio n in g and management. Vol. I.
C am bridge U niv. P r e s s . C am bridge London New York M elb o u rn e.
IBP pp. 6 2 7 -6 4 5 .
149
M iic g g ler, W.F. I 966. V ole dam age to b ig s a g e b r u s h i n s o u th w e s te r n
Montana. J. Range Manage. 2 0 :8 8 -9 0 .
N o b le, J . C., A.D. B e l l , and J.L . H a rp e r. 1979. The p o p u l a t i o n b io lo g y
o f p l a n t s w ith c l o n a l g ro w th . I . The m o rp h o lo g y and s t r u c t u r a l
demography o f Carex a r e n a r i a . J. Ecol. 67:963-1008.
Nosova, L I . 1973. P o te n tia l seed p r o d u c tiv ity o f A rtem is ia rh o d an th a.
B o t a n i c h e s k i i Z hurnal. 58(6):899-904.
N um ata, M., A. K o b a y a sh i, and N. Ohga . 1975. S t u d i e s on th e r o l e o f
a l l e l o p a t h i c su b sta n c e s. .%&: S tu d ie s i n Urban E cosystem s, ed. by
M. N um ata. pp. 3 8 -4 1 .
N u t t a l l , T. 1841. A f t e m l s j a and P ic ro th a m n u s . T ra n s . Am. P h i l . Soc.
I I . 7 :3 9 8 , 417.
01 so n , K.C. 1 982. E f f e c t o f p r e c i p i t a t i o n on m ix ed g r a s s p l a n t
c o m m u n itie s o f S o u t h e a s t e r n M ontana and i t s i m p l i c a t i o n s f o r
g ra z in g i n t e n s i t y . M. S. T h e sis. Montana S ta te Univ. 205p.
P a rm a r, M.T., and R.P. M oore. 1966. E f f e c t s o f s im u l a t e d d ro u g h t by
p o ly e th y le n e g ly c o l s o lu tio n s on co rn (Zea mavs L ) g e rm in a tio n
and s e e d lin g developm ent. A groa J. 58:391-392.
P e c h a n e c , J .F ., A.P. Plum m er, J.H. R o b e rts o n , and A.C. H a ll. 1 965.
S a g e b ru s h c o n t r o l on r a n g e la n d s . USDA Agr. H andbook No. 2 77.
40p.
F i j i , L. v a n d e r, 1982. P r i n c i p l e s o f d i s p e r s a l i n h ig h e r p l a n t s . 3 rd
e d i t i o a S p rin g er-V e rla g . B e r lin H eid elb e rg New York. 215p.
R o ath , L R ., and W.C. K ru e g e r. 1982. C a t t l e g r a z in g i n f l u e n c e on a
m ountain r i p a r i a n zone. J. Range M anage. 3 5 (1 ): 100- 103.
Sabo, D.G., G.V. J o h n s o n , W.C. M a r t i n , an d E .F . A ld o n . 1 9 7 9 .
G erm in atio n re q u ire m e n ts o f 19 a r id la n d ,p la n ts . R esearch Paper,
Rocky Mtn. F o r e s t and Range Exp. S ta ., USDA F o r e s t S e r v ic e , No.
RM-210. 26 p.
S a lis b u ry , E.J. 1942. The re p ro d u c tiv e c a p a c ity o f p la n ts ; s tu d ie s i n
q u a n t i t a t i v e b io lo g y . 224p. London, G. B e ll and Sons, Ltd.
S c h o ll, J .P ., R.G. K e ls e y , and F. S h a f i z ad eh . 1977. In v o lv e m e n t o f
v o l a t i l e com pounds o f A r t e m i s i a i n b ro w se p r e f e r e n c e by m u le
d e e r . B iochem . Sys. and E c o l. 5 :2 9 1 -2 9 5 .
S h a f iz a d e h , F ., and A.B. M e ln ik o f f . 1970. C o u m arin s o f A r te m is ia
tJlid .en t^tq ssp. _v_aseyana. P h y to c h e m istry 9:1311-1316.
150
S h e e h y , D.P., and A.H. Winwa rd . 1981. R e l a t i v e p a l a t a b i l i t y o f s e v e n
A r t e m i s i a t a x a t o m u le d e e r a n d s h e e p . J . R an g e M an ag e.
3 4 ( 5 ) :397-399.
S h e tle r, S.G., and L.E. Skog. 1978. A p ro v is io n a l c h e c k lis t o f s p e c ie s
f o r F lo ra N orth America. F lo ra N orth America R eport 84. M isso u ri
B o ta n ic a l Garden. 199p.
S te v e n s , R., and E.D. M cA rthur. 1 974. A s im p le f i e l d te c h n iq u e f o r
i d e n t i f i c a t i o n o f som e s a g e b r u s h t a x a . J . R an g e M anage.
2 7 (4 ):3 2 5 -3 2 6 .
S tid h a m , N.D., R.M. A h rin g , J . P o w e ll, and P.L. Cl ay p o o l. 1 980.
Chemical s c a r i f i c a t i o n , m o ist p r e c h i l l i n g and th io u r e a e f f e c t s on
g e rm in a tio n o f 18 shrub s p e c ie s . J. Range Manage. 33(2): 115-118.
S tu rg e s, D.L. 1977a. S o il m o is tu re re sp o n se to sp ra y in g b ig sag eb ru sh :
A s e v e n y e a r s tu d y and l i t e r a t u r e i n t e r p r e t a t i o n . USDA F o r e s t
S e rv ic e R esearch Paper, RM-188. 12p.
S tu rg e s, D.L. 1977b. S o il w a ter w ith d ra w a l and r o o t c h a r a c t e r i s t i c s o f
b ig sagebrush. Amer. Mid. Nat. 98(2):257-274.
T h a tc h e r , A.P. I 959. D i s t r i b u t i o n o f s a g e b ru s h a s r e l a t e d to s i t e
d if f e r e n c e s i n Albany County, Wyoming. J, Range Manage. 12:55-60.
T i s d a l e , E .W., and M. H iro n a k a . 1981. The s a g e b r u s h —g r a s s r e g i o n : A
re v ie w o f th e e c o l o g i c a l l i t e r a t u r e . F o r e s t , W ild l. and Range
Exp. S t a ., U niv. Id a h o . No. 20 9 . 3 Ip .
V asek, F.C. 1980. C re o s o te b u sh : lo n g l i v e d c lo n e s i n
D e s e r t. Amer. J. B ot. 6 7 (2 ):2 4 6 -2 5 5 .
th e M ojave
W a lle r , S.S., D.K. S c h m id t, J . S tu b b e n d ie c k , C.M. B r i t t o n , and F.A.
Sneva. 1980. G erm ination o f Kochia p r o s ta ta (L.1. Schrad. S o c ie ty
o f Range M anage., 3 3 rd a n n u a l m e e tin g , San D ie g o , C a l i f .
A b s tra c t.
W eaver, T.W., and D. K lo v ic h . I 977. A l l e l o p a t h i c e f f e c t s o f v o l a t i l e
su b sta n c e s from A rte m is ia t r i d e n t a t a . Amer. Mid. Nat. 97(2):508512.
W elch, B.L., and E.D. M cA rthur. 1 979. F e a s i b i l i t y o f im p r o v in g b ig
s a g e b r u s h f o r u se on m ule d e e r w i n t e r r a n g e s . JEn: ( J . R. G oodin
a n d D.K. N o r t h i n g t o n , e d . ) , P r o c e e d i n g s A r id L a n d P l a n t
R esources. Texas Tech. Univ., Lubbock.
W eldon, L.W., D.W. Bohm ont, and H.P. A lle y . 1959. The i n t e r r e l a t i o n o f
th re e en v iro n m e n ta l f a c t o r s a f f e c t i n g g e r m in a tio n o f s a g e b r u s h
s e e d . J . Range Manage. 12:236-238.
151
Went, F.W. 1 979. G e rm in a tio n and s e e d l i n g b e h a v io r o f d e s e r t p l a n t s .
Jo.: A rid -la n d E cosystem s: s tr u c tu r e , fu n c tio n in g and management.
IBP. V ol. I . C am bridge U niv. P r e s s . C am bridge London New York
M elbourne, pp. 477- 479.
W h ite , R.S., and P.0. C u r r ie . I 983» The e f f e c t s o f p r e s c r i b e d b u rn in g
on s i l v e r sag eb ru sh . J . Range Manage. 36:611-613.
W ils o n , R.G. I 982. G e rm in a tio n and s e e d l i n g d e v e lo p m e n t o f f r i n g e d
sagew ort (A rte m is ia f r i e i d a ) . Weed S c i. 30:102-105.
W ils o n , R.W. I 977. S a g e b ru s h u t i l i z a t i o n by m ule d e e r and a n te l o p e .
J n : Wyoming S h r u b la n d s — p r o c e e d in g s o f s i x t h Wyoming S hrub
E co lo g y Workshop, pp. 25-34.
W inw ard, A,H. 1 980. Taxonomy and e c o lo g y o f s a g e b r u s h i n Oregon.
O regon Agr. Exp. S ta . B u l l . 6 4 2 , 15p.
W inw ard, A.H., and E.W. T i s d a le . I 969. A s i m p l i f i e d c h e m ic a l m ethod
f o r s a g e b r u s h i d e n t i f i c a t i o n . U niv. Id a h o . S ta . N o te. No. 11. 2p.
W o o lle y , J.T ., and E.W. S t o l l e r . 1 978. L ig h t p e n e t r a t i o n and l i g h t
in d u ced seed g e rm in a tio n i n s o i l . P la n t P h y sio l. 61:597-600.
W rig h t, H.A., L.F. N euenschw a n d e r , and C.W. B r i t t o n . 1979. The r o l e
and u se o f f i r e i n s a g e b r u s h - g r a s s and p i n y o n - j u n i p e r p l a n t
com m unities: a s t a t e of th e a r t rev iew . USDA Gen. Tech. Rep. No.,
IN T -58. 48p.
Young, J.A ., and R.A. E vans. 1972. P o p u la tio n d y n a m ic s o f g re e n
r a b b i t b r u s h . J n : P r o c e e d in g s o f th e W e s te rn S o c i e t y o f Weed
S c ie n c e . V ol. 2 4 :1 3 .
Young, J.A ., and R.A. E vans. I 975. G e r m i n a b i l i t y o f s e e d r e s e r v e s i n a
b ig sagebrush community. Weed S c i. 23(5):358-364.
Young, J.A ., and R.A. E vans. 1 979. A rro w le a f b a s a m ro o t and m u le s e a r
seed g e rm in a tio n . J. Range M anage. 3 2 (1 ):7 1 -7 4 .
152
APPENDICES
153
I
APPENDIX A
PRECIPITATION AND TEMPERATURE DATA FOR THE YEARS
1981, 1982 AND 1983
154
Sum m arization o f c lim a tic d a ta p re s e n te d i n two ta b le s . Table 7
i s the p r e c i p i t a t i o n and te m p e ra tu re a v erag e s f o r th e summer months
f o r th e y e a rs o f 1981 through 1983 a t M iles C ity , Montana. Table 8 i s
maximum te m p e ra tu re s and days above 90 F d u rin g th e summer months a t
M iles C ity .
Table 8. P r e c i p i t a t i o n and te m p e ra tu re av erag es by month f o r th e y e a rs
1981, 1982 and 1983 a t M iles C ity , Montana.
Year
1981
Month
January
F ebruary
March
A p ril
May
June
J u ly
August
September
O ctober
November
December
Tem perature
(F)
(C)
D ep artu re
(F)
(C)
.13
.15
.71
.51
7.29
6.53
.91
2.84
1.83
3.53
1.98
.58
-.4 4
- .4 5
- .3 7
—1.06
.81
- .7 5
-1 .1 9
—.08
-.4 7
.68
.27
- .2 5
- 1.12
-1 .1 4
- .9 4
-2 .6 9
2.06
- 1 .91
- 3.02
-.2 0
-1 .1 9
1.73
.69
- .6 4
31.0
27.9
40.7
51.3
57.1
63.9
75.1
74.7
63.8
45.0
37.0
21.9
—,6
- 2 .3
3 .8
10.8
14.1
17.9
24.1
23.9
17.8
7 .3
2 .8
- 5 .7
10.63
27.00
-3 .3 0
-8 .3 8
49.1
9.6
Jan u a ry
F ebruary
March
A p ril
May
June
J u ly
August
Septem ber
October
November
December
.96
2.44
.20
.51
.73
1.85
.53
1.35
2.61
6.63
5.10 12.95
.69
1.75
.61
1.55
5.66
2.23
1.61
4.09
.10
.25
1.01 2.57
.47
-.3 1
.08
- .7 3
.55
1.78
- .8 6
- .5 9
1.04
.91
-.4 1
.53
1.19
- .7 9
.20
-1 .8 5
1 .40
4 .5 2
-2 .1 8
- 1 .50
2.64
2.31
- 1 .04
1.35
1.9 -1 6 .9
17.2 - 8 .3
30.8
- .7
41.9
5 .5
52.6 11.5
63.7 17.8
73.1 23.0
74.2 23.6
59.4 15.3
8 .2
46.7
28.4 - 2 .0
2 1.4 - 5 .9
ANNUAL
16.38 41.61
2.4 5
6.22
42.6
5 .9
- 2 .7 - 1 .5
-.3 1
- .4 7
.36
-1 .3 5
-.9 5
- 1 .1,9
- .7 9
- 1 .19
.91
-3 .4 3
-2.41
- 3 .02
27.7
34.9
36.5
44 .9
53.7
65.7
- 2 .4
1.6
2 .5
7 .2
12.2
18.9
13.6 7.6
12.8 7 .2
5 .2 2.9
0 .0 0.0
-3 .1 -1 .7
- .7 - .4
.66
.23
2.41
.05
3.45
3.96
-1 3 .5
—4.4
.6
-3 .4
-3 .7
- 1.2
- 1 .3
1.7
-.5
- 2.1
- 4 .0
-.6
5
.26
.09
.95
.02
1.36
1.56
OQ
January
F ebruary
March
A p ril
May
June
15.6 8.7
6 .3 3 .5
10.5 5 .9
6 .0 3 .4
.8
.5
■*1 • 0 —• 6
.7
.4
2 .2 1.2
3 .9 2 .2
- 3 .8 - 2.1
4 .6 2.6
—. I - . I
OO
1983
D ep artu re
( in ) (cm)
.05
.06
.28
.20
2.87
2 .5 7
.36
1.12
.72
1.39
.78
.23
ANNUAL
1982
P r e c ip ita tio n
( in )
(cm)
-7 .6
-2 .5
.3
-1 .9
- 2.1
-.7
-.7
1.0
-.3
- 1.2
- 2 .2
-.3
155
Table 8 . c o n tin u e d .
Year
Month
P r e c ip ita tio n
( in ) (cm)
J u ly
August
September
O ctober
November
December
1.89
.33
1.36
.26
.43
.28
ANNUAL
8 .7 9 22.33
4.80
.84
3.45
.66
1.09
.71
D ep artu re
( in )
(cm)
.37
- .9 3
.28
- .6 4
—.17
- .3 2
.94
- 2.36
.71
- I „63
—.43
-.8 1
-4 .6 7 -1 1 .8 6
Tem perature
(F)
(C)
76.1 24 .7
80.4 27.1
58.3 15.8
49 .9 10.0
34.0
1.1
0 .9 -1 7 .4
46.9
D ep artu re
(F)
(C)
1.5
.8
8.1 4 .5
—I .8 —I .0
,1.5
.8
2 . 0 1.1
- 2 0 . 6 - 11.1
8 .3
1.6
.9
T a b le 9. Maximum te m p e r a t u r e s and d a y s a b o v e 90 F (50.4 C) d u r in g
_________
June; J u ly and August o f 1982 and 1983 a t M iles C ity , Mont.
Maximum Tem perature
(F)
(C)
Days above 90 F
(5 0 .4 C)
Year
Month
1982
June
J u ly
August
94
99
101
52.6
55.4
56.6
2
11
14
1983
June
J u ly
August
100
108
105
56.0
60.5
58.8
20
3
25
156
APPENDIX B
DISPERSAL ANALYSIS OF VARIANCE TABLE
/
157
S um m arization o f a n a ly s is o f v a ria n c e o f seed d is p e r s a l d a ta i n
w hich th e s i x t r a n s e c ts and fo u r d is ta n c e s a re c o n sid e re d s p l i t p lo ts
and d a te o f d is p e r s a l as a c o v a ria n t. Sources o f v a r ia tio n , deg rees o f
freedom , F -r a t i o and s ig n if ic a n c e a re p re s e n te d .
Table 10. Sum m arization o f d is p e r s a l a n a ly s is o f v a ria n c e .
Source o f
v a ria tio n
Degrees o f
freedom
F -r a t i o
S ig n ific a n c e
le v e l
Study a re a
2
.40
T ra n se c ts
( d ir e c tio n )
5
6.58
D istan c e from
p la n t
3
11.71
.0
Date of seed
drop
4
6.36
.0
T ran se ct &
D istan c e
15
5.19
.0
Study a re a
& Date
8
2.73
.006
D istan c e &
Date
12
5.45
.0
T ra n s e c t, D istan ce
& Date
60
1.44
.018
.68
.0001
158
APPENDIX C
GERMINATION FACTORIAL ANALYSIS OF VARIANCE TABLE
I
J
159
S u m m a riz a tio n o f a n a l y s i s o f v a ria n c e i n g e rm in a tio n f a c t o r i a l
ex p erim en t. F iv e f a c t o r s w ere exam ined in d iv id u a lly and in t e r a c t i o n s
among f a c t o r s w e re a l s o e x a m in e d . N ote t h a t i n t e r a c t i o n s t h a t
in c lu d e d s t r a t i f i c a t i o n a re n o t in c lu d e d i n t h i s ta b le .
Table 11. Sum m arization of g e rm in a tio n a n a ly s is o f v a ria n c e .
Source of
v a ria tio n
D egrees o f
freedom
F -r a t i o
S ig n ific a n c e
le v e l
Date o f seed
c o lle c tio n
2
72.3
S tra tific a tio n
I
.0015
L ig h t/D ark
I
58.4
.0
Tem perature
2
90.0
.0
Osmotic P o te n tia l
3
890.7
.0
L ig h t/d a rk & D ate
2
16.2
.0004
Tem perature &
Date
4
16.9
.0
L ig h t/d a rk &
Osmotic p o te n tia l
3
79.1
.0
L ig h t/d a rk &
Tem perature
2
93.5
.0
L ig h t/d a r k , Date
& Tem perature
4
5.6
.0009
Tem perature &
Osmotic p o t e n t i a l
6
4.6
.0002
12
4.9
.0
L ig h t/d a rk , Tem perature
& Osmotic p o t e n t i a l
6
12.5
.0
L ig h t/d a rk , T em perature,
Osmotic p o te n tia l &
Date
12
2.6
g
Tem perature, D ate &
Osmotic p o t e n t i a l
.0007
.97
CO
APPENDIX D
CONSTRUCTION OF DISPERSAL FIGURES
161
Example o f c o n s t r u c t i o n o f d i s p e r s a l g r a p h s . S c a l e on a x e s are
numbers o f s e e d s d i s p e r s e d in each o f s i x d i r e c t i o n s . At each d i s t a n c e
from the p a ren t p l a n t ( 0 , I , 2 , and 3 m ), the number o f s e e d s t h a t f e l l
a t t h a t d i s t a n c e were graphed and c o n n e c te d to approxim ate th e degree
o f d i s p e r s a l in each d i r e c t i o n .
prevailing
NW wind
1-3 .96
Area of dispersal
I and 3 m, respectively
TRANSECT
A
MONTANA STATE UNIVERSITY LIBRARIES
3 1762 10020952 5
MAIN LIB.
N378
W178 W alton,
c o p .2
Of8S
T.
r
p
^
r
h aoisn =
F378
W178
cop. 2