Growth responses of Agropyron smithii and Bouteloua gracilis to simulated grazing and water
treatments
by Stephen Dale McClelland
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Range Science
Montana State University
© Copyright by Stephen Dale McClelland (1983)
Abstract:
Plant growth responses to simulated grazing and supplemental water application influenced forage
yield and canopy structure. These observations were made in vegetation representing two important
grassland communities of the Northern Great Plains and were studied from 1979 to 1981 in eastern
Montana. One study site was dominated by western wheatgrass (Agropyron smithii), the other by blue
grama (Bouteloua gracilis). At each site, two grazing and two water treatments were applied in a 2x2
design. Repeated clipping at three-week intervals was compared with one terminal (season’s end)
clipping to a stubble height of 7.6 and 5.0 cm (western wheatgrass and blue grama sites, respectively).
Each simulated grazing treatment included plots receiving only natural precipitation, and others
receiving 2.5 cm per week of sprinkler irrigation water. Total yields of plots clipped at three-week
intervals were compared with total yields of plots clipped only at season’s end. Canopy structures were
compared with an inclined point-contact system to record the vertical distribution of foliar density,
leaf-stem ratios, and green surface area (photosynthetic surface). Grazable forage production (i.e. above
clipping height) of plots harvested at season’s end averaged 15% more than plots harvested
periodically throughout the season. Total above ground production was not significantly affected by
harvest method. Simulated grazing also reduced canopy height, leaf-stem ratios and photosynthetic
surface. Application of supplemental irrigation resulted in significant increases in total above ground
production, grazable forage production, foliar density, leaf-stem ratios, and photosynthetic surface.
GROWTH RESPONSES OF
AGROPYRON SMITHII AND BOUTELOUA GRACILIS
TO SIMULATED GRAZING AND WATER TREATMENTS
by
S t e p h e n D a le M c C le lla n d
S
A t h e s i s su b m itte d i n p a r t i a l f u l f i l l m e n t
o f th e re q u ire m e n ts f o r th e d eg ree
of
M aster o f S cien c e
in
Range S c i e n c e
)
MONTANA STATE UNIVERSITY
Bozeman, M ontana
A p r i l 1983
WaiN LiB.
N 37%
Cop. <2
ii
APPROVAL
o f a t h e s i s s u b m i t t e d by
S t e p h e n D a le M c C le lla n d
T h i s t h e s i s h a s b e e n r e a d by e a c h member o f t h e t h e s i s c o m m i t t e e
a n d h a s b e e n f o u n d t o 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 l i s h
u s a g e , f o r m a t , c i t a t i o n s , b i b l i o g r a p h i c s t y l e , and c o n s i s t e n c y , and i s
rea d y f o r s u b m is s io n t o th e C o lleg e o f G ra d u a te S tu d ie s .
25
/oas
^ p f a l r p e r s o n , Graduprf^e Com m ittee
, D a te
Approved f o r t h e M a jo r D e p a r tm e n t
H ead, M ajor D e p a r tm e n t
D a te ^
A pproved f o r t h e C o l l e g e o f G r a d u a te S t u d i e s
r -z 'f-FJ
D a te
___
G r a d u a t e Dean
ill
STATEMENT OF PERMISSION TO USE
In p re se n tin g t h is th e s is in p a r t i a l
f u lf il lm e n t o f th e r e q u ir e ­
m e n t s f o r a m a s t e r ’s d e g r e e a t M ontana S t a t e . U n i v e r s i t y ,
I ag ree th a t
t h e L i b r a r y s h a l l m ake i t a v a i l a b l e t o b o r r o w e r s u n d e r r u l e s o f t h e
L ib ra ry .
B r i e f q u o t a t i o n s from t h i s t h e s i s a r e a l l o w a b l e w i t h o u t
s p e c ia l p erm issio n ,
is
p r o v i d e d t h a t a c c u r a t e a c k n o w le d g e m e n t o f s o u r c e
made.
P e r m i s s i o n f o r e x t e n s i v e q u o t a t i o n fro m o r r e p r o d u c t i o n o f t h i s
t h e s i s may be g r a n t e d by my m a j o r p r o f e s s o r ,
o r i n h i s a b s e n c e , by t h e
D i r e c t o r o f L i b r a r i e s w hen, i n t h e o p i n i o n o f e i t h e r ,
of th e m a te r ia l i s f o r s c h o la r ly purposes.
m a te ria l
in
th is
th e sis
for
w i t h o u t my w r i t t e n p e r m i s s i o n .
S ig n a tu re
D ate.
th e proposed u se
Any c o p y in g o r u s e o f t h e
f in a n c ia l g a in s h a ll
n o t be a llo w e d
iv
D e d i c a t e d i n L o v in g Memory
o f ay M o th e r
26 December 1982
V
VITA
S t e p h e n D a le M c C l e l la n d w as b o r n i n D over, Ohio on S e p t e m b e r 28,
1 955 t o C u r t i s D a l e a n d N a o m i R u t h M c C l e l l a n d . A f t e r g r a d u a t i n g i n
1 9 7 4 f r o m New P h i l a d e l p h i a H i g h S c h o o l i n New P h i l a d e l p h i a , O h i o ,
S te v e a tte n d e d Kent S t a t e U n iv e r s ity b e fo r e c o m p le tin g h i s B a c h e lo r o f
S c i e n c e i n F i s h and W i l d l i f e M anagem ent a t M ontana S t a t e U n i v e r s i t y i n
1979. I n S e p t e m b e r o f 1982, S t e v e m a r r i e d P a t r i c i a L o r e e n W a lle n m e y e r
i n M c M i n n v i l l e , O re g o n . S t e v e ’s M a s t e r o f S c i e n c e i n R ange S c i e n c e
w as c o m p l e t e d i n 1983 a t M ontana S t a t e U n i v e r s i t y .
vi
ACKNOWLEDGEMENTS
I w i s h t o e x p r e s s my a p p r e c i a t i o n t o t h e f o l l o w i n g :
T a y l o r f o r s e r v i n g a s c h a i r m a n o f my c o m m i t t e e ,
g u id an ce,
D r. J o h n
h is p ro fe ssio n a l
f i n a n c i a l s u p p o r t , and r e v i e w o f t h e s i s ; Dr. T h e o d o re W eaver
f o r t h e i n t r o d u c t i o n i n t o t h e H i p l e x W e a th e r M o d i f i c a t i o n P r o j e c t , h i s
p r o f e s s io n a l g u id an ce,
th e sis;
Dr.
a n a ly sis;
a b id in g i n s p i r a t io n ,
frie n d sh ip ,
and re v ie w o f
R i c h a r d Lund f o r h i s p r o f e s s i o n a l g u i d a n c e i n s t a t i s t i c , a l
th e fa c u lty
and g r a d u a t e s t u d e n t s o f t h e Range and B i o l o g y
D e p a r t m e n t s w i t h whom I h a v e s h a r e d m e m o r a b le m om ents d i s c u s s i n g many
a s p e c t s o f Range S c i e n c e ;
b e lie f,
d e v o te d
a n d p e r s o n a l s a c r i f i c e s w h i c h e n a b l e d c o n t i n u a t i o n o f my
e d u c a t i o n ; an d f i n a l l y ,
s u p p o r t and g u i d a n c e
rev iew
my p a r e n t s . f o r t h e i r e n c o u r a g e m e n t ,
I w o u ld l i k e t o t h a n k my w i f e P a t r i c i a f o r h e r
d u r i n g the, l a s t m o n th s o f t h e s i s p r e p a r a t i o n and
v ii
TABLE OF CONTENTS
PAGE
LIST OF TABLES ............................................................... ............................
. . . . . .
LIST OF FIGURES ..................................................................................................... ....
ABSTRACT ....................................... ....
. . ........................................................................
ix
xi
x ii
INTRODUCTION ..........................................................................................................
1
LITERATURE REVIEW.......................................................................................................
'
3
C l i p p i n g E f f e c t s on P r o d u c t i o n ...........................................................................
3
Canopy S t r u c t u r e E f f e c t s o n P r o d u c t i o n .........................................
W ater E f f e c t s o n Canopy S t r u c t u r e a n d P r o d u c t i o n . . . . . . . 8
6
METHODS.................................................................................................................
S tu d y D e s c r i p t i o n . . . ..................................................................................
L o c a t i o n . . , . ..........................................................................................
V e g e t a t i o n . . ................................................................................
G r a z in g H i s t o r y ........................
P . . .
............................................10
C l i m a t e ............................................................................................................................10
S o i l s . . ............................................................................
E x p e r i m e n t a l D e s ig n ............................................................................. ....
12
Canopy S t r u c t u r e A n a l y s i s ................................................................
B io m ass P r o d u c t i o n A n a l y s i s
.................... . . . . . .
.................... 16
S t a t i s t i c a l A n a l y s i s ..............................................................
9
9
9
9
14
17
RESULTS AND DISCUSSION..............................................................................
Canopy S t r u c t u r e ..................................................................................
D i s t r i b u t i o n o f L e a f - S t e m S u r f a c e a n d B iom ass ............................... 18
F a c t o r s A f f e c t i n g Canopy S t r u c t u r e . . . . . . . . . . . . .
20
S e a s o n ..............................................................................
S p e c i e s ............................. .... . . !....................................................................23
W a t e r ........................................................................................... '........................... 23
G r a z in g ........................................................................................... . . . . .
23
L e a f - S t e m Canopy S t r u c t u r e ................................................................................ 24
P h o t o s y n t h e t i c Canopy S t r u c t u r e ............................................ . . . . 28
W a te r an d S e a s o n .....................................................................
G r a z in g . ............................................. ..................................................... .... . 28
T o t a l A bove-G round P r o d u c t i o n . ...........................................................
G r a z a b l e F o r a g e P r o d u c t i o n ............................................................................. . 33
18
18
28
33
v iii
TABLE OF CONTENTS-Confcinued
O
CONCLUSIONS. . o .
LITERATURE C I T E D .......................................................... .... ...............................................
APPENDICES
. 44
51
/
ix
LIST OF TABLES
TABLE
,
page
1
E i g h t C h a r a c t e r i s t i c s I n Which G r a z i n g a n d C l i p p i n g '
E f f e c t s D i f f e r ( C u l l y e t a l . 1933, Jam eson 1963,
W h ite 1973, McWaughton 1979) . . " .....................................................4
2
P r e c i p i t a t i o n (cm) and A ve ra g e T e m p e r a tu r e ( D e g r e e s '
C e l s i u s ) a t M i l e s C i t y , M ontana 1 9 7 8 -1 9 8 1 . .............................
11
3
Summer N a t u r a l and S u p p l e m e n ta l M o i s t u r e (cm)
R e c e iv e d by W e s te r n W h e a t g r a s s (AGSM) an d B lu e
Grama (BOGR) S i t e s , 1 9 7 9 - 1 9 8 1 . . . .
............................................ 15
4
T o t a l L e a f - S t e m R a t i o s o f t h e W e s te r n W h e a t g r a s s and
B lu e Grama S i t e s , 1 9 8 1 ............................. .... .......................................... 25
5
-
S t r a t i f i e d L e a f - S t e m R a t i o s From t h e W e s te rn W h e a tg r a s s
S i t e , 1981 ............................................................................................................. 26
6
S t r a t i f i e d L e a f - S t e m R a t i o s o f B l u e Grama, 1981.
R a t i o s C a l c u l a t e d from P i n C o n t a c t s ............................................ 27
7
T o t a l P h o t o s y n t h e t i c S u r f a c e ( L iv e / D e a d P i n C o n t a c t
R a t i o ) o f t h e W e s te r n W h e a t g r a s s an d B lu e Grama
S i t e s , 1 9 8 1 .......................................................................................
8
9
S t r a t i f i e d P h o t o s y n t h e t i c S u r f a c e ( L iv e - D e a d R a t i o ) o f
t h e W e s t e r n W h e a t g r a s s S i t e , 1981. . . . . . . . . . . .
29
30
S t r a t i f i e d P h o t o s y n t h e t i c S u r f a c e ( L iv e - D e a d R a t i o s ) o f
t h e B l u e Grama S i t e , 1 9 8 1 ........................ ............................................... 31
10
T o t a l Above Ground P r o d u c t i o n ( g / p 2 ) f o r t h e W e s te r n
W h e a t g r a s s an d B l u e Grama S i t e s , 1 9 8 1 .............................................. 33
11
G r a z a b l e F o r a g e P r o d u c t i o n (g /m 2 ) o f t o e W e s te r n
W h e a t g r a s s a n d B l u e Grama S i t e s , 1979-1981 . . . . . . .
35
T o t a l P r o d u c t i o n (g/m 2 ) Below G r a z in g H e i g h t f o r t h e
W e s t e r n W h e a t g r a s s and B l u e Grama S i t e s , 1981. . . . . .
38
12
13
B a s a l A rea M e a s u r e s ( P e r c e n t ) f o r t h e W e s te r n W h e a t g r a s s
a n d B l u e Grama S i t e s , 1981. . M e a s u re s Taken a t S e a s o n 's
End C o r r e s p o n d i n g t o L a s t G r a z i n g Sam ple C o l l e c t i o n
D a te
. . 38
i
X
LIST OF TABLES-Continued
TABLE
14
15
16
17
Page
Mean P i n C o n t a c t s (From T r e a t m e n t P l o t s ) o f W e s t e r n
W h e a t g r a s s , 1981 .......................................................................................
52
Mean P i n C o n t a c t s (From T r e a t m e n t P l o t s ) o f B lu e
Grama, 1981. ................................................................................................
53
S t r a t i f i e d C u m u la tiv e P h o t o s y n t h e t i c S u r f a c e ( L i v e Dead R a t i o s ) o f t h e W e s te rn W h e a tg ra s s S i t e , 1981. . .
54
S t r a t i f i e d C u m u la tiv e P h o t o s y n t h e t i c S u r f a c e (L iv e -D e a d
R a t i o s ) o f t h e B lu e Grama S i t e , 1981 ..............................
55
Xi
LIST OF FIGURES
FIGURE
Page
.
1
/
E x p e r i m e n t a l P l o t D e s ig n f o r W e s t e r n W h e a t g r a s s
a n d B l u e G r a m a , 1 9 7 9 - 1 9 8 1 .........................................................
2
V e r t i c a l S t r a t i f i c a t i o n o f Canopy Cover From t h e
W e s te rn W h e a t g r a s s a n d B l u e Grama S i t e s , P e r c e n t
P i n C o n t a c t s (% P i n C o n t a c t s P l u s S t a n d a r d E r r o r ) ,
L e a f - S t e m . R a t i o s ( x ) , and T o t a l Above Ground Y i e l d
( g ra m s /m 2 ) a t Maximum S t a n d i n g C ro p , 1981.
Y ie ld s
a r e P r e d i c t e d From R e g r e s s i o n A n a l y s i s .
(F ig u re I ) .
'
13
. . 19
3
R e g r e s s i o n s a n d C o r r e l a t i o n s From W e s te rn W h e a t g r a s s
and B l u e Grama S i t e s , 1981 . ( P i n C o n t a c t s / P l o t Above
G r a z i n g H e i g h t w i t h G r a z a b l e F o r a g e Y i e l d / P l o t ) .................... 21
4
Growing S e a s o n V e r t i c a l S t r a t i f i c a t i o n o f W e s te r n
W h e a t g r a s s an d B l u e Grama Canopy C o v e r.
T o ta l P in
C o n t a c t s f o r Each T r e a t m e n t an d S a m p lin g D a t e . . . .
22
S t r a t i f i e d C u m u lativ e P h o to s y n th e tic S u rfa c e P in
C o n t a c t s F o r W e s t e r n W h e a t g r a s s an d B lu e Grama
S i t e s , 1981.
C u m u lativ e P in C o n ta c ts a r e C a lc u la te d
by Summed T o t a l P i q C o n t a c t s o f L a y e r s Below ,
E x c l u d i n g Those Above............................. ............................ ....
. 32
5
6
T o t a l G r a z a b l e F o r a g e Y i e l d s From B ly e Grama and
W e s t e r n W h e a t g r a s s S i t e s , 1 9 7 9 -1 9 8 1 . Means o f
Growth Form C a t e g o r i e s and S t a n d a r d E r r o r s o f
T o ta l Y ie ld s P re se n te d . . . . . . . . . . .
........................
I
34
x ii
ABSTRACT
P la n t g ro w th re s p o n s e s to s im u la te d g ra z in g and s u p p le m e n ta l
w a te r a p p lic a tio n
in flu e n c e d
f o r a g e y i e l d and canopy s t r u c t u r e . ,
T hese o b s e r v a t i o n s w e r e made i n v e g e t a t i o n r e p r e s e n t i n g tw o i m p o r t a n t
g r a s s la n d co m m u n ities o f th e N o rth e rn G re a t P la in s and w ere s tu d i e d
f ro m 1979 t o 1981 i n e a s t e r n M ontana. One s t u d y s i t e w as d o m i n a t e d by
w e s t e r n w h e a t g r a s s ( A a r o o v r o n s m i t h ! ! ) , t h e o t h e r by b l u e g r a m a
(B o u te lo u a g r a c i l i s ).
At e a c h s i t e , t w o g r a z i n g a n d t w o w a t e r
t r e a t m e n t s w e r e a p p l i e d i n a 2x2 d e s i g n .
R e p e a te d c l i p p i n g a t t h r e e week i n t e r v a l s w as c o m p a re d w i t h o n e t e r m i n a l ( s e a s o n ’s end) c l i p p i n g
t o a s t u b b l e h e i g h t o f 7.6 a n d 5.0 cm ( w e s t e r n w h e a t g r a s s a n d b l u e
gram a s i t e s , r e s p e c t i v e l y ) .
Each s i m u l a t e d g r a z i n g t r e a t m e n t i n c l u d e d
p l o t s r e c e i v i n g o n l y n a t u r a l p r e c i p i t a t i o n , and o t h e r s r e c e i v i n g 2.5
cm p e r w e e k o f s p r i n k l e r i r r i g a t i o n w a t e r .
T o tal y i e l d s o f p l o ts
c li p p e d a t th r e e - w e e k i n t e r v a l s w ere com pared w ith t o t a l y i e l d s o f
p l o t s c l i p p e d o n l y a t s e a s o n ’s end.
Canopy s t r u c t u r e s w e r e c o m pared
w ith an i n c l i n e d p o i n t - c o n t a c t sy ste m to r e c o r d th e v e r t i c a l
d is trib u tio n of f o lia r
d e n s i t y , l e a f - s t e m r a t i o s , and g r e e n s u r f a c e
a re a (p h o to sy n th e tic su rfa c e ).
G ra z a b le f o r a g e p r o d u c tio n ( i .e . above
c l i p p i n g h e i g h t ) o f p l o t s h a r v e s t e d a t s e a s o n ’s end a v e r a g e d 15% m ore
th an p l o ts h a rv e s te d p e r io d ic a lly th ro u g h o u t th e season.
T o ta l above
g r o u n d p r o d u c t i o n w a s h o t s i g n i f i c a n t l y a f f e c t e d by h a r v e s t m ethod.
S im u la te d g r a z in g a ls o re d u c e d canopy h e i g h t , l e a f - s t e m r a t i o s and
p h o to sy n th e tic su rfa c e .
A p p lic a tio n o f su p p le m e n ta l i r r i g a t i o n
r e s u lte d in s ig n if ic a n t i n c r e a s e s i n t o t a l above ground p ro d u c tio n ,z
g r a z a b l e f o r a g e p r o d u c t i o n , f o l i a r d e n s i t y , l e a f - s t e m r a t i o s , and
p h o to sy n th e tic s u r f a c e .
s
I
INTRODUCTION
S e a s o n a l p l a n t c o m m u n ity d e v e l o p m e n t a n d g r o w t h a r e i m p o r t a n t
a s p e c ts o f w e ste rn ran g e lan d fo ra g e p ro d u ctio n .
Com m unity d e v e lo p m e n t
a n d g r o w t h r e s p o n s e s a r e o f t e n m e a s u r e d by p l a n t y i e l d s a n d / o r canopy
stru c tu re .
A l t h o u g h m any f a c t o r s a f f e c t y i e l d a n d c a n o p y s t r u c t u r e ,
none
h a v e m ore i m p o r t a n t i n f l u e n c e s t h a n w a t e r and g r a z i n g ( C la r k e t a l .
19^3,
H u r t t 1951,
Reed and P e t e r s o n 1961).
g e n e ra liz e d id e a s
P re se n tly ,
t h e r e a r e many
o f w a t e r and g r a z i n g i m p a c ts oh y i e l d and canopy
s t r u c t u r e ( P e r r y 1976,
J a m e s o n 1963).
T hese a r e d e r i v e d
o f g r a z i n g an d w a t e r i m p a c t s on y i e l d
fro m s t u d i e s
and canopy s t r u c t u r e
t h a t have
a s s e s s e d r e s p o n s e s f ro m e i t h e r a g r a z i n g o r a w a t e r a s p e c t .
However,
by d e t e r m i n i n g r e s p o n s e s o f y i e l d and can o p y s t r u c t u r e a s a f f e c t e d by
b o th g r a z i n g an d w a t e r , a m o re c o m p l e t e u n d e r s t a n d i n g o f c o m m u n ity
a n d / o r s p e c i e s r e l a t i o n s t o r a n g e e c o s y s t e m d y n a m ic s c a n be r e a l i z e d .
■
i
W h ile a s s e s s i n g r a n g e c o m m u n ity r e s p o n s e s t o s u p p l e m e n t a l w a t e r
i n e a s t e r n M o ntana,
t h e High P l a i n s
W e a th e r M o d i f i c a t i o n E x p e r im e n t
(W eaver and H a g lu n d 1981) s o u g h t i n f o r m a t i o n on t h e i n t e r a c t i o n o f
g r a z i n g a n d / w a t e r m an a g e m e n t p r a c t i c e s .
L i v e s t o c k and Range R e s e a r c h S t a t i o n
Two s i t e s l o c a t e d on t h e USDA
w ere s e le c te d
to
g r a s s la n d c o m m u n itie s of th e N o rth e rn G re a t P la in s .
r e p r e s e n t tw o
One s i t e w a s
d o m i n a t e d by w e s t e r n w h e a t g r a s s (A a ro o v r o n s m i t h ! ! ) , t h e o t h e r by b l u e
g r a m a (JB outeloua g r a c i l i s ) .
2
The s t u d y h a d two o b j e c t i v e s :
1)
£t
D e t e r m i n e how s i m u l a t e d g r a z i n g a n d s u p p l e m e n t a l s u m m e r
irrig a tio n
w o u ld a l t e r
th e p ro d u c tio n o f w e s te rn w h eatg rass
and b l u e g r a m a c o m m u n i t i e s .
2)
D e t e r m i n e how s i m u l a t e d g r a z i n g a n d s u p p l e m e n t a l s u m m e r
irrig a tio n
a v a ila b ility .
w o u ld
a lte r
canopy
stru c tu re
and
fo rag e
3
LITERATURE REVIEW
x
The s p e c i e s o f p r i m a r y c o n c e r n i n t h i s s t u d y w ere, w e s t e r n w h e a t g r a s s and b l u e g r a m a ,
w h ic h a r e w i d e l y d i s t r i b u t e d i n t h e G r e a t P l a i n s
( H itc h c o c k an d C hase 1971), a ssu m e d o m in a n c e o v e r l a r g e a r e a s t h e r e
(K u c h le r
d iffe r
1964),
in
and a r e
m o rp h o lo g y
im p o rta n t fo ra g e
(H itc h c o c k
and
p ro d u cers.
C hase
1971),
The s p e c i e s
p h o to sy n th e tic
p a th w a y ( W a l l e r and L e w is 1979), a n d , a t l e a s t i n t h e c e n t r a l p l a i n s ,
i n s e a s o n o f g r o w t h (Kemp an d W i l l i a m s 1980).
T h i s p a p e r w i l l e x a m in e r e s p o n s e s o f t h e s e p l a n t s , t o tw o l e v e l s
o f g r a z i n g a n d tw o l e v e l s o f w a t e r s t r e s s .
D e s p i t e d i f f e r e n c e s i n m o r p h o l o g y , p h o t o s y n t h e t i c p a th w a y , and
p h e n o lo g y o f w e s t e r n w h e a tg r a s s and b lu e g ram a,
a f f e c t e d ' by g r a z i n g a n d w a t e r s u p p l e m e n t a t i o n .
su p p le m e n t
can a f f e c t
riu trie n t c o n te n t,
p la n t
c o m m u n ity
s p e c ie s c o m p o sitio n ,
b io m ass p r o d u c tio n ,
1976).
m any
an d o t h e r s
b o th s p e c i e s a r e
G ra z in g and w a te r
responses
re p ro d u c tio n ,
(J a m e s o n 1963,
in c lu d in g
ca n o p y s t r u c t u r e ,
McWaughton 1979,
P erry
H ow ever, t h e p r i m a r y r e s p o n s e s o f g r a z i n g an d w a t e r s u p p l e m e n t
a re a lte r a tio n s in :
I) b i o m a s s p r o d u c t i o n ,
a n d 2 ) ca n o p y s t r u c t u r e .
C l i p p i n g E f f e c t s on P r o d u c t i o n
)
'
M ost s t u d i e s o f p l a n t r e s p o n s e s t o g r a z i n g a r e b a s e d upon d a t a
from
s im u la te d
g raz in g
e x p e rim e n ts.
c lip p in g a re s im ila r but not id e n tic a l
The e f f e c t s
( W h i t e 1973 ).
o f g ra z in g
C o m p a ris o n s , o f
g r a z i n g and c l i p p i n g a r e t h o r o u g h l y r e v i e w e d by C u l l e y e t a l .
Jam eso n (1 9 6 3 ),
W h i t e ( 1 9 7 3 ) , a n d M c W a u g h to n ( 1 9 7 9 ) .
p r e s e n t e d i n T a b l e I.
and
(1933),
A sum m ary i s
4
T able I .
E i g h t C h a r a c t e r i s t i c s I n Which G r a z i n g and C l i p p i n g E f f e c t s
D i f f e r ( C u lly e t a l . 1933, J a m e s o n 1963, W h ite 1973,
, M cW aughton 1979).
1.
U tiliz a tio n e ffe c ts
G razin g rem oves h e rb a g e a t h e i g h t s v a ry in g
fro m p l a n t t o p l a n t and e v e n w i t h i n t h e
sam e p l a n t .
C lip p in g rem oves a l l h erb ag e
above a g iv e n h e ig h t from a l l p l a n t s .
2.
T r a m p lin g e f f e c t s
G r a z in g p r o v i d e s m o re m e c h a n i c a l dam age
and s o i l c o m p a c ti o n .
3.
M e c h a n ic a l e f f e c t s
4.
S a liv a e f f e c ts
May s t i m u l a t e r e g r o w t h o f p l a n t p a r t s ;
absent in c lip p in g stu d ie s.
5.
S e le c tio n p referen ces
T he p l a n t s we s e l e c t f o r s t u d y ( s p e c i e s ,
a g e , s i z e , m i c r o s i t e , e t c . ) , m ay n o t b e
t h e sam e p l a n t s g r a z e d and r e g r a z e d by t h e
h erb iv o res.
6.
N u trie n t tr a n s p o r t
G r a z e r s may f a c i l i t a t e a n e t i n f l u x o r
e f f l u x o f n u t r i e n t s fro m a s i t e and
p o t e n t i a l l y on a l a r g e s c a l e , w h e re as
c lip p in g s tu d ie s g e n e r a lly
rem ove
n u t r i e n t s ( l e a v e s ) fro m a s i t e on a s m a l l
sc ale .
7.
C o m p e titio n
G ra z in g o f t e n re m o v e s h e rb a g e fro m one
p l a n t and n o t fro m s u r r o u n d i n g p l a n t s .
U n g ra z ed p l a n t s may t h e n o u t c o m p e t e g r a z e d
p l a n t s f o r w a t e r and n u t r i e n t s .
C lip p in g
i s le s s se le c tiv e .
8.
T ra n slo c atio n
S h r e d d i n g , r i p p i n g , p u l l i n g , s t r i p p i n g and
t e a r i n g o f t i s s u e by a n i m a l a r e c o n t r a s t e d
. w i t h t h e c l e a n c u t by s c i s s o r s o r s h e a r s .
G r a z i n g m ay b e l e s s d e t r i m e n t a l t h a n
, c l i p p i n g by l e a v i n g s o m e t i l l e r s i n a
t i l l e r s y s t e m u n g r a z e d . C a r b o h y d r a t e s may
be t r a n s f e r r e d fro m u n g r a z e d t o g r a z e d
tille rs.
5
M ost c l i p p i n g s t u d i e s c o m p a re y i e l d r e s p o n s e s o f p l o t s c l i p p e d a t
some s p e c i f i e d h e i g h t ,
d ev elo p m en t w it h
some f r e q u e n c y o f r e m o v a l a n d / o r some s t a g e o f
an u n t r e a t e d
c o n tro l.
J a m e s o n (1963) s u g g e s t s t h a t
c l i p p i n g when r e g r o w t h r e a c h e s a p r e d e t e r m i n e d h e i g h t o r grow th' s t a g e
may h a v e s p e c i a l
m e r i t when t h e o b j e c t i v e i s
p r a c t i c e s o f hay h a r v e s t in g .
to d e te rm in e d e s ir a b le
C l i p p i n g a t s p e c i f i e d t i m e i n t e r v a l s may
be m ore u s e f u l f o r s t u d y i n g g r a z i n g s y s t e m s .
v
The l i t e r a t u r e sh o w s t h a t c l i p p i n g e f f e c t s v a r y among s p e c i e s and
g r a s s l a n d c o m m u n ities.
C l i p p i n g s t u d i e s o f B i s w e l l and W eaver (1 9 3 3 ),
Cook a n d S t o d d a r t ( 1 9 5 3 ) , B r a n s o n ( 1 9 5 6 ) , H e a d y ( 1 9 6 1 ) , D w y e r e t a l .
(1 9 6 3 ),
and
S m o li a k
T rlic a
c o n c lu d e d
c o n tro ls.
(1 9 6 5 ),
(1 9 7 6 ),
th a t
D i t t m e r (1 9 7 3 ), B e a ty and P o w e l l (1 9 7 6 ), Buwai
a n d m any o t h e r s
d e fo lia tio n
and b lu e g ram a .
as
D elay ed
th is
sp e c ific a lly
On t h e o t h e r h a n d ,
s h o w n by C a n f i e l d
( 1 9 7 2 ) , E ck e t a L
(1953)
b e lo w
th e g r e a te r th e re d u c tio n in y ie ld .
E v e r s o n (1966) d e m o n s t r a t e d
g rasses,
red u ced y ie ld
resp o n ses
and
th a t of u n d ip p e d
They a l s o s h o w e d t h a t t h e m o r e f r e q u e n t a n d s e v e r e t h e
c lip p in g ,
y ie ld s,
com pared y i e l d
H d ls c h e r (1945) and
for
w estern
c li p p in g so m e tim e s in c r e a s e s
(1939),
Lodge ( I 9 6 0 ) ,
D ra w e e t
a l.
(1 9 7 5 ), and o t h e r s .
responses
to
c lip p in g
w ere
e v id e n t
p a r t i c u l a r l y b u f f a l o g r a s s and b l u e gram a.
show ed
w h eatg rass
p ro d u c tio n
of
b lu e
gram a
and
in
lo w
g ro w in g
A lb e rtso n e t a l.
b u ffa lo
g rass
w as
u n a f f e c t e d i n t h e y e a r o f c l i p p i n g b u t w as a f f e c t e d i n s u b s e q u e n t
y ears.
6
G ra z in g
and
c lip p in g
b o th
d isru p t
norm al
p la n t
reso u rce
a l l o c a t i o n by r e m o v a l o f p h o t o s y n t h e t i o a l l y a c t i v e t i s s u e ( C a l d w e l l e t
a l.
1981 ) w h ic h d i r e c t l y r e d u c e s a c q u i s i t i o n o f r e q u i r e d m a t e r i a l s and
e n e r g y ( C o n a n t and R i s s e r 1974).
P l a n t s c o p in g w ith th e e f f e c t s o f
d e f o l i a t i o n m u s t c o m p e n s a t e f o r l o s t p h o t o s y n t h e t i c t i s s u e by r a p i d
rep la ce m e n t of p h o to sy n th e tic
tissu e
(C a ld w e ll e t
al
1981) u s in g
e i t h e r s t o r e d c a r b o n r e s e r v e s (Cook 1966» D o n a r t and Cook 1970,
an d Chapman 1974» Owensby e t a l .
1974, B uw ai a n d T r l i c a 1976), a n d / o r
a p p r o p r i a t e a l l o c a t i o n s o f n e w ly f i x e d c a r b o n (W h ite 1973).
et
a l.
( 1981) show ed
th a t
le a f-
and
p r i m a r i l y i n t h e f o rm o f c a r b o h y d r a t e s ,
by c l i p p i n g .
P erry
s te m -so lu b le
C a ld w ell
carb o n
p o o ls,
a r e a l m o s t c o m p l e t e l y rem o v e d
L e a f r e g r o w t h i s s u p p o r t e d p r i m a r i l y by c ro w n r e s e r v e s .
C a rb o h y d rate p o o ls o f d i f f u s e
r o o t sy ste m s a re r e s e r v e d f o r r o o t
s y s te m a c t i v i t i e s when th e s u p p ly o f p h o t o s y n t h a t e s fro m th e s h o o t
sy ste m i s c u r t a i l e d .
o b serv ed
a fte r
C u r ta ilm e n t o f r o o t g ro w th h as n e v e r t h e l e s s been
c lip p in g
(W eaver
1 930»
B isw e ll
S t o d d a r t and S m i t h 1955» B u r l e s o n and H e w i t t 1982).
a m ec h a n ism
for
c o n serv in g
p la n t reso u rces
and
and
W eaver
1933»
T h is c o n s t i t u t e s
a id s
in
th e
re­
e s ta b lis h m e n t o f a p ro p e r r o o t- s h o o t b a la n c e .
Canopy S t r u c t u r e E f f e c t s on P r o d u c t i o n
K n i g h t ( 1 9 6 9 ) , R i s s e r ( 1 9 7 1 ) , a n d C o n a n t a n d R i s s e r ( 1 9 7 4 ) sh o w
canopy s t r u c t u r e
is
an
n u trie n t a v a ila b ility
s tru c tu re i s
(W atso n
w ith in th e e co sy stem .
because
it
p h o to sy n th e sis
in flu e n c e s
w a te r,
and
In p a r t i c u l a r , canopy
a n i m p o r t a n t d e t e r m i n a n t o f c r o p an d p a s t u r e
1952)
co n seq u e n tly ,
im p o rta n t m o d ifie r of en erg y ,
lig h t
p ro d u ctio n
in te rc e p tio n ,
( W a r r e n - W i l s o n 1965).
and
P e r io d ic m easures
7
o f canopy s t r u c t u r e d u r in g th e g ro w in g s e a s o n t h e r e f o r e i l l u s t r a t e
g r a s s l a n d co m m u n ity r e s p o n s e s t o m a n i p u l a t i o n , s u c h a s g r a z i n g and
w a t e r (C o n a n t an d R i s s e r 1974).
P r o d u c t i v i t y o f m ost c ro p s i n c r e a s e s
a s l e a f a r e a i n c r e a s e s ( J a m e s o n 1963) u n t i l l i g h t ,
lim it
th e
g ro w th
of
a c tiv e
p la n t tis s u e
(W a tso n 1952, D o n a ld a n d B l a c k 1958,
w ater,
or n u trie n ts
and p r o d u c t i o n d e c l i n e s
C a ld w e ll e t a l .
1981).
I n r e g i o n s o r s e a s o n s w h e r e w a t e r and n u t r i e n t s a r e n o t l i m i t i n g
p r o d u c t i o n , g r a s s l a n d e c o s y s t e m s a r e d e p e n d e n t on t h e q u a n t i t y and
v e rtic a l
d istrib u tio n
of
fo lia r
m a te ria l.
D onald (1951) s t a t e s
th e u l t i m a t e c a p a c ity o f a s p e c i e s f o r b io m ass p ro d u c tio n ,
th at
when w a t e r
and n u t r i e n t s a r e i n a d e q u a t e s u p p l y , d e p e n d s o n t h e d e g r e e t o w h ic h a
c o m m u n ity
p ro d u ctio n
can
e x p lo it
w ill
th e
depend
lig h t
on th e
fa llin g
sta tu re
on
it.
T h is
and h a b i t
of
lev e l
th e
of
sp e cie s.
S p e c ie s o f p r o s t r a t e h a b i t and d e n se h o r i z o n t a l l y
d isp o se d le a v e s
a c h ie v e
lig h t
a
fu ll
co m p arativ ely
h e ig h t,
low
canopy
and
sta tu re .
and l e a v e s a t
fu ll
T a ll
e x p lo ita tio n
sp ecies,
w ith
v a r i o u s l e v e l s an d a n g l e s ,
of
erect
h a b it,
at
g rea ter
do n o t r e a d i l y fo rm
a c o n t i n u o u s f o l i a g e c o v e r , a n d s o do n o t i n t e r c e p t a l l
lig h t.
w h ile
a v a ila b le
S t u d i e s by W a t s o n ( 1 9 5 2 ) a n d D o n a l d a n d B l a c k ( 1 9 5 8 ) show a n
in te rre la tio n s h ip of lig h t,
l e a f a r e a , and p ro d u c tio n .
They c o n c lu d e d
t h a t i f l e a f a r e a i s l e s s t h a n t h e p o i n t c o r r e s p o n d i n g w i t h o p t im u m
y i e l d , p r o d u c t i o n w i l l be r e d u c e d by d e f o l i a t i o n
d epends on l e a f s u r f a c e to i n t e r c e p t l i g h t .
sin c e p ro d u c tiv ity
If le a f area is g re a te r
t h a n t h e p o i n t o f o p tim u m y i e l d , d e f o l i a t i o n w i l l r e d u c e l e a f a r e a and
p r o d u c t i o n may i n c r e a s e .
8
f e t m L J ^ X ^ .f c . 8^jnL-CanQP.v. S t r u c t u r e and P r o d u o t i o n
In a r id re g io n s o r seasons,
w a te r l i m i t s gro w th .
The m a j o r r o l e
o f w a t e r s u p p l e m e n t a t i o n on n a t i v e r a n g e i s t o a l l o w ( p h o t o s y n t h e s i s - i n
d r y p e r i o d s . The w a t e r economy o f a n
tec h n iq u e s
sp read in g ,
in c lu d in g
c o n to u r
w e a th er
fu rro w in g ,
S u p p le m e n ta l w a te r s t u d i e s
(1 9 6 5 ),
S m ik a e t a l .
a r e a may be a u g m e n te d by v a r i o u s
m o d ific a tio n ,
p ittin g ,
irrig a tio n ,
or scalp in g
by B r a n s o n ( 1 9 5 6 ) ,
(1 9 6 5 ),
(V a lle n tin e
w a te r
1971).
K la g e s and R yerson
J o h n s an d L a zen b y (1 9 7 3 a,, 1 9 7 3 b ), and
L a v e n w o r th a n d S im s (1973) show ed i n c r e a s e s i n y i e l d r a n g i n g f ro m 50
/
-
to 330 p e r c e n t o v e r c o n t r o l s .
W eaver (1 9 8 1 ) w o rk in g w i t h w e s t e r n
w h e a t g r a s s and b l u e g r a m a , u n d e r w e e k ly sum m er w a t e r s u p p l e m e n t s o f 6 ,
12,
and
25 m i l l i m e t e r s
i n c r e a s e s o f 22 %,
p e r g ro w in g
season-w eek,
show ed a v e ra g e
45%, 246% r e s p e c t i v e l y f o r b l u e g r a m a a n d 17%, 58 %,
338 % r e s p e c t i v e l y f o r w e s t e r n w h e a t g r a s s .
B e s i d e s e f f e c t s on f o r a g e y i e l d , t h e r e a r e o b v io u s e f f e c t s o f
w a t e r a d d i t i o n s on canopy s t r u c t u r e .
D o nald and B l a c k (1958) w o r k in g
w i t h p a s t u r e c r o p s show ed i n c r e a s e s i n d e n s i t y
o f ground s u r f a c e ) .
W eaver (1 9 8 1 )
(p la n ts per u n it are a
w o rk in g i n w e s te r n w h e a tg ra s s
c o m m u n i t i e s w i t h w a t e r a d d i t i o n s o f 25 m i l l i m e t e r s p e r g r o w i n g s e a s o n w eek,
show ed i n c r e a s e d d e n s i t i e s
(p la n ts or p a rtg of p la n ts per u n it
a re a ) a t gro u n d s u r f a c e and i n v e r t i c a l l a y e r s above th e s u r f a c e , a s
w e l l a s t h e u s u a l i n c r e a s e i n canopy h e i g h t .
9
METHODS
S tu d y D e s c r i p t i o n
L o o a tI p n.
I n 1977s a n i r r i g a t i o n s t u d y w a s i n i t i a t e d a s p a r t o f
t h e High P l a i n s W e a th e r M o d i f i c a t i o n E x p e r i m e n t nHIPLEXn (W eaver and
H a g lu n d ,
1981),
t o d e t e r m i n e t h e e f f e c t s o f i n c r e a s e d m o i s t u r e on t h e
v e g e ta tio n of th e N o rth ern G reat P la in s .
The s i m u l a t e d g r a z i n g a n d
su p p le m e n ta l
w as c o n d u c te d d u r in g t h e
w a te r
s tu d y r e p o r te d
here
s u m m e rs o f 1979 t h r o u g h 1981 a t t h e DSDA L i v e s t o c k a n d Range R e s e a r c h
S t a t i o n , M i l e s C i t y , M ontana.
Two g r a s s l a n d e c o s y s t e m s , o n e 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 an d t h e o t h e r by b l u e g r a m a , w h ic h c o m p r i s e o v e r
1.16 m i l l i o n km ^ ( K u o h l e r 1 9 6 4 ) o f t h e N o r t h e r n G r e a t P l a i n s w e r e
rep resen ted .
The w e s t e r n w h e a t g r a s s s i t e
an a l l u v i a l
flo o d
p la in
w as 4 km s o u t h w e s t o f M i l e s C i t y on
of th e
Y e llo w sto n e
a p p r o x i m a t e l y 150 m e t e r s by 300 m e t e r s .
R iv er.
The s i t e
w as
The b l u e g r a m a s i t e was 6 km
s o u t h e a s t o f M il e s C ity on a f l o o d p l a i n o f t h e T ongue R iv e r.
The
s i t e w as a p p r o x i m a t e l y 50 m e t e r s by 150 m e t e r s .
V e g e tatio n .
and
b lu e
gram a
Over 97% o f t h e p r o d u c t i o n o f t h e w e s t e r n w h e a t g r a s s
c o m m u n itie s
w as
by p e r e n n i a l
grass
sp e c ie s.
By
c o m p o s i t i o n , i t w as s u b j e c t i v e l y e s t i m a t e d t h a t w e s t e r n w h e a t g r a s s an d
b l u e g r a m a c o m p r i s e d 90% o f t h e i r r e s p e c t i v e
g r a s s e s in c lu d e d n e e d le a n d th r e a d ( S t i o a o o m a t a ).
( S t i o a v i r i d u l a ). b u f f a l o g r a s s
c o m m u n itie s.
O th er
g ree n n e e d le g ra ss
( B u c h l o e d a c t v l o i d e s ) . J a p a n e s e brom e
(Brom us . i a p o n i c u s ). c h e a t g r a s s ( B r o m u s t e o t o r u m ) . a n d s a n d d r o p s e e d
(S o o ro b o lu s c r v o ta n d r u s ) .
The p r i n c i p a l f o r b s w e r e y e l l o w s w e e t c l o v e r
10
(M-e_J.JLJ,-0 _ tu 3
o o c c l n e a ).
and
sc a rle t
g lo b e m a llo w
The m o s t c o n s p i c u o u s h a l f - s h r u b
(S p h a e ra lce a
w as cu d w eed s a g e w o r t
( A r te m is ia lu d o v ic ia n a ).
V e g e t a t i o n o f t h e M i l e s C i t y a r e a i s d e s c r i b e d i n m o re d e t a i l by
H o l s c h e r (1 9 4 5 ),
d e sc rip tio n s
H o u s to n an d Woodward (1 9 6 6 ),
are
put
in
a
N i c h o l s o n a n d H u l e t t (1 9 6 9 ),
G ra z in g .H isto ry .
c o n te x t
by
C o u p lan d
G razin g a t
(1961),
ha d p r e v i o u s l y r e c e i v e d g r a z i n g
th e w e ste rn w h eatg rass s i t e
d u r in g sum m er and w as c o n s id e r e d l i g h t
p e r s o n a l c o m m u n ic a t io n ) .
T hese
a n d K iic h le r (196-4).
B oth s t u d y s i t e s
by d o m e s t i c a n i m a l s .
c o w -c a lf p a ir s
re g io n a l
a n d O lso n (1 9 8 2 ).
G r a z i n g was d i s c o n t i n u e d i n
(R.
was by
W h ite
1975. . G r a z in g
a t t h e b l u e g r a m a s i t e w as by c o w - c a l f p a i r s d u r i n g t h e l a t e summer e a r l y a u tu m n , an d w as c o n s i d e r e d h e a v i e r ,
m ete rs
of
a sto c k
w a te r
ta n k
G r a z i n g was d i s c o n t i n u e d i n
C lim a te .
T he
(R.
s i n c e i t w a s w i t h i n 100
W h ite p e r s o n a l
c o m m u n ic a tio n ).
1976.
c l i m a t e o f t h e s t u d y a r e a i s s e m i a r i d w i t h a m ean
a n n u a l p r e c i p i t a t i o n o f 35.5 cm.,
76% o f w h ic h f a l l s d u r i n g t h e A p r i l
t o S e p t e m b e r g r o w i n g s e a s o n ( U n i t e d S t a t e s D e p a r t m e n t o f C o m m e rc e .
C lim a to lo g ic a l
D a ta
-
M o n ta n a
(M iles
C ity
FFA
AP)
19 7 9 -1 9 8 1 ).
C l i m a t o l o g i c a l d a t a a r e s u m m a riz e d i n T a b l e 2.
S o ils.
c la ssifie d
S o ils of th e
by S o i l
C i t y , M o n ta n a ).
d rain e d ,
fin e ,
i d e n t i f i e d a s a,
w e s t e r n w h e a t g r a s s and b l u e g r a m a s i t e s w e r e
C o n s e r v a t i o n S e r v i c e p e r s o n n e l (M.
N ic h o ls,
M ile s
The s o i l o f t h e w e s t e r n w h e a t g r a s s s i t e i s a w e l l m o n tm o r ilI o n i t i c B o r o l l i c C a m b o rth id s p e c i f i c a l l y
K obar s i l t y
cm, a n d r o o t s t o 1 50 cm .
c l a y lo a m ,
w i t h c a l c i u m c a r b o n a t e a t 20
I t d e v e lo p e d on a llu v iu m l y i n g i n s im p le
T a b l e 2 . P r e c i p i t a t i o n (cm) and A verage T e m p e r a tu r e ( D e g r e e s C e l s i u s ) a t M il e s C i t y ,
M ontana 1 9 7 8 - 1 9 8 1 .
Jan
Feb
Mar
Apr
1 .3 0
3.02
2.9 0
0 .8 4
0 .1 5
1 .6 5
0.30
0 .6 6
0 .7 1
0 .7 1
3.20
1 .1 9
1.93
1.68
0 .5 1
May
Jun
Jly
Aug
Sep
Oct
Nov
Dec
8 .4 3
3 .5 3
1 .96
7 .7 2
6 .5 3
3 .9 4
6 .3 7
7 .0 9
1 .3 5
0 .91
3 .0 5
2 .0 5
3.02
8 .6 3
0 .0 8
1 .8 5
1 .8 3
1.80
0 .6 8
0.81
4 .0 9
3 .5 3
1 .3 0
5 .5 1
0 .51
0 .7 4
1 .9 8
1.22
1.60
0 .1 3
0 .8 4
0.58
A nnual
P re c ip ita tio n
Normal
1978
1979
1 .2 4
1 .3 0
0 .8 4
0 .8 4
0 .1 3
1980
1981
5 .2 3
1 7.30
3 .4 5
0 .7 1
7 .2 9
1.70
5 .1 8
2 .8 4
1980
1981
-9 .2
-1 6 .3
-1 7 .7
-1 0 .3
—0 • 6
27 .0 0
A v e ra g e
T e m p e r a tu r e
Normal
1978
1979
3 5 .3 8
5 1 .5 1
2 2 .0 5
2 6 .5 4
-5 .8
-1 1 .4
-1 3 .3
-4 .4
-2 .3
—1 .0
-0 .3
—1 • 2
—0 . 2
4 .8
7 .4
8.2
5 .2
1 1 .7
1 0 .7
1 3 .5
1 3 .7
12.1
16.8
13 .9
1 8 .3
18.8
1 9 .8
20 .0
1 7 .7
23.6
2 1 .9
2 3 .7
2 4 .7
2 3 .9
2 2 .5
2 1 .3
22 .2
1 9 .7
2 3 .7
1 5 .5
1 7 .2
1 8 .7
16.0
1 7 .7
9 .3
9 .2
10 .4
9 .6
7 .2
0.2
-5 .2
—1.2
3 .6
2. 8
-5 .6
-1 0 .7
—1.6
-4 .2
-5 .6
7 .3 9
5 .5
6 .4 2
8.58
9 .4 9
12
r e l i e f w ith a
2% n o r t h s l o p e .
w e ll-d ra in e d ,
fin e ,
s p e c ific a lly
lo am y ,
id e n tifie d
as
The s o i l o f t h e b l u e g r a m a s i t e i s a
frig id
a
c a r b o n a t e a t 75 cm , a n d r o o t s
c a lc a re o u s
H avre
to
v a ria n t
105 cm.
U stic
lo am ,
T o rrio rth e n t
w ith
c a lc iu m
I t d e v e lo p e d on a
a l l u v i a l t e r r a c e ly in g i n sim p le r e l i e f w ith a
h ig h
e a s t slo p e .
E x p e rim e n ta l- D e s ig n
The e x p e r i m e n t a l d e s i g n a t e a c h s t u d y s i t e was a 2 x 2 s y s t e m a t i c
b l o c k w i t h tw o s i m u l a t e d g r a z i n g an d tw o w a t e r t r e a t m e n t s ( F i g u r e I).
D ep en d in g u p o n ,s p a c e
re p lic a te s;
re p lic a te s
th at is,
a v a ila b le ,
each t r e a tm e n t had f i v e
to seven
t h e b l u e g ra m a s i t e h a d a n u n b a l a n c e d d e s i g n o f 5
o f w e t g r a z e d / u n g r a z e d t r e a t m e n t s and 7 r e p l i c a t e s o f d r y
g r a z e d /u n g r a z e d t r e a t m e n t s , w h ile th e w e s te r n w h e a tg ra s s s i t e had
b a la n c e d d e s ig n o f 6 r e p l i c a t e s p e r t r e a tm e n t.
Each e x p e r i m e n t a l p l o t
w as 2 x 6 m e t e r s .
The s i m u l a t e d g r a z i n g t r e a t m e n t s w e r e :
p l o t s r e p e a t e d l y c l i p p e d e v e r y 21 d a y s ( i . e . ,
S ep tem b er g ro w in g s e a s o n ),
I) G r a z e d ,
c o n sisted of
4 tim e s in th e June -
2) U n g r a z e d , c o n s i s t i n g o f p l o t s c l i p p e d a t
th e end o f th e g ro w in g s e a s o n ( i n S e p te m b e r, c o r r e s p o n d in g w ith th e
fo u rth
"grazed" c l i p
b a g g in g T oro
1
d a te ).
l a w n mower.
7.6 cm a n d 5.0 cm ,
a fte r
w e s t e r n w h e a t g r a s s and
" G r a z in g " was a c c o m p l i s h e d w i t h a r e a r -
(
G r a z in g h e i g h t s w e re a r b i t r a r i l y
su rv e y in g
su rro u n d in g
p a stu re s
b l u e g ra m a s i t e s , r e s p e c t i v e l y .
d e s c r i b e d by H o l s c h e r and M o o k fo lk (1953)
by w e i g h t w i t h s u c h g r a z i n g h e i g h t s
chosen a t
fo r
th e
U s in g m e th o d s
av erag e p e rc e n t u t i l i z a t i o n
w e r e e s t i m a t e d t o r e s u l t i n 64%
‘M e n tio n o f a nam em ark d o e s n o t i m p l y i t s a p p r o v a l t o t h e e x c l u s i o n
o f o t h e r p r o d u c t s t h a t may a l s o be s u i t a b l e .
13
F ig u re I.
E x p e rim e n ta l P lo t D e sig n f o r W e s te rn W h e a tg r a s s and
B lu e Grama, 1 9 7 9 -1981.
BLUE GRAMA SITE
DRY
WET
WESTERN WHEATGRASS SITE
DRY
WET
GRAZED
REPLICATE I
G RA ZED
R EPLIC A TE I
GRAZBD
GRAZED
REPLICATE I
REPLICATE I
UNGRAZED
R E PU C A T E I
UNGRAZED
REPLICATE I
UNGRAZED
REPLICATE I
UNGRAZED
REPLICATE I
GRAZED
REPLIC A TE 2
G RAZED
REPLICA TE 2
GRAZED
R EPLICA TE 2
GRAZED
REPLICATE 2
UNGRAZED
REPLICATE 2
UNGRAZED
R EPL IC A TE 2
UNGRAZED
R E PU C A T E 2
UNGRAZED
REPLICATE 2
- I —
V
DC
“ I -
LU
DC
LU
LU
LU
LU
LU
D
CO
D
CO
- I "
n
u tiliz a tio n
o f w e s t e r n w h e a t g r a s s a n d 30$ f o r b l u e g r a m a .
a u th o rs
suggest
av erag e
w e ste rn
w h e a tg ra ss
^p ro p er” u t i l i z a t i o n
and
b lu e
gram a
su b ty p e s
45$ and
of
T hese
41$
re sp e c tiv e ly ,
for
under
c o n t i n u o u s sum m er g r a z i n g (May t o November) i n e a s t e r n M ontana.
T he
w a te r
p re c ip ita tio n .
1979
-
1982
tre a tm e n ts
w ere:
1)
D rvf
re c e iv e d
P r e c i p i t a t i o n was b e lo w a v e r a g e f o r
(T a b le
2),
2)
W etf
re c e iv e d
o n ly
n a tu ra l
th e s tu d y p e rio d
su p p le m e n ta l
sp rin k le r
i r r i g a t i o n w a t e r o f 2.5 cm p e r week d u r i n g t h e g r o w i n g s e a s o n .
p l o t s w ere in te n d e d t o r e p r e s e n t w et y e a r s o r i r r i g a t e d
They a l s o
s e r v e d to p r o t e c t th e i n v e s t i g a t o r from
p o ssib le
d ro u g h t
c o n d itio n s
S u p p le m e n ta l w a te r a p p l i c a t i o n s
w in d less c o n d itio n s.
re c e iv e d
found
w e re a p p l i e d
in
in
c o m m u n ities.
fa ilu re
e a ste rn
ea rly
due to
M o n ta n a .
m o rn in g u n d e r
Wedge g a u g e s w e r e u s e d t o r e c o r d a v e r a g e w a t e r
by t r e a t m e n t s .
W eaver (1 9 8 1 ).
o fte n
T hese
W a te r a p p l i c a t i o n s a r e f u r t h e r d e s c r i b e d by
S p e c i f i c a m o u n ts o f w a t e r r e c e i v e d by t r e a t m e n t p l o t s
a r e s u m m a r i z e d i n T a b l e 3.
Canopy S t r u c t u r e A n a l y s i s
Canopy s t r u c t u r e w i l l be d e f i n e d a s t h e v e r t i c a l d i s t r i b u t i o n o f .
f o l i a r m a te ria l d if f e r e n tia te d as to le a f ,
stem , o r i n f l o r e s c e n c e .
P o i n t c o n t a c t d a t a w e re r e c o r d e d d u r in g 1981, j u s t b e f o r e e a c h
g r a z in g sam p le c o l l e c t i o n d a te , f o r a l l t r e a t m e n t s and b o th s i t e s .
S a m p le s w e re t a k e n w i t h a m o to r iz e d i n c l i n e d p o i n t - c o n t a c t s y s te m
d e s c r i b e d by K n i g h t (1 973).
f ro m
th e h o r iz o n ta l.
The p i n ' s a n g l e o f i n c l i n a t i o n was 3 2 .5 °
T hree sa m p lin g p o s i t i o n s w ere ran d o m ly
a t th e 2 m ete r edge in each tre a tm e n t.
c o lle c tio n
w ith o u t d istu rb a n c e
p laced
T h is p la c e m e n t a llo w e d d a ta
o f b io m a ss c o l l e c t i o n p ro c e d u re s.
T a b l e 3*
Summer N a t u r a l a n d S u p p l e m e n ta l M o i s t u r e (cm) R e c e iv e d By
W e s te r n W h e a t g r a s s (AGSM) and B lu e Grama (BOGR) S i t e s ,
1 9 7 9 -1 9 8 1 .
Mav
1979
N atu ral*
Jun
Jlv
Aue
T o tal
3 .4 5
1.96
7 .0 9
1 .7 0
1 4.20
N a tu ral
0 .7 1
7 .7 2
1 .3 5
5 .1 8
1 4.96
AGSM I r r i g a t i o n
AGSM T o t a l
2.31
3.02
10.90
18.62
10.52
1 1 .8 7
7 .9 2
1 3 .1 0
3 1 .6 5
4 6 .6 1
BOGR I r r i g a t i o n
BOGR T o t a l
2 .6 4
3 .3 5
7 .2 9
15.01
1 4 .1 7
1 5 .5 2
1 0 .4 4
15.62
3 4 .5 4
4 9 .5 0
N a tu ral
7 .2 9
6 .5 3
0 .91
2 .8 4
1 7 .5 7
AGSM I r r i g a t i o n
AGSM T o t a l
#*
7 .2 9
2 .5 7
1 0 .8 7
1 1 .7 8
11.66
1 4 .5 0
2 5 .1 0
4 2 .6 7
BOGR I r r i g a t i o n
BOGR T o t a l
2 .3 4
9 .3 6
2 .1 3
10.16
11.06
1 0 .4 9
1 3.33
2 5 .1 2
4 2 .6 9
1980
1981
9.10
8.66
• Though a s i m i l a r i r r i g a t i o n r e g i m e was a p p l i e d i n 1 9 7 9 -1 9 8 0 - 1981 ,
1979 r e c o r d s a r e n o t a v a i l a b l e .
• • I r r i g a t i o n M o i s t u r e Not A p p l i e d .
16
S a m p li n g p o s i t i o n s w e r e m ark e d w i t h i r o n n a i l s d r i v e n i n t o t h e g ro u n d
f o r ea se o f fram e r e lo c a tio n .
E x a c t r e p o s i t i o n i n g o f t h e f ra m e on
s u c c e s s iv e sam p le d a te s e li m i n a te d p l o t to p l o t v a r i a t i o n a s a so u rc e
of erro r.
E a c h s a m p l e c o n s i s t e d o f 15 p i n s l o c a t e d 5 cm a p a r t f o r a
t o t a l o f 45 p i n s p e r t r e a t m e n t .
v e rtic a l
c o n d itio n ,
h e ig h t
of
c o n ta c t,
A ll p in c o n t a c t s w ere r e c o rd e d a s t o
sp e cie s,
p la n t
p a rt,
and
p h y sic a l
d e fin e d a s l i v e o r dead p l a n t t is s u e .
B io m ass P r o d u c t i o n A n a l y s i s
G ra z a b le f o ra g e h e re i s d e f in e d as b io m ass p ro d u ced above th e
c l i p p i n g h e i g h t s o f f .6 cm f o r t h e w e s t e r n w h e a t g r a s s a n d 5.0 cm f o r
th e
b lu e
gram a
site .
T o ta l
above-g ro u n d
b io m ass
is
d e fin e d
as
p r o d u c t i o n b o t h a b o v e a n d b e lo w c l i p p i n g l e v e l s .
G ra z a b le f o r a g e s a m p le s w e re h a r v e s t e d from a l l t r e a t m e n t s a t
b o t h s i t e s d u r i n g t h e sum m er m o n th s o f 1979 - 1981.
The " g r a z e d " p l o t
s a m p l e s w e r e c o l l e c t e d f o u r t i m e s , e v e r y 21 d a y s , e x c e p t i n
w h ic h had t h r e e s a m p lin g p e r i o d s .
1979,
The " u n g r a z e d " p l o t s a m p l e s w e r e
c o l l e c t e d a t s e a s o n ’s e n d w h i c h c o r r e s p o n d e d w i t h t h e l a s t g r a z i n g
sam ple c o l l e c t i o n .
S a m p le s w e re s e p a r a t e d i n t o g r a s s ,
c a t e g o r i e s i n a l l y e a r s e x c e p t 1979» w h e r e t o t a l s
f o r b , and s h r u b
w ere used.
S a m p le s
w e r e b a g g e d an d d r i e d t o c o n s t a n t w e i g h t a t 50° C e l s i u s .
The s a m p l e s
w e r e s i f t e d i n a 35 mesh s c r e e n t o re m o v e s o i l m a t e r i a l ,
t h e n w e ig h e d
t o t h e n e a r e s t 0.1 gram .
Tc e s t i m a t e
from
a ll
produced
to ta l
a b o v e -g ro u n d b io m ass,
t r e a t m e n t s a t b o th s i t e s
b e lo w
th e
g raz in g
i n O c t o b e r o f 1981
h e ig h t.
r e g u l a r l y p l a c e d f r a m e s (2 x 5 dm.,
sam p les w ere c o ll e c t e d
S a m p le s
w ere
fo r
b io m ass
tak en
2 per p lo t) per tre a tm e n t.
fro m
8
T o tal
17
p la n t m a te ria l
w a s c l i p p e d t o g r o u n d l e v e l by h a n d ,
and d r i e d and
w e ig h e d j u s t a s w as t h e g r a z a b l e f o r a g e m a t e r i a l .
S t a t i s t i c a l A n a ly sis
Mean b i o m a s s p r o d u c t i o n v a l u e s w e r e c a l c u l a t e d f o r e a c h t r e a t m e n t
and
a n a ly z e d
fo r
s ig n ific a n t
d iffe re n c e s
at
th e
99% l e v e l
of
c o n f i d e n c e u s i n g a n A n a l y s i s o f V a r i a n c e M u l t i - F a c t o r a n d LSD m e a n
se p a ra tio n t e s t s .
Means a n d s t a n d a r d e r r o r s w e re c a l c u l a t e d fro m t h e
can o p y s t r u c t u r e f r e q u e n c y d a t a f o r e a c h t r e a t m e n t .
fo rm u la te d
u sin g
b io m a ss p r o d u c tio n
f re q u e n c y d a ta .
(
/
v a lu e s
and
R e g re ssio n s w ere
canopy
stru c tu re
18
RESULTS AND DISCUSSION
A 2x2 f a c t o r i a l e x p e r i m e n t was c a r r i e d o u t t o d e t e r m i n e e f f e c t s
o f g r a z i n g o n tw o m a j o r g r a s s l a n d c o m m u n i t i e s u n d e r d r y and w e t y e a r
i
c o n d itio n s.
The u n i r r i g a t e d p l o t s r e c e i v e d l e s s t h a n l o n g - t e r m
av erag e
p re c ip ita tio n
(T a b le
2)
d u rin g
th e
stu d y
p e rio d .
The
i r r i g a t e d p lo ts re c e iv e d w ater e q u iv a le n t to th e w e tte s t y e a rs in th e
reg io n .
G r a z in g p l o t s i n e a c h t r e a t m e n t w e r e C lip p e d a t t h r e e week
i n t e r v a l s t o a h e i g h t o f 5 .0 cm ( b l u e g r a m a s i t e ) o r 7 .6 cm ( w e s t e r n
w h e a tg ra ss s ite ).
Com m unity r e s p o n s e s w e r e m e a s u r e d i n t e r m s o f t o t a l a b o v e g ro u n d
p ro d u ctio n ,
g ra z a b le p ro d u c tio n (i.e .
canopy s t r u c t u r e
p la n t area).
(i.e .
t h a t ab o v e c l i p p i n g h e i g h t ) ,
and
v e r t i c a l d i s t r i b u t i o n o f b io m a s s and t o t a l
S t r u c t u r a l c o m p o n e n ts w e r e s u b d i v i d e d a c c o r d i n g t o l e a f -
s t e m - f r u i t an d l i v e - d e a d .
T hese p a r a m e t e r s a r e t r e a t e d s e p a r a t e l y i n
th e fo llo w in g s e c tio n s.
Canopy S t r u c t u r e
D i s t r i b u t i o n o f L e a f Stem S u r f a c e and B iom ass
The v e r t i c a l d i s t r i b u t i o n
o f p l a n t l e a f and s te m
su rface
c o n t a c t s ) a t maximum s t a n d i n g c r o p i s show n i n f i g u r e 2.
c o n ta c ts are u s u a lly
1964,
c o n ta c ts
S in ce p o in t
w e l l - c o r r e l a t e d w i t h b io m a s s ( G re ig - S m ith
C o n a n t a n d R i s s e r 1974), i t i s
of p o in t
(p o in t
in
15 p r o b e s
(or
d e s i r a b l e t o r e g r e s s t h e num ber
p ercen t
p in
c o n ta c t)
a g a in st
b io m a s s e s r e c o r d e d t o a llo w s im u l ta n e o u s d i s c u s s i o n o f s u r f a c e and
b io m a ss s t r u c t u r e .
R e s u l t a n t c o n v e r s i o n s c a l e s ( F i g u r e 2) w i l l b e
a v e ra g e s c a l e s f o r l e a f ste m s u r f a c e v e r s u s b io m a ss th r o u g h o u t th e
19
FiS'Jf'® 2 .
V e r t i c a l S t r a t i f i c a t i o n o f Canopy Cover From t h e W e s te rn
W h e a t g r a s s and B lu e Grama S i t e s , P e r c e n t P i n C o n t a c t s (%
P i n C o n t a c t s P l u s S t a n d a r d E r r o r ) , L e a f- S te m R a t i o s ( x ) ,
an d T o t a l Above Ground Y i e ld (g ra m s/m ^ ) a t Maximum
S t a n d i n g C ro p , 1981.
Y i e l d s a r e P r e d i c t e d From R e g r e s s i o n
A n a ly s is . (F ig u re I ) .
DRY GRAZED
DRY UNGRAZED
WET GRAZED
PERCENT PIN HITS
28.0
76.9
125.8
28.0
76.9
125.8
YIELD ( G / M 1)
DRY GRAZED
DRY UNGRAZED
■
LEAF
□
STEM
WET UNGRAZED
30
50
70
WET GRAZED
C
PERCENT PIN HITS
57.2
90.5
123.8
157.1
21.9
YIELD ( G / M l)
40.5
59.1
77.7
20
canopy b ecau se
no e f f o r t w as made t o d e v e l o p s e p a r a t e r e g r e s s i o n s f o r
e a c h canopy l a y e r .
D a ta fro m l e a f s te m
f i t lin e a r reg re ssio n s
s u r f a c e c o n t a c t s a g a i n s t b i o m a s s ( F i g u r e 3)
b e t t e r th an c u r v i l i n e a r r e g r e s s io n s a tte m p te d .
C o r r e l a t i o n c o e f f i c i e n t s f o r w e s t e r n w h e a t g r a s s and b l u e g r a m a r a n g e d
f r o m 0 .8 7 t o 0 . 9 0 .
W este rn w h e a tg ra s s r e g r e s s i o n s had th e h ig h e s t
c o r r e l a t i o n c o e f f i c i e n t s when d a t a f ro m w a t e r and g r a z i n g t r e a t m e n t s
w e r e c o m b in e d , w h i l e b l u e g r a m a v a l u e s w e r e h i g h e s t when t h e d a t a w e re
s e p a r a t e d by g r a z i n g t r e a t m e n t .
W h ile i t
w as n o t d i r e c t l y p e r t i n e n t t o t h e i m m e d i a t e s t u d y g o a l ,
one c a n n o t h e l p a s k i n g why t h e r e g r e s s i o n l i n e s d i f f e r .
D ifferen ces
b e t w e e n t h e s p e c i e s a r e p r o b a b l y due t o g r o w t h fo rm d i f f e r e n c e s ,
w ith
w e s te r n w h e a tg ra s s h a v in g a g r e a t e r w e ig h t (g ra m /p in c o n ta c t) th a n
b l u e gram a.
lo n g er,
F i e l d o b s e r v a t i o n s s u g g e s t t h a t w e ste rn w h e a tg ra ss has
co arser
c o n trib u te
to
ste m s
th an
b lu e
gram a
th e h ig h w e ig h ts o b served.
and
if
so,
S im ila rly ,
th e se
t h e low w e i g h t
( g r a m s / p i n c o n t a c t ) o f g r a z e d b l u e g r a m a may be due t o
ste m s r e l a t i v e
m ig h t
th e r a r i t y
of
to p r o p o r tio n s p r e s e n t i n ungrazed p l a n t s .
F a c t o r s A f f e c t i n g Canopy S t r u c t u r e
T h i s s t u d y e x a m in e d c h a n g e s i n
sp e cie s,
w a te r le v e l,
s im p lifie d i f
Season.
ca n o p y s t r u c t u r e
g razin g le v e l,
an d s e a s o n .
L ater d isc u ssio n i s
se aso n a l e f f e c t s a re c o n sid e red f i r s t .
L a te ra l b ars in fig u re
4 in d ic a te
p r e s e n t i n e a c h 5 cm l a y e r o f e a c h s p e c i e s fo u r d a te s.
w ith re s p e c t to
th e amount o f m a t e r i a l
t r e a t m e n t c o m m u n ity a t
The s i m i l a r i t y o f m o s t s e t s o f b a r l e n g t h s b e tw e e n e a r l y
J u l y and e a r l y S e p t e m b e r show t h a t b a s i c canopy s t r u c t u r e s ha d e v o l v e d
21
F ig u re 3.
R e g r e s s i o n s a n d C o r r e l a t i o n s From W e s te rn W h e a t g r a s s and
B lu e Grama S i t e s , 1981.
( P i n C o n t a c t s / P l o t Above G r a z in g
H eig h t w ith G ra z ab le Forage Y i e l d / P l o t ) .
Y= 16.3 X + 3. 6
0.87
BOGR SI TE
UNGRAZED
Y = II.IX +4 0 . 6
R2=O.90
IOO
YI EL D
( G/ M2)
200
AGSM S I T E
GRAZED
Y= 6.2 X + 12.6
R2= 0 87
+ - UNGRAZED
• - GRAZED
PIN HI TS
5
IO
PIN HI T S
22
CANOPY HEIGHT (CM)
F i g u r e 4.
Growing S e a s o n V e r t i c a l S t r a t i f i c a t i o n o f W e s te rn
W h e a t g r a s s and B lu e Grama Canopy C over. T o t a l P in
C o n t a c t s f o r Each T r e a t m e n t P l o t and S a m p lin g D a t e .
O
"f
AGSM
AGSM
WET
UNGRAZED
WET
GRAZED
IO
IO
O
IO
■r 3
IO
CU
O 222220
CU■g
■ 'V.".":'"//'.I
pSBBEBBEBBB3S5BSB
20 30
IO 2 0 30
CANOPY HEIGHT (CM)
P I N HI TS
23 by J u l y 4 and r e m a i n e d l i t t l e
c h a n g e d f o r t h e r e s t o f t h e summ er.
p r in c ip a l e x c e p tio n to t h i s s ta te m e n t i s
The
seen in b la c k b a rs (e a rly
J u l y ) o n g r a z e d p l o t s ; t h e s e show t h e p r e s e n c e o f p l a n t m a t e r i a l i n
upper la y e rs
w h ic h w as t o
be c u t i n
th e
first
g ra z in g
and n ev er
re a p p e a re d t h e r e due to re p e a te d c lip p in g o f th e s e p l o ts .
s h o w e d no c h a n g e s o c c u r r e d i n t h e s e a s o n s t u d i e d ;
R e su lts
h o w ever,
it
is
o b v i o u s t h a t c h a n g e s o c c u r o v e r a l o n g e r t e r m ( H a r p e r 1977).
S p e c ie s.
The f a c t t h a t w e s t e r n w h e a t g r a s s and b l u e g r a m a d i f f e r i n
t h e i r m o r p h o l o g i c a l g r o w t h c h a r a c t e r i s t i c s i s w e l l - k n o w n ( H i tc h c o c k
a n d Chase 1971),
an d h a s b e e n . f u r t h e r d e m o n s t r a t e d w i t h s t u d y r e s u l t s
( F ig u r e 4).
W a te r.
A p p lic a tio n of su p p le m e n ta l w a te r to u n g razed w e ste rn
w h e a t g r a s s and b l u e g ra m a c o m m u n i t i e s d i d n o t s i g n i f i c a n t l y
can o p y h e i g h t o f e i t h e r c o m m u n ity ( F i g u r e 4 ).
in c re a se
S u p p le m e n ta l w a te r
i n c r e a s e d canopy h e i g h t s o f g r a z e d c o m m u n i t i e s s l i g h t l y
by s u p p o r t i n g
g r o w th i n t o t h e g r a z e d l a y e r ( F i g u r e 4 ). T o t a l l e a f s te m s u r f a c e and
b i o m a s s i n c r e a s e d i n b o t h s p e c i e s ( F i g u r e 4) a s a r e s u l t o f i n c r e a s e d
f o l i a r d e n s i t y i n a l l ca n o p y l a y e r s .
The f a c t t h a t w a t e r a d d i t i o n s d i d n o t s i g n i f i c a n t l y i n c r e a s e
canopy
h e ig h t
and
v e rtic a l
d istrib u tio n
of
b io m ass
in
w e stern
w h e a t g r a s s and b l u e g r a m a c o m m u n i t i e s i s i n c o n t r a s t w i t h t h e r e s u l t s
o f W eaver e t a l . (1 9 8 1 ).
G ra z in g .
W h i l e p r e g r a z i n g m e a s u r e s ( F i g u r e 4 , e a r l y J u l y ) show
t h a t p l a n t s o f g r a z e d p l o t s a r e c a p a b l e o f r e a c h i n g i n t o h i g h e r canopy
lay ers,
l a t e r m e a s u r e s show t h a t g r a z i n g e s s e n t i a l l y e l i m i n a t e s g r o w t h
V
24
a b o v e t h e g r a z i n g h e i g h t (5 cm i n b l u e g r a m a , a n d 7.6 cm i n w e s t e r n
w h e a t g r a s s ) i n d r y p l o t s and g r e a t l y r e d u c e s i t i n i r r i g a t e d
As a r e s u l t o f g r a z i n g ,
p lo ts.
p l a n t s becom e m ore p r o s t r a t e by r e d u c i n g
p l a n t s i z e , th e re b y a p p e a r in g to c o n c e n tr a te m a t e r i a l i n th e u n c lip p e d
canopy l a y e r ( F ig u r e 4).
Such c o n c e n t r a t i o n s o f l e a f s u r f a c e i n t h e
u n c l i p p e d l a y e r w o u ld m a x im iz e p h o t o s y n t h e s i s i n a g r a z i n g - s t r e s s e d
sy ste m .
T o tal q u a n t i t i e s o f l e a f s u rfa c e i n th e f i r s t la y e r o f grazed
p l o ts a re n o t,
how ever,
T here
to
appears
be
in c r e a s e d over ungrazed
little
tru e
c o n tro ls
c o m p e n sa tio n
in
(F ig u re
th e se
2).
w e stern
w h e a t g r a s s and b l u e g ra m a c o m m u n i t i e s .
L e a f - S t e m Canoov S t r u c t u r e
W a te r and g r a z i n g m ig h t a f f e c t l e a f - s t e m r a t i o s ( a l l o c a t i o n o f
c a r b o n ) a s w e l l a s c o m m u n ity h e i g h t and b i o m a s s .
im p o r ta n t b oth because o f th e r e l a t i v e l y
L e a f-ste m r a t i o s a r e
h igh n u t r i t i o n a l
q u a lity
of
t h e l e a v e s a n d b e c a u s e g r a z i n g a n i m a l s p r e f e r l e a v e s t o s t e m s (Cook
and H a r r i s
1950,
A r n o ld 1964).
G ra z in g had l i t t l e
e f f e c t on s e a s o n a l d e c l i n e s o f
r a t i o s un d er dry c o n d itio n s ,
w hereas w ith su p p le m e n ta l m o is tu re ,
g ra z in g m a in ta in e d h ig h le a f - s te m
4).
A p p a re n tly ,
lea f-stem
r a t i o s t h r o u g h o u t t h e s e a s o n ( T a b le
under dry c o n d itio n s se n esc e n c e o f le a v e s o c c u rre d a t
a h ig h e r r a t e th a n under m o ist c o n d itio n s .
S u p p le m e n ta l w a te r f u r t h e r
s u p p o r t e d g r o w t h o f new l e a v e s on s h o r t e n e d s t e m s .
L e a f-ste m
6 ).
(T a b le s 5,
ra tio s
ten d
T h e se low
to
be lo w
ra tio s
are
in th e lo w e s t canopy la y e r s
a n ecessary
s u p p o r t f u n c t i o n s o f s t e m s i n any c o m m u n ity .
be c o u n t e r a c t e d
I
to
c o rre la te
However,
some e x t e n t i n some g r a s s l a n d
of
th e
t h i s t r e n d may
c o m m u n i t i e s by t h e
25
T a b le 4.
T o t a l L e a f - S te m R a t i o s o f t h e W e s te rn W h e a tg r a s s and
B lu e Grama S i t e s i, 1981.
W e s te rn W h e a tg r a s s
Ju ly 4
D a te
J u l y 25
August 14
S e p tem b e r 5
0.1
1.0
2. 2
1.8
0. 0
0.8
2 .4
1 .3
A ugust 12
S e p te m b e r 2
1.4
0 .9
5 .8
T reatm en t
Dry
Dry
Wet
Wet
G razed
U ngrazed
G razed
U ngrazed
4 .3
2 .5
.
2.8
1.8
v
1.2
4 .5
1.6
1 .3
B lu e Grama
J u n e 30
D a te
J u l y 22
T reatm en t
Dry
Dry
Wet
Wet
G razed
U ngrazed
G razed
U ngrazed
1.8
1 4 .0
3 .0
1 .9
1 .9
1 .9
0.8
1 2 .5
2.2
0.8
4.1
1. 2
1.8
26
T able 5.
S t r a t i f i e d L e a f - Stem R a t i o s From t h e W e s te rn W h e a tg ra s s
S i t e , 1981.
D a te
T reatm en t
J u ly 4
H e ig h t
Dry
G razed
5
10
15
20
25
cm
cm
cm
cm
cm
Dry
U ngrazed
5
10
15
20
25
30
35
40
Wet
G razed
Wet
U ngrazed
Leaf
J u l y 25
Stem
Leaf
Stem
8
9
3
7
5
0
I
0
I
5
I
4
I
cm
cm
cm
cm
cm
cm
cm
cm
6
9
5
3
0
2
0
5
2
I
I
0
0
I
I
6
3
2
4
5
2
2
I
I
5
10
15
20
25
30
35
cm
cm
cm
cm
cm
cm
cm
6
17
10
I
I
I
0
5
10
15
20
25
30
35
40
cm
cm
cm
cm
cm
cm
cm
cm
9
10
15
8
I
I
0
3
A ugust 14
Leaf
0
0
4
3
2
4
2
I
I
4
0
0
4
5
4
4
I
I
I
4
5
3
7
3
I
I
I
I
8
3
0
12
9
I
9
5
4
3
13
8
2
15
9
7
3
0
I
0
0
0
0
2
I
5
I
Stem
5
5
8
9
I
5
3
4
3
Leaf
I
0
0
5
3
I
I
I
I
I
Stem
S eptem ber 5
10
7
I
4
0
0
2
0
2
3
9
I
19
5
7
4
0
2
0
7
6
I
2
2
2
I
7
9
3
7
8
7
9
2
0
0
2
I
0
3
27
T a b le 6 .
S t r a t i f i e d L e a f - Stem R a t i o s o f B lu e Grama, 1981.
R a t i o s C a l c u l a t e d fro m P i n C o n t a c t s .
D a te
T reatm en t
Dry
G razed
J u n e 30
H e ig h t
J u l y 22
S e p te m b e r 2
Leaf
Stem
Leaf
Stem
Leaf
Stem
Leaf
Stem
14
I
21
7
10
7
3
I
3
3
19
I
0
0
0
5
6
7
4
4
12
0
0
I
0
9
I
2
I
0
0
I
12
0
0
0
0
0
0
2
I
2
3
23
7
29
2
2
0
27
6
2
I
4
2
3
2
0
0
2
20
14
3
0
0
0
0
0
4
0
4
I
2
2
I
I
23
14
14
4
4
4
24
10
2
6
0
I
I
5
10
15
20
25
30
cm
cm
cm
cm
cm
cm
19
I
3
3
0
0
0
0
2
I
I
I
5
10
15
20
25
30
35
cm
cm
cm
cm
cm
cm
cm
18
I
0
0
0
0
0
5
I
Wet
G razed
5
10
15
20
25
30
cm
cm
cm
cm
cm
cm
20
11
4
0
0
0
Wet
U ngrazed
5
10
15
20
25
30
35
40
cm
cm
cm
cm
cm
cm
cm
cm
24
2
10
3
I
0
0
0
4
Dry
U ngrazed
A ugust 12
2
3
6
2
3
,
2
2
2
2
I
0
0
2
4
8
3
I
0
0
28
appearance
o f s te m s w h ic h l i f t
r e p r o d u c tiv e s t r u c t u r e s above th e
canopy f o r b e t t e r w in d p o l l i n a t i o n a n d / o r s e e d d i s p e r s a l .
P h o t o s v n t h e t i c Canopy S t r u c t u r e
B ecause
p h o to sy n th e sis
m o rp h o lo g y ,
th e
depends
d istrib u tio n
m ore
and
on
am ount
green
of
su rface
g reen
th an
su rface
( p h o t o s y n t h e t i c s u r f a c e ) i n t h e v a r i o u s c a n o p i e s ( T a b le 7) a s a f f e c t e d
by w a t e r a v a i l a b i l i t y ,
d isc u ssio n
is
g razin g ,
sim p lifie d
if
and se aso n ,
may be i m p o r t a n t .
w a t e r and s e a s o n e f f e c t s
L ater
a r e c o n sid e re d
first.
. a M _S_e.aaon.
(liv e -d e a d r a tio s )
W ith a d e q u a t e w a t e r , p h o t o s y n t h e t i c s u r f a c e
(T a b le 7),
in c re a se d as season p ro g ressed
r e s u lt of in c re a s e s in p h o to sy n th e tic s u rfa c e in a l l
( T a b l e s 8 , 9).
S im ila rly ,
( T a b le 7 ).
B o k h a r i (1976) show ed t h a t t h e c h l o r o p h y l l c o n t e n t o f
w h e a tg ra ss
su p p le m e n ta l
canopy la y e r s
H ow ever, i f w a t e r b eco m es l i m i t i n g , l e a v e s d ie and
p h o to sy n th e tic su rfa c e d e c lin e s
w e ste rn
as a
w as
m o istu re ,
m a in ta in e d
w h ile
Rauzi
th ro u g h o u t
and
th e
D obrenz
season
(1970)
by
show ed
c h l o r o p h y l l c o n t e n t d e c l i n e d w i t h s e a s o n i n w e s t e r n w h e a t g r a s s and
b lu e gram a w i t h o u t a d d i t i o n a l w a te r.
G ra z in g .
P h o to sy n th e tic
e x p o n e n tia lly as h e ig h t
w h e a tg ra ss i t
m axim um
su rface
,
in
ungrazed
p lo ts
d ecreased
d e c r e a s e d i n b lu e gram a w h i l e i n w e s te r n
te n d e d t o d e c l i n e b o th a b o v e and b e lo w t h e l e v e l o f
canopy
d e n s ity
(F ig u re
5).
G ra z in g
c o n v e rts
th e
p h o to s y n th e tic s u rfa c e o f w e ste rn w h e a tg ra ss to an e x p o n e n tia lly
d e c l i n i n g one,
s i m i l a r t o t h a t o b s e r v e d i n b l u e g ra m a ( F i g u r e 5).
29
T a b l e 7»
T o t a l P h o t o s y n t h e t i c S u r f a c e ( L iv e / D e a d P in C o n t a c t
R a t i o ) o f t h e W e s te rn W h e a t g r a s s and B lu e Grama S i t e s ,
1981.
W e s te rn W h e a tg r a s s
Sam ple D a te
Dry
Dry
Wet
Wet
G razed
U ngrazed
G razed
U ngrazed
J u ly 4
J u l y 25
A ugust 14
36.0
1 6 .5
6. 0
1 0 .3
0.1
1 .3
6 .3
4 .3
0.1
0.8
7 .0
6 .3
S e p te m b e r 2
0.2
0 .3
11.3
1 1 .5
B lu e Greuna
Sam ple D a te
Dry
Dry
Wet
Wet
G razed
U ngrazed
G razed
U ngrazed
J u n e 30
31 / 0 *
1 3.5
1 6 .7
5 9 .0
J u l y 22
August 12
2.8
0.1
0 .9
1 2 .5
6 .4
0 .4
*31 L iv e P i n C o n t a c t s / 0 Dead P i n C o n t a c t s
8. 0
4 .6
S e p tem b e r 2
0. 0
0.2
1 6 .0
4.3
30
T a b le 8 .
S t r a t i f i e d Phot o s y n t h e t i c S u r f a c e ( L iv e - D e a d R a t i o ) o f t h e
W e s te rn W h e a t g r a s s S i t e , 1981.
T reatm en t H e ig h t
Dry
G razed
5 cm
10 cm
15 cm
20 cm
25 cm
Dry
U ngrazed
5 cm
10 cm
15 cm
20 cm
25 cm
30 cm
35 cm
40 cm
Wet
G razed
Wet
U ngrazed
Ju ly
Ju ly 4
D a te
5
10
15
20
25
30
35
L iv e
Dead
7
I
8
10
3
8
0
0
0
0
9
2
0
0
0
0
0
0
11
6
4
0
2
I
L iv e
25
Dead
I
0
8
2
2
4
4
4
3
2
4
2
I
I
15
9
I
I
3
11
2
2
2
I
6
I
0
0
0
0
0
11
15
18
12
4
I
I
6
0
0
0
0
0
0
8
15
10
7
4
I
5
I
3
5
3
cm
cm
cm
cm
cm
cm
cm
5
19
5 cm
10 cm
15 cm
20 cm
25 cm
30 cm
35 cm
40 cm
0
0
I
0
0
0
August 14
L iv e
Dead
S e p tem b e r 5
L iv e
Dead
0
0
6
5
I
0
3
3
2
4
6
3
0
2
0
0
3
0
I
I
2
0
2
2
9
8
6
I
I
I
I
2
2
0
24
2
I
0
3
I
I
I
11
10
14
11
3
0
3
3
I
2
3
I
I
I
19
8
I
7
18
10
8
3
6
I
0
0
0
8
2
5
I
0
0
0
0
0
31
T able 9.
S t r a t i f i e d P h o t o s y n t h e t i c S u r f a c e ( L iv e - D e a d R a t i o s ) o f
t h e B l u e Grama S i t e , 1981.
D a te
J u n e 30
T reatm en t H eig h t
Ju ly
L iv e
Dead
L iv e
22
Dead
A ugust 12
L iv e
Dead
S e p tem b e r 2
L iv e
Dead
Dry
G razed
5
10
15
20
25
30
cm
cm
cm
cm
cm
cm
22
4
2
I
I
I
0
0
0
0
0
0
11
4
2
26
0
17
Dry
U ngrazed
5
10
15
20
25
30
35
cm
cm
cm
cm
cm
cm
cm
21
2
2
I
0
0
I
2
0
0
0
0
0
0
4
0
I
3
2
I
2
11
I
2
0
0
I
0
3
0
2
4
4
21
7
5
0
0
I
I
19
I
0
I
0
0
2
2
I
0
0
0
Wet
G ra z ed
5
10
15
20
25
30
cm
cm
cm
cm
cm
cm
21
16
6
I
4
2
2
I
0
0
0
0
23
2
0
30
4
0
30
0
2
2
0
0
Wet
U ngrazed
5
10
15
20
25
30
35
40
cm
cm
cm
cm
cm
cm
cm
cm
25
14
5
4
I
0
0
0
0
0
0
23
14
5
I
I
0
2
0
2
0
I
I
34
15
4
3
I
3
3
3
28
10
7
I
I
0
8
0
2
0
0
I
6
2
3
2
0
2
0
0
2
0
0
2
2
I
I
0
I
32
S t r a t i f i e d C u m u l a t i v e P h o t o s y n th e t ic S u rfa c e P in C o n ta c ts
F o r W e s t e r n W h e a t g r a s s and B lu e Grama S i t e s , 1981.
Cumula­
t i v e P i n C o n t a c t s a r e C a l c u l a t e d by
Summed T o t a l P i n
C o n t a c t s o f L a y e r s B elow , E x c l u d i n g Those Above.
DRY GRAZED
15
10
5
CANOPY
5
o 10
E
n.
5
HEIGHT
(CM)
F ig u re 5.
DRY GRAZED
I _______________
DRY UNGRAZED
20
15
10
WET GRAZED
5
WET UNGRAZED
5 30
CO 2 5
O
20
< 15
’2
10
20
30
40
50
60
70
CUMULATIVE PIN HITS
CUMULATIVE PIN HITS
33
T o t a l Above-Ground P r o d u c t i o n
T o t a l a b o v e - g r o u n d p r o d u c t i o n w a s m e a s u r e d i n 1981 a t s e a s o n ' s
end.
S u p p le m e n ta l
w a te r
s ig n ific a n tly
in c re a se d
w e s te r n w h e a tg r a s s and b lu e gram a c o m m u n itie s ,
ungrazed
(T a b le
10).
T o ta l
y ie ld s
from
y ie ld s
in
b o th
w h eth er g razed or
grazed
p lo ts
w ere
not
s i g n i f i c a n t l y d i f f e r e n t fro m t h o s e i n u n g r a z e d p l o t s ( T a b l e 10).
T a b le 10.
T o t a l Above Ground P r o d u c t i o n (g/m ^) f o r t h e W e s te rn
W h e a t g r a s s a n d B lu e Grama S i t e s , 1981
W e s te rn W h e a tg r a s s
Dry
Wet
G ra z ed
U ngrazed
G razed
U ngrazed
1 5 2 .2 * *
1 4 8 .5 *
3 2 9 .I b
3 35. 3b
3 06 . Ob
2 9 9 . 4b
T o ta l Y ield
B lu e Grama
T o ta l Y ield
100 . 6 *
1 0 7 .9 *
"Means w i t h i n row s w h ic h s h a r e t h e same s u p e r s c r i p t s do n o t d i f f e r
s i g n i f i c a n t l y LSD ( P ^ . 0 1 ) .
O ra z ah le Forage P ro d u c tio n
I t s e e m s o b v i o u s t h a t f o r a g e w e l l a b o v e g ro u n d l e v e l w i l l be use d
first
and
th a t
fo rag e
at
ground
le v e l
w ill
be l e s s
su rv e y in g g ra z in g h e ig h ts in su rro u n d in g p a s tu r e s ,
a rb itra rily
w h e a tg ra ss.
used.
A fter
g r a z i n g h e i g h t was
d e f i n e d a s 5 cm f o r b l u e g r a m a a n d 7.6 cm f o r w e s t e r n
U sin g t h e m eth o d d i s c r i b e d
by H o l s c h e r a n d W o o l f o l k
( I 9 5 3 ) s u c h g r a z i n g h e i g h t s w e r e e s t i m a t e d t o r e s u l t i n 3 0 $ a n d 64$
34
F ig u re 6 .
T o t a l G r a z a b l e F o r a g e Y i e l d s From B lu e Grama and
W e s te rn W h e a t g r a s s S i t e s , 1 9 7 9 -1 9 8 1 . Means o f
Growth Form C a t e g o r i e s and S t a n d a r d E r r o r s o f
T o ta l Y ie ld s P re s e n te d .
BOGR
n GRASS
■
FORB
Y I E L D (G/M )
M SHRUB
G - GRAZED
U - UNGRAZED
AGSM
DRY
WET
1979
DRY
WET
1980
DRY
WET
1981
35
T a b l e 11.
G r a z a b l e F o r a g e P r o d u c t i o n ( g /m 2 ) o f t h e W e s te r n
W h e a t g r a s s and B lu e Grama S i t e s , 1 9 7 9 -1 9 8 1 .
W e s te rn W h e a t s r a s s
Dry
G r a s s 1980
G r a s s 1981
Wet
G razed
U ngrazed
G razed
Ungrazed
4 .9 * "
111 . 6 *
3 .8 *
120 . 1*
102 . 8 b
127.1®
1 3 7 .4 °
2 0 1 .4 °
F o rb 1980
F o rb 1981
0 . 0a
4 .3 a
0 . 0*
0 .7 *
2 . 0*
4 5 . 6b
1 7 .2b
3 4 . 5b
S h ru b 1980
S hrub 1981
0 .7 *
8 . 1*
0 . 0*
7 .9 *
0 . 0*
0 . 0*
0 . 0*
0 . 0*
T o t a l 1979
T o t a l 1980
T o t a l 1981
1 1 4 .2 *
5 .6 *
1 2 4 .0 *
1 5 0 .2b
1 0 4 . 8b
1 7 2 .7b
1 8 7 .9 °
1 5 4 .5 °
2 3 5 .5 °
1 4 6 . Ob
3 .8 *
1 2 8 .7 *
B lu e
G r a s s 1980
G r a s s 1981
G ram a
4 .6 *
6 2 . 8*
3 .7 *
7 0 .5 *
4 1 . 6b
15 0 . 2b
5 4 .3 °
1 6 4 .9 °
F o r b 1980
F o rb 1981
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
S h ru b 1980
S hrub
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
0 . 0*
T o t a l 1979
T o t a l 1980
T o t a l 1981
4 0 .2 *
4 .6 *
6 2 .8 *
5 2 .3b
3 .7 *
7 0 .5 *
6 5 .3 °
4 1 . 6b
1 5 0 .2b
7 1 . 2°
5 4 .3 °
1 6 4 .9 °
•M eans w i t h i n ro w s w h ic h s h a r e t h e same s u p e r s c r i p t s do n o t d i f f e r
s i g n i f i c a n t l y LSD ( P i . 0 1 ) .
36
u tiliz a tio n
re sp e c tiv e ly .
by
w e ig h t
fo r
b lu e
A ctu al u t i l i z a t i o n ,
gram a
and w e s t e r n
w h e a tg ra ss
d e f in e d a s th e am ount o f m a t e r i a l
by w e i g h t re m o v e d a t t i m e o f s a m p l i n g was m e a s u r e d i n 1981 u s i n g t h e
' g r a z e d / u n g r a z e d h e i g h t - w e i g h t m eth o d d e s c r i b e d by Lommasson a n d J e n s e n
(1943).
h e ig h t
T he a s s u m p t i o n s a r e t h a t o b s e r v a t i o n s b e m ad e a t m axim um
in
g ro w th
w h ic h
co rresp o n d s
to
m axim um
w e ig h t.
m e th o d o lo g y d o e s n o t a c c o u n t f o r g r o w t h f o rm d i f f e r e n c e s ,
T h is
changes in
b a s a l c o v e r , q u i e s c e n c e , s e n e s c e n c e , Or t i m e o f p e a k s t a n d i n g c r o p ,
a ll
o f w h i c h may b e a f f e c t e d
by g r a z i n g a n d / o r w a t e r s u p p l e m e n t .
W ith o u t c o n s i d e r a t i o n o f th e s e f a c t o r s , ,u n d e re s tim a te s o f u t i l i z a t i o n
w i l l o ccur.
T re atm e n t
x
u tiliz a tio n
m easures
tak e
at
s e a s o n 's
end
(e a rly
S e p t e m b e r ) f o r b l u e g r a m a s h o w e d 2k% a n d 26% f o r d r y a n d w e t p l o t s
re sp e c tiv e ly .
W e s te r n w h e a t g r a s s m e a s u r e s w e r e 51% and 48% f o r d r y
and w et r e s p e c t i v e l y .
Dry p l o t s may u n d e r e s t i m a t e u t i l i z a t i o n i f p e a k
s ta n d in g c ro p was e a r l y
senescence ( le a f f a l l ,
in th e s e a s o n and l o s s e s o c c u rr e d th ro u g h
seed s h a tte r )
gro u n d p r i o r to c o l l e c t i o n d a te .
or tra n sp o rt of m ate ria l
R eg ro w th
f u r th e r r e s u l t in u n d e re stim a te s of t o t a l
p lo ts
may u n d e r e s t i m a t e
sam ple c o l l e c t i o n d a te .
if
u tiliz a tio n
if
below
a f t e r c o l l e c t i o n w o u ld
seasonal u tiliz a tio n .
Wet
w a t e r p r o l o n g s g r o w t h beyond
G r a z in g may a l s o a f f e c t u t i l i z a t i o n m e a s u r e s
m a t e r i a l i s c o n c e n t r a t e d below g r a z i n g h e i g h t t h e r e b y a l t e r i n g t h e
h e ig h t-w e ig h t cu rv e.
tille rs
C h a n g e s may a l s o o c c u r i f g r a z i n g i n c r e a s e d
(b a s a l cover) a s se aso n p ro g re s s e d .
H o lsc h e r and
W o o lfo lk
(1 9 5 3 )
recom m ended
w h e a t g r a s s a s 45% an d 41% f o r b l u e g r a m a .
use
P roper use i s
of
w e ste rn
t h e maximum
37
d e g r e e a n d t i m e o f u s e o f c u r r e n t y e a r ’s g r o w t h w h i c h w i l l e i t h e r
m a in ta in o r im p ro v e ra n g e c o n d itio n .
A c tu a l u t i l i z a t i o n
s u g g e s t o y e r - u s e f o r w e s t e r n w h e a t g r a s s and u n d e r - u s e
fig u re s
f o r b l u e g ra m a
c o n s i d e r i n g t h e r e c o m m e n d a tio n s o f H o ls c h e r and W o o lfo lk (1953).
S tu d y
r e s u l t s sh o w t h a t g r a z i n g d i d r e d u c e t h e p r o d u c t i v i t y o n w e t
p l o t s b u t d i d n o t a f f e c t i t o n d r y p l o t s ( F i g u r e 6 ).
c o v e r (T a b le
13) i n c r e a s e d on a l l
p lo ts.
H ow ever, b a s a l
T h is i m p l i e s t h a t w e s t e r n
w h e a t g r a s s may h a v e b e e n u n d e r - u s e d r e g a r d l e s s o f w a t e r t r e a t m e n t .
A
c a r e f u l c o n s i d e r a t i o n o f m e th o d o lo g y an d t h e i n t e r p r e t a t i o n o f r e s u l t s
m u s t f o l l o w any m e a s u r e o f u s e .
U sin g
th e se
d e fin itio n s,
c o m p a riso n s
o f g ra z a b le
fo rag e
p r o d u c t i o n on b l u e g ra m a an d w e s t e r n w h e a t g r a s s c o m m u n it i e s i n t h e
th re e y ears,
1979 - 1981 w e r e made.
U nder d r y - y e a r c o n d i t i o n s , g r a z a b l e f o r a g e p r o d u c t i o n i n u n g r a z e d
p l o t s exceeded p ro d u c tio n o f g ra z e d p l o t s f o r b o th w e s te r n w h e a tg ra s s
a n d b l u e g r a m a c o m m u n i t i e s i n tw o o f t h r e e y e a r s ( F i g u r e 6 ; T a b l e 11).
T o t a l f o r a g e p r o d u c t i o n w as c o m p r is e d p r i m a r i l y
i n s i g n i f i c a n t a m o u n ts o f f o r b s and s h r u b s .
of g rasses,
w ith
No s i n g l e c o m p o n e n t o f t h e
t o t a l f o r a g e p r o d u c t i o n ( F i g u r e 6 ; T a b l e 11) d i f f e r e d s i g n i f i c a n t l y
b e tw e en g r a z in g t r e a t m e n t s .
Under w e t-y e a r * " jo n d itio n s ( i . e . w ith s u p p le m e n ta l w a te r ) t o t a l
p r o d u c t i o n f ro m b l u e g r a m a ( e x c e p t 1979) a n d w e s t e r n w h e a t g r a s s g r a z e d
p l o t s w ere s i g n i f i c a n t l y
l e s s th a n th e u n g razed p l o t s i n a l l stu d y
y e a r s ( F i g u r e 6 , T a b le 11).
One may s p e c u l a t e t h a t c l i p p i n g r e m o v e d s o much l e a f s u r f a c e t h a t
p la n ts
c o u ld
not
m ax im ize
use
of
a v a ila b le
w a te r
and
n u trie n t
38
T a b l e 12.
T o t a l P r o d u c t i o n (g /m 2 ) Below G r a z in g H e i g h t f o r t h e
W e s te r n W h e a t g r a s s and B lu e Grama S i t e s , 1981.
W e s te rn W h e a t g r a s s
Dry
G ra z ed
T o ta l
Wet
O ngrazed
1 9 .8 *
2 8 . 3a *
G razed
U ngrazed
1 5 6 .4 ^
9 9 .3 °
1 5 5 .8b
1 3 4 .5 ^
B lu e Grama
T o tal
3 7 .8 *
3 7 .4 *
•Means W i t h i n Rows Which S h a r e t h e Same S u p e r s c r i p t s Do Not D i f f e r
S i g n if i c a n t ly ( P i 0 .0 1 ) , S tu d en t t - t e s t .
T a b l e 13.
B a s a l Area M e a s u re s ( P e r c e n t ) f o r t h e W e s te rn W h e a tg r a s s
and B lu e Grama S i t e s , 1981. M e a s u re s Taken a t S e a s o n ' s
End C o r r e s p o n d i n g t o L a s t G r a z i n g Sample C o l l e c t i o n D a ta .
W estern W heatgrass
Dry
W e s te rn W h e a t g r a s s
O ther P l a n ts
L itte r
B a r e Ground
Wet
G ra z ed
U ng ra z ed
4 .0
0 .4
1 5 .5
1.2
0.0
1 4 .6
8 4 .2
80.0
G razed
U ngrazed
8 .5
3 -7
1.6
14.6
7 5 .2
17 .9
7 6 .4
2.0
B lu e Grama
B lu e Grama
O ther P l a n ts
L itte r
B a r e Ground
1 5 .3
0.0
3 3 .5
5 1 .2
8.0
0.0
3 2 .1
5 9 .6
2 3 .4
1.0
2 0 .0
5 5 .6
12.2
0 .5
20.0
6 7 .3
39
resources.
C o n siste n t w ith
th is
h y p o th esis,
H o l s c h e r ( 1945 ) ,
B ra n s o n
(1 9 5 6 ), D w yer e t a l . ( 1 9 6 3 ), S m o lia k ( 1 9 6 5 ), E v e r s o n ( 1 9 6 6 ), D i t t m e r
(1 9 7 3 ),
O w e n sb y e t a l .
(1 9 7 4 ),
B eaty and P o w e ll (1 9 7 6 ), and o t h e r s
have o b se rv e d lo w e r p ro d u c tio n due to c lip p in g
v e g e ta tio n .
in , t h i n s t a n d s o f
I n d e n s e o r t a l l e r g r a s s r e g i o n s c l i p p i n g may i n c r e a s e
p r o d u c t i o n a s s h o w n by C a n f i e l d ( 1 9 3 9 ) ,
Lodge ( I 9 6 0 ) ,
( 1 9 7 2 ) , Eck e t a l . ( 1 9 7 5 ) , a n d S i n g h a n d M a l l ( 1 9 7 6 ) .
D raw e e t a l .
These r e s u l t s
a r e p ro b a b ly due to r e d u c t io n s in i n t e r n a l s h a d in g a n d /o r in c r e a s e d
r e s p i r a t i o n w i t h i n t h e canopy.
I f we a s s u m e t h a t 1981 d a t a f o r t o t a l a b o v e - g r o u n d s t a n d i n g c r o p
a r e t y p i c a l , we m u st c o n c l u d e t h a t w h i l e g r a z a b l e f o r a g e p r o d u c t i o n i s
reduced
by g r a z i n g
w a te r),
t o t a l ab o v e-g ro u n d p ro d u c tio n i s
occu r,
equal
(b u t
p r o d u c t i o n b e lo w
or exceed
e x p la in e d
if
th a t
sig n ific a n tly
so o n ly w ith
u n a ffe c te d .
su p p le m e n ta l
For th is
to
t h e g r a z i n g h e i g h t o f g r a z e d p l o t s had to
o f ungrazed
p lo ts
(T a b le
12).
T h i s may b e
g ra z e d p l o t s had a c o m p e t it iv e a d v a n ta g e f o r g ro w th
a n d /o r b io m a ss p ro d u c tio n .
G r a z e d p l o t s do i n f a c t sh o w a t l e a s t
t w i c e t h e b a s a l a r e a ( T a b l e 13) a n d h i g h e r l e a f - s t e m r a t i o s ( T a b l e s
5 ,6 ,
l a s t sam p le d a te ) th a n u n g razed p l o t s .
One may s p e c u l a t e
on t h e a p p a r e n t u n d e r - u t i l i z a t i o n
w e s t e r n w h e a t g r a s s a n d b l u e g ra m a w i t h r e s p e c t t o
p ro d u ctio n r e s u l ts .
In creases in
o f b o th
in te rp re ta tio n
of
u t i l i z a t i o n w o u ld r e s u l t i n t h e
e x p e c te d i n c r e a s e i n g r a z a b l e f o r a g e p r o d u c tio n o f b o th g ra z e d and
u n g ra z e d p l o t s due to lo w e r c l i p p i n g l e v e l s .
B ecause o f s p e c ie s '
m o r p h o l o g i c a l d i f f e r e n c e s , on e m ig h t e x p e c t b l u e g ra m a t o be l e s s
a f f e c t e d by r e p e a t e d c l i p p i n g s i n c e g r o w i n g p o i n t s a r e n e a r e r t h e s o i l
40
su rface.
B o th
g ro w th fo rm .
s p e c i e s h a v e show n a r e s i s t a n c e t o g r a z i n g by a l t e r e d
One m i g h t e x p e c t t h i s p r o s t r a t e f o r m t o c o n t i n u e a s
c lip p in g l e v e l s a re lo w e re d u n t i l s p e c ie s v ig o r i s red u ced .
re s u lts
resp o n se
in d ic a te
in
th a t c lip p in g
p ro d u c tio n .
produced b o th a n e g a tiv e
A n e g a tiv e
resp o n se
S tu d y
an d p o s i t i v e
o ccu rred
above th e
g r a z i n g h e i g h t by d e c r e a s i n g p r o d u c t i v i t y , a n d a p o s i t i v e r e s p o n s e
o c c u r r e d b e lo w
If
w e ste rn
by i n c r e a s i n g p r o d u c t i o n t h r o u g h i n c r e a s e d b a s a l a r e a .
w h e a tg ra ss
p r o s t r a t e g ro w th fo rm ,
in cre ase
p ro d u c tio n .
and
b lu e
are
lim ite d
S tu d y
re s u lts
of
w a te re d
a m in im u m
p lo ts
suggest
r e d u c e l e a f a r ^ a b e l o w t h e o p t im u m
I f u t i l i z a t i o n w as i n c r e a s e d ,
may i n c r e a s e p r o d u c t i o n .
to
t h e n r e p e a t e d c l i p p i n g a t . l o w e r l e v e l s may
u t i l i z a t i o n w as n o t enough to
l e v e l s f o r g ro w th .
gram a
re p e a te d
c lip p in g
41
CONCLUSIONS
D ata
p rese n ted
p ro d u ctio n .
sh o w
th a t
g ra z in g
lo w ered
g ra z a b le
fo rag e
T he l o s s o f p r o d u c t i o n m i g h t b e d u e t o I ) r e d u c t i o n o f
p h o t o s y n t h e t i c s u r f a c e t o l i m i t i n g v a l u e s a n d / o r 2) l o w e r i n g o f t h e
ca n o p y t o s u b - g r a z i n g l e v e l s .
On t h e o t h e r h a n d ,
g r a z i n g p r o d u c e d no
s i g n i f i c a n t d i f f e r e n c e s in t o t a l ab o v e-g ro u n d p ro d u c tio n .
T h is i s
a p p a r e n t l y due t o r e l a t i v e l y h i g h p r o d u c t i o n below t h e g r a z i n g h e i g h t ,
w here g ra z e d p l o t p r o d u c tio n e q u a lle d o r exceeded u n g raz e d p l o t s .
so,
grazed p lo ts
If
may h a v e h a d a c o m p e t i t i v e a d v a n t a g e f o r g r o w t h
a n d / o r p r o d u c t i o n by i n c r e a s e d b a s a l a r e a a n d / o r g r e a t e r l e a f s u r f a c e .
Community d e v e l o p m e n t a s m e a s u r e d by canopy s t r u c t u r e showed t h e
b a s i c s t r u c t u r e h a d e v o lv e d by e a r l y J u l y an d r e m a i n e d l i t t l e
as th e season p rogressed.
canopy
h e ig h t,
c h a ra c te ris tic s .
c h a nged
G r a z in g p r o d u c e d t h e e x p e c t e d l o w e r i n g o f
re s u ltin g
in
p la n ts
w ith
p ro stra te
g ro w th
D a t a f u r t h e r sh o w t h a t g r a z i n g w as i n e f f e c t i v e i n
/
m a i n ta i n in g e a r l y s e a s o n l e v e l s o f l e a f - s t e m r a t i o s and p h o t o s y n t h e ti c
su rface.
One a l s o
p ro d u ctio n
s ig n ific a n t
p ro d u ctio n .
e x p e cts
and
su p p le m e n ta l
augm ent
in c re a se s
canopy
in
m o istu re
stru c tu re .
g ra z a b le
fo rag e
A dded w a t e r d i d n o t i n c r e a s e
i n c r e a s e can o p y d e n s i t y .
to
D ata
in c re a se
b io m ass
p rese n ted
and t o t a l
show
abo v e-g ro u n d
canopy h e i g h t ,
bu t d id
D a ta f u r t h e r show t h a t w a t e r p r o l o n g e d , e a r l y
s e a s o n l e v e l s o f l e a f - s t e m r a t i o s an d p h o t o ^ y n t h e t i c s u r f a c e .
42
T hese r e s u l t s s u p p o r t no c o n c r e t e c o n c l u s i o n s a b o u t be lo w g r o u n d
p ro d u c tio n .
I t i s c o n c e iv a b le th a t g ra z in g
tr a n s p o r t o f p h o to sy n th a te s
as
in d u c e d a n e t dow nw ard
a g ra z in g -re sista n c e
stra te g y
or th a t
n e t m ovem ent was u p w a rd t o r e b u i l d t h e p h o t o s y n t h e t i c c anopy.
D a ta p r e s e n t e d h e r e s u g g e s t t h a t i n y e a r s o f a v e r a g e o r b e lo w
av erag e p r e c i p i t a t i o n ,
p e rio d ic g ra z in g w i l l lo w er fo ra g e p ro d u ctio n
w ith o u t in c re a s e s in fo rag e q u a lity .
W ith w a t e r s u p p l e m e n t a n d / o r i n
y e a r s o f h ig h p r e c i p i t a t i o n f o r a g e q u a l i t y ( l e a f i n e s s ) and q u a n ti ty
i
'
r
w i l l i n c r e a s e , th o u g h p e r i o d i c g r a z i n g r e d u c e s t h e l a t t e r .
W e lk e r
11 j
( 1982 ) show ed t h a t f o r a g e 1d i g e s t i b i l i t y d i d n o t i n c r e a s e w i t h w a t e r
1'
s u p p l e m e n t s o f 6 , 12, o r 25 mm p e r g r o w i n g s e a s o n - w e e k . M ost r a n c h i n g
o p e r a t i o n s w o u ld
u n a v a ila b ility
c o n s id e r w a te r 'a p p lic a tio n i m p r a c t i c a l ,
due to
o f w a t e r a p d e c o n o m i c c o s t s o f i r r i g a t i o n e q u ip m e n t.
W e a th e r m o d i f i c a t i o n p r o g r a m s may p r o v i d e t h e r e s o u r c e .
G ra z in g
and w a te r
s u p p le m e n ts
may h a v e
w e s t e r n w h e a t g r a s s and b l u e g ra m a c o m m u n i t i e s .
n e g a tiv e
e ffe c ts
C o n tin u e d g r a z i n g i n
s u c c e s s i v e y e a r s o f low p r e c i p i t a t i o n may r e d u c e p l a n t v i g o r ,
cau sin g
c h a p g e s i n c o m m u n ity c o m p o s i t i o n t o l e s s d e s i r a b l e s p e c i e s .
w a te r
over
th e
lo n g
term
w ill
m ost
on
c e rta in ly
a llo w
Added
changes
in
c o m m u n ity c o m p o s i t i o n t o m o re m e s i c a n d / o r o p p o r t u n i s t i c s p e c i e s .
Y ellow s w e e t c l o v e r and s c a r l e t g l o b e m a l l o w w e r e tw o s p e c i e s w h ic h w e re
o b serv ed to in c r e a s e w ith added w a te r d u rin g th e s tu d y p e rio d .
The
e x a c t e x t e n t o f c o m m u n ity c h a n g e s w i l l d e p e n d upon t i m i n g a n d am ount
o f w a te r re c e iv e d .
W a t e r a d d i t i o n s may a l s o r e s u l t i n c o m m u n i t i e s
t h a t a r e l e s s a b le to w ith s ta n d e x tre m e
(i.e .
d ro u g h t)
flu c tu a tio n s in p re c ip ita tio n
43
The
w e ste rn
w h e a tg ra ss
and
b lu e
gram a
c o m m u n itie s
w ere
r e p r e s e n t a t i v e o f a r e a s o f t e n fo u n d i n t h e N o r t h e r n G r e a t P l a i n s .
The
r e s p o n s e s o f t h e s e tw o c o m m u n i t i e s t o s u p p l e m e n t a l w a t e r a n d s i m u l a t e d
g r a z i n g h a v e a l l o w e d a m ore c o n c i s e u n d e r s t a n d i n g o f c o m m u n ity a n d / o r
s p e c i e s r e l a t i o n s t o ra n g e e co sy stem dynam ics.
a llo w
im p ro v ed m anagem ent p r a c t i c e s
c o m m u n it i e s .
in
T h is u n d e r s t a n d i n g may
th e se
or o th e r g rasslan d
44
LITERATURE CITED
45
LITERATURE CITED
A l b e r t s o n , F.W„, A. R i e g e l , . a n d J .L . L a u n c h b a u g h , J r .
1953.
E ffe c ts
o f d i f f e r e n t i n t e n s i t i e s o f c l i p p i n g on s h o r t g r a s s e s i n w e s t
c e n t r a l K a n sa s.
E c o lo g y 3 4 : 1 - 2 0 .
A r n o l d , G.
1964.
b e h a v io r and
( e d . ) . 1 96 4.
BES Sym posium
F a c to rs w ith in p la n t a s s o c ia tio n s a ff e c tin g th e
p erfo rm an ce o f g ra z in g a n im a ls.
D. C r i s p
G ra z in g i n T e r r e s t r i a l and M a rin e E n v iro n m e n ts .
No. 4.
B l a c k w e l l S c i . P u b l. 332 pp.
B r a n s o n , F.A.
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f i v e r a n g e g r a s s e s . J. Range M a n a g e . 2 7 : 3 0 8 - 3 0 9 .
tre a tm e n ts
in
B e a t y , E.R., and J.D. P o w e l l .
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^gjLrgatmn L.) t o c l i p p i n g f r e q u e n c y .
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E f f e c ts o f d i f f e r e n t frequency
o f c l i p p i n g s on th e d e v e lo p m e n t o f r o o t s and to p s o f g r a s s e s i n
p r a i r i e sods.
E c o lo g y ' 1 4 :4 4 7 -4 5 6 .
B o k h a r i , M.G. 1 9 7 6 .
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w h e a t g r a s s . J. Range M anage. 2 9 : 1 2 7 - 1 3 1 .
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Responses o f N e e d lean d th read
and W e s t e r n W h e a t g r a s s t o d e f o l i a t i o n by g r a s s h o p p e r s .
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f iv e range s p e c ie s.
J. Range Manage. 3 0 :1 6 ^ - 1 7 1 .
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c l i p p i n g on d e n s i t y and y i e l d o f b la c k gram a and to b o s a g r a s s .
U.S. D e p t . A gr. T e c h . B u l l . 6 8 1 . 3 2 pp .
C l a r k , S .E ., E.W.
c l i m a t e an d
in so u th e rn
A g ric . Tech.
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B u l l . 4 6 . 53 p p .
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J.
6 :2 6 7 -2 7 0 .
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4 9 :1 3 5 -1 6 7 .
responses of
Range Manage.
A re c o n s id e ra tio n of g rasslan d c la s s if ic a tio n
G r e a t P l a i n s o f N o rth A m erica.
J. E co lo g y .
C u l l e y , M .J ., R.S. C a m p b e l l , a n d R.H. C a n f i e l d .
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E c o lo g y 1 4 :3 5 -3 9 .
D i t t m e r , H .J .
1973.
C lip p in g e f f e c t s
E c o lo g y 5 4 : 2 1 7 - 2 1 9 .
V alu es and
on B erm uda g r a s s
b io m ass.
D o n a ld ,
C.M.
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C o m p e ti ti o n am ong p a s t u r e p l a n t s I .
I n t r a s p e c i f i c c o m p e t i t i o n among a n n u a l p a s t u r e p l a n t s .
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R esponses o f
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1964.
Q u a n tita tiv e
256 pp .
P la n t
E c o lo g y .
B u tterw o rth
and
47
H a r p e r , J .L .
1977.
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A cad em ic P r e s s ,
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D e f o lia tio n , l e a f a re a in d ex ,
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E c o lo g y 6 1 :8 4 6 -8 5 8 .
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E f f e c t s o f n i t r o g e n and
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L eaf a r e a d y n am ics o f a s h o r t g r a s s p r a i r i e i n
C o lo r a d o . E c o lo g y 5 4 : 8 9 1 - 8 9 6 .
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K n i g h t , D.H.
1969. Some i n f l u e n c e s o f v e g e t a t i o n s t r u c t u r e on e n e r g y
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P o t e n t i a l n a t u r a l v e g e ta ti o n o f th e c o n te rm in o u s
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Am. G e o g r . S o c . S p e c i a l P u b l . No. 3 6 . New Y o rk .
154 p p . a n d m ap.
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* .
L a v e n w o r th , W.K., and P.L. S im s.
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Colo. S t a t e U niv., IBP
G r a s s l a n d s B i o m e . T e c h . Rep. No. 2 3 2 .
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E f f e c t s o f b u r n i n g , c u l t i v a t i n g , a n d mowing on t h e
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13 :3 1 8 -3 2 1 .
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1943. D e t e r m i n i n g u t i l i z a t i o n o f r a n g e
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J. F o r e s t r y .
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Am er. N a t u r . 1 1 3 : 6 9 1 703.
N i c h o l s o n , R.A., and G.K. H u l e t t .
196 9.
Remnant g r a s s l a n d v e g e t a t i o n
i n t h e C e n t r a l G r e a t P l a i n s o f N o r th A m e ric a .
J. E c o lo g y 6 7 :5 9 9 612.
O l s o n , K.
1982.
E f f e c t o f p r e c i p i t a t i o n on m ix e d g r a s s p l a n t ,
c o m m u n i t i e s o f s o u t h e a s t e r n M o n ta n a a n d i t s i m p l i c a t i o n s f o r
g r a z in g i n t e n s i t y ( M a s te r 's T h e s is ) .
M o n ta n a S t a t e U n iv .,
Bozeman, M ontana.
200 pp.
O w e n s b y , C .E ., J .R . R a i n s , a n d J.D . M c K u n d r i c k , 1 9 7 4 . E f f e c t s o f o n e
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J . R a n g e M a n ag e .
27:3 4 1 -3 4 3 .
P e r r y , D.A. I 9 7 6 . The e f f e c t s o f w e a t h e r m o d i f i c a t i o n o n N o r t h e r n
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J. Range
M anage.
2 9 : 2 7 2 -2 7 8 .
P e r r y , L . J . , a n d S .R . C h a p m a n .
1974.
E ffe c ts of c lip p in g
c a rb o h y d ra te r e s e r v e s in b a s in w ild ry e .
Agron. J . 6 6 :6 7 -7 0 .
on
R a u z i, F., and A.K. Dobrenz=
1970.
Seasonal v a r ia tio n of c h lo ro p h y ll
i n w e s t e r n w h e a t g r a s s an d b l u e g r a m a . J. Range M anage. 2 3 : 3 7 2 373.
/
49
Reed, M .J ., a n d R.A. P e t e r s o n .
1961. V e g e t a t i o n , s o i l s , and c a t t l e
r e s p o n s e s t o g r a z i n g on N o r t h e r n G r e a t P l a i n s r a n g e .
U.S. Dept.
A g r. F o r . S e r v . T e c h . B u l l . 1 2 5 2 . 7 9 pp.
R i s s e r , P.G.
1971.
P l a n t c o m m u n ity s t r u c t u r e , p. 4 1 -5 8 .
I n : N.
F r e n c h ( e d .) .
P r e l i m i n a r y a n a l y s i s of S t r u c t u r e and F u n c t i o n i n
G r a s s l a n d s . R a n g e S c j.. D e p t . S e r . No. 10. C o l o r a d o S t a t e O n i v .,
F o r t C o l l i n s , C o lo r a d o .
S c h u s t e r , Ji,L., a n d R.C. D e L e o n G a r c i a .
1973. P h e n o lo g y and f o r a g e
p ro d u c tio n o f co o l se aso n g r a s s e s in th e s o u th e rn p la in s .
J . Range M anage. 2 6 : 3 3 6 - 3 3 9 .
S i n g h , V .P., a n d L.P. M a l l .
1976.
R e s p o n s e s o f A ndrooogon p u m llu s
Roxb. t o v a r i o u s h e i g h t s a n d i n t e r v a l s o f c l i p p i n g .
J. Range
M a n a g e . '2 9 : 1 3 5 - 1 3 7 .
S m i k a , D.E., H .J. H a a s , a n d J . F . P o w e r .
19 6 5 .
E f fe c ts o f m o istu re
an d n i t r o g e n f e r t i l i z e r on g r o w t h a n d w a t e r u s e by n a t i v e g r a s s .
A gron. J . 5 7 : 4 8 3 - 4 8 6 .
S m o l i a k , S.
1965.
A c o m p a ris o n o f u n g ra z e d and l i g h t l y g ra z e d
S t i n a - B o u te lo u a p r a i r i e i n s o u t h e a s t e r n A lb e rta .
Can. J. P l a n t
S c i. 4 5 :2 7 0 -2 7 5 .
S t o d d a r t , L.A., and A.D. S m ith .
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Range M anagem ent.
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V a l l e n t i n e , J.F.
1971.
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1979.
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J. Range
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1965.
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A n a ly sis o f p o in t q u a d ra ts .
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I.
W a ts.o n , D .J.
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1930.
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N a t . R e s , a n d C o n s ., H e l e n a , M o n t a n a .
2 8 7 PP.
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W e a v e r , T., a n d B. H a g lu n d o
1981.
A sso c ia te d im p a c t a sse ssm e n t
s t u d i e s , p p . 6 5 - 8 0 . I n ; G. K n u d s e n a n d R. Moy ( e d . ) 1 9 8 1 . S t a t e
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287 PP.
W e l k e r , J.M.
1982. F o ra g e d i g e s t i b i l i t y o f A e ro o v ro n s m i t h i i and
B o u te lo u a g r a c i l i s to s ix w a te r
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L.M.
1973.
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Range M anage. 2 6 ; 1 3 - 1 8 .
of g rasses;
a rev ie w .
APPENDICES
52
Appendix I
T a b le 14.
Mean P i n C o n t a c t s (From T r e a t m e n t P l o t s ) o f W e s te r n
W h e a tg ra s s , 1981.
Ju ly 4
T reatm en t
H e i g h t ( cm)
X
J u l y 25
S.E.
X
S.E.
A ugust 14
X
S.E.
S e p te m b e r 5
X
S.E.
Dry
G ra z ed
5
10
15
20
25
2 .7
2 .7
3 .3
1 .0
2 .7
1 .8
0 .9
1 .2
1 .0
0 .7
3 .0
0 .7
1 .7
0 .3
2 .0
1 .7
1 .2
0 .9
1 .3
1 .0
0 .3
0 .6
Dry
U ngrazed
5
10
15
20
25
30
35
40
3 .7
3 .7
2 .0
1 .3
0 .0
0 .7
0 .3
0 .3
1 .3
1 .0
0 .7
0 .0
0 .7
0 .3
2 .0
2 .7
1 .7
1 .0
1 .7
0 .6
0 .3
0 .9
1 .0
0 .9
2 .0
3 .0
1 .3
0 .7
1 .7
0 .3
0 .3
1.3
1 .2
2 .1
0 .3
0 .3
0 .9
0 .3
0 .3
0 .9
3 .0
3 .0
2 .3
1 .0
0 .3
1 .0
1 .0
1 .2
0 .6
0 .7
0 .6
0 .3
0 .6
0 .0
Wet
G razed
5
10
15
20
25
30
35
3 .7
6 .7
3 .7
0 .7
0 .7
0 .7
0 .3
1 .2
2 .4
1.5
0 .3
0 .6
0 .6
0 .3
5 .3
4 .0
0 .3
0 .9
0 .6
0 .3
7 .0
3 .3
0 .3
1 .5
0 .9
0 .3
8 .7
3 .0
0 .7
2 .0
0 .6
0 .3
Wet
U ngrazed
5
10
15
20
25
30
35
40
5 .7
5 .0
6 .0
4 .0
1 .3
0 .3
0 .3
2 .3
1 .0
1 .5
1 .7
0 .3
0 .3
0 .3
3 .7
6 .7
4 .3
2 .3
1 .7
0 .3
1 .7
0 .3
0 .7
1 .3
1 .7
0 .7
0 .9
0 .3
0 .9
0 .3
3 .3
6 .3
3 .7
3 .0
1.0
2 .0
0 .3
1 .5
1 .9
0 .7
1 .2
0 .0
1 .0
0 .3
5 .3
3 .7
4 .7
3 .7
1 .0
0 .0
1.0
2 .0
1 .2
1.8
0 .3
0 .6
0 .0
0 .6
53
Appendix 2
T a b l e 15.
Mean P in C o n t a c t s (From T r e a t m e n t P l o t s ) o f B l u e Grama,
1981
J u n e 30
T reatm en t
H e i g h t (cm )
X
S.E.
J u l y 22
X
S.E.
A ugust 12
X
S.E.
S e p te m b e r 2
X
S.E.
Dry
G razed
5
10
15
20
25
30
7 .3
1 .3
0 .7
0 .3
0 .3
0 .3
0 .9
0 .9
0 .3
0 .3
0 .3
0 .3
5 .0
0 .6
9 .3
1 .9
5 .7
0 .9
Dry
U ngrazed
5
10
15
20
25
30
35
7 .7
0 .7
0 .7
0 .3
0 .0
0 .0
0 .3
0 .7
0 .3
0 .3
0 .3
0 .0
0 .0
0 .3
5 .0
0 .3
1 .0
1 .0
0 .7
0 .7
0 .7
0 .0
0 .3
0 .6
1 .0
0 .7
0 .7
0 .7
8 .0
2 .3
2 .3
1.3
1.3
1 .7
0 .9
0 .9
1 .3
0 .9
7 .0
0 .3
0 .7
0 .7
0 .0
0 .0
0 .7
1 .5
0 .3
0 .7
0 .7
0 .0
0 .0
0 .7
Wet
G ra z ed
5
10
15
20
25
30
7 .7
5 .7
2 .0
0 .3
1 .3
0 .7
2 .0
2 .6
1 .0
0 .3
0 .3
0 .3
8 .3
0 .7
0 .3
0 .7
1 1 .3
0 .7
0 .9
0 .7
1 0 .7
0 .7
0 .9
0 .3
Wet
U ngrazed
5
10
15
20
25
30
35
40
8 .7
4 .7
1 .7
1 .3
2 .0
0 .7
1 .0
1 .2
1 .5
0 .9
0 .3
1.0
0 .7
1 .0
8 .0
4 .7
2 .3
0 .3
0 .7
0 .7
0 .3
0 .3
1 .7
0 .7
0 .9
0 .3
0 .7
0 .7
0 .3
0 .3
12.3
6 .0
2 .0
1 .7
0 .7
1.3
0 .0
0 .3
2 .3
4 .0
0 .0
1 .2
0 .3
0 .9
0 .0
0 .3
11.3
3 .3
3 .0
0 .3
0 .3
0 .3
1 .2
1 .2
2.1
0 .3
0 .3
0 .3
54
Appendix 3
T a b l e 16.
T reatm en t
S t r a t i f i e d C u m u l a t iv e P h o t o s y n t h e t i c S u r f a c e ( L i v e Dead R a t i o s ) o f t h e W e s te rn W h e a t g r a s s S i t e , 198 1 .
D ates
H e i g h t (cm)
J u ly 4
L iv e
Dead
Ju ly
L ive
25
Dead
A ugust 14
L iv e
Dead
S e p te m b e r 5
L iv e
Dead
Dry
G razed
5
10
15
20
25
36
29
21
11
8
I
0
0
0
0
I
0
10
2
I
0
11
5
I
0
6
3
Dry
U ngrazed
5
10
15
20
25
30
35
40
33
24
13
7
3
3
I
2
0
0
0
0
0
0
15
13
9
6
4
12
8
4
2
I
14
12
9
8
6
3
2
I
18
14
8
5
5
3
3
3
8
8
7
6
4
4
2
27
18
10
4
3
2
I
Wet
G razed
5
10
15
20
25
30
35
42
37
18
7
5
3
I
7
I
0
0
0
0
0
25
10
I
4
3
0
28
9
I
4
2
0
34
10
2
3
I
0
Wet
U ngrazed
5
10
15
20
25
30
35
40
62
51
36
18
6
2
I
6
0
0
0
0
0
0
51
42
28
18
11
7
6
I
12
9
4
I
I
0
0
0
53
46
28
18
10
7
I
6
3
2
I
0
0
0
52
41
31
17
6
3
3
6
I
0
0
0
0
0
55
Appendix 4
T a b le 17.
T reatm ent
S t r a t i f i e d C u m u lativ e P h o to s y n th e tic S u r f a c e
Dead R a t i o s ) o f t h e B lu e Grama S i t e , 1981.
D a te s
H e i g h t (cm)
J u n e 30
J u l y 22
(L iv e -
A ugust 12
S e p te m b e r 2
L iv e
Dead
L iv e
11
4
2
26
0
17
13
9
9
8
5
3
2
15
4
3
I
I
I
0
13
10
10
8
4
33
12
5
0
0
5
4
3
3
2
2
23
4
3
I
0
0
Dead
L iv e
Dead
L iv e
Dead
Dry
G razed
5
10
15
20
25
30
31
9
5
3
2
I
0
0
0
0
o
0
Dry
U ngrazed
5
10
15
20
25
30
35
27
6
4
2
I
I
I
0
0
0
0
0
0
Wet
G razed
5
10
15
20
25
30
50
29
13
7
6
2
3
I
0
0
0
0
25
2
2
0
32
2
4
0
32
2
2
0
Wet
U ngrazed
5
10
15
20
25
30
35
40
59
34
20
15
11
5
3
I
0
0
0
0
0
0
45
22
8
3
2
2
0
0
7
6
6
4
4
2
2
I
60
26
11
7
4
3
0
0
13
10
7
5
3
2
I
I
47
19
9
2
I
0
11
3
3
I
I
I
M ON TA N A ST A T E U N IV E R SIT Y L IB R A R IE S
stks N378.M133@Theses
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Growth responses of Agropyron smithii an
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