Geographic Variation in Seedling Douglas-Fir (Pseudotsuga Menziesii) from the Western
Siskiyou Mountains of Oregon
Author(s): Frank C. Sorensen
Source: Ecology, Vol. 64, No. 4 (Aug., 1983), pp. 696-702
Published by: Ecological Society of America
Stable URL: http://www.jstor.org/stable/1937191 .
Accessed: 20/01/2015 16:27
Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .
http://www.jstor.org/page/info/about/policies/terms.jsp
.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of
content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms
of scholarship. For more information about JSTOR, please contact support@jstor.org.
.
Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.
http://www.jstor.org
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
l:"l'olo:~.ty.
64(4). 1981. pp. 090-702
,·1 1%1 by tht: Ecologi~.:al Society of America
GEOGRAPHIC VARIATION IN SEEDLING DOUGLAS-FIR
(PSEUDOTSUGA MENZIES/I) FROM THE WESTERN
SISKIYOU MOUNTAINS OF OREGON 1
FRANK
C.
SORENSEN
Pacific Northwesr Foresr and Ran{?e Experimenr Srarion, Unired Srares Deparrmenr of'
ARricu/rure. Fore.\1 Service , Corvallis, Ore{?on 97331 USA
Ahstracr. Patterns of geographic variation for seed and seedling traits of Douglas-fir from four
elevations on west and east aspects of first and second ridges away from the ocean (latitude = 42°30' N)
were observed under two air-temperature regimes in a common garden. Size and germination rate
were recorded for seeds; phenological and size data were recorded on seedlings through two growing
seasons.
The pattern of genetic variation appeared to be determined by adaptation to local moisture and
temperature regimes. ln east-west comparisons (inland ridge vs. coastal ridge or east aspect vs. west
aspect), seeds of east aspect or inland origin were larger and germinated more rapidly than seeds of
more westerly origin. Similarly, plants of inland origin or from east aspects tended to start and end
elongation earlier and have smaller top: root ratios , compared to plants from the coastal ridge or
west aspects. Genetic differences were generall y greater between the west and east aspects of the
coastal ridge than between the two aspects of the inland ridge.
Variation in date of bud set and plant size was al so related to elevation. The change associated
with elevation was greater on the coastal ridge than on the inland ridge. Evidence is presented that
indicates length of growing season and heat accumulation may change more with elevation and latitude
near the ocean than inland in the Pacific Northwest. This in turn may result in steeper elevational
and latitudinal gradients of genetically based variabilit y near the ocean than inland.
Key words: adaptarion ; {?ermination rare; grmvrh ; moisrure srres.1·; phenology; seed siz.e; rem­
perature.
INTRODUCTION
The Klamath Region of southwestern Oregon and
northwestern California, USA, embracing the Siski­
you and Trinity Mountains, has been an area of par­
ticular ecological interest because of its geologic age
and vegetational , edaphic, topographic , and climatic
complexity (Engelbrecht 1955, Whittaker 1960, Bald­
win 1964, Wolfe 1969, Franklin and Dyrness 1973).
Nevertheless , with the exception of Griffin ' s recent
work with Douglas-fir (Pseudotsuxa menziesii [Mirb.j
Franco) (Griffin 1974, 1978, Griffin and Ching 1977)
and studies on genetic adaptation to ultramafic soils
(e.g., Kruckeberg 1967, Jenkinson 1974), little re­
search has been done on local genetic differentiation
in the plants of the region, a lthough this would seem
basic to ecological interpretations.
Griffin ( 1974) and Griffin and Ching ( 1977) compared
the effects of latitude, elevation, and distance from the
ocean on patterns of geographic variation of seed and
seedling characteristics of Douglas-fir from northern
California . Distance from the ocean had the greatest
influence and the response was significantly curvilin­
ear, that is, the rate of change in expression of a char­
acter decreased with increasing distance from the
ocean.
The purpose of my study was to describe genetic
differentiation of Douglas-fir in the lower Rogue River
' Manuscript received 14 September 1981; revised 12 July
1982; accepted 23 July 1982.
watershed of southwestern Oregon and to investigate
the degree to which genetic variation is associated with
topographic variables of ridge, aspect , and elevation.
MATERI A LS AND METHODS
Seed samples and seedlinu culture
The location of the cone-collection sites and their
topographic position are shown in Fig. I a nd Table I.
Each location-sample was represented by wind-pol­
lination seed from mature cones collected from five or
six trees. Depending upon the road system and avail­
ability of cone-bearing trees, individual trees for a sin­
gle elevational sample were either scattered over sev­
eral kilometres , or were restricted to a spread of a few
hundred metres . The collection goal was a balanced
set of samples from 150, 455,760, and 1065 m on west­
and east-facing slopes on the first two ridges inland
from the ocean. Areas with ultramafic soils, as iden­
tified by the Geologic Ma p of Oregon (Peck 1961) and
on-site inspection, were avoided . Locations I through
4 (Fig. I) a re on slopes descending to the ocean; other
locations were on slopes descending to the valley of a
river flowing towa rd the ocean.
Cones were collected in August and September 1976.
Seeds were extracted and placed in cold storage
(- I0°C). The following spring seeds were stratified 60
d at 3-4°, germinated on filter paper in Petri dishes and
sown 17-19 May into raised coldframes at Corva llis,
Oregon (44°35'N , I23°15'W, 75 m).
Coldframes were covered from 20 May to 5 Septem-
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
August 19H3
697
GEOGRAPHIC VARIATION IN DOUGLAS-FIR
To Umpqua
River
~
Glendale •
~
42°30'N
I
~
t- Gold Beach
.
3
Illinois River
I
124°20'W
FiG. I. Collection locations in relation to coastline, main ridges, and the Rogue River Valley. • indicate average position
of the collections (numbers by the circles are indexed to Table 1), • = weather stations, and topographic features are identified
as coastline(//////), main ridges(>>>>), and named rivers(->). Latitudes and longitudes are given in the left and bottom
margins. Seed zone boundaries, revised 1973 from a map adopted 1966 (Western Forest Tree Seed Council 1973), are shown
with wide black lines.
ber the 1st yr with two layers of shade cloth (single
layer rated by the manufacturer at 30o/r; shade) and left
uncovered the 2nd yr.
Because patterns of genetic vmiation have been
found to vary with test environment (Campbell and
Sorensen 1978), two air temperatures, normal and
warm, were included in this study. Warm-air environ­
ment was created by placing a plastic tent over the
plots. The tent was in place for the duration of the
test. All plots were fertilized periodically and hand­
watered on a schedule based on size of plants and
weather conditions.
DesiRn and analysis
The sampling pattern included two ridges, coastal
and inland; two aspects, west and east on each ridge;
and four elevations between 150 and 1065 m. Because
elevations were nearly equally spaced, linear and non­
linear trends associated with elevation could be tested,
as well as ridge and aspect effects and their interac­
tions.
For determination of seed mass and germination rate,
progeny from individual seed trees (families) were kept
separate, and genetic effects were subdivided into those
among locations (as listed on Fig. 1, hereafter called
provenance) and those among families within prove­
nances. Families were not kept separate in the seed­
ling test.
The design model used in the coldframe test planting
was a split-plot with normal and warm air temperature
mainplots randomized in four replications. Prove-
nance subplots were completely randomized within
mainplots. Each provenance subplot contained 10
seedlings, 2 from each of five families. Main plots were
separated by 30 em and surrounded by two rows of
border seedlings. Spacing between seedlings was 8 em
within rows and 7.5 em between rows.
Air temperature and all sample location effects were
considered fixed. If provenance x air-temperature in­
teraction was not significant, response patterns were
TABLE I. Ridge, aspect, elevation, and distance inland of
collection sites. Collection number refers to number on
map in Fig. I.
Collection
number
I
2
3
4
5
6
7
8
9
10
II
12
13
14
15
16
Ridge
Aspect
Elevation
(m)
Coastal
Coastal
Coastal
Coastal
Coastal
Coastal
Coastal
Coastal
Inland
Inland
Inland
Inland
Inland
Inland
Inland
Inland
West
West
West
West
East
East
East
East
West
West
West
West
East
East
East
East
!50
450
760
1060
1070
770
450
150
180
460
770
1060
1070
830
400
210
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
Distance
from
ocean
(km)
I
II
14
19
25
26
30
30
31
34
35
39
57
62
68
70
Ecology , Vol. 64 , No.4
FRANK C. SORENSEN
698
B. Germination rate
A. Seed Mass
..,
7
16
~g
Q)
5:
c.
14
~:::
0 ~
6
~Q;
5
-;;;E
E
WE
0
"'(
~
6
,.,
11
M
-
5
~
~
-
4
~~--~W~E~--~W~E~
Coastal
10
E
_g
"'
9
-"
Q)
~
8
.,
35
Inland
E. Bud flush, year 2, normal air
.,
45
.ri
40
,f
~
E
_g
"',.,
~
35
-
~---
F. Bud flush, year 2, warm air
.g"'
30
_g
25
~
20
u.
E
"',.,
30
OL-~~W~E~--~W~E~
Coastal
Inland
2.5
a::
,....-1--
O~-;~W~E~--~W~E~
Inland
H. Top: root dry mass ratio,
warm air
3.6
2.6
.!:!
- --Coastal
G. Top: root dry mass ratio,
normal air
..
WE
D. Bud set, year 2, normal air
C. Bud set, year 1, normal air
7
WE
0'L-~C~o~aLs~ta~l--~ln~la~n~d
Inland
"'
~
..
3.5
.!:!
2.4
2.3
oL---C~o~a~s~ta~~--~~~
a::
3.4
3.3
oi'-~C~o~a~s+:ta,-1--~~~
FIG. 2. Average values for several traits from west and east aspects of the coastal and inland ridges. Only traits with
significant ridge, aspect , or ridge x aspect interaction effects are listed. Arrow indicates the mean value for the ridge. Because
neither aspect nor ridge x aspect were significant for top: root ratio (traits G and H) , only the ridge means are presented.
based on the mean values over both air-temperature
treatments. If provenance x air-temperature interac­
tion was significant (and it was for most traits) sub­
sequent conditional analyses were conducted sepa­
rately for each temperature treatment , and response
patterns were determined for each air temperature.
Uni- and multivatiate analyses of variance were made
on seedling traits. Testing levels for the rejection of
the null hypothesis were P = .05 .
The following characters were measured:
I) Seed mass: grams per 100 filled seeds.
2) Germination rate (time to 50Cio germination [Camp­
bell and Sorensen 1979]) at 23° after 60 d stratifi­
cation.
3) Date of bud set in both first and second growing
seasons: date when terminal bud could first be seen.
If terminal bud broke a second time in one summer,
the date that the final bud appeared was recorded .
Observations were made every 7 d .
4) Total height to base of terminal bud after first and
second growing seasons.
5) Date of bud break in the second season : date when
green needles could first be seen extending from
the bud scales . Observations made every other day .
6) Diameter below cotyledons: measured in October,
= 2 mo after bud set of the 2nd yr.
7) Top and root dry masses . Plants were harvested,
one replication at a time , during December and Jan­
uary after the second growing season, separated
into tops and roots at the ground line , dried at 50°
for 7 d in a forced-air drying room, and weighed.
Ratios of top: root dry mass were calculated.
RES U LTS
The three 2nd-yr growth traits (height, top dry mass,
and top : root ratio) were significantly and positively
intercorrelated , as were the three phenological traits
(dates of bud set both years and date of bud break) .
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
August 1983
GEOGRAPHIC VARIATION IN DOUGLAS-FIR
699
26
Sept 16
o
•
o
•
250
.S!
(ll
Coastal ridge, west aspec t (1)
Coastal ridge, east aspect (2)
Inland ridge, west aspect (3)
Inland ridge, east aspect (4)
Sept. 6
240
Aug . 27
230
Aug. 17
'0
....
(ll
~
220
1
210
Aug. 7
July 28
150
455
760
1065
Elevation (metres)
FiG. 3. The relation between mean date of bud set (year 2, warm environment) and elevation of provenance for west and
east aspects of a coastal and inland ridge in the western Siskiyou Mountains of Oregon. Solid lines represent significant
linear trends. Observed values are indicated by circles and squares. Standard error is 1.3 d.
To simplify the presentation, particularly if interac­
tions are significant, top : root ratio is used as repre­
sentative of growth traits and date of bud set in year
2 as representative of phenological traits.
Significant variation among provenances was pres­
ent for all traits, and much of this variation was related
to topographic variables. Effects associated with dif­
ferent topographic variables are presented separately.
Ricft.:e and aspect effects
For seed traits and all phenological traits, sources
of variation associated with both ridge and aspect were
significant. The ridge effect alone was significant for
top : root ratio. Neither ridge nor aspect significantly
affected seedling size traits.
Seeds from the west or coastal ridge were lighter
and germinated more slowly. Except for bud break in
the warm air temperature, seedlings from the coastal
ridge flushed and set buds later and had larger top :
root ratios than seedlings from the inland ridge. Av­
erage values associated with the two ridges and west
and east aspects of each ridge are shown in Fig. 2 for
several characters .
The differences associated with aspect were, again
with the exception of bud break, in the same direction
as the ditferences resulting from ridges . For example ,
if seeds from the coastal ridge germinated more slow­
ly , then seeds from the west aspect of each ridge also
germinated more slowly.
Interactions between ridge and aspect were signifi­
cant for phenological, but not for seed characteristics,
nor for top : root ratio. If the interaction was signifi­
cant, the average difference between aspects was al­
ways greater on the coastal ridge than on the inland
ridge.
E/e\'{/fion ejf'ects
Most significant elevation effects occurred only as
interactions with ridge, aspect, or both. Exceptions
were date of bud break and top dry mass in warm air
temperature, and even for these traits the interactions
with ridge, aspect, or both were significant.
Interactions
Two interaction s occurred most frequently: as­
pect x elevation and ridge x aspect x elevation. The
interactions tended to be larger when plants were grown
in warm air than when they were grown in norma l air
temperatures. The topographic patterns of two pre­
sumably important adaptive characters, date of bud
set and top: root ratio, are shown in Figs. 3 and 4,
respectively.
Bud set (year 2, warm environment) occurred earlier
with increasing elevation for samples from the west
aspect of the west ridge, but the trend was reversed
for population samples from the east aspect of the same
ridge (Fig. 3). On the other hand , relativel y little dif­
ference in the elevation trends was associated with
the two aspects of the inland (east) ridge.
A similar pattern of interactions was found with top :
root ratios (Fig. 4). Again, the average trends with
elevation were quite different for the two as pects of
the coastal ridge, but not for the two aspects of the
inland ridge.
Interaction patterns were quite consistent for the
different traits. This is shown by a listing of the signs
(plus or minus) of the coefficients for two interaction
terms . Signs a re li sted in Table 2 for the interactions
ridge (R) x aspect (A), aspect x elevation (E), and
ridge x aspect x elevation-linear. The absence of a
sign means the etlect was not significant for that par­
ticular trait. In all significant R x A interactions , the
difference between aspects is greater on the coastal
ridge than on the inla nd ridge, which is shown by the
consistent sign. Significant A x E interactions res ult
from the opposing elevation trends on west and east
aspects of the ridges . The opposing elevation trends
are, for all traits except bud break, more strongly ex-
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
0
•
o
•
4.0
~
3.9
E
3.8
rn
rn
3.7
E
3.6
Ill
~
"'C
3.5
0
3.4
e
ii
t2
Ecology, Vol. 64, No.4
FRANK C. SORENSEN
700
Coastal ridge, west aspect (1)
Coastal ridge, east aspec t (2)
Inland ridge, west aspec t (3)
Inland ridge, east aspect (4)
.
3.3
3.2
3. 1
150
455
760
1065
Elevation (metres)
FIG. 4. The relation between top : root dry mass ratio
(warm environment) and elevation of provenance for west
and east aspects of a coastal and inland ridge in the western
Siskiyou Mountains of Oregon. Solid lines represent signifi­
cant linear trends. Observed values are indicated by circles
and squares. Standard error is 0.056 units.
pressed on the two aspects of the coastal ridge than
they are on the two aspects of the next major ridge
inland. This gives rise to the significant R x A x E
interactions, as illustrated for traits in Figs . 3 and 4.
Air temperature
The air temperature in which the seedlings were
raised had a significant effect on all traits except root
dry mass. Warm relative to normal air temperature
increased plant size and top : root ratio, advanced date
of bud break and delayed date of bud set in year 2,
but not year I.
DISCUSSION
Three interaction patterns were of particular inter­
est: (I) on the ave rage, a greater difference in phe­
nology was found between plants from the west and
east aspects of the coastal ridge than between com­
parable aspects of the inland ridge : (2) elevation trends,
when significant, were steeper on the slopes of the
coastal ridge than on the slopes of the inl and ridge:
and (3) the elevation trends on the two aspects of
the coastal ridge were opposite in direction. Associ­
ated with this last interaction were comparatively large
differences between the high-elevation locations west
and east of the coastal summit.
Traits such as date of bud set, top length , top mass,
and top : root ratio appear to indicate adaptation to
length of growing season (Isaac 1949, Levitt 1966,
Hermann and Lavender 1968, Alden and Hermann
1971, Griffin 1974) . Earlier bud set, smaller tops and
top : root ratio are associated with sites having shorter
growing seasons either because of moisture stress or
length of the frost-free period .
The interactions noted above suggest that site se­
verity differs more between the two aspects of the
coastal ridge than between the two aspects of the in-
land ridge , that site severity changes more with ele­
vation on the coastal ridge than on the inland ridge,
and that it appears to increase with increasing eleva­
tion on the west as pect of the coastal ridge and with
decreas ing elevation on the east aspect of the same
ridge . Because of lack of long-term weather data in
the forest zone, I will try to interpret the genetic pat­
terns from generalizations about the climate of the area
and from three valley-bottom weather stations.
The entire Klamath Region is an area of rugged
mountains, deeply dissected, with steep slopes and
narrow valleys. Mountain crests range in elevation from
600 to II 00 m near the coast and to 1200 m and higher
farther inland.
The prevailing wind direction is from west to east.
Thus, air masses moving across the land are predom­
inantly of marine origin (Sternes 1968). Ridges paral­
leling the coast reduce the maritime influence inland
and produce rapid climatic changes toward drier,
warmer, and more continental conditions (Whittaker
1960) . I stress the word "rapid," because it indicates
that the greatest west-east transition in climate should
be associated with two aspects of the coastal ridge, as
it was in this test (Fig. 2)
Air masses are modified in moving inland by their
asce nt over the ridges. Cooling causes much of the
moisture in the incoming air to precipitate so that pre­
cipitation both increases with elevation and is greater
on the windward aspects (Engelbrecht 1955) . Air
reaching the lower inland slopes and valley floor is
much drier than the original maritime air to which the
windward aspect of the coastal ridge is exposed.
Additionally, fog frequently forms near the coastline
and is carried inland to the tops of the coastal hills
and into the valleys that open to the west. Because of
mixing of the air in the layer near the ground, the fog
is often raised 100m and more otT the ground (Engel­
brecht 1955). Although the lower elevations would be
shaded when fog is present , they would not be mois-
TABLE 2. Signs (plus or minus) of the contrast for three
interaction terms from the a nalyses of variance. A sign is
given only if the interaction is significant. Interpretation is
in the text. R , A, and E 1 stand for ridge, aspect, and ele­
vation-linear, respectively.
Interac tion
Traits
Bud break, year 2, normal
air temperature
Bud set, year I, both
air temperature s
Bud set, year 2, normal
Bud set, year 2, warm
Height , year 2, warm
Top dry mass, year 2, warm
Top : root ratio, year 2, warm
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
R x A
A
X
+
+
+
+
+
+
+
+
+
El
R X A X
E1
August 1983
GEOGRAPHIC VARIATION IN DOUGLAS-FIR
tened by the fog, and this could further contrast levels
of moisture stress on lower slopes relative to middle
and upper slopes that are in contact with the fog. The
significant trend of earlier bud set, smaller top: root
ratio (Figs. 3 and 4) and smaller top size associated
with decrea sing elevation on the east a spect of the
coastal ridge appear to be genetic responses to the
increasing and earlier moisture stress with decreasing
elevation along that slope.
Root: shoot ratio (Fig. 4) and size of seedlings rep­
resenting the two high elevations, east aspect, coastal
ridge (locations 5 and 6, Fig. I) were large compared
with like elevations on the other three slopes. This
performance indicated a milder than expected envi­
ronment for the elevations of those locations. No ex­
planation is available except to suggest again that the
high coastal ridge has a marked effect on the climate
immediately to its lee, even at high elevation. More
sampling across the coastal ridges would be worth­
while.
Because of abundant precipitation on the windward
aspect of the coastal ridge (Engelbrecht 1955), the steep
elevational cline in growth and phenological traits on
the west aspect of the coastal ridge (Figs. 3 and 4)
appears to be related to a temperature gradient.
Comparable interactions have been reported previ­
ously in Douglas-fir. For example, Campbell and So­
rensen ( 1978) found north-south clines for several traits
to be steeper along the coast than inland, and Griffin
(1974:81-4, and A. R. Griffin, personal communica­
tion) observed a linear latitudinal cline for cold har­
diness in coastal, but not in inland, seedlings.
Observations by Manley ( 1945) on the effect of At­
lantic maritime climates on the elevation of tree line
suggest an explanation for different temperature gra­
dients near the coast and inland. Because climatic ex­
tremes are less where the maritime etTect is greater,
much flatter annual temperature curves will be found
near the water than at a distance from it. Fig. 5 shows
the average annual temperature plots for the Gold
Beach and lllahe weather stations (Johnsgard 1963). A
horizontal line has been drawn on the figure at 9°C.
This value was chosen beca use it appears to be about
the average air temperature at which 2nd-yr bud flush
occurs in our coldframes at Corvallis. Using this base­
line for illustration, estimates of growing season length
and heat accumulation can be calculated for the two
stations. For Gold Beach, these estimates are 280 d
(the period that the average temperature curve is > 9°)
and 1915 degree days (the area in degree days under
the curve and above the baseline). For Illahe, the es­
timates are 239 d and 3360 degree days .
A change in latitude or elevation can be simulated
at the two locations by upward or downward move­
ment of the temperature curves. For illustration, I will
assume an elevational or latitudinal change that lowers
the curves by an average of 2°. At Gold Beach, this
change would reduce length of growing season by 49
701
25
OJ~~F--~M--~A--~
M~~J~-J~-A~~S--~O~~N~~D~~
Month
FIG. 5. Plots of mean monthly temperature at a coastal
location (Gold Beach) and an inland location 28 km air dis­
ta nce from the coast and behind the first range of mountains
(lllahe). A horizontal line has been drawn at 9°C as a baseline
for computing length of growing season and heat-unit accu­
mulation. Further explanation in text.
d and heat accumulation by 510 degree days : at Illahe
by 20 d and 455 degree days. In both measures , the
change is greater for a curve of the Gold Beach type
than for a curve of the Illahe type.
Zobel and Hawk ( 1980) reported several weather
characteristics for two forested sites , Pine Point (620
m, II km from the ocean) and Game Lake ( 1280 m,
28 km from the ocean) near the latitude of my transect.
They quantified temperature with an "October drop
index," the ratio of " temperature decrease from Sep­
tember to October" to " total decrease from warmest
month to October. " A high ratio indicated a warm
September, or a relatively flat or coastal type of curve.
Using 2 yr of field records, they obtained an October
drop index of 0.97 for Pine Point and 0.72 for Game
Lake. Values for Gold Beach and lllahe, based on
long-term weather records, were 0.87 and 0.69. These
figures indicate that temperature curve forms associ­
ated with distance from the ocean at low-elevation sta­
tions also may be associated with distance from the
ocean at higher elevations and on forested sites.
Thus, the evidence indicates that in this region el­
evational and latitudinal differences will result in greater
differences in temperature climate near the coast than
inland. This should result in steeper genetic clines,
both elevational and latitudinal, along the coast than
inland. Results of Douglas-fir population studies 111
common gardens seem to substantiate this .
Practical implications
Transfer of seeds and seedlings in artificial refores­
tation of western forests is based on prescribed seed
zones and elevation bands within which relatively little
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions
702
FRANK C. SORENSEN
adaptive genetic differentiation is anticipated. For the
western Siskiyous, the seed-zone ma p designates a
Coastal Region extending from the ocean to a set of
ridges = 60 km inland (Western Forest Tree Seed
Council 1973 and Fig. I). Generally, this line runs along
the ma in eastern ridges of the Coast Ranges. The
Coastal Region is then further divided into zones and
subzones based on latitude , but not based on the to­
pography between the north-south zone line and the
coast.
My results are preliminary, but they indicate that a
subzone should be considered to separate the coastal
ridge and perhaps even the west side of the coastal
ridge from the rest of the Coastal Region. Currently
the Gold Beach Cooperative makes this breakdown in
designating breeding zones for their applied Douglas­
fir Tree Improvement Program (Roy R. Silen, Forestry
Sciences Laboratory, Corvallis, personal communi­
cation). The justifications are (I) the significant aver­
age difference in seedling growth and phenology be­
tween the west and east slopes of the coastal ridge and
(2) the steeper genetic gradient associated with ele­
vation on the west aspect of the coastal ridge.
Extrapolation north and south of the latitude of this
transect in Oregon is speculative, but might be worth­
while to indicate hypotheses for further testing . The
height of the coastal hills and their position rel ative to
the ocean and other ridges are of critical importance
in determining patterns of adaptive variation for coast­
al Douglas-fir in this region . High coastal hills are gen­
erally present north to = 43°N , the northern edge of
the western Siskiyous. From there to = 4SON, the Coast
Ranges are generally lower and the summit generally
closer to the ocean. Less genetic differentiation be­
tween the east- and west-facing coastal slopes may
have occurred in this area , and the need for a separate
subzone west of the coastal ridge also may be less.
Between 4SON and the Columbia River, the main crest
of the Coast Ranges is again higher and occurs further
east, but with intervening high hills also occurring be­
tween the main crest a nd the ocean. Increased genetic
differentiation close to the ocean might be anticipated,
which again would increase restrictions on east-west
seed movement.
ACKNOWLEDGMENTS
Andreas Regehr , as a volunteer, ass isted with the cone
collections, and Richard Miles maintained the test plots and
supervised data collection. Their help is greatly appreciated.
Helpful reviews were provided by W. T. Adams , A. R. Grif­
fin , D. Minore, and D. B. Zobel. I am particularly grateful
to Dr. Zobel for drawing my attention to his temperature
records.
LITERATURE CITED
Alden, J ., and R. K. Hermann. 1971. Aspects of the cold
hardiness mechanism in pla nts . Botanical Review 37:37142.
Baldwin , E. M. I964. Geology of Oregon. University of
Oregon Cooperative Book Store, Eugene, Oregon, USA.
Ecology, Vol. 64, No.4
Campbell , R. K. , and F. C. Sorensen. 1978. Effect of test
environment on expression of clines and on delimitation of
seed zones in Douglas-fir . Theoretical and Applied Ge­
netics 51:223-246.
Campbell, R. K., and F. C. Sorensen. 1979. A new basis for
characterizing germination data. Journal of Seed Technol­
ogy 4:24-34.
Engelbrecht, H. H. 1955. The climatology and ecology of
the Pacific Coast. National Shade Tree Conference Pro­
ceedings 31:7-24.
Franklin , J. F., and C. T . Dyrness. 1973. Natural vegeta­
tion of Oregon and Washington. Forest Service General
Technical Report PNW-8, Pacific Northwest Forest and
Range Experiment Station, Portland, Oregon, USA.
Griffin , A. R. 1974. Geographic variation in juvenile growth
characteristics of Douglas-fir (Pseudotsuga menziesii [Mirb.]
Franco) from the Coastal Ranges of California. Disserta­
tion. Oregon State University, Corvallis, Oregon, USA.
- - -. 1978. Geographic variation in Douglas-fi r from the
Coastal Ranges of California. II . Predictive value of a
regression model for seedling growth variation. Silvae Ge­
netica 27:96-101.
Griffin , A. R. , and K. K. Ching. 1977. Geographic variation
in Douglas-fir from the Coastal Ranges of California. I.
Seed, seedling growth and hardiness characteristics. Silvae
Genetica 26:149-157.
Hermann , R. K. , and D. P. Lavender. 1968. Early growth
of Douglas-fir from various altitudes and aspects in south­
ern Oregon . Silvae Genetica 17: 143-151.
Isaac , L. A. 1949. Better Douglas-fir forests from better
seeds. University of Washington Press, Seattle , Washing­
ton, USA.
Jenkinson, J. L. 1974. Ponderosa pine progenies: differ­
entiation responses to ultramafic and granitic soils. Forest
Service Research Paper PSW-101 , Pacific Southwest For­
est and Range Experiment Station, Berkeley, California,
USA.
Johnsgard, G. A. 1963. Temperature and the water balance
for Oregon weather stations. Special Report 150, Agricul­
ture Experiment Station , Oregon State University, Cor­
vallis, Oregon , USA.
Kruckeberg, A. R. 1%7.
lypic response to ultramafic
soils by some plant specie'
.wrthwestern United States.
Brittonia 19: 133-151.
Levitt , J . 1966. Winter hardiness in plants . Pages 495-563
in H. T. Meryman, editor. Cryobiology. Academic Press,
New York, New York , USA.
Ma nley, G. 1945 . The effective rate of altitudinal change
in temperate Atlantic climates. Geographical Review 34:
308-417.
Peck , D. L. compiler. 1961. Geological map of Oreg'on west
of the 121 st meridian . Geological Survey , United States
Department of Interior, Washington , D.C ., USA.
Sternes, G. L. 1968. The climate of the Rogue Basin. United
States Environmental Science Services Administration,
Portland, Oregon, USA.
Western Forest Tree Seed Council. 1973. Tree seed zone
map. State of Oregon. Revi sed July 1973 from a map adopt­
ed April 1966. United States Department of Agriculture,
Forest Service, Portland, Oregon , USA.
Whittaker, R. H. 1960. Vegetation of the Siskiyou Moun­
tains , Oregon and California. Ecological Monographs 30:
279-338.
Wolfe , J . A. 1969. Neogene floristic and vegetational his­
tory of the Pacific Northwest. Madroiio 20:83-110.
Zobel, D. B. , and G. M. Hawk. 1980. The environment of
Chamaecyparis /a wsoniana . American Midl a nd Naturalist
103:280-297.
This content downloaded from 166.6.105.57 on Tue, 20 Jan 2015 16:27:31 PM
All use subject to JSTOR Terms and Conditions