1 

1 

United States 

Department of 

Agriculture 

Forest Service 

Intermountain 

Forest and Range 

Experiment Station 

Ogden, UT 84401 

Research Paper 

INT-295 

July 1982 

Ecological 

Adaptations 

in Douglas-fir 

Populations. II. 

Western Montana 

Gerald E. Rehfeldt 

This file was created by scanning the printed publication.

Errors identified by the software have been corrected;

however, some errors may remain.
THE AUTHOR 

GERALD E. REHFELDT is a plant geneticist at the 

Forestry Sciences Laboratory, Moscow, Idaho. His 

research includes studies of the ecological genetics of 

Northern Rocky Mountain conifers, primarily Douglas-fir. 

RESEARCH SUMMARY 

Seedlings from 50 populations of Douglas-fir 

(Pseudotsuga menziesii var. g/auca) from Montana west of 

the Continental Divide were compared in nursery, 

laboratory, and shadehouse studies. Analyses of variance 

indicated significant differences among populations in six 

traits: bud burst, bud set, 3-year height, growth rate, cold 

injury, and flushing periods during the first or third 

growing season. Most traits were highly intercorrelated; 

thus, populations that expressed a high growth potential 

also set buds late, flushed twice, grew at a rapid rate, but 

were most severly injured by freezing. Consequently, 

adaptation of populations for numerous traits is viewed 

as a balance between selection of high growth potential 

in relatively mild environments and selection for cold 

hardiness in severe environments. 

Multiple regression analyses related genetic differentation of populations to geographic and ecologic conditions of the seed source. The regression model that best 

fit the data described adaptive variation according to two 

physiographic zones, elevation within each zone, and 

latitude within zones. Patter'ns of adaptive differentiation 

were used to develop seed transfer guidelines for reforestation and tree improvement. 

ACKNOWLEDGMENT 

I appreciate the excellent technical assistance of S. P. 

Wells, and the thoughtful criticism of D. T. Lester and 

R. K. Campbell. . 

Approved for publication by 

Intermountain Station 

January 1982 
United States 

Department of 

Agriculture 

Forest Service 

Intermountain 

Forest and Range 

Experiment Station 

Ogden, UT 84401 

Ecological 

Adaptations 

Research Paper 

INT-295 

July 1982 

in Douglas-fir 

Populations. II. 

Western Montana 

INTRODUCTION 

Genetic differentiation among populations of Douglasfir (Pseudotsuga menziesil) is closely related to the 

environment. In the coastal variety (Pseudotsuga 

menziesii var. menziesil), genetic variation within a single 

drainage was clearly related to elevation and topographic 

setting (Campbell 1979; Campbell and Franklin 1981). For 

the Rocky Mountain variety (Pseudotsuga menziesii var. 

glauca), the growth potential and cold hardiness of 

populations depends on geographic origin: populations 

from northern Idaho tend to be faster growing and less 

hardy than those from western Montana which in turn 

are faster growing and less hardy than populat'ions fro~ southern Idaho (Rehfeldt 1979b). Within northern Idaho 

alone, differences among populations are closely related 

to the elevation, latitude, and longitude at the seed origin 

(Rehfeldt 1979a). 

The main objective of the present study is to describe 

patterns of genetic variation among Douglas-fir populations from Montana west of the Continental Divide (fig. 

1). The study excludes the extreme northwest portion of 

the area which presents patterns of enVironmental variation (Pfister and others 1977) and genetic differentiation 

(Rehfeldt 1979a,b) that are similar to those of northern 

Idaho. Patterns of variation will be used to: (1) develop 

guidelines for the transfer of seeds that should limit 

maladaptation in reforestation, and (2) delineate the 

breeding zones within which genetic gains from tree improvement will accrue. 

Western Montana (fig. 1), a region of diverse montane 

environments, is separated from contiguous areas by the 

Continental Divide on the east and south, the Cabinet 

and Bitterroot Mountains on the west, and a political 

boundary to the north. Within this region, climatic, physiographic and ecologic conditions follow a well-described 

pattern from the west and northwest toward the Continental Divide (Pfister and others 1977). Remnants of a 

maritime climate in the northwest are gradually lost as 

the general climate becomes continental. The elevation of 

valley floors increases from about 2,000 ft to 4,000 ft 

(600 m to 1 200 m). Concomitant changes in the frequency 

of particular habitat types largely reflect a gradual 

decrease in species most common in moist environments. 

Finally, effects of topography are superimposed on 

general environmental trends to produce the extreme 

environmental heterogeneity that characterizes the region. 

And within this region, Douglas-fir occupies a range of 

sites from the relatively warm, near lower timberline, to 

relatively cold subalpine environments above 6,500 ft 

(2 000 m) elevation (Pfister and others 1977). 

MATERIALS AND METHODS 

To assess population differentiation, cones were 

collected from several squirrel caches in each of 50 

populations from western Montana (fig. 1). Populations, 

selected to represent the ecological amplitude of the 

species within the region, differed in elevation by as much 

as 4,300 ft (1 300 m); and represented habitats (Pfister and 

others 1977) as dry and warm as the Pseudotsuga 

menziesiilAgropyron spicatum, as cool as the Abies 

lasiocarpalVaccinium globulare, or as moist as the Thuja 

plicatalClintonia uniflora habitat types. In addition to 

populations from western Montana, some populations 

from adjacent geographic provinces (fig. 1) were included 

in separate studies of (1) growth potential and phenology, 

(2) cold hardiness, and (3) patterns of first-year shoot 

elongation. Data from all studies were used to assess 

patterns of geographic and ecologic variation. 

Growth and Phenology 

Seedlings from 54 populations were grown for 1 year in 

plastic tubes (4 in3, 65 cm3) in a shadehouse at Moscow 

Idaho. In autumn of the first growing season, seedlings' 
were transplanted into six environments (table 1) on the 

Priest River Experimental Forest in northern Idaho (fig. 1). 

While two plantings were in a nursery, four were established on various forest sites. Although plantings on these 

four sites were made in the residual soil, rocks, roots, and 

competing vegetation had been removed before tilling. All 

plantings received natural precipitation. Twelve seedlings 

from each population were planted in row plots in each of 

two replicates in all environments. Rows were separated 

by 4 in (10 cm); 3 in (8 cm) separated seedlings within 

rows. 

Growth potential and phenology of seedlings was 

assessed from the following scores and measurements 

obtained for each population in all replicates: 

1. Bud burst: the day after April 1 by which 50 percent 

of the seedlings had burst terminal buds during the 

third growing season. 

2. Bud set: the week by which 50 percent of the 

seedlings had set terminal buds during the third 

growing season. 

3. Two flushes: the proportion of seedlings that 

flushed more than once during the third growing 

season. 

4. Height: average seedling height after 3 years. 

5. Growth rate: deviation from regression of 3-year 

height on 2-year height; an index to the rate of 

growth from a constant height at age 2. 

Population differentiation was assessed from the model 

of random effects: 

Yijk = !1 + Pi + ej + rjk + gij + d ijk 

where Yijk is the performance of population i in replicate k 

of environment i; !1 is the overall mean; Pi is the effect of 

population i; ej is the effect of environment i; gij is the 

interaction of population i in environment i; and dijk is the 

residual variation. While most analyses were made on the 

original variables, proportions were transformed to arcsin 

..rx:- and bud set was transformed to ~ 1f2 .• 

Cold Hardiness 

Tolerance to freezing was studied with 50 seedlings 

from each of 58 populations that had been growing for 2 

years in plastic containers (9 in3; 150 cm3) in a shadehouse at Moscow, Idaho. In general accordance with procedures outlined by Levitt (1972), freezing tests were made 

to assess hardiness of each population in mid-September 

when first autumnal frosts can be expected. This single 

date was chosen because northern Idaho populations 

expressed greatest differentiation in cold hardiness after 

bud set but prior to the first frost of autumn and because 

previous tests indicated that the ranking of populations 

according to hardiness did not change in subsequent 

sampling dates (Rehfeldt 1979d). 

Terminal shoots from each of the 58 populations were 

cut and arranged into 5 sets of 10 shoots (3 in; 8 cm 

long). Each set was mOistened, packaged in a plastic bag, 

and stored overnight at 37 0 F (3 0 C). The following 

morning, plastic bags were suspended in a freezing 

chamber equipped with two fans for providing circulation. 

One set of shoots from each population was frozen at the 

rate of 9 0 F (50 C)/h to one of five test temperatures 

2 

between 7 0 F and 0 0 F (-14 0 C and -18 0 C). While 

within the plastic bags, shoots were removed from the 

freezer when remote temperature sensors indicated that 

internal air temperatures had reached desired levels, were 

thawed for 24 h at 37 0 F (3 0 C), and were placed on a 

shaded greenhouse bench. After 2 days, the presence or 

absence of injury to each shoot was scored by 

discoloration of leaves. For each population, the number 

of seedlings exhibiting leaf injury was recorded for each 

test temperature. 

Differentiation of populations was assessed by an 

analysis of variance of random effects on the percentage 

of shoots of each population exhibiting injury at each test 

temperature: 

Yij = !1 + Pi + tj + gij + e 

where Yij is the percentage of twigs injured from 

population i at temperature i; !1 is the overall mean; Pi is 

the effect of population i; tj is the effect of temperature i; 

gij is the interaction of population i at temperature i; and 

e is the theoretical variance of an observation in a 

binomial distribution (Steele and Torrie 1960). Percentages 

were transformed to arcsin VX before analyses were 

made. 

Patterns of First-Year Growth 

Douglas-fir seedlings exhibit contrasting patterns of 

growth during the first growing season (Rehfeldt 1979c). 

For essentially all seedlings from western Montana. a 

terminal bud is set about 1 month after germination. But, 

only a portion of these seedlings burst bud and resume 

growth in late July or August. To test for differences 

among Montana populations in patterns of first-year 

elongation, 30 to 40 seedlings from 50 populations were 

grown in plastic containers (4 in3; 65 cm3) in each of four 

replicates. The proportion of seedlings that exhibited a 

single growth period was recorded for each population in 

all replicates. Proportions were transformed (arcsin 'v'"X) 

before statistical analyses that followed a model identical 

to that used for freezing tolerance. 

Patterns of Variation 

Data from the separate studies were used to assess 

differentiation in relation to geographic and ecologic 

criteria of the seed sources according to the general 

model: 

where Yi is the mean performance of population i; b's are 

regression coeffiCients; and X's are various independent 

variables (table 2). Qualitative independent variables were 

included in the model by fitting constants, values of zero 

or one (Draper and Smith 1966). Of the independent 

variables, habitat types included five major series on 

which Douglas-fir is common (Pfister and others 1977); 

Idaho departure is distance from the State line; and 

northwest departure is an imaginary grid distance from 

northwest to southwest through western Montana. 
Table t.- Trait means according to environment 

Bud Bud 

Environment burst set 

Days Weeks 

Nursery shade, 730 m 33.4 2.9 

Nursery sun, 730 m 31.7 5.5 

Reservoir, 790 m 31.4 5.4 

M-2 Road, 1 100 m 35.8 5.7 

North Ridge west, 1 520 m 60.8 9.4 

North Ridge east, 1 580 m 66.3 11.9 

'Deviation from regression of 3-year height on 2-year height. 

1170 

1160 

1150 

49" + 

• 

48" + 

47 0+ 

o MOSCOW 

NORTH IDAHO 

• 

• 

Saltnon R 

450+ CENTRAL IDAHO 

\ 

• 

Figure t.-Major drainages of western Montana and adjacent 

regions showing location of populations. 

3 

Trait 

Two 

flushes 

Percent 

24.5 

54.8 

51.6 

38.3 

44.3 

61.1 

1140 

Growth 

Height rate1 

----------------cm-------------

1130 

+ 

MONTANA 

18.6 

17.2 

15.4 

11.6 

12.6 

10.6 

• 108" 

45" + 

10.8 

7.9 

4.3 

-7.8 

-4.9 

-10.4 
For all regression models, residuals from regression 

were examined visually in relation to observed and 

predicted values to assess homogeniety of error variances 

and the fit of data to regression models (Draper and 

Smith 1966). Thus, seven regression models were fitted to 

the data (table 2). Adequacy of a model was judged 

according to the goodness of fit (R2), residual variance 

(Sy. x), and geographic or ecologic patterns displayed by 

residuals. 

RESULTS 

Six environments exerted considerable influence on the 

growth and phenology of seedlings (tables 1 and 3). Most 

of this influence was directly related to elevation. As 

compared to seedlings growing in the nursery at low 

elevation, seedlings growing at high elevations on North 

Ridge burst bud about 4 weeks later, set buds about 6 

weeks later, grew at a slower rate (negative deviation from 

regression), and, consequently, were about 3 in (7.5 cm) 

smaller. Only the proportion of seedlings that flushed 

twice seemed to be independent of elevation, but perhaps 

not independent of shade. The two environments with the 

lowest proportion of seedlings that flushed twice included 

Table 2.-lndependent variables included in various models for 

relating population differentiation to geographic and 

ecologic conditions of the seed source 

Independent 

variable 

Latitude 

Longitude 

Habitat types 

Elevation 

Northwest departure 

Idaho departure 

Three major 

drainages 

Elevation within 

drainages 

East and west 

physiographic 

zones 

Elevation within 

zones 

Northwest departure 

in zones 

Latitude in zones 

x 

x 

x 

x 

Variables included in model: 

23456 

x 

x 

x 

x 

x x 

x 

x 

x x 

x 

x x 

7 

x 

x 

x 

the nursery that received 50 percent shade and M-2 Road 

that received afternoon shade. 

Populations differed greatly in phenology and growth 

potential (table 3). In the average environment, 

populations from western Montana differed by as much 

as 6 days in bud burst, 6.2 weeks in bud set, 53 percent in 

seedlings that flushed twice, 2.7 in (7 cm) in height, and 

1.2 in (3 cm) in growth rate (third-year growth from a 

constant height at age 2). In addition, populations 

performed essentially the same in all environments. 

Interactions of genotype and environment were detected 

for only bud burst and height. While accounting for little 

variance, these interactions, like those detected for north 

Idaho populations (Rehfeldt 1979a), resulted from mean 

differences not associated with changes in the ranking of 

populations. 

Laboratory studies of freezing tolerance revealed 

significant differences among 58 populations (table 4A). 

Even though test ~emperatures spanned only 90 F (50 C), 

percentage of injury to all twigs ranged from 19 percent at 

70 F (-14 0 C) to 75 percent at 0 0 F (-18 0 C). Across this 

range of temperatures, mean injury to populations from 

western Montana ranged from 16 to 69 percent. 

Shadehouse studies of the pattern of first-year 

elongation revealed significant differences among populations in the proportion of seedlings that exhibited a single 

growth period (table 48). Mean values for Montana populations ranged from 24 to 74 percent. 

Table 4.-Analyses of variance for freezing injury (A) and one 

period of growth (B) 

Source of variance 

A. Freezing injury 

Temperatures 

Populations 

Temperature x Population 

Sampling error1 

B. One period of growth 

Replication 

Populations 

Replication x Population 

Sampling error1 

Degrees Mean 

of freedom square 

4 

57 

228 

3 

49 

147 

6.2206* * 

.1280* * 

.0424 

.0250 

0.0478** 

.0499** 

.0155 

.0148 

lTheoretical variance of a binomial distribution. 

* *Statistical significance at the 0.01 level of probability. 

Table 3.-Mean squares from analyses of variance for population performance in nursery environments 

Source of variation 

Environments 

Repslenvironment 

Populations 

Pops. x environment 

Residual 

Degrees of freedom 

5 

6 

53 

265 

318 

Bud burst 

27,290.59* * 

10.22* * 

20.54* * 

1.78 

1.92 

lDeviation from regression of 3-year height on 2-year height. 

• ·Significant at the 0.01 level of probability. 

·Significant at the 0.05 level of probability. 

Bud set 

38.400* * 

1.079* * 

1.499* * 

0.312* 

.247 

4 

Two flushes Height Growth rate1 

1.9907* * 1097.39* * 84.64* * 

0.2538** 23.25* * 21.33* * 

.3116* * 95.51* * 6.43* * 

.0433 5.36* * 1.53 

.0447 2.07 1.57 
Variation in growth, phenology, cold hardiness, and 

first-year flushing of western Montana populations formed 

an intercorrelated network of traits to which only bud 

burst was unrelated (table 5). This network, like that for 

northern Idaho populations (Rehfeldt 1979a), seems keyed 

to adaptation to the cold. Populations that set buds early 

were also characterized by a low proportion of seedlings 

that flushed twice, a low growth rate, a short height, but a 

high tolerance to freezing. 

Because of strong intercorrelations, results of the 

series of regression analyses (table 6) showed similar 

patterns for all traits. In general, the sequence of 

regression models shows an increase in values of R2 and 

a decrease in residual variances. Regression model 1 

(table 2) indicated that (1) genetic variation was related to 

elevation; (2) geographic patterns of variation followed a 

grid that was oblique to latitude and longitude; and (3) 

habitat types were related to neither dependent nor independent variables. A lack of association between habitat 

types and genetic variation in western Montana corresponds with results for Douglas-fir populations from 

northern Idaho (Rehfeldt 1979a) and for Pinus ponderosa 

from southern Idaho (Rehfeldt 1980). 

Residuals from model 2 suggested that geographic 

patterns of variation were discontinuous at 40 to 60 mi (60 

to 100 km) from the Idaho state line, a boundary that 

roughly follows the crests of the Cabinet and Bitterroot 

Mountains. Populations from the Bitterroot and west 

Clark Fork drainages differed from eastern populations 

representing similar latitudes and elevations. This 

discontinuous pattern of variation was incorporated in 

models 3 to 6, which represent sequential steps toward 

the model that best represented the data. Regression 

model 7 generally produced the highest fit and lowest 

residual variance. But also, residuals displayed no 

obvious geographic or ecologic patterns. 

In model 7, genetic variation is described according to 

six independent variables: two physiographic zones, 

elevation within each zone, and latitude within zones. The 

western physiographic zone includes the Bitterroot and 

west Clark Fork drainages; the eastern zone is composed 

of the Flathead and east Clark Fork drainages (fig. 1). 

Results of multiple regression analyses are presented 

graphically for each variable (fig. 2). These graphs were 

generated by predicting population performance (Y) from 

multiple regression equations. Because of high 

Table 5.-Matrix of simple correlation coefficients among population means 

BS TWF H GR OP FZ 

Bud burst (BB) -0.13 -0.22 0.12 -0.02 0.21 -0.05 

Bud set (BS) .91 * * .72** .49* * -.45** .49* * 

Two flushes (TWF) .61 * * .54* * - .44* * .40* * 

Height (H) .25 -.26 .45* * 

Growth rate (GR) - .42* * .28* * 

One period (OP) -.31* 

Freezing injury (FZ) 

*Statistical significance at the 0.05 level of probability . 

• ·Statistical significance at the 0.01 level of probability. 

Table 6.-Results of several multiple regression models (table 2) for relating genetic variation to geographic and ecologic conditions of the 

seed source 

Regres- Bud burst Bud set Two flushes Height Growth rate One period Cold hardiness 

sion 

model R2 Syex R2 Syex R2 Syex R2 Syex R2 Syex R2 Syex R2 Syex 

1 0.26* * 1.021 0.30 0.2435 0.32* * 0.1044_ 0.60* * 1.138 0.11 0.5500 0.12 0.0980 0.23* * 0.1199 

2 .30** .991 .38* * .2299 .38** .1003 .61 * * 1.127 .10 .5534 .13 .0975 .31 * * .1148 

3 .23 1.039 .42* * .2225 .45* * .0939 .58** 1.167 .10 .5534 .12 .0982 .31 * * .1145 

4 .31 * * 1.011 .48* * .2146 .50* * .0916 .59** 1.177 .27* .5095 .17 .0975 .37** .1121 

5 .28** 1.011 .46* * .2166 .49** .0917 .68** 1.031 .18 .5355 .13 .0984 .34** .1130 

6 .32* * 1.005 .49* * .2126 .51 * * .0909 .70** 1.006 .21 .5300 .18 .0970 .35** .1136 

7 .32** 1.003 .52** .2071 .52** .0900 .72** .978 .23* .5245 .19 .0964 .35* * .1131 

·Statistical significance at the 0.05 level of probability . 

• • Statistical significance at the 0.01 level of probability. 

5 
intercorrelations among dependent variables, similar 

results of regression models (fig. 2) were expected for bud 

set, two flushes, height, growth rate, and freezing injury. 

But the same model was also effective for bud burst 

largely because of strong effects of latitude and elevation 

within the western zone. Similarly, elevation within the 

western zone was the only independent variable 

significantly associated with the proportion of seedlings 

that displayed one growth period. Consequently, results of 

the multiple regression for the latter variable are 

presented even though the entire model was not 

significant. 

The regression models generally depict: (1) decreasing 

growth potential and increasing hardiness of populations 

in association with increasing elevation of the seed origin; 

(2) greater growth potential but lesser hardiness of 

populations in the western zone than in the eastern zone; 

(3) effects of elevation on genetic differentiation that are 

generally stronger in the western zone than in the eastern 

zone; and (4) effects of latitude in the west that are the 

reverse of those in the east. Thus, at a constant elevation, 

hardiness of populations increases while growth potential 

decreases northward through the western zone and then 

southward through the eastern zone. Thereby, genetic 

differentiation in populations from different physiographic 

zones is greater in the southern portion of we~tern 

Montana that in the northern portion. 

Finally, since nursery and laboratory studies included a 

few populations from geographic regions adjacent to 

western Montana, geographic variation can be assessed 

further. As noted previously (Wright and others 1971; 

BUD BURST BUD SET ;r;'ccc,- 11 

, ~- 0l-f., 

~~~OOOc -::;:::::. 

43 

:/ 9 Vl 

Vl 

'],c:§::i ~ 

w >- w <{ .-- 3 7 CJ 

41 ,c() o~ 

~ 

. W....- QQ~""- j....--

.........- .........- , 46° 47" 48° 49° 46° 47" 48° 49~ 

20 

16 

~ 

u 

12 

Rehfeldt 1979b), populations from northern IdahG express 

greater growth potential but lesser hardiness than 

western Montana populations from comparable elevations 

(table 7). In addition, populations from the severe 

environments of central Montana and central Idaho 

express an extremely low growth potential but high 

hardiness. 

DISCUSSION 

By illustrating strong geographic and ecologic patterns 

in genetic differentiation, the present results further 

exemplify intense physiological attunement of Douglas-fir 

populations to their environment. Adaptation of populations is readily interpreted as a balance between selection 

of high growth potential in mild environments and selection for cold hardiness in severe environments. Montana 

populations, like those from northern Idaho, were readily 

differentiated by a network of intercorrelated traits: 

populations of high growth potential were tall, set buds 

late, grew at a rapid rate, expressed pronounced tendencies for multiple flushing, but suffered the most injury 

from freezing. Accordingly, as compared to populations 

from western Montana, those from northern Idaho expressed adaptations to a milder climate; and those from 

southern Idaho and central Montana expressed adaptations to a more severe climate. 

In addition, patterns of genetic variation depicted by 

multiple regression models seem uniquely suited to the 

climate and physiography of western Montana. A western 

physiographic zone contained populations of higher 

HEIGHT 

lOOOW 

46· 47° 48~ 49° 

70 

~ 

z 

w 

~50 

w 

0.. 

30 

TWO flUSHES 

~ 

46° 47" 48° 49° 

GROWTH RATE 

FREEZING INJURY 1.0 

~ 0 

20 -1.0 

46° 47° 48° 49· 46° 47" 48· 49° 

~ 50 

u 

ae: 

w 

0.. 

30 

ONE PERIOD 

,OOOW 

46° 47~ 48· 49· 

----------------------------------------LATITUDE----------------------------------------

Figure 2.-Results of multiple regression mode! 7 (table 2) depicting the predicted 

performance (ordinate) in relation to the latitude (abscissa), geographic zone (E = 

eastern, W = western), and the elevation (1 000 m or 2 000 m) of the seed source. 

6 
Table 7.-Average deviation in performance of populations from peripheral areas from the predicted performance of western Montana 

populations at comparable elevations 

Geographic area 

Northern Idaho 

Central Idaho 

Central Montana 

Sample 

populations 

Number 

3 

3 

Bud 

burst 

Days 

-0.6 

-2.2 

-2.0 

growth potential and lesser hardiness than populations 

from similar elevations and latitudes in an eastern zone. 

The boundary between eastern and western zones generally follows the crest of the Sapphire Mountains, which 

separate the Bitterroot Drainage from the eastern Clark 

Fork, and includes the Jocko Range and the Cabinet 

Mountains, which separate the Flathead Drainage from 

the western Clark Fork (fig. 1). Moreover, a climate with 

considerable maritime influence in the west and northwest becomes decidedly more continental as the Continental Divide is approached; this climatic pattern is 

reflected in the distribution of plant communities (Pfister 

and others 1977; Arno 1979). Consequently, it is appropriate for Douglas-fir populations from the western zone 

to express adaptations to a milder climate than populations from the eastern zone. 

For genetiC variation to be related to elevation of the 

seed source is not surprising: growing seasons generally 

decrease with increasing altitude; an intercorrelated 

network of traits is keyed to adaptations to the cold; and 

for both Oregon (Campbell and Sorensen 1978; Campbell 

1979) and northern Idaho (Rehfeldt 1979a) popu lations, 

genetic variation has been related to elevation. However, 

the strength of the relationship between differentiation 

and elevation depended on the physiographic zone. For 

instance, in the western zone, 3-year height of populations 

decreased by about 26 percent over an elevational difference among seed sources of 3,280 ft (1 000 m). The 

corresponding decrease for the eastern zone amounted to 

about 14 percent while that for the northern Idaho 

populations was about 28 percent (Rehfeldt 1979a). Thus, 

in areas where climatic gradients in altitude should be the 

steepest, the strongest associations between differentiation and elevation were apparent. Near the Continental 

Divide, the difference in environmental severity between 

high and low elevations, judged by the distribution of 

habitat types (Pfister and others 1976), is the least, and 

clinal gradients are relatively flat. 

In the Northern Hemisphere, populations of woody 

plants from southern latitudes generally show higher 

growth rates and lesser hardiness than populations from 

northern latitudes. Thus, differentiation among Douglas-fir 

populations in northern Idaho (Rehfeldt 1979a) and in 

Montana's western physiographic zone followed the expected trend even though the latitudinal interval was 

small (3.5 degrees). However, patterns of population differentiation in the eastern physiographic zone followed a 

contrasting pattern: northern populations were of the 

highest growth potential and lowest hardiness. Again, 

patterns of latitudinal differentiation in the eastern zone 

Bud Two Growth One Freezing 

set flushes Height rate period injury 

Weeks Percent ------cm------ - - - - Percent - - - -

1.9 6.3 5.6 0.51 4.6 

-1.5 -17.0 -2.6 -.34 5.2 -11.0 

-.8 -10.4 -3.5 -.52 11.9 -15.0 

7 

are readily interpreted by climatic patterns imposed by 

the unique physiognomy of the region: not only does a 

maritime climatic influence decrease from the northwest 

toward the southwest, but also, elevation of valley floors 

increases greatly toward the southeast. Consequently, 

much of the region drained by the eastern Clark Fork 

represents an ecotone between the relatively moist environment to the west and north and the severely cold and 

dry habitats to the east. Thus, it is appropriate for (1) 

northern populations of the eastern zone to be of higher 

growth potential and lower hardiness than southern populations, and (2) for genetic differentiation among populations from different zones to be greater in the southern 

portion of western Montana than in the northern. 

Regression models accounted for only a portion of the 

variance among populations. However, a perfect fit of 

regression models to data cannot be expected even if all 

relevant independent variables could be assessed. High 

levels of genetic variability exist within populations 

regardless of geographic origin (Campbell 1979, Rehfeldt 

1979b). Natural sampling errors coupled with selection 

pressures that vary in time and space can account for 

random patterns of differentiation within single drainages 

(Rehfeldt 1974). Moreover, experimental errors, including 

sampling errors, can account for additional extraneous 

variance. Perhaps it is surprising that regression models 

accounted for as much as 72 percent of the variance 

among populations. 

Patterns of adaptive differentiation of forest trees 

determine the distance of seed transfer in reforestation 

for which maladaptation of planted trees is minimal. As 

proposed previously (Rehfeldt 1979a), Isd(0.2)/b [where 

Isd(0.2) = least significant difference among populations 

at the 80 percent level of probability, as estimated from 

analyses of variance, and b = regression coefficients 

from multiple regression models] estimates a geographic 

or elevational interval associated with differences among 

populations that are significant with a probability of about 

80 percent. These intervals (table 8) imply that seed zones 

for reforestation or tree improvement should be limited to 

about one degree latitude and 920 ft (280 m) elevation in 

the Bitterroot and western Clark Fork drainages; and by 

about 1.5 degrees latitude and 2,100 ft (650 m) elevation in 

the Flathead and eastern Clark Fork drainages. Or, as 

general guidelines, the transfer of seed from a single 

source should be within ± 460 ft (140 m) elevation and 

± 30 miles (50 km) north or south in the western physiographic zone, and within ± 1,050 ft (325 m) and ± 45 miles 

(75 km) in the eastern zone. 
Table B.-Geographic and elevational distances associated with mean differences among seed sources that correspond to a significance 

level of BO percent 

Western zone 

Trait Elevation Latitude 

Meters Degrees 

Bud burst 474 0.8 

Bud set 422 1.9 

Two flushes 359 1.5 

Height 278 11.4 

Growth rate 782 2.0 

One period 586 11.5 

Freezing injury 1 924 7.4 

PUBLICATIONS CITED 

Arno, s. F. Forest regions of Montana. Res. Pap. INT-218. 

Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Intermountain Forest and Range Experiment 

Station; 1979.39 p. 

Campbell, R. K. Genecology of Douglas-fir in a watershed 

in the Oregon Cascades. Ecology 60: 1036-1050; 1979. 

Campbell, R. K.; Franklin, J. F. A comparison of habitat 

type and elevation for seed zone classification of 

Douglas-fir in western Oregon. For. Sci. 27: 49-59; 1981. 

Campbell, R. K.; Sorensen, F. C. Effect of test environ· 

ment on expression of clines and on delimitation of 

seed zones in Douglas-fir. Theoretical and Applied 

Genetics 51: 233-246; 1978. 

Daubenmire, R.; Daubenmire, J. B. Forest vegetation of 

eastern Washington and northern Idaho. Tech. Bull. 60. 

Pullman, WA: Washington State University, Washington 

Agricultural Experiment Station; 1968. 104 p. 

Draper, N. R.; Smith, H. Applied regression analyses. New 

York: John Wiley and Sons; 1966.407 p. 

Levitt, J. Responses of plants to environmental stresses. 

New York: Academic Press; 1972.697 p. 

Pfister, R. D.; Kovalchik, B. L.; Arno, S. F.; Presby, R. C. 

Forest habitat types of Montana. Gen. Tech. Rep. 

INT-34. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and Range Experiment Station; 1977. 174 p. 

Rehfeldt, G. E. Local differentiation of populations of 

Rocky Mountain Douglas-fir. Can. J. For. Res. 4: 

399-406; 1974. 

8 

Eastern zone 

Elevation Latitude 

km Meters Degrees km 

94 2567 2.5 296 

222 1 195 2.3 266 

171 708 3.8 448 

1 337 656 1.3 149 

234 6578 2.0 229 

1 350 9928 3.5 414 

866 1 001 3.9 460 

Rehfeldt, G. E. Ecological adaptations in Douglas-fir 

(Pseudotsuga menziesii var. g/auca) populations. I. 

North Idaho and northeast Washington. Heredity 43: 

383-397; 1979a. 

Rehfeldt, G. E. Genetic differentiation of Douglas-fir populations from the northern Rocky Mountains. Ecology 

59: 1264-1270; 1979b. 

Rehfeldt, G. E. Patterns of first-year growth in populations 

of Douglas-fir (Pseudotsuga menziesii var. g/auca). Res. 

Note INT-255. Ogden, UT: U.S. Department of 

Agriculture, Forest Service, Intermountain Forest and 

Range Experiment Station; 1979c. 7 p. 

Rehfeldt, G. E. Variation in cold hardiness among populations of Pseudotsuga menziesii var. g/auca. Res. Pap. 

INT-233. U.S. Department of Agriculture, Forest Service, 

Intermountain Forest and Range Experiment Station; 

1979d. 11 p. 

Rehfeldt, G. E. Genetic gains from tree improvement of 

ponderosa pine in southern Idaho. Res. Pap. INT-263. 

Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Intermountain Forest and Range Experiment 

Station; 1980.9 p. 

Sorensen, F. C. Provenance variation in Pseudotsuga 

menziesii seedlings from the var. menziesii var. g/auca 

transition zone in Oregon. Silvae Genetica 28: 37-119; 

1979. 

Steele, R. G. D.; Torrie, J. H. Principles and procedures of 

statistics. New York: McGraw-Hili; 1960.481 p. 

Wright, J. W.; Kung, F. H.; Read, R. A.; Lemmine, W. A.; 

Bright, J. N. Genetic variation in Rocky Mountain 

Douglas-fir. Silvae Genetica 20: 54-60; 1971. 

-It u.s. GOVERNMENT PRINTING OFFICE: 1982-0-576-026/9 
Rehfeldt, Gerald E. Ecological adaptations in Douglas-fir populations. II. Western 

Montana. Res. Pap. INT-295. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Forest and- Range Experiment Station; 1982. 

8 p. 

Populations of Douglas-fir (Pseudotsuga menziesii var. g/auca) from Montana I 

west of the Continental Divide were compared in common environments. 

Differentiation was observed for six variables reflecting growth potential, 

phenology and cold hardiness. Adaptation of populations for numerous traits is 

viewed as a balance between selection of high growth potential in relatively mild 

environments and selection for cold hardiness in severe environments. Adaptive 

variation is described according to two physiographic zones, elevation within each 

zone, and latitude within zones. 

KEYWORDS: Douglas-fir, ecological genetics, growth potential, cold hardiness, 

phenology, tree improvement 
1 

The Intermountain Station, headquarted in Ogden, 

Utah, is one of eight regional experiment stations charged 

with providing scientific knowledge to help resource 

managers meet human needs and protect forest and range 

ecosystems. 

The Intermountain Station includes the States of 

Montana, Idaho, Utah, Nevada, and western Wyoming. 

About 231 million acres, or 85 percent, of the land area in 

the Station territory are classified as forest ~nd rangeland. 

These lands include grasslands, deserts, shrublands, alpine 

areas, and well-stocked forests. They supply fiber for 

forest industries; minerals for energy and industrial 

development; and water for domestic and industrial consumption. They also provide recreation opportunities for 

millions of visitors each year. 

Field programs and research work units of the Station 

are maintained in: 

Boise, Idaho 

Bozeman, Montana (in cooperation with 

Montana State University) 

Logan, Utah (in cooperation with Utah State 

U ni versi ty) 

Missoula, Montana (in cooperation with the 

University of Montana) 

Moscow, Idaho (in cooperation with the 

University of Idaho) 

Provo, Utah (in cooperation with Brigham 

Young University) 

Reno, Nevada (in cooperation with the University of Nevada)