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INT. 356

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Ecological Genetics of
Pinus contorta in the
Upper Snake River
Basin of Eastern Idaho
and Wyoming

G. E. Rehfeldt

sqod?

THE AUTHOR

G. E. REHFELDT is a plant geneticist at the Inter-
mountain Research Station’s Forestry Sciences
Laboratory in Moscow, ID. He has been studying the
ecological and quantitative genetics of Rocky Mountain
conifers since 1968.

RESEARCH SUMMARY

Genetic differentiation of 60 populations of Pinus
contorta primarily from eastern Idaho and adjacent
Wyoming was assessed in three studies involving (1)
growth and development in field environments, (2) the
periodicity of shoot elongation in the greenhouse, and
(3) freezing tolerance in the laboratory. Genetic
differentiation between populations was observed for
traits that included 3-year height, leaf length, freezing
tolerance, and the pattern of shoot elongation. Regres-
sion models related as much as 83 percent of the vari-
ation between populations to the elevation and geo-
graphic location of the seed origin. Elevational clines
were particularly steep. Consequently, if maladaptation
is to be controlled in artificial reforestation, seed
transfer should be restricted severely for elevation but
geographically may be relatively liberal. Detailed prac-
tical guidelines will be presented separately.

Ecological Genetics of Pinus
contorta in the Upper Snake
River Basin of Eastern Idaho
and Wyoming

G. E. Rehfeldt

INTRODUCTION

Ecological genetics is devoted to exploring the ecologi-

cal bases for adaptive differentiation between popula-
tions. In lodgepole pine (Pinus contorta var. latifolia
Engelm.), differentiation of populations from both
Canada (Lindgren and others 1980; Hagner 1980; Ying
and others 1985) and the United States (Rehfeldt 1985b)
is related to the geographic origin and elevation of the
seed source. Adaptive clines, however, reflect environ-
mental gradients. As a result, clines in British Columbia
reflect the relatively gentle environmental gradients
associated with a region of dissected plateaus. But in

the rugged Rocky Mountains of the United States, adap-

tive clines tend to be steep for a variety of traits that
include growth potential, morphology, and cold hardi-
ness (Rehfeldt 1980, 1983), patterns of shoot elongation
(Rehfeldt and Wykoff 1981; Stoneman 1985; Rehfeldt
1985a), and resistance to insects and diseases (Hoff
1985). Regardless of geographic region, populations
appear as physiologicai specialists for relatively small
segments of the environmental gradient.

Figure 1.—Geographic distribution of
Pinus contorta (shading according to
Little 1971) within the region of study
and location of populations.

Steep adaptive clines have direct relevance to forest
management. Artificial reforestation carries the implicit
goal of maximizing productivity while maintaining
adaptedness. Steep clines require that seed for reforesta-
tion be transferred only short distances along the
environmental gradient if maladaptation and resultant
losses in productivity are to be controlled.

The present study is part of a series that (1) examines
adaptive variation between lodgepole pine populations,
(2) relates patterns of variation to geography, topogra-
phy, physiography, and climate, and (3) develops seed
transfer guidelines for reforestation.

MATERIALS AND METHODS

The study of population differentiation included seed-
lings from 60 populations, 51 of which represented the
geographic distribution and ecologic amplitude of the
species in the upper Snake River Basin (fig. 1). Addi-
tional populations from peripheral areas provided a link
to other studies in this series: four were from the
Wasatch Mountains of Utah and southeastern Idaho;

MONTANA

three were from the lower Snake River basin of central
Idaho; and two were from a small disjunct population
from Deadline Ridge in south-central Idaho (fig. 1). Seed-
lings from the 60 populations were used in separate
studies of (1) growth and development in field environ-
ments, (2) periodicity of shoot elongation in a green-
house, and (3) cold hardiness in the laboratory. Because
cone collections, experimental procedures, and statistical
analyses are detailed in the first paper of this series,
which involved populations from the Wasatch and Uinta
Mountains of Utah (Rehfeldt 1985a), only an outline of
these procedures follows.

Growth and Development

One set of seedlings from each of the 60 populations
grew for 6 months in plastic containers (10 in’) in a
shadehouse at Moscow, ID (lat. 48.5° N., long. 116.7°
W.). In the fall, seedlings were transplanted into two
environments, 2,200 and 5,000 feet elevation, at the
Priest River Experimental Forest, 150 miles north of
Moscow. Eight seedlings, spaced at 1.0 foot and 0.5 foot
at low and high elevation sites, respectively, were
planted in row plots, separated by 1.5 feet and 1.0 foot
at the respective sites. Three blocks were established at
each site, and both plantings were maintained under
intensive culture.

The performance of each seedling was described by
four variables for which differentiation of Utah popula-
tions had been pronounced: (1) height—seedling height
after 3 years; (2) late growth—amount of the 3-year
predetermined shoot that elongated after the fourth
week of elongation in the respective environments;

(3) leaf length—the length of a leaf near the center of the
3-year shoot; and (4) adjusted height—3-year height
adjusted by regression on 2-year height. By representing
the increment from a common 2-year height, adjusted
height is relatively independent of previous environmen-
tal (such as transplanting shock) and genetic effects and
thereby is capable of reflecting adaptation of populations
to a particular environment for a single growing season.

In addition, scores were made for the presence or
absence of injury from a freeze (16 °F) that occurred in
mid-May at the low-elevation site. Injuries ranged from
death of the developing shoot to reductions in internode
lengths near the shoot tip.

To account for heterogeneous variances at the two test
environments, data were transformed to standard normal
deviates (Steel and Torrie 1960) for each test site and
the deviates were analyzed according to a model of ran-
dom effects. The model estimated: (1) main effects for
test environments, blocks within environments, and
populations; (2) the interaction of populations X environ-
ments; (3) an experimental error, composed of the inter-
action of populations X blocks within environments; and
(4) a residual error. As a result of the transformations,
mean squares associated with the main effects of test
environments were zero. A harmonic mean of 7.20
reflected the number of seedlings representing each
population in each block.

Injury from the spring frost was analyzed according
to a model of random effects, which estimated main
effects for blocks and populations, plus an error.

Periodicity of Shoot Elongation

Another set of seedlings grew for 1 year in plastic con-
tainers (45 in*) in a shadehouse at Moscow. Nine seed-
lings from each population grew in each of three blocks.
In early March of the second growing season, seedlings
were moved into a greenhouse before shoot elongation
had begun. Greenhouses were maintained under natural
lighting; temperatures were about 75 °F during the day
and 55 °F at night. All seedlings were measured three
times each week until elongation of the preformed bud
had ceased.

As described by Rehfeldt and Wykoff (1981), shoot
elongation of individual trees was expressed mathemati-
cally by a logistic function that included a hyperbolic
time term. Regression statistics allowed calculation of
the following variables for describing periodicity of shoot
elongation of individual seedlings: (1) initiation of
growth—the day on which 0.1 inch of cumulative growth
had occurred; (2) cessation of growth—the day on which
all but 0.1 inch of growth had occurred; (3) duration of
growth—the number of days between initiation and ces-
sation; (4) rate of growth—elongation per day during the
period of maximum elongation; and (5) total elongation.

Population differentiation was assessed according to
least squares analyses of random effects that estimated
main effects for populations and blocks, the interaction
of populations X blocks, and an error. A harmonic mean
of 8.81 reflected the number of seedlings representing
each population in each block.

Cold Hardiness

To estimate the relative cold hardiness of populations
in early autumn, laboratory tests of freezing tolerance
were made according to the general procedures of Levitt
(1972). Mature leaves were collected in late September
from near the center of the 3-year shoot of trees planted
at 5,000 feet elevation in the study of growth and
development.

Four sets of eight leaves were collected from each
eight-tree plot; each set contained one leaf from each
tree. One set of leaves from each plot was exposed to
one of four test temperatures (—4 °F,—6 °F,—10 °F,
and—12 °F) by cooling at the rate of 10 °F/h. Injured
leaves were identified visually by the presence of dis-
colored and flaccid tissue (Rehfeldt 1980). Population
differentiation for the proportion of injured leaves from
each plot was assessed from a model of random effects
that allowed estimation of main effects for populations,
blocks, and test temperatures; three two-way interac-
tions; and a residual.

Patterns of Variation

Geographic patterns of genetic variation were assessed
from a series of regression analyses that fit independent
variables describing the origin of populations to the
array of population means. Because the primary purpose
of these analyses was to describe genetic patterns of
variation for the upper Snake River Basin, regression
analyses considered only the 51 representative popula-
tions. The sequence of regression analyses concentrated
first on the relationship between performance and eleva-

tion of the seed source, and second on geographic pat-
terns of variation that were independent of elevation.
Adequacy of a model was judged according to the good-
ness of fit (R*), residual variance (s,.,), and geographic or
ecologic patterns displayed by residuals (Draper and
Smith 1966).

Elevational models considered both a linear and quad-
ratic relationship between performance and elevation of
the seed source. Deviations from the best fitting eleva-
tional regressions were then used as dependent variables
for considering geographic patterns of variation that
were independent of elevation. The geographic model
included four independent variables, plus their squares:
latitude, longitude, northwest departure, and northeast
departure. The latter two variables were obtained by
rotating the grid of latitude and longitude by 45°. Thus,
eight independent variables were included in the model,
which was fit with a stepwise regression program for
maximizing R? (Barr and others 1979). Finally, for those
variables in which both the elevational and geographic
models had been significant, elevation of the seed source
was added to the independent variables of the best fit-
ting geographic model in order to estimate the joint
determination of performance by geography and
elevation.

RESULTS

Because each study was autonomous, the results of
each are presented separately but are considered jointly
in establishing patterns of genetic variation.

Growth and Development

The effects of planting environment on growth and
development of seedlings were pronounced for all traits
(table 1). Compared to trees growing at high elevation,
trees at low elevation were much taller and had longer
leaves. In addition, late growth, defined as the propor-
tion of the predetermined shoot that elongated after the
fourth week, was measured approximately 5 weeks
earlier at low elevation than at high and therefore was
affected tremendously by the environment. Adjusted
heights show that even if all trees had been the same
height at age 2, those growing at low elevation would
still have been tallest after 3 years.

For nearly all variables, the range in population mean
values was considerably different at the two planting
environments (table 1). For these ranges to differ greatly
illustrates the heterogeneous variances that required
adjustment before statistical analyses were made.

By accounting for more than 20 percent of the total
variance, effects of populations were pronounced for
3-year height and injury from a spring frost (table 2).
These strong effects are illustrated by mean differences
between populations of as much as 0.8 foot in height
and 50 percent in trees injured by frost. On the average,
trees damaged by frost were 3.2 inches shorter after
3 years than uninjured trees from the same population.
Relatively weak effects for late growth are likely due to
the relatively late stage of elongation at which measure-
ments were begun: the average tree produced only 10
percent of the 3-year shoot as late growth. Consequently,

Table 1.—Mean values according to test environment and range of population

means in each environment

Mean values

Range in population means

Variable 2,200 ft 1,500 ft 2,200 ft 5,000 ft
Late growth (inches) et 0.7 0.8 0.4
Leaf length (inches) 2.9 2.7 1.1 0.8
Height (inches) 17.1 13.9 12.2 5.8
Adjusted height (inches) 16.2 14.7 5.7 1.8
Frost injury (percent) 22 — 56 —

Table 2.—Results of analyses of variance for growth and development
presented as intraclass correlations, the ratio of individual

variance components to the sum of all components

Frost
injury

Variable

Source of Late Leaf Adjusted
variance growth length Height height
Environments 0 0 0 0
Blocks in

environment 0.03** 0 0.02** 0
Populations .06** 0.08** eshte 0.02*
Environment x

population 0 .02 01 1092”.
Experimental O70"? 07 03** OA ter

error
Within plots 84 83 Roy 84

“Statistical significance of the F-value at the 5 percent level of probability.
**Statistical significance of the F-value at the 1 percent level of probability.

mean values for populations ranged from only 0.7 to 1.2
inches. Significant effects of populations in leaf length
reflected mean differences as large as 0.8 inch. And
finally, the significant effects of populations for adjusted
height show that populations would have differed in
3-year height even if all trees had been the same height
at age 2, even though 2-year height accounted for 64
percent of the variance in 3-year height of individual
trees.

Significant interactions of populations and environ-
ments were detected only for adjusted height; conse-
quently, main effects for this variable were significant
with a rather low level of probability (table 2). The inter-
action was caused by (1) a lack of differences between
populations in the environment at high elevation, com-
bined with (2) statistically detectable differences at low
elevation. Consequently, subsequent analyses for
adjusted height use only those data from the low-
elevation site.

Periodicity of Shoot Elongation

The logistic function described periodicity of shoot
elongation of individual trees nearly perfectly. Values of
R* ranged from 0.94 to essentially 1.0 while averaging
0.99. Analyses of variance detected strong effects of
populations for duration, rate, cessation, and amount of
shoot elongation (table 3). These effects accounted for 21
to 38 percent of the total variance and are illustrated in
figure 2. Differences between populations were as large
as 15 days in cessation, 16 days in duration, 0.1
inch/day in rate, and 3.4 inches in the amount of elonga-
tion. Populations differed by only 0.8 day in the initia-
tion of shoot elongation, and, consequently, no differ-
ences could be detected statistically.

Cold Hardiness

Effects of test temperatures dominated analyses of
variance (table 4). These effects are associated with a
range in injury from 36 percent at —4 °F to 78 percent
at —12 °F. Effects of populations were significant but
accounted for only 5 percent of the total variance. Mean
differences between populations amounted to as much as
55 percent injury.

Table 3.—Results of analyses of variance for periodicity of shoot

pososon== 5440

Cd
o*

eoee==7350

8000

==='8690
o"

ELONGATION, IN

fe) 10 20 30 40 50
DAYS
Figure 2.—Periodicity of shoot elongation for
populations from a range of elevations (feet)
that represented maximum differences in
response.

Patterns of Variation

Elevation of the seed source had a pronounced effect
on population performance (table 5, fig. 3). Elevational
models accounted for more than 70 percent of the vari-
ance between populations for five variables and were
statistically significant for all variables except the initia-
tion of shoot elongation. As elevation increases, growth
potential decreases, largely because of an associated
decline in late growth and in the rate, duration, and ces-
sation of shoot elongation. Leaf lengths also decline with

elongation presented as intraclass correlations, the ratio of a

variance component to the sum of all components

Source of

variance Initiation Duration Rate Cessation Elongation
Blocks O:110"* 0.04** OL03e* 0 0.01
Populations 02 sophie! Bl pes O23%= oOtns
Interaction "1533 0 .06 0: O35
Within plots w3 eS. 70 ATATE 58

“Statistical significance of the F-value at the 5 percent level.
**Statistical significance of the F-value at the 1 percent level.

Table 4.—Results of analyses of variance of freezing tests
presented as intraclass correlations, the ratio of a
variance component to the sum of all components

Source of Intraclass

variance correlation
Blocks 0.06*
Temperatures les
Populations 1050"
Populations x temperatures 0
Residual! .68

*Statistical significance of the F-value at the 5 percent level.
**Statistical significance of the F-value at the 1 percent level.
1Composed of the interactions involving blocks.

Table 5.—Coefficients of determination (R2) for regression analyses relating genetic
variation to geographic and physiographic variables

Elevational model Geographic Combined

Variable Linear Quadratic model model
Growth and development

Late growth 0.26** 0.27** 0.04

Leaf length so2n Se ag 26" 0.49**

Height tQF* 0** .24* 18"*

Adjusted height (2,200 ft) ‘50** 53** ei ale .66**

Frost injury at" * 22 0 =
Periodicity of shoot elongation

Duration Sala 4** 3" 63°"

Rate tae 4** .09 —

Cessation BAtlas ie4e* .29* .80**

Elongation 1B"? WY AS aad 19 —
Cold hardiness

Injury Agi 13" 33"* .43**

*Statistical significance at the 5 percent level of probability.
**Statistical significance at the 1 percent level of probability.

CESSATION OF
ELONGATION

DAYS

1.2 LATE GROWTH

INCHES

Figure 3.—Population means for four variables
plotted by elevation of the seed source. Symbols
code geographic origins: ® = Upper Snake River
Basin; O = Lower Snake River, ® = Wasatch
Mountains, & = Deadline Ridge.

5900 7200 8500

21 3-YR HEIGHT

18
wn”
Ww
5
2 15
12
0.25; e RATE OF
ELONGATION
>
<q
=
>= -20
Ww
=
oO
z

5900 7200 8500

ELEVATION OF SEED SOURCE, IN

increasing elevation of the seed source, but freezing DURATION OF ELONGATION LEAF LENGTH
tolerance increases. The strong relationship between ele-
vation and adjusted height indicates that, at the low
elevational planting, populations from mild environments
still would have been tallest even if all trees had been
the same height at age 2. Quadratic models provided a
significant reduction in the residual mean square of the
linear model for only the cessation and duration of
elongation.

The geographic model (table 5) was statistically signifi-
cant for only half of the variables. At most, this model
accounted for less than a third of the variance in the
dependent variables that was not explained by elevation.
Consequently, geography accounted for less than 25 per-
cent of the variance among populations. Thus, eleva-
tional clines tend to be steep, and geographic clines are
relatively gentle. Nevertheless, geographic variables plus
elevation (the combined model) accounted for 43 to 83
percent of the variance of populations.

Geographic patterns of genetic variation that are
independent of elevation are presented in figure 4 for
several traits. These patterns were generated from
values predicted by the geographic model. The contour
interval is scaled to a value equaling half the least sig-
nificant difference (Steel and Torrie 1960) between popu-
lations at the 80 percent level of probability [2 /sd(0.2)].
Because values of /sd were calculated from the analysis
of variance (table 2), contours represent about half the
geographical distance associated with population
differentiation at the 80 percent level of probability.
Contouring was begun with the overall mean, the zero
deviation from the elevational regression.

All variables for which the geographic model was sig-
nificant presented similar patterns of genetic variation.

Ci=0.9 DAYS Ci=0.08 INCHES

3-YEAR HEIGHT FREEZING INJURY

Those variables selected for figure 4 illustrate patterns ChE OA TSINCBES ee

of greatest divergence. In general, populations in the Figure 4.—Geographic patterns of variation
west-central regions are of highest growth potential and that are independent of elevation. Shading
lowest hardiness. From this area, growth potential marks the distribution of lodgepole pine in
decreases and hardiness increases in all directions. The reference to the Teton Range. C.|. = the con-
general pattern, however, is influenced greatly by the tour interval, which is scaled to a value of
rugged Teton Range. Populations of relatively high Y2\sd(0.2). The zero contour represents the

mean of all populations standardized for

growth potential and low hardiness extend into the
elevation.

Table 6.—Correlation matrix relating population means for all studies’

Variable Code LL H AH FI I D R Cc EL IN
Growth and development
Late growth LG 0.56 0.68 0.61 0.34 —0.24 0.54 0.61 0.53 0.61 0.13
Leaf length LL 62 +53 .33 —.27 62 59 62 64 21
Height H 81 56 —.21 84 87 85 90 36
Adjusted height (2,200 ft) AH 44 — .32 atl 71 70 =(hs) .20
Frost injury Fl .08 42 43 43 44 Xf
Periodicity of shoot elongation
Initiation | —.33 — .23 —.27 —.31 10
Duration D 84 .99 93 27
Rate R .84 97 40
Cessation Cc .93 28
Elongation EL i
Cold hardiness
Injury IN

‘Coefficients of absolute value >0.27 are statistically significant at the 5 percent level.

6

Table 7.—Average difference between the observed performance of peripheral populations and

that expected from the elevational regressions

Lower Snake Wasatch Deadline

Variable River Mountain Ridge
Growth and development

Late growth (inches) —0.07 —0.00 —0.07

Leaf length (inches) — .08 .05 13

Height (inches) — 2.48 —.71 57

Adjusted height (inches) -—.41 — .86 1.27

Frost injury (percent) -9.3 —8.7 —3.0
Periodicity of shoot elongation

Initiation (days) 0 —.1 “3

Duration (days) —1.9 1.6 3.3

Rate (inches/days) —.01 —.01 01

Cessation (days) -1.8 1.6 3.6

Elongation (inches) — .35 —.02 58
Cold hardiness

Injury (percent) —3.1 —1.6 Sat

drainages east of the Tetons. Significant intercorrela-
tions between variables (table 6) produce the similar
elevational and geographic clines. Particularly note-
worthy are the correlations among variables associated
with growth potential. Whether measured in the field or
greenhouse, these correlations were extremely strong

(r >0.8).

The performance of populations from geographic
regions peripheral to the region of study is presented in
table 7, relative to that expected for populations from
the upper Snake River drainage at similar elevations.
Populations from the Wasatch Mountains are of slightly
lesser growth potential and slightly higher hardiness
than populations from the upper Snake. But, the popula-
tions tested from the lower Snake were of considerably
lesser growth potential and higher hardiness than those
from the upper Snake. However, disjunct populations
from Deadline Ridge are of higher growth potential and
lesser hardiness than populations from similar elevations
in the upper Snake.

DISCUSSION

Genetic differentiation between populations from the
upper Snake River Basin, like that for populations from
northern Idaho (Rehfeldt 1983), Utah (Rehfeldt 1985a),
and Oregon (Stoneman 1985), occurs along relatively
steep clines. Differentiation was detected for a variety of
traits, most of which were intercorrelated. Strong inter-
correlation of adaptive traits results from either or both
genetic linkage and parallel selection. Regardless, coher-
ence (Clausen and Hiesey 1960) typifies the system of
genetic variability for a species such as lodgepole pine
that is physiologically specialized for specific environ-
ments. Populations from mild environments display a
high growth potential and relatively low hardiness; popu-
lations from severe environments express high hardiness
and low growth potential. Adaptation can be viewed as a
balance between selection for high growth potential in
mild environments and selection for high cold hardiness
in severe environments.

Adaptive clines parallel environmental gradients.
Temperatures and frost-free periods sharply decrease as
elevation increases. Consequently, elevational clines are
steep. On the average, populations separated by 3,000
feet elevation are expected to differ, for example, by 42
percent in 3-year height, by 20 percent in both spring
and fall frost injury, and by 0.3 inch in leaf length.

A comparison of figures 4 and 5 shows that geo-
graphic patterns of genetic variation closely parallel
environmental gradients in temperature but are poorly
related to precipitation gradients. In fact, the geographic
patterns presented in figure 4 nearly duplicate the
environmental gradients represented by the length of the
frost-free period (fig. 5). Patterns of genetic variation
that arc to the east of the rugged Teton Range respond
to the relatively mild climates that also extend east of
this mountain range.

FROST-FREE DAYS

PRECIPITATION, INCHES

Figure 5.—Geographic patterns in precipita-
tion and the frost-free period for the upper
Snake River Basin (from U.S. Department of
Commerce 1968).

Elevational clines are much steeper than the geo-
graphic. A comparison of these clines can be made by
noting that in figure 4, each geographic band, situated
between any two contours, is standardized for elevation.
Each band is equivalent to the amount of genetic
differentiation that occurs across 302 feet elevation for
3-year height, 315 feet for duration of elongation, 935
feet for leaf length, and 1,377 feet for fall freezing
injury, respectively. Thus, in a region approximately 200
miles from north to south, the geographic clines (fig. 4)
in those variables for which population differentiation
was pronounced (table 5) are equivalent to the genetic
differentiation that occurs within about 1,000 feet eleva-
tion at a single locality.

Patterns of adaptive variation between populations
have direct implications in forest management. To limit
maladaptation in planted trees, seed transfer guidelines
must reflect adaptive variation. One estimate of an
appropriate limit to seed transfer involves the smallest
geographic or elevational interval across which differenti-
ation can be detected (Rehfeldt 1979). This interval is
estimated by the ratio /sd(0.2)/b, where b is the regres-
sion coefficient and /sd(0.2) is derived from the analysis
of variance as the least significant difference between
population means at the 80 percent level of probability.
(A rather low level of probability is used to avoid accept-
ing no differences when differences actually exist.)

Elevational intervals associated with /sd(0.2) include,
for example, 604 feet for 3-year height, 738 feet for rate
of elongation, 1,788 feet for late growth, and 2,752 feet
for injury from fall freezing. These intervals suggest
that the maximum elevational limits for biologically
sound seed zones should not be much greater than 600
feet. This means that the transfer of seed from a single
source should be limited to +300 feet. Nevertheless, con-

siderable genetic differentiation occurs across seed zones
that occupy only 600 feet. These differences, for
instance, amount to 9 percent in 3-year height and 5 per-
cent in susceptibility to injury from the cold. Therefore,
transfers of seeds beyond these limits can result in con-
siderable productive losses in artificial reforestation.

Geographic patterns of variation (fig. 4) were scaled to
a value of 2 Isd(0.2), and therefore lateral transfers of
seed should be limited to about +1 contour. This means
that two geographic zones are sufficient for the upper
Snake River Basin.

The appropriate size of seed zones should be practical
operationally and economically. Thus, limits to seed
transfer must accommodate biology, operational feasibil-
ity, and economics. When, however, administration
demands an alteration in the guidelines proposed above,
it should be remembered that each geographic band in
figure 4 is equivalent genetically to a relatively small
elevational interval within a band. Consequently, the
geographic limits should be compromised. From the bio-
logical viewpoint, seed zones for the upper Snake River
Basin should be considered as elevational zones with
geographic stratification.

Regardless, populations of lodgepole pine from the
drainages of the upper Snake River display patterns of
genetic variation that typify the adaptation of the spe-
cies to heterogeneous environments in other geographic
localities. Populations appear to be physiologically
attuned to specific environments, clines are steep, and
genetic differences occur across relatively small environ-
mental intervals. Differentiation between populations is
easy to detect experimentally and is closely related to
geography and elevation of the seed origin. Therefore,
seed transfer in artificial reforestation should be greatly
limited.

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U.S. GOVERNMENT PRINTING OFFICE: 1985-0-676-039/20030

Rehfeldt, G. E. Ecological genetics of Pinus contorta in the upper Snake River
Basin of eastern Idaho and Wyoming. Research Paper INT-356. Ogden, UT:
U.S. Department of Agriculture, Forest Service, Intermountain Research
Station; 1986. 9 p.

Genetic differentiation of 60 populations of Pinus contorta primarily from
eastern Idaho and western Wyoming was studied in field, greenhouse, and
laboratory tests. Analyses of variables reflecting growth potential, morphology,
cold hardiness, and periodicity of shoot elongation revealed population differen-
tiation for a variety of traits. Regression models related as much as 83 percent
of the variance of population means to the elevation and geographic location of
the seed source. For genetic variation to be arranged along relatively steep
environmental clines implies pronounced adaptive differentiation. As a result,
seed transfer in reforestation should be restricted severely if maladaptation is
to be controlled.

KEYWORDS: microevolution, adaptation, population differentiation, seed zones,
seed transfer

INTERMOUNTAIN RESEARCH STATION

The Intermountain Research Station provides scientific knowledge and
technology to improve management, protection, and use of the forests and
rangelands of the Intermountain West. Research is designed to meet the
needs of National Forest managers, Federal and State agencies, industry,
academic institutions, public and private organizations, and individuals.
Results of research are made available through publications, symposia,
workshops, training sessions, and personal contacts.

The Intermountain Research Station territory includes Montana, Idaho,
Utah, Nevada, and western Wyoming. Eighty-five percent of the lands in
the Station area, about 231 million acres, are classified as forest or range-
land. They include grasslands, deserts, shrublands, alpine areas, and
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energy and industrial development, water for domestic and industrial con-
sumption, forage for livestock and wildlife, and recreation opportunities for
millions of visitors.

Several Station units conduct research in additional western States, or
have missions that are national or international in scope.

Station laboratories are located in:

Boise, Idaho

Bozeman, Montana (in cooperation with Montana State University)
Logan, Utah (in cooperation with Utah State University)

Missoula, Montana (in cooperation with the University of Montana)
Moscow, Idaho (in cooperation with the University of Idaho)
Ogden, Utah

Provo, Utah (in cooperation with Brigham Young University)

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