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

 that expected from the elevational regressions 



Variable 



Lower Snake 

 River 



Wasatch 

 Mountain 



Deadline 

 Ridge 



Growth and development 



Late growth (inches) 



Leaf length (inches) 



Height (inches) 



Adjusted height (inches) 



Frost injury (percent) 



Periodicity of shoot elongation 



Initiation (days) 



Duration (days) 

 Rate (inches/days) 



Cessation (days) 



Elongation (inches) 



Cold hardiness 



Injury (percent) 



-0.07 

 -.08 



-2.48 

 -.41 



-9.3 







-1.9 

 -.01 



-1.8 

 -.35 



-3.1 



-0.00 

 .05 

 -.71 

 -.86 



-8.7 



-.1 

 1.6 



-.01 

 1.6 



-.02 



-1.6 



0.07 

 .13 

 .57 

 1.27 

 -3.0 



.3 

 3.3 



.01 

 3.6 



.58 



5.1 



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 relati'/ely 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. 



PRECIPITATION, INCHES FROST-FREE DAYS 



Figure 5.— Geographic patterns in precipita- 

 tion and ttie frost-free period for ttie upper 

 Snal<e River Basin (from U.S. Department of 

 Commerce 1968). 



7 



