Figure 4 — Geographic patterns that are independent of elevation 

 as predicted by regression models. Patterns are relative to the 

 distribution of the species (shading), the Bitterroot Range, and 

 the Salmon River. Isopleths are positioned relative to the mean 

 value (x) with an interval scaled to V2/sd (0.05). 



of relatively equal predicted performance for the mean 

 elevation (1,625 m). Contouring was begun with the mean 

 value, and the interval between isopleths was scaled to 

 Vzlsd (.05). Thus, populations separated by two isopleths 

 are expected to differ at about the 95 percent level of 

 probability. The pattern for late growth duplicates that of 

 7-year height and is not presented. 



When comparing populations from the same elevation, 

 those from the north were the tallest and had the most 

 late growth; populations from central Idaho were the 

 shortest and exhibited httle late growth. The percentage 

 of trees infected with needle cast or infested with mites 

 was directly related to the geographic distance that the 

 seed was transferred to the planting site. Populations of 

 highest adjusted heights at Lost Valley (1,500 m) tended 

 to be from the north where growth potentials were 

 highest. 



DISCUSSION 



The results illustrate differentiation of populations for 

 numerous traits which together determine adaptedness, 

 the degree by which populations are physiologically at- 

 tuned to their environment. Genetic differentiation was 

 readily detected experimentally, and patterns of genetic 

 variation were closely associated with the elevation and 

 geographic location of the seed source. Pronounced clines 

 tend to typify genetic differentiation in montane popula- 

 tions of P. contorta spp. latifolia (Ying and others 1985; 

 Rehfeldt 1983a, 1985a; Stoneman 1985). 



That the clines reflect adaptation to natural environ- 

 ments is demonstrated both directly, as differential fitnesi 

 in contrasting environments, and indirectly, as genetic 

 responses that parallel environmental gradients. Thus, in- 

 direct support is provided by the steep elevational clines 



7 



