Ecological adaptations in Douglas-fir (Pseudotsuga menziesii var. glauca). IV. Montana and Idaho near the Continental Divide

Seventy-seven seedling populations of Douglas-fir (Pseudotsuga menziesii var. glauca) sampled from near the Continental Divide in Idaho and Montana exhibited pronounced genetic differences when compared in three common enwronments. Differentiation i volved several traits that are components of an annual developmental cycle that must be completed within a growing season of finite length. Consequently, the elevational and geographic dines of genetic variation tend to parallel variation in the length of the growing season at the seed source. Such clines uggest that maladaptation in artificial reforestation can be controlled by hmiting the transfer of seeds. While geographic transfers can be relatively liberal, elevational transfers hould be limited to -+90 m (300 ft) from the seed source at elevations below 1,400 m (4,600 ft), to -+125 m (410 ft) for elevations between 1,400 and 2,000 m (4,600 and 6,550 ft), and -+200 m (560 ft) for devations above 2,000 m (6,550 ft). West. J. Appl. For. 3(4):101-105, October 1988. bud development, lignification, and cold acclimation are sequential events that must be completed within the frost-free period. For populations within a species to differ in the timing and duration of•such events implies that natural selection has attuned the entire cycle to the local climate (Dietrichson 1964, Rehfeldt 1983a, Campbell 1986). Patterms of genetic variation in Douglas-fir thus parallel variation in the length of the growing season (Rehfeldt 1983b, Sorensen 1983, Campbell 1986), a period that is truncated by frost but often interrupted by drought. Patterns of adaptive variation are used to estimate the distance that seeds can be transferred before maladaptations begin limiting the productivity of artificial regeneration. This