Populations of Douglas-fir (Pseudotsuga menziesii var. glauca) from Montana 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.
Rehfeldt, Gerald E. 1982. 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. 8 p.