Geographic Variation in Seedling Douglas‐Fir (Pseudotsuga Menziesii) from the Western Siskiyou Mountains of Oregon

Patterns of geographic variation for seed and seedling traits of Douglas—fir from four elevations on west and east aspects of first and second ridges away from the ocean (latitude °42°30'N) were observed under two air—temperature regimes in a common garden. Size and germination rate were recorded for seeds; phenological and size data were recorded on seedlings through two growing seasons. The pattern of genetic variation appeared to be determined by adaptation to local moisture and temperature regimes. In east—west comparisons (inland ridge vs. coastal ridge or east aspect vs. west aspect), seeds of east aspect or inland origin were larger and germinated more rapidly than seeds of more westerly origin. Similarly, plants of inland origin or from east aspects tended to start and end elongation earlier and have smaller top : root ratios, compared to plants from the coastal ridge or west aspects. Genetic differences were generally greater between the west and east aspects of the coastal ridge than between the two aspects of the inland ridge. Variation in data of bud set and plant size was also related to elevation. The change associated with elevation was greater on the coastal ridge than on the inland ridge. Evidence is presented that indicates length of growing season and heat accumulation may change more with elevation and latitude near the ocean than inland in the Pacific Northwest. This in turn may result in steeper elevational and latitudinal gradients of genetically based variability near the ocean than inland.