Gradient analysis of vegetation on the north wall of the Columbia River Gorge, Washington

摘要

The Columbia River Gorge represents an ecocline of shifting environmental factors, species populations, and vegetation associations. Combinations of wind, temperature, and precipitation create different environmental regimes from the west to the east. The north wall of the Gorge supported four physiognomic associations: western conifer forest, central mixed forest, central broadleaf forest, and eastern steppe. Each association comprised species distributed individually along the ecocline. Douglas-fir, western redcedar, bigleaf maple, dull Oregongrape, sword fern, bracken, vine maple, and red bilberry were centered in the western conifer forest. Garry oak, ponderosa pine, poison oak, and snowberry were centered in the central mixed forest. Cheatgrass, northern buckwheat, Wyeth's lupine, western serviceberry, mockorange, and Sandberg's bluegrass were centered in the eastern steppe. Although the center of distribution for each species was in one of the associations, few were confined to a specific association. The Columbia River Gorge is analogous to a mountain turned on its side, with the cool, moist summit to the west and the warm, dry base to the east. Plant species have migrated both eastward and westward along this ecocline during the lifetime of the Gorge, and each association has combinations of species derived from surrounding regions in Washington and Oregon.