Temperature inversions, frequent in upland areas in winter, result in warmer temperatures on lower slopes than in bottom lands. The undergrowth is dense shrubbery formed by green and thinleaf alder, willow, dogwood, and berries. The outer valley edges support evergreen and coniferous forests, often with pure stands of black spruce. The undergrowth consists of willow, dwarf birch, crowberry, fern, blueberry, lichens, and mosses. Pure stands of white spruce grow near streams.
Typical undergrowth includes willow, alder, fern, berries, grasses, and mosses.
Root systems are shallow. Water balance is likely the factor limiting growth in most of these areas because of the hot, dry summer climate. Old river terraces, ponds, and sloughs contain scattered but extensive bogs where the vegetation is chiefly sphagnum and other mosses, sedges, bog rosemary, and Labrador-tea. Marginal areas may support willow and alder. Permafrost is discontinuous in major river valleys.