An estimated 76 percent of Boise National Forest is forest, which according to the Forest Service is considered land capable of supporting trees on at least 50 percent of its area. The forests are primarily coniferous evergreens, dominated by Douglas fir and ponderosa and lodgepole pines at lower elevations and Engelmann spruce, subalpine fir, and whitebark pine at higher elevations. Grand fir and western larch (a coniferous deciduous tree) grow in the northern part of the forest where there are moister conditions. Quaking aspen, a broadleaf deciduous tree, grows both in stands among conifers and in monotypic stands throughout the forest at elevations above . Non-forested areas occupy 23 percent of the forest, primarily on south-facing slopes, lower elevations in the forest's southern latitudes, or high-elevation areas and are dominated by grasses, forbs, or shrubs.