 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 <unk> , dominated by Douglas fir and ponderosa and lodgepole pines at lower elevations and Engelmann spruce , subalpine fir , and <unk> pine at higher elevations . Grand fir and western <unk> ( a coniferous deciduous tree ) grow in the northern part of the forest where there are moister conditions . <unk> <unk> , a broadleaf deciduous tree , grows both in stands among conifers and in monotypic stands throughout the forest at elevations above 5 @,@ 000 feet ( 1 @,@ 500 m ) . 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 . 
