Our focus is on the Pacific Northwest and Intermountain Region including the Great Basin, Columbia Plateau, Colorado Plateau, and surrounding areas. The climate of this large, arid to semiarid region is defined by generally low and highly variable precipitation. Much of the yearly precipitation arrives as winter snow because most of the moisture comes as frontal storms in winter instead of convective storms in summer. Strong gradients in both temperature and precipitation exist with mountainous areas receiving as much as 127 cm (50 inches) of precipitation a year, and lower elevation cold deserts receiving only about 13 to 18 cm (5 to 7 inches). The distribution of both species and vegetation communities is determined by these gradients. At low to mid-elevations, cold desert vegetation dominates including salt desert shrub, sagebrush steppe and sagebrush semiarid desert, and pinyon and juniper woodlands. At the periphery of the cold deserts and on mountain ranges, diverse forest types occur, including pines, firs, and spruce. Riparian areas, aspen ecosystems, and inter-basin forests dominated by drought-tolerant pines comprise smaller land areas, but support much of the region's biodiversity.