Environment

The Boise Area from a Biologist’s Perspective

Of the eight ecoregions encountered in Idaho, five are within a day’s drive of Boise. The city itself is situated in the Snake River Basin / High Desert region. This area is characterized by flat bottomland plains leading into gently rolling foothills (2500 to 5000 feet above sea level). Average rainfall in this area is between 8-15 inches per year. This domain is drained primarily by intermittent, ephemeral, and small perennial streams (at high elevations) coalescing into the Boise River (on the plain). Sagebrush steppe dominates the region, with cottonwood, alder, and willow lining the riparian areas along the Boise River. The river itself is impounded upstream of Boise, forming Lucky Peak, Arrowrock, and Anderson Ranch Reservoirs.

In a 2-3 hour drive to northeast, the Northern Rocky Mountain ecoregion begins. Rugged high mountains are the dominant feature. These mountains have sharply-crested ridges and steep slopes cut by steep-walled, narrow stream valleys. Elevation varies from 1300 to 8000 feet. Conifers include Douglas fir, subalpine fir, Englemann spruce, western hemlock, and western larch; Ponderosa pine is found in lower areas. Shrubs, forbs, and grasses represent forest understory vegetation. Perennial and ephemeral streams are usually high gradient and fast flowing. Stream density can range from less than one to as many as three miles of perennial stream flow per square mile. Lakes are common in higher glaciated areas. Both the Boise and Payette National Forests lie within part of this area. Timber harvest is the major economy, but wildlife habitat, recreation and mining are also important land uses. The multiple use of these forests provide diverse habitat types for scientific study.

In a 3-4 hour drive to the northwest, the Blue Mountains ecoregion begins. This region is comprised of several mountain ranges (Blue, Ochoco, Wallowa, Strawberry, Aldrich) separated by fault valleys and synclinal basins. Elevation varies from 2700 feet in low lying valleys to 7000-10,000 feet on mountain peaks. Rainfall averages 10 to 20 inches annually in lower valleys and basins, and greater than 40 inches in the mountains. Stream drainage density varies from one and a half to two miles of perennial streams per square mile in wetter areas, to no perennial stream flow in drier areas. Numerous springs are scattered throughout the region, and a few clusters of alpine glacial lakes occur in the higher mountains. The mountainous portions of the region support forests of grand fir, Douglas fir, ponderosa pine, and Englemann spruce. Stands of larch and lodgepole pine also occur. At lower elevation areas and foothills support large tracts of sagebrush/wheatgrass steppe and wheatgrass/bluegrass grasslands.

To the southwest of Boise lies the arid High Desert ecoregion. This area is characterized by smooth, flat topography occasionally dissected by lava and basalt plains and sand dunes giving way to the Owyhee Mountains. Large tracts of saltbush/greasewood, sagebrush, and wheatgrass vegetation occur throughout the region and along the streams due to their intermittent and ephemeral nature.

To the southeast of Boise begins the Northern Basin and Range ecoregion marking the start of the Great Basin Region. This region consists of numerous sub-basins and mountain ranges which present an extremely diverse physical setting. Surface water of the Basin include perennial, intermittent, and ephemeral streams; freshwater and saline lakes; playa lakes; freshwater and saline wetlands and thermal springs associated with faulting and volcanic activity.

Finally, in a day’s drive due east, the middle Rockies ecoregion is encountered. Within this region Yellowstone and Grand Teton National Parks occur.