The Idaho Batholith ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) in the U.S. states of Idaho and Montana. It is contained within the following biomes (or major habitat types) designated by the World Wild Fund for Nature (WWF): temperate coniferous forests; temperate grasslands, savannas, and shrublands; and deserts and xeric shrublands.
Setting
The Idaho batholith ecoregion is bordered on the north by the Northern Rockies, on the east by the Middle Rockies, on the south by the Snake River Plain, on the west by the Blue Mountains, and partially on the northwest by the Columbia Plateau. It has been subdivided into eleven Level IV ecoregions in Idaho and Montana. As defined by the EPA, ecoregions are, "Areas of similarity regarding patterns in the mosaic of abiotic and biotic, aquatic and terrestrial ecosystem components, including geology, physiography, vegetation, climate, soils, hydrology, land use, and wildlife, with humans being considered as part of the biota."
The ecoregion is found within the Nearctic realm as designated by WWF, which covers most of North America. Realms are the broadest way of breaking up the Earth's land surface biogeographically. Realms characterize large amounts of habitat that contain organisms that have been evolving together in relative isolation for long time periods.
The most prevalent geological feature in this ecoregion is its namesake, the Idaho batholith. A batholith is a body of intrusive igneous rock formed by the cooling of magma under the Earth's surface. Igneous rocks are those formed by magma cooling and solidifying, while intrusive rocks are igneous rocks that form beneath the Earth's surface. The Idaho batholith is fundamentally different from other batholiths of the North American Cordillera in that it is mostly made up of peraluminous granites and positioned completely within the Precambrian continental crust. Peraluminous granites are those that contain more aluminum oxide than sodium oxide, potassium oxide, and calcium oxide combined. The batholith is composed of the Bitterroot lobe in the north and the larger Atlanta lobe in the south. The major mountain ranges in the region are part of the Rocky Mountains; they include the Bitterroot Range, Clearwater Mountains, Salmon River Mountains, and the Sawtooth Range. Major mountain peaks include 10,201 ft (3,085 m) tall Trapper Peak in the Bitterroot Mountains in Montana and 12,009 ft (3,660 m) tall Hyndman Peak in the Pioneer Mountains in Idaho.
Soils derived from the granite that characteristically underlays the ecoregion tend to retain water poorly and be limited in fertility. The removal of vegetation causes these soils to be highly erodible.
The rivers that flow through the ecoregion include the Payette, Selway, Salmon, Lochsa, Clearwater, Boise in Idaho, and the Bitterroot in Montana. The region lies within the Columbia and Missouri Watersheds for named rivers as designated by the United States Geological Survey (USGS). The Idaho Batholith ecoregion lies within the following WWF freshwater ecoregions: the Upper Snake, the Upper Missouri, and the Columbia Unglaciated. Lake Cascade, the fourth largest lake or reservoir in the state of Idaho is situated on the North Fork of the Payette River.
Level IV Ecoregions
Eastern Batholith(16a)
The Eastern Batholith ecoregion is located in the easternmost portion of the Idaho Batholith, which is just northwest of the Continental Divide. The region is forested and mountainous. Its surface waters tend to be very low in alkalinity, which is caused by its underlain intrusive rocks of the Cretaceous Idaho Batholith. Alkalinity is the measure of a solution's capacity to neutralize or buffer acids. The average annual precipitation ranges from 16-55 inches (40.6-139.7 cm). Climax vegetation includes subalpine fir (Abies lasiocarpa), Douglas-fir (Pseudotsuga menziesii), and ponderosa pine (Pinus ponderosa). Logging, grazing, mining, and recreation illustrate some of the more common land uses of the area.
Lochsa Uplands (16b) The Lochsa Uplands ecoregion is mountainous and dissected. Granitic rocks underlay the region which is spread out by volcanic ash deposits that help improve the soil fertility and water retention in the uplands. Grand fir (Abies grandis) and Douglas-fir are common throughout the region. Engelmann spruce (Picea engelmannii) and subalpine fir grow at high elevations, while cedar-hemlock-pine forests are found in canyons and on north-facing slopes.