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 tall
Trapper Peak in the
Bitterroot Mountains in Montana and 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 .
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.
Lochsa-Selway-Clearwater Canyons (16c) The Lochsa-Selway-Clearwater Canyons ecoregion features fast-flowing rivers transporting cold water. As the depths of canyons increase, they become warmer and drier. The ecoregion is dominated by Douglas-fir, grand fir,
western redcedar (
Thuja plicata),
western larch (
Larix occidentalis), and
western white pine (
Pinus monticola). Ponderosa pine is found on lower, drier sites. There are large tracts of
wilderness here and the
Selway River watershed is located within the region. Logging is common in non-wilderness areas. Granitics are less likely to be found here than in any other part of the Idaho Batholith ecoregion, which is uncharacteristic. This region is on the
leeward (or downwind) side of the mountains, meaning it is dry and receives very little precipitation. Unlike any other parts of the Idaho Batholith ecoregion, there is a mosaic of
shrubland, open Douglas-fir forests, and
aspen occurs. Mining is affecting water quality, and rapid residential and commercial growths are occurring near the city of
Ketchum, Idaho. The region also contains
terraces, wetlands, and hills.
Sedges (
Cyperaceae) and
rushes (
Juncaceae) originally grew commonly in wet soils. In drier soils,
bunch grasses and
mountain big sagebrush (
A. tridentata subsp.
vaseyana) originally occurred.
Lodgepole pine (
Pinus contorta subsp.
latifolia) and ponderosa pine originally grew in valley floors. Cold and snowy winters occur here. Large amounts of runoff from melting snow in the mountains occur during the spring. The region serves as pasture for livestock during the summer months. Land is also used for cropland and developments for recreation. Streams suffer raised sediment and nutrient (phosphorus) levels from flood irrigation and grazing. Annual precipitation is greater than surrounding ecoregions at lower
elevations and the mountains are often capped with snow. The soils are shallow, contain many stones, and have a cryic (cold) temperature regime. The region includes
alpine areas,
subalpine parkland, and open, windblown forests of mostly non-marketable trees such as
subalpine fir and
whitebark pine at very high elevations. Above
treeline,
tundra, alpine
grasslands,
subirrigated meadows, and
wetlands are found.
South Clearwater Forested Mountains (16i) The South Clearwater Forested Mountains ecoregion experiences
maritime influences at a lower rate than ecoregions to the north, but at a higher rate than ecoregions to the south. Grand fir, found at elevations between where Douglas-fir and subalpine fir grow, is the only tree species in the region that receives maritime influences. Instability of slopes and sedimentation of streams is caused by logging. Rivers are also heavily impacted by various types of gold mining.
Hot Dry Canyons (16j) The Hot Dry Canyons ecoregion is heavily dissected by the occurring canyons.
Relief (or local relief) can reach . Relief is the difference between the highest and lowest elevations in a given area. Much like the canyons in ecoregion 16c, the canyons here become drier and warmer as depth increases. This region receives little snowfall in the winter. Widespread vegetation includes mountain sagebrush, ponderosa pine, and various grasses. Vegetation on south-facing slopes is less than on north-facing slopes to the increased impact of the
Sun due to the Earth's tilt in the
Northern Hemisphere. This effect also causes the sites on south-facing slopes to be drier. Douglas-fir can also be found, but is less common than in nearby ecoregions. The bottoms of canyons have been impacted by mining. Some of these canyon bottoms are used as transportation corridors.
Southern Forested Mountains (16k) Soils derived from granitic rocks, which are characteristically poor at retaining water spread out the Southern Forested Mountains ecoregion. This region receives marginal influence from maritime events. Ponderosa pine can be found growing in canyons, while grand fir and subalpine fir grow at higher elevations. Douglas-fir in open settings is common in the region, while sagebrush and forests can be found in the south. Like much of the Idaho Batholith ecoregion, soil disturbance results in high amounts of sediment being deposited in streams. ==Climate==