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Blue Mountains Ecoregion: Biodiversity

Map: WA Department of Natural Resources

Washington’s smallest ecoregion, the rugged Blue Mountains are a rolling high plateau dotted with ponderosa pine forests, vestiges of Palouse prairie, and steeply cut rimrock canyons.

Location

The Blue Mountains spill over into Washington’s extreme southeastern corner. Just 1% of Washington lies within the Blue Mountains.

They are the westernmost ranges of the Middle Rockies that extend south into Oregon and east across central Idaho and into Montana.

Highway 129 is the only road through Washington’s portion of the ecoregion. It heads south along the Snake River from Clarkston through Asotin and Anatone. Then it climbs over Rattlesnake Pass before descending the precipitous switchbacks to the Grande Ronde River and continuing to Enterprise, Oregon.

Outstanding Biodiversity Features

• High plateaus and deep canyons foster diverse plant communities. Vegetation varies dramatically on the steep, river-cut gradients in this highland ecoregion. Elevations range from 750 to nearly 6,400 feet.

• Old-growth forests host high bird diversity. The ecoregion’s remaining patches of old-growth forest provide a wealth of habitat for birds, from predators like the bald eagle, goshawk, and Northern spotted owl to songbirds like the golden-crowned kinglet, Townsend’s warbler, and Swainson’s thrush.

Landforms

Like the Cascades, the Blue Mountains are largely volcanic, the result of the upward thrust of Columbia River basalt. On the plateau, the upland soils are fertile, owing to a generous covering of volcanic ash and windblown silts.

The peaks of the Blue Mountains rise from a plateau above the Snake River. The highland undulations are deeply fissured by both the Snake and the Grande Ronde Rivers.

Carved by the two rivers, this dramatic landscape includes steep, deep hillsides, bluffs, and sheer rimrock faces. The river bottoms are dramatically lower: elevations range from 750 feet along the Snake to nearly 6,400 feet at Mt. Misery.

Climate

Temperature and precipitation correlate strongly with elevation in the Blue Mountains ecoregion. Higher reaches are wetter and colder than lower ones.

Along the river valleys, precipitation ranges from 9 to 18 inches annually, while in the nearby mountains it can reach more than 100 inches a year.

Average temperatures vary from 28 to 52 degrees annually. Summers, particularly at lower elevations, can be very hot and dry.

Vegetation

Photo: WA Department of Fish and Wildlife

Coniferous forests dominate much of the Blue Mountains. At higher elevations subalpine fir and Engelmann spruce are common. At mid-elevations Western larch, western white pine and lodgepole pine can be found, especially on slightly moister sites.

At mid-elevations Douglas-fir and ponderosa pine become prevalent. Open, park-like stands of ponderosa pine, with a snowberry and bunchgrass understory, host more vertebrate species than any other eastside forest.

Vegetation changes dramatically as hillsides plunge toward river bottoms along the Grande Ronde and Snake. In the higher canyons, shrublands can be found. Western juniper, snowberry, mountain mahogany, bitterbrush, and sage are among the shrubs found in the Blue Mountains.

At lower elevations grasslands are common. The famed Palouse prairie extends into the Blue Mountains, as do patches of shrub-steppe. Much of the grasslands and shrub-steppe have been displaced by agricultural operations.

Streamside areas covered in mountain alder, willows, and quaking aspen offer support for more wildlife species than any plant community type in the ecoregion. Of the Blue Mountains’ estimated 246 wildlife species, roughly a third are found in riparian wetland areas.

Terrestrial Wildlife

A range of mammals, large and small, find home in the Blue Mountains. Ungulates, like mule deer and Rocky Mountain elk, omnivores like black bear, coyotes, and raccoons, and predators like cougars make use of the ecoregion’s forests and river valleys.

Snags in the dry forest supply habitat to cavity nesters, such as bluebirds, chickadees, and woodpeckers. Steep cliff faces and rocky slopes attract raptors, including the golden eagle.

Coho salmon, Chinook salmon, and steelhead trout make runs in the Grande Ronde and Snake Rivers, though in substantially fewer numbers than historically. Rivers also support resident populations of rainbow and bull trout.

People in the Ecoregion

The Blue Mountains have been inhabited by humans for at least 12,000 years. The ecoregion is an ancestral home for the Nez Perce people (Nimi'ipuu), renowned across the West as horse breeders and traders. Bands camped along river bottoms in winter and left seasonally to hunt bison on the Montana high plains.

The first rush of Euro-Americans came to the Blue Mountains in search of gold in the 1860s. The hydraulic and hardrock mining that followed scoured and poisoned parts of the landscape. Mining opened the region to subsequent settlement. In the late 1800s, ranching became a predominant livelihood.

Roughly two-thirds of the region is in public ownership. The Umatilla Forest holds more than half the ecoregion’s lands. More than 111,000 acres of it in Washington is the Wenaha-Tucannon Wilderness, which straddles the Washington-Oregon border.

The state of Washington manages more than 32,000 acres, including the Asotin Wildlife Area, a major elk calving range, and the Chief Joseph and William T. Wooten Wildlife Areas, both of which contain important riparian areas.

Many of the river valley bottoms in the Blue Mountains are privately owned and used for ranching and forage crop production.

Activities such as hunting, fishing, snowmobiling and skiing make this sparsely populated ecoregion increasingly popular. It faces growing pressures from low-density vacation home development.

Human Impact

Ongoing challenges to the native biodiversity and ecological integrity of the Blue Mountains include:

• Changes in fire regime. Past forest practices and a century of fire suppression have substantially altered function and composition of the ecoregion’s ponderosa pine and Douglas-fir forests. The loss of mature stands reduce habitat for cavity nesters, such as the pygmy nuthatch and flammulated owl. Overstocked forests of smaller trees increase the danger of large-scale fires.

• Excessive grazing. Overgrazing of the ecoregion’s grasslands has changed the plant composition dramatically and allowed invasive cheatgrass to gain a hold.

• Agricultural conversion. Nearly all the remaining interior grasslands have been converted to dryland wheat, irrigated field crops, or hay and alfalfa. Many of the ecoregion’s low-lying wetlands, home to the Columbia spotted frog, have been drained for agricultural uses.

Despite these impacts, natural or semi-natural vegetation is dominant in Washington's Blue Mountains, a tiny piece of a much larger ecoregion. Public-private partnerships and stewardship efforts will go a long way toward conserving the rich native biodiversity here.