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Okanogan Ecoregion: Biodiversity

Map: WA Department of Natural Resources

In north-central Washington, the Cascades, the Rockies, and the Columbia Plateau converge to form the Okanogan ecoregion, which boasts highland landscapes and lowland waterways, grizzly bears and sage grouse.

Location

The Okanogan ecoregion could be called the mountains between mountains—the broad highland area separating the North Cascades and the Northern Rockies.

In Washington, the ecoregion covers about 14% of the state. It extends significantly into the sage-steppe country of south-central British Columbia.

Scenic river valleys, like the Methow, the Okanogan, and the Colville, run north-south. Highway 97 threads through the Okanogan Valley, connecting the towns of Omak and Oroville.

State Route 20 links the Puget Trough and the North Cascades to Methow Valley communities like Winthrop and Twisp. It continues on through the Okanogan to Republic and Kettle Falls. On the ecoregion’s eastern edge, Highway 395 links Spokane, Colville, and Kettle Falls.

Outstanding Biodiversity Features

• Large tracts of little disturbed land. Much of the Okanogan ecoregion’s vegetation remains in a natural, or at least semi-natural, state. It hosts 100 wildlife habitat types, from alpine grasslands and upland aspen forests to shrub-steppe.

• North meets south in a diverse landscape. Boreal species like snowshoe hares and northern flying squirrels share the ecoregion with Great Basin species like pallid bats and burrowing owls.

• Park-like stands of ponderosa pine and Douglas-fir. The Okanogan’s dry climate results in open grassy stands of ponderosa pine and Douglas-fir.

• Wide-roaming carnivores still find a home. Though diminished in numbers, grizzly bears, wolves, and wolverines all range through large areas of Okanogan wild lands.

Landforms

Geologically, the Okanogan ecoregion is a complex story of plate tectonics, volcanic eruptions, and ice age sculpting. The Okanogan was once its own micro-continent.

This micro-continent collided 100 million years ago with the mass of North America, resulting in the highlands of today. Some of Washington’s oldest Precambrian metamorphic and sedimentary rock underlies the eastern part of the Okanogan.

Over the following tumultuous eons, Cambrian sandstone and limestone have layered over the region. They’ve left it rich in minerals such as gold, lead, zinc, and quartzite.

Fossils, too, are found near Republic, where an ancient lake bed holds the fossilized remains of plants, fish, and insects.

During the Pleistocene, glaciers covered much of the Okanogan. Their final retreat shaped the face of the ecoregion today. Evidence of glaciers can be seen along the mile-wide floodplain of the Okanogan River. Glaciers left terraces of till (sand and gravel) standing up to 500 feet above the river.

Photo: Scott Fitkin

Mountaintops that rise above 8,000 feet and broad river valleys that dip below 800 feet reflect the diversity of the Okanogan landscape. The alpine peaks of the Pasayten Wilderness in the west are separated from the Kettle Range by the low-lying Okanogan Valley.

The Columbia River forms the ecoregion’s southern boundary. At the Grand Coulee Dam it becomes Franklin D. Roosevelt Lake. This waterway takes a northward turn toward its headwaters in Canada, dividing the Kettle Range and the Selkirk Mountains.

Climate

Hot, dry summers and cold, snowy winters distinguish the Okanogan from its neighboring ecoregions.

In the west, the Okanogan Valley lies under the Cascade Mountains’ rain shadow. Annual precipitation measures less than 12 inches. On the ecoregion’s eastern edge, precipitation roughly doubles as storm fronts bump up against the rise of the Canadian Rocky Mountains.

In the summer, hot air flows northward from the Columbia Plateau, driving daily highs into the 90s and even the triple digits.

In the winter, cold, dense Arctic air can stream out of Canada. In 1968 this dropped temperatures to -48º F at Mazama and Winthrop, a record for Washington State.

Vegetation

In the Okanogan ecoregion, native plant cover ranges from alpine tundra to semi-arid shrub. The ecoregion’s plant communities vary with elevation.

At the highest elevations, alpine and subalpine meadows intermix with whitebark pine, lodgepole pine, and subalpine larch. These yield to stands of Engelmann spruce and subalpine fir at slightly lower elevations.

Photo: Clay Antieau

Lower still, and extending down into the valleys, are the ecoregion’s distinctive grassy-floored forests of ponderosa pine, Douglas-fir, western larch, western white pine, and quaking aspen.

Fire has always played an important role in ecoregion’s forests. Historically, regular low-intensity fires cleared out undergrowth, especially diseased or insect infested trees. For roughly a century, natural fires have been disrupted by timber management practices.

Fire suppression has caused forests to become overstocked with smaller trees and downed wood. This has created a greater risk of large, stand-replacing fires. The Tripod Complex Fire burned more than 175,000 acres northeast of Twisp in 2006.

The low river country of the Okanogan is essentially a long finger of shrub-steppe that extends northward. It reaches into Canada’s only desert, British Columbia’s arid Okanagan Valley. (Note that north of the border, it’s spelled with an ‘a.’). In the river valleys, fruit orchards and alfalfa fields mix with sagebrush and grasslands.

Terrestrial Wildlife

The Okanogan hosts high numbers of butterflies, birds, and mammals.

More than 200 species of birds, from sage thrashers in the shrub-steppe to ptarmigans in the alpine areas, spend some part of their lives in the Okanogan. Waterways offer quality habitat for harlequin ducks, ospreys, and eagles.

The Pasayten Wilderness, in the ecoregion’s northwestern corner, still retains its full complement of large herbivores, such as moose, mountain goats, and bighorn sheep.

Its more carnivorous inhabitants include wolves, grizzly bears, and lynx. Small populations and a dwindling gene pool raise conservation concerns for these and other mammals.

A broad range of amphibians and reptiles, among them western rattlesnakes, painted turtles, and Great Basin spade foot toads, can also be found in the Okanogan.

Biologists have identified several priority habitat types in the Okanogan.

Riparian areas and wetlands in the Okanogan play many vital ecological roles. They are habitat for tiger salamanders, Columbia spotted frogs, great blue herons, and sandhill cranes. Columbia River wildlife habitats have been inalterably changed by the Grand Coulee Dam, which blocked anadromous fish runs and inundated riparian zones.

Photo: WDFW

The Okanogan valley shrub-steppe is an important migration corridor for animals moving between the grassy interior of British Columbia and the sagebrush sea of the Great Basin.

Ponderosa pine stands host arboreal biodiversity like Northern goshawks, white-headed woodpeckers, and Western gray squirrels.

The tender buds and shoots of aspen forests provide important food source for songbirds, sharptail grouse, and deer. Regenerating lodgepole forests offer ideal habitat for snowshoe hares and, their chief predator, the lynx.

People in the Ecoregion

Numerous Interior Salish tribes have made their homes in the Okanogan for millennia. Okanogan tribes wintered in permanent camps, living in longhouses made of tules (hardstem bulrush), bark, and hides. They harvested scores of types of berries, nuts, and roots.

Traveling seasonally, they hunted bear, deer, and other game. Tribes gathered at Kettle Falls on the Columbia to fish for salmon and to trade.

The mapmaker and fur trader David Thompson visited Kettle Falls in 1811, and the Hudson Bay Company established a trading post there in 1825.

Gold was discovered near Republic in the 1890s and a mining boom followed. The timber industry developed in the ecoregion about the same time. Homesteading began in earnest at the beginning of the twentieth century.

Land use varies in the Okanogan and depends largely on elevation. The high country is devoted to mostly recreational uses, though mineral exploration and development continue. At mid-elevations, logging and grazing occur in the Okanogan’s pine forests.

In the valleys, milder temperatures support ranching and agriculture. Hay, alfalfa, and tree fruit (apples, apricots, cherries, peaches, pears) are primary products.

The sunny climate and ample recreation opportunities make the Okanogan ecoregion popular for vacation homes and tourists. The Grand Coulee Dam and miles of boating opportunities along Franklin D. Roosevelt Lake draw people to the ecoregion.

Roughly two-thirds of the Okanogan ecoregion is in state, federal, or tribal ownership. The Colville and Spokane tribes own 2,100 square miles and the state has 835 square miles.

The Forest Service controls 3,100 square miles (just under a third of the total). In addition to the federally protected 529,000-acre Pasayten Wilderness Area, there are more than a dozen designated Natural Areas in the Okanogan.

Human Impact

The human impact on the Okanogan may be lighter when compared to other ecoregions, but its biodiversity still faces numerous challenges.

• Invasive Plant and Animal Species. Spotted knapweed, Dalmatian toadflax, and cheatgrass invade lands formerly covered in shrub-steppe, increasing likelihood of fires in a fire-intolerant system. Canary reedgrass clogs waterways. Bullfrogs and bass both prey on native amphibians.

• Changes in Fire Regime. A vigilant fire suppression policy has caused the overstocking of many Douglas-fir and ponderosa pine stands. This increases the risk of more frequent large, stand-replacing—even catastrophic—fires.

• Overgrazing. Areas of shrub-steppe in the Okanogan have been damaged by excessive grazing or poor grazing practices. These have been especially harmful in biologically rich riparian areas.

• Sprawling Development. With its ample recreation opportunities, the Okanogan ecoregion is seeing flourishing residential development—especially second homes. These often encroach on native plant cover and wildlife habitat.

• Recreation. Motor boating along waterways disturbs feeding and nesting western grebes, common loons, great blue herons, and bald eagles. In the high country, hikers, skiers, snowmobilers, and ATV riders may encroach on grizzlies, wolverines, lynx, golden eagles, and peregrine falcons.

People living in the ecoregion and partners like The Nature Conservancy are working to keep the rich biodiversity of the region healthy. Continuing to develop innovative partnerships and conservation incentives offer opportunities for this richly diverse ecoregion.