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West Cascades Ecoregion: Biodiversity

Map: WA Department of Natural Resources

Rumbling volcanoes, ancient forests, and a wealth of amphibian diversity distinguish Washington’s West Cascades ecoregion.

Location

The West Cascades ecoregion encompasses the westside midsection of the great Cascades cordillera.

In Washington, the West Cascades run southward from Snoqualmie Pass to the Columbia Gorge, the only lowland divide in the range. Across the Columbia, the West Cascades ecoregion extends south into Oregon.

The crest of the Cascades marks the ecoregion’s eastern edge. The western boundary dips to meet the foothills of the Puget Trough at about 1,000 feet. The ecoregion covers about 8% of state.

On the road map, Interstate 90 forms the north boundary of the ecoregion. Highways 12 and 410 both traverse the Cascades. Highway 14 follows the north side of the Columbia River, the ecoregion’s southern boundary in Washington.

Within the sparsely populated ecoregion lie only a few towns, among them Ashford, Morton, Packwood, Randle, and Stevenson.

Outstanding Biodiversity Features

• A great forested mountain range. The West Cascades still retain significant tracts of natural, or at least semi-natural, forest, although management practices have altered forest structure at lower elevations.

• Spectacular—and active—volcanoes host lowland to alpine species. Mount Rainier is home to 723 native plants, amounting to 30% of the flora found in Washington. Mount Rainier and Mount Saint Helens are natural laboratories for studying how ecosystems respond to eruptions.

• Columbia Gorge: a mountain range divided. The Columbia Gorge, the ecoregion’s low point at roughly 50 feet above sea level, splits the Cascades. It is notable as a place where coastal and inland species converge.

Landforms

At Snoqualmie Pass, the rugged North Cascades begin to soften. Older and more weathered, the West Cascades form part of the Cascade-Sierra mountain range that runs the length of the United States. The West Cascades are a glaciated landscape with numerous river valleys.

Photo: Ben Legler

At the heights, peaks approach 7,000 feet. Much taller stratovolcanoes— Mount Rainier, Mount Saint Helens, Mount Adams in the East Cascades, and Mount Hood in Oregon dramatically punctuate the ecoregion. Mount Rainier tops them all at more than 14,000 feet.

These volcanic peaks are part of the intercontinental Ring of Fire that rims the Pacific Ocean. They vary in activity, ranging from long dormant to increasingly lively. The eruption of Mount Saint Helens in 1980 blew out a tremendous plume of ash and reshaped its surrounding landscape.

The Columbia River, at some fifty feet above sea level, bisects the Cascades. The gorge developed at roughly the same time the Cascades began to uplift. The gorge itself was shaped by cataclysmic floods caused by the breakup of Glacial Lake Missoula.

Climate

The West Cascades catch Pacific maritime weather systems that roll over the ecoregion from fall through spring. Temperatures are cool but moderate. Precipitation is high, from 55 to 140 inches annually. Lower elevations in the Cascades will see much of this as rain, while a rain and snow mix prevails at mid-elevations.

A blanket of snow often covers the higher elevations through much of the winter. Snowfall on higher slopes can be staggering: more than 93 feet of snow fell at Paradise on the slopes of Mount Rainier in the winter of 1971-72.

Typically, winters are cold and wet and summers can be cool and drier, sometimes foggy. July and August are driest months, particularly when high-pressure systems form east of the Cascade crest.

Vegetation

The wet and relatively mild conditions in the West Cascades support magnificent conifer forests. Forests of Douglas-fir and western hemlock predominate on the lower slopes, with western red cedar growing in moist sites.

In lowland areas of Mount Rainier National Park, patches of old growth rainforest still support trees up to a 1,000 years old. These ancient Douglas-firs offer habitat for dozens of additional plant and fungal species.

Photo: Ben Legler

At mid-elevations Douglas-fir and western hemlock are joined by Pacific silver fir and noble fir. Lush wildflower meadows occur in these subalpine areas.

The highest reaches of the West Cascades are characterized by stands of mountain hemlock and subalpine fir. At timberline, these trees can form low-lying, gnarled stands of krummholz. In areas prone to avalanches, stands of flexible Sitka alder can thrive.

Up to elevations of roughly 11,000 feet, the volcanoes in the West Cascades host alpine meadows and heath fields. Some of these heath fields have been around for some 10,000 years. Mount Rainier is home to 30% of the species in Washington’s native flora.

A number of broad leaf trees line the ecoregion’s river valleys. Among them are black cottonwood, bigleaf maple, red alder, and Oregon ash.

Terrestrial Wildlife

Black bears and cougars still roam in the West Cascades ecoregion although grizzlies and wolves are no longer found. Mammals that are receiving particular conservation efforts include the fisher, the wolverine, and the western gray squirrel (not to be confused with its invasive cousin, the eastern gray squirrel).

Other vertebrates of concern include the Cascades torrent salamander, bull trout, Chinook salmon, spotted owl, and marbled murrelet.

Map: WA Department of Natural Resources

The Washington Department of Fish and Wildlife has identified four priority wildlife habitats in the West Cascades. Lowland conifer-hardwood forests, particularly remnants of old-growth forest, are critical for dependent species, such as the spotted owl, the fisher, and a slug known as the blue-gray taildropper. In addition, old-growth forest supplies significant ecosystem services.

Garry oak woodlands and dry Douglas-fir forests are another priority. These drier site forests supply habitat to pileated woodpeckers and Johnson’s hairstreak butterflies.

Herbaceous balds, another priority habitat, are those south- to west-facing hillsides covered in bunchgrass. These host to western bluebirds and Mardon skipper butterflies.

Riparian wetlands, an additional priority habitat, exist in mosaics with lowland conifer-hardwood forests. They are inhabited by great blue herons, western pond turtles, and western toads.

People in the Ecoregion

The West Cascades ecoregion is sparsely populated but long utilized. Human history in the West Cascades dates back at least 8,500 years when the montane glaciers began to recede.

Tribes from both the west and east sides of the Cascades gathered huckleberries in the summer and fall. They hunted large and small game, from elk and mountain goats, to pikas and porcupines.

The Nisqually, Puyallup, Squaxin Island, Muckleshoot, Yakama, and Cowlitz are among the peoples with long ties to the ecoregion.

Photo: Ben Legler

The search for a wagon route over the Cascades led to some exploration of the West Cascades near Mount Rainier in the 1860s. That effort eventually resulted in settlement near Packwood in the 1880s.

In the generations since, the timber industry has provided livelihoods. Agriculture, particularly grazing and hay production, continues in the river valleys. Tourism has played an increasingly important role in recent years.

Nearly two-thirds of the ecoregion is public land, most of it federal. The ecoregion features numerous protected areas, including Mount Rainier National Park, Mount Saint Helens National Volcanic Monument, and several Forest Service wilderness areas.

Human Impact

The low elevation ecosystems of the West Cascades have borne the greatest changes from human activities. Threats to biodiversity include:

• Past forest management practices. Extensive timber harvesting and its accompanying road building have altered the complex ecological functions of lowland forests. Multi-aged forests have been replaced with even-aged stands.

• Habitat fragmentation and loss. Patchworks of ownership and management at lower elevations complicate biodiversity conservation efforts. Conversion to residential and commercial uses puts landscape continuity in jeopardy.

• Invasive species. Non-native and invasive plant and animal species pose a serious threat to ecoregional biodiversity.

This forested and mountainous ecoregion is near several urban centers, creating challenges to its future ecological integrity. Forward-thinking partnerships are looking for ways to conserve both the vitality of farms and working forests and the biodiversity of this ecoregion.

Definitions:

Stratovolcano: A volcano, often conical in shape, composed of layers of ash, lava, and other volcanic debris. >back

Krummholz: German for "twisted wood," this term applies to low-growing trees near timberline; their growth is shaped by harsh and windy conditions . >back