Modoc Plateau and East Cascades

Description & Physiography

The Upper Klamath Basin and the Modoc Plateau are large land forms that characterize the southern portion of the ecoregion. The Modoc Plateau has a diverse geography, with portions draining into closed basins such as Goose Lake and Surprise Valley, and most of the remainder draining into the Pitt River, a tributary of the Sacramento River. These areas contain a series of broad, relatively flat mid-elevation valleys that once supported a vast expanse of lakes and marshes that drained into the Klamath River. Upper Klamath Lake is Oregon’s largest lake and is the biggest remnant of this wetland system. Most of these wetlands have been drained and converted to agriculture. Much of the remainder of the East Cascades to the north in Oregon is drained by the Deschutes River system, which includes a series of large lakes and reservoirs near its headwaters.

The East Cascades in Washington and northern Oregon resulted from tectonic uplift and subsequent erosion by alpine glaciers and landslides. The combination of these processes and volcanic activity created rugged ridges extending southeast to east from the Cascade crest. Broad valleys occupy the lowlands between the mountain ridges. Isolated volcanic cones occupy steep mountain ridges, but tend to be smaller than those in the Western Cascades with the exception of Mount Adams.

Climate

There is a dramatic moisture gradient across the ecoregion as the precipitation diminishes from the cold, wet Cascade crest (up to 120 inches of precipitation per year) to the warm, dry eastern border with the Columbia Plateau and Great Basin (less than 20 inches per year). Most precipitation accumulates from November through April. A snow pack develops at higher elevations. Precipitation also changes significantly from north to south, with annual rainfall below 12 inches per year in portions of the Modoc Plateau in California.

Plants & Animals

The variety of habitat types in the East Cascades has led to a unique and diverse flora and fauna. An abundance of species are supported by high elevation meadows, parklands and forests: low-elevation dry forests, oak woodlands, cliffs and talus slopes, riparian corridors, and a variety of aquatic habitats. Numerous lakes, reservoirs and marshes characterize the East Cascades, providing exceptional habitat for waterfowl, shorebirds and wading birds, aquatic mammals, amphibians, fish, aquatic plants and invertebrates. In fact, the East Cascades support an unusually high aquatic biodiversity among ecoregions in the U.S., including a large number of endemic freshwater snails and fish.

This ecoregion has one of the most extensive Ponderosa pine forests in the western U.S., occurring in all parts of the ecoregion, from Wenatchee to Mount Lassen. At mid elevations, there are areas of Douglas-fir and grand fir (Abies grandis) forests to the north, and white fir and Douglas-fir forests to the south. The ecoregion includes a large pumice zone in central Oregon, dominated by lodgepole pine (Pinus contorta), one of the very few places where the species is the climax tree (not replaced by other conifers if fire is suppressed). Oregon white oak (Quercus garryana) woodlands occupy lower elevations near the Columbia River in the central portion of the ecoregion and also the western parts of the Modoc and Upper Klamath Basin sections in the south. Subalpine fir (Abies lasiocarpa), mountain hemlock (Tsuga mertensiana) and Engelmann spruce (Picea engelmannii) are found at higher elevations, with mountain hemlock replaced by Shasta red fir in the Upper Klamath Basin. Whitebark pine (Pinus albicaulis), lodgepole pine, and western larch (Larix occidentalis) are common components of many of these forests. In the Modoc Plateau, Douglas-fir becomes less important, western white pine (Pinus monticola) woodlands dominate many areas, and Jeffrey pine (Pinus jeffreyi) and Washo pine (Pinus washoensis) occur with or replace ponderosa pine.

Large mammals are emblematic of the ecoregion, which supports populations of elk, blacktail deer, mule deer, bighorn sheep, mountain lions, and black bears. Mountain goats inhabit high elevations in the central and northern part of the ecoregion in Washington, but are largely absent from the southern portion of their range, and absent from Oregon. Grizzly bears and gray wolves no longer occur in the ecoregion, however lynx and wolverines may occasionally visit the northernmost portions. Fisher, once common in this ecoregion, now occurs only in the extreme southwestern portion of the East Cascades. The western gray squirrel is at-risk within the ecoregion in Washington as it is restricted to two isolated populations, but populations in Oregon and California are more robust.

Wetlands in the ecoregion are home to many birds including bald eagles, geese, ducks, herons, cranes, rails, and various songbirds. Golden eagles (Aquila chrysaetos) inhabit a small portion of their historical ranges and are limited in distribution while the peregrine falcon (Falco peregrinus) is making a comeback. The threat of catastrophic wildfire and competition with barred owls (Strix varia) are concerns for the conservation of the spotted owl, a federally listed species that occurs within the ecoregion. The western pond turtle is listed as an endangered species in Washington, although it has more robust populations in the Oregon and California portions of its range. The largest wild population in Washington occurs within the ecoregion in the Columbia River Gorge. Anadromous fish such as steelhead, coho and Chinook salmon inhabit East Cascade streams and rivers. Their distribution and numbers are significantly reduced, particularly due to dams that restrict their passage through much of the ecoregion. Rainbow (Oncorhynchus mykiss) and cutthroat trout are the common cold water inhabitants. Bull trout occur within the ecoregion but their range has been significantly reduced. Kokanee (Oncorhynchus nerka) can be found in lakes in the northern and central portions of this ecoregion in Washington. The federally-listed Lost River sucker (Deltistes luxatus), and shortnose sucker (Chasmistes brevirostris), bull trout, and salmon stocks drive many of the conservation activities in the ecoregion.

Humans & History

Historically, fires occurred at irregular intervals from under 10 years in the lowland foothills to 150 years or more at high elevations. Forest stand patterns on the landscape often reflect this complex fire history. In some areas, decades of fire suppression have resulted in large areas of dense, fire-prone forest. Shrub-steppe vegetation composed of big sagebrush (Artemesia tridentata) or antelope bitterbrush (Purshia tridentata) and native bunchgrasses occurs along the foothills and higher south-facing slopes. The southern portion of the ecoregion has extensive valleys and flatlands between the forested mountains and foothills, which include large marshes, irrigated meadows and pastures, and arid juniper and sagebrush steppes. These habitats are a critical part of the Pacific flyway, supporting vast numbers of shorebirds and waterfowl, the densest wintering concentration of bald eagles in the world, and many other wildlife species.

Today

In Washington, much of the ecoregion is within the ceded lands and usual and accustomed fishing areas of tribes. The tribes manage tribally-owned lands on reservations and are also involved in monitoring and research activities on ceded lands. Tribes are active participants in discussions about natural resources management and conservation activities within their usual and accustomed areas. Dominant land uses are forestry, livestock grazing, recreation and conservation. In Washington and the rapidly developing areas around Bend in Oregon, timber companies have recently begun to sell their lands in the mid-elevation forest and transition zones to developers. In Washington and California, less than 2% of the ecoregion had been converted to agricultural or human uses by the early 1990s.

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