Eastern Cascades forests

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Near Bend, Oregon, United States. (Photograph by John Morrison)

The Eastern Cascades forests span the eastern slopes of the Cascade Mountains in Oregon and Washington, from the southern reaches of the Cascade Mountains Leeward Forests to northern California. Vegetation is highly variable throughout this ecoregion, being influenced chiefly by edaphic processes and disturbance regimes. Several ecotones exist, particularly along the Cascade crest where western Cascade forest types overlap with eastern Cascade forests (e.g., the Wenatchee National Forest in Washington has conifer species present on both sides of the Cascades) and along the lower timberline, where forest species mix with shrub and shrub-steppe communities.

This ecoregion is considered part of the Nearctic Realm, and is given the ecocode NA0512 by the World Wildlife Fund; it is within the Temperate Coniferous Forests biome. The Eastern Cascades forests covers a lond area of approximately 21,300 square miles.

caption WWF

Geology and climate

The geomorphology of the region is characterized by a series of steep, rugged mountains with the interior Cascade range rising to 2700 meters (m) and volcanic peaks extending to 4300 m (e.g., Mt. Rainier, Washington). Soil types are primarily andisols underlain by volcanic ash and other dry soils. Serpentine soils also occur in some areas (e.g., Wenatchee National Forest) and may support rare community types. Climate is generally mild with precipitation averaging less than 511 millimeters (mm) annually for the region.

Vegetation and disturbance regimes

The natural vegetation of the region is a complex mosaic of shrublands, grasslands, and coniferous forests. The dominant forest type along the eastern slopes of the Cascades is Ponderosa pine (Pinus ponderosa). Within forested landscapes, species composition (forest type) varies along environmental gradients defined by physical factors such as temperature and moisture. Topographic-moisture gradients (e.g., from sheltered valleys to exposed ridges) and soil conditions further determine the distribution of vegetation types. Fire resistance among different communities varies considerably. Seven forest zones and numerous plant associations have been recognized, including the Juniperus occidentalis zone (driest type receiving 200-250 mm precipitation), P. ponderosa (dry, warm areas from 600 to 2000 m elevation), Douglas fir (Pseudotsuga menziesii) in mesic areas, Abies grandis (predominates midslopes), P. contorta (wide ecological amplitude receiving 1200-1525 mm precipitation), Tsuga heterophylla (eastern extension of west Cascade forest), and Abies lasiocarpa (subalpine zone, coolest and wettest forest type). In addition, A. concolor and A. magnifica shastensis associations, which are widespread in California and southwestern Oregon, occur along the eastern slopes of the Southern Oregon Cascades, reflecting another ecotonal zone in this region.

Prior to European settlement (pre-1850), a wide variety of disturbances characterized the region, ranging from frequent small-scale and localized events such as treefall gaps to rare, large-scale events such as stand-replacing fires and epizootic outbreaks. Such disturbances resulted in a dynamic equilibrium between patch creation and loss. This active disturbance regime has resulted in a larger proportion of younger seral stages than in areas west of the Cascade Mountains. However, the low-elevation (900-1500 m) forests, which experienced frequent low-intensity fires, were predominantly (up to 90 percent) old growth ponderosa pine. In general, forest ecosystems in this region are adapted to more frequent fire disturbances than mesic westside forests. Natural fire cycles range from periodic (five to fifteen years) surface fires in dry and warm ponderosa pine and Douglas-fir types, to infrequent (more than 100 years and up to 900 years) stand-replacement crown fires (greater than 100 square kilometers) in mesic and cool western redcedar (Thuja plicata), western hemlock, and cedar/spruce forest types. Such disturbances played a crucial role in maintaining inland forest structure, species composition, and ecosystem processes (e.g., species interactions, epizootics, plant species adaptations to fire, nutrient cycling, succession). A new anthropogenic regional landscape mosaic has now replaced this dynamic equilibrium that was once maintained by natural forces. Logging and fire suppression have shifted disturbance regimes and landscape dynamics to less frequent and more intense fires, and frequent and large-scale anthropogenic disturbances have disrupted natural processes and led to declines in various ecosystem types and species.

Biological distinctiveness

This ecoregion contains important habitat for up to 268 taxa that have federal listing status, including 45 native fish species (recognized by federal and state agencies as sensitive or special concern) and ten listed or candidates for listing under the Endangered Species Act. The total number of species in this region, however, is intermediate when compared to other coniferous forests within its major habitat type (MHT). Birds make up the majority (42 percent) of the faunal taxa evaluated, followed by butterflies (28 percent), and mammals (14 percent). There are a total of 323 vertebrate species that have been observed in the ecoregion.

Conifer richness is intermediate compared to other coniferous forests in this major habitat type, however, beta diversity is locally high in ecotones along the crest of the Cascades (e.g., Wenatchee National Forest). Within this ecoregion, elements from many adjacent regions, such as the Klamath-Siskiyou, Great Basin, and Sierra Nevadas, intermingle in a complex mosaic of communities.


There are numerous mammalian species found in this ecoregion. Some of the larger mammals are: Black bear (Ursus americanus); Bobcat (Lynx rufus);  Representative small mammals occurring in the Eastern Cascades forests are: Cinereus shrew (Lampropeltis zonata);


caption Olive sided flycatcher. Source: Jerry Oldenettel A variety of avifauna species are found in the ecoregion, including: Northern flicker (Colaptes auratus); the Near Threatened Olive-sided flycatcher (Contopus cooperi); the Near Threatened Greater sage grouse (Centrocercus urophasianus); the Vulnerable Pinyon jay (Gymnorhinus cyanocephalus); and the Endangered Tricolor blackbird (Agelaius tricolor).


A moderate number of reptile species occurs within the ecoregion. Snakes are the California mountain kingsnake (Lampropeltis zonata); Western rattlesnake (Crotalus viridis); Sharp-tailed snake (Contia tenuis); Yellow-bellied racer (Coluber constrictor); Common garter snake (Thamnophis sirtalis); Gopher snake (Pituophis catenifer). Other reptiles present are the Northern alligator lizard (Elgaria coerulea); Western fence lizard (Sceloporus occidentalis) and the Side-blotched lizard (Uta stansburiana).


There is a paucity of amphibians within the Eastern Cascades forests. Salamanders present are: Long-toed salamander (Ambystoma macrodactylum). The only anuranAn amphibian that has limbs but no tail (includes all frogs and toads) species in the ecoregion are the Pacific chorus frog (Pseudacris regilia) and the Vulnerable Oregon spotted frog (Rana pretiosa).

Conservation status

Habitat loss

caption Golden eagle (Aquila chrysaetos), California, United States. Source: Lloyd Glenn Ingles, California Academy of Sciences and CalPhotos

The forests of eastern Oregon and Washington have experienced dramatic changes in the past fifty years. Of particular concern is the loss of old-growth forest types such as low-elevation ponderosa pine, western larch (Larix occidentalis), and Douglas-fir. Only about one-fourth of the remaining late-seral/old growth (LSOG) has been protected administratively or by statute (in some areas less than three percent of LSOG remains) and from 75-90 percent of remaining patches in the region are too small (less than .4 km2) to conserve LSOG dependent species or processes. Continued logging in these areas could further reduce LSOG types to seven to thirteen percent of their original extent. Other losses identified in this ecoregion include degradation of shrub-steppe caused by extensive livestock grazing and invasion of exotic species, degradation of riparian, wetlands, and aquatic ecosystems, and reductions in habitat quality caused by invasive species. While habitat loss has been extensive within the ecoregion, the ecoregion was given a vulnerable rating compared to other coniferous forests within its MHT that had higher losses.

Remaining Blocks of Intact Habitat

Maps of remaining LSOG, wilderness, roadless areas, aquatic diversity areas, and designated old growth (note, not all areas designated as old growth by the USDA Forest Service meet old growth criteria) are available in Henjum et al. These maps, together with state GAP analyses of vegetation coverage, provide regional information needed in conservation reserve planning. In addition, the workshop participants identified the following intact blocks:

  • Gearhart Mt. Wildnerness and surrounding intact forest areas - 160 km2 wilderness and intact forest
  • Deschutes National Forest - west of Bend, Oregon - approximately 800 km2
  • Bear Valley National Wildlife Refuge - south-central Oregon - 43 km2
  • Tule Lake National Wildlife Refuge - northern California -170 km2 (primarily wetlands)
  • Clear Lake National Wildlife Refuge - northeastern California - 176 km2 (primarily wetlands)
  • Oak Creek Washington State Recreation Area - central Washington - 137 km2
  • South Warner Wilderness Area - northeastern California - 217 km2 (the area has been grazed but not logged)
  • Lake Murry Washington State Recreation Area - central Washington - 128 km2
  • Indian Heaven Wilderness Area, Gifford Pinchot National Forest - south-central Washington
  • Mt. Adams Wilderness Area, Gifford Pinchot National Forest - south-central Washington
  • William O. Douglas Wilderness Area, Wenatchee National Forest - central Washington
  • Norse Peak Wilderness Area, Wenatchee National Forest - central Washington

Degree of fragmentation

Fragmentation has been extensive in the region, particularly in the southern portion because of agriculture and clearcut logging. Few blocks greater than twenty square kilometers remain.

Degree of protection

The greatest threat in the region is continued logging, particularly salvage logging. Several areas of ecological importance were proposed for salvage logging, including old-growth forests with live trees greater than two meters in diameter breast height; late-seral reserves and key watersheds previously protected under the President's Northwest forest plan; habitat previously protected because of concerns over listed or candidate species; areas abutting wilderness; sacred Native American sites; Wild and Scenic Rivers; roadless areas; and steep slopes previously removed under forest plans. The Western Ancient Forest Campaign (Washington DC), local Audubon Society, and Sierra Club have more detailed information on the location of salvage logging operations in the region.

Ecological threats

The major types of threat in the ecoregion include the following: (1) logging; (2) livestock overgrazing in riparian areas and native shrub-steppe; (3) overly aggressive fire suppression; (4) spread of alien species of weeds exacerbated by road-building and fragmentation; and (5) hydroelectric dams and flood control. Federally imposed salvage logging levels under the Obama administration remain the greatest threat to protecting biodiversity in the region.

Suite of priority activities to enhance biodiversity conservation

Most of the forests in this region are publicly owned (USDA Forest Service lands). Thus, the key to conservation of biological diversity lies in how the national forests are managed. The Forest Service and Bureau of Land Management are currently preparing an Environmental Impact Statement (EIS) that will determine the fate of many remaining roadless areas and LSOG in the region. This EIS should remain a priority for conservation organizations, particularly those concerned about the need for a conservation reserve network and restoration of degraded ecosystems. The following conservation activities were recommended by DellaSala et al. and generally apply to this ecoregion:

  • Determine where the most natural conditions persist (e.g., existing parks, wilderness, and roadless areas)
  • Assemble or develop the necessary geo-referenced data and information to determine the status of ecosystem representation (e.g., GAP analysis)
  • Identify hot spots of species richness and endemism for the region (e.g., Wenatchee National Forest, crest of the Cascades)
  • Identify areas most threatened by human activities
  • Describe existing spatial patterns of regional biodiversity and reconstruct historic patterns where  possible
  • Examine historic records of vegetation at appropriate ecological scales (e.g., across regional landscapes) to determine which ecosystems have lost critical components or have been most degraded
  • Determine necessary size, level of redundancy, and distribution of core areas to meet well-defined conservation goals
  • Conduct population viability studies for forest carnivores, e.g. Wolverine (Gulo gulo); Marten (Martes americana); Fisher (Martes penanti); Lynx (Lynx lynx); Flammulated owl (Otus flammeolus); Boreal owl (Aeoius funereus); and Great gray owl (Strix nebulosa)
  • Examine landscape pattern and linkages, paying particular attention to the interfaces between patches
  • Conduct watershed assessments so as to complement the greater regional planning effort
  • Consider both aquatic and terrestrial conservation requirements and their interaction
  • Integrate public lands management with conservation of important biodiversity features on private lands through the use of economic incentives and cooperative agreements
  • Restore fire-suppressed ecosystems through ecologically appropriate silviculture (e.g., thinning from below the canopy) and prescribed fire.

Conservation partners

  • Inland Empire Public Lands Council
  • Kettle Range Conservation Group
  • National Wildlife Federation - Western Division
  • Northwest Ecosystem Alliance
  • Oregon Natural Resources Concil
  • Selkirk-Priest Basin Association

Relationship to other classification schemes

The Eastern Cascades Forest ecoregion delineated in this assessment is concordant with Omernik's ecoregion #9. However, the Eastern Cascades ecoregion is herein split from the northern portion of Bailey's ecoregion, #M242, placing that northern portion into the Cascade Mountains Leeward Forests. In addition, Bailey's ecoregion includes both slopes of the Cascades, while the authors feel the plant series and climate were different enough to warrant splitting along the Cascade crest.

Neighboring ecoregions

The following ecoregions have a border with the Eastern Cascades forests:

  • Southern and Central  Cascades forests, to the west and northwest
  • Klamath-Siskiyou forests, to the southwest
  • Sierra Nevada forests, at the extreme south
  • Snake-Columbia shrub steppe, to the east
  • Cascade Mountains leeward forests, at the extreme north


  • Ron Adkison. 2001. Wild Northern California The Globe Pequot Press
  • Charles L. Bolsinger and Karen L.Waddell. 1993. Area of old-growth forests in California, Oregon, and Washington (PDF). United States Forest Service, Pacific Northwest Research Station. Resource Bulletin PNW-RB-197.
  • Daryl W. Fedje, James M. White, Michael C. Wilson, D. Erle Nelson, John S. Vogel, John R. Southon. 1995. Vermilion Lakes Site: Adaptations and Environments in the Canadian Rockies during the Latest Pleistocene and Early Holocene. American Antiquity 60 (1): 81–108.
  • Sylvie Gauthier et al., eds. 2009. Ecosystem management in the Boreal forest. Presses de l'Universite du Quebec


Disclaimer: This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.






Fund, W., & Hogan, C. (2015). Eastern Cascades forests. Retrieved from


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