Eastern Cascades forests

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 [NA0507] to northern California. Vegetation is highly variable throughout this ecoregion and are influenced primarily by edaphic processes and disturbance regimes (Franklin and Dyrness 1973:160). 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 (Franklin and Dyrness 1973:160).

The geomorphology of the region is characterized by a series of steep, rugged mountains with the interior Cascade range rising to 2,700 m and volcanic peaks extending to 4,300 m (e.g., Mt. Rainier, Washington, Bailey 1995). Soil types are primarily andisols underlain by volcanic ash and other dry soils (Bailey 1995). 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 mm annually for the region.

The natural vegetation of the region is a complex mosaic of shrublands, grasslands, and coniferous forests (Küchler 1966, Franklin and Dyrness 1973:160, Bailey 1995). The dominant forest type along the eastern slopes of the Cascades is ponderosa pine (Pinus ponderosa) (Franklin and Dyrness 1973:160). Within forested landscapes, species composition (forest type) varies along environmental gradients defined by physical factors such as temperature and moisture (DellaSala et al. 1996). 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 (Habeck and Mutch 1973). Seven forest zones and numerous plant associations have been recognized, including Juniperus occidentalis (driest type receiving 200-250 mm precipitation), P. ponderosa (dry, warm areas from 600-2,000 m elevation), Pseudotsuga menziesii (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) (Franklin and Dyrness 1973:161). 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 (Franklin and Dyrness 1973:160).

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 (DellaSala et al. 1995, 1996). Such disturbances resulted in a dynamic equilibrium between patch creation and loss (Everett et al. 1994). This active disturbance regime has resulted in a larger proportion of younger seral stages than in areas west of the Cascade Mountains (Hejl 1992). However, the low-elevation (900-1500 m) forests, which experienced frequent low-intensity fires, were predominantly (up to 90%) old growth ponderosa pine (Henjum et al. 1994). In general, forest ecosystems in this region are adapted to more frequent fire disturbances than mesic westside forests. Fire cycles range from periodic (5-15 years) surface fires in dry and warm ponderosa pine and Douglas-fir types, to infrequent (more than 100 yrs and up to 900+ yrs) stand-replacement crown fires (greater than 1,00 km2) in mesic and cool western redcedar (Thuja plicata), western hemlock, and cedar/spruce forest types (Agee 1993:13). 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; DellaSala et al. 1995, 1996). 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 (Henjum et al. 1994, DellaSala et al. 1996).

  • Scientific Code
  • Ecoregion Category
  • Size
    21,300 square miles
  • Status
  • Habitats

Biological Distinctiveness
This ecoregion contains important habitat for up to 268 taxa that have federal listing status, including 45 native fish (recognized by federal and state agencies as sensitive or special concern) and 10 listed or candidates for listing under the Endangered Species Act (Thomas and DellaSala 1996). The total number of species in this region, however, is intermediate when compared to other coniferous forests within its MHT. Birds make up the majority (42%) of the taxa evaluated, followed by butterflies (28%), and mammals (14%). Conifer richness is intermediate compared to other coniferous forests in this MHT, 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.

Conservation Status

Habitat Loss
The forests of eastern Oregon and Washington have experienced dramatic changes in the past 50 years (Henjum et al. 1994, DellaSala et al. 1995, 1996). Of particular concern is the loss of old growth forest types such as low-elevation ponderosa pine, western larch (Larix occidentalis), and Douglas-fir (Henjum et al. 1994). Only about one-fourth of the remaining late-seral/old growth (LS/OG) has been protected administratively or by statute (in some areas less than 3% of LS/OG remains) and from 75-90 percent of remaining patches in the region are too small (less than .4 km2) to conserve LS/OG dependent species or processes (Henjum et al. 1994). Continued logging in these areas could further reduce LS/OG types to 7-13 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 (DellaSala et al. 1995, 1996). 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 (e.g., [32] and [38]).

Remaining Blocks of Intact Habitat
Maps of remaining LS/OG, 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. (1994). These maps, together with state GAP analyses of vegetation coverage, provide regional information needed in conservation reserve planning (see DellaSala et al. 1996 for models). 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 (Henjum et al. 1994). Few blocks greater than 20 km2 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 2m 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 (DellaSala et al. 1995, 1996, DellaSala and Olson in press). 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.

Types and Severity of Threats
The major types of threat in the ecoregion include the following: (1) logging; (2) livestock grazing in riparian areas and native shrub-steppe; (3) fire suppression; (4) spread of noxious weeds exacerbated by road building and fragmentation; and (5) hydroelectric dams and flood control (Henjum et al. 1994, DellaSala et al. 1995, 1996). Congressionally imposed salvage logging levels 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 that will determine the fate of many remaining roadless areas and LS/OG 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 (see DellaSala et al. 1995, 1996). The following conservation activities were recommended by DellaSala et al. 1996 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)
•determine areas most threatened by human impacts
•describe existing spatial patterns of regional biodiversity and attempt to reconstruct historic patterns where and when 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) (Ruggiero et al. 1994; Hayward & Vernor. 1994)
•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 (DellaSala et al. 1995, 1996).

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, we split this ecoregion from the northern portion of Bailey's ecoregion #M242 and put this portion into the Cascade Mountains Leeward Forests [NA0507]. In addition, Bailey's ecoregion includes both slopes of the Cascades, while we felt the plant series and climate were different enough to warrant splitting along the Cascade crest.

Prepared by: D. DellaSalla


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