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The Central and Southern Cascades span several physiographic provinces in Washington and Oregon, including the southern Cascades, the Western Cascades, and the High Cascades (Franklin and Dyrness 1973:21-26). This ecoregion extends from Snoqualmie Pass in Washington to just north of the California border. The region is characterized by accordant ridge crests separated by steep, deeply dissected valleys (Franklin and Dyrness 1973:21), strongly influenced by historic and recent volcanic events (Mt. Saint Helens). Ridge elevations in the northern section are as high as 2,000m with three dormant volcanoes ranging from 2,550m (Mt. Saint Helens) to 4,392m (Mt. Rainer) (Franklin and Dyrness 1973:21). The stratigraphy dates back to Precambrian-Cenozoic epochs (McNab and Bailey 1994). Pleistocene glacial activity has been widespread, creating numerous lakes and mountain valleys. However, most glaciers were restricted to small alpine areas (Franklin and Dyrness 1973:22). The region is characterized by numerous perennial streams and lakes maintained by abundant annual precipitation (1270-3048 mm, McNab and Bailey 1994). Soils are generally andisols and spodsols; however, soil series vary considerably across the region in association with local climatic differences and edaphic processes (Franklin and Dyrness 1973:21-26, McNab and Bailey 1994). Potential vegetation includes the western hemlock (Tsuga heterophylla), Pacific silver fir (Abies amabilis), and western red cedar series (Thuja plicata) (McNab and Bailey 1994). Predominant natural disturbances include fire, wind, floods, and volcanoes (McNab and Bailey 1994). Extensive logging and fire suppression have substantially altered natural disturbance regimes, shifting regional landscapes from those with a full range of seral stages to highly fragmented landscapes where late-seral stages are rapidly being replaced by monocultural tree plantations (see DellaSala et al. 1995 for basin-wide declines and USDA For. Serv. and USDI Bur. Land Mange. 1996 for ecoregional declines).
When compared to other ecoregions within the Temperate Coniferous Forest Major Habitat Type, this ecoregion contains intermediate levels of biodiversity (e.g., total species richness=493). Birds represent the majority (41%) of taxa evaluated, followed by butterflies (26%), and mammals (13%). This ecoregion contains one of the highest levels of endemic amphibians (5 of 11 endemics are amphibians) of any ecoregion within its major habitat type. Several taxa, including salamanders (e.g., Pacific giant salamander (Dicamptodon ensatus) and Ensatina spp.), frogs (e.g., tailed frog (Ascaphus truei)), fishes (e.g., chinook salmon (Oncorhynchus tshawytscha), bull trout (Salvelinus confluentus), and birds (e.g., northern spotted owl (Strix occidentalis caurina), northern goshawk Accipiter gentilis)) have been the focus of conservation attention in this region because of their close association with declining habitat types such as aquatic areas, seeps, talus slopes, old growth, and riparian forests (Bury and Corn 1988, USDA For. Serv. 1994). The threatened northern spotted owl has been used as an indicator species in environmental impact assessments because its range overlaps with 39 listed or proposed species (10 of which are late-seral associates) and 1,116 total species associated with late-seral forests (USDA For. Serv. 1994:S-15). Late-seral forests in general are of national and global importance because they provide some of the last refugia for dependent species, and perform vital ecological services, including sequestration of carbon, cleansing of atmospheric pollutants, and maintenance of hydrological regimes. At finer mapping scales, the USDA Forest Service and USDI Bureau of Land Management (1996:98) have identified two hot biodiversity spots within the Southern Cascades and Upper Klamath Ecological Reporting Units (overlaps with this ecoregion). These areas contain unusually high levels of species richness for diverse taxa (e.g., invertebrates, bryophytes, lichens, fungi, vascular plants, and vertebrates) relative to other ecological reporting areas within the Columbia River Basin. One of the two hot spots also received a relatively high composite ecological integrity ranking, meaning that the area still consists of a mosaic of plant and animal communities maintained by well-connected, high-quality habitats (USDA For. Serv. and USDI Bur. Land Manage. 1996:115). Habitat Loss and Degradation Habitat loss within late-seral forests and aquatic areas have been extensive throughout this ecoregion (see USDA For. Serv. and USDI Bur. Land Manage. 1996 for portions of this ecoregion that lie within the Columbia River Basin analysis area). In particular, late-seral multi- and single-story forests have declined basin-wide to as much as 40 percent of their original extent (see USDA For. Serv. and USDI Bur. Land Manage. 1996:81). Late-seral forests in general have experienced sharp declines in many other ecoregions within the temperate coniferous forest major habitat type and are therefore a national as well as ecoregional priority (e.g., see ecoregions 23,24, 29-35, 37-39, 42, 44). In addition, mid-seral subalpine forests have experienced a 35 percent decrease while late-seral montane multi-story forests have increased by 35 percent (USDA For. Serv. and USDI Bur. Land Manage. 1997:2-88). Moreover, many terrestrial and aquatic areas within this ecoregion have relatively low composite ecological integrity rankings due primarily to cumulative impacts of extensive logging, road building, and hydroelectric development (USDA For. Serv. and USDI Bur. Land Mange. 1996:109, 118, 121, 124, 127). Declines in salmonid populations have been severe throughout the ecoregion and basin-wide (USDA For. Serv. and USDI Bur. Land Manage. 1996:109); however, a few aquatic strongholds and areas of very low road densities still persist within the ecoregion (USDA For. Serv. and USDI Bur. Land Manage. 1996:110). In addition to the above declines, ecological processes in this region have been altered by a century of fire suppression activities that have increased the severity and extent of fires and altered fire-dependent plant communities (see DellaSala et al. 1995, 1996 for general discussions of basin-wide fire suppression effects, and USDA For. Serv. and USDI Bur. Land Manage. 1996:90, 91, 127 for regional discussions). The absence of periodic fires also has resulted in declines in rangeland integrity and increases in exotic species invasions (USDA For. Serv. and USDI Bur. Land Manage. 1996:88). Remaining Blocks of Intact Habitat Both the Oregon and Washington GAP projects provide more detailed information on remaining intact blocks of habitat and areas of high biological importance outside protected areas. In addition, the USDA Forest Service and USDI Bureau of Land Management (1996) identified other key areas of importance to fish and terrestrial biodiversity, particularly the aquatic strongholds and biodiversity hot spots discussed above. The workshop participants provided the following local knowledge of relatively intact habitats that should be added to these sources:
Degree of Fragmentation Fragmentation has been extensive throughout this region, as indicated by the few remaining intact late-seral forests, high road densities, and low ecological integrity rankings discussed above. Degree of Protection Protected sites in this ecoregion primarily include the remaining intact habitat blocks identified above. In addition, several late-seral forest reserves have been administratively protected under the President's Northwest Forest plan (USDA For. Serv. 1994) for forests within the range of the northern spotted owl. However, many of these administratively protected areas as well as the aquatic diversity areas remain vulnerable to Congressionally-mandated salvage logging under the timber salvage rider. Types and Severity of Threats Logging is the primary threat to biodiversity in this region. Fire suppression, exotic species invasions, and road building have caused extensive damage to key watersheds, late-seral forests, and rangelands in this ecoregion.
 Relationship to other classification schemes This ecoregion corresponds to Omernik's Level III ecoregion 4 (Cascades). There is high concordance in the centroids of this ecoregion when compared to McNab and Bailey's (1994) classification (ecoregion 242B). However, their delineation of this ecoregion continues further north, encompassing the entire Cascade Mountain range within the U.S. (i.e., includes the southern portion of ecoregion 33). In addition, this ecoregion overlaps with three physiographic provinces identified by Franklin and Dyrness (1973), including the Southern, Western, and High Cascades. Prepared by: D. DellaSala, J. Strittholt, R. Noss, and G. Orians This text was originally published in the book Terrestrial ecoregions of North America: a conservation assessment from Island Press. This assessment offers an in-depth analysis of the biodiversity and conservation status of North America's ecoregions. All text by World Wildlife Fund © 2001 For more general information on this ecoregion, go to the WildWorld version of this description.
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