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LEVEL III AND IV ECOREGIONS OF OREGON
Description:
Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources; they are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components. By recognizing the spatial differences in the capacities and potentials of ecosystems, ecoregions stratify 1999). Ecoregions are critical for structuring and implementing ecosystem management strategies across federal agencies, state agencies, and nongovernment organizations that are responsible for different types of resources within the same geographical areas (Omernik and others, 2000). The approach used to compile this map is based on the premise that ecological regions can be identified through the analysis of the spatial patterns and the composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity (Wiken, 1986; Omernik, 1987, 1995). These phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The relative importance of each characteristic varies from one ecological region to another regardless of the hierarchical level. A Roman numeral hierarchical scheme has been adopted for different levels of ecological regions. Level I is the coarsest level, dividing North America into 15 ecological regions. Level II divides the continent into 52 regions (Commission for Environmental Cooperation Working Group, 1997). At level III, the continental United States contains 104 ecoregions and the conterminous United States has 84 ecoregions (United States Environmental Protection Agency [USEPA], 2000). Level IV is a further subdivision of level III ecoregions. Explanations of the methods used to define the USEPA's ecoregions are given in Omernik (1995), Omernik and others (2000), Griffith and others (1994), and Gallant and others (1989). Oregon contains forested mountains, woodland- shrubland- and forest-covered hills, shrub- and grass-covered plains, agricultural valleys, glaciated peaks, volcanic plateaus, coastal headlands, marine terraces, beaches, playas and wetlands. Ecological diversity is enormous. The west receives plentiful precipitation during the fall, winter, and spring. The eastern 2/3 in the rain shadow of the Cascade Range and is much drier than the west. There are 9 level III ecoregions and 65 level IV ecoregions in Oregon and many continue into ecologically similar parts of adjacent states (Bryce and others, in press). This level III and IV ecoregion map was compiled at a scale of 1:250,000. The western part was originally published as part of Pater and others (1998). The level IV lines in the Columbia Plateau and Blue Mountains were originally published in Clarke and Bryce (1997). Ecoregion boundaries in the remainder of Oregon depict revisions and subdivisions of earlier level III ecoregions that were originally compiled at a smaller scale (USEPA, 1996; Omernik, 1987). This poster is the product of a collaborative effort primarily between the USEPA Region X, the USEPA National Health and Environmental Effects Research Laboratory (Corvallis, Oregon), the Oregon Natural Heritage Program, the United Department of Agriculture-Natural Resources Conservation Service (NRCS) (formerly the Soil Conservation Service), and the United States Department of the Interior-Geological Survey (USGS)-Earth Resources Observation Systems (EROS) Data Center. The Oregon ecoregion project is associated with an interagency effort to develop a common framework of ecological regions. Reaching that objective requires recognition of the differences in the conceptual approaches and mapping methodologies applied to develop the most common ecoregion-type frameworks, including those developed by the USFS (Bailey and others, 1994), the USEPA (Omernik, 1987, 1995), and the NRCS (U.S. Department of Agriculture- Soil Conservation Service, 1981). As each of these frameworks is further refined, their differences are becoming less discernible. Regional collaborative projects such as this one in Oregon, where agreement has been reached among multiple resource management agencies, are a step toward attaining consensus and consistency in ecoregion frameworks for the entire nation.