Ecoregions of Oregon, and of Western Oregon and Washington

Introductory text
Literature cited


(NOTE: maps and GIS files may differ. To make sure you are using the most current ecoregion data, download shapefiles of ecoregions)

GIS data (shapefiles, metadata and symbology):
Ecoregions of Oregon--poster front side

Map (available in PDF format):

Ecoregions of Oregon--poster back side

Map (available in PDF format):

Level III and IV Ecoregions of Oregon

Map (available in PDF format):

Level III and IV Ecoregions of Oregon

Map (available in PDF format):

Ecoregions of Western Oregon and Washington--poster front side

Map (available in PDF format):

Ecoregions of Western Oregon and Washington--poster back side

Map (available in PDF format):

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 the environment by its probable response to disturbance (Bryce and others, 1999). Ecoregions are directly applicable to the immediate needs of state agencies, including the development of biological criteria and water quality standards and the establishment of management goals for nonpoint-source pollution (Omernik and Griffith, 1991; Hughes and others, 1990; Whittier and others, 1988). They are also relevant to integrated ecosystem management, an ultimate goal of many federal and state resource management agencies.

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 distributions, 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], 2003). 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 is ecologically diverse. The west side of the state has a marine-influenced climate and receives plentiful precipitation three seasons of the year. In contrast, eastern Oregon lies in the rain shadow of the Cascades and is much drier. The climatic gradient is evident in the state's landscapes: forested mountains, glaciated peaks, shrub- and grass-covered plains, agricultural valleys, beaches, desert playas, and wetlands. 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, 2003; McGrath and others, 2002; Pater and others, 1998).

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 coarser scale (Omernik, 1987; USEPA, 2003).

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 States Department of Agriculture–Forest Service (USFS), the United States 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 part of an interagency effort to develop a common framework of ecological regions for the United States. 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.

Literature Cited:

Bailey, R.G., Avers, P.E., King, T., and McNab, W.H., eds., 1994, Ecoregions and subregions of the United States (map) (supplementary table of map unit descriptions compiled and edited by McNab, W.H. and Bailey, R.G.): Washington, D.C., USFS, scale 1:7,500,000.

Bryce, S.A., Omernik, J.M., and Larsen, D.P., 1999, Ecoregions – a geographic framework to guide risk characterization and ecosystem management: Environmental Practice, v. 1, no. 3, p. 141-155.

Bryce, S.A., Woods A.J., Morefield, J.D., Omernik, J.M., McKay, T.R., Brackley, G.K., Hall, R.K., Higgins, D.K., McMorran, D.C., Vargas, K.E., Petersen, E.B., Zamudio, D.C., and Comstock, J.A., 2003, Ecoregions of Nevada: Reston, Virginia, U.S. Geological Survey, map scale 1:1,350,000.

Clarke, S.E., and Bryce, S.A., eds., 1997, Hierarchical subdivisions of the Columbia Plateau and Blue Mountains Ecoregions, Oregon and Washington: Portland, Oregon, USFS, Pacific Northwest Research Station, General Technical Report PNW-GTR-395.

Commission for Environmental Cooperation Working Group, 1997, Ecological regions of North America – toward a common perspective: Montreal, Commission for Environmental Cooperation, 71 p.

Gallant, A.L., Whittier, T.R., Larsen, D.P., Omernik, J.M., and Hughes, R.M., 1989, Regionalization as a tool for managing environmental resources: Corvallis, Oregon, U.S. Environmental Protection Agency, EPA/600/3-89/060, 152 p.

Griffith, G.E., Omernik, J.M., Wilton, T.F., and Pierson, S.M., 1994, Ecoregions and subregions of Iowa – a framework for water quality assessment and management: Journal of the Iowa Academy of Science, v. 101, no. 1, p. 5-13.

Hughes, R.M., Whittier, T.R., Rohm, C.M., and Larsen, D.P., 1990, A regional framework for establishing recovery criteria: Environmental Management, v. 14, no. 5, p. 673-683.

McGrath, C.L., Woods A.J., Omernik, J.M., Bryce, S.A., Edmondson, M., Nesser, J.A., Shelden, J., Crawford, R.C., Comstock, J.A., and Plocher, M.D., 2002, Ecoregions of Idaho: Reston, Virginia, U.S. Geological Survey, map scale 1:1,350,000.

Omernik, J.M., 1987, Ecoregions of the conterminous United States (map supplement): Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125, scale 1:7,500,000.

Omernik, J.M., 1995, Ecoregions – a framework for environmental management, in Davis, W.S. and Simon, T.P., eds., Biological assessment and criteria-tools for water resource planning and decision making: Boca Raton, Florida, Lewis Publishers, p. 49-62.

Omernik, J.M., Chapman, S.S., Lillie, R.A., and Dumke, R.T., 2000, Ecoregions of Wisconsin: Transactions of the Wisconsin Academy of Sciences, Arts, and Letters, v. 88, p. 77-103.

Omernik, J.M. and Griffith, G.E., 1991, Ecological regions vs. hydrologic units: frameworks for managing water quality: Journal of Soil and Water Conservation, v. 46, no. 5, p. 334-340.

Pater, D.E., Bryce, S.A., Thorson, T.D., Kagan, J., Chappell, C., Omernik, J.M., Azevedo, S.H., and Woods, A.J., 1998, Ecoregions of Western Washington and Oregon: Reston, Virginia, U.S. Geological Survey, map scale 1:1,350,000.

U.S. Department of Agriculture–Soil Conservation Service, 1981, Land resource regions and major land resource areas of the United States: Agriculture Handbook 296, 156 p.

U.S. Environmental Protection Agency, 2003, Level III ecoregions of the continental United States (revision of Omernik, 1987): Corvallis, Oregon, USEPA – National Health and Environmental Effects Research Laboratory, Map M-1, various scales.

Wiken, E., 1986, Terrestrial ecozones of Canada: Ottawa, Environment Canada, Ecological Land Classification Series no. 19, 26 p.

Whittier, T.R., Hughes, R.M., and Larsen, D.P., 1988, Correspondence between ecoregions and spatial patterns in stream ecosystems in Oregon: Canadian Journal of Fisheries and Aquatic Sciences, v. 45, p. 1264-1278.

PRINCIPAL AUTHORS: Thor D. Thorson (NRCS), Sandra A. Bryce (Dynamac Corporation), Duane A. Lammers (USFS), Alan J. Woods (Dynamac Corporation), James M. Omernik (USEPA, retired), Jimmy Kagan (Oregon Natural Heritage Program), David E. Pater (Water Quality Program, Washington Department of Ecology), and Jeffrey A. Comstock (Indus Corporation).

COLLABORATORS AND CONTRIBUTORS: Thomas Atzet (USFS), Hugh Barrett (U.S. Department of Interior, Bureau of Land Management), Rick Hafele (Oregon Department of Environmental Quality), Charles Johnson (USFS), Thomas Loveland (USGS), Robert Meurisse (USFS, retired), Chad L. McGrath (NRCS), and Robert Ottersberg (Cordilleran Services, Inc.).

REVIEWERS: Sharon E. Clarke (Oregon State University), Robert M. Hughes (Dynamac Corporation), and Michael A. Bollman (Dynamac Corporation).

CITING THIS POSTER: Thorson, T.D., Bryce, S.A., Lammers, D.A., Woods, A.J., Omernik, J.M., Kagan, J., Pater, D.E., and Comstock, J.A., 2003. Ecoregions of Oregon (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000).

This project was partially supported by funds from the USEPA–Office of Research and Development's Environmental Monitoring and Assessment Program through contract 68-C6-005 to Dynamac Corporation. Partial funding was also provided by the Oregon Watershed Enhancement Board.

Ecoregion Links

Ecoregion Home  |  Level I  |  Level IILevel III  |  Level IV  |  Publications  |  Download Site  |  Links  |  Contacts