EcoregionSplit

Ecoregions are areas where ecosystems (and the type, quality, and quantity of environmental resources) are
generally similar. They are designed to serve as a spatial framework for the research, assessment,
management, and monitoring of ecosystems and ecosystem components. These Level III and IV ecoregions,
compiled at a scale of 1:250,000, revise and subdivide an earlier, smaller-scale national ecoregion map
(Omernik, 1987). The ecoregions were identified by analyzing the spatial patterns and the composition of
biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity (Omernik,
1987, 1995). These phenomena include geology, landforms, soils, vegetation, climate, land use, wildlife,
and hydrology. The relative importance of each characteristic varies from one ecological region to another
regardless of the hierarchical level. An ecoregion framework is 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 geographic areas (McMahon and others,
2001; Omernik and Griffith, 2014).
A Roman numeral hierarchical scheme has been adopted for different levels of ecological regions. Level I
is the most general level, dividing North America into 15 ecological regions. Level II divides the continent
into 50 regions (Commission for Environmental Cooperation, 1997, 2006). At level III, the continent contains
183 ecological regions of which 105 occur in the continental United States (United States Environmental
Protection Agency [U.S. EPA], 2013; Wiken and others, 2011).
The Level III and IV ecoregions of the Pacific Northwest were mapped in state-level projects in Idaho
(McGrath and others, 2001), Oregon (Thorson and others, 2003) and Washington (Clarke and Bryce, 1997;
Pater and others, 1998). These projects were conducted primarily by the U.S. EPA National Health and
Environmental Effects Research Laboratory (Corvallis, Oregon) in collaboration with U.S. EPA Region 10,
state resource management agencies, and other federal agencies, such as the U.S. Department of Agriculture
(USDA)–Natural Resources Conservation Service, USDA–Forest Service, U.S. Geological Survey, and the
Bureau of Land Management. The mapping was associated with an interagency effort to develop a common
framework of ecological regions (McMahon and others, 2001). Although there are differences in the
conceptual approaches and mapping methodologies used by the different federal agencies for developing
their own regional frameworks, these collaborative ecoregion projects were a step toward attaining
consensus and consistency in ecoregion frameworks for the entire nation.
Explanations of the methods used to define these ecoregions are given in Omernik (1995, 2004) and
Omernik and Griffith (2014). Additional maps, publications, and GIS data for U.S. and North American
ecoregions can be obtained at www.epa.gov/eco-research/ecoregions.

Clarke, S.E., and Bryce, S.A., eds., 1997, Hierarchical subdivisions of the Columbia Plateau and Blue Mountains
Ecoregions, Oregon and Washington. Portland: U.S. Department of Agriculture-Forest Service General Technical
Report PNW-GTR-395, 114 p.
Commission for Environmental Cooperation, 1997, Ecological regions of North America – toward a common
perspective: Montreal, Quebec, Canada, Commission for Environmental Cooperation, 71 p. (map revised 2006),
www.epa.gov/eco-research/ecoregions-north-america.
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 (color poster with map, descriptive text, summary
tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,350,000).
McMahon, G., Gregonis, S.M., Waltman, S.W., Omernik, J.M., Thorson, T.D., Freeouf, J.A., Rorick, A.H., and Keys,
J.E., 2001, Developing a spatial framework of common ecological regions for the conterminous United States:
Environmental Management, v. 28, no. 3, p. 293-316.
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., 2004, Perspectives on the nature and definition of ecological regions: Environmental Management, v. 34,
Supplement 1, p. s27-s38.
Omernik, J.M., and Griffith, G.E., 2014, Ecoregions of the conterminous United States ‒ evolution of a hierarchical spatial
framework: Environmental Management, v. 54, no. 6, p. 1249-1266, https://dx.doi.org/10.1007/s00267-014-0364-1
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 (2 sided color poster with map, descriptive text, summary tables, and
photographs). U.S. Geological Survey, Reston, VA. Scale 1:1,350,000.
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).
U.S. Environmental Protection Agency, 2013, Level III ecoregions of the continental United States: Corvallis, Oregon,
US EPA, Western Ecology Division, National Health and Environmental Effects Research Laboratory,
www.epa.gov/eco-research/level-iii-and-iv-ecoregions-continental-united-states.
Wiken, E., Jiménez Nava, F., and Griffith, G., 2011, North American Terrestrial Ecoregions - Level III. Commission
for Environmental Cooperation, Montreal, Canada. 149 p.,
https://ecologicalregions.info/htm/pubs/NA_TerrestrialEcoregionsLevel3_Final-2june11_CEC.pdf<div><br /></div><div><br /></div><div><span style='font-family:&quot;Avenir Next W01&quot;, &quot;Avenir Next W00&quot;, &quot;Avenir Next&quot;, Avenir, &quot;Helvetica Neue&quot;, sans-serif; font-size:17px;'>To view this in the larger story map with other ecoregions in Washington State, please go to here: </span><font face='Avenir Next W01, Avenir Next W00, Avenir Next, Avenir, Helvetica Neue, sans-serif'><span style='font-size:17px;'>https://fws.maps.arcgis.com/apps/Shortlist/index.html?appid=44c1fb1ebd69415689b9f6823f29595f</span></font><br /></div>