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, Omernik, and Larsen, 1999).

Ecoregions are general purpose regions that 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 in the same geographical areas (Omernik and others, 2000). 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 (U.S. Environmental Protection Agency [USEPA], 2003). Level IV ecoregions are further subdivisions of level III ecoregions. Explanations of the methods used to define the USEPA’s ecoregions are given in Omernik (1995), Omernik and others (2000), and Gallant and others (1989).

The approach used to compile the ecoregion map of Arkansas 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 characteristics that affect or reflect differences in ecosystem quality and integrity (Wiken, 1986; Omernik, 1987, 1995). These characteristics include geology, physiography, climate, soils, land use, wildlife, fish, hydrology, and vegetation (including “potential natural vegetation” defined by Küchler (p. 2, 1964) as “vegetation that would exist today" if human influence ended and "the resulting plant succession" was "telescoped into a single moment”). The relative importance of each characteristic varies from one ecological region to another regardless of ecoregion hierarchical level.

In Arkansas, there are 7 level III ecoregions and 32 level IV ecoregions; all but four level IV ecoregions continue into ecologically similar parts of adjacent states (Chapman and others, 2002, 2004a, 2004b; Griffith, Omernik, and Azevedo, 1998). Arkansas’ ecological diversity is strongly related to regional physiography, geology, soil, climate, and land use. Elevated karst plateaus, folded mountains, agricultural valleys, forested uplands, and bottomland forests occur. Fire-maintained prairie was once extensive in several parts of the state.

The ecoregion map on this poster was compiled at a scale of 1:250,000, and depicts revisions and subdivisions of earlier level III ecoregions that were originally compiled at a smaller scale (U.S. Environmental Protection Agency, 2003; Omernik, 1987). It is part of a collaborative project primarily between USEPA Region 6, USEPA–National Health and Environmental Effects Research Laboratory (Corvallis, OR.), and the Multi-Agency Wetland Planning Team (MAWPT), which comprises representatives of six Arkansas state agencies (Arkansas Natural Heritage Commission, Arkansas Soil and Water Conservation Commission, Arkansas Game and Fish Commission, Arkansas Department of Environmental Quality, Arkansas Forestry Commission, and University of Arkansas Cooperative Extension Service). Collaboration and consultation also occurred with the U.S. Army Corps of Engineers (USACE), U.S. Department of Agriculture–Natural Resources Conservation Service (NRCS), U.S. Geologic Survey (USGS), U.S. Fish and Wildlife Service, USGS–Earth Resources Observation Systems Data Center, and University of Arkansas–Center for Advanced Spatial Technologies.

This project is associated with an interagency effort to develop a common framework of ecological regions (McMahon and others, 2001). 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 U.S. Department of Agriculture–Forest Service (Bailey and others, 1994), the USEPA (Omernik 1987, 1995), and the U.S. Department of Agriculture–Soil Conservation Service (1981). As each of these frameworks is further refined, their differences are becoming less discernible. Each collaborative ecoregion project, such as this one in Arkansas, is 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., editors, 1994, Ecoregions and subregions of the United States (map): Washington, D.C., U.S. Department of Agriculture–Forest Service, map 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.

Chapman, S.S., Griffith, G.E., Omernik, J.M., Comstock, J.A., Beiser, M.C., and Johnson, D., 2004a, Ecoregions of Mississippi (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey, map scale 1:1,000,000.

Chapman, S.S., Kleiss, B.A., Omernik, J.M., Foti, T.L., and Murray, E.O., 2004b, Ecoregions of the Mississippi Alluvial Plain (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey, map scale 1:1,150,000.

Chapman, S.S., Omernik, J.M., Griffith, G.E., Schroeder, W.A., Nigh, T.A., and Wilton, T.F., 2002, Ecoregions of Iowa and Missouri (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey, map scale 1:1,800,000.

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., Omernik, J., and Azevedo, S., 1998, Ecoregions of Tennessee (color poster with map, descriptive text, summary tables, and photographs): Reston, U.S. Geological Survey, scale 1:940,000.

Küchler, A.W., 1964, Potential natural vegetation of the conterminous United States (map and manual): American Geographic Society, Special Publication 36, map scale 1:3,168,000.

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, p. 118-125, map scale 1:7,500,000.

Omernik, J.M., 1995, Ecoregions – a framework for environmental management, in Davis, W.S., and Simon, T.P., editors, 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.

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, Western Ecology Division, Map M-1, various scales.

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

PRINCIPAL AUTHORS: Alan J. Woods (Oregon State University), Thomas L. Foti (Arkansas Natural Heritage Commission), Shannen S. Chapman (Dynamac Corporation), James M. Omernik (USEPA, retired), James A. Wise (Arkansas Department of Environmental Quality), Elizabeth O. Murray (Arkansas Multi-Agency Wetland Planning Team), William L. Prior (Arkansas Geological Commission), Joe B. Pagan, Jr. (U.S. Department of Agriculture–Natural Resources Conservation Service), Jeffrey A. Comstock (Indus Corporation), and Michael Radford (Arkansas Soil and Water Conservation Commission).

COLLABORATORS AND CONTRIBUTORS: Ken Brazil (Arkansas Soil and Water Conservation Commission), Kenneth Colbert (Arkansas Soil and Water Conservation Commission), Philip Crocker (U.S. Environmental Protection Agency), Brian Culpepper (University of Arkansas–Center for Advanced Spatial Technologies), Billy Justus (U.S. Geological Survey), Barbara A. Kleiss (USACE, ERDC–Waterways Experiment Station), Bob Leonard (Arkansas Game and Fish Commission), Thomas R. Loveland (U.S. Geological Survey), Larry Nance (Arkansas Forestry Commission), and Rex Roberg (Arkansas Cooperative Extension Service).

REVIEWERS: John Giese (Arkansas Department of Pollution Control and Ecology, retired), Robert J. Lillie (Professor, Department of Geosciences, Oregon State University), and Kenneth Smith (Executive Director, Audubon Arkansas).

CITING THIS POSTER: Woods A.J., Foti, T.L., Chapman, S.S., Omernik, J.M., Wise, J.A., Murray, E.O., Prior, W.L., Pagan, J.B., Jr., Comstock, J.A., and Radford, M., 2004, Ecoregions of Arkansas (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,000,000).

This project was partially supported by funds from the USEPA Region 6, Biocriteria Program and USEPA–Office of Science and Technology through a contract with Dynamac Corporation. It was also partially supported by funds from the Arkansas Soil and Water Conservation Commission through grants provided by the USEPA Region 6 under the provisions of Section 104(b) (3) of the Clean Water Act (through the wetlands grant program).