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Ecoregions of the Conterminous United States: Evolution of a Hierarchical Spatial Framework

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Abstract

A map of ecological regions of the conterminous United States, first published in 1987, has been greatly refined and expanded into a hierarchical spatial framework in response to user needs, particularly by state resource management agencies. In collaboration with scientists and resource managers from numerous agencies and institutions in the United States, Mexico, and Canada, the framework has been expanded to cover North America, and the original ecoregions (now termed Level III) have been refined, subdivided, and aggregated to identify coarser as well as more detailed spatial units. The most generalized units (Level I) define 10 ecoregions in the conterminous U.S., while the finest-scale units (Level IV) identify 967 ecoregions. In this paper, we explain the logic underpinning the approach, discuss the evolution of the regional mapping process, and provide examples of how the ecoregions were distinguished at each hierarchical level. The variety of applications of the ecoregion framework illustrates its utility in resource assessment and management.

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Acknowledgments

The authors would like to thank the numerous people who helped map, author, review, fund, promote, or otherwise provide support in the development of the ecoregion framework discussed in this paper. While there are many individuals who should be acknowledged, special thanks are given (alphabetically) to the other members of our geography team who did large portions of the research, writing, and mapping of the nation, especially Sandy Bryce, Shannen Chapman, Alisa Gallant, and Alan Woods; to those who provided other technical, research, or organizational support including Sandy Azevedo, Doug Brown, Sharon Clarke, Jeff Comstock, Jerry Freeouf, Andy Herstrom, Hoke Howard, Colleen Burch Johnson, Duane Lammers, Chad McGrath, Henry McNab, Brian Moran, David Pater, Sue Pierson, Ben Sleeter, Dave Smith, Thor Thorson, Marc Weber, Denis White, and Ed Wiken; and to those who helped with the institutional support and fundamental design including Mike Beiser, Phil Crocker, Jack Gakstatter, Jim Harrison, Bob Hughes, Phil Larsen, Rick Linthurst, Tom Loveland, Jerry McMahon, Tony Olsen, Steve Paulsen, Tony Selle, Safa Shirazi, John Stoddard, Tom Wilton, and Chris Yoder.

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  1. U.S. Geological Survey, c/o US EPA, 200 SW 35th Street, Corvallis, OR, 97333, USA

    James M. Omernik & Glenn E. Griffith

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Omernik, J.M., Griffith, G.E. Ecoregions of the Conterminous United States: Evolution of a Hierarchical Spatial Framework. Environmental Management 54, 1249–1266 (2014). https://doi.org/10.1007/s00267-014-0364-1

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