EPA Level III and IV Ecoregions of EPA Region 3

The U.S. Environmental Protection Agency (EPA) denotes ecoregions as areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources. Federal and state agencies also use this resource as a spatial framework for the assessment, management, and monitoring of ecosystems and its components. The approach used to compile ecoregion maps is based on the premise that ecological regions can be identified by analyzing the patterns and composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity. These phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology, which are examined for patterns of coincidence that cause or reflect differences in ecosystem characteristics. Level III is a class that divides the continental United States into 104 ecoregions and Level IV ecological regions are further subdivisions of Level III units. The exact number of ecological regions at each hierarchical level is still changing slightly as the framework undergoes development at the international, national, and local levels.

Courtesy of the U.S. Environmental Protection Agency.