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In the United States, the EPA and the United States Geological Survey (USGS) are the principal federal agencies working with the CEC to define and map ecoregions. Ecoregions may be identified by similarities in geology , physiography , vegetation , climate , soils , land use , wildlife distributions, and hydrology .
A map of the United States showing the 10 regions of the Environmental Protection Agency. Key: Region 1: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont.
Terrestrial Ecoregions of the World (Olson et al. 2001, BioScience) WWF terrestrial ecoregions of the world One way of mapping the world into 18 terrestrial vegetation biomes, each containing one or more ecoregions EPA level III ecoregions in the contiguous United States. Alaska ecoregions (102-120) not shown.
Ecoregions of North America, featuring the 50 United States, the District of Columbia and the five inhabited territories. The following is a list of ecoregions in the United States as identified by the World Wide Fund for Nature (WWF). The United States is a megadiverse country with a high level of endemism across a wide variety of ecosystems.
U.S. Census Bureau regions and divisions. Since 1950, the United States Census Bureau defines four statistical regions, with nine divisions. [1] [2] The Census Bureau region definition is "widely used... for data collection and analysis", [3] and is the most commonly used classification system.
"Level I" divides North America into 15 broad ecoregions. "Level II" subdivides the continent into 52 smaller ecoregions. "Level III" subdivides those regions again into 182 ecoregions. [1] [2] "Level IV" is a further subdivision of Level III ecoregions. Level IV mapping is still underway but is complete across most of the United States.
The system dates to Nevin Fenneman's report Physiographic Divisions of the United States, published in 1916. [2] [3] The map was updated and republished by the Association of American Geographers in 1928. [4] The map was adopted by the United States Geological Survey by publication in 1946. [5]