"The Omernik ecoregion system is hierarchical and considers the spatial patterns of both the living and non-living components of the region, such as geology, physiography, vegetation, climate, soils, land use, wildlife, water quality, and hydrology. The patterns affect or reflect differences in ecosystem quality and integrity. All the components are considered when determining the location of ecoregion boundaries. The relative importance of each component may vary from one ecoregion to another, regardless of the level of the hierarchy. For example, for one ecoregion, geology may be the primary characteristic that determines the ecoregion boundaries. For another, a combination of soils and climate may be what defines the ecoregion. This is true whether the ecoregion is continental in scale, local in scale, or falls somewhere in between." - National Atlas of the United States
BRDC uses this version of defining ecoregions because it prefers the “weight-of-evidence” approach offered by Omernik for educational interpretive purposes. Other means of interpreting ecoregions are weighted to further other specific causes, such as protection of rare and endangered species or conservation planning.
For maps showing the Ecoregions of North America, visit:
Levels I, II, and III resolution: http://www.epa.gov/wed/pages/ecoregions/na_eco.htm#Level%20I
Level III and IV resolution: http://www.epa.gov/wed/pages/ecoregions/level_iv.htm