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Level 3 Ecoregions of the United States
Learn more about:
- Ecoregions of the US
- Ecological Regions within the Mid-Atlantic
- Major
Ecoregions of Washington State
- Alaska
Ecoregion Mapping
- Ecoregions
of Minnesota and Associated Wetlands
- Ecoregions
of North and South Dakota
- Ecoregions
of the White River Basin, Indiana
- Forest
Service Ecoregions
- Natural
Regions of Texas
- Ecoregions
of the Red River Valley, Minnesota
(adpated from Omernik 1995)
The first compilation of ecoregions of the conterminous United States by EPA was performed at a relatively cursory 1:3,168,000 scale and was published at a smaller 1:7,500,000 scale (Omernik 1987). The approach recognized that the combination and relative importance of characteristics that explain ecosystem ecosystem regionality vary from one place to another and from one hierarchical level to another. This is similar to to the approach used by Environment Canada (Wiken 1986). In describing ecoregionalization in Canada, Wiken (1986) stated:
"Ecological land classification is a process of delineating and classifying ecologically distinctive areas of the earth's surface. Each area can be viewed as a discrete system which has resulted from the mesh and interplay of the geologic, landform, soil, vegetative, climatic, wildlife, water, and human factors which may be present. The dominance of any one or a number of these factors varies with the given ecological land unit. This holistic approach to land classification can be applied incrementally on a scale-related basis from very site-specific ecosystems to very broad ecosystems."
Hence, the difference between this approach to defining ecoregions and most preceding methods is that it is based on the hypothesis that ecological regions gain their identity through spatial differences in a combination of landscape characteristics. The factors that are more or less important vary from one place to another at all scales. One of the strengths of the approach lies in the analysis of multiple geographic characteristics that are believed to cause or reflect differences in the mosaic of ecosystems, including their potential composition. All maps of particular characteristics (e.g., soils, physiography, climate, vegetation, geology, and land use) are merely representations of aspects of that characteristic.