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A map location of the Amazon Rainforest ecoregions. The yellow line encloses the ecoregions per the World Wide Fund for Nature.
A map of North America's Bioregions

An ecoregion (ecological region) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are larger than an ecosystem.[citation needed] Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remain relatively constant, within an acceptable range of variation (largely undefined at this point). Three caveats are appropriate for all biogeographic mapping approaches. Firstly, no single biogeographic framework is optimal for all taxa. Ecoregions reflect the best compromise for as many taxa as possible. Secondly, ecoregion boundaries rarely form abrupt edges; rather, ecotones and mosaic habitats bound them. Thirdly, most ecoregions contain habitats that differ from their assigned biome. Biogeographic provinces may originate due to various barriers. Some physical (plate tectonics, topographic highs), some climatic (latitudinal variation, seasonal range) and some ocean chemical related (salinity, oxygen levels).

Definition and categorization[edit]

A conifer forest in the Swiss Alps (National Park).

An ecoregion is a "recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region"[1] Omernik (2004), elaborates on this by defining ecoregions as: “areas within which there is spatial coincidence in characteristics of geographical phenomena associated with differences in the quality, health, and integrity of ecosystems[2] “Characteristics of geographical phenomena” may include geology, physiography, vegetation, climate, hydrology, terrestrial and aquatic fauna, and soils, and may or may not include the impacts of human activity (e.g. land use patterns, vegetation changes). There is significant, but not absolute, spatial correlation among these characteristics, making the delineation of ecoregions an imperfect science. Another complication is that environmental conditions across an ecoregion boundary may change very gradually, e.g. the prairie-forest transition in the midwestern United States, making it difficult to identify an exact dividing boundary. Such transition zones are called ecotones.

Ecoregions can be categorized using an algorithmic approach or a holistic, “weight-of-evidence” approach where the importance of various factors may vary. An example of the algorithmic approach is Robert Bailey’s work for the U.S. Forest Service, which uses a hierarchical classification that first divides land areas into very large regions based on climatic factors, and subdivides these regions, based first on dominant potential vegetation, and then by geomorphology and soil characteristics. The weight-of-evidence approach is exemplified by James Omernik’s work for the United States Environmental Protection Agency, subsequently adopted (with modification) for North America by the Commission for Environmental Cooperation.



(b) Share similar environmental conditions, and;














Marine ecoregions are: “Areas of relatively homogeneous species composition, clearly distinct from adjacent systems….In ecological terms, these are strongly cohesive units, sufficiently large to encompass ecological or life history processes for most sedentary species.”[4] They have been defined by The Nature Conservancy (TNC) and World Wildlife Fund (WWF) to aid in conservation activities for marine ecosystems. Forty-three priority marine ecoregions were delineated as part of WWF’s Global 200 efforts.[5] The scheme used to designate and classify marine ecoregions is analogous to that used for terrestrial ecoregions. Major habitat types are identified: polar, temperate shelves and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic (trades and westerlies), abyssal, and hadal (ocean trench). These correspond to the terrestrial biomes.


See Global 200 Marine ecoregions for a full list of marine ecoregions.[6]






A new map of Freshwater Ecoregions of the World, released in 2008, has 426 ecoregions covering virtually the entire non-marine surface of the earth.[7]



See also[edit]


  2. ^ Omernik, J. M. (2004). "Perspectives on the Nature and Definition of Ecological Regions". Environmental Management. p. 34 - Supplement 1, pp.27–38. 
  3. ^ WWF: Terrestrial Ecoregions
  5. ^ Olson and Dinerstein 1998 and 2002
  7. ^ "Freshwater Ecoregions of the World". WWF. 

Further reading[edit]

  • Olson, DM, E Dinerstein, ED Wikramanayake, ND Burgess, GVN Powell, EC Underwood, JA D’Amico, HE Strand, JC Morrison, CJ Loucks, TF Allnutt, JF Lamoreux, TH Ricketts, I Itoua, WW Wettengel, Y Kura, P Hedao, and K Kassem. 2001. Terrestrial ecoregions of the world: A new map of life on Earth. BioScience 51:933-938.
  • Mark D. Spalding, Helen E. Fox, Gerald R. Allen, Nick Davidson, Zach A. Ferdaña, Max Finlayson, Benjamin S. Halpern, Miguel A. Jorge, Al Lombana, Sara A. Lourie, Kirsten D. Martin, Edmund McManus, Jennifer Molnar, Cheri A. Recchia, and James Robertson. 2007. Marine Ecoregions of the World: A Bioregionalization of Coastal and Shelf Areas. BioScience 57:573-583.

External links[edit]