Ecoregion

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 either less or greater than an ecosystem. 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 remains relatively constant, within an acceptable range of variation (largely undefined at this point).A large area of land or water that contains a geographically distinct assemblage of natural communities that: 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 either less or greater than an ecosystem. 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 remains relatively constant, within an acceptable range of variation (largely undefined at this point). Three caveats are appropriate for all bio-geographic mapping approaches. Firstly, no single bio-geographic 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). The history of the term is somewhat vague, and it had been used in many contexts: forest classifications (Loucks, 1962), biome classifications (Bailey, 1976, 2014), biogeographic classifications (WWF/Global 200 scheme of Olson & Dinerstein, 1998), etc. The concept of ecoregion of Bailey gives more importance to ecological criteria, while the WWF concept gives more importance to biogeography, that is, distribution of distinct biotas. An ecoregion is a 'recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region'. 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'. '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. The intended purpose of ecoregion delineation may affect the method used. For example, the WWF ecoregions were developed to aid in biodiversity conservation planning, and place a greater emphasis than the Omernik or Bailey systems on floral and faunal differences between regions. The WWF classification defines an ecoregion as: