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An ecoregion (ecological region), sometimes called a bioregion, is the next smallest ecologically and geographically defined area beneath "realm" or "ecozone". Ecoregions cover relatively large area of land or water, and contain characteristic, geographically distinct assemblage of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tend to be distinct from that of other ecoregions.

Contents 1 Overview of definitions 2 World Wildlife Fund's definition 2.1 Terrestrial ecoregions 2.2 Marine ecoregions 2.3 Freshwater ecoregions 3 See also 4 Sources 5 External links

When defined by the WWF, the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. The WWF has identified 825 terrestrial ecoregions, and approximately 450 freshwater ecoregions across the Earth.

Another way of defining an ecoregion is as a "recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region" (Brunckhorst, 2000).

Others have defined ecoregions as areas of ecological potential based on combinations of biophysical parameters such as climate and topography.^{[citation needed]}

World Wildlife Fund's full definition of an ecoregion, which is widely accepted and used, is the following:

A large area of land or water that contains a geographically distinct assemblage of natural communities that

(a) share a large majority of their species and ecological dynamics;

(b) share similar environmental conditions, and;

(c) interact ecologically in ways that are critical for their long-term persistence.

--World Wildlife Fund - Ecoregions

The use of the term ecoregion is an outgrowth of a surge of interest in ecosystems and their functioning. In particular, there is awareness of issues relating to spatial scale in the study and management of landscapes. It is widely recognized that interlinked ecosystems combine to form a whole that is "greater than the sum of its parts." There are many attempts to respond to ecosystems in an integrated way to achieve "multi-functional" landscapes, and various interest groups from agricultural researchers to conservationists are using the ecoregion as a unit of analysis.

The Global 200 is the list of ecoregions identified by the World Wildlife Fund (WWF) as priorities for conservation.

Terrestrial ecoregions are land ecoregions, as distinct from freshwater ecoregions and marine ecoregions.

World Wildlife Fund ecologists currently divide the land surface of the Earth into 8 major ecozones containing 825 smaller terrestrial ecoregions (see list). The WWF effort is a synthesis of many previous efforts to define and classify ecoregions. Many consider this classification to be quite decisive, and some propose these as stable borders for bioregional democracy initiatives.

The eight terrestrial ecozones follow the major floral and faunal boundaries, identified by botanists and zoologists, that separate the world's major plant and animal communities. Ecozone boundaries generally follow continental boundaries, or major barriers to plant and animal distribution, like the Himalayas and the Sahara. The boundaries of ecoregions are often not as decisive or well recognized, and are subject to greater disagreement.

Ecoregions are classified by biome type, which are the major global plant communities determined by rainfall and climate. Forests, grasslands (including savanna and shrubland), and deserts (including xeric shrublands) are distinguished by climate (tropical and subtropical vs. temperate and boreal climates) and, for forests, by whether the trees are predominantly conifers (Gymnosperms), or whether they are predominantly broadleaf (Angiosperms) and mixed (broadleaf and conifer). Biome types like Mediterranean forests, woodlands, and shrub, Tundra, and Mangroves host very distinct ecological communities, and are recognized as distinct biome types as well.

Ecologically-based movements like bioregionalism maintain that ecoregions, rather than arbitrarily-defined political boundaries, provide a better foundation for the formation and governance of human communities, and have proposed ecoregions and watersheds as the basis for bioregional democracy initiatives.

In this context, terrestrial is used to mean "of land" (soil and rock), rather than the more general sense "of Earth" (which includes land and oceans). Terrestrial planets, for example, include not only the earth, but all planets which have surfaces composed mostly of rock, as distinct from planets without a solid surface.

Marine ecoregions are regions of the world's oceans, as defined by the World Wildlife Fund (WWF), to aid in conservation activities for marine ecosystems.

The scheme used to designate and classify marine ecoregions is analogous to the classification system used by WWF 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) —which correspond to the terrestrial biomes. Major biogeographic realms, analogous to the seven terrestrial ecozones, represent large regions of the ocean basins: North Temperate Atlantic, Eastern Tropical Atlantic, Western Tropical Atlantic, South Temperate Atlantic, North Temperate Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Western Indo-Pacific, South Temperate Indo-Pacific, Southern Ocean, Antarctic, Arctic, and Mediterranean.

The classification of Marine ecoregions is not developed to the same level of detail and comprehensiveness as that of the terrestrial ecoregions; only the priority conservation areas of the Global 200 are listed.

See Global 200 Marine ecoregions for a full list of marine ecoregions (World Wildlife Fund).

A similar system of identifying areas of the oceans for conservation purposes is the system of large marine ecosystems (LMEs), developed by the US National Oceanic and Atmospheric Administration (NOAA).

Freshwater ecoregions represents the freshwater habitats of a particular geographic area, including rivers, streams, lakes, and wetlands. Freshwater ecoregions are distinct from terrestrial ecoregions, which identify biotic communities of the land, and marine ecoregions, which are biotic communities of the oceans.

The WWF identifies seven major habitat types of freshwater ecoregions: Large rivers, large river headwaters, large river deltas, small rivers, large lakes, small lakes, and xeric basins.

Several freshwater ecoregions are listed in the Global 200, the WWF's priority ecoregions for conservation of biodiversity.

• Ecozone
• Ecotope
• Biome
• Habitat
• List of biogeographic provinces
• Bioregionalism
• List of ecoregions
• Lists of ecoregions by country
• Global 200
• Biosphere reserve
• World Network of Biosphere Reserves

• Brunckhorst, D. 2000. Bioregional planning: resource management beyond the new millennium. Harwood Academic Publishers: Sydney, Australia.

• World Wildlife Fund: ecoregions
• Sierra club: ecoregions
• Activist network cultivating Ecoregions/Bioregions
• A National Ecological Framework for Canada
• Ecoregions of North America
• Interactive map and images of North American ecoregions at bioimages.vanderbilt.edu
• Map of the ecozones