Ecoregions are defined by the World Wildlife Fund as "relatively large units of land or water containing a distinct assemblage of natural communities and species, with boundaries that approximate the original extent of natural communities prior to major land-use change". Terrestrial ecoregions are land ecoregions, as distinct from freshwater ecoregions and marine ecoregions.

World Wildlife Fund (WWF) ecologists currently divide the land surface of the Earth into 8 major ecozones, containing 867 smaller terrestrial ecoregions. The WWF effort is a synthesis of many previous efforts to define and classify ecoregions, and the Wikipedia uses the WWF scheme to organize its articles about ecoregions.

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.

Terrestrial as used here differs slightly with use of terrestrial as a synonym for "terran" ("of Earth" in general, whether land or oceans). It follows its alternate meaning, roughly "of land" (soil and rock). 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.

List of the Global 200

World Wildlife Fund's list of the 200 most endangered ecoregions or groups of ecoregions.

External link

Map of the ecozones (http://www.panda.org/about_wwf/where_we_work/ecoregions/global200/pages/mainmap.htm)