A biome (also called a biotic area) may be defined as a major region of distinctive plant and animal groups well adapted to the physical environment of its distribution area. The biome concept embraces the idea of community, of interaction among vegetation, animal populations, and soil. The biosphere consists of three major biome classes: the sea, the terrestrial biomes and azonally-occurring biomes (e.g. fluviatile, limnic, cave). The same biome may occur in different parts of the world; for example the temperate grasslands biome is found on most continents.
A biome characterizes a biogeographic province (a subdivision of a biogeographic realm). A biome is thus a considerable geographical area and is characterized by the occurrence of one or more ecologic associations that differ, at least in proportional area covered, from the associations of adjacent provinces.
Each biogeographic province is characterized by a dominant ecosystem (also called a major biome or biome-complex). Provincial boundaries can subdivide the area of a biome where significant faunal or floral differences occur. Also large areas of relatively uniform faunas and/or floras are subdivided on the basis of changes in the structure of vegetation. Biogeographical, faunistic or vegetational criteria may enable the division of biogeographical provinces into subprovinces, districts and subdistricts.
In some regions of the world (notably North and South America) biotic provinces based on faunistic criteria (sometimes called faunal provinces) have been clearly described and these are generally considered synonymous with biotic provinces. Elsewhere in the world, floristic provinces (usually called floral regions) have been described and mapped based on dominant or major vegetation types and the regional climate, and these are used by zoologists. They are identified according to the climax vegetation type. However, a biome is composed not only of the climax vegetation, but also of associated successional communities, persistent subclimax communities, fauna, and soils.
A given biome may be composed of different taxa on different continents. Continent-specific associations of species within a given biome are known as formations and often are known by different local names. For example, the temperate grassland biome is variously called prairie, steppe, pampa, or veld, depending on where it occurs (North America, Eurasia, South America, and southern Africa, respectively).
Regional climate is an important determinant of the character of a biome by imposing limitations or requirements of temperature and/or precipitation. Soil type is also an important characteristic. However, other aspects of the physical environment may exert a stronger influence than climate in determining common plant growth forms and/or subclimax vegetation. Usually these factors are conditions of the substrate (e.g. waterlogged, excessively droughty, nutrient-poor) or of disturbance (e.g. periodic flooding or burning).