In ecology, a biome is a major regional group of distinctive plant and animal communities best adapted to the regions physical natural environment, latitude, elevation, and terrain.
A biome is made up of ecoregions or settlements at stable steady state and all associated transitional, disturbed, or degraded, vegetation, fauna and soils, but can often be identified by the climax vegetation type.
The biodiversity characteristic of each biome, especially the diversity of fauna and subdominant plant forms, is a function of abiotic factors and the biomass productivity of the dominant vegetation. Terrestrial biomes with higher net primary productivity, moisture availability, and temperature.
A fundamental classification of biomes is into:
- Terrestrial land biomes and
- Aquatic water biomes.
Biomes are often given local names. For example, a temperate grassland or shrubland biome is known commonly as steppe in central Asia, savanna or veld in southern Africa, prairie in North America, pampa in South America and outback or scrub in Australia. Sometimes an entire biome may be targeted for protection, especially under an individual nations Biodiversity Action Plan.
1. Terrestrial biomes
Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:
- dry summer, wet winter: most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.
- seasonal variation: rainfall may be distributed evenly throughout the year, or be marked by seasonal variations.
- latitude: arctic, boreal, temperate, subtropical, tropical.
- humidity: humid, semi-humid, semi-arid, and arid.
- elevation: increasing elevation causes a distribution of habitat types similar to that of increasing latitude.
Biodiversity generally increases away from the poles towards the equator, and increases with humidity.
The most widely used systems of classifying biomes correspond to latitude or temperature zoning and humidity.
1.1. Terrestrial biomes Bailey system
Robert G. Bailey developed a biogeographical classification system for the United States in a map published in 1975. Bailey subsequently expanded the system to include the rest of North America in 1981, and the world in 1989. The Bailey system is based on climate, and is divided into four domains, with further divisions based on other climate characteristics.
1.2. Terrestrial biomes WWF system
A team of biologists developed an ecological land classification system for the World Wide Fund for Nature WWF that identified 14 biomes, called major habitat types, and further divided the worlds land area into 867 terrestrial ecoregions. This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation. The WWF major habitat types are as follows:
- Tropical and subtropical coniferous forests tropical and subtropical, semihumid
- Temperate coniferous forests temperate, humid to semihumid
- Forests broadleaf = Angiosperm trees
- Tropical and subtropical dry broadleaf forests tropical and subtropical, semihumid
- Boreal forests/taiga subarctic, humid
- Tropical and subtropical moist broadleaf forests tropical and subtropical, humid
- Temperate broadleaf and mixed forests temperate, humid
- Mediterranean forests, woodlands, and scrub or sclerophyll forests temperate warm, semihumid to semiarid with winter rainfall
- Tropical and subtropical grasslands, savannas, and shrublands tropical and subtropical, semiarid
- Montane grasslands and shrublands: alpine above the tree line or montane below the tree line, and hence with trees.
- Temperate grasslands, savannas, and shrublands temperate, semiarid
- Flooded grasslands and savannas temperate to tropical, fresh or brackish water inundated
- Deserts and xeric shrublands temperate to tropical, arid
- Mangrove subtropical and tropical, salt water inundated
- Tundra Arctic
2. Aquatic biomes
- pack ice
- benthic zone
- littoral/intertidal zone
- continental shelf
- cold seeps
- coral reef
- pelagic zone
- hydrothermal vents
- kelp forest
- neritic zone
3. Other biomes
The Endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered and does not fit well into most classification schemes.