biome n : a major biotic community characterized by the dominant forms of plant life and the prevailing climate
A biome is a climatically and geographically defined area of ecologically similar communities of plants, animals, and soil organisms, often referred to as ecosystems. Biomes are defined based on factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), plant spacing (forest, woodland, savanna), and climate. Unlike ecozones, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation.
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. Species diversity tends to be higher in terrestrial biomes with higher net primary productivity, moisture availability, and temperature.
Ecoregions are grouped into both biomes and ecozones.
A fundamental classification of biomes is into:
- Terrestrial (land) biomes
- Freshwater biomes
- Marine biomes
Biomes are often given local names. For example, a Temperate grassland or shrubland biome is known commonly as steppe in central Asia, prairie in North America, and pampas in South America. Tropical grasslands are known as savanna or veldt in southern Africa and outback or scrub in Australia. Sometimes an entire biome may be targeted for protection, especially under an individual nation's Biodiversity Action Plan.
Climate is a major factor determining the distribution of terrestrial biomes. Among the important climatic factors are:
- latitude: Arctic, boreal, temperate, subtropical, tropical.
- humidity: humid,
semi-humid, semi-arid, and arid.
- seasonal variation: Rainfall may be distributed evenly throughout the year or be marked by seasonal variations.
- 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.
- 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.
Map of Biomes
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 (Polar, Humid Temperate, Dry, and Humid Tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical; marine and continental; lowland and mountain).
- 100 Polar Domain
- 120 Tundra Division
- M120 Tundra Division - Mountain Provinces
- 130 Subarctic Division
- M130 Subarctic Division - Mountain Provinces
- 200 Humid Temperate Domain
- 210 Warm Continental Division
- M210 Warm Continental Division - Mountain Provinces
- 220 Hot Continental Division
- M220 Hot Continental Division - Mountain Provinces
- 230 Subtropical Division
- M230 Subtropical Division - Mountain Provinces
- 240 Marine Division
- M240 Marine Division - Mountain Provinces
- 250 Prairie Division
- 260 Mediterranean Division
- M260 Mediterranean Division - Mountain Provinces
- 300 Dry Domain
- 310 Tropical/Subtropical Steppe Division
- M310 Tropical/Subtropical Steppe Division - Mountain Provinces
WWF systemA team of biologists convened by the World Wildlife Fund (WWF) developed an ecological land classification system that identified fourteen biomes, called major habitat types, and further divided the world's land area into 825 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:
- Tundra (Arctic)
- Boreal forests/taiga (subarctic, humid)
- Temperate coniferous forests (temperate, humid to semi-humid)
- Temperate broadleaf and mixed forests (temperate, humid)
- Temperate grasslands, savannas, and shrublands (temperate, semi-arid)
- Mediterranean forests, woodlands, and shrub (temperate warm, semi-humid to semi-arid with winter rainfall)
- Tropical and subtropical coniferous forests (tropical and subtropical, semi-humid)
- Tropical and subtropical moist broadleaf forests (tropical and subtropical, humid)
- Tropical and subtropical dry broadleaf forests (tropical and subtropical, semi-humid)
- Tropical and subtropical grasslands, savannas, and shrublands (tropical and subtropical, semi-arid)
- Montane grasslands and shrublands (alpine or montane climate)
- Deserts and xeric shrublands (temperate to tropical, arid)
- Mangrove (subtropical and tropical, salt water inundated)
- Flooded grasslands and savannas (temperate to tropical, fresh or brackish water inundated)
Freshwater biomesAccording to the World Wildlife Fund:
- Large lakes
- Large river deltas
- Polar freshwaters
- Montane freshwaters
- Temperate coastal rivers
- Temperate floodplain rivers and wetlands
- Temperate upland rivers
- Tropical and subtropical coastal rivers
- Tropical and subtropical floodplain rivers and wetlands
- Tropical and subtropical upland rivers
- Xeric freshwaters and endorheic basins
- Oceanic islands
Global 200 marine major habitat types
- Temperate shelves and sea
- Temperate upwelling
- Tropical upwelling
- Tropical coral
Other marine habitat types
Anthropogenic biomes provide an alternative view of the terrestrial biosphere based on global patterns of sustained direct human interaction with ecosystems, including agriculture, human settlements, urbanization, forestry and other uses of land. Anthropogenic biomes offer a new way forward in ecology and conservation by recognizing the irreversible coupling of human and ecological systems at global scales and moving us toward an understanding how best to live in and manage our biosphere and the anthropogenic biosphere we live in.
Major Anthropogenic Biomes
- Dense Settlements
Other biomesThe 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.
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