Biome
In ecology, a biome is a major regional group of distinctive plant and animal communities well adapted to the region's physical environment. The concept of a biome highlights the interaction among plant and animal populations, soil, water and air. A biome is discernible at a global scale, and a biotic area is the geographical area occupied by a particular biome. The Earth's biomes comprise the biosphere.
Biomes are defined by the global pattern of species. This pattern is influenced by regional climate, soil characteristics, substrate condition (due to periodic flooding for example), and other physical environment factors. In turn, climate and soil partly depend on latitude, altitude and slope.
A biome is composed of the climax flora and all associated subclimax, or degraded, flora, fauna and soils, but can often be identified by the climax flora type, vertical stratification or vegetation adaptation.
Biomes may be divided into:
- Terrestrial (also called continental) biomes and
- Aquatic biomes.
Often, a type of biome in a particular area is given a local name. For example, a Temperate grassland or shrubland biome is known as steppe in central Asia, savanna or veld in southern Africa, prairie in North America, pampa in South America and outback in Australia.
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Latitude Classification
Latitude is a major factor defining biomes. There is a good correlation between the distribution of climates with latitude, and homogenous vegetation bands. Another major factor is humidity. This can be illustrated by the fact that biodiversity increases away from the poles towards the equator, and increases with humidity.
The most widely used classification of biomes is related to latitude (or temperature zoning) and humidity :
Arctic or Subarctic area
- humid type : Tundra
Subarctic and Boreal area
- humid type: taiga or boreal forest
Temperate cold
Temperate warm or sub-tropical
- humid: subtropical moist broadleaf forest
- semi-humid: Subtropical dry broadleaf forests, Subtropical coniferous forests
- semi-arid: Mediterranean forests, woodlands, and shrub, Temperate grasslands, savannas, and shrublands
- Arid: Temperate deserts and xeric shrublands
Tropical
- humid area : Tropical forest or Rainforest
- Semi-arid area : Tropical Grasslands -- Tropical Savannas
- Arid area : Desert
Aquatic
- continental shelf
- littoral
- riparian
- pond
- lake
- coral reef
- kelp forest
- pack ice
- hydrothermal vents
- cold seeps
- benthic zone
- pelagic zone
Altitude and Latitude Classification
Another system of classification takes into account altitude and humidity, ignoring temperature as a factor. This classification is used to define the Global 200 list of ecoregions identified by the World Wildlife Fund (WWF) as priorities for conservation.
This classification gives the following terrestrial biomes :
- Tundra (arctic, humid)
- Boreal forests/taiga (subarctic, humid)
- Temperate coniferous forests (temperate cold, 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)
- Deserts and xeric shrublands (temperate to tropical, arid)
- Mangrove (subtropical and tropical, salt and brackish water inundated)
- Flooded grasslands and savannas (temperate to tropical, fresh water inundated)
- Montane grasslands and shrublands (temperate to tropical, high altitude)
Imperfect Clasification
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.