Biomes are large regions of the earth that share similar characteristics such as climate, soils, precipitation, plant communities, and animal species. Biomes are sometimes referred to as ecosystems or ecoregions. Climate is perhaps the most important factor that defines the nature of any biome but it is not the only one—other factors that determine the character and distribution of biomes include topography, latitude, humidity, precipitation, and elevation.
Scientists disagree as to exactly how many biomes there are on Earth and there are many different classification schemes that have been developed to describe the world's biomes. For the purposes of this site, we distinguish five major biomes. The five major biomes include aquatic, desert, forest, grassland, and tundra biomes. Within each biome, we also define numerous different types of sub-habitats.
The aquatic biome includes the habitats around the world that are dominated by water—from tropical reefs, to brackish mangroves, to Arctic lakes. The aquatic biome is divided into two main groups of habitats based on their salinity—freshwater habitats and marine habitats.
Freshwater habitats are aquatic habitats with low salt concentrations (below one percent). Freshwater habitats include lakes, rivers, streams, ponds, wetlands, swamps, lagoons, and bogs.
Marine habitats are aquatic habitats with high salt concentrations (more than one percent). Marine habitats include seas, coral reefs, and oceans. There are also habitats where freshwater mixes with saltwater. In these places, you'll find mangroves, salt marshes, and mud flats.
The various aquatic habitats of the world support a diverse assortment of wildlife including virtually every group of animals—fishes, amphibians, mammals, reptiles, invertebrates, and birds.
The desert biome includes terrestrial habitats that receive very little rainfall throughout the year. The desert biome covers about one-fifth of the Earth's surface and is divided into four sub-habitats based on their aridity, climate, location, and temperature—arid deserts, semi-arid deserts, coastal deserts, and cold deserts.
Arid deserts are hot, dry deserts that occur at low latitudes around the world. Temperatures remain warm year-round, although they are hottest during the summer months. There is little rainfall in arid deserts and what rain does fall is often exceeded by evaporation. Arid deserts occur in North America, Central America, South America, Africa, southern Asia, and Australia.
Semi-arid deserts are generally not as hot and dry as arid deserts. Semi-arid deserts experience long, dry summers and cool winters with some precipitation. Semi arid deserts occur in North America, Newfoundland, Greenland, Europe, and Asia.
Coastal deserts generally occur on the western edges of continents at approximately 23°N and 23°S latitude (also known as the Tropic of Cancer and the Tropic of Capricorn). In these locations, cold ocean currents run parallel to the coast and produce heavy fogs that drift over the deserts. Although the humidity of coastal deserts may be high, rainfall remains rare. Examples of coastal deserts include the Atacama Desert of Chile and the Namib Desert of Namibia.
Cold deserts are deserts that have low temperatures and long winters. Cold deserts occur in the Arctic, Antarctic, and above the treelines of mountain ranges. Many areas of the tundra biome can also be considered cold deserts. Cold deserts often have more precipitation than other types of deserts.
The forest biome includes terrestrial haibtats that are dominated by trees. Forests extend over about one-third of the world's land surface and can be found in many regions around the globe. There are three main types of forests—temperate, tropical, boreal—and each has a different assortment of climate characteristics, species compositions, and wildlife communities.
Temperate forests occur in temperate regions of the world including North America, Asia, and Europe. Temperate forests experience four well-defined seasons. The growing season in temperate forests lasts between 140 and 200 days. Rainfall occurs throughout the year and soils are nutrient-rich.
Tropical forests occur in equatorial regions between 23.5°N and 23.5°S latitude. Tropical forests experience two seasons, a rainy season and a dry season. Day length varies little throughout the year. The soils of tropical forests are nutrient-poor and acidic.
Boreal forests, also known as tiaga, are the largest terrestrial habitat. Boreal forests are a band of coniferous forests that encircle the globe in the high northern latitudes between about 50°N and 70°N. Boreal forests form a circumpolar band of habitat that extends right across Canada and stretches from northern Europe all the way to eastern Russia. Boreal forests are bordered by tundra habitat to the north and temperate forest habitat to the south.
Grasslands are habitats that are dominated by grasses and have few large trees or shrubs. There are three main types of grasslands, temperate grasslands, tropical grasslands (also known as savannas), and steppe grasslands. Grasslands experience a dry season and a rainy seasons. During the dry season, grasslands are susceptible to seasonal fires.
Temperate grasslands are dominated by grasses and have lack trees and large shrubs. The soil of temperate grasslands has an upper layer that is nutrient-rich. Seasonal droughts are often accompanied by fires that prevent trees and shrubs from growing.
Tropical grasslands are grasslands that are located near the equator. They have warmer, wetter climates than temperate grasslands and experience more pronounced seasonal droughts. Tropical grasslands are dominated by grasses but also have some scattered trees. The soil of tropical grasslands are very porous and drain rapidly. Tropical grasslands occur in Africa, India, Australia, Nepal, and South America.
Steppe grasslands are dry grasslands that border on semi-arid deserts. The grasses found in steppe grasslands is much shorter than that of temperate and tropical grasslands. Steppe grasslands lack trees except along the banks of rivers and streams.
Tundra is a cold habitat characterized by permafrost soils, low temperatures, short vegetation, long winters, brief growing seasons, and limited drainage. Arctic tundra is located near the North Pole and extends southward to the point where coniferous forests grow. Alpine tundra is located on mountains around the world at elevations that are above the tree line.
Arctic tundra is located in the Northern Hemisphere between the North Pole and the boreal forest. Antarctic tundra is located in the Southern Hemisphere on remote islands off the coast of Antarctica—such as the South Shetland Islands and the South Orkney Islands—and on the Antarctic peninsula. Arctic and Antarctic tundra supports about 1,700 species of plants including mosses, lichens, sedges, shrubs, and grasses.
Alpine tundra is a high-altitude habitat that occurs on mountains around the world. Alpine tundra occurs at elevations that lie above the tree line. Alpine tundra soils differ from the tundra soils in polar regions in that they are usually well-drained. Alpine tundra supports tussock grasses, heaths, small shrubs, and dwarf trees.