Biome

Biome, large ecosystem characterized by similar vegetation, animals, and climate. A biome's abiotic (non-living) factors, such as light intensity, wind, soil quality, amount of rainfall, temperature, and nutrients, determine what plants and animals inhabit the zone.

There are various terrestrial and two aquatic (freshwater and salt-water) biomes. While scientists do not agree on the number of land-based biomes, the six most widely accepted biomes are: tundra, taiga, grassland, deciduous forest, desert, and tropical rainforest.

The tundra, the biome with the coldest climate, spans a huge portion of land just below the poles, and in high mountain environments at other latitudes. The tundra generally receives 10 to 40 cm (4 to 16 in) of precipitation (mostly snow) annually, with long, severe winters and cool, brief summers. At its warmest, the ground only thaws about 1m (3 ft) down; below this is permanently frozen ground, called permafrost. The most typical plants are mosses, lichens, and other small plants that can survive the extreme cold. Polar bears, musk-oxen, reindeer, caribou, arctic foxes, arctic hares, and lemmings all inhabit the northern tundra, while the fringes of Antarctica support various species of seal and penguin.

The taiga, also known as the boreal forest, covers the upper portions of Europe, Russia, and North America, and the Andean foothills of southern South America. Boreal forests experience lengthy, snowy, cold winters and short, mild summers with about 20 to 60 cm (8 to 24 in) of rainfall per year (in some places as much as 100 cm/39 in). Cone-bearing evergreen trees dominate the landscape but spongy bogs also distinguish taigas. Various types of large deer, particularly elk and wapiti, dominate this biome, but lynx, wolves, porcupines, wolverines, hares, and several species of bear also frequent these areas.

Deciduous forests are marked by deciduous trees (that is, trees that shed their leaves annually). The deciduous, or temperate forest biome, encompasses the eastern half of North America from southern Ontario and Quebec to northern Florida, most of Europe, eastern China, and Japan. In the southern hemisphere, in parts of southern Australia, New Zealand, South Africa, and South America, similar broad-leaved trees have adapted to different rainfall patterns, both drier and wetter. This biome receives 60 to 100 cm (24 to 40 in) of precipitation each year (in some places up to 150 cm/60 in) and winters are long but not as harsh as the boreal forest. Animal life is varied and includes ground squirrels, foxes, bear, mice, snakes, rabbits, chipmunks, lizards, and deer.

Grasslands comprise the largest of several biomes in North America, covering much of the central part of the continent, and cover large areas of eastern and southern Africa, South America, and Central America, and vast areas of Central Asia. Rainfall ranges from 10 to 60 cm (4 to 24 in) annually. Large parts of North American grasslands are now planted with oats, wheat, barley, and maize. Grasslands in North America, which used to be dominated by the bison, now contain prairie dogs, coyotes, and badgers, while those in central Asia also support wild horses. Savannahs are a type of grassland located in tropical or subtropical areas, such as the Serengeti Plain of East Africa, which supports buffalo, wildebeest, zebra, antelopes, elephants, lions, and cheetahs.

Tropical rainforests, characterized by rapid plant growth, thick forest canopy, a profusion of flowering trees, and a huge diversity of animal species, occur in equatorial areas where more than 500 cm (200 in) of rain may fall per year, as well as in tropical areas which may include a dry season. A multitude of insects and other invertebrates thrive along with birds, monkeys, snakes and lizards.

The desert is the hottest and driest biome, receiving less than 25 cm (10 in) of rain annually. There are deserts in North America and South America, Asia, Australia, and Africa. Plants are well adapted to the dry conditions. Mesquite and creosote bushes have long root systems that tap water deep in the ground. Cactuses store water in stems and leaves, while in Africa and Australia, the acacia tree flourishes. Insects, reptiles (especially lizards), birds and small mammals reside in the desert, many active only at night.