Biome
A biome is a large geographical region characterized by particular kinds of plants and animals and maintained by a distinct climate and soil conditions. There are eight generally recognized biomes throughout the world. The six terrestrial biomes (those found on land) are the rain forest, desert, grasslands, temperate deciduous forest, taiga, and tundra. The two aquatic biomes are the freshwater and marine biomes.
Rain forests are most commonly found in tropical regions close to the equator in areas of very heavy rainfall, at least 150 in (381 cm) per year, and with relatively constant warm temperatures. They are often recognized as one of the most biologically diverse habitats on Earth. Deserts are the driest biome with only an average annual rainfall of 10 in (25 cm). Organisms living in the desert must have special adaptations to survive in these dry conditions. Grasslands are the prairies. They can be found in both temperate and tropical climates; however, there is not enough rainfall in grasslands for many large trees to survive. Rainfall in temperate grasslands (those lying between 25 and 65 degrees latitude) ranges from 10-30 in (25-75 cm) per year. At tropical and subtropical latitudes, annual precipitation averages 24-59 in (60-150 cm). As a result, grasslands are dominated by grasses. The temperate deciduous forest is dominated by deciduous trees, those that lose their leaves in autumn. Examples include maple, oak, beech, birch, and hickory. This biome is generally warm in the summer and cold in the winter. The taiga has extremely cold winters, with a relatively short growing season. The taiga is dominated by forests with conifer trees, such as pine, fir, and spruce. The tundra is the coldest of all of the terrestrial biomes. It has such a short growing season that the subsoil never thaws. As a result, no trees or shrubs can survive. The vegetation in the tundra is dominated by mosses, lichens, and other plants that do not grow very large and can reproduce very quickly during the short growing season. The freshwater biome includes creeks, rivers, ponds, and lakes. The marine biome includes all of the areas of salt water in the world, in particular, the oceans. The marine biome is the largest of all of the biomes, covering approximately 71% of Earth.
As one increases in latitude from the equator, the terrestrial biomes change in a relatively predictable pattern. Closest to the equator, the rain forest is most common. As one moves to higher latitudes the deciduous forest becomes more common. At still higher latitudes the taiga is most prominent due to the decreases in temperature. Finally, closest to the poles, in the coldest regions, one finds tundra. A similar, generalized pattern is observed going up a very tall mountain from low to high altitudes. The rain forest is dominant at the warmer bottom of the mountain, and at the highest altitudes a tundra-like community is found. Neither desert nor grasslands are included in this pattern because the predominant factor limiting their distribution is precipitation rather than temperature.
The terrestrial biomes are not necessarily completely distinct from each other. Two neighboring biomes blend together at their edges. For example, at the northern edge of the temperate deciduous forest biome in North America, both deciduous trees and conifers are present, which are characteristic of the taiga biome. A little farther north, the conifers will be dominant.
While biomes have recognizable types of vegetation, species will vary with location. For example, the vegetation in a North American and African desert will be similar and have similar adaptations. However, there will be different species in these two locations. For example, each location might have different species of cactus-like, succulent plants.
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