Savannas are the tropical version of the temperate grasslands. Most savannas are caused by climatic patterns where there is a strong dry season for a large part of the year. Few trees survive in these regions, but most savannas do have some form of trees that scatter the landscape. If you look at the map below you'll realize that a large part of Africa, nearly half its landmass, is covered in some sort of savanna. Large tracks of savanna are also found in South America, India and Australia.
The annual rainfall in a savanna is from 50.8 to 127 cm of rain a year (20-50 inches). The rain must be concentrated in one season with a long period of drought in between. This drought causes the habitat to dry out which provides kindle for fires. These fires burn through the region and kill trees that may be trying to invade the grasslands.
Certain savannas are caused because of shallow or clayish soils. These savannas are called edaphic savannas.
Most savanna soils however, are very porous and have only a very thin layer of organic matter. This allows the rains to drain quickly.
In any one savanna the vegetation consists primarily of grasses and small forbes (such as wildflowers that grow with the grasses). Often one or a few dominant grasses make up the bulk of the vegetation. This isn't to say that the flora lacks diversity though.
Since savannas are spread around the globe there are many different types of animals that have become successful. For instance, in Australia one can find different types of kangaroos and wallabies that mingle with emus and frilled lizards. In South America roams the large rhea, which is the flightless equivalent of Africa's ostrich. Yet, it is the African animals that most people think about when they hear the word savanna.
The African savannas are home to many large herbivores. The common ones include several species of zebra (see the video), lions, giraffes, rhinos, elephants, hyenas (listen to the research), gazelles, and more.
The animals of the savanna play an important roll in maintaining the grasslands. Because the large herds eat the seeds and leaves from trees and trample the ground, grasslands are protected. A large population of elephants for instance can quickly turn a forest into a savanna as it breaks branches and topples trees.
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