The savanna is a type of tropical biome with large stretches of grasslands mixed with sparse trees and shrubs. It is an intermediate terrain between tropical forest and desert. Not enough rain falls to support a forest biome. Climatic savannas is the term for savannas that are the result of climate conditions. Edaphic savannas are caused by soil conditions, and derived savannas are the result of forest clearing by humans.
Africa contains more savanna terrain than any other continent. The Serengeti Plains of Tanzania are well-known for diverse wildlife. According to the website Blue Planet Biomes, "In Brazil, Colombia, and Venezuela, savannas occupy some 2.5 million square kilometers, an area about one-quarter the size of Canada." Other savannas exist in northern Australia and India.
Savannas only occur in warm or hot climates with annual rainfall of 20 to 50 inches. According to the University of California Museum of Paleontology, "Climate is the most important factor in creating a savanna. It is crucial that the rainfall is concentrated in six or eight months of the year, followed by a long period of drought when fires can occur." Fires kill enough trees to prevent savannas from becoming tropical forest.
Climatic savannas have porous soil with only a thin layer of humus, the organic part of soil created by plant and animal decomposition. This allows the seasonally heavy rains to drain quickly, preventing swampy conditions. Edaphic savannas have shallow or clayish soil that inhibit tree growth.
Savanna plants must be adapted to deal with long periods of drought. Many types of grasses exist, along with associated wildflowers. East African savannas are known for the occasional grove of acacia trees. Elephant grass can grow up to 10 feet tall, thriving in the savannas of Africa near rivers and lakes. Baobab trees are found on the plains of Africa and India, and can grow up to 80 feet tall and live for thousands of years. Eucalyptus trees are found in the tropical grasslands of Australia.
African savannas support many grazing animals such as gazelles, zebra, giraffes, elephants and rhinos, and predators such as lions and hyenas. The Egyptian mongoose also inhabits African savanna areas, and is known for killing poisonous snakes. The koala bear inhabits Australians savannas, feeding on Eucalyptus leaves and climbing the trees with sharp claws. Another Australian savanna animal is the emu, a flightless bird about 5.7 feet tall.