Biome: Tropical Savanna

Biogeographical Patterns of diversity

Tropical savanna is one of the largest global vegetation types (biomes), potentially occurring over about 20% of the land surface in the tropics and subtropics between 30° north and south of the equator in South America, Africa, South Asia, and Australia. Major savannas are mapped in South America, where densely wooded grasslands dominate in the “cerrados” of northeastern Brazil, the grass-dominated “campo” in southeast Brazil, and the “llanos del Orinoco” in Venezuela. In Africa, tropical savanna is most extensive, predominating across a broadband between the west-central equatorial tropical rain forest to the Sahara Desert in the north and Kalahari Desert in the south, continuing across plains in equatorial East Africa, and dominating much of the landscape in Western Madagascar. When mapped with the distribution of tropical deciduous forest and tropical thorn-scrub, tropical savanna covers approximately 65% of the African continent. Much of the Indian subcontinent is also mapped as savanna and small patches occur in southeast Asia and on the islands of the East Indies and the Pacific. In Australia, tropical savanna occurs in the north and extends southeast between the more arid central plains and the humid tropical and subtropical forests along the east coast.

Tropical savanna, therefore, shows a disjunct distribution across the continents in the tropical realm. While savanna vegetation may be similar in its overall structure as a mixed system with grasses and woody plants, the composition of plants species that occur in the region can also influence its appearance. For example, evergreen Acacia trees dominate the savannas of the new world tropics in South America, just as evergreen eucalyptus trees occur across a broad moisture gradient on the continent of Australia. In Africa, evergreen Acacia trees can predominate, but much of the region shows a mixed composition with some evergreen trees (e.g., Acacia species, Balanites aegyptica), deciduous trees (Commiphora species, Delonix elata, Sclerocarya birrea), and evergreen (e.g., Croton) or deciduous (e.g., Combretum) shrubs. In Africa, baobob (Adansonia digitata) is a prominent deciduous tree in savanna that varies its deciduous habit in relation to changes in the occurrence of rains across the region. The plants that make up the tropical savanna are much more diverse than temperate grasslands. About half of the plant species on the African continent occur in this vegetation type.

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