Tropical+Grassland+Soil

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Characteristics of Soil
The soil of the tropical grassland, or savanna, is porous and drains rapidly (G1). The layer closest to the top of the soil contains a thin layer of humus, an organic substance made of decomposed animal and plant material (G2). Humus provides the vegetation of the ecosystem with nutrients, though tropical grassland soil as a whole is not as rich as the soil of other biomes due to the comparably low amount of humus and nutrients (G3).

Vegetation that Soil Supports
The most common types of vegetation in tropical grasslands are grasses, forbs (small, leafy plants that grow alongside grasses) and shrubs (G2). The type of grass that dominates the savanna depends on the location, as differences in precipitation and soil conditions cause different grasses to be more successful (G4). In drier savannas like those on the Serengeti, red oat grass and Rhodes grass are dominant due to the high drainage of the soil there. In East Africa, star grasses are dominant, and lemon grasses are the most common in western Ugandan savannas (G3, G5). Grasses typically grow from 3-6 feet tall. Deciduous trees and shrubs are common as well, and are usually scattered throughout the landscape. For trees to be successful, they sometimes must be drought and fire-resistant, due to commonality of forest fires and droughts (G5). In some savannas, usually located in southwestern Kenya, Tanzania, and Uganda, called a "grouped-tree grassland", trees only grow on termite mounds, because the other soil is too thin and poorly drained to allow tree growth (G3). The most common tree species in African savannas are the baobab and acacia trees, while Australian savannas consist of mostly baobab and eucalyptus trees (G3, G5).

Types of Savannas and Effect on Soil
Edaphic savannas, which are savannas caused by soil conditions (not very rich in nutrients, thin, and excessively dry or wet), can occur on hills or ridges due to the shallow nature of soil, or in valleys where soil becomes oversaturated with water in periods with excessive rainfall. This type of savanna usually covers a smaller area than savannas of the other 2 varieties (climatic and derived savannas), and exists in warm climates. In climatic savannas, the soil becomes so dry from a lack of rainfall that many types of trees cannot grow, resulting in less species diversity. Derived savannas are manmade, and result from people clearing forest land for their own cultivation. These are created by cutting down all the vegetation in a forest, burning it, and planting crops in the ashes, which act as fertilizer. Thus, soil quality and characteristics differ based on the type of savanna that exists in an area (G5).

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