For example, in drier savannas such as those on the Serengeti plains or Kenya's Laikipia plateau, the dominant grasses on well-drained soils are Rhodes grass and red oat grass throughout the East African savannas, star grasses are dominant the lemon grasses are common in many western Uganda savannas. Because the savanna supports such a large number of species competing for living space, usually only one or a few kinds of grass are more successful than the others in a particular area. Different savannas support different grasses due to disparities in rainfall and soil conditions. The predominant vegetation consists of grasses and forbs (small broad-leaved plants that grow with grasses). Savannas are sometimes classified as forests. It has only a thin layer of humus (the organic portion of the soil created by partial decomposition of plant or animal matter), which provides vegetation with nutrients. The soil of the savanna is porous, with rapid drainage of water. Savanna in the Samburu Game Preserve, Kenya.

Annual fires then maintain the area as a savanna. Elephants can convert a dense woodland into an open grassland in a short period of time. In Africa, a heavy concentration of elephants in protected parkland have created a savanna by eating leaves and twigs and breaking off the branches, smashing the trunks and stripping the bark of trees. Then, the field is abandoned and, although forest trees may recolonize, grass takes over on the bare ground (succession), becoming luxuriant enough to burn within a year or so. Farmers fell a tract of forest, burn the dead trees, and plant crops in the ashes for as long as the soil remains fertile. A third type of savanna, known as derived savanna, is the result of people clearing forest land for cultivation.

These can occur on hills or ridges where the soil is shallow, or in valleys where clay soils become waterlogged in wet weather. Savannas that are caused by soil conditions and that are not entirely maintained by fire are called edaphic savannas. Savannas which result from climatic conditions are called climatic savannas. If the rain were well distributed throughout the year, many such areas would become tropical forest. 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. Savannas are always found in warm or hot climates where the annual rainfall is from about 50.8 to 127 cm (20-50 inches) per year. Climate is the most important factor in creating a savanna. Savannas of one sort or another cover almost half the surface of Africa (about five million square miles, generally central Africa) and large areas of Australia, South America, and India. Savanna is grassland with scattered individual trees. There are two main divisions of grasslands: Following the Pleistocene Ice Ages, grasslands expanded in range as hotter and drier climates prevailed worldwide. Ancient forests declined and grasslands became widespread. In the Miocene and Pliocene Epochs, which spanned a period of about 25 million years, mountains rose in western North America and created a continental climate favorable to grasslands. Grasslands are characterized as lands dominated by grasses rather than large shrubs or trees. A grassland west of Coalinga, California.

Blue planet biomes grassland