Savannas that are caused by soil conditions and that are not entirely maintained by fire are called edaphic savannas . These can occur on hills or ridges where the soil is shallow, or in valleys where clay soils become waterlogged in wet weather. A third type of savanna, known as derived savanna , is the result of people clearing forest land for cultivation. Farmers fell a tract of forest, burn the dead trees, and plant crops in the ashes for as long as the soil remains fertile. 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.
Elephants can convert a dense woodland into an open grassland in a short period of time.
Annual fires then maintain the area as a savanna. The soil of the savanna is porous, with rapid drainage of water. Savannas are sometimes classified as forests. Different savannas support different grasses due to disparities in rainfall and soil conditions. 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.