Savannas are warm throughout the year. Dry and wet seasons alternate, often with severe drought during the dry season. During the rainy season, there is a rapid spurt of growth. Some of the larger grasses can grow 2-3 cm in just 24 hours. In Africa, heavy concentrations of elephants can cause savanna.
Large herds can quickly destroy an area of dense woodland.
After the elephants have stripped off the bark, eaten the leaves, broken branches and knocked down the trees, fire then maintains the area as savanna. Fire occurs naturally in the savanna, and keeps the habitat from developing into forest. Grasses can cope with fire because their roots travel deeply underground, enabling them to regrow after the exposed parts of the plant have been burnt. Grazing also serves to ensure grass remains the dominant vegetation, but overgrazing by domestic stock encourages scrub plants to dominate. This is because the bare patches of ground caused by overgrazing mean that fire cannot spread and so plants other than grasses can take over.