A Look at the savanna
...ing the dry season to allow trees to grow more densely and to form a canopy, shading out the grasses. In regions of higher rainfall, such as eastern Africa, periodic fires maintain savanna vegetation. Consuming dry grass at the end of the rainy season, the fires burn back the forest vegetation, check the invasion of trees and shrubs, and stimulate new grass growth. Large grazing mammals such as wildebeest and zebra also influence these savannas. When abundant, the animals can so reduce the vegetation that the grassy cover cannot carry a fire. Woody vegetation then increases, changing savanna to woodland. Large browsers such as elephants help to control these areas. Shrub Life Although few in numbers, shrubs are an important factor in the savanna, because they support primary consumers during dry spells. Shrubs are more successful than grass and trees. Shrubs put more of their nutrients and energy into the growth of roots than into the growth of aboveground stems. The extensive root systems enable shrubs to reach moisture deep in the ground. Some shrub species inhibit competing herbs by secreting substances toxic to other plants. Shrub lands support their own distinctive animal life. Frequently, however, these lands are considered worthless and are converted to other uses, which eliminates wildlife and plant species associated with them. ...