Plants of the African Savanna (Photo: )
Savannas encompass almost 50 percent or about 5 million square miles of land in Africa. Also known as tropical grasslands, savannas receive between 20 and 50 inches of rainfall on average annually, all of which falls in a six- to eight-month period. Some savannas receive as little as 6 inches of precipitation annually. The wet period is followed by a period of drought. Some plants that survive in the savanna use the rainy season to grow while relying on special adaptations to survive the dry season.
The soil found on the savanna stays very porous, allowing for fast water drainage during the rainy season. The plants get most of their nutrients from a thin layer of humus made up of partially decomposed plant or animal matter. Most savannas include grasses and a few species of trees. Savannas differ from one another in terms of exactly what grasses thrive based on that region’s rainfall and whether or not the soil drains well. Thanks to seasonal fires and large animals foraging on the savannas, many seedlings never reach maturity, helping to keep the trees and shrubs to a minimum.
On the East African savannas, the dominant grass consists of star grasses. Rhodes grass and red oat grass dominate the savannas of the Serengeti plains and the Laikipia plateau in Kenya. In the western Uganda savannas, lemon grasses prevail. When the rains come, the grasses start to rapidly grow, many gaining an inch or more in just 24 hours.
Several species of trees have adapted to the savanna, including the baoba tree. The tree produces small leaves during the wet season that keep water loss to a minimum when the dry season occurs. The tree stores large amounts of water in its large trunk to help it survive the long dry spell. The long tap roots of the acacia tree help it take in water from sources deep underground. The sharp thorns on the tree’s branches stop animals from eating all of its leaves. The tree produces a poisonous alkaloid when giraffes start eating the leaves from the top of the tree. The giraffe takes a few bites, then moves away because the leaves rapidly become inedible. The affected tree takes things one step further by emitting a chemical into the air that indicates nearby acacia trees should also start sending alkaloid into their leaves.
Some plants in the African savanna only grow on termite mounds since the surrounding soil is too thin or drains so poorly that it cannot sustain plants. Instead, the mounds provide the nutrients and water the plants need to survive. Mopane, also known as the turpentine tree, thrives on termite mounds. The multi-stemmed tree features leaves that resemble butterfly wings. The vegetation turns green when it rains, but during the dry season, the leaves turn shades of yellow and orange.
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