A savannah is an grassland ecosystem with a thin distribution of trees. Over a third of Africa, approximately 5 million square miles, is savannah, with tropical grasslands covering the central portion of the continent. The savannah does not experience cold weather and has only two seasons, a wet and a dry season. The ecosystem of the savannah presents a unique food web in which species have become adapted to an often harsh environment.
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The soil of the savannah is volcanic sand that is rich in nutrients but dry for more than half the year. Fires are frequent. The plants are rugged, fire-resistant, water-retaining, woody plants with deep root systems and tough skins. There are 55 species of acacia on the plains. Tough tall grasses such as Bermuda and elephant grass cover the savannah land. Trees such as candenelabras and jackalberry dot the landscape providing shade and a layer of food source for browsing animals but do not grow thickly enough to form a forest-like canapy cover that blocks the sun from lower growing plants.
Grazing animals such as antelope, gazelle and zebras have teeth that are adapted for chewing tough savannah grasses. Browsers, giraffes and elephants, eat high tree branches and leaves grazers can't reach. Herbivores have adapted protections from swift and large predator species such as lions and cheetahs. Rhinoceroses and ostriches have tough, hard-to-penetrate skin. Giraffes have long legs and elephants are too big for predators. Grazers run rapidly and burrowing animals hide. Many animals migrate during the dry season. Some small animals eat water-retaining plant roots. Elephants break water-retaining tree trunks to drink from, leaving rubble for lizard habitats. Scavengers such as jackals and buzzards feast on the carrion other animals won't eat.
In the savannah, insects are important in ecosystem maintenance. Termites play an important role in savannah ecosystem maintenance. Their mounds, which are regularly dispersed throughout the land, are rich in phosphorus and nitrogen and other nutrients. Termites also import coarse soil particles, which increase water infiltration and decrease the swelling and shrinking of the soils during dry and wet seasons. Not only plants benefit from the termites, however. Lizards, aardwolves, rodents, birds and other insectivores feed on the termites, which number into the millions per mound. Fire ants also play a part in habitat preservation by protecting trees from being stripped by elephants, which will stay away from leaves and branches with ants on them to keep them out of their trunks.
Human activities -- starting fires, poaching and agricultural land clearing and livestock grazing -- has fragmented and endangered the African savannahs. Efforts are being made to mitigate damage to the savannah ecosystem. Controlled burns are taking place to inhibit larger fires. Corridors are being preserved for migrating animals. About 2 million acres of savannah is now designated wildlife preserve. Tourism provides work and economic support to the savannahs' people while giving them an incentive to preserve the land. At present only 5 per cent of the savannah lands are preserved. Continued efforts are necessary if this unique ecosystem is to thrive.
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- Science Daily: Ecosystem Engineers: Elephant Eating Habits Influence Lizard Habitat Choices; January 31, 2008
- Science Daily: Ants Take on Goliath Role in Protecting Trees in the Savanna from Elephants; September 3, 2010
- Blueplantebiomes: African Savanna
- Science Daily: Star of Africa's Savanna Ecosystems May Be the Lowly Termite: Regularly Spaced Termite Mounds Are Key to Maintaining Ecological Function; May 26, 2010
- Savannah Biome