Kalahari Desert ecosystem

• Category: Desert Biomes.
• Geographic Location: Africa.
• Summary: The vast red sand country of the Kalahari Desert supports some of Africa’s most iconic wildlife.

The Kalahari Desert is a vast region of porous, sandy soils that covers much of south-central Africa, from the Orange River in South Africa through Botswana, Zimbabwe, Namibia, and Angola, to the Congo. This 965,255-square-mile (2.5 million-square-kilometer) region is 10 times the size of Great Britain. The southern section of the Kalahari supports iconic rolling red dunes that are intersected by ancient dry riverbeds lined with camelthorn acacia trees 49 feet (15 meters) tall.

The Kalahari generally exists in drought, with an average of 10 inches (250 millimeters) of annual rainfall in the southwest region, to approximately 26 inches (650 millimeters) in northeastern Botswana. Occasional thunderstorms during the wet season, October to March, bring life to the dry earth. The northeast Kalahari is not classified as a true desert because it receives more than 10 inches of annual precipitation. It is a large, semiarid, grassy plain.

The Kalahari was formed during the breakup of the Gondwana supercontinent, and by 65 million years ago, it had begun to assume its modern dry and dusty character. The desert is cut by two dry rivers: the Nossob and the Auob. These rivers flowed until the tectonic movements that created Africa’s Great Rift 10–15 million years ago tilted the ground in such a way that the rivers lost momentum, and their water soaked into the Kalahari sands.

Biodiversity

Despite the aridity of the environment, the Kalahari supports diverse fauna that are adapted to desert conditions. Large herbivores like the gemsbok (Oryx gazella), a large antelope with 3-foot- (1-meter-) long spear-like horns to provide protection against lions, are adapted to survive long dry periods when temperatures here exceed 113 degrees F (45 degrees C).

Ground squirrels of the Kalahari have an innovative way to keep cool. They protect themselves from the sun by holding their bushy tails over their heads like a parasol on hot days. This behavior allows them to be active in the sun for longer periods. Some arid-adapted mammals, like springbok and gemsbok, possess pelage (hair) patterns that are thought to reflect heat.

The southern parts of the Kalahari were once home to one of the world’s greatest animal migrations. Springbok, blue wildebeest, and red hartebeest once moved from the Orange River in the northern part of the Kalahari in numbers that were estimated to be 80 million animals covering 130 miles (210 kilometers), with a 14-mile (22-kilometer) front. Although these estimates may be exaggerated, the migration clearly was an impressive sight, with people sitting on their doorsteps watching the herds travel by for three days. Hunting and human expansion have decimated these herds.

Giraffes have been reintroduced to the Kalahari. Lions, leopards, brown and spotted hyenas, cheetahs, and (on the more mesic, or moist, eastern side) African wild dogs prey on the still-rich supply of herbivore fauna. Smaller and more unusual predators abound, including Cape foxes, black-backed jackals, caracals, African wildcats, and honey badgers. Other animals of the Kalahari include black-footed cats, yellow mongoose, insect-eating aardwolf, and velvet monkey.

Boreholes sunk along the dry riverbeds of the Auob and Nossob rivers 100 years ago in search of water have proved to be beneficial to wildlife today; for example, they have sustained Burchell’s sandgrouse. Normally, these birds get enough water from the seeds they feed on, but during the breeding season, males fly on a 75-mile (120-kilometer) round trip daily from their nests across the desert to collect water around these boreholes and then return to their chicks. The feathers of the sandgrouse have special barbs that act like a sponge to hold up to 1.4 ounces (40 milliliters) of water. Raptors like lanner falcons rocket like fighter planes into the midst of the drinking birds, looking for a meal.

Hundreds of arid-adapted plant species exist in the Kalahari, the best-known of which is the camelthorn (Acacia erioloba), which has numerous uses, from candy and a coffee surrogate, to beams for fencing posts and firewood, with the plant’s roots used to help alleviate toothaches and as a drink to ward against tuberculosis. The pods are fodder for elephants. Other plants include black thorn (Acacia mellifera), shepherd’s tree (Boscia albitrunca), tsama melon (Citrullus roastes), belle mimosa (Dichrostachys cinerea), Kalahari currant (Searsia tenuinervis), and buffalo thorn (Ziziphus mucronata).

Human Settlement

Humans have inhabited the Kalahari at least since the San, or Khoisan, bushmen settled there more than 3,000 years ago. They are renowned for their prowess in hunting large and dangerous prey with the aid of small poison arrows. When an animal such as an eland or gemsbok was hit with the arrow, the San people would track the animal over many miles (kilometers) until it succumbed to the poison.

The Khoisan knew where to obtain water from the environment and from plants such as tsamma melon, gemsbok cucumber, and wild cucumber, and they stored and carried the water in blown ostrich eggs. While the people and animals of the Kalahari benefit from the water stored in plants, the plants themselves benefit by having their seeds transported in the dung of the animals that eat them.

The Khoisan people were followed into the Kalahari by Bantu, and then by European pastoralists starting in the 1600s. The Europeans classified the bushmen as “vermin” and killed an estimated 200,000 within the first two centuries of their occupation of the Capeland. A people of hunter-gatherers then, only a small number of the San follow their traditional way of life in the Kalahari today. Modern civilization has invaded the Kalahari and is threatening the natural resources and habitats of the area. Mineral companies have discovered large coal, copper, and nickel deposits in the region; one of the largest diamond mines in the world is located at Orapa in the Makgadikgadi, a depression of the northeastern Kalahari.

Protected Areas

The core Kalahari Desert is largely protected in Kgalagadi Transfrontier Park, which is composed of the Gemsbok National Park in Botswana and the Kalahari Gemsbok National Park in South Africa. The transfrontier park is a large wildlife preserve and conservation center that is jointly managed. The ecosystem extends through Botswana to the Nxai and Makgadikgadi salt pans and the Central Kalahari Game Reserve.

Kalahari Gemsbok National Park receives 50,000 visitors each year. Its aim is to be a self-contained ecosystem, but even at the size of 8.9 million acres (3.6 million hectares), the park is not large enough to support a viable population of lions, because predator population density is related to resources, and deserts are resource-poor areas. This situation is increasingly problematic, as much of the park is fenced to minimize human-animal conflict.

The effect of artificial waterholes is another problem faced in the region. These areas create halos of overgrazing around them. Most mammals can persist only with regular access to water, so they graze all vegetation in the vicinity of the bore. This overgrazing leads to erosion, salinity problems, and altered vegetation communities. Scientists are analyzing the effects of rising temperatures as a result of climate change, and already have noticed how rising atmospheric carbon dioxide levels are impacting the soil, advancing the leaching of nutrients in some cases. This type of adverse condition can upset subsistence pastoral farming and natural grazing patterns, adding to habitat stress on a range of plant and animal species. Changes in climate also exacerbate drought conditions. A drought in the Southern Kalahari from 2014-2020 was the longest and most intense drought recorded in that region in 60 years. The drought caused a number of mortalities among animals and plants. Scientists fear conditions could worsen as the effects of climate change continue to be felt.

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