Kalahari xeric savanna

• Category: Grassland, Tundra, and Human Biomes.
• Geographic Location: Africa.
• Summary: The Kalahari Xeric Savanna biome hosts a low variety of plant and animal species with multiple adaptations to harsh environmental conditions; it is increasingly in danger of desertification.

The Kalahari Xeric Savanna ecosystem is one of the least biodiverse regions in southern Africa, as it is one of extremes: highly variable low mean annual rainfall that occurs primarily during winter months, and high temperature differences between day and night. These climatic conditions create a harsh environment, requiring both plant and animal species to develop specific adaptations to survive and reproduce.

This biome extends throughout the Kalahari Desert from the northern Cape region in South Africa, north to the Democratic Republic of Congo, covering large expanses of land in northwestern South Africa, southern Botswana, and southeastern Namibia. The term xeric refers to dry; these savannas exist around the core of the extremely arid Kalahari Desert, and many species here have evolved to survive in such conditions.

The area is characterized by large night-day temperature fluctuations, with daytime highs up to 113 degrees F (45 degrees C), and after-dark lows falling near freezing. Rainfall often comes during short and infrequent, but powerful, thunderstorms. Rainfall is regionally highly variable, ranging from 6 inches (150 millimeters) in the northeast to up to 20 inches (500 millimeters) in the southwestern Kalahari. The Kalahari Desert consists primarily of reddish-brown, highly oxidized, and nutrient-poor soils.

Biodiversity

Typical savanna vegetation is represented by open grasses from families Aristinda, Eragrostis, and Stipagrostis, along with scattered trees and shrubs. Although very low in endemic (found only here) species, the Kalahri is well known for such plants as the camelthorn tree (Acacia erioloba)—the largest and best-adapted tree species in this biome—interspersed with silver cluster-leaf, umbrella thorn, shepherd’s tree, and many types of shrubs.

Among the animals are gemsbok (Oryx gazella), Kalahari lion (Panthera leo), cheetah, leopard, spotted and brown hyena, wild dog, and jackal. Birds here include the secretary bird, sociable weaver (Philetairus socius), and raptors such as eagles, owls, falcons, and kites. Most of these species, even though they are not different from those in adjoining regions, have developed a set of special adaptations. The Kalahari lion, for example, has larger spatial ranges, hunts smaller prey, and lives in smaller groups than its neighbors.

The sociable weaver builds immense communal nests up to 20 feet (6 meters) long and 7 feet (2 meters) high, weighing as much as 1.1 tons (1,000 kilograms). These structures house up to 300 laying birds and their young at a time. These giant nests are well insulated to buffer the extreme temperature swings.

The wild dog, an endangered species, is the Kalahari’s most threatened carnivore. Although restrictive measures such as tracking collars are in place to protect their dwindling numbers, local farmers admit to shooting the dogs and destroying their collars. Also affecting the dog population is rising temperatures from climate change, which can reduce the abundance of prey, and sharper competition among higher-up predators such as lions and leopards.

Protected Areas and Human Activity

Approximately 18 percent of the Kalahari Xeric Savanna ecoregion falls within protected areas, the largest of which is Central Kalahari Game Reserves in Botswana. Kgalagadi Transfrontier Park, shared by Botswana and South Africa, is Africa’s first Peace Park. This transboundary park was created to enable better animal and human movement across protected areas; it has so far been a successful conservation and rural development strategy in both countries.

Human settlements expanding into these regions, as well as the fences people build (primarily to separate cattle from wildlife for fear of foot-and-mouth disease), have had detrimental effects on a number of the wildlife species that need to migrate long distances to obtain water, such as the wildebeest and hartebeest. The problem is especially serious in Botswana, where the beef industry is a major source of revenue.

Degradation of vegetation, sometimes leading to desertification, is a major concern. According to the United Nations Convention to Combat Desertification, four main processes are primarily responsible for the condition: deforestation; overharvesting of high-value timber products, medicinal plants, and large fauna; soil erosion; and nutrient depletion. The underlying causes of these include rapid population growth, inappropriate government policies, poor agricultural practices in unsuitable regions, overgrazing, woodcutting, environmental change, and mining.

A first diagnostic signal of degradation is an increasing rate of thorny-shrub establishment, a process referred to as bush encroachment. This problem is especially severe throughout southern Africa, primarily because it means that large grazing areas are lost (or reduced in carrying capacity), accompanied by a degradation of habitats and a reduction in species diversity.

Climate change is becoming an increasing threat to the area. The Kalahari is warming at more than twice the global rate and scientific projections indicate the area is facing more intense droughts. This shift also affects water availability, creating a scarcity that negatively impacts biodiversity.

Conservation Efforts

A fair proportion of this biome is under conservation and protection, but far from all or even most of it. As a result, wide areas are experiencing increasing land degradation. One of the main approaches to improving the state of degraded shrublands is the mechanical removal of encroaching species and controlled burns. Alternatively, some areas that become bush-encroached in riparian grasslands can more easily be returned to a nonwoody state after large floods drown the woody species; they are then removed mechanically.

A race against time is developing, as global warming adds to the encroachment threats, disrupts growing seasons, and exerts pressure on growers and herders, who in turn are likely to support poaching, water diversion, and less than ideal, short-term land-use practices.

Bibliography

Knight, M. and P. Joyce. The Kalahari: Survival in a Thirstland Wilderness. Cape Town, South Africa: Struik Publishers, 1997.

Liu, Xuan, and Jie Zhou. "Assessment of the Continuous Extreme Drought Events in Namibia During the Last Decade." Water, vol. 13, no. 20, 2021. DOI: 10.3390/w13202942. Accessed 18 Nov. 2024.

Munday, Callum, Sebastian Engelstaedter, and Richard Washington. “SoGE Climate Research in the Kalahari Desert: The KAPEX Field Campaign.” School of Geography and the Environment, 2 Feb. 2024, www.geog.ox.ac.uk/news/soge-climate-research-kalahari-desert-kapex-field-campaign. Accessed 18 Nov. 2024.

Schulze, R. E. “Climate.” Vegetation of Southern Africa. Cambridge, UK: Cambridge University Press, 1997.

Van der Walt, P. and E. Le Riche. The Kalahari and Its Plants. Pretoria, South Africa: Van der Walt and Le Riche, 1999.