Kalahari Sands

A
lthough the Kalahari Sand areas of western Zambia are part of the southern African plateau, the soils and vegetation are so different from those elsewhere that they are always treated as a distinct entity by ecologists. Kalahari Sand derives its name from the Kalahari Desert, which has undergone considerable expansions many times during its geological history. The Kalahari Sands, which have been described as the largest sand sea in the world, extends from the northern Cape Province, in South Africa, to well north of the equator. They are recognized by microscopic examination of the sand grains, which are rounded and pitted as a result of abbrasion while being blown about. In the present Kalahari Desert of Botswana significant dune movement only occurs where the annual rainfall is less than 150mm. The expansions of desert on either side of the equator have depleted the African flora, which is not nearly as rich as South America and other tropical regions.

The main differences between the Kalahari Sands and the rest of the Zambian plateaux are attributable to the very deep, free-draining soil with virtually no clay or silt. Such soils provide an excellent growing medium for deep-rooting woody plants. Since it is deficient in clay the soil can only hold nutrients where there is organic matter. Exposure of the soil surface to the sun destroys much of the organic matter and such areas tend to remain bare.

Kalahari Sand Wetlands

On the west side of the Zambezi, where the relief is low, there are large plains which barely rise above the high flood level. In Liuwa National Park near the Angolan border there are treeless plains where there is no tree visible above the flat horizon in all directions.

Although the topland areas are deficient in clay and soil nutrients this is not the case with the plains and dambos, which are of great importance for grazing cattle and crop growing. In Sesheke and Senanga Districts the sand overlies old river beds which are rich in clay and lime. These areas can usually be recognised by the presence of termite mounds.

Kalahari Sand Vegetation Types

There are two types of dryland forest, mavunda or Cryptosepalum forest, which occurs mainly in the northern higher-rainfall areas, and mukushi (Baikiaea plurijuga or Zambezi Teak) forest, which occurs mostly in Sesheke, Senanga and Kalomo Districts, as well as in the adjacent areas of neighbouring countries.

Mavunda

Mavunda is classed as a dry-evergreen forest type, consisting of a very dense evergreen shrub matrix, mostly about 4m in height, with a fairly light overwood in which Cryptosepalum exfoliatum subsp. pseudotaxus (mukwe) is the dominant tree. The two main blocks of mavunda, occurring respectively to the north and south of the Kabompo river, constitute the largest area of tropical evergreen forest in Africa (and probably in the world) outside the equatorial zone. Small outliers of mavunda occur as far south as Sesheke District.

Mukushi Forest

Mukushi Forest is deciduous and occurs in an area of much lower rainfall than the mavunda forests. Again it consists of a dense thicket with a lighter overwood, but the species are entirely different. The dominant tree species is mukusi (Zambezi teak). It is deciduous and occurs in an area of much lower rainfall than the mavunda forests. Again it consists of a dense thicket with a lighter overwood, but the species are entirely different.

Zambezi (or Rhodesian) teak supported a major timber industry in the first half of the century, supplying enormous quantities of railway sleepers and parquet flooring. Without this timber resource the rail through to the Copperbelt and Lubumbashi, in Zaire, would undoubtedly have taken much longer to complete. Production of mukusi timber peaked at 100,000 cubic metres per annum in the 1930s and again in 1964. Since then there has been a steady decline, and a recent inventory undertaken by the Japanese aid agency found no further exploitable reserves in the prime teak forest areas of Sesheke District.

As with other indigenous African timbers, exploitation has destroyed the forests, with little hope of recovery. Any opening up of the forest results in the invasion of grasses and fires. Mukusi will survive as a woodland tree, but in this habitat it never achieves the same size as in the forests. A German aid agency has embarked on a 15-year programme to try to find out how to rescue what remains of the teak forests.

Kalahari Woodland, Dambos and Pans

Most upland Kalahari sand carries woodland vegetation which is similar to miombo. On the deep sands of the plain east of the Zambezi there are a few major rivers in the form of wide dambos. These are highy productive areas. Also on this plain are numerous “blow-outs”, or wind-scoured pans, which are remnants from previous desert conditions. Many are seasonal swamps. These dambos and pans of the Kalahari Sand provide a fine thatch grass, Loudetia simplex (mwange in Lozi) for which Western Province is famous.

The Bulozi Floodplain
This vast area of wetland is one of the most important areas for the production of fish and cattle in southern Africa. The depth of flooding of the Zambezi and its tributaries varies considerably from year to year, which makes both cropping and cattle keeping somewhat dependent on chance. In years of high rainfall the floods recede slowly and the cattle suffer, because the grazing off the plain is of poor quality.

Western Province is the source of some of the finest crafts in southern Africa. The most skilled are the Mbunda and Nkoya people, both of whom use mukenge, the root fibres of the tree Combretum zeyheri for weaving basket work which is much sought after on international markets. These tribes also make very fine bows and arrows, which are still used in hunting.