Ecology and dynamics of the woody vegetation on the Kalahari Sands in Hwange National Park, Zimbabwe

Abstract

The woody vegetation on Kalahari sand deposits in Hwange (ex-Wankie) National Park, Zimbabwe was classified into nine types on the basis of species composition. Ordination of the data showed that the types which occupy the ends of the major (soil-type) gradient are easily distinguishable, viz. well developed, mature Baikiaea plurijuga woodlands on deep sands, and scrub Terminalia sericea and mixed woodland on soils with a higher clay content or compact layer. The central groups of stands, involving mixed woodlands and scrub, were less easy to interpret, and previous logging disturbance is involved.

In the disturbed Baikiaea woodlands recruitment appears to be less than is required for long-term maintenance, even given that some of the measurements may have led to underestimates. Elephants were shown to have only a minor effect, and are relatively insignificant as agents of change in the woodlands. Depth of sand and soil moisture regime are the predominant factors determining overall vegetation structure. Fire is a dominant feature in scrub areas and interacts with frost, which has a periodic severe effect on developing saplings in scrub and in some disturbed woodlands. Although the relief is very flat there is a marked frost gradient from ‘ridge’ areas with mature woodland into the slightly lower-lying scrub areas. A conceptual model of the dynamics of the vegetation, based on the above features, is described.