Vegetation types of mountain tops in Damaraland, Namibia

Abstract

The vegetation of flat-top mountains (mesas) was investigated in northwest Namibia. The main questions were: (1) Are there differences between vegetation types on mountain tops and what is the composition of mountain top vegetation? (2) Do rare species affect the floristic relationship between mountain tops? and (3) What are the likely factors determining the vegetation on mountain tops? Seven vegetation types were described, comprising a sparse to medium cover mix of mainly shrubs and grasses. Vegetation types differed remarkably between mountain tops, even within the proximity of a few kilometres. No single environmental driver can explain the vegetation on the investigated mountain tops. Biogeographic influences (distance to other mountain habitat, size of habitat per se, position within phytogeographic zones), as well as physical variables such as soil properties, elevation (height above surroundings), a westeast gradient of increasing rainfall, and possible rain shadows were considered of importance in determining the documented vegetation types. Accessibility to large herbivores, hence grazing impacts, are other factors possibly influencing the derived vegetation types. Multivariate analyses with and without weightings of rare plant species showed that rare species had a significant influence on the results.The following practical considerations emanate from this study: (1) Extrapolation of mountain top vegetation in the general area will be difficult and more individual mountains, particularly higher ones, will need to be investigated. (2) The data analyses stressed the importance of rare species in determining floristic relationships.Complete botanical surveys, rather than surveys of general descriptors as in many environmental assessments in Namibia should thus be undertaken for management purposes in this area. (3) High mountain tops in Damaraland are relatively species rich and are prone to harbour species at their limit of distribution. These are of particular conservation importance.