Weed flora of South Africa 3: more power shifts in the veld

Abstract

This paper deals with shifts towards plants with particular life cycles, growth forms, or from particular geographic areas.

Exotics probably have their greatest impact in the aquatic habitat where they almost equal in number of species (the ratio is 3:5) and out-perform the indigenous aquatic flora. In the streambank habitat exotic weed species, mostly trees, outnumber indigenous weed species by more than 3 to 1. They are completely replacing indigenous streambank communities in many places. An investigation of their effect on stream flow and water loss is urgently required.

The problems of the winter rainfall area are highlighted by the fact that it has 300% more indigenous species and 109% more weed species per unit area than the summer and all year rainfall areas. In the veld as a whole there is a significant and so far unremarked invasion by exotic annuals.

The major invasive weed groupings are herbs from Europe and Asia and trees from Australia but South America probably has the greatest potential to provide us with new and dangerous weeds. A comparison of the weed floras of the southern continents could contribute much to an understanding of our own weed flora.