A DESCRIPTION OF THE FUNCTIONAL VEGETATION PATTERN OF A SEMIARID FLOODPLAIN, SOUTH-AFRICA

The floodplain ecosystem of the Nyl River is located in a semi-arid re gion of South Africa where water limits both human development and eco system functioning. Proposed upstream impoundments threaten the ecosys tem's functioning and hence its conservation value and eco-tourist pot ential. Articulation of these threats to the floodplain ecosystem requ ires a predictive understanding of the relationships between the biota and hydro-geomorphic processes. This study provides the basis for the establishment of these relationships by presenting a description of t he plant assemblages of the Nyl River floodplain, identifying environm ental correlates of this vegetation pattern, and by distinguishing fun ctional plant groups. A correspondence analysis identified three major vegetation associations on the floodplain ecosystem: near-channel sit es, hydromorphic sites and sodic sites, Geomorphic landform type, soil moisture and soil texture were the best correlates of the vegetation pattern. Elevation above the channel and distance from the channel wer e poor correlates of vegetation pattern. The distribution of functiona l groups, which were defined by plant life forms, showed that the near -channel sites were dominated by prostrate and decumbent grasses, hydr omorphic sites by erect grasses, and sodic sites by a variety of succu lent life forms. The plant-environment relationships recognized sugges t that future distributions of functional plant groups may provide a s ensitive index of the impacts of anticipated reductions in run-off.