Changes in woody community structure and composition under constrasting landuse systems in a semi-arid savanna, South Africa

We aimed to explore the farm scale effects of three landuse types, communal grazing, wildlife management and commercial cattle farming, on the woody v egetation of a semiarid savanna. Location The study farms were located within a single bioclimatic zone in s emiarid savanna, South Africa. Methods The species composition and structure of woody vegetation on three farms of each of three landuse types were sampled. Results We found that communal grazing land sites were classified outside t he topland-bottomland vegetation dichotomy characteristic of this region. C omparisons of size class distributions showed the communal grazing lands ha d fewer small and large individuals; suggesting both lower levels of regene ration and regenerative capacity in the communal grazing lands. The species richness and biomass of woody plants was lower on communal grazing lands t han on private game reserves and commercial cattle farms. The longevity of tree species explains the observed lag between changes in abundance and spe cies loss; we consequently predict that there will be future losses of spec ies in the communal grazing lands. By classifying species into a range of u se-categories we showed that utilization and species loss was not limited t o certain plant use categories. Higher levels of wood harvesting measured i n the communal grazing lands are likely to be responsible for the observed differences. Main conclusions It is concluded that communal grazing management at this s tudy site has substantially changed the composition and structure of woody plant communities, and that these changes have reduced the current availabi lity of natural resources and will reduce resource production in the future .