Alien plant infestations

Assessing impacts of alien plant infestations on river systems in the Southern Cape using cost-benefit analyses

This project aimed to improve the scientific basis for quantifying impacts of alien riparian vegetation on water quality, in particular, water temperature, on aquatic macroinvertebrate diversity in the Southern Cape region of South Africa. Alien vegetation in the riparian zone can impact on water temperatures, flow patterns, degree of shading, channel modification, and changes to natural sediment loads. Climate change is likely to exacerbate the problem both directly through its amplification of thermal extremes in aquatic systems, and indirectly through its impacts on dispersal patterns of alien invasive vegetation. Freshwater systems in the Garden Route Initiative planning domain are of particular conservation value because of their rich Gondwanaland relict aquatic macroinvertebrate fauna found in these rivers, which are vulnerable to thermal changes. This study analysed information on the costs of clearing alien riparian vegetation relative to the ecological benefits, as assessed by convergence of water temperatures to target values. It also examined the impacts on aquatic macroinvertebrate community structure in response to increasing alien plant densities in the riparian zone versus major vegetation type (fynbos and forest).





Project Leader
Nick Rivers-Moore