The ecological effect of Acacia saligna in a sand plain fynbos ecosystem of the Western Cape, South Africa

[摘要] ENGLISH ABSTRACT:The invasive Australian acacia, A. sa ligna, is widespread in the Western Cape, South Africa, andis widely used by local communities. Not surprisingly, the introduction of the biological controlagent, the fungus Uromycladium tepperianum in 1987 was received with mixed emotions. In aneffort to determine the socio-economical and ecological impact of the fungus, the Department ofWater Affairs and Forestry has commissioned a study, of which this thesis forms part.For this thesis, a number of parameters, environmental as well as biological, were sampled,analyzed and compared with existing data from previous studies. The goal was to obtain acomprehensive estimation of the effect of A. saligna on a Sand Plain Fynbos community nearAtlantis and to assess whether or not, the detrimental effect A. saligna has on plant biodiversity,has reached the stage where it has become irreversible. The floristic data confirmed results fromearlier studies, that invasion of A. saligna in Fynbos communities induces a decline in plantdiversity, especially in dense acacia thickets. This study mainly revealed structural changes ratherthan community shifts. The enrichment of the soil as noted by others authors was also confirmedfor the study area. However, it was outside the scope of this study to determine the long-termeffects of this enrichment on the Sand Plain Fynbos communities. Soil moisture content wassampled on three different occasions, in densely invaded and uninvaded study plots. The aim wasto see if A. saligna had any influence on the availability of water in the upper soil. Contrary toexpectations, moisture content under acacia stands was higher in spring and early summer in thetop soil than in pristine fynbos. Pitfall traps were used to sample the arthropods that dwell thesurface of the study area. For arthropods in general, the survey did not produce conclusive data,but spider species seem to be positively affected by the presence of A. saligna, probably due tothe structural diversity they add to the fynbos. This study revealed that the full ecological impactof A. saligna on its environment is far from understood, mainly due to the richness andcomplexity of the fynbos communities and a lack of research about faunal aspect of the Fynbosecosystem.

[发布机构] Stellenbosch University