Species richness of alien plants across protected areas in northern KwaZulu-Natal, South Africa: environmental and anthropogenic correlates

Previous studies have highlighted several factors that contribute to the invasiveness of a reserve, e.g. the native plant species richness, the age of the reserve and human population densities next to reserves. Some areas or ecosystems are more susceptible to invasions than others; this is due to the dynamics of alien plant invasion as well as different characteristics found in different ecosystems. To examine which factors are contributing to the invasiveness of a reserve, characteristics concerning biotic and abiotic variables representing human dynamics, reserve specific dynamics, climate and native biodiversity were obtained within each of 12 protected areas located within the northern region of KwaZulu-Natal. Two response variables, namely alien species richness and proportion of alien species richness, were also obtained for each protected area. From the different predictor groups, variation in alien species richness correlated more strongly with variables associated with human dynamics compared to proportion of alien richness, which showed a strong association with the year of reserve proclamation. I conclude that, in addition to processes and dynamics associated with the reserve per se, it is more specifically those associated with the outside periphery of protected areas that are having a significant influence on the spread of alien plant species into protected areas; and that reserves cannot be managed as small, independent entities.