Alien plant invasions in South Africa: driving forces and the human dimension

Invasive alien plants pose a substantial threat to the rich biodiversity of South Africa, and to the sustained delivery of a wide range of ecosystem services. Biological invasions are driven by human activities and mediated by culturally shaped values and ethics. This paper explores the human dimensions of alien plant invasions in South Africa. We consider four primary forces, those which directly influence the likelihood and rate of invasion - arrival of propagules; changes in disturbance regimes; changes in the availability of limiting factors; and fragmentation of the landscape - and the roles of 22 secondary driving forces in shaping the outcomes of the four primary driving forces. Human societies and their dynamics and activities are an integral part of each of the secondary driving forces. A map of the interactions between and among the primary and secondary driving forces shows how they are interlinked and influence each other-either positively or negatively, or switching between the two. There are two key points for intervention: prevention of the introduction of propagules of potentially invasive species and developing collaborative initiatives with enterprises that rely largely on alien species (for example, horticulture, agriculture and forestry, including community forestry) to minimize the introduction and use of potentially invasive species. An example of the first type of intervention would be to implement more effective inspection systems at international border and customs posts. This type of intervention can only be effective if those who are directly affected-whether businessmen, tourists or migrants - understand the requirement for these measures, and collaborate. The need to build public awareness of the critical importance of the human dimension of invasions emerges as a key theme from this analysis and is the basis for better-informed decisions, more effective control programmes and a reduction of further invasions.