Alien plant invasions, their impacts and effective responses

Biodiversity and Ecosystem Services, CSIR, Stellenbosch and Centre for Invasion Biology, Department of Botany and Zoology, University of Stellenbosch

This presentation focuses on key shifts in the perceptions of alien plant invasions in South Africa, growing understanding of their impacts and the progress that is being made towards effective solutions. The first clear warning came from a report in 1948, which noted the serious implications of invasions of the fynbos, aided by fires, for both the flora and for water supplies. Even at that stage, the report recognised that control measures might have to be limited to selected areas. Despite these warnings, research on, and effective actions to address these invasions only began in the late 1960s, including biological control. Control programmes implemented by the forestry department made good progress until the mid-1980s. They were restarted following the establishment of the Working for Water programme in 1995, which was motivated by the potential for water savings and gainful employment. The savings were demonstrated based on catchment studies of plantations of the same species that were invading and have been supported by subsequent research. However, the clearing projects were not optimally located for maximising the gains, but the shift began when the importance of prioritising clearing to optimise the benefits was accepted. Some progress has been made in shifting the investment focus into priority areas, such as Water Source Areas for surface and for groundwater. The option of selecting some areas, and abandoning others, modelled on the medical practice of triage, has been revived. However, this must be carefully thought through or it could simply result in cleared areas being swamped by a sea of unmanaged invasions. The Knysna fires highlighted the hazards posed by alien tree invasions to many towns, a threat which will make triage more risky. Successful control will require more emphasis on behavioural change and coordinating efforts by all land owners and land management agencies.