The management of invasive alien plants in South Africa: strategy, progress and challenges.
Almost 900 species of alien plants have escaped cultivation and established populations in the wild in South Africa. About two thirds of these established alien species have become invasive, spreading into natural ecosystems. Many of them still have relatively restricted distributions in South Africa, but a growing number are becoming alarmingly widespread. These widespread species include many alien trees, such as pines (Pinus species), wattles (Acacia species) and mesquite (Prosopis species), as well as a host of shrubby, herbaceous and succulent species. In South Africa, alien plants are estimated to cover almost 7% of the country, and many species are now entering a phase of exponential growth. This problem has been recognised for over a century in South Africa, mainly because of the negative impact that alien plants have had on rangelands utilised for livestock production. However, it was the realization that alien plants, and especially alien trees, were responsible for the reduction of streamflow from water catchment areas that triggered a large expansion in control efforts in 1995. This article provides a brief description of the policies and strategies adopted in South Africa to address this problem, reviews the progress that has been made with control efforts, and outlines the main challenges that face the managers of alien plant control projects.