South African contributions to the understanding of plant invasion ecology and management

Abstract

This paper provides a brief selective history of research into the ecology and management of alien plant invasions in South Africa. Over 2000 alien plant species have been introduced to the country, and over 750 species are known to have become naturalized or invasive. A striking feature of this naturalized flora is the unusually high dominance of trees and shrubs, making South Africa the world capital of tree invasions. Research into the ecology and management of these invasions began over 100 years ago. In the first half of the 20th century the focus was almost exclusively on biological control and invasive species in the fynbos biome. A broadening research agenda in the second half of the 20th century was facilitated by several initiatives, including the Scientific Committee on Problems of the Environment’s (SCOPE) global project on “The Ecology of Biological Invasions” (which had its origins in South Africa), the CSIR’s National Programs for Ecosystem Research, and the Working for Water program. In 2004, the world’s first (and until recently only) research institute devoted solely to all facets of biological invasions was established in South Africa. This institute (the DST-NRF Centre of Excellence for Invasion Biology) made a substantial contribution to improving the understanding of alien plant invasions, and to building capacity to manage them. The true extent of invasions has proven difficult to estimate, but indications are that 10 % of the surface area of the country has been invaded, and that this is increasing. The most invaded biome is the Indian Ocean coastal belt (11 % invaded) followed by the fynbos biome (5 % invaded). Ecological impacts on biodiversity, water resources, livestock production and the severity of wildfires have been reported. Taken together, these impacts are estimated to be costing the country around USD 875 million (approximately ZAR 17 billion) per year, but data on costs are scant. Extensive control programs aimed at eliminating invasive trees and shrubs from the water catchment areas of the fynbos were initiated in the early 1970s. These efforts were expanded in the 1990s by the Working for Water program which operated at a national level with the dual goals of controlling invasive alien plants and creating employment. There have been few robust attempts to monitor the effectiveness of these interventions. Some studies have found that the extent of invasion has been reduced in selected areas while in others control has been ineffective. When assessed at a national scale, it appears that invasions have continued to grow despite control efforts. Populations have declined at a national level for some species under biological control, illustrating the important role that this practice has played. South African scientists have made substantial contributions to the field of invasion science, punching above their weight compared to better-funded developed nations. Challenges to the management of alien plant invasions in future include declining funding and a realisation of the complex social-ecological nature of the problem. Given the capacity and understanding that has been built, South Africa is comparatively well placed to address these challenges.