Controlling Invasive Australian Acacia Species: The South African Story

Australian Acacia species (‘wattles’) were introduced to South Africa for a range of purposes from the early 19th century onwards. Some wattle species continue to be grown and utilized for timber and bark products, but since the mid-20th century management has increasingly had a focus on reducing their impacts as invasive species. Wattles are thus ‘conflict species’ that generate both positive benefits and negative impacts, and management and legislation have had to accommodate the often opposing views and needs of various stakeholders. Proposals to introduce biological control agents in the 1970s were initially strongly resisted, and only ten seed-feeding and flower-galling insects and one gall-forming rust fungus have been released between 1982 and 2020, although several other agents are currently under consideration for future release. Released agents provide various levels of control against ten wattle species. Legislation was passed in 1983 that required landowners to manage wattles as invasive species, but also allowed for the continued growing of some species for commercial purposes. In 1995, the South African government initiated nationwide control campaigns against invasive alien plants, including wattles, to both reduce negative impacts and create employment. To date, ZAR 1.4 billion has been spent on physical and chemical control of wattles through this programme (2020 ZAR values), but this control has reached < 6% of the estimated invaded area. The effectiveness of control is not monitored, so the outcomes of this investment are largely unknown. Seven wattle species that have limited distributions have been systematically controlled with a view to achieving nationwide eradication, but extirpating even small populations could take decades given that many invasive wattles have large persistent seed banks. When cleared of wattles, ecosystems are largely left to self-recover, although active restoration of the historically displaced vegetation is clearly needed in many instances. Future management of wattles in South Africa will have to build on the lessons learnt over the past century, and will continue to be constrained by insufficient funds and competing interests. The development of national species-level policies, with clear and attainable goals, will be needed to guide integrated management into the future.