Acacia implexa in South Africa: an emerging invader and potential candidate

Invasive alien plant species have major impacts on biodiversity and ecosystem functioning in most parts of the world. Early detection and rapid response is a crucial part of management programmes. Eradication of invasive species at the early stage of invasion is a very cost-effective intervention, but not all species can be eradicated. This paper reports on a study of Acacia implexa, the screw-pod wattle from Australia, an emerging invader, to determine whether it is a suitable candidate for eradication in South Africa. The species was introduced to South Africa in around 1986. Its current range comprises three populations: in Stellenbosch, Tokai and Wolseley. The populations sizes ranges between 100 and 200ha, with the Tokai population covering the largest area but comprising the fewest plants. The density of the plants ranges from very high to very low, with Stellenbosch (Papegaaiberg) having the highest density. The plants reproduce vegetatively (through suckering and resprouting) and sexually (via seeds). A very high occurrence of suckering was present and few seedlings were observed. Spread is mainly along rivers. Current treatments by area managers are unsuccessful for controlling the species. I consider that eradication of this species is feasible. The eradication plan should place strong emphasis on the effective use of herbicides, communication and cooperation between different managerial organizations, and prioritization of treatment efforts.