Managing invasive alien plants on private land in the Western Cape : insights from Vergelegen Estate

[摘要] ENGLISH ABSTRACT: Invasive alien plants (IAPs) are a major threat to biodiversity and ecosystem services in South Africa and are particularly widespread and damaging in the Cape Floristic Region (CFR). Activities such as agricultural development, the establishment of forestry plantations and urbanization can change environments and provide opportunities for IAPs to spread. Large-scale government-funded management initiatives are underway to reduce the extent of invasions in this region, but they face many challenges. Among these challenges are the huge spatial extent of the invasions and difficulties in coordinating management efforts across large areas of invaded land in private ownership. Scarce funds for large-scale clearing operations need to be optimally used, but little information is available on which to base the planning of such complex undertakings.This investigation used Vergelegen Wine Estate near Somerset West as a case study to investigate the factors that contributed to alien plant invasion on private land. I studied the effectiveness of one large project that set out to reduce alien plant cover, the challenges that the project faced, and the costs associated with long-term operations to clear IAPs on privately-owned land in the CFR. I documented the current (2016) extent of the problem at Vergelegen and estimated the time and resources that would be required to reduce the remaining invasions to a level where the minimum amount of resources are required to maintain the plants at a low density at low cost ('maintenance level'). Evaluation of this project provides insights into how to better manage IAPs on private land in the CFR.I found a clear link between human activities, changes in land-use, and the spread and proliferation of IAPs. The area occupied by IAPs increased with increasing land-use change, from 8 % cover in 1938 to 40 % in 2004. The management interventions initiated in 2004 reduced dense stands of IAPs by 70 % over the next 10 years. The challenges associated with managing IAPs on private land included multiple interacting environmental and socio-economic factors. The total cost required to clear Vergelegen to a maintenance level was estimated to be between R55 and 80 million (2015-equavalent Rands; R49 million already spent prior to 2016, plus R6 – 30 million that still will be needed, depending on the scenario). Maintaining the estate was estimated to be R5.9 million per 15-year cycle, amounting to between 7.3 and 10.7 % of the cost to bring the estate to a maintenance level.Using a wide range of research methods and techniques, I have shown that controlling IAPs at the scale of the operation at Vergelegen is possible, but at a significant cost to landowners. The effectiveness of projects, typically constrained by limited funds, could be increased by adopting an outcomes-based approach to ensure that objectives are achieved. Novel funding pathways need to be investigated by government to support clearing initiatives on private land that form part of larger priority areas to ensure success.

[发布机构] Stellenbosch University