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Dr Willem de Lange is senior environmental economist at CSIR's Natural Resources and the Environment Unit in Stellenbosch. |
CSIR ecologist Dr Brian van Wilgen |
Dr Brian van Wilgen is chief ecologist at the CSIR's Natural Resources and the Environment Unit in Stellenbosch, where he has devoted more than thirty years of research to the management of invasive alien plants. Behind him in the picture is part of the Kogelberg Fynbos Reserve - a World Heritage Site in the Western Cape. |
If there had been no biological control of invasive alien plants in South Africa, the country would have lost R48.2 billion per year in terms of the services provided by ecosystems such as water, grazing and biodiversity.
The value of these ecosystem services, provided by Mother Nature herself, amounts to an estimated R152 billion per year.
According to CSIR environmental economist Dr Willem de Lange and CSIR ecologist Dr Brian van Wilgen, biological control of invasive alien plants pays not only in terms of monetary values, but especially in terms of protecting the resilience of ecosystems to handle impacts like climate change.
"If we allow aliens to dominate our natural ecosystems, the systems will lose their ability to deliver many of the benefits on which we depend for our livelihoods. Invasive alien plants use excessive amounts of water and smother our remarkable biodiversity, resulting in reduced river flow, a loss of grazing and a loss of harvested products from the veld," they explain.
In a paper delivered at the International Conference for Ecology and Management of Alien Plant Invasions this year, De Lange and Van Wilgen for the first time provided a programme-level economic evaluation of South Africa's endeavours to manage invasive alien plants using biological control. Biological control, as opposed to chemical or manual control, is (if executed properly) a safe and sustainable form of control that relies on insects and plant pathogens.
The researchers focused on the delivery of ecosystem services in biomes invaded by groups of weeds, rather than by individual weed species: "We established the present net value of biological control research for four invasive alien plant groups (pines and hakeas, acacias, succulents and subtropical shrubs), which amounted to R102 million/year in 2008, and derived benefit:cost ratios by comparing this value to the estimated savings in the value of ecosystem services directly attributable to biological control," they explain.
The impact of the various groups of invasive alien plants varied amongst the different biomes: Fire-adapted trees (pines and hakeas) contributed 20% of the relative impact in fynbos ecosystems, and relatively little elsewhere, while invasive Australian acacia trees dominated in all ecosystems except savanna and thicket by contributing 78-96% of the impact. Savanna ecosystems suffered impacts from all groups of plants.
De Lange and Van Wilgen are unanimous in their belief that more research funding for the study of biological control of invasive aliens is required. "In our study, biological control was estimated to have resulted in substantial levels of protection of ecosystem services such as water, grazing and biodiversity. The annual value of services from ecosystems that would have been invaded by invasive Australian trees amounted to R8.3 billion, with savings of R2.6 billion and R1.1 billion arising from the protection of water and grazing resources in grasslands and R1.4 billion from the protection of biodiversity in the fynbos.
"The biological control of invasive succulents was also estimated to have protected services that deliver a value of R2.9 billion, mostly in the savanna and thicket biomes. With a minimum benefit:cost ratio of 50:1 (for subtropical shrubs) it should be clear that biological control is a cost-effective control mechanism. This kind of economic evaluation of biological control is necessary, inter alia, for deciding on appropriate levels of funding to support further research," they conclude.
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