Restoration of water resources (natural capital) through the clearing of invasive alien plants from riparian areas in South Africa — Costs and water benefits

AbstractWorking for Water forms part of the Expanded Public Works Programme of the South African Government, aimed at the sustainable management of natural resources through the control and management of invasive alien plants while enhancing socio-economic empowerment in South Africa. The programme's name was taken from one of the original motivations: namely, reducing the impacts of invasive alien trees on water resources. A number of studies have looked at the potential impacts of the programme but only one or two have used actual management data to quantify its costs and benefits. This paper is the first, in hopefully a series of papers, on the costs and impacts of the programme over recent years. The paper focuses on the extent, costs and impacts of clearing invasive alien plants from riparian areas. Data were extracted from the Working for Water Information Management System (WIMS) and analysed to assess clearing costs and estimated impacts of clearance on water resources. Some of the most significant findings of the study again illustrate the need to treat invasions as early as possible. Very scattered (1–5%) invasions of selected species for example were between 3 and 25 times cheaper to clear than closed canopy stands (75–100%). On the other hand, unit reference values, used to compare clearing operations in terms of cost efficiency in generating extra water yield, were much higher for low levels of invasion than denser invasions, to the extent that the former's viability could be questioned by the uninformed. However, this was only assessed in terms of extra water generated and not in terms of volumes of water secured, as invasive alien plants spread and become denser if not actively controlled. If left unchecked, water losses increase, which makes the clearing of light infestations much more viable. Overall, it is estimated that around 7% of riparian invasions have been cleared, resulting in significant yield increases. The increased estimated yield of 34.4 million m3 is about 42% of the yield of the new Berg River Scheme in the Western Cape (81 million m3). The investment in clearing species known for excessive water use from riparian areas, at a cost of R116 million, was found to be a very good investment. However, it is important to note that the clearing of invasive alien plants will seldom result in the total elimination of shortfalls in water supply and should be seen as part of a package of water resource options to optimize supply, aimed at minimizing wastage of water