Clearing invasive alien plants as a cost-effective strategy for water catchment management: The case of the Olifants river catchment, South Africa

Abstract

Invasive alien plants have a negative impact on ecosystem goods and services derived from ecosystems. Consequently, the aggressive spread of invasive alien plants (IAPs) in the river catchments of South Africa is a major threat to, inter alia, water security. The Olifants River catchment is one such a catchment that is under pressure because of the high demand for water from mainly industrial sources and unsustainable land-use, which includes IAPs. This study considered the cost-effectiveness of clearing IAPs and compared these with the cost of a recently constructed dam. The methods used for data collection were semistructured interviews, site observation, desktop data analysis, and a literature review to assess the impact of IAPs on the catchment’s water supply. The outcomes of this study indicate that clearing invasive alien plants is a cost-effective intervention with a Unit Reference Value (URV) of R1.44/m3, which compares very favourably with that of the De Hoop dam, the URV for which is R2.93/m3. These results suggest that clearing invasive alien plants is a cost-effective way of catchment management, as the opportunity cost of not doing so (forfeiting water to the value of R2.93/m3) is higher than that of protecting the investment in the dam.

Impacts of Plant Invasions on Terrestrial Water Flows in South Africa

“…This has generally been done using the unit reference value, which provides an estimate of the unit cost of supplying a cubic meter of water at the required assurance over the portion of the water management or augmentation project's lifespan during which it produces economic benefits for society (van Niekerk 2013). It has been used to show that clearing invasive alien plants can be more cost-effective than other water supply options such as building a dam (van Wilgen et al 1997;Larsen et al 2001;Hosking and Preez 2002;Marais and Wannenburgh 2008;Blignaut et al 2010;DWS 2014;Preston 2015;Vundla et al 2016;Morokong et al 2016;Mander et al 2017;Nkambule et al 2017). None of these studies assessed the financial impacts of impacts on yields (Table 15.2) so this is an opportunity for further research.…”

The Extent and Effectiveness of Alien Plant Control Projects in South Africa

“…Finally, the potential returns on investment from invasive plant control operations have been the subject of several recent studies that compared the outcomes of various management scenarios (Vundla et al 2016;Mudavanhu et al 2016;Morokong et al 2016;Nkambule et al 2017). The scenarios included different rates of spread, included or excluded value-added products using biomass from invasive plants, and included or excluded private sector co-funding.…”

Reducing the costs of landscape restoration by using invasive alien plant biomass for bioenergy

“…Assuming 3303 million m 3 of water per year and assigning the tier‐1 water resource management charge (R1.50/m 3 ), the net present value would be between R12.8 billion and R29.5 billion . A study of the Olifants River catchment suggests that clearing IAPs to improve the flow of water was a more cost‐effective option to secure water resources than building the De Hoop dam …”