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

Tshepo Morokong,Thulile Vundla,Shepherd Mudhavanhu,James Blignaut,Nonophile Nkambule

doi:10.4102/sajems.v19i5.1594

Tshepo Morokong, Thulile Vundla + Show 3 more

Open Access

https://doi.org/10.4102/sajems.v19i5.1594

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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.

Highlights

Invasive alien plants (IAPs), as biological invaders, negatively affect water sources (Ghahramanzadeh, 2013)
The impact of IAPs on water sources is a threat to water security and the sustainability of water bodies
The outcomes of this study indicate that clearing IAPs is a very cost-effective strategy

Summary

Introduction

Invasive alien plants (IAPs), as biological invaders, negatively affect water sources (Ghahramanzadeh, 2013). Woody IAPs negatively affect water sources, biodiversity, and land productivity (Mugido et al, 2014). These include Acacia mearnsii, Acacia saligna, Eucalyptus, Hakea and Pinus IAPs, which had a total evaporation (ET) of 895 mm in the Western Cape. The Olifants River catchment includes hard rock formations, with Bushveld igneous complex being the most dominant (Water Institute of Southern Africa, 2013); “[t]he soils are erodible due to intensive cultivation and grazing” (www.csir.co.za). One activity making a negative impact on this catchment is coal mining, which is reported to alter the natural hydrological systems by disturbing the overlying rock and soil strata, resulting in increased filtration and release of groundwater (Water Institute of Southern Africa, 2013). Most of the groundwater is used for supplying the rural area and for stock watering

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