Alien plants and their impact on Agulhas Plain rivers

Rivers on the Agulhas Plain are losing up to 10 percent of their water to invasive alien plants. According to David le Maitre of the Council for Scientific and Industrial Research at the ABI (Agulhas Biodiversity Initiative) annual general meeting, should rivers such as the Heuningnes and Nuwejaars on the Plain be completely cleared of aliens, enough water to fill around 33,000 Olympic size swimming pools would become available per year.


Le Maitre was a guest speaker at ABI’s first annual general meeting as a voluntary association. The meeting was held on 28 August in Bredasdorp.  ABI Partners and stakeholders across the Agulhas Plain and Overberg, where ABI operates, attended the event. ABI is working as a landscape initiative in the region – allowing partners operating in conservation and social development spheres to share information and work together.


According to Le Maitre, the removal of invasive aliens would  hold massive economic advantages to the Agulhas Plain. Based on economic modeling over the next 50 years (and at net present value), flower harvesting could see additional returns of R376-million should the veld be cleared of aliens. The return on investment in terms of water would equate to some R177-million. He says, “There is no doubt that you would get a positive return  for the economy should invasive aliens be removed.”


Most recent studies have found that should the invasive aliens in the country be condensed together, they would cover 1.5 million hectares. That’s slightly down from a 1998 national study, which put that figure at 1.78 million hectares. Black wattle is the worst invader, covering around 500,000 hectares in the country, followed by Pine trees and Eucalyptus (or Gum) trees.


ABI is currently coordinating the ABI Alien Clearing Project through funding secured from the Department of Environmental Affairs’ Land User Incentive Scheme. In the first year alone, some 28,000 hectares will  undergo follow up clearing work, on the Agulhas Plain creating around  270 jobs. The project has allowed government, private land users, parastatal organisations and non-governmental organisations to work together to strategically plan and implement the activities.


Le Maitre said that monitoring and evaluating the impact of alien clearing has been lacking in past government-run alien clearing projects. He suggested taking photos before  starting to clear and as you go along. It’s an inexpensive and effective way to see progress being made. Deciding on where to clear needs to be guided by what’s best for ecosystem services – water quality and quantity, as well as impacts on conservation priorities (critical biodiversity).



abi alien clearing

Francis Steyn of the Department of

Agriculture, at the ABI AGM


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