Pine trees in the Tokai Forest, Cape Town. (Tiyese Jeranji)
  • Alien plants use more water than indigenous plants, and in South Africa they consume up to 2,450-million mof surface runoff water. The Western Cape’s 44 dams together contain just over half of that when full.
  • Invasive species are plants, animals, and organisms that have been introduced to and established themselves in a new environment, often at the expense of local species.
  • They cost South Africa’s economy about R6.5-billion a year, despite the R1.5-billion government spends trying to manage the problem.


Invasive alien plants threaten up to 30% of the water supply in major cities in the Western and Eastern Cape, such as Cape Town and Port Elizabeth, according to a new government report.

The Status of Biological Invasions and their Management 2017, produced by the South African National Biodiversity Institute and the Centre for Invasion Biology at Stellenbosch University, estimates that currently invasive alien plants, such as pine and wattle trees, consume between 1,450- and 2,450-million m3 of surface runoff water each year. For some context, 44 dams supply water to the Western Cape, with a maximum storage capacity of 1,870.4-million m3.

These invasive shrubs and trees invade the catchment areas, where rainwater naturally collects into rivers and dams. The report estimates that if the Western and Eastern Cape’s catchments are fully invaded, they will deliver 30% less water to the cities of Cape Town, George, Mossel Bay, Knysna, Plettenberg Bay, and Port Elizabeth.

Invasive species are plants, animals, and organisms that have been introduced to and established themselves in a new environment, often at the expense of local species. In fact, the comprehensive scientific report - which is the first of its kind in the world - found that invasive species are responsible for about a quarter of the country’s indigenous biodiversity loss. Many of the country’s invasive species were introduced for cultivation (like pine trees), recreational fishing (like trout), or pets, for example, but they also stowaway in luggage, vehicles, or even ships.

The report estimates that invasive species costs the country R6.5 billion each year, despite the R1.5 billion spent on trying to combat the problem

“The known and potential impacts of invasive species in South Africa are staggering,” says Jasper Slingsby, an ecologist who was not involved in the report. “And we've had limited success stemming the spread of established invasives due underfunding, lack of coordination among institutions and various levels of government and mixed incentives.”

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