Alarming growth in invasive species

George Hendrickse and David Whitelaw, Claremont

As residents of Cape Town with an interest in the environment, we were gratified to read the article, “Invasive aliens threaten biodiversity”, published in the Tatler on June 10, which hopefully will help to alert the population to this problem.

We had a number of concerns regarding what was stated in this article, such as the number of aliens increasing at an alarming rate.

The article said the number of aliens introduced has increased by an alarming 15%. Over what period did this take place and is there any evidence of how they were introduced? One would assume that attempting to stop the introduction would form part of the strategy to minimise the problem.

It is also disturbing that employees at Kirstenbosch import potentially invasive plants, if this is intentionally done.

The article was an interesting introduction for the public, and we would suggest that follow-up articles covering the points listed above would be beneficial in combating the problem of invasive aliens.

Nolwethu Tshali, regional coordinator at the South African National Biodiversity Institute’s Directorate on Biodiversity Evidence, responds: Invasive alien species are intentionally or unintentionally introduced into new areas by humans for various reasons. For example, some alien species are deliberately introduced to new areas as garden ornamentals and for timber and firewood, agricultural crops, animal fodder, hedge plants and for other purposes.

Invasive animals are introduced mainly for the pet trade, ornamental purposes and for the game-farming industry. Many are also introduced accidentally, as contaminants on vehicles and traded goods.

Employees at Kirstenbosch who import potentially invasive plants to the area must be accidental introductions.

Sanbi’s Directorate on Biodiversity Evidence has a mandate to monitor, assess and report on biological invasions in South Africa. The Biological Invasions Directorate focuses on detection and eradicating emerging invasive alien species. These are species listed as category 1a on the National Environmental Management: Biodiversity Act (NEM:BA) regulations and as “suspects”, which are those species that are not yet listed on NEM:BA but are suspected to become problematic invaders in future.

These suspected species have not reached their full invasive potential and occur as relatively small populations.

The removal of these populations at an early stage of invasion will limit spread to other areas, save on future costs of control and contribute to the goal of eradication of these species from South Africa.

For more information on invasive alien species in South Africa, visit and to report invasive species contact Ms Tshali at 0834791955 or