war on aliens

Invasive Alien Plants

Invasive alien plants are one of the greatest threats to water security and are the cause for significant destruction of natural habitat in the region.  Their removal, with follow-up rehabilitation of the natural environment, offers considerable employment potential for local people. Various products from the biomass (expanded upon below) can provide income for rural communities. The Gouritz Cluster Biosphere Reserve will identify and implement innovative projects that make productive use of invasive alien plants, simultaneously removing a dangerous threat to aquatic ecosystems and providing valuable work opportunities for local communities.

Different threats are associated with different alien species, e.g. blocking of rivers, displacement of biodiversity, fire threat, invasion of floodplains, shading of watercourses, toxicity and water use. Landscape (as opposed to riverine) species include pines and Hakea spp. Their seeds are blown in by wind, so it is very hard to remove them permanently as there is always a source of seeds within wind distance. In the late 1980s and early 1990s the Swartberg were cleared completely, but now there are some dense stands of Hakea again and pines are slowly marching back. The main threat from these aliens is water use and the displacement of indigenous fynbos.


The first step in the fight against invasive alien plants is to get to know them. Ena and Bob McIntyre of the Botanical Society of South Africa (BOTSOC) have compiled a series of documents in which the most aggressive invasive alien plant species are illustrated and discussed. Some of them can be downloaded here:

Invasive Alien Animals

Several alien invertebrates are threatening the biodiversity of the Gouritz domain. Foreign invertebrates are attacking indigenous bees and the Argentine ant poses a serious threat to fynbos biodiversity as they prevent seed dispersal of many endemic plant species.

The European paper wasp (Polistes dominula), often incorrectly cited as P. dominulus, is a recently recorded alien invasive species in South Africa. It competes directly with our native species (eg. Polistes fastidiousus and P. marginalis) for food and shelter to the extent of reducing the numbers of natives and disrupting natural processes and arthropod numbers. Read more about these beasts in the following brochures: 


Alien fish are a major threat to indigenous species in the rivers, and to river functioning in general. Problem species include bass, bluegill sunfish, trout, and the Mozambique Tilapia. Considering the high levels of endemism of freshwater fish in the Cape fold mountains, alien fish are considered as a serious threat.