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Alien Invasive Plants in South Africa

Author: David J McDonald ~ Botanical Society of SA

( Article Type: Explanation )

Many plant species have a strong ability to grow in similar situations but away from their native habitats. The result is that many plants are now found in places where they did not originate. This process of global distribution of plants has been happening for millions of years. In the past 1 000 years – as people have dispersed across the globe – this has speeded up, escalating still further over the past 300 years as modern world travel has developed. Plants have been distributed as crop plants and ornamentals to foreign lands, often displacing the local flora with negative consequences. In many, if not most, cases invasive alien plants that have originated from horticulture are plants selected by gardeners for the same qualities that make them potentially invasive. Some of these characteristics are rapid growth, early maturity, large quantities of seeds that are easily dispersed, the ability to out-compete other plants and disease, and pest resistance. Like many other parts of the world, southern Africa has also been affected by the global distribution of plants. With its diverse natural environment, southern Africa provides habitats suitable for many species ranging in origin from the tropics to Mediterranean-type environments and deserts. In South Africa 198 plant species have been declared weeds and invaders. These plants are termed ‘invaders’ because they spread and displace the indigenous plants. The question then is ‘Why are invasive alien plants such a problem?’ Apart from displacing the natural flora and therefore impacting negatively on biodiversity they also use more water than the better-adapted natural flora. They also intensify wild fires should these occur. These negative impacts call for concerted action for the control of these invasive alien plants.

What is being done to combat the spread of invasive alien plants?
The major group of offending plant species in southern Africa has been identified, and the Working for Water Programme is active throughout South Africa in clearing alien plant species. Legislation has now been enacted to combat the problem of invasive plant species that threaten the natural flora of the country and, in turn, valuable water resources. Some of the most widespread offending species in random order are Acacia mearnsii (Black Wattle), Saligna (Port Jackson Willow), Cyclops (Rooikrantz), Melanoxylon (Blackwood), Lantana camara (Lantana), Chromolaena odorata (Triffid weed), Solanum mauritianum (Bugweed), Hakea sericea (Silky hakea), Pinus pinaster (Cluster pine), and Melia azedarach (Syringa or Persian lilac). The problem of invasive plants is large, and it requires active public and private participation to combat this ‘growing’ threat. Agricultural landowners need to familiarise themselves with those species that pose a threat on their own land and eradicate them. The gardening public, in turn, should be aware of those invasive alien plant species that they may have on their suburban properties and remove them. Local hack-groups exist whose purpose is to clear invasive alien plants from public land for the benefit of local communities and their environment. This activity should be greatly encouraged to increase awareness of the increasing threat of invasive plant species and to ensure that action is taken against this threat at the local level.