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National Department of Agriculture
Department of Water Affairs and Forestry

Invading alien plants

A great deal of South Africa's water is used by plants that do not belong here. They are called "invading alien" plants. These plants are invasive because they spread and displace our natural trees and plants. They have invaded large areas of good agricultural land and some of our most scenic areas.

Where do invading alien plants come from?

Many invading alien plants were brought into the country for practical purposes such as for forestry plantations.

Why do invading alien plants grow so well?

In South Africa these plants have no natural enemies such as insects, animals and diseases that would have controlled them in their own countries.

Not all invading alien plants are harmful

Oak trees, bottlebrush, azaleas and most fruit trees are aliens that do not spread aggressively. Certain pines are important forestry trees that are grown in special areas. They are used for the production of paper and wood products, saving our local trees.

Problem invading alien trees

Some examples are:

black wattle.JPG (25065 bytes)Black wattle Silver wattle 1.JPG (31760 bytes)Silver wattle


Blackwood.JPG (27748 bytes)Blackwood pinus.JPG (27236 bytes)Pines

Castor-oil plant
Port jackson
Mauritius thorn



Reasons why alien invaders are a problem

They use a lot of water

Invading alien plants use much more water than indigenous trees and plants. They prevent rainwater from reaching rivers and deprive people and ecosystems of much needed water. Many springs and streams have already dried up because of invading alien trees.

They displace indigenous plants

Large areas of our country have been infested with invading alien plants. They destroy precious vegetation such as fynbos in the Western Cape.

They cause devastating fires

When invading alien trees burn, the flames can be up to 15 m high, often destroying houses and damaging the soil. In the case of fynbos the flames only reach 5 m. Invading alien plants grow in denser stands than natural shrub preventing firefighters from putting out a fire.

They cause soil erosion

Fires in invading alien vegetation are more intense than those in natural vegetation, resulting in damage to the soil. With the first rains the soil is then washed into rivers causing the rivers and dams to fill up with sand.

How can you help to solve the problem?

         Look for invading alien trees and plants in your area and cut them down.

         Ask your neighbours to do the same.

         Plant indigenous trees and plants in your garden.

How do we benefit?

         By clearing invading alien vegetation we improve water supplies.

         It will not be necessary to build so many dams; this will save money.

         We protect our local plants and trees.

         We help to prevent fires and erosion.

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For further information contact

The Working for Water Programme Communication Project,
P.O. Box 95823, Waterkloof 0145


Compiled by Directorate Communication, National Department of Agriculture
in cooperation with
the Department of Water Affairs and Forestry

Printed and published by National Department of Agriculture
and obtainable from
Resource Centre, Directorate Communication, Private Bag X144, Pretoria 0001, South Africa