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PLAAGBEHEER/
PEST CONTROL
Five of the ten main alien
trees in South Africa
Invader plants – and particularly alien trees – are a growing problem in South Africa. It would be easy to
pass it off as the natural flow of things – if these plants did not have such a major economic impact on
farming operations. Allegedly, 20 million hectares of land in South Africa have already been taken over by
invader plants – 10 million hectares by alien trees. If all these trees were to be combined to represent 100%
invasion, they would cover 1,7 million hectares – an area bigger than Gauteng. The effect of these alien
trees on the eco system and eco-system services is enormous. Usually, they first displace the indigenous veg-
etation, reduce the biodiversity, increase the fire hazard, change the course of streams and often use a lot of
water – to mention only a few disadvantages. Much has been done to try and control these alien trees – the
Working for Water programme has already cleared more than 2 million hectares. However, if one considers
the rapid invasion of the trees, as well as the fact that they have few if any natural enemies that can control
them, the control programmes are only a drop in the ocean.
It is therefore the duty of every farmer to
actively control these plants where they occur – not only to preserve the eco system, but also because it
re-invests millions of rands in eco-system services.
The five of the top ten alien trees mentioned here are not necessarily the biggest problem plants in your
area. They are, however, a problem in terms of the area they have invaded, as well as the volume of water
they consume.
Acacia cyclops
A. Cunn. ex G. Don
Rooikrans or red eye wattle is an evergreen, rounded shrub or small tree that branches out low, at the bot-
tom of the stem. It can become between 1,5 m and 4,0 m tall. This plant is indigenous to South-Western
Australia and was brought to South Africa in 1886 – mainly to stabilise dunes. It grows primarily in sandy
and loam soils and prefers sunny habitats. It is moderately frost resistant, but handles droughts well. It
grows relatively slowly and takes seven to ten years to reach maturity. Habitats that have already been in-
vaded by this tree include fynbos, spaces between plantations, dunes, road reserves and water courses. The
seed of the plant is interesting because it is surrounded by a double row of red or orange succulent stems.
The negative aspects of rooikrans include the following: They compete for light, space, water and nutrients;
change the landscape and habitat; displace and replace the indigenous vegetation and change the sedi-
ment dynamics of sand dunes. The seed is a contaminant – where it occurs it forms an obstruction (vision
and access), and the tree consumes large volumes of water. This tree is known to have invaded
1 855 792 ha
already. If all the trees are placed in one spot, they would occupy
339 153 ha
. The
estimated annual water consumption of rooikrans is
487 million m
3
.
Biological control agents occur on this plant and have a very effective control action – they should therefore
always be the first choice for controlling this plant. Fire or mechanical control (cutting down trees) can be
used to control these trees, as they seldom regrow. If the trees are cut down, it should be done close to the
soil surface. Young seedlings of this plant can also be pulled out by hand. Various chemicals are registered
to control this plant and they can be used effectively in combination with mechanical control to get rid of the
plants. According to the CARA Act, rooikrans is a category 2 plant – it therefore has an economic use, but
the plants may occur only in demarcated areas, and with the necessary permission. According to NEMBA
(National Environmental Management Biodiversity Act), rooikrans is a category 1b plant – it is therefore an
alien species that should be controlled, removed and destroyed if possible. No trading in this plant may
take place.
Acacia cyclops