Importance of eradication of alien vegetation in South Africa

First of several feature articles on the eradication of alien plants in the country

Rooikrans (acacia cyclops) is a tree originally from Australia, brought to Cape Town as an ornamental in the 1800s, and later used for dune stabilisation on the Cape Flats. Here in the St Francis Bay area rooikrans, among other aliens, was used by the Department of Forestry in response to farmers’ fear of desertification, and it spread to adjacent areas.

In the 1950s Leighton Hulett, the founder of St Francis bay more than 60 years ago, planted rooikrans on the dune system in what is now Santareme, as did John Booysen in Cape St Frances — anywhere where plots were planned. This massive population invaded the surrounding areas, especially in disturbed areas.

Since then we understand that the movement of sand is natural and important, and that interfering with it can have huge and disastrous effects, i.e. ruin our beaches. But in the 20th century it was a common practice worldwide.

The rooikrans tree reaches 5m and has woody stems, tapered narrow supple green 1cm x 8cm leaves with a rounded point and three mid-veins, 1cm round yellow flowers and 10cm long curved seed pods. The seeds are dispersed by birds (long distance) and ants (short distance) and are able to lie dormant in sand for 40 years!!
FOSTER spends much time and money clearing this growth from the reserves.

When FOSTER was started, a large grant from the World Wildlife Fund enabled reclamation of the areas which had become overwhelmed with acacia cyclops. Now there is little in sight, and what re-grows is cleared by our team on an annual basis(see pics.)

This species uses large amounts of water compared to fynbos, creates a canopy impenetrable by sunlight over natural vegetation leading to the death of the natural vegetation, stabilises dunes, out-competes natural vegetation and contributes to a loss in biodiversity. It makes nitrates available to the soil which our natural vegetation cannot tolerate and creates a serious fire hazard due to a massive fuel load and highly flammable oils. Due to the highly flammable oils found in living trees, they are just as flammable as a dead Rooikrans.

Rooikrans has been placed by CARA (The Conservation of Agricultural Resources Act, species list 2016) in Category 1b, which simply put, means that it is a prohibited species, but individuals already present may be left alive if control measures are in place.

The methods through which it can be controlled are mechanical, chemical or biological. The seed weevil, Melanterius servulas I, was introduced from Australia in the 90s but only has a 5% reduction in seeds.
The gall forming midge Dasineura dielsi was introduced after the millennium and has a very successful effect in reducing the seed production by 95%. The midge taints the flower at an early age resulting in the formation of a fertile 1.5cm twisted ball of deformed seeds instead of pods.

There is also an indigenous root fungus at work. The root fungus, first noted at Great Brak River, attacks the roots of the tree, eventually leading to its death. The fungus thrives in hot weather when the elements converge to provide the right conditions, killing off patches of Rooikrans in dense stands or individual trees in mixed stands of alien and indigenous vegetation.

On the positive side, Rooikrans is an excellent braai wood. Its collection has provided livelihoods for many people

(Original Article by Wayne Meyer Mosselbaai Nuus – edited by Foster and Bev Mortimer
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Thanks to Pam Golding St Francis Bay for support of this series.


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