Understanding and controlling alien vegetation in South Africa

March 18, 2020

What is alien vegetation?

Alien vegetation is plants and trees that are native in another country and came over to our country where they settled between our indigenous vegetation. Some alien vegetation was brought to South Africa centuries ago intentionally as these plants possess many beneficial properties: they make great timber, are fast growing, stabilize sandy soil, are excellent for honey production, produce pods which are a good food source for animals etc. Some aliens, however, have been spread unintentionally over the years, entering our country on people’s shoes, tents, ships, animals, imported plants and airplanes. But since these species are not indigenous to South Africa they pose the following risks:

Many alien species easily settle in river systems and on river banks. Since most alien vegetation consumes more water than our indigenous plants, it can threaten underground water and river systems. We lose billions of liters of our precious and limited water supply annually due to this.
This overcrowding of the river system can also cause severe flooding when rivers come down after heavy rains.
Since these invasive species do not have any natural enemies here they have a much higher growth rate than our indigenous species.
They also spread quicker and easier than our native plants making them very difficult to control.
It is labour intensive, costs a lot of money and is extremely hard work to do alien clearing – which discourages lots of people from removing alien vegetation.
It grows very densely and invades the space of our indigenous trees.
It costs government and private land owners millions of rands every year to clear and manage alien vegetation
Thousands of hectares of agricultural land are lost annually due to the uncontrolled growth of these species – indirectly wasting millions of rands in the agricultural sector, seeing that the land cannot be used anymore by anyone.

Left: Understanding and controlling alien vegetation in South Africa. Right: A photo taken of Presopis Trees / Suidwesdoring growing inside a river. Notice how completely green it is given the fact that it was in the middle of a 7 year drought. These are being cut down and used as cattle feed (Bos tot Kos)

How bad is the alien vegetation problem in South Africa?

In the Western Cape the predominant species are Black Wattle (Acacia Aulacocarpa), Port Jackson (Acacia Saligna), Rooikranz (Acacia Cyclops), Hakea (Hakea Sericea), Spider Gum (Eucalyptus conferruminata), Cluster Pine (Pinus Pinaster) and Blackwood (Acacia Melanoxylon). Black Wattle trees are visible in almost in every river system and mountain range in the Western Cape. At the coast Rooikranz overtook the natural fynbos especially in areas such as Witsand, Hangklip, Gouritsmond and Stilbaai. Hakea is widely spread throughout the mountain ranges of Worcester, Villiersdorp, Slanghoek, Paarl and Ceres. Port Jackson is also widespread around the Cape, up the West Coast, in Cape Agulhas and all the way to the Breederiver Valley and beyond.

In the Southern Cape & Eastern Cape the predominent species is Black Wattle (Acacia Aulacocarpa), Port Jackson (Acacia Saligna), Rooikranz (Acacia Cyclops) and also Blackwood (Acacia Melanoxylon). The natural forest in Knysna and ravines appears beautiful from a distance. It is only upon closer inspection that you realize that most of the material is not indigenous.

In the North Eastern part of the Eastern Cape & KwaZulu-Natal Black Wattle (Acacia Aulacocarpa) and Port Jackson (Acacia Saligna) is also clearly visible.

In the Northern Cape, Prosopis Glandulosa (Honey Mesquite, Muskietboom, Suidwedoring, Peulboom) trees cover the entire river systems and the banks completely. It is so dense that animals cannot even walk through it, which means that although it rains, the grass will not grow.

The positive side to this is that the problem can be controlled and the wood from alien species can be used.

Left: A photo taken of Presopis Trees / Suidwesdoring growing extremely dense in the Kimberley area in the Northern Cape. Right: Bloekom (Gum) trees – felled and neatly stacked ready for a wood chipper. The woodchips will be used as mulch on the fruit orchards

How can we control the alien vegetation?

It is extremely important to know the different alien species in your area. Identification is the first step. Small invaders can easily be pulled out by hand while they are still young. When these trees get bigger they are more difficult to control. They can be taken down by using a panga, axe, bowsaw, brush-cutter or chainsaw.

Lots of mountain climbing clubs in South Africa have monthly “hacking” sessions where they will go out into the mountains in a group and target a specific specie for example, Hakea Sericea or Black Wattle (Acacia Aulacocarpa).

When you take down trees the stumps must be treated with the correct herbicide to ensure that there will be zero regrowth. The branches must be stacked neatly in piles. These neatly stacked piles are much easier to work with than messy heaps, when you want to chip the branches or maybe transport them to a different location where they can be processed further.

It is important to remember that when foreign trees are taken out of the river system, they must be replaced by indigenous trees and shrubs. The area where they are removed should not be left empty as this can lead to soil erosion.

Left: Rooikrans branches that is left behind in an untidy heap after wood cutters came through to make firewood – leaving a huge fire risk behind. Right: Gum, Wattle and Pine cleared in Plettenberg Bay in the Western Cape to be used as mulch (ground cover).

What can the alien vegetation be used for?

Here are some of the most popular uses:

Bigger trees especially Gum trees grow quickly and reach large diameters especially in river beds. Gum trees have got a beautiful grain and are a great wood to work with. Gum trees can be exported to foreign countries where they will be used to make furniture. They can also be cut using a sawmill machine or large chainsaw to turn large diameter logs into slabs. The slabs can then be turned into coffee tables, bar counters or dining room tables.
Alien trees can be cut down to size, split using an axe or a hydraulic log splitter, and then used for braaiwood. Black Wattle and Rooikranz make good quality braaiwood. Spider Gum, Port Jackson and Pine Trees are good for kaggelwood (firewood) to keep you warm during those cold winter nights.
When firewood is made a lot of branches are left behind in the field that are too small and cannot be used. If they are left in heaps in the field this is a big fire hazard. The best environmentally friendly solution is to process the branches through a wood chipper. A small to medium sized wood chipper will be sufficient, depending on the amount of the material that needs to be chipped. Wood chips can be spread out and left in the field instead of leaving the branches to dry and rot over time.
The wood chips can then be used as mulch, compost, bio-fuel and some species, such as black wattle can even be used for cattle feed.
Sheep farmers who own land next to the Sakriver in and around Williston in the Northern Cape clear sections of the river from Presopis (Suidwesdoring) and use the branches for animal feed for their sheep. The nutritional value inside the Prosopis pods are extremely high and this is the main reason why it was imported from Australia a couple of decades ago.