Focus On Invasive Trees

But Trees are Good for the Planet

When it comes to the Gauteng grasslands, not all trees are created equal. Trees endemic to our grasslands, like Wild Olive, Karee, Buffalo Thorn and so forth, all have a role to play in our landscape. However, invasive tree species do a lot more harm than good to intact grasslands.

The Crocodile River Reserve certainly has its fair share of invader species and in this article we look at the invasive tree species found here.

Why should we care, aside from the legal requirement that requires landowners to remove and control all declared invader species? As invader species have no natural predators, they tend to establish themselves quickly and outcompete indigenous plant species. Many invader trees are a lot thirstier than their indigenous counterparts. A bluegum tree consumes between 80 and 200 litres of water per day which is relatively little in comparison with Acacia mearnsii’s (black wattle) thirsty habit of in excess of 500 litres per day.

Not only do invader tree species use more water than indigenous species, they pose a massive threat to biodiversity and particularly in the species rich grasslands of the CRR. Some invasives change soil chemistry, resulting in soils unsuitable for indigenous species. Eucalyptus trees release chemicals which inhibit indigenous plant growth and may result in severe erosion due to the lack of native vegetation cover. Likewise, the tree of heaven releases toxins into the soil that inhibits the growth of native species, and as if that is not enough, produces thousands of seeds and sends out underground suckers to reproduce vegetatively.

Fire plays a huge role in grassland regeneration, but with the increased fire load represented by invader species, fires might get out of hand faster and burn hotter than can be tolerated by fire-adapted indigenous species found in the grasslands.

During 2022, GDARDE assisted us to do a high-level map of all invader species that occur within our borders. Each of these species threaten biodiversity in its own unique way, but together they pose a huge threat to our water resources, biodiversity and safety. Their efforts revealed that the following tree species have taken root throughout the Reserve:

The following links take you to descriptions and pictures of the plants in question. Permission was granted by the owner of the website, Kay Montgomery, to use the links in this article.

Melia azedarach – (Syringa),

Salix babylonica – (Weeping willow),

Morus alba –  (White mulberry)

Pinus sp. 

Ailanthus altissima – (Tree of heaven) 

Pyracantha angustifolia – (Fire thorn) 

Here is how we can help you:

  • Free training: Look out for dates in upcoming newsletters
  • The GSA can help you: Ask for an assessment and quotation
  • Herbicide: The GSA buys in bulk. You can buy it from the GSA at a reduced price

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