Weeds in our Area (Part Four) By Bob and Ena McIntyre – Garden Route Branch.

Why do we need to control invasive alien vegetation??

The question is often asked ‘Why do we need control of Alien Invader Weeds, after all are they not just another plant serving a similar purpose?’ The simple answer is a categorical NO. Plant species are not listed in the Official Weed list unless the negative impacts of the plant on people and/or the environment outweigh other useful attributes of the species.

Weeds may have many different impacts on agriculture, livestock, people and the environment. Some impacts can negatively affect our economy while others may impact on the integrity of the biodiversity of our natural environment. Many invader species, without any natural enemies in our environment, outgrow and outperform our indigenous flora to the extent that many precious indigenous species are totally displaced and in fact lost in this way.

Too frequently we overlook the importance of our actions in the bigger scheme of things based on the notion that our impact as individuals is minimal. Witness an area of natural vegetation that has been disturbed by man and becomes infested by Acacia mearnsii (Black Wattle). The stand of wattle is a mono culture with very few, if any bird species as opposed to an adjacent undisturbed area of natural vegetation which may have 30 to 40 or more species of trees and shrubs and numerous bird species. This is a very simplistic example as a thorough study will also show a lack of diversity of other organisms in degraded areas.

It has also been proven that a mature Black Wattle consumes up to 150 litres of water per day - about 5 times the requirement of a similar size indigenous tree. The consumption of a mature Eucalyptus (Blue Gum) is about 1000 litres of water per day. It is common knowledge that South Africa is water poor and at our current growth-rate could face major water shortages within the next 50 years. Allowing the depletion of our water resources by means of these very effective “pumps” invading watercourses and dispersing this precious resource into the atmosphere, is unwise.

The sobering fact that most woody invader species burn with a heat intensity of about 5 times that of our indigenous species was proven at the time of the severe fires in the Cape some years ago. Locally we also too have first hand knowledge. Many of us still clearly remember the devastating fires in Wilderness Heights on 03 August 1998 with the tragic loss of property. An interesting observation at that time was how the fire slowed after moving into pristine indigenous scrub forest from areas heavily infested with alien species. The sad part is that some fearful landowners misguidedly cleared the protective scrub vegetation around their properties. Such actions in fact aggravate the fire threat unless infestation by alien invader species is strictly controlled in the long term.

Fortunately the realisation that the future of mankind is indeed dependent on the preservation of the biodiversity of our world is gradually dawning. Learn to know, grow and above all to love and respect our indigenous flora and rid our area of alien invader weeds.