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October 2013

In the first article in this series, we mentioned that the biggest threats to biodiversity are habitat loss and degradation. We will now focus on one of the prime causes of habitat degradation - namely the introduction of alien plant species.


These plants that become weeds are usually vigorous growers that compete with indigenous vegetation for water, light, space and nutrients. They are adaptable and easily invade a wide range of ecological niches. Most are exotic or of foreign origin producing an abundance of fertile seed, often with efficient methods of dispersal. Most alien plant invaders will suppress or replace indigenous species and, as this flora declines, so also does the fauna that has evolved to depend on it - resulting in a reduction of species diversity. As an ecosystem weakens, its stability declines and it becomes more susceptible to catastrophic events such as fires, floods (and associated soil erosion) and disease epidemics.


The Conservation of Agricultural Resources Act (Act 43 of 1983) was revised and amended in 2000. This was done because, in 1996, South Africa became a signatory to the Convention of Biological Diversity, undertaking to “prevent the introduction of and control or eradicate those alien species which threaten ecosystems, habitats and species”. In 1995, the “Working for Water” campaign was launched and became the largest alien plant clearing program. Further changes brought about were the creation of three categories of alien plants:

  • Category 1: Declared weeds

These are prohibited plants which must be controlled or eradicated. Well known examples in our area are: Lantana, Bugweed, Prickly Pear, etc.

  • Category 2: Declared invader plants with commercial value

These plants are allowed in demarcated areas under controlled conditions. Examples are: commercial Eucalyptus, Pine and Wattle species

  • Category 3: Ornamental plants

Alien plants presently growing in or having escaped from gardens. No further planting is allowed and spread of existing plants must be prevented. Examples are: Cotoneaster, Jacaranda, Privets, Syringa, Sword Fern etc.

In future articles we will learn to identify our worst alien invader plants and discuss methods to control or eradicate them.
Reference: Problem Plants of S.A. Clive Bromilow

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January 2014

After Indonesia and Brazil, South Africa is the third-most biologically diverse country in the world. Occupying only 1% of the world’s terrestrial land area it is home to...

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December 2013

Since 2013 marks the 100th anniversary of Biological Control of IAP’s in South Africa, it is appropriate that we take a closer look at this programme in this, the last issue of 2013.

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November 2013

This month, we describe the first two alien invaders that are currently quite evident in our area as they are early spring bloomers

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October 2013

One of the prime causes of habitat degradation - namely the introduction of alien plant species.

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September 2013

Biodiversity is the all-encompassing term to describe the variety of all life on Earth.

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February 2014

This month, we revert to our series on Alien Invader Plants (AIP’s) and how to identify and eradicate them.

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March 2014

As promised last month, our next “candidate” is the notorious weed Lantana camara.

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