Invasive alien plants, or IAPs, are plants that are not native to a specific area and often have a significant negative impact on the environment by causing habitat destruction, reducing the availability of water, and increasing the risk and intensity of wildfires.

As stated by the National Environmental Management: Biodiversity Act 10 of 2004 (NEMBA), landowners are under a legal obligation to control IAPs that occur on their property. Therefore, it is a minimum requirement that management is in possession of a formalised IAP clearing plan that provides strategic direction to the farm’s IAP clearing.

The Alien and Invasive Species Regulations (AIS) of 2014 list four different categories of IAPs that must be managed, controlled or eradicated. Landowners should ensure that IAP control plans identify and classify the IAP species present on the property according to these categories, as this will have an impact on which species should be prioritised for clearing first. The categories are as follows:

  • Category 1a: Most harmful species which requires immediate action to control and to eradicate. Any form of trade or planting is strictly prohibited.
  • Category 1b: Invasive species that must be controlled and, wherever possible, removed and destroyed. Any form of trade or planting is strictly prohibited.
  • Category 2: Invasive species or species deemed to be potentially invasive, for which a permit is required to carry out a restricted activity. This category includes commercially important species such as pine, wattle, and gum trees.
  • Category 3: Invasive species that may remain in prescribed areas or provinces. Further planting, propagation or trade is, however, prohibited.

Category 2 IAPs are deemed to be potentially invasive and may be cultivated under special circumstances, for example, Beefwood trees (Casuarina cunninghamiana) used as windbreaks between orchards, and Gum trees (Eucalyptus spp.) used for honey production. According to NEMBA, the cultivation of these plants is a restricted activity and therefore requires a permit, irrespective of when they were planted. Where Category 2 species are cultivated, a demarcation permit is required if a landowner wants to retain these plants for commercial purposes. Demarcation permits for retaining IAP species are issued by the Department of Agriculture Land Reform and Rural Development (DALRRD).

A suitable IAP clearing plan should contain a map of IAP coverage, as well as a worksheet with the following information:

  • Dominant IAP species present on site, as well as their NEMBA categories
  • Density of IAP infestation
  • Maturity of IAPs
  • Methods of clearing

Data collected around the location, density, and maturity of the IAPs will be useful when formalising an IAP clearing plan and should prioritise the phasing of IAP clearing. Areas that should be prioritised are mountain catchment areas, riparian areas, critical biodiversity areas, and areas that pose a fire risk. If IAPs are located within or alongside a river, it is recommended to start clearing in the headwaters, moving downstream. Ideally, dense, mature stands should be cleared last, as their density is unlikely to increase.

To ensure that IAPs are effectively eradicated, relevant staff should be adequately trained in the safe and appropriate IAP clearing methods. The control methods for IAP clearing can be broadly classified into these three categories:

  • Mechanical (e.g., felling, strip-barking, hand-pulling, and mowing)
  • Chemical (e.g., the foliar spray of herbicides on targeted plants)
  • Biological (e.g., release of natural enemies that will reduce population vigour to a level comparable to that of the natural vegetation).

Always remember that environmental safety should be prioritised when using herbicides for IAP clearing. Management and herbicide operators must have a basic understanding of herbicides and their functions, as this will guide the correct selection of herbicides for the targeted plant. If used incorrectly, herbicides can do more harm than good, especially when working in riparian areas.