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What is an invasive plant

What is an invasive plant?

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In many ways, invasive species are very similar to foreigners. Both are aliens to the land they find themselves in and because they are not familiar with the land, they tend to work harder to compete for the same resources. As a result, they end up out performing the natives. The local government then intervenes with laws and special programs to protect the natives because they are unable to compete with the aliens for the same resources.     

Just like invasive species, foreigners outcompeting the natives is a global problem. Stories of xenophobia are constantly making headlines from “building the wall” to “the refugee and migrant crisis”. Invasive species management programs, like Xenophobia attacks, are an attempt to manage the aliens. 

What is an invasive species?

Whenever a species is living in a particular environment, it is there because it is either native (or indigenous) to that environment or it was introduced there. A species that is introduced to a particular environment and causes ecological and or socio-economic harm is called an invasive species. Not all introduced species are invasive. To be considered invasive, a species must be a threat to the particular environment.  

The term “species” refers to a living organism. It is not reserved to a particular organism, i.e., it can be used to mean a plant, human, or animal.  Hence, there are invasive species that are animals, such as fish species such as salmonids and black bass, and plants, such as acacia, eucalyptus, and pines. Plants that are considered invasive are called invasive plants. 

How are invasive species introduced?

It is estimated that about 400, 000 plant species exist in the world. However, all these species are not equally distributed in every part of the globe. Consequently, if a species that is considered essential is not found in a particular area it will be introduced to that area. 

The primary reasons for introducing species to a particular area is to provide raw materials and food via horticulture. Species that are introduced for raw material and food have a high societal value and are widely disseminated across the country and in some areas they are conspicuous components of natural ecosystems. 

Species are also introduced for recreational purposes such as gardening, and for environmental restoration. For example, in South Africa, acacias were introduced for erosion control and dune stabilisation. 

There are also cases where species have been introduced in an environment accidentally, known as unintentional introductions. This occurs due to the increase in travel and trade causing travellers and transported goods to serve as pathways for introducing invasive species.  

Introducing the right species to an environment can have considerable socio-economic benefits. However, when a  species becomes invasive, it can have an adverse ecological and socio-economic impact. Invasive species are considered the single biggest threat to plant and animal biodiversity. They can cause changes to the functioning of the ecosystem. In some cases, they can impact human health. 

Invasive species in South Africa

As a country, South Africa is dry and classified as semi-arid. According to Hendrik Venter (2005), in South Africa there are approximately 750 trees and 8, 000 herbaceous species that have been introduced. Of which, 1, 000 have been naturalised and 200 are considered invasive. It is estimated that about 10 million hectares of the land is covered by invasive plants, which waste 7% of water resources. Thus, negatively impacting agriculture and farming and leading to natural events, such as floods, fires, and erosion.     

Managing invasive species in South Africa

Invasive species have a long history and there have been many intervention methods that have been employed to manage them. According to Hendrik Venter (2005), the cost of controlling invasive plants in South Africa is estimated to be R600 million a year over 20 years (approximately US$ 100 million annually). Management is important because if these plants are left uncontrolled, the problem will double within 15 years.

In 1995, the government of South Africa created a conservation programme called Working for Water. This programme supports a range of labour-intensive projects aimed at eradicating invasive alien plants using mechanical methods, chemical methods, and biological control. The main purpose of the project is to conserve water through the eradication of invasive species as part of the Reconstruction and Development Programme initiative. 

The departments of agriculture, department of environmental Affairs, and department of tourism were integrated in the programme, causing these departments to respond by developing legislation on invasive species in relation to imports, agriculture and the environment. The programme also drew in other departments that were involved operationally, such as the department of social development, department of health, department of arts and culture, department of science and innovation, department of labour, department of education, department of trade and industry, and department of finance.  

The legislation for the management of invasive species in South Africa, includes:

  • Agricultural Pests Act, 1983 (Act No. 36 of 1983) – prevents the introduction of agricultural pests and organisms associated with agriculture. This involves the control of importation of plants and plant products and organisms associated with agricultural activities, such as biological control agents.
  • Conservation of Agricultural Resources Act, 1983 (Act No. 43 of 1983) – provides control over the utilization of the natural agricultural resources of South Africa in order to promote the conservation of the soil, the water sources, and the vegetation as well as fight against weeds and invader plants. 
  • National Environmental Management Act, 1998 (Act No. 107 of 1998) – provides an institutional framework for environment protection in South Africa. It also provides implementation of international agreements and compliance and enforcement in general.
  • Environment Conservation Act, 1989 (Act No. 73 of 1989) – provides for the effective protection and controlled utilization of the environment and for matters incidental thereto. 
  • National Water Act, 1998 (Act No. 36 of 1998) – provides for fundamental reform of the law relating to water resources; to repeal certain laws; and. to provide for matters connected therewith.
  • National Veld and Forest Fire Act, 1998 (Act No. 101 of 1998) – prevents and combats veld, forest and mountain fires throughout the country.

Reference and further reading

  • Ellender, B.R. and Weyl, O.L.F., 2014, ‘A review of current knowledge, risk and ecological impacts associated with non-native freshwater fish introductions in South Africa’, Aquatic Invasions 9, pp.117–132.
  • Hendrik Venter, J., 2005. Invasive species and the Working for Water programme in South Africa.
  • Holmes, T.P., Aukema, J.E., Von Holle, B., Liebhold A. & Sills, E., 2009, ‘Economic impacts of invasive species in forests: Past, present, and future’, Annals of the New York Academy of Sciences 1162, pp.18–38.
  • Hulme, P.E., 2014, ‘Invasive species challenge the global response to emerging diseases’, Trends in Parasitology 30, pp. 267–270.
  • Lehan, N.E., Murphy, J.R., Thorburn, L.P. and Bradley, B.A., 2013. Accidental introductions are an important source of invasive plants in the continental United States. American journal of botany, 100(7), pp.1287-1293.
  • Powell, K.I., Chase, J.M. & Knight, T.M., 2013, ‘Invasive plants have scale-dependent effects on diversity by altering species-area relationships’, Science 339, pp. 317–319.
  • Rejmanek, M. and Richardson, D.M., 1996. What attributes make some plant species more invasive?. Ecology, 77(6), pp.1655-1661.
  • Richardson, D.M., Cambray, J.A., Chapman, R.A., Dean, W.R.J., Griffiths, C.L., Le Maitre, D.C. 2003, ‘Vectors and pathways of biological invasions in South Africa – past, future and present’, in G. Ruiz & J. Carlton (eds.), Invasive species: Vectors and management strategies, pp. 292–349, Island Press, Washington, DC.
  • Richardson, D.M., Wilson, J.R.U., Weyl, O.L.F. and Griffiths, C.L., 2011, ‘South Africa: Invasions’, in D. Simberloff & M. Rejmánek (eds.), Encyclopedia of biological invasions, pp. 643–651, University of California Press, Berkeley, CA.
  • van Wilgen, B.W. and Richardson, D.M., 2014, ‘Challenges and trade-offs in the management of invasive alien trees’, Biological Invasions 16, pp.721–734.
  • Working for Water. 2000. The Working for Water programme annual report 1999/2000. Cape Town, South Africa, Department of Water Affairs and Forestry (available at
  • Working for Water. 2001. The Working for Water programme annual report 2000/2001. Cape Town, South Africa, Department of Water Affairs and Forestry.
  • Zengeya, T., Ivey, P., Woodford, D.J., Weyl, O., Novoa, A., Shackleton, R., Richardson, D. and Van Wilgen, B., 2017. Managing conflict-generating invasive species in South Africa: challenges and trade-offs. Bothalia 47 (2): a2160.

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