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City of Johannesburg declares war on alien invasive species

Alien invasive plants are a global phenomenon, which directly affects the socio-economic activities and threatens biodiversity with extinction (McFadyen, 1998). Alien invasive plant species refer to introduced plants, either accidentally or deliberately, that are not natural occurring in an area and posing an environmental risk by invading or having a potential of invasion.

In urban areas such as the City of Johannesburg, biological invasion affects passive recreational activities such as fishing, water sports, canoeing, bird life and species diversity (Kowarik,2011). Challenges with alien invasive plants are escalating worldwide resulting in vast environmental damage as natural functioning of ecosystems is negatively affected (McFadyen, 1998). Ecosystems on various continents have been biologically invaded, excluding the Antarctic (Cronk, 1995).

Alien invasive plants (AIS) have the ability to reproduce and spread prolifically, invading and displacing indigenous plants in the new areas of introduction.

How alien plants have been introduced into South Africa

Alien plants are plants that have been brought to South Africa from other countries for their beauty, economic value or ecological purpose. Some are brought in unintentionally and without their natural enemies, are able to reproduce and spread prolifically.

These plants or seeds enter the country in a number of ways: for example, by clinging to people’s shoes, tents, by mail order on ships, planes, etc. Even animals that cross the borders can bring in seeds. The invader plants and seeds spread rapidly and compete for the growing space of our own indigenous plants.

Legislative framework

In South Africa, invasive species are regulated by National Environmental Management: Biodiversity Act (NEM:BA), Act 10 of 2004: Government Gazette No. 36683 of 19 July 2013; which became law on 1 August 2014

(Irlich et al., 2017). Section 4 (2) (a) of NEM:BA, Act 10 of 2004 requires that local municipalities conserve and manage biological diversity;ensuring that programmes to eradicate and control AIS are implemented.

Why AIS should be eradicated:

  • It can colonise quickly and aggressively.
  • Occur in an area without being put there.
  • AIS are harmful to wildlife.
  • AIS are poisonous to people.
  • AIS are aesthetically unattractive.
  • Alien plants threaten the indigenous vegetation as they use up valuable and limited water resources.
  • Most of them consume more water than indigenous plants and are depleting the valuable underground water resources.
  • Many alien plants are also responsible for causing exceptionally hot fires and affect the makeup of the soil structure.
  • AIS compete with indigenous plants for growth (space, light, etc.)
  • AISare excessively aggressive and competitive in an area.

How can AIS be eradicated?

AIS regulations, NEM:BA, Act 10 of 2004, requires that property owners develop and implement management plans for infested sites. Property owners are required to control, manage and eradicate listed invaders or infestations control, especially water hyacinth and yellow flower water-lilies, to acceptable levels (below an ecological threshold of 10%), (NEM:BA, Act 10 of 2004).

There are four control methods of alien plants – physical or mechanical, chemical, biological and integrated control methods (Byrne et al. 2010).

Physical or mechanical control involves removal by hand and the use of machinery which makes it highly labour-intensive and not cost-effective.

Chemical control involves foliar spraying of herbicide on leaf surfaces of floating and emergent weeds, or inoculation with the chemicals underwater to control submerged plants (van Wyk & van Wilgen, 2002). This technique is cost- effective, and saves time. However, only registered and environmentally friendly herbicides can be used in aquatic ecosystems and labels should be followed thoroughly to avoid non-target effects on aquatic plants and animals. Integrated control that combines herbicides with mechanical and biological control methods is considered the preferred contemporary control measure (Byrne et al., 2010).

South Africa is amongst the countries leading with biological control of alien invasive species, through the implementation of the Working for Water Programme financed by the National Department of Environmental Affairs (SAPIA, 2010).

In conclusion, the City of Johannesburg, through Johannesburg City Parks and Zoo as its custodian of green open spaces, has adopted an integrated approach as the best tool to fight the biological invasion in ecological systems. The method is environmentally friendly, effective and efficient (Julien et al., 1996; Julien, 2001; van Wyk & van Wilgen, 2002). The integrated method linked to the use of remote sensing makes the scientific research, management and optimal maintenance of ecologically sensitive ecosystems achievable.


Alien and Invasive Species Regulations (AIS), National Environmental Management Biodiversity Act (Act no 10 of 2004). (2014). Department of Environmental Affairs, South Africa.

Byrne, M.J., Hill, M.P., Robertson, M., King, A., Jadhav, A., Katembo, N., Wilson, J., Brudvig, R. and Fisher, J. (2010). Integrated Management of Water Hyacinth in South Africa: Development of an integrated management plan for water hyacinth control, combining biological control, herbicidal control and nutrient control, tailored to the climatic regions of South Africa. Report to the Water Research Commission, Pretoria, South Africa.

Cronk, Q.C.B., (1995). Changing worlds and changing weeds. Proc. BCPC Symp.: Weeds in a Changing World, 64:3-13. Farnham: Br. Crop Prot. Counc.

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Department of Justice and Constitutional Development, (1996). Constitution of the Republic of South Africa No. 108 of 1996.

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Irlich, U.M., Potgieter, L., Stafford, L. and Gaertner, M. (2017). Recommendations for municipalities to become compliant with national legislation on biological invasions, Bothalia 47(2), a2156.

Julien, M.H. (2001). Biological control of water hyacinth with arthropods: A review to 2000. In: Julien MH, Hill MP, Center TD & Ding Jianqing (Eds) Biological and integrated control of water hyacinth, Eichhornia crassipes. ACIAR Proceedings 102: 8 -20.

Julien, M.H., Harley, K.L.S., Wright, A.D., Cilliers, C.J., Hill, M.P., Cordo, H.A., Gunther, T. and Cofrancesco, A. (1996). International cooperation and linkages in the management of water hyacinth with emphasis on biological control. In: Moran VC & Hoffmann JH (Eds) Proceedings of the IX International Symposium on Biological Control of Weeds, 21-26 January 1996, Stellenbosch. University of Cape Town. Cape Town, South Africa, pp. 273282.

Kowarik, I. (2011). Novel urban ecosystems, biodiversity, and conservation, Environmental Pollution 159(8/9), 1974–1983. envpol.2011.02.022 .

McFadyen, R.E.C. (1998). Cooperative Research Centre for Tropical Pest Management and Queensland Department of Natural Resources, Alan Fletcher Research Station, PO Box 36, Sherwood, Q 4075 Australia.

National Environmental Management: Biodiversity Act (2004): Alien and Invasive Species List, 2014, Pretoria, South Africa.

SAPIA, (2010). Southern African Plant Invaders Atlas News. ARC - Plant Protection Research Institute. Pretoria.

Southern African Plant Invaders Atlas (SAPIA). (2010). Newsletter No. 17. ARC-PPRI, Weeds Research Programme c/o SANBI, Pretoria.

van Wyk, E.V. and van Wilgen, B.W. (2002). The cost of water hyacinth control in South Africa: a case study of three options. African Journal of Aquatic Science 27: 141-149.