Alien Grass Working Group

Alien Grass Working Group

Who are we?

The South African National Alien Grass Working Group was jointly initiated by the South African Biodiversity Institute (SANBI) and the Centre for Excellence in Invasion Biology (C·I·B) in August 2013 by a group of researchers and managers concerned about the impacts of alien grasses in the country.

Our aims are detailed in our Terms of Reference, but in short, they are to:

  • Strategically monitor and coordinate information on invasive alien grasses in South Africa
  • Provide a collaborative approach to alien grass research and management
  • Raise awareness of new alien species and new incursions
  • Produce a list of priority invasive alien grasses and priority areas for management
  • Assess the risks posed by alien grasses and the feasibility of management
  • Develop best practice control methods of target grass species
  • Facilitate better communication between research institutes, invasive species managers and relevant government departments
  • Provide information for queries on grass introductions/permits
  • Provide policy recommendations

So far, members of the Working Group have published three peer-reviewed papers on the subject of alien grasses:

Global Ecology and Biogeography:   Much more give than take: South Africa as a major donor but infrequent recipient of invasive non‐native grasses by Vernon Visser, John R. U. Wilson, Lyn Fish, Carly Brown, Garry D. Cook, David M. Richardson.

ABC Bothalia:  Grasses as invasive plants in South Africa revisited: Patterns, pathways and management by Vernon Visser; John R.U. Wilson; Kim Canavan; Susan Canavan; Lyn Fish; David Le Maitre;  Ingrid Nänni; Caroline Mashau; Tim G. O’Connor; Philip Ivey; Sabrina Kumschick; David M. Richardson.

AoB plants: The global distribution of bamboos: assessing correlates of introduction and invasion by Susan Canavan; David M. Richardson; Vernon Visser; Johannes J. Le Roux; Maria S. Vorontsova; John R. U. Wilson.

And one popular article on the subject of alien grasses:

Quest: Invasive grasses : Africa burns and why this matters for grasses by Vernon Visser and Susan Canavan. Stellenbosch University.  Source : Quest, Volume 11, Issue 2, Jun 2015, p. 24 – 26.

Why? ( focus species / area )

The grass family (Poaceae) is the fourth largest plant family with over 11,000 species and with some of the most important crop and pasture species. It is therefore not surprising that many grass species have been extensively moved around the world. Some alien grass species have caused major ecosystem transformation—e.g. radically altered fire regimes—with grasses of African origin often having the largest impacts.

Comparatively, Africa appears to have suffered far fewer and less severe impacts from invasive grasses, with some notable exceptions, e.g. giant reed (Arundo donax), Kikuyu grass (Pennisetum clandestinum) and a number of annual grasses of Eurasian origin.

In South Africa, grasses seemingly have had little impact on ecosystems, but this lack of an observed impact may be largely due to the fact that this group of plants has received so little attention from invasion researchers and managers.

There is very good reason to be concerned because South Africa is comparable to countries like Australia and the USA in terms of numbers of grass species introduced, and has at least 122 species that are surviving and reproducing in the wild, but that have yet to become serious invaders.

Our research

1.  Grasses as invasive plants in South Africa revisited

One of the main outputs of this Working Group has been to compile a comprehensive review of alien grasses in South Africa (Visser et al. 2017).
This revealed that there are at least 256 alien grass species in South Africa, of which 122 have naturalised and 37 have become invasive (this represents an 8% increase in the number of naturalised species since 2004).

Alarmingly, more recently many grass species appear to have been introduced accidentally, suggesting the possibility for new invasions.
Our review highlighted the need for much greater investment in alien grass management, research and legislation, particularly since we appear to be saddled with a large grass invasion debt, i.e. a large number of species likely to become invasive in the future.

2. Biocontrol of grasses

Dr. Kim Canavan and PhD student, Guy Sutton from the Centre for Biological Control, Rhodes University are currently involved in researching the prospects for classical biological control of grasses. Their work hopes to address the current lack of biological control of grasses worldwide, with only one grass, Arundo donax having had releases of biological control agents to date.

Guy’s research explores whether or not invasive grasses will make suitable targets for biological control with a focus on invasive rat’s tail grasses (Sporobolus spp.) as models. Kim’s focus has been on invasive reed populations in South Africa with particular attention on exploring the potential for biological control of A. donax (see Canavan et al. 20172018)

3. Bamboos

In 2014, the Alien Grass group identified the need for research on the increasing popularization of bamboos in South Africa, and the potential for new invasion risks. This work was taken up by PhD student Susan Canavan at Stellenbosch University, jointly funded by the C·I·B and SANBI.

Susan has reviewed the global transfer of bamboos, her work has included producing a complete species list of bamboos (c. 1600 species), mapping the native and introduced and distribution of bamboo, reviewing impacts, as well as exploring correlates (traits, phylogeny, cultivar diversity) of invasion success. She has also looked at the introduction history of bamboos in South Africa, and the perceptions of landowners on its value.

4. Risk & impact assessments

Khensani has done detailed impact analyses for selected grasses recorded as alien in South Africa and elsewhere in the world. Her research has shown that grasses score similarly for impacts, regardless of where they occur as aliens. This highlights the dangers posed by the many alien grasses in South Africa that are, as yet, not widespread but already established in the country.

She has also investigated the risk posed by Paspalum quadrifarium, a species with a relatively restricted distribution in South Africa and first recorded in only 2003. Her research clearly shows that areas invaded by this species are undergoing a complete transformation in the plant community, with uninvaded, invaded and cleared areas all having almost completely different groups of plant species.

Khensani’s research will provide valuable scientific support for the listing of alien grass species under the NEM:BA regulations.

Current status and regulations of alien grasses in SA

The status, management and control of alien grass species in South Africa is regulated by the National Environmental Management: Biodiversity Act (Act No. 10 of 2004) Alien and Invasive Species Regulations (of 2014).

At present 14 species are listed under these regulations (with varying requirements for controls on their importation, possession, sale, cultivation and management), and a further 38 species are prohibited from being introduced into South Africa (See Appendix 6 of our paper for full details on these species).

Student bursaries


So far the Alien Grass Working Group has met four times.

Our next meeting is scheduled for 25-27 September 2018 in Cape Town.

Get in contact:

Chair: Vernon Visser

Secretary: Ingrid Nanni