Bothalia - African Biodiversity & Conservation ISSN: (Online) 2311-9284, (Print) 0006-8241 Page 1 of 29 Original Research Grasses as invasive plants in South Africa revisited: Patterns, pathways and management Authors: Background: In many countries around the world, the most damaging invasive plant species 1,2,3,4 Vernon Visser are grasses. However, the status of grass invasions in South Africa has not been documented John R.U. Wilson3,4 Kim Canavan5 recently. Susan Canavan3 Lyn Fish6 Objectives: To update Sue Milton’s 2004 review of grasses as invasive alien plants in South David Le Maitre3,7 Africa, provide the first detailed species level inventory of alien grasses in South Africa and Ingrid Nänni4 assess the invasion dynamics and management of the group. Caroline Mashau6 Tim G. O’Connor8 Method: We compiled the most comprehensive inventory of alien grasses in South Africa to 4 Philip Ivey date using recorded occurrences of alien grasses in the country from various literature and Sabrina Kumschick3,4 David M. Richardson3 database sources. Using historical literature, we reviewed past efforts to introduce alien grasses into South Africa. We sourced information on the origins, uses, distributions and Affiliations: minimum residence times to investigate pathways and patterns of spatial extent. We 1 SEEC – Statistics in Ecology, identified alien grasses in South Africa that are having environmental and economic impacts the Environment and Conservation, Department of and determined whether management options have been identified, and legislation created, Statistical Sciences, University for these species. of Cape Town, South Africa Results: There are at least 256 alien grass species in the country, 37 of which have become 2African Climate and invasive. Alien grass species richness increased most dramatically from the late 1800s to about Development Initiative, 1940. Alien grass species that are not naturalised or invasive have much shorter residence University of Cape Town, South Africa times than those that have naturalised or become invasive. Most grasses were probably introduced for forage purposes, and a large number of alien grass species were trialled at 3Centre for Invasion Biology, pasture research stations. A large number of alien grass species in South Africa are of Eurasian Department of Botany and origin, although more recent introductions include species from elsewhere in Africa and from Zoology, Stellenbosch Australasia. Alien grasses are most prevalent in the south-west of the country, and the Fynbos University, South Africa Biome has the most alien grasses and the most widespread species. We identified 11 species 4Invasive Species Programme, that have recorded environmental and economic impacts in the country. Few alien grasses South African National have prescribed or researched management techniques. Moreover, current legislation neither Biodiversity Institute, adequately covers invasive species nor reflects the impacts and geographical extent of these Kirstenbosch Research Centre, South Africa species. Conclusion: South Africa has few invasive grass species, but there is much uncertainty 5Department of Zoology and Entomology, Rhodes regarding the identity, numbers of species, distributions, abundances and impacts of alien University, South Africa grasses. Although introductions of alien grasses have declined in recent decades, South Africa has a potentially large invasion debt. This highlights the need for continued monitoring and 6 National Herbarium, South much greater investment in alien grass management, research and legislation. African National Biodiversity Institute (SANBI), South Africa 7Natural Resources and the Introduction Environment, Stellenbosch, In many parts of the world, grasses are among the most damaging and widespread alien plant South Africa species (D’Antonio, Stahlheber & Molinari 2011; D’Antonio and Vitousek 1992; Gaertner et al. 8South African Environmental 2014). In the Americas, Australia and on many tropical islands, grasses have transformed Observation Network ecosystems, usually by altering the natural fire cycle (D’Antonio and Vitousek 1992; Gaertner (SAEON), Pretoria, et al. 2014). By contrast, South Africa has fewer invasive grasses, and alien plant control efforts are South Africa dedicated primarily to combating woody plant invasions. The only grass species that has been widely targeted for control operations by the Working for Water Programme is Arundo donax, Corresponding author: Vernon Visser, [email protected] Read online: Dates: Received: 05 Sep. 2016 Accepted: 06 Dec. 2016 Published: 31 Mar. 2017 Scan this QR How to cite this article: Visser, V et al., 2017, ‘Grasses as invasive plants in South Africa revisited: Patterns, pathways and management’, code with your Bothalia 47(2), a2169. https://doi.org/10.4102/abc.v47i2.2169 smart phone or mobile device Copyright: © 2017. The Authors. Licensee: AOSIS. This work is licensed under the Creative Commons Attribution License. to read online. Note: This paper was initially delivered at the 43rd Annual Research Symposium on the Management of Biological Invasions in South Africa, Goudini Spa, Western Cape, South Africa on 18-20 May 2016. http://www.abcjournal.org Open Access Page 2 of 29 Original Research although < 0.5% of the total budget for alien plant control and climate change could have differential consequences for was allocated to managing this species (Table 2 in van Wilgen grasses of particular phylogenetic clades. et al. 2012). Grasses also do not feature in the National Strategy for Dealing with Biological Invasions in South Africa Since 2004, an increasing amount of information on alien (Department of Environmental Affairs [DEA] 2014). The grass distributions, origins, traits and impacts in South Africa relative paucity of grass invasions in South Africa might be has become available from online databases, surveys and because of high fire frequencies in African grasslands and research projects. The legal framework for alien grass savannas excluding alien grasses (Visser et al. 2016). It would, management in South Africa has also changed substantially therefore, seem that grass invasions in South Africa are with the introduction of the Alien and Invasive Species generally neither common nor widespread and that they do (A&IS) regulations under the National Environmental not pose a major risk. However, there are several reasons to Management: Biodiversity (NEM:BA) Act 10 of 2004. A number be concerned about undetected and possible future grass of alien grasses were listed as invasive in 2014 (NEM:BA invasions. Alien and Invasive Species List 2016; A&IS regulations) and now have specific management requirements or are The last review of alien grasses in South Africa was published prohibited from being imported. Moreover, the A&IS more than a decade ago (Milton 2004). This review highlighted regulations require the publication of a national status report major gaps in our knowledge. We do not know how many on listed invasive species every 3 years, the purpose of which alien grasses are in South Africa nor their identity or status is to monitor the status of listed species and the effectiveness on the introduction-naturalisation-invasion (INI) continuum of the regulations and associated control measures (Wilson (Blackburn et al. 2011; Richardson and Pyšek 2012). While it et al. 2017). appears that South Africa experienced lower introduction Given the demonstrated potential for alien grasses to become effort of alien grasses relative to other regions of the world, it problematic invaders elsewhere in the world, the increased was one of the countries most actively engaged in trialling availability of data in South Africa and new legislation alien grasses at pasture research stations (Visser et al. 2016). regarding alien species, we aim to provide an updated review However, there is no consolidated inventory of species of the status of alien grasses in South Africa. To this end, we cultivated in these pasture research trials. Without a collate the first detailed species-level inventory of alien comprehensive (or as near as possible) inventory of alien grasses in South Africa. We use this inventory, together with grasses, it is impossible to ascertain all the risks. other literature, to address some of the information gaps identified above, including investigating (1) minimum We also have inadequate knowledge of the introduction residence times (MRTs) of alien grasses in South Africa, (2) pathways of alien grasses, which is needed to determine pathways of introduction and spread, (3) areas that are ‘introduction debt’, the number of species that are likely to be potentially being most impacted by alien grasses, (4) introduced to South Africa in the future (Rouget et al. 2016). impacting species and the nature of their impacts and (5) Introduced but not yet naturalised or invasive grasses might information on management of alien grasses. This information also represent an invasion debt as they might invade in the is needed to make recommendations for future management future, while current invasions might spread to new areas of alien grasses in South Africa. and cause increasing negative impacts (Rouget et al. 2016). However, we need information on the origins of alien grasses, their residence times (Wilson et al. 2007) and propagule Methods pressure to be able to estimate establishment and spread Inventory debts (Rouget et al. 2016). We also have very poor knowledge We produced an inventory of alien grasses in South Africa