Grasses as invasive plants in South Africa revisited: Patterns, pathways and management

Abstract

Background: In many countries around the world, the most damaging invasive plant species are grasses. However, the status of grass invasions in South Africa has not been documented recently. Objectives: To update Sue Milton’s 2004 review of grasses as invasive alien plants in South Africa, provide the first detailed species level inventory of alien grasses in South Africa and assess the invasion dynamics and management of the group. Method: We compiled the most comprehensive inventory of alien grasses in South Africa to date using recorded occurrences of alien grasses in the country from various literature and 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 minimum residence times to investigate pathways and patterns of spatial extent. We identified alien grasses in South Africa that are having environmental and economic impacts and determined whether management options have been identified, and legislation created, for these species. Results: There are at least 256 alien grass species in the country, 37 of which have become invasive. Alien grass species richness increased most dramatically from the late 1800s to about 1940. Alien grass species that are not naturalised or invasive have much shorter residence 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 pasture research stations. A large number of alien grass species in South Africa are of Eurasian origin, although more recent introductions include species from elsewhere in Africa and from Australasia. Alien grasses are most prevalent in the south-west of the country, and the Fynbos Biome has the most alien grasses and the most widespread species. We identified 11 species that have recorded environmental and economic impacts in the country. Few alien grasses have prescribed or researched management techniques. Moreover, current legislation neither adequately covers invasive species nor reflects the impacts and geographical extent of these species. Conclusion: South Africa has few invasive grass species, but there is much uncertainty regarding the identity, numbers of species, distributions, abundances and impacts of alien 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 much greater investment in alien grass management, research and legislation.

An Evaluation of the Impacts of Alien Species on Biodiversity in South Africa Using Different Assessment Methods

“…The Environmental Impact Classification for Alien Taxa has been applied to various taxa that are known to occur as alien species in South Africa including grasses (Visser et al 2017;Nkuna et al 2018;Canavan et al 2019), amphibians (Kumschick et al 2017), birds (Evans et al 2016), mammals (Hagen and Kumschick 2018), fish (Marr et al 2017), gastropods (Kesner and Kumschick 2018), and some other invertebrates (Nelufule 2018). Most EICAT assessments performed to date have been done at a global scale, i.e.…”

“…It is important to note that although global assessments are comprehensive, there will need to be regularly updated as further assessments are done at national scales. In South Africa, national-level EICAT assessments have been done for some alien grasses (Visser et al 2017) and fishes (Marr et al 2017) (Table 17.1).…”

“…There are six grass species that have had EICAT assessments done at a national scale for South Africa, with Arundo donax (Giant Reed) and Glyceria maxima (Reed Meadow Grass) evaluated as having major impacts (Visser et al 2017;Nkuna et al 2018;VK Nkuna, unpublished data). These two species have been implicated in competitively displacing native species; A. donax, for example, dominates riparian areas and can locally exclude native plants (Holmes et al 2005;Guthrie 2007), while G. maxima has locally displaced some native wetland species (Mugwedi 2012).…”

Global environmental and socio-economic impacts of selected alien grasses as a basis for ranking threats to South Africa

“…species have not reached their full impact potential in South Africa (yet), as species with more information in South Africa did not show higher similarities in impact magnitudes to elsewhere. Finally, South Africa might be more resilient to grass invasions, and impacts are actually lower here (Visser et al 2017). These hypotheses warrant more research and can only be disentangled once more data become available.…”

“…There are approximately 256 alien grasses introduced into South Africa (Visser et al 2017). Of these, we assessed impacts for the 58 species that occur as aliens in at least one of the other following regions: Australia, Chile, Europe or the USA.…”