Grasses as invasive alien plants in South Africa

7that alien grasses can transform ecosystems. At present only five grass species, all large conspicuous perennials, are declared weeds in South Africa. 8 However, perennials and annuals are equally represented in the alien grass flora. The annuals, largely of European origin, are widespread and sometimes abundant in winter rainfall and arid parts of southern Africa, whereas the perennial species have successfully invaded both winter and summer rainfall regions, particularly in wetlands and riparian areas. Most alien grass species are too poorly known to evaluate their ecological and economic impact or to recommend control measures. This preliminary review of the processes and influences of perennial and annual grass invasions seeks to address this gap. Because of the dearth of local research on this topic, information is largely drawn from studies of invasive behaviour by the same (or related) grass species in Australia and North America.