Grasses as invasive alien plants in South Africa

Grasses are important, but often overlooked, elements of the South African alien flora. Current information shows that 15% of the grass genera and 12% of grass species in southern Africa are naturalized aliens. Many of these species are invasive in other parts of the world, where they are reducing the biodiversity of indigenous communities, changing ecosystem processes, retarding ecosystem restoration and reducing profits from ranching and arable agriculture. Their spread has been facilitated by domestic livestock, disturbance, long-distance transport and nitrogen addition to soils. Control is complicated by abundant seed production, persistent seed banks, positive response to disturbance, a dearth of biocontrol research and, in some cases, by herbicide resistance. This review of the impacts of alien grasses in other parts of the world suggests that alien grasses will become increasingly prevalent in South Africa, and that more research, aimed at identifying appropriate management responses, would be justified.