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

Grasses as invasive plants in South Africa revisited: patterns, pathways and management
Vernon VISSER1,2,3,4, Kim Canavan5, Susan Canavan3,4, Lyn Fish6, Philip Ivey4Sabrina Kumschick3, David C. Le Maitre7, Ingrid Nänni4, Tim O'Connor8, Sebataolo Rahlao4, David M. Richardson3, John R. Wilson3,4
1SEEC - Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Rondebosch 7701, South Africa
2African Climate and Development Initiative, University of Cape Town
3Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University
4South African National Biodiversity Institute, Kirstenbosch Research Centre
5Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown
6National Herbarium, Pretoria, South African National Biodiversity Institute, Pretoria
7Centre for Invasion Biology, CSIR Natural Resources and the Environment, Stellenbosch
8SAEON, PO Box 2600, Pretoria 0001, South Africa

In many countries around the world the most damaging invasive plant species are grasses.  However, the group has received little attention in South Africa. Here we expand upon Sue Milton’s 2004 review of grasses as invasive alien plants in South Africa. Specifically we provide the first detailed species-level inventory of introduced grasses in South Africa, and use this and other literature sources to elucidate the history of grass introductions, identify possible pathways of introduction and spread, determine which species are having impacts, and predict possible future trends.

We found that over 200 non-native grass species have been introduced to the country, 37 of which have become invasive. This reflects in part an extensive historical effort to introduce non-native grasses via formal pasture introduction programmes, but more recently an increasing number of horticultural species have been introduced. Most grass introductions into South Africa have been of species native to Eurasia, although more recent introductions have often been from regions other than Eurasia.

Non-native grass species richness and abundance is highest in the south-west of the country, but has recently increased much more in other parts of the country.

We found at least 21 species with recorded environmental and economic impacts in South Africa. There is little literature on the management of these species, and current legislation does not adequately cover these species.

We discuss our results with regards to previous findings on grass invasions and make suggestions for possible future problems with non-native grasses in South Africa.