their detrimental impact far outweighs advantages as their abundance increases,
resulting in a net negative value. An escalating threat of alien plants to rangelands
demands innovative responses in addition to biological control and clearing
programmes.
16.1 Introduction
Rangelands are areas of natural or semi-natural vegetation that support large mammalian herbivores. They cover >70% of the land surface of South Africa, and
include grassland, savanna, thicket, and karroid shrubland vegetation. This diversity
of vegetation supports a richness of domestic and native large mammalian herbivores that consume graminoid plants, herbaceous dicotyledons, and woody plants in
different proportions depending on whether they are grazers, browsers, or mixed
feeders. Ecosystems dominated by woody plants therefore support more browsers,
while grasslands support only grazers. Production or subsistence rangelands are used
for the rearing of 40.7 million head of livestock (cattle, 12.8 million; sheep, 22.5
million; goats, 5.4 million; Department of Agriculture, Forestry and Fisheries 2018).
In addition, over 60,000 km
2 is set aside either as protected areas (Department of
Environmental Affairs 2018a), or for farming game animals (~3 million head,
Meissner et al. 2013).
Alien plants can provide novel foodstuffs for herbivores, but they also alter
vegetation structure and composition in ways that can negatively affect herbivores.
Despite their prominence, there have been few studies of the impact of alien plants
on South African rangelands (Richardson and van Wilgen 2004). Impacts of invasive alien species on the ecosystem services provided by rangelands (livestock
production and conservation), catchments (water supply), and biodiversity
(harvested products and non-use activities) are of particular concern (van Wilgen
et al. 2008).
In this chapter we assess the impact of invasive alien plants on South African
rangelands. We review the types, extent, economic importance, and key ecological
processes relevant to invasions of South African rangelands, and identify the status
of important alien species in each biome. We address the question of whether
rangeland management has influenced the success of alien plants, and consider
their ecological and economic impact, illustrated by case studies. We conclude
with a distillation of key features concerning the ingress of alien plants into
rangelands and how effective rangeland management could be used for their
control.
460
T. G. O’Connor and B. W. van Wilgen
resulting in a net negative value. An escalating threat of alien plants to rangelands
demands innovative responses in addition to biological control and clearing
programmes.
16.1 Introduction
Rangelands are areas of natural or semi-natural vegetation that support large mammalian herbivores. They cover >70% of the land surface of South Africa, and
include grassland, savanna, thicket, and karroid shrubland vegetation. This diversity
of vegetation supports a richness of domestic and native large mammalian herbivores that consume graminoid plants, herbaceous dicotyledons, and woody plants in
different proportions depending on whether they are grazers, browsers, or mixed
feeders. Ecosystems dominated by woody plants therefore support more browsers,
while grasslands support only grazers. Production or subsistence rangelands are used
for the rearing of 40.7 million head of livestock (cattle, 12.8 million; sheep, 22.5
million; goats, 5.4 million; Department of Agriculture, Forestry and Fisheries 2018).
In addition, over 60,000 km
2 is set aside either as protected areas (Department of
Environmental Affairs 2018a), or for farming game animals (~3 million head,
Meissner et al. 2013).
Alien plants can provide novel foodstuffs for herbivores, but they also alter
vegetation structure and composition in ways that can negatively affect herbivores.
Despite their prominence, there have been few studies of the impact of alien plants
on South African rangelands (Richardson and van Wilgen 2004). Impacts of invasive alien species on the ecosystem services provided by rangelands (livestock
production and conservation), catchments (water supply), and biodiversity
(harvested products and non-use activities) are of particular concern (van Wilgen
et al. 2008).
In this chapter we assess the impact of invasive alien plants on South African
rangelands. We review the types, extent, economic importance, and key ecological
processes relevant to invasions of South African rangelands, and identify the status
of important alien species in each biome. We address the question of whether
rangeland management has influenced the success of alien plants, and consider
their ecological and economic impact, illustrated by case studies. We conclude
with a distillation of key features concerning the ingress of alien plants into
rangelands and how effective rangeland management could be used for their
control.
460
T. G. O’Connor and B. W. van Wilgen