(Visser et al. 2017). Examples include invasive Paspalum and Bromus species,
Pennisetum clandestinum (Kikuyu Grass) and Lolium multiflorum (Ryegrass), all
palatable species. By contrast, grazing capacity has been reduced by the unpalatable
perennials Nasella trichotoma (Nasella Tussock) and Nasella tenuissima (White
Tussock) in mountain grassland in the Eastern Cape Province, Pennisetum setaceum
(Fountain Grass) in grassland and the Nama-Karoo, and by the annual Stipa capensis
(Mediterranean Needle Grass), which damages wool, in the Succulent Karoo.
However, even the normally unpalatable P. setaceum can serve as fodder during
drought. We found no studies concerning the impact of alien species on wildlife
systems, or which had quantified the impact of alien grasses on livestock production
or on wildlife in southern Africa.
Invasion of grassland or savanna by alien trees and shrubs will markedly depress
grass production as occurs with encroachment by native woody species (O’Connor
and Stevens 2017). This negative impact is offset to some extent when the woody
species offer palatable forage for browsers or mixed feeders. Most of the woody
invasive species (legumes in the genera Acacia and Prosopis, and Chromolaena
odorata, Triffid Weed) (see below) do not offer palatable foliage, although some of
the legume species were introduced for their palatable pods. Cattle and browsers
consume and effectively disperse the pods of, for example, Gleditsea triancanthos
(Honey Locust), Leucaena leucocephala (Leucaena) and Prosopis species, and this
has contributed to their recent increase in distribution (Table 16.2; 94.4% increase
for L. leucocephala) although these foodstuffs can be harmful when large quantities
are consumed (Binggeli 2001). The foliage of all woody species listed in Table 16.2
is not considered as quality forage, although a few of these species [e.g., Acacia
mearnsii, Morus alba (White Mulberry), Psidium guajava (Guava), Robinia
pseudoacacia (Black Locust), Salix babylonica (Weeping Willow)] may be browsed
incidentally. Schinus molle (Pepper Tree) seedlings are palatable and consequently
may experience potentially high levels of mortality when exposed to sheep grazing
in semi-arid savanna (Iponga et al. 2009), and this offers an approach for controlling
this species which threatens to expand considerably its distribution (Rouget et al.
2004). However, even species providing poor-quality forage may be used by
livestock, especially goats, under intensive stocking; examples include Acacia
dealbata (Silver Wattle), Populus X canescens (Grey Poplar) (Du Toit 2016), and
Lantana camara (Lantana) (T. O’Connor, pers. obs.). Atriplex species and the
succulent species Agave americana (American Agave), Opuntia ficus-indica (Mission Prickly Pear) and Opuntia monocantha (Cochineal Prickly Pear) are commonly
used as forage (Henderson 2001), and Melia azedarach (Syringa) has been made
into silage.
Woody alien species that possess deterrents such as thorns may form impenetrable thickets that prevent access to forage, as is evident for drainage lines in the
Succulent Karoo Biome, which harbours key forage resources that have been
invaded by Prosopis spp. (van den Berg 2010). Dense infestations of Opuntia
ficus-indica, a succulent shrub protected by thorny cladodes, had occurred in the
16 The Impact of Invasive Alien Plants on Rangelands in South Africa
475
Pennisetum clandestinum (Kikuyu Grass) and Lolium multiflorum (Ryegrass), all
palatable species. By contrast, grazing capacity has been reduced by the unpalatable
perennials Nasella trichotoma (Nasella Tussock) and Nasella tenuissima (White
Tussock) in mountain grassland in the Eastern Cape Province, Pennisetum setaceum
(Fountain Grass) in grassland and the Nama-Karoo, and by the annual Stipa capensis
(Mediterranean Needle Grass), which damages wool, in the Succulent Karoo.
However, even the normally unpalatable P. setaceum can serve as fodder during
drought. We found no studies concerning the impact of alien species on wildlife
systems, or which had quantified the impact of alien grasses on livestock production
or on wildlife in southern Africa.
Invasion of grassland or savanna by alien trees and shrubs will markedly depress
grass production as occurs with encroachment by native woody species (O’Connor
and Stevens 2017). This negative impact is offset to some extent when the woody
species offer palatable forage for browsers or mixed feeders. Most of the woody
invasive species (legumes in the genera Acacia and Prosopis, and Chromolaena
odorata, Triffid Weed) (see below) do not offer palatable foliage, although some of
the legume species were introduced for their palatable pods. Cattle and browsers
consume and effectively disperse the pods of, for example, Gleditsea triancanthos
(Honey Locust), Leucaena leucocephala (Leucaena) and Prosopis species, and this
has contributed to their recent increase in distribution (Table 16.2; 94.4% increase
for L. leucocephala) although these foodstuffs can be harmful when large quantities
are consumed (Binggeli 2001). The foliage of all woody species listed in Table 16.2
is not considered as quality forage, although a few of these species [e.g., Acacia
mearnsii, Morus alba (White Mulberry), Psidium guajava (Guava), Robinia
pseudoacacia (Black Locust), Salix babylonica (Weeping Willow)] may be browsed
incidentally. Schinus molle (Pepper Tree) seedlings are palatable and consequently
may experience potentially high levels of mortality when exposed to sheep grazing
in semi-arid savanna (Iponga et al. 2009), and this offers an approach for controlling
this species which threatens to expand considerably its distribution (Rouget et al.
2004). However, even species providing poor-quality forage may be used by
livestock, especially goats, under intensive stocking; examples include Acacia
dealbata (Silver Wattle), Populus X canescens (Grey Poplar) (Du Toit 2016), and
Lantana camara (Lantana) (T. O’Connor, pers. obs.). Atriplex species and the
succulent species Agave americana (American Agave), Opuntia ficus-indica (Mission Prickly Pear) and Opuntia monocantha (Cochineal Prickly Pear) are commonly
used as forage (Henderson 2001), and Melia azedarach (Syringa) has been made
into silage.
Woody alien species that possess deterrents such as thorns may form impenetrable thickets that prevent access to forage, as is evident for drainage lines in the
Succulent Karoo Biome, which harbours key forage resources that have been
invaded by Prosopis spp. (van den Berg 2010). Dense infestations of Opuntia
ficus-indica, a succulent shrub protected by thorny cladodes, had occurred in the
16 The Impact of Invasive Alien Plants on Rangelands in South Africa
475