et al. 2020; Chap. 12). Gwen Shaughnessy (1980) provided a detailed documentation of the factors that led to the introduction, widespread dissemination and further
spread of 13 woody alien species in the Cape Town area in the 1800s. Trees and
shrubs in the genera Acacia, Hakea, Leptospermum, Paraserianthes and Pinus were
introduced for display in botanical gardens, for sand stabilisation, climatic amelioration and economic gain. The government programs to establish these species were
considerable, often involving the removal of native vegetation, ploughing, digging
of pits and ridging of the soil. In addition, government supplied “massive” quantities
of seeds to private landowners. Government plantations were later abandoned,
leaving large areas dominated by alien species. Shaughnessy’s study is a rare
example of the meticulous historical documentation of the processes that led to the
establishment of invasive alien species. Brett Bennett has documented what he
termed a “globally unique and ultimately successful research programme” in
which South African foresters used climate matching to select candidate alien trees
for introduction, and then tested them in experimental plantings across South Africa
to select candidates to grow commercially (Bennett 2011). While this led to the
successful establishment of plantation forestry in South Africa, the species themselves often became invasive, not surprisingly given the care taken to match them to
local conditions. These invasions led to changing views about the forest industry
(see, for example, Johns 1993; Cellier 1994), and Bennett (2011) concludes that “the
currently popular anti-exotic rhetoric of many South Africans is at odds with the
contribution of plantations and timber products to South Africa’s economy and the
more nuanced scientific findings about biological invasion held by the scientific
community”.
Van Sittert (2002) documented in graphic detail the devastations to communities
and to their social structures, from 1870–1910, through the invasions of Opuntia
ficus-indica which at that time densely covered nearly 1 million hectares of land in
the Karoo Biome of the Eastern Cape. The distribution of the plant was subsequently
reduced to about 10% of its original range through biological control that was
initiated in 1932 (Pettey 1948; Annecke and Moran 1978). These stark historical
perspectives are often overlooked or ignored in present-day commentaries (see also
Hill et al. 2020, Sect. 19.3 in Chap. 19). In a detailed social analysis of the control of
O. ficus-indica, Beinart and Wotshela (2011) maintain that while control of this plant
has been beneficial for native biodiversity, it has had major costs for poor rural
people, who no longer can benefit from prickly pears for fruit. They conclude
that the value of useful invasive plants such as prickly pear should be given
greater weight in comparison to their environmental costs. This is also in line with
the view that local benefits are often underestimated when assessing the costs
of invasive or alien species (Shackleton et al. 2007). Beinart (2014) also discusses
the case of Acacia mearnsii in South Africa, and notes that black wattle is one
of the few species for which a systematic cost benefit analysis has been attempted
(De Wit et al. 2001). Despite this, Beinart remains sceptical about De Wit et al.’s
conclusions, arguing that the social costs of removing a useful species had not
been adequately estimated.
56
B. W. van Wilgen
spread of 13 woody alien species in the Cape Town area in the 1800s. Trees and
shrubs in the genera Acacia, Hakea, Leptospermum, Paraserianthes and Pinus were
introduced for display in botanical gardens, for sand stabilisation, climatic amelioration and economic gain. The government programs to establish these species were
considerable, often involving the removal of native vegetation, ploughing, digging
of pits and ridging of the soil. In addition, government supplied “massive” quantities
of seeds to private landowners. Government plantations were later abandoned,
leaving large areas dominated by alien species. Shaughnessy’s study is a rare
example of the meticulous historical documentation of the processes that led to the
establishment of invasive alien species. Brett Bennett has documented what he
termed a “globally unique and ultimately successful research programme” in
which South African foresters used climate matching to select candidate alien trees
for introduction, and then tested them in experimental plantings across South Africa
to select candidates to grow commercially (Bennett 2011). While this led to the
successful establishment of plantation forestry in South Africa, the species themselves often became invasive, not surprisingly given the care taken to match them to
local conditions. These invasions led to changing views about the forest industry
(see, for example, Johns 1993; Cellier 1994), and Bennett (2011) concludes that “the
currently popular anti-exotic rhetoric of many South Africans is at odds with the
contribution of plantations and timber products to South Africa’s economy and the
more nuanced scientific findings about biological invasion held by the scientific
community”.
Van Sittert (2002) documented in graphic detail the devastations to communities
and to their social structures, from 1870–1910, through the invasions of Opuntia
ficus-indica which at that time densely covered nearly 1 million hectares of land in
the Karoo Biome of the Eastern Cape. The distribution of the plant was subsequently
reduced to about 10% of its original range through biological control that was
initiated in 1932 (Pettey 1948; Annecke and Moran 1978). These stark historical
perspectives are often overlooked or ignored in present-day commentaries (see also
Hill et al. 2020, Sect. 19.3 in Chap. 19). In a detailed social analysis of the control of
O. ficus-indica, Beinart and Wotshela (2011) maintain that while control of this plant
has been beneficial for native biodiversity, it has had major costs for poor rural
people, who no longer can benefit from prickly pears for fruit. They conclude
that the value of useful invasive plants such as prickly pear should be given
greater weight in comparison to their environmental costs. This is also in line with
the view that local benefits are often underestimated when assessing the costs
of invasive or alien species (Shackleton et al. 2007). Beinart (2014) also discusses
the case of Acacia mearnsii in South Africa, and notes that black wattle is one
of the few species for which a systematic cost benefit analysis has been attempted
(De Wit et al. 2001). Despite this, Beinart remains sceptical about De Wit et al.’s
conclusions, arguing that the social costs of removing a useful species had not
been adequately estimated.
56
B. W. van Wilgen