Eucalyptus (Gums) for forestry were successful (Bennett 2011). Australian Acacia
species were planted en masse (more than 300 million seeds) to stabilise sand on the
Cape flats, and prizes were offered to individuals for successful planting and
establishment (van Sittert 2000; Bennett and van Sittert 2019), leading to substantial
invasions as a result of this high propagule pressure (Donaldson et al. 2014).
Similarly, people made substantial efforts to ensure the establishment of Prosopis
trees during the mid-twentieth century for silviculture (Shackleton et al. 2015a).
Some farmers recount childhood memories of putting Prosopis seedlings by the Aga
stove in winter and only planting them out in spring to ensure survival. But, in the
hot summers, one farmer recounts how during the school holidays he was required to
go out and water Prosopis seedlings to ensure their survival.
Significant research went into discovering how to introduce fishes for sport and
recreation by British colonists, and how to ensure their survival. Tens of thousands
of O. mykiss and Salmo trutta (Brown Trout) eggs were sent from the UK to
South Africa in the late 1800s and early 1900s, which failed to establish, but efforts
continued until appropriate strategies were implemented to ensure survival during
transport (also see Weyl et al. 2020, Chap. 6). In the Cape, special hatcheries were
built and a bounty was even established for killing otters that were presumed to pose
a threat to the newly introduced fish (Britz 2015). In KwaZulu-Natal, railway sidings
were built specifically to ensure that the water did not have time to heat up during
transport (Alletson 1997). The time and money that went into ensuring introduction
and survival must have helped to promote invasions in the long run.
The available evidence and examples above support the proposition that great
perseverance and effort to ensure the survival and establishment of some non-native
species was important for facilitating invasions. The degree of human tenacity
during the pre-introduction and post-introduction stages is typically poorly
accounted for in purely ecological models of invasion dynamics.
24.2.3 Proposition 1c: Human-Mediated Modifications Help
Invasive Species to Establish
Humans can modify both species and landscapes, which may facilitate or limit the
invasion of some species (Kueffer 2017; Shackleton et al. 2018). Human agency is
often not well acknowledged in the biological sciences, often being treated as an
“unwelcome extraneous variable”, but is actually a key factor in explaining many
biological invasion processes (van Sittert 2002).
Le Roux et al. (2013) show how humans have altered the genetic make-up of
Acacia pycnantha (Golden wattle) through artificial selection both prior to and after
introduction, which may facilitate its invasiveness. At a broader scale, human
alteration or disturbance of landscapes has facilitated invasions. Initially, many
invasive species can only survive and proliferate in human-altered landscapes. For
example, the creation of ponds, urban garden microclimates and farm dams has
24 The Social Dimensions of Biological Invasions in South Africa
707
species were planted en masse (more than 300 million seeds) to stabilise sand on the
Cape flats, and prizes were offered to individuals for successful planting and
establishment (van Sittert 2000; Bennett and van Sittert 2019), leading to substantial
invasions as a result of this high propagule pressure (Donaldson et al. 2014).
Similarly, people made substantial efforts to ensure the establishment of Prosopis
trees during the mid-twentieth century for silviculture (Shackleton et al. 2015a).
Some farmers recount childhood memories of putting Prosopis seedlings by the Aga
stove in winter and only planting them out in spring to ensure survival. But, in the
hot summers, one farmer recounts how during the school holidays he was required to
go out and water Prosopis seedlings to ensure their survival.
Significant research went into discovering how to introduce fishes for sport and
recreation by British colonists, and how to ensure their survival. Tens of thousands
of O. mykiss and Salmo trutta (Brown Trout) eggs were sent from the UK to
South Africa in the late 1800s and early 1900s, which failed to establish, but efforts
continued until appropriate strategies were implemented to ensure survival during
transport (also see Weyl et al. 2020, Chap. 6). In the Cape, special hatcheries were
built and a bounty was even established for killing otters that were presumed to pose
a threat to the newly introduced fish (Britz 2015). In KwaZulu-Natal, railway sidings
were built specifically to ensure that the water did not have time to heat up during
transport (Alletson 1997). The time and money that went into ensuring introduction
and survival must have helped to promote invasions in the long run.
The available evidence and examples above support the proposition that great
perseverance and effort to ensure the survival and establishment of some non-native
species was important for facilitating invasions. The degree of human tenacity
during the pre-introduction and post-introduction stages is typically poorly
accounted for in purely ecological models of invasion dynamics.
24.2.3 Proposition 1c: Human-Mediated Modifications Help
Invasive Species to Establish
Humans can modify both species and landscapes, which may facilitate or limit the
invasion of some species (Kueffer 2017; Shackleton et al. 2018). Human agency is
often not well acknowledged in the biological sciences, often being treated as an
“unwelcome extraneous variable”, but is actually a key factor in explaining many
biological invasion processes (van Sittert 2002).
Le Roux et al. (2013) show how humans have altered the genetic make-up of
Acacia pycnantha (Golden wattle) through artificial selection both prior to and after
introduction, which may facilitate its invasiveness. At a broader scale, human
alteration or disturbance of landscapes has facilitated invasions. Initially, many
invasive species can only survive and proliferate in human-altered landscapes. For
example, the creation of ponds, urban garden microclimates and farm dams has
24 The Social Dimensions of Biological Invasions in South Africa
707