21.3 Alien Plant Eradication Projects
The Working for Water programme (WfW) explicitly took an area-based, as opposed
to a species-based, approach to management (see Faulkner et al. 2020, Chap. 12, for a
discussion on pathway-based approaches). Invaded areas were demarcated, estimates
of the overall density of all alien plants in those areas were made, and contracts issued
to clear all the alien plants in the specified areas. Classical biological control aside,
individual species were not explicitly targeted. To address this gap, in 2008, the
South African National Biodiversity Institute (SANBI) was contracted by WfW to
develop species-specific control programmes focusing on alien plant species that
were not yet widespread invaders (Wilson et al. 2013). Over time, this mandate has
narrowed so that the focus of control efforts is on species where the possibility of
national-scale eradication has not been ruled out (see Sect. 21.6 for a discussion of
species-specific management programmes where the goal is not eradication).
There have been several documented plant eradication attempts in continental
South Africa, all initiated by the government, but none of which succeeded (cf. work
on the sub-Antarctic Islands, Greve et al. 2020, Chap. 8). Intensive programmes
were initiated in the early 1960s to remove Alhagi camelorum (Camel Thorn) from
irrigation schemes. However, the systemic herbicides available at the time were
ineffective for dealing with the extensive underground root systems (Erasmus and
Viljoen 1993; Jooste 1965). In 1968 an eradication programme was initiated against
Solanum elaeagnifolium (Satansbos) (Wasermann et al. 1988). Despite some local
successes, by 1972 the eradication campaign was cancelled; failure was ascribed to
inadequate biological knowledge, ineffective herbicides and application techniques,
and a lack of cooperation from many farmers. The most extensive eradication
campaign in South Africa was against Opuntia aurantiaca (Jointed Cactus)
(Moran and Annecke 1979), but despite significant governmental support, apparently not a single farm was fully cleared.
These efforts focussed on alien plants that were already widespread in the
country, and basic requirements to achieve eradication were not always in place,
e.g. no new immigration of propagules, all populations delimited, sufficient
resources available to complete eradication, and adequate monitoring and evaluation
in place (Wilson et al. 2017).
There are 42 alien plant species listed as Category 1a in South Africa’s Alien &
Invasive Species Regulations, published in 2014 under the National Environmental:
Biodiversity Act (NEM:BA, Act 10 of 2004) (i.e. deemed as nation-wide eradication
targets). On investigation, several of these species have been found to be present at
many sites across the country (e.g. Iris pseudacorus (Yellow Flag) (Jaca and Mkhize
2015), and Furcraea foetida (Mauritian Hemp), although the formal process of
documenting the evidence and transfer of these species to more appropriate management categories has not been completed yet (see Chap. 20; Kumschick et al. 2020).
Several of the Category 1a species [Cabomba caroliniana, (Cabomba) and Euphorbia
esula (Leafy Spurge)] have not been found again, and might simply not be in the
country, while others are not known to have become invasive and were listed for
precautionary purposes (Henderson and Wilson 2017). Several of the species are found
21 The Extent and Effectiveness of Alien Plant Control Projects in South Africa
607
The Working for Water programme (WfW) explicitly took an area-based, as opposed
to a species-based, approach to management (see Faulkner et al. 2020, Chap. 12, for a
discussion on pathway-based approaches). Invaded areas were demarcated, estimates
of the overall density of all alien plants in those areas were made, and contracts issued
to clear all the alien plants in the specified areas. Classical biological control aside,
individual species were not explicitly targeted. To address this gap, in 2008, the
South African National Biodiversity Institute (SANBI) was contracted by WfW to
develop species-specific control programmes focusing on alien plant species that
were not yet widespread invaders (Wilson et al. 2013). Over time, this mandate has
narrowed so that the focus of control efforts is on species where the possibility of
national-scale eradication has not been ruled out (see Sect. 21.6 for a discussion of
species-specific management programmes where the goal is not eradication).
There have been several documented plant eradication attempts in continental
South Africa, all initiated by the government, but none of which succeeded (cf. work
on the sub-Antarctic Islands, Greve et al. 2020, Chap. 8). Intensive programmes
were initiated in the early 1960s to remove Alhagi camelorum (Camel Thorn) from
irrigation schemes. However, the systemic herbicides available at the time were
ineffective for dealing with the extensive underground root systems (Erasmus and
Viljoen 1993; Jooste 1965). In 1968 an eradication programme was initiated against
Solanum elaeagnifolium (Satansbos) (Wasermann et al. 1988). Despite some local
successes, by 1972 the eradication campaign was cancelled; failure was ascribed to
inadequate biological knowledge, ineffective herbicides and application techniques,
and a lack of cooperation from many farmers. The most extensive eradication
campaign in South Africa was against Opuntia aurantiaca (Jointed Cactus)
(Moran and Annecke 1979), but despite significant governmental support, apparently not a single farm was fully cleared.
These efforts focussed on alien plants that were already widespread in the
country, and basic requirements to achieve eradication were not always in place,
e.g. no new immigration of propagules, all populations delimited, sufficient
resources available to complete eradication, and adequate monitoring and evaluation
in place (Wilson et al. 2017).
There are 42 alien plant species listed as Category 1a in South Africa’s Alien &
Invasive Species Regulations, published in 2014 under the National Environmental:
Biodiversity Act (NEM:BA, Act 10 of 2004) (i.e. deemed as nation-wide eradication
targets). On investigation, several of these species have been found to be present at
many sites across the country (e.g. Iris pseudacorus (Yellow Flag) (Jaca and Mkhize
2015), and Furcraea foetida (Mauritian Hemp), although the formal process of
documenting the evidence and transfer of these species to more appropriate management categories has not been completed yet (see Chap. 20; Kumschick et al. 2020).
Several of the Category 1a species [Cabomba caroliniana, (Cabomba) and Euphorbia
esula (Leafy Spurge)] have not been found again, and might simply not be in the
country, while others are not known to have become invasive and were listed for
precautionary purposes (Henderson and Wilson 2017). Several of the species are found
21 The Extent and Effectiveness of Alien Plant Control Projects in South Africa
607