in private gardens [e.g. Triplaris americana (Ant Tree)]. While this does not preclude
eventual eradication, it complicates both control efforts and our ability to declare a
species eradicated. A few Cactaceae species have (or will likely in future have) effective
biocontrol agents, such that nation-wide eradication would probably not be required for
adequate control to be effected. Consequently, only around a third of the species listed
in Category 1a are still the focus of on-going eradication efforts. By contrast, many
other taxa that are not yet listed in the regulations have been identified as eradication
targets and are subject to control efforts [e.g. Acacia viscidula (Sticky Wattle), and
Melaleuca parvistaminea (Rough-barked Honey Myrtle) (Magona et al. 2018; Jacobs
et al. 2014)].
The mismatch between legal status and feasibility of eradication discussed above
highlights the need to set eradication as the management goal only once a formal
detailed assessment of eradication feasibility has been conducted. Such assessments
require investment in delimitation and pilot control measures (Wilson et al. 2017). It
is also clear that there is a substantial invasion debt in the country (Rouget et al.
2016)—many alien plants have only naturalised or invaded a few sites, and there are
likely to be many that are still to be detected.
In the decade that the SANBI programme has been active, no alien plant species
had been formally declared as eradicated. The project closest to achieving eradication is probably that against Spartina alterniflora (Smooth Cordgrass), a grass
invading the Knysna estuary in the Western Cape. However, the conditions under
which eradication can be declared have not been specified, nor is it clear why the
plant was introduced in the first place, so the possibility of reintroduction has not
been ruled out (Riddin et al. 2016). Detailed point patterns have been produced for a
number of species (Wilson et al. 2013), and insights have been gained in terms of
efforts to delimit populations (Jacobs et al. 2014), produce risk maps (Kaplan et al.
2014), estimate the costs of eradication (Moore et al. 2011), and the continuing need
for morphological and molecular taxonomy (Magona et al. 2018; Jacobs et al. 2017).
The SANBI programme has funded postgraduate students to work on particular
species or taxa, and produced an increasing number of published analyses of risk
analyses, impact assessments, and estimates of eradication feasibility (Kumschick et
al. 2020). However, the programme has suffered from similar issues to other projects
funded under the WfW umbrella. The onus has been to report on input indicators
(e.g. person days of employment), and few or no data are routinely collected on
output indicators (e.g. the number of plants present). When assessed against the
requirements set by the National Status Report on Biological Invasions (van Wilgen
and Wilson 2018), the project planning was evaluated as being inadequate across the
board. These are solvable issues, but will require a shift in approach to ensure that
dedicated teams focus on specific targets year on year, that data are collected, and
that monitoring data feed back into decision-making both at a project level and as
input to the regulatory changes. If the global best practices regarding alien plant
incursion response are applied (e.g. Wilson et al. 2017), then we can expect to see an
increasing number of declared alien plant eradications in the next decade. For some
taxa, particularly those with long-lived seed-banks (Zenni et al. 2009; Wilson et al.
2011), eradication might only be achieved far in the future, but it is feasible given
persistence and effective monitoring.
608
B. W. van Wilgen et al.
eventual eradication, it complicates both control efforts and our ability to declare a
species eradicated. A few Cactaceae species have (or will likely in future have) effective
biocontrol agents, such that nation-wide eradication would probably not be required for
adequate control to be effected. Consequently, only around a third of the species listed
in Category 1a are still the focus of on-going eradication efforts. By contrast, many
other taxa that are not yet listed in the regulations have been identified as eradication
targets and are subject to control efforts [e.g. Acacia viscidula (Sticky Wattle), and
Melaleuca parvistaminea (Rough-barked Honey Myrtle) (Magona et al. 2018; Jacobs
et al. 2014)].
The mismatch between legal status and feasibility of eradication discussed above
highlights the need to set eradication as the management goal only once a formal
detailed assessment of eradication feasibility has been conducted. Such assessments
require investment in delimitation and pilot control measures (Wilson et al. 2017). It
is also clear that there is a substantial invasion debt in the country (Rouget et al.
2016)—many alien plants have only naturalised or invaded a few sites, and there are
likely to be many that are still to be detected.
In the decade that the SANBI programme has been active, no alien plant species
had been formally declared as eradicated. The project closest to achieving eradication is probably that against Spartina alterniflora (Smooth Cordgrass), a grass
invading the Knysna estuary in the Western Cape. However, the conditions under
which eradication can be declared have not been specified, nor is it clear why the
plant was introduced in the first place, so the possibility of reintroduction has not
been ruled out (Riddin et al. 2016). Detailed point patterns have been produced for a
number of species (Wilson et al. 2013), and insights have been gained in terms of
efforts to delimit populations (Jacobs et al. 2014), produce risk maps (Kaplan et al.
2014), estimate the costs of eradication (Moore et al. 2011), and the continuing need
for morphological and molecular taxonomy (Magona et al. 2018; Jacobs et al. 2017).
The SANBI programme has funded postgraduate students to work on particular
species or taxa, and produced an increasing number of published analyses of risk
analyses, impact assessments, and estimates of eradication feasibility (Kumschick et
al. 2020). However, the programme has suffered from similar issues to other projects
funded under the WfW umbrella. The onus has been to report on input indicators
(e.g. person days of employment), and few or no data are routinely collected on
output indicators (e.g. the number of plants present). When assessed against the
requirements set by the National Status Report on Biological Invasions (van Wilgen
and Wilson 2018), the project planning was evaluated as being inadequate across the
board. These are solvable issues, but will require a shift in approach to ensure that
dedicated teams focus on specific targets year on year, that data are collected, and
that monitoring data feed back into decision-making both at a project level and as
input to the regulatory changes. If the global best practices regarding alien plant
incursion response are applied (e.g. Wilson et al. 2017), then we can expect to see an
increasing number of declared alien plant eradications in the next decade. For some
taxa, particularly those with long-lived seed-banks (Zenni et al. 2009; Wilson et al.
2011), eradication might only be achieved far in the future, but it is feasible given
persistence and effective monitoring.
608
B. W. van Wilgen et al.