et al. 2017). One estimate (McConnachie et al. 2016) suggested that the invaded
area in the fynbos-clad Hawequas mountains would have been almost 50% higher
if control operations had not been carried out. Ongoing control has also reduced
the extent of invasions of several species in savanna ecosystems, including
Lantana camara, Opuntia stricta, and Chromolaena odorata (van Wilgen et al.
2017; Dew et al. 2017; te Beest et al. 2017). At several localised sites, therefore,
control measures have been effective. The picture changes when progress is
assessed at a national scale, however, because plant invasions have generally
continued to grow, some substantially (Henderson and Wilson 2017). Meaningful
progress in reducing widespread invasions to a maintenance level, therefore, can
arguably only be made if the available funding is focused on priority sites and
species (Box 21.2). Essentially, the conscious practice of conservation triage
(Bottrill et al. 2008) will need to be introduced, and this will require agreement
on which species, and which areas, to target for control. Because alien plants
spread more rapidly than they are being removed, current control efforts could fail
if funds are spread too thinly, as suggested by modelling exercises (Higgins et al.
1997; van Wilgen et al. 2016). If adequate funding were re-directed to agreed
priority areas, then the chances of achieving control in those areas would increase.
Similarly, by focussing on priority species, scarce funds could be concentrated
where they would be most effective. For example, funding for the control of Pinus
and Australian Acacia species in fynbos is divided equally between these two taxa
(van Wilgen et al. 2016). Pinus species, however, will eventually cover a much
larger area than Acacia species if allowed to spread. If funds were diverted from
Acacia species (which are under more effective biological control) to Pinus, then
the eventual outcome would be far more favourable. Although prioritisation
studies have already been initiated (e.g. Forsyth et al. 2012), it is going to be
challenging to get managers to accept the need for triage, because terminating
projects where funds have already been expended will understandably meet with
resistance (see also Foxcroft et al. 2020, Chap. 28, Sect. 28.7). In conclusion, the
implementation of focused, well-funded and well-managed control measures
should bring invasions down to a maintenance level in many priority areas.
Such interventions should bring very attractive returns on investment, but they
will require some fundamental changes to the current modus operandus.
Box 21.2 Wisdom from the Past
Alien plant control has been considered, and practiced, in South Africa for
many decades. The question arises as to whether we can learn from this
experience. Two quotes, in particular, seem relevant.
In his report on the conservation of the vegetation of the Cape Floristic
Region, Prof. C.L. Wicht noted that “it seems, at present, that unless enormous sums of money are expended on their [invasive alien plant] eradication
or control they will become dominant everywhere except in nature reserves
and other selected areas where they will constantly be destroyed”
(continued)
622
B. W. van Wilgen et al.
area in the fynbos-clad Hawequas mountains would have been almost 50% higher
if control operations had not been carried out. Ongoing control has also reduced
the extent of invasions of several species in savanna ecosystems, including
Lantana camara, Opuntia stricta, and Chromolaena odorata (van Wilgen et al.
2017; Dew et al. 2017; te Beest et al. 2017). At several localised sites, therefore,
control measures have been effective. The picture changes when progress is
assessed at a national scale, however, because plant invasions have generally
continued to grow, some substantially (Henderson and Wilson 2017). Meaningful
progress in reducing widespread invasions to a maintenance level, therefore, can
arguably only be made if the available funding is focused on priority sites and
species (Box 21.2). Essentially, the conscious practice of conservation triage
(Bottrill et al. 2008) will need to be introduced, and this will require agreement
on which species, and which areas, to target for control. Because alien plants
spread more rapidly than they are being removed, current control efforts could fail
if funds are spread too thinly, as suggested by modelling exercises (Higgins et al.
1997; van Wilgen et al. 2016). If adequate funding were re-directed to agreed
priority areas, then the chances of achieving control in those areas would increase.
Similarly, by focussing on priority species, scarce funds could be concentrated
where they would be most effective. For example, funding for the control of Pinus
and Australian Acacia species in fynbos is divided equally between these two taxa
(van Wilgen et al. 2016). Pinus species, however, will eventually cover a much
larger area than Acacia species if allowed to spread. If funds were diverted from
Acacia species (which are under more effective biological control) to Pinus, then
the eventual outcome would be far more favourable. Although prioritisation
studies have already been initiated (e.g. Forsyth et al. 2012), it is going to be
challenging to get managers to accept the need for triage, because terminating
projects where funds have already been expended will understandably meet with
resistance (see also Foxcroft et al. 2020, Chap. 28, Sect. 28.7). In conclusion, the
implementation of focused, well-funded and well-managed control measures
should bring invasions down to a maintenance level in many priority areas.
Such interventions should bring very attractive returns on investment, but they
will require some fundamental changes to the current modus operandus.
Box 21.2 Wisdom from the Past
Alien plant control has been considered, and practiced, in South Africa for
many decades. The question arises as to whether we can learn from this
experience. Two quotes, in particular, seem relevant.
In his report on the conservation of the vegetation of the Cape Floristic
Region, Prof. C.L. Wicht noted that “it seems, at present, that unless enormous sums of money are expended on their [invasive alien plant] eradication
or control they will become dominant everywhere except in nature reserves
and other selected areas where they will constantly be destroyed”
(continued)
622
B. W. van Wilgen et al.