3. More emphasis and research efforts are needed on detailed plant-population-level
evaluations of the outcomes of biological control. But patience and persistence
are the key: too many biological control efforts are perceived as failures because
not enough time has elapsed, at least 10 years in many cases (McFadyen 1998),
for the agents to have built up sufficiently in numbers and to have had an impact
on target-plant populations. For example, an agent released against Pereskia
aculeata (Cactaceae; Barbados Gooseberry), at a limited number of sites in
South Africa, took 25 years, with numerous interventions to bolster its numbers,
before it had a significant impact on its target host.
4. The economic costs and benefits of biological control of invasive plants and gains
for agriculture, conservation, ecosystem services, and water supply in
South Africa are discussed by van Wilgen et al. (2004), De Lange and van
Wilgen (2010), van Wilgen and De Lange (2011), van Wilgen et al. (2012) and
by Zachariades et al. (2017). These authors reach consensus that biological
control of invasive plants is often more successful than other management
practices, is prominently used against some of South Africa’s worst invasive
species, and is highly cost-effective. Certainly, the interactions of scientists with
economists, over the last 25 years, has been crucial in convincing decisionmakers and managers that biological control is essential in efforts to suppress
problem plants.
5. Martin et al. (2018) have recently demonstrated the potential for extension of
research and implementation practices in biological control of invasive plants to
the wider community through employment opportunities and via innovative
educational and outreach programmes. These precedents should be more widely
applied in biological control and formally assessed for their socio-economic
benefits.
6. Biological control is seldom a ‘silver-bullet-solution’: it is one of several options
and strategies for the suppression of invasive alien plants. Early interventions
using biological control, before the problem has been allowed to escalate, may
maximise the suppression of plant invasions. South Africa has tried to adopt this
as an approach for biological control (Olckers 2004) but has not always
succeeded, largely because it is difficult to convince funders, landowners, and
conservationists to commit resources to an invasive-plant problem that seems
trivial and might never materialise.
7. Further, successful biological control is sometimes thwarted because other alien
plants replace those that have been controlled. For example, when floating,
aquatic invasive plant species are successfully controlled they may be replaced
by submerged aquatic invaders (Coetzee et al. 2011b), or in the case of the
suppression of invasive Acacia species, they are sometimes replaced by
Leptospermum laevigatum (Australian Myrtle) which itself is refractory to biological control (Gordon 2011). Implementation and optimal integration of biological control with other forms of management, and close monitoring to
document changes in populations of the invasive and the native flora, following
biological control, remain an ongoing challenge and goal for researchers and
managers.
19 Biological Control Against Invasive Alien Plants
567
evaluations of the outcomes of biological control. But patience and persistence
are the key: too many biological control efforts are perceived as failures because
not enough time has elapsed, at least 10 years in many cases (McFadyen 1998),
for the agents to have built up sufficiently in numbers and to have had an impact
on target-plant populations. For example, an agent released against Pereskia
aculeata (Cactaceae; Barbados Gooseberry), at a limited number of sites in
South Africa, took 25 years, with numerous interventions to bolster its numbers,
before it had a significant impact on its target host.
4. The economic costs and benefits of biological control of invasive plants and gains
for agriculture, conservation, ecosystem services, and water supply in
South Africa are discussed by van Wilgen et al. (2004), De Lange and van
Wilgen (2010), van Wilgen and De Lange (2011), van Wilgen et al. (2012) and
by Zachariades et al. (2017). These authors reach consensus that biological
control of invasive plants is often more successful than other management
practices, is prominently used against some of South Africa’s worst invasive
species, and is highly cost-effective. Certainly, the interactions of scientists with
economists, over the last 25 years, has been crucial in convincing decisionmakers and managers that biological control is essential in efforts to suppress
problem plants.
5. Martin et al. (2018) have recently demonstrated the potential for extension of
research and implementation practices in biological control of invasive plants to
the wider community through employment opportunities and via innovative
educational and outreach programmes. These precedents should be more widely
applied in biological control and formally assessed for their socio-economic
benefits.
6. Biological control is seldom a ‘silver-bullet-solution’: it is one of several options
and strategies for the suppression of invasive alien plants. Early interventions
using biological control, before the problem has been allowed to escalate, may
maximise the suppression of plant invasions. South Africa has tried to adopt this
as an approach for biological control (Olckers 2004) but has not always
succeeded, largely because it is difficult to convince funders, landowners, and
conservationists to commit resources to an invasive-plant problem that seems
trivial and might never materialise.
7. Further, successful biological control is sometimes thwarted because other alien
plants replace those that have been controlled. For example, when floating,
aquatic invasive plant species are successfully controlled they may be replaced
by submerged aquatic invaders (Coetzee et al. 2011b), or in the case of the
suppression of invasive Acacia species, they are sometimes replaced by
Leptospermum laevigatum (Australian Myrtle) which itself is refractory to biological control (Gordon 2011). Implementation and optimal integration of biological control with other forms of management, and close monitoring to
document changes in populations of the invasive and the native flora, following
biological control, remain an ongoing challenge and goal for researchers and
managers.
19 Biological Control Against Invasive Alien Plants
567