alternate stable states, one dominated by floating invasive plants and the other by
submerged invasive plants, with biological control triggering the shift between these
stable states (Strange et al. 2018).
4.8 Discussion
We have shown that biological control has played a significant role in the recovery of
aquatic biodiversity (Midgley et al. 2006; Coetzee et al. 2014), but such biodiversity
benefits will be short-lived in impacted ecosystems unless integrated catchment
management addresses eutrophication. If not, new invasions will replace the plants
that have been cleared. To minimise the impacts of invasive submerged plants,
research in South Africa must now focus on understanding the mechanisms facilitating these new invasions, and on devising successful management strategies. Such
strategies must also address ecosystem-level responses to control to improve the
chances of long-term success. Traditionally, intervention has been aimed at restoring
ecosystems dominated by an invasive species by removing the invader (Dobson
et al. 1997; Prach et al. 2001; Young 2000). However, when we consider such
restoration in the context of regime shifts between degraded stable states, there is a
clear need to adopt a more holistic approach. It is important to consider the effect that
invasive species have upon the multitrophic interactions that define ecosystem
structure and functioning. Further multitrophic studies could also help to elucidate
the drivers that determine levels of success and failure in the establishment of both
invasive species, and their biological control agents (Harvey et al. 2010).
Identifying management interventions that will be both successful and economically justifiable will require a thorough understanding of the affected ecosystem as a
whole. The most efficient management can be obtained by prioritising those systems
where management interventions would be most likely to succeed. South Africa is in
the relatively early stages of research into the control of submerged invasive
macrophytes. Experience gained in South Africa in the successful biological control
of floating invasive plants may well be the route to follow. It can be a lengthy
process, but could well deliver excellent results.
The single most important mitigation measure to reduce further impacts of
invasive macrophytes is prevention of invasions at the outset (Tamayo and Olden
2014). Although legislation to prevent introduction and enforce management of
invasive alien species does exist, the lack of financial resources and manpower to
implement these legal requirements remains a challenge. Furthermore, it is important
to coordinate actions against invasive macrophytes in neighbouring countries, otherwise a species that is being controlled or eradicated in one country might simply
reinvade from an invaded neighbouring country through shared watersheds, rendering all efforts futile (Faulkner et al. 2017). This would require an effective
biosecurity approach that builds on knowledge of potential invaders and invadable
systems, and pathways of introduction and spread, incorporated into early detection
and rapid response programmes (Hussner et al. 2017). Recent improvements in
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M. P. Hill et al.
submerged invasive plants, with biological control triggering the shift between these
stable states (Strange et al. 2018).
4.8 Discussion
We have shown that biological control has played a significant role in the recovery of
aquatic biodiversity (Midgley et al. 2006; Coetzee et al. 2014), but such biodiversity
benefits will be short-lived in impacted ecosystems unless integrated catchment
management addresses eutrophication. If not, new invasions will replace the plants
that have been cleared. To minimise the impacts of invasive submerged plants,
research in South Africa must now focus on understanding the mechanisms facilitating these new invasions, and on devising successful management strategies. Such
strategies must also address ecosystem-level responses to control to improve the
chances of long-term success. Traditionally, intervention has been aimed at restoring
ecosystems dominated by an invasive species by removing the invader (Dobson
et al. 1997; Prach et al. 2001; Young 2000). However, when we consider such
restoration in the context of regime shifts between degraded stable states, there is a
clear need to adopt a more holistic approach. It is important to consider the effect that
invasive species have upon the multitrophic interactions that define ecosystem
structure and functioning. Further multitrophic studies could also help to elucidate
the drivers that determine levels of success and failure in the establishment of both
invasive species, and their biological control agents (Harvey et al. 2010).
Identifying management interventions that will be both successful and economically justifiable will require a thorough understanding of the affected ecosystem as a
whole. The most efficient management can be obtained by prioritising those systems
where management interventions would be most likely to succeed. South Africa is in
the relatively early stages of research into the control of submerged invasive
macrophytes. Experience gained in South Africa in the successful biological control
of floating invasive plants may well be the route to follow. It can be a lengthy
process, but could well deliver excellent results.
The single most important mitigation measure to reduce further impacts of
invasive macrophytes is prevention of invasions at the outset (Tamayo and Olden
2014). Although legislation to prevent introduction and enforce management of
invasive alien species does exist, the lack of financial resources and manpower to
implement these legal requirements remains a challenge. Furthermore, it is important
to coordinate actions against invasive macrophytes in neighbouring countries, otherwise a species that is being controlled or eradicated in one country might simply
reinvade from an invaded neighbouring country through shared watersheds, rendering all efforts futile (Faulkner et al. 2017). This would require an effective
biosecurity approach that builds on knowledge of potential invaders and invadable
systems, and pathways of introduction and spread, incorporated into early detection
and rapid response programmes (Hussner et al. 2017). Recent improvements in
110
M. P. Hill et al.