more susceptible to alien plant invasions (Macdonald 1984). An unusual feature of
plant invasions in the fynbos is the prominence of alien trees and shrubs originating
from other Mediterranean-climate regions of the globe (Richardson et al. 1997).
Owing to the negative impacts of these alien species on ecosystem services, particularly water supply, and locally endemic and highly threatened biodiversity (the
Fynbos Biome has 38% of the country’s critically endangered ecosystems and 67%
of threatened plant taxa; Raimondo et al. 2009), research to document these impacts
was intensified (Richardson and van Wilgen 2004). A motivation to the national
government by stakeholders in the Fynbos Biome for a large-scale intervention for
alien control resulted in the “Working for Water” programme being initiated in 1995
(Marais and Wannenburgh 2008). This programme stimulated continued research
into the impacts of invasion and invasive alien control methods, including
restoration.
A significant discovery that revolutionised restoration in fynbos and other fireprone ecosystems is that chemicals in smoke stimulate germination in many taxa
(Brown 1993). This cue promotes seedling recruitment in the immediate post-fire
environment and can be used as a pre-treatment for seeds, in combination with heat
shock for some taxa, to optimise native species establishment in restoration projects
(Hall et al. 2017).
23.3 Restoration After Biological Invasion
23.3.1 The Restorative Continuum
An overarching goal of managing biological invasions is to halt or slow the spread of
the invaders, which entails intercepting invasion pathways and managing invaded
landscapes in an integrated way. For ecological restoration, however, the overarching goal is to optimise ecosystem recovery, i.e. structure and functioning, using
spontaneous regeneration or active interventions as the situation requires (McDonald
et al. 2016a, b; Aronson et al. 2017). These two goals can be synergistic, and optimal
restoration outcomes are most likely to result from good planning and implementation that integrates the research findings from both invasion biology and restoration
ecology.
If one considers the restorative continuum in relation to biological invasions, the
costs of ecosystem repair increase as a function of the extent, duration and intensity
of environmental damage caused by the invasive alien (Milton et al. 2003; Holmes
et al. 2007). It is therefore important to act early in the invasion process, before biotic
and abiotic thresholds have been crossed, as costs increase according to the number
of interventions required to restore a resilient, functional ecosystem (Aronson et al.
2007). In the case of highly modified habitats, such as road embankments or
quarries, removal of invasive alien species may be the only action needed to attain
the optimal goal, i.e. to halt spread of the invader. Active restoration interventions
such as native species re-introduction may not be warranted in such situations,
23 Biological Invasions and Ecological Restoration in South Africa
671
plant invasions in the fynbos is the prominence of alien trees and shrubs originating
from other Mediterranean-climate regions of the globe (Richardson et al. 1997).
Owing to the negative impacts of these alien species on ecosystem services, particularly water supply, and locally endemic and highly threatened biodiversity (the
Fynbos Biome has 38% of the country’s critically endangered ecosystems and 67%
of threatened plant taxa; Raimondo et al. 2009), research to document these impacts
was intensified (Richardson and van Wilgen 2004). A motivation to the national
government by stakeholders in the Fynbos Biome for a large-scale intervention for
alien control resulted in the “Working for Water” programme being initiated in 1995
(Marais and Wannenburgh 2008). This programme stimulated continued research
into the impacts of invasion and invasive alien control methods, including
restoration.
A significant discovery that revolutionised restoration in fynbos and other fireprone ecosystems is that chemicals in smoke stimulate germination in many taxa
(Brown 1993). This cue promotes seedling recruitment in the immediate post-fire
environment and can be used as a pre-treatment for seeds, in combination with heat
shock for some taxa, to optimise native species establishment in restoration projects
(Hall et al. 2017).
23.3 Restoration After Biological Invasion
23.3.1 The Restorative Continuum
An overarching goal of managing biological invasions is to halt or slow the spread of
the invaders, which entails intercepting invasion pathways and managing invaded
landscapes in an integrated way. For ecological restoration, however, the overarching goal is to optimise ecosystem recovery, i.e. structure and functioning, using
spontaneous regeneration or active interventions as the situation requires (McDonald
et al. 2016a, b; Aronson et al. 2017). These two goals can be synergistic, and optimal
restoration outcomes are most likely to result from good planning and implementation that integrates the research findings from both invasion biology and restoration
ecology.
If one considers the restorative continuum in relation to biological invasions, the
costs of ecosystem repair increase as a function of the extent, duration and intensity
of environmental damage caused by the invasive alien (Milton et al. 2003; Holmes
et al. 2007). It is therefore important to act early in the invasion process, before biotic
and abiotic thresholds have been crossed, as costs increase according to the number
of interventions required to restore a resilient, functional ecosystem (Aronson et al.
2007). In the case of highly modified habitats, such as road embankments or
quarries, removal of invasive alien species may be the only action needed to attain
the optimal goal, i.e. to halt spread of the invader. Active restoration interventions
such as native species re-introduction may not be warranted in such situations,
23 Biological Invasions and Ecological Restoration in South Africa
671