required to test optimal treatment combinations. Examples of where this has been
explored for the Fynbos Biome in South Africa include: (1) highly degraded, alien
grass-dominated renosterveld shrubland, where a combination of fire or tillage and
herbicide treatments followed by active restoration sowing met the desired outcomes
(Waller et al. 2016); (2) mountain fynbos densely invaded by woody alien pines and
wattles, where alien clearance resulted in good spontaneous regeneration from the
soil-stored seed bank, but ecosystem structure was improved by sowing the seeds of
additional species that had been displaced (Holmes 2001b); and (3) lowland fynbos
that was densely invaded by alien wattles, where native seed banks were too depleted
to support spontaneous regeneration, necessitating active sowing to restore vegetation
structure after alien clearance (Hall 2018). These examples illustrate that even within
the same biome, different approaches may be required, depending on the ecosystem
affected, the invasive alien species and the type of degradation that has occurred at a
site. However, resource-intensive, active restoration interventions, such as comprehensive species sowing, may only be justifiable for priority threatened ecosystems.
Richardson et al. (2007) reviewed studies of riparian vegetation restoration
following alien plant invasions. They recommended that a framework for restoration
should consider biogeographical processes at different spatial scales, and specific
relationships between invasive alien plants, resilience and ecosystem functioning.
For example, large-scale, human-mediated changes, such as impoundments, can
alter downstream river geomorphology in favour of the invasive alien species and
limit the outcomes of reach-scale restoration (Rouwntree 1991).
23.2.4 Biological Invasions and Restoration Ecology
in South Africa
South Africa has been a prominent contributor to global invasion science since the
1980s (Macdonald et al. 1986; Richardson et al. 1997; Wilson et al. 2014), and the
management of invasions has been a strong component of this research (van Wilgen
2018). Given the importance of catchment areas for providing water and conserving
the country’s rich biodiversity, coupled with the escalating threat posed by alien
plant invasions in these areas, it is not surprising that ecological restoration has
developed here as a complementary research stream to invasion biology (van Wilgen
et al. 2016). The past two decades have seen a closer integration of the two
disciplines, in both theoretical and empirical research aspects (Gaertner et al.
2012a). Restoration ecology studies have enabled us to test our understanding of
ecosystem structure and functioning (Gaertner et al. 2011; Holmes and Richardson
1999), and to explore ways of improving restoration when managing alien-invaded
ecosystems (Holmes 2001b; Waller et al. 2016).
Disproportionate research attention has focussed on the Fynbos Biome, which
covers only 4% of South Africa. Early analyses showed that this Mediterraneanclimate biome was more severely invaded than other biomes, though not necessarily
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P. M. Holmes et al.
explored for the Fynbos Biome in South Africa include: (1) highly degraded, alien
grass-dominated renosterveld shrubland, where a combination of fire or tillage and
herbicide treatments followed by active restoration sowing met the desired outcomes
(Waller et al. 2016); (2) mountain fynbos densely invaded by woody alien pines and
wattles, where alien clearance resulted in good spontaneous regeneration from the
soil-stored seed bank, but ecosystem structure was improved by sowing the seeds of
additional species that had been displaced (Holmes 2001b); and (3) lowland fynbos
that was densely invaded by alien wattles, where native seed banks were too depleted
to support spontaneous regeneration, necessitating active sowing to restore vegetation
structure after alien clearance (Hall 2018). These examples illustrate that even within
the same biome, different approaches may be required, depending on the ecosystem
affected, the invasive alien species and the type of degradation that has occurred at a
site. However, resource-intensive, active restoration interventions, such as comprehensive species sowing, may only be justifiable for priority threatened ecosystems.
Richardson et al. (2007) reviewed studies of riparian vegetation restoration
following alien plant invasions. They recommended that a framework for restoration
should consider biogeographical processes at different spatial scales, and specific
relationships between invasive alien plants, resilience and ecosystem functioning.
For example, large-scale, human-mediated changes, such as impoundments, can
alter downstream river geomorphology in favour of the invasive alien species and
limit the outcomes of reach-scale restoration (Rouwntree 1991).
23.2.4 Biological Invasions and Restoration Ecology
in South Africa
South Africa has been a prominent contributor to global invasion science since the
1980s (Macdonald et al. 1986; Richardson et al. 1997; Wilson et al. 2014), and the
management of invasions has been a strong component of this research (van Wilgen
2018). Given the importance of catchment areas for providing water and conserving
the country’s rich biodiversity, coupled with the escalating threat posed by alien
plant invasions in these areas, it is not surprising that ecological restoration has
developed here as a complementary research stream to invasion biology (van Wilgen
et al. 2016). The past two decades have seen a closer integration of the two
disciplines, in both theoretical and empirical research aspects (Gaertner et al.
2012a). Restoration ecology studies have enabled us to test our understanding of
ecosystem structure and functioning (Gaertner et al. 2011; Holmes and Richardson
1999), and to explore ways of improving restoration when managing alien-invaded
ecosystems (Holmes 2001b; Waller et al. 2016).
Disproportionate research attention has focussed on the Fynbos Biome, which
covers only 4% of South Africa. Early analyses showed that this Mediterraneanclimate biome was more severely invaded than other biomes, though not necessarily
670
P. M. Holmes et al.