may be based on a historically-informed reference ecosystem (Prins et al. 2004), but
must also be realistic—i.e. they must consider the intensity of past degradation and
the ecological interventions necessary to promote recovery. Social and budgetary
constraints should also be considered to ensure that realistic goals are set.
There are many different contexts and goals for ecological restoration of alieninvaded sites. In degraded ecosystems that retain intact soils, the first restoration
action is usually to remove the invasive species, which may differ in structure and
functioning from the dominant components of the native vegetation, and to re-instate
ecosystem structure, either by stimulating the residual native seed bank or by
re-introducing propagules of representative guilds. In so doing, it is anticipated
that ecosystem functions and ecosystem services linked to these structural components will self-restore. However, it is important to collect baseline data on key
functions and services and to monitor changes after the interventions, to test these
assumptions and to modify the interventions as required. This approach is particularly important for invaded sites in areas identified as ecological infrastructure
(e.g. water catchments) or high importance for ecosystem-based adaptation to
climate change. In areas of high biodiversity importance, such as critically endangered ecosystems in global biodiversity hotspots, longer-term goals following the
control of invasive alien plants may include the restoration of community composition and viable species populations.
23.4.2 Prioritisation
Resources are limited, so prioritisation is key to efficient restoration. An objective
protocol that incorporates best-practice knowledge should be used, such as the
Analytical Hierarchical Process (AHP), to select those restoration projects of the
highest priority and/or likelihood of success (Mostert et al. 2018). AHP uses inputs
from key stakeholders, who may participate in defining and scoring criteria for
prioritisation, thus promoting a co-production approach during the planning process.
An important principle in prioritising restoration projects is to first target the least
degraded areas that have the highest potential for autogenic recovery (Holmes and
Cowling 1997; Strydom et al. 2017).
23.4.3 Costs and Benefits of Restoration Projects
Intact ecosystems comprise the natural capital that in economic terms represents the
stocks (i.e. component species) and the flows of ecosystem services upon which
society depends. Degradation by invasive alien species disrupts these stocks and
flows, and ecological restoration is required to reverse the impacts. However, what
are the costs and benefits of doing so, and are the costs justified? Examples are not
restricted to the improved ecosystem services delivered by the restored ecosystems,
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P. M. Holmes et al.
must also be realistic—i.e. they must consider the intensity of past degradation and
the ecological interventions necessary to promote recovery. Social and budgetary
constraints should also be considered to ensure that realistic goals are set.
There are many different contexts and goals for ecological restoration of alieninvaded sites. In degraded ecosystems that retain intact soils, the first restoration
action is usually to remove the invasive species, which may differ in structure and
functioning from the dominant components of the native vegetation, and to re-instate
ecosystem structure, either by stimulating the residual native seed bank or by
re-introducing propagules of representative guilds. In so doing, it is anticipated
that ecosystem functions and ecosystem services linked to these structural components will self-restore. However, it is important to collect baseline data on key
functions and services and to monitor changes after the interventions, to test these
assumptions and to modify the interventions as required. This approach is particularly important for invaded sites in areas identified as ecological infrastructure
(e.g. water catchments) or high importance for ecosystem-based adaptation to
climate change. In areas of high biodiversity importance, such as critically endangered ecosystems in global biodiversity hotspots, longer-term goals following the
control of invasive alien plants may include the restoration of community composition and viable species populations.
23.4.2 Prioritisation
Resources are limited, so prioritisation is key to efficient restoration. An objective
protocol that incorporates best-practice knowledge should be used, such as the
Analytical Hierarchical Process (AHP), to select those restoration projects of the
highest priority and/or likelihood of success (Mostert et al. 2018). AHP uses inputs
from key stakeholders, who may participate in defining and scoring criteria for
prioritisation, thus promoting a co-production approach during the planning process.
An important principle in prioritising restoration projects is to first target the least
degraded areas that have the highest potential for autogenic recovery (Holmes and
Cowling 1997; Strydom et al. 2017).
23.4.3 Costs and Benefits of Restoration Projects
Intact ecosystems comprise the natural capital that in economic terms represents the
stocks (i.e. component species) and the flows of ecosystem services upon which
society depends. Degradation by invasive alien species disrupts these stocks and
flows, and ecological restoration is required to reverse the impacts. However, what
are the costs and benefits of doing so, and are the costs justified? Examples are not
restricted to the improved ecosystem services delivered by the restored ecosystems,
676
P. M. Holmes et al.