circumstances do negative impacts become apparent? (4) How can thresholds be
determined beyond which specific management plans should be implemented?
(Willis and Birks 2006: 1264). These questions lead us to various key concepts, as
outlined below.
5.1.1 Baseline and Range of Natural Variability
A central aspect of any analysis is determining the ‘baseline’ or ‘reference’ conditions against which current changes can be assessed (Willis and Birks 2006;
Froyd and Willis 2008; Willis and Bhagwat 2010; Willis et al. 2010; Bradshaw
et al. 2015). Froyd and Willis (2008) agree with Lindbladh et al. (2007) that the
“baseline is perceived as the ecosystem present before human influence became
pronounced on the landscape” (Lindbladh et al. 2007). “Baselines are especially
common in environmental regulation and ecosystem services” (Froyd and Willis
2008: 1724).
Closely related to this concept, Froyd and Willis (2008) also highlight the
‘Range of Natural Variability’ (RNV) of ecological systems; the central premise is
that “resilient ecosystems will be maintained if land management activities operate
within the range of conditions that would be expected under the natural disturbance
regime” (Froyd and Willis 2008: 1725). This concept is promoted by managers with
a vocation based on ecology, geography, etc. As these authors further explain,
“application of the RNV incorporates the ideas of a historical baseline period or
reference condition, but in addition the concept includes the implicit acknowledgement that ecological systems are not static and management applications
should therefore vary, yet within a defined boundary range” (Froyd and Willis
2008: 1725). The question of how far back we should set the baseline is not exempt
from dispute because it involves choosing a particular point on the space-time
continuum, and this choice is not easy when we know that the landscape has never
been static at any time in history. As Jackson and Hobbs (2009) point out,
ecosystems are dynamic, fluid, and ever-changing, making it difficult to identify
one moment in time to serve as a reference condition for the present situation.
5.1.2 Thresholds and Ecological Resilience and Persistence
In any case, it seems essential to set some thresholds, as Froyd and Willis (2008:
1726) indicated: “paleoecology holds great potential to inform conservation practice (…) through the identification of ecological thresholds, where the threshold is
an abrupt change in an ecosystem and a switch from one stable state to another. The
threshold concept is of particular interest to natural resource managers and policy
makers because of the potential to define limits on the amount of ‘acceptable’
change an ecosystem can withstand.”
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determined beyond which specific management plans should be implemented?
(Willis and Birks 2006: 1264). These questions lead us to various key concepts, as
outlined below.
5.1.1 Baseline and Range of Natural Variability
A central aspect of any analysis is determining the ‘baseline’ or ‘reference’ conditions against which current changes can be assessed (Willis and Birks 2006;
Froyd and Willis 2008; Willis and Bhagwat 2010; Willis et al. 2010; Bradshaw
et al. 2015). Froyd and Willis (2008) agree with Lindbladh et al. (2007) that the
“baseline is perceived as the ecosystem present before human influence became
pronounced on the landscape” (Lindbladh et al. 2007). “Baselines are especially
common in environmental regulation and ecosystem services” (Froyd and Willis
2008: 1724).
Closely related to this concept, Froyd and Willis (2008) also highlight the
‘Range of Natural Variability’ (RNV) of ecological systems; the central premise is
that “resilient ecosystems will be maintained if land management activities operate
within the range of conditions that would be expected under the natural disturbance
regime” (Froyd and Willis 2008: 1725). This concept is promoted by managers with
a vocation based on ecology, geography, etc. As these authors further explain,
“application of the RNV incorporates the ideas of a historical baseline period or
reference condition, but in addition the concept includes the implicit acknowledgement that ecological systems are not static and management applications
should therefore vary, yet within a defined boundary range” (Froyd and Willis
2008: 1725). The question of how far back we should set the baseline is not exempt
from dispute because it involves choosing a particular point on the space-time
continuum, and this choice is not easy when we know that the landscape has never
been static at any time in history. As Jackson and Hobbs (2009) point out,
ecosystems are dynamic, fluid, and ever-changing, making it difficult to identify
one moment in time to serve as a reference condition for the present situation.
5.1.2 Thresholds and Ecological Resilience and Persistence
In any case, it seems essential to set some thresholds, as Froyd and Willis (2008:
1726) indicated: “paleoecology holds great potential to inform conservation practice (…) through the identification of ecological thresholds, where the threshold is
an abrupt change in an ecosystem and a switch from one stable state to another. The
threshold concept is of particular interest to natural resource managers and policy
makers because of the potential to define limits on the amount of ‘acceptable’
change an ecosystem can withstand.”
110
A. Pèlachs et al.