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Chapter
ECOLOGICAL RESILIENCE: IS IT READY FOR OPERATIONALISATION IN
FOREST MANAGEMENT?
Gerardo Reyes1,2* and Daniel Kneeshaw
2
1Department of Interdisciplinary Studies, Lakehead
University,
Orillia, Ontario, Canada 2Centre for Forest Research, Department
of Biological Sciences,
University of Quebec in Montreal, Montreal, Quebec, Canada
ABSTRACT
Given the physiographic variability, variation in
socio-political landscapes, and
differences in connectedness of people and communities
associated with boreal forest
ecosystems, approaches to forest management that are flexible
enough to accommodate
this variation are needed. Moreover, to ensure sustainable
forest resource use, we need to
embrace the inherent complexity of boreal forest ecosystems
rather than eliminate it, and
be prepared to adapt and adjust as environmental conditions
change. While ecological
resilience may be a useful forest management objective to this
end, developing general
guidelines to integrate it into practice remains elusive. We
address a number of questions
often posed by managers when attempting to include ecological
resilience into forest
management planning. Our goal is to determine if the theoretical
foundation of ecological
resilience is sufficiently developed to provide a general
framework that can be applied for
boreal forest management.
Keywords: Boreal forests, ecological resilience, stability and
change, adaptation, forest
ecosystem management
* E-mail : [email protected];
[email protected].
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Gerardo Reyes and Daniel Kneeshaw 2
1. INTRODUCTION
Given the overwhelming environmental, social, and economic
importance of forests to
humankind, preoccupation is growing for promoting the
sustainable use of forest ecosystem
resources. Because of expected rapid changes in global
conditions over the next century
(Sokolov et al. 2009) and the potential consequences of these
changes to our well-being, it is
imperative that we develop and implement forest management
strategies that ensure forests
will continue to provide us with needed resources and services.
Ecological resilience, an
ecosystems ability to re-organize and adapt to disturbance or
environmental change without
shifting to an undesirable alternative state (Holling 1973,
Gunderson 2000), is a concept that
has been proposed to help us to achieve this objective.
Ecological resilience was conceptualized to help explain
unexpected and nonlinear
dynamics observed in complex adaptive systems (Holling 1973,
Gunderson and Holling
2002), thus providing a theoretical foundation towards
spatio-temporal understanding of how
boreal forest ecosystems may respond to any changes in climate,
natural and anthropogenic
disturbances, invasive species, resource utilisation, and so
forth. Managing for ecological
resilience is said to promote sustainability by enhancing a
forest ecosystems adaptive
capacity (Gunderson 2000, Allen and Holling 2010), defined as
the magnitude of an
ecosystems component species ability to respond and adapt to
disturbance or change before
collapsing and shifting to a new stability domain, even as the
shape or breadth of the domain
changes (Figure 1). In other words, maintaining or improving the
ability of species within
ecosystems to respond to episodic disturbances or gradual change
will improve an
ecosystems chance of avoiding progression towards an unwanted
ecological state (Holling
1973, Walker et al. 2004). Thus, forest ecosystems adapted to
natural as well as imposed
anthropogenic disturbance regimes will have greater capacity to
re-organize and retain
desired characteristics and functions, and by consequence be
more resilient. Central to this
tenet is that while post-disturbance conditions in resilient
ecosystems are not expected to be
exactly like those that existed prior to disturbance, as
structural and compositional changes
occur, the same critical processes driving the system are upheld
(e.g., photosynthetic capacity,
nutrient cycling, disturbance regime, etc.). Changes in critical
processes can drive an
ecosystem into a new stability domain and thus it is imperative
that we focus our attention on
understanding their roles in ecosystem maintenance.
Along with the direct changes to forest structure and natural
ecological processes caused
by forest management, climate change presents new and unique
challenges that will make
sustainable management of boreal forest ecosystems far more
difficult to achieve given the
potential for it to interact with processes such as nutrient and
hydrological cycling,
disturbance regimes, pollination, etc. (Bonan 2008, Berggren et
al. 2009, Huntington et al.
2009). Even now, fundamental changes to environmental conditions
are occurring at an
unprecedented rate (Bentz et al. 2010, Kilpelinen et al. 2010,
Fettig et al. 2013) and we are
uncertain about the nature, magnitude, and timing of the
effects. Given this uncertainty, an
adaptive approach for boreal forest ecosystem management is
essential. To this end, the idea
of making forest ecosystems resilient to these challenges is
certainly appealing. However,
operationalizing the concept; i.e., actively managing for
resilience has a number of stumbling
blocks that require attention.
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Ecological Resilience 3
Figure 1. Ball and cup conceptual model of ecological resilience
and ecosystem state change. Balls
represent different stable ecological states, each within a
domain of attraction controlled by a unique set
of processes. A threshold point is exceeded when a disturbance
or change is so intense, severe, or
frequent that an ecosystem is driven into a qualitatively
different stable ecosystem state and controlled
by a different set of ecological processes. In this example,
grassland, boreal forest, and heathland
ecosystems are shown. In (A) ecological states shift into
alternate stable states when disturbances of
sufficient magnitude or gradual changes drive them beyond
ecological threshold points and into
different domains of attraction; (B) the domain itself can
change in depth or width over time due to
slow changes in controlling processes (e.g., climate, acid
rain), also potentially causing shifts in
ecological state as well as changing an ecosystems overall
resilience. Red arrows with solid lines indicate changes within an
ecosystems natural range of variation. These shifts may be caused
by natural disturbances such as fire or insect outbreaks for which
ecosystem components have developed
adaptations to; i.e., the disturbances have historical
precedents. Red arrows with dotted lines indicate
that restoration effort may be required if attempting to shift a
system from an unwanted ecological state
back into another.
Modified from Gunderson (2000)
Our purpose here is to examine the applicability of ecological
resilience as a management
option in boreal forest ecosystems. We address a number of
questions directly related to
putting the concept on the ground for a hypothetical forest
management unit. Ultimately, we
wish to determine if the theoretical foundation of ecological
resilience is developed enough to
provide a general framework that can be applied for any boreal
forest management unit.
A
B
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Gerardo Reyes and Daniel Kneeshaw 4
2. INTEGRATING ECOLOGICAL RESILIENCE
INTO FOREST MANAGEMENT
Those involved with boreal forest management decisions usually
raise questions such as:
i. For what components of an ecosystem should we build
ecological resilience?
ii. What do we need to know to manage for ecological
resilience?
iii. At what spatio-temporal scales should we focus our
management efforts? and
iv. How do we determine if a system is resilient or not?
Proponents of resilience thinking have responded by stating
that:
managing for ecological resilience requires:
i. clearly defined stakeholder objectives;
ii. knowledge of critical processes and drivers that promote
ecosystem stability or
ecosystem change;
iii. knowledge of the ecological impacts of cultivating,
harvesting, or using various
ecosystem resources or services at multiple scales; and
iv. indicators of the adequacy of resilience via proxies such as
biological diversity,
structural heterogeneity, response diversity, and ecological
redundancy.
(Fischer et al. 2006, Campbell et al. 2009, Thompson et al.
2009)
For the remainder of this section, we address each of the above
questions in relation to
the responses in more detail.
2.1. For What Components of an Ecosystem Should We Build
Ecological
Resilience?
A starting point for operationalising ecological resilience is
for stakeholders to determine
what objectives to manage for. The question of resilience of
what to what? (Carpenter et al.
2001) forces managers to clearly define objectives for the
entire forest management unit and
explicitly specify their relative importance and spatio-temporal
impacts across the landscape.
This can include managing for timber supply, maintaining
biodiversity or old-growth forest,
provisioning of water, or providing opportunities for
recreational activities. However, it
should be recognized that managing for one desired aspect of an
ecosystem may reduce
resilience of another. This apparent paradox stems from what
Holling and Meffe (1996)
called a command and control approach to managing resources.
They note that managers
have simplified ecosystems to maximize the production of a
desired resource; and that it this
simplification that reduces the adaptability of a system and
thus the resilience of its non-
targeted components.
When entire forest management units are managed for only one
purpose, tradeoffs are
inevitable. We cannot maintain resilience for everything
everywhere because of fundamental
differences in species life history requirements, feedbacks and
interactions among species,
and conflicting stakeholder interests. For example, management
plans may include provisions
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Ecological Resilience 5
to enhance white-tailed deer (Odocoileus virginianus) habitat.
Large herd sizes provide
greater opportunities for hunters and naturalists but also
result in heavy browsing damage to
regenerating commercial tree species (Rooney and Waller 2003).
Moreover, improving
hunting opportunities entails having a mix of favorable habitat
types across the landscape that
includes conifer forest cover for shelter during winter, an
abundance of clearings that provide
herbaceous plants, forbs, and browse for deer to forage, as well
as maintaining logging roads
for human access (Voigt et al. 1997). Conversely, protecting
pine marten (Martes americana)
populations in the same forest management unit may require
maintaining large tracts of intact
mature mixed-coniferous forest containing spruce (Picea spp.),
fir (Abies spp.), or cedar
(Thuja occidentalis), and limiting the fragmentation across the
landscape that favours deer
(Watt et al. 1996). Many other associated plant and animal
species also draw benefits or are
negatively impacted by conditions that promote elevated deer
population densities (de Calesta
1994, Gill and Beardall 2001). Extremely high population
densities have, for example, shifted
the forest state on Anticosti Island from a balsam fir (Abies
balsamea) to white spruce (Picea
glauca) dominated forest with concomitant losses or decreases of
many herbaceous species
palatable to deer (Potvin et al. 2003, Morissette et al. 2009) .
Managing for a single resource
invariably reduces habitable conditions for other elements in
the ecosystem and may be a
critical driver for shifting ecological states.
2.2. What Do We Need to Know to Manage for Ecological
Resilience?
Whether our desire is to simply maintain a functioning forest
ecosystem or to maintain a
specific type of forest ecosystem, building ecological
resilience entails identifying the critical
processes that drive the ecosystem (Table 1). Species and
ecosystems are adapted to
ecological processes that have historical precedents (Peterson
2000, Read et al. 2004,
Johnstone et al. 2010). Retaining these processes is thus an
approach that can be proactively
used to maintain ecological resilience. This is in fact, the
original premise behind the
Emulating Natural Disturbance (END) concept (Gauthier et al.
2008). Moreover, if the focus
is centered on emulating processes rather than patterns END
would escape some (but perhaps
not all) of the critiques of managing for past patterns in a
changing environment.
Understanding the natural variability in processes and species
adaptations to them can
identify the type and range of processes that will maintain the
stability of a desirable state, as
well as those that will lead to unwanted ecosystem state
changes.
Natural processes that can lead to an ecosystem state change
includes paludification,
which results in the conversion of conifer forests in to peat
bogs over time (Lavoie et al.
2005). The process can be magnified by human activity when
dominant or correcting
processes are not understood. For example, severe fires that
burn into the moss layer can
reduce or reverse paludification whereas partial or less severe
disturbances such as windthrow
or senescence (e.g. pathogen caused tree mortality) that do not
disturb the soil (moss) layer
accelerate the process. Consequently, the blanket approach of
using harvesting that protects
soils and advance regeneration (Leblanc and Pouliot 2011)
creates conditions favourable for
stand conversion whereas more aggressive silvicultural
techniques that include scarification
would better emulate the soil disturbing processes that
naturally control paludification.
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Gerardo Reyes and Daniel Kneeshaw 6
Table 1. Factors that impact ecological resilience at various
spatial scales in boreal
forest ecosystems
scale Process Structure Other
environmental
factors
anthropogenic
impacts
Stand seed dispersal,
natural
regeneration,
competition,
pollination,
herbivory, disease,
photosynthesis,
respiration, evapo-
transpiration,
nutrient cycling,
allelopathy,
mycorrhizal
association
vertical,
horizontal, stand
density, relative
species mixes,
patch size &
shape
soil moisture,
pH, light
availability,
temperature,
nutrient
availability,
slope-aspect,
altitude, latitude,
Timber harvest,
soil erosion,
compaction,
land conversion,
invasive species,
climate change,
conversion,
structural and
compositional
simplification,
pollution
Landscape Natural
disturbance,
succession,
nutrient cycling,
hydrological
cycling,
paludification
Variation in
forest types &
age class, stand
pattern &
connectivity
Soil moisture,
nutrient
availability,
physiography
Fragmentation,
homogenization,
sedimentation &
waterflow
alteration,
climate change,
pollution
Region Primary
production climate
regulation
Variation in
forest types &
age class, patch
pattern &
connectivity
temperature,
precipitation,
CO2, ozone, N
deposition &
uptake,
physiography
Fragmentation,
homogenization,
sedimentation &
waterflow
alteration,
climate change,
pollution
Understanding the dominant processes and their interactions is
clearly an important step
to effective management. Such an understanding will be critical
when dealing with novel
combinations of disturbances such as the interaction of
allelopathy, clearcutting, and fire that
have resulted in some conifer forest ecosystems to be converted
to heathlands (Mallik 1995,
Payette and Delwaide 2003), invasive insect pests that can
substantially alter forest structure
and composition (Dukes et al 2009), and use of other
inappropriate harvesting analogues
(Nitschke 2005, Salonius 2007, Taylor et al. 2013).
Unprecedented changes to the historical frequency or severity of
natural disturbances is
also problematic. Fire regimes that are more frequent than the
age of sexual maturity of tree
species, for example, can lead to ecosystem change. Increased
frequency of stand-replacing
fires has resulted in conversion of aspen woodland to conifer
forest (Strand et al. 2009) and
conifer forests to grasslands (Heinselman 1981, Hogg and Hurdle
1995, Beckage and
Ellingwood 2008). Noble and Slatyer (1980) used knowledge of
these processes and tree
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Ecological Resilience 7
functional attributes to identify when and why species shifts
would occur as disturbance
processes changed. In fact, ecological research throughout
history has been about identifying
shifts in ecosystem states due to changes in natural
disturbances as well as those caused by
humans (Frelich and Reich 1998). Clements (1928) was concerned
about how the agricultural
practices of his time influenced the integrity of mid-plains
ecosystems. Holling (1978)
identified the importance of disturbance in maintaining
resilience; exemplified by the spruce
budworm (Choristoneura fumiferana) maintaining balsam fir
forests in the Maritimes by
killing the canopy and releasing understory trees whereas fire,
which is a rare disturbance in
this ecosystem, can lead to a different forest type. Thus,
processes that can cause ecosystem
collapse usually do not have historical precedents and are often
the result of anthropogenic
changes to the timing or severity of natural processes.
Accordingly, human disturbances
should be evaluated in light of the processes they affect and
the subsequent impacts on
species present across the landscape.
2.3. At What Spatio-temporal Scales Should We Focus Our
Management
Efforts?
Ecological resilience changes over time and space. Thus,
understanding the critical
processes driving a system must include knowledge of the
spatio-temporal scales over which
they operate and interact (e.g., Heinselman 1981, Gunderson and
Holling 2002, Mladenov et
al. 2008). Different ecological processes influence community
structure and composition at
different spatial and temporal scales (Ricklefs 1987, Herzog and
Kessler 2006, Sepp et al.
2009) (Figure 2). Certain processes can also have impacts across
scales of measure. These
processes often do not function in a simple linear fashion, nor
do they function independently
of one another (Peterson et al. 1998, Frelich and Reich 1999,
Groffman et al. 2006).
Extrapolating ecosystem responses to these processes by scaling
up or down may result in
erroneous assumptions and predictions due to non-linear
relationships, differences in
environmental characteristics at different scales, and emergent
properties (Peterson 2000,
Turner et al. 2001). Therefore, we need to understand if and how
critical processes impact our
forests at stand, management unit, and regional levels.
Effective management requires careful planning of how each
desired objective is
distributed across the forest management unit. Thus, the scope
should be large enough to
generate region-wide ecological benefits that compensate for
impacts of an objective at a
single site as well as the cumulative impacts of multiple
interventions of this and various
other objectives over time. For example, while the effects of
logging are site specific, we need
to consider the spatio-temporal impacts on the forest management
unit as a whole; not just
accommodate short-term and local needs or demands. If an
associated objective is to maintain
structural complexity across the landscape, including large
tracts of mature forest to provide
core habitat for wildlife and various aesthetic values, then a
mixture of large and small cuts
arranged in an aggregated pattern across the management unit
could allow for more intact,
interior forest conditions to be retained across the landscape
relative to a strategy creating
smaller, uniform patches distributed systematically. Over time,
a more fragmented landscape
with a greater edge-to-interior ratio may develop utilising the
systematic approach (Turner et
al. 2001).
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Gerardo Reyes and Daniel Kneeshaw 8
Figure 2. Some important processes affecting boreal forest
ecosystems across spatio-temporal scales.
2.4. How Do We Determine If a System Is Resilient or Not?
At this time, ecological resilience can only be coarsely
quantified using a proxy; i.e.,
measured in terms of the amount of biodiversity, structural
heterogeneity, response diversity,
and ecological redundancy. Biodiversity and structural
heterogeneity are defined as the
amount of variation in biological (genes, species, and
ecosystems) and structural elements
(vertical strata of extant vegetation, spatial arrangement of
patches, snags, coarse woody
debris, pit & mound topography, etc.), respectively (Hunter
1999). Response diversity is the
variation in responses of functionally similar species to
disturbance (Elmqvist et al. 2003); for
example, black spruce (Picea mariana) regenerates almost
exclusively from the abundant
seed rain after severe fire while white birch (Betula
papyrifera) and poplars (Populus spp.)
can reproduce via seed, but can also regenerate vegetatively.
Ecological redundancy is the
extent to which a forest ecosystem structure, process, or
function is substitutable if a
degradation or loss in the main species that provides that
particular attribute occurs (Folke et
al. 2004). A system having greater quantities of a proxy is
thought to be more resilient
(Loreau et al. 2003, Fischer et al. 2006). Response diversity
and ecological redundancy are
deemed particularly important as multiple species performing the
same critical function can
replace or compensate for substantial losses in a dominant
species, as well as display
variation in responses to disturbance or gradual change
(Thompson et al 2009).
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Ecological Resilience 9
An abundance of research shows that the chances of shifting into
another stability domain
increase when removal, reduction, or drastic changes to any of
these proxies occurs (e.g.,
Naeem et al. 1995, Loreau et al. 2003, Contamin and Ellison
2009). Larger impacts on critical
ecosystem processes are typically observed when there are fewer
species present, when the
dominant or keystone species are strongly affected, or when
functional redundancy is low
(Pastor et al. 1996, Lavorel et al. 2007, Rinawati et al. 2013).
Thus, greater species diversity
may confer greater ecological resilience (Hooper et al. 2005,
Fischer et al. 2006). Yet this
may not always be the case (e.g., Petchey and Gaston 2009). Some
boreal systems with
relatively low species diversity levels are also resilient. For
example, black spruce (Picea
mariana) and balsam fir (Abies balsamea) forest ecosystems both
have low functional
diversity and redundancy, yet are both highly resilient to
catastrophic fire and insect
disturbance, respectively (Pollock and Payette 2010, Boiffin and
Munson 2013).
Black spruce and balsam fir trees are well adapted to these
severe disturbances and have
a broad genetic diversity that can tolerate a wide range of
habitat conditions (Thompson et al.
2009). Thus, while high levels of diversity may not be expressed
at the species or community
levels of organization, at the genetic level, these species have
the necessary components for
renewal and reorganization. However, questions remain as to how
these ecosystems will
respond to climate change. Balsam fir, for example, regenerates
poorly after fire (Asselin et
al. 2001) while jack pine (Pinus banksiana) regenerates poorly
in its absence (Parisien et al.
2004). Boiffin and Munson (2013) observed shifts in species
dominance from black spruce to
jack pine after a period of unusually high fire activity that
caused changes in microhabitat
suitability for germination. Large scale changes to species
distribution patterns will likely
occur across the landscape if these periods of large fire years
become more frequent. Other
concomitant effects of climate change are also of concern.
Changes to habitat suitability for a
number of spruce beetle species (Dendroctonus spp.) along the
west coast of North America
have expanded the potential for their impacts in both altitude
and latitude (Bentz et al. 2010)
for example.
So how much diversity is enough to maintain resilience? Clearly
there is still much to be
resolved with this aspect of ecological resilience. It is
difficult to ascertain the quantity of a
proxy required for stability or which proxy is most important
for any particular forest
management unit given that differences in local physiographic
attributes, disturbance regimes,
and the spatial or temporal scale of measurement can change
expected contributions (Loreau
et al. 2002, Lavorel et al. 2007). Further, knowledge of the
functional roles of many species
remains incomplete (Grime 1998, Scherer-Lorenzen et al. 2005),
and thus it can be difficult to
judge the adequacy of response diversity or ecological
redundancy.
Management is facilitated by clear objectives and by concrete
numbers that support and
validate them; and ecological resilience theory, at this stage
of its conceptual development
cannot provide them. In the ball and cup model of Figure 1, this
equates to determining
exactly how close to a threshold edge an ecosystems current
state is, how quickly it can
tumble towards it, and how much a proxy can keep it from drawing
nearer or can drive it
away from collapse. Modeling that projects changes in critical
processes into the future is
only beginning (e.g., Hirota et al. 2011, Gustafson 2013, Lafond
et al. 2013) so detecting or
predicting critical changes such as shifts between stable
ecosystem states is still problematic.
Thus, it remains an enormous task to shift knowledge of the
adequacy of ecological resilience
from hindsight to a useful predictive tool as we still dont know
where thresholds are until
after they are crossed.
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Gerardo Reyes and Daniel Kneeshaw 10
But do we really need to know exactly where thresholds lie or
just the impacts of the
processes that lead to them? Shouldnt we be able to identify
signals of tumbling towards
shifts in forest ecosystem states, and use these signals as
qualitative indicators of the risks of
surpassing undesirable threshold points? As it is, we are not
even able to effectively identify
key species or their response functions (e.g., whole plant, stem
and below ground, or
regeneration traits) (Grime 1998, Scherer-Lorenzen et al. 2005,
Lavorel et al. 2007). Thus, the
precautionary principle; n.b., Leopolds (1949) argument that the
intelligent rule to tinkering
is not to get rid of any of the pieces, suggests that all
species should be maintained. Moreover,
a recent synthesis (Cardinale et al. 2012) suggests that
increased diversity also begets
increased ecosystem productivity, which implies that a call for
maintaining biodiversity does
not need to be based on altruism or ethical considerations but
may be for our own best
interest.
Perhaps another issue is that were expecting that managing for
ecological resilience (or
any other management option) should account for everything a
priori. Questions arise such
as: is management that promotes maintaining processes such as
disturbance regimes within
natural historical ranges of variation even useful if the
resultant patterns and relationships are
expected to change or decouple altogether with global change?
How do we know if oncoming
novel disturbance types and/or disturbance interactions will be
beyond what our forest
management unit can absorb? These are questions that perhaps no
amount of management or
management approach can truly account for a priori. This may
also require us to accept that
domain shifts will occur as conditions exceed the adaptations of
local species. For example, if
conditions become too xeric for moisture sensitive species such
as balsam fir. The ability to
adapt human institutions that depend on natural ecosystems will
thus be tantamount to socio-
ecological resilience as the ecosystems themselves
re-organize.
3. PUTTING IT ALL TOGETHER: THE WAY FORWARD
Ecological resilience may eventually be an important management
option. But at its
current conceptual iteration, there are too many details that
require development or resolution
prior to it being used as a general operational tool. In
particular, the lack of knowledge of a
number of critical processes and how they function and interact
across spatio-temporal scales,
the uncertainty associated with relationships between resilience
and the quantity of
biodiversity needed to maintain stability, as well as the lack
of quantitative approaches to
determine an ecosystems position in state space relative to
threshold points need addressing.
Despite this, there are several elements of ecological
resilience that are already being used in
contemporary forest management. Many of the requirements to
maintain ecological resilience
are the same factors central to other forest management
paradigms. For example,
contemporary forest management approaches guided by knowledge of
ecosystem processes
and functioning such as Ecosystem Management, Emulating Natural
Disturbance, and
Managing for Complexity are consistent with ecological
resilience principles (Holling 1978,
Grumbine 1994, Perera et al. 2007, Gauthier et al. 2008).
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Ecological Resilience 11
Figure 3. Conceptual diagram of the balance of social, economic,
and environmental objectives under
Forest Ecosystem Management linked across scales. We cannot
manage for everything everywhere. In
our example here, the ball represents an objective. In (a) an
economic objective takes precedence but
overall effects are beyond the adaptive capacity of the
ecosystem at the microsite scale but since there
are many sites within a stand if we manage at the stand scale
then the impacts at some sites will be
balanced out by others for stand level resilience (b) effects
can be balanced by applying conservation on
some sites and more intensive forestry somewhere else across the
landscape; (c) shows multiple
objectives across the region, each having a specific focus, but
impacts on other objectives are always
considered. Ecosystem function is maintained by processes that
can interact and affect the ecosystem at
one or a number of scales. Elimination of an objective occurs
when disturbance or slow change drives
species responsible for providing objective beyond the tipping
point (i.e., threshold limit of resilience) at the regional scale
(indicated by the dashed arrow). Restoration is now required to
re-introduce source
or basis of objective. Ecosystem collapse can occur when
detrimental impacts of an objective are
beyond the adaptive capacity of the groups of species
responsible for regulation of key ecosystem
processes driving the system. Link between scales is dependent
on the connectivity and pattern of forest
patches across scales and the processes controlling them.
An approach based on Ecosystem Management (Grumbine 1994), one
that integrates
various aspects of other contemporary paradigms at multiple
scales of focus will help
minimize risk of changing stability domains as well as maintain
processes and attributes
identified when asking from what to what. Managing forest
resources so that processes
remain within historic natural ranges of variability are
stressed, but stakeholders should be
flexible enough to adapt strategies as more information becomes
available. As in the TRIAD
approach to forestry management (Seymour and Hunter 1992), the
forest management unit
could be partitioned into zones where either social, economic,
or conservation objectives are
emphasized, the proportion of which are pre-determined by
stakeholder agreement, and this
pattern repeated across the landscape at various spatio-temporal
scales (Figure 3). At each
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Gerardo Reyes and Daniel Kneeshaw 12
scale of focus, an adaptive strategy is used. This is an
iterative approach wherein the effects
of management policy and stakeholder actions are periodically
evaluated and modified as
necessary; essentially, as outcomes from natural events and
management actions become
better understood (Holling 1978). Thus, it is a
multidisciplinary, dynamic, and multi-scalar
approach to Ecosystem Management based on processes responsible
for natural historic
ranges of variation. It emphasizes frequent communication,
research, and information
exchange among stakeholders. The use and modification of
procedures derived from
continuously updated knowledge of ecosystem dynamics is the
underlying premise for
stakeholder exchanges.
Consistent with the requirements for building ecological
resilience, this strategy
recognizes the importance of a range of variability in natural
processes in contributing to
forest ecosystem functioning. The strength of the approach would
be in the ability to identify
changes in conditions created by anthropogenic disturbances from
multiple viewpoints and at
multiple scales. Moreover, complexity and variation of forest
ecosystems are emphasized
rather than avoided while modeling and forecasting could
incorporate spatial structure and
processes, in addition to traditional modeling parameters
(Baskent and Yolasimaz 2000). So rather than focusing on attaining
a single optimal ecosystem condition, a range of acceptable
outcomes is managed for, and thus, potentially reducing
vulnerability to unforeseen
disturbance and gradual change across the entire forest
management unit; n.b., similar to the
ball and cup metaphor, this is analogous to having a number of
balls moving around in the
desired ecosystem state space at the same time (Figure 3).
CONCLUSION
Operationalising ecological resilience is an admirable goal. But
at this stage of its
conceptual development, its use in management planning is
limited. Instead it is perhaps best
used as a monitoring tool to evaluate the success of other
strategies (e.g., TRIAD, Ecosystem
Management, Emulating Natural Disturbances). Until our
understanding of critical processes
and ability to predict shifts in ecological states improves,
current management approaches
that draw attention to the processes driving ecosystem dynamics
across spatio-temporal
scales, as well as linking these processes with societal uses
and values should be emphasized.
ACKNOWLEDGEMENTS
Lively discussions and feedback from a number of individuals,
including H. Archibald,
H. Chen, B. Freedman, T. Gooding, B. Harvey, K. Hylander, T.
Jain, M. Kennedy, H.
Kimmins, N. Klenk, D. Kreutzweiser, L. Leal, C. Messier, A.
Miller, A. Mosseler, A. Park,
K. Peterson, K. Puettmann, M. Willison, L. Van Damme, S.
Woodley, and R. Tittler were
important in helping to develop ideas and clarify concepts
presented here.
-
Ecological Resilience 13
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