Conservation triage at the trailing edge of climate
Sophie L. Gilbert ,1Kate Broadley,2Darcy Doran-Myers,2Amanda Droghini,2
Jessica A. Haines ,2Anni H¨
ainen,3Clayton T. Lamb,2Eric W. Neilson,2and Stan Boutin2
1Department of Fish & Wildlife Sciences, University of Idaho, Moscow, ID, 83844, U.S.A., email firstname.lastname@example.org
2Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G0C5, Canada
3School of Optometry, Universit´
eal, QC CAN, H3T1P1, Canada
Species protection via geographically fixed conservation
actions is a primary tool for maintenance of biodiversity
worldwide (Pimm et al. 2014). Yet, for many species,
the assumption that currently suitable sites will remain
so is undermined by climate change (Urban 2015; Wiens
2016). Climate-change-associated range shifts (Chen et al.
2011), a process driven by populations at the trailing
edge of the climate envelope going extinct or moving and
those at the leading edge becoming established, are be-
coming widespread around the world (Wiens 2016). We
argue that conservation of populations of at-risk species
should be prioritized across each species’ range based on
future climatic suitability of an area with the goal of main-
taining or increasing the number of viable populations
range wide. Such range-wide prioritization could help
conserve species in a changing climate when resources
are limited; effort would be reallocated to viable popu-
lations (Oliver et al. 2012; Alagador & Cerdeira 2016).
Promisingly, resistance to this approach (Oliver et al.
2016) may be waning. Many nongovernment organiza-
tions (e.g., International Panel on Climate Change, World
Wildlife Fund) now use climate-informed range-wide ap-
proaches, as do some national and state agencies (e.g.,
Association of Fish & Wildlife Agencies 2018; Cornwall
2018). We aimed to advance discussion and implemen-
tation of climate-informed prioritization across species’
ranges and considered when populations behind the trail-
ing edge of climate change should be deprioritized.
Article impact statement: Resources should target leading edges of species’ climate envelopes rather than populations at the trailing edge of
Paper submitted November 25, 2017; revised manuscript accepted June 22, 2019.
An Urgently Needed Approach
Deprioritizing populations that are no longer viable under
climate change is critical but remains rarely discussed.
Most decision tools and conservation plans focus on en-
hancements within and on the leading edge of climate
envelopes (connectivity, habitat improvement, refugia
protection, and assisted migration [Jones et al. 2016]),
whereas decisions for trailing-edge populations are rarely
discussed. As climate conditions worsen at the trailing
edge, affected populations will near extinction despite
conservation actions (e.g., threat mitigation, protection
of habitat). Nevertheless, species-specific, geographically
static conservation actions are status quo and common.
One-fifth of protected areas worldwide aim to protect
specific species (IUCN 2008; Supporting Information).
For example, protection and restoration designed to stop
declines of woodland caribou (Rangifer tarandus cari-
bou) do not consider that these populations may already
be outside their climate envelope (Murray et al. 2015);
likewise, sea-level rise will eventually drive Florida key
deer (Odocoileus virginianus clavium) to extinction,
yet in situ conservation actions continue (Maschinski
et al. 2011).
Principles of conservation prioritization could be used
to reallocate resources from climate-change unviable
to climate-change viable populations within each at-
risk species’ shifting climate envelopes, which we term
trailing-edge triage. Unlike multispecies conservation
triage, in which resources are reallocated among species
2019 Society for Conservation Biology
Climate is driving decline of
a trailing-edge population?
Continue in situ
Population still present?
within the climate
Is remaining population
within the climate
Is there viable habitat within
the climate envelope?
intervention in situ
(a) (b) (c) (d) (e)
within the climate
Figure 1. Conceptual diagram of 4 primary scenarios (rectangles) and actions (ovals) resulting from the
difference between a protected-area (PA) designated for a population of a target species (solid-line polygon) and
the PA designed to encompass the species’ climate envelope (dashed-line polygon). Shown as an example are a
population of woodland caribou and their northward-shifting climate envelope. Scenarios are (a) no range shift;
(b) population shifts range, leaving unoccupied, but protected habitat; (c) population does not shift range, but is
not essential for species persistence; (d) protected population does not shift range, is essential, and viable habitat
exists elsewhere; and (e) protected population does not shift range, is critical, and no habitat exists elsewhere.
(Hobbs & Kristjanson 2003; Bottrill et al. 2008; Gerber
2016), trailing-edge triage allocates resources within the
range of a target species toward populations likely to
remain viable under future climate change and away from
those at the trailing edge, where efforts are least likely to
be effective (Oliver et al. 2012; Alagador et al. 2014). Such
an approach should maximize the preservation of biodi-
versity with limited resources in a changing climate. Four
primary scenarios could occur for populations behind the
trailing edge (Fig. 1). These scenarios and potential triage
actions do not encompass all the social, economic, and
political complexities inherent in conservation decision
making (Wintle et al. 2011; Hagerman & Satterfield 2014),
which are beyond the scope of this article but are critical
to resolve if trailing-edge triage is to succeed in the long
term (Sinclair et al. 2018). Further, our arguments also
apply to species assemblages of conservation concern
(e.g., coral reefs, short-grass prairie).
Determining which populations to deprioritize requires
species-specific, range-wide analysis of climate vulner-
ability to identify climate-change unviable and viable
populations so that resources can be reallocated. Range-
wide vulnerability analysis currently encompasses several
approaches (e.g., correlative, mechanistic, or trait-based
[Pacifici 2015]), and recent advances show promise for
integrating these approaches (Razgour et al. 2018). The
potential for in situ evolutionary adaptation to climate
change should simultaneously be facilitated and thresh-
olds for decline agreed on by decision makers prior to
prioritization (Doak & Morris 2010; Boutin & Lane 2014).
Careful analysis and decision making should be used to
disentangle interactive effects, reduce attribution uncer-
tainty, and make robust, adaptive decisions (Oliver &
Several frameworks exist that can inform decisions
about how to address climate-change unviable popula-
tions. They offer practical, detailed guidance (e.g., Oliver
et al. 2012; Alagador & Cerdeira 2016); therefore, we
only highlight the general process (Fig. 1). First, if a
population shifts range to keep pace with its climate
envelope, then what remains behind the trailing edge
is a remnant population and potentially a relict, species-
specific protected or management area (Fig. 1b). In this
situation, conservation actions, including continued habi-
tat protection, would likely cease (but not in multispecies
protected areas such as national parks) (Schneider et al.
2010; Alagador et al. 2014).
If a population cannot track the climate envelope and is
not critical to the persistence of the species (Fig. 1c), then
active management of that population would likewise
cease, although considerations such as maintenance of
genetic diversity must be taken into account. In contrast,
populations unable to follow their moving climate enve-
lope but deemed critical and with viable habitat (i.e.,
areas with suitable environmental and socioeconomic
conditions [Schneider et al. 2010; Corlett 2016]) else-
where (Fig. 1d) would require ex situ management, such
as assisted migration or captive breeding (Dawson et al.
2011). Finally, some populations deemed critical to the
persistence of a species would become stranded outside
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Gilbert et al. 3
their climate envelopes and would lack viable habitat
elsewhere (Fig. 1e). In this case, drastic and ongoing
interventions would be required (e.g., maintenance of
a conservation-reliant population [Shoo et al. 2013]).
Seizing the Opportunity
Unless geographically static conservation policies are
adapted to include trailing-edge triage, increasing con-
servation failures and economic costs are likely as popu-
lations fall behind the trailing edge of climate envelopes
and the cost of conserving them escalates. Yet, depriori-
tizing trailing-edge populations that are no longer climate-
change viable is so far a rarely adopted strategy.
We see a number of barriers to adoption, foremost
among which may be trepidation and loss aversion within
the conservation community. We acknowledge that triag-
ing trailing-edge populations is unsettling and therefore
suggest that further research into understanding and mit-
igating resistance to prioritization and triage is key to
further progress. There is a growing recognition of the
joint need to both increase and better allocate total con-
servation resources within the conservation community
(Hagerman & Satterfield 2014), which has sparked a sub-
sequent resurgence in discussions of conservation triage
(Cornwall 2018). Yet, some level of uncertainty will al-
ways remain when determining whether a population is
climate-change unviable, which points to the need for
involvement of social scientists (e.g., decision science,
behavioral economics, etc.) in the conservation prioriti-
zation process. Further, we see the evaluation of these
populations and their responses to climate change as
an ongoing process to be incorporated into an adaptive-
management framework. Regular monitoring and adap-
tive management will increase the chance of success.
Another key challenge to adoption of trailing-edge
triage is the multijurisdictional nature of prioritization
decisions. Inevitably, some target species will shift range
across intra- and international boundaries, challenging
resource-reallocation efforts, although existing multina-
tional agreements could be adapted or serve as a produc-
tive starting point (e.g., The Migratory Bird Treaty Act,
UN Convention on Migratory Species, Convention on Bi-
ological Diversity, and the Convention on International
Trade in Endangered Species).
Adoption of trailing-edge triage is urgent. Range shifts
are occurring faster than anticipated (Chen et al. 2011),
and protective policies that are spatially static could
erode public support due to real or perceived conser-
vation failure behind the trailing edge (Tam & McDaniels
2013). As the no-analog climate future unfolds, novel
tools such as trailing-edge triage could increase conserva-
tion success for at-risk species and provide a mechanism
for funding conservation efforts elsewhere in species’
ranges. Given the increasing interest in climate-informed
prioritization and the escalating costs of continued in-
vestment in trailing-edge populations, we suggest that
now is the time for rapid investment into all aspects of
trailing-edge triage and subsequent widespread adoption.
We thank, R. Serrouya, C. DeMars, M. Dickie, M. Peers, Y.
Majchrzak, and R. Schneider for productive discussions
of these ideas.
Calculations regarding species-specific protected areas
(Appendix S1) are available online. The authors are solely
responsible for the content and functionality of these
materials. Queries (other than absence of the material)
should be directed to the corresponding author.
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