Introduction
Wetlands such as swamps, marshes, and bogs contain a wealth of
biodiversity including many endemic and rare species (McLaughlin et al.
2017; Cartwright 2019). They also provide critical ecosystem services
such as water quality improvement, flood damage reduction, and
recreation and education opportunities (Randolph 2012). The unique
features of wetland landscapes support unusual local environments and
provide opportunities for species to survive in changing conditions,
making them candidates for climate refugia (Morelli et al. 2016;
McLaughlin et al. 2017). However, more research on the impacts of
climate change and the conservation management of these unique
ecosystems is needed (Cartwright and Wolfe 2016), in order to identify
appropriate climate-change adaptation strategies. This need is
pronounced for conventional reserve networks including protected
wetlands, because these conservation areas have typically not been
designated to address climate change (Araújo et al. 2011; Game et al.
2011; Schneider and Bayne 2015).
As climate conditions shift across continents, much conservation
research has focused on tracking analog climates (Carroll et al. 2018;
Parks et al. 2018; Fitzpatrick and Dunn 2019). Studies have examined
landscape connectivity among reserves with climate change (Andrello et
al. 2015), and projections of species future-ranges (Ramirez-Villegas et
al. 2014; Choe et al. 2017) or vegetation shifts (Powers et al. 2018) to
model theoretical networks of future conservation that incorporate
climate change (Heller et al. 2015). However, there is a need for a more
unified approach to analyzing climate connectivity across protected
areas such as national parks, nature reserves, and multiple-use
conservation areas (Belote et al. 2017) and for insular or rare
ecosystems (Cumming et al. 2010; Cartwright 2019) to inform questions
such as to which conservation areas might species need to move (Hannah
et al. 2007; Lawler and Hepinstall-Cymerman 2010) and whether dispersal
would result in species arriving at suitable, or analogous, climates to
those being lost.
We used a discrete network-based analysis to examine climatically
suitable arrival points for species being climatically dislodged from
wetland nodes in a climatic network of conservation areas. We used
wetlands in the United States National Wildlife Refuge System (NWRS)
that span the California floristic region (Burge et al. 2016), part of
the Pacific Northwest’s temperate coniferous forest region, and parts of
the desert ecosystems of Nevada to model analogous climates through
time. We considered the wetland in each NWRS unit (hereafter refuge) a
node within the network analysis, and the links are the climate
relations between nodes. The NWRS administers a network of lands and
waters for the conservation and management of wildlife species and their
habitats (U.S. Code 1997). Currently, the refuges in USA provide
habitats for over 700 bird species, 220 mammals, 250 reptiles and
amphibians, and 1000 fish species (National Wildlife Refuge System,
2016). Refuges from the NWRS system are particularly suitable for a
network analysis because they are spatially and environmentally isolated
by large intervening areas.
Climate change impacts are expected to be significant (Rannow et al.
2014) and some refuges may become climatically unsuitable for the
species the units were created to protect (Jewitt et al. 2017). This
research was motivated by the question of whether suitable
climate-conditions for dislodged protected species might occur or emerge
at other nodes in the network, thereby making those nodes candidates for
possible species relocations. In such cases, some nodes may lose their
functions as habitats, but others may become more climatically suitable
as species’ habitats. Thus, developing a climate classification of nodes
within a conservation network of wetlands is useful for conservation
management.
We focused on the site-level climate conditions of refuges and examined
the climate networks among 48 existing refuges (43 national wildlife
refuges and 5 wildlife management areas) for present and future periods
from the “climate-analog” point of view. Climate-analog analysis has
the advantage that it does not need to make assumptions about the
tolerances of species (Veloz et al. 2012), and can help to identify the
most important or highly exposed areas among the refuges for resource
management. For example, Parks et al. (2018) identified the
climate-analog of mountainous ecoregions of the western US to evaluate
how climate change may influence fire regime and vegetation shifts. The
climate-analog approach can be applicable to other environments or
regions (Veloz et al. 2012), but we have not seen the application of
this approach to conservation area networks.
Here we ask how many types of temporal climate connections exist for a
set of wetland conservation areas? We define the current climate
conditions of each refuge and identify others with analogous climates.
Then, we identify where each refuge’s current climate can be found in
the future using climate change projections to understand the climate
network of each unit. Our objectives are to identify the temporal
climate networks among the refuges under future climate projections, to
classify the units using their relative climate importance based on
their climate classes for efficient conservation management of the NWRS
system, and to consider the utility of climate analog classifications
within a conservation network.