| Abstract: | Motivated by declines in biodiversity exacerbated by climate change, we identified a network of conservation sites designed to provide resilient habitat for species, while supporting dynamic shifts in ranges and changes in ecosystem composition. Our 12-y study involved 289 scientists in 14 study regions across the conterminous United States (CONUS), and our intent was to support local-, regional-, and national-scale conservation decisions. To ensure that the network represented all species and ecosystems, we stratified CONUS into 68 ecoregions, and, within each, we comprehensively mapped the geophysical settings associated with current ecosystem and species distributions. To identify sites most resilient to climate change, we identified the portion of each geophysical setting with the most topoclimate variability (high landscape diversity) likely to be accessible to dispersers (high local connectedness). These “resilient sites” were overlaid with conservation priority maps from 104 independent assessments to indicate current value in supporting recognized biodiversity. To identify key connectivity areas for sustaining species movement in response to climate change, we codeveloped a fine-scale representation of human modification and ran a circuit-theory-based analysis that emphasized movement potential along geographic climate gradients. Integrating areas with high values for two or more factors, we identified a representative, resilient, and connected network of biodiverse lands covering 35% of CONUS. Because the network connects climatic gradients across 250,000 biodiversity elements and multiple resilient examples of all geophysical settings in every ecoregion, it could form the spatial foundation for targeted land protection and other conservation strategies to sustain a diverse, dynamic, and adaptive world.Conservationists in the United States are not winning the battle to sustain biological diversity. Despite broad public support and unprecedented bipartisan agreement on Earth Day 1970, followed by landmark environmental laws, expanded regulatory efforts, and the establishment of hundreds of private conservation organizations, the species and ecosystems that characterize the natural world continue to decline. In North America, the abundance of birds has fallen 29% since 1970 (1); 32% of insect taxa are in decline (2); and 56% of mammalian carnivore and ungulates have shown notable range contractions since 1950 (3). Amphibians have declined an average (avg.) of 33% since 2002 (4). Of the 51,936 species of plants, vertebrates, and macroinvertebrates tracked by NatureServe for the conterminous United States (CONUS), 9% are ranked vulnerable, 12% imperiled, and 1% possibly extinct (5).*Changes in climate are exacerbating species declines, especially for small, isolated populations. As temperature and moisture regimes change, species ranges are shifting with speed and magnitude unprecedented in recent millennia. In the eastern United States, trees have shifted their centers of distribution 10 km north and 11 km west per decade since 1980 (6). Southern bird ranges have shifted northward by an avg. of 23.5 km per decade (7). These changes are on par with global shifts of 10 km north and 11 m upslope per decade across taxa groups (8).A primary driver of biodiversity decline is habitat loss and degradation resulting from land-use change (9, 10). Land- and water-conservation efforts can reverse these trends when strategically located and enabled by the necessary investments. In North America, billions of dollars spent on wetland restoration and management, combined with more stringent hunting regulations, reversed bird-abundance declines in wetlands (1). Globally, conservation investment from 1996 to 2008 reduced the extinction risk for mammals and birds by a median value of 29% (10). However, the effectiveness of land and water conservation in sustaining biodiversity depends on the representativeness of the conserved area network, the resilience and condition of the sites, and the connectivity between sites to allow for movement and adaptation (11, 12).To sustain biodiversity and facilitate adaptation of species to a changing climate, the Convention on Biological Diversity (CBD) Target 2 (13) calls for the protection of well-connected and effective systems of protected areas covering at least 30% of the planet. However, as climate change drives changes in species distributions and ecosystem composition, conservation plans based on current biodiversity patterns may become less effective at sustaining species (14). In particular, the current configuration of protected areas may fail to adequately provide access to the diverse climatic conditions needed for species populations to persist amid changing regional climates (12, 15, 16). Accordingly, conservation planners are beginning to focus on conserving sites that represent the earth’s eco-physiographic regions (hereafter “ecoregions”) and the spectrum of geophysical variation and a diversity of connected topographic microclimates (hereafter “topoclimates”) to allow species to adapt in situ or move to newly favorable areas, an approach known as Conserving Nature’s Stage (CNS) (15–19).Most studies of climate effects on biota use regional-scale climate-projection models combined with species vulnerability assessments to identify areas of relatively high threat or stability at a coarse scale. Here, we take a different approach. By focusing on geophysical diversity that shapes species distributions and fine-scale climate variation directly relevant to species persistence (20, 21), we aimed to identify enduring climate strongholds relevant under many climate scenarios and to map them at scales appropriate for land-conservation decisions.For species in topographically diverse locations, variability in temperature locally may exceed the degree of warming expected over the next century (22, 23). These areas have the potential to provide species with microclimatic buffering from regional climatic change by allowing local dispersal to more favorable microclimates or providing stepping stones to facilitate longer-distance range shifts (24, 25). Paleoecological records highlight the dynamic nature of species responses to Quaternary climate change, including the role of topography in creating climate refugia (26–28), and suggest that the CNS strategy may be appropriate for many taxa if it is purposefully designed to accommodate species responses to climate change (29).Species persisted under past climatic changes through in situ refugia combined with range shifts to track suitable climates (30–32). Rapid warming projected for the next century will likely require many species to adapt in a similar way (33–35), and many species’ ranges are already shifting (8). However, high levels of habitat loss and fragmentation due to anthropogenic activities are isolating populations and creating barriers to species movement that were not present during past periods of rapid climate change (29, 36, 37). Thus, conservation actions that maintain or increase connectivity are essential for effective conservation under climate change, as connectivity facilitates movement and gene flow, bolstering adaptive capacity by maintaining genetic diversity (38–40).To sustain biodiversity, a conservation network must also include sites that support living biotic assemblages reflecting each ecoregion’s geophysical properties, such as dominant habitats, unique communities, and viable examples of rare and specialist species populations. We refer to these as sites with “recognized biodiversity value.” Including them in a conservation network ensures that it is embedded with species and habitats that provide the capacity for adapting to climate change (41, 42). In the United States, state agencies and nongovernment organizations (NGOs) have identified over a thousand areas with recognized biodiversity value through comprehensive ecoregional or state-based assessments specifically targeting viable rare species populations, exemplary natural communities, and intact ecosystems. Integrating the footprint of these sites with spatial information on connected topoclimates and representative geophysical features helps confirm that the sites are collectively distributed across all abiotic “stages” needed to sustain biodiversity into the future. |
