Tess O’Sullivan slips off her daypack and reclines against a white-barked tree. The shade of this aspen grove dissipates the August heat. It’s an ideal spot to break after a morning’s hike in the high desert sagebrush of Idaho’s Pioneer Mountains. O’Sullivan, the land conservation strategy lead for The Nature Conservancy in Idaho, sifts through her pack just as three dusky grouse flush out from a patch of brush. Overhead, chickadees flit from branch to branch. Elk droppings are scattered in moist seeps throughout the thicket.
It’s not difficult to see the appeal of aspen in the high desert, whether you’re a human on a hike or a foraging elk. But this stand of trees is more than an oasis. Scientists call it a microhabitat, and this variation in the landscape—like a steep slope, a deep snowdrift or a pool of water—may be the key to helping species adapt to climate change.
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Conservation has traditionally focused on where the wild things are. (Want to protect spotted owls? Preserve a stand of old-growth forest in the Pacific Northwest.) But it’s increasingly becoming clear that to protect biodiversity in the face of climate change, conservationists need to focus on where the wild things are going to be.
Many of the world’s species are already on the move. In North America, species have shifted their ranges approximately 11 miles north and 36 feet in elevation each decade. Some species are approaching the limit of where they can go to find hospitable climates—and some can’t move as fast as they need to. A United Nations report released in 2019 estimated about half a million of the planet’s terrestrial species lack sufficient habitat to survive long-term.
For more than a decade, Mark Anderson, TNC’s director of science for the eastern United States, has helped the organization develop an innovative and dynamic approach to conserving land so species have room to thrive. “To discover what makes one area more resilient than the next, we looked at the properties of the land itself,” says Anderson. “We need to protect nature in a way that allows species to move and change regardless of the exact climate scenarios.”
Instead of predicting how high temperatures will rise, how much precipitation will fall or how soon snowpacks will melt, a cohort of more than 150 TNC scientists led by Anderson identified a spectrum of habitats best equipped to support species through climate shifts.
The 2.4 million acres from the peaks of the Pioneer Mountains to the lava fields of Craters of the Moon National Monument and Preserve are part of this newly mapped network of resilient lands. These safe havens—like O’Sullivan’s stomping grounds in the south central part of the state—boast a variety of microhabitats, are rich in biodiversity and allow species to freely move to adjacent strongholds.
“A map of resilient places helps us prioritize land conservation in Idaho,” says O’Sullivan. “This isn’t just about protecting land that is important to wildlife now; it’s about protecting land that is going to be important for the future.”
To identify which lands in the United States are most resilient to climate change and can support the most diverse range of plants and animals, Anderson and his team started by combing through a vast database of spatial information, some of which has been collected across TNC’s nearly 70-year history. Researchers profiled every acre of land in the lower 48 states, noting ecological features (such as landforms, elevation zones and wetlands) and cataloging land use (including the presence of development, agriculture and energy infrastructure). In the process, a handful of characteristics surfaced that scientists began to recognize as the hallmarks of resilience.
One strong indicator is the availability of local habitats with varying topography, soil composition and elevation, which offer a range of climates for flora and fauna. In Idaho’s Pioneers, they could be isolated meadows or the canopy cover furnished by aspen groves.
“The direction a slope faces, low wet basins, little islands of habitat—these all influence the temperature near the ground,” says Anderson. As the world warms, he says, landscapes that offer a range of physical environments and corresponding temperature gradients will allow communities of species to move around without having to move on.
Another sign of resilience is biodiversity. For decades, TNC has focused on preserving areas with intact habitats and populations of rare species.
In Idaho, a rocky moonscape of former lava flows transforms into sagebrush prairie before giving way to the undulating, conifer-studded foothills of the Pioneers. This varied landscape of public wildlands and private working lands supports sage grouse and redband trout, badgers and beavers, wolves and wolverines.
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But a place bursting with biodiversity and marked with microhabitats is not enough. Take the aspen grove: It provides food and cover for animals like elk and mule deer. But if wildlife has to traverse highways and developments to reach it, it’s less of a refuge and more of a risk. To be resilient, a landscape needs to be connected to others like it.
“A wild animal isn’t perceiving long-term shifts in climate,” says Anderson. “It’s perceiving subtle shifts around it. It moves not because the temperature is increasing every year, but because it needs to find food, water and cover.”
Each spring, about 500 pronghorn migrate west across Idaho from their wintering range at the base of the Continental Divide, through a bottleneck at the north end of Craters of the Moon—driven by a biological need to breed and feed on nutrient-dense vegetation found in the foothills of the Pioneers. This Pleistocene mammal, known for its ability to run up to 60 miles per hour, executes one of the longest large-mammal migrations on the continent. The connectivity that makes its 160-mile round trip possible is thanks, in part, to a 13-year effort by TNC, partners and landowners to protect more than 95,000 acres of mostly contiguous private ranchland from development.
Not all landscapes that have emerged as resilient are as remote as Idaho’s Pioneer Mountains. Some, like the Appalachians, which stretch from central Alabama into Canada, are bordered by densely populated cities. Others, like Nebraska’s Central Platte River, which includes TNC’s Platte River Prairies, may not have the elevation of mountainous regions, but possess topography so complex (in this case, a chain of grasslands and wetlands) that they can support a wide array of wildlife, like the 1 million or so sandhill cranes that stop over during their spring migration.
To showcase the nationwide distribution of these resilient sites and natural corridors, Anderson’s team mapped what’s known as the Resilient and Connected Lands Network (see map on page 57). The network contains examples of all habitat types in each region, accounts for 250,000 locations of rare species and unique natural communities, covers 33% of the contiguous United States—and serves as a north star for the conservation of the country’s most climate-resilient land.
Anderson concedes that making a map and producing on-the-ground conservation are two very different things—but in this case they are intertwined. The Resilient and Connected Lands Network was built on a ground-up effort from scientists across the United States, so conservation action informed by the project is already in the works.
Roughly 44% of the lands in the network are currently secured by a mix of public and private ownerships, including easements and other restrictions. Numerous state and local agencies, particularly across the eastern U.S., are using this science to shape local conservation plans.
In 2017, the state of Massachusetts used the network to guide the distribution of more than $3 million in grants for the state’s landscape-preservation program. State officials funded the protection of the Brewer Brook Forest, 1,033 acres of unfragmented forestland in western Massachusetts.
Last year, TNC spent $4 million to purchase another resilient site—Vermont’s Glebe Mountain. The 3,500-acre forest sustains beechnut-loving black bears and the black-throated blue warbler.
And protecting climate-resilient land is a boon for more than just biodiversity. These lands are also vital for people. The network of climate-resilient lands mapped in the eastern United States contains 75% of the sources of clean drinking water in the region, produces oxygen for 1.8 billion people and supports a multibillion-dollar outdoor recreation industry. Efforts are underway to map the resilience of Alaska and Hawaii, as well as freshwater and coastal habitats.
Anderson is quick to note, though, that this science is not a silver bullet: Landscapes identified as resilient and connected are not infallibly so. Factors like fire and development can alter a landscape’s ability to sustain plants and animals as the climate changes. Yet identifying and conserving these places may still be our best shot at protecting the bulk of North America’s rich natural heritage for the long haul: “Nature is changing and we can’t hold it steady,” says Anderson. “So we have to find a way to protect it while it shifts.”
In the Pioneers, O’Sullivan reflects on the changes she’s seen in her 18 years exploring this landscape, first as a steward for a conservation-focused sheep ranch and now as a TNC staffer. She’s toured its nooks and crannies by foot and on horseback. She knows the slopes where snow melts more slowly, the springs, the aspen groves, even the large boulders that provide welcome shade.
“If you’re driving through this area at 65 miles an hour, it just looks like brown hills,” says O’Sullivan. “But when you walk around, these microhabitats start to show themselves. You might even say you gravitate toward them.”
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