As the climate changes, plants and animals worldwide are migrating to follow their preferred conditions. Human activity, however, can impede these movements. Now researchers are mapping out ways to help species escape to more suitable climes. The scientists detailed their findings online June 13 in PNAS.

Species have already begun shifting their populations. These migrations have generally been poleward and to higher elevations. However, roads, cities, and farms have fragmented the American landscape. This disconnected patchwork of natural lands presents challenges to migrating species. And some species may have to move hundreds of kilometers over the course of the coming century due to warming temperatures.

To learn more about the problems that species might face due to climate change, scientists analyzed the contiguous United States, focusing on habitats that have stayed relatively unchanged by human activity. They next partitioned these natural regions into patches characterized by 1 degree C increments. They then examined how these patches would change over time based on temperature forecasts from 15 climate models running up to the end of the century, and how well each patch was connected to cooler patches.

They found that only 41 percent of these relatively natural areas have climate connectivity—that is, are sufficiently connected to each other to allow plants and animals to escape to favorable temperatures as the planet warms over the next 100 years or so. This problem was especially pronounced in the eastern United States—natural areas there had a climate connectivity of less than 2 percent.

“The eastern United States was settled by Europeans earlier—as a result, it has many more dense urban areas and areas otherwise impacted by humans,” says study lead author Jenny McGuire, a spatial ecologist at the Georgia Institute of Technology in Atlanta. “Thus there are fewer natural areas left in the east, and therefore fewer places for species to live and move through.” Plus, because the Appalachian Mountain range is ancient and low, it doesn’t get as cool as western mountain ranges. So the East doesn’t have as many cool areas for plants and animals to retreat to.

In contrast, the western United States possesses a greater range of temperatures and less in the way of human interference. As such, 51 percent of the western United States provides the kind of climate connectivity needed by species that will likely need to migrate, according to the study.

“Back about 10 or 15 years ago, connectivity emerged as a major issue in conservation biology—promoting gene flow between patches,” says ecologist David Ackerly at the University of California, Berkeley, who did not take part in this research. “Bringing together the problem of connectivity with the long-term problem of climate change is an exciting direction.”

To find ways to facilitate animal movements in problem areas, McGuire and her colleagues examined ways to devise corridors between habitats, such as planting natural habitats next to large farms or building natural overpasses or underpasses to help animals avoid vehicles while crossing highways. The researchers found that such corridors could boost climate connectivity to 65 percent across the country. “Given that climate is changing so quickly, and species will therefore need to disperse equally rapidly to keep up, corridors will be an important tool to allow species to survive,” McGuire says.

The greatest gains would be seen in low-lying areas, particularly in the southeastern United States. For instance, the Texas-Louisiana coastal plains and Mississippi alluvial and southeast coastal plains could experience 64 and 57 percent improvements in climate connectivity, respectively, via pathways to cooler inland mountainous regions such as the Ozarks and Appalachians. “We can be strategic about figuring out where species will be most benefitted by increasing connectivity between natural lands,” McGuire says.

The researchers cautioned that this work only looks at average annual temperatures. “Many other aspects of climate, particularly precipitation and maximum temperatures, may affect where species can live and thrive,” McGuire says.

A dearth of climate connectivity will affect some species more than others, McGuire adds. For instance, species with small ranges or those with specialist diets or habitats will struggle the most, a problem that will likely be the focus of future research.

“We want to know where animal’s movement needs may conflict with human development needs, and determine strategies to ease these conflicts,” says McGuire. In particular, she emphasizes the need for more local studies that use regional species and climate data to help determine corridor placements.