As climates change over the next century, many species of plants and animals will be forced to change their habitat ranges to survive. According to the first continent-wide geospatial study of climate connectivity—a measure of the migratory routes between warm and cool zones—only 2% of the eastern United States contains the connected green space needed for animals to find new homes. The findings appeared on 13 June in the Proceedings of the National Academy of Sciences of the United States of America.
“The East Coast is in dire shape because habitat is already in very small patches,” says study author Jenny McGuire, a research scientist at Georgia Tech in Atlanta. “We have a nice swath of intact land around the Appalachian Mountains, but other natural areas are patchy and fragmented.” This keeps animals—and the plant seeds they may carry—from moving to cooler areas where they can maintain a temperature similar to the climate in their current habitat.
Fragmented Green Space
McGuire and her colleagues set out with an ambitious plan to identify all spans of green space in the United States where species can migrate from a warmer to a cooler habitat without having to traverse extreme deserts, cold mountain peaks, or disturbed areas like cities and agricultural routes.
They used an algorithm to consider temperature change over time and then mapped cooler areas that species in warming locations could access. Then they measured how close populations are to where they could go, using corridor lengths of no longer than 100 kilometers.
According to their findings, about 50% of the American West can support migration. However, the landscape on the East Coast remains too fragmented for plants and animals to change their range—only 2% of the eastern plains and coastal areas have cool sites adjacent to warm zones.
Eastern species able to traverse 10-kilometer corridors can enjoy 16% climate connectivity, and those that migrate more than 100 kilometers will find 27% of the landscape to be accessible. In contrast, when allowing for 100-kilometer migratory routes in the West, climate connectivity rose to a more robust 75%.
Although surprised by the dire state in the East, David Ackerly of the University of California, Berkeley, predicted that connectivity would be better in the West because of the rugged terrain. “If you live in a mountain range and temperatures begin to warm, you just move a short distance uphill,” said Ackerly, who is not affiliated with the study. “But on a large span of flat landscape, like the plains or coastal hills, you have to traverse a greater distance to reach higher altitude and cooler climate.”
Connecting Shrinking Habitats
Prior studies have mapped routes between dwindling populations to help increase interbreeding and genetic diversity. This strategy supports a long list of species, including threatened plants, which disperse to moist areas by spreading pollen, and predators like foxes and mountain lions, which migrate according to the shifting ranges of food species and distant mates.
It also helps local species like the gopher tortoise (Gopherus polyphemus), which is currently protected by the Endangered Species Act because of the disturbance of sandy pine forests in Florida and Georgia, where it digs burrows that shelter more than 300 other types of animals. The threatened seepage salamander (Desmognathus aeneus) is similarly found only in small areas of Tennessee, North Carolina, Georgia, and Alabama, but these ranges are predicted to shrink because of climate change.
Corridor projects that create greenways for migration can help such isolated populations breed, but they rarely consider long-term range changes that will alter habitat boundaries as temperatures warm.
However, “the current findings give us a 30,000 foot view of the problem” because they consider climate conditions, says Ackerly. “By tracing connectivity across coastal and mountainous regions, we can see areas where restoration work would significantly expand connectivity in the East.”
—Amy Coombs, Editorial Intern