Climate change is reshaping our coasts and, as it turns out, the forests that live there. A new study published April 4 in the journal Ecological Applications found that over the past few decades, a sizable portion of forested wetlands at a coastal wildlife refuge on the North Carolina Coastal Plain has been turned into “ghost forests.” staggeringly large masses of dead and leafless trees. trees.
“North Carolina’s forested wetlands are extremely vulnerable to climate change,” says lead author Emily Ury, a recent Duke University biology graduate. Using satellite imagery from the US Geological Survey, Ury and his co-authors found that between 1985 and 2019, up to 11 percent of the area that was once covered by forest had deteriorated into a “ghost forest,” which which marks a shift from bald cypress trees and hardwood swamp trees to woody shrub lands or salt marshes. In that time frame, about 30 percent of the wildlife refuge area changed to a different type of vegetation, and nearly 3,000 acres of land completely disappeared into the ocean.
Environmentalists say more changes could be coming to the area.
“This will be part of a major ecological transition on our coasts as we move toward our climate future,” says lead author Emily Bernhardt, an ecologist at Duke University.
Most trees do not like to drink salt water. “A tree is constantly trying to absorb nutrients through its roots,” says Bernhardt. “And when there is too much salt, they end up consuming a lot of salt instead of nutrients.” Additionally, seawater adds sulfate to the soil, which can become toxic to trees.
The marshes that take over these wetland forests are incredibly important ecosystems. But the possible loss of forests remains a major concern, says Bernhardt. Their disappearance will also mean the loss of many of the creatures that depend on them.
Trees and the soil beneath them also contain a large amount of carbon, says Ury. “Keeping that soil in place will be really important in the future to prevent the release of that carbon into the atmosphere, which will exacerbate climate change.”
Several overlapping factors have contributed to these changes, including constant sea level rise, historical agricultural stressors like ditches and canals, and extreme weather, all combined to push salt water inland. In particular, ghost forests appear to have been buoyed by a series of extreme weather events including several years of drought (preventing fresh water from flushing out accumulated salt), fires, and, in August 2011, Hurricane Irene.
“One of the really nice things about this study is that it showed that that gradual transition from forest to swamp that you would expect with rising sea levels was really marked by Hurricane Irene,” says Matt Kirwan, associate professor at the Virginia Institute. Marine Science that was not involved in the investigation.
The authors had already seen these ghost forests along the sides of roads and canals, Ury says, and had suspected they were due to saltwater intrusion. But from space, “you can really see the extent of these dying stands, and it extends beyond what we had originally thought.” And while maps of projected sea level rise often focus on the outer margins of the coast, Bernhardt says, salt water can seep further inland than you might imagine. Some of this loss of forests and changes in flora was occurring, for example, near canals more than half a mile from the water’s edge.[Related: Forest fires leave behind charcoal—and it might be toxic for years]
The area the researchers were studying is protected, making the death of the trees even more distressing. “We have worked very hard through legislation and protection to keep these remaining forested coastal wetlands, and now they are threatened by something that does not respect those limits,” says Bernhardt.
And these results are not necessarily unique to North Carolina, says Kirwan. This pattern is being observed throughout the Atlantic coast of the United States, particularly in the mid-Atlantic and the southeast.
“The findings that they have historically observed are only going to intensify,” he said. “In the future, salt marshes will replace coastal forests at an increasingly rapid rate.” The marshes themselves, of course, are not infinitely hardy.
“If there is no room for the marshes to migrate, if there are cities or infrastructure along the way, then the continued loss of the existing marsh could exceed the capacity of the marshes to migrate inland.”
Going forward, Ury wants ecologists to focus more on potential strategies to mitigate problems like the loss of wetland forests.
“As ecologists and environmental scientists, we spend a lot of time quantifying the bad. And I think it is time that we began to exercise our capacity and creativity to find solutions. “