‘Ghost forests’ are spreading in coastal areas of the United States

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‘Ghost forests’ are spreading in coastal areas of the United States

Climate change is reshaping our coasts and, ultimately, the forests that live there. A new study published April 4 in the journal Ecological Applications found that over the past several decades, a significant portion of the forested wetlands at a coastal wildlife refuge on the North Carolina Coastal Plain have become “ghost forests.” – very large stands of dead and leafless. trees.

“The forested wetlands of North Carolina are extremely vulnerable to climate change,” says lead author Emily Ury, a recent PhD in biology from Duke University. Using satellite images from the US Geological Survey, Ury and his co-authors found that between 1985 and 2019, up to 11 percent of the area once covered by forest had deteriorated into “ghost forest,” marking the passage of bald cypress trees and trees from deciduous swamps to woody shrub lands or salt marshes. During this time, about 30% of the wildlife refuge area changed to a different type of vegetation, and nearly 3,000 acres of land disappeared entirely into the ocean.

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Environmentalists say more changes could be made in the region.

“This is going to be part of a major ecological transition on our shores as we move towards our climate future,” says lead author Emily Bernhardt, ecologist at Duke University.

Most trees don’t like to drink salt water. “A tree is constantly trying to absorb nutrients through its roots,” says Bernhardt. “And when there’s too much salt, they end up taking in a lot of salt instead of nutrients.” Additionally, seawater adds sulfate to the soil, which can become toxic to trees.

The marshes that invade these humid forests are extremely important ecosystems. But the potential loss of forests remains a major concern, says Bernhardt. Their demise will also mean the loss of many of the creatures who rely on them.

Trees and the soil beneath them also contain a lot of carbon, Ury says. “Keeping this soil in place will be very important in the future to prevent the release of this carbon into the atmosphere, which will only worsen climate change.”

A number of overlapping factors have contributed to these changes, including steadily rising sea levels, historic agricultural stressors like ditches and canals, and extreme weather conditions, all mixing together to push l salt water inland. In particular, the ghost forests appear to have been encouraged by a series of extreme weather events, including several years of drought (which prevents fresh water from flushing out accumulated salt), fires and, in August 2011, Hurricane Irene. .

“One of the advantages of this study is that it showed that the gradual transition from forest to swamp that one would expect with rising sea levels was really punctuated by Hurricane Irene,” says Matt Kirwan, an associate professor at the Virginia Institute of Marine Science who was not involved in the research.

The perpetrators had seen these ghost forest stands along roadsides and canals before, Ury says, and they suspected it was due to saltwater intrusion. But from space, “you can really see the extent of these dying stands, and it’s beyond what we originally thought.” And while maps of projected sea level rise often focus on the outer fringes of the coast, Bernhardt says salt water can seep further inland than you might think. . Some of this forest loss and change in flora was happening, 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 studied by the researchers is protected, which makes the death of trees even more distressing. “We have worked very hard through legislation and protection to conserve these remaining coastal wooded wetlands, and now they are threatened by something that does not respect these boundaries,” says Bernhardt.

And these results aren’t necessarily unique to North Carolina, Kirwan says. This trend is observed throughout the Atlantic coast of the United States, particularly in the central Atlantic and the southeast.

“The discoveries that they have observed historically will only intensify,” he said. “In the future, swamps will replace coastal forests at an increasingly rapid rate.” The swamps themselves, of course, are not endlessly resistant.

“If there is no room for the swamps to migrate, if there are towns or infrastructure in the way, then the continued loss of the existing swamp could exceed the swamp’s ability to migrate inland. lands.”

Going forward, Ury wants conservationists to focus more on potential strategies to mitigate problems like forest loss in wetlands.

“As ecologists and environmental scientists, we spend a lot of time quantifying the bad. And I think it’s high time we started to exercise our capacity and creativity to find solutions.