Up and down the East Coast, a phantom phenomenon is spreading.
Rising sea levels and flooding push saltwater inland, killing coastal trees not equipped to withstand it. The resulting stands of pale and leafless trees are known as “ghost forests.”
A team at the University of Virginia recently published research documenting the extent of the problem, using artificial intelligence to uncover expanses of ghost forests from Maine to South Carolina.
“We found out the traditional way of detecting ghost forests missed out a lot of them,” said Henry Yeung, a doctoral student who helped lead the project. “We found lots of undocumented hotspots throughout the coastal plain.”
The group mapped more than 10 million dead trees, about 6 million of which are concentrated in low-lying areas most vulnerable to rising waters.
“These findings highlight the alarming decline of coastal forests and the need for strategic actions to preserve their critical ecosystem services,” researchers wrote.
The project grew out of broader discussions at UVA about water-related issues, said Xi Yang, associate professor in the Department of Environmental Sciences.
Several years ago, he participated in the Water Futures Initiative, collaborating with experts in and outside of the university. His group focused on saltwater intrusion from sea level rise.
“People were talking about ghost forest formation, and a lot of those are anecdotal,” Yang said. “People driving in the neighborhood, they saw ghost forests. But what is the true extent and what are the major drivers, at that time, was unclear.”
A post-doctoral researcher first used coarse-resolution satellite data to look at the trend. But Yeung was tasked with diving deeper to document each dead tree.
The Atlantic coastal plain, including eastern Virginia, is ripe for research on the topic. Much of the East Coast is considered a sea level rise hotspot. The rate of rise in Hampton Roads, for example, is accelerating faster than the global average, largely because of sinking land and changing ocean currents and wind patterns.
The changing conditions kill trees in three main ways, Yang said: underground, with soil and water becoming increasingly salty; at the surface, from flooding; and in the air, through sea spray and storms. Droughts and insect infestations can also contribute.
Ghost forests usually form in a narrow line along the boundary between intact forest and salt marshes, Yeung said. That can make them difficult to see from coarse-resolution satellites, which capture broader-scale imagery with less fine detail.
The UVA team used high-resolution imagery to find individual dead trees, Yeung said. They trained an AI system to detect ghost forests using those images and other modeling techniques.
Coastal forests have a range of important benefits, such as storing carbon, slowing erosion and supporting wildlife, he said.
Researchers hope the data will be a resource for scientists studying ghost forests and officials who could “do some damage control.” Identifying ghost trees on people’s property or agricultural land could help warn them of encroaching sea levels.
“It’s not just about the forest. It is an indicator of the underground saltwater intrusion,” Yeung said. “If people can look at the map and see, ‘OK, my nearby forest is already converting to a ghost forest,’ they may know that the land, as well, may soon get salinized.”
