Ghost forests, the cemetery-like groupings of dead trees killed by saltwater intrusion, have become haunting symbols of sea level rise overtaking land along the Mid-Atlantic coast. But a new study in Nature Sustainability led by William & Mary’s Batten School & VIMS points to even more dramatic land losses in the region’s coastal farmlands, where the rate of marsh encroachment is happening nearly twice as fast.
Using satellite data spanning decades as well as recent field measurements, the study’s authors found that between 1984 and 2022 approximately 25,000 acres of farmland was lost to sea level rise in the Chesapeake and Delaware Bay watersheds, despite preventative measures taken by local farmers.
“There's this assumption that we'll never let sea level rise consume farmland, that people will protect valuable land. And it's just wrong,” said Matt Kirwan, co-author and professor of marine science at the Batten School of Coastal & Marine Sciences & VIMS. “We found lots of examples where small levees were built at the edges of fields to prevent saltwater intrusion, but they only slowed down the loss. They couldn’t stop it.”
Measuring marsh encroachment
As sea levels continue to rise due to human-driven climate change, saltwater creeps farther inland through groundwater, tidal creeks and storm surges. This process, known as saltwater intrusion, gradually kills freshwater plants and replaces them with salt-tolerant marsh grasses. Scientists track this transformation by measuring how the boundary between dry land and marsh shifts over time, a metric known as retreat.
Rather than measuring only how far inland the marsh boundary moved, which can depend on how flat or steep the land is, the authors tracked the elevation of the boundary as well. This approach accounts for differences in terrain and allows for a more direct comparison of marsh encroachment between farmland and forest.
The mid-Atlantic coast experiences sea level rise at roughly double the global average, making it both a hotspot for these changes and an ideal location to study them.
The study shows that marsh encroachment can be up to 7 times more frequent on agricultural land compared to forestland in the mid-Atlantic and that, regionally, agricultural land appears to have accelerated the impacts of saltwater intrusion.
“We hypothesized, and most people would intuitively expect, that marshes would migrate slower into farmland, that forests are more vulnerable than farmland. But we found the opposite,” Kirwan said. “On farmland, it’s much more subtle. It’s a row of crops at the edge of the field that’s brown instead of green, but it still adds up to thousands of acres of lost agricultural production.”
Why coastal farmlands are vulnerable
The study references an assumption that coastal farmland’s economic value incentivizes flood mitigation strategies to protect against sea level rise. In point of fact, mid-Atlantic farmers have built levees or earthen berms around their land to reduce inundation, along with other mechanisms like ditches.
However, because Virginia and Maryland made tidal wetlands protected ecosystems in the 1970s, few structural interventions have been built since then, raising doubts about whether coastal farmlands are as protected as presumed.
“Some of the berms are still being used and maintained, but a lot of them have been abandoned and are now surrounded by marsh,” said the study’s lead author and Batten School Ph.D. graduate Grace Molino ’25.
To conduct field surveys for the study, Molino visited six farm sites on the Eastern Shore along with co-author and former Batten School & VIMS student intern Grace Levins. They found that levees and other structural interventions did mitigate saltwater intrusion, bringing the vertical retreat rate in line with that of forests in the same area.
While these individual efforts did reduce marsh encroachment locally, the study found that regionally farmland was still more vulnerable to saltwater intrusion than forests. New construction is limited because of complicated permitting requirements, and the ones that are maintained cannot fully prevent land conversion to marsh. Additionally, crops are biologically less resilient than trees.
“It’s not that farmland is flat and therefore it retreats faster,” Kirwan said. “Trees have lifespans of hundreds of years. It can take decades to kill a tree. Agricultural crops have lifespans of less than a year.”
The overlooked impact of farmland on coastal resilience
Discussions around the impact of human development on coastal habitats have traditionally been focused on urban flood prevention methods like hardened shorelines and seawalls, which have been shown to prevent wetlands from migrating inland as seas rise. And yet, less than 15% of coastal watersheds in the United States are heavily developed. The vast majority of the nation's coastline is rural, and the human footprint on those landscapes has been largely overlooked.
“It's really underappreciated how large human impacts can be even in rural areas where you don't have the big beach houses, you don't have the big seawalls,” Kirwan said. “Everything's more subtle, but they're still having a big impact."
Rural communities are often not included in conversations about future flood infrastructure or coastal adaptation. The study argues that a paradigm shift is needed to understand the responses of these areas and the people who live in them.
Investigating these rural responses to marsh encroachment can be difficult. Researchers typically work on public land, where there is little barrier to entry. To access privately-owned farmland, Molino had to make old-fashioned cold calls and knock on doors. The effort was well worth it, she said.
“The landowners there have this unbelievable wealth of knowledge,” Molino said. “Most of them have lived on the land for several generations and know a lot about the neighboring properties and how things have changed.”
At one site in Maryland, a landowner who uses the property as a weekend hunting retreat during waterfowl season gave Molino a tour of two massive impoundment structures he had built on fields that were too salty to farm. One had been partially funded through a U.S. Department of Agriculture program that pays landowners to create wildlife habitat.
Molino said she was struck by how this landowner had independently adapted to saltwater intrusion by completely changing his land use, and that a federal program existed to support that decision.
“Individual landowner decisions have such a strong influence on the changes that we're seeing on the coast,” Molino said. “It's so important to actually get out into the field and talk with them and understand what's driving these decisions.”
Marshes are also under threat from sea level rise. If they can’t build soil fast enough to keep pace with rising tides, they must move to higher ground. So what may be bad for farmers in terms of land loss can at the same time be good for marshes, because agricultural land represents a new and faster pathway for them to migrate inland, potentially bolstering coastal resilience overall. But that comes directly at the expense of farmers’ livelihoods.
Molino believes that science can help figure out a solution for all. She cited the mission of the Batten School & VIMS to provide solutions-based science and how these farmers are exactly the kind of people she hopes science can serve.
In carrying out this study, science already has benefited these landowners. During one field visit, a landowner asked Molino to let him know if she found any breaches in his levees so he could plug them. When she got back to the lab, she called him and gave him the breaches’ exact GPS coordinates.
Nature Sustainability
Sea-level-driven land conversion amplified by coastal agriculture
18-May-2026
The authors declare no competing interests.