'Ghost forests' could be key to understanding coastal resilience to climate change

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Rising sea levels are contributing to a phenomenon called "ghost forests," which are groups of dead and dying standing trees that have been drowned by intruding saltwater. And all along the eastern U.S. where there used to be vibrant green trees, clusters of bare gray trunks appear. Now, researchers say studying how water cycles through ghost forests may hold the key to understanding how coastal forest ecosystems respond to climate change.

Samantha Chittakone, an undergraduate student in environmental engineering at the University of Delaware, will present the research team's results at the spring meeting of the American Chemical Society (ACS 2026), held in Atlanta, March 22–26. The study is titled "Linking stemflow to groundwater in ghost forests: Accessing tracers and impacts of tree health on dissolved organic carbon composition."

Ghost forests serve as powerful, visible warnings of climate change. Encroaching ocean waters are poisoning salt-intolerant trees, leaving behind eerie skeletal remains. Researchers from the University of Delaware are wading through these surreal landscapes along the mid-Atlantic coastline to better understand the environmental impact of this climate-driven phenomenon.

"Walking through these coastal forests, surrounded by nature, is beautiful," says Chittakone. "However, it is disheartening to see the healthy trees becoming less prevalent as you approach the shoreline and the effects of rising sea levels become apparent."

Ghost forests mark hidden shifts in how trees process carbon and nutrients belowground. So, Chittakone, with her supervisors Robyn O'Halloran, Delphis Levia and Yu-Ping Chin, and other colleagues, chose to collect and study sweetgum tree stemflow, which is the rainwater that travels down branches and the trunk of this common mid-Atlantic coastal tree. They say stemflow is a useful diagnostic tool for understanding rapid changes to forest ecosystems because the water running down the trees acts like a funnel to concentrate water and mobilize nutrients near the roots.

"Stemflow is basically injecting nutrients and really important chemicals into the forest ecosystem so the microbiome there can thrive," Chin says. He further explains that stemflow color can vary greatly, ranging from intense dark brown, like rich coffee, to pale tan, like weak tea, depending on the bark texture and concentration of nutrients and other substances picked up from the bark.

The researchers collected stemflow from healthy, dead and stressed sweetgum trees to determine if stressed trees could cause cascading impacts in forest ecosystems. For example, changes in stemflow from dead or dying trees may change the soil and consequently impact other organisms such as moss and understory vegetation. When they analyzed their samples, the researchers found significantly less stemflow made it to the forest floor from the dead trees. Another finding was unexpectedly high sugar concentrations in stemflow from dead and stressed trees.

What's the potential cause and effect of the stemflow changes? "The stemflow's being absorbed by the dead trees. They're acting like sponges," says Chin. "Suddenly you cut off water, nutrients and dissolved organic carbon to the forest floor. Not only is this changing the health of the trees, but it changes the health of the forest floor." And Levia speculates that the high sugar transport by stemflow from dying trees could alter microbial communities in near-trunk soil.

"Our results signify that the transition from healthy trees to ghost forests changes the magnitude and chemistry of stemflow, leading to pronounced differences in dissolved carbon inputs," shares Levia. "Further research will better contextualize these changes in stemflow chemistry on the overall cycling of carbon in coastal forests."

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These underground changes ultimately affect how coastal forests store carbon, and understanding these processes could help scientists predict which forests are most vulnerable as sea levels continue to rise.

This research is one piece of the work that the team is doing to investigate stemflow, including how stemflow is impacted by wildfires. "People are beginning to understand the role that stemflow plays in forest floor carbon cycling," adds Chin. "We're kind of preaching the gospel, not just to the general community, but our own scientific community."

"Stemflow is a significant transporter of nutrients and other important chemicals in these coastal forests. It's something that we should study more and not overlook whenever it comes to carbon cycling, especially in these vulnerable ecosystems," says Chittakone.

More information

Linking stemflow to groundwater in ghost forests: Accessing tracers and impacts of tree health on dissolved organic carbon composition: acs.digitellinc.com/live/36/session/574925

Key concepts

effects of climate changecarbon cyclingcoastal ecosystemsfire damageforest ecosystems

Provided by American Chemical Society