Along the Eastern Seaboard of the United States, rising sea levels have fostered an ominous and striking environmental phenomenon known as “ghost forests.” These are areas where once-lush coastal woodlands have succumbed to increasing saltwater intrusion, leaving behind stands of dead and dying trees. This stark transformation vividly signals the advancing effects of climate change on coastal ecosystems. Recent scientific investigations have begun to delve into an underexplored aspect of this change: how water flows through these ghost forests and the consequential shifts in nutrient cycling, carbon processing, and forest floor health.
The ghost forests are characterized by trees, primarily sweetgum (Liquidambar styraciflua) in the mid-Atlantic, that suffer from saltwater inundation. These salt-intolerant trees experience physiological stress, culminating in their decline and death, producing ghostly, skeletal remains of trunks and branches. While visibly arresting, the implications of this landscape transformation extend profoundly beneath the surface. Scientists have become especially interested in stemflow—a process where rainwater funnels down tree branches and trunks to the forest floor—because it plays a pivotal role in transporting water, nutrients, and organic compounds that sustain soil microbial communities and influence carbon dynamics.
At the University of Delaware, a research team led by environmental engineering student Samantha Chittakone and her supervisors has pioneered efforts to quantify and characterize stemflow in these sensitive coastal forest settings. Their work involves collecting stemflow samples from healthy, stressed, and moribund sweetgum trees within ghost forests along the mid-Atlantic coast. This approach provides insight into how tree health affects the volume and chemical composition of stemflow. Notably, they observed that dead and dying trees deliver less stemflow to the forest floor, suggesting a disruption in nutrient and water transfer, which could cascade through the ecosystem and alter soil chemistry and biotic communities.
One of the study’s most intriguing findings relates to the variations in dissolved organic carbon (DOC) and sugar concentrations within stemflow from different tree health categories. Dying and dead trees exhibited unusually high sugar levels in their stemflow, a phenomenon thought to result from these trees acting as sponges that absorb water but release accumulated organic compounds as they decay. This absorption limits the amount of water, nutrients, and carbon reaching the soil microbes and understory vegetation, potentially impairing microbial activity and altering carbon cycling processes critical to forest function and regenerative capacity.
Moreover, the color variability of stemflow—from dark brown to pale tan—correlates with the chemical richness and bark texture of the trees, indicating that stemflow chemistry is tightly linked to both biological and physical tree characteristics. These nuanced variations offer promising diagnostic tools for assessing forest health and predicting ecosystem responses to climate-induced stressors. Understanding these dynamics could help scientists identify which coastal forest stands are more vulnerable and how these ecosystems might evolve as sea levels continue to rise.
Complementing their stemflow sampling, the researchers deployed groundwater wells near tree trunks to examine interactions between stemflow and the water table. Measurements revealed that groundwater levels adjacent to both healthy and moribund trees consistently rose after precipitation events, reflecting stemflow’s direct contribution to local hydrology. This is particularly significant in coastal forests, where groundwater tables often hover near the surface, enabling a close coupling between precipitation filtered through trees and subsurface water processes.
Fluorescence indices of dissolved organic matter (DOM) in groundwater samples highlighted contrasting sources and transformations of organic material. Groundwater influenced by stemflow displayed fluorescence signatures indicative of allochthonous, or externally-derived, organic precursors typically associated with surface plant materials. In contrast, groundwater less affected by stemflow manifested fluorescence characteristic of microbially processed DOM, signifying different degrees of organic matter breakdown. These findings underscore how stemflow mediates the quality and origin of carbon inputs entering coastal subsurface environments.
Further chemical analysis focused on quantifying dissolved lignin products, key biomarkers of tree-derived organic matter, within groundwater samples. Results demonstrated higher concentrations of lignin derivatives in stemflow-influenced groundwater near healthy trees compared to unimpacted sites. This pattern reinforces the notion that stemflow serves as a conduit not only for water and nutrients but for significant quantities of organic carbon that shape coastal forest biogeochemical cycles.
Altogether, these findings paint a complex picture of rapid ecological transition. As healthy trees give way to ghost forests, changes in stemflow quantity and quality alter soil chemistry, microbial activity, and ultimately, the carbon storage capacity of these critical ecosystems. This research shines a spotlight on previously overlooked pathways of carbon and nutrient transport, urging ecologists to incorporate stemflow dynamics into models predicting forest resilience and carbon sequestration under climate stress.
Understanding the fate of carbon as it travels from canopy to soil and groundwater is crucial for forecasting broader ecosystem responses to climate change-induced disturbances. The interplay of rising seas, saltwater intrusion, tree mortality, and stemflow-mediated organic matter fluxes creates feedback loops that could accelerate forest degradation or, conversely, reveal resilience mechanisms. Deciphering these processes will be fundamental to developing adaptive management strategies and conservation efforts aimed at preserving coastal forests and the ecosystem services they provide.
The impact of this research extends beyond coastal environments. It aligns with a growing scientific awareness of the importance of stemflow in forest ecology globally, including its role in post-disturbance scenarios such as wildfires. By elucidating how stemflow characteristics vary with tree health and environmental conditions, scientists aim to improve understanding of nutrient and carbon cycling in diverse forest systems, further informing ecological restoration and climate mitigation policies.
Samantha Chittakone, alongside her mentors Robyn O’Halloran, Delphis Levia, and Yu-Ping Chin, advocates for a heightened focus on stemflow studies, describing the process as a critical but underappreciated mechanism in forest floor nutrient and carbon dynamics. Their research effort represents a shift toward integrating hydrological, chemical, and biological perspectives to address pressing questions about ecosystem function amidst unprecedented environmental change.
Funded by the U.S. National Science Foundation, this work was recently presented at the American Chemical Society’s Spring 2026 meeting, spotlighting its significance within the scientific community. As coastal areas face escalating threats from climate pressures, investigations like these offer vital insight into the hidden transformations underway in forest ecosystems, charting a path forward for research and stewardship in a warming world.
Subject of Research: Changes in stemflow chemistry and hydrology in coastal sweetgum forests affected by rising sea levels and saltwater intrusion, with implications for carbon cycling and forest ecosystem health.
Article Title: Linking stemflow to groundwater in ghost forests: Accessing tracers and impacts of tree health on dissolved organic carbon composition
News Publication Date: March 26, 2026
Web References: https://acs.digitellinc.com/live/36/page/1271
Image Credits: Samantha Chittakone
