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A new study finds that climate change may have a range of contrasting effects on coastal forests, both slowing and enabling growth in areas where sea levels are rising and storms are more common.

Researchers compared a decade of forest growth data from two types of environments across the mid-Atlantic, southeastern, and Gulf coasts of the United States: coastal areas less than five meters (20 feet) above sea level and inland areas between 30 and 50 meters (more than 100 feet) in elevation. They found that while forests have expanded in both environments in the last 10 years, some coastal areas have seen significantly lower tree growth and higher mortality than areas of higher elevation.

Marcelo Ardón, associate professor in the North Carolina State University College of Natural Resources, is the lead author of a paper on the study. He said that the expansion of forests in both middle and lower elevations was unexpected. The work is in the journal PLOS Climate.

"We were a little surprised that we found increased forest area and forest biomass in both elevations, and that could be to do with the abandonment of agricultural land," Ardón said. "Despite that expansion, we found that low-lying areas exposed to rising seas still had less overall biomass growth than those at higher elevation."

Researchers were also surprised to find a positive correlation between forest growth and increased coastal storms. Despite also resulting in large numbers of dead trees, the newly cleared space left behind may allow new growth to flourish, Ardón said.

"In a way, these storms may serve a similar function to a controlled burn," he said, referencing the forestry practice of using targeted fires to thin out dense, overgrown areas of vegetation.

"By knocking down these older trees, they clear out the canopy overhead and allow more light to reach the forest floor. It resets the succession for younger trees."

Researchers used data from the United States Department of Agriculture's Forest Inventory and Analysis program, which is unique in that it relies on hand-collected field data rather than satellite monitoring. This allowed the researchers to analyze the carbon storage capacity of the trees knocked down by coastal storms, which the study highlights as an important area for future research.

"In the process of studying these other effects of climate change, we also learned that we really need to spend more time understanding this dead wood," Ardón said. "There is a lot of carbon in those dead trees, both standing and on the ground, and we don't understand it very well."