Mangrove forests and salt marshes perform a variety of beneficial functions: they protect coastlines from storms and erosion, improve water quality, and offer habitat for fish and wildlife. As winter temperatures become warmer and there are fewer freeze events in the southeastern U.S., mangrove forests are expected to expand their range and replace salt marshes.

Scientists are beginning to unpack what this transition means for coastal wetland ecosystems. In a newly released publication in the Journal of Ecology, scientists from the University of Louisiana at Lafayette and the U.S. Geological Survey point out that changes from mangrove expansion will likely occur not only above ground, but also below. Mangrove forests tend to have more vegetation above ground than salt marshes, as well as (for some) more peat development in the soil. Such differences are relevant in the context of climate change because both above-ground vegetation and below-ground peat act as carbon sinks.  

However, one key finding of the researchers is that there’s no one-size-fits-all model for what will happen when mangroves encroach. Instead, the types and extent of changes (especially below ground) are highly dependent on the existing characteristics of the site – for example, its salinity and annual rainfall. In particular, dry, high salinity locations may experience the biggest soil changes (more peat) in response to mangrove arrival. These results are important for helping natural resource managers predict and plan for how coastal wetland ecosystems will respond to climate change in the southeastern U.S.

These findings are part of a larger study investigating the ecological changes associated with mangrove expansion. The study is supported by the Department of Interior Southeast Climate Science Center, which is managed by the USGS National Climate Change and Wildlife Science Center. The center is one of eight that provides scientific information to help natural resource managers and communities respond effectively to climate change.