Squeezed between rising seas and landward development, many of our nation’s tidal marshes are in danger of disappearing. Deciding how to protect them requires the ability to conduct “apples to apples’’ comparisons of marsh condition across broad landscapes. A new study out of the National Estuarine Research Reserve System (NERRS) and the National Oceanic and Atmospheric Administration (NOAA) is meeting that need by using geographic information system (GIS) data to provide a first-ever assessment of marsh resilience at multiple geographic scales.

“There are many reasons to protect tidal marshes and everyone wants to invest their resources where they can do the most good,” says Rachel Stevens, co-lead of the study and stewardship coordinator at New Hampshire’s Great Bay Reserve. “This assessment can help us understand what drives not just one marsh’s ability to survive, but all the marshes in a particular geographic area. Research and monitoring design, selecting the right restoration approach, deciding which lands to protect to allow migration—all of this depends on being able to see the big picture of marsh resilience.”

The team analyzed tidal marsh resilience—the ability to persist in place or migrate to another location—as rates of sea level rise accelerate. Different factors influence resilience, and the study looked at 13 GIS-based measures of current marsh conditions, vulnerability to sea level rise, and capacity to adapt in the future. Region by region, they found marshes in the Southeast to be the most resilient and those in the Northeast the least.

 In every region, the study identified undeveloped lands with the capacity to support healthy tidal marshes as they migrate landward in the future. Only 53% of these lands have already been protected by fee or easement. 

“Healthy marshes contribute to community resilience,” says Rebecca Roth, director of the National Estuarine Research Reserve Association (NERRA). “As the climate changes, we need science-based tools like these to support marsh conservation efforts around the country. This work is more important than ever as we push to conserve 30% of the world’s lands and waters by 2030.” 

Understanding resilience at the landscape scale helps natural resource managers determine which marshes need help and the kind of help they need. For example, highly resilient marshes that are likely to persist in place are strong candidates for protection. Marshes that are vulnerable to sea level rise but in good condition with a high adaptation potential, might be appropriate for restoration. Those in poor condition with nowhere to migrate as sea levels rise may be too expensive to save. Scientists also can use the analysis to help target fieldwork and monitoring and strengthen experimental design. 

“With state and local budgets stretched thin by the pandemic, it’s important to make sure that every dollar invested in coastal resource management and science counts,” says Roth. “When you combine on the ground knowledge, a strong national network, and expertise from a federal partner like NOAA, you can deliver tools like these that not only help efforts to protect beloved salt marshes, they make the coasts a better place to live and work. It’s what the NERRS was created to do.”

The study provides a strong foundation for states and communities to create targeted tools that meet local priorities. To make this study more actionable for New Hampshire, for example, the team used high-resolution land cover data from NOAA’s Coastal Change Analysis Program (C-CAP) and locally relevant metrics, like the presence of invasive species, to develop parcel scale tools. 

“With these tools, we can compare the feasibility and the likelihood of success of specific restoration and conservation projects,” says Cory Riley, manager of New Hampshire’s Great Bay Reserve. “They are informing a more comprehensive marsh management plan for Great Bay, ordinance language for local communities, and a new tidal wetland reporting methodology for New Hampshire’s Department of Environmental Services.”