We’re excited to share that the Great Bay National Estuarine Research Reserve (GBNERR) has wrapped up our work on the Pathways to Salt Marsh Resilience Project. This initiative focused on identifying and advancing efforts across coastal New Hampshire that will help protect the natural pathways salt marshes need to migrate as sea levels rise.
The final report and key findings are now available to help spark and inform next steps:
Executive Summary (3 pages)
Report with all appendices included (127 pages)
Report with links to appendices (32 pages)
To support the release of this report, we are hosted a webinar on June 12, 2025.
Over the past ten years, the Great Bay NERR has been leading efforts locally and nationally to monitor coastal habitat change, assess the resilience of salt marshes, and model the impacts of sea level rise. It has become increasingly clear that salt marshes in many parts of the country are threatened by future sea level rise and increased coastal development. Without the space to migrate inland, salt marshes may drown and get squeezed out of existence.
There is an urgent need to focus on the places, ecological processes, and management actions that can help salt marshes migrate into adjacent upland areas as sea level rises, thus supporting the long term persistence of this important habitat. Building on the results of a recent literature review, Salt marsh migration into coastal uplands and application for conservation in New Hampshire, we teamed up with five other reserves (See: Pathways to Resilience) to identify and advance projects – including conservation, restoration and land use management – that can enable marshes to migrate inland as seas rise.
Over the course of the 18-month project, we consulted with 58 individuals from 30 partner organizations through a series of workshops and small meetings and asked them:
- What spatial, field and practical considerations can help us identify promising areas to invest in marsh migration projects?
- Given the spatial information we compiled and your local knowledge, where should we invest in marsh migration projects?
- What specific strategies should be promoted in each priority location?
Partners brainstorming marsh migration ideas with large maps at the project kick-off workshop in October 2023.
The NH Marsh Migration Mapping Tool was created for this project to pull together key spatial data to help GBNERR and partners identify promising locations for marsh migration projects (see screenshot below). Included in this mapping was a new NH Fish & Game Landcover Resistance Spatial Analysis, which models how easily marshes could migrate into different areas based on slope and land cover type, and the results of the 2022 Sea Level Affecting Marshes Model (SLAMM), which maps how estuarine habitats could shift in response to sea level rise.
To learn more about the data layers used in the mapping tool, view the Data Notes.
Example screenshot of the NH Marsh Migration Mapping Tool created for this project, showing existing marsh (green) and the land cover resistance scores within the marsh migration space (yellow to orange) along the mouth of the Squamscott River.
Through this collaborative process, we identified 23 promising areas for marsh migration in coastal New Hampshire (see map below at left), along with important information about potential projects and partnerships for these areas. After reviewing the 23 promising areas, we chose to scope out and explore site specific strategies for 12 projects where we felt we could advance work over the short term, for example, by supporting a grant application, adding a new dimension to an on-going initiative, or jumpstarting action in a priority area (see map below at right).
At left, promising areas for investing in salt marsh migration projects in coastal New Hampshire identified through this collaborative process. At right, locations where we developed site specific strategies and marsh migration opportunity maps.
For 10 of the projects, we developed a summary product called a Marsh Migration Opportunity Map – a succinct project profile to support planning and implementation. These profiles offer an interpretation of maps and spatial data for the site and summarize local knowledge and ideas generated by partners. In addition to the mapping products, we also offered customized support to advance the 12 projects, including proposal writing assistance, convening partners to brainstorm strategies, and developing customized analyses.
Marsh Migration Opportunity Maps were generated for 10 sites and are available in the report appendices.
In addition, GBNERR continues to work on protection and restoration of salt marshes and migration space though:
- Assistance for organizations interested in using the New Hampshire Salt Marsh Plan;
- Development of standardized protocols for monitoring how coastal habitats are shifting with sea level rise; and
- Support of the newly reinvigorated New Hampshire Salt Marsh Task Force, with the goal of strengthening collaborative relationships among people involved in salt marsh monitoring, restoration, and protection efforts in NH.
Example of coastal habitat change happening along Great Bay in Newmarket, NH. Dashed lines show forest die off and formation of a ghost forest as salt water flooding increases. From McKnown and Burdick, 2024.
Explore the final report and watch the webinar recording.
Executive Summary (3 pages)
Report with all appendices included (127 pages)
Report with links to appendices (32 pages)
