Developing Monitoring Protocols to Document Marsh Migration
Have you noticed that the vegetation at the upland edge of salt marshes is changing? Trees are dying, undergrowth is flooding, and marsh plants are sprouting in forests or agricultural fields. This change is driven by sea level rise and storm surges, which are creating saltier and wetter conditions in previously terrestrial landscapes that are allowing marsh plants to move, or “migrate,” into adjacent woods and fields.
Forest changes observed at Great Bay Reserve properties showing (left) ghost forests now turned into salt marsh meadows and (right) evidence of storm surges depositing wrack, which is ocean plant debris brought in by tides, at eye level in the forest.
Land managers and researchers in New Hampshire have observed this change as well and have used computer models to predict where salt marshes are likely to migrate in the coming decades due to sea level rise. However, until recently, researchers had not developed a method for quantifying and monitoring marsh migration over time and determining if marsh migration pathways were behaving as predicted by the models.
The Need to Monitor Marsh Changes
To address these knowledge gaps, a Marsh Migration Monitoring Workgroup led by Great Bay National Estuarine Research Reserve and The Nature Conservancy was convened as a technical sub-group of the NH Salt Marsh Task Force, and includes researchers from:
- University of New Hampshire
- NH DES Coastal Program
- Piscataqua Region Estuaries Partnership
- NH Natural Heritage Bureau
- US Fish and Wildlife Service
- Environmental Protection Agency
Over the last few years, this group has worked to develop a standardized method for monitoring marsh migration in New Hampshire. These protocols combine elements of existing national and regional vegetation monitoring protocols from key partners (e.g., National Estuarine Research Reserve System and US Fish and Wildlife Service), as well as upland forest monitoring. Monitoring methods help address key research questions, such as:
- How much marsh are we losing vs gaining?
- How do plant communities compare in newly created marsh to current marsh?
- What factors are accelerating or halting marsh migration (slope, land cover, hydrology)?
The Workgroup piloted the monitoring methods in the field with partners to refine the protocols based on collective input.
Explore the current monitoring protocols, which may be updated over time:
Putting the Protocols into Action
Members of the Workgroup have started implementing the New Hampshire Marsh Monitoring Protocols at several coastal sites, continuing and adding to the process of building a long-term dataset on how marshes migrate over time due to sea level rise. These protocols give researchers a consistent way to document, understand, and predict change and compare on-the-ground observations with marsh migration modeling results. The mechanisms of salt marsh migration are not well studied in New England and implementing a monitoring program provides a platform for advancing the collective knowledge about drowning and migrating marshes, and how to best manage these rare coastal habitats in our state.
Field measurements of (a) shrub and (b) tree percent cover declines from 2014 to 2019 at four salt marshes scattered across Great Bay NH and southern ME, indicating a transition from upland to marsh. This data is from a prior, related study, authored by C. Peter, S.Adamowicz, R. Tiner, T. Leitch, K. O’Brien, N. Pau, R. Stevens, and B. Benvenuti.
Outreach and Next Steps
To share the protocols with others in the area, the Marsh Migration Monitoring Workgroup has conducted training with researchers and land managers, and has presented their methodology to the NH Salt Marsh Task Force. In addition, these protocols are currently being considered as the National Estuarine Research Reserve System looks to adopt a national ecotone protocol.
Photos from a recent NH Salt Marsh Task Force meeting, during which members of the Marsh Migration Monitoring Workgroup discussed how to apply the new protocols in the field.
Funding
This work has been funded by grants from the Infrastructure Investment and Jobs Act and the NERRS Capacity Building Grants Program.
Contact
For more information, contact Chris Peter, Great Bay National Estuarine Research Reserve Research Coordinator, at Christopher.R.Peter@wildlife.nh.gov.
