Site Resilience is the ability of a site to support biological diversity and ecological functions even as it changes in response to climate change and sea level rise (Anderson et al. 2016). We expect coastal sites to change dramatically over the next century. Many of our existing marshes are already converting to open water and new tidal habitats are forming or migrating into adjacent low lands where suitable space is available to accommodate them. Identifying places where conservation can succeed, and restoration actions could help sites adapt to change, is a necessary step in sustaining the diversity and functions of coastal habitats.
To identify resilient sites, we evaluated three components of a coastal site: tidal complexes (interconnected tidal habitats such as salt marsh, tidal flat, and brackish marsh), the adjacent migration space (suitable low-lying areas that could accommodate future tidal habitats), and the buffer area (natural and agricultural lands surrounding a site).
For each site, we assessed its physical properties for characteristics that would allow for habitat migration: size of migration space, number of tidal zones, amount of shared edge, etc. We also assessed condition characteristics that would facilitate migration: absence of barriers, adequate sediment supply, suitable water quality, etc. We combined the normalized scores for the physical and condition factors to calculate an index of site resilience.
To account for uncertainty, we calculated the resilience scores for multiple sea level rise scenarios (scenarios vary by study region, please refer to the report for your region of interest), assessed the trend in migration space size over time, and evaluated the physical and condition characteristics of the surrounding buffer area. The final scores are given for the highest sea level rise scenario (varies by study region) as these sites are likely to be robust to the most extreme, but possible, conditions.
Final scores indicate the relative resilience of the site in comparison to all other sites within its respective Coastal Shoreline Region. Scores indicate the standard deviations above or below the average score (0) for the Shoreline Region. For example, a score of 1.5 SD means the site scores 1.5 standard deviations above the average score for the Shoreline Region. In other words, the site scores higher than 69% of the other sites in its Shoreline Region.
Migration space is the area of adjacent low-lying land that is potentially suitable for supporting tidal habitats in the future as sea levels rise, and into which the current habitats could migrate. The left image illustrates how current tidal marsh is expected to move into its migration space, while the existing marsh is lost to inundation. The image on the right shows the current marsh and migration space (orange) for a section of Great Marsh, MA.
Anderson, M.G., Barnett, A., Clark, M., Prince, J., Olivero Sheldon, A. and Vickery B. 2016. Resilient and Connected Landscapes for Terrestrial Conservation. The Nature Conservancy, Eastern Conservation Science, Eastern Regional Office. Boston, MA. link
Anderson, M.G. and Barnett, A. 2019. Resilient Coastal Sites for Conservation in the South Atlantic US. The Nature Conservancy, Eastern Conservation Science. Boston, MA. link
Anderson, M.G. and Barnett, A. 2019. Resilient Coastal Sites for Conservation in the Gulf of Mexico. The Nature Conservancy, Eastern Conservation Science. Boston, MA.link
Heady, W. N., B. S. Cohen, M. G. Gleason, J. N. Morris, S. G. Newkirk, K. R. Klausmeyer, H. Walecka, E. Gagneron, M. Small. 2018. Conserving California’s Coastal Habitats: A Legacy and a Future with Sea Level Rise. The Nature Conservancy, San Francisco, CA; California State Coastal Conservancy, Oakland, CA. 143 pages. link