This indicator depicts the capacity of coastal habitats to migrate to adjacent lowlands in order to sustain biodiversity and natural services under increasing inundation from sea-level rise. It is based on the physical and condition characteristics of current tidal complexes, their predicted migration space, and surrounding buffer areas. These characteristics include marsh complex size, shared edge with migration space, sediment balance, water quality, natural landcover, landform diversity, and many others. This indicator originates from The Nature Conservancy’s Resilient Coastal Sites project.
Reason for Selection
The resilient coastal sites indicator seeks to capture features of salt marshes that are important for salt marsh species and ecosystem function both now and in the future. Many of these characteristics, like water quality and landform diversity, also serve as indicators of a site’s potential future habitat quality once the salt marsh is fully inundated and transitions to a new estuarine or marine habitat.
Input Data
- Base Blueprint 2022 extent
- Base Blueprint 2022 subregions
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This indicator combines data from the following TNC projects:
From the South Atlantic and Gulf of Mexico Resilient Coastal Sites projects, we used:
- The “RESILB1stC” field of the “Tidal_Complex_Resilience_Score_SLR65” layers: Final resilience score within existing tidal complexes in a 6.5 ft of SLR scenario.
- The “RESILB1stC” field of the “Migration_Space” layers ending in _SLR15, _SLR30, _SLR40, and _SLR65: Final resilience score within the migration space associated with each tidal complex in 1.5, 3, 4, and 6.5 ft of SLR scenarios. Migration space consists of low-lying areas adjacent to current tidal complexes that may support future tidal habitats as current habitats migrate due to SLR.
- The “RESILB1stC” field of the “Additional_Migration_Space” layers ending in _SLR15, _SLR30, _SLR40, and _SLR65: Final resilience score within additional migration space units in 1.5, 3, 4, and 6.5 ft of SLR scenarios. Additional migration space units capture portions of the migration space that do not spatially intersect current tidal marshes, but may provide additional landscape context.
From the Northeast and Mid-Atlantic Resilient Coastal Sites projects, we used:
- The “RESILssBZ” field of the “slr06_stratified_resilience” layer: Final resilience score within existing tidal complexes in a 6 ft of SLR scenario.
Mapping Steps
To capture the resilience of existing tidal complexes in the highest SLR scenario (6.5 ft for South Atlantic and Gulf of Mexico, 6 for Northeast and Mid-Atlantic):
- Convert the South Atlantic and Gulf of Mexico “Tidal_Complex_Resilience_Score_SLR65” layers from vector to a 30 m raster data using the “RESILB1stC” field.
- Convert the Northeast and Mid-Atlantic “slr06_stratified_resilience” layers from vector to a 30 m raster using the “RESILssBZ” field. Areas that overlapped with the South Atlantic were removed from this input.
To capture the resilience of the migration space and additional migration space associated with each tidal complex across all SLR scenarios (1.5 ft, 3 ft, 4 ft, and 6.5 ft):
- Convert all of the South Atlantic and Gulf of Mexico “Migration_Space” and “Additional_Migration_Space” layers for each SLR scenario (ending in _SLR15, _SLR30, _SLR40, and _SLR65) from vector to a 30 m raster using the “RESILB1stC” field. Note: The Northeast and Mid-Atlantic data does not provide resilience scores for migration space or additional migration space.
To create a combined coastal resilience layer:
- Combine the coastal resilience layers produced in the previous steps using the cell statistics function in ArcGIS with the overlay statistic Maximum. This creates a layer depicting the highest possible resilience score for each pixel from the above sea- level rise layers.
- Clip to the ‘Atlantic Coastal Plain’, ‘Central Gulf Coastal Plain’, ‘East Gulf Coastal Plain’, ‘Florida Peninsula’, ‘Gulf Coastal Prairies’, ‘Mid East Gulf Coastal Plain’, ‘Mississippi Alluvial Valley’, and ‘West Gulf Coastal Plain’ subregions. The source data also covers a few pixels in the Piedmont subregion. We didn’t include data in those subregions due to an oversight in which indicators were used for the Blueprint priorities in those subregions.
- As a final step, clip to the spatial extent of Base Blueprint 2022.
Note: For more details on the mapping steps, code used to create this layer is available in the Southeast Blueprint 2022 Data Download under BlueprintInputs > BaseBlueprint2022 > 6_Code
Final Indicator Values
Indicator values are assigned as follows:
- 7 = Most resilient
- 6= More resilient
- 5 = Slightly more resilient
- 4 = Average/median resilience
- 3 = Slightly less resilient
- 2 = Less resilient
- 1 = Least resilient
Known Issues
- Resilience scores on some indigenous lands are still under review, and are not included in this indicator.
- This indicator does not account for the occurrence and timing of disturbance processes, like prescribed fire, which impact resilience.
- Accretion rates were not incorporated into the marsh migration data.
- The source data from TNC assesses costal resilience and sea-level rise slightly differently in a portion of coastal Virginia that falls into the Northeast and Mid-Atlantic region, where TNC conducted its first coastal resilience assessment. In the Northeast and Mid-Atlantic, TNC data only assessed coastal resilience within the existing tidal complex and did not score migration space as it does in in the Gulf of Mexico and South Atlantic regions. Therefore, migration space along the North Virginia coast will appear as NoData.
- Also, TNC assessed sea-level rise in the Northeast and Mid-Atlantic region in 1 foot increments (ranging from 1-6 ft) as opposed to 1.5 ft increments (ranging from 1.5-6.5 ft) in the Gulf and South Atlantic regions. As a result, this indicator likely underestimates the extent of resilient areas in this portion of coastal Virginia.
- Because resilience was only assessed for tidal marsh and its migration space, there will be areas of NoData in the coastal zone. Places that do not receive a resilience score are urban areas or non-marsh habitat in the coastal zone, but outside of the migration space. While the indicator source data extends into a few pixels in the Piedmont, those pixels are not included in the indicator because they were not used in the Blueprint priorities for that subregion. We didn’t include those pixels due to an oversight in which indicators were used for the Blueprint priorities in the Piedmont subregion. Those pixels are just southeast of where I-95 crosses the Occoquan River in Virginia.
Disclaimer: Comparing with Older Indicator Versions
There are numerous problems with using Southeast Blueprint indicators for change analysis. Please consult Blueprint staff if you would like to do this (email hilary_morris@fws.gov).
Literature Cited
Anderson, M.G., Ferree, C.E., 2010. Conserving the stage: climate change and the geophysical underpinnings of species diversity. PLoS One 5, e11554. [https://doi.org/10.1371/journal.pone.0011554].
Anderson, M.G. and Barnett, A. 2017. Resilient Coastal Sites for Conservation in the Northeast and Mid-Atlantic US. The Nature Conservancy, Eastern Conservation Science.[http://easterndivision.s3.amazonaws.com/coastal/Resilient_Coastal_Sites_for_Conservation_NE_Mid_Atlantic.pdf].
Anderson, M.G. and Barnett, A. 2019. Resilient Coastal Sites for Conservation in the South Atlantic US. The Nature Conservancy, Eastern Conservation Science. [https://www.conservationgateway.org/ConservationByGeography/NorthAmerica/UnitedStates/edc/Documents/SouthAtlantic_Resilient_Coastal_Sites_31Oct2019.pdf].
Anderson, M.G. and Barnett, A. 2019. Resilient Coastal Sites for Conservation in the Gulf of Mexico US. The Nature Conservancy, Eastern Conservation Science. [https://www.conservationgateway.org/ConservationByGeography/NorthAmerica/UnitedStates/edc/Documents/GulfOfMexico_Resilient_Coastal_Sites_31Oct2019.pdf].
