Due to their position at the land-sea interface, barrier islands experience a combination of oceanic and atmospheric drivers of change (i.e. relative sea level rise, temperature warming, coastal storms). Barrier island sediment overwashes on to back-barrier marsh in response to increased sea level and storm surge. The vegetative-topographic relationships of these coastal landforms may affect resistance/responsiveness to migration of the marsh-upland boundary. We used Landsat imagery to assess how vegetation area and island area of the Virginia Coast Reserve Long-Term Ecological Research site has changed over a 32-year period (1984-2016) and during a storm event. We quantified transitions between landcover (bare, grassland, woody vegetation, marsh, and ocean) and the marsh-upland boundary in this microtidal system between different time periods for the entire system and through 1 km sub-sections. We assessed areas that changed in landcover and those that remained stable. Storms between 2013 – 2016 were classified using storm duration and storm surge, with imagery pre-and post-storm included in this analysis.
Results/Conclusions
Throughout the 1984 – 2016 time interval, 11.8% of upland and 7.3% of marsh vegetation were lost from the system. As upland area was reduced, we found a 41% increase of woody vegetation, primarily driven by the expansion of the native-invasive, Morella cerifera, attributed to warming temperatures and microclimate modification. Through 1km subsampling we found marsh to upland conversion occurred between 0 – 7 m yr-1 , depending on elevation and vegetative composition. In areas with low elevation and low woody vegetation, the rate of ecosystem change was highest. Conversely, we found that there was a decrease of marsh to upland conversion behind foredunes greater than 2.5 m, which were also associated with higher woody cover. We found that areas with higher elevation and woody cover were more resistant to change during a storm event. Our analysis demonstrates how the importance of vegetation-topographic interactions influencing barrier island response to sea-level rise and storm events and highlights how ecological processes impact coastal change.