Variations in Persistence and Regenerative Zones in Coastal Forests Triggered by Sea Level Rise and Storms

Abstract

Retreat of coastal forests in relation to sea level rise has been widely documented. Recent work indicates that coastal forests on the Delmarva Peninsula, United States, can be differentiated into persistence and regenerative zones as a function of sea-level rise and storm events. In the lower persistence zone trees cannot regenerate because of frequent flooding and high soil salinity. This study aims to verify the existence of these zones using spectral remote sensing data, and determine whether the effect of large storm events that cause damage to these forests can be detected from satellite images. Spectral analysis confirms a significant difference in average Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) values in the proposed persistence and regenerative zones. Both NDVI and NDWI indexes decrease after storms triggering a surge above 1.3 m with respect to the North American Vertical Datum of 1988 (NAVD88). NDWI values decrease more, suggesting that this index is better suited to detect the effect of hurricanes on coastal forests. In the regenerative zone, both NDVI and NDWI values recover three years after a storm, while in the persistence zone the NDVI and NDWI values keep decreasing, possibly due to sea level rise causing vegetation stress. As a result, the forest resilience to storms in the persistence zone is lower than in the regenerative zone. Our findings corroborate the ecological ratchet model of coastal forest disturbance.

Salt Marsh Dynamics in a Period of Accelerated Sea Level Rise

“…A pulse disturbance can have severe impacts on a landscape, causing widespread plant mortality as well as geomorphic change. However, if conditions return to their previous state after the pulse, upland plant communities can likely recover and the total amount of land cover change is likely to be small (Fagherazzi, Nordio, et al, 2019). However, gradual presses can change landscape conditions and prevent recovery after a pulse disturbance.…”

“…Sea level rise will trigger ecosystem shifts in wetlands, with salt marshes transgressing in upland areas (Fagherazzi, Anisfeld, et al, 2019; Fagherazzi, Nordio, et al, 2019) and, in warm climates, mangroves replacing salt marshes at the marine edge (Saintilan et al, 2014). The migration of marshes into uplands changes the ecosystem services that humans obtain from coastal landscapes (Feagin et al, 2010; Schmidt et al, 2014).…”

Spatio-Temporal Analysis of Oil Spill Impact and Recovery Pattern of Coastal Vegetation and Wetland Using Multispectral Satellite Landsat 8-OLI Imagery and Machine Learning Models

“…As depicted in Figure 5a, the comparison of the pre-and post-oil-spill status of the vegetation area showed a general decrease in vegetation health with respect to 15 of the indices. However, the NDWI after oil pollution shows an increase in value, which is likely due to the high absorption and presence of surface water that changed over time [63,93]. Further analysis with the use of paired T-Test (Table 9) indicated that nine of the fifteen indices that reflect deterioration in post oil spill vegetation health (RVI, CVI, GCI, GNDVI, NDVI, MSI, MDWI, SARVI2 and SAVI) were statistically significant with p-value < 0.05.…”

Modeling Marsh‐Forest Boundary Transgression in Response to Storms and Sea‐Level Rise

“…Marsh migration into retreating upland forests is considered to be primarily controlled by the local rate of SLR and the slope of adjacent uplands (Brinson et al, 1995; Kirwan, Temmerman, et al, 2016). However, the pace and mechanisms of ecosystem change are likely controlled by a more complex interplay between gradual SLR and episodic events (Fernandes et al, 2018; Fagherazzi, Anisfeld, et al, 2019; Fagherazzi, Nordio, et al, 2019; Schieder and Kirwan, 2019). Soils and herbaceous vegetation respond quickly (Anisfeld et al, 2017), but the extent of mature forests may lag behind SLR (Kirwan et al, 2007; Williams et al, 1999).…”