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Mangrove forests play a critical role in coastal ecosystems by buffering shorelines against the destructive forces of storms and storm surges, but in doing so, they often endure significant structural damage, including defoliation, tree snapping, and branch loss. Using decade-long remote sensing Landsat 8 data, we calculated the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Moisture Index (NDMI) to assess patterns and trends within the decade-long time series for each index in mangrove forests of southwestern Florida Everglades. Before calculating NDVI and NDMI, we cloud-filtered and calculated the monthly spectral means of the study region from March 2013 to March 2023. Using both NDVI and NDMI, we found seasonal variations in the value of both indices, in which the value increased during the wet season and decreased during the dry season of the Everglades. We also detected the impact of Hurricane Irma on mangroves in 2017 due to a sudden drop in the indices’ values right after the storm. The time series showed a slow recovery of indices values compared to pre-storm values. Using an exponential recovery model, we calculated that most mangrove areas recovered within two to four years. However, some small mangrove areas show no recovery, which we attribute to saltwater ponding and areas without freshwater flow and hydrological connectivity. 

In September 2017, Hurricane Irma made landfall in South Florida, causing a great deal of damage to mangrove forests along the southwest coast. A combination of hurricane strength winds and high storm surge across the area resulted in canopy defoliation, broken branches, and downed trees. Evaluating changes in mangrove forest structure is significant, as a loss or change in mangrove forest structure can lead to loss in the ecosystems services that they provide. In this study, we used lidar remote sensing technology and field data to assess damage to the South Florida mangrove forests from Hurricane Irma. Lidar data provided an opportunity to investigate changes in mangrove forests using 3D high-resolution data to assess hurricane-induced changes at different tree structure levels. Using lidar data in conjunction with field observations, we were able to model aboveground necromass (AGN; standing dead trees) on a regional scale across the Shark River and Harney River within Everglades National Park. AGN estimates were higher in the mouth and downstream section of Shark River and higher in the downstream section of the Harney River, with higher impact observed in Shark River. Mean AGN estimates were 46 Mg/ha in Shark River and 38 Mg/ha in Harney River and an average loss of 29% in biomass, showing a significant damage when compared to other areas impacted by Hurricane Irma and previous disturbances in our study region. 

ABSTRACT Mangrove forests are typically considered resilient to natural disturbances, likely caused by the evolutionary adaptation of species‐specific traits. These ecosystems play a vital role in the global carbon cycle and are responsible for an outsized contribution to carbon burial and enhanced sedimentation rates. Using eddy covariance data from two coastal mangrove forests in the Florida Coastal Everglades, we evaluated the impact hurricanes have on mangrove forest structure and function by measuring recovery to pre‐disturbance conditions following Hurricane Wilma in 2005 and Hurricane Irma in 2017. We determined the “recovery debt,” the deficit in ecosystem structure and function following a disturbance, using the leaf area index (LAI) and the net ecosystem exchange (NEE) of carbon dioxide (CO₂). Calculated as the cumulative deviation from pre‐disturbance conditions, the recovery debt incorporated the recapture of all the carbon lost due to the disturbance. In Everglades mangrove forests, LAI returned to pre‐disturbance levels within a year, and ecosystem respiration and maximum photosynthetic rates took much longer, resulting in an initial recovery debt of 178 g C m⁻²at the tall forest with limited impacts at the scrub forest. At the landscape scale, the initial recovery debt was 0.40 Mt C, and in most coastal mangrove forests, all lost carbon was recovered within just 4 years. While high‐intensity storms could have prolonged impacts on the structure of subtropical forests, fast canopy recovery suggests these ecosystems will remain strong carbon sinks. 

Abstract Mangroves buffer inland ecosystems from hurricane winds and storm surge. However, their ability to withstand harsh cyclone conditions depends on plant resilience traits and geomorphology. Using airborne lidar and satellite imagery collected before and after Hurricane Irma, we estimated that 62% of mangroves in southwest Florida suffered canopy damage, with largest impacts in tall forests (>10 m). Mangroves on well-drained sites (83%) resprouted new leaves within one year after the storm. By contrast, in poorly-drained inland sites, we detected one of the largest mangrove diebacks on record (10,760 ha), triggered by Irma. We found evidence that the combination of low elevation (median = 9.4 cm asl), storm surge water levels (>1.4 m above the ground surface), and hydrologic isolation drove coastal forest vulnerability and were independent of tree height or wind exposure. Our results indicated that storm surge and ponding caused dieback, not wind. Tidal restoration and hydrologic management in these vulnerable, low-lying coastal areas can reduce mangrove mortality and improve resilience to future cyclones.