Storm surge and ponding explain mangrove dieback in southwest Florida following Hurricane Irma

David Lagomasino,Christopher S R Neigh,Temilola Fatoyinbo,Selena Chavez,Lawrence A Corp,Lesley E Ott,Douglas C Morton,Bruce D Cook,Edward Castañeda-Moya,Paul M Montesano

doi:10.1038/s41467-021-24253-y

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.

Highlights

Mangroves buffer inland ecosystems from hurricane winds and storm surge
Damage to mangrove forests from tropical cyclones varies from temporary defoliation to widespread tree mortality[6,7]
In the first 15 months after Irma, 10,760 ha of mangroves showed evidence of complete dieback, with little to no greening (Fig. 2, Supplementary Fig. 3). These low resilience areas were marked by a 0.2 drop in Normalized Difference Vegetation Index (NDVI) and recovery times that exceeded 15 years (Materials and methods are available as Supplementary materials)

Summary

Introduction

Mangroves buffer inland ecosystems from hurricane winds and storm surge. Their ability to withstand harsh cyclone conditions depends on plant resilience traits and geomorphology. Human development has hemmed in much of the remaining mangroves, limiting landward migration, and altered coastal hydrology, increasing vulnerability to sea level rise, salt water intrusion, and ponding[13,14]. These chronic stressors are compounded by strong and sustained winds, storm surge, and prolonged flooding during hurricane events, pushing mangroves to the brink of collapse[7,10]. Spatial variability in the risk of mangrove dieback depends on how specific characteristics of each hurricane[15] interact with forest structure, species composition, geomorphology, and elevation[8,10], and prior hydrologic connectivity[16]

Methods

Results

Conclusion