An official website of the United States government
The capacity of coastal wetlands to stabilize shorelines and reduce erosion is a critical ecosystem service, and it is uncertain how changes in dominant vegetation may affect coastal protection. As part of a long-term study (2012–present) comparing ecosystem functions of marsh and black mangrove vegetation, we have experimentally maintained marsh and black mangrove patches (3 m × 3 m) along a plot-level (24 m × 42 m) gradient of marsh and mangrove cover in coastal wetlands near Port Aransas, TX. In August 2017, this experiment was directly in the path of Hurricane Harvey, a category 4 storm. This extreme disturbance event provided an opportunity to quantify differences in resistance between mangrove and marsh vegetation and to assess which vegetation type provided better shoreline protection against storm-driven erosion. We compared changes in plant cover, shoreline erosion, and accreted soil depth to values measured prior to storm landfall. Relative mangrove cover decreased 25–40% after the storm, regardless of initial cover, largely due to damage on taller mangroves (> 2.5 m height) that were not fully inundated by storm surge and were therefore exposed to strong winds. Evidence of regrowth on damaged mangrove branches was apparent within 2 months of landfall. Hurricane-induced decreases in mangrove cover were partially ameliorated by the presence of neighboring mangroves, particularly closer to the shoreline. Marsh plants were generally resistant to hurricane effects. Shoreline erosion exceeded 5 m where mangroves were absent (100% marsh cover) but was relatively modest (< 0.5 m) in plots with mangroves present (11–100% mangrove cover). Storm-driven accreted soil depth was variable but more than 2× higher in marsh patches than in mangrove patches. In general, mangroves provided shoreline protection from erosion but were also more damaged by wind and surge, which may reduce their shoreline protection capacity over longer time scales.
more »
« less
Storm surge and ponding explain mangrove dieback in southwest Florida following Hurricane Irma
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.
more »
« less
- PAR ID:
- 10253192
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The capacity of coastal wetlands to stabilize shorelines and reduce erosion is a critical ecosystem service, and it is uncertain how changes in dominant vegetation may affect coastal protection. As part of a long-term study (2012–present) comparing ecosystem functions of marsh and black mangrove vegetation, we have experimentally maintained marsh and black mangrove patches (3 m × 3 m) along a plot-level (24 m × 42 m) gradient of marsh and mangrove cover in coastal wetlands near Port Aransas, TX. In August 2017, this experiment was directly in the path of Hurricane Harvey, a category 4 storm. This extreme disturbance event provided an opportunity to quantify differences in resistance between mangrove and marsh vegetation and to assess which vegetation type provided better shoreline protection against storm-driven erosion. We compared changes in plant cover, shoreline erosion, and accreted soil depth to values measured prior to storm landfall. Relative mangrove cover decreased 25–40% after the storm, regardless of initial cover, largely due to damage on taller mangroves (> 2.5 m height) that were not fully inundated by storm surge and were therefore exposed to strong winds. Evidence of regrowth on damaged mangrove branches was apparent within 2 months of landfall. Hurricane-induced decreases in mangrove cover were partially ameliorated by the presence of neighboring mangroves, particularly closer to the shoreline. Marsh plants were generally resistant to hurricane effects. Shoreline erosion exceeded 5 m where mangroves were absent (100% marsh cover) but was relatively modest (< 0.5 m) in plots with mangroves present (11–100% mangrove cover). Storm-driven accreted soil depth was variable but more than 2× higher in marsh patches than in mangrove patches. In general, mangroves provided shoreline protection from erosion but were also more damaged by wind and surge, which may reduce their shoreline protection capacity over longer time scales.more » « less
-
Hurricanes are recurring high-energy disturbances in coastal regions that change community structure and function of mangrove wetlands. However, most of the studies assessing hurricane impacts on mangroves have focused on negative effects without considering the positive influence of hurricane-induced sediment deposition and associated nutrient fertilization on mangrove productivity and resilience. Here, we quantified how Hurricane Irma influenced soil nutrient pools, vertical accretion, and plant phosphorus (P) uptake after its passage across the Florida Coastal Everglades in September 2017. Vertical accretion from Irma’s deposits was 6.7 to 14.4 times greater than the long-term (100 y) annual accretion rate (0.27 ± 0.04 cm y−1). Storm deposits extended up to 10-km inland from the Gulf of Mexico. Total P (TP) inputs were highest at the mouth of estuaries, with P concentration double that of underlying surface (top 10 cm) soils (0.19 ± 0.02 mg cm−3). This P deposition contributed 49 to 98% to the soil nutrient pool. As a result, all mangrove species showed a significant increase in litter foliar TP and soil porewater inorganic P concentrations in early 2018, 3 mo after Irma’s impact, thus underscoring the interspecies differences in nutrient uptake. Mean TP loading rates were five times greater in southwestern (94 ± 13 kg ha−1d−1) mangrove-dominated estuaries compared to the southeastern region, highlighting the positive role of hurricanes as a natural fertilization mechanism influencing forest productivity. P-rich, mineral sediments deposited by hurricanes create legacies that facilitate rapid forest recovery, stimulation of peat soil development, and resilience to sea-level rise.more » « less
-
Abstract Hurricanes are among the most destructive natural disturbances in mangroves, altering community structure and ecological processes. Despite their impacts, few studies have assessed changes in belowground root processes (i.e., biomass, production, decomposition) following major hurricanes. Here, we quantified and compared changes in mangrove root processes in the Florida Coastal Everglades before (pre‐hurricane period: 2000–2004) and after post‐hurricane periods (post‐Wilma, May 2012; immediate‐post‐Irma, March 2018; post‐Irma, March 2023). We assessed spatiotemporal patterns in root dynamics across four mangrove sites (upstream, midstream, downstream, and estuary mouth) along a well‐defined soil phosphorus fertility gradient in the Shark River estuary. Root biomass carbon stocks were highest in the immediate‐post‐Irma and post‐Irma periods. The midstream site had the highest root C stocks, whereas the downstream site had the lowest across periods. Root size class distribution shifted considerably post‐hurricane, with fine roots accounting for 32% (post‐Wilma) to 66% (immediate‐post‐Irma and post‐Irma) of the total root C stocks across sites. However, root production did not vary among periods at any site, although estimates were higher midstream compared to upstream or downstream. Root total nitrogen and P were ~1.3 times higher in the post‐Irma period compared to other periods, with root P consistently increasing from upstream to the estuary mouth. Fine root turnover rates were lower post‐hurricane compared to pre‐hurricane across sites. Root decay rates declined post‐Irma at all sites, except at the midstream site. Our findings suggest that P‐rich sediments deposited by hurricanes can enhance belowground C allocation by increasing root biomass and nutrient uptake, while reducing root turnover to facilitate forest recovery. These responses underscore the strong phenotypic plasticity and resilience of mangrove roots in P‐limited carbonate settings, highlighting their critical role in C sequestration, resilience, and ecosystem stability as climate‐related disturbances and sea‐level rise intensify.more » « less
-
Mangrove forests along the coastlines of the tropical and sub-tropical western Atlantic are intermittently impacted by hurricanes and can be damaged by high-speed winds, high-energy storm surges, and storm surge sediment deposits that suffocate tree roots. This study quantified trends in damage, delayed mortality, and early signs of below- and aboveground recovery in mangrove forests in the Lower Florida Keys and Ten Thousand Islands following direct hits by Hurricane Irma in September 2017. Mangrove trees suffered 19% mortality at sites in the Lower Florida Keys and 11% in the Ten Thousand Islands 2–3 months post-storm; 9 months post-storm, mortality in these locations increased to 36% and 20%, respectively. Delayed mortality of mangrove trees was associated with the presence of a carbonate mud storm surge deposit on the forest floor. Mortality and severe branch damage were more common for mangrove trees than for mangrove saplings. Canopy coverage increased from 40% cover 1–2 months post-storm to 60% cover 3–6 months post-storm. Canopy coverage remained the same 9 months post-storm, providing light to an understory of predominantly Rhizophora mangle (red mangrove) seedlings. Soil shear strength was higher in the Lower Florida Keys and varied with depth; no significant trends were found in shear strength between fringe or basin plots. Rates of root growth, as assessed using root in-growth bags, were relatively low at 0.01–11.0 g m−2 month−1 and were higher in the Ten Thousand Islands. This study demonstrated that significant delayed mangrove mortality can occur 3–9 months after a hurricane has passed, with some mortality attributable to smothering by storm surge deposits.more » « less
