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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 FROM AUTHOR]

We investigated how mangrove-island micro-elevation (i.e. habitat: center vs edge) affects tree physiology in a scrub mangrove forest of the southeastern Everglades. We measured leaf gas exchange rates of scrub Rhizophora mangle L. trees monthly during 2019, hypothesizing that CO2 assimilation (A net) and stomatal conductance (g sw) would decline with increasing water levels and salinity, expecting more considerable differences at mangrove-island edges than centers, where physiological stress is greatest. Water levels varied between 0 and 60 cm from the soil surface, rising during the wet season (May–October) relative to the dry season (November–April). Porewater salinity ranged from 15 to 30 p.p.t. being higher at mangrove-island edges than centers. A net maximized at 15.1 μmol m−2 s−1, and g sw was typically <0.2 mol m−2 s−1, both of which were greater in the dry than the wet season and greater at island centers than edges, with seasonal variability being roughly equal to variation between habitats. After accounting for season and habitat, water level positively affected A net in both seasons but did not affect g sw. Our findings suggest that inundation stress (i.e. water level) is the primary driver of variation in leaf gas exchange rates of scrub mangroves in the Florida Everglades, while also constraining A net more than g sw. The interaction between inundation stress due to permanent flooding and habitat varies with season as physiological stress is alleviated at higher-elevation mangrove-island center habitats during the dry season. Freshwater inflows during the wet season increase water levels and inundation stress at higher-elevation mangrove-island centers, but also potentially alleviate salt and sulfide stress in soils. Thus, habitat heterogeneity leads to differences in nutrient and water acquisition and use between trees growing in island centers versus edges, creating distinct physiological controls on photosynthesis, which likely affect carbon flux dynamics of scrub mangroves in the Everglades. [ABSTRACT FROM AUTHOR]

To determine whether mangrove soil accretion can keep up with increasing rates of sea level rise, we modeled the theoretical, steady-state (i.e., excluding hurricane impacts) limits to vertical soil accretion in riverine mangrove forests on the southwest coast of Florida, USA. We measured dry bulk density (BD) and loss on ignition (LOI) from mangrove soils collected over a period of 12 years along an estuarine transect of the Shark River. The plotted relationship between BD and LOI was fit to an idealized mixing model equation that provided estimates of organic and inorganic packing densities in the soils. We used these estimates in combination with measures of root production and mineral deposition to calculate their combined contribution to steady-state, vertical soil accretion. On average, the modeled rates of accretion (0.9 to 2.4 mm year−1) were lower than other measured rates of soil accretion at these sites and far less than a recent estimate of sea level rise in south Florida (7.7 mm year−1). To date, however, no evidence of mangrove "drowning" has been observed in this region of the Everglades, indicating that assumptions of the linear accretion model are invalid and/or other contributions to soil accretion (e.g., additional sources of organic matter; feedbacks between physical sedimentation processes and biological responses to short-term environmental change) make up the accretion deficit. This exercise highlights the potential positive impacts of hurricanes on non-steady-state soil accretion that contribute to the persistence of neotropical mangroves in regions of high disturbance frequency such as the Gulf of Mexico and the Caribbean region. [ABSTRACT FROM AUTHOR]

Ecosystems across the United States are changing in complex ways that are difficult to predict. Coordinated long‐term research and analysis are required to assess how these changes will affect a diverse array of ecosystem services. This paper is part of a series that is a product of a synthesis effort of the U.S. National Science Foundation's Long Term Ecological Research (LTER) network. This effort revealed that each LTER site had at least one compelling scientific case study about "what their site would look like" in 50 or 100 yr. As the site results were prepared, themes emerged, and the case studies were grouped into separate papers along five themes: state change, connectivity, resilience, time lags, and cascading effects and compiled into this special issue. This paper addresses the time lags theme with five examples from diverse biomes including tundra (Arctic), coastal upwelling (California Current Ecosystem), montane forests (Coweeta), and Everglades freshwater and coastal wetlands (Florida Coastal Everglades) LTER sites. Its objective is to demonstrate the importance of different types of time lags, in different kinds of ecosystems, as drivers of ecosystem structure and function and how these can effectively be addressed with long‐term studies. The concept that slow, interactive, compounded changes can have dramatic effects on ecosystem structure, function, services, and future scenarios is apparent in many systems, but they are difficult to quantify and predict. The case studies presented here illustrate the expanding scope of thinking about time lags within the LTER network and beyond. Specifically, they examine what variables are best indicators of lagged changes in arctic tundra, how progressive ocean warming can have profound effects on zooplankton and phytoplankton in waters off the California coast, how a series of species changes over many decades can affect Eastern deciduous forests, and how infrequent, extreme cold spells and storms can have enduring effects on fish populations and wetland vegetation along the Southeast coast and the Gulf of Mexico. The case studies highlight the need for a diverse set of LTER (and other research networks) sites to sort out the multiple components of time lag effects in ecosystems. [ABSTRACT FROM AUTHOR]

Highlights • Hurricane Wilma (2005) did not impact mangrove forest structure or stem productivity. • There was a negative relationship between leaf NPP and foliar residence time. • This relationship is a good proxy of canopy recovery for global mangrove NPP studies. Abstract Mangrove wetlands along coastal regions in neotropical northern latitudes are exposed to frequent hurricanes and therefore depend on resistant and resilient attributes to persist after these extreme events. However, few long-term studies have documented mangrove forest dynamics following hurricane disturbance to determine how species-specific phenotypic plasticity, species range shifts, and environmental stress interact to determine recovery trajectories. We present here a comprehensive analysis of Hurricane Wilma's (hereafter, "Wilma") impact (category 3, October 2005) on mangrove forest demography and aboveground net productivity in the Everglades, Florida (USA). We determined spatiotemporal patterns over a 15-year period (5 pre- and 10 post-Wilma) in three impacted sites on a productivity gradient along the Shark River Estuary. Hurricane resistance was evident in the low cumulative tree mortality and long-term recovery from defoliation (∼10 years). Aboveground standing carbon stocks were not significantly reduced, as mortality ranged only from 3 to 10%. A negative linear relationship between Leaf Net Primary Productivity (NPP L) and foliar residence time along the estuary shows that an increase in foliar production results in shorter residence time, which is defined by the interannual variation in NPP L rates and recovery periods across sites. We propose this relationship as a proxy of canopy recovery in latitudinal comparative studies across mangrove ecotypes and coastal settings. This work advances ecological disturbance theory and ecological modeling of mangrove forests; specifically, we provide quantitative relationships among structural properties and dynamic processes to validate agent-based demographic and biogeochemical models to forecast the impact of natural and human disturbances on mangrove wetlands under climate change. [ABSTRACT FROM AUTHOR]

We evaluated mangrove forest resilience in the Florida Coastal Everglades (FCE) by analyzing long-term (2001–2014) spatial and temporal patterns of litterfall net primary productivity (NPP L ), including the impact and recovery from two natural disturbance events: Hurricane Wilma (October-2005) and a cold snap (January-2010). Specifically, we tested whether the disturbance driven recovery trajectory of mangrove forests (i.e. recovery duration and rate) depends on the disturbance impact magnitude and initial forest structure in three study sites. Hurricane Wilma caused canopy defoliation at all sites and was a function of the wind-field strength such that higher wind speeds at the SRS-6 site (30–40 m s −1 ) induced greatest defoliation (4.7 Mg C ha −1 yr −1 ). Disturbance magnitude (decrease in NPP L from 2005 to 2006) was higher in SRS-6 (7.8 Mg C ha −1 yr −1 ), followed by SRS-4 (5.7 Mg C ha −1 yr −1 ) and SRS-5 (5.5 Mg C ha −1 yr −1 ). We observed differential NPP L recovery times among sites and species, where sites SRS-5 and SRS-6 returned to pre-Wilma NPP L rates by 2010 while SRS-4 has not yet fully recovered. In contrast, the cold snap had significant disturbance impact, yet recovery occurred within one month across all sites. We conclude that differential resilience to Hurricane Wilma was a result of a synergy of local changes in hydrology, salinity and storm impact. The long-term ability of subtropical mangroves to recover to pre-disturbance production rates within a short period (<5 years) demonstrates their resilience capacity in cases where massive defoliation occurs as result of natural disturbances. [ABSTRACT FROM AUTHOR]

The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0-10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30± 0.03 cm year-1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm-3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm-3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise. [ABSTRACT FROM AUTHOR]

• A mass balance-based hydrological model was modified to simulate soil porewater salinity in riverine mangrove forests. • The seasonal and annual interaction between freshwater inflow and sea level rise controls soil porewater salinity values in Everglades mangrove forests. • Hydrological restoration decisions and a warming climate can trigger vegetation species composition/dominance shifts by changing the soil porewater salinity regime and its interaction with fertility gradients. • The model can serve as a tool to guide wetland restoration management decisions. Hydrology is a critical driver controlling mangrove wetlands structural and functional attributes at different spatial and temporal scales. Yet, human activities have negatively affected hydrology, causing mangrove diebacks and coverage loss worldwide. In fact, the assessment of mangrove water budgets, impacted by natural and human disturbances, is limited due to a lack of long-term data and information that hinders our understanding of how changes in hydroperiod and salinity control mangrove productivity and spatial distribution. In this study, we implemented a mass balance-based hydrological model (RHYMAN) that explicitly considers groundwater discharge in the Shark River estuary (SRE, southwestern Everglades) located in a karstic geomorphic setting and influenced by regional hydrological restoration. We used long-term hydroperiod and porewater salinity (PWS) datasets obtained from 2004 to 2016 for model calibration and validation and to determine spatiotemporal variability in water levels and PWS at three riverine mangrove sites (downstream, SRS-6; midstream, SRS-5; upstream, SRS-4) along SRE. Model results agree with a distinct PWS pattern along the estuarine salinity gradient where the highest PWS occurs at SRS-6 (mean: 25, range: 22–30 ppt), followed by SRS-5 (17, 14–25 ppt) and SRS-4 (5, 3–13 ppt). A commensurate increase in PWS over a thirteen-year period indicates a long-term reduction in freshwater inflow coupled with sea-level rise (SLR). Increasing freshwater scenario simulation results show a significant reduction (17–27%) in PWS along the estuary in contrast with a high SLR scenario when salinity increases up to 1.1 to 2.5 times that of control values. Model results show that freshwater inflow and SLR are key drivers controlling mangrove wetlands PWS in this karstic coastal region. Given its relatively simple structure, this mass balance-based hydrological model could be used in other environmental settings to evaluate potential habitat and regime shifts due to changes in hydrology and PWS under regional hydrological restoration management. [ABSTRACT FROM AUTHOR]