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Freeze events govern the distribution and structure of mangrove ecosystems, especially in tropical‐temperate transitional zones. Understanding mangrove responses to freezing is crucial for predicting their poleward expansion under climate change. However, there is a need for field‐based measurements of mangrove freeze resistance and resilience. After an extreme winter storm in December 2022, we measured mangrove post‐freeze damage and recovery (January and November 2023), building on a pre‐freeze baseline assessment conducted in July 2022 across 12 sites along the temperature gradient of Florida's Gulf of Mexico coast (USA). Low‐temperature thresholds for leaf damage to Avicennia germinans, Rhizophora mangle and Laguncularia racemosa were quantified near −6, −4 and − 4°C, respectively. Thresholds for mortality were found to be near −6 to −7°C for A. germinans and −4 to −5°C for R. mangle. A threshold for loss of reproductivity in A. germinans was identified near −6 to −7°C. Resprouting was observed in all three species but limited to just one individual for R. mangle. Surviving A. germinans resprouted vigorously and had the greatest number of resprout branches, which was proportional to leaf damage. Tall A. germinans had a higher resprout percentage than short trees. Strata‐specific differences in freeze damage were most pronounced for R. mangle, with higher damage in tall versus short trees, while no difference was found between A. germinans strata. These results suggest that R. mangle population recovery may depend on the growth of short trees, while A. germinans can recover from all strata. Minimum air temperature was strongly correlated with mangrove height and above‐ground biomass. Projections of future minimum temperature and species‐specific freeze degree days predict warming winters, suggesting further mangrove development and range expansion under climate change. Synthesis: Collectively, our study advances understanding of mangrove responses to freezing and identifies low‐temperature thresholds for each species, aiding predictions of mangrove range expansion. [ABSTRACT FROM AUTHOR]

Abstract Although mangrove forests are great carbon sinks, they also release carbon dioxide (CO2) from soil, plants, and water through respiration. Many studies have focused on CO2 effluxes only from soils, but the role of biogenic structures such as pneumatophore roots has been poorly studied. Hence, CO2 effluxes from pneumatophores were quantified at sediment-air (non-flooded sediment) and water–air (flooded sediment) interfaces along a salinity gradient in three mangrove types (fringe, scrub, and basin) dominated by Avicennia germinans during the dry and rainy seasons in Yucatan, Mexico. Pneumatophore abundance explained up to 91% of CO2 effluxes for scrub, 87% for fringe, and 83% for basin mangrove forests at the water–air interface. Overall, CO2 effluxes were inversely correlated with temperature and salinity. The highest CO2 effluxes were in the fringe and the lowest were in the scrub mangrove forests. Flooding decreased CO2 effluxes from the dry to the rainy season in all mangrove forests. These results highlight the contribution of pneumatophores to mangrove respiration, and the need to include them in our current carbon budgets and models, but considering different exchange interfaces, seasons, and mangrove ecotypes.

Although mangrove forests are great carbon sinks, they also release carbon dioxide (CO2) from soil, plants, and water through respiration. Many studies have focused on CO2 effluxes only from soils, but the role of biogenic structures such as pneumatophore roots has been poorly studied. Hence, CO2 effluxes from pneumatophores were quantified at sediment-air (non-flooded sediment) and water–air (flooded sediment) interfaces along a salinity gradient in three mangrove types (fringe, scrub, and basin) dominated by Avicennia germinans during the dry and rainy seasons in Yucatan, Mexico. Pneumatophore abundance explained up to 91% of CO2 effluxes for scrub, 87% for fringe, and 83% for basin mangrove forests at the water–air interface. Overall, CO2 effluxes were inversely correlated with temperature and salinity. The highest CO2 effluxes were in the fringe and the lowest were in the scrub mangrove forests. Flooding decreased CO2 effluxes from the dry to the rainy season in all mangrove forests. These results highlight the contribution of pneumatophores to mangrove respiration, and the need to include them in our current carbon budgets and models, but considering different exchange interfaces, seasons, and mangrove ecotypes. [ABSTRACT FROM AUTHOR]

Climate change is reshaping coastal wetlands worldwide, driving ecosystem shifts like mangrove poleward expansion into saltmarshes in tropical‐temperate transitional zones. Though warming is recognized as the primary driver, a lack of detailed field studies limits our ability to predict mangrove responses to rapid climate warming.Here, we characterized how mangroves vary across a temperature gradient at 18 sites along Florida's Gulf of Mexico coast (USA). We used minimum air temperature (Tmin) derived from daily data from 1989 to 2021 as the independent variable and applied plot‐based and synoptic approaches to quantify species‐specific mangrove variation at community, population, and individual levels. We then used these results to spatially project future mangrove ecosystem properties under multiple warming scenarios.Across the Tmin gradient from −10.8 to −1.4°C, mangrove canopy height and coverage ranged from 0.4 to 11.5 m and 15% to 98%, respectively, with both exhibiting sigmoidal increases with Tmin. Estimated mangrove aboveground biomass ranged from 0 to 496.7 Mg/ha and showed a positive linear relationship with Tmin due both to the tall tree stratum's increased biomass per tree and higher abundance.While the population abundance and coverage of Rhizophora mangle and Laguncularia racemosa had positive linear relationships with Tmin, Avicennia germinans exhibited a significant quadratic relationship, reflecting the higher freeze tolerance of this species. Such tolerance may stem from A. germinans' higher morphological plasticity observed at the individual level, adapting to cold stress by exhibiting a more shrub‐like architecture at colder sites.Based on these field‐derived quantitative relationships, we projected substantial increases in mangrove coverage and canopy height near current range limits, with tall A. germinans dominating in the north and R. mangle dominating the centre and south of the study region.Synthesis. To better predict the ecological consequences in coastal wetlands under future climate change, it is essential to understand how mangroves respond to winter temperature regimes across a temperature gradient. Collectively, these cross‐level and species‐specific results advance our understanding of mangrove temperature sensitivity and provide information about the future of coastal wetland structure and function in response to a changing climate. [ABSTRACT FROM AUTHOR]

Determining the factors that set species' range limits is of critical importance in an era of rapid climate and biotic change. Mangroves dominate global tropical coastlines, but their subtropical range limits are thought to be mainly constrained by cold air. However, several tropical mangrove range limits are conspicuously warm, arid, and dominated by cold water countercurrents. Despite speculation that the combination of cold water and aridity controls these range limits, investigations of this phenomenon are rare.Here, we conducted an experimental study examining the separate and interactive effects of cold water and aridity on survival, growth, and ecophysiological traits of three mangrove species from the arid, countercurrent range limit in Baja California, Mexico. It is one of the few range edges worldwide where red and white mangroves (Rhizophora mangle and Laguncularia racemosa, respectively), not the putatively stress‐tolerant black mangroves (Avicennia germinans), are the most poleward distributed mangroves, providing further opportunity to examine how mangrove ecophysiological traits affect species‐specific range limits.Black mangroves were surprisingly intolerant of cold water regardless of aridity, with no seedlings surviving in the lowest water temperature (13°C) after 8 months. In contrast, both white and red mangrove seedlings were able to survive at 13°C when humidity was 65% (but not 40%).In cold water and arid conditions, leaf stomatal conductance was consistently lowest for white mangroves, intermediate for red mangroves, and highest for black mangroves, suggesting that white mangroves were the most resistant to transpiration water loss in the arid conditions typical of Baja.Similarly, when exposed to drought after the eight‐month experiment, white mangroves grown in cold water survived longer than red and black mangroves.Synthesis: Ultimately, our results suggest that the species‐specific range limits of mangroves in Baja California reflects their species‐specific adaptations (or lack thereof) to cold water and aridity, with white and red mangroves surprisingly outperforming black mangroves. Further, the difference in our results compared to the same species in other ranges underscores the need to incorporate species and range‐specific traits when conducting distribution modelling to predict the effects of climate change on organism range limits. [ABSTRACT FROM AUTHOR]

Abstract Mangrove leaves have unique features that enable them to cope with shifting environmental conditions while preserving their general functionality and efficiency. We examined the morphological characteristics and chlorophyll content (spectroscopically) of 600 mature Avicennia germinans leaves selected from 30 trees located in one degraded, one restored, and one natural mangrove ecosystem along Guyana's coastline. Systematic sampling was carried out using the closest individual sampling method in the wet and dry seasons. We hypothesized that both habitat type and seasonality influence the leaf traits and chlorophyll content of A. germinans. Our findings showed that A. germinans leaves are mesophyllous, and traits such as leaf perimeter, area, length, width, dry mass, wet mass, turgid mass, leaf‐specific area, and relative water content showed fluctuations in ecosystems (one‐way ANOVA, p .75) were also established for over 10 leaf parameters in both seasons while PCA and multiple regression analyses further confirmed the strong relationships between leaf morphological features and their respective locations. Changes in chlorophyll concentration were most noticeable in the degraded ecosystem while variations in leaf traits were more pronounced in the restored mangrove area. This may be due to the various disturbances found in each ecosystem coupled with fluctuations in the seasons. Our results demonstrate that mangroves, to some extent, alter their plant structures to cope with environmental stressors present in the various ecosystems they thrive in to maintain their survival.

Climate change is altering the frequency and intensity of extreme weather events. Quantifying ecosystem responses to extreme events at the landscape scale is critical for understanding and responding to climate-driven change but is constrained by limited data availability. Here, we integrated remote sensing with ground-based observations to quantify landscape-scale vegetation damage from an extreme climatic event. We used ground- and satellite-based black mangrove (Avicennia germinans) leaf damage data from the northern Gulf of Mexico (USA and Mexico) to examine the effects of an extreme freeze in a region where black mangroves are expanding their range. The February 2021 event produced coastal temperatures as low as − 10 °C in some areas, exceeding thresholds for A. germinans damage and mortality. We used Sentinel-2 surface reflectance data to assess vegetation greenness before and after the freeze, along with ground-based observations of A. germinans leaf damage. Our results show a negative, nonlinear threshold relationship between A. germinans leaf damage and minimum temperature, with a temperature threshold for leaf damage near − 6 °C. Satellite-based analyses indicate that, at the landscape scale, damage was particularly severe along the central Texas coast, where the freeze event affected > 2000 ha of A. germinans-dominated coastal wetlands. Our analyses highlight the value of pairing remotely sensed data with regional, ground-based observations for quantifying and extrapolating the effects of extreme freeze events on mangroves and other tropical, cold-sensitive plants. The results also demonstrate how extreme freeze events govern the expansion and contraction of mangroves near northern range limits in North America. [ABSTRACT FROM AUTHOR]

Mangrove leaves have unique features that enable them to cope with shifting environmental conditions while preserving their general functionality and efficiency. We examined the morphological characteristics and chlorophyll content (spectroscopically) of 600 mature Avicennia germinans leaves selected from 30 trees located in one degraded, one restored, and one natural mangrove ecosystem along Guyana's coastline. Systematic sampling was carried out using the closest individual sampling method in the wet and dry seasons. We hypothesized that both habitat type and seasonality influence the leaf traits and chlorophyll content of A. germinans. Our findings showed that A. germinans leaves are mesophyllous, and traits such as leaf perimeter, area, length, width, dry mass, wet mass, turgid mass, leaf‐specific area, and relative water content showed fluctuations in ecosystems (one‐way ANOVA, p <.05) as well as seasonally (paired t‐test, p <.05). Substantial, positive correlations (p <.05, R >.75) were also established for over 10 leaf parameters in both seasons while PCA and multiple regression analyses further confirmed the strong relationships between leaf morphological features and their respective locations. Changes in chlorophyll concentration were most noticeable in the degraded ecosystem while variations in leaf traits were more pronounced in the restored mangrove area. This may be due to the various disturbances found in each ecosystem coupled with fluctuations in the seasons. Our results demonstrate that mangroves, to some extent, alter their plant structures to cope with environmental stressors present in the various ecosystems they thrive in to maintain their survival. [ABSTRACT FROM AUTHOR]

Mangroves are vital ecosystems that help mitigate climate change and natural hazards, despite representing only 0.5% of the world's coastlines. Recent studies have provided empirical evidence of the ongoing over-exploitation of mangrove forests in West Africa. Understanding the impact of such harvesting on mangroves’ carbon potential is essential to inform decision-making for management and carbon economy policies. This study investigated the impacts of harvesting intensity on (i) carbon allocation to species, size class, soil depth and pool (standing live trees, standing dead trees, litter and soil); and (ii) carbon stock in the different carbon pools, and its relationships with stand structural attributes, using the case study of Benin coastal line. Data were collected in 600 plots of 0.015 ha across 20 mangrove sites in high and low-harvesting-intensity areas. Sixty litter quadrats were also established to sample litter, while 160 soil samples were collected for soil carbon content analysis.Regardless of the harvesting intensity, two mangrove species, Rhizophora racemosa and Avicennia germinans, contributed more than 98% of the tree carbon. Small (1–10 cm) and medium (10–20 cm) size classes dominated tree carbon in high and low harvesting sites, respectively. Soil carbon up to 1 m depth had the greatest share (55%-70%) of the total carbon stock, followed by standing live trees (26%-40%) and litter, and was not influenced by harvesting intensity. Harvesting intensity influenced the carbon stocks in standing live and dead trees, with greater values in low and high harvesting sites. The total carbon stock was ∼ 1.46-fold higher in low harvesting sites (308.54 ± 32.74 MgC.ha−1) than in high harvesting sites (211.40 ± 14.91 MgC.ha−1). Mixed effect models showed that stand density and proportion of R. racemosa related positively with tree carbon stock, especially on low harvesting sites. Multiple factorial analyses revealed that carbon stocks in dead trees, litter and soil are high in low harvesting areas where stand densities are also high. However, in high harvesting sites, carbon stock in litter was positively related to relative density of A. germinans. This study expands our understanding of the carbon stock potential in a West African mangrove subject to different levels of disturbance and its contribution to mitigating greenhouse gas emissions. The implications for management were further discussed.

Background and Aims How well plants reproduce near their geographic range edge can determine whether distributions will shift in response to changing climate. Reproduction at the range edge can be limiting if pollinator scarcity leads to pollen limitation, or if abiotic stressors affect allocation to reproduction. For many animal-pollinated plants with expanding ranges, the mechanisms by which they have overcome these barriers are poorly understood. Methods In this study, we examined plant–pollinator interactions hypothesized to impact reproduction of the black mangrove, Avicennia germinans , which is expanding northward in coastal Florida, USA. We monitored insects visiting A. germinans populations varying in proximity to the geographic range edge, measured the pollen loads of the most common insect taxa and pollen receipt by A. germinans stigmas, and quantified flower and propagule production. Key Results We found that despite an 84 % decline in median floral visits by insects at northernmost versus southernmost sites, range-edge pollen receipt remained high. Notably, local floral visitor assemblages exhibited substantial turnover along the study's latitudinal gradient, with large-bodied bees and hover flies increasingly common at northern sites. We also observed elevated flower production in northern populations and higher per capita reproductive output at the range edge. Furthermore, mean propagule mass in northern populations was 18 % larger than that from the southernmost populations. Conclusions These findings reveal no erosion of fecundity in A. germinans populations at range limits, allowing rapid expansion of mangrove cover in the region. These results also illustrate that substantial turnover in the assemblage of flower-visiting insects can occur at an expanding range edge without altering pollen receipt. [ABSTRACT FROM AUTHOR]

Mangroves are unique coastal ecosystems, which have many important ecological functions, as they are a reservoir of many marine species well adapted to saline conditions and are fundamental as sites of carbon storage. Although the microbial contribution to nutrient cycling in these ecosystems has been well recognized, there is a lack of information regarding the microbial composition and structure of different ecological types of mangrove forests. In this study, we characterized the microbial community (Bacteria and Archaea) in sediments associated with five ecological types of mangrove forests in a coastal lagoon dominated by Avicennia germinans and Rhizophora mangle, through 16S rRNA-V4 gene sequencing. Overall, Proteobacteria (51%), Chloroflexi (12%), Gemmatimonadetes (5%) and Planctomycetes (6%) were the most abundant bacterial phyla, while Thaumarchaeota (30%), Bathyarchaeota (21%) and Nanoarchaeaeota (18%) were the dominant archaeal phyla. The microbial composition associated with basin mangroves dominated by Avicennia germinans was significantly different from the other ecological types, which becomes relevant for restoration strategies. [ABSTRACT FROM AUTHOR]

Nutrient enrichment is a major driver of environmental change in mangrove ecosystems. Yet, nutrient enrichment impacts on physiological processes that regulate CO2 and water fluxes between mangrove vegetation and the atmosphere remain unclear. We measured peak growing season photosynthesis (A) and respiration (R) in black mangrove (Avicennia germinans) leaves that had been subjected to long-term (8-year) nutrient enrichment (added N, added P, control) in north Florida. Previous results from this site indicated that Avicennia productivity was N-limited, but not P-limited. Thus, we expected that N addition would increase light saturated net photosynthesis at ambient CO2 (Anet), intrinsic water-use efficiency (iWUE), maximum rate of Rubisco carboxylation (Vcmax), and leaf dark respiration (R), while P addition would have little effect on any aspect of photosynthesis or respiration. We expected that increased photosynthesis and respiration would be most apparent immediately after N addition and in newly formed leaves. Indeed, Anet and Vcmax increased just after N addition in the N addition treatment; these increases were limited to leaves formed just after N addition. Nonetheless, over time, photosynthetic parameters and iWUE were similar across treatments. Interestingly, R measured at 25 °C increased with N addition; this effect was consistent across time points. P addition had little effect on R. Across treatments and time points, Vcmax,25 (Vcmax standardized to 25 °C) showed no relationship with R at 25 °C, but the maximum rate of electron transport for RuBP regeneration standardized to 25 °C (Jmax,25) increased with R at 25 °C. We conclude that N addition may have small, short-lived effects on photosynthetic processes, but sustained effects on leaf R in N-limited mangrove ecosystems. [ABSTRACT FROM AUTHOR]

This study examined species composition and occurrence pattern among mangroves across the Western Niger Delta. Vegetation measurements were carried out in one hundred quadrats of 20m by 20m. Rhizophora spp was dominant in Burutu, Opuama, Kurutie, Control (Importance Value Index =300, 177.28, 237.65, 300). A.germinans was dominant in Agge (IVI =183.03). Adult Rhizophora spp were dispersed in Agge, Burutu, Control (Morisita Index =0.25, 1.02, 0.025). Adult A. germinans were dispersed in Kurutie, Opuama, Agge (MI =0.07, 0.08, 0.26). Rhizophora spp juveniles were clustered in Agge, Burutu, Opuama, Kurutie, Control (MI =1.17, 1.86, 1.47, 1.9, 1.14). A. germinans juveniles were dispersed in Kurutie, Agge (MI =0.06, 0.69). Restoration and conservation programs should be established. [ABSTRACT FROM AUTHOR]

Mangroves are unique coastal ecosystems, which have many important ecological functions, as they are a reservoir of many marine species well adapted to saline conditions and are fundamental as sites of carbon storage. Although the microbial contribution to nutrient cycling in these ecosystems has been well recognized, there is a lack of information regarding the microbial composition and structure of different ecological types of mangrove forests. In this study, we characterized the microbial community (Bacteria and Archaea) in sediments associated with five ecological types of mangrove forests in a coastal lagoon dominated by Avicennia germinans and Rhizophora mangle, through 16S rRNA-V4 gene sequencing. Overall, Proteobacteria (51%), Chloroflexi (12%), Gemmatimonadetes (5%) and Planctomycetes (6%) were the most abundant bacterial phyla, while Thaumarchaeota (30%), Bathyarchaeota (21%) and Nanoarchaeaeota (18%) were the dominant archaeal phyla. The microbial composition associated with basin mangroves dominated by Avicennia germinans was significantly different from the other ecological types, which becomes relevant for restoration strategies.

Background and Aims Trees interconnected through functional root grafts can exchange resources, but the effect of exchange on trees remains under debate. A mechanistic understanding of resource exchange via functional root grafts will help understand their ecological implications for tree water exchange for individual trees, groups of trees and forest stands. Methods To identify the main patterns qualitatively describing the movement of sap between grafted trees, we reviewed the available literature on root grafting in woody plants that focus on tree allometry and resource translocation via root grafts. We then extended the BETTINA model, which simulates mangrove (Avicennia germinans) tree growth on the individual tree scale, to synthesize the available empirical information. Using allometric data from a field study in mangrove stands, we simulated potential water exchange and analysed movement patterns between grafted trees. Key Results In the simulations, relative water exchange ranged between −9.17 and 20.3 %, and was driven by gradients of water potential, i.e. differences in tree size and water availability. Moreover, the exchange of water through root grafts alters the water balance of trees and their feedback with the soil: grafted trees that receive water from their neighbours reduce their water uptake. Conclusions Our individual-tree modelling study is a first theoretical attempt to quantify root graft-mediated water exchange between trees. Our findings indicate that functional root grafts represent a vector of hydraulic redistribution, helping to maintain the water balance of grafted trees. This non-invasive approach can serve as a basis for designing empirical studies to better understand the role of grafted root interaction networks on a broader scale. [ABSTRACT FROM AUTHOR]

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Mangroves is an ecosystem which plays an economical role in Gabon for its watercourses where are used for fishing and marine traffic or as little bin for garbage and waste water disposal. These bad practices destroy that fragile ecosystem, perturbing like this carbon sequestration and biodiversity protection. Hence, the impact of the anthropogenic pollution stress of fishing engine oils so called hydrocarbons pollution on the chemical, microstructure and natural durability of Avicennia. germinans (L.)L. from Ambowé mangrove of the Estuary region of Gabon was studied. The results were compared with samples from Oveng and Mamboumba, two unpolluted sites of Libreville. Dichloromethane and hexane soluble extractives content decreased significantly (p < 0.05) in the polluted heartwoods, 5 ± 0,007 % et 2.11 ± 0,2 %, respectively. Confocal microscopy revealed for the first time the occurrence of rays and vessels opening in the polluted heartwood which could explain the loss of some extractives. That loss of extractives was supported by UV where a dramatic decrease of extractives was observed in the heartwood exposed to pollutants while no changes occurred in lignin. These changes on extractives content and wood microstructures would explain the high mass loss of the polluted heartwood exposed to Trametes versicolor (35.69 ± 6.27 %) and Rhodonia placenta (11.65 ± 6.62 %), these rot fungi provoked only mass losses <10 and 5 %, respectively for the unpolluted heartwoods. • Oil pollution is a danger for mangrove trees. • Oil pollution alters the properties of the wood at the macroscopic and microscopic levels in Avicennia germinans. • Oil pollution decreases the extractives content in Avicennia germinans wood. • Oil pollution decreases the content of lapachol in Avicennia germinans wood. • Oil pollution reduces the durability of Avicennia germinans wood. [ABSTRACT FROM AUTHOR]

Neotropical black mangrove (Avicennia germinans) is expanding poleward into temperate salt marsh along Atlantic Florida, USA, with field evidence of trait shifts consistent with greater cold tolerance within range margin populations. However, whether these shifts have a genetic basis remains unanswered. To address this gap, we measured multiple phenotypic traits of twenty A. germinans maternal cohorts from areas in both the Atlantic Florida range core and margin in a 2-year greenhouse common garden with annual temperatures analogous to range margin conditions. Compared to those from the range core, range margin cohorts survived in greater numbers, established (i.e., produced first true leaves) more quickly, and were less stressed under winter temperatures. Range margin cohorts were not taller, but invested more into lateral growth and biomass accumulation that presumably reflects adaptation to their colder and open-canopy environment. Range margin cohorts also exhibited leaf traits consistent with greater resource acquisition that may compensate for a shorter growing season and reduced light quality at higher latitude. Our results suggest that genetically based phenotypic differences better enable these range margin mangroves to thrive within their stressful environment and may facilitate further poleward expansion. An improved understanding of adaptive trait variation within ecologically important mangrove foundation species should also help inform coastal restoration initiatives. [ABSTRACT FROM AUTHOR]

Mangroves are one of the most threatened ecosystems globally. Likewise, they benefit many restoration efforts. However, these efforts have often disregarded potential effects of climate change on selected species and foreseen changes in physico-chemical conditions of mangrove ecosystems. This study aimed to model current and future climatic and physico-chemical conditions in occupied mangroves' niche, in order to derive implications for successful long-term restorations. Presence records of mangroves' indicator species and corresponding physico-chemical variables were collected. Bioclimatic data were obtained from Africlim. Kruskal–Wallis and Nemenyi pairwise tests for multiple comparisons were used to test the among sites (spatial) variations of climatic and physico-chemical variables within mangroves' niche. Multiple linear regression (MLR) and artificial neural network (ANN) were used to build predictive models of salinity, dissolved oxygen, and conductivity; using most meaningful climatic variables to tropical mangroves—potential evapotranspiration, temperature seasonality, mean temperature of the warmest quarter, moister index of the moist quarter, and moister index of the driest quarter as predictors. Results showed that there are strong spatial variations of climatic and physico-chemical variables within mangroves' niche. ANN outperformed MLR and was then used to predict trends in salinity, dissolved oxygen, and conductivity by year 2055. Based on foreseen trend in bioclimatic variables, conductivity, salinity, and dissolved oxygen will experiment significant changes under Representative Concentration Pathways 4.5 and 8.5, with most severe changes in case the later scenario occurs. Foreseen salinization of sites may be at the advantage of Avicennia germinans but to the prejudice of Rhizophora spp. [ABSTRACT FROM AUTHOR]

Mangrove ecosystems are estimated to have a high impact potential on the global carbon cycle because of their high organic matter content (Dittmar y col., 2006), and consequently a significant importance in CO2 flow as the greenhouse gas with the greatest impact on global warming (Benavides y León, 2007; Caballero, Lozano y Ortega, 2007; CESPA, 2013). In Venezuela, however, studies focusing on this issue are scarce, hence the aim of this research was to specify significant differences in the flow of CO2 in soil colonized by Avicennia germinans, as well as non-rizospheric located in Los Totumos sector. Research developed in three phases was applied: (a) fieldwork, in order to collect 120 surface soil samples (0-20 cm), (b) laboratory, with the purpose of estimating the CO2 flow from the basal breathing method (Anderson, 1982) and (c) statistical analysis, to identify significant differences based on the ANOVA and Tukey test. It is evident that there are significant differences, with flows of 7.51 mg C-CO2 g/24h in the rhyspheric area and 1.49 mg C-CO2 g/24h for non-rizospheric. It is concluded that: (a) microbial activity in the soil, induced by the presence of Avicennia germinans, is possibly contributing to its evolution, and (b) it is reaffirmed that mangrove ecosystems are a source of CO2 and reservoir gas to the impact of climate change. [ABSTRACT FROM AUTHOR]

Changes in species distributions and disturbances have complex impacts on ecosystem functioning. In many subtropical coastal wetlands, plant identity and cover are changing, as salt marshes dominated by low‐stature herbaceous species transition to woody mangroves. These systems are also subject to frequent and potentially more intense hurricanes, which can alter a range of ecosystem structures and functions. We examined how changes in dominant plant species affected carbon processing in coastal wetlands following a hurricane. We experimentally manipulated cell‐scale (3 × 3 m) cover of black mangroves (Avicennia germinans) and salt marsh plants (e.g., Spartina alterniflora and Batis maritima) in fringe and interior locations of 10 plots (24 × 42 m) to create a gradient in mangrove cover in coastal Texas, USA. Hurricane Harvey made direct landfall over our site on 25 August 2017, uniformly decreasing soil nutrients and impacting the spatial patterns of total soil sulfide accumulation (δ34S). To test how mangrove cover affected carbon processing and retention after the hurricane, we measured litter breakdown rates (k) of A. germinans and S. alterniflora in surface soils and associated microbial respiration rates, and fast‐ and slow‐decomposing standard litter substrates (green and red tea, respectively) in subsurface soils (15 cm depth). Soil temperatures were lower in mangrove than marsh cells, and A. germinans litter k increased linearly with plot‐level mangrove cover. Breakdown rates of S. alterniflora and fast‐decomposing green tea litter increased nonlinearly with mangrove cover (highest k at intermediate % cover). Slow‐decomposing red tea had similar k in all plots and was highest where soil δ34S was greatest. Microbial respiration rates (R) did not change with plot‐level mangrove cover for either S. alterniflora or A. germinans litter. Respiration associated with S. alterniflora litter was highest in interior marsh cells, and R associated with A. germinans litter was similar between fringe and interior mangrove cells. Despite widespread declines in soil nutrient concentrations and increases in δ34S, all predicted to decrease R and k, post‐hurricane carbon processing increased with mangrove cover in coastal wetlands. Our results indicate that disturbances can reduce local plant identity effects and may enhance carbon loss. [ABSTRACT FROM AUTHOR]

Geographic and environmental differences have been identified as factors influencing Brazilian mangrove trees' genetic diversity. Geographically, distinct species have convergent spatial genetic structures, indicating a limited gene flow between northern and southern populations. Environmentally, genomic studies and common garden experiments have found evidence of local adaptations along the latitudinal gradient of the Brazilian coast. However, little is known about how such adaptive heterogeneity could be affected by a rapidly changing climate in the coming decades, and the combination of deforestation and climate-induced habitat loss may affect these forests and their genetic diversity. Here, we applied two genomic-environmental association methods to model the turnover of potentially adaptive alleles for two dominant mangrove trees: Avicennia germinans and A. schaueriana. We analyzed a total of 134 individuals from six populations of A. germinans and 10 populations of A. schaueriana spanning the Brazilian coast from 1 °S to 28 °S. Gradient forest models identified temperature-related variables as the most important predictors for A. germinans outlier loci, whereas both temperature and precipitation were important for A. schaueriana. We modeled allele frequencies and projected them for future climatic scenarios to estimate adaptively driven vulnerability. We assessed climate-driven habitat loss through climate-only distribution models and calculated annual deforestation rates for each sampled region. Finally, to assess the vulnerability of individual populations, we combined the environmental suitability, deforestation data, and adaptive vulnerability projections. For both species, subtropical populations presented a higher vulnerability than equatorial populations to climate-driven habitat loss. We also identified deforestation rates at the sampled sites that were alarmingly higher than the global average mangrove deforestation rate. Our results provide improved estimates of the impacts of ongoing climate change and human-caused habitat loss on the distribution of mangroves and highlight the importance of site-based conservation strategies that consider individual subtropical and equatorial mangrove forests.

Abstract Changes in species distributions and disturbances have complex impacts on ecosystem functioning. In many subtropical coastal wetlands, plant identity and cover are changing, as salt marshes dominated by low‐stature herbaceous species transition to woody mangroves. These systems are also subject to frequent and potentially more intense hurricanes, which can alter a range of ecosystem structures and functions. We examined how changes in dominant plant species affected carbon processing in coastal wetlands following a hurricane. We experimentally manipulated cell‐scale (3 × 3 m) cover of black mangroves (Avicennia germinans) and salt marsh plants (e.g., Spartina alterniflora and Batis maritima) in fringe and interior locations of 10 plots (24 × 42 m) to create a gradient in mangrove cover in coastal Texas, USA. Hurricane Harvey made direct landfall over our site on 25 August 2017, uniformly decreasing soil nutrients and impacting the spatial patterns of total soil sulfide accumulation (δ34S). To test how mangrove cover affected carbon processing and retention after the hurricane, we measured litter breakdown rates (k) of A. germinans and S. alterniflora in surface soils and associated microbial respiration rates, and fast‐ and slow‐decomposing standard litter substrates (green and red tea, respectively) in subsurface soils (15 cm depth). Soil temperatures were lower in mangrove than marsh cells, and A. germinans litter k increased linearly with plot‐level mangrove cover. Breakdown rates of S. alterniflora and fast‐decomposing green tea litter increased nonlinearly with mangrove cover (highest k at intermediate % cover). Slow‐decomposing red tea had similar k in all plots and was highest where soil δ34S was greatest. Microbial respiration rates (R) did not change with plot‐level mangrove cover for either S. alterniflora or A. germinans litter. Respiration associated with S. alterniflora litter was highest in interior marsh cells, and R associated with A. germinans litter was similar between fringe and interior mangrove cells. Despite widespread declines in soil nutrient concentrations and increases in δ34S, all predicted to decrease R and k, post‐hurricane carbon processing increased with mangrove cover in coastal wetlands. Our results indicate that disturbances can reduce local plant identity effects and may enhance carbon loss.

Temperature acclimation of leaf respiration (R) is an important determinant of ecosystem responses to temperature and the magnitude of temperature‐CO2 feedbacks as climate warms. Yet, the extent to which temperature acclimation of R exhibits a common pattern across different growth conditions, ecosystems, and plant functional types remains unclear. Here, we measured the short‐term temperature response of R at six time points over a 10‐month period in two coastal wetland species (Avicennia germinans [C3 mangrove] and Spartina alterniflora [C4 marsh grass]) growing under ambient and experimentally warmed temperatures at two sites in a marsh–mangrove ecotone. Leaf nitrogen (N) was determined on a subsample of leaves to explore potential coupling of R and N. We hypothesized that both species would reduce R at 25°C (R25) and the short‐term temperature sensitivity of R (Q10) as air temperature (Tair) increased across seasons, but the decline would be stronger in Avicennia than in Spartina. For each species, we hypothesized that seasonal temperature acclimation of R would be equivalent in plants grown under ambient and warmed temperatures, demonstrating convergent acclimation. Surprisingly, Avicennia generally increased R25 with increasing growth temperature, although the Q10 declined as seasonal temperatures increased and did so consistently across sites and treatments. Weak temperature acclimation resulted in reduced homeostasis of R in Avicennia. Spartina reduced R25 and the Q10 as seasonal temperatures increased. In Spartina, seasonal temperature acclimation was largely consistent across sites and treatments resulting in greater respiratory homeostasis. We conclude that co‐occurring coastal wetland species may show contrasting patterns of respiratory temperature acclimation. Nonetheless, leaf N scaled positively with R25 in both species, highlighting the importance of leaf N in predicting respiratory capacity across a range of growth temperatures. The patterns of respiratory temperature acclimation shown here may improve the predictions of temperature controls of CO2 fluxes in coastal wetlands. [ABSTRACT FROM AUTHOR]

Se estima que los ecosistemas de manglar tienen un elevado potencial en el ciclo global de carbono por su alto contenido de materia orgánica (Dittmar et al., 2006), y en consecuencia una relevante importancia en el flujo del CO2 como el gas invernadero de mayor impacto en el calentamiento global (Benavides and León, 2007; Caballero et al., 2007; CESPA, 2013). No obstante, en Venezuela los estudios centrados en este asunto son escasos, es por ello que la presente investigación tuvo como propósito precisar diferencias significativas en el flujo de CO2 en suelo colonizado por Avicennia germinans, así como no rizosférico, emplazado en el sector Los Totumos. Se asumió una investigación desarrollada en tres fases: (a) trabajo de campo, a fin de colectar 120 muestras de suelo superficial (0-20 cm), (b) laboratorio, con el propósito de estimar el flujo de CO2 a partir del método de respiración basal (Anderson, 1982) y (c) análisis estadístico, para identificar con base en el ANOVA y prueba de Tukey, diferencias significativas. Se evidencia que existen diferencias significativas, con flujos de 7,51 mg C-CO2 g/24h en la zona rizosférica y 1,49 mg C-CO2 g/24h para la no rizosférica. Se concluye que: (a) la actividad microbiana en el suelo, inducida por las condiciones edáficas que genera la presencia de la Avicennia germinans posiblemente está contribuyendo con la evolución del mismo, y (b) se reafirma que los ecosistemas de manglar constituyen fuente de CO2 y sumidero del gas ante el impacto del cambio climático.

The niche-centroid hypothesis states that populations that are distributed near the centroid of the species' ecological niche will have higher fitness-related attributes, such as population abundance and genetic diversity than populations near the edges of the niche. Empirical evidence based on abundance and, more recently, genetic diversity data support this hypothesis. However, there are few studies that test this hypothesis in coastal species, such as mangroves. Here, we focused on the black mangrove Avicennia germinans. We combined ecological, heterozygosity, and allelic richness information from 1,419 individuals distributed in 40 populations with three main goals: (1) test the relationship between distance to the niche centroid and genetic diversity, (2) determine the set of environmental variables that best explain heterozygosity and allelic richness, and (3) predict the spatial variation in genetic diversity throughout most of the species' natural geographic range. We found a strong correlation between the distance to the niche centroid and both observed heterozygosity (Ho; ρ2 = 0.67 P < 0.05) and expected heterozygosity (He; ρ2 = 0.65, P < 0.05). The niche variables that best explained geographic variation in genetic diversity were soil type and precipitation seasonality. This suggests that these environmental variables influence mangrove growth and establishment, indirectly impacting standing genetic variation. We also predicted the spatial heterozygosity of A. germinans across its natural geographic range in the Americas using regression model coefficients. They showed significant power in predicting the observed data (R2 = 0.65 for Ho; R2 = 0.60 for He), even when we considered independent data sets (R2= 0.28 for Ho; R2 = 0.25 for He). Using this approach, several genetic diversity estimates can be implemented and may take advantage of population genomics to improve genetic diversity predictions. We conclude that the level of genetic diversity in A. germinans is in agreement with expectations of the niche-centroid hypothesis, namely that the highest heterozygosity and allelic richness (the basic genetic units for adaptation) are higher at locations of high environmental suitability. This shows that this approach is a potentially powerful tool in the conservation and management of this species, including for modelling changes in the face of climate change.

Predictions of climate-related shifts in species ranges have largely been based on correlative models. Due to limitations of these models, there is a need for more integration of experimental approaches when studying impacts of climate change on species distributions. Here, we used controlled experiments to identify physiological thresholds that control poleward range limits of three species of mangroves found in North America. We found that all three species exhibited a threshold response to extreme cold, but freeze tolerance thresholds varied among species. From these experiments, we developed a climate metric, freeze degree days (FDD), which incorporates both the intensity and the frequency of freezes. When included in distribution models, FDD accurately predicted mangrove presence/absence. Using 28 years of satellite imagery, we linked FDD to observed changes in mangrove abundance in Florida, further exemplifying the importance of extreme cold. We then used downscaled climate projections of FDD to project that these range limits will move northward by 2.2-3.2 km yr(-1) over the next 50 years.

Abstract Information on plant phenological patterns aids in understanding the structure and functioning of ecosystems and support restoration projects in degraded areas. The aim of this study was to characterize the reproductive phenology of Avicennia germinans and Laguncularia racemosa in a mangrove forest in the Mamanguape River estuary in northeastern Brazil. The characterization was performed monthly from July 2016 to June 2017. We applied circular statistics to detect seasonal trends, calculated intra-specific synchrony, and performed regressions between the reproductive phenophases and the abiotic variables. Avicennia germinans exhibits seasonal responses to floral buds, flowers at anthesis, and fruit, with one reproductive episode per year (annual pattern). Laguncularia racemosa has no seasonal response, with one reproductive episode per year for floral buds (annual pattern) and two episodes for flowers at anthesis and fruits (subannual pattern). Reproductive phenophases of A. germinans exhibited higher intra-specific synchrony than L. racemosa. We provide evidence that temperature, solar radiation and rainfall are important drivers of the flowering rhythm in both species. In conclusion, the results of this study showed that the species exhibited different phenological responses, even though they were subjected to the same abiotic conditions.

Premise: Host‐plant genetic variation can shape associated communities of organisms. These community‐genetic effects include (1) genetically similar hosts harboring similar associated communities (i.e., the genetic similarity rule) and (2) host‐plant heterozygosity increasing associated community diversity. Community‐genetic effects are predicted to be less prominent in plant systems with limited genetic variation, such as those at distributional range limits. Yet, empirical evidence from such systems is limited. Methods: We sampled a natural population of a mangrove foundation species (Avicennia germinans) at an expanding range limit in Florida, USA. We measured genetic variation within and among 40 host trees with 24 nuclear microsatellite loci and characterized their foliar endophytic fungal communities with internal transcribed spacer (ITS1) gene amplicon sequencing. We evaluated relationships among host‐tree genetic variation, host‐tree spatial location, and the associated fungal communities. Results: Genetic diversity was low across all host trees (mean: 2.6 alleles per locus) and associated fungal communities were relatively homogeneous (five sequence variants represented 78% of all reads). We found (1) genetically similar host trees harbored similar fungal communities, with no detectable effect of interhost geographic distance. (2) Host‐tree heterozygosity had no detectable effect, while host‐tree absolute spatial location affected community alpha diversity. Conclusions: This research supports the genetic similarity rule within a range limit population and helps broaden the current scope of community genetics theory by demonstrating that community‐genetic effects can occur even at expanding distributional limits where host‐plant genetic variation may be limited. Our findings also provide the first documentation of community‐genetic effects in a natural mangrove system. [ABSTRACT FROM AUTHOR]

Increases in minimum air temperatures have facilitated transitions of salt marshes to mangroves along coastlines in the southeastern United States. Numerous studies have documented mangrove expansion into salt marshes; however, a present‐day conversion of oyster reefs to mangrove islands has not been documented. Using aerial photographs and high‐resolution satellite imagery, we determined percent cover and number of mangrove patches on oyster reefs in Mosquito Lagoon, FL, USA over 74 years (1943–2017) by digitizing oyster reef and "mangrove on oyster reef" areas. Live oyster reefs present in 1943 were tracked through time and the mangrove area on every reef calculated for seven time periods. There was a 103% increase in mangrove cover on live oyster reefs from 1943 (6.6%) to 2017 (13.4%). Between 1943 and 1984, the cover remained consistent (~7%), while between 1984 and 2017, mangrove cover increased rapidly with a 6% year−1 increase in mangrove area on oyster reefs (198% increase). In 1943, 8.7% of individual reefs had at least one mangrove patch on them; by 2017, 21.8% of reefs did. Site visits found at least one mature Avicennia germinans on each tracked mangrove reef, with large numbers of smaller Rhizophora mangle, suggesting the post‐1984 mangrove increases were the result of increased R. mangle recruitment and survival. Escalation in the coverage and number of mangrove stands on oyster reefs coincided with a period that lacked extreme freeze events. The time since a temperature of ≤−6.6°C (A. germinans mortality threshold) and ≤−4°C (R. mangle mortality threshold) were significantly correlated with the increased ratio of mangrove area:oyster area, total mangrove area, and number of mangrove patches, with greater variation explained by time since ≤ −4°C. The lack of freezes could lead globally to an ecosystem shift of intertidal oyster reefs to mangrove islands near poleward mangrove range limits. [ABSTRACT FROM AUTHOR]

Ongoing losses to mangrove forests globally have prompted increased interest in restoration programs that seek to restore vital ecosystem functions and services. In many cases, data on local‐scale environmental tolerances of mangrove species used in reforestation efforts is lacking, and failure of restoration projects has been attributed to incorrect species selection in plantations. Here, we assess the impact of soil salinity on the early establishment success of monospecific red mangrove Rhizophora mangle reforestation projects in the Saloum Delta, Senegal, a region where widespread mangrove restoration efforts are ongoing. At soil salinities >60 ppt, stomatal conductance, photosystem II operating efficiency, and growth of planted R. mangle seedlings were severely reduced. Similarly, after 1–3 years, survival of mangrove seedlings decreased in soil salinities of >60 ppt. In contrast, we recorded naturally occurring black mangrove Avicennia germinans growing in exceptionally hypersaline conditions (90 ppt), representing some of the most saline vegetated ecosystems on Earth. The findings reported herein can be used to inform species choice in reforestation projects and help improve success rates of coastal wetland restoration projects in semiarid regions. [ABSTRACT FROM AUTHOR]

Information on plant phenological patterns aids in understanding the structure and functioning of ecosystems and support restoration projects in degraded areas. The aim of this study was to characterize the reproductive phenology of Avicennia germinans and Laguncularia racemosa in a mangrove forest in the Mamanguape River estuary in northeastern Brazil. The characterization was performed monthly from July 2016 to June 2017. We applied circular statistics to detect seasonal trends, calculated intra-specific synchrony, and performed regressions between the reproductive phenophases and the abiotic variables. Avicennia germinans exhibits seasonal responses to floral buds, flowers at anthesis, and fruit, with one reproductive episode per year (annual pattern). Laguncularia racemosa has no seasonal response, with one reproductive episode per year for floral buds (annual pattern) and two episodes for flowers at anthesis and fruits (subannual pattern). Reproductive phenophases of A. germinans exhibited higher intra-specific synchrony than L. racemosa. We provide evidence that temperature, solar radiation and rainfall are important drivers of the flowering rhythm in both species. In conclusion, the results of this study showed that the species exhibited different phenological responses, even though they were subjected to the same abiotic conditions. [ABSTRACT FROM AUTHOR]

El bosque salado o Manglar de Barra Salada con 454 has., ubicado en el departamento de Sonsonate, es considerado un ecosistema de importancia ambiental y socioeconómica; sin embargo, está siendo alterado por factores físico-químicos y antrópicos. Este bosque está ubicado en la parte sur de la cuenca Mandinga, con una extensión de 86.51 km², una elevación máxima de 600 msnm y drenado por los ríos Mandinga y Pululuya, que se extienden a través de los territorios municipales de San Julián, Cuisnahuat y Sonsonate. La cuenca presenta el 92% de su área para la producción agrícola (granos básicos abarcan: 29.1 km², siendo este el rubro más representativo, establecido en pendientes entre el 15% a más de 70%), hay una densidad poblacional de 173 hab./km²; estos, entre otros factores, son las causas que impiden el desarrollo de bienes y servicios ambientales, importantes para el buen funcionamiento de los ecosistemas en este territorio. Por ejemplo, el Índice de Calidad del agua (ICA), indica que aguas drenadas al manglar tienen calidad regular a pésima; los ríos, sin agua en época seca, facilitan el taponamiento de la bocana, y con ello, se elevan (30-33‰) o disminuyen (0.15-0.45‰) periódicamente, la concentración salina en las aguas del Estero, incrementándose además la temperatura en esta, por largos períodos de tiempo; a lo anterior, se suma la usurpación del manglar para construcción de viviendas (13.1 has.) o crecimiento agropecuario (22.01 has.). Estos factores, están promoviendo el desarrollo de bosques monoespecíficos de Avicennia germinans, que además se encuentran poco desarrollados y deteriorados, según se define por el índice de complejidad de Holdrige (ICH) que tuvo un valor de 0.094. De igual manera, el bosque salado se ha reducido en área, desde 1954 al 2018 en un 33.21% (260.01 has.), es decir, de 620.41 has. a 414.4 has. respectivamente, un área menor a la manejada oficialmente por el Ministerio del Ambiente y Recursos Naturales (MARN).

In the northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss of protective barrier islands. These barrier islands provide critical habitat for wildlife, including globally significant populations of marsh and shorebirds. We investigated salt marsh restoration on two Louisiana barrier islands using presence of eight marsh bird species as an index to evaluate restoration success. Land loss was extensive for both islands prior to restoration, with submerged marsh restored by backfilling sediment into the marsh platform. Restoration methods were similar between the two islands, although Raccoon Island was built to a higher elevation (1.1 m) than Whiskey Island (0.8 m). Avian presence was estimated via passive acoustic monitoring and point counts. To evaluate restoration success, we modeled influence of habitat covariates on index species presence in restored and reference (intact) sites over three breeding seasons and modeled occupancy for six species. On Whiskey Island, index richness was higher in restored sites. Marsh specialists Seaside Sparrows (Ammospiza maritima) and Least Bitterns (Ixobrychus exilis) had higher occupancy in restored areas on Whiskey, while generalist species showed no response to site. These results are likely due to a strong association between habitat and vegetation type, with restored sites dominated by Spartina alterniflora and reference sites by Avicennia germinans. On Raccoon Island, species richness was low across all sites. Our results suggest that restoration efforts were successful in creating salt marsh habitat on Whiskey but not Raccoon as of the time of our study. [ABSTRACT FROM AUTHOR]

Aim: Climate change is expected to result in the tropicalization of coastal wetlands in the northern Gulf of Mexico, as warming winters allow tropical mangrove forests to expand their distribution poleward at the expense of temperate salt marshes. Data limitations near mangrove range limits have hindered understanding of the effects of winter temperature extremes on mangrove distribution and structure. Here, we investigated the influence of extreme freeze events on the abundance, height and coverage of black mangroves (Avicennia germinans) near their northern range limit in Louisiana. Location: Coastal Louisiana, USA. Methods: We quantified the relationships between the frequency of extreme freeze events and A. germinans abundance, height and coverage using: (a) mangrove observation points recorded via aerial surveys from a fixed‐wing aircraft; (b) 30 years of temperature data; and (c) mangrove mortality and leaf damage temperature thresholds. We used freeze frequency data and mangrove–climate relationships to evaluate and spatially depict the risk of A. germinans freeze damage across Louisiana. Results: We identified strong negative relationships between the frequency of extreme freeze events and A. germinans abundance, height and coverage. Avicennia germinans is most abundant, tall and continuous along the south‐eastern outer coast of Louisiana, where the frequency of extreme freeze events is reduced (i.e., lower risk of mangrove freeze damage) by the buffering effects of comparatively warm Gulf of Mexico waters. Conversely, the risk of A. germinans freeze damage has historically been very high across Louisiana's Chenier Plain and within more inland wetlands in the Deltaic Plain. Main conclusions: Our analyses advance understanding of how the frequency of extreme freeze events controls the distribution, height and coverage of A. germinans near its northern range limit. In addition to informing climate‐smart coastal restoration efforts, our findings can be used to better anticipate and prepare for the tropicalization of temperate wetlands due to climate change. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Climate change and nutrient enrichment are two phenomena impacting coastal ecosystems. In coastal wetlands, mangroves in temperate–tropical ecotones are encroaching on adjacent saltmarshes, a pattern that is primarily attributed to warmer winter temperatures. Climate change is also expected to increase the vulnerability of coastal wetlands to eutrophication, and increases in nutrient availability may further mediate the rate of mangrove expansion. We investigated the consequences of nutrient enrichment on coastal wetlands in the mangrove–saltmarsh ecotone near the temperate edge of mangrove distribution along the northeast coast of Florida. We tested the hypothesis that nutrient enrichment enhances the ongoing, climate-driven expansion of mangroves into areas historically dominated by saltmarshes by increasing mangrove growth and cover, allowing them to outcompete and overgrow adjacent saltmarsh plants. We manipulated nitrogen (N) and phosphorus (P) availability and measured the effects on growth, cover, diversity, leaf traits, and nutrient dynamics of Avicennia germinans. We found that A. germinans shrubs growing in the saltmarsh–mangrove ecotone in northern Florida grew taller, increased their canopies, and had higher reproductive output when enriched with N compared to control plants and P-enriched plants. Nutrient enrichment did not alter Sarcocornia perennis growth and increased Batis maritima height but did not alter density or biomass. Nitrogen addition caused an increase in A. germinans cover and decrease in B. maritima cover and Simpson's index of diversity, suggesting that N enrichment, an ongoing phenomenon, can hasten the invasion of mangroves into saltmarshes by favoring mangrove growth and reproduction without significantly enhancing saltmarsh plant growth. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are present in a great variety of ecosystems, including wetlands. However, little is known regarding the environmental factors that affect their abundance, diversity and development within the rhizosphere of their hosts in flooded soils. This study had the objective of describing the edaphic environment and the mycorrhizal status of two mangrove species: Avicennia germinans (L.) L. and Conocarpus erectus L., and to identify the edaphic variables that determine the percentage of mycorrhizal colonization, spore density and AMF species richness on their rhizospheres. To accomplish this, roots and rhizospheric soil of A. germinans and C. erectus were collected on the coastal lagoon "La Carbonera", Yucatán, Mexico. Soil analyses were conducted, the percentage of root fungal colonization was determined and the spores isolated, identified and quantified. Structural equation models were elaborated for each mangrove species to determine the relationship between the edaphic environment and the arbuscular mycorrhizal association. The rhizospheres of the mangroves differ physico-chemically and, while mycorrhizal colonization occurs in both species and spores are present in their rhizospheres, the results indicate higher values in C. erectus compared to A. germinans. Substrate water content and pH are the edaphic variables that determine the AMF variation in the analyzed mangrove rhizospheres. [ABSTRACT FROM AUTHOR]

Key message: Wood density varies among mangrove tree species and diameter size classes, reflecting ontogenetic strategies influenced by environmental conditions, such as the salinity gradient. Wood density is one of the most widely used parameters for the description of the structure of a plant and its production of biomass/carbon, as well as its strategies of growth and survival in the context of varying environmental conditions. Data were compiled on the wood density of the three mangrove tree species [Rhizophora mangle L., Avicennia germinans (L.) L., and Laguncularia racemosa (L.) C. F. Gaertn.] that predominate on the Ajuruteua Peninsula in Bragança on the Amazon coast of the Brazilian state of Pará, focusing on the stem position and diameter classes. The influence of the salinity gradient on the wood density of A. germinans was analyzed based on the definition of the three zones of salinity defined from the mean salinity values ascertained from the principal tidal channels found on the peninsula. Wood density varied significantly among species, diameter classes, and saline zones, but not in relation to the position on the stem. Our findings indicate that the inter- and intra-specific variation found in the wood density of the mangrove trees is the result of the different levels of salinity found in the study area, mediated by the variation in the growth of the plant in response to desiccation and hypersalinity that occur at higher elevation in the intertidal zone. In addition, the A. germinans trees with the highest wood density were found in the most saline zone, where these mangrove trees present a reduced assimilation of carbon, which affects the spatial distribution of this species, its production of biomass, and carbon storage. [ABSTRACT FROM AUTHOR]

The objective of this work was characterize the floristic diversity and the phytosociological structure of the mangrove in the São Francisco River estuary in order to contribute to the conservation of this ecosystem. Thirtyfour sampling sites were selected, according to ongoing structural mosaic in the region ranging from 100 to 400 m between themselves, in a total useful area of 0.7625 ha. The evaluated parameters were: density of live and dead trunks; living and dead Basal Area; Absolute Frequency, Relative Frequency and Importance Value. Three typical mangrove species of the São Francisco estuary were found such as Avicennia germinans (L.) Stearn, Rhizophora mangle L. and Laguncularia racemosa (L.) Gaertn. F. Gaertn. The forest height ranged from 2.88 to 15.63 m, the DBH from 3.95 to 19.74 cm, live basal area from 4.22 to 47.83 m² ha-1 and dead basal area from 0.50 to 59.63 m² ha-1. The living trunks density ranged from 375.00 to 9100.00 trunks ha-1 and dead trunk density from 100-2800 trunks ha-1. The described results in this study demonstrated that the mangrove forests presents a structural variability that may be associated with environmental characteristics (marine erosion) and anthropogenic factors. The peculiarities of each site emphasize the importance of preventive actions in the ecosystem conservation. [ABSTRACT FROM AUTHOR]

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Crown displacement in trees is an adaptive response driven by neighbours that optimizes space use and reduces competition. But it can also be the result of wind force. Although morphological responses to neighbours have been well studied, the interplay between neighbours and wind in driving crown shape, and the implications for plant interactions remain poorly understood. However, it is crucial to predict such changes in vegetation structure and function under the scope of global change. We test the hypothesis that aboveground interactions are reduced with increasing soil stress and that wind becomes the main driver of crown shape in mangrove forests.We investigated the effect of neighbours and wind intensity and direction on crown displacement of mangrove canopy and below canopy trees along a salinity gradient, and assessed crown asymmetry for three mangrove tree species, as well as the contribution of crown displacement on reducing crown‐projected area overlap and thus neighbourhood competition.Results show that crown displacement of canopy trees is strongly influenced by winds at all salinities. At low salinities, competition for space accounted for 48% of crown displacement away from neighbours, compared to 49% found for the synthetized effects of wind and neighbours. While trees below the canopy displace their crowns away from their neighbours, no response to wind could be detected. This can be due to the wind protection conferred by a dense canopy stand related to bigger crowns that effectively reduce wind drag. At higher salinities, there was a reduction in canopy overlap due to crown displacement, which suggests reduced aboveground plant interactions with increasing soil stress.While neighbourhood avoidance is a fundamental strategy for optimal light foraging, this study shows that wind strength and directionality are main drivers of crown shape with increasing stress and highlights their potential influence in plant interactions and forest structure, pointing to an increased susceptibility of trees to disturbances that should be further studied. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

• Rhizophora racemosa and Avicennia germinans contributed most of the tree carbon stock. • Soil had the greatest share of the total carbon stock, followed by live trees and litter. • Total carbon stock (all pools combined) was higher on low harvesting sites. • Tree density generally enhanced tree carbon stock, but more so on low harvesting sites. • Carbon stocks in dead trees, litter and soil are high in low harvesting areas where stand densities are also high. Mangroves are vital ecosystems that help mitigate climate change and natural hazards, despite representing only 0.5% of the world's coastlines. Recent studies have provided empirical evidence of the ongoing over-exploitation of mangrove forests in West Africa. Understanding the impact of such harvesting on mangroves' carbon potential is essential to inform decision-making for management and carbon economy policies. This study investigated the impacts of harvesting intensity on (i) carbon allocation to species, size class, soil depth and pool (standing live trees, standing dead trees, litter and soil); and (ii) carbon stock in the different carbon pools, and its relationships with stand structural attributes, using the case study of Benin coastal line. Data were collected in 600 plots of 0.015 ha across 20 mangrove sites in high and low-harvesting-intensity areas. Sixty litter quadrats were also established to sample litter, while 160 soil samples were collected for soil carbon content analysis. Regardless of the harvesting intensity, two mangrove species, Rhizophora racemosa and Avicennia germinans, contributed more than 98% of the tree carbon. Small (1–10 cm) and medium (10–20 cm) size classes dominated tree carbon in high and low harvesting sites, respectively. Soil carbon up to 1 m depth had the greatest share (55%-70%) of the total carbon stock, followed by standing live trees (26%-40%) and litter, and was not influenced by harvesting intensity. Harvesting intensity influenced the carbon stocks in standing live and dead trees, with greater values in low and high harvesting sites. The total carbon stock was ∼ 1.46-fold higher in low harvesting sites (308.54 ± 32.74 MgC.ha−1) than in high harvesting sites (211.40 ± 14.91 MgC.ha−1). Mixed effect models showed that stand density and proportion of R. racemosa related positively with tree carbon stock, especially on low harvesting sites. Multiple factorial analyses revealed that carbon stocks in dead trees, litter and soil are high in low harvesting areas where stand densities are also high. However, in high harvesting sites, carbon stock in litter was positively related to relative density of A. germinans. This study expands our understanding of the carbon stock potential in a West African mangrove subject to different levels of disturbance and its contribution to mitigating greenhouse gas emissions. The implications for management were further discussed. [ABSTRACT FROM AUTHOR]

Accurate estimation of biomass and carbon stocks in mangrove forests is a prerequisite for a better understanding of their role in climate regulation. Allometric equations remain appropriate tools in this context but are lacking for many mangrove species and sites across Africa. In this study, we destructively sampled 68 individual trees of the two dominant West African mangrove species (Rhizophora racemosa and Avicennia germinans) to (i) determine species-specific height-diameter allometry; (ii) evaluate biomass allocation to stem, branches, leaves and roots components; (iii) establish species-specific aboveground-, belowground- and total biomass allometric equations; and (iv) examine the accuracy of our best biomass model against existing equations for mangroves. Diameter at breast height (Dbh), total height (H), wood density and crown diameter were used as predictors in the models. Results showed that Dbh explained 53% and 62% of height variation for R. racemosa and A. germinans , respectively. Stems stored the highest biomass fractions (84.30% for R. racemosa and 52.80% for A. germinans), followed by branches, while the belowground compartment contributed to 19%–22% of the total biomass. Among the candidate biomass models, the models incorporating Dbh and height as a compound variable (Dbh2H) were the most suitable for estimating aboveground and total biomass, with 87–92% of explained variance. For the root components, wood density and crown diameter were additionally found to improve model performance for R. racemosa and A. germinans , respectively. Our study revealed that biomass in West African mangrove forests was more accurately predicted using the established equations than with the existing models. • Height and biomass allometric models were developed for West African mangrove species. • The highest biomass fractions were stored in stems, followed by branches and leaves. • Models with Dbh2H were the most suitable for aboveground/total biomass estimation. • Selected biomass allometric models performed better than the existing models. • Selected models are recommended for future use in West African mangrove forests. [ABSTRACT FROM AUTHOR]

Los manglares son los principales reservorios de biomasa aérea (BA) y carbono (C) sobre el suelo entre los ecosistemas marino-costeros tropicales. A partir de datos estructurales de campo y de ecuaciones alométricas publicadas, se estiman los reservorios de BA y C en la vegetación de las cuatro áreas de manglar más extensas del golfo de Urabá. Los manglares del delta del río Atrato mostraron los mayores reservorios de BA y C (165 y 83 t/ha, respectivamente) concentrados en árboles de Rhizophora mangle, al igual que los de la ensenada de Rionegro (115 y 58 t/ha, respectivamente). En el costado suroriental del Golfo, los mayores valores se obtuvieron en los manglares de Puerto César-Punta Coquito (85 y 43 t/ha, respectivamente), y por último los de Turbo (76 y 38 t C/ha, respectivamente), ambos dominados por Avicennia germinans. En Turbo predominaron árboles de R. mangle y Laguncularia racemosa de diámetros < 5 cm, reflejo de la fuerte intervención antrópica y los reservorios de BA y C son menores que los de Puerto César-Punta Coquito, más alejado de la cabecera urbana. Los reservorios de biomasa de los manglares del Golfo se encuentran dentro del rango observado en todo el mundo, pero los del delta del río Atrato se acercan más al límite superior registrado. Los manglares mejor conservados del golfo de Urabá son reservorios importantes de C en la BA. La magnitud del reservorio está inversamente relacionada con la distancia a los dos principales centros poblados.