Mangrove Expansion Research Articles

Stocks and soil-plant transfer of macro-nutrients and trace metals in temperate New Zealand estuarine mangroves

Rapid expansion of temperate mangroves in New Zealand over the last decades has prompted an increase in resource consents for removal. However, little is known about the capacity of temperate mangroves to store elements, including pollutants. The main objectives of this study were to assess the stocks and soil-plant transfer of macro-nutrients (C, N, P, K, Mg, Ca, S) and trace metals (Fe, Mn, Al, Ni, Cu, Zn, Co, Cr) within temperate mangrove soils. Soil samples and root, leaf and wood tissues were analysed for their total and available elemental concentrations over a wide range of environmental conditions along the head-mouth textural, salinity and nutrient gradients of the estuary. Physico-chemical characteristics of the soil of the different sites studied were also determined. Mangrove soils with lower Eh and currents upstream of the estuary trapped larger amount of macro-nutrients and heavy metals in the soils than downstream. This results in higher translocation of macro elements from the soil toward the above-ground biomass and higher translocation of heavy metals from the soil toward the litterfall, likely as a mechanism to avoid long term metal toxicity in the root system. This multi-elemental study provides a comprehensive understanding of soil- plant transfers in temperate mangroves and can be used to better evaluate the ecological services of these ecosystems.

Measuring mangrove carbon loss and gain in deltas

Demand for mangrove forest resources has led to a steady decline in mangrove area over the past century. Land conversions in the form of agriculture, aquaculture and urbanization account for much of the deforestation of mangrove wetlands. However, natural processes at the transition zone between land and ocean can also rapidly change mangrove spread. In this study, we applied a robust field-based carbon inventory and new structural and temporal remote sensing techniques to quantify the magnitude and change of mangrove carbon stocks in major deltas across Africa and Asia. From 2000–2016, approximately 1.6% (12 270 ha) of the total mangrove area within these deltas disappeared, primarily through erosion and conversion to agriculture. However, the rapid expansion of mangroves in some regions during this same period resulted in new forests that were taller and more carbon-dense than the deforested areas. Because of the rapid vertical growth rates and horizontal expansion, new mangrove forests were able to offset the total carbon losses of 5 332 843 Mg C by 44%. Each hectare of new mangrove forest accounted for ∼84% to ∼160% of the aboveground carbon for each hectare of mangrove forest lost, regardless of the net change in mangrove area. Our study highlights the significance of the natural dynamics of erosion and sedimentation on carbon loss and sequestration potential for mangroves over time. Areas of naturally regenerating mangroves will have a much larger carbon sequestration potential if the rate of mangrove deforestation of taller forests is curbed.

The role of atmospheric-tropospheric rivers in partitioning coastal habitats and limiting the poleward expansion of mangroves along the southeast coast of Brazil

The role of atmospheric-tropospheric rivers in partitioning coastal habitats and limiting the poleward expansion of mangroves along the southeast coast of Brazil

Does Sea Surface Temperature Contribute to Determining Range Limits and Expansion of Mangroves in Eastern South America (Brazil)?

Low Sea Surface Temperature (SST) is a climate barrier because it may inhibit and reduce seedling growth of mangrove propagules upon dispersal through seawater. Our objective is to analyze the spatio-temporal series of daily SST data from the Multi-scale Ultra-high Resolution (MUR)-SST in order to identify the occurrence of chilling events for mangrove plants at the Eastern South America mangrove limit and beyond. We focus our study on three key sites: (i) the Rhizophora mangle L. distribution limit (Praia do Sonho: 27°53′S), (ii) the Eastern South America mangrove limit (Laguna: 28°30′S) and (iii) one beyond mangrove areas, in Araranguá (28°55′S). Our results show that, in Araranguá, chilling events are more intense and occur more frequently than in the other two sites that have a mangrove cover. We conclude that, the chilling events of SST may play a role in restricting mangroves within their actual limits. In this sense, higher occurrences of chilling events of SST could be an explanation for the absence of R. mangle in Laguna. However, Laguncularia racemosa (L.) C.F. Gaertn. was reported to be tolerant to low temperatures, and yet it is absent from the southernmost study site. This may be an indication of the role of other factors than SST in determining a mangrove range expansion, such as dispersal constraints.

Remote sensing of unhelpful resilience to sea level rise caused by mangrove expansion: A case study of islands in Florida Bay, USA

Previous studies have found that vegetated coastal areas can increase their elevation indicating resilience to inundation by sea level rise (SLR), but the potential resilience were ignored or showed controversial results (i.e., soil accretion of vegetated areas vs. SLR). To estimate the resilience influences on 15 islands in Florida Bay (Florida, U.S.), our study used indicators (areas of the 15 islands and their mangrove forests) by analyzing 61-yr high-resolution historical aerial photographs and a 27-yr time-series of Landsat images. In these islands, coastal fringes are dominated by mangroves, and inland parts are dominated by brackish or freshwater species. Our results showed that: (1) despite rising sea levels, these low-lying islands significantly increased in area; (2) all of these islands had significant mangrove expansion, and the landward part of expansion led to the replacement of inland non-mangrove habitats; (3) there was a positive relationship between the increase of island area and mangrove expansion in these islands; (4) without the mangrove expansion, simulations showed that all of the islands had decreased areas by 2014 compared with that in 1953. On the basis of our spatial analyses and previous field studies in our study areas, these islands showed resilience to inundation and the mangrove expansion contributed to processes stabilizing these islands under SLR. Meanwhile, the mangrove expansion were partly at the expense of the habitats previously covered by non-mangrove species, thus potentially leading to a loss of plant diversity. Therefore, the mangrove expansion increased unhelpful resilience to maintain islands in a degraded state losing biodiversity, which should be considered in conservation accounting for future SLR. Moreover, the unhelpful resilience can be monitored by remote sensing based indicators, such as island area.

Changes in arthropod communities as black mangroves Avicennia germinans expand into Gulf of Mexico salt marshes

Climate change is driving poleward shifts in species distributions worldwide. In the Gulf of Mexico (GOM), warming temperatures foster black mangrove (Avicennia germinans L.) expansion into GOM wetlands replacing wetland plants including Spartina alterniflora Loisel, Salicornia depressa L., and Batis maritima L. We investigated insect community assemblages in wetlands with and without A. germinans to assess potential effects of A. germinans expansion on insect fauna. Insect abundance, biomass, richness, diversity, community structure, and feeding guild composition were measured in both the spring and the fall across three levels of A. germinans abundance. Insect abundance and biomass were larger in both the spring and the fall in wetlands where A. germinans abundance was low. Significant differences in community structure were associated with the presence of A. germinans. Feeding guild composition was also different in wetlands containing A. germinans, having less predator biomass. Shifting vegetation caused by climate change can alter insect communities in coastal wetlands, illustrating the need for a more comprehensive understanding of climate change effects on fauna in response to shifting foundation plant species.

Mangrove forests in a rapidly changing world: Global change impacts and conservation opportunities along the Gulf of Mexico coast

Mangrove forests are highly-productive intertidal wetlands that support many ecosystem goods and services. In addition to providing fish and wildlife habitat, mangrove forests improve water quality, provide seafood, reduce coastal erosion, supply forest products, support coastal food webs, minimize flooding impacts, and support high rates of carbon sequestration. Despite their tremendous societal value, mangrove forests are threatened by many aspects of global change. Here, we examine the effects of global change on mangrove forests along the Gulf of Mexico coast, which is a valuable region for advancing understanding of global change impacts because the region spans multiple ecologically-relevant abiotic gradients that are representative of other mangrove transition zones across the world. We consider the historical and anticipated future responses of mangrove forests to the following aspects of global change: temperature change, precipitation change, accelerated sea-level rise, tropical cyclone intensification, elevated atmospheric carbon dioxide, eutrophication, invasive non-native species, and land use change. For each global change factor, we provide an initial global perspective but focus primarily on the three countries that border the Gulf of Mexico: United States, Mexico, and Cuba. The interactive effects of global change can have large ecological consequences, and we provide examples that highlight their importance. While some interactions between global change drivers can lead to mangrove mortality and loss, others can lead to mangrove expansion at the expense of other ecosystems. Finally, we discuss strategies for using restoration and conservation to maximize the adaptive capacity of mangrove forests to global change. To ensure that the ecosystem goods and services provided by mangrove forests continue to be available for future generations, there is a pressing need to better protect, manage, and restore mangrove forests as well as the adjacent ecosystems that provide opportunities for adaptation in response to global change.

Warming accelerates mangrove expansion and surface elevation gain in a subtropical wetland

Abstract Climatic warming can change how coastal wetland plants grow, thus altering their capacity to build land and keep pace with rising seas. As freeze events decline with climate change, mangroves expand their range to higher latitudes and displace salt marsh vegetation. Warmer air temperatures will likely alter above‐ and below‐ground plant dynamics as this dramatic coastal wetland biome shift proceeds, which in turn may result in changes in ecosystem function such as sediment building. We used a large scale in situ warming experiment in a subtropical wetland to increase both marsh and mangrove ecosystem air temperatures. We assessed how 2 years of continuous warming influenced above‐ and below‐ground plant growth and surface elevation relative to sea level. We found that chronic warming doubled plant height and accelerated the expansion of mangrove into salt marsh vegetation, as indicated by a sixfold greater increase in mangrove cover in warmed plots compared to ambient temperature plots and a corresponding loss in salt marsh cover. Surface elevation gain, a measure of soil‐building capacity, increased due to warming over a 2‐year period and these changes in surface elevation were driven by increased mangrove root production in warmed plots. Synthesis. Our findings suggest that, in some coastal wetlands, warming can facilitate plant community changes from marsh to mangrove, with corresponding increases in growth that help coastal wetlands to keep pace with sea‐level rise.

Moving from Generalisations to Specificity about Mangrove –Saltmarsh Dynamics

Spatial and temporal variability in factors influencing mangrove establishment and survival affects the distribution of mangrove, particularly near their latitudinal limit, where mangrove expansion into saltmarsh is conspicuous. In this paper the spatial variability in mangrove distribution and variability in factors influencing mangrove establishment and survival during the Quaternary period are reviewed, focussing on research at latitudinal limits in Australia and mainland USA. Despite similarities in the response of mangrove to some drivers, the expression of these drivers is both spatially and temporally variable, demonstrating the need for analyses of mangrove-saltmarsh dynamics to move beyond generalisations and incorporate regional and local-scale specificity. We propose i) that precursory recognition that ‘correlation does not mean causation’ is inadequate and assumptions, caveats, and limitations should be clearly articulated in correlative studies; ii) experimental design in manipulative experiments must also articulate the spatial and temporal scale to which the analysis is relevant; and iii) analyses that draw from a range of methods will provide greater confidence. Integrated research programs that transect spatial and temporal scales and incorporate a range of techniques are essential to improve projections. Mangrove-saltmarsh distribution research should move beyond simple models that assume equilibrium between realised and fundamental niches.

Sensitivity of mangrove range limits to climate variability

AbstractAimCorrelative distribution models have been used to identify potential climatic controls of mangrove range limits, but there is still uncertainty about the relative importance of these factors across different regions. To provide insights into the strength of climatic control of different mangrove range limits, we tested whether temporal variability in mangrove abundance increases near range limits and whether this variability is correlated with climatic factors thought to control large‐scale mangrove distributions.LocationNorth and South America.Time period1984–2011.Major taxa studiedAvicennia germinans, Avicennia schuaeriana, Rhizophora mangle, Laguncularia racemosa.MethodsWe characterized temporal variability in the enhanced vegetation index (EVI) at mangrove range limits using Landsat satellite imagery collected between 1984–2011. We characterized greening trends at each range limit, examined variability in EVI along latitudinal gradients near each range limit, and assessed correlations between changes in EVI and temperature and precipitation.ResultsSpatial variability in mean EVI was generally correlated with temperature and precipitation, but the relationships were region specific. Greening trends were most pronounced at range limits in eastern North America. In these regions variability in EVI increased toward the range limit and was sensitive to climatic factors. In contrast, EVI at range limits on the Pacific coast of North America and both coasts of South America was relatively stable and less sensitive to climatic variability.Main conclusionsOur results suggest that range limits in eastern North America are strongly controlled by climate factors. Mangrove expansion in response to future warming is expected to be rapid in regions that are highly sensitive to climate variability (e.g. eastern North America), but the response in other range limits (e.g. South America) is likely to be more complex and modulated by additional factors such as dispersal limitation, habitat constraints, and/or changing climatic means rather than just extremes.

Operationalizing Blue Carbon in the Mission-Aransas National Estuarine Research Reserve, Texas

Recently, greater interest in the resilience of coastal habitat ecosystem services in the northern Gulf of Mexico has emerged due in part to an expansion of mangroves into areas previously dominated by salt marshes. To operationalize coastal wetland ecosystem services for decision-making, there is a need to clarify how salt marshes and mangroves function in this region. The goal of this research is to operationalize blue carbon (carbon stored in coastal habitats) within the Mission-Aransas National Estuarine Research Reserve, TX by documenting what we know about blue carbon within the study area, identifying data gaps and future research needs, and using available knowledge to inform management and decision-making within the Reserve. Our research shows that there is a lack of data within the Reserve on mangrove aboveground biomass, belowground biomass and soil carbon and on salt marsh soil carbon. There is also a dearth of information on wetland carbon sequestration and emission rates within the Reserve, making it challenging to inform management and develop a market for blue carbon.

Assessing changes of mangrove forest in a coastal region of southeast China using multi-temporal satellite images

Mangroves provide many ecological, economic, and social benefits to humans. In the Jiulong River Estuary of Fujian Province, China, many mangroves have been lost largely due to human activities and so artificial planting has been implemented. However, the spatial and temporal dynamics of mangrove forests are still largely unknown at this location. This study aimed to identify changes to mangrove distribution and aboveground biomass (AGB) in three periods (1995–2004, 2004–2014 and 1995–2014) in order to influence mangrove management. Landsat satellite imagery and the threshold value method were used to classify mangroves. Landsat satellite imagery, field-based biomass investigations, elevation data and an allometric biomass equation were employed to develop an AGB model using a multiple linear regression method. Both mangrove area and AGB increased from 1995 to 2014 with an increase rate of 5.5% and 7.2% for mangrove area and AGB, respectively. Mangrove expansion was the main cause for AGB and area increase. In addition, AGB increase due to the growth of mangroves without extending the area also has great potential in AGB increase. Similar to AGB, above-ground carbon increased from 57 t C/ha in 1995 to 79 t C/ha in 2014, which demonstrated that mangroves in this region can help to mitigate climate warming. However, a large-scale continuous decrease of mangrove forest in the JRE was observed, likely caused by growing human activities. Moreover, tidal range change during 2004–2014 resulted in a more adverse impact on mangroves.

Effects of oil exposure, plant species composition, and plant genotypic diversity on salt marsh and mangrove assemblages

AbstractClimate change is causing shifts in the distribution and abundance of many species. Because species vary in the rate and degree of these shifts, novel transition zones have developed where new combinations of species overlap. If climate‐mediated range shifts result in greater diversity, transition communities could have enhanced resistance and/or resilience, particularly if the resident and colonizing species differ in their response to environmental change. The range expansion of the tropical black mangrove, Avicennia germinans, into salt marshes dominated by the temperate cordgrass, Spartina alterniflora, provides an opportunity to examine the responses of climate‐mediated transition zones to disturbance. We conducted a yearlong mesocosm experiment testing the effects of plant species identity and composition (A. germinans, S. alterniflora), as well as plant genotypic diversity (S. alterniflora only), on the response of coastal wetlands to oiling disturbance. Oil negatively impacted S. alterniflora and A. germinans both above‐ and belowground, though the timing of these effects varied, with S. alterniflora showing more immediate declines than A. germinans. As hypothesized, the magnitude of the oil effect was reduced in the mixed plant species treatment compared to the single species treatment for A. germinans survival (12% vs. 21% reduction) and belowground biomass (19% vs. 71% reduction). In addition, when exposed to oil, A. germinans crown area and volume were greater in the mixed species treatment compared to the single species treatment at the end of the experiment. However, we did not detect any benefit of mixed species communities or S. alterniflora genotypic diversity for the S. alterniflora response to oil. Our results suggest that transition habitats in the northern Gulf of Mexico where A. germinans and S. alterniflora co‐occur will be negatively impacted by future oiling events, but that they are no more susceptible, and perhaps slightly less so, than habitats dominated by either individual species.

A Review on Biodiversity, Ecosystem Services, and Perceptions of New Zealand’s Mangroves: Can We Make Informed Decisions about Their Removal?

Mangrove cover is increasing in estuaries and harbours in many areas on North Island, New Zealand. The expansion of mangroves has been attributed to anthropogenic land-use change, including urbanisation and conversion of land to agriculture. Rapid expansion of mangroves in the coastal landscape has created discord in local communities over their importance in terms of the services they deliver to both wildlife and people. Some community groups have been advocates for the large-scale removal of mangrove habitat, whilst other local residents oppose this removal. This review paper investigated and discussed pertinent biodiversity and ecosystem services studies based in New Zealand mangroves from 1950 to 2017. Results showed that the majority of biodiversity studies have targeted particular species or groups of organisms, with a focus on benthic invertebrate communities. Deficits remain in our knowledge of this expanding forest and shrub ecosystem, notably the terrestrial component of biodiversity, species community-shifts with landscape fragmentation, and associated cultural values. It is recommended that broader species assessments and a longer-term approach be applied to biodiversity monitoring in mangroves, coupled with Mātauranga Māori (Māori knowledge) and western science for holistic management of this coastal ecosystem.

Microspatial ecotone dynamics at a shifting range limit: plant–soil variation across salt marsh–mangrove interfaces

Ecotone dynamics and shifting range limits can be used to advance our understanding of the ecological implications of future range expansions in response to climate change. In the northern Gulf of Mexico, the salt marsh-mangrove ecotone is an area where range limits and ecotone dynamics can be studied in tandem as recent decreases in winter temperature extremes have allowed for mangrove expansion at the expense of salt marsh. In this study, we assessed aboveground and belowground plant-soil dynamics across the salt marsh-mangrove ecotone quantifying micro-spatial patterns in horizontal extent. Specifically, we studied vegetation and rooting dynamics of large and small trees, the impact of salt marshes (e.g. species and structure) on mangroves, and the influence of vegetation on soil properties along transects from underneath the mangrove canopy into the surrounding salt marsh. Vegetation and rooting dynamics differed in horizontal reach, and there was a positive relationship between mangrove tree height and rooting extent. We found that the horizontal expansion of mangrove roots into salt marsh extended up to eight meters beyond the aboveground boundary. Variation in vegetation structure and local hydrology appear to control mangrove seedling dynamics. Finally, soil carbon density and organic matter did not differ within locations across the salt marsh-mangrove interface. By studying aboveground and belowground variation across the ecotone, we can better predict the ecological effects of continued range expansion in response to climate change.

Mangrove swamp expansion controlled by climate since 1988: a case study in the Nanliu River Estuary, Guangxi, Southwest China

In the Nanliu River Estuary of Guangxi, China, the naturally expanding process of a mangrove swamp (primarily consist of Aegiceras corniculatum) over past decades is studied by satellite images. From 1988 to 2013, the area of studied mangrove swamp increased significantly from 60 hm2 to 134 hm2. The expanding process is not gradual and the significant expansion only took place in some special periods. To reveal the dynamic of mangrove swamp expansion, the evolution of tidal flat elevation and the climate change in past decades are studied respectively. The hydrodynamic condition and nutrient supply are also analysed. The study results show that the climate factors of typhoon intensity and annual minimum temperature are crucial for controlling mangrove expansion. A large number of mangrove seedlings on bare tidal flats can survive only in special climate optimum periods, which are continuous years of low typhoon intensity and high annual minimum temperature. In past decades, the scarcity of climate optimum periods resulted in a non-gradual process of mangrove expanding and a time lag of 30 years between the elevation reaching the low threshold for mangrove seedling survival and the eventual emergance of the mangrove. Compared with the climate factors, the hydrodynamic condition and nutrient supply are not important factors affecting mangrove expansion. In the future, combined with global warming, the enhanced frequency and energy of landing typhoons will most likely restrain the further expansion of this mangrove swamp.

Mangrove microclimates alter seedling dynamics at the range edge.

Recent climate warming has led to asynchronous species migrations, with major consequences for ecosystems worldwide. In woody communities, localized microclimates have the potential to create feedback mechanisms that can alter the rate of species range shifts attributed to macroclimate drivers alone. Mangrove encroachment into saltmarsh in many areas is driven by a reduction in freeze events, and this encroachment can further modify local climate, but the subsequent impacts on mangrove seedling dynamics are unknown. We monitored microclimate conditions beneath mangrove canopies and adjacent open saltmarsh at a freeze-sensitive mangrove-saltmarsh ecotone and assessed survival of experimentally transplanted mangrove seedlings. Mangrove canopies buffered night time cooling during the winter, leading to interspecific differences in freeze damage on mangrove seedlings. However, mangrove canopies also altered biotic interactions. Herbivore damage was higher under canopies, leading to greater mangrove seedling mortality beneath canopies relative to saltmarsh. While warming-induced expansion of mangroves can lead to positive microclimate feedbacks, simultaneous fluctuations in biotic drivers can also alter seedling dynamics. Thus, climate change can drive divergent feedback mechanisms through both abiotic and biotic channels, highlighting the importance of vegetation-microclimate interactions as important moderators of climate driven range shifts.

Establishment and Biomass Allocation of Black and Red Mangroves: Response to Propagule Flotation Duration and Seedling Light Availability

ABSTRACT Simpson, L.T.; Osborne, T.Z., and Feller, I.C., 2017. Establishment and biomass allocation of black and red mangroves: Response to propagule flotation duration and seedling light availability. Global climate change is driving the expansion of mangroves into salt-marsh habitats around the world, and the ability of mangroves to displace salt marsh is attributable to a combination of factors. Early life history is critical to initial establishment; the mangroves' hydrochorous propagules allow for long-distance dispersal, and plasticity allows for establishment in varying environmental conditions. To examine differences in propagule flotation duration and the influence of light availability on seedling establishment and growth, the growth dynamics of Avicennia germinans (black mangrove) and Rhizophora mangle (red mangrove) seedlings were documented in a manipulative laboratory experiment. Propagules were collected on the Atlantic coast of Florida and were grown under two light levels (sun and shade) ...

Coastal dynamics of Northern Australia – Insights from the Landsat Data Cube

We demonstrate the capacity of detailed time-series of remotely sensed data to identify notable changes and trends in coastal morphology and vegetation over the last three decades, and illustrate how these data can help identify drivers of change, and areas that require further investigation. Time-series analysis (1987–2016) of the Australian Landsat archive is enabled by the Australian Geoscience Data Cube (AGDC), in which the data has been processed and restructured. We use Hovmoller plots to graphically display this time series for three test sites on the tropical coast of northern Australia. Initial results reveal distinct differences between sites: 1. Abrupt loss of mangrove cover (2004, 2006), which clearly relates to the passage of cyclones (Junction Bay); 2. Gradual seawards expansion of mangrove (1987–1996), and subsequent rapid narrowing of the mangrove zone (2013–2016; Burketown); 3. Minor seawards expansion of mangrove (1987–2004) in a stable embayment (Darwin Harbour). The density and duration of the time series enables clear links to be made to recorded events (e.g. cyclones), and identifies focus areas that exhibit unprecedented patterns of change (e.g. loss of mangrove) where regional or global environmental processes may be driving local change.

Carbon Storages along a Climate Induced Coastal Wetland Gradient

Across the globe, coastal wetland vegetation distributions are changing in response to climate change. In the southeastern United States, increased winter temperatures have resulted in poleward range expansion of mangroves into pure salt marsh habitat. Climate change-induced expansion of mangroves into salt marsh will significantly alter carbon (C) storage capacity of these wetlands, which currently store the highest average C per land area among unmanaged terrestrial ecosystems. Total ecosystem C stocks were measured along a 342 km latitudinal gradient of mangrove – to – marsh dominance in Florida. Carbon stocks were quantified through measurements of above- and belowground biomass and soil C. Interior mangrove C stocks were greater than both salt marsh and ecotonal C stocks and soil C comprised the majority of each ecosystem C component (51–98%). The wetlands investigated in this study cover 38,532 ha, and store an average of 215 Mg of C ha−1. Currently, mangroves cover 31% of the land area studied, storing 44% of the total C, whereas salt marshes occupy 68% of the wetland area and only store 55% of the C. Total conversion of salt marsh to mangrove may increase C storage by 26%, predominately due to increases in aboveground biomass.