Boxplot of differences in species richness of emergent assemblages of major wetland habitat types between water and salinity treatments

Boxplot of differences in species richness of emergent assemblages of major wetland habitat types between water and salinity treatments

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Coastal freshwater wetlands are amongst the world’s most modified but poorly researched ecosystems and some of the most vulnerable to climate change. Here, we examine vegetation resilience in coastal wetlands of subtropical Australia to altered salinity and flooding regimes likely to occur with climate change. We conducted field surveys and glassho...

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... A paucity of woody species emerging from soil seed banks have been similarly. Observed in other studies in arid and semi-arid savannas (Capon & Brock 2006, Tessema et al. 2012, tropical forests (Jara 2006) and subtropical coastal freshwater wetlands (Grieger et al. 2019). These relatively low numbers indicate that tree species may store viable seeds in other seed banks, if at all (e.g., aerial seed banks), but are unlikely to rely on seed stores in soil or litter for regeneration (Roberts & Marston 2000). ...
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Revegetating abandoned agricultural lands is vital to restoring critical ecological functions and services. Natural regeneration, whereby vegetation regrows via the seeds already present within the landscape, has shown to be an effective approach to restoring large agricultural areas, although more research is required to understand the regenerative capacity of the various seed sources. Here, we investigate the regenerative capacity of old‐fields of semi‐arid floodplains of eastern Australia in a year‐long seedling emergence experiment. We examined the germinable seed banks from three potential propagule sources (soil, leaf litter, and animal scats) collected across 24 field sites, comprising 12 old‐fields and 12 adjacent remnant vegetation patches, distributed across four regions. Soil seed banks stored the most germinable species of the three seed bank types, although these were dominated largely by annual herbaceous species. High abundances of seedlings emerged from scat samples, indicating that native animals, such as kangaroos and emus, play a role in transporting seeds in these landscapes. Finally, leaf litter stored the most germinable propagules of woody species, therefore representing a vital mechanism for woody vegetation regeneration. There were few differences in emerging seedling assemblages in terms of species richness, abundance or composition between seed banks of old‐fields and adjacent remnant vegetation, suggesting that old‐field seed banks have a high level of resilience. Our findings suggest that these seed banks can make an important contribution to natural regeneration of these old‐fields, but mainly with respect to understory and midstory species, with overstory tree species mostly absent from these seed sources. This article is protected by copyright. All rights reserved.
... Various studies have been carried out to evaluate the response of biomass gain and growth in height or diameter to the increase in salinity of swamp tree species that are distributed in the southeastern United States such as Cephalanthus occidentalis L., Fraxinus pennsylvanica, Nyssa aquatica, Nyssa sylvatica, Quercus lyrate Walter, Quercus michauxii, Quercus nigra, Quercus nuttallii, Sapium sebiferu and Taxodium distichum (Allen et al. 1994;Conner 1994;Conner et al. 1998Conner et al. , 1997McCarron et al. 1998;Pezeshki 1990;Pezeshki et al. 1989), in the Caribbean such as Pterocarpus officinalis Jacq. (Bompy et al. 2015;Rivera-Ocasio et al. 2007), and in southeastern Australian wetlands such as Melaleuca ericifolia (Salter et al. 2007) and Eucalyptus tereticornis Sm. (Grieger et al. 2019). In these studies, it was observed that the seedlings biomass, height, and diameter were greater in the treatments with no or low salinity compared to the high salinity treatments. ...
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During the last century the mean sea level has been increasing at a rate of 0.2–0.4 mm·year−1, and that rate is expected to accelerate during this century. Coastal wetland ecosystems are sensitive to the potential changes and impacts resulting from a rise in sea level. In the coastal region of the Gulf of Mexico, freshwater swamps are wetlands located further inland than mangroves, and while influenced by the tides, maintain freshwater conditions. Due to their location, the rise in sea level could increase the levels of flooding and salinity in these ecosystems. The objective of this study was to evaluate, under greenhouse conditions, the effect of nine flood and salinity treatments on the survival, growth, and increase in the biomass of Annona glabra (pond apple) seedlings (average height: 18.6 ± 1.61 cm). The treatments combined two factors: water level (Saturation, Flood, Flood-Drought) and salinity (0, 5 and 15‰). Seedling survival was greater under freshwater conditions. Increases in height and diameter, and leaf and biomass gain, were more significant under saturation and freshwater conditions. Based on our results, we conclude increased flood levels and salinity will negatively affect the natural establishment of A. glabra seedlings in freshwater swamps under a scenario of rising sea level.
... Human changes applied to agriculture reduce the resilience of wetland ecosystems' structure and functionality. Disturbances in the hydrological regime can exceed the limits of resilience mechanisms and, consequently, transform the structure, functionality, and identity of ecosystems (Grieger et al., 2019). ...
... Bad weather conditions (INMET, 2020) and low soil moisture -both caused by Banhado Grande's severe drought -were the determining factors for the rapid burning that has devastated 702 ha of emergent vegetation in less than 24 h. Grieger et al. (2019) found that soil seed banks are essential for the resilience of freshwater marshes after fire or flooding hazardous episodes. However, climate change and soil degradation can drastically affect seed availability and, consequently, the resilience of marshes. ...
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Resilience is the ability of a system to absorb disturbances, rearrange itself, and adapt in order to maintain its functionality, structure, identity, and feedback. Research involving fire resilience in subtropical wetlands (SW) allows us to understand the dynamics of these ecosystems, measure impacts on fauna and flora, and promote policies for the management and protection. The aim of the present study is to assess the fire resilience of SW. The study was divided into three steps: (i) burned area classification, (ii) vegetation pattern classification, and (iii) temporal analysis of SW fire resilience based on NDVI calculation. Our results show that (a) high resilience potential of emerging plants, which developed green leaves in less than 90 days after the fire; (b) poor recovery of peatlands with underground fire history. Daily coverage of high spatial resolution PlanetScope images has great potential for classification and monitoring of land use in areas where there are rapid changes, such as after a fire event, explosions, and dam ruptures with ore tailings, for example.
... These results should be interpreted with caution, however, since, to achieve optimal discriminating accuracy, we had to group some disparate wetland classes, which may mask some of the salt-freshwater wetland transitions. Although there are significant differences in the floral composition and vegetation structure [7,88], determinant factors, such as freshwater inputs and groundwater availability [2,26], might not closely associate with the hydro-geomorphological variables considered in this study. Again, further studies with long-term imagery are required to investigate the interchange of freshwater wetlands due to SLR. ...
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Many coastal wetlands are under pressure due to climate change and the associated sea level rise (SLR). Many previous studies suggest that upslope lateral migration is the key adaptive mechanism for saline wetlands, such as mangroves and saltmarshes. However, few studies have explored the long-term fate of other wetland types, such as brackish swamps and freshwater forests. Using the current wetland map of a micro-tidal estuary, the Manning River in New South Wales, Australia, this study built a machine learning model based on the hydro-geomorphological settings of four broad wetland types. The model was then used to predict the future wetland distribution under three sea level rise scenarios. The predictions were compared to compute the persistence, net, swap, and total changes in the wetlands to investigate the loss and gain potential of different wetland classes. Our results for the study area show extensive gains by mangroves under low (0.5 m), moderate (1.0 m), and high (1.5 m) sea level rise scenarios, whereas the other wetland classes could suffer substantial losses. Our findings suggest that the accommodation spaces might only be beneficial to mangroves, and their availability to saltmarshes might be limited by coastal squeeze at saline–freshwater ecotones. Furthermore, the accommodation spaces for freshwater wetlands were also restrained by coastal squeeze at the wetland-upland ecotones. As sea level rises, coastal wetlands other than mangroves could be lost due to barriers at the transitional ecotones. In our study, these are largely manifested by slope impacts on hydrology at a higher sea level. Our approach provides a framework to systematically assess the vulnerability of all coastal wetland types.
... These coastal forests are dynamic and are highly responsive to changing conditions, and in extreme conditions (e.g. storm surges and large tides), can experience periods of elevated salinities and waterlogging due to marine and groundwater interactions (Grieger et al., 2019;Krauss et al., 2009). If such conditions prevail, tidal freshwater forested wetlands can undergo structural and physiological changes in their transition to a more saline environment (Duberstein et al., 2020;Krauss et al., 2009). ...
... In palustrine forests, specific-specific hydrological thresholds influence based on flooding and influence growth and establishment of Casuarina and Melaleuca (Grieger et al., 2019), and forested communities in the US (Hough-Snee, 2020). However, we are uncertain as to whether the characteristics of CSOF observed on the Minnamurra floodplain reflects controls on growth (species hydrological thresholds), or simply is representative of an immature forested community. ...
Article
Coastal Swamp Oak Forest (CSOF), a supratidal wetland community dominated by Casuarina glauca, is a widely distributed coastal ecosystem along Australia's east coast. These wetland communities are highly valuable for providing ecosystem services, including carbon sequestration. Positioned within the supratidal zone of estuaries – and often abutting upper intertidal saltmarsh and/or mangrove – CSOF may be vulnerable to salinity intrusion and increased tidal inundation due to sea-level rise. To understand spatial patterns of vegetation composition and structure in CSOF, field-based (in-situ) and remote-sensing approaches were employed on the Minnamurra floodplain, New South Wales, Australia. In-situ vegetation surveys within 23 field plots located along seaward to landward transects revealed large variations in mean tree height (2.5–13.1 m) and tree densities (100–8700 trees/ha). Unmanned Aerial Vehicles with Structure from Motion (UAV-SfM), and airborne Light Detection and Ranging (LiDAR) approaches returned mean plot canopy height estimates ranging between 0.1 and 12.8 m. Comparison of vegetation metrics between remote sensors (UAV-SfM and LiDAR) demonstrated similar capacities (R² values > 0.85) to capture CSOF vegetation height. Comparison of field and spatial metrics elucidated a moderate correlation between the datasets for maximum canopy height (R² > 0.6) which can be partially explained by the different spatial scales of measurement among these approaches. Canopy height, Normalised Difference Vegetation Index (NDVI), and point density (i.e., vegetation density) estimates were each positively correlated with elevation above mean sea-level. This coincides with indications of plant stress and/or mortality at the seaward edge of CSOF, and in topographic depressions. These findings suggest physico-chemical gradients exert a strong control on CSOF vegetation structure and health, with implications for the current acceleration of sea-level rise. When combined, remote sensing and field-based datasets are useful to characterise and quantify CSOF structure and distribution and can therefore be employed in future assessments of this understudied ecosystem.
... Improved coastal modelling, experiments and in situ studies are reducing uncertainties at a local scale about the impact of future sea level rise (SLR) on coastal freshwater terrestrial wetlands (medium confidence) (Shoo et al., 2014;Bayliss et al., 2018;Grieger et al., 2019). Low-lying coastal wetlands are susceptible to saltwater intrusion from sea level rise (SLR) (Shoo et al., 2014;Kettles and Bell, 2015;Finlayson et al., 2017) with consequences for species dependent on freshwater habitats (Houston et al., 2020). ...
... Landscape planning (Bond et al., 2014;McCormack, 2018) helps reduce habitat loss, facilitates species dispersal and gene flow (McLean et al., 2014;Shoo et al., 2014;Lowe et al., 2015;Harris et al., 2018;McCormack, 2018) and allows for new ecological opportunities (Norman and Christidis, 2016). Coastal squeeze is a threat to freshwater wetlands and requires planning for the potential inland shift (Grieger et al., 2019). Adaptations that maintain critical volumes and periodicity of environmental flows will help protect freshwater biodiversity (Box 11.3) (Yen et al., 2013;Barnett et al., 2015;Wang et al., 2018b). ...
... For example, measuring and evaluating the composition and structure of soil seed banks may be more informative than solely observing extant vegetation dynamics with respect to assessing the vulnerability of herbaceous wetland plant communities to climate change (e.g. Grieger et al. 2019). Similarly, objectives for environmental flows should also include measures of resistance or recovery of various vegetation attributes to other disturbances (e.g. ...
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Evaluating wetland vegetation responses to flow regimes is challenging because of the inherently complex, variable and dynamic nature of wetland vegetation in space and time. We propose four principles to guide the development of management objectives and evaluation approaches to support adaptive management of wetland vegetation in flow-managed systems. First, we assert a need for more explicit, direct and defensible alignment of management objectives, targets and indicators to reflect broader ecological, sociocultural and economic values, and the underlying ecosystem functions that support them. Second, we propose a framework for indicator selection across multiple spatiotemporal scales and levels of ecological organisation, from individuals to landscape mosaics (vegscapes). Third, we emphasise the need to evaluate vegetation condition and responses to environmental flows in relation to a more nuanced understanding of temporal flow dynamics. Finally, we discuss the importance of considering the effects of non-flow variables that can modify vegetation responses to environmental flows. We highlight key knowledge needs required to support the implementation of these principles, particularly the urgency of improving our understanding of ecological, sociocultural and economic values of wetland vegetation and the attributes and functions that support these values.
... Coastal plant communities accumulate sediment organic carbon (SOC) at different rates and therefore spatial shifts in the ecological landscape induced by SLR are accompanied by changes in the accumulation of SOC (Watanabe et al. 2019;Gonneea et al. 2019;Dontis et al. 2020). Along subtropical and tropical coastlines, SLR has stimulated the horizontal and vertical expansion of mangrove plant communities and associated sediments at the expense of other coastal plant communities (Krauss et al. 2011;Saintilan et al. 2014;Armitage et al. 2015;Grieger et al. 2019). Because mangroves accumulate more SOC than freshwater and salt marshes, quantifying these changes is fundamental to understanding how future SLR will affect the resilience of mangrove plant communities and their capacity to function as blue carbon ecosystems (Donato et al. 2011;Alongi 2014;Atwood et al. 2017). ...
Article
Mangroves can store more sediment organic carbon (SOC) than freshwater and salt marshes. Understanding how mangroves have responded to historical sea-level rise (SLR) is fundamental to assessing their resilience and capacity to store carbon as SLR accelerates. We quantified landscape-level temporal and spatial trends in historical coastal wetland sediment accumulation and associated SOC content (i.e., storage) along coastal-to-inland gradients in Southeast Florida. The observed trends were transgressive and attributed to the historical rise in sea level. Our results indicate an overall significant increase in the SOC content of the historic wetland sediment succession caused by the vertical accumulation and landward migration of carbon-rich mangrove-dominated plant communities (mean = 0.08 g cm−3) into and over carbon-poor wet prairie plant communities (mean = 0.02 g cm−3). The observed historical increase in SOC is predicted to diminish over time as the difference between rates of SLR and vertical sediment accumulation increases and because the landward migration of mangrove-dominated plant communities is now obstructed by a shore-parallel flood-control levee. These results are likely to unfold in other low-latitude coastal wetlands where they are sandwiched between rising seas and an urbanized landscape.
... While SLR is the most recognizable climate change-related threat in tidal marsh seascapes causing increased erosion to shorelines, emerging evidence suggests that it could actually be advantageous for some tidal marshes. For example, while SLR changes inundation patterns causing a redistribution of marsh plants, increased inundation can lead to more marsh area becoming available for fish (Grieger et al. 2019;Abbott et al. 2020). Note that restoring the lowest, most frequently inundated marsh areas substantially improves value of the restoration, including nekton use, of the marsh as a whole. ...
Article
Tidal marshes (including saltmarshes) provide remarkable value for many social (cultural, recreational) and environmental (fish production, water quality, shoreline protection, carbon sequestration) services. However, their extent, condition, and capacity to support these services are threatened by human development expansion, invasive species, erosion, altered hydrology and connectivity, and climate change. The past two decades have seen a shift toward working with managers to restore tidal marshes to conserve existing patches or create new marshes. The present perspective examines key features of recent tidal marsh restoration projects. Although optimism about restoration is building, not all marshes are the same; site-specific nuances require careful consideration, and thus, standard restoration designs are not possible. Restoration projects are effectively experiments, requiring clear goals, monitoring and evaluation, and adaptive management practices. Restoration is expensive; however, payment schemes for ecosystem services derived from restoration offer new ways to fund projects and appropriate monitoring and evaluation programs. All information generated by restoration needs to be published and easily accessible, especially failed attempts, to equip practitioners and scientists with actionable knowledge for future efforts. We advocate the need for a network of tidal marsh scientists, managers, and practitioners to share and disseminate new observations and knowledge. Such a network will help augment our capacity to restore tidal marsh, but also valuable coastal ecosystems more broadly.
... For example, bald cypress Taxodium distichum swamps, common in TFFWs of the south-east US, exhibit greater basal areas and growth rates in areas of lower salinity and shorter flood periods (Krauss et al. 2009). Composition also differed from marsh to eucalypt forest across a salinefresh tidal gradient in south-east Queensland, Australia (Grieger et al. 2019). Significant changes in salinity or hydrology due to disturbance events (e.g. ...
... TFFWs in the southern US are similarly structured along a tidal gradient of differing salinity and flooding (Mitsch and Gosselink 2015c), reflected by variation in vegetation structure, species richness and diversity and tree regeneration (Baldwin 2007;Krauss et al. 2009;Anderson et al. 2013;Liu et al. 2017). Within subtropical Australia, dominant CFW canopy species shift along landward elevational gradients, reflecting changes in salinity and flooding (Grieger et al. 2019). For example, the structure of Melaleuca swamp forests in northern Australia differs with the duration of seasonal flooding, with denser canopies generally occurring in areas that are inundated for up to 8 months (Finlayson et al. 1989). ...
... As a result, successive disturbance events (e.g. storms, further saline intrusion) can trigger the death of the canopy, resulting in a ghost forest of standing dead trees and a salt marsh understorey (Grieger et al. 2019;Kirwan and Gedan 2019). Similar responses have been observed in coastal Melaleuca forests of northern Australia, where Traditional Owners and scientists attribute the forest dieback to increased salinity from rising sea levels and the effects of feral ungulates (Bowman et al. 2010;Sloane et al. 2019). ...
Article
Coastal freshwater wetlands (CFWs) are among the most understudied wetlands globally and are highly vulnerable to projected climate changes. To address CFW knowledge gaps in south-east Queensland, Australia, we surveyed the floristic composition and structure of wooded CFWs and explored variation in vegetation patterns in relation to selected environmental drivers. Understorey and shrub assemblages were surveyed using a cover-class scale and stem counts for tree species abundance. Vegetation structure attributes (stem density, basal area) were calculated from survey data. Redundancy analysis was used to investigate drivers of vegetation structure and the species composition of each stratum. Vegetation structure patterns were associated with gradients of rainfall, soil moisture, salinity and pH. Understorey species composition was associated with wallum wetland species, native perennial grass and herb species, and vegetation patterns of the canopy. Common CFW species, namely Melaleuca quinquenervia and Eucalyptus tereticornis, dominated tree assemblage variation. Overall, CFW vegetation exhibited strong associations with gradients of salinity, rainfall, groundwater dependence and disturbance. Alterations to key drivers of vegetation pattern with future climate changes are likely to markedly influence the composition, structure and function of CFW vegetation communities. Action is therefore required to maintain CFW vegetation communities and ecological function in these diverse and unique wetland systems.