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Wetland vegetation regeneration in response to tidal reinstatement on an abandoned sugar cane farm

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Abstract

Supratidal wetlands are threatened by agricultural production and are highly vulnerable to climate change, particularly through sea level rise (SLR). While vegetation structure and composition of supratidal wetlands will likely change under projected SLR with run‐on effects for ecosystem service provision, these changes can provide opportunities for restoration of adjacent agricultural land. Here, we investigated the natural regenerative potential of supratidal wetlands on abandoned agricultural land in Southeast Queensland, Australia, specifically, responses of wetland vegetation communities to simulated SLR, through tidal reinstatement. In 15 years since crop abandonment, distinct communities of typical supratidal wetland vegetation have naturally re‐established, in predominately freshwater conditions, with minimal management intervention. Reinstating tidal floodwater increased the flooded extent and permanence of brackish water. Four repeat surveys of vegetation composition, structure, and condition were conducted in permanent plots established in Casuarina swamp, Melaleuca swamp, herbaceous marsh, and riparian zone vegetation communities, to observe change over time. Species richness decreased in all regenerating communities (Herbaceous marsh, Casuarina, and Melaleuca) post flood gate removal. Understorey vegetation cover also decreased in Melaleuca and Casuarina plots, but increased in herbaceous marsh plots, with increased cover of salt tolerant species throughout. Changes in woody vegetation community and structure were not observed during this short study (2.5 years), although the regenerative capacity of woody and herbaceous species was reduced. Supratidal wetland vegetation communities can naturally re‐establish in areas of abandoned agricultural land, however, increased saltwater flooding (likely with SLR) will put these communities at risk of transition to salt‐tolerant vegetation. This article is protected by copyright. All rights reserved.

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Eutrophication of coastal and nearshore receiving environments downstream of intensive agricultural production areas is a global issue. The Reef 2050 Water Quality Improvement Plan (2017-2022) sets ambitious targets for reducing pollutant loads entering the Great Barrier Reef from contributing agricultural catchments. At a regional scale, the Wet Tropics end-of-catchment target load reduction for dissolved inorganic nitrogen (DIN) is 60% from the 2012-2013 anthropogenic load level. However, not even with the combined efforts of the Reef Regulations (December 2019) mandate and adoption of best practice nutrient management on farm, is it likely that these DIN targets will be reached. Thus, there is a need for innovative and cost-effective approaches to deliver further water quality improvement. Transitioning low-lying, marginal sugarcane land to alternative land uses that require lower or no nitrogen inputs, but still provide farmers with income streams, is a potentially attractive solution. In this study, a multi-criteria analysis was conducted to identify sites suitable for such alternative land uses. The cost-effectiveness of DIN reductions from these land use changes were calculated, accounting for reductions in annuity gross margins and land conversion cost. In certain locations (where conversion costs are low and DIN reductions are high) treatment wetlands and no-input cattle grazing offer cost-effective DIN reduction in the range of 20-26$/kg DIN. This compares favourably with existing agricultural extension-based approaches (c. $50/kg DIN reduction). Ecosystem service wetlands (i.e., wetland restoration for fish production) - again when appropriately situated - offer the prospect of even more cost-effective performance (11-14 $/kg DIN reduction). These results, in conjunction with best management practices, support the premise that alternative land uses are cost-effective options for improving water quality in certain areas of low-lying, low productivity sugarcane land. On-going investments by government in addition to private market funding mechanisms could be appropriate for supporting such land use transitions. These approaches need to be tested and refined via targeted pilot projects, as part of a whole-of-landscape approach to achieve broader reef water quality targets.
Article
Background & aims: The capacity of dispersal to promote or hinder species' responses to global change remains a major question in ecology. One ecosystem experiencing rapid change is the tidal marsh, which is migrating inland in response to accelerated sea level rise. Few studies to date have investigated the ecological dynamics that impact this large-scale migration. Seed dispersal and persistence in the soil seed bank is a component that can be strongly indicative of community trajectories. With this in mind, the aim of our study was to characterize the germinable seed bank across a marsh-forest ecotone in the Chesapeake Bay. Methods: Soil samples were collected across transects that ran from the high marsh to the coastal loblolly pine forest in a brackish marsh in Blackwater National Wildlife Refuge, Maryland, USA. Samples were grown in a greenhouse and watered with either freshwater or 3 ppt seawater solution. We compared community composition across transects and between salinity treatments. Additionally, we compared the seed bank to standing vegetation and used seed trait data from the TRY Database to investigate changes in functional traits along this ecotone. Key results: We found halophytic species dispersing up to 15 m into the forest and a general lack of obligate upland species, including near absence of Pinus taeda, the dominant species in the forest canopy. A majority of species detected in the seed bank were wetland species of various types, with species with wide salinity tolerance arising most frequently. Salinity addition had a significant negative influence on seed bank diversity. Conclusion: Overall, our seed bank results suggest dispersal and germination under the conditions of saltwater intrusion will limit forest regeneration and favor marsh plant dispersal. This indicates that the ecological processes that determine the soil seed bank community will support continued migration of marsh species into uplands.
Chapter
This introductory chapter defines the key subjects for this volume of ecological studies and briefly presents the common context and the cohesion of the contents of the various chapters. It gives a definition of wetland ecosystem services and outlines briefly the 17 services that have been identified in ecosystems globally and are generally considered as being of major importance. Provisioning wetland ecosystem services such as food chain support, regulating services such as climate cooling, and the enhancement of biodiversity are prime examples. Definitions are also given for wetland character and wise use, as adopted by the Ramsar Convention on Wetlands. New developments in wetland restoration to enhance wetland ecosystem services, as they are described in this volume, are outlined briefly. The overview also pays attention to the chapters on the latest developments of our understanding of water quality enhancement services and climate regulation services of wetlands; on threats and resilience to disturbances such as climate change and invasion of exotic species; on new initiatives for wise use of large, internationally divided wetlands in the Yellow Sea; and on restoration and creation of wetlands in urban environments, in particular in China.
Article
We compiled available data and information on the global and regional areas (Ramsar regions), and changes in area, of 22 classes of marine or coastal and inland wetlands. From those classes for which there is information, inland natural surface wetlands (forming ,77% of total surface wetland extent) are dominated by non-forested peatlands, marshes and swamps on alluvial soils, with peatlands forming ,33% of natural inland wetlands. The smaller area of marine or coastal wetlands (,10% of total wetland extent) is dominated by unvegetated tidal flats and saltmarshes. Largest areas of human-made wetlands for which there is information are rice paddy and water storage bodies, with a much smaller area of tropical oil palm and pulpwood plantations. These human-made wetlands are all increasing in area. The reported decline in global natural wetland area is occurring across almost all classes of inland and marine or coastal natural wetlands. Total global wetland area estimated from these wetland classes is between 15.2 Â 10 6 and 16.2 Â 10 6 km 2 , similar to recent global wetland area estimates derived from remote sensing. Given the considerable data gaps for area of wetland classes, even the most recent other estimates of global wetland extent are likely to be underestimates.
Article
We measured plant community composition and productivity, soil accretion, and C, N, and P burial in a tidal freshwater forest of the Altamaha River, Georgia to gain a better understanding of the ecosystem services they deliver and their ability to keep pace with current and future rates of sea level rise. Ten species were identified in two 0.1 ha plots. Nyssa aquatica (Tupelo Gum) made up 50% of the density and 57% of the total basal area. Nyssa biflora, Liquidambar styraciflua, and Fraxinus pennsylvanica were the next dominant species, collectively accounting for 37% of the density and 26% of the total basal area. Taxodium distichum only accounted for 3% of the density, but 12% of the total basal area. Aboveground productivity, measured as litterfall and stem wood growth, averaged 927 and 1030 g/m² in 2015 and 2016, respectively, with litterfall accounting for 60% of the total. Tidal forest soils in the streamside and the interior (0–60 cm) contained 3–6% organic C, 0.20–0.40% N, and 270–540 µg/g P. Soil accretion based on ¹³⁷Cs was 4.0 mm/year on the streamside and 0.2 mm/year in the forest interior. The rate of accretion in the interior is considerably less than the current rate of sea level rise (3.1 mm/year) along the Georgia coast. Because the accretion rate was much higher on the streamside, rates of C sequestration, N and P accumulation, and mineral sediment deposition also were much greater. Low accretion rates in the interior of the forest that accounts for most of the acreage suggests that accelerated sea level rise is likely to lead to foreseeable death of tidal forests from saltwater intrusion and submergence.
Article
The Australian continent spans coastal wetland settings ranging from extensive mangrove forest and sabkha plains occupying in the tropical north, to the southern half of the continent, where high wave energy constrains wetlands within numerous barrier-fronted estuaries, drowned river valleys and coastal embayments. Only on the island of Tasmania are mangroves absent; elsewhere mangroves, Casuarina, Melaleuca and saltmarsh interact in ways illustrative of the effects of ongoing climate, tidal and sea-level change. Observations over several decades have suggested that recent anthropogenic climate change may already be impacting Australian coastal wetlands in important ways. A period of accelerating sea-level rise has been associated with saline intrusion, mangrove encroachment and Melaleuca dieback in the tropical north, punctuated by widespread mangrove mortality in drought periods. The consistent trend of mangrove encroachment and replacement of saltmarsh in the south, is associated with an “accretion deficit” in saltmarsh during contemporary sea-level rise. We review the ecological and cultural implications of these changes, including impacts on habitat provision for migratory birds, fisheries values, carbon sequestration and Indigenous cultural values. Current legislative and policy protections may not be sufficient to meet the increasingly dynamic impacts of climate change in altering wetland boundaries, composition and function.
Article
A decade-long examination was made of recruitment and establishment in a tidal freshwater high marsh along the Delaware River. Over the 10 yr of the study, seed bank, field seedlings, and vegetation showed variable patterns and significant year-to-year fluctuations. Patterns of each species were unique, perhaps the result of specific germination and/or establishment requirements and seedling morphology. For a given species there was little correlation among seed bank, seedling, and vegetation patterns, and germination success did not guarantee establishment. Species diversity showed significant year-to-year fluctuation, but there was no trend, and perennials did not change in importance during the 10-yr period. Because four annual species (Bidens laevis, Cuscuta gronovii, Impatiens capensis, and Polygonum arifolium) composed over 90% of the seed bank and field seedlings, and 58-89% ( = 70 ± 4) of the cover, community dynamics were dependent on seedling recruitment. For a given species life history stages (seed bank, field seedlings, and vegetation) were not predictable over the temporal scale of a decade. It is predicted, however, that if hydrology remains unchanged, the same suite of species will persist. The importance of the parasite Cuscuta gronovii is noteworthy.
Article
Depletion during spring germination (turnover), longevity, and successional relationships were studied at High Marsh (HM), Cattail (CT), and Shrub Forest (SF) sites in a freshwater tidal wetland over three years. There was significant seasonal reduction in size and composition of seed banks from all sites. Turnover was greatest in HM surface (0–2 cm) samples where 29 x more seeds germinated in March than in June. In CT and SF samples turnover was considerably less. Magnitude (34–97%) was related to species composition and factors affecting field germination. Decrease in density with depth (0–10 cm) was log-linear in March samples. Except for SF 30–32 cm, few seeds and species were found at 8–10, 15–17, or 30–32 cm. Three seed bank strategies were distinguished: (a) complete turnover (Type II, sensu Thompson and Grime 1979), (b) high turnover with some reserve (Type III), and (c) large long-term seed reserve (Type IV). Longevity of many species appeared to be restricted; 31–56% at each site were present only in surface samples, and 29–52% germinated only in March samples. Although some species were important at all three sites, the seed bank composition of each was distinct, and was related to vegetation composition at each site. Because the bulk of the seed bank at each site resembles its site vegetation more than that of another site, it is not possible to predict succession.
Article
Describes the seed bank in a Fraxinus caroliniana dominated floodplain swamp of the St. Johns River. The seed bank was dominated by Ulmus americana in spring and Cephalanthus occidentalis in autumn. Mean density of seeds in both the top 5 cm of substrate and at 5-10 depth decreased significantly from spring to autumn, principally due to germination of Ulmus americana seeds. The highest viable seed density was on stump microsites (611 seeds/m² in spring and 0 seeds/m² in autumn) and the lowest viable seed density was on logs (127 seeds/m² in spring and 25 seeds/m² in autumn). Seeds of most of the dominant tree species in the floodplain were absent from the seed bank. -from Author
Article
Drainage schemes to reclaim land or improve the productivity of waterlogged land in Queensland’s sugar-producing districts occurred overwhelmingly between 1920 and 1990. To understand the motivations for and timings of these schemes the discussion begins by defining drainage, examining its purpose and establishing how drainage in the sugar-producing lands of Queensland occurred at different geographic scales and involved various combinations of structures and co-operative arrangements. Next, consideration is given to why poor drainage retards the growth of sugar cane and how better drainage improves yields and reduces disease outbreaks. The analysis then considers how floodplain topography and the presence of soils with poor internal drainage, combined with high to very high annual rainfall, contributed to drainage problems in the sugar-producing lands of Queensland. The fifth section contains an examination of what drainage activities occurred throughout the sugar-cane-growing lands of Queensland, particularly after 1950. The environmental consequences of these drainage activities such as the loss of freshwater wetlands and the creation of sites where weeds have flourished are considered in the final section. Three important themes in the environmental and agricultural history of Australia will be explored in this article: the role of the State; knowledge and technology transfer; and human mastery over nature and its environmental consequences.
Article
Sea level rise elicits short- and long-term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014-2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; ten plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22-117%, corresponding with substantial declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long-term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re-shaping the unique coastal landscape of the Big Bend. This article is protected by copyright. All rights reserved.
Article
Tidal freshwater forested wetlands (TFFW) of the southeastern United States are experiencing increased saltwater intrusion mainly due to sea-level rise. Inter-annual and intra-annual variability in forest productivity along a salinity gradient was studied on established sites. Aboveground net primary productivity (ANPP) of trees was monitored from 2013 to 2015 on three sites within a baldcypress (Taxodium distichum) swamp forest ecosystem in Strawberry Swamp on Hobcaw Barony, Georgetown County, South Carolina. Paired plots (20 × 25-m) were established along a water salinity gradient (0.8, 2.6, 4.6 PSU). Salinity was continuously monitored, litterfall was measured monthly, and growth of overstory trees ⩾10 cm diameter at breast height (DBH) was monitored on an annual basis. Annual litterfall and stem wood growth were summed to estimate ANPP. The DBH of live and dead individuals of understory shrubs were measured to calculate density, basal area (BA), and important values (IV). Freshwater forest communities clearly differed in composition, structure, tree size, BA, and productivity across the salinity gradient. The higher salinity plots had decreased numbers of tree species, density, and BA. Higher salinity reduced average ANPP. The dominant tree species and their relative densities did not change along the salinity gradient, but the dominance of the primary tree species differed with increasing salinity. Baldcypress was the predominant tree species with highest density, DBH, BA, IV, and contribution to total ANPP on all sites. Mean growth rate of baldcypress trees decreased with increasing salinity, but exhibited the greatest growth among all tree species. While the overall number of shrub species decreased with increasing salinity, wax myrtle (Morella cerifera) density, DBH, BA, and IV increased with salinity. With rising sea level and increasing salinity levels, low regeneration of baldcypress, and the invasion of wax myrtle, typical successional patterns in TFFW and forest health are likely to change in the future.
Article
Coastal floodplains are among the most modified landscapes in southeastern Australia. We used available vegetation survey data for coastal alluvium and other unconsolidated Quarternary sediments to construct a diagnosis of the major plant communities and document their flora. We used soil landscape maps and historical portion plans to gain an understanding of the distribution and environmental relationships of the communities. The flora of coastal floodplains includes more than 1000 native vascular plant taxa and more than 200 introduced taxa. The introduced flora is likely to be considerably larger, given that sampling was biased toward the least disturbed sites. Six major plant communities were diagnosed including a rainforest found north from the Shoalhaven floodplain, a mixed forest of eucalypts and melaleucas found north from Jervis Bay, a casuarina forest (sometimes with melaleuca) found throughout the coast, one open eucalypt forest found principally south from the Hunter region, another open eucalypt forest found north of the Hunter region and a complex of treeless wetland assemblages scattered throughout the coast. The extent and spatial arrangement of these communities varies between floodplains, with landform, rainfall, water regime and soil properties including moisture, fertility and salinity thought to be important factors mediating their distribution patterns. All six assemblages are listed as Endangered Ecological Communities under Threatened Species legislation. The coastal floodplain communities continue to be threatened by land clearing and crop conversion, fragmentation, changes to water flows, flooding and drainage, input of polluted runoff, weed invasion, activation of acid sulphate soils, climate change and degradation through rubbish dumping and other physical disturbances.
Article
Premise of the study: Species richness and diversity may increase with spatial scale related to increased area and heterogeneity of habitat. Yet, in bidirectional hydrologically connected tidal ecosystems, secondary dispersal via hydrochory has the potential to homogenize seed banks, and both life history characteristics and tolerances to environmental conditions influence the composition of plant communities. How species richness, diversity, and composition of seed banks and vegetation change along environmental gradients and at different spatial scales is not well understood. Methods: We explored the relationships of seed bank and vegetation diversity across 135 plots along a tidal freshwater river in the Delaware Estuary, USA. Species richness and diversity were partitioned across three hierarchical spatial scales: individual plots, transects perpendicular to the tidal channel, and river kilometers. Community structure was also examined as it related to distance from the tidal channel and location along the tidal river. Key results: Species richness was 89 in the seed bank and 54 in the vegetation. Species-area relationships revealed that species richness reached a near maximum asymptote inland (20 m from channel) for the seed bank and at the edge (0 m) for the vegetation. Rare occurrences of species in the seed bank and vegetation were greatest 5 m from the channel edge. As spatial scale increased, seed bank richness increased, associated with the progressive accumulation of species. Seed bank diversity, however, was maximized within small plot areas and along the river. Diversity of the vegetation was maximized locally due to the abundance of a few common species. Conclusions: These findings suggest that suites of common species contributed to high localized vegetation diversity, yet large spatial scales maximized the number and diversity of species in the seed bank and vegetation through rare encounters, as well as the complexity of the landscape.
Article
The Gippsland Lakes, listed under the Ramsar Convention in 1982, have undergone chronic salinization since the cutting in 1889 of an artificial entrance to the ocean to improve navigational access, exacerbated in the mid-late 20th century by increasing regulation and extraction of water from inflowing rivers. Both developments have had substantial ecological impacts: a marked decline in the area of reed (Phragmites australis) beds; the loss of salt-intolerant submerged taxa such as Vallisneria australis, causing a shift to a phytoplankton-dominated system in Lake Wellington; and, nearer the entrance, an expansion in the area of seagrasses. Mangroves (Avicennia marina) first appeared in the late 1980s or early 1990s. Since 1986 recurring blooms of Nodularia spumigena have led to loss of recreational amenity and to the periodic closure of recreational and commercial fisheries. Changes to hydrological and salinity regimes have almost certainly shifted the contemporary fish community away from the pre-entrance state. Rises in eustatic sea levels and increases in storm surges will exacerbate the issue of chronic salinization. Whether or not managers choose to intervene to prevent, or at least minimize, ongoing environmental change will inevitably prove controversial, and in some cases no socially or technologically feasible solutions may exist.
Article
1. The survival and growth of 15 species and provenances of Australian trees planted on a saline site in dry tropical northern Australia was examined. The study site was divided between high, moderate and low salinity subsites. A randomized complete block design was used for each subsite. 2. Tree survival and height were measured at 3 and 24 months. Measurements of diameter at breast height, tree crown size, branch number per tree, growth form, fork numbers per tree, and leaf length, width and thickness were conducted at 24 months. Soil salinity was measured at 3, 12 and 24 months. These data were statistically analysed to examine the effect of salinity on tree survival and growth and the differences in response between taxa. 3. The survival and growth varied with salinity and species. Trees grown on the high salinity subsite had the lowest survival and poorest growth rate. Casuarina cunninghamiana, C. glauca and Eucalyptus camaldulensis achieved the highest survival, fastest growth rate and best growth form. Acacia aulacocarpa showed the poorest performance. 4. It is suggested that species selection for utilization of saline sites should be made according to salinity, species salt tolerance and management objectives. Plant height and diameter, crown size and branch number are important characteristics which indicate salt tolerance. Those species with an ability to maintain a relatively large crown and a high number of branches when subjected to salinity are most likely to be highly tolerant to salt.
Article
Recent evidence from field surveys suggests that periodic saline intrusions into tidal freshwater wetlands may not reduce plant species richness and that reductions in richness may not occur until a more consistent brackish salinity regime develops. In a greenhouse experiment using tidal wetland mesocosms, we tested the hypothesis that plant species richness of coastal marshes (wetlands dominated by herbaceous plants) would be similar under oligohaline (0.5–5) and freshwater conditions (<0.5) (psu; practical salinity units), provided that propagules of salt-tolerant species were present. We also hypothesized that plant community responses would depend on inundation frequency. Species richness was highest in fresh and oligohaline treatments (<5, 11–13 species per mesocosm) and decreased with increasing salinity up to 12. Inundation frequency did not significantly influence species richness. Aboveground biomass decreased weakly as salinity increased, but the difference between salinity treatments was significant only at the 0.1 level. Flooding did not significantly alter aboveground biomass, and belowground biomass was not significantly influenced by either salinity or flooding treatments (P < 0.05). Biomass of individual species and non-metric multidimensional scaling (NMS) analysis indicated a shift toward salt-tolerant plant communities with increasing salinity, but detected little influence of inundation. These findings suggest that species composition shifts may prevent strong reductions in biomass due to loss of individual species as salinity increases, and that community composition will change more rapidly in response to increases in salinity than to inundation increases. Also, saltwater intrusions into low-salinity marshes of up to 6 will not create an immediate and significant reduction in species richness assuming propagules of salt-tolerant plants are available and given the tolerance of many Fresh/Oligohaline species observed in this study to salinity levels ≥6. However, the species composition of fresh and oligohaline wetlands can shift toward a less species-rich brackish plant community within a single growing season under prolonged salinity exposures of 12.
Article
The discharge of agriculture irrigation runoff containing large amounts of suspended particles resulted in a high sediment accumulation rate (0.3–1.0 cm yr−1) in the receiving wetland upstream of Lake Xingkai, Northeast of China and may create negative ecological impacts to the wetland system, particularly the vegetation community. In this study, we conducted a germination experiment and a vegetation survey to evaluate the effects of different sediment loads on the seed banks of three wetland communities (dominated by Glyceria spiculosa, Zizania latifolia and Pycreus korshinskyi, respectively) under two hydrological regimes (0 and 10 cm water depth). Results revealed significant differences in seed germination rates among the three plant communities and significant effects of sediment load on the germination rates. Species richness and seedling emergence decreased significantly at 0.5–0.75 cm of sediment addition. Species responded differently to the addition of sediment. The number of seedlings of P. korshinskyi, Sagittaria trifolia, Alisma orientale, Monochoria vaginalis, Carpesium macrocephalum decreased gradually as the sediment addition increased from 0 to 2 cm, while the number of seedlings of Fimbristylis dichotoma, Eleocharis ovata, Bidens bipinnata decreased to zero at 0.5 cm of sediment addition. The number of species germinated under the non-flooded conditions was significantly higher than that under flooded condition. All plant communities showed a similar response to the sediment load under the two water regimes. Despite low similarity, the number of species germinated from seed banks was higher than the original number of species present in each plant community. To protect and restore the wetland vegetation community in the Sanjiang Plain, irrigation and land management strategies will need to be implemented to reduce the sediment load from the paddy fields to the wetlands.
Article
Five species of Casuarina were grown under non-saline drained, saline drained, non-saline waterlogged and saline waterlogged conditions in a glasshouse and their tolerance assessed by survival and relative growth after 12 weeks. Salinity tolerance of C. obesa, C. glauca and C. equisetifolia was associated with exclusion of Na and Cl while relatively sensitive species, C. cunninghamiana and C. cristata, accumulated salt in the shoots.High waterlogging tolerance of all species was related to the large proportion of aerenchyma in the roots. Waterlogging with saline water increased salt uptake to the shoot and was the most severe treatment imposed. Casuarina obesa and C. glauca were most tolerant of saline waterlogged conditions.
Article
Responses to salt in soil interstitial water were studied experimentally for nine populations of Phragmites australis (Cav.) Trin. ex Steud. from coastal Mediterranean marshes in France. The effects of exposure to salinity ranging from 0 to 25‰ were measured on germination of seeds collected in each site. Germination was up to 100% and was affected by salinity above 10‰. Variation in germination among populations was small in freshwater (ranging from 89 to 99% on average) but saline conditions increased the contrast (5–60% at 25‰).Growth of seedlings in shoot and biomass production were measured during a 2-month exposure to constant saline solutions, ranging from 0 to 20‰. The effects on the number and length of shoots from a 25-day temporary exposure at 25‰ followed by recovery in freshwater were measured. Growth decreased with increasing salinity (50% decrease at 7.5‰ when compared to freshwater) and 7–100% mortality depending on population, occurred at 15 and 20‰. Cumulative shoot length and biomass production varied significantly among populations in freshwater, but the difference was small in saline conditions, significant for biomass but not for length. The 25-day exposure at 25‰ stopped growth and plants recovered after flushing with freshwater. The stress effect was significant for shoot length but not for shoot number. Twenty-five days after the treatment ended, the numbers of shoots were not different between exposed seedlings and controls. The temporary stress suppressed the differences among populations but they were restored during subsequent growth in freshwater. None of the variation patterns observed during the experiment were related to the present condition of the site of origin.
Article
The phosphorus (P) requirements of Australian plants are reviewed. Many Australian plants have highly developed abilities for acquiring and conservatively using P. This is seen as an evolutionary response to the combined environmental pressures of fire, soil P levels that are in the lower part of the range for world soils, and low and eratic rainfall. In natural Australian ecosystems, more than 50% of the P in the A horizon is in organic combination. Organic matter is the main source for the growth of perennial plants, so the only successful assessments of 'available' P measure labile organic P and microbial P. However, the inorganic P of ashbeds is essential to the rapid establishment of fire ephemerals and tree seedlings in natural ecosystems. Almost all Australian plants develop associations with mycorrhizal fungi, or produce hairy roots, as ways of increasing P uptake. Highly developed abilities to redistribute P from ageing to young tissues enable Australian plants to have a low P requirement per unit of biomass production. This also results in low P losses in sawlogs from natural forests, but not necessarily from short-rotation plantations. The special role of P in the ecology and conservation of heathlands is reviewed. Finally,an overview is given of the P requirements of Australian plants being grown in soil-less media in nurseries.
Article
The relationship between above and belowground species composition has been researched in forests, grasslands, and wetlands to understand what mechanisms control community composition. I thoroughly reviewed 108 articles published between 1945 and 2006 that summarized and provided specific values on similarities between above and belowground communities to identify common trends among ecosystems. Using Sørenson's index of similarity, I found that standing vegetation and its associated seed bank was the least similar in forest ecosystems, most similar in grasslands, and of intermediate similarity in wetlands. I also discovered that species richness was not related to seed bank – vegetation similarity in any of the three ecosystems. Disturbances were a common mechanism driving community composition in all ecosystems, where similarity decreased with time since disturbance in forest and wetland ecosystems and increased with time since disturbance in grasslands. Knowing the relationships between seed bank and standing vegetation may help conservationists to manage against exotic species, plan for community responses to disturbances, restore diversity, and better understand the resilience of an ecosystem.
Article
1. When using the seedling-emergence method to analyse a soil seed bank the greenhouse conditions should match the germination requirements of the species involved. Although the seedling-emergence method is common practice in ecological studies, the germination characteristics of many species are not known, or are only partly known. 2. Before carrying out a large-scale seed-bank study in a wet dune slack, we tested the water requirements of the species in the seed bank, comparing a waterlogged soil with a moist soil. Four species germinated in significantly larger numbers in a waterlogged soil, seven species in a moist soil and 11 species showed no significant difference. When a species was present in low densities, it was often missed using the less appropriate treatment. 3. These results emphasize the need for a preliminary study before carrying out a seed-bank analysis and show the danger of using a ‘standard’ method to analyse soil samples from different habitats.
Article
Summary • Changes in farming practice provide an opportunity to restore once extensive forested wetlands on agricultural land. In some parts of the world, however, it has proved difficult to restore the full complement of plant species through natural regeneration. Similarly, the restoration of forested wetlands by replanting has often resulted in ecosystems of low diversity. Better methods of restoring these important ecosystems are now required and baldcypress swamps provide an opportunity to investigate alternative approaches to the restoration of forested wetlands. This study examined the composition of seed banks of farmed fields to determine their value in restoring swamps in the south-eastern United States. • A seed bank assay of soils from baldcypress swamps was conducted to determine the extent to which seeds are maintained during farming for various lengths of time. Soils from swamps that were farmed for 0–50 years were collected near the northern boundary of the Mississippi Alluvial Valley along the Cache River, Illinois. Soils were placed in a glasshouse setting in flooded and freely drained conditions, and the numbers and species of seeds germinating were recorded. • Woody species including trees, shrubs, and vines were poorly represented in seed banks of both farmed and intact sites (51 and 9 sites, respectively). Missing dominants in the seed banks included tree species with short-lived seeds such as Taxodium distichum and Nyssa aquatica. Cephalanthus occidentalis constituted the most abundantly dispersed seed of all woody species. • Herbaceous species were well represented in the seed banks of both farmed and intact swamps (species richness of 207 vs. 173 species, respectively) suggesting that herbaceous species may live longer than woody species in seed banks. Few of the herbaceous species decreased in seed density in seed banks with time under cultivation, although seed density was lower at sites that had not been farmed. Species that relied on vegetative organs for dispersal were absent in the seed banks of farmed sites including Heteranthera dubia, Hottonia inflata, Lemna minor, Lemna trisulca and Wolffia columbiana. These species may require active reintroduction during restoration. • Synthesis and applications. Both restoration ecologists and managers of nature conservation areas need to be cognisant of seed bank and dispersal characteristics of species to effectively restore and manage forested wetlands. In the case of baldcypress swamps, critical components of the vegetation are not maintained in seed banks, which may make these floodplain wetlands difficult to restore via natural recolonization. Ultimately, the successful restoration of abandoned farm fields to forested wetlands may depend on the re-engineering of flood pulsing across landscapes to reconnect dispersal pathways. Journal of Applied Ecology (2003) 40, 1025–1034
Article
Question: Community structure may be influenced by patterns of dispersed seeds (seed rain) because they contribute to the template of plant community development. We explored factors influencing seed rain in a system dominated by tidal water, where direction and magnitude of water flow are difficult to predict, unlike many other hydrochorous systems where water flow is directional. We posed three main questions: (1) are patterns in seed rain linked to effects of hydrodynamic variability; (2) do these patterns in seed rain reflect distribution of seed sources and seed production; and (3) what are the implications for the assembly of tidal communities?Location: Salt marshes on the Wadden island of Schier-monnikoog, The Netherlands.Methods: Species compositions of vegetation, seed rain, seed production and driftlines along a chronosequence of communities were compared. We also studied seed movement by sowing Astroturf® mats with seeds and checking for seeds remaining after a single tidal inundation.Results: Storm surges had a significant effect on seed-rain patterns as the highest density and diversity of captured seeds were found during a stormy period. Seed rain of the youngest communities was more influenced by storms than that of older communities. Patterns in seed rain generally followed similar patterns in the distribution of established plants, and seed production.Conclusions: Results suggested mostly local dispersal of seeds. However, there was some evidence of long-distance dispersal occurring during storm surges in younger communities that are regularly inundated with tidal water. The possible role of seed retention in constraining community development, rather than dispersal per se, is further discussed.