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Does cereal crop agriculture in dry swamps damage aquatic plant communities?
Abstract
The response of swamp vegetation to cropping was measured by analysis of the seed bank present (as a measure of swamp resilience) and a survey of the extant vegetation (as a measure of swamp integrity). Samples of seed bank were exposed to a germination stimulus, the plants that germinated and established were identified, and the density of emergent vegetation was assessed. Surveys of the extant vegetation after flooding in cropped and uncropped swamps indicated that the plant communities establishing after the different treatments were different. Cropping results in a reduced diversity and density of plants, although swamp plant communities retain some resilience to such disturbances. Cropping also affects germination from the seed bank of these wetlands. The degree to which cropping is a threatening process to swamp plant communities and their dependent fauna will depend on whether vulnerable elements can return to swamps, which in turn depends on swamp management, connectivity and landscape level processes. As the climate changes and wetlands become more temporary and flooding less reliable, recognition and conservation of the processes that maintain biodiversity in the landscape will become more important.
... 4. Wetlands have a high degree of inherent resilience. The plants and animals in them have adaptations such as germination cues and/or breeding triggers as responses to disturbances such as drought, high flows, physical changes, and grazing (Brock et al., 2003;Casanova, 2012). In many cases, it has been found that some disturbance is required to maintain biodiversity. ...
... In addition, they contain significant areas of native vegetation in an otherwise highly utilised agricultural landscape (Willis, 1964). Recognition of their intrinsic ecological values (Casanova, 2012;Casanova & Powling, 2014) coincided with one of the longest droughts in the region's history; from 1998 to 2010. During this time, these areas were rarely filled with water and were often completely dry for long periods, and as a consequence, many were easily converted to cropping land (Casanova & Casanova, 2016). ...
... Moderate grazing by native or domesticated animals (sheep, cattle), together with the variable water regime, represent disturbances that can support the coexistence of a diverse range of plants and animals. Initial attempts to conserve and restore these wetland systems entailed scientific studies to document (i) their biological values (Casanova & Powling, 2014), (ii) the threats to their existence (Casanova, 2012;Casanova & Casanova, 2016), and (iii) their geographical distribution and their size (Papas & Moloney, 2012). ...
For successful restoration of wetland and riparian systems, we need to recognise several key points: Wetland systems exist because of, and are governed by hydrology, so hydrological restoration is imperative. Wetlands always have been and need to be temporally and spatially variable, changes in flow and water availability are natural; so restoration of those characters are necessary for successful wetland restoration. Wetlands are closely linked to their surrounding environment as a water and nutrient source; where possible they should be restored in relation to whole landscape restoration. Wetland systems can be resilient and are capable of recovery to a functioning state; the recovery goal, appropriate methods, available resources and subsequent management and monitoring are vital to success.
... There were relatively few studies on temporary wetlands in Victoria undertaken before the Millennium Drought (Corrick and Norman 1980, Corrick 1981, Corrick 1982, Corrick 1992, Roshier et al. 2001, Butcher 2003, Robson and Clay 2005, but these studies indicate the general high biodiversity and functional values of temporary wetlands in the landscape. Even during the Millennium Drought, temporary wetlands retained high biodiversity values when they filled (Casanova 2012, Casanova andPowling 2014). ...
... The Millennium Drought stimulated a steady increase in cropping area in Victoria (van Dijk et al. 2013), 6 including an increase of 6.7 % in area cropped in the south-west of Victoria over the decade to 2003(WatLUC 2005. Some of that increase occurred in areas occupied by temporary wetlands (Casanova 2012). ...
... Unless there is a strong case to value a wetland in its own right, it can be devalued or ignored (Fellows and Buhl 1995), or thought of as being 'undeveloped'. This suite of attitudes, combined with technological advancements (such as GPS steering and zero tillage), as well as drier than average seasons, have combined to result in an increased incidence of cropping in wetlands, and a substantial risk from cropping to wetlands that remain unimpacted (Casanova 2012). ...
Victoria has over 35,000 wetlands, of which approximately 25,000 are defined as “naturally occurring”. These wetlands provide a number of ecosystem services and values. Many of these values are reliant on maintenance of the condition of wetlands.
Wetlands in Victoria are managed in accordance with the Victorian Waterway Management Strategy (VWMS). The VWMS identifies cropping as a threatening process to wetlands in fragmented landscapes and specifies a number of actions to address the risks to wetlands from cropping. Consistent with achieving the vision and actions of the VWMS, this project provides a review of the knowledge related to wetland values and cropping in the Victorian landscape. The information contained in this report can be used to inform policy development, prioritise research and develop management guidance for natural resource managers and landholders.
This review obtained information in three ways:
• literature review of written resources in grey and refereed published literature, unpublished reports and websites
• consultation with wetland managers (including farmers) and wetland researchers; and
• geospatial analysis of wetland distribution and cropping.
This information was used in a vulnerability assessment framework to assess the vulnerability of wetlands to cropping in Victoria at two spatial scales: site scale (individual wetlands) and landscape scale (regions or clusters of wetlands).
Wetland vulnerability at the site scale
Cropping in Victoria is generally a dryland activity, with broadacre production of grains such as wheat and barley, covering over 3 million hectares. These crop species are intolerant of long-term waterlogging and high salinities. Therefore, wetlands that are most likely to be exposed to cropping are frequently dry, generally shallow, and fresh to brackish. In addition, cropping does not occur on very steep or heavily forested land, so wetlands at risk identified in this study usually occur on plains areas with endorheic (internal) drainage patterns.
The factors that influence the likelihood that a farmer can and will crop a wetland include:
• the physical attributes of the wetland, e.g. wetland size (smaller wetlands are more likely to be cropped than larger wetlands) and soil constraints (the presence of heavy clay reduces the likelihood of cropping)
• the likelihood of economic gain, i.e. the potential crop yield versus the potential return on expenditure
• the risk of crop failure, e.g. frost, droughts and waterlogging risks
• legal limitations such as protection of endangered or rare species, and government legislation; and
• the farmer’s attitude towards conservation.
The overall aim of cropping practices is to produce a plant monoculture that results in a high yield of seed or grain. Broadacre cropping entails soil preparation (chemical amelioration, cultivation), sowing seed, application of biocides and fertilisers, and harvest. Each of these activities has the potential to impact on the biota and processes of wetlands.
There are multiple ecological consequences from cropping of wetlands. Cropping in wetlands has been found to reduce the germination of plants from the seed bank, and reduce the diversity of plants that establish. Invertebrate diversity and abundance can be impacted by the physical changes associated with cropping, as well as changes in hydrology that occur when wetlands are modified to enhance their value as cropland. Chemical and physical disturbances associated with cropping wetlands can modify food availability and reduce the numbers of amphibians, reptiles and mammals that use dry wetlands as a refuge. Cropped wetlands support fewer waterbirds that rely on a mosaic of wetlands for feeding and breeding.
The inherent resilience (or ‘adaptive capacity’) of temporary wetland plant and animal communities allows them to tolerate disturbance of different kinds. The seed bank, the high levels of biodiversity in the plant, plankton and invertebrate communities, as well as connectivity with other wetlands convey resilience and can ameliorate some potential impacts. Despite this, wetlands are highly vulnerable to cropping because a large number of their attributes (soil, seed bank, vegetation, invertebrates, vertebrates, water regime, water quality) and processes (germination, establishment, trophic interactions) are sensitive to the physical and chemical disturbances applied in cropping.
Therefore, although temporary wetlands are naturally resilient to disturbance, repeated and widespread cropping is likely to have a negative effect on their condition, and therefore the values and services they provide. Cropping has the capacity to remove shallow, temporary wetlands from the landscape altogether.
Wetland vulnerability at the landscape scale
At a landscape scale, wetlands are exposed to cropping in those agricultural areas of high wetland density where the topography, soil characters and rainfall are amenable to cropping. There is a low likelihood of cropping and impacts of cropping to wetlands on public land. The approximately 20,000 privately owned wetlands of natural origin are at the highest risk.
Geospatial analysis identified seven clusters of Victoria’s wetlands that could be exposed to the impacts of cropping. The incidence of cropping in the southern Victorian landscape is limited by a combination of landform and alternate agricultural enterprises. Wetland clusters at Bessiebelle and near Mt Gambier in western Victoria are currently only lightly impacted by cropping, but are potentially vulnerable to cropping in the future (with higher temperatures and more evaporation due to climate change).
Two of the wetland clusters in western Victoria (South East Grampians and West Wimmera) are currently impacted by cropping and were examined in detail to determine the scale of that impact. The results of this analysis indicate that changes in cropping practices and machinery that have occurred in the past decade (e.g. rock removal, direct-drill sowing, landscape clearance, use of airseeders with 20 m widths, sprayers with 33 m span), have increased the amount of cropping in wetlands in these regions.
A comparison of data collected for this study and data collected in c. 2010 revealed that the incidence of cropping in wetlands is now much higher than was previously recorded, with nearly 45 % of wetlands sampled in the South East Grampians cluster of wetlands impacted by cropping to some degree, compared to an estimate of 2 % in 2010. In the South East Grampians cluster cropping occurs on freshwater, rain-filled wetlands on volcanic-derived soils. There do not appear to be any substantial physical restrictions to an increase in the incidence of cropping in South East Grampians wetlands in dry years. In contrast, the percentage of wetlands cropped in the West Wimmera has remained relatively stable since 2010, at approximately 20 %. The West Wimmera cluster of wetlands occurs on a mosaic of undulating farmland and forested land, where wetlands are formed from groundwater and rainfall. Wetland cropping in the West Wimmera occurs at the edges of saline and fresh permanent wetlands, as well as in temporary wetlands. Cropping in the West Wimmera region is restricted by soil type, and the presence of trees and shrubs.
In both the East Grampians and West Wimmera regions the likelihood that a wetland will be cropped is related to:
• surrounding land use - wetlands adjacent to crop land are highly likely to be cropped
• wetland size and depth - shallow wetlands up to approximately 8 ha are more vulnerable than are larger wetlands
• wetland water regime - permanent wetlands are less likely to be fully cropped than temporary ones
• water quality - saline wetlands are not much cropped, brackish and freshwater more so
• presence of trees and shrubs across the wetland - wetlands dominated by non-woody vegetation are more likely to be cropped than those dominated by woody vegetation; and
• the conservation ethic of the land manager.
Wetlands, like all ecosystems, have some degree of adaptive capacity or resilience that allows them to withstand disturbance. One of the mechanisms that provides adaptive capacity in temporary wetlands is the connectivity among individual wetlands in a wetland mosaic. Cropping can increase fragmentation of that mosaic by reducing wetland size, removing smaller wetlands, and increasing the distances and resistance to dispersal among wetlands, thereby reducing wetland resilience at a landscape scale.
The outcomes of this review were used to briefly explore management recommendations for natural resource managers. There are three management options in relation to cropping in wetlands: do nothing, conserve what remains, or conserve and try to restore wetlands that are already impacted. Given the value of temporary wetlands in the Victorian landscape and their capacity to support high biodiversity and cultural values it is recommended that management should seek to conserve and improve the condition of the remaining unimpacted wetlands, and restore wetlands that are currently impacted where they contribute to landscape connectivity.
Actions could include:
• developing guidelines for management of unimpacted wetlands in cropping landscapes
• establishing buffers between cropping activities and wetlands
• identifying and preserving connectivity among wetlands; and
• prioritising wetlands and wetland mosaics for restoration.
There are significant barriers to the implementation of management actions. These barriers include:
• the fact that most of the wetlands are privately owned
• their dispersed nature across the landscape
• the availability of funding
• the lack of knowledge among landowners; and
• the difficulties in implementation of effective communication with landowners.
It is recommended that management actions target the economic and social drivers that make cropping in wetlands profitable and acceptable to farmers. The rapid rate of change that has been detected makes it necessary to implement conservation measures as soon as possible, before the majority of wetlands are removed from the landscape altogether, and the species dependent on them become rarer, more threatened or extinct.
... The major land use has been grazing by sheep and occasionally cattle, and for the development of water storages, dams or tanks, within the body of the swamp. Despite the surrounding land use and the impact of grazing, until the 2000s many swamps retained high biodiversity values because of the resilience conveyed by seed, tuber and propagule banks (Casanova 2012). When swamps are inundated by rainwater the seeds and eggs in the soil germinate or hatch, tubers sprout and the vegetation re-establishes. ...
... According to the EPBC Act listing advice (Commonwealth of Australia 2012), they become flooded with rainwater annually, except in drought years. The frequency of inundation appears to have become lower in recent decades and, as a consequence, some farmers have started to cultivate swamps for crop production (Casanova 2012). There are no formal records of swamp flooding frequency in any public repository, and the only sources of information about the water regime in these water bodies come from local maps (based on aerial photography) and local memories. ...
... Where hydrological measurements are not available, models of wetland filling can be developed from rainfall and climatic records (Roshier et al. 2001). The vegetation of swamps is generally tree-less (fringing Eucalytpus camaldulensis can occur) and dominated by emergent grasses and herbs, although there have been few investigations into individual swamps (Butcher 2003; Robson and Clay 2005; Casanova 2012) and no published records of the microalgae associated with these wetlands. The listing of these wetlands under the EPBC Act is based on the contention that swamps have high biodiversity values, although such values are poorly documented. ...
Freshwater temporary wetlands are a little-studied ecosystem world-wide. They have been recognised as critically endangered in south east Australia under Australian biodiversity conservation legislation. However, little has been recorded about their hydrology, functioning or biodiversity values; i.e. the factors that make them intrinsically âswampyâ. In this paper we develop a simple threshold model of wetland hydrology based on historical rainfall records and calculated evaporation records matched to records and recollections of the owners of swamps, and document water plant and microalgal species richness. The model indicates that swamps were inundated to at least 10 cm depth in an average of 6.3 years per decade for most of the 20th century. The average dry time between inundations was 1.27 years (maximum of 4.5 years). Since 1998 the frequency of inundation appears to have decreased, and the average dry times have increased. Despite, or because of, their temporary nature, these swamps have high biodiversity values among the vegetation and the microalgae, more than has been recorded for near-by permanent wetlands. There is no evidence that a drier and warmer climate will impact negatively on biodiversity values, however land management is likely to be important for maintaining these systems as the climate changes.
... Moreover, wet grasslands show limited topographic variation (Ward et al. 2013) so that species may lack refuges from floods or climate warming. In addition, many remaining wet grasslands are fragmented or isolated (Casanova 2012) and the characteristic and rare plant species of diverse communities (e.g., orchids) tend to lack mobility due to low dispersal rates (Joyce 2014). Thus, wet grasslands might provide an early warning of climate change impacts upon ecology, especially as diverse systems can allow small or rapid responses to be discriminated (Joyce 2001). ...
... Historical average inundation was six or seven years of flooding in every decade (Casanova and Powling 2014), but in the last two decades these wetlands have only been inundated approximately four times per decade. One consequence of fewer filling events has been to encourage a change in land use from grazing to cropping, which had significant effects on the biodiversity and ecological integrity of these wet grasslands (Casanova 2012). Reduced water supply to wet grasslands could also initiate a negative feedback loop in which these wetlands would be unable to recover, favoring a more terrestrial community (Čížková et al. 2013) and leading to changes in nutrient cycling, decomposition, soil microbes, and primary production (Öquist and Svensson 1996). ...
Wet grasslands are threatened by future climate change, yet these are vital ecosystems for both
conservation and agriculture, providing livelihoods for millions of people. These biologically diverse,
transitional wetlands are defined by an abundance of grasses and periodic flooding, and maintained
by regular disturbances such as grazing or cutting. This study summarizes relevant climate change
scenarios projected by the Intergovernmental Panel on Climate Change and identifies implications for
wet grasslands globally and regionally. Climate change is predicted to alter wet grassland hydrology,
especially through warming, seasonal precipitation variability, and the severity of extreme events
such as droughts and floods. Changes in the diversity, composition, and productivity of vegetation
will affect functional and competitive relations between species. Extreme storm or flood events will
favor ruderal plant species able to respond rapidly to environmental change. In some regions, wet
grasslands may dry out during heatwaves and drought. C4 grasses and invasive species could benefit
from warming scenarios, the latter facilitated by disturbances such as droughts, floods, and possibly
wildfires. Agriculture will be affected as forage available for livestock will likely become less reliable,
necessitating adaptations to cutting and grazing regimes by farmers and conservation managers,
and possibly leading to land abandonment. It is recommended that agri- environment schemes,
and other policies and practices, are adapted to mitigate climate change, with greater emphasis on
water maintenance, flexible management, monitoring, and restoration of resilient wet grasslands.
... Ecological changes in regulated river systems include massive loss of wetlands, decline of riparian forests, invasion of dewatered river channels and wetlands by vegetation, changes in aquatic plant community structure, population and diversity declines of invertebrates, fish and waterbirds, and several invertebrate extinctions (Arthington and Pusey, 2003;Kingsford, 2000). Additionally, a greater frequency and duration of drought in temporary wetlands (Driver et al., 2011;Casanova, 2012) along with an increase in the profitability of grain and oil-seed production (Tostovrsnik et al., 2010) has led to a change in land-use from biodiverse pasture grazing to monoculture cropping, with consequent threats to temporary wetlands as habitat for birds, frogs, plants and algae (EPBC_Act, 1999). ...
... In many temporary wetlands plant, algal and invertebrate populations re-establish when inundated, through germination or hatching from a bank of desiccation-resistant seeds, eggs or propagules in the soil. This bank of propagules conveys a degree of resilience in temporary wetlands (Casanova, 2012), and many species can remain dormant in the soil for years or decades (Brock, 2011). ...
... Infrequently flooded floodplain seedbanks are more likely to reflect what would be found in terrestrial environments; however, some floodplain seedbanks have been shown to also contain comparable numbers of riparian plants species as in-channel features (O'Donnell et al. 2013). The lower taxa richness and seed abundances of riparian plant species found in our floodplain samples may be a result of their agricultural legacy, which has been demonstrated to adversely affect riparian plant soil seedbanks (Casanova 2012;Dawson et al. 2017aDawson et al. , 2020. In addition, cultivation is likely to promote the predominance of terrestrial species in the soil seed bank, such as we observed (Dawson et al. 2017a). ...
Flow regulation impacts on riparian vegetation composition, often increasing the prevalence of exotic and terrestrial plant species. Environmental flows may benefit native riparian vegetation via the promotion of plant recruitment from riparian soil seedbanks, but this is dependent on an intact native seedbank. Thus, we assessed the composition of the soil seedbank of different riverine geomorphic features to determine its potential response to environmental flows. Soil seedbank samples were taken from channel bars, benches and floodplains at six sites along the Campaspe River, Australia, a heavily regulated river that receives environmental flows. These geomorphic features represent a gradient in elevation and thus flooding frequency from frequently flooded (bars) to infrequently flooded (floodplain). Seedbank samples were ‘grown out’ in a glasshouse, and seedlings identified and classified according to taxa, flood tolerance and origin (native or exotic). We identified 6515 seedlings across all geomorphic features and sites, with monocots most abundant. Soil seedbank composition varied between geomorphic features. Overall, seedling abundances were greater for in-channel features (bars and benches) than floodplains, but taxa richness did not vary likewise. Soil seedbanks of in-channel features were dominated by flood tolerant and native taxa, while flood intolerant and exotic taxa were generally associated with floodplains. The dominance of native flood tolerant taxa in the soil seedbanks of in-channel geomorphic features suggest these seedbanks can play an important role in the resilience of native riparian plant communities. Moreover, environmental flows are likely to play a positive role in maintaining native riparian plant communities given such conditions.
... Although significant differences were found between inundation regime (F, flooded; W, waterlogged; R, rain), there was no significant differences between land-use zones. and Vandervelde 1995) and their phenotypic response to inundation (Brock and Casanova 1997;Casanova 2012;Bell and Clarke 2004). Of the three inundation treatments used in this study (regardless of historical land use), the submerged functional groups (Se, Sk and Sr; WPIL ,2) emerged only from the flooded treatments, suggesting that this functional group only germinated following flooded conditions of at least 9 weeks. ...
Ephemeral floodplain lakes are an integral component of inland wetland ecosystems and experience highly variable hydrology and prolonged dry periods. Although wetland soil seed banks are highly resilient to drought and floods, anthropogenic land use may add an additional stress. Understanding the recovery potential of wetland soil seed banks to different historical land uses helps manage and prioritise environmental water. In this study we explored the resilience of the wetland plant community in an ephemeral floodplain lake (Ita Lake, NSW, Australia). We collected soil samples during an extended dry phase (10 years) from two distinct zones within the lake, one of which was subjected to historical grazing and the other to lakebed ploughing and cropping. The samples were inundated under multiple inundation regimes to assess soil seed bank response. We found that the soil seed bank was viable, indicating a level of resilience not previously recorded for some plant species, namely Ricciocarpus natans, Chara spp., Nitella spp., Alternanthera denticulata and Eleocharis acuta. Although the results highlight the resilience of ephemeral wetland plant communities, intensive land uses such as ploughing and cropping will limit the availability of seeds to germinate, and the inundation regime will influence species composition and the subsequent likelihood of restoration.
... Although there is little knowledge of how the propagulebank depth profile changes with land use, there is a greater understanding of how land uses discussed here affects propagule banks in the top 5 cm. The findings of the present study are consistent with those of a previous study in the same wetland (Dawson et al. 2017a) and another study on the effect of cultivation in floodplain wetlands (Casanova 2012). All three studies found fewer amphibious species or numbers in cultivated areas, but there were also indications that recovery may be possible, depending on future flooding. ...
Many studies have investigated the effects of human disturbances on floodplain propagule banks, but few have examined how these propagule banks change down the soil depth profile. Changes in soil propagule banks with depth can indicate the state of past vegetation and potentially demonstrate the effects of different land uses on the soil profile. Here, we examined changes in soil propagule banks down the soil-depth profile in an Australian floodplain wetland with five different land-use histories, ranging from a, in this case, relatively minor disturbance (clearing) through to more major disturbance (continuous cultivation). Land use had a larger influence than floodplain geomorphology on the propagule distribution of wetland plant-group numbers. An observed decrease in individuals over the depth profile also altered terrestrial plant groups in fields with longer land-use histories. Overall, soil-propagule profiles for terrestrial plants were not as affected by land use as were those of wetland plants. The geomorphological position on the floodplain also altered the soil propagule bank, with areas subject to the most flooding having the highest number of wetland species and retaining more of these species with greater depths. In conclusion, land-use impacts alter soil-propagule banks down the profile, despite most studies focussing on the top few centimetres.
... Recent investigations suggest that herbicides discharged into natural aquatic systems, primarily through water runoff, could be one of the highest risk factors for plant species survival (Eullaffroy et al., 2009;Casanova, 2012). Paddy herbicides are a high-risk concern for aquatic plants not only in the paddy system but also in the surrounding wetlands, because these herbicides readily flow out of paddy fields into rivers causing toxic effects (Nagai et al., 2011). ...
Although rice production provides stable environments for aquatic plants, the wide use of herbicides is a concern for wild plants inhabiting the surroundings of rice paddies. Because commercial herbicides are typically a cocktail of chemicals, they may pose a threat to wild plants even when the constituent chemicals do not individually have detrimental effects. We sampled water from a rice paddy and a river receiving the paddy drainage immediately after the transplanting period to identify and compare the concentrations of herbicides. We also examined the effect of the sampled water on the germination of two plants: Ammannia multiflora(hygrophyte) and Vallisneria asiatica(submerged). We found that the concentrations of glufosinate in the paddy and river waterswere 0.0015 and 0.0013mgL-1, respectively, and those of pyraclonil were 0.0010 and 0.0009 mg L-1in the same waters, indicating that these chemicals persist outside the rice paddy. The germination rate of A.multiflorawas significantly diminished with exposure to river and paddy water under fluctuating temperature conditions, whereas no difference was observed for V. asiatica. For a comprehensive understanding of the influences of residual herbicides on wetland biodiversity, it is necessary to analysethe effects of herbicides on a wide range of aquatic plants and at various stages of growth.
... Viable seeds of aquatic macrophytes can persist in the seed bank for decades, ensuring regeneration of aquatic communities following extended dry periods (Wienhold & van der Valk, 1989; Rogers, 1998;Brock et al., 2003). Furthermore, Casanova (2012) demonstrated that seed banks of some aquatic plants in farmed wetlands exhibited resiliency to such extreme disturbances such as drought and tillage. As submersed aquatic and persistent emergent vegetation have substantially declined in the IRV since the mid-1900s (Stafford et al., 2010), it is noteworthy that these vegetation communities developed at Emiquon without supplemental seeding or planting by managers. ...
More than half of the natural wetlands in the Illinois River valley (IRV) have been lost through conversion of floodplain wetlands and lakes to drainage and levee districts for agricultural production. During 2007–2013, we monitored the response of wetland vegetation communities to restoration at Emiquon Preserve, a former floodplain that was drained and farmed for more than 80 years. Spatial coverage of wetland vegetation and other cover types rapidly expanded from 252 ha in 2007 to 1,944 ha in 2013 (mean 1,512 ± 239 ha) with little supplemental planting or hydrological management. Restored vegetation emulated aquatic plant communities that were largely eliminated from the IRV, most importantly floating-leaved and submersed aquatic vegetation. Mean annual wetland cover included aquatic bed (44%), open water (20%), persistent emergent vegetation (10%), hemi-marsh (10%), and nonpersistent emergent vegetation (9%). Average moist-soil seed and tuber density was similar to managed wetlands in the IRV (mean 724 ± 224 kg/ha). A viable option for restoration of diverse aquatic macrophyte communities within degraded wetlands of large river systems includes passive restoration of hydrology and vegetation behind levees while maintaining infrastructure to facilitate drawdowns when necessary or to mimic historical conditions.
... Adaptive management may facilitate the establishment of a series of alternating communities, thus, maximising plant diversity over time. Many conservation studies have assessed the soil seed bank and its importance for the conservation and restoration of wetlands in agricultural landscapes (Bissels et al. 2005;Casanova 2012). In the prairie pothole region and in coastal plain depressions in the United States, for example, several studies have focused on different approaches to restore the natural vegetation after long-term agricultural use of these wetlands (De Steven et al. 2006;Galatowitsch and van der Valk 1996). ...
Temporarily flooded depressions in arable fields support populations of specialised plant species that are affected by flooding and agricultural management. Depending on the degree of flooding, different proportions of wetland and arable species contribute to the seed bank. This is reflected by high inter-annual variations in plant communities with a high conservation value. Due to ongoing agricultural intensification, the biodiversity of temporarily flooded depressions has declined, and several plant species have become regionally extinct. Because seed banks harbour persistent seeds over long periods, they play a crucial role in the conservation and restoration of temporary wetland vegetation. This study focuses on the effects of different flooding regimes on plant species emerging from seed banks of temporarily flooded depressions in arable fields in northeast Germany. We cultivated soil samples from upper and lower wetland zones under short, intermediate and long-term flooding (5, 15 and 40 cm above soil surface) in a common garden experiment over 2 years. We observed significant changes in species composition depending on the flooding duration. Species richness declined and evenness increased with increasing flooding duration. Upper and lower zones showed similar species richness and evenness, but species compositions differed. Red List species emerged from all treatments although the species differed, indicating that all communities emerging under different flooding regimes have a high conservation value. Seed banks under fluctuating site conditions can constitute a series of alternating plant communities. This could be used to develop management strategies that benefit different communities with high conservation values.
... Second, we evaluated the anthropogenic and natural pressures that threaten the survival of this species. Recent investigations suggest that herbicides discharged into natural aquatic systems, primarily through water runoff, could be one of the top risk factors for species survival (Eullaffroy et al., 2009;Casanova, 2012). Accordingly, we tested the effect of the most common and modern-day European herbicides on M. quadrifolia. ...
This study investigated the conservation status of Marsilea quadrifolia, an endangered fern found in paddy fields, irrigation ditches and ponds. An evaluation at the European level based on IUCN criteria showed that the extent of occurrence (EOO) of M. quadrifolia has decreased from 5,930,000 km2 to 5,774,000 km2 during the past decade, whereas its area of occupancy (AOO) has decreased from 620 to 400 km2 (approximately 35.5%). These findings allowed the species to be upgraded from the IUCN classification of Near Threatened to Vulnerable. The agricultural chemical treatments seem to be the main extinction cause of M. quadrifolia, therefore we performed toxicological with 7 most common rice herbicides. Young plantlets were incubated for 96 h with each herbicide at three different concentrations: TQ (Tale Quale, chosen in accordance with the suggested dose for rice fields described on the product label), 1:100 and 1:1.000. Results suggested that survival of the plantlets depended on the herbicide and concentration used, and ranged between 0 and 80%, and no survival at ambient concentrations for 4 (Aura, Aura + Dash, Clincher and Viper) out of the 8 chosen herbicides. We conclude that herbicides represent one of the principal threats to the survival of this species. Finally, a DNA analysis using the AFLP approach was employed to identify the most suitable genetic pool for plant reintroduction efforts. The data show that the analysed populations of M. quadrifolia suffered from low genetic variability (Nei's gene diversity varied from 0.025 to 0.036). However, the analysis of the distribution of genetic variability suggested that 4 populations were characterised by different genetic traits that are useful in defining a genetic pool for plant conservation. This study highlights a strategy for implementing a plan of action for species growing in agro-ecosystems based on an integrated approach that is able to clarify the species conservation status, the principal threat factor and the genetic pool to be used for species conservation and reintroduction.
Some landholders who have cropping enterprises utilise wetlands on their properties, even where such actions are unlawful. The ecological impacts of cropping or draining these environmental assets will vary, but the outcomes can be dramatic and irreversible. This article examines the judgements of rural landholders about the acceptability of cropping or draining wetlands. Data were gathered through a survey of rural landholders in western Victoria. Rural landholders were more likely to judge cropping or draining wetlands to be unacceptable than acceptable. Respondents who found these practices acceptable were more likely to have a business orientation and be farmers by occupation. Almost a third of respondents indicated they were ‘unsure’, suggesting there is an opportunity to influence their attitudes. However, the ‘unsure’ were more similar to those who found cropping or draining wetlands acceptable. Economic opportunities provided by these practices are an important barrier to conservation efforts. We suggest that management agencies target landholders with wetlands and offer financial incentives for their active management beyond that required by law, and provide learning opportunities around wetlands. It may also be necessary to more actively monitor and prosecute illegal activity to complement the existing focus on extension and cost sharing for on-ground work.
Global acknowledgement of climate change and its predicted environmental consequences has created a need for practical management techniques that increase a landscape’s ability to capture and store atmospheric carbon (C). Globally, wetlands sequester disproportionally more C per unit surface area than many other components of the landscape. However, wetlands vary in their capacity to store C and regulate greenhouse gas emissions. Hydrology, in particular, is a critical driver of wetland C capture and storage. Rain-filled wetlands offer a challenge for the management of C sequestration and storage because the hydrology of these systems is almost entirely driven by rainfall. We present a conceptual model of how management options, including weed and pest control, grazing and crop management and revegetation, will affect C sequestration and storage in rain-filled wetlands. Given the intensive nature of agricultural activities in areas where rain-filled wetlands are common, further work is needed to increase our understanding of the effects of these activities on wetland C capture and storage. Key knowledge gaps relating to the effect of management actions on wetland C sequestration include: (a) the benefits of integrated wetland management; (b) the appropriateness of different grazing regimes and the effect of total grazing pressure; (c) the effects of fire; and (d) the extent to which wetland function (C storage) can be restored following agricultural activities, such as cropping.
Australian species of Chara L. sect. Charopsis (Kütz.) Leonh. are revised. Multivariate analysis supports recognition of four species: Chara braunii C.C.Gmel., C. evanida Casanova, C. karolii Casanova and C. muelleri (A.Braun) F.Muell. These taxa are described and illustrated, and a key is provided.
A new locality of Chara baueri A. Braun (Chara scoparia Bauer ex Reichenbach) in a mid-field pond localized near Cedynia (western Poland) was found in August 2008 to be the first known locality of this species in Poland. Specimens were found on mineral substratum at the depth of 0-40 cm among patches of Ceratophyllum submersum L. and Chara globularis Thuill. The species is one of the rarest charophytes all over the world and known from few sites only in Europe and Asia.
3 Office of Environment & Heritage, Baradine, NSW 2396 AUSTRALIA Abstract: The floristic composition and vegetation partitioning of the ephemeral wetlands of the Pilliga Outwash within the Pilliga National Park and Pilliga State Conservation Area (30˚30'S, 149˚22'E) on the North Western Plains of New South Wales are described. SPOT5 imagery was used to map 340 wetlands across the Pilliga Outwash. A total of 240 plots within 31 wetlands explored composition and species richness in relation to water depth and wetland size. The predominant community described is the species-rich herbfield of shallow basin wetlands, along with the structurally distinct but the less common sedgeland/herbfield of the deeper 'tank' wetlands and a single wetland with a floristically depauperate Diplachne fusca wet grassland. A total of 131 taxa were recorded including three species listed under the NSW Threatened Species Conservation Act (1995): Eriocaulon australasicum, Lepidium monoplocoides and Myriophyllum implicatum. New records for an additional six taxa were recorded for the North Western Plains. 11% of taxa were exotic in origin.
Australia has a long history of taxonomic research on charophytes, and approximately 95 species have been described over the years. In Wood's revision of Australian charophytes (1972), several species were not recognised because the material was missing or destroyed. Some of these species have been recently rediscovered. This paper focusses on the taxa Nitella hookeri A. Br. var. arthroglochin A.Br. Lychnothamnus barbatus (Meyen) Leonh. and Nitella partita Nordst. N. hookeri var. arthroglochin has only been collected in Australia in 1854 and 1887 and not again until 1989. It was rediscovered in high-altitude, temporary streams on granitic soil in New South Wales. L. barbatus was collected for the first time by R.D.Wood in 1960, and then again after intensive surveys in 1996. It grows in subtropical episodic streams in south-east Queensland. N. partita was collected once in the Georgina river region of arid central Queensland in 1889, then again more than 100 years later from temporary wetlands in arid north-west New South Wales. A combination of factors led to the initial discovery of these species, their apparent extinction in the intervening years, and recent discover. The apparent extinction and rediscovery of these taxa highlights the importance of temporary wetlands to many members of Characeae and the necessity for conservation of these habitats.
Charophytes (family Characeae) are a cohesive group within the green algae. The genus Chara is abundant and diverse in a variety of Australian habitats. Approximately 37 taxa of Chara have been described on the basis of Australian collections. The current status of charophyte taxonomy is confused. RD Wood revised Australian charophytes in 1972 on the basis of an erroneous species concept, and charophytes are rarely identified lower than genus by ecologists and water managers. Many species were described by overseas experts in the mid-1800s, and this trend continues to the present day. Typically, species descriptions have been based on examination of few specimens, and sometimes not even fertile representatives of each species. In this study Wood's (1972) taxonomic treatment of Australian members of the genus Chara is examined and analysed in relation to historical species concepts and more recent experimental taxonomy and oospore morphology. Thorough studies based on determination of reliable indicators of genetic incompatibility through culture studies, including oospore morphology and genetic analysis and objective analysis of fertile specimens, are now required. Introduction Limnologists and aquatic botanists in Australia will be familiar with family Characeae (commonly called charophytes), a group of macroscopic green algae that grow in fresh, brackish and saline non-marine waters throughout Australia (and the rest of the world). They are similar in appearance to the submerged angiosperms Myriophyllum and Ceratophyllum, with long axes and whorls of leaf-like structures (branchlets) at the nodes. However, their basic construction consists of large, multinucleate, haploid cells joined end-on-end, and each node has a complex of branchlets and accessory cells. Their sexual reproductive organs (oogonia and antheridia) are also different from angiosperm flowers. They can reproduce vegetatively (by bulbils and contracted, starch-filled branches) and sexually through diploid oospores. They can be annual or perennial, but most collectors would agree that they are unreliable in their occurrence. Reproductive organs can be ephemeral also, so collecting a charophyte with oogonia, antheridia and oospores can be a lucky occurrence. Consequently, only about 60% of specimens in Australian herbaria are sufficiently mature to be used in a taxonomic study. Five of the six recognised genera of charophytes occur in Australia,. Australian charophytes suffer from a long and confusing taxonomic history. The first Australian charophytes to be described were collected by Robert Brown, Chara australis R. Br. and Nitella congesta (R. Br.) A. Braun. (Brown 1810). Early collectors like Gunn, Preiss and Drummond (Braun 1849) included charophytes in their exsiccatae and Ferdinand von Mueller encouraged collectors and was an avid collector himself. Most of the specimens collected were sent to Alexander Braun in Germany (e.g. Braun 1843, 1849, 1852). When Braun died, Otto Nordstedt became the overseas expert (Braun and Nordstedt 1882; Nordstedt 1891, 1918), followed by James Groves and GO Allen in Britain (Groves and Allen 1935) and eventually, Richard Wood. Wood came from Rhode Island on a Fullbright Scholarship to collect and examine Australian charophytes to complete his world monograph (Wood and Imahori 1965) and was the first of these specialists who actually visited Australia and saw live material. Before Wood's visit, Beth Williams (nee Macdonald) worked on Australian charophyte taxonomy (Macdonald and Hotchkiss 1956; Chambers and Williams 1959; Williams 1959), until her work was interrupted by the Armidale fire. The most recent monographic treatment was undertaken by Joop van Raam, working in The Netherlands, who revised the charophytes of Tasmania after a collecting visit (van Raam 1995). Other local species have been described by Hotchkiss and Imahori (1988), García (1996) and García and Casanova (2004), and distributional studies have been undertaken (Brock and Lane 1983; Brock and Sheil 1983; Casanova 1993; García 1999; Casanova 2004a, 2004b; Casanova and Dugdale 2004). Many specimens deposited in German herbaria have been lost, presumably during the bombing of Berlin, and
In many temporary wetlands such as those on the Northern Tablelands of New South Wales Australia, the develop-ment of plant communities is largely the result of germination and establishment from a long-lived, dormant seed bank, and vegetative propagules that survive drought. In these wetlands the pattern of plant zonation can differ from year to year and season to season, and depth is not always a good indicator of the plant community composition in different zones. In order to determine which aspects of water regime (depth, duration or frequency of flooding) were important in the development of plant communities an experiment using seed bank material from two wetlands was undertaken over a 16 week period in late spring–early summer 1995–1996. Seed bank samples were exposed to 17 different water-level treatments with different depths, durations and frequencies of flooding. Species richness and biomass of the communities that established from the seed bank were assessed at the end of the experiment and the data were examined to determine which aspects of water regime were important in the development of the different communities. It was found that depth, duration and frequency of inundation influenced plant community composition, but depth was least important, and also that the duration of individual flooding events was important in segregating the plant communities. Species were grouped according to their ability to tolerate or respond to fluctuations in flooding and drying. The highest biomass and species richness developed in pots that were never flooded. Least biomass and species richness developed in pots that were continuously flooded. Short frequent floods promoted high species richness and biomass especially of Amphibious fluctuation-tolerator species and Amphibious fluctuation-responder species that have heterophylly. Terrestrial species were able to establish during dry phases between short floods. Depth was important in determining whether Amphibious fluctuation-tolerator or Amphibious fluctuation-responder species had greater biomass. Longer durations of flooding lowered species richness and the biomass of terrestrial species. Experiments of this kind can assist in predicting vegetation response to water-level variation in natural and modified wetlands.
1. The ability of seeds to survive periods of drying and wetting that do not lead to seed production will determine the potential species pool for future plant communities of temporary wetlands. I investigated characteristics of the seed banks in sediment from Australian temporary wetlands that might contribute to the ability of aquatic plants to re-establish after extended drought.
2. Experimental investigation into germination from sediment from six sites in five Australian temporary wetlands, with various water regimes, examined two sources of seed bank depletion: (i) length of time dry (longevity up to 12 years) and (ii) successive annual wetting and germination events (up to seven) with intervening periods dry (leaving a residual seed bank), both without any opportunity for replenishment of the seed bank.
3. These wetlands had species-rich, long-lived seed banks that were not exhausted by successive germination events. After three years of dry storage, 90% of the original seed bank species germinated, after six years 75% and after 12 years 20%. After seven successive wetting and drying events without seed bank replenishment, 48% of the original species still germinated. The mean survival time dry for seed bank species, 7.4 years, was longer than the duration of recent droughts.
4. Seed bank composition varied among wetlands and over time; most species did not occur in all wetlands and many occurred in one wetland only. The germination patterns of different species, although differing in detail, tended to be consistent in that all species could survive long dry periods and several wetting and drying events. However, experimental drought significantly diminished species richness and abundance, indicating limits to seed bank persistence.
5. Data from such long-term studies of seed bank persistence should allow prediction of the species richness and composition of the germinating communities in a wetland whose water regime is intentionally or unintentionally altered. This ability to forecast may become particularly important under climate change and the need to predict future wetland conditions.
1. A long-lived bank of propagules consisting of eggs, seeds and spores is one mechanism that allows aquatic communities to survive drought. A drying (drought) event is, for aquatic organisms in a temporary wetland, a phase from which communities must recover. Such a dry phase is often considered a disturbance but should not be considered adverse or catastrophic for the organisms that have evolved to live in temporarily wet habitats.
2. This paper explores the parallels between the egg bank of zooplankton and the seed bank of aquatic plants as means of survival in temporary wetlands. The resilience of communities in temporary wetland ecosystems is assessed by examining dormancy, hatching, germination, establishment and reproduction of animals and plants from the egg and seed banks of wetlands with a range of wetting and drying regimes.
3. Both the zooplankton and aquatic plants of the temporary wetlands studied rely on their egg and seed banks as a means for surviving drying. These communities recover after the disturbance of drying by means of specific patterns of dormancy, dormancy breakage, hatching, germination, establishment and reproduction. Spatial and temporal patterns of species richness allow resilience through dormancy, as not all species are present at all sites and not all species hatch and germinate at the same time. Multiple generations in the egg and seed bank and complexity of environmental cues for dormancy breakage also contribute to the ecosystem's ability to recover after a drying event. A persistent egg and seed bank allows species-rich communities to hatch, germinate and develop rapidly once dormancy is broken. Rapid establishment of species-rich communities that reproduce rapidly and leave many propagules in the egg and seed bank also facilitates community recovery on flooding of a temporary wetland after a drying event.
4. To maintain the diversity of temporary wetland communities through droughts and floods we need to manage the dry and wet phases of wetlands. To conserve a wide range of wetland types, we need to maintain a variety of hydrological patterns across the landscape.
In many temporary wetlands such as those on the Northern Tablelands of New South Wales Australia, the development of plant communities is largely the result of germination and establishment from a long-lived, dormant seed bank, and vegetative propagules that survive drought. In these wetlands the pattern of plant zonation can differ from year to year and season to season, and depth is not always a good indicator of the plant community composition in different zones. In order to determine which aspects of water regime (depth, duration or frequency of flooding) were important in the development of plant communities an experiment using seed bank material from two wetlands was undertaken over a 16 week period in late spring–early summer 1995–1996. Seed bank samples were exposed to 17 different water-level treatments with different depths, durations and frequencies of flooding. Species richness and biomass of the communities that established from the seed bank were assessed at the end of the experiment and the data were examined to determine which aspects of water regime were important in the development of the different communities. It was found that depth, duration and frequency of inundation influenced plant community composition, but depth was least important, and also that the duration of individual flooding events was important in segregating the plant communities. Species were grouped according to their ability to tolerate or respond to fluctuations in flooding and drying. The highest biomass and species richness developed in pots that were never flooded. Least biomass and species richness developed in pots that were continuously flooded. Short frequent floods promoted high species richness and biomass especially of Amphibious fluctuation-tolerator species and Amphibious fluctuation-responder species that have heterophylly. Terrestrial species were able to establish during dry phases between short floods. Depth was important in determining whether Amphibious fluctuation-tolerator or Amphibious fluctuation-responder species had greater biomass. Longer durations of flooding lowered species richness and the biomass of terrestrial species. Experiments of this kind can assist in predicting vegetation response to water-level variation in natural and modified wetlands.
Aquatic plant communities in arid zone wetlands underpin diverse fauna populations and ecosystem functions yet are relatively
poorly known. Erratic flooding, drying, salinity and turbidity regimes contribute to habitat complexity, creating high spatial
and temporal variability that supports high biodiversity. We compared seed bank density, species richness and community composition
of aquatic plants (submergent, floating-leaved and emergent) among nine Australian arid zone wetlands. Germinable seed banks
from wetlands within the Paroo and Bulloo River catchments were examined at nested scales (site, wetland, wetland type) using
natural flooding and salinity regimes as factors with nondormant seed density and species richness as response variables.
Salinity explained most of the variance in seed density (95%) and species richness (68%), with flooding accounting for 5%
of variance in seed density and 32% in species richness. Salinity-flooding interactions were significant but explained only
a trivial portion of the variance (<1%). Mean seed densities in wetlands ranged from 40 to 18,760m−2 and were highest in wetlands with intermediate levels of salinity and flooding. Variability of densities was high (CVs 0.61–2.66),
particularly in saline temporary and fresh permanent wetlands. Below salinities of c. 30 gl−1 TDS, seed density was negatively correlated to turbidity and connectivity. Total species richness of wetlands (6–27) was
negatively correlated to salinity, pH and riverine connectivity. A total of 40 species germinated, comprising submergent (15
species), floating-leaved or amphibious (17 species), emergent (6 species) and terrestrial (6 species) groups. Charophytes
were particularly important with 10 species (five Chara spp., four Nitella spp. and Lamprothamnium macropogon), accounting for 68% of total abundance. Saline temporary wetlands were dominated by Ruppia tuberosa, Lamprothamnium macropogon and Lepilaena preissii. Variable flooding and drying regimes profoundly altered water quality including salinity and turbidity, producing distinctive
aquatic plant communities as reflected by their seed banks. This reinforces the importance of hydrology in shaping aquatic
biological communities in arid systems.
Vernal pools, broadly defined as ephemeral wetlands that predictably form in permanent basins during the cooler part of the
year but which dry during the summer months, are distributed throughout the world. In the U. S., they are particularly abundant
on the Pacific Coast and in various forms in the glaciated landscapes of the north and northeast. Vernal pools are ecosystems
that have evolved in a balance between isolation and connectedness. Because of isolation at several scales, the vernal pools
biota includes many regionally endemic species. Because of connectedness, vernal pools also share many taxa with continent-spanning
distributions at the generic and species level. Vernal pools serve an important local biodiversity function because of their
connection to surrounding terrestrial habitats. Along with other ephemeral wetlands, they are the primary habitat for animal
species that require relatively predator-free pools for feeding or breeding, including many amphibians. The recent U. S. Supreme
Court decision (SWANCC), which deemed “isolated” wetlands to be outside the class of “waters of the United States,” places
some significant but unknown proportion of vernal pools at risk. In the worst case, the consequences could be immediate reductions
in biodiversity at a local level, and regional reductions over longer periods of time. Ideally, federal law should be rewritten
to establish unambiguously the value of ephemeral wetlands. It will also be necessary for conservationists to educate the
public and to bring the issue of vernal pool protection to the notice of their local and state governments.
Soil seed banks are an important component of plant community diversity in ephemeral wetlands, allowing many species to persist
through unpredictable periods of flood and drought. Spatial variation of extant vegetation in such habitats commonly reflects
patterns of flood history and often varies predictably between broadly differing hydro-geomorphic habitat types. Here we investigate
whether spatial variation of soil seed banks is similarly controlled by fluvial processes at this scale. Results are presented
from a seedling emergence trial using samples collected from a range of habitat types, and at different scales within these,
in the ephemeral Narran Lakes system in semi-arid Australia. Composition and structure of soil seed banks varied significantly
between habitat types reflecting broad differences in flood frequency. As predicted, germinable seed abundance was found to
be highest in intermediately flooded habitats. Variability in soil seed bank composition at a local scale was also found to
be influenced by hydrology with greater spatial heterogeneity evident in the river channel as well as amongst the least frequently
inundated riparian and floodplain habitats.
Because few collections of Nitella macounii exist and early descriptions were largely based on dried herbarium material, a number of morphological features such as type and form of branching have been reinterpreted suggesting reclassification into Section Palia from Section Nitella. Earlier observations that the species may be related to N. stuartii are supported and a potential disjunct range with Argentina seems a possibility. Oospore membrane decoration is described in detail and conflicting earlier reports clarified. Especially significant is the first report that this species is tetrascutate, only the sixth charophyte known to be so. The ephemeral habitat and the ecology of N. macounii in Saskatchewan are discussed in light of the recent charophytivory hypothesis which predicts that such species are restricted to habitats where aquatic invertebrate herbivores are absent or present in low numbers. The dynamic nature of ephemeral habitats both in time and space is postulated to be a prime factor in the distribution and rarity of this species throughout its range. It is suggested that because of its unexpected ephemeral ecology, N. macounii may be more widespread across the Great Plains of North America than is presently known. Currently it must be considered globally and nationally very rare with only 16 known collection sites.
From sixty-four playas (temporary lakes) on the Llano Estacado of the Texas panhandle, eleven charophytes are reported, plus and additional nine from permanent bodies of water in the same area. Virtually no overlap of species exist between the two habitats. Dominating the playas, but never present in permanent bodies of water, was eurythermic and opportunistic Chara braunii Gm. Also present in approximately 25% or more of the playas, but no permanent bodies, were c. haitensis Turpin, C. foliolosa Muhl. es Willd. and C. hydropitys Reich., all of tropical affinity. Playas are normally inundated only during the summer months. Permanent bodies of water in the area are dominated by cool-temperate charophytes, e.g. C. contaria Br. ex Kutz and `C. globularis' (Proctor, 1971), none of which even colonizes playas. Bulbil-forming Characeae are absent from playas, and dioecius species of little significance in terms of total biomass, as both generally are on oceanic islands as well. The total of twenty of Llano Estacado, considerably higher than previously reported for most areas of North America, is thought to reflect the dual nature of the habitats, i.e. temporary and permanent. The maximum number of charophytes per playa was seven; the mode 2. Undisturbed playas, though transient in nature, apparently support charophyte floras that are fairly stable from year to year.
1. Analysis of the distribution and abundance of water plants can be a useful tool for determining the ecological water requirements of sites in a catchment.
2. Seed-bank and vegetation surveys of wetland and riparian sites were undertaken in the Angas River catchment in South Australia to determine the distribution and abundance of plants associated with riparian habitats. Plant species were allocated to water plant functional groups (WPFGs sensu Brock and Casanova, Frontiers in Ecology; Building the Links, 1997, Elsevier Science). In addition to the seven functional groups already recognised, three new groups containing submerged and woody growth forms were included in this study.
3. Cluster analysis of sites on the basis of species presence/absence was compared with site clustering obtained from analysis of representation of WPFGs. Functional group analysis provided a similar segregation of species-poor sites to that resulting from analysis of species presence/absence, but provided better resolution of clusters for species-rich sites. Three clusters of species-rich sites were delineated: riparian sites that require year-round permanent water but have fluctuating water levels, spatially and temporally variable riparian sites with shrubs and trees and temporary wetlands that dry annually.
4. Segregation of sites on the basis of functional group representation can provide information to managers about the water requirements of suites of species in different parts of the catchment. Knowledge of the environmental water requirements of sites within a catchment can help managers to prioritise water management options and delivery within that catchment.
Restoration of species-rich flood meadows impoverished by agricultural intensification is an important challenge. The relationships between flooding regime and soil seed bank were compared in three successive meadow communities (hygrophilic, mesohygrophilic and mesophilic) distinguished along a topographic and hydric gradient. Differences in flood duration and frequency between the three associations allowed the study of the contribution of floods to soil seed bank richness and density. No significant difference was found in species richness among the three soil seed banks, whereas the densities were significantly higher in the wettest community. The three seed bank compositions were clearly distinguished along the hydric gradient. In fact, the three seed bank types constituted a species poor version of the meadow communities to which they belong. Flood contributions appear to play a minor role in seed bank enrichment. Thus, seed dispersal by flood water would probably be insufficient to enable the restoration of alluvial meadows.
The genus Nitella Ag. in algal family Characeae is characterised by furcate (forked) branchlets, compressed oospores (i.e. oval in cross-section), terminal antheridia and a 10-celled coronula on the oogonium. Species of Nitella are submerged plants that grow in a variety of wetland and riverine habitats. Approximately 89 taxa of Nitella (species, subspecies, varieties and forms) have been described on the basis of Australian collections, and published estimates of the number of species range from 18 to >35. The lower value is based on the assumption that infra-specific variation is great, species have a wide distribution, monoecy and dioecy are not indicative of speciation and the number of furcations and the ratio of branchlet segment lengths vary for a species owing to the environment in which they grow. The higher value is based on evidence that morphological characters are relatively constant for a species, that oospore variation is a good indication of speciation and that monoecious and dioecious entities are not inter-fertile. An overview of Australian members of the genus is presented here as a framework for further taxonomic work. Representatives of all three subgenera of Nitella occur in Australia, with subgenus Nitella poorly represented, and subgenera Tieffallenia and Hyella equally speciose. The subgenera are defined here in relation to the Australian taxa they contain. In the present treatment, section Migularia is transferred from subgenus Tieffallenia to subgenus Hyella, and several species are transferred to subgenus Tieffallenia. Within subgenus Tieffallenia, variation in vegetative and oospore morphology is useful for distinguishing among sections and species. However, although members of subgenus Hyella display a similar range of variation in vegetative morphology, most of the species have similar, reticulate, oospore ornamentation. Australia is home to a large number of endemic species of Nitella, many of which are dioecious. The total number of species and the degree of endemism have been underestimated in earlier studies, and it is likely that more than 50 species of Nitella will be recognised on the basis of Australian specimens. A key to the subgenera, and keys to sections in the subgenera are provided.
An account is given of a typical rainfed waterbody in the Al-Ammariyah Wadi
(Saudi Arabia), with special reference to charophyte vegetation, water
chemistry and topography of the area, which was studied from April 1996 to
July 1997. Recurring patterns following rainfall and inundation of the
waterbody are described as a model of temporal succession of biotic
communities. Unispecific Chara braunii Gm. meadows were
the first aquatic vegetation to emerge and overwhelmingly dominated the
freshwater lentic ecosystem. This was followed by plankton and desert plants
as the waterbody dried out. Chara braunii is reported as
a new record for the Saudi Arabian charoflora. The species is characterised as
stenohaline and tends to grow in vivo and
in vitro in the salinity range of 0.2–0.8‰.
A gradual increase in elements and ions (Si 20–31 mg
L–1 and pH 6.8–7.6) in the water was
demonstrated as the waterbody desiccated. As a result of the increasing
concentration of ions and pH, C. braunii developed heavy
encrustation, and hastened fructification prior to desiccation of the
waterbody between June and July 1997. Survival and emergence of
C. braunii is positively correlated with drought
resistant-oospores, specificity to hyposalinity, water-level fluctuations, and
absence of herbivores.
The charophytes Chara corallina Kl. ex Willd. and Nitella sustilissima A. Br. are present in temporary wetlands in Australia. The mean maximum percentage germination of these two species and the number of oospores in the seed bank are compared using germination and total count methods of seed bank analysis. The pattern of germination in both field and laboratory studies and the fate of individual sporelings of both species is examined. C. corallina showed a pattern of later germination of 5% of the seed bank, a high rate of establishment and early reproduction, whereas N. subtilissima had earlier 13% germination, poor establishment and did not reproduce during the experimental period. The life history patterns of these species are compared.
Charophytes ( family Characeae) are a cohesive group within the green algae. The genus Chara is abundant and diverse in a variety of Australian habitats. Approximately 37 taxa of Chara have been described on the basis of Australian collections. The current status of charophyte taxonomy is confused. RD Wood revised Australian charophytes in 1972 on the basis of an erroneous species concept, and charophytes are rarely identified lower than genus by ecologists and water managers. Many species were described by overseas experts in the mid-1800s, and this trend continues to the present day. Typically, species descriptions have been based on examination of few specimens, and sometimes not even fertile representatives of each species. In this study Wood's ( 1972) taxonomic treatment of Australian members of the genus Chara is examined and analysed in relation to historical species concepts and more recent experimental taxonomy and oospore morphology. Thorough studies based on determination of reliable indicators of genetic incompatibility through culture studies, including oospore morphology and genetic analysis and objective analysis of fertile specimens, are now required.
Charophyte oospore banks have been studied in different habitat types, whereas only one detailed study of bulbil banks has been recorded from the literature. The density of oospore banks generally appears to be very high, dominating the propagule bank in many wetlands. Oospore banks are characterised by high spatial variability within and between the sites. Bulbils and oospores are not uniformly distributed with sediment depth, oospores being generally more numerous in thetop few centimetres. Animal activities can mix the sediment, bury propagules and/or homogenise their distribution. Burial deeper than 2 cm limits oospore germination, but burial to a depth of 5mm can improve their germination capacities. Oospore banks are highly variable between years.
They are generally perennial, cumulating several generations of oospores, and buffering the risk of reproductive failure with time. The limited germination rates recorded for oospores from the bank could be related to this perennial strategy, whereas up to 100% of freshly harvested oospores may germinate. Germination rates and patterns and the conditions required for germination vary greatly from one study to another as a result of the large range of species and habitats investigated. Certain water birds consume charophytes and could be efficient dispersal agents for oospores. Various abiotic factors can affect the charophyte biomass and therefore the oospore production which then in turn could affect the propagule bank.
The oospore bank density appears to influence charophyte abundance in the field, but above a threshold, its abundance is not related to the number of oospores in the soil. Below a threshold of density, charophytes may be unable to establish dense stands of vegetation.
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.
There has been little research examining the soil seed banks of degraded floodplain wetlands and their contribution to wetland
rehabilitation in Australia. Our aim was to assess the establishment of plants from the seed bank that may occur following
the delivery of an environmental water allocation to Kanyapella Basin, a 2950ha wetland located on the floodplain of the
Goulburn and Murray Rivers in northern Victoria, Australia. Two hypothetical water regimes were investigated (flooded and
dry) in a glasshouse experiment, where plants were left to establish from the seed bank over a period of 124days. Differences
in the establishment of plants from the seed bank indicated that the return of a flooding regime is likely to have a significant
effect on the composition of the wetland vegetation. Mapping of the distribution of plant species indicated that propagules
were highly dispersed across the wetland for the majority of taxa, in contrast to the localised distribution of many of the
plant species represented in the extant vegetation. Inundation favoured the establishment of native wetland and floodplain
plants, although many areas of Kanyapella Basin that are currently ‘weed-free’ have the potential to become colonised and
potentially dominated by introduced plants if the wetland is not managed appropriately. Overall, results supported the aim
of management to reestablish a wetting and drying regime through use of an environmental water allocation. This study presents
a significant example of the application of seed bank investigations in wetland ecology and management.
Germination from the seed banks of ephemeral floodplain wetlands of the Nyl River in South Africa was quantified in a glasshouse experiment to examine the potential of the seed bank for revegetation. Sediments from three sites with different wetting and drying histories (permanent, seasonal and occasional inundation) were collected in late summer after flooding and germination but before the seed bank was replenished. Samples were flooded artificially after dry, wet or wet/dry pretreatment and germination was recorded. Samples were then dried and reflooded to assess germination from the residual seed bank. All sites had a species-rich germinable seed bank. The water regime history of each site did not influence the number of species or individuals present in any trial or pretreatment. More species and individuals germinated in the first germination trial than the second. Fewer species germinated from the samples collected from above the water line than from underwater. Sixteen species (12 aquatic) and 1392 individuals germinated in the first trial. Most species from the field communities also germinated from the seed bank. Twelve species, including 2 new species, germinated from the residual seed bank. Many of the species from these wetlands have persistent seed banks with staggered germination of propagules. Species maintain themselves over space (sites), conditions (water regimes) and time (trials) by a range of life-cycle patterns. Wetland communities that depend on their seed banks for revegetation between wetting and drying events may be altered by human-induced changes to water regimes.
1. This paper explores soil seed bank composition and its contribution to the vegetation dynamics of a hydrologically variable desert floodplain in central Australia: the Cooper Creek floodplain. We investigated patterns in soil seed bank composition both temporally, in response to flooding (and drying), and spatially, with relation to flood frequency. Correlations between extant vegetation and soil seed bank composition are explored with respect to flooding.
2. A large and diverse germinable soil seed bank was detected comprising predominantly annual monocot and annual forb species. Soil seed bank composition did not change significantly in response to a major flood event but some spatial patterns were detected along a broad flood frequency gradient. Soil seed bank samples from frequently flooded sites had higher total germinable seed abundance and a greater abundance of annual monocots than less frequently flooded sites. In contrast, germinable seeds of perennial species belonging to the Poaceae family were most abundant in soil seed bank samples from rarely flooded sites.
3. Similarity between the composition of the soil seed bank and extant vegetation increased following flooding and was greatest in more frequently flooded areas of the floodplain, reflecting the establishment of annual species. The results indicate that persistent soil seed banks enable vegetation in this arid floodplain to respond to unpredictable patterns of flooding and drying.
Ecological responses to inun-dation of sediments from grazed and ungrazed areas of Thegoa Lagoon, NSW Seed banks in arid wetlands with contrasting flooding, salinity and turbidity regimes
- S Muston
- J Nicol
- B Mccarthy
- S Zukowski
- Mildura
- J L Porter
- R T Kingsford
- M A Brock
Muston, S., Nicol, J., McCarthy, B., Zukowski, S., 2004. Ecological responses to inun-dation of sediments from grazed and ungrazed areas of Thegoa Lagoon, NSW. Technical Report 3/2004. Murray Darling Freshwater Research Centre, Lower Basin Laboratory, Mildura. Porter, J.L., Kingsford, R.T., Brock, M.A., 2007. Seed banks in arid wetlands with contrasting flooding, salinity and turbidity regimes. Plant Ecology 188, 215–234.
Draft Report on Wetlands of the Wannon. Glenelg-Hopkins Catchment Management Authority
- M T Casanova
Casanova, M.T., 2012. Draft Report on Wetlands of the Wannon. Glenelg-Hopkins Catchment Management Authority, Hamilton, Victoria.
A Directory of Important Wetlands in Australia PATN version 3.12. Blatant Fabrications Pty Ltd Ephemeral wetlands of the Pilliga Outwash, northwestern NSW
- Canberra Anca
- L Belbin
- A Collins
- D M Bell
- J T Hunter
- L Montgomery
Australian Nature Conservation Agency, 1996. A Directory of Important Wetlands in Australia. ANCA, Canberra. Belbin, L., Collins, A., 2009. PATN version 3.12. Blatant Fabrications Pty Ltd. Bell, D.M., Hunter, J.T., Montgomery, L., 2012. Ephemeral wetlands of the Pilliga Outwash, northwestern NSW. Cunninghamia 12, 177–186.
Glenelg Hopkins Regional Wetlands Status Report Glenelg Hopkins Catchment Management Authority New and noteworthy South African Charophyta I
- Victoria Groves
- J Stephens
GHCMA, 2006. Glenelg Hopkins Regional Wetlands Status Report, 2006. Glenelg Hopkins Catchment Management Authority, Victoria. Groves, J., Stephens, E.L., 1926. New and noteworthy South African Charophyta I. Transactions of the Royal Society of South Africa 13, 145–158.
Water and Land Use Change Study, Stage 2: community report. Water and Land Use Change Study Steering Committee and Sinclair-Knight-Metz
- Watluc
WatLUC, 2006. Water and Land Use Change Study, Stage 2: community report. Water and Land Use Change Study Steering Committee and Sinclair-Knight-Metz. www.Glenelg-hopkins.vic.gov.au/imageandfileuploads/ GHCMA WATER%20LAND%20USAGE.pdf.
Deposition, germination and spatio-temporal patterns of charophyte propagule banks: a review
- Bonis
Drought and aquatic community resilience: the role of eggs and seeds in sediments of temporary wetlands
- Brock
The first locality of Chara bauera (Characeae) in Poland
- Pucacz
Glenelg Hopkins Catchment Management Authority
Spatial variability of the soil seed bank in a heterogenous wetland system in semi-arid Australia
- James
Seed banks in arid wetlands with contrasting flooding, salinity and turbidity regimes
- Porter
New and noteworthy South African Charophyta I
- Groves