Seasonal flooding,topography, and organic debris interact to influence the emergence and distribution of seedlings in a tropical grassland

In seasonally flooded wetlands, inundation and associated organic debris deposition followed by a drawdown period can promote plant community diversity across space and time. Post‐flood regeneration might be influenced by the direct effect of flooding on seed dispersal and seedling emergence, as well as the indirect effect of organic debris on seed trapping and germination. Our objective was to examine the influence of seasonal flooding, topography, and organic debris cover on seedling distribution in a seasonally flooded grassland. We measured species richness, seedling abundance, and organic debris cover for 3 yr in a seasonally flooded grassland in the Pantanal, Brazil, at three topographic levels at the end of the flood season and during the dry season when there was no debris deposition. A total of 43 species were recorded, with no difference in species richness detected between seasons. However, the abundance of some species was higher post‐flood than during the dry period. The greatest seedling abundance and richness were found post‐flood at intermediate elevations, followed by high and the lowest elevations. Seed germination and seedling establishment were likely suppressed at low topographic positions due to shading from organic debris and poor drainage. Therefore, areas with predictable annual floods promote diversity by creating spatial and temporal variations in environmental conditions.     

Effect of flooding and draw‐down disturbance on germination from a seashore meadow seed bank

Abstract. The objective of this study was to investigate the effects of flooding and draw‐down on the germination from the coastal grassland seed banks and to determine whether the effect of flooding varies between the delta and the seashore. Seed bank samples were collected from three shore transects in SW Finland, two on the shore of the Baltic Sea and one on the delta of River Kokemäenjoki. Samples were germinated in non‐flooded and flooded conditions for over a month, after which both treatments were maintained in non‐flooded conditions. A total of 9267 seedlings of 47 species germinated and mean density of seeds in the soil was ca. 84 000/m². Most of the seedlings were monocots (98%) and perennials (98%). Ca. 30–40% of the species found in the above‐ground vegetation had a seed bank including the majority of the most abundant species. The number of seeds and species richness increased as the organic layer became thicker. The organic layer was thicker in the seashore samples and the seed bank was significantly larger than in the delta. The flooding and draw‐down treatment significantly increased the number of germinating seedlings in the seashore and also increased species richness in two transects, one in the delta and the other in the seashore. Two species, Schoenoplectus tabernaemontani and Typha latifolia, had significantly higher germination in the flooded treatment than in the non‐flooded. Apparently, many species in these coastal grasslands have adapted to flood disturbance and for seeds of some species flooding may work as a positive signal, possibly breaking dormancy.     

Impact of flooding on potential and realised grassland species richness

In order to reduce flood risk, river management policies advise floodplain restoration and the recreation of water retention areas. These measures may also offer opportunities for the restoration of species-rich floodplain habitats through rewetting and the restoration of flood dynamics. The potential to enhance biodiversity in such flood restoration areas is, however, still subject to debate. In this paper we investigate whether flooding along a small altered lowland river can contribute to the potential and realised species richness of semi-natural meadows. We compare the seed bank and vegetation composition of flooded and non-flooded semi-natural meadows and test the hypothesis that flooding contributes to an input of diaspores into the meadow seed banks, thereby promoting seed density and potential species richness. Furthermore we hypothesise that, where habitat conditions are suitable, flooding leads to a higher realised species richness. Results showed that seed densities in flooded meadows were significantly higher than in non-flooded meadows. The seed banks of flooded meadows also contained a higher proportion of exclusively hydrochorous species. However, the seed bank species richness, as well as the species richness realised in the vegetation did not differ significantly between flooded and non-flooded meadows. Finally, the seed bank and standing vegetation of flooded sites showed larger differences in species composition and Ellenberg nitrogen distribution than non-flooded sites. From these results we conclude that, although flooding does contribute to the density and composition of the seed bank, most imported seeds belong to only a few species. Therefore, it is unlikely that flooding substantially enhances the potential species richness. Furthermore, even if new species are imported as seeds into the seed bank, it seems unlikely that they would be able to establish in the standing vegetation. However, it is unclear which factors impede the establishment of imported species in the vegetation. The implications of our findings for flood meadow restoration are discussed.     

Changes along a disturbance gradient in the density and composition of propagule banks in floodplain aquatic habitats

This study used germination methods to examine the density, species composition and functional composition of propagule banks in a series of riverine wetland aquatic habitats subject to varying degrees of hydrological and management-related disturbance. Under permanent inundation (the conditions prevailing at most sites during the growing season) propagule germination and species richness was low, with floodplain perennials and helophytes particularly affected. Densities of floodplain annuals were largely maintained through continued germination of a few flooding tolerant species. On damp mud (conditions associated with hydrological instability) total seedling number and species richness increased significantly, but species richness of germinating hydrophytes declined. Mean seedling density at 0–0.1m depth was 15450 ± 4400 m–2, reaching a maximum (162 050 m–2) in temporary backwaters. Annual (e.g., Lindernia dubia, Cyperus fuscus) and facultative ruderal species (e.g., Lythrum salicaria and Alisma plantago-aquatica) predominated. Vertical zonation of the propagule bank was weakly developed. The numbers of individuals and species germinating varied significantly between sites. The seasonal, most intensely disturbed sites (temporary backwaters) supported a numerically large, species-rich propagule bank based on floodplain annuals, while the permanent, less disturbed sites (ditches and an oxbow pond) had a small, species-poor propagule bank composed of hydrophytes and helophytes supplemented by allochthonous seed inputs. Sites intermediate on the gradient had a propagule bank dominated by facultative amphibious, ruderal hydrophytes. The composition of the seed bank and the established vegetation was most similar at the heavily disturbed sites where the seed bank was maintained by vigorously fruiting annuals and supplemented by inputs from temporary habitats upstream. At permanent sites much of the propagule bank composition could be accounted for by inputs of floodborne seed from the immediately adjacent floodplain. The established vegetation at such sites appeared to be maintained mainly by vegetative propagation with recruitment from the propagule bank likely only after severe disturbance. The potential contribution of functionally diverse propagule banks to sucessional processes within fluvially dynamic floodplain aquatic habitats is emphasised.     

Flooding, soil seed bank dynamics and vegetation resilience of a hydrologically variable desert floodplain

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.     

How do depth,duration and frequency of flooding influence the establishment of wetland plant communities?

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.     

Inter-annual variation in the soil seed bank of flood-meadows over two years with different flooding patterns

Persistent soil seed banks are presumed to play a significant role in bridging and exploiting the effects of major flood disturbances in riparian systems. However, presently there is little empirical data on the correlation between flooding and seed bank dynamics. The objective of this study was to assess the impact of inter-annual flooding variation on soil seed bank dynamics in flood-meadows. We analysed seed bank composition at 46 plots along the northern Upper Rhine River, Germany, after two periods with contrasting flooding conditions (1996–1997: low and rare flooding; 1998–1999 high and very frequent flooding). Between both sampling occasions the total number of seedlings emerging from the seed bank decreased by 50% and average species-richness per sample by 30%, irrespective of the sampling depth. Similar decline occurred in mesophytes and wetland species as well as over different functional groups, with the exception of legumes. Considerable compositional changes in the seed bank were also indicated by shifts in DCA ordination and by the comparison of similarity matrices from both years with the Mantel test. The Mantel test also confirmed that compositional changes were more pronounced in the seed bank than in aboveground vegetation. There was poor correlation between the decline in total seed densities and species in the soil seed bank and environmental variables such as flooding duration and ecological groupings such as floodplain compartment and seed bank community types. Further distinct patterns of decline and persistence were evident only at the species level. While 21 species displayed a significant decline, only two species increased. Annual arable weeds and perennial ruderals with high temperature or nutrient requirements to break dark dormancy were amongst the most significantly declining species. In contrast, there was no decline in typical winter annuals and certain perennials that preferably germinate in autumn and fall into dormancy at the beginning of the warm period. Generally, differences in germination requirements and dormancy cycles of species gave the best explanation for the patterns of decline and persistence after intense flooding. Given these findings, the heavy depletion of the persistent soil seed bank we observed is most likely attributed to a post-flood germination flush due to very favourable recruitment conditions prevailing during the draw-down period after early summer flooding in 1999. The results of our study suggest that persistent soil seed banks are of outstanding importance to bridge and exploit the highly variable hydrological conditions that are typical of flood-meadows. Thus, they play a significant role in maintaining the floristic diversity of this habitat type over time and space. This revised version was published online in June 2006 with corrections to the Cover Date.     

The impact of flooding regime on the soil seed bank of flood‐meadows

Abstract. We assessed the significance of flooding for the floristic composition of seed banks in flood‐meadows of the northern valley of the Upper Rhine. We compared three hydrological compartments of the alluvial plain, consisting of the regularly flooded land between the river and low summer dykes (functional flood‐plain), the occasionally flooded land between summer dykes and high winter dykes (hybrid floodplain) and the land behind the winter dykes, which is now only submerged by ascending groundwater (fossil flood‐plain). Due to their different flooding regime, the three compartments should differ with respect to the prevailing conditions of diaspore input. The seed density of soil samples increased with the duration of flooding in the three compartments, while species richness and the proportion of species not occurring in the vegetation was constant. The increase in seed density can be largely attributed to an increase of disturbance indicators, which are present in the above‐ground vegetation and capable of forming a long‐term persistent seed bank. No effects of flooding on the composition of seed banks in the three flood‐plain compartments were found. The differences in seed bank composition can be largely explained by corresponding differences in above‐ground vegetation and former and present‐day meadow management. Seeds of species absent from above‐ground vegetation can be attributed to the local species pool present in the immediate vicinity of the study plots. We discuss consequences of the results for the restoration of species‐rich flood‐plain meadows.     

The influence of vegetation,salinity, and inundation on seed banks of oligohaline coastal marshes

Sea level rise may alter salinity and inundation regimes and create patches of open water in oligohaline coastal marshes, potentially affecting the composition and germination of seed bank species. We conducted seedling emergence experiments to: (1) examine the effects of standing vegetation on the seed banks of three oligohaline marsh communities in coastal Louisiana (dominated by Paspalum vaginatum Sw., Sagittaria lancifolia L., or Spartina patens (Ait.) Muhl., respectively); and (2) investigate the effects of salinity and inundation regime on germination of seed bank species. We also studied the effect of a temporary increase in salinity (to simulate a salt water intrusion event) on the viability of buried seeds. We found that the presence or absence of vegetation within a community affected the abundance of some species in the seed bank but had little effect on species composition. Also, the seed banks of the three communities exhibited considerable overlap in species composition and had similar species richness (10–11) and diversity (antilog Shannon-Weaver diversity index = 6.5–7.1), despite differences in vegetation type. Higher salinities and flooding reduced seedling emergence for most species; few species emerged at salinities above four parts per thousand (ppt), and only Sagittaria lancifolia and Eleocharis parvula germinated well under flooded conditions. A temporary increase in salinity did not affect species richness or seedling emergence of most species. Our results suggest that differences in vegetation may have little effect on the composition of seed banks of oligohaline marshes. However, higher salinities and greater depth and duration of inundation (anticipated as global sea level continues to rise) may decrease recruitment of seed bank species, reducing their abundance in oligohaline marsh communities.     

Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatum

Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring‐summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C₄ grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species.     

Managed flooding can augment the benefits of natural flooding for native wetland vegetation

Managed flooding is increasingly being used to maintain and restore the ecological values of floodplain wetlands. However, evidence for its effectiveness is sometimes inconsistent and water available for environmental purposes often limited. We experimentally inundated a floodplain wetland (or “billabong”) in late spring by pumping water from its adjacent creek, aiming to promote the native wetland flora and suppress terrestrial exotics. Vegetation was surveyed before (spring) and after (late summer) the managed flood in the experimental billabong and in three control billabongs. Floodplain water levels were continuously monitored. Wet conditions caused two of the control billabongs to also flood, but to a lesser extent than the experimental billabong. We therefore assessed vegetation changes relative to flooding duration. With increasing flooding duration, the cover of wetland vegetation (amphibious and aquatic species) increased and the cover of terrestrial and exotic vegetation decreased, with these effects largest in the deliberately flooded billabong. Flooding durations greater than 20 days generally resulted in increased cover of wetland plants and restricted the growth of terrestrial plants. Reinstatement of more appropriate flooding regimes can thus promote native wetland plants, while suppressing terrestrial exotic species. Our study also provides evidence for the use of modest water allocations to augment the benefits of natural flooding in the maintenance and restoration of native wetland plant communities.     

Seed Bank Effects on Recovery after Disturbance in Reconstructed Tallgrass Prairies

Litter‐removing disturbances such as fire in grasslands temporarily increase available resources for plants, opening a window of opportunity for new establishment as communities recover. At this time, new individuals or species could be added to the community as a result of germination from the local seed bank. In reconstructed grasslands this may be problematic, as the seed bank may contain a suite of undesired species reflective of prior and surrounding land uses. In two, 25‐year‐old, low‐diversity reconstructed grasslands, we tested the effect of local seed bank establishment following litter‐removing disturbance using seedling removal plots (1 m²) and plots where natural seedling establishment was allowed. Following disturbance, the vegetation was either left intact or hayed to enhance seedling establishment (a common practice following inter‐seeding efforts). Although the seed bank and seedling community were dominated by resident grasses (Andropogon gerardii and Poa pratensis), recruitment from the seed bank increased species richness and reduced evenness through the addition of forb species (including Cirsium arvense) in one of the study sites. Haying temporarily altered the abundances of the dominant grasses, but did not consistently affect seedling recruitment. Disturbances that facilitate seed bank recruitment may promote establishment of undesired species within reconstructed grassland communities, and we need to take steps to better manage the contributions into and recruitment from the seed bank to reconstruct sustainable grasslands.     

Plant species richness in ephemeral and perennial reaches of a dryland river

Ephemeral reaches are common along desert rivers but are less well studied than those with perennial stream flow. This study contrasted riparian plant species richness and composition (extant vegetation and soil seed bank) between stream reaches with different low-flow conditions (perennial vs. ephemeral flow) but similar flood patterns and similar watershed-derived species pools. Data were collected at Cienega Creek (Arizona, USA) over a 2 year period spanning drought conditions and wetter conditions. Consistent with expectations relating to water limitation effects on diversity, species richness in the riparian zone was lower at ephemeral-flow sites during a season with minimal precipitation and no overbank flooding; under these conditions, the more permanent water sources of the perennial-flow sites sustain the larger number of species. During seasons with greater precipitation and elevated stream flows, in contrast, species richness at ephemeral-flow sites increased to levels at or slightly above those of perennial-flow sites. For values pooled across two wet seasons of a calendar year, year-round richness was greater at the two ephemeral-flow sites (total of 92 vascular plant species) than at the two perennial-flow sites (68 species). This greater year-round richness was a combination of multiple factors: greater light, space, and bare ground, a diverse soil seed bank (with the seed banks equally species-rich among hydrologic types), and moderately abundant precipitation and flooding sufficient to stimulate establishment of opportunistic species (mainly annuals) during the bimodal wet seasons. These results indicate that long-term patterns of site water availability, by influencing woody plant cover, mediate the diversity response to episodic water pulses in dryland rivers. The results also have implications for riparian conservation efforts, which to date have focused primarily on perennial stream reaches: ephemeral reaches of spatially intermittent rivers harbor many riparian plant species, and warrant conservation efforts, as well.     

Seed Banks in Arid Wetlands with Contrasting Flooding,Salinity and Turbidity Regimes

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 18,760 m⁻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 g l⁻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.     

Changes in biotic communities developing from freshwater wetland sediments under experimental salinity and water regimes

1. Reduction in diversity of both freshwater aquatic and terrestrial ecosystems has been attributed to salinity increase and such increases are a symptom of changes to land use. Hydrological alteration to ground and surface water are likely to be associated with salinity increase and its influence on biodiversity. However the combined effects of salinity and hydrology on aquatic biodiversity have not been elucidated fully in either field or experimental situations. 2. The effect of salinity and water regime on the biota in sediments from seven wetlands from inland south‐eastern Australia was tested experimentally using germination of aquatic plant seeds (five salinity and two water levels) and emergence of zooplankton eggs (five salinity levels). Salinity levels were <300, 1000, 2000, 3000, 5000 mg L^?1 and water regimes were damp (waterlogged) and submerged. 3. Aquatic plant germination and zooplankton hatching was not consistent for all seven wetland sediments. Four of the wetland sediments, Narran Lakes, Gwydir Wetlands, Macquarie Marshes and Billybung Lagoon showed similar responses to salinity and water regime but the other three wetland sediments from Lake Cowal, Great Cumbung Swamp and Darling Anabranch did not. 4. As salinity increased above 1000 mg L^?1 there was a decrease in the species richness and the abundance of biota germinating or hatching from sediment from four of the wetlands. 5. Salinity had a particularly strong effect in reducing germination from sediments in damp conditions when compared to the flooded conditions. In parallel, salts accumulated in the sediment in damp conditions but did not in flooded conditions. 6. There is potential for increasing salinity in freshwater rivers and wetlands to decrease the species richness of aquatic communities and thus of the wetland community as a whole, resulting in loss of wetland biodiversity. This reduction in diversity varies between wetlands and is at least partly related to hydrology. For aquatic plants the reduction in diversity will be more marked for plants germinating from seed banks at the edges of wetlands where plants are not completely submerged than for the same seed bank germinating in submerged conditions.     

Germinable soil seed banks in a tropical savanna: seasonal dynamics and effects of fire.

Abstract The germinable soil seed bank of a tropical eucalypt savanna of north‐eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire‐related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta, Pycnospora lutescens and Triumfetta rhomboidea. Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus. The germinable soil seed bank varied seasonally, increasing from the mid wet season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.     

Seed bank potential of moist-soil managed wetlands in east-central Texas

Proper management techniques on moist-soil wetlands provide methods for enhancement of established wetlands, restoration of former wetlands, and creation of new wetland habitat. These techniques also create suitable wetland habitat for non-breeding waterfowl and other wetland dependent species during winter. To understand moist-soil managed wetland vegetative patterns, aspects such as plant species distribution, reproductive strategy, seed bank composition and viability should be thoroughly characterized. We investigated soil seed bank potential of moist-soil managed wetlands on Richland Creek Wildlife Management Area, Texas to determine which treatment (i.e., drawdown or flooded) produced the most desirable moist-soil plants. A total of 27 species germinated, producing 3,731 and 3,031 seedlings in drawdown and flooded treatments, respectively. There were also differences in stem densities between treatments of desirable and non-desirable species. Drawdown treatments had more seedlings germinate than flooded treatments, validating the notion that drawdown treatments provide favorable conditions for seed germination. Drawdown and flooding techniques, when properly timed, will allow managers to drive and directly influence managed wetland plant communities based on seed bank composition and response to presence or absence of water during the germination period.     

Drought and aquatic community resilience: the role of eggs and seeds in sediments of temporary wetlands

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.     

Persistence of seed banks in Australian temporary 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.     

Immediate and longer-term effects of managed flooding on floodplain invertebrate assemblages in south-eastern Australia: generation and maintenance of a mosaic landscape

1. We compared assemblages of ground‐active, terrestrial beetles and spiders from different areas of river red gum Eucalyptus camaldulensis floodplain forest in subhumid, south‐eastern Australia before and for 2 years following a managed flood to determine whether the Flood Pulse Concept is an appropriate ecological model for this regulated, lowland river‐floodplain system. 2. Immediately following flooding, the abundance, species richness and biomass of beetles were greatest at sites that had been inundated for the longest period (approximately 4 months). The abundance, species richness and biomass of spiders were not reduced at sites that were flooded for 4 months compared with unflooded or briefly flooded areas. Sites recently flooded for several months had high densities of predatory, hygrophilic beetles (Carabidae) and spiders (Lycosidae). 3. Over the 2 years following the flood, beetles generally were more abundant at sites that had been inundated for longer. At all sampling times, the species richness of beetles at sites increased with the length of time sites were inundated, even before the flood. Neither the abundance nor species richness of spiders was related to duration of flooding. 4. The structure of beetle and spider assemblages at sites that were flooded for different lengths of time did not appear to converge monotonically over the 2 years after the flood. 5. Managed flooding promotes diversity of beetles and spiders both by providing conditions that create a ‘pulse’ in populations of hygrophilic specialists in the short term, and by creating subtle, persistent changes in forest‐floor conditions. Despite its monotypic canopy, river red gum floodplain forest is a habitat mosaic generated by differing inundation histories.