Unrealized Expectations for Restoration of a Floodplain Plant Community

The ongoing restoration of the channelized Kissimmee River is expected to promote reestablishment of the prolonged, deep inundation regimes that sustained broadleaf marsh as the dominant wetland plant community on the historical floodplain. The success of the restoration was evaluated at locations on the remnant floodplain where broadleaf marsh had been replaced by a mesophytic shrub community, and on the lower portion of the reconstructed floodplain, which was recreated by backfilling of a flood control canal and degradation of associated spoil mounds. During the 8‐year post‐restoration period (2001–2008) mean annual hydroperiods and depths on the restored floodplain were not significantly different from pre‐channelization hydrologic conditions at historical reference sites. Increased hydroperiods and depths eliminated the mesophytic shrub (primarily Myrica cerifera) and associated fern cover, and led to colonization of floating and mat‐forming species, but did not result in the reestablishment of a broadleaf marsh community. Signature broadleaf marsh species, Sagittaria lancifolia and Pontederia cordata, were found in all remnant floodplain plots and colonized 8 of the 10 reconstructed floodplain plots, but had mean cover ranging from only 0.9 to 6.1%. Several factors may have contributed to unsuccessful reestablishment of broadleaf marsh, including unfavorable edaphic conditions, brief drawdown (low stage) periods for establishment of seedlings, flood induced mortality, and an invasion of the exotic shrub, Ludwigia peruviana, which had post‐restoration mean cover of 17–19%. Study results indicate hydrologic restoration of floodplain plant communities can be influenced by more discrete aspects of the river flood pulse than average hydroperiods and depths.     

Response of floodplain grassland plant communities to altered water regimes

Floodplain grasslands are often composed of a mosaic of plant communities controlled by hydrological regime. This article examines the sensitivity of floodplain grassland plant communities to water regime using reciprocal transplantation of an inundation grassland and a flood-meadow within an English floodplain. Experimental treatments comprised control, transplanted and lifted plots; the last treatment, in order to elucidate any disturbance effects of transplantation. Plant community response was analysed using species abundance and their ecological traits. Results from both communities showed substantial annual variations related to hydrology, including significant species changes, but generally, vegetation seemed to be responding to drier conditions following a major flood event. This ‘drying’ trend was characterised by increased species diversity, a greater abundance of competitive species and fewer typical wetland plants. Transplanted community composition increasingly resembled receptor sites and transplant effects were most pronounced the first year after treatment for both vegetation types. Differential responses to water regime were detected for the two plant communities. The inundation grassland community was particularly dynamic with a composition that rapidly reflected drying conditions following the major flood, but transplantation into a drier flood-meadow site prompted little additional change. The flood-meadow community appeared more resistant to post-inundation drying, but was sensitive to increased wetness caused by transplantation into inundation grassland, which significantly reduced six species while none were significantly favoured. The effects of disturbance caused by lifting the transplants were limited in both communities, although five species showed significant annual fluctuations. The study shows that small alterations in water regime can prompt rapid vegetation changes and significant plant species responses in floodplain grasslands, with effects probably magnified through competitive interactions. The dynamic properties of floodplain vegetation demonstrated by this study suggest that its classification, management and monitoring are challenging and ideally should be based on long-term studies.     

Bottomland hardwood forest species responses to flooding regimes along an urbanization gradient

Urbanization alters stream hydrology, hence flooding frequency and duration in floodplain wetlands. Potential impacts include shifts in species composition and survival, making restoration and selection of wetland species difficult. Cephalanthus occidentalis, Fraxinus pennsylvanica, and Quercus shumardii seedlings were subjected to experimental flooding regimes typical of floodplain forests in rural and urban settings. Treatments included a rural flood regime with three 7-day floods, an Urban-short flood regime with six 4-day floods, and an Urban-long flood regime with six 10-day floods over a growing season. Specific responses, measured by stem length, leaf area, and leaf, stem, and root biomass, varied between species from different wetland indicator classes. C. occidentalis, a wetland obligate, was well adapted to both urban flooding regimes, whereas productivity of F. pennsylvanica, a facultative wetland species, and Q. shumardii, a facultative species, was significantly reduced by the Urban-long treatment. Growth rates also varied over time, indicating the importance of temporal flooding patterns on species productivity. Because urban flooding regimes directly and selectively alter species productivity, proper restoration methods in urbanizing environments should include species selection based on current and potential future hydrologic conditions and use of reference standards from reference sites subjected to similar urban hydrologic regimes.     

Interim Responses of Floodplain Wetland Vegetation to Phase I of the Kissimmee River Restoration Project: Comparisons of Vegetation Maps from Five Periods in the River's History

Phase I of the Kissimmee River Restoration Project (KRRP) reestablished intermittent inundation of the river's floodplain by backfilling 12 km of the C‐38 flood control canal in 2001. We compared floodplain vegetation maps based on 2003 and 2008 aerial imagery (2 and 7 years following completion of Phase I, respectively) to vegetation maps from 1954 (pre‐channelization), 1974 (3 years after channelization), and 1996 (25 years after channelization) to evaluate broad‐scale vegetation responses to Phase I restoration. Results indicate that the extent of wetland plant communities expanded rapidly, more than doubling in area within 2 years after completion of Phase I, and that by 2008 wetlands had nearly recovered to pre‐channelization levels. However, full reestablishment of the pre‐channelization wetland mosaic has not yet occurred. Prior to channelization, much of the floodplain was dominated by a broadleaf marsh (BLM) community associated with extended, deep annual flooding, while shorter‐hydroperiod communities dominated the floodplain in 2003 and 2008. Prior to restoration construction, the reestablishment of BLM was predicted to be slow because suitable hydrology is dependent on project components that will not be in place until all restoration components are completed (projected for 2019). Hydrologic data indicate that the duration and variability of floodplain inundation have not yet achieved restoration targets over the entire Phase I study area. Other factors affecting vegetation responses are likely involved, including the age and viability of soil seed banks, the rarity of relict propagule sources following the channelized period, and competition from an invasive wetland shrub species.     

内蒙古高原典型草原区河漫滩湿地植物群落退化表征

草原区河流河漫滩草甸是生物多样性表现最充分和生物生产力最高的地段, 但由于过度放牧利用, 绝大部分草甸处于退化状态。该文以锡林河流域中游的河漫滩草甸为研究对象, 比较分析了围封保育湿地与放牧退化湿地的群落组成、地上生物量, 以及共有植物种的植株高度、节间长、叶长、叶宽, 土壤含水量、容重, 群落地下根量及根的分布, 土壤微生物生物量碳、氮的变化。结果表明: 1)放牧使得湿地植物群落优势种发生变化, 原有湿生植物逐渐向旱生化转变, 同时地上及地下生物量明显降低。2)退化湿地的植物呈现显著小型化现象。3)放牧退化湿地的土壤含水量较围封保育湿地低, 其垂直分布及地下根的垂直分布也发生变化。在低河漫滩, 土壤水分随土层的增加而增加, 根量也趋于深层化。但在高河漫滩湿地, 土壤含水量接近典型草原, 根未出现深层化分布趋势。4)放牧践踏引起土壤容重和土壤紧实度增加。5)放牧使得低河漫滩湿地土壤微生物生物量增加, 而在过渡区及高河漫滩湿地, 放牧使得土壤微生物生物量碳、氮含量显著降低。     

Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States

Flooding and salinity stress are predicted to increase in coastal Louisiana as relative sea level rise (RSLR) continues in the Gulf of Mexico region. Although wetland plant species are adapted to these stressors, questions persist as to how marshes may respond to changed abiotic variables caused by RSLR, and how herbivory by native and non-native mammals may affect this response. The effects of altered flooding and salinity on coastal marsh communities were examined in two field experiments that simultaneously manipulated herbivore pressure. Marsh sods subjected to increased or decreased flooding (by lowering or raising sods, respectively), and increased or decreased salinity (by reciprocally transplanting sods between a brackish and fresh marsh), were monitored inside and outside mammalian herbivore exclosures for three growing seasons. Increased flooding stress reduced species numbers and biomass; alleviating flooding stress did not significantly alter species numbers while community biomass increased. Increased salinity reduced species numbers and biomass, more so if herbivores were present. Decreasing salinity had an unexpected effect: herbivores selectively consumed plants transplanted from the higher-salinity site. In plots protected from herbivory, decreased salinity had little effect on species numbers or biomass, but community composition changed. Overall, herbivore pressure further reduced species richness and biomass under conditions of increased flooding and increased salinity, supporting other findings that coastal marsh species can tolerate increasingly stressful conditions unless another factor, e.g., herbivory, is also present. Also, species dropped out of more stressful treatments much faster than they were added when stresses were alleviated, likely due to restrictions on dispersal. The rate at which plant communities will shift as a result of changed abiotic variables will determine if marshes remain viable when subjected to RSLR. Received: 8 April 1998 / Accepted: 15 June 1998     

Effects of hydrological variation on the aquatic plant community in a floodplain palustrine wetland of southern Brazil

This study analyzed macrophyte richness, biomass, and composition under flooding of brief duration (less than 3 days) and drawdown events over an annual cycle in a floodplain palustrine wetland in the south of Brazil. The study was carried out to test the hypothesis that floods of brief and very brief duration are not long enough to compromise the richness and the biomass of aquatic macrophytes and that the alternation between wet and drawdown phases may cause variations in the macrophyte richness and composition. A total of 26 aquatic macrophyte species were observed from April 2003 to May 2004: 13 species were observed during the wet phase, and 24 during the drawdown phase. The mean richness was higher during the drawdown phase than during the wet phase, however, the mean biomass was similar in both phases. Although macrophyte richness was not modified after the three flooding events, mean biomass was modified after two events. The number of macrophyte species of which the biomass was modified after the first flooding event increased with subsequent floods. These results illustrate the importance of the dynamics between brief floods and drawdown events to the aquatic plant community in floodplain wetlands in southern Brazil.     

Effects of raised water levels on wet grassland plant communities

Questions: What are the effects of raised water levels on wet grassland plant communities and dynamics? To what extent do time since raised water levels, vegetation management and water regime influence community composition? Location: Pevensey Levels, southeast England, UK. Methods: Plant communities and hydrology were monitored during 2001‐03 within 23 wet grassland meadows and pastures where water levels had been raised for nature conservation at different times over 21 years. Community variations were examined using species abundance and ecological traits. Results: Water regime, measured as duration of flooding, groundwater level and soil moisture was significantly related to plant community variation. Communities were divided into grasslands where inundation was shallow (≤8 cm) and relatively short (≤3 months) and sites where deeper flooding was prolonged (≥5 months), supporting a variety of wetland vegetation. With increasing wetness, sites were characterised by more bare ground and wetland plants such as sedges, helophytes and hydrophytes, and species with a stress‐tolerating competitive strategy. All sites showed considerable annual dynamics, especially those with substantially raised water levels. There were no significant relationships between time since water levels were raised and plant community composition. Grassland management exerted a limited influence upon vegetation compared to water regime. Conclusions: Grassland plant communities are responsive to raised water levels and have potential for a rapid transition to wetland vegetation, irrespective of grazing or cutting management. Creation or restoration of wet grasslands by (re)wetting is feasible but challenging due to the high dynamism of wetland plant communities and the need for substantially raised water levels and prolonged flooding to produce significant community changes.     

Predictability of flood pulse driven assembly rules for restoration of a floodplain plant community

Community assembly rules were formulated to evaluate the restoration of wet prairie along the periphery of the floodplain of the Kissimmee River in central Florida. Restoration of this plant community is expected to be driven by the reestablishment of flood pulse hydrology following the ongoing dechannelization of the river. Assembly rules were assessed with plant species composition and cover data from 15 permanent plots on the restored floodplain and 6 control plots on the channelized floodplain. These sites were sampled biannually from 1998 to 2010. Mean annual hydroperiods and depths confirmed that the frequency, duration and amplitude of post-restoration flood pulses at study sites were similar to historic reference locations. Elimination of pasture grasses (primarily Paspalum notatum Flüggé) following restoration of the flood pulse validated the hypothesized deletion rule for initial transformation of the wet prairie zone. Predicted increased dominance of obligate and facultative wetland species, a “community addition rule”, also was confirmed. An index of weighted averages of wetland indicator taxa showed significant short-term responses to antecedent hydroperiods and depths, and a restoration trajectory for wetland plant species. As predicted, recruitment of wet prairie indicator species from the extant seed bank correlated with reestablishment of the flood pulse, but was greatest when inundation extended from the wet season into the dry season. Restoration of a wetland plant community did not result in the predicted increase in species richness and diversity. Colonization and expansion of the exotic grass, Hemarthria altissima (Poir.) Stapf & C.E. Hubb., disrupted community reassembly processes. By summer 2007, mean cover of this species and several other exotic grasses increased to 24%, and necessitated herbicide treatments. Assembly rules provided useful predictions for the initial restoration of wet prairie vegetation, but were eventually confounded by the spread of an exotic species that was new to the regional flora.     

Landscape-scale variation in the seed banks of floodplain wetlands with contrasting hydrology in China

1. At a local scale, the species composition, diversity and spatial variation of wetland plant communities are determined primarily by spatial and temporal heterogeneity in their environments. Less is known about variation at a landscape‐level. The floodplain of the Changjiang (Yangtze) River in China includes hydrologically connected, subtropical wetlands with different hydrological characteristics. 2. We examined seed‐bank species composition and richness in marshes of two contrasting hydrological types: permanent marshes, fed by local runoff, and lakeshore marshes more closely connected to the regulated river. Lakeshore marshes are flooded annually to depth of approximately 1 m and during flooding they support an alternate, aquatic vegetation type. The soil seed bank in March was a comparative estimator of species diversity. At the beginning of the growing season it included seeds from both phases of alternating vegetation types associated with the annual hydrological cycle. 3. A regional pool of 101 species was detected in the seed banks of six wetlands associated with the river and its tributaries: 56 occurred in permanent marshes and 59 in lakeshore marshes, with only 15 common to both. Species rarefaction curves indicated that more species occurred in permanent than lakeshore marshes at equal numbers of individuals sampled. However, the more heterogeneous lakeshore seed banks were estimated (Chao 2) to have greater total species richness (81) than permanent marsh (60). 4. Analysis using Sørensen's coefficient of similarity and DCA ordination revealed complex variation, with much greater differences between hydrological types than within them, irrespective of geographical distance. The types also differed significantly in the composition of four functional groups of species. 5. Despite the potential for dispersal of propagules via the annually pulsing river system (hydrochory), at a regional and landscape scale, diversity is maintained largely by large‐scale temporal hydrological heterogeneity and smaller scale spatial and topographic heterogeneity.     

Managing plant species diversity under fluctuating wetland conditions: the case of temporarily flooded depressions

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.     

Alterations in flood frequency increase exotic and native species richness of understorey vegetation in a temperate floodplain eucalypt forest

The delivery of environmental flows for biodiversity benefits within regulated river systems can potentially contribute to exotic weed spread. This study explores whether exotic plants of a floodplain forest in Victoria, Australia, are characterised by specific functional groups and associated plant traits linked to altering hydrological conditions over time. Permanently marked 20 × 20 m² plots from five wetland sites in Eucalyptus camaldulensis floodplain forest were sampled twice, first in the early 1990s (1993–1994) and then 15 years later (2007–2008). Species cover abundance data for understorey vegetation communities were segregated by season and analysed using ordination analysis. Exotic species richness was modelled as a function of site flooding history and native species richness using general linear models. Site ordinations by detrended correspondence analysis showed differential community compositions between survey dates, but native and exotic species were not clearly differentiated in terms of DCA1 scores. Most exotics belonged to functional groups containing annual species that germinate and reproduce under drier conditions. Exotics reproducing under wetter conditions were in the minority, predominantly perennial and capable of both sexual and asexual reproduction. Site flooding history and native species richness significantly predicted exotic species richness. Vegetation changes are partially structured by reduced flood frequency favouring increased abundance of exotic, sexually reproducing annuals at drier sites. Sites of low flood frequency are more sensitive to future exotic weed invasion and will require targeted management effort. Flow restoration is predicted to benefit propagule dispersal of species adopting dual regeneration strategies, which are predominantly natives in this system.     

Response of Plant Height,Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands,Northeast China

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region.     

Conservation of Leafhoppers in Floodplain Grasslands – Trade-off between Diversity and Naturalness in a Northern German National Park

The impacts of mowing and of flooding on the leafhopper communities of a river flood plain were investigated. Samples were taken by a motor-driven suction apparatus. In 2001 leafhoppers were collected in a variety of sites differing in land use (fallows, mown sites) and in flood intensity (high, medium, low, none). In 2002 samples were only taken in fallows subject to different flooding regimes.In fallows, more species (43) were collected than in mown sites (33). Flooding had an effect only in fallows. Here, the most species-rich (29) communities occurred in sites not subject to flooding, whereas fewest species (21) were found in sites subject to regularly occurring long lasting winter floods. Mown sites were dominated by pioneer species. In fallows, the communities differed in respect to flood intensity. In fallows that were subject to summer and winter floods pioneer species prevailed. In contrast, in fallows that were flooded a long time during winter but not in summer, communities of very specialised species were found which were not very species-rich.For the conservation of the typical leafhopper communities of floodplain grassland, management by mowing should be at least reduced if not totally stopped and natural flooding dynamics should be restored.     

Variant restoration trajectories for wetland plant communities on a channelized floodplain

Restoration efforts are typically based on an assumption that reestablishment of altered determinants of ecological structure and function will lead to a predictable reestablishment of populations and reassembly of communities. Dechannelization and reestablishment of natural hydrologic regimes provide the basis for the ongoing restoration of the Kissimmee River in Central Florida, United States. The expected reestablishment of historically dominant broadleaf marsh (BLM) and buttonbush shrub (BB) communities was evaluated over a 10‐year period following implementation of the first phase of the restoration project. Plant species composition and cover were assessed during dry (spring) and wet (summer) season sampling periods at five sites on the restored floodplain, and four “control” sites on the channelized floodplain. Mean daily stage data from nearby gauges indicated hydroperiods and depths on the reflooded floodplain were within the range of historic hydrologic conditions that selected for BLM and BB communities on the pre‐channelization floodplain. After reflooding, pasture grass and upland shrub communities rapidly transitioned to a fluid mix of obligate and facultative wetland species. Although signature BLM and BB species, Sagittaria lancifolia (bulltongue arrowhead), Pontederia cordata (pickerel weed), and Cephalanthus occidentalis (buttonbush), recolonized all study sites, the expected reestablishment of dominant cover of these species did not occur. Results indicate that restoration of BLM and BB communities has been impeded by deep flood pulse disturbances, establishment of invasive wetland grasses, and mineralized soil characteristics of the drained floodplain.     

Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

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The Significance of Meander Restoration for the Hydrogeomorphology and Recovery of Wetland Organisms in the Kushiro River,a Lowland River in Japan

The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6‐km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4‐km meander channel was restored. Additionally, flood levees were removed to promote river–floodplain interactions. There were four objectives of this restoration project: to restore the in‐stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river–floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment‐laden floodwater spread over the floodplain, and approximately 80–90% of the fine sediment carried by the water was filtered out by the wetland vegetation.     

Eutrophication,agriculture and water level control shift aquatic plant communities from floating-leaved to submerged macrophytes in Lake Chini,Malaysia

In this study we: (1) present a quantitative spatial analysis of the macrophyte communities in Lake Chini with a focus on the biogeographical distributions of the native Nelumbo nucifera and the invasive Cabomba furcata; (2) examine the environmental changes that affect plant community composition; and (3) outline a conceptual model of the variation of ecological processes that shape the macrophyte communities. Plant species cover, biomass of C. furcata and N. nucifera, and water quality and environmental variables were measured before and after monsoonal floods in September 2009 and April 2010. Permutational multivariate analysis was used to examine the significance of the invasion of C. furcata at different spatial scales. Relationships between plant species cover and environmental variables before and after flooding were examined using principal coordinates analysis and non-parametric multivariate multiple regressions. Our findings suggest that (1) Variation in plant communities was significant at the lake scale and the distribution of plant species changed after annual floods. (2) Invasion by C. furcata significantly affected the overall plant community composition. (3) C. furcata biomass increased after the monsoonal season, which indicates that C. furcata is adapted to flooding events and that it is becoming increasingly abundant. (4) In addition to the strong monsoonal effect, total depth, nutrient concentration, and sediment type were important environmental variables that significantly affected plant community composition. The macrophyte community in Lake Chini is highly dynamic. The spatial and temporal plant community dynamics are associated with flood regime, water quality, and substrate. Human-induced changes in these parameters are likely shifting the macrophyte dominance from floating-leaved to submerged species.     

Turlough ground beetle communities: the influence of hydrology and grazing in a complex ecological matrix

Turloughs are groundwater dependent grazed wetlands of conservation importance that occur in limestone depressions in the karst landscape, mostly in the west of Ireland. Data on Carabidae, hydrological regime, soils and management (using grazing exclosures) were collected to assess the effects of both hydrological regime and grazing management on ground beetles of Skealoghan turlough. Distinct ground beetle communities have been found associated with different hydrological regimes with carabid beetle community composition sensitive to both changes in hydrological regime and vegetation structure. The hydrological regime is the primary factor controlling the carabid species composition of this grazed wetland. Grazing, particularly selective grazing by animals plays an important but subordinate role to hydrology in providing suitable habitat conditions for many species of conservation importance. This paper provides a detailed assessment of species responses to wetland management and demonstrates the need to maintain a range of hydrological and grazing regimes.     

Base-line variations in stable isotope values in an Arctic marine ecosystem: effects of carbon and nitrogen uptake by phytoplankton

Floods are fundamental for the maintenance of floodplain biodiversity. As a result, well-functioning floodplains are characterized by a high spatio-temporal heterogeneity. Most floodplain-organisms need this shifting landscape mosaic to fulfil their environmental requirements and display a range of adaptations to survive floods. However, in temperate areas, where winter floods are common, extraordinary floods occurring in summer, a period of high physiological activity, may seriously impact the floodplain fauna. This is especially true for guilds characterized by low mobility, such as molluscs. Here we examined the immediate and longer-term response of Elbe grassland molluscs to the extreme 2002 Elbe summer flood in terms of abundance, diversity, and community composition by comparing pre- and post-flood data collected with identical methods. The flood favoured the colonization of aquatic species and led to a shift of the community towards a more hydrophilic composition. Both diversity and abundance increased significantly in the first year following the flood but decreased later gradually to the pre-flood levels. The high spatio-temporal habitat heterogeneity played an important part in the maintenance of mollusc diversity by increasing refuge opportunities and favouring the maintenance of various mollusc communities with different environmental requirements within the floodplain. Handling editor: S. I. Dodson