Floodplain Grasslands Research Articles

The application of geospatial analyses to support an integrated study into the ecological character and sustainable use of Lake Chilwa

Wetlands, which occupy a considerable proportion of Malawi, are an important resource for the rural-poor. In regions of low and erratic rainfall, they provide important opportunities for agriculture and fisheries and are often vital for food security. However, overutilization and some farming practices can result in environmental degradation and the loss of valuable ecosystem services. The Lake Chilwa wetland, a complex aquatic ecosystem comprising a shallow open water lake surrounded by marsh and floodplain grassland, is one of the most important wetlands in Malawi. Most of the 1 million people who live in the vicinity of the lake derive their livelihoods from the wetland. Increases in population in recent decades have increased the pressures on the wetland. In light of continued population growth, it is anticipated that some levels of resource use may be difficult to sustain in the long-term. Consequently, planning the use of wetland resources is a priority if the diverse benefits that local communities presently receive are to be sustained. Baseline wetland information is needed to determine appropriate sustainable management plans, as well as to identify limits to resilience. However, for many wetlands in southern and eastern Africa, these data are lacking, or not available to those who need them. This paper provides an overview of the distribution and characteristics of wetlands in Malawi. Using Lake Chilwa as an example, it illustrates how Earth Observation data, in combination with hydrometric and botanical data, can be used to provide information crucial for sustainable wetland management.

Species introduction in restoration projects – Evaluation of different techniques for the establishment of semi-natural grasslands in Central and Northwestern Europe

Abstract During recent decades, many studies have shown that the successful restoration of species-rich grasslands is often seed-limited because of depleted seed banks and limited seed dispersal in modern fragmented landscapes. In Europe, commercial seed mixtures, which are widely used for restoration measures, mostly consist of species and varieties of non-local provenance. The regional biodiversity of a given landscape, however, can be preserved only when seeds or plants of local provenance are used in restoration projects. Furthermore, the transfer of suitable target species of local provenance can strongly enhance restoration success. We review and evaluate the success of currently used near-natural methods for the introduction of target plant species (e.g. seeding of site-specific seed mixtures, transfer of fresh seed-containing hay, vacuum harvesting, transfer of turves or seed-containing soil) on restoration sites, ranging from dry and mesic meadows to floodplain grasslands and fens. Own data combined with literature findings show species establishment rates during the initial phase as well as the persistence of target species during long-term vegetation development on restoration sites. In conclusion, our review indicates that seed limitation can be overcome successfully by most of the reviewed measures for species introduction. The establishment of species-rich grasslands is most successful when seeds, seed-containing plant material or soil are spread on bare soil of ex-arable fields after tilling or topsoil removal, or on raw soils, e.g. in mined areas. In species-poor grasslands without soil disturbance and on older ex-arable fields with dense weed vegetation, final transfer rates were the lowest. For future restoration projects, suitable measures have to be chosen carefully from case to case as they differ considerably in costs and logistic effort. Long-term prospects for restored grassland are especially good when management can be incorporated in agricultural systems.

Vertebrate herbivores influence soil nematodes by modifying plant communities

Abiotic soil properties, plant community composition, and herbivory all have been reported as important factors influencing the composition of soil communities. However, most studies thus far have considered these factors in isolation, whereas they strongly interact in the field. Here, we study how grazing by vertebrate herbivores influences the soil nematode community composition of a floodplain grassland while we account for effects of grazing on plant community composition and abiotic soil properties. Nematodes are the most ubiquitous invertebrates in the soil. They include a variety of feeding types, ranging from microbial feeders to herbivores and carnivores, and they perform key functions in soil food webs. Our hypothesis was that grazing affects nematode community structure and composition through altering plant community structure and composition. Alternatively, we tested whether the effects of grazing may, directly or indirectly, run via changes in soil abiotic properties. We used a long-term field experiment containing plots with and without vertebrate grazers (cattle and rabbits). We compared plant and nematode community structure and composition, as well as a number of key soil abiotic properties, and we applied structural equation modeling to investigate four possible pathways by which grazing may change nematode community composition. Aboveground grazing increased plant species richness and reduced both plant and nematode community heterogeneity. There was a positive relationship between plant and nematode diversity indices. Grazing decreased the number of bacterial-feeding nematodes, indicating that in these grasslands, top-down control of plant production by grazing leads to bottom-up control in the basal part of the bacterial channel of the soil food web. According to the structural equation model, grazing had a strong effect on soil abiotic properties and plant community composition, whereas plant community composition was the main determinant of nematode community composition. Other pathways, which assumed that grazing influenced nematode community composition by inducing changes in soil abiotic properties, did not significantly explain variation in nematode community composition. We conclude that grazing-induced changes in nematode community composition mainly operated via changes in plant community composition. Influences of vertebrate grazers on soil nematodes through modification of abiotic soil properties were of less importance.

Effects of bryophytes and grass litter on seedling emergence vary by vertical seed position and seed size

Establishment of plants through seeds is often constrained by the quality of microsites, which is in part controlled by the nature and amount of ground cover. The latter consists of living shoots of vascular plants or bryophytes and/or the dead remains of the dominant species. In the present article, we report the results of a controlled pot experiment with five species characteristic of floodplain grasslands. We manipulated the amounts of grass litter and/or mosses to study (1) differences between ground cover types with respect to their effects on microenvironment and seedling emergence and (2) how these effects interact with seed size and seed sowing position. Increasing amounts of both cover types led to increasing soil humidity, whereas temperature amplitude and illumination were decreased. However, since grass litter decomposed much faster than bryophytes, light conditions for germination under grass litter improved considerably with time. Although seedling emergence varied significantly between species, ground cover types and cover amounts, seed position alone explained about 50% of the variation in the data set. Additionally, we found an important interaction between seed size, seed position and cover type: large-seeded species showed a fitness advantage when seeds were situated beneath a cover, irrespective of cover type, which disappeared when seeds were shed on top of a cover layer. We suggest that this interaction may be ecologically and evolutionarily relevant because it may lead to changes in species composition and diversity of plant communities as a consequence of changes in the amount and type of ground cover.

Vegetation structure and heavy metal uptake by plants in the mining-impacted and non mining-impacted sites of Southern Lake Victoria Wetlands

This study assessed the plant species composition and the heavy metal uptake by plants in the mining-impacted and non mining-impacted areas of the southern Lake Victoria basin. The vegetation of the wetlands was stratified into riverine forest, riverine thickets, swampy grassland, open woodland and floodplain grassland. Plant diversity at Nyamtukuza ranged between 2.34 to 2.70; at Geita was 2.29 to 2.57 and Mwakitolyo was between 1.08 to 1.70, which was significantly lower than the other two sites; whereas variation in plant species richness was not significant. TWINSPAN classification resulted into four clusters of the vegetation communities. Cluster A, a shrubby community with Combretum molle, Bersama abyssinica, Acalypha ornata and Acacia brevispica indicated previous cutting of woody species from the area. Cluster B was a severely disturbed community with Bidens pilosa and Anthocleista grandiflora as early successors. Cluster C was a community with moderate disturbance levels and cluster D was of wetland vegetation community types with indicator species such as Pistia stratiotes and Corchorus aestuans that are characteristic permanent wetland species. CCA ordination showed a significant positive correlation of the soil mineral elements to those in plants at axis 1. The influence of soil minerals on plant species distribution pattern was not significant at axis 1. Tanzania Journal of Science Vol. 32 (2) 2006: pp. 39-50

The decline of metallophyte vegetation in floodplain grasslands: Implications for conservation and restoration

AbstractQuestion: Which biogeochemical processes are responsible for the decline of endemic metallophyte vegetation in floodplain grasslands?Location: Floodplain grasslands along the River Geul (the Netherlands) and metalliferous mine spoils near the River Geul (Belgium).Methods: In order to find factors and soil processes that have caused a decline of metallophytes and an increase of pseudo‐metallophytes in floodplain grasslands, a soil study was done at locations currently and formerly dominated by metallophytes. In addition, changes in soil chemistry in recent decades in floodplain grasslands were investigated. Finally, a 2‐year plant growth experiment was performed in the field, to test the effects of improving soil conditions by topsoil removal.Results: Metallophytes only occur on acidic floodplain soils (pH‐H2O 5.0‐5.5) with relatively high Zn availability (total Zn >40 μmol g−1; Zn/Ca>0.8; Zn‐H2O>59 μmol kg−1) combined with low phosphate availability (Olsen‐P≪1250 μmol kg−1). The Olsen‐P and total Ca concentrations were relatively high in topsoil (0‐20 cm), while total Zn was high throughout the soil profile (0‐50 cm). Removal of topsoil led to recovery of P and Zn availability. Under the new soil conditions there was almost no growth and expansion of pseudo‐metalliferous grasses in time, wheras metallophytes easily established, maintained and reproduced with significant increases in cover over time.Conclusions: On a global scale, metallophyte vegetation types are increasingly under threat of extinction. Our study shows that factors leading to higher soil alkalinity inhibit Zn availability at the expense of the metallophyte vegetation. Factors leading to a higher Olsen‐P concentration stimulate the growth of more competitive pseudo‐metallophyte grasses. Both eutrophication and alkalinisation have contributed to the decline of metallophyte vegetation in floodplains of the River Geul. Removal of the alkaline‐ and phosphate‐enriched soil top layer restores the original soil chemistry and enables re‐colonisation by the metallophyte vegetation. The results can be applied in conservation and restoration strategies for such sites.

Succession of floodplain grasslands following reduction in land use intensity: the importance of environmental conditions, management and dispersal

Summary Classical ecological theory predicts a succession towards plant communities that are determined by environmental conditions. However, in ecological restoration, species composition often remains different from the predicted target community, compromising the success of restoration measures. We analysed the relative importance of environmental conditions, management and distance to source populations for floodplain grassland succession following re‐conversion from intensive to traditional use. The study was established at 33 grassland sites in central German river valleys. Species composition, environmental variables, past and current management, and the distance to source populations of characteristic species of traditional management (indicator species) were recorded and compared using multivariate statistics. We further tested the speed of colonization by two indicator species, Silaum silaus and Serratula tinctoria, along transects from source populations into unoccupied fields. The species composition of the successional grassland was mainly determined by elevation, total soil nitrogen, distance to remnant species‐rich grasslands and frequency of mowing or grazing. Elevation and distance were negatively, and frequency was positively related to the occurrence of late successional species. Colonization by indicator species was only dependent on the distance to source populations; other explanatory variables were not significant. Migration from adjacent source sites of S. silaus and S. tinctoria into re‐converted grasslands was slow, reaching only 40 m and 15 m after 15 years. Synthesis and applications. The results demonstrated the limitations of the deterministic view on plant succession and the high relative importance of propagule availability in grassland restoration. Natural colonization will only be successful if source populations of the target species are adjacent to the restoration sites. Artificial introduction techniques are recommended to overcome dispersal barriers.

What drives plant biodiversity in the clay floodplain grasslands of NSW?

An assessment of the relative influences of management and environment on the composition of floodplain grasslands of north-western New South Wales was made using a regional vegetation survey sampling a range of land tenures (e.g. private property, travelling stock routes and nature reserves). A total of 364 taxa belonging to 55 different plant families was recorded. Partitioning of variance with redundancy analysis determined that environmental variables accounted for a greater proportion (61.3%) of the explained variance in species composition than disturbance-related variables (37.6%). Soil type (and fertility), sampling time and rainfall had a strong influence on species composition and there were also east–west variations in composition across the region. Of the disturbance-related variables, cultivation, stocking rate and flooding frequency were all influential. Total, native, forb, shrub and subshrub richness were positively correlated with increasing time since cultivation. Flood frequency was positively correlated with graminoid species richness and was negatively correlated with total and forb species richness. Site species richness was also influenced by environmental variables (e.g. soil type and rainfall). Despite the resilience of these grasslands, some forms of severe disturbance (e.g. several years of cultivation) can result in removal of some dominant perennial grasses (e.g. Astrebla spp.) and an increase in disturbance specialists. A simple heuristic transitional model is proposed that has conceptual thresholds for plant biodiversity status. This knowledge representation may be used to assist in the management of these grasslands by defining four broad levels of community richness and the drivers that change this status.

Constructing a policy and institutional framework for an ecosystem-based approach to managing the Lower Amazon floodplain

A regional experiment in co-management is underway in the Lower Amazon that is developing the basic policy and institutional elements for an ecosystem-based approach to floodplain management. This initiative grew out of the grassroots movement of floodplain communities who, concerned with excessive commercial fishing pressure on local fisheries, took control of local lakes and implemented collective agreements regulating fishing activity. This paper describes the main elements of the evolving regional management system. This process has focused on four main dimensions of floodplain settlement and resource use: development of sustainable management systems for floodplain resources, policies and institutions for fisheries co-management, collective agreements for grazing cattle on floodplain grasslands, and a land tenure policy consistent with the objectives of the evolving co-management system. Over the last year INCRA, the National Institute for Colonization and Agrarian Reform, has begun implementation of a comprehensive new land tenure policy that could resolve structural deficiencies in the existing co-management system and provide the basis for the ecosystem-based management of the Lower Amazon floodplain.

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.

Flood events overrule fertiliser effects on biomass production and species richness in riverine grasslands

AbstractQuestion: Do severe winter flood events lift the nutrient limitation of biomass production in a river floodplain? How does this affect plant species richness? How long do the effects last?Location: Floodplain grassland on calcareous sandy loam near river Rhine in The Netherlands.Methods: Plots were fertilised with four treatments (control, N, P, N+P) for 21 years; plant species composition, vegetation biomass and tissue nutrient concentrations were determined every year between 1985 and 2005.Results: Fertilisation with N generally increased biomass production and reduced species richness, but these effects varied over time. During the first four years of the experiment, biomass production appeared to be co‐limited by N and P, while N fertilisation dramatically reduced plant species richness; these effects became weaker subsequently. Following two extreme winter floods in 1993–94 and 1994–95 and a drought in spring 1996, the effects of fertilisation disappeared between 1998 and 2001 and then appeared again. Flooding caused an overall reduction in species richness (from c. 24 to 15 species m‐2) and an increase in biomass production, which were only partly reversed after ten years.Conclusions: Long time series are necessary to understand vegetation dynamics and nutrient limitation in river floodplains, since they are influenced by occasional flood and drought events, whose effects may persist for more than ten years. A future increase in flooding frequency might be detrimental to species richness in floodplain grasslands.

Flood events overrule fertiliser effects on biomass production and species richness in riverine grasslands

Question: Do severe winter flood events lift the nutrient limitation of biomass production in a river floodplain? How does this affect plant species richness? How long do the effects last? Location: Floodplain grassland on calcareous sandy loam near river Rhine in The Netherlands. Methods: Plots were fertilised with four treatments (control, N, P, N+P) for 21 years; plant species composition, vegetation biomass and tissue nutrient concentrations were determined every year between 1985 and 2005. Results: Fertilisation with N generally increased biomass production and reduced species richness, but these effects varied over time. During the first four years of the experiment, biomass production appeared to be co-limited by N and P, while N fertilisation dramatically reduced plant species richness; these effects became weaker subsequently. Following two extreme winter floods in 1993–94 and 1994–95 and a drought in spring 1996, the effects of fertilisation disappeared between 1998 and 2001 and then appeared again. Flooding caused an overall reduction in species richness (from c. 24 to 15 species m-2) and an increase in biomass production, which were only partly reversed after ten years. Conclusions: Long time series are necessary to understand vegetation dynamics and nutrient limitation in river floodplains, since they are influenced by occasional flood and drought events, whose effects may persist for more than ten years. A future increase in flooding frequency might be detrimental to species richness in floodplain grasslands.

Earthworm communities of flooded grasslands in Matsalu, Estonia

Earthworm communities in the soil of flooded (coastal and floodplain grasslands) and non-flooded (boreo-nemoral) meadows were studied. The average number of species in coastal and floodplain meadows was low, earthworm communities of boreo-nemoral meadows were diverse and the average number of species was high. Specific composition of earthworm communities varied between the three types of meadows. Earthworm communities of flooded meadows possess specific characteristics being low in both numbers and species due to periodical anaerobic conditions during over flooding and negative effect of sea water in coastal meadows.

The Performance of Plants, Molluscs, and Carabid Beetles as Indicators of Hydrological Conditions in Floodplain Grasslands

AbstractFloodplain systems are among the most complex ecosystems. To assess their ecological condition, several indicator systems have been developed. However, none of them quantifies environmental factors related to the dynamics of water levels, which is a major driver for the occurrence and distribution of species in floodplains. We present a new bioindicator system for the duration of inundation per year and mean depth of groundwater during the vegetation period. The new indicator system is based on carabid beetles, molluscs, and plants. The indicator system generally proved to be precise as well as temporally and spatially transferable within the same river system, the Elbe River in Germany. The indication based on plants was clearly most precise and transferable. The results are discussed in terms of application of the indicator system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carabid Beetles (Coleoptera, Carabidae) as Indicatorsof Hydrological Site Conditions in Floodplain Grasslands

AbstractThe relationship of carabid beetle species occurrence patterns and environmental variables characterising the hydrological regime has been studied at the River Elbe in Central Germany. Both flood duration and groundwater depth had major influence on species assemblages as the ordination of study plots mainly followed a gradient along these two variables. The simultaneous ordination of the plots according to species occurrence and environmental parameters showed a highly significant joint structure with the first two axes of a co‐inertia analysis, explaining >98% of the variance. A total of 27 species out of 129 caught fulfilled criteria of fidelity and specificity to the plots of the five clusters revealed by their abiotic conditions and were sufficiently abundant to be suitable indicators for one or a combination of clusters of plots. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Scenarios of the impact of local and upstream changes in climate and water use on hydro-ecology in the Okavango Delta, Botswana

Summary Changes in hydrological inputs to the flood-pulsed Okavango Delta result in changes in such flooding characteristics as floodplain water depth, inundation duration and frequency. A mathematical model is used to assess impacts of changing hydrological inputs on flooding in the Okavango Delta. Future conditions are simulated by superimposing simulated abstractions, upstream developments and climate change effects on the observed time series of hydrological inputs. The effects of change in inputs are then determined by comparing hydrological characteristics such as inundation duration and frequency derived from the original and modified time series of model outputs. Simulations show that upstream abstractions are likely to have small short-term effects on the flooding pattern in the Delta, while other upstream developments such as damming or deforestation have more pronounced effects. All of these effects are relatively small, however, when compared to changes resulting from existing climatic variability, and those from the possible effects of future climate change. The combined effects of human abstraction and climate change, manifested as increased temperatures, decreased rainfall, and reduction in river flows, may result in significant Delta drying. The simulated hydrological changes affect the Delta floodplain ecosystems, with anticipated changes in the area and proportions of permanent swamp, areas covered by sedge and grass vegetation (seasonal floodplains) and floodplain grasslands (intermittently flooded areas). These will have varied effects on ecological processes in the Delta, in particular vegetative succession, primary production, and relationships of floodplains with the surrounding woodland and savannah. Additional ripple effects up trophic levels can also be expected. There may also be downstream impacts on tourist facilities presently on the fringes of the seasonal swamps as a result of reduced or increased flooding. As a result of altered flood regime, some effects are also anticipated with respect to the recharge of aquifers, which are currently used for drinking water supply around the Delta.

Regularities of wind-erosion of different land-use types in Yongding River sandy land, Beijing

The threshold wind velocity of a number of variables was studied in four different land-use types: farm land, forestland, wild grassland and a flood plain in the Yongding River sandy land in Beijing. The variables studied were transport of sand, underlying surface roughness, windblown sediment, wind-sand flow structure, soil mechanical composition and amount of wind erosion. The following conclusions were drawn: 1) The order of decreasing threshold of wind speed for sand displacement and surface roughness were forestland, wild grassland, farm land, sparse wild grassland and flood plain. 2) There were significant differences in sand flux among different ground covers. At a height of 0–20 cm, the height increased while the sediment discharge percent of sand flux decreased; there were significant differences in the sand flow formation under different land-use types. 3) The mechanical composition of sand particles consisted mainly of silver sand in the flood plain and sparse wild grassland, and of silver sand, particle silver sand and floury sand in other land-use types. 4) The amounts of wind erosion and sand sediment were different among different land-use types. Increased vegetation cover and change in farming techniques were suggested to prevent and control wind erosion of sand and soil.

Soil characteristics of a hyperseasonal cerrado compared to a seasonal cerrado and a floodplain grassland: implications for plant community structure

Savannas may be divided according to their seasonality into semi-seasonal, seasonal, hyperseasonal, or marshy savannas. Hyperseasonal savannas are characterized by the alternation of two contrasting stresses during each annual cycle, one induced by drought and fire and the other, by waterlogging. In South America, the largest savanna region is the Brazilian cerrado, in which there are few hyperseasonal areas that become waterlogged in the rainy season. The cerrado soils are generally well drained, but in central Brazil there is a small cerrado area in which the soil is poorly drained and which becomes waterlogged in the middle of the rainy season, allowing the appearance of a hyperseasonal cerrado. As long as soil is important in the ecology of the cerrado vegetation, we asked whether the waterlogging in this hyperseasonal cerrado implied that there were differences in soil characteristics in relation to a seasonal cerrado, which is not waterlogged in the rainy season, and to a floodplain grassland, which remains waterlogged throughout the year. In each environment, we randomly selected ten points, in which we collected soil samples in the mid-rainy season for chemical and granulometric analyses. For all variables, we found significant differences among the three environments, at least at one of the depths. Nevertheless, when we took into account all the variables together, we observed that the soils under the hyperseasonal and seasonal cerrados were similar and both were different to the soil under the floodplain grassland. The soil under the floodplain grassland was related to larger amounts of clay, silt, organic matter, phosphorus, aluminium, aluminium saturation, cation exchange capacity, and sum of bases, whereas soils under hyperseasonal and seasonal cerrados were related to higher pH values, base saturation, calcium, magnesium, and sand. As long as the soil under both cerrados was chemically and physically similar, the duration of waterlogging in the hyperseasonal cerrado is not long enough to alter its soil characteristics. Limitations to the plants growing on the hyperseasonal cerrado soil must be a consequence of the direct effects of flooding. Since cerrado plant species are dryland ones, the hypoxia caused by waterlogging may limit the number of cerrado species able to withstand these conditions.

Vegetation responses to environmental conditions in floodplain grasslands: Prerequisites for preserving plant species diversity

Summary We studied plant species responses to environmental conditions in floodplain grasslands (alliance Cnidion ) of the river Elbe (northern Germany) in order to describe relationships between species composition/diversity and underlying site gradients. We analysed a total area of 639 ha of floodplain grasslands, using 98 sampling plots. Vegetation responses to environmental conditions were examined by means of DCA. The relationships between species diversity and environmental conditions were examined using regression analyses. Our results show that species composition and species richness are mainly affected by present-day utilization, by the phosphate supply and by the productivity of stands. Species richness decreases significantly under grazing, with increasing phosphate supply and productivity of stands. Intermediate productivity levels, mowing and high inundation frequencies promote floodplain target species. N inorg availability and base availability have only a minor impact on species composition/species diversity. Productivity is closely related to the amount of plant available phosphate. Low phosphate concentrations in the topsoil are particularly characteristic of Cnidium dubium floodplain meadows. Therefore, it is likely that in floodplain grasslands with low to intermediate productivity, phosphate is the most important factor influencing plant competition and plant species diversity. We hypothesize that an increased phosphate supply increases stand productivity and, hence, the competition for light, thus excluding weak competitors. This interpretation is supported by the present-day distribution of C. dubium floodplain meadows of the river Elbe: these are concentrated in the hybrid (between summer and winter dykes) and fossil floodplain (landward side of winter dykes), but have been replaced in the functional floodplain by grass-dominated plant communities as a result of a steady increase in the river water phosphate content. It is, therefore, only in the hybrid and fossil floodplain grasslands that species diversity may be preserved in the long term, as the P input is lower here than in the functional floodplain.

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.