Release of inorganic N,P and K in peat soils; effect of temperature,water chemistry and water level

In the Netherlands, fens that are fed by polluted river water are often eutrophic, whereas fens fed by calcium-rich groundwater often are mesotrophic. Differences in trophic status can not always be attributed to differences in the nutrient load of the water. In this paper we try to determine if the inflow of river water in fens, in fact, accelerates the soil nutrient release, thereby creating more eutrophic conditions (‘internal eutrophication’). For this purpose, we compared nutrient release rates (N, P and K) in soil cores fromSphagnum peat andCarex peat saturated with different media, that were artificially created to mimic the three basic water sources: polluted river water, unpolluted calcium-rich groundwater and rainwater. In addition, we studied the effect of temperature and water level on nutrient release rates. The experiments proved thatSphagnum peat released much more P and ammonium thanCarex peat. The strong site effect proved consistent throughout the water chemistry treatments, which indicates that soil quality may be the most important agent determining nutrient release rates. Nevertheless, it was established that water chemistry and water level are of significant influence on nutrient release rates in peat soils. In particular, river water stimulated P release by the peat, most notably in theSphagnum peat. P-release in both soils was only minor when the soils were incubated in clean Ca-rich groundwater. It is suggested that P release is strongly associated with soil chemical processes, and that high P release rates after incubation in river water are due to the high sulphate content of the water. The net release from the soil of ammonium, potassium and phosphate increased with increasing temperature. A freezing treatment significantly increased nutrient availability. The results of the experiments are examined in the context of hydrologic management strategies for the conservation of fens in agricultural landscapes.     

Variation in species composition and species richness within Phragmites australis dominated riparian zones

In riparian wetlands total standing crop often fails to account for a significant part of the observed variation in species richness and species composition within communities. In this study, we used abundance of the dominant species instead of total standing crop as the biotic predictor variable and investigated its relationships with species composition and species richness in communities dominated by Phragmites australis (Cav.) Trin. ex Steudel. This was done by measuring soil organic matter content, litter cover and elevation, Phragmites abundance (standing crop and stem density) and species composition in 78 relevés. In addition, we tried to identify the environmental boundaries of Phragmites communities by sampling relevés in neighbouring communities.Two gradients were related to a decline in Phragmites abundance: one gradient, perpendicular to the shoreline, was mainly related to increased elevation and the second gradient ran parallel to the shoreline and was related to increased amounts of soil organic matter. Within the relevés dominated by Phragmites, stem density of Phragmites and litter cover were the only factors significantly related to species composition in the RDA solution. Litter cover and standing crop of the dominant accounted for 64% of the variation in species richness within the Phragmites-dominated community. These results show that dead and living biomass of the dominant species may account for a substantial part of the variation in species composition and species richness within a single community.     

Habitat engineering under dry conditions: The impact of pikas (Ochotona pallasi) on vegetation and site conditions in southern Mongolian steppes

Question: Does ecosystem engineering by small mammals have a significant influence on vegetation patterns in the arid steppe vegetation of southern Mongolia? Location: Gobi Altay Mountains, southern Mongolia. Methods: We assessed the impact of the small lagomorph Ochotona pallasi on plant community composition, nutrient levels and biomass production in montane desert steppes. Data were derived from vegetation relevés, harvests of above‐ground standing crop and a bioassay, followed by analyses of soil and plant nutrient contents. Results: Although the local climate is arid with <150 mm annual precipitation, clear evidence of allogenic ecosystem engineering was found. Plant communities on burrows differed from those on undisturbed steppe in that they contained more species of annuals and dwarf shrubs, and a greater abundance of the important fodder grass Agropyron cristatum. Standing crop and nutrient concentrations were higher for plants growing on burrow soil. In situ measurements and a pot experiment showed that this effect was related to increased levels of soil nutrients (P, K, N) rather than moisture availability. Conclusions: The study confirms that O. pallasi positively influences soil nutrient levels on its burrows, which leads to increased grassland productivity even under dry conditions. Thus, O. pallasi does not deteriorate site conditions, and the need for presently applied pest control schemes aimed at this species should be reassessed.     

Marshland vegetation of the class <Emphasis Type="Italic">Phragmito-Magnocaricetea</Emphasis> in northwest Croatia (Krapina river valley)

Marshland vegetation of the class Phragmito-Magnocaricetea in the Krapina river valley was investigated during 2006 and 2007, and some sporadic investigations were made earlier. Phytosociological studies were carried out in accordance with the standard Braun-Blanquet methodology. As a result of the field work, and a small amount of data from the literature, 120 relevés were collected and 18 communities were established. For the purposes of comparison, the relevés were also classified using numerical methods. The clusters obtained mostly correspond to specific associations, but do not confirm the division into traditional vegetation alliances and orders. In the analysis of the ecological factors it is established that separation of the relevés is influenced by nutrient content, soil reaction, soil moisture, depth of water, and type of management. Analysis of the plant life forms shows, in all marshland communities, a prevalence of hemicryptophytes, geophytes and hydrophytes. The most widespread marshland communities of the investigated area are: Phalaridetum arundinaceae, Phragmitetum australis and Galio palustris-Caricetum ripariae. Furthermore, Carex randalpina community is recorded for the first time in Croatia. The most threatened marshland communities could be considered to be: Carex randalpina community, Caricetum vesicariae, Leersietum oryzoidis and Oenantho-Rorippetum. They are selected because of their very small surfaces in the investigated area and the small number of known localities within the territory of Croatia. The most invasive alien plant species in the Krapina river valley is Solidago gigantea. It spreads in potential habitats of marshland vegetation, and it is recorded in the species composition of many marshland communities. For the preservation of marshland vegetation, and especially threatened types, it is necessary to maintain the water regime of the habitats, to not remove natural plant cover due to spreading of neophytes, and to provide occasional mowing and burning.     

Hydro-ecological analysis of the Biebrza mire (Poland)

Vegetation composition and structure of 58 sites along gradients in the valley mire of Biebrza, Poland, are related to physical and chemical variables of groundwater and peat. The three most prominent hydrochemical processes in the valley are (a) dissolution of calcite; (b) dissolution of iron, manganese and aluminium; and (c) enrichment with nitrogen and potassium. Major factors determining these processes are vertical flow of the groundwater and river flooding.Within the rheophilous zone of the mire, calcium-richness of the shallow groundwater and base-saturation of the peat are caused by upward seepage of groundwater originating from adjacent higher grounds. This groundwater movement keeps the larger part of the mire saturated with calcium.Good correlations exist between hydrochemistry and vegetation patterns. Groundwater-fed sites support a characteristic rich fen vegetation (Caricetum limoso-diandrae) with a low biomass production. The flood-plain vegetation consists of highly-productive communities of Glycerietum maximae and Caricetum elatae. In a belt in the Upper Basin where neither flooding nor upward seepage occurs, succession, probably caused by intensified drainage, leads to a dwarf-shrub vegetation (Betuletum humilis; poor fen).     

黑河河岸植被与环境因子间的相互作用

2009-2010年,对黑河流域河岸植被分季节进行了详细调查,并实地测定各样点环境因子数据,采用PC-ORD和Canoco软件对数据进行分类排序与环境因子的指示种分析:(1)黑河河岸带植被分为4个植被型和6个群系,位于黑河上游的高山苔草+矮嵩草群系植被种类和数量最为丰富,草本层盖度最大,也是唯一没有乔木分布的群系;金露梅+沙棘+膜荚黄芪+针茅群系是灌木层密度和盖度最大的群系,草本植物种类相对较丰富;位于湿地的沙枣+水柏枝+芦苇+香蒲群系,土壤养分含量最高;(2)影响黑河河岸带植被分布的主要环境因子是海拔、降水、温度、土壤有机质、含水率以及全氮含量,其中,海拔、降水和温度为最重要的影响因子,土壤影响因子中土壤含水率>有机质>全氮,而全磷和速效氮没有显著影响;(3)在黑河河岸带共有20种植物是环境因子指示种,柽柳和苦豆子是温度、降水指示种,胡杨对海拔和降水有很强的指示作用,草本植物中没有土壤含水率和海拔指示种,而在乔灌木中没有土壤有机质指示种,这为气候、土壤条件的变化提供了很好的参考价值。     

Seed banks of a rare wetland plant community: distribution patterns and effects of human-induced disturbance

Seed banks in rare shoreline communities (Nova Scotia, Canada), were examined in order to determine their role in the persistence of rare plant species. A pristine shoreline which supports globally and nationally significant Atlantic coastal plain species averaged 8500 seeds/m². Seedsweremost abundant high on the shore and where standing crop was greatest. Rare species, which made up 22% of the standing crop and litter of the adult vegetation, comprised only 4% of the seed bank. Common rushes such as Juncus canadensis and J. filiformis, were not well represented in the adult vegetation (5% of the standing crop and litter) but were abundant in the seed bank (52% of all seeds). Seed densities were on average, much lower on an intensely disturbed shoreline (1000 seeds/m²), where heavy all-terrain vehicle traffic had destroyed the adult vegetation. These results suggest that intense disturbances will destroy both existing vegetation and the seed bank and moderate disturbances will alter community composition so that common rushes will replace already endangered Atlantic coastal plain species.     

The grassland communities of the southeastern basin of the Labe river 2. Synecology

This part of the study, referring to the previous syntaxonomic part (Ková? 1981), presents the results of a synecological examination of nine grassland communities of the Labe river basin covering roughly the following gradient of the alluvial hydrosere: theCerastio arvensi-Festucetum trachyphyllae trifolietosum pratensis, theArrhenatheretum elatioris typicum, theAlopecuretum pratensis, theStellario-Deschampsietum caespitosae phalaridetosum, theSerratulo-Festucetum commutatae, theMolinietum coeruleae brometosum, theAngelico-Cirsietum oleracei, theCaricetum gracilis typicum, theCaricetum buekii. The long-term study of ground-water level fluctuations showed their close connection to other characteristics of the meadow soils (soil type, moisture content, granulometric composition, capillary water-holding capacity, porosity, acidity, mineral nutrient contents, microbial activity, soil temperature) as well as to the development and distribution of the grassland communities associated with ecosystems of river alluvia. The formation and dynamics of the vegetation in the large river floodplain (at present exposed to the impact of far-reaching hydrological alteration) are explained as a consequence of changes in the natural ecocycles supporting the long-term stable character of the large river basin within the landscape.     

Dynamics of Nutrient Contents (Phosphorus,Nitrogen) in Water,Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.     

Factors Controlling Compositional Changes in a Northern Andean Páramo (La Rusia,Colombia)

In this study, we aimed to assess the processes controlling compositional change in a Northern Andean páramo highly affected by human‐induced disturbances over the last few decades (La Rusia, Colombia). Along the 3000–3800 m asl altitudinal range, we randomly sampled fifty 10 × 10 m plots. Therein, we measured altitude and variables related to soil conditions (i.e., moisture, nutrient contents, bulk density, and texture), occurrence of human‐induced disturbances (i.e., fire, vegetation clearing, potato cultivation, and cattle grazing), and land‐use history. We also recorded richness and abundance of plant species, identifying them as exotic or native. We differentiated four groups of plots according to their species composition. The groups had significant differences in altitude, soil conditions, land‐use history, and particularly, in richness of exotic species and exotic/native cover ratio. They could be ascribed to shrub‐ and grass‐páramo vegetation types based on their relative dominance of woody and herbaceous species; however, these groups were not arranged according to the hypothetical composition of altitudinal belts, but rather formed a mosaic of patches. This mosaic was determined not only by altitude but also by soil conditions and disturbance history of sites. Our results corroborate recent findings which highlight shrub‐ and grass‐páramo vegetation types as patches of contrasting species composition and structure that depend on local environmental variables, as well as human‐induced disturbances as a major determinant of compositional discontinuities in these ‘high mountain’ tropical ecosystems.     

Flooding and groundwater dynamics in fens in eastern Poland

Abstract. Dynamics in hydrology and water chemistry in the Biebrza mires (Poland) were examined by means of a sampling survey that was repeated four times between 1987 and 1992. The dynamics in the vertical stratigraphy of water types in the peat profile are considerable from close to the mire surface to a depth of 50 cm. Water composition in the root zone correlated best with vegetation types during extremely dry or wet conditions. In the root zone of groundwater-fed rich fens with Caricetum limoso-diandrae and Calamagrostietum strictae vegetation, specific groundwater types evolve from the interaction of discharging groundwater from below the root zone and the temporal influence of precipitation and evapotranspiration. The Caricetum limoso-diandrae is fed by the continuous discharge of nutrient-poor, relatively mineral-rich water. The site conditions in the Calamagrostietum strictae are determined by occasional flooding and the presence of discharging mineral-poor groundwater in the lower part of the root zone. In the Caricetum limoso-diandrae and the Calamagrostietum strictae the maximum variations in water level were 56 and 86 cm, respectively. The composition of shallow groundwater of the Betuletum humilis/Caricetum rostratodiandrae fen is diluted most compared to other vegetation types by rainwater in wet periods. In periods of prolonged drought it has a water type that is affected by evapotranspiration and peat mineralisation. The water level varies by only 33 cm. In the Magnocaricion and Glycerietum maximae in the floodplain the water composition is determined by spring flooding of the river and the natural draw-down that occurs in the following summer. Here, maximum variations in water level were 108 and 117 cm, respectively.     

Impact of the Invasive Alien Plant Solidago Giganteaon Primary Productivity, Plant Nutrient Content and Soil Mineral Nutrient Concentrations

Invasion by alien plants can alter ecosystem processes and soil properties. In this study, we compared aboveground productivity, nutrient pools in standing biomass and topsoil (0–0.10 m) mineral nutrient concentrations between plots invaded by Early Goldenrod (Solidago gigantea) and adjacent, uninvaded, vegetation at five sites in Belgium. The five sites were characterised by a resident perennial herbaceous vegetation and spanned a wide range in soil fertility level and floristic composition. Invaded stands consistently had higher (2–3-fold) aboveground productivity and lower mineral element concentrations in standing phytomass. Nutrient pools (calculated as concentration × phytomass) was ca. twice higher in invaded plots, suggesting that S. gigantea might enhance nutrient cycling rates. Impacts on topsoil chemistry were surprisingly modest, with slightly higher nutrient concentrations under the invader. A noticeable exception was phosphorus, which showed higher concentrations of ammonium acetate-extractable fraction in invaded plots in four of five sites. It appears that S. gigantea does not significantly contribute to nutrient uplift from deep soil layers to topsoil, possibly because it does not root much deeper compared to resident vegetation.Equally contributing authors: S. Vanderhoeven, N. Dassonville     

The roles of elevation and salinity as primary controls on living foraminiferal distributions: Cowpen Marsh, Tees Estuary, UK

Benthic foraminiferal assemblages in subrecent deposits are commonly used to reconstruct past sea level. Interpretations are generally made by comparison with either modern dead or total (live plus dead) assemblages. In both cases there will have been post-mortem changes that have differentially affected preservation. It is therefore important to establish the primary ecological controls by analysis of the living assemblages. We have determined the spatial and temporal variability of intertidal benthic foraminifera in the surface (0–1 cm) sediments from a time series survey of 31 sampling stations at Cowpen Marsh, for a period of 12 months. We counted 112,067 live foraminifera assigned to 28 species. The fauna was dominated by two agglutinated species (Jadammina macrescens and Trochammina inflata) on the high and middle marshes, and three calcareous species (Elphidium williamsoni, Haynesina germanica and Quinqueloculina spp.) on the low marsh and tidal flat.The standing crop of the whole intertidal zone, including the high, middle, low marsh and tidal flat habitats, and the individual species varied both temporally and spatially. The standing crop of the intertidal zone as a whole was greatest in the summer months and showed a positive correlation with elevation. The standing crops of the high and middle marshes showed similar temporal variation with peaks in summer and autumn and a trough in winter. The low marsh showed numerous peaks and troughs of standing crop during the year, whereas the tidal flat showed a single peak in summer. The standing crops of Jadammina macrescens and Trochammina inflata on the high and middle marshes peaked from April to May and August to October with troughs in winter. These agglutinated species showed a strong correlation with elevation. Haynesina germanica peaked in May to August and November to January on the low marsh, whereas on the tidal flat there was a single peak in July. The standing crops of E. williamsoni on the low marsh and tidal flat were relatively high in June and May, and July, respectively. Quinqueloculina spp. peaked in May to July on the low marsh and July on the tidal flat. The species was also found in the middle marsh from July to May and high marsh from September to November. Haynesina germanica showed a strong negative correlation with elevation, whereas the other two dominant calcareous species demonstrated weak negative correlations with both elevation and salinity.Reconstructing former sea level depends primarily on the recognition of high and middle marsh assemblages and in this study these are shown to be strongly controlled by elevation rather than salinity. Caution may be needed in interpreting low marsh and tidal flat data as salinity plays a more important role here.     

Dominant environmental factors in wetland plant communities invaded by Phragmites australis in East Harbor, Ohio, USA

Elevation, standing crop, disturbance and soil fertility often emerge from studies of freshwater plant communities as the dominant environmental factors determining both species richness and species composition. Few studies in North America have investigated the relationship between these factors and species abundance (standing crop) and species composition in the context of invasion by Phragmites australis. This study explores the influence of key abiotic and biotic variables on species abundance and composition across three Lake Erie wetlands differing in hydrology and Phragmites abundance in East Harbor, Ohio, USA. Standing crop for 92 species was related to standard sediment analyses, wave exposure, distance to shoreline, elevation, light interference, species density, and Phragmites standing crop in each of 95 1 × 1 m quadrats by using canonical correspondence analysis (CCA). Elevation (Axis I) and Phragmites standing␣crop-soil fertility (Axis II) explained 35.7 and 26.2%, respectively, of the variation in the species–environment relationships. Wave exposure was not a primary component of the first four canonical axes. Axis I was instrumental in describing species composition, separating wet meadow species from marsh species. Axis II was inversely related to species density for both wet meadow and marsh species. These findings generally support prevailing models describing the distribution of wetland plants along environmental gradients. Two discrepancies were noted, however: (1) species density was highest in the most sheltered sites and (2) wave exposure was directly associated with Phragmites standing crop-soil fertility gradient. The structural integrity of Phragmites stems, topographic heterogeneity and differential responses to anthropogenic disturbance may contribute to departure from prevailing multivariate models. This information has direct implications for local and regional wetland managers.     

The Role of Soil Seed Banks in the Rehabilitation of Degraded Hillslopes in Southern Wello,Ethiopia1

The species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0‐to 5‐cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m². Mean species richness also differed significantly among the vegetation classes. Forty‐two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.     

Vegetation and ecological characteristics of the northernmost salt marshes of the European continent

We surveyed 17 locations of salt marshes along the Barents Sea coast in northern Norway (Finnmark, Nordkinnhalvøya and Varangerhalvøya), where 86 phytosociological relevés were recorded and analyzed. Two main vegetation groups were identified: Caricion glareosae and Puccinellion phryganodis, both alliances belonging to the class Juncetea maritimi, order Puccinellietalia phryganodis. The first, Caricion glareosae (upper marshes) is subject to shorter‐term flooding and is saturated by brackish water in river estuaries on sandy or sandy gravel soils. Four units were distinguished: Festuceto‐Caricetum glareosae, Caricetum mackenzie, Caricetum salinae and the Plantago maritima × borealis community. The second group (lower marshes on fine muddy surface, higher salinity, inundated for a longer period directly by the sea) belongs to the alliance Puccinellion phryganodis which encompasses two units: the associations Caricetum subspathaceae and Puccinellietum phryganodis. The floristic composition and habitat preferences of each vegetation cluster are described and our study revealed that there are no significant differences in the vegetation composition of salt marshes beyond the Arctic line and the southern subarctic sites. The observed variations are related to the geomorphology of the sites rather than to their latitude. The comparison of historical records with our recent data demonstrates the great stability of habitat conditions and species composition. The salt marshes studied meet all criteria of good quality and we found no evidence for any threatening trends like those seen in most other habitats in Europe.     

Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

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.     

Patterns of tree species richness in relation to environment in southeastern New South Wales,Australia

Abstract We present regression models of species richness for total tree species, two growth forms, rainforest trees (broadleaf evergreens) and eucalypts (sclerophylls), and two large subgenera of Eucalyptus. The correlative models are based on a data set of 166 tree species from 7208 plots in an area of southeastern New South Wales, Australia. Eight environmental variables are used to model the patterns of species richness, four continuous variables (mean annual temperature, rainfall, radiation and plot size), plus four categorical factors (topographic position, lithology, soil nutrient level and rainfall seasonality). Generalized linear modelling with curvilinear and interaction terms, is used to derive the models. Each model shows a significant and differing response to the environmental predictors. Maximum species richness of eucalypts occurs at high temperatures, and intermediate rainfall and radiation conditions on ridges with aseasonal rainfall and intermediate nutrient levels. Maximum richness of rainforest species occurs at high temperatures, intermediate rainfall and low radiation in gullies with summer rainfall and high nutrient levels. The eucalypt subgenera models differ in ways consistent with experimental studies of habitat preferences of the subgenera. Curvilinear and interaction terms are necessary for adequate modelling. Patterns of richness vary widely with taxonomic rank and growth form. Any theories of species diversity should be consistent with these correlative models. The models are consistent with an available energy hypothesis based on actual evapotranspiration. We conclude that studies of species richness patterns should include local (e.g. soil nutrients, topographic position) and regional (e.g. mean annual temperature, annual rainfall) environmental variables before invoking concepts such as niche saturation.     

Seed bank,seed dispersal and vegetation cover: Colonization along a newly‐created river channel

Question : What is the relative importance of the initial seed bank and subsequent seed dispersal for floristic composition of bank vegetation two years after creation of a newly‐cut reach of a river channel? Location : River Cole, West Midlands, United Kingdom. Methods : We took bank and bed sediment samples from a 0.5‐km reach of a new river channel cut into intact flood‐plain. After river diversion, seed samples deposited on artificial turf mats placed on the river banks and flood‐plain edge were taken in summer and winter 2002 and 2003. Seed rain samples from funnel traps were taken during summer 2002 and 2003. We undertook greenhouse germination trials to assess viable seed species within these samples. In summer 2004, we surveyed river bank vegetation. Agglomerative cluster analysis was used to investigate floristic similarity between seed bank, seed rain, seed deposition samples and final bank vegetation cover. DCA was used to explore contrasts between the samples and to assess whether these reflected interpretable environmental gradients. Results : Seed rain samples contained a small subset of species in the summer depositional samples. 38 species were found within the final vegetation, the seed bank, and at least one of the four sets of depositional samples; a further 30 species not present in the seed‐bank samples were present in at least one of the four sets of depositional samples and the final vegetation. Floristic composition of the vegetation was most similar to the depositional samples from winter 2002 and 2003 and summer 2003. DCA axis 1 reflected a time sequence from seed‐bank samples through depositional samples to the final vegetation. Conclusions : Newly cut river banks were colonized rapidly. Seed remobilization and hydrochorous transport from the upstream catchment are important for colonization. Species richness was highest in samples deposited during winter when high river flows can remobilize and transport viable seeds from upstream. This process would also have enhanced the species richness of seed production along the banks during the second summer (2003).