The interpretation of fen carr pollen diagrams: pollen–vegetation relationships within the fen carr

Sediments deposited in fen carr environments are frequently used in pollen-based reconstructions of vegetation history, although few studies of modern pollen–vegetation relationships in fen carr have been undertaken to aid the interpretation of fossil assemblages. It is often assumed that the wetland pollen signal will reflect the overall composition of the fen carr system although, given the closed canopy context, it may actually be dominated by local vegetation elements. This paper seeks to determine whether the vegetation heterogeneity within a modern fen carr is reflected in the pollen signal of the wetland taxa. Vegetation composition was recorded around a series of moss polster sample points at Calthorpe and Wheatfen, two areas of fen carr in the Norfolk Broadland, UK. The spatial interrelationship between the wetland components of the vegetation and their palynological equivalents in the moss polster pollen assemblages is explored through trend surfaces and a correlation based statistical test (the Mantel Test). The representation of the major vegetation components in the pollen record is highly variable. Values for Alnus glutinosa, a dominant canopy species, range from 5.3% to 73% of total land pollen (TLP) at Calthorpe and 2.5–61% TLP at Wheatfen. In part, this variation reflects the enhanced input of pollen from dry land sources close to the wetland edge although the variation recorded at points equidistant from the dry land margin suggests that other processes are also influential. The strongest positive associations in the Mantel Test are for under-storey and ground flora elements that are poorly represented in the pollen record. Taxa for which there is no association include those with few vegetation occurrences and those for which a large proportion of the pollen appears to have been derived from outside the study areas. We conclude that modern pollen samples collected from fen carr broadly reflect the vegetation composition of the study areas. However, the input of pollen from fen carr species is spatially inconsistent. Differences between the sample points can be attributed to the distribution and pollination biology of the under-storey and ground flora elements and the structure of the vegetation around sites. The results caution against assuming that changes in the pollen representation of wetland taxa, in fossil sequences constructed from fen carr deposits, necessarily reflect changes in the overall composition of the community.     

Hydrological landscape settings of base‐rich fen mires and fen meadows: an overview

Question: Why do similar fen meadow communities occur in different landscapes? How does the hydrological system sustain base‐rich fen mires and fen meadows? Location: Interdunal wetlands and heathland pools in The Netherlands, percolation mires in Germany, Poland, and Siberia, and calcareous spring fens in the High Tatra, Slovakia. Methods: This review presents an overview of the hydrological conditions of fen mires and fen meadows that are highly valued in nature conservation due to their high biodiversity and the occurrence of many Red List species. Fen types covered in this review include: (1) small hydrological systems in young calcareous dune areas, and (2) small hydrological systems in decalcified old cover sand areas in The Netherlands; (3) large hydrological systems in river valleys in Central‐Europe and western‐Siberia, and (4) large hydrological systems of small calcareous spring fens with active precipitation of travertine in mountain areas of Slovakia. Results: Different landscape types can sustain similar nutrient poor and base‐rich habitats required by endangered fen meadow species. The hydrological systems of these landscapes are very different in size, but their ground water flow pattern is remarkably similar. Paleoecological research showed that travertine forming fen vegetation types persisted in German lowland percolation mires from 6000 to 3000 BP. Similar vegetation types can still be found in small mountain mires in the Slovak Republic. Small pools in such mires form a cascade of surface water bodies that stimulate travertine formation in various ways. Travertine deposition prevents acidification of the mire and sustains populations of basiphilous species that elsewhere in Europe are highly endangered. Conclusion: Very different hydrological landscape settings can maintain a regular flow of groundwater through the top soil generating similar base‐rich site conditions. This is why some fen species occur in very different landscape types, ranging from mineral interdunal wetlands to mountain mires.     

Experimental restoration of a fen plant community after peat mining

Question: Which restoration measures (introduction of donor diaspore material, application of straw mulch, alteration of residual peat depths) contribute to the establishment of a fen plant community on minerotrophic surfaces after peat mining? Location: Rivière‐du‐Loup peatland, southern Québec, Canada at 100 m a.s.1. Methods: The effectiveness of introducing fen plants with the application of donor diaspore material was tested. The donor diaspore material, containing seeds, rhizomes, moss fragments, and other plant propagules, was collected from two different types of natural fens. We tested whether the application of straw mulch would increase fen species cover and biodiversity compared to control plots without straw mulch. Terrace levels of different peat depths (15 cm, 40 cm, and 56 cm) were created to test the effects of different environmental site conditions on the success of re‐vegetation. Results: Applying donor seed bank from natural fens was found to significantly increase fen plant cover and richness after the two growing seasons. Straw mulch proved to significantly increase fen plant richness. The intermediate terrace level (40 cm) had the highest fen plant establishment. Compared to reference sites, the low terrace level (15 cm) was richer in base cations, whereas the high terrace level (56 cm) was much drier. Conclusions: The application of donor diaspore material was demonstrated as an effective technique for establishing vascular fen plants. Further re wetting measures are considered necessary at the restoration site to create a fen ecosystem rather than simply restoring some fen species.     

Anaerobic consumers of monosaccharides in a moderately acidic fen

16S rRNA-based stable isotope probing identified active xylose- and glucose-fermenting Bacteria and active Archaea, including methanogens, in anoxic slurries of material obtained from a moderately acidic, CH(4)-emitting fen. Xylose and glucose were converted to fatty acids, CO(2), H(2), and CH(4) under moderately acidic, anoxic conditions, indicating that the fen harbors moderately acid-tolerant xylose- and glucose-using fermenters, as well as moderately acid-tolerant methanogens. Organisms of the families Acidaminococcaceae, Aeromonadaceae, Clostridiaceae, Enterobacteriaceae, and Pseudomonadaceae and the order Actinomycetales, including hitherto unknown organisms, utilized xylose- or glucose-derived carbon, suggesting that highly diverse facultative aerobes and obligate anaerobes contribute to the flow of carbon in the fen under anoxic conditions. Uncultured Euryarchaeota (i.e., Methanosarcinaceae and Methanobacteriaceae) and Crenarchaeota species were identified by 16S rRNA analysis of anoxic slurries, demonstrating that the acidic fen harbors novel methanogens and Crenarchaeota organisms capable of anaerobiosis. Fermentation-derived molecules are conceived to be the primary drivers of methanogenesis when electron acceptors other than CO(2) are absent, and the collective findings of this study indicate that fen soils harbor diverse, acid-tolerant, and novel xylose-utilizing as well as glucose-utilizing facultative aerobes and obligate anaerobes that form trophic links to novel moderately acid-tolerant methanogens.     

Responses of fen plant species to groundwater level and light intensity

Characteristic species of sedge-moss fen communities occur in constantly wet, nutrient-poor sites with a high penetration of light through the vegetation canopy. We studied the effects of water table depth and differences in light intensity on the performance of fen species. Three fen species (Carex curta, Viola palustris, Hydrocotyle vulgaris) and one species with a wide range of occurrence (Poa trivialis) were grown for 10 weeks in a sedge-moss peat substrate at 4 different water levels and 3 light intensities. In all species differences in light availability had a larger effect on biomass production than differences in water level. Under a light availability reduced to only 10% the root weight ratio of all the species decreased while leaf weight ratio increased. The biomass allocation ratios were hardly affected by differences in water level. For Viol a and Hydrocotyle an interaction between the two factors was observed. Poa did not show particular differences compared to the other species. We discuss the results in the context of the establishment of fen species in riparian vegetation. It is suggested that the occurrence of fen species in the landscape is directly related to the availability of light, whereas the relationship between fen species occurrence and hydrological conditions seems to be an indirect one.     

沼肥与化肥在大白菜、花椰菜上的应用效果比较研究

以大白菜、花椰菜为试材 ,研究了沼肥、化肥两种肥料在高量、中量、低量 3个施用水平下的施用效果。结果表明 ,从株高指标上看 ,大白菜施沼肥以低量为佳 ,花椰菜以高量为好 ;从开展度指标上看 ,大白菜、花椰菜施沼肥均以低量为好 ;从单球净重上看 ,两种蔬菜均以施沼肥中量利于提高单球净重 ;从提高净菜率来看 ,大白菜以沼肥中量处理为好 ,花椰菜以沼肥高量处理为佳 ;从两种蔬菜的产量来看 ,施沼肥处理均显著高于施化肥处理 ,其中沼肥高量与沼肥中量处理之间无显著差异 ,而它们与沼肥低量处理之间存在显著差异 ;大白菜中的总糖含量以沼肥低量处理为最高 ,而花椰菜则以沼肥中量处理最高 ;两种蔬菜中的Vc含量均以化肥高量处理为最高 ;从两种蔬菜收获时霜霉病的发病情况来看 ,均以沼肥中量处理发病最轻。施用沼肥利于改善土壤理化性状 ,利于大白菜、花椰菜对土壤中营养元素的吸收 ,从而致使土壤中营养元素的积累量减少。     

Shrub removal facilitates recovery of wetland species in a rewetted fen

Drainage and shrub expansion are the main threats to the biodiversity of fens and fen meadows, whereas rewetting and the removal of shrubby species are frequently applied restoration measures. We examine whether removal of shrubs enhances recovery of target species in a degraded fen subjected to moderate rewetting. The study was located in the drained fen Ca?owanie (central Poland), where remnants of open fen communities and willow-invaded fens exist in former turf-pits, surrounded by degraded meadows on dried peat. All these three habitat types were included in a monitoring grid, which covered an area of 2.2 ha. Within 55 quadrats of 20 m × 20 m we monitored occurrence of 52 species, i.e. two groups of target species (fen indicators and wet meadow indicators) and indicators of two failure scenarios (degraded fen indicators and eutrophic wetland indicators), during six years following shrub removal, rewetting and re-application of conservational mowing, using a 3-step ordinal abundance scale. NMDS ordination revealed a gradual convergence of shrub removal plots and reference plots. We noticed significant effects of year and habitat type on all indicator groups, but only fen indicators have shown a clear (increasing) trend within shrub removal plots. Degraded fen indicators (ruderal and opportunistic species) initially expanded on shrub removal plots, but this effect disappeared in the following years. We conclude that shrub removal enhances establishment of target species in a moderately drained and then rewetted fen and attribute this effect to lowered competition for light. However, given high costs of this method and long-lasting problems with shrub resprouts, we recommend applying shrub removal only to recently overgrown sites, which still retained high botanical diversity. Heavily degraded fen meadows did not react on the increase of moisture, which indicates that more advanced restoration measures, such as top soil removal are needed there.     

Litter controls plant community composition in a northern fen

The accumulation of litter or thatch can affect plant community composition by affecting the temperature, nutrient availability, and light availability of the soil environment, thereby forming a potentially important linkage between recent productivity and current ecosystem processes. To investigate the importance of litter on a fen peatland plant community, we conducted a litter addition and removal experiment in a fen in northern Minnesota, USA, between 1998 and 2001. The addition of litter had little effect on fen plant community composition or microenvironmental variables, despite a two-fold increase in litter mass compared to control plots. However, the removal of litter dramatically increased cover of Rhynchospora fusca and R. alba , and reduced cover of Carex exilis . Litter removal also increased availability of light and soil temperature and increased the phosphorus content of aboveground plant biomass. Our results indicate that litter is an important control of plant community composition in this northern fen.     

Insect conservation in Michigan prairie fen: addressing the challenge of global change

Prairie fen is a globally rare, groundwater dependent peatland community restricted to discrete portions of the glaciated north central USA. Prairie fen harbours a diverse flora composed of sedge wetland and tallgrass prairie species, which in turn support a diversity of rare insects. In Michigan, USA over 20% of the state’s insects of conservation concern are associated with prairie fen, including the globally imperilled Mitchell’s satyr butterfly, Neonympha mitchellii mitchellii (Lepidoptera: Nymphalidae). Here we investigate how global change drivers, including land use change, climate change, and invasive species, may interact to threaten this important community. Specifically, we examine how characteristics of prairie fen habitats—e.g., formation and distribution—interact with the biology of rare fen insects to suggest appropriate short to long term conservation strategies. Our results suggest that prairie fen associated insects are rare for a variety of reasons, including host plant specialization, habitat specialization, and shifting landscape context that limits opportunities for dispersal. We recommend that current conservation efforts focus on stabilization and restoration of existing prairie fens, coupled with directed surveys to monitor population change in insects of concern, and restoration of the landscape matrix to facilitate metapopulation dynamics. In the future, due to the severely fragmented nature of Michigan landscapes, captive rearing and assisted migration may be necessary to conserve some prairie fen insect species. Overall, the effective conservation of fen associated insects will require a shared vision by multiple actors and a willingness to purse that vision over a long time frame.     

Depth related diversity of methanogen Archaea in Finnish oligotrophic fen

The annual rate of CH₄ release and potential CH₄ production has recently been studied in the Salmisuo fen in eastern Finland but the microbiota responsible for the CH₄ production has not been examined. The diversity of the methane producing Archaea was analysed, at different depths, in the most representative microsite (Eriophorum lawn) of the fen. Methanogen populations were studied using primers amplifying a region of the methyl-coenzyme M reductase gene. PCR products were analysed by denaturing gradient gel electrophoresis and restriction fragment length polymorphism (RFLP) analysis of clone libraries. A representative of each RFLP group was sequenced. The study revealed a change of the methanogen populations with depth. Sequences from the upper layers of the fen grouped in a novel ‘Fen cluster’ and were related to Methanomicrobiales. Sequences retrieved from the deeper layers of the fen were related to Methanosarcinales via the Rice Cluster-I.     

The relation between vegetation and soil chemistry gradients in a ground water discharge fen

Abstract. The soil chemistry of a headwater valley fen is influenced by local ground water discharge that supplies base cations and alkalinity to the fen. An irrigation canal just upward of the fen is the source of this alkalinity. The ecological consequences of this artificial system are studied both on the soil and vegetation level. Rich-fen species of the alliance Caricion davallianae are connected to soil water alkalinity and soil base status. They depend directly on the alkaline ground water discharge. In addition, the local input of this water causes a gradient-rich pattern from poor to rich fen, and it is therefore concluded that it is responsible for the presence of intermediate fen vegetation too. High nutrient levels in the irrigation water have not influenced the fen until now. This case study illustrates the possibility for rich fen restoration after acidification. Irrigation with alkaline water is efficient if excess nutrients can be removed.     

In search of a hydrological explanation for vegetation changes along a fen gradient in the Biebrza Upper Basin (Poland)

The understanding of succession from rich fen to poorer fen types requires knowledge of changes in hydrology, water composition, peat chemistry and peat accumulation in the successional process. Water flow patterns, water levels and water chemistry, mineralisation rates and nutrient concentrations in above-ground vegetation were studied along a extreme-rich fen-moderate-rich fen gradient at Biebrza (Poland). The extreme-rich fen was a temporary groundwater discharge area, while in the moderate-rich fen groundwater flows laterally towards the river. The moderate-rich fen has a rainwater lens in spring and significant lower concentrations of calcium and higher concentrations of phosphate in the surface water. Mineralisation rates for N, P and K were higher in the moderate-rich fen. Phosphorus concentrations in plant material of the moderate-rich fen were higher than in the extreme-rich fen, but concentrations of N and K in plant material did not differ between both fen types. Water level dynamics and macro-remains of superficial peat deposits were similar in both fen types.We concluded that the differences observed in the moderate-rich and the extreme-rich fens were caused by subtile differences in the proportion of water sources at the peat surface (rainwater and calcareous groundwater, respectively). Development of an extreme-rich fen into a moderate-rich fen was ascribed to recent changes in river hydrology possibly associated with a change in management practices. The observed differences in P-availability between the fen types did not result in significantly different biomass. Moreover, biomass production in both fen types was primarily N-limited although P-availability was restricted too in the extreme-rich fen. Aulacomnium palustre, the dominant moss in the moderate-rich fen, might be favoured in competition because of its broad nutrient tolerance and its quick establishment after disturbance. It might outcompete low productive rich fen species which were shown to be N-limited in both fens. We present a conceptual model of successional pathways of rich fen vegetation in the Biebrza region.     

Stand structure and vegetation dynamics of a subalpine wooded fen in Rocky Mountain National Park,Colorado

Abstract. The tree population size structure and relationship between tree diameter and age were examined in a subalpine fen and surrounding Picea-Abies forest in northern Colorado. The fen grades from a sedge fen, through an ecotone, to a treed fen. Tree growth rate varies across the vegetational gradient, with the sedge fen having the slowest growth, and the upland forest having the fastest growth. Differences in growth rate are related to the average size of peat hummocks, with areas containing tall hummocks exhibiting the highest tree growth rates. Size structures display the characteristic reverse-J distribution generally indicative of stable populations, but forest vegetation is expanding into the open regions of the fen, and within the treed fen an increase in Abies lasiocarpa is occurring. These changes are primarily attributed to a positive feedback situation wherein the fen's surface is built up by peat accumulation. Distinct hummocks form first on the open fen but then coalesce to form raised peat islands in the treed fen. This new substrate provides habitat with a comparatively low water table and allows the growth of mesophytic forest vegetation. A pathway for this vegetational development is proposed.     

Microsite-dependent changes in methanogenic populations in a boreal oligotrophic fen

Wetlands, including peatlands, are the main source of natural methane emission. Well-defined fen microsites have different methane emissions rates, but it is not known whether the methane-producing Archaea communities vary at these sites. Possible horizontal variations of communities, in a natural oligotrophic fen, were analysed by characterizing the methanogens from two well-defined microsites: Eriophorum lawn and Hummock. Community structures were studied at two different layers of the fen, showing, respectively, high and low methane production. The structure of methanogen populations was determined using molecular techniques targeting the 16SrRNA gene and combined denaturing gradient gel electrophoresis (DGGE) and restriction fragment length polymorphism (RFLP) analysis. Results subjected to non-metric multidimensional scaling (MDS), diversity indices calculation and phylogenetic analysis revealed that upper layer communities changed with site while deeper layer communities remained the same. Phylogenetic analyses revealed six different clusters of sequences grouping with only two known orders of methanogens. Upper layers of Hummock were dominated by sequences clustering with members of Methanomicrobiales and sequences dominating the upper part of the Eriophorum lawn were related to members of the order Methanosarcinales. Novel methanogenic sequences were found at both sites at both depths. Vegetation characterizing the microsites probably influences the microbial communities in the layers of the fen where methane is produced.     

Experimental investigation of drought induced acidification in a rich fen soil

Intact rich fen soil cores with controlled water levels near thesurface were installed in an open greenhouse. To simulate short termsummer drought, water levels were lowered (20 cm) after two weeks inhalf of the cores (experimental cores) and remained near the surface inthe other half (blanks). After two more weeks, the water levels werebrought back to the surface in the experimental cores and remainedthere for another two weeks. In the blanks, reduction and alkalinizationof the top peat layer occurred. In the experimental soil cores oxidationand acidification started within one week after drawdown. An indicationfor a drought induced rise in soluble reactive phosphorus has beenfound. The velocity of the acidification process illustrates the dynamicnature of the hydrochemical conditions in fen soils during drought. Theprocesses controlling the acid/base status of rich fen, the effect ofdrought induced acidification on P availability and the significance forthe vegetation are discussed.     

Groundwater and surface water hydrology of a small groundwater-fed fen

The hydrology of a small quaking fen was investigated by measuring all components of the water budget. Water-level measurements indicated that the fen is a focus for groundwater discharge, and that there is a lateral (subsurface) flow from the fen toward surrounding areas during most of the year. The hydrology, however, is strongly influenced by man, as water tables are maintained during dry periods by pumping water into the area. This action results in a reversal of flow patterns as surface water from a ditch infiltrates the fen and groundwater recharge occurs.Two approaches for calculation of groundwater and surface water terms were compared. The two procedures differ in the way that vertical and horizontal hydraulic conductivity of the soil is calculated. Hydraulic conductivity estimated from in situ tube experiments was one to two orders of magnitude lower than hydraulic conductivity estimates from numerical water budget analyses.Four one-month periods were selected for calculations of complete water budgets. Results of calculations of water flow were compared in respect to the overall error in the water budget (calculated as percent difference between inputs and outputs). Water budgets calculated from data on hydraulic conductivity gave high residual errors (56.% ± 16.3%). When hydraulic conductivity was derived from numerical analyses, the errors were very small (2.8% ± 3.1%) and the difference between inputs and outputs over a period of 127 days was only 2.6 mm (0.45%).     

Impact of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve (the Netherlands)

Restoration of rich fens is commonly attempted through local-scale measures, such as removal of sod or blockage of ditches. However, regional-scale restoration measures, that aim to re-establish the original hydrology in which rich fens developed, might have a more long-lasting effect. We investigated the effect of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve in the Netherlands. We compared water quality and vegetation composition of the fen before and after the restoration measures, almost 30 years apart. Overall rich fen species increased and although this indicates the desired increased supply of fresh mineral-rich groundwater to the fen, continued succession towards poor fen vegetation has not been prevented in the entire fen. Despite sod layer removal, we observed an increase in a Polytrichum-dominated vegetation in patches that are primarily fed by rainwater. Our findings confirm results from a previous study which showed that brackish palaeo-groundwater is still contributing substantially to the water balance of the fen, especially in periods of precipitation deficit. We conclude that the local- and regional-scale restoration measures have been successful in increasing the abundance of rich fen species in parts of the fen. However, considering the pressures of climate change and high atmospheric N-deposition on the fen, it is uncertain whether rich fen species can be sustained in quite nutrient-poor conditions in the future. Therefore, there is a need for continued management that keeps the nutrient-poor and mineral-rich conditions of the fen intact.

     

Differential and reversible responses of common fen meadow species to abandonment

Abstract. We studied the effects of abandonment on two common fen plant species. In mown and a chronosequence of abandoned fen meadows spanning 35 yr, we measured fitness traits of the sedge Carex davalliana and the forb Succisa pratensis. Cessation of mowing had little effect on fitness traits and seed production of C. davalliana, but seedling density decreased more than threefold. Population density of S. pratensis decreased with increasing community biomass, but was not affected by the cessation of mowing. However, flowering frequency increased threefold and seed production was 20% higher in fallow meadows. Consequently, seedling density of S. pratensis increased nearly threefold after abandonment. However, these changes were not dependent on the age of the fallow. In a common garden and germination experiment, we found no differences in either species between plants from fallows and mown fen meadows, except for the height of the flowering stalk of S. pratensis. The combined results from the common garden experiment and the field studies indicate that changes in fitness traits observed in fallows were mostly phenotypic and likely to be reversible. If other species react in similar ways, there is a high potential for re‐establishing traditional fen meadow communities from fallows by mowing.     

Species trait shifts in vegetation and soil seed bank during fen degradation

Fens in Central Europe are characterised by waterlogged organic substrate and low productivity. Human-induced changes due to drainage and mowing lead to changes in plant species composition from natural fen communities to fen meadows and later to over-drained, degraded meadows. Moderate drainage leads to increased vegetation productivity, and severe drainage results in frequent soil disturbances and less plant growth. In the present article, we analyse changes in plant trait combinations in the vegetation and the soil seed bank as well as changes in the seed bank types along gradient of drainage intensity. We hypothesize that an increase in productivity enhances traits related to persistence and that frequent disturbance selects for regeneration traits. We use multivariate statistics to analyse data from three disturbance levels: undisturbed fen, slightly drained fen meadow and severely drained degraded meadow. We found that the abundance of plants regenerating from seeds and accumulating persistent seed banks was increasing with degradation level, while plants reproducing vegetatively were gradually eliminated along the same trajectory. Plants with strong resprouting abilities increased during degradation. We also found that shifts in trait combinations were similar in the aboveground vegetation and in soil seed banks. We found that the density of short-term persistent seeds in the soil is highest in fen meadows and the density of long-term persistent seeds is highest in degraded meadows. The increase in abundance of species with strong regeneration traits at the cost of species with persistence-related traits has negative consequences for the restoration prospects of severely degraded sites.