Calcareous Fens Research Articles

Survival of an Endangered OrchidLiparis loeseliiin Habitats with Different Water Level Fluctuations

Liparis loeselii (L.) Rich. is an endangered orchid species which occurs in wetland habitats. For successful conservation of this orchid it is necessary to recognize its adaptive traits and special habitat requirements. Therefore, we examined morphological and anatomical traits in relation to the water level, cover of vascular plants and seed viability of L. loeselii in habitats with different water level fluctuations. Field studies of L. loeselii were carried out in nine localities and four habitat types: alkaline fen, calcareous fen with Cladium mariscus, transition mire and quaking bog. The fluctuations of seasonal water level were defined in the range from dry substrate to short time flooding (up to two weeks). Leaf length and width of 30 flowering specimens of L. loeselii as well as angle between the leaf blade and the axis of the inflorescence were measured at each locality. Seed viability and root anatomy were examined in the laboratory. The leaf angle was significantly affected (P < 0.05) by water level in the studied habitat. The leaf length to width ratio in each population of L. loeselii did not show significant differences between the years, but was characteristic for the habitat type. L. loeselii sensitivity to the long-term flooding in the habitat is associated with a lack of aerenchyma in its roots. During short-term flooding specimens of L. loeselii can survive due to a shallow root system and hyponastic leaf movements. As evidenced by seed viability, the most favourable growth conditions for L. loeselii are in the habitats with partially water saturated substrate with balanced water supply.

Early and middle Holocene ecosystem changes at the Western Carpathian/Pannonian border driven by climate and Neolithic impact

Travertine deposits are unique archives for multidisciplinary studies of past climate changes, associated vegetation development and the evolution of human societies. Despite their high potential in palaeoecological and palaeoclimate reconstructions, investigations of travertines are rather scarce in central Europe and particularly in Slovakia. Therefore, this study focused on a travertine deposit situated on the border between the Pannonian Basin and the Western Carpathians in a small valley in Santovka village (SW Slovakia), which is unique due to the presence of archaeological artefacts with known radiocarbon ages in the palaeoecological profile. Using a multidisciplinary approach combining macrofossil, pollen, mollusc, lithological and geochemical analyses, this study investigated climate–human–vegetation interactions. The Holocene onset was marked by the early arrival of oak trees; however, forest‐steppe with a high representation of pine predominated until 9880 cal. a BP, followed by an expansion of temperate trees. The local ecosystem changed around 8600 cal. a BP when the valley was probably dammed by a travertine accumulation, probably resulting in the existence of a small travertine lake. This was associated with wetter climatic conditions, which were also documented in other sites in the Western Carpathians at that time. Surrounding temperate forest possibly retained a certain degree of openness, or local steppe habitat may have persisted on adjacent loess terraces until the neolithization of the area. Archaeological evidence represented by a ceramic shard dated to 7339 cal. a BP suggests the first appearance of humans at the site, yet pollen analysis records a significant change in vegetation first at 6650 cal. a BP. The local ecosystem records an abrupt change linked with human settlement earlier, at c. 7000 cal. a BP. Deforestation activities of the Neolithics resulted in the formation of an open calcareous fen occupied by numerous light‐demanding mollusc species. The present study provides new important data about the spread of temperate trees at the onset of the Holocene, about further vegetation changes caused by activities of the first Neolithic farmers and about climate changes in the region of southwestern Slovakia.

Floristics of the Abrams Creek Wetlands, a Calcareous Fen Complex in Winchester City and Frederick County, Virginia

ABSTRACT The 24-ha Abrams Creek Wetlands (Winchester City and Frederick County, Virginia) is an array of fen, swamp, and disturbed transitional ecosystems underlain by limestone and dolostone bedrock. Soils of the area are generally characterized by exceptionally high levels of calcium (>10,000 ppm). Floristic data were collected through monthly surveys during the 2012–14 growing seasons and plot sampling in representative locations. We documented 296 vascular plant species during the inventory period; eight species found previously were not relocated. The 304 total species comprised 206 genera in 78 families. Of these, 55 species were graminoids (27 grasses, 21 sedges, 7 rushes). Obligate or facultative wetland species comprised 43% of the list. The 216 native species represented 71% of the total and included 20 listed as rare in Virginia. Plot data revealed that native species represented 72–99% of the total vegetative cover in the communities sampled. Floristic quality of the 12 constituent sites was ...

Arcto-Alpine Species at Their Niche Margin: the Western Carpathian Refugia of Juncus castaneus and J. triglumis in Slovakia

Juncus castaneus and J. triglumis are umbrella species of moist calcareous tundra and arctic-alpine initial fens (the Caricion atrofusco-saxatilis alliance), considered to be glacial relicts in the central-European Mts. Here we report new findings from the Western Carpathians (Slovakia). We analysed species composition of plant communities with the target Juncus species in a wide geographical context, using 20 available vegetation-plot records from the Carpathians, 711 records from other European regions, and formal definitions of fen alliances taken from a pan-European vegetation synthesis. The first gradient of non-metric multidimensional scaling (NMDS) differentiated alpine and arctic samples. The second principal gradient between Caricion atrofusco-saxatilis and other vegetation types was of similar importance. Records from the Western Carpathians assumed a marginal position in the gradient space, while records from the Eastern Carpathians (Romania) appeared to be similar to those from the Alps. Generally, Carpathian records did not match the formal definition of the Caricion atrofusco-saxatilis alliance. Although the arctic-alpine rush species persist occasionally in spring, fen and tundra microrefugia in the Carpathians, they do not belong in similar plant communities as in the Alps or in the Arctic.

Natura 2000 protected habitats, Massaciuccoli Lake (northern Tuscany, Italy)

ABSTRACTThe Massaciuccoli Lake (northern Tuscany, Italy) Natura 2000 habitat map (1:10,000) was compiled from photo-interpretation and recent phytosociological studies, integrated by field surveys of the vegetation units. Conventional geographical information system procedures were used to select and manage spatial information. The following attributes were assigned to each map polygon: (i) vegetation type, (ii) habitat typology and (iii) percentage cover of the habitat type. Habitat types covering polygons smaller than 50 m2 were treated as points. A total of nine Natura 2000 habitat types were identified and mapped; they cover almost 20% of the study area. The results show that of all sites on the Italian peninsula, Lake Massaciuccoli Calcareous fens with Cladium mariscus covers the largest surface area and is crucial for the national conservation of this habitat type. It is also of priority importance in Europe.

Effect of environmental factors on growth and physiological status of generative shoots of Cladium mariscus in a protected calcareous fen habitat

Effect of environmental factors on growth and physiological status of generative shoots of Cladium mariscus in a protected calcareous fen habitat

Sphagnum establishment in alkaline fens: Importance of weather and water chemistry.

Sphagnum expansion to alkaline fens has accelerated during the last decades in Europe, leading to changes in diversity, habitat distributions and carbon storage. The causes are still not clearly understood and involve an interplay between climate change, hydrology, nutrient supply and Sphagnum physiology. We conducted a 4-year field experiment in eight fens in Central European highlands and assessed survival and establishment of individual apical shoot fragments of S. flexuosum, S. warnstorfii and S. squarrosum transplanted along the microtopographical gradient. In a laboratory experiment, we tested combined effects of desiccation and high calcium bicarbonate concentration on Sphagnum survival. We found that in unflooded positions, living shoots of Sphagnum and brown mosses lowered [Ca2+] and pH in their capillary water, in contrast to dead fragments; yet without differences between species. Survival and expansion of Sphagnum fragments, which did not die of acute calcium toxicity during first weeks/months, was negatively affected by dry weather and alkaline water chemistry, reflecting Sphagnum intolerance to desiccation and to combined high [Ca2+] and pH. Shoot fragments expanded to patches only when precipitation was high. Interestingly, non-toxic concentration of calcium bicarbonate reduced desiccation damage in Sphagnum, probably through protection of membranes or other cell components. This mechanism would facilitate Sphagnum survival in elevated, frequently desiccated microhabitats of calcareous fens such as brown-moss hummocks. However, since water-retaining capacity of few Sphagnum shoots is insufficient to change water chemistry in its surroundings, surface acidification may occur only once the environment (e.g. sufficient humidity) enabled expansion to larger mats. Then, the retained rainwater together with hardly decomposable Sphagnum litter would separate mire surface from groundwater, speeding up successional shift towards poor fens. Sphagnum expansion to alkaline fens is therefore more likely in humid regions.

Anticipating extinctions of glacial relict populations in mountain refugia

Glacial relict populations at the rear-edge of species' distributions are expected to respond dramatically to climate warming, yet very few studies have compared their conservation status in current refugia. Here we combine population genetics with species distribution modelling to assess patterns and causes of extinction or persistence in two cold-adapted species, Salix hastata and Juncus balticus, which survived post-glacial retractions in calcareous fens of the Iberian Peninsula. In both species, we detected extremely-low genetic diversity and clonal strategies in red-listed populations of the most marginal region (Cantabrian Range), but high genetic diversity linked with sexual reproduction in populations from a less marginal region of the rear edge (Pyrenees). Genetic patterns were partially explained by past and present species´ climatic niches, more remarkably in the arctic-alpine S. hastata than in the boreo-atlantic J. balticus, suggesting different biogeographic history but similar sensitivity to global change. Our results show different magnitudes of extinction debt in regional populations that have survived in mountain refugia since the Last Glacial Maximum. Functional extinction of the most marginal populations can be explained by postglacial climate change and the historical decline of mire habitats. In contrast with the current trend of predicting future effects of climate change, we highlight that glacial relict populations might be currently going into extinction in climatically marginal regions. These populations can provide valuable information about the processes involved in species extinctions, improving our capacity to anticipate the effect of global change across regions and habitats.

Storage and release of road-salt contamination from a calcareous lake-basin fen, western Massachusetts, USA

Road salt (NaCl) applications to highways have increased stream sodium and chloride concentrations due to retention within watersheds. The mechanisms for retention and export of Na+ and Cl− from different environments are not fully understood. This field study examines the hydrologic and cation exchange processes that store and release Na+ and Cl− from a calcareous fen adjacent to a highway. Despite high concentrations of Ca2+ and Mg2+, elevated salt concentrations enable Na+ to occupy up to 15% of the cation exchange capacity of shallow peat. Calculations of selectivity coefficients show that Na+ preferentially exchanges with Mg2+, and Na+ can be desorbed under more dilute conditions caused by precipitation and snowmelt.Detailed sampling of surface and ground waters during three snowmelt events illustrate early releases of Na+ and Cl− at the onset of melting, with maximum fluxes coinciding with peak discharge. From 7 March through 4 April 2005, the flux of dissolved salt exiting the wetland amounts to 13% (Na) and 17% (Cl) of annual rock salt applied to the highway. For all of 2005, the total salt mass leaving the wetland via Kampoosa Brook is similar to the amount of road salt applied; 50% of the annual salt efflux occurred during the snowmelt season of March through May. In general, exported Na+ and Cl− correlate with the number of lane miles of highway crossing the watershed. Large rain events outside of winter months are more effective than snowmelt with reducing dissolved salts because snowmelt also introduces contamination. For this and other wetlands having alkaline geochemistry and high flushing rates, management strategies that reduce rock salt amounts to roadways will assist with reducing salt contamination to levels less toxic to vegetation and aquatic organisms.

The influence of vegetation structure on spider species richness, diversity and community organization in the Apšuciems calcareous fen, Latvia

La influencia de la estructura de la vegetacion en la riqueza de especies, la diversidad y la organizacion de las comunidades de aranas en el pantano en terreno calcareo de Apsuciems, en Letonia Se considera que los pantanos en terrenos calcareos son uno de los ecosistemas mas amenazados de Europa. Asimismo, son uno de los habitats con mayor diversidad, puesto que albergan una variedad de especies de plantas y animales increiblemente rica y diversa. No obstante, a pesar de su diversidad, los pantanos en terrenos calcareos se han estudiado poco, especialmente por lo que hace a los invertebrados, como las aranas. Debido a que son buenos indicadores, es interesante conocer su ecologia en habitats singulares y amenazados. Este estudio tiene como finalidad documentar la composicion y diversidad de las especies, familias y gremios de alimentacion de aranas en los estratos edafico y herbaceo del pantano calcareo de Apsuciems, y evaluar la influencia de la estructura de la vegetacion en la organizacion de las comunidades de aranas. En verano de 2012, recogimos aranas que habitan en el suelo utilizando trampas de caida y aranas que habitan en la hierba con redes entomologicas. En total, en el pantano de Apsuciems se recogieron 2.937 aranas pertenecientes a 19 familias y 80 especies. Nuestros resultados indican que las especies y familias de aranas tienden a estratificarse a lo largo de la estructura vertical del habitat; la composicion de aranas en el estrato edafico diferia de la del estrato herbaceo. Por el contrario, la estructura de los gremios de alimentacion era parecida en el estrato edafico y el estrato herbaceo. Cada uno de los dos estratos estudiados presentaba gremios parecidos en proporciones similares. Nuestros resultados tambien pusieron de manifiesto que la composicion de aranas diferia considerablemente entre distintas partes del gremio y que gran parte de esta variabilidad se podia explicar por las propiedades arquitectonicas del habitat. En general, cuanto mas diversa era la vegetacion, mayor era el numero de aranas.

Environmental predictors of woody plant encroachment in calcareous fens are modified by biotic and abiotic land‐use legacies

Summary Woody plant encroachment in grasslands is a world‐wide concern. Assertions that abiotic stress reduction facilitates encroachment are not universally supported. To devise restoration and management strategies, the ability of stress reduction, in the context of co‐occurring biotic land‐use legacies, needs to be assessed to predict shrub cover. We determined whether legacy‐induced reduction in Carex stricta (a potential facilitator of shrub encroachment and attractor of animal dispersers) and an increase in herbaceous invaders (potential competitors) altered the ability of stress reduction to predict woody plant cover in ploughed and never‐ploughed plots within 11 Wisconsin (USA) calcareous fens. We hypothesized that drier conditions (low saturation stress) and higher nutrient availability associated with ploughing would be associated with high woody plant cover; that higher cover of herbaceous invaders associated with ploughing would predict low woody plant cover, and C. stricta cover predicts high woody plant cover in saturated, never‐ploughed plots. Restricted maximum‐likelihood (REML) multiple regression was used to determine the importance of interactions among ploughing, saturation, nutrients and the two biotic legacies in predicting woody richness and cover, as well as cover by dispersal syndromes and individual species. Unexpectedly, encroachment by animal‐dispersed species was higher in never‐ploughed plots, while wind‐dispersed species had no relationship with ploughing. Animal‐dispersed species cover decreased with saturation stress in never‐ploughed plots, only. Carex cover was associated with increased encroachment by animal‐dispersed species, mainly in never‐ploughed highly saturated plots. Herbaceous‐invasive cover was associated with decreased encroachment. Wind‐dispersed species cover declined with increasing saturation stress, with responses varying among species. Synthesis and applications. The results suggest that the impacts of stress reduction on encroachment are not uniform and are modified by biotic legacies. We suggest that impacts of restoring stressful abiotic conditions on encroachment may not be known until the impacts on competitors and facilitators are understood.

Testing inter‐regional variation in pH niches of fen mosses

AbstractQuestionMosses are important ecosystem engineers in mires. Their pH optima and tolerances presented in the literature differ between regions, even though the high dispersal ability of mosses should prevent local adaptations. Nutrient availability is sometimes suggested as a reason for local niche differentiation. Are patterns in moss niche diversification, optima and tolerance with respect to pH consistent between regions differing in nutrient availability and abundance of calcareous bedrock?LocationWestern Carpathians (Slovakia, a predominantly calcareous P‐ and K‐poor region), Bohemian Massif (Czech Republic, a predominantly crystalline, P‐ and K‐rich region).MethodsAnalyses of an original stratified data set and a large database using species response curves.ResultsAlthough the above two regions differ in abundance of calcareous fens, species pH optima (either original or adjusted according to calcium level) were consistent between the regions and data sets. Calcium‐tolerant peat mosses (Sphagnum warnstorfii, S. contortum, S. teres) showed an optimum at pH 6 and rather narrow niches. Sphagnum fallax was the most acidophilous, and both S. palustre and S. flexuosum had rather wide intermediate niches. The pH amplitudes were largely consistent between the regions (especially when adjusted pH was used), but S. fallax and Aulacomnium palustre exhibited wider niches in the Bohemian Massif. Despite no significant difference in niche optimum and width, some more nutrient demanding and more generalist species occurred at higher frequency in specific parts of the pH gradient in the Bohemian Massif, while some fen specialists showed the opposite pattern.ConclusionsThe small stratified data set and the database data set yielded rather consistent results regarding fen moss niches in the Bohemian Massif and the Western Carpathians. The consistency in pH niches corresponds to the lack of large‐scale genetic differentiation in moss species. The observed inter‐regional differences in species response curves may thus reflect an increased frequency of competitively strong species in certain parts of the pH/Ca gradient in the nutrient‐richer Bohemian Massif rather than genetically conditioned niche shifts. Expansion of these species was probably triggered by potassium enrichment that took place in the 1970s–1980s. Inter‐regional differences in species response curves were observed in both data sets, but in the large database data set they were more frequently statistically significant.

Soil thermal buffer and regeneration niche may favour calcareous fen resilience to climate change

Calcareous fens are azonal habitats permanently saturated by groundwater. This is expected to have a buffer effect on soil temperature, alleviating climate changes and allowing plant communities to occupy diverse climatic regions. We analysed the extent of such buffering and its relation with a relevant plant trait, the seed germination niche breadth, along altitudinal gradients in fens of the Cantabrian Mountains (Spain) and the Western Carpathians (Slovakia). In each fen we recorded soil temperature for several years and compared it with WorldClim predictions for air temperature. We also collected seeds from five Cyperaceae fen specialists to evaluate the influence of soil temperature on germination. Although the soil temperatures and WorldClim predictions were strongly correlated, their absolute values differed substantially, showing a narrower thermal amplitude and warmer minimum winter temperature in the soil. The greatest differences in soil temperature and germination niche breadth were those between mountain regions. Narrower germination niches correlated with the colder Slovak winter. Our results suggest that the soil thermal buffer allows species to escape frost temperatures in winter, but also high summer temperatures in warm regions, explaining their wide distribution ranges. The warm regeneration niche does not match the cooler soils, but shows variability and potential for adaptation. While these findings support resilience to climate warming, changes in precipitation rather than temperature seem to be the main threat for fen persistence.

Drivers of aquatic macroinvertebrate richness in spring fens in relation to habitat specialization and dispersal mode

AbstractAimsThe aim was to identify the main drivers of aquatic macroinvertebrate species richness in spring‐fen habitats (i.e. groundwater seepage wetlands) because these habitats are among the most threatened temperate biodiversity hotspots.LocationIsolated spring fens in the western Carpathian Mountains.MethodsAssemblages of Tricladida, Clitellata, Mollusca, Ephemeroptera, Plecoptera, Trichoptera and Diptera were sampled at 48 fens distributed evenly along a gradient of water mineral richness and grouped according to habitat specialization and dispersal mode. Several physicochemical parameters that have been reported to be the main drivers of species distribution were recorded for each site, along with radiocarbon measurements of the absolute age of the sites. The numbers of species in the taxonomic groups analysed were modelled as a function of the predictors via multiple linear regressions.ResultsWe achieved a notably higher sampling efficiency than had been used in previous spring aquatic macroinvertebrate studies. In total, we collected and identified 255 species within 331 taxa from &gt; 235,000 individuals. The number of species in all taxonomic groups increased with water discharge but the highest predictive power was obtained with water redox potential, which explained as much as 55.7% of the specialist species richness variance. We found contrasting and systematic differences in the importance of predictors related mainly to the level of species habitat specialization. Species richness of spring‐fen specialists was strongly determined by the main environmental gradient of change in groundwater chemistry, while generalists primarily reflected habitat stability linked to higher water discharge, habitat size and absolute age.Main conclusionIsolated island‐like spring fens can harbour unusually species‐rich assemblages of aquatic macroinvertebrates, the species richness of which is shaped by contrasting mechanisms dependent mainly on habitat specialization and also partly on dispersal mode. The richness of habitat specialist species seen at calcareous fens indicates their conservation priority.

Multi‐species competition experiments with peatland bryophytes

AbstractQuestionSpecies interactions are one of the processes determining composition of plant communities. We used the community density series method to study competition in a multi‐species community of bryophytes common in calcareous fens. The succession of mires is driven by Sphagnum species, which are supposedly superior to brown mosses in competition for resources and space, but little is known about the environmental conditions in which brown mosses can prevail when subject to neighbour interactions. How are interactions among peatland bryophytes affected by the environment?LocationField and garden experiments near Uppsala in mid‐eastern Sweden.MethodsTo examine the effects of environment on competition and competitive hierarchies we assembled multi‐species communities of ten bryophyte species from shoot fragments (brown mosses and Sphagnum species) at two densities and grew them on three types of peat (representing poor, intermediate and rich fens) under dry or wet conditions in a garden experiment and along pH and wetness gradients in the field.ResultsA multivariate analysis of the garden experiment showed that community composition was affected by peat type and wetness and their interactions. The brown mosses performed better in wet and rich fens, the Sphagnum species in drier and poorer fens. The Sphagnum species were overall the best competitors.ConclusionsThe experiments demonstrated contrasting responses of brown mosses and Sphagnum to properties of the microhabitat. Sphagnum species were generally less affected by competition than the brown mosses. Sphagnum species were competitive in habitats typically dominated by brown mosses and even responded positively to crowding. This can explain why Sphagnum can invade calcareous fens. In contrast, brown mosses performed poorly in habitats more typical of Sphagnum species.

Explaining species distributions by traits of bryophytes and vascular plants in a patchy landscape

The species pool theory helps us understand species distributions at different geographical scales. In theory, species pools consist of species passing the filters between different geographical scales. Filters of dispersal and environment act between the regional and local pools, while filters of biotic interactions act between the local and the community pools. We studied bryophytes and vascular plants restricted to rich (calcareous) fens that occur as patches in a forested landscape. We then examined their frequencies and abundances at the local and regional scales and related the results to traits important for dispersal and competition. Our results show that weft-forming bryophytes and vascular plants with far-creeping rhizomes have higher local frequency than predicted from their regional frequency. Dispersal traits did not explain any variation in the distributions. This indicates that environmental and biotic filters are more important than dispersal limitation at the regional scale, and that clonal expansion is the most important factor for high frequency and abundance at the local scale in these nutrient poor habitats.

Restoration mowing of a calcareous fen — response of species to re-applied management measures

AbstractCalcareous fens are habitats that are well-adapted to extreme ecological conditions (water with a very high calcium content). The vegetation response following the application of restoration measures (mowing, removal of shrubs) in a calcareous fen (site Sliačske travertiny, western Carpathians) was observed over six years in six permanent plots. Three plots were established in an area strongly invaded by reeds (Phragmites australis), where restoration mowing was introduced, and three plots were established in an area overgrown by willows, where the shrubs were partly removed at the beginning and no other management measures were subsequently applied. Indirect and direct gradient analyses (Principal Component Analysis and Redundancy Analysis) and General Linear Models showed that species composition in the mown reed area evolved towards the typical composition of calcareous fens, although reeds were still dominant in the canopy. The overall species richness, as well as number of fen indicator species increased here, especially on the most-detailed scale of 0.25 × 0.25 m. In contrast, the species composition in the unmown area with willows developed towards a higher abundance of wetland generalists. The species richness of vascular plants increased on the scale of 2 × 2 m, but the number of bryophyte species decreased on the scale of 0.25 × 0.25 m and the number of fen indicators species remained unchanged. Our survey showed that mowing can be used for the restoration of calcareous fens invaded by reed, but the total supression of reed can not be achieved in short time period. Furthermore, the occasional removal of shrubs on overgrown calcareous fens is not a feasible method of habitat management.

Using multi-proxy palaeoecology to test a relict status of refugial populations of calcareous-fen species in the Western Carpathians

The distribution pattern of relict and specialised species in calcareous fens was revealed to be non-stochastic, with ancient fens harbouring more of these species than younger ones. This phenomenon could be caused by long-lasting in situ survivals over millennia, but direct palaeoecological evidence is lacking. We addressed the question whether at least some ancient calcareous fens indeed retained open-fen patches throughout the Holocene, using a palaeoecological approach involving proxies with different taphonomies (pollen, vascular plants, bryophytes, molluscs). We identified three old fens in the Western Carpathians, where several postglacial relict species have recently been found, and we reconstructed their histories with respect to sedimentary processes, vegetation structure and dynamics of relict species. The development at all the sites started with a (semi)-open fen community dominated by sedges and brown mosses. The site with the highest recent number of relict species was reconstructed to harbour open patches continually since the late Glacial to the present, including the middle Holocene when open-fen patches were restricted. By contrast, at the site with the lowest recent number of relict species, a large sedimentary hiatus suggested peat mineralisation or erosion that prevented the survival of light-demanding species. At all the sites, characteristic snails of European Glacial periods occurred during fen initiation, but disappeared around the early/middle Holocene transition. The probability of a relict species being present in a modern fen community increases with fen age, but it also depends on the continual existence of open-fen patches and peat accumulation throughout the middle Holocene.

Stress and land‐use legacies alter the relationship between invasive‐ and native‐ plant richness

AbstractQuestionsDoes the driver of native richness impact invasion–diversity relationships? In high stress systems, do negative invasion–diversity relationships emerge from biotic resistance (as predicted by the diversity–resistance hypothesis) or from stress acting as a selective driver of native richness? Do invasion–diversity relationships change when abiotic and biotic legacies, rather than stress, act as non‐selective drivers of richness?LocationCalcareous fens, Wisconsin, USA.MethodsWe compared plot‐level relationships between native and invasive species richness in 220 plots in 11 calcareous fens, six of which had stress alleviation and community impoverishment due to historic ploughing. We measured nutrient availability (resource stress) and saturation stress (non‐resource stress), native richness and invasive richness in each plot.ResultsResidual maximum likelihood (REML) regression found a negative correlation between native and invasive richness in never ploughed plots, but no relationship was found in ploughed plots. REML multiple regression found that after accounting for saturation and nutrients, there was no relationship between native and invasive richness in ploughed or never ploughed plots. Saturation stress predicted low invasive richness and high native richness in never ploughed plots. Time since abandonment did not predict invasive richness. Non‐metric multidimensional scaling (NMDS) found most invasive species present only in areas with the least saturation stress.ConclusionsNegative relationships between native and invasive richness can result when the main driver of native richness favour native species (such as stress), and therefore may not support the diversity–resistance hypothesis. When the main driver of native richness does not select between native and invasive richness, there may be no relationship between native and invasive richness, even at very small spatial scales.

Diversity of grass-dwelling spiders (Arachnida: Araneae) in calcareous fens of the Coastal Lowland, Latvia

Calcareous fens have a high conservation priority in the European Union. They are very unique, very sensitive and very rare habitats in Latvia as well as in many other European countries. Because of their rarity, many organisms living in calcareous fens are nowadays considered threatened. The same is applied to spiders. Spiders have been suggested as good biodiversity indicators because they have numerous direct and indirect relationships with other organisms. Only few investigations have been carried out on fen inhabiting spiders. The knowledge of grass-dwelling spiders is especially lacking. Thus the aim of this study was to evaluate grass-dwelling spider diversity in several calcareous fens of Latvia, compare these fens and to find out the habitat features that might affect grass-layer inhabiting spiders. The research was carried out in eight calcareous fens located in the Coastal Lowland of Latvia. A total of 760 spiders from nine families and 20 species were collected with a sweep net. Two of the most abundant spider species were Dolomedes fimbriatus (Clerck, 1757) and Tibellus maritimus (Menge, 1875). Diversity indices suggested that the grass-dwelling spider community consists of few abundant species and numerous rare species. Correlation analysis as well as DCA showed that plant species diversity did not significantly affect spider species richness and diversity, although at the same time there were a lot of significant associations between spiders and individual plant species. It was shown that various spider species responded very differently to the presence of particular plant species, and thus habitat structural heterogeneity emerges to be an important factor influencing the grass-dwelling spider diversity and community structure. Correlation analysis also revealed that spider abundance was negatively affected by the vegetation height and wind speed.