Recent changes in the plant composition of wetlands in the Jura Mountains

Aim

To assess vegetation changes in montane fens and wet meadows and their causes over 38 years.

Location

Wetlands, Jura Mountains (Switzerland and France).

Methods

Plots were inventoried in 1974 and re‐located in 2012 (quasi‐permanent plots) on the basis of sketches to assess changes in plant communities. The 110 plots belonged to five phytosociological alliances, two in oligotrophic fens (Caricion davallianae, Caricion fuscae) and three in wet meadows (Calthion, Molinion, Filipendulion). Changes between surveys were assessed with NMDS, and changes in species richness, Simpson diversity, species cover and frequency and the causes of these changes were evaluated by comparing ecological indicator values.

Results

Changes in species composition varied between alliances, with a general trend towards more nutrient‐rich flora with less light at ground level. Species diversity declined, with a marked decreasing trend for the typical species of each alliance. These species were partly replaced by species belonging to nitrophilous and mesophilous grasslands. However, no trend towards drier conditions was detected in these wetlands. The largest changes, with an important colonization by nitrophilous species, occurred in the Swiss sites, where grazing was banned 25 years ago. As a result of floral shifts, many plots previously belonging to fens or wet mesotrophic meadows shifted to an alliance of the wet meadows, generally Filipendulion. Moreover, communities showed a slight trend towards more thermophilous flora.

Conclusions

The investigated wetlands in the Jura Mountains have suffered mainly from eutrophication due to land‐use abandonment and N deposition, with a loss of typical species. Areas with constant land use (grazing or mowing) showed less marked changes in species composition. The most important action to conserve these wetlands is to maintain or reintroduce the traditional practices of extensive mowing and livestock grazing in the wetlands, especially in areas where they were abandoned 25 years ago. This previous land‐use change was intended to improve fen conservation, but it was obviously the wrong measure for conservation purposes.     

Plant communities along environmental gradients of high‐arctic mires in Sassendalen,Svalbard

Abstract. The wet to moist bryophyte‐dominated vegetation of Sassendalen, Svalbard, was classified into seven communities. These communities were grouped into (1) Cardamino nymanii‐Saxifragion foliolosae marsh; (2) Caricion stantis fen; (3) Luzulion nivalis snowbed – including manured vegetation corresponding to moss tundras. All communities have a basically arctic distribution. Marshes are developed in habitats with a water table above the bryophyte vegetation surface and fens on sites with a water table level high above the permafrost but below the bryophyte surface. Moss tundras normally have no standing water table, but in Sassendalen they have a low water table due to their development on less steep slopes than in their normal habitat near bird cliffs. CCA confirms that the standing water level is the prime differentiating factor between the alliances, while aspect favourability and permafrost depth differentiate between the fen communities and temporary desiccation is important for the Catoscopium nigritum community. Carex subspathacea is a characteristic fen species in the absence of other Carex species dominating elsewhere in the Arctic. Arctic marshes are linked to an extremely cold environment. They have a very low species diversity with a few species dominating; Arctophila fulva, Pseudocalliergon trifarium, Scorpidium scorpioides and Warnstorfia tundrae are character species. Moss tundra as defined here appears to be restricted to Svalbard and, probably, neighbouring Novaya Zemlya. This may be due to the absence of rodents and the high seabird density, which is related to the mild sea currents reaching further to the north here and which implies manuring of surrounding ecosystems. Manuring in a very cold environment produces moss carpets with a thin active layer and accumulation of thick peat layers without a standing water level. In Sassendalen the role of arctic seabirds is replaced by Svalbard reindeer which are nonmigratory and are concentrated to favourable grazing areas where their manuring effect is intense. Their long‐term manuring effect probably explains the occurrence of moss tundras in this weakly rolling landscape where seabird colonies are absent.     

Patterned fens in Scotland: evidence from vegetation and water chemistry

Mires with attributes similar to the patterned fens of boreal continental regions have recently been reported from northern Scotland. This paper reports on the vegetation and water chemistry of 18 of these sites. Most of the 18 mires displayed remarkable uniformity in their vegetation, with Carex lasiocarpa being a main character species. Major variation of plant communities is associated with microtopographical niches, similar to those found on ombrotrophic mire systems and secondarily with pH and conductivity of surface waters. Nine vegetation noda are described and compared with existing phytosociological associations and National Vegetation Classification (NVC) communities. The dominant Sphagnum - Carex communities are intermediate between the Oxycocco-Sphagnetea and the Caricion lasiocarpae and are thus difficult to assign to existing associations or to NVC communities. Although there is a large variation in pH of surface waters (3.9–6.6), mean measurements for terrestrial and aquatic communities are 5.12 and 5.51 respectively. pH levels are comparable with poor fen systems elsewhere in Britain and slightly higher than patterned fens in continental regions of Europe and North America. The vegeta-tional and chemical attributes of these sites therefore confirm the existence of true patterned fen systems in the British Isles.     

Secondary succession in a Swiss mire after a bog burst

Severe natural disturbances can lead to the recovery of the original vegetation or the shift to new vegetation types. While post-disturbance succession is well documented for regularly disturbed ecosystems, little is known about the pathways and rapidity of vegetation dynamics after rare events such as peat mass movements in bogs. We monitored the floristic changes in a mire subject to a bog burst in 1987 for two decades through the repeated sampling of permanent plots. The mean species number per plot increased continuously, while the evenness increased only in the first decade and then slightly decreased. Declining species were mostly mire species, while colonist species were mostly wet meadow species. Species turnover was higher in the first decade after the disturbance, and was also higher in the area of peat erosion than in the area of peat accumulation. Changes in plant species composition indicate a succession towards tall-forb vegetation (Filipendulion), acidic fen vegetation (Caricion fuscae) and swamp willow forest (Salicion). We conclude that the effects of the disturbance are still ongoing, and that the mire’s potential for recovery is therefore difficult to predict.     

Dynamics or constancy in Sphagnum dominated mire ecosystems? A 40‐year study

Traditionally mire ecosystems (especially bogs) have been viewed as stable systems with slow changes in the vegetation over time. In this study the mire Åkhultmyren, south‐central Sweden was re‐investigated in 1997 after 40 yr of continued natural development. The results show a high degree of dynamics in a Sphagnum dominated bog and fen. Altogether 97 vascular plant and bryophyte species were recorded in the two inventories of the bog and poor fen vegetation. pH and electrical conductivity in the mire water were also surveyed. In 1997 we found 10 new species and that 8 species had disappeared since 1954 but the over‐all mean number of species per plot (size 400 m²) had hardly changed. However, 21% of the species increased and 21% decreased significantly in frequency. Most of the species that decreased in frequency were low‐grown vascular plants, most common in wet microhabitats. Vascular plant species that increased in frequency included trees (defined as >1.3 m in height) and were generally taller than the unchanged or decreasing species. The frequency of dwarf shrubs and hummock bryophytes increased too. Areas with an initial pH of 4.5–5.0 showed the strongest decrease in pH, coinciding with an enlarged distribution of some Sphagnum species. The species diversity increased on the bog, but decreased in the wettest parts of the fen, where the pH also decreased. Species with unchanged or increasing frequency often showed high capacity to colonise new plots. On average the sum of gains and losses of species in the plots in 1997 was ca 50% of the species number in 1954. The vegetation changes indicate a drier mire surface and an increased availability of nitrogen. The increased tree cover may have triggered further changes in the plant cover.     

Differential recovery of above‐ and below‐ground rich fen vegetation following fertilization

Abstract. For seven years we studied the recovery of vegetation in a Belgian P limited rich fen (Caricion davallianae), which had been fertilized with nitrogen (200 g.m^?2) and phosphorus (50 g.m^?2) in 1992. The vegetation in this fen has low above‐ground biomass production (< 100 g m^?2) due to the strong P limitation. Above‐ground biomass was harvested from 1992 to 1998 and P and N concentrations measured. In 1998, below‐ground biomass was also harvested. The response to fertilization differed markedly between below‐ and above‐ground compartments. Above‐ground, P was the single most important factor that continued to stimulate growth 7 yr after fertilization. Below‐ground, N tended to decrease live root biomass and increase dead root biomass and seemed to have a toxic effect on the roots. In the combined NP treatment the stimulating effect of P (an increase of live root biomass) was countered by N. The 1998 soil analysis showed no difference in soil P in the plots. Thus, Fe hydroxides are not capable of retaining P in competition with fen vegetation uptake. However, higher capture of P in root Fe coatings from N plots may partially explain this negative N effect. The results suggest that N root toxicity will be amplified in strongly P limited habitats but that its persistence will be less influenced by P availability. This mechanism may be a competitive advantage for N₂ fixing species that grow in strongly P limited wetlands.     

Nutrient limitation in species-rich lowland fens

Abstract. Nitrogen, phosphorus and potassium were supplied to some Belgian fens of varying nutrient status and productivity. Plant growth in the lowest productive fen with a species-rich Caricion davallianae vegetation was strongly P-limited. N was ineffective when applied alone, but increased the effect of P-addition when applied together. Summer biomass and plant nutrient concentrations were monitored for four years, and showed partial recovery of nutrient limitation. In a more productive fen dominated by Carex lasiocarpa and in a fen meadow, nutrient limitation was less strong. N limited growth in the productive fen, and N and K were co-limiting in the fen meadow. The P-concentration in the productive fen vegetation showed a marked increase after P-fertilization, but it did not result in higher standing crop. The significance of P-limitation for the conservation of species rich low productive fens is discussed. P-limitation may be an essential feature in the conservation of low productive rich fens: because it is less mobile in the landscape than N and/or because it is an intrinsic property of this vegetation type. Plant nutrient concentrations and N:P-ratios may be used as an indication for the presence and type of nutrient limitation in the vegetation. We found N:P-ratios of 23 to 31 for a P-limited site and 8 to 15 in N-limited sites. This was in agreement with critical values from the literature: N:P > ca. 20 for P-limitation and N:P < 14 for N-limitation. Thus, this technique appears valid in the vegetation types that were studied here.     

Long‐term effects of drainage and initial effects of hydrological restoration on rich fen vegetation

Questions: What vegetational changes does a boreal rich fen (alkaline fen) undergo during a time period of 24 years after drainage? How is plant species richness affected, and what are the changes in composition of ecological groups of species? Is it possible to recover parts of the original flora by rewetting the rich fen? Which are the initial vegetation changes in the flora after rewetting? What are the major challenges for restoration of rich fen flora after rewetting? Location: Eastern central Sweden, southern boreal vegetational zone. Previously rich fen site, drained for forestry purposes during 1978–1979. The site was hydrologically restored (rewetted) in 2002. Method: Annual vegetation survey in permanent plots during a period of 28 years. Results: There were three successional stages in the vegetational changes. In the first stage there was a rapid (< 5 years) loss of rich fen bryophytes. The second step was an increase of sedges and early successional bryophytes, which was followed by an increase of a few emerging dominants, such as Molinia caerulea, Betula pubescens and Sphagnum spp. After rewetting, there are indications of vegetation recovery, albeit at slow rates. Depending on, for instance, initial species composition different routes of vegetation change were observed in the flora after drainage, although after 24 years, species composition became more homogenous and dominated by a few species with high cover. Conclusion: Major changes have occurred after changes in the hydrology (drainage and rewetting) with a severe impact on the biodiversity among vascular plants and bryophytes. Several rich fen bryophytes respond quickly to the changes in water level (in contrast to vascular plants). The recovery after rewetting towards the original rich fen vegetation is slow, as delayed by substrate degradation, dispersal limitation and presence of dominant species.     

Groundwater chemistry and vegetation of gradients from rich fen to poor fen in the Naardermeer (the Netherlands)

In the eastern part of the Naardermeer peatlands (the Netherlands) a regional calcium-rich groundwater flow discharges (here often called the seepage area), whereas in the western part infiltration takes place. The ecological consequence of this hydrological pattern is reflected by the pattern in reedland communities. In the seepage area, which is characterized by Thelypteris-reedlands including many rare and endangered species (Caricion davallianae, Calthion palustris), there is a complex gradient of water types. The lime potential in the peat soil is clearly influenced by the hydrological gradient. In the ombrotrophic (poor fen) part of the gradient (containing species of Caricion curto-nigrae) the lime potentials are low and the groundwater contains low amounts of dissolved ions. The rare and endangered species (Caricion davallianae) are restricted to a small area with high lime potentials which is nourished by regional calcium-rich groundwater. High lime potentials were also measured in eutrophic reedlands influenced by brackish groundwater. Several species which generally occur in wet meadows even show a preference for this brackish environment.In a part of the seepage area succession from rich fen to poor fen and Alnus wood has taken place over a period of 40 years. This development has been caused by the diminishing amount of fresh seepage due to a lowering of the water levels in the surrounding area.The characteristics of poikilotrophic zones (contact zones between water flows) are discussed in relation to their significance for the preservation of endangered marsh species.Abbreviations EC₂₅= Electrical conductivity measured at 25 °C     

Early succession on plots with the upper soil horizon removed

Abstract. Succession was studied on plots with the upper soil horizon removed in an area affected by acidic air pollution in the Kru?né Hory Mts., Czech Republic. 10 permanent 1‐m² plots were marked and vegetation recorded annually using a grid of 100 subplots from 1989 to 1995. Constrained ordination analyses showed that soil texture is the most important environmental factor influencing the course of succession. Its effect on species composition increases with successional age of the plant community. On fine‐grained soils species‐poor communities dominated by grasses (Calamagrostis villosa, Deschampsiaflexuosa) and on coarse‐grained soils species‐rich communities dominated by heather (Calluna vulgaris) developed. Succession proceeded from communities where species composition was determined by diaspore availability towards communities where species composition depended on environmental conditions. Successional communities after 10 yr are more dependent on soil characteristics and consequently environmental determination increases over the course of succession and causes the communities to diverge.     

Nutrient limitation in boreal plant communities and species influenced by scything

Abstract. The nutrient status was studied in permanent plots of four plant communities, two rich-fen communities and two wooded grassland communities, all formerly used for haymaking. The concentrations of N, P and K in plant material of dominant and subdominant species (above- and below-ground) were measured in plots experimentally scythed annually or biennially for two decades, and in plots unscythed for four decades. Three of the communities had an N:P ratio of 14 or less, indicating N-limitation; the most fertile grassland community had particularly low values for the N:P ratio (6–12), as did a majority of the species, including all tall-herb species. A species-rich community of fen-margin vegetation in the lowest productive rich fen, had an N: P ratio of 17–19 in the above-ground biomass, which indicates P-limitation of nutrients. Molinia caerulea and Thalictrum alpinum were found to be the vascular plants with the highest N:P ratio, indicating P-limitation of nutrients. Calculations of N:K and K:P ratios indicated possible K-limitation in the rich-fen communities, especially for Thalictrum alpinum, the species with the highest N:K value. No expected change from N- to P-limited growth was found; in contrast, a reduction in the N:P ratio was found in the annually scythed plots of the rich fens, suggesting that reduced biomass production is mainly a result of disturbance by scything. As expected, a reduction in the concentration of K was detected in the scythed plots.     

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.     

Shading by Phragmites australis: a threat for species-rich fen meadows?

Abstract. Common reed (Phragmites australis Trin.) has spread in fen meadows on the Swiss Plateau during the last decades. An increased dominance of this tall grass may reduce the plant species richness and displace rare or endangered species because of the additional shade. To investigate whether this has actually happened and whether shading by Phragmites was likely to be responsible for the reduction, the plant species composition was surveyed in 241 plots (4 m²) with differing above-ground biomass of Phragmites (ABP). Species richness and the occurrence of characteristic fen species were negatively related to site productivity (total above-ground biomass), but correlations with ABP were generally weaker. The main change associated with increasing ABP within species-rich fens (alliances Molinion and Caricion davallianae) was an increase of species characteristic of the more species-poor alliance Filipendulion. Thus, Phragmites did apparently not play a disproportionate role in the reduction of species richness in the plant communities studied. Selective clipping experiments and light measurements also indicated that shading by Phragmites does not have a strong effect upon the performance of other species in the community, at least in the short term. The reason appeared to lie in the later seasonal growth of Phragmites compared with the other species. These results suggest that the direct impact of shading by Phragmites on the species richness of fen meadows is probably lower than has been assumed. However, possible long-term or indirect effects still need to be investigated.     

Conversion of sagebrush shrublands to exotic annual grasslands negatively impacts small mammal communities

Aim The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long‐term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass‐dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods At two sites in Tooele County, Utah, USA, we investigated with Sherman live trapping whether intact sagebrush vegetation and nearby converted Bromus tectorum‐dominated vegetation differed in rodent abundance, diversity and community composition. Results Rodent abundance and species richness were considerably greater in sagebrush plots than in cheatgrass‐dominated plots. Nine species were captured in sagebrush plots; five of these were also trapped in cheatgrass plots, all at lower abundances than in the sagebrush. In contrast, cheatgrass‐dominated plots had no species that were not found in sagebrush. In addition, the site that had been converted to cheatgrass longer had lower abundances of rodents than the site more recently converted to cheatgrass‐dominated plots. Despite large differences in abundances and species richness, Simpson’s D diversity and Shannon‐Wiener diversity and Brillouin evenness indices did not differ between sagebrush and cheatgrass‐dominated plots. Main conclusions This survey of rodent communities in native sagebrush and in converted cheatgrass‐dominated vegetation suggests that the abundances and community composition of rodents may be shifting, potentially at the larger spatial scale of the entire Great Basin, where cheatgrass continues to invade and dominate more landscape at a rapid rate.     

Changes in forest understorey vegetation in Norway related to long‐term soil acidification and climatic change

Question: Does the understorey vegetation of Norwegian boreal forests change in relation to broad‐scale, long‐term changes? Location: Norway. Methods: Permanently marked 1‐m² vegetation plots from 17 monitoring reference areas in forests dominated by Picea abies (11 areas, 620 plots) and Betula spp. (six areas, 300 plots) were analysed twice, at the start in 1988–1997 and 5 yr later (1993–2002). Species subplot frequency data were analysed separately for each area by univariate and multivariate statistical methods; 5‐yr changes in single species abundances, species number per plot and species composition were tested. Results: Two distinct patterns of change were found: 1. Abundance of several vascular plant species decreased in SE Norwegian Picea forests, most noticeably of species with a preference for richer soils, such as Oxalis acetosella. 2. Abundance of many bryophyte species as well as bryophyte species number per plot increased in forests of both types over most of Norway. Conclusions: The pattern of vascular plant changes is probably a time‐delayed response of long‐lived, mainly clonal, populations to acidified soils resulting from deposition of long‐distance airborne pollutants. The pattern bryophyte changes, with reference to the close link between climatic conditions for growth and abundance changes for Hylocomium splendens established in previous demographic studies, is related to climatic conditions favourable for bryophyte growth. We conclude that many forest understorey plants are sensitive indicators of environmental change, and that the concept used for intensive monitoring of Norwegian forests enables early detection of changes in vegetation brought about by broad‐scale, regional, impact factors.     

Diversity and productivity of plant communities across the Inland Northwest,USA

No definitive explanation for the form of the relationship between species diversity and ecosystem productivity exists nor is there agreement on the mechanisms linking diversity and productivity across scales. Here, we examine changes in the form of the diversity–productivity relationship within and across the plant communities at three observational scales: plots, alliances, and physiognomic vegetation types (PVTs). Vascular plant richness data are from 4,760 20 m² vegetation field plots. Productivity estimates in grams carbon per square meter are from annual net primary productivity (ANPP) models. Analyses with generalized linear models confirm scale dependence in the species diversity–productivity relationship. At the plot focus, the observed diversity–productivity relationship was weak. When plot data were aggregated to a focus of vegetation alliances, a hump-shaped relationship was observed. Species turnover among plots cannot explain the observed hump-shaped relationship at the alliance focus because we used mean plot richness across plots as our index of species richness for alliances and PVTs. The sorting of alliances along the productivity gradient appears to follow regional patterns of moisture availability, with alliances that occupy dry environments occurring within the increasing phase of the hump-shaped pattern, alliances that occupy mesic to hydric environments occurring near the top or in the decreasing phase of the curve, and alliances that occupy the wettest environments having the fewest species and the highest ANPP. This pattern is consistent with the intermediate productivity theory but appears to be inconsistent with the predictions of water–energy theory.     

Continental rain forest fragments in Singapore resist invasion by exotic plants

Abstract Aim In general, the plant communities of oceanic islands suffer more from exotic plant invasions than their continental equivalents. At least part of this difference may be contributed by differences in non‐biological factors, such as the antiquity and intensity of human impacts and the absence of internal barriers to dispersal, rather than differences in inherent invasibility. We tested the resistance of species‐rich continental rain forests to plant invasion on a small, continental island that has been subject to prolonged and intensive human impact. Location Singapore is a 683‐km² equatorial island <1 km from the Asian mainland and with a population of 4 million people. It has a continental biota but has been subject to human impacts as intense as on any oceanic island. Methods We sampled twenty‐nine sites in seven vegetation types, ranging from urban wasteland to fragments of primary lowland rain forest. In each sample plot, all plant species were identified, exotic cover was estimated, and a range of environmental variables measured. Additional qualitative surveys for exotic invasion were made in other forest areas in Singapore. The data were analysed by Spearman's rank correlation coefficient. Results The number of exotic species recorded at a site was unrelated to the number of native species. Across all sites, percentage canopy opening had the highest correlation with the number of exotic species, while soil pH (which largely reflects the incorporation of calcareous construction wastes) had the highest correlation if the mangrove sites were excluded. There were no exotics in mangrove forest and only a tropical American, bird‐dispersed shrub, Clidemia hirta (L.) D. Don (Melastomataceae: Koster's Curse), in primary and tall secondary forest patches. The species‐poor early stages of woody plant succession on highly degraded soils were also very resistant to exotic plant invasion. Main conclusions Long‐isolated rain forest fragments in an exotic‐dominated continental island landscape resist invasion by exotic plants, suggesting that the problems on oceanic islands may reflect an inherently greater invasibility. This study also adds to the increasing evidence that the floras of tropical rain forest fragments in South‐east Asia are remarkably resilient on a time‐scale of decades to a century or more.     

Effectiveness of Turf Stripping as a Measure for Restoring Species-Rich Fen Meadows in Suboptimal Hydrological Conditions

Most species‐rich fen meadows in nature reserves in The Netherlands are acidified due to weaker upwelling of base‐rich groundwater. The present study investigated whether and why turf stripping combined with superficial drainage might promote the long‐term recovery of such meadows and restore the nutrient‐poor, buffered conditions they require. In a field experiment, we analyzed changes in vegetation composition, soil parameters, and soil water chemistry in stripped plots of degraded Cirsio‐Molinietum vegetation over 12 years. After the first five years, many species from the target communities occurred in stripped plots. Both vegetation and soil data showed positive effects of turf stripping on the acid‐buffering capacity. Because sulfate concentration in the soil water decreased over time, whereas the bicarbonate concentration increased, we inferred that there was internal alkalinization driven by sulfate reduction in low‐lying stripped plots. However, the succession toward more acidophilus plant communities, in both control and stripped plots, indicated gradual acidification. This may be caused by a continuing weakening of the upward seepage of base‐rich groundwater as shown by declining calcium concentrations in the soil water. Though turf stripping exposed a nutrient‐poor soil layer with a greater acid‐buffering capacity, these positive effects might not be sufficient to combat the ongoing acidification in the long term.