Higher acidification rates in fens with phosphorus enrichment

Question: Why is bryophyte succession in eutrophicated fens faster than in natural fens? Location: Mineral‐rich fens in The Netherlands and NW Europe. Methods: Literature review on the ecology of four bryophyte species in various successional types as observed in Dutch fens. Results: Bryophyte succession in eutrophicated fens from the brown moss Calliergonella cuspidata to Sphagnum squarrosum is much faster than in natural fens with species shifts from Scorpidium scorpioides to Sphagnum subnitens. Under P‐poor conditions, the brown moss stage is stabilized as long as mineral‐rich water is supplied. This is because S. scorpioides is tolerant of rainwater, is a strong competitor and can counteract acidification to some extent while S. subnitens is intolerant to groundwater and has low growth rates and low acidification capacity. In contrast, the Sphagnum stage is stable after rapid succession from rich‐fen mosses under P‐rich conditions. Calliergonella cuspidata has suboptimal growth in rainwater, possibly due to ammonium toxicity, while the high growth rates of S. squarrosum in nutrient‐rich and highly acidic groundwater allow early establishment and rapid expansion. Conclusions: If measures to improve fen base status occur in environments of increased nutrient (P) availability, the management may not lead to the desired restoration of brown moss stages, but instead to rapid acidification by S. squarrosum.     

Growing season carbon gas exchange from peatlands used as a source of vegetation donor material for restoration

The moss layer transfer technique removes the top layer of vegetation from donor sites as a method to transfer propagules and restore degraded or reclaimed peatlands. As this technique is new, little is known about the impacts of moss layer transfer on vegetation and carbon fluxes following harvest. We monitored growing season carbon dioxide (CO₂) and methane (CH₄) fluxes as well as plant communities at donor sites and neighbouring natural peatland sites in an ombrotrophic bog and minerotrophic fen in Alberta, Canada from which material was harvested between 1 and 6 years prior to the study. Plant recovery at all donor sites was rapid with an average of 72% total plant cover one growing season after harvest at the fen and an average of 87% total plant cover two growing seasons after harvest at the bog. Moss cover also returned, averaging 84% 6 years after harvest at the bog. The majority of natural peatlands in western Canada are treed and tree recruitment at the donor sites was limited. Methane emissions were higher from donor sites compared to natural sites due to the high water table and greater sedge cover. Carbon budgets suggested that the donor fen and bog sites released higher CO₂ and CH₄ over the growing season compared to adjacent natural sites. However, vegetation re-establishment on donor sites was rapid, and it is possible that these sites will return to their original carbon-cycle functioning after disturbance, suggesting that donor sites may recover naturally without implementing management strategies.     

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.     

Geothermal bryophyte habitats in the South Sandwich Islands,maritime Antarctic

Question: How does geothermal activity influence terrestrial plant colonization, species composition and community development in the Antarctic? Location: South Sandwich Islands, maritime Antarctic. Methods: Bryophytes were documented during a biological survey of the archipelago in January and February 1997. Particular attention was given to sites under current or recent influence of geothermal activity. Temperature profiles obtained across defined areas of activity on several islands were linked with the presence of specific bryophytes. Results: Greatest bryophyte richness was associated with geothermally influenced ground. Of 35 moss and nine liverwort species recorded, only four mosses were never associated with heated ground, while eight of the liverworts and 50% of the mosses were found only on actively or recently heated ground. Some species occur in unheated sites elsewhere in the maritime Antarctic, but were absent from such habitats on the South Sandwich Islands. Several species occurred in distinct zones around fumaroles. Maximum temperatures recorded within the upper 0.5 cm of the vegetation surface were 40 ‐ 47 °C, with only Campylopus introflexus tolerating such temperatures. Maximum temperatures 2.5 or 5 cm below the vegetation surface of this moss reached 75 °C. Other bryophytes regularly present in zoned vegetation included the mosses Dicranella hookeri, Sanionia georgico‐uncinata, Pohlia nutans and Notoligotrichum trichodon, and the liverworts Cryptochila grandiflora and Marchantia berteroana. Surface temperatures of 25 ‐ 35 °C and subsurface temperatures of 50 ‐ 60 °C were recorded in these species. Conclusions: These exceptional plant communities illustrate the transport of viable propagules into the Antarctic. Individually ephemeral in nature, the longer term existence of geothermal habitats on islands along the Scotia Arc may have provided refugia during periods of glacial expansion, facilitating subsequent recolonization of Antarctic terrestrial habitats.     

Mosses modify effects of warmer and wetter conditions on tree seedlings at the alpine treeline

Climate warming enables tree seedling establishment beyond the current alpine treeline, but to achieve this, seedlings have to establish within existing tundra vegetation. In tundra, mosses are a prominent feature, known to regulate soil temperature and moisture through their physical structure and associated water retention capacity. Moss presence and species identity might therefore modify the impact of increases in temperature and precipitation on tree seedling establishment at the arctic‐alpine treeline. We followed Betula pubescens and Pinus sylvestris seedling survival and growth during three growing seasons in the field. Tree seedlings were transplanted along a natural precipitation gradient at the subarctic‐alpine treeline in northern Sweden, into plots dominated by each of three common moss species and exposed to combinations of moss removal and experimental warming by open‐top chambers (OTCs). Independent of climate, the presence of feather moss, but not Sphagnum, strongly supressed survival of both tree species. Positive effects of warming and precipitation on survival and growth of B. pubescens seedlings occurred in the absence of mosses and as expected, this was partly dependent on moss species. P. sylvestris survival was greatest at high precipitation, and this effect was more pronounced in Sphagnum than in feather moss plots irrespective of whether the mosses had been removed or not. Moss presence did not reduce the effects of OTCs on soil temperature. Mosses therefore modified seedling response to climate through other mechanisms, such as altered competition or nutrient availability. We conclude that both moss presence and species identity pose a strong control on seedling establishment at the alpine treeline, and that in some cases mosses weaken climate‐change effects on seedling establishment. Changes in moss abundance and species composition therefore have the potential to hamper treeline expansion induced by climate warming.     

Isoprene emission from a subarctic peatland under enhanced UV-B radiation

Isoprene is a reactive hydrocarbon with an important role in atmospheric chemistry, and emissions from vegetation contribute to atmospheric carbon fluxes. The magnitude of isoprene emissions from arctic peatlands is not known, and it may be altered by increasing UV-B radiation. Isoprene emission was measured with the dynamic chamber method from a subarctic peatland under long-term enhancement of UV-B radiation targeted to correspond to a 20% loss in the stratospheric ozone layer. The site type of the peatland was a flark fen dominated by the moss Warnstorfia exannulata and sedges Eriophorum russeolum and Carex limosa. The relationship between species densities and the emission was also assessed. Isoprene emissions were significantly increased by enhanced UV-B radiation during the second (2004) and the fourth (2006) growing seasons under the UV-B exposure. Emissions were related to the density of E. russeolum. The dominant moss, W. exannulata, proved to emit small amounts of isoprene in a laboratory trial. Subarctic fens, even without Sphagnum moss, are a significant source of isoprene to the atmosphere, especially under periods of warm weather. Warming of the Arctic together with enhanced UV-B radiation may substantially increase the emissions.     

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.     

Turnover of recently assimilated carbon in arctic bryophytes

Carbon (C) allocation and turnover in arctic bryophytes is largely unknown, but their response to climatic change has potentially significant impacts on arctic ecosystem C budgets. Using a combination of pulse-chase experiments and a newly developed model of C turnover in bryophytes, we show significant differences in C turnover between two contrasting arctic moss species (Polytrichum piliferum and Sphagnum fuscum). ¹³C abundance in moss tissues (measured up to 1 year) and respired CO₂ (traced over 5 days) were used to parameterise the bryophyte C model with four pools representing labile and structural C in photosynthetic and stem tissue. The model was optimised using an Ensemble Kalman Filter to ensure a focus on estimating the confidence intervals (CI) on model parameters and outputs. The ratio of aboveground NPP:GPP in Polytrichum piliferum was 23% (CI 9–35%), with an average turnover time of 1.7 days (CI 1.1–2.5 days). The aboveground NPP:GPP ratio in Sphagnum fuscum was 43% (CI 19–65%) with an average turnover time of 3.1 days (CI 1.6–6.1 days). These results are the first to show differences in C partitioning between arctic bryophyte species in situ and highlight the importance of modelling C dynamics of this group separately from vascular plants for a realistic representation of vegetation in arctic C models.     

Plant recruitment in the High Arctic: Seed bank and seedling emergence on Svalbard

Abstract. Composition and density of the soil seed banks, together with seedling emergence in the field, were examined on Svalbard. 1213 soil samples were collected from six drymesic habitats in three regions representing various stages of colonization from bare moraines to full vegetation cover and spanning a range of typical nutrient and thermal regimes. Of the 165 vascular plant species native to Svalbard, 72 were present as mature plants at the study sites and of these 70% germinated seed. Proglacial soil had 12 seedlings per m², disturbed Dryas heath 131, intact Dryas heath 91, polar heath 715, thermophilic heath 3113, and a bird cliff 10437 seedlings. Highest seed bank species richness was at the thermophilic heath (26 species). Seedlings of 27 species emerged in the field, with fewer seedlings in disturbed habitats (60 seedlings per m²) than in intact Dryas heath (142), suggesting that an absence of ‘safe sites’ limited seedling establishment in disturbed habitats. Measurement of seedling emergence in the field increased awareness of which species are able to germinate naturally. This may be underestimated by up to 31% if greenhouse trials alone are used, owing partly to unsuitability of greenhouse conditions for germination of some species and also to practical limitations of amount of soil sampled. Most thermophilic species failed to germinate and some species present at several sites only germinated from the thermophilic heath seed bank, suggesting that climate constrains recruitment from seeds in the High Arctic.     

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.     

Contrasting Species—Environment Relationships in Communities of Testate Amoebae, Bryophytes and Vascular Plants Along the Fen–Bog Gradient

We studied the vegetation, testate amoebae and abiotic variables (depth of the water table, pH, electrical conductivity, Ca and Mg concentrations of water extracted from mosses) along the bog to extremely rich fen gradient in sub-alpine peatlands of the Upper Engadine (Swiss Alps). Testate amoeba diversity was correlated to that of mosses but not of vascular plants. Diversity peaked in rich fen for testate amoebae and in extremely rich fen for mosses, while for testate amoebae and mosses it was lowest in bog but for vascular plants in extremely rich fen. Multiple factor and redundancy analyses (RDA) revealed a stronger correlation of testate amoebae than of vegetation to water table and hydrochemical variables and relatively strong correlation between testate amoeba and moss community data. In RDA, hydrochemical variables explained a higher proportion of the testate amoeba and moss data than water table depth. Abiotic variables explained a higher percentage of the species data for testate amoebae (30.3% or 19.5% for binary data) than for mosses (13.4%) and vascular plants (10%). These results show that (1) vascular plant, moss and testate amoeba communities respond differently to ecological gradients in peatlands and (2) testate amoebae are more strongly related than vascular plants to the abiotic factors at the mire surface. These differences are related to vertical trophic gradients and associated niche differentiation.     

Key variables controlling the vegetation of a cool-temperate mire in northern Japan

Abstract. In the cool-temperate Bibi Mire, Hokkaido, Japan, valley fens and flood-plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood-plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood-plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone. The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire -where the non-inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.     

Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

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Life syndrome of the bryophyte communities as an adaptative pattern in the Mediterranean temporary ponds of Italy

An ecological and biological investigation on the bryophyte communities of the Mediterranean temporary ponds was carried out in Italy. Here, the occurrence of a rich set of liverworts is very significant, as several species of Riccia characterize the communities from a physiognomical, ecological and syntaxonomical point of view. The moss component is represented only by acrocarpous mosses, e.g. Archidium alternifolium and Pleuridium acuminatum which play an important phytosociological role. In this study, the bryophyte communities are used to identify a pattern, corresponding to a “functional type” which reflects the correlated response of the bryophyte communities toward the prevalent ecological parameters of the habitat. The individuated functional type assembles life strategy, life form, lifespan, spore size, dispersal strategy, reproduction effort, independently from the taxonomical relationship of the species characterizing the communities. It represents an adaptative pattern of coevolved characters, adopted by the bryophyte communities for the habitat establishment and re-establishment following the seasonal water fluctuations typical of the investigated habitat.     

Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

Vegetation pattern of mountains in West Greenland – a baseline for long-term surveillance of global warming impacts

Background: Steep environmental gradients, coupled with predicted high temperature rises in the Arctic make arctic mountain vegetation highly suitable for surveillance of changes related to global warming. However, guidelines and baselines for such a purpose are widely lacking since arctic mountain vegetation has been little explored.

Aims: We explore options for long-term surveillance on the basis of a detailed analysis of extant plant community patterns and their underlying environmental conditions in the mountainous inland of West Greenland.

Methods: Distribution, abundance and site conditions of vegetation types were analysed, using 664 vegetation samples and detailed vegetation maps in four altitudinal belts.

Results: Most plant communities had a restricted elevation distribution and were confined to special habitats predominantly defined by mesotopography and soil moisture.

Conclusions: Based on the strong linkage to habitat conditions, horizontal and vertical changes of species distribution and vegetation pattern are excellent indicators for inferring underlying environmental changes on three different scales. The recommendations given concerning climate sensitive species and plant communities, ecotones for setting up observation sites as well as stratification of analysis by habitats can be the basis for establishing long-term surveillance programmes on arctic mountain vegetation.     

Methane dynamics of recolonized cutover minerotrophic peatland: Implications for restoration

In North America, mulching of vacuum-harvested sites combined with blocking of the drainage system is widely used for peatland restoration to accelerate Sphagnum establishment. However, peat extraction in fen peatlands or exposure of deeper minerotrophic peat layers results in soil chemistry that is less suitable for re-establishment of Sphagnum moss. In this situation, restoration of plant species characteristic of minerotrophic peatlands is desirable to return the site to a carbon accumulating system. In these cases, it may be worthwhile to maintain spontaneously revegetating species as part of restoration if they provide desirable ecosystem functions. We studied the role of six spontaneously recolonizing vegetation communities for methane (CH₄) emissions and pore water CH₄ concentration for two growing seasons (2008 and 2009) at an abandoned minerotrophic peatland in southeastern Quebec. We then compared the results with bare peat and adjacent natural fen vegetation. Communities dominated by Eriophorum vaginatum, Carex aquatilis and Typha latifolia had CH₄ flux an order of magnitude greater than other cutover vegetation types and natural sites. In contrast, Scirpus atrocinctus and Equisetum arvense had CH₄ emission rates lower than natural hollow vegetation. We found seasonal average water table and vegetation volume had significant correlation with CH₄ flux. Water table and soil temperature were significantly correlated with CH₄ flux at plots where the water table was near or above the surface. Pore water CH₄ concentration suggests that CH₄ is being produced at the cutover peatland and that low measured fluxes likely result from substantial oxidation of CH₄ in the unsaturated zone. Understanding ecosystem functions of spontaneously recolonizing species on cutover fens can be used to help make decisions about the inclusion of these communities for future restoration measures.     

Differential effects of ammonium and nitrate deposition on fen phanerogams and bryophytes

Question: High atmospheric nitrogen (N) deposition has been shown to affect productivity and species composition of terrestrial ecosystems. This study focused on the differential effects of the two inorganic N forms in atmospheric deposition (i.e. ammonium and nitrate). Methods and location: Nutrient addition experiments were carried out during 4 years in a mesotrophic fen in a low‐deposition area in Ireland. In a factorial design, plots were fertilized with ammonium and/or nitrate, in two doses comparable with 35 and 70 kg N ha^?1 y^?1 and compared with an unfertilized control. Results: Vascular plant biomass as well as bryophyte biomass were not affected by N dose but showed significantly different responses to the N form. In the ammonium‐fertilized plots, vascular plant biomass was higher and moss biomass was lower than the control, while nitrate additions had no effect. Vascular plant species density was high (16 species per 0.49 m²) and was not affected by any of the treatments; bryophyte species density was also high (seven species per 0.04 m²) but showed a significant decrease upon ammonium fertilization. Conclusion: The vulnerability of the mesotrophic vegetation to enhanced atmospheric N deposition depends strongly on the N form. If N would be mainly deposited as NO_x, no detrimental effects on the vegetation will occur. If, however, the deposition is mainly in the form of NH_y, the bryophyte vegetation will be seriously damaged, while the vascular plant vegetation will show an increased biomass production with possible shifts in dominance from Carex and herb species to grasses and shrubs.     

Plant community composition along a peatland margin follows alternate successional pathways after hydrologic disturbance

Hydrological disturbances can alter the structure and function of ecosystems by changing plant species composition over time. Peatlands in the northern hemisphere are particularly sensitive to global change drivers related to soil water availability, such as drought and drainage, because of important ecohydrological feedbacks between species composition and water table position. Here, we examined the plant community structure and environmental drivers of species distributions over two growing seasons along a bog – margin gradient, pre- and post-disturbance by beaver activity. Pond drainage resulted in seasonal average water table depth 8–24 cm lower in the second season. Five plant communities corresponded to changes in water table depth and acidity: bog, poor fen, meadow, mudflat and pond. Plant cover increased in meadow and mudflat communities, decreased in the pond community and did not differ between years in bog and poor fen communities. Changes in species abundance between years showed signs of alternate successional pathways: one that favors Sphagnum moss and bog community expansion and another pathway that favors meadow and mudflat expansion. This study highlights the non-linear successional trajectory of plant communities with changes in water table depth, which has implications for land management goals that aim to conserve the ecological integrity of peatland ecosystems.