Mire Margin Research Articles

Recent hummock establishment in the margin of a subarctic fen, Finnish Lapland

Northern fens, that host unique biota and form a remarkable carbon stock, are sensitive to changes in the moisture balance and, therefore, may be strongly affected by climatic fluctuations. However, long‐term monitoring and palaeoecological studies of fens are relatively rare and, as a result, their responses to past and current climatic fluctuations are poorly known. In this study, we examined the recent vegetation change as well as changes in testate amoeba communities in the mire margin of a subarctic fen in Finnish Lapland with four peat profiles. Testate amoebae were used as indicators of past fluctuations in water table depth. The vegetation showed a drastic shift from sedge‐dominated fen to Sphagnum‐dominated communities during the late 20th and the early 21st centuries. This shift was accompanied by a turnover in the testate amoeba community. Testate amoeba‐based water table reconstructions indicated recent drying. This may be due to the lowering of the water table either from accelerated Sphagnum increment or enhanced evaporation. The observed hummock establishment concurs with the documented hemisphere‐wide expansion trend of hummock communities in fens. This change may strengthen the carbon sink and storage capacity of these peatlands, which could be viewed as a welcome negative feedback process to the ongoing climate warming. However, the change also poses a threat to biodiversity since fens are not only species‐rich habitats but are also endangered ecosystems.

Biodiversity of a boreal mire, including its hydrographic network (Shichengskoe mire, north-western Russia).

BackgroundThe paper is based on the dataset whose purpose was to deliver, in the form of GBIF-mediated data, diverse materials on the biodiversity of a large mire, Shichengskoe mire (Vologda Region, north-western Russia), including its various mire sites and intra-mire water bodies. The dataset was based on our materials collected for two decades (from 2000 to 2021) in different parts and biotopes of the Shichengskoe mire and complemented by scarce data obtained previously by other researchers. The data contain materials on the diversity of Animalia (2886 occurrences), Bacteria (22), Chromista (256), Fungi (111), Plantae (2463) and Protozoa (131). Within the study period, the most detailed and long-term biodiversity studies were carried out for higher plants and invertebrates. On the other hand, the data on the composition of lichens, protozoa, algae, basidiomycetes, some groups of invertebrates and, to a lesser extent, lichens and vertebrates are far less comprehensive and require further substantial research efforts. The list includes occurrences from both the peatland (mire sites and mire margins different in typology) and the objects of the mire hydrographic network. In a standardised form, this article summarises both already published (mainly in Russian) and unpublished materials.New informationThe paper summarises the results of long-term research on the biodiversity of a boreal mire, including its hydrographic network. A total of 5869 occurrences were included in the dataset published in the Global Biodiversity Information Facility (GBIF, gbif.org) for the first time. According to the GBIF taxonomic backbone, the dataset covers 1358 taxa, including 1250 lower-rank taxa (species, subspecies, varieties, forms) and 108 taxa identified to the genus level. Several species found in the Shichengskoe mire, mainly belonging to Bacteria, Chromista and Protozoa, have never been listed in GBIF for the territory of Russia before. The overwhelming majority of occurrences and identified species came from the territory of Shichengskiy Landscape Reserve. Due to our work, this Reserve is now the most studied regional reserve in the Vologda Region with respect to biodiversity. By the number of revealed species, it is close to two federal protected areas: Darwinskiy State Nature Biospheric Reserve and National Park "Russkiy Sever".

Diversity of lichens, mosses and vascular plants in the paludified herb-rich spruce forests of the Pinego-Mezen watershed (Arkhangelsk Region)

The paludified herb-rich spruce forests of the Pinego-Mezen watershed are characterized by a high speciesand coenotical diversity. The habitat type (floodplain, stream valley, mire margin) is the main compositional gradientfor vascular plant and moss diversity. The density, basal area and proportion of spruce and deciduous species in thetree stand are less significant. The main compositional gradient of the lichen diversity is the tree stand structure, whichprovides the availability and quality of the substrate for the epiphytic and epixilic lichens that prevail in such communities.The gradient of paludified herb-rich spruce forests from floodplain habitat to mire margins is less significant for thecomposition of lichen flora.

Spring water table depth mediates within‐site variation of soil temperature in groundwater‐fed mires

AbstractGroundwater‐dependent ecosystems represent globally rare edaphic islands of scattered distribution, often forming areas of regionally unique environmental conditions. A stable groundwater supply is a key parameter defining their ecological specificity, promoting also soil thermal buffering. Still, a limited number of studies dealt with the importance of water temperature in mire ecosystems and virtually no data exist on within‐site variation in the temperature buffer effect. Three temperature dataloggers, placed in patches potentially differing in groundwater supply, were installed in each of 19 Western Carpathian spring mire sites from May 2019 to July 2020. Spring source plots statistically differed in water temperature parameters from the plots located towards the spring mire margin, which did not significantly differ from one another. At the majority of sites, the temperature values changed gradually from spring source to mire margins, fitting the pattern expected in the groundwater temperature buffering scenario. Dataloggers placed in the spring sources were the most distinctive from the others in thermal buffering parameters in conditional principal component analysis. The difference between the spring source and its margin was on average 3.25 °C for 95th percentile of the recorded water temperature data points (i.e. warm extremes) and 1.91 °C for 5th percentile (i.e. cold extremes). This suggests that if the temperature at spring source area is considered, thermal buffering within a site may mitigate mainly warm extremes. Thus, our data may provide an important baseline for predictions of possibly upcoming changes in spring mire hydrology caused by climate change. Both warming and precipitation decrease can give rise to the loss or substantial reduction of buffering effect if the contrasting parameters now recorded at the central part shift to those found towards the margins of groundwater‐fed areas.

Quantifying groundwater fluxes from an aapa mire to a riverside esker formation

Abstract Water flows in peatland margins is an under-researched topic. This study examines recharge from a peatland to an esker aquifer in an aapa mire complex of northern Finland. Our objective was to study how the aapa mire margin is hydrogeologically connected to the riverside aquifer and spatial and temporal variations in the recharge of peatland water to groundwater (GW). Following geophysical studies and monitoring of the saturated zone, a GW model (MODFLOW) was used in combination with stable isotopes to quantify GW flow volumes and directions. Peatland water recharge to the sandy aquifer indicated a strong connection at the peatland–aquifer boundary. Recharge volumes from peatland to esker were high and rather constant (873 m3 d−1) and dominated esker recharge at the study site. The peat water recharging the esker boundary was rich in dissolved organic carbon (DOC). Stable isotope studies on water (δ18O, δ2H, and d-excess) from GW wells verified the recharge of DOC-rich water from peatlands to mineral soil esker. Biogeochemical analysis revealed changes from DOC to dissolved inorganic carbon in the flow pathway from peatland margin to the river Kitinen. This study highlights the importance of careful investigation of aapa mire margin areas and their potential role in regional GW recharge patterns.

Modelling the hydrological interactions between a fissured granite aquifer and a valley mire in the Massif Central, France

Abstract. We developed a high-resolution MIKE SHE/MIKE 11 model of a 231.3 ha headwater catchment in the granitic uplands of the French Massif Central to estimate the contribution of groundwater upwelling to the water balance of the Dauges mire, an acidic valley mire of international importance for nature conservation. We estimated that groundwater upwelling from the underlying weathered granite formations – mostly an approximately 55 m deep fissured zone – provides 27.1 % of total long-term inflows to the mire. This contribution increases to 37.2 % in September when total inflows are small. Overland boundary inflow accounts for an average of 40.2 % of total inflows. However, most of this originates from groundwater seepage through mineral soils along the mire margins or in small non-channelised valleys upslope of the mire. A sensitivity analysis showed that model performance in terms of the simulation of mire groundwater levels was most sensitive to parameters describing the mineral soils and weathered granite formations rather than the overlying peat layer. Variation partitioning demonstrated that groundwater upwelling was the most important factor driving simulated monthly groundwater table depth within the mire. Sustained groundwater upwelling maintains the mire water table close to or at ground level for most of the year. As a result, precipitation and overland boundary inflows quickly leave the wetland as saturation-excess runoff. There was close agreement between the observed distribution of mire habitats and areas where the simulated long-term groundwater seepage rate was larger than zero in September. Our results demonstrate that, contrary to the assumed small contribution of groundwater to the hydrology of hard-rock regions, groundwater upwelling from underlying weathered formations can be a quantitatively important and functionally critical element of the water balance of valley mires in granitic headwater catchments. These results have important legal and management implications.

Sphagnum divinum (sp. nov.) and S. medium Limpr. and their relationship to S. magellanicum Brid.

Sphagnum magellanicum has been viewed as being a predominantly circumpolar species in the northern hemisphere, but it occurs in the southern hemisphere and was originally described from the southern parts of Chile. It is an ecologically important species in mire ecosystems and has been extensively used as a model to study processes of growth, carbon sequestration and peat decomposition. Molecular and experimental studies have, however, revealed genetic structure within S. magellanicum, and morphological differences associated with these genetic groups. Here we describe Sphagnum divinum in Sphagnum subgenus Sphagnum (Sphagnaceae, Bryophyta) as a new species, based on molecular and morphological evidence. Sphagnum medium is reinstated as a distinct species and is epitypified. Consequently, a new species concept of S. magellanicum is presented including an epitypification. Important morphological characters to separate these three species in the field and under the microscope are presented. Ecology and distribution differ among the species; S. divinium has a wide habitat range including mire margin, forested peatlands and moist heaths, and a circumpolar distribution around the northern hemisphere. Sphagnum medium seems to be more restricted to ombrotrophic mire expanse habitats and shows an amphi-Atlantic distribution in the northern hemisphere. Sphagnum magellanicum has a very broad ecological niche in peatlands and is found in most mire habitats in Tierra del Fuego on the southern tip of South America.

Ecological, topographic and successional patterns across wetlands in a rugged land uplift coast in Nyby, northern Finland

We studied 45 mid-boreal wetlands in a rugged land uplift coast with a thin cover of till. Wetlands ranged from 1 to 53 m a.s.l. and were of highly various sizes. Our aims were to examine, if vegetation types are valid in comparing wetlands, what kind of ecological major pattern the vegetation type composition of wetlands shows and how vegetation types distribute across altitudes. On those ground we discuss the wetland succession of the study area. We used the Finnish mire site types as vegetation types. Mire site types could be used for an ecological classification and ordination of the wetlands. As was expected, the major gradient consisted of the transition from mire margin (swamp) to expanse. The distribution of the Major Vegetational Wetland Groups (MVWG) responded to a general water-flow pattern in the landscape. Partly different peatland succession sequences occur in areas with small mire basins and in areas with larger mire basins with evolving mire complexes. Sequences of small wetlands and those of mire complexes follow the same trajectory only as far as the major gradient is considered while they differ with regard to the vegetation type composition of locally rare vegetation types and with regard to peatland morphology. Trajectories of mire complexes at catchment divides differ from those at catchment centers where the waters in the landscape tend to gather. Peatland forms of aapa mires experience a change reaching altitudes of 30–50 m a.s.l. Small bog complexes at catchment divides reach a stage of an unpatterned Sphagnum fuscum bog in the study area. Mature mixed complexes with aapa-mire parts and patterned sloping-bog parts only occur at altitudes higher than 60 m a.s.l. Peculiarities in the succession of the wetlands of Nyby, which include the presence of separate incomplete successional sequences in the same area, are mainly caused by the peculiar topography with various sub-areas and with an abundance of rock outcrops.

Paradise (and Herrin) lost: Marginal depositional settings of the Herrin and Paradise coals, Western Kentucky coalfield

This is the fourth installment in a series of papers on the Asturian (Westphalian D) disrupted mire margins, termed the “ragged edge” in previous papers, and limestone distributions in the Herrin–Baker coal interval in the Western Kentucky extension of the Illinois Basin. New data, indicating in-situ peat development and marine influence, collected from the first in-mine exposure of this interval are presented. Borehole data from the region are examined in the context of “ragged edge” exposures and a carbonate platform depositional model for this portion of the Illinois Basin is presented. This shows that deposition of the sequence was influenced both by the underlying sediments and by a marine transgression. The former influence is seen in variations in coal and limestone thickness over sandstone-filled channels versus over shale bayfill deposits. The latter is marked by the progressive upwards loss of coal benches (i.e., the bottom bench of both coals is the most extensive and the Herrin coal is more extensive than the overlying Paradise coal) and by marine partings in both coals. Further, the brecciated margins seen in both coal seams are similar to brecciated peats encountered along the Everglades margins of Southwest Florida. Overall coal distributions are similar to both those along the Everglades margins and those along a transect from the Belize coast to Ambergis Caye.

Subalpine gully‐head ribbon fens of the Lammerlaw and Lammermoor Ranges, Otago, New Zealand

Vegetation patterns of subalpine gully‐head mires were investigated in the flat‐topped Lammerlaw and Lammermoor Ranges, South Island, New Zealand. Two intensively studied mires each consist of a series of peaty terraces and scarps. Terraces may contain pools, elongated downslope in the narrow, lower altitude mire, but across slope in the broader, upper mire. A crest occurs on some terrace lips, and marginal “spillways” (channel‐like zones) occur down some scarps. Some mires have drained by subsurface pipes. Vegetation analysis distinguished between grassland or herbfield on gully sides, vegetation of mire margins, showing aspect differences on the steeper, lower mire, and the vegetation of gully floors, including oligotrophic mire centre vegetation and species‐poor pools. The crests, though warmer, bore no special vegetation type. Mineral soil beneath the peat indicates a previous non‐mire vegetation, which has subsequently paludified. Scarp slumps indicate downslope creep of organic material. Peat fissures, and mineral, vegetation, and erosion dams all appear to have initiated development of some pools. Mires are designated gully‐head ribbon fens. Patterning appears to be accentuated because of the mires’ gully‐head location on broad‐topped ranges, and drainage of soligenous water from upslope gully sides. These apparently unique fens give insight into patterning in aapa mires, and merit special conservation.

Multiple gradients in mire vegetation: a comparison of a Swedish and an Italian bog

The major environmental gradients underlying plant species distribution were outlined in two climatically and bio-geographically contrasting mires: a Swedish bog in the boreo-nemoral zone, and an Italian bog in the south-eastern Alps. Data on mire morphology, surface hydrology, floristic composition, peat chemistry and pore-water chemistry were collected along transects from the mire margin (i.e., the outer portion of the mire in contact with the surrounding mineral soil) towards the mire expanse (i.e., the inner portion of the mire). The delimitation and the extent of the minerotrophic mire margin were related to the steepness of the lateral mire slope which, in turns, controls the direction of surface water flow. The mineral soil water limit was mirrored in geochemical variables such as pH, alkalinity, Ca2+, Mg2+, Al3+, Mn2+, and SiO2 concentrations in pore-water, as well as Ca, Al, Fe, N and P contents in surface peat. Depending on regional requirements of plant species, different species were useful as fen limit indicators at the two sites. The main environmental factors affecting distribution of habitat types and plant species in the two mires were the acidity-alkalinity gradient, and the gradient in depth to the water table. The mire margin – mire expanse gradient corresponds to a complex gradient mainly reflected in a differentiation of vegetation structure in relation to the aeration of the peat substrate.

Vegetation of high-altitude fens and restio marshlands of the Hottentots Holland Mountains, Western Cape, South Africa

Seepages occurring at high altitudes in the Hottentots Holland Mountains (HHM) (Western Cape Province. South Africa) were subject to a phytosociological survey. Relevé sampling method and classification procedures of the floristic-sociological (Braun-Blanquet) approach as well as numerical data analyses (numerical classification and ordination) were used to reveal syn- taxonomic patterns and characterize the position of the syntaxa along major environmental gradients. Nine plant communities were recognized, three of which were classified as associations, following formal syntaxonomic and nomenclatural rules of the floristic-sociological approach Most of the studied mire communities were dominated by low-growing clonal restios (Restionaceae). whereas some consisted of other types of graminoids. The most important species determining the structure (and function) of the mire communities on sandstones of the HHM include restios Anthochortus crinalis, Chondropetalum deustum.C. mucronatum, Elegia intermedia. E. thyrsifera. Restio subtilis. R. purpurascens. cyperoids Epischoenus villosus. Ficinia argy-ropa, grasses Ehrharta setacea subsp. setacea. Pentameris hirtiglumis as well as shrubs Berzelia squarrosa. Cliffortia tricuspi- data. Erica intenallaris and Grubbia rosmarinifolia. Protea lacticolor and Restio perplexus dominate a rare shale band seep­age community. There are two major groups of communities—the fens (dominated by carpets of Anthochortus crinalis and other low-growing species) and the restio marshlands (mosaics of low tussocks of Restio subtilis and tall Chondropetalum mucrona­tum). The degree of soil (and water) minerotrophy was found to be the most important differentiating feature between the mire (fen and restio marshland) communities studied. The soils in the centre of mires were found to have high contents of peat and showed very little influence from the underlying sandstone. The soils along the mire margins had a greater admixture of mineral soil derived from the sandstone or shale bedrock.

The Upper Hance coal bed in southeastern Kentucky: palynologic, geochemical, and petrographic evidence for environmental succession

The Upper Hance coal bed in Bell County, eastern Kentucky exhibits considerable variation in depositional setting on a mine scale. Palynology and geochemistry of the coal are examined in order to supplement previous petrographic examinations. The various depositional settings of the Upper Hance mire progress from the pioneer, possibly partially allochthonous, settings at the mire margins and base; to the well-developed, planar to domed main body of the mire; and finally to the terminal events of flooding, clastic influx, and temporary reestablishment of mires now seen as the thin rider coals. Palynologic diversity generally decreases upwards from the basal lithotype through the main body of the coal bed. The cannel and rider lithologies represent distinct depositional events.

Ecohydrological characterisation of a degenerated valley peatland in Northern Germany for use in restoration

Present environmental policy aims to restore wetlands for multifunctional purposes and requires quantitative information on the spatially interrelated biohydrochemical processes which allow wetlands to regulate water- and nutrient flow on different scales. For this purpose, this study presents an ecohydrological system analysis as a basis for a future management concept of the Eider valley peatland. This study combines field data with existing knowledge to set up different modelling techniques to study hydrological processes and nitrogen transformations. The Eider valley of northern Germany is a riverine freshwater wetland of 150 ha. Mire genesis was dominated first by river water inflow from the upstream catchment area, and in a later successional stage by groundwater inflow at the mire margins. Drainage, land use intensification and river regulation have resulted in severe degeneration of the peatland. Altering of the water flow patterns led to the mobilisation of nutrients and resulted in eutrophication of the sites. Abandonment of the mown or grazed sites led to the establishment of species poor Urtica dioica stands. The scenario calculations of the nitrogen budget of the peatland with a process oriented nitrogen model indicate that a water level increase of 30 cm is not sufficient to reduce peat loss due to oxidation. On the basis of the system analysis, restoration prospects for the Eider valley peatland are discussed where the historical subsurface flow pattern can be a long term restoration goal. Due to irreversible changes in peat hydraulic conductivities combined with subsidence, it is only possible to restore surface flow on top of the peat. Raising river water level will result in a shallow lake system. The limnic stage is a draw-back in the genesis of the valley, but necessary for the restoration of wetlands as self-evolving landscape entities.

Луга Северо-Восточного Алтая

The North-Eastern Altai is an ultra-humid area with climax vegetation represented by tall-herb fir (Abies sibirica) dark-coniferous forest. Its meadows belong to the class Molinio-Arrhenatheretea. The typical asso­ciation Aegopodio podagrariae—Dactyletum glomeratae originates in the watershed clearings after climax forests whereas ass. Hyperici perforati—Agrostietum giganteaereplaces the previous one under mowing and grazing. The Molinietalia wet meadows are widespread in the river valleys. The meadows of ass. Cirsio heterophylli—Calama­grostietum langsdorffii occur on wet soils in small depressions and along floodplain mire margins, and ass. Ca­rici ovalis—Deschampsietum cespitosae comprises typical floodplain hay-meadows on moist, nutrient-rich soils.

Carbon accumulation in West Siberian Mires, Russia Sphagnum peatland distribution in North America and Eurasia during the past 21,000 years

The rates of carbon (C) accumulation and the role of fires in the C dynamics of the major types of boreal West Siberian mires were investigated. Detailed analysis of dry bulk density, C, and N concentration and age of the peat layers were used to determine C accumulation rates throughout the Holocene. The average long‐term apparent rate of carbon accumulation (LORCA) at 11 studied sites was 17.2±1.0 (SE) g m−2 yr−1, ranging from 12.1 to 23.7 g m−2 yr−1, and the total apparent carbon sink 11.8 Tg yr−1 (1 Tg = 1012 g) for Russian raised string bogs (68.5 million hectares). These estimates of C accumulation in West Siberian mires are roughly a half of the earlier estimates for these boreal mires. Differences in LORCA for three major mire types in the study area, the ridge‐hollow pine bogs, Sphagnum fuscum pine bogs, and dwarf‐shrub pine bogs, were not significant. The age versus depth (measured as cumulative carbon from the surface downward) curve was slightly convex, indicating a general declining trend in LORCA with decreasing age. About 55% of the present carbon store was already accumulated about 6000 cal. BP. The most intensive expansion phase of the study area occurred between 7000 and 8000 cal. BP. The subsequent lateral expansion has been very slow in the later Holocene. The charcoal data indicated that these mires have burned only 2–3 times during the past 7000–8000 cal. BP, and only a strip of a few meters along the mire margins has burned relatively frequently. No evidence of significant carbon losses due to fires could be found. The charcoal layers at the mire margins suggest a declining trend in burning rates during the later Holocene.

Reconstruction of local vegetation in AD 915 at an oligotrophic mire in northern Japan from pollen, present‐day vegetation and tephra data

The use of data for present‐day vegetation, modern and pretephra pollen have, together, allowed reconstruction of the spatial pattern of the vegetation of an oligotrophic mire, Shimo‐kenashi Mire, in AD 915. The modern pollen data were compared with the surrounding vegetation, showing that pollen of Ericaceae, Rosaceae (excluding Sanguisorba), Sphagnum and Liliaceae, together with trees and shrubs, which form scrub or thicket, indicate the limits of the mires. Shimo‐kenashi Mire was narrower in AD 915 and had more islands and peninsulas of scrub. Subsequently, the mire margin has advanced and the scrub islands and peninsulas have disappeared at some sites. The fact that the mire is spreading implies that conditions are wetter since AD 915, caused by changes in local hydrology. This history of vegetation at the site will contribute to the conservation and management of the mire as trends in vegetational change provide the basic information for conservation strategy.

A Scandinavian perspective on ecological gradients in north‐west European mires: reply to Wheeler and Proctor

In their recent review of gradient relationships in mires, Wheeler & Proctor (2000) question the central paradigm in Scandinavian mire ecology that there are three major gradients in mires, which relate to nutrient richness, water-table depth and proximity to the mire margin (see Sjors 1948; Malmer 1962; 0kland 1989a). Wheeler & Proctor (2000) propose that the simple 'poor-rich' gradient should be replaced by a dual system considering '... [first] variation in pH and concentrations of metallic cations [and, second] variation in the availability of limiting nutrients, primarily phosphorus (P) and nitrogen (N)'. They further suggest that the current practice of using the mineral soil water limit that distinguishes between ombrotrophic and minerotrophically influenced sites 'as a general main division within mires' should be discontinued because this limit 'is not sharp, and cannot be related to consistent differences in either

Vegetation-environment relationships of boreal spruce swamp forests in Østmarka Nature Reserve, SE Norway

Abstract Swamp forests dominated by Picea abies contribute strongly to the total plant species richness in boreal forests. The variation in species composition and environmental conditions in swamp forests and the relationships of swamp forests to mires and upland forest, have, however, remained insufficiently known. From a preliminary survey of 57 spruce swamp forests, eleven localities were selected to represent the variation in the study area with respect to size and nutrient status, and altitude and position in the landscape. Physiographic and hydrotopographic descriptions were made. A total of 150 1-m2 plots were distributed on the localities by a restricted random procedure. In each plot, the abundance of all vascular plants, bryophytes and macrolichens was recorded as frequency in 16 subplots, 53 variables (topographic and geographic, tree influence, water-table, water chemical and physical, and soil chemical and physical) were measured. The gradient ( coenocline) structure of vegetation was found by parallel DCA and LNMDS ordinations, interpreted ecologically by analysis of correlations and geostatistical patterns. The two main coenoclines were the same for the full species composition and for vascular plant and cryptogams considered separately. The first gradient was related to soil acidity and nutrient concentrations: plots segregated into relatively poor (and intermediate) and richer swamp forests. Nitrogen availability is considered a decisive factor for species’ responses to this gradient. The second gradient was related to depth to the water table and mesotopographic relief of the swamp-forest surface, varying mostly on fine (0.75-1.5 m) scales. Vascular plants segregate along this gradient due to a trade-off between tolerances to waterlogging and drought, bryophyte are influenced by a complex set of factors. Two minor vegetation gradients were also found; one related to microtopography (extending from flat, lawn-like areas dominated by large bryophytes to more strongly sloping sites dominated by small mosses and hepatics; ‘pocket species’) and one weakly related to the annual water-table amplitude. Relatively strong coenoclines were found that separated entire swamp forests but were uncorrelated with measured variables. These occurred because all swamp forests, notably the richer, had a strong element of uniqueness in species composition, probably because species are recruited from a large species pool during thousands of years. Swamp forest is proposed as a broad term for all peatlands with trees, including mire margin, from which it is essentially indistinguishable. Similarities with, and differences from, open mire and forest on mineral soil are discussed. Some unique features of swamp forests are pointed out. A classification of swamp forests into eight site-types by division of the two main gradients is proposed. Descriptions are provided for the six site-types encountered in the study area. All intact richer swamp forests and a representative selection of poor swamp forests should be protected if maintenance of the biological diversity of (coniferous) forests in general, and swamp forests in particular, is aimed at.

Spatial patterns of plant species in a poor mire on the Southern Alps (Italy)

In a poor mire on the southern Alps of Italy the local distribution of plant species was related to the main hydrological and hydrochemical gradients of the study site. A consistent trend of decreasing water‐table depth was observed from the mire margin towards the mire expanse. Water pH did not show any significant pattern, while electrical conductivity, calcium and magnesium concentrations in pore water decreased from the mire margin towards the mire expanse. The vascular and bryophyte species were divided into three groups on the basis of their distribution on the mire, as defined using a kriging interpolation analysis: 1) species located on the mire margin (i.e., Vaccinium myriillus, Vaccinium vitis‐idaea and Vaccinium uliginosum); 2) species located on the mire expanse (i.e., Drosera rotundifolia, Trichophorum caespttosum, Scheuchzeria palustris, Carex limosa, Drepanocladus fluitans and Sphagnum compactant); 3) species evenly distributed over the mire (i.e., Carex rostrata, Calluna vulgaris, Eriophorum vaginatum, Carex pauciflora, Sphagnum magellanicum, Sphagnum capillifolium, Sphagnum russowii and Polytrichum strictum). Water‐table depth was as the main factor controlling the local distribution of plant species. Vascular species reflected more accurately the boundary between the mire margin and the mire expanse, their distribution probably being affected to a greater extent by waterlogging and dehydration. Among bryophytes, Sphagnum species were less predictive in delimiting the mire margin as a probable consequence of low interspecific competition.