Vegetation change in an ombrotrophic mire in northern England after excluding sheep

Abstract. The role of sheep grazing on vegetation change in upland mires removed from livestock farming and surrounded by conifer plantation was investigated with a grazing trial at Butterburn Flow in northern England. Paired grazed and ungrazed plots from central and peripheral locations were compared over 14 yr. Vegetation data from 34 mires in Kielder Forest provided an ordination framework within which vegetation trends were investigated. A gradient from dry moorland/hummock to wet mire/hollow vegetation dominated this framework and may reflect hydrological variability and structural vegetation differences between the mires. Some species were significantly affected by change in grazing intensity and there were differences between the edge and the centre of the mire. Overall vegetation change depended upon the grazing management and the position of the plots such that the removal of sheep grazing decreased the cover of species typical of wet ombrotrophic conditions, but only at the periphery of the mire. The vegetation in one plot became very similar to that of mires elsewhere in Kielder Forest where sheep were removed several decades ago. Cessation of grazing on upland mires is likely to lead to slow structural and species change in vegetation at the mire edge with a long‐term loss of ombrotrophic species. The nature conservation significance of these changes will depend upon whether or not management objectives target natural conditions or wish to maximize ombrotrophic vegetation. The context of external factors such as climate and pollution may, however, be more important in determining site condition on the wettest mires.     

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.     

Types of Scottish bog vegetation

Summary

The main types of ombrotrophic mire vegetation in Scotland are described with reference to selected mire sites of national importance. The range of variation is controlled by two main environmental gradients, climate and altitude. In particular the degree of oceanicity is crucial, influencing both the vegetation and the hydro-morphology of individual mires. The framework described provided the basis for selection of 31 nationally important mire sites in Scotland identified in the Nature Conservation Review in 1977. Protection of these sites has been successful, except for two sites now afforested. Current threats to Scottish peatlands mainly relate to lowland raised mires.     

Microsite variation and climate result in stand dynamics variation in pristine Pinus sylvestris mires: Evidence from a stand structure study

Questions: How do climate conditions and the site's ecohy‐ drological properties affect the age and size structure of natural Pinus sylvestris stands on pristine boreal mires? How do the long‐term stand dynamics on mires proceed as stands age? Do the mire stands reach a balanced, old‐growth stage? Location: Boreal mire forests in southern and northern Finland. Methods: Tree age and diameter distributions were analysed in 52 stands in two climate areas and in two mire site types with different ecohydrological properties. Temporal stand dynamics were examined by (1) comparing the graphs of the stands’ mean tree ages by diameter at breast height (1.3 m) classes and (2) describing the changes in stand characteristics and stand age and size structures as a function of stand dominant age in a chronosequence. Results: In the south, the DBH distributions were mostly unimodal and bell‐shaped in both site type groups. Age distributions were multimodal and flat in fully‐stocked sites but more uneven in sparsely forested composite sites. In the north, both the age and size distributions were clearly uneven in both site type groups. Tree age and size variation increased with stand age, but levelled out in the long term. Particularly in the south, the abundance of small trees decreased as stand age increased. Conclusions: The pine stands on pristine boreal mires are more dynamic than anticipated and are generally not characterised by a balanced, self‐perpetuating structure. Their dynamics reflect differences in climate and ecohydrology: on stocked sites in favourable boreal conditions, the stands showed structures typically resultant of inter‐tree competition processes that control tree growth and regeneration, whereas in harsh boreal climates, the tree regeneration process is ongoing diversifying the stand structure.     

Impact of rewetting on the vegetation of a cut‐away peatland

Abstract. We tested whether rewetting improved environmental conditions during peatland restoration and promoted colonization and development of mire vegetation. Vegetation change was monitored in a cut‐away peatland one year before, and four years after, rewetting. Colonizers before rewetting were perennials, mostly typical of hummocks or bare peat surfaces. The main variation in vegetation was related to variation in the amounts of major nutrients and water table level. The wettest site with the highest nutrient level had the highest total vegetation cover and diversity, as well as some species typical of wet minerotrophic mires. Raising the water table level above, or close to, the soil surface promoted development of wet minerotrophic vegetation. Diversity initially decreased because of the disappearance of hummock vegetation but started to recover in the third year. Eriophorum vaginatum and Carex rostrata were both favoured, and bryophytes typical of wet habitats colonized the site. Moderate rewetting promoted the development of Eriophorum vaginatum seedlings and an increase in the cover of tussocks. Bryophytes typical of disturbed peat surfaces spread. In the control site development continued slowly towards closed hummock vegetation. The study showed that raising the water level to, or above, soil surface promotes conditions wet enough for a rapid succession towards closed mire vegetation.     

Recent vegetation history of Drygarn Fawr (Elenydd SSSI), Cambrian Mountains,Wales: implications for conservation management of degraded blanket mires

Many areas of blanket mire in Britain display apparently degraded vegetation, having a limited range of ericaceous and Sphagnum species. Data are presented here from Wales from the upland locality of Drygarn Fawr (Elenydd SSSI), which is dominated overwhelmingly by Molinia caerulea. Palaeoecological techniques were used to chronicle vegetation history and to determine the nature and timing of vegetation changes, as an aid to devising conservation management and restoration strategies. Although for the past 2000 years the pollen and plant macrofossil data indicate some evidence for cyclic vegetation change, they demonstrate that here the major vegetation change post-dated the start of the industrial revolution. The palaeoecological data show a greater proportion of Sphagnum than currently. Local extinction of some species (e.g., Myrica gale) apparently took place in Medieval times, but most of the degradation and floral impoverishment apparently occurred during the 20th Century. The implications for conservation management are far-reaching. The overwhelming dominance of Molinia is clearly unprecedented. While it was locally present for hundreds of years, some factor(s)—possibly a change in grazer and grazing regime—encouraged its recent ascendancy in the 20th Century. Consequently, any management attempts to reduce the pre-eminence of Molinia would not be countering an ingrained, long-established dominance. It is suggested that investigation of degraded blanket mires elsewhere by historical and multi-proxy palaeoecological techniques—through multiple, dated cores to track species extinctions and directional vegetation changes—would help ascertain previous mire floras and so indicate a range of restoration targets for mire vegetation.     

Improving predictive mapping in Swiss mire ecosystems through re‐calibration of indicator values

Question: How may Landolt indicator values be re‐calibrated to improve the performance of predictive models? Location: Mires Gross Moos Schwändital (1250 m a.s.l.) in the Prealps, Burgmoos (465 m. a.s.l.) on the Central Plateau and La Burtignière (1000 m a.s.l.) in the Jura, Switzerland. Methods: Habitat distribution models based on high resolution remotely sensed data and vegetation field data are applied to monitor 130 mires. Instead of plant species or communities we used mean indicator values of vegetation records as response variables. To improve the differential power of indicator values for wetland habitat conditions, we calibrated these values using field data. Different methods were tested with our predictive models in three mires to see which calibration method is best in enhancing model performance. To assess the effect of the uneven distribution of vegetation records along environmental gradients, calibrations based on random and evenly distributed samples were compared. As a test of the predictive power of the models we used r² between ground truth and model prediction. This approach is illustrated through an application with nutrient indicator values in the mire La Burtignière. Results: Model performances were not the same for the three mires. The predictive power was better for the nutrient values, soil reaction and humus values than for light and moisture values. 2000 records were sufficient as basis for re‐calibration. Models based on original Landolt indicator values were overall the weakest compared with re‐calibrated values. By comparing the predictive power of Models based on randomly or evenly selected records were about equally predictive. Conclusions: 1. Ahabitat‐specific re‐calibration of the Landolt indicator values enhances the predictive mapping of the Swiss mire ecosystems. 2. The re‐calibration based on weighted averaging gives a better performance than the one based on Gaussian logistic regression. 3. The uneven distribution of indicator values due to the over‐representation of mire habitats does not hamper model performance. 4. 2000 vegetation records are a sufficient basis for an optimal re‐calibration of the vegetation types. An illustration of the method is given by using the soil fertility pattern of the mire La Burtignière.     

Ecological processes and trophic status of two low-alpine patterned mires,south-central South Island,New Zealand

Abstract Vegetation and environmental patterns, and associated ecological processes, were quantified from 42 sites on several transects in each of two extensive (5 and 220 ha) low-alpine patterned mires in the same region of south-central New Zealand. Plant communities, as derived from multivariate analyses, were correlated with 15 physical and chemical environmental factors. Various measures of water availability and chemistry were consistently the most significant factors in relation to vegetation patterns in both mires. In the smaller mire, plant cover adjacent to pools, which were partly or completely drained through underground tunnels, dominated the overall correlations. The nutrient status of surface water had a consistent negative relationship with water availability. No consistent spatial or temporal patterns were found in the concentrations of Ca, Mg, K or Na, nor pH or conductivity in pool water. Evaporative enrichment of cations on the surface of both mires was noted, with levels consistently higher in surface than in adjacent pool water. The somewhat higher nutrient status in the smaller mire may be a result of the size and/or the amounts of run-off from the surrounding slopes onto the mire surface or through the underground pipe system. Hydrogen (D) and oxygen (¹⁸O) isotopic compositions in water from pools, the mire surface and below ground from the smaller mire, suggested that there was negligible mixing of evaporation-enriched surface water with groundwater. Differences in overall nutrient levels in the two mires were relatively small and indicative of mesotrophic or marginally ombrotrophic status for these mires. Although of international significance, the wetland complex currently has inadequate formal protection. Possible options are assessed.     

Classification of boreal mires in Finland and Scandinavia: A review

Mires have been classified in northern Europe at two levels: (1) mire complexes are viewed as large landscape units with common features in hydrology, peat stratigraphy and general arrangement of surface patterns and of minerogenous vs. ombrogenous site conditions; (2) mire sites are considered as units of vegetation research and used in surveys for forestry and conservation. This paper reviews the development of site type classifications in Fennoscandia (Finland, Sweden, Norway), with a discussion on circumboreal classification and corresponding mire vegetation types in Canada. The scale of observation affects classifications: small plot size (0.25–1 m²) has been used in Scandinavia to make detailed analyses of ecological and microtopographical variation in mostly treeless mire ecosystems, while larger sampling areas (up to 100–400 m²) have been commonly employed in Finnish studies of forested peatlands. Besides conventional hierarchic classifications, boreal mires have been viewed as an open, multidimensional, non-hierarchic system which can be described and classified with factor, principal component or correspondence analyses. Fuzzy clustering is suggested as an alternative method of classification in mire studies where only selected environmental and vegetational parameters are measured or estimated.Nomenclature: Lid, J. (1987) Norsk, svensk, finsk flora (vascular plants). Corley et al. (1981) Journal of Bryology 11: 609–689 (bryophytes)     

Species diversity,niche metrics and species associations in harvested and undisturbed bogs

Abstract. Competition is considered an important force in structuring plant communities and in governing niche relations, but communities recovering from disturbance, may be less governed by species interactions and less orderly organized. To address this issue, we studied species richness, abundance and patterns of association between plant species at three spatial scales (1 m², 1/25 m², 1/625 m²) in two ombrotrophic mires in east-central Sweden. One was at a secondary successional stage following peat extraction 50 yr ago and the other was undisturbed. Peat extraction leads to a change in hydrology which is slowly restored by the formation of new peat. Niche breadth and niche overlap along the gradient of height above the water table were calculated for the five common Sphagnum species occurring at both mires in an attempt to better understand differences in species co-occurrence at each mire. Species cover differed between the mires, and the number of species per plot was higher in the undisturbed community at all scales, suggesting that the degree of species intermingling was greater than at the harvested site. At all scales, the number of non-random associations was higher, and niche overlap lower among ecologically similar species (e.g. hollow Sphagnum species) in the undisturbed mire. These differences indicate that random events are important in colonization, and that biotic interactions between neighbours later result in a higher degree of non-randomness. In addition, we surveyed a number of abandoned peat pit sites to test the effect of disturbance for species composition at a regional scale. Ombrotrophic peat pits contained several Sphagnum species normally associated with minerotrophic mires, and species of wooded mires occurred frequently in peat pits, making them more species-rich than undisturbed bogs. There were also Sphagnum species new to, or rare in, this part of Sweden which indicates effective long-distance dispersal. Even 50 yr after peat extraction had ceased, the vegetation had not recovered to its original composition.     

Cranefly (Diptera: Tipuloidea) fauna of a boreal mire system in relation to mire trophic status: implications for conservation and bioassessment

Craneflies (Diptera Tipuloidea) are a typical but poorly known insect group in various moist environments, such as mires. The area of natural mires has strongly decreased in Finland, and there is an urgent need to study and describe the fauna of mires and to determine whether different mire categories support different assemblages of craneflies that might have indicator value. Craneflies were studied using Malaise traps in the Kauhaneva mire system in minerotrophic and ombrotrophic sites, the former subdivided into meso- and oligotrophic sites. A total of 29 cranefly species were recorded. Species richness was highest in mesotrophic sites while the number of species was equally low in oligo- and ombrotrophic sites. Phylidorea squalens, Erioptera flavata, Pedicia rivosa and Tricyphona immaculata were identified as indicators for mesotrophic sites, but no indicators were found for oligo- or ombrotrophic sites. No differences between the species composition of minerotrophic (meso- and oligotrophic combined) and ombrotrophic sites were detected, but when three classes of trophic status were compared, a statistical difference was found. Cranefly species richness in Kauhaneva was low compared to pristine spring habitats. Our results imply, that a focus towards conservation and restoration of mire types with high trophic status would benefit also the conservation of cranefly diversity in the boreal ecoregion. Bioassesments and ecological surveys of craneflies should be designed to cover adequately all trophic status classes within a mire, and especially the mire types with highest trophic status. We also review the distribution and ecology of some potentially regionally threatened cranefly species.     

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.     

Long-term ecological study (palaeoecology) to chronicle habitat degradation and inform conservation ecology: an exemplar from the Brecon Beacons, South Wales

For ecosystems perceived as degraded, but for which the causal factors or timescales for the degradation are disputed or not known, long-term (palaeo-)ecological records may aid understanding and lead to more meaningful conservation approaches. To help ‘bridge the gap’ between (very) long-term ecology and contemporary ecology for practical application, there have been calls for working relationships to be established between palaeoecologists and conservation ecologists. One environment in which this has been attempted is blanket mire. Many blanket mires in Europe are degraded and contain few sphagna. In South Wales, almost all exhibit symptoms of degradation, with dominance by purple moor grass (Molinia caerulea) widespread. We used palaeoecological techniques on three peat profiles in the Brecon Beacons to investigate vegetation history of high-altitude blanket mire to help assess the relative contribution of various factors in mire degradation and to inform strategies for mire conservation and restoration management. We found that declines in sphagna preceded the rise to dominance of monocotyledons. Macrofossil records showed that although Molinia was already present on the Beacons before the start of the industrial revolution, its major rise to dominance in one profile was within the 20th Century, coincident with evidence for local fire. In another profile, it was out-competed by Eriophorum vaginatum after the start of the industrial revolution; there is circumstantial evidence to suggest that a reduction in burning contributed to the rise in E. vaginatum. Conservation management to reduce the current local dominance of both Eriophorum and Molinia is supported by the palaeoecological data, but severe erosion and hagging of peat will constrain practical methods for achieving this on the Beacons until the peat is stabilised. We suggest that palaeoecological techniques have wider applicability in conservation.     

Disjunct Occurrences of Plant Species in the Refugial Mires of Bulgaria

Many mire vascular plant and bryophyte species have disjunct occurrences in Bulgaria despite that most of south-eastern Europe is not suitable for the occurrence of permanently waterlogged and nutrient-limited wetlands due to the current and glacial dry climate conditions as well as prevailing limestone bedrock. Unfortunately, such important distributional data are scattered throughout numerous papers and reports, and are not adequately provided even by national checklists and floras. No attempt to summarize them has been done yet. Therefore, the main aim of this paper is to review and enlarge such data, and to use the resulting data set to address the question whether the disjunctly occurring rare species are concentrated in certain mire complexes or even in particular vegetation plots and if they do characterize such localities. Our current research shows that the phenomenon of isolated occurrences of mire plants in Bulgaria is even more widespread than previously thought. Seventeen species were found as new for Bulgaria with their distribution range limits there, and distributional data of many other species, including some previously considered extinct, were enlarged. Fifty-four mire species were found at only three or fewer sites. Our analyses showed a conspicuous concentration of rare, disjunctly occurring species at a few sites, which are, however, largely unexplored in terms of palaeoecology or ecology, not legally protected and currently threatened by human activities. The distributions of target rare species within Bulgarian mires were significantly nested, which means that more species-poor assemblages were subsets of richer ones. Nestedness was significantly related to the estimated area of mire complex, but not all high-diversity mires were large. Disjunctly occurring rare species were more concentrated in particular vegetation plots at lower altitudes and in mineral-rich fens. Fragmentary data about the ecology and history of Bulgarian refugial mires suggest that these mires harbour specific ecotypes and genotypes, contain specifically distributed biogeographic groups of species, provide an opportunity to test biogeographical hypotheses and shelter crucial information about the history of European mires. Thus, these sites have a potential to become a source of very important information for biogeographical, palaeoecological, and phylogeographical analyses.     

Human and climatic impact on mires: a case study of Les Amburnex mire,Swiss Jura Mountains

Modern period long-term human and climatic impacts on a small mire in the Jura Mountains were assessed using testate amoebae, macrofossils and pollen. This multiproxy data analysis permitted detailed interpretations of local and regional environmental change and thus a partial disentanglement of the different variables that influence long-term mire development. From the Middle Ages until a.d. 1700 the mire vegetation was characterised by ferns, Caltha and Vaccinium, but then abruptly changed into the modern vegetation characterised by Cyperaceae, Potentilla and Sphagnum. The cause for this change was most probably deforestation, possibly enhanced by climatic cooling. A decrease in trampling intensity by domestic animals from a.d. 1950 onwards allowed Sphagnum growth and climatic warming in the a.d. 1980s and 1990s may have been responsible for considerable changes in the species composition. The mire investigated is an example of the rapid changes in mire vegetation and peat development that occurred throughout the central European mountain region during the past centuries as a result of changing climate and land-use practice. These processes are still active today and will determine the future development of high-altitude mires.     

长白山区苔草泥炭沼泽植物物种多样性

本研究以长白山区典型苔草沼泽为对象,分析了密丛型苔草(瘤囊苔草、乌拉草)沼泽和疏丛型苔草(毛苔草)沼泽的植物物种多样性.结果 表明:3种苔草沼泽植物群落共有83个物种,隶属于36科59属.其中,乌拉草沼泽有71个物种,瘤囊苔草沼泽有61个物种,毛苔草沼泽有26个物种.密丛型苔草沼泽植物物种数和物种丰富度明显高于疏丛型苔...     

Diversity and pH changes after 50 years on the boreal mire Skattlösbergs Stormosse,Central Sweden

Abstract. The Skattlösbergs Stormosse mire was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providing a unique opportunity to quantify long‐term mire dynamics. The results show decreased pH in the richer (high‐pH) parts of the mire, but little or no change in the poor fen and ombrotrophic parts. 14 species had disappeared while two new species were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in 10m x 10m plots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 73% of other bryophyte species and 38% of vascular plant species had decreased by more than 20% in plot frequency. There was a strong relationship between number of species and pH‐value. The mean and standard deviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in more polluted areas.     

A phytosociological classification of Swiss mire vegetation

The mapping and monitoring of Swiss mires has so far relied on a classification system based on expert judgement, which was not supported by a quantitative vegetation analysis and which did not include all wetland vegetation types described in the country. Based on a spatially representative sample of 17,608 relevés from 112 Swiss mires, we address the following questions: (1) How abundant are wetland vegetation types (phytosociological alliances) in Swiss mires? (2) How are they distributed across the country––is there a regional pattern? (3) How clearly are they separated from each other? (4) How clear and reliable is their ecological interpretation? Using published wetland vegetation relevés and lists of diagnostic species for phytosociological units (associations and alliances) established by experts, we developed a numerical method for assigning relevés to units through the calculation of similarity indices. We applied this method to our sample of 17,608 relevés and estimated the total area covered by each vegetation type in Switzerland. We found that vegetation types not included in previous mapping were either rare in Switzerland (partly due to mire drainage) or poorly distinguished from other vegetation units. In an ordination, the Swiss mire vegetation formed a triangular gradient system with the Sphagnion medii, the Caricion davallianae and the Phragmition australis as extreme types. Phytosociological alliances were clearly separated in a subset of 2,265 relevés, which had a strong similarity to one particular association, but poorly separated across all relevés, of which many could not be unequivocally assigned to one association. However, ecological gradients were reflected equally well by the vegetation types in either case. Overall, phytosociological alliances distinguished until now proved suitable schemes to describe and interpret vegetation gradients. Nevertheless, we see the urgent need to establish a data base of Swiss wetland relevés for a more reliable definition of some vegetation units.