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.     

Patch dynamics and local succession in a sandstone area with frequent disturbance

Abstract. A system of sand talus cones in a small forested rocky sandstone area was investigated to determine the importance of disturbance‐related dynamics and mesoclimate to vegetation differentiation. These cones (usually 3–12 m long) are formed by the accumulation of sand at the foot of sandstone rocks and are subject to frequent disturbance by the transport of sand. Vegetation was recorded both at the whole‐cone level and at the within‐cone level; the latter was approached by means of a transect of small squares along each cone. Soil profiles were recorded at the upper, centre and bottom parts of the cones. To express mesoclimatic differentiation among the cones within the rocky area, the potential insolation was calculated from the horizon angular height and the likelihood of thermal inversions was estimated by the height of the cones above the valley bottom. The major environmental factor correlated with variation in cone vegetation is the disturbance dynamics as determined by the structure of the soil profile; active cones (with sand at the surface) are colonized by different species as compared with non‐active cones (with surface covered by humus sediments). There is a clear primary succession gradient from plants able to cope with continuous sand transport to stands of tall bryophytes, small shrubs and herbs. Quite often the same gradient is found within cones, with late successional vegetation confined to the lower, stabilized parts of the cones, while the upper part is still being affected by sand transport. The differentiation along the gradient of disturbance is much stronger than the differentiation due to climatic or other gradients. Indirect data indicate that the long‐term average rate of sand accumulation is ca. 1 mm/yr. If sand transport ceases, Sphagnum peat accumulates on some of the cones; the depth of accumulated Sphagnum remains may reach 50 cm. The development of the peat layer is but weakly correlated with the measured variables suggesting that random processes at the beginning of Sphagnum establishment may be a driving force. By measuring Sphagnum growth and decomposition, and the peat density, we estimated the time needed for their development to be several hundreds of years.     

Nitrogen concentration and δ15N signature of ombrotrophic Sphagnum mosses at different N deposition levels in Europe

Alteration of the global nitrogen (N) cycle because of human‐enhanced N fixation is a major concern particularly for those ecosystems that are nutrient poor by nature. Because Sphagnum‐dominated mires are exclusively fed by wet and dry atmospheric deposition, they are assumed to be very sensitive to increased atmospheric N input. We assessed the consequences of increased atmospheric N deposition on total N concentration, N retention ability, and δ¹⁵N isotopic signature of Sphagnum plants collected in 16 ombrotrophic mires across 11 European countries. The mires spanned a gradient of atmospheric N deposition from about 0.1 up to about 2 g m^?2 yr^?1. Mean N concentration in Sphagnum capitula was about 6 mg g^?1 in less polluted mires and about 13 mg g^?1 in highly N‐polluted mires. The relative difference in N concentration between capitulum and stem decreased with increasing atmospheric N deposition, suggesting a possible metabolic mechanism that reduces excessive N accumulation in the capitulum. Sphagnum plants showed lower rates of N absorption under increasing atmospheric N deposition, indicating N saturation in Sphagnum tissues. The latter probably is related to a shift from N‐limited conditions to limitation by other nutrients. The capacity of the Sphagnum layer to filter atmospheric N deposition decreased exponentially along the depositional gradient resulting in enrichment of the mire pore water with inorganic N forms (i.e., NO₃^?+NH₄⁺). Sphagnum plants had δ¹⁵N signatures ranging from about ?8‰ to about ?3‰. The isotopic signatures were rather related to the ratio of reduced to oxidized N forms in atmospheric deposition than to total amount of atmospheric N deposition, indicating that δ¹⁵N signature of Sphagnum plants can be used as an integrated measure of δ¹⁵N signature of atmospheric precipitation. Indeed, mires located in areas characterized by greater emissions of NH₃ (i.e., mainly affected by agricultural activities) had Sphagnum plants with a lower δ¹⁵N signature compared with mires located in areas dominated by NO_x emissions (i.e., mainly affected by industrial activities).     

Sphagnum distribution patterns along environmental gradients in Bulgaria

Abstract

The distribution patterns of 18 Sphagnum species along base-richness and altitudinal gradients were studied in Bulgarian treeless wetlands which are noteworthy because of the edge-of-range occurrence of many mire species including Sphagnum. Of 483 spring and mire sites studied, 202 samples contained some Sphagnum species. The most common species were S. subsecundum (n=85), S. platyphyllum (46), S. contortum (41), S. teres (40) and S. capillifolium (26). The significance of Sphagnum responses to environmental gradients was tested by comparing generalized additive models against the null model. Many Sphagnum species displayed a significant response to the altitudinal gradient. Several species were clearly linked to low or to high altitudes, but the realized niche of other species was wide with respect to altitude. Most species significantly responded to water pH, both above and below the timberline. The same result was obtained for water conductivity below the timberline, whereas only a few species had a significant response to conductivity above the timberline. The highest water conductivity under which Sphagnum species occurred was 280 μS cm^?1. Sphagnum contortum was the species occupying the mires with the highest mineral content. On the contrary, Sphagnum warnstorfii, one of the most calcitolerant species in many regions of Europe, often occurred in extremely mineral-poor mires above the timberline. Some other Sphagnum species growing in mineral-rich mires below the timberline, also inhabited extremely mineral-poor mires above the timberline. This could be explained by adaptation to local conditions during long-term isolation on mineral-poor bedrock or by changed competition pressure.     

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.     

Techniques for restoring fen vegetation on cut‐away peatlands in North America

Question: Which restoration measures (reintroduction techniques, reintroduction timing and fertilization) best enable the establishment of fen species on North American cut‐away peatlands? Location: Rivière‐du‐Loup peatland, southern Québec, Canada. Methods: In total, eight treatments which tested a combination of two reintroduction techniques, two reintroduction timings and the use of phosphorus fertilization were tested in a field experiment within a completely randomized block design. Results: Sphagnum transfer, a reintroduction technique commonly used for bog restoration in North America, was effective for establishing Sphagnum and Carex species. The hay transfer method, commonly used for fen restoration in Europe, was much less successful, probably due to questionable viability of reintroduced seeds. The treatments which included light phosphorus fertilization, had a higher Carex cover after three growing seasons. The timing of the reintroductions had no impact on the success of vegetation establishment. However, vegetation reintroduction should be carried out in the spring while the ground is still frozen to minimize other ecological impacts. Conclusions: The success of the diaspore reintroduction technique on small‐scale units indicates that a large‐scale restoration of fens using this technique is feasible.     

Ion flux from precipitation to peat soil in spruce forest–<Emphasis Type="Italic">Sphagnum</Emphasis> bog communities in the Ochiishi district,eastern Hokkaido,Japan

To evaluate the contribution of proton flux from precipitation on peat acidification in mire ecosystems, we estimated ion fluxes to peat soils from bulk deposition in Sphagnum-dominated bogs and from throughfall plus stem flow in spruce forests in three cool-temperate ombrogenous mires in the Ochiishi district, northeastern Japan. We tested the hypothesis that proton fluxes from the atmosphere to peat soils are affected by vegetation types, leading to the consequent difference in soil acidity. The proton flux in bulk deposition was higher than that in throughfall plus stem flow, but the concentration of H⁺ in the peat surface water in Sphagnum bogs was lower than that in spruce forests. The inverse relationship between proton flux and soil water acidity means that the soil water acidity could not be explained quantitatively by proton flux from the atmosphere to the peat surface. The ion fluxes of sea-salt components were dependent on the distance from the coast to the mires. This means that the sea-salt accumulation in the peat surface soil can be directly attributed to the high flux of sea-salt from precipitation. The flux of sea-salts deposited on the mires positively correlated with the H⁺ concentration of the peat surface water in each community, implying that the acidity of peat surface water depends on the cation fluxes from precipitation.     

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.     

Rockin' in rhythm,growth dynamics of the peat moss Sphagnum

The genus Sphagnum is an essential component in the formation and maintenance of high latitude peatlands, bogs and mires. The species grows in dense, extended mats of agglomerated shoots that allow it to retain water necessary for its growth. These mats are partly responsible for maintaining the right conditions for other species in these wetlands to thrive. In this issue of Physiologia Plantarum, Mironov et al. (2020) monitored the growth of Sphagnum riparium for a period of 4 years and revealed three distinct growth rhythms: a seasonal temperature dependent, a circalunar and a third one, synchronized with the circalunar. This synchronised nature of Sphagnum growth could contribute to its position as a key species in the maintenance of peatlands.     

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.     

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.     

A model of alpine species distribution in relation to snowmelt time and altitude

Abstract. The focus of this study is the response of species to time of snowmelt and altitude in alpine areas and an examination of changes in species response to snowmelt as altitude increases and temperature decreases. Transects (n= 43) were placed evenly along an altitudinal gradient at Finse, Hardanger‐vidda, western Norway, from ridges to late snowbeds. These gradients were systematically sampled (‘Repeated Gradient Analysis, RGA’) and an adjusted F‐test was used to determine repeated trends in species distribution along the transects. Of the 41 taxa analysed 22 showed a significant change in expected occurrence in response to time of snowmelt (when a site becomes free of snow) as altitude increased. Three types of response were observed: (1) no change in response: (2) increased occurrence as altitude increases, i.e. the taxon invades snow‐free sites as altitude increases, and (3) decreased occurrence as altitude increases, i.e. the taxon retreats from snow covered areas. It is suggested that the changes in response are due to both environmental factors (temperature related) and biological interactions. Decreases in expected occurrence are probably due to increased environmental severity as altitude increases (temperature related decreases). These species are represented by taxa preferring intermediate cover of snow. The invasion of earlier snow‐free sites is probably due to reduced competition from lee‐side taxa as altitude increases. A predictive model based on the species‐environmental relationships suggests that a 1°K temperature increase changes the limits of occurrence in response to time of snowmelt from 3 to 20 days for the different taxa.     

Numerical syntaxonomy of the Asplenietalia petrarchae in the Iberian Peninsula

Abstract. A numerical syntaxonomic study of rupicolous vegetation of the Asplenietalia petrarchae in the Iberian Peninsula is described. The study is based on 37 local tables (OSUs) of different rupicolous communities from limestone cliffs found in the eastern half of the Iberian Peninsula. Three classification approaches were followed: (1) ‘hard partition’ techniques, (2) ‘fuzzy partition’ and (3) ordination partition. In order to find a direct solution, we tried an evaluation system based on the inertia associated with a CCA, Canonical Correspondence Analysis, and its relationships with the inertia of a similar CA, Correspondence Analysis. The most effective solutions were found through spatial partitions, and the best partition was obtained with CA considering five segments per axis. Among the fuzzy partitions the best solution was obtained with two clusters and a fuzziness value of 1.20. The best hierarchical partition was Complete Linkage with Chord Distance as a resemblance function. With the GRID procedure applied to the CA diagram, three different groups were distinguished. The first group is related to the Saxifragion boisseriano-reuterani, including five OSUs from Baetic ranges; the second group is very close to the Cosentinio-Lafuenteion rotundifoliae and includes 11 OSUs from thermo-mediterranean areas; the third group, including 21 OSUs basically related to meso-mediterranean areas, is strongly related to the Teucrion buxifolii.     

The influence of altitude on the distribution of subterranean organs and humus components in Vaccinium myrtillus carpets

Abstract. Humus profiles were sampled along an altitudinal gradient in the Macot‐La‐Plagne Forest (France, northern Alps) to investigate variation occurring under carpets of Vaccinium myrtillus present within Picea abies forests. The vertical distribution of subterranean organs of V. myrtillus was compared with (1) that of P. abies roots and other accompanying vegetation and (2) other components of humus profiles, in particular humified organic matter mainly consisting of animal faeces. It was shown that V. myrtillus roots were mostly concentrated in mineral horizons, while P. abies roots and V. myrtillus rhizomes occupied litter horizons. This was interpreted in terms of competition for nutrient capture between P. abies and V. myrtillus. The effects of altitude were (1) a change in the vegetation accompanying V. myrtillus in dense V. myrtillus carpets, bryophytes at the montane level being replaced by forbs at the sub‐alpine level and (2) a decrease in the thickness of ecto‐organic horizons. This was interpreted as a shift from a moder system characterized by recalcitrant litter (moss) processed by an active faunal community (stabilized in the form of animal faeces) to a mor system characterized by low animal abundance but with litter of better quality which is easily leached in the absence of prominent faunal activity.     

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.     

Large‐scale changes in abundance of terricolous bryophytes and macrolichens in Finland

Abstract. Major changes in forest floor vegetation were identified on the basis of three nationwide surveys conducted as part of national forest inventories in 1951–1953, 1985–1986 and 1995. These surveys provided objectively selected, statistically representative samples of all forested land in Finland. The 1951–1953 data consist of over 10000 sample plots, while the later surveys were conducted on ca. 3000 permanent plots. Changes in relative abundance of dominant species (i.e. in the proportions of species of the total cover of forest floor vegetation) were analysed across biogeographical provinces. Spatial correlation, systematic sampling, partial re‐measurement and multiple testing were taken into account in assessment of the statistical significance of the observed changes. The most notable changes in forest floor vegetation were a decrease in the relative abundance of Hylocomium splendens and an increase in Dicranum polysetum. In N Finland, where forests are grazed by semi‐domestic reindeer, we observed a decline in the abundance of Cladina lichens and an increase in Dicranum mosses. Peltigera aphthosa declined throughout the country. Polytrichum juniperinum, Pohlia nutans, and Brachythecium species, which occupy disturbed sites or grow on litter, increased in abundance. The relative abundance of Sphagnum species decreased, particularly in W Finland, where Pleurozium schreberi was favoured. A major decline in S. fuscum was also recorded in C and E Finland. Many of the changes detected in this study are apparently related to intensified forest management; but solely on the basis of this study, its effects cannot be distinguished from those of other large‐scale environmental changes.     

长白山哈泥泥炭地丘间生境泥炭藓孢子的寿命

长寿有性繁殖体对于植物种群的长存具有重要意义,迄今,泥炭地苔藓植物孢子长寿性研究还很少。在长白山哈泥泥炭地钻取丘间表层泥炭样品,测定泥炭腐殖化度和烧失量,逐层提取和培养泥炭藓孢子,研究埋藏时间对孢子萌发的影响。结果表明,丘间泥炭藓孢子埋藏环境中,随着埋深的增加即埋藏年限的增加,泥炭腐殖化度和烧失量总体上分别呈现增加和递减的趋势,而地层泥炭藓孢子萌发率呈现直线递减的规律,但在埋藏近150余年后孢子萌发率仍可达40%。研究进一步证明泥炭藓具有长期持久孢子库,根据推算,泥炭地丘间埋藏环境中,泥炭藓孢子最大寿命可超过400a。     

Post‐fire bryophyte establishment in a continental bog

Questions : What is the mechanism of bog ground layer colonization post‐fire? Is species colonization stochastic or does facilitation occur? Location : Boreal bog peatland near Crow Lake, Alberta, Canada. Methods : Diaspore‐addition treatments were applied in 2003 to autoclaved peat samples from high and low microtopographic positions within a recently burned bog. Colonization was assessed within the plots in 2005 and compared to control plots to determine treatment success and patterns of colonization. Results : A significant degree of ground layer colonization was found two years after fire, with Polytrichum strictum dominating the site. Colonization was greater in low (wet) plots, although only P. strictum and Sphagnum angustifolium had significant colonization. No effect of diaspore addition was observed and Sphagnum was only found in conjunction with P. strictum. Conclusions : Environmental conditions and species life history strategy are more important than diaspore availability for post‐fire colonization. True mosses (e.g. P. strictum) appearto facilitate Sphagnum colonization.     

Dwarf-shrub-<Emphasis Type="Italic">Sphagnum</Emphasis> mires in taiga zone: Comparison of phytomass structure and productivity

The study compared phytomass structure (percentages of phytomass fractions) and annual primary production of mesotrophic dwarf-shrub-Sphagnum mires—the most widespread mires in Karelia, West Siberia, and Priamur’e. The analysis showed similarities and differences in phytomass structure among the regions. Fire-disturbed and undisturbed mires of Priamur’e were compared. The study revealed high productivity of underground phytomass of vascular plants and its close relation to water regime of mesotrophic mires in general and those of Priamur’e in particular.