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Heathland vegetation has undergone significant changes in the past century, e.g., due to airborne pollutants and a lack of proper management. Understanding the interactions between these factors in combination is pivotal for heathland conservation. Here, we studied the vegetation changes at a dune heath in a four-year manipulation experiment analysing the combined effects of nitrogen deposition, mowing, and deer grazing. Our results showed no significant effect of nitrogen deposition and deer grazing on plant growth and cover of dwarf shrubs within the experimental plots. However, high loads of nitrogen decreased bryophyte cover and increased the growth and cover of sand sedge Carex arenaria L. Mowing adversely affected the dwarf shrub community, e.g., the dwarf shrub species crowberry Empetrum nigrum L., and facilitated increased cover and plant growth of graminoids. Plant growth and the cover of C. arenaria increased in plots without deer grazing, whereas bryophyte cover decreased significantly without grazing. We do not recommend intensive mowing of vegetation as a conservation method for dune heaths because it promotes graminoids. From a conservation aspect, it is essential to consider the effect of deer on heathlands because they both impede some species and benefit others and mitigate the adverse effects of nitrogen deposition on dune heaths. [ABSTRACT FROM AUTHOR]

Heathland vegetation has undergone significant changes in the past century, e.g., due to airborne pollutants and a lack of proper management. Understanding the interactions between these factors in combination is pivotal for heathland conservation. Here, we studied the vegetation changes at a dune heath in a four-year manipulation experiment analysing the combined effects of nitrogen deposition, mowing, and deer grazing. Our results showed no significant effect of nitrogen deposition and deer grazing on plant growth and cover of dwarf shrubs within the experimental plots. However, high loads of nitrogen decreased bryophyte cover and increased the growth and cover of sand sedge Carex arenaria L. Mowing adversely affected the dwarf shrub community, e.g., the dwarf shrub species crowberry Empetrum nigrum L., and facilitated increased cover and plant growth of graminoids. Plant growth and the cover of C. arenaria increased in plots without deer grazing, whereas bryophyte cover decreased significantly without grazing. We do not recommend intensive mowing of vegetation as a conservation method for dune heaths because it promotes graminoids. From a conservation aspect, it is essential to consider the effect of deer on heathlands because they both impede some species and benefit others and mitigate the adverse effects of nitrogen deposition on dune heaths.

Aim: Ground lichens have declined in boreal and temperate Europe. The potential causes of the decline were explored by analysing the response of lichen cover to forest management, site and stand variables as well as co-existing plants in different boreal vegetation subzones. Location: Finland. Methods: Understorey vegetation was surveyed on a systematic network of 1721 sample plots in forests on mineral soil. The response of macrolichen cover to explanatory variables was analysed by generalised linear mixed models (GLMMs). Results: Ground lichens favoured old Pinus sylvestris forests on xeric sites with sufficient light conditions. Intensive forest management regimes, such as regeneration cutting and soil ploughing decreased lichen cover, while lighter scarification methods had less effect on lichens. Lichens benefitted from intermediate cutting on sites with low bryophyte cover. Lichens responded similarly to site and stand variables in all boreal subzones, showing that despite heavy reindeer grazing these response patterns apply also in the northern boreal subzone. Lichens showed both negative (Vaccinium myrtillus, Empetrum nigrum and Calluna vulgaris) and positive (Vaccinium vitis-idaea) responses to increasing dwarf shrub cover. Generally, lichens negatively responded to increasing bryophyte cover, indicating either that bryophytes benefit from a decline of lichens or that there is real competition between these groups. The negative relationship between bryophytes and lichens strengthened as the tree canopy becomes denser. Conclusions: Our study provides new quantitative insights into the effects of forest management and changes in forest structure as underlying factors for lichen decline both inside and outside the reindeer-herding area (i.e., the northern boreal subzone). These factors include increased canopy cover with increased shading as well as disturbance caused by regeneration cutting and soil preparation. The possible effects of the long-term legacy of nitrogen deposition, lack of forest fires and climate change are also discussed. [ABSTRACT FROM AUTHOR]

The lowering of water level caused by bog drainage increases the exposure of the upper layers of peat deposits to oxygen, which leads to an increase in the degree of peat decomposition. Elements become more readily available to plants and their biological absorption increases. The aim of this study is to estimate the differences in element accumulation by plants in pristine and drained areas of bogs. We conducted a study of otherwise similar drained and pristine bog sites. We took samples of four plant species (Chamaedaphne calyculata, Andromeda polifolia, Eriophorum vaginatum and Rhododendron tomentosum) and of the peat in which these plants were growing. We analysed the plants and peat for Zn, Cd, Pb and Cu content. We found an increase in the elemental content of plants in drained areas, but the increase was not always significant. We developed, and tested on our data, a coefficient that takes into account both the ability of a species to absorb elements from peat and differences in element content between the pristine and drained areas, to indicate the effect of drainage.

Iceland, located in the climatologically sensitive subarctic zone, is one of the key areas for studying climate change and the current Arctic warming. Poor and rich heathland covers approximately 30% of Iceland, with heath vegetation being the area's most important vegetation type. Prostrate and erect dwarf shrub and shrub species are the primary sources of dendrochronological information on the changes and characteristics of Iceland's climate. Here, we investigate the dendrochronological potential of seven common Icelandic heathland species (Dryas octopetala , Calluna vulgaris , Salix arctica , Salix herbacea , Empetrum nigrum , Juniperus communis nana , and Betula nana) and explore the impact of climate conditions on their growth, particularly with regard to extreme meteorological events. We conducted comparative analyses among species and observed their climatic responses in a climatically, morphologically, and geologically homogeneous setting in north-eastern Iceland. After sampling, measurements, and cross-dating, we constructed local chronologies for the seven species. Of approximately 200 samples, only 113 were included in the final shrub chronologies. All chronologies covered at least 50 years, with few of them exceeding 100 years. Dendroclimatological analysis indicated that above-average temperatures in June and summer positively influence the growth of D. octopetala (June–September), J. communis (July–August), B. nana (July–August), C. vulgaris (June–August), and S. arctica (August–September). The opposite is observed for S. herbacea and E. nigrum. Climate–growth correlations indicate that the growth of these species is negatively correlated with temperature and positively correlated with winter and summer precipitation. Furthermore, among the long-lived woody species growing in Iceland, seven common species were used to assess the impact of extreme meteorological conditions on their growth. The most pronounced extreme year in the wood anatomy of Icelandic shrubs was 1979, depicted as very narrow or missing rings and as the blue ring in J. communis. [ABSTRACT FROM AUTHOR]

This article aims at revising the nomenclature of the Italian syntaxa belonging to the Festuco hystricis-Ononidetea striatae and Rumici-Astragaletea siculi classes according to the EuroVegChecklist at the ranks of class, order and alliance. The correct syntaxon names, authors' citations, nomenclatural types and causes of invalidity and illegitimacy are identified and reported. Two classes (Cerastio-Carlinetea nebrodensis, Festuco hystricis-Ononidetea striatae), two orders (Erysimo-Jurineetalia bocconei, Euphorbietalia myrsinitae) and three alliances (Cerastio-Astragalion nebrodensis, Armerio denticulatae-Stipion etruscae, Sideritidion italicae), treated as valid syntaxa in the EuroVegChecklist, turned out to be invalidly published. The new class Helianthemo cani-Seslerietea nitidae is here described to replace the Festuco hystricis-Ononidetea striatae. The Erysimo bonanniani-Jurineetalia bocconei is validated to contain the new alliance Odontarrheno nebrodensis-Koelerion splendentis and the validated Cerastio tomentosi-Astragalion nebrodensis. Since the Koelerio brutiae-Astragalion calabrici turned out to be a superfluous name, the Plantaginenion serpentinae is here raised to the rank of alliance to include the silicicolous pulvinate scrub of the Sila Mountains. The order Festuco-Seslerietalia nitidae, previously deemed invalid, is proven to be validly published, and it is the earliest available name for the supra- and oromediterranean xeric calcicolous grasslands of the Italian Peninsula. Three mutations of names are provided, and the Astragaletum calabrici is lectotypified. [ABSTRACT FROM AUTHOR]

Abstract Background Alpine alder vegetation acts upon the nearby grass and dwarf shrub vegetation by the nitrogen supply from the symbiotic bacteria Frankia alni of Alnus viridis. This has been studied in two transects concerning plant distribution, plant diversity, nitrate concentration in soil and photosynthetic performance of specific marker plants. Results Away from the alder stand, a band of some meters was dominated by Calamagrostis varia which then was followed by alpine dwarf shrub vegetation. Nitrate in the soil showed a concentration decrease away from the alder stand leading to values near the detection limit in the dwarf shrub zone. Within these three zones, plant species were distributed according to their N-index, given in the ecological literature. Three dominant species, Calamagrostis varia, Rhododendron ferrugineum and Vaccinium myrtillus were examined at sites of different N-availability in the horizontal transect for their photosynthetic performance, by measuring the prompt fluorescence, the OJIP named polyphasic rise of chlorophyll-a fluorescence. All three plant species showed signs of stress in the fluorescence rise kinetics at decreased nitrate availability. These are similar to other known stress effects such as faster reduction of the primary acceptor or an electron supply limitation on the donor site of photosystem II. Conclusion Prompt chlorophyll-a fluorescence data of the examined leaves in a natural vegetation system showed the effects of a decrease in the essential nutrient nitrogen and in a manner parallel to changes in plant diversity. The selected marker plants behaved differently towards decreasing nitrogen concentrations in soil.

In the tundra, woody plants are dispersing towards higher latitudes and altitudes due to increasingly favourable climatic conditions. The coverage and height of woody plants are increasing, which may influence the soils of the tundra ecosystem. Here, we use structural equation modelling to analyse 171 study plots and to examine if the coverage and height of woody plants affect the growing-season topsoil moisture and temperature (< 10 cm) as well as soil organic carbon stocks (< 80 cm). In our study setting, we consider the hierarchy of the ecosystem by controlling for other factors, such as topography, wintertime snow depth and the overall plant coverage that potentially influence woody plants and soil properties in this dwarf shrub-dominated landscape in northern Fennoscandia. We found strong links from topography to both vegetation and soil. Further, we found that woody plants influence multiple soil properties: the dominance of woody plants inversely correlated with soil moisture, soil temperature, and soil organic carbon stocks (standardised regression coefficients = − 0.39; − 0.22; − 0.34, respectively), even when controlling for other landscape features. Our results indicate that the dominance of dwarf shrubs may lead to soils that are drier, colder, and contain less organic carbon. Thus, there are multiple mechanisms through which woody plants may influence tundra soils. [ABSTRACT FROM AUTHOR]

In the UK, the majority of peatlands have been damaged by drainage, agriculture, forestry plantations or erosion, compromising the ecosystem services they deliver including carbon sequestration. On the other hand, since the 1990s many projects have carried out a range of interventions to restore peatlands. In forest-to-bog restoration, tree removal and drain blocking lead to immediately visible changes. However, while some key plant species return within years, they may continue to exhibit differences in how they perform and interact with their environment. To investigate this, plant functional traits were measured and compared for Calluna vulgaris, Erica tetralix, Eriophorum angustifolium, Eriophorum vaginatum, Sphagnum capillifolium and Sphagnum papillosum collected in an open blanket bog, a forestry plantation and two forest-to-bog restoration sites in northern Scotland. Significantly lower specific leaf area and chlorophyll content, and higher leaf dry matter content, were found in the open bog site compared with plantation and forest-to-bog sites. This could be related to nutrient enrichment derived from brash and needle decomposition in the latter sites, suggesting a lasting effect of coniferous plantations even after decades of restoration management. Altered plant functional traits may have feedbacks on ecosystem processes such as litter decomposition and peat formation.

The lowering of water level caused by bog drainage increases the exposure of the upper layers of peat deposits to oxygen, which leads to an increase in the degree of peat decomposition. Elements become more readily available to plants and their biological absorption increases. The aim of this study is to estimate the differences in element accumulation by plants in pristine and drained areas of bogs. We conducted a study of otherwise similar drained and pristine bog sites. We took samples of four plant species (Chamaedaphne calyculata, Andromeda polifolia, Eriophorum vaginatum and Rhododendron tomentosum) and of the peat in which these plants were growing. We analysed the plants and peat for Zn, Cd, Pb and Cu content. We found an increase in the elemental content of plants in drained areas, but the increase was not always significant. We developed, and tested on our data, a coefficient that takes into account both the ability of a species to absorb elements from peat and differences in element content between the pristine and drained areas, to indicate the effect of drainage. [ABSTRACT FROM AUTHOR]

In the Nama-Karoo, South Africa, rainfall and grazing by livestock are two important drivers of botanical composition. Summer rains are advantageous particularly to the grass layer, whereas the characteristic dwarf shrubs survive better than grasses during drought, and benefit from rainfall during cool months. Heavy grazing by livestock during summer reduces the abundance of grasses, whereas winter grazing increases it. This study examined the influences of season of grazing (summer vs winter) and rainfall on botanical composition at two long-term grazing trials at Grootfontein in the eastern Karoo from 1949 to 1967. Severe summer grazing strongly reduced grass abundance and slightly increased the abundance of both palatable and unpalatable dwarf shrubs. High previous-season rainfall strongly promoted short-lived grasses. Dwarf shrubs and grasses declined in response to a decline in annual rainfall over the study period, except for the creeping grass Tragus koelerioides that increased in abundance, possibly in response to decreased competition and an increase in available gaps in the vegetation layer. Results indicate that grazing systems that exclude repeated summer-only grazing maintain ecological health, and that rainfall is the main driver of composition unless extreme grazing systems are employed. [ABSTRACT FROM AUTHOR]

Background: Alpine alder vegetation acts upon the nearby grass and dwarf shrub vegetation by the nitrogen supply from the symbiotic bacteria Frankia alni of Alnus viridis. This has been studied in two transects concerning plant distribution, plant diversity, nitrate concentration in soil and photosynthetic performance of specific marker plants. Results: Away from the alder stand, a band of some meters was dominated by Calamagrostis varia which then was followed by alpine dwarf shrub vegetation. Nitrate in the soil showed a concentration decrease away from the alder stand leading to values near the detection limit in the dwarf shrub zone. Within these three zones, plant species were distributed according to their N-index, given in the ecological literature. Three dominant species, Calamagrostis varia, Rhododendron ferrugineum and Vaccinium myrtillus were examined at sites of different N-availability in the horizontal transect for their photosynthetic performance, by measuring the prompt fluorescence, the OJIP named polyphasic rise of chlorophyll-a fluorescence. All three plant species showed signs of stress in the fluorescence rise kinetics at decreased nitrate availability. These are similar to other known stress effects such as faster reduction of the primary acceptor or an electron supply limitation on the donor site of photosystem II. Conclusion: Prompt chlorophyll-a fluorescence data of the examined leaves in a natural vegetation system showed the effects of a decrease in the essential nutrient nitrogen and in a manner parallel to changes in plant diversity. The selected marker plants behaved differently towards decreasing nitrogen concentrations in soil. [ABSTRACT FROM AUTHOR]

Nitrogen fertilization can increase above- and belowground forest growth and carbon storage in low nitrogen (N) environments. However, it may also induce changes in other parts of the ecosystem, such as altered composition and diversity of the ground vegetation. These changes may occur, for example, because of increased availability of nitrogen and light depletion due to a denser tree canopy. We studied vegetation changes at 11 experimental sites in Pinus sylvestris stands with low N-deposition, along a south–north gradient in Sweden. We estimated the relative cover of individual species and the data were analysed with a linear model, using total amount of fertilizer-N added, years since last fertilization, site and site index as independent variables. The relative cover of the dominant dwarf shrubs (Vaccinium myrtillus and Vaccinium vitis-idaea) increased following fertilization. In the bottom layer, N significantly increased the total cover of two of the three dominant species (Pleurozium schreberi and Dicranum spp.). For the third species (Hylocomium splendens) no detectable effect was found. For lichens as a group, the cover decreased following N fertilization. No effect of N fertilization on species diversity was detected at any of the sites, and the forest vegetation types remained unchanged. [ABSTRACT FROM AUTHOR]

Premise: Mountain ecosystems are particularly sensitive to climate change. However, only a very small number of studies exist so far using annually resolved records of alpine plant growth spanning the past century. Here we aimed to identify the effects of heat waves and drought, driven by global warming, on annual radial growth of Rhododendron ferrugineum. Methods: We constructed two century‐long shrub ring‐width chronologies from R. ferrugineum individuals on two adjacent, north‐ and west‐facing slopes in the southern French Alps. We analyzed available meteorological data (temperature, precipitation and drought) over the period 1960–2016. Climate–growth relationships were evaluated using bootstrapped correlation functions and structural equation models to identify the effects of rising temperature on shrub growth. Results: Analysis of meteorological variables during 1960–2016 revealed a shift in the late 1980s when heat waves and drought increased in intensity and frequency. In response to these extreme climate events, shrubs have experienced significant changes in their main limiting factors. Between 1960 and 1988, radial growth on both slopes was strongly controlled by the sum of growing degree days during the snow free period. Between 1989 and 2016, August temperature and drought have emerged as the most important. Conclusions: Increasing air temperatures have caused a shift in the growth response of shrubs to climate. The recently observed negative effect of high summer temperature and drought on shrub growth can, however, be buffered by topographic variability, supporting the macro‐ and microrefugia hypotheses. [ABSTRACT FROM AUTHOR]

Mammalian herbivores shape the structure and function of many nutrient-limited or low-productive terrestrial ecosystems through modification of plant communities and plant–soil feedbacks. In the tundra biome, mammalian herbivores may both accelerate and decelerate plant biomass growth, microbial activity and nutrient cycling, that is, ecosystem process rates. Selective foraging and associated declines of palatable species are known to be major drivers of plant–soil feedbacks. However, declines in dominant plants of low palatability often linked with high herbivore densities may also modify ecosystem process rates, yet have received little attention. We present data from an island experiment with a 10-year vole density manipulation, to test the hypothesis that herbivores accelerate process rates by decreasing the relative abundance of poorly palatable plants to palatable ones. We measured plant species abundances and community composition, nitrogen contents of green plant tissues and multiple soil and litter variables under high and low vole density. Corroborating our hypothesis, periodic high vole density increased ecosystem process rates in low-productive tundra. High vole density was associated with both increasing relative abundance of palatable forbs over unpalatable evergreen dwarf shrubs and higher plant N content both at species and at community level. Changes in plant community composition, in turn, explained variation in microbial activity in litter and soil inorganic nutrient availability. We propose a new conceptual model with two distinct vole–plant–soil feedback pathways. Voles may drive local plant–soil feedbacks that either increase or decrease ecosystem process rates, in turn promoting heterogeneity in vegetation and soils across tundra landscapes. [ABSTRACT FROM AUTHOR]

The Natura 2000 network is crucial to conserve biodiversity in the European Union and provides hotspots for certain ecosystem services. Grazing, a common land use in different Natura 2000 habitat types, may contribute to the maintenance of protected plant communities and reduce fuel loads and wildfire hazard. Our study aims to assess the effects of grazing on plant composition and conservation status of calcareous shrub-grassland Natura 2000 habitat types, as well as its effects on fire hazard reduction and aboveground carbon storage. We surveyed plant communities grazed by goats in fenced (ungrazed) and open (grazed) plots in a mosaic of calcareous shrub-grassland habitat types and assessed plant species composition and habitat conservation status. We also assessed aboveground plant biomass in grazed and ungrazed plots and modelled potential fire behaviour in those plots for each habitat. With the exception of cryptogams, grazing did not affect plant cover, but positively affected species richness (mean ± SD: 26.80 ± 11.65 vs. 29.37 ± 8.59, P = 0.01; fenced vs. unfenced) and Shannon diversity (2.11 ± 0.81 vs. 2.33 ± 0.55, P < 0.01) in the habitat mosaic. Furthermore, grazing did not affect the conservation status of two out of three of the studied habitat types. Additionally, grazing decreased the fire hazard in grass and dwarf shrub communities without reducing aboveground carbon stocks significantly. Our results show that moderate grazing is a management practice that effectively contribute to the conservation of Natura 2000 shrub-grassland habitat types through reduction of wildfire hazard and maintenance of habitat conservation status. [ABSTRACT FROM AUTHOR]

High Arctic is an intensively explored region in relation to predicted global warming. Its long-term impact is analysed in dwarf-shrubs, such as a widely distributed and pioneering species Salix polaris (polar willow). Understanding the functioning of lateral meristems in these dwarf-shrubs is however limited, affecting interpretation of the data. The presented study focused on the formation and anatomy of the derived secondary tissues in the stems of S. polaris from polar habitats. The entire branches of the polar willow were collected in five vegetation types of tundra located in SW Spitsbergen (Svalbard) and analysed on the series of transverse and longitudinal sections. Our analyses showed that the periderm developed in two or three-year old stems as the secondary protective tissue, and that the multiple epidermis, typical of many willow species, was not formed in S. polaris. The secondary xylem in the polar willow stems showed considerable differences in diameter and length of vessel elements within a single stem. Importantly, the size of the vessel elements differed also depending on the tundra vegetation type. Our findings suggest that the soil moisture was a main factor determining the size of vessels, and that their size was not correlated to the nitrogen supply. Our study thus demonstrated the usefulness of different anatomical features of wood, in above-ground organs, in High Arctic research. [ABSTRACT FROM AUTHOR]

Almost all natural terrestrial ecosystems are nutrient limited in terms of growth, and we expect treeline vegetation to be no exception. However, direct constraints of low temperature on tissue formation may superimpose effects of low nutrient availability.We examined growth responses of two tree (Larix decidua and Pinus uncinata) and two dwarf shrub species (Vaccinium myrtillus and Vaccinium gaultherioides) to 12 years of moderate fertilizer addition (NPK applied at a rate of 15 and 30 kg nitrogen ha−1 a−1) along an elevation gradient within the treeline ecotone in the Swiss Alps (2,083 to 2,225 m a.s.l.). We measured annual top‐ and side‐shoot increments as well as stem ring width in trees and shoot increments in dwarf shrubs.Fertilizer addition increased soil nutrient availability, indicated by enhanced soil extractable N, higher concentrations of N, P and K in leaves and higher foliar δ15N.Fertilizer addition stimulated annual growth of all four species: by 11%–20% for L. decidua and 15%–36% for P. uncinata (depending on trait) and by 8%–16% for the two dwarf shrub species. Growth stimulation by the higher fertilizer dose was not significantly stronger than by the lower dose (except for V. gaultherioides), suggesting an overall low nutrient demand for growth and saturation at a rather low nutrient input.Synthesis. Even slightly enhanced nutrient availability can stimulate growth of trees and dwarf shrubs in an alpine treeline ecosystem. Ongoing atmospheric nutrient deposition, in conjunction with global warming, may accelerate plant growth at the treeline. Twelve years of low‐dose nutrient addition showed that even slightly enhanced nutrient availability stimulates growth of two tree (Larix decidua and Pinus uncinata) and two dwarf shrubs species (Vaccinium myrtillus and Vaccinium gaultherioides) in an alpine treeline ecosystem. Ongoing atmospheric nutrient deposition, in conjunction with global warming, may therefore accelerate plant growth at the treeline. [ABSTRACT FROM AUTHOR]

The facilitation mechanism maintains ecosystem richness by increasing seedling recruitment. Overgrazed grasslands of northwestern Patagonia are invaded by shrubs that could promote the seedling recruitment of forage species. We investigated the role of Acaena splendens shrubs on the maintenance of diversity and its usefulness as a nurse shrub in the recruitment of Festuca pallescens, a grass of high forage value present with a low cover in degraded grasslands. To test the performance of A.splendens as a nurse plant in non-degraded grassland, we recorded the species richness four years inside of A. splendens senescent shrubs and in gaps among dominant tussock grasses. Species were grouped in four functional groups: annual and biannual herbs and grasses, perennial herbs, perennial grasses and shrubs. To test the usefulness of A. splendens in the restoration of degraded grassland, we monitored the seedling emergence and survival of F. pallescens inside A. splendens and in gaps. We related seedling survival to meteorological and microenvironmental conditions. Species richness was higher in Acaena nurse plants than in gaps. The frequency of functional groups, with exception of annual and biannual herbs and grasses, were higher in Acaena than in gaps. Seedling emergence and survival of F. pallescens were higher in Acaena, but the seedlings died in summer in both microsites. Mean maximum temperature was higher and mean minimum humidity lower in gaps than in Acaena during spring. However, the spring-summer season in which we monitored F. pallescens survival, was exceptionally dry and hot, affecting the survival of F. pallescens seedlings. Our results show that A. splendens act as a nurse species increasing the richness in the non-degraded grassland and facilitating the seedling recruitment of an important forage species in the degraded grassland. Nevertheless, the facilitation mechanism will fail in drought conditions, indicating that this restoration tool is limited by climate. [ABSTRACT FROM AUTHOR]

Lateglacial submarine lake sediments are reported for the first time from the Kattegat Sea in southern Scandinavia. The Lateglacial sediments were collected from a vibrocore that contained, from top to bottom, Holocene marine muddy sand, Holocene brackish‐water mud, Early Holocene peat with remains of Betula pubescens and telmatic plants, Lateglacial lake deposits that are the focus of this paper, and homogenous sand. Radiocarbon dating of terrestrial plant remains from the Lateglacial sediments gave ages between 12 400 and 12 800 cal a bp, corresponding to the Younger Dryas. The Lateglacial sediments contain remains of Betula nana and other plants indicating a tundra‐like open landscape with dwarf shrub heaths, which is typical for the region. Remains of macrolimnophytes indicate shallow carbonate‐rich, cool lake waters. Remains of larvae of Trichoptera and Chironomidae dominate the invertebrate fauna and indicate a fairly species‐rich fauna. Half of the trichopteran taxa today have their distribution north of Denmark or show a generally northern distribution in Europe. The lake sediments are found at ∼ 24 m below sea level, and the presence of lake sediments shows that this part of Kattegat had not been transgressed by the sea during the Younger Dryas. [ABSTRACT FROM AUTHOR]

Sphagnum mosses mediate long-term carbon accumulation in peatlands. Given their functional role as keystone species, it is important to consider their responses to ecological gradients and environmental changes through the production of phenolics. We compared the extent to which Sphagnum phenolic production was dependent on species, microhabitats and season, and how surrounding dwarf shrubs responded to Sphagnum phenolics. We evaluated the phenolic profiles of aqueous extracts of Sphagnum fallax and Sphagnum magellanicum over a 6-month period in two microhabitats (wet lawns versus dry hummocks) in a French peatland. Phenolic profiles of water-soluble extracts were measured by UHPLC-QTOF-MS. Andromeda polifolia mycorrhizal colonization was quantified by assessing the intensity of global root cortex colonization. Phenolic profiles of both Sphagnum mosses were species-, season- and microhabitat- dependant. Sphagnum-derived acids were the phenolics mostly recovered; relative quantities were 2.5-fold higher in S. fallax than in S. magellanicum. Microtopography and vascular plant cover strongly influenced phenolic profiles, especially for minor metabolites present in low abundance. Higher mycorrhizal colonization of A. polifolia was found in lawns as compared to hummocks. Mycorrhizal abundance, in contrast to environmental parameters, was correlated with production of minor phenolics in S. fallax. Our results highlight the close interaction between mycorrhizae such as those colonizing A. polifolia and the release of Sphagnum phenolic metabolites and suggest that Sphagnum-derived acids and minor phenolics play different roles in this interaction. This work provides new insight into the ecological role of Sphagnum phenolics by proposing a strong association with mycorrhizal colonization of shrubs. [ABSTRACT FROM AUTHOR]

A study of relationships between the micromosaic structure of vegetation and the composition of L layer of the litter of automorphous dwarf shrub-green moss spruce forests of the northern taiga has been carried out on the Kola peninsula. The analysis is performed based on the total content of secondary metabolites (phenolic compounds including lignin and tannins), carbon, as well as, nitrogen, and other nutrients in either L layer or senescent photosynthetic organs of dominating plant species forming an active litterfall fraction. The contribution of these species to the phytomass of mosaic components is considered, as is the micromosaic structure of vegetation. A trend in the growth of the content of mineral nutrients, phenols, and condensed tannins in the forest litter has been revealed in the case of an increase in their content in senescent plant organs. The content of lignin and the C/N ratio in the top litter depends less on the lignin concentration in senescent plant organs and may be determined by the conditions of the further plant litter decomposition, including microbiological activity, differences in water and light regimes, etc. [ABSTRACT FROM AUTHOR]

Tundra vegetation dynamics are an excellent indicator of Arctic climate change. In many places in the Arctic, greening of tundra has been observed since the 1980s due to rapid increases in temperature. However, in some areas the opposite process has taken place in connection with a reduction in biomass production. The spatial patterns of tundra ‘greening’ and ‘browning’ constitute important issues in the contemporary analysis of polar ecosystems. The aim of our study was to assess recent tundra vegetation dynamics on the basis of changes in annual growth ring widths of the polar willow. Bjørnøya (Bear Island), located in the western part of the Barents Sea is an important site in the transition zone between the high and low Arctic. No dendrochronological studies have been conducted to date due to the island’s isolation, which makes access very difficult. In 2012 and 2016, 43 samples of Salix polaris Wahlenb. were taken from the south-eastern part of Bear Island. An average chronology of the 29 most closely correlated measurement series was then compiled, covering 95 years (1922–2016); however, the time span 1946–2016 was used for the climate-growth analysis. Beginning in the mid-1980s, an increase in the width of annual increments was observed, whereas over the last decade (since 2005) the growth rate has declined rapidly. Simple correlation analyses showed that temperatures in spring and summer had the positive influence on the radial growth of the polar willow; however, the results of the moving correlation analysis made it possible to conclude that this relationship is more complex and time-dependent. Sensitivity of radial growth to temperature was strongest in the years 1955–2005, whereas the decrease in the strength of positive correlation with temperature since 2005 has been accompanied by a significant increase in the importance of summer precipitation.

The probabilistic cellular-automata model of development and long-time dynamics of dwarf shrub populations and communities is developed. It is based on the concept of discrete description of the plant ontogenesis and joint model approaches in terms of probabilistic cellular automata and L-systems by Lindenmayer. Short representation of the basic model allows evaluation of the approach and software implementation. The main variables of the model are a number of partial bushes in clones or area projective cover. The model allows us to investigate the conditions of self-maintenance and sustainability population under different environmental conditions (inaccessibility of the territory for settlement, mosaic moisture conditions of soil and wealth). The model provides a forecast of the total biomass dynamics shrubs and their fractions (stems, leaves, roots, fine roots, fruits) on the basis of the data obtained in the discrete description of ontogenesis and further information on the productivity of the plant fractions. The inclusion of the joint dynamics of biomass of shrubs and soil in EFIMOD models cycle of carbon and nitrogen to evaluate the role of shrubs in these circulations, especially at high impact, such as forest fires and clear cutting, allow forecasting of the dynamics of populations and ecosystem functions of shrubs (regulation of biogeochemical cycles maintaining biodiversity, participation in the creation of non-wood products) with changing climatic conditions and strong damaging effects (logging, fires); and application of the models developed to investigate the stability and productivity of shrubs and their participation in the cycle of carbon and nitrogen in different climatic and edaphic conditions.

Abstract Ericaceous dwarf shrubs, such as bilberry, Vaccinium myrtillus , have an important role in nutrient cycling of boreal forests, but in metal polluted environments they also form a link between heavy metal pool of the soil, primary consumers and upper trophic levels. From the viewpoint of metal transfer in a food chain, we document metallic element (As, Ca, Cd, Co, Cu, Mn, Mo, Ni, Pb, Se, Zn) concentrations in leaves, berries and herbivorous larvae of V. myrtillus around a Finnish copper-nickel smelter and compare those with levels in relatively unpolluted reference sites, and with levels documented in soil and feces (a proxy of dietary levels) of an insectivorous bird, the pied flycatcher, Ficedula hypoleuca. Herbivorous larvae of the autumnal moth, Epirrita autumnata (Lepidoptera: Geometridae), grown experimentally on V. myrtillus , showed slower growth rate but not higher mortality in the polluted area. In general, metal levels in leaves, berries and larvae were higher in the polluted area and comparable to those reported at other smelter sites in Europe. The levels of the main toxic metals (As, Cd, Cu, Ni, Pb) followed the general pattern: soil > bird feces > leaves > larvae = berries, and levels in V. myrtillus , E. autumnata and F. hypoleuca reflected soil metal levels. The lowest levels were found in those matrices that are most important sources of food for birds and humans, i.e. leaf-eating larvae and berries, reducing a risk of toxic effects. Highlights • Metal levels in bilberry reflect soil concentrations near a copper-nickel smelter. • Growth of leaf-chewing lepidopteran larvae was retarded on exposed plants. • Toxic metals followed the pattern: soil > bird feces > leaves > larvae = berries. • Current metal levels do not pose a toxicological risk for wildlife or humans. [ABSTRACT FROM AUTHOR]

Question: Vascular plant productivity of arctic tundra has often been viewed as varying little between years and thus being largely insensitive to the high inter‐annual variation in summer weather conditions. Yet, remote‐sensing data and retrospective growth analyses of the circumpolar dwarf shrub, Cassiope tetragona, commonly show considerable between‐year variability in plant growth in response to variation in summer temperature. Given that both Cassiope growth and vascular plant biomass production share a common environmental driver, summer temperature, we would expect positive co‐variation between them. Here we investigate whether this is indeed the case and if so over what spatial scale. Location: Nordenskiöldland, high arctic Svalbard. Methods: We brought dendroecology and plot‐based field estimation methodologies together in an empirical study using retrospective analysis of Cassiope growth and annual estimation of above‐ground vegetation biomass production to investigate their temporal and spatial co‐variation and sensitivity to summer weather conditions. Results: Despite substantial small‐scale heterogeneity, we found spatial co‐variation in Cassiope growth patterns, which weakened as distance between sampling sites increased from 0 to 25 km. Furthermore, we found a strong positive correlation between annual estimates of above‐ground live vascular plant biomass and Cassiope shoot growth over a 12‐year period at a local scale. The correlation declined with distance, likely due to increasing differences in local weather conditions. Conclusions: We demonstrate that Cassiope growth can be used as a proxy for above‐ground tundra vegetation productivity at the local scale. Our findings suggest that Arctic plant productivity is as sensitive to between‐year variation in summer temperature as the well‐established growth response of Cassiope. This challenges the view that tundra plant productivity varies little between years and provides a mechanistic understanding that helps reconcile field‐ and satellite‐based annual estimation methods. Arctic above‐ground vascular plant productivity and annual growth of the dwarf shrub Cassiope tetragona share a common environmental driver, summer temperature. We found local‐scale positive covariation between them over a 12‐year period in high arctic Svalbard, suggesting tundra plant productivity is as sensitive to between‐year variation in summer temperature as the well‐established growth response of Cassiope. [ABSTRACT FROM AUTHOR]

Warming-induced biological and ecological responses have been reported from high-northern latitude sites, where changes in dwarf shrub communities translate into complex vegetation-climate feedbacks. Most of the available Arctic tree-ring evidence is, however, restricted to a limited number of species and locations. A combination of wood anatomical and ‘dendro’-ecological techniques provides insights into past growth rates, recruitment dynamics and even community assemblages of Arctic vegetation. Here, we use thin sectioning and ring counting of 1432 dwarf shrub samples from eight species and two tundra regions in coastal east Greenland to assess community recruitment history and its relation to climate. Site and species-specific annual stem increments, as well as estimated plant ages, range from 0.013-0.720 mm and from 4 to 204 years, respectively. The mean ring width is 0.086 mm, with a mean age of 50 years. Decadal-scale recruitment dynamics of the studied vegetation cover respond to Greenlandic summer temperature variations back to the late 19th century ( r  = 0.7; 1881–2000). [ABSTRACT FROM AUTHOR]

Seed dispersal is a key process in plant community dynamics, and soil seed banks represent seed dispersal in time rather than in space. Despite their potential importance, seed bank dynamics in the Arctic are poorly understood. We investigated soil seed banks and corresponding plant community composition in three contrasting vegetation types in West Greenland, viz. dwarf shrub heaths, herb slopes and fell‐fields. Through germination testing, 31 species were documented in soil seed banks. All of these were herbaceous, while no dwarf‐shrub species, which represents the dominating growth form in the above‐ground vegetation, were emerging from the seed bank. Consequently, across vegetation types, the lowest similarity between seed bank and above‐ground vegetation was found in dwarf shrub heath. Nine plant species were exclusively found in seed bank, all of which were non‐clonal forbs. Seed bank size (total number of seeds) and species richness seemed to increase with the level of natural disturbance. Additionally, we examined the effect of different experimental light and temperature conditions on the quantity and diversity of germinating seeds. The difference in diversity in vegetation and seed bank at the species level will impact population dynamics, regeneration of vegetation after disturbances and its potential to respond to climate change. [ABSTRACT FROM AUTHOR]

Warming may lead to a cover increase of tundra shrubs and a north- and upward shift of treelines. The latter may be inhibited by a densification of shrub stands. However, the climatic drivers of neartreeline shrub growth are relatively unexplored, especially that of shrub species from different functional groups growing intertwined, in competition for light and resources. We measured ring widths from two dominant dwarf shrubs species, the deciduous Betula nana and the evergreen Empetrum nigrum ssp. hermaphroditum from a near-treeline alpine ridge in the Central Norwegian Scandes, and tested the influence of on-site and regional climate, and changes therein, over the past 55 yr. Radial growth of B. nana was found to be negatively influenced by early summer (June–July) precipitation, possibly related to low amounts of photosynthetically active radiation and nitrogen leaching, and positively by July temperatures. That of E. hermaphroditum was positively correlated with late summer (July–August) temperatures. In recent decades, the influence of summer climate on both species’ growth has declined and been replaced by a negative influence of May temperatures. Rising spring temperatures in recent decades have likely advanced key phenology events in B. nana and E. hermaphroditum, such as budburst and flowering. This may have left the shrubs’ soft tissues vulnerable to late frost events, which in recent decades occur more frequently after the advanced start of the growing season, resulting in suppressed growth. [ABSTRACT FROM AUTHOR]

Non-random patterns in the functional structure of communities are often interpreted as evidence for different forces governing their assemblage. However, community assembly processes may act antagonistically, countering each other's signatures on the functional structure of communities, which may lead to spurious inferences on the underlying mechanisms. To illustrate this issue, we assessed the joint effects of environmental filtering and facilitative interactions on a key leaf functional trait (i.e. specific leaf area, SLA) in Mediterranean dwarf-shrub communities, using a two-scale sampling approach. Specifically, we analyzed differences in community-weighted mean SLA values (CWM-SLA) between communities (community-scale) and between guilds within communities (guild-scale, i.e. individuals sampled in understorey, overstorey and open-ground conditions) across contrasted soil environments and elevational gradients. We found that communities on harsh edaphic conditions (i.e. dolomite habitats) showed significantly lower CWM-SLA values than communities on more fertile habitats. In contrast, elevation was a poor predictor of differences in CWM-SLA between the communities. This suggests that environmental filtering may influence leaf trait variation along soil gradients irrespective of elevation. On the other hand, communities on dolomite habitats showed strong differences in CWM-SLA between understorey (higher CWM-SLA) and either open-ground and overstorey guilds (lower CWM-SLA), whereas communities on more fertile soils showed no differences between the guilds. The strong differences in CWM-SLA between understorey and non-understorey guilds in dolomite communities suggest that facilitative interactions may be particularly at stake under stressful edaphic conditions, thus partially mitigating the effect of environmental filtering (i.e. low SLA values) on communities growing in harsh soils. [ABSTRACT FROM AUTHOR]

Abstract: Questions: The rapid climate warming in tundra ecosystems can increase nutrient availability in the soil, which may initiate shifts in vegetation composition. The direction in which the vegetation shifts will co‐determine whether Arctic warming is mitigated or accelerated, making the understanding of successional trajectories urgent. One of the key factors influencing the competitive relationships between plant species is their access to nutrients, depending on the depth where they take up most nutrients. However, nutrient uptake at different soil depths by tundra plant species that differ in rooting depth is unclear. Location: Kytalyk Nature Reserve, northeast Siberia, Russia. Methods: We injected 15N to 5 cm, 15 cm and the thaw front of the soil in a moist tussock tundra. The absorption of 15N by grasses, sedges, deciduous shrubs and evergreen shrubs from the three depths was compared. Results: The results clearly show a vertical differentiation of N uptake by these plant functional types, corresponding to their rooting strategy. Shallow‐rooting dwarf shrubs were more capable of absorbing nutrients from the upper soil than from deeper soil. Deep‐rooting grasses and sedges were more capable of absorbing nutrients from deeper soil than the dwarf shrubs. The natural 15N abundances in control plants also indicate that graminoids can absorb more nutrients from the deeper soil than dwarf shrubs. Conclusions: Our results show that graminoids and shrubs in the Arctic differ in their N uptake strategies, with graminoids profiting from nutrients released at the thaw front, while shrubs mainly forage in upper soil layers. Our results suggest that tundra vegetation will become graminoid‐dominated as permafrost thaw progresses and nutrient availability increases in the deep soil. [ABSTRACT FROM AUTHOR]

Dwarf shrubs are a dominant plant type across many regions of the Earth and have hence a large impact on carbon and nutrient cycling rates. Climate change impacts on dwarf shrubs have been extensively studied in the Northern Hemisphere, and there appears to be large variability in response between ecosystem types and regions. In the Southern Hemisphere, less data are available despite dwarf shrub vegetation being a dominant feature of southern South America and mountainous regions of the Southern Hemisphere. Here, we present the response of an Empetrum rubrum dwarf shrub and a Poa grass community to 12 years of experimental climate manipulation achieved using open top chambers on the Falkland Islands, a cold temperate island group in the South Atlantic. The dwarf shrub and grass vegetation did not change significantly in cover, biomass or species richness over the 12 years period in response to climate warming scenarios of up to 1°C reflecting annual warming levels predicted in this region for the coming decades. The soil microarthropod community, however, responded with declines in abundance (37%) under warming conditions in the grass community, but no such changes were observed in the dwarf shrub community. Overall, our data indicate that dwarf shrub communities are resistant to the levels of climate warming predicted over the coming decades in the southern South America region and will, therefore, remain a dominant driver of local ecosystem properties. [ABSTRACT FROM AUTHOR]

Our work aims to investigate whether herbaria resources can be used for the extension of Arctic dwarf shrub chronologies. The current use of herbaria reaches far beyond their initially aims; among the new applications, phenology observations and conservation biology can be mentioned. However, to this date, no studies on the use of herbarium specimens for dendrochronological research have been published. Examples of perennial plants from herbarium sheets that could potentially be used for such studies are dwarf shrubs, samples of which often consist of whole specimens, including the root system, the root collar and branches. Here, we present a protocol for the selection and processing of historical material. Based on the collections from Kew and Copenhagen, which are among of the largest herbaria with Arctic plants, a database of 25 areas from the Atlantic sector of the Arctic was created. Material from the following most common species was collected: grey willow (Salix glauca L.), polar willow (Salix polaris Wahlenb.), dwarf willow (Salix herbacea L.), net-leaved willow (Salix reticulata L.), arctic willow (Salix arctica Pall.), mountain avens (Dryas octopetala L.), dwarf birch (Betula nana L.). We present the preliminary results of a case study using historical samples of Salix arctica from the Thule (Qaanaaq) area, NW Greenland. Dwarf shrubs can commonly reach the age of 80–100 years or beyond, while herbaria resources may allow the extension of such series over the last centuries. Therewith, these resources may provide an excellent proxy data source on the changing natural environment beyond the northern and upper tree limits, where well-replicated proxy time-series remain sparse. [ABSTRACT FROM AUTHOR]

Rapid climate warming has resulted in shrub expansion, mainly of erect deciduous shrubs in the Low Arctic, but the more extreme, sparsely vegetated, cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. Dwarf shrub dendrochronology may reveal climatological causes of past changes in growth, but is hindered at many High Arctic sites by short and fragmented instrumental climate records. Moreover, only few High Arctic shrub chronologies cover the recent decade of substantial warming. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the northernmost polar desert at 83°N in North Greenland. We analysed climate-growth relationships over the period with available instrumental data (1950-2012) between a 102-year-long C. tetragona shoot length chronology and instrumental climate records from the three nearest meteorological stations, gridded climate data, and North Atlantic Oscillation ( NAO) and Arctic Oscillation ( AO) indices. July extreme maximum temperatures (JulTemx), as measured at Alert, Canada, June NAO, and previous October AO, together explained 41% of the observed variance in annual C. tetragona growth and likely represent in situ summer temperatures. JulTemx explained 27% and was reconstructed back to 1927. The reconstruction showed relatively high growing season temperatures in the early to mid-twentieth century, as well as warming in recent decades. The rapid growth increase in C. tetragona shrubs in response to recent High Arctic summer warming shows that recent and future warming might promote an expansion of this evergreen dwarf shrub, mainly through densification of existing shrub patches, at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost, contrasting earlier notions of limited shrub growth sensitivity to summer warming in the High Arctic. [ABSTRACT FROM AUTHOR]

Carbon (C) allocation is a key determinant of plant functioning and ecosystem processes. Its dynamic responses to environmental conditions and global change are still poorly understood. This holds particularly true for dwarf shrubs, which are an important component of high mountain vegetation. We studied the short-term C allocation dynamics in two dominant dwarf shrub species, Vaccinium myrtillus and Vaccinium uliginosum, at two subalpine sites, in the Pyrenees and in the Alps, and additionally performed an experimental rain exclusion to simulate summer drought at the site in the Alps. We compared net assimilation rates ( A max ), stomatal conductance ( g s ) and shoot water potentials ( Ψ S ) between the two species and carried out a 13 C pulse labelling experiment to trace their C allocation dynamics, both under natural conditions and in the drought experiment. Under ambient conditions, V. uliginosum showed higher A max and g s and used recent assimilates as a respiratory substrate more slowly than V. myrtillus . C allocation dynamics in current-year shoots differed significantly between the species, showing a progressive decrease after the pulse labelling in V. uliginosum shoots but a progressive increase in V. myrtillus shoots. In the drought experiment, a significant reduction of soil moisture caused predawn Ψ S below −1.2 MPa in both species, which is considered close to the turgor loss point. However, the stomatal conductance and the speed of transfer of newly assimilated C to belowground organs decreased in V. uliginosum only. We found a strong coupling in C allocation dynamics between xylem and phloem tissues of the rhizome, which was maintained under drought. Although both species were largely tolerant to the drought imposed, our results indicate a higher drought sensitivity of V. uliginosum compared to V. myrtillus , with potential implications for community composition and ecosystem C cycling in a future climate. [ABSTRACT FROM AUTHOR]

Although soil invertebrates play a decisive role in maintaining ecosystem functioning, little is known about their structural composition in Alpine soils and how their abundances are affected by the currently ongoing land-use changes. In this study, we re-assessed the soil macrofauna community structure of managed and abandoned Alpine pastureland, which has already been evaluated 14 years earlier. Our results confirm clear shifts in the community composition after abandonment, in that (1) Chilopoda and Diplopoda were recorded almost exclusively on the abandoned sites, (2) Coleoptera larvae and Diptera larvae were more abundant on the abandoned than on the managed sites, whereas (3) Lumbricidae dominated on the managed sites. By revisiting managed and abandoned sites, we infer community patterns caused by abandonment such as changes in the epigeic earthworm community structure, and we discuss seasonal and sampling effects. Our case study improves the still limited understanding of spatio-temporal biodiversity patterns of Alpine soil communities. [ABSTRACT FROM AUTHOR]

Rhododendron ferrugineum L. is a widespread dwarf shrub species growing in high-elevation, alpine environments of the Western European Alps. For this reason, analysis of its growth rings offers unique opportunities to push current dendrochronological networks into extreme environments and way beyond the treeline. Given that different species of the same genus have been successfully used in tree-ring investigations, notably in the Himalayas where Rhododendron spp. has proven to be a reliable climate proxy, this study aims at (i) evaluating the dendroclimatological potential of R. ferrugineum and at (ii) determining the major limiting climate factor driving its growth. To this end, 154 cross-sections from 36 R. ferrugineum individuals have been sampled above local treelines and at elevations from 1800 to 2100 m asl on northwest-facing slopes of the Taillefer massif (French Alps). We illustrate a 195-year-long standard chronology based on growth-ring records from 24 R. ferrugineum individuals, and document that the series is well-replicated for almost one century (1920–2015) with an Expressed Population Signal (EPS) > 0.85. Analyses using partial and moving 3-months correlation functions further highlight that growth of R. ferrugineum is governed by temperatures during the growing season (May–July), with increasingly higher air temperatures favoring wider rings, a phenomenon which is well known from dwarf shrubs growing in circum-arctic tundra ecosystems. Similarly, the negative effect of January–February precipitation on radial growth of R. ferrugineum , already observed in the Alps on juniper shrubs, is interpreted as a result of shortened growing seasons following snowy winters. We conclude that the strong and unequivocal signals recorded in the fairly long R. ferrugineum chronologies can indeed be used for climate–growth studies as well as for the reconstruction of climatic fluctuations in Alpine regions beyond the upper limits of present-day forests. [ABSTRACT FROM AUTHOR]

Climate warming can lead to changes in alpine plant species interactions through modifications in environmental conditions, which may ultimately cause drastic changes in plant communities. We explored the effects of 4 years of experimental warming with open-top chambers (OTC) on Vaccinium myrtillus performance and its interaction with neighbouring shrubs at the Pyrenean treeline ecotone. We examined the effects of warming on height, above-ground (AG) and below-ground (BG) biomass and the C and N concentration and isotope composition of V. myrtillus growing in pure stands or in stands mixed with Vaccinium uliginosum or Rhododendron ferrugineum. We also analysed variations in soil N concentrations, rhizosphere C/N ratios and the functional diversity of the microbial community, and evaluated whether warming altered the biomass, C and N concentration and isotope composition of V. uliginosum in mixed plots. Our results showed that warming induced positive changes in the AG growth of V. myrtillus but not BG, while V. uliginosum did not respond to warming. Vaccinium myrtillus performance did not differ between stand types under increased temperatures, suggesting that warming did not induce shifts in the interaction between V. myrtillus and its neighbouring species. These findings contrast with previous studies in which species interactions changed when temperature was modified. Our results show that species interactions can be less responsive to warming in natural plant communities than in removal experiments, highlighting the need for studies involving the natural assembly of plant species and communities when exploring the effect of environmental changes on plant-plant interactions. [ABSTRACT FROM AUTHOR]

Detailed descriptions of individual vegetation types shown on vegetation maps can improve the ways in which the composition and spatial structure within the types are understood. The authors therefore examined dwarf shrub heath, a vegetation type covering large areas and found in many parts of the Norwegian mountains. They used data from point samples obtained in a wall-to-wall area frame survey. The point sampling method provided data that gave a good understanding of the composition and structure of the vegetation type, but also revealed a difference between variation within the vegetation type itself (intra-class variation) and variation resulting from the inclusion of other types of vegetation inside the map polygons (landscape variation). Intra-class variation reflected differences in the botanical composition of the vegetation type itself, whereas landscape variation represented differences in the land-cover composition of the broader landscape in which the vegetation type was found. Both types of variation were related to environmental gradients. The authors conclude that integrated point sampling method is an efficient way to achieve increased understanding of the content of a vegetation map and can be implemented as a supporting activity during a survey. [ABSTRACT FROM PUBLISHER]

PREMISE OF THE STUDY: Vegetative reproduction and spread through clonal growth plays an important role in arctic-alpine ecosystems with short cool growing seasons. Local variation in winter snow accumulation leads to discrete habitat types that may provide divergent conditions for sexual and vegetative reproduction. Therefore, we studied variation in clonal structure of a dominant, evergreen, dwarf shrub (Empetrum nigrum s.l. with the two taxa E. nigrum L. s.s. and E. hermaphroditum Hagerup) along a snow cover gradient and compared clonal diversity and spatial genetic structure between habitats. METHODS: We studied 374 individual shoots using 105 polymorphic AFLP markers and analyses based on hierarchical clustering, clonal diversity indices, and small-scale spatial genetic structure with pairwise kinship coefficient. We used two approaches to define a threshold of genotypic distance between two samples that are considered the same clone. Clonality was examined among three habitats (exposed ridges, sheltered depressions, birch forest) differing in snow conditions replicated in four study regions in Norway and Sweden. KEY RESULTS: Clonality of E. hermaphroditum differed between habitats with an increase in clonal diversity with decreasing snow depth. Small-scale spatial genetic structure increased with decreasing clonal diversity and increasing clone size. In three study regions, E. hermaphroditum was the only species, whereas in one region E. nigrum also occurred, largely confined to exposed ridges. CONCLUSIONS: Our results demonstrated that snow cover in conjunction with associated habitat conditions plays an important role for the mode of propagation of the dwarf shrub E. hermaphroditum. [ABSTRACT FROM AUTHOR]

The efficacy of using vegetative clumps derived from seeds with a variety of origins to establish nuclei for regeneration of bog vegetation on abandoned peat mines in Nova Scotia and New Brunswick (Canada) was tested using seeds within scats (excrement) and seeds from berries, various techniques for creating clumps, and different clump sizes. Direct placement of scat pieces on peat in the field did not produce successful colonisation. Vegetative clumps begun in a greenhouse, whether from seeds extracted from scats or berries, were 60–100 % successful when transplanted into abandoned peat mines depending on the initial size of the transplant. Based on annual growth rate, Vaccinium oxycoccos has the greatest capacity to quickly colonise abandoned peat mines. Other promising taxa were Vaccinium vitis-ideae and the genus Empetrum.

• Many parts of Iceland are affected by the severe aeolian erosion. • Dendrochronological analyses of dwarf shrubs provided reliable data on rates and timing of aeolian erosion. • Erosion rates (post-1990′s) ranged from 1.0 cm yr−1 in the 1970 s to 4.4–5.4 cm yr−1. • Reconstructed erosion rates in NE Iceland compared well to observations of dusty conditions (from the 1970′s to the present) • Increased erosion rates of small erosional escarpments coincide with dust storm activity. Iceland is known for having strong aeolian erosion events, as evidenced by erosional escarpments on the soil surface; these are known locally as rofabards. The aim of the study was to estimate aeolian erosion rates at two research plots affected by severe erosion, using anatomic features of the roots of Arctic, woody, dwarf shrubs. Ours is the first study to utilize dendrochronological analyses of exposed roots of dwarf willows (Salix herbacea L.) as an indicator of aeolian erosion. When dwarf shrub roots are exposed to the atmosphere by erosion, cell sizes are reduced by >50 %, with maximum changes in individual plants exceeding 150–200 %. We detected the erosion signal by analyzing changes in cell-size and width of growth rings in the roots. Using this relationship, were able to estimate erosion rates (the retreat of escarpments) since the 1970s for the study area. During the 1970s and 1980s, erosion rates were fairly constant, with retreat ranging from 1.0 to 2.5 cm yr−1. Rapid increases in erosion rates were observed after the late 1990s, occasionally as much as 4.4–5.4 cm yr−1. Increased aeolian erosion rates may be linked to continuous heavy grazing by sheep and climate change, as this period coincides with increased numbers of hot and warm, and dusty days. Our results indicate that dendrochronological methods can be highly useful in determining past geomorphic activity, due to modern environmental changes observed in the Arctic. The methods employed here can be applied even in treeless areas. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated the camels’ (1) dietary preference for perennial plants, (2) low selectivity among perennial species, and (3) ability to remove large amounts of perennial biomass, thus causing irreversible damage on the landscape. We studied the activity and feeding behaviour of camels on coastal sand dunes dominated by the dwarf shrub Artemisia monosperma , as well as the short-term impacts of camel foraging on perennial vegetation. The herd foraged on four semi-stabilised dunes during summer, when the available biomass was composed almost entirely of perennials. We recorded the activity and feeding selectivity of the camels, as well as the consumption and recovery of the common perennial plant species. The camels were selective foragers and spent relatively little time feeding when the more palatable perennial species became scarcer. Most of the more palatable (herbaceous) species were consumed, and these plant species recovered faster and more abundantly than the less palatable (both woody and herbaceous) species, which were hardly consumed. A. monosperma was practically avoided despite its dominance, even when more palatable species were nearly absent. In conclusion, results suggest that camels are selective feeders, and will not cause irreversible damage to the local vegetation. [ABSTRACT FROM AUTHOR]

Natural floodplains belong to the most species-rich ecosystems worldwide. However, over the last decades there has been a strong decrease in the extent of natural floodplains. As a consequence, the biodiversity of these ecosystems has experienced a dramatic decline. In this study, we investigated the habitat and food preferences of the grasshopper species Chorthippus binotatus on gravel banks of a nearly natural river system in the Spanish Pyrenees. The studied plots on the alluvial gravel banks in the Spanish Pyrenees were characterised by strong differences in habitat structure. However, C. binotatus only occurred in sparsely-vegetated sub-Mediterranean dry grasslands. The abundance of the grasshopper species was also strongly related to habitat structure and cover of the main food source and dominant plant species of these open grasslands, the dwarf shrub Genista scorpius. Concerning habitat structure, the grasshopper species preferred habitats with sparse and low-growing vegetation with a high cover of bare ground and gravel/stones. C. binotatus occupies a very narrow ecological niche within the studied floodplain. It requires sparsely-vegetated gravel banks that ensure sufficient oviposition sites and a favourable ambient temperature for optimal development. G. scorpius dwarf shrubs have to be considered as multi-functional key elements in the habitats of C. binotatus. They offer high-quality food, shelter against predators and allow thermoregulation in a hot and dry Mediterranean environment. For the conservation of C. binotatus, we recommend maintaining and restoring both natural floodplain dynamics as well as traditional grazing systems. [ABSTRACT FROM AUTHOR]

Plant-plant interactions are key drivers of treeline dynamics. At the Pyrenean treeline, the dwarf shrub Vaccinium myrtillus grows in pure stands or in mixed stands with Vaccinium uliginosum or Rhododendron ferrugineum. They form sparse shrub patches that colonize subalpine grasslands, having dramatic impacts on their structure and functioning. We investigated the role of the two co-occurring shrubs as possible modulators of the structure and performance of V. myrtillus in the Central Pyrenees. We analysed biomass, growth, functional parameters, age distribution, N and C concentrations and isotope compositions (δN and δ C) of V. myrtillus ramets in pure stands, and stands mixed with V. uliginosum or R. ferrugineum. Volume, above-ground biomass and age of the ramets did not differ between stand types. We found lower δC values, indicative of lower water-use efficiency (WUE), in leaves and shoots of V. myrtillus in stands with R. ferrugineum than in pure stands. The N content and δN of V. myrtillus leaves and shoots in pure stands were higher than in mixed stands, pointing to a competition for N in mixed stands. Our results indicate that V. myrtillus competes for nutrients with its neighbours, but neither this competition nor the lower WUE affect its above-ground performance. Therefore, the interaction with co-occurring shrubs does not have a major effect on V. myrtillus structure and functioning at treeline and, consequently, should not be considered as a key driver on the dynamics of this species in the encroachment of subalpine grasslands. [ABSTRACT FROM AUTHOR]

Questions To what extent may impact vary according to the invaded community, region or sites? Do impact thresholds exist, above which native species richness and/or cover declines rapidly? Does impact following invasion by the exotic shrub Baccharis halimifolia differ from that of a native shrub ( Tamarix gallica) during natural successions? Location Mediterranean coast, SE France. Methods Vegetation was sampled on 120 4-m² quadrats, half of which were in areas invaded by B. halimifolia and the other half in nearby non-invaded areas, in two distinct community types nested in three sites in each of two regions. Mixed models were built to explain variations in impacts on native vegetation according to community types, sites and regions. Next, 85 additional plots variously invaded by B. halimifolia were used to assess the nature of the relationships between B. halimifolia cover and impact in Juncus communities. Linear regressions were compared to polynomial regressions, and when relevant, regression trees were built to identify threshold values. Finally, we compared the vegetation from 90 plots either dominated by B. halimifolia, by T. gallica (a native shrub) or without a shrub layer (control) using dissimilarity indices in wet meadows. Results The magnitude of B. halimifolia impacts depended mainly on community type, with no differences between regions. Community structure (species richness, Shannon's diversity) declined linearly with increasing cover of B. halimifolia, with the most rapid decline in annual species. Native species cover fitted better with a cubic regression, with an impact threshold of around 86% cover of B. halimifolia. Impact of B. halimifolia on community diversity was higher than that of the native shrub T. gallica. While the magnitude of species composition changes was comparable for both shrubs, the higher nestedness component of dissimilarity found for B. halimifolia may indicate a higher short-term impact. Conclusion Improved understanding of the impacts of exotic shrubs on community structure and composition can be gained via comparisons with the impacts caused by native shrubs. Higher impacts of the exotic B. halimifolia on Mediterranean salt marsh vegetation are likely explained by a denser canopy, shorter juvenile period and more frequent recruitment. [ABSTRACT FROM AUTHOR]