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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]

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]

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]

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]

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]

The dynamics and structure of the phytomass and production of an undisturbed mesotrophic dwarf shrub-sphagnum phytocenosis and one burned by fire have been compared. The net primary production (NPP) of both sites of phytocenoses in the postpyrogenic period is estimated by direct field determination of the productivity parameters, and C emission from the fire is assessed. The obtained data on emission (0.7 kg/m) differ from the results obtained in the peatlands of western Canada (3.2 kg/m). [ABSTRACT FROM AUTHOR]

Rates of decomposition in Arctic soils are regulated by temperature and moisture, but substrate availability is dictated by vegetation inputs, which are also subject to biotic influences. Here, we examine how leaf and litter inputs from individual dwarf shrub species influence soil enzyme activity in a sub-Arctic heath community in Abisko, Sweden. We further consider how foliar damage via insect herbivory (and outbreak) affects the soil community and decomposition. During the peak growing season (July 2011), we assessed how shrub community composition ( Empetrum hermaphroditum, Vaccinium myrtillus, V. uliginosum and V. vitis- idaea) determined litter and soil phenol oxidase activity. A periodic severe outbreak of autumn moth larvae ( Epirrita autumnata) affected this community in the following year (July 2012), and we used this to investigate its impact on relationships with phenol oxidase activity, soil respiration, soluble NH and soluble phenolics; the soluble factors being directly associated with inputs from insect larval waste (frass). Pre-outbreak (2011), the strongest relationship observed was higher phenol oxidase activity with E. hermaphroditum cover. In the outbreak year (2012), phenol oxidase activity had the strongest relationship with damage to the deciduous species V. myrtillus, with greater herbivory lowering activity. For the other deciduous species, V. uliginosum, soil NH and phenolics were negatively correlated with foliar larval damage. Phenol oxidase activity was not affected by herbivory of the evergreen species, but there was a strong positive relationship observed between E. hermaphroditum community abundance and soil respiration. We highlight the dominant role of E. hermaphroditum in such sub-Arctic shrub communities and show that even during insect outbreaks, it can dictate soil processes. [ABSTRACT FROM AUTHOR]

A set of characters has been used to evaluate transformations in forest phytocenoses and their small mammal communities affected by urbanization, compared to conditionally undisturbed phytocenoses (communities). In park forests of the city of Yekaterinburg, the understory and subordinate shrub and herb-dwarf shrub layers of phytocenosis are transformed to a greater extent. The undergrowth of conifer forestforming species is as a rule sparse or absent, and that of deciduous trees often consists mainly of invasive species. Small mammal communities in pine forests transformed under the effect of urbanization also undergo changes leading to the formation of relatively stable (for an urbanized environment) zoocenoses differing both in species composition and in parameters characterizing community diversity. [ABSTRACT FROM AUTHOR]

Aims: Plant species and functional groups are known to drive the community of belowground invertebrates but whether their effects are consistent across environmental gradients is less well understood. We aimed to determine if plant effects on belowground communities are consistent across a successional gradient in boreal forests of northern Sweden. Methods: We performed two plant removal experiments across ten stands that form a 364-year post-fire boreal forest chronosequence. Through the removal of plant functional groups (mosses or dwarf shrubs) and of individual species of dwarf shrubs, we aimed to determine if the effects of functional groups and species on the soil micro-arthropod community composition varied across this chronosequence. Results: Removal of mosses had a strong negative impact on the abundance and diversity of Collembola and Acari and this effect was consistent across the chronosequence. Only specific Oribatid families declined following dwarf-shrub species removals, with some of these responses being limited to old forest stands. Conclusions: Our results show that the impacts of plants on micro-arthropods is consistent across sites that vary considerably in their stage of post-fire ecosystem development, despite these stages differing greatly in plant productivity, fertility, humus accumulation and moss development. In addition, mosses are a much stronger driver of the micro-arthropod community than vascular plants. [ABSTRACT FROM AUTHOR]

Alpine dwarf shrub communities are phenologically linked with snowmelt timing, so early spring exposure may increase risk of freezing damage during early development, and consequently reduce seasonal growth. We examined whether environmental factors (duration of snow cover, elevation) influenced size and the vulnerability of shrubs to spring freezing along elevational gradients and snow microhabitats by modelling the past frequency of spring freezing events. We sampled biomass and measured the size of Salix herbacea, Vaccinium myrtillus, Vaccinium uliginosum and Loiseleuria procumbens in late spring. Leaves were exposed to freezing temperatures to determine the temperature at which 50 % of specimens are killed for each species and sampling site. By linking site snowmelt and temperatures to long-term climate measurements, we extrapolated the frequency of spring freezing events at each elevation, snow microhabitat and per species over 37 years. Snowmelt timing was significantly driven by microhabitat effects, but was independent of elevation. Shrub growth was neither enhanced nor reduced by earlier snowmelt, but decreased with elevation. Freezing resistance was strongly species dependent, and did not differ along the elevation or snowmelt gradient. Microclimate extrapolation suggested that potentially lethal freezing events (in May and June) occurred for three of the four species examined. Freezing events never occurred on late snow beds, and increased in frequency with earlier snowmelt and higher elevation. Extrapolated freezing events showed a slight, non-significant increase over the 37-year record. We suggest that earlier snowmelt does not enhance growth in four dominant alpine shrubs, but increases the risk of lethal spring freezing exposure for less freezing-resistant species. [ABSTRACT FROM AUTHOR]

Adaptive reactions of the pigment system in assimilating shoots of evergreen dwarf shrub Ephedra monosperma J.G. Gmel. ex C.A. Mey. were studied under natural conditions of Central Yakutia. Seasonal changes in the content and ratio of green and yellow pigments were revealed; their relation to the stage of plant development and formation of cold tolerance was shown. The decrease in chlorophyll content started in September when the natural photoperiod became shorter and the air temperature lower; the chlorophyll concentration in winter was 30% lower than in summer. The content of β-carotene decreased twofold. The xanthophyll cycle pigments increased in content and deepoxidation level by a factor of 1.7 and 3.6, respectively. In peripheral cells of assimilating parenchyma, accumulation of a secondary carotenoid, rhodoxanthin was noted. In the period of active plant growth (from June to August), rhodoxanthin was absent, while its concentration in shoots in winter was 75 μg/g dry wt. It is concluded that changes in the pigment pool reflect structural and functional reorganization of photosynthetic machinery and are an indispensable part of the intricate process of plant hardening. Activation of energy-dissipating and antioxidant pigment systems, together with accumulation of the light-screening secondary carotenoid rhodoxanthin, promote the retention of photosynthetic apparatus and the survival of Ephedra monosperma plants under extreme conditions of cryolithozone of Yakutia. [ABSTRACT FROM AUTHOR]

The effect of sheep grazing on species richness, higher order diversity measures, inequality, species composition, functional diversity and allometric relationships at a coastal dune heathland site was investigated. After a prescribed fire in 2002, the site was divided into two parts, where one of the parts was unmanaged and the other part was fenced and grazed by sheep. Sheep grazing had a positive effect on species richness as well as a significant positive effect on the functional diversity at the coastal dune heathland site. Generally, the cover of dwarf shrubs was negatively affected by grazing, whereas the cover of sedges and grasses was positively affected by grazing. There is a need for comparative investigations of the effect of different management methods not only on floristic biodiversity, but on all relevant kinds of biodiversity as well as on soil structure, soil chemistry and habitat micro- and macrostructure. Consequently, we advocate the initiation of an international systematic investigation of the effect of different management methods. [ABSTRACT FROM AUTHOR]

Arctic ecosystems are important carbon sinks. Increasing temperatures in these regions might stimulate soil carbon release. Evidence suggests that deciduous shrubs might counteract these carbon losses because they positively respond to increasing temperature, but their role in ecosystem carbon budgets remains uncertain. Many studies dealing with large-scale tundra greening and carbon sequestration in relation to increasing temperature have usually based their estimations on the aboveground components, but very little is known about belowground growth. In this context, annual rings can provide a retrospective insight into intra-plant temperature responses and seasonal growth allocation. This study presents a 70-year-long and annually resolved intra-plant analysis of ring width and missing ring distribution from a comprehensive serial sectioning, including 142 cross-sections and the measurements of 471 radii from ten Salix polaris Wahlenb. dwarf shrubs growing in the high Arctic on Svalbard. Results indicate a high intra-plant and inter-annual growth variation, characterized by a high proportion of partially (13.6 %) and completely (11.2 %) missing rings. The annual growth and the frequency of completely missing rings were evenly distributed inside the plant and mainly controlled by summer temperatures. Radial growth in the belowground parts appeared to be proportionally higher during long and warm summers and lower in cold early growing seasons than in the aboveground parts. The results reveal a diverging allocation between aboveground and belowground growth depending on the climatic conditions. Favorable years promoted root allocation since root radial growth occurs after aboveground growth. The observed belowground responses suggest that shrub carbon allocation might be higher than estimated only from the aboveground compartments. [ABSTRACT FROM AUTHOR]

Background and aims: Shrublands are ecosystems vulnerable to climate changes, with key functions such as carbon storage likely to be affected. In dwarf shrublands dominated by Calluna vulgaris, the aboveground carbon allocation is associated with community age and phase of development. As the Calluna community grows older, a shift to net biomass loss occurs and it was hypothesized this would result in carbon stock increases within the soil. Methods: The interaction of community age with ecosystem carbon stocks was investigated through a chronosequence study on three Calluna communities, aged 11, 18 and 27 years. Results: Aboveground Calluna carbon stock increased significantly from the 11 year community (0.73 kg C m) to the 18 year community (1.11 kg C m) but did not significantly change from 18 to 27 years (1.0 kg C m), indicating a net carbon gain that corresponded with the growth phase of the Calluna plants. Moss was also found to be a relatively large contributor to aboveground carbon stock (e.g. 30 % in the Young community). Moss has often been excluded in aboveground assessments on Calluna heathlands which may have led to previous stock underestimation. Belowground carbon stocks to 25 cm were six to nine times greater than in the aboveground pools. For example in the Young community, 8 % of the carbon stock was located aboveground, 35 % in the organic layer and 55 % in the mineral soil. Conclusions: Increased heathland age resulted in increased aboveground carbon stock until peak production was reached at approximately 18 years of age. However, the proportionally large belowground carbon stock eclipsed any aboveground effect when total carbon stocks were considered. The investigation emphasized both the importance of including the mineral soil in sampling programs and of consider all major species, such as bryophytes, and vegetation age in carbon stock assessments. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore the effects of heavy rain and drought on the flowering phenology of two shrub species Genista tinctoria and Calluna vulgaris. We conducted a field experiment over five consecutive years in Central Europe, applying annually recurring extreme drought and heavy rain events on constructed shrubland communities and recorded the flowering status. Further, we correlated spring temperature and precipitation with the onset of flowering. Both species showed a response to extreme weather events: drought delayed the mid flowering date of Genista tinctoria in 3 of 5 years by about 1 month and in 1 year advanced the mid flowering date by 10 days, but did not affect the length of flowering. Mid flowering date of Calluna vulgaris was not affected by drought, but the length of flowering was extended in 2 years by 6 and 10 days. For C. vulgaris the closer the drought occurred to the time of flowering, the larger the impact on the flowering length. Heavy rainfall advanced mid flowering date and reduced the length of flowering of Genista tinctoria by about 2 months in 1 year. Mid flowering date of Calluna vulgaris was not affected by heavy rain, but the length of flowering was reduced in 1 year by 4 days. Our data suggest that extreme weather events, including alterations to the precipitation regime, induce phenological shifts of plant species of a substantial magnitude. Thus, the impacts of climate extremes on plant life cycles may be as influential as gradual warming. Particularly, the variability in the timing of precipitation events appears to have a greater influence on flowering dynamics than the magnitude of the precipitation. [ABSTRACT FROM AUTHOR]

The dynamics of northern forest boundary and the state of vegetation in the tundra-taiga ecotone in the northwestern Kola Peninsula have been evaluated using Landsat satellite images obtained in 1986 and 2005, the years encompassing the period of recent climate warming. Values of the normalized difference vegetation index (NDVI) in these years have been calculated to construct a differential index image reflecting changes in the vegetation. Its analysis has revealed an increase in the density of open forests and in the thickness of dwarf shrub vegetation, which has expanded to the lichen tundra. [ABSTRACT FROM AUTHOR]

Tundra vegetation is responding rapidly to on-going climate warming. The changes in plant abundance and chemistry might have cascading effects on tundra food webs, but an integrated understanding of how the responses vary between habitats and across environmental gradients is lacking. We assessed responses in plant abundance and plant chemistry to warmer climate, both at species and community levels, in two different habitats. We used a long-term and multisite warming (OTC) experiment in the Scandinavian forest-tundra ecotone to investigate (i) changes in plant community composition and (ii) responses in foliar nitrogen, phosphorus, and carbon-based secondary compound concentrations in two dominant evergreen dwarf-shrubs ( Empetrum hermaphroditum and Vaccinium vitis-idaea) and two deciduous shrubs ( Vaccinium myrtillus and Betula nana). We found that initial plant community composition, and the functional traits of these plants, will determine the responsiveness of the community composition, and thus community traits, to experimental warming. Although changes in plant chemistry within species were minor, alterations in plant community composition drive changes in community-level nutrient concentrations. In view of projected climate change, our results suggest that plant abundance will increase in the future, but nutrient concentrations in the tundra field layer vegetation will decrease. These effects are large enough to have knock-on consequences for major ecosystem processes like herbivory and nutrient cycling. The reduced food quality could lead to weaker trophic cascades and weaker top down control of plant community biomass and composition in the future. However, the opposite effects in forest indicate that these changes might be obscured by advancing treeline forests. [ABSTRACT FROM AUTHOR]

Northern peatlands are recognized as globally important stores of terrestrial carbon (C), yet we have limited understanding of how global changes, including land use, affect C cycling processes in these ecosystems. Making use of a long-term (>50 year old) peatland land management experiment in the UK, we investigated, using a CO pulse chase approach, how managed burning and grazing influenced the short-term uptake and cycling of C through the plant-soil system. We found that burning affected the composition and growth stage of the plant community, by substantially reducing the abundance of mature ericoid dwarf-shrubs. Burning also affected the structure of the soil microbial community, measured using phospholipid fatty acid analysis, by reducing fungal biomass. There was no difference in net ecosystem exchange of CO but burning was associated with an increase in photosynthetic uptake of CO and increased transfer of C to the soil microbial community relative to unburned areas. In contrast, grazing had no detectable effects on any measured C cycling process. Our study provides new insight into how changes in vegetation and soil microbial communities arising from managed burning affect peatland C cycling processes, by enhancing the uptake of photosynthetic C and the transfer of C belowground, whilst maintaining net ecosystem exchange of CO at pre-burn levels. [ABSTRACT FROM AUTHOR]

Due to their diversity and dominance in environmentally harsh sites, Mediterranean dwarf shrubs are a valuable tool to understand the consequences of climatic variability on radial growth in woody plants. We evaluate the dendrochronological potential of three Mediterranean dwarf shrubs versus three coexisting tree species inhabiting cold- ( Hormathophylla spinosa vs . Pinus sylvestris), mesic- ( Ononis fruticosa vs . Abies alba), and xeric sites ( Linum suffruticosum vs . Pinus halepensis). Cross-sectional wood sections of the three shrub species and cores in the case of trees were visually cross-dated and ring-widths were measured and converted into residual growth indices. We used linear mixed-effects models to assess how growth indices respond to local factors and climatic variables. The radial growth of the three dwarf shrub species was more asynchronous, i.e., ring-width series differed among conspecific individuals, than that of coexisting tree species. Growth asynchrony was higher for H. spinosa than for O. fruticosa and L. suffruticosum. Similarly, the ring-width series of O. fruticosa and L. suffruticosum was strongly correlated with that of coexisting tree species, while growth series of H. spinosa and P. sylvestris was not related at all. The growth of the three dwarf shrub species was influenced by the regional climatic conditions, but to a lesser degree than coexisting tree species. The highest responsiveness of growth to climate was observed in Mediterranean dwarf shrubs from xeric sites. However, local conditions are also major drivers of growth in Mediterranean dwarf shrubs as indicated by the stronger asynchrony in ring formation of these species as compared with coexisting trees, particularly in cold sites. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a critical resource for plant growth in tundra ecosystems, and species differences in the timing of N uptake may be an important feature regulating community composition and ecosystem productivity. We added N-labelled glycine to a subarctic heath tundra dominated by dwarf shrubs, mosses and graminoids in fall, and investigated its partitioning among ecosystem components at several time points (October, November, April, May, June) through to the following spring/early summer. Soil microbes had acquired 65 ± 7% of the N tracer by October, but this pool decreased through winter to 37 ± 7% by April indicating significant microbial N turnover prior to spring thaw. Only the evergreen dwarf shrubs showed active N acquisition before early May indicating that they had the highest potential of all functional groups for acquiring nutrients that became available in early spring. The faster-growing deciduous shrubs did not resume N acquisition until after early May indicating that they relied more on nitrogen made available later during the spring/early summer. The graminoids and mosses had no significant increases in N tracer recovery or tissue N tracer concentrations after the first harvest in October. However, the graminoids had the highest root N tracer concentrations of all functional groups in October indicating that they primarily relied on N made available during summer and fall. Our results suggest a temporal differentiation among plant functional groups in the post-winter resumption of N uptake with evergreen dwarf shrubs having the highest potential for early N uptake, followed by deciduous dwarf shrubs and graminoids. [ABSTRACT FROM AUTHOR]

Winter climate and snow cover are the important drivers of plant community development in polar regions. However, the impacts of changing winter climate and associated changes in snow regime have received much less attention than changes during summer. Here, we synthesize the results from studies on the impacts of extreme winter weather events on polar heathland and lichen communities. Dwarf shrubs, mosses and soil arthropods were negatively impacted by extreme warming events while lichens showed variable responses to changes in extreme winter weather events. Snow mould formation underneath the snow may contribute to spatial heterogeneity in plant growth, arthropod communities and carbon cycling. Winter snow cover and depth will drive the reported impacts of winter climate change and add to spatial patterns in vegetation heterogeneity. The challenges ahead lie in obtaining better predictions on the snow patterns across the landscape and how these will be altered due to winter climate change. [ABSTRACT FROM AUTHOR]

Alpine landscapes are heavily influenced by ski run management, which can have severe impacts on alpine biodiversity. To assess these impacts on alpine Orthoptera, we compared species richness and species abundance in 41 plot pairs on ski runs and adjacent off-slope control plots in three ski resorts in Austria and Germany. A mixed modelling approach was used to assess the impacts of ski run preparation, artificial snow-making and environmental variables such as altitude, cover of dwarf shrubs and the application of fertilizer. Ski run plots showed a significantly lower species richness and number of individuals than control plots. Moreover, artificial snow led to a further decrease in species number. Hierarchical variance partitioning revealed that Orthoptera community composition is best predicted by environmental variables indirectly related to ski run management (fertilization, cover of dwarf shrubs) and to altitude. Only one out of five species significantly decreased in abundance after artificial snow-making. Other species were more sensitive to fertilizing and altitude. Dwarf shrubs were negatively associated with ski run management but positively associated with abundance of three species and species richness. Our data provide evidence for both direct and indirect consequences of ski runs and artificial snow-making on alpine Orthoptera. Overall, Orthoptera communities are suitable indicators for human-induced changes in alpine environments. In particular, a shift towards generalist species such as Chorthippus parallelus along with a decrease in typical alpine species gives cause for concern as this implies a homogenisation of biodiversity owing to ski run management. [ABSTRACT FROM AUTHOR]

In northern Fennoscandia, the spatial and temporal grazing practices of semi-domesticated reindeer ( Rangifer tarandus tarandus) vary, which implies different grazing effects dependent on natural conditions as well as management regime (i.e., timing and intensity of grazing). We compared density and biomass of main plant groups in semi-dry mountain birch forests exposed to either long-term summer or winter grazing in three reindeer herding districts in the northernmost Finland. Percent plant cover, height, and biomass of reindeer lichens ( Cladonia spp.) and dwarf shrubs ( Vaccinium uliginosum, Calluna vulgaris, and Betula nana) were lower on summer ranges compared with winter ranges. The biomass of other dwarf shrubs ( Vaccinium myrtillus and V. vitis- idaea), and graminoids and herbs, and the % cover of non-vegetated bare soil and litter were, however, higher on summer ranges than on winter ranges. Young mountain birch shoots ( Betula pubescens ssp. czerepanovii) were less frequent on summer ranges than on winter ranges. The total leaf biomass under the browsing height of reindeer (<1.5 m) was also lower on summer ranges compared with winter ranges. Especially in drier and nutrient poor mountain birch forests, intensive summer grazing reduces the quantity of lichens and total plant biomass which affects the ecological state and productivity of these forests and also reduces especially their winter grazing value for reindeer. Therefore, in addition to regulating the maximum sustained numbers of reindeer, pasture rotation systems that effectively protect dry and nutrient poor vegetation from summer grazing and trampling should be encouraged. [ABSTRACT FROM AUTHOR]

Ischnura pumilio is threatened in the UK and its habitat requirements are not well understood. This study tests previously held notions of the habitat requirements of I. pumilio, investigates the features of a habitat influencing odonate species composition and provides recommendations for habitat creation and management for I. pumilio persistence. Thirty-one sites across south west England with past I. pumilio records were surveyed in 2006. Environmental variables and odonate abundance were recorded. Odonate species composition and I. pumilio abundance were related to environmental variables using multivariate techniques and GLM. Ischnura pumilio was found at a wide variety of habitat types; key habitat features were a muddy substrate with some open ground, turbid water, and low levels of shade. It was associated with increased structural diversity of vegetation away from water but low maximum height; characteristic of early-successional sites. The variables predicting odonate composition were location, shade, level of disturbance, water depth, and cover of terrestrial dwarf shrubs and Sphagnum species. Vegetation height and structure were also highly influential to at least 20 m from water. This study indicates that odonate habitat management should include adjacent hinterland. Management for I. pumilio may be complicated by the species' use of two habitat types, each with associated problems. Furthermore, odonate species diversity was negatively associated with I. pumilio abundance, which may cause conflict of interest when managing habitats. [ABSTRACT FROM AUTHOR]

A large proportion of northern peatlands consists of Sphagnum-dominated ombrotrophic bogs. In these bogs, peat mosses ( Sphagnum) and vascular plants occur in an apparent stable equilibrium, thereby sustaining the carbon sink function of the bog ecosystem. How global warming and increased nitrogen (N) deposition will affect the species composition in bog vegetation is still unclear. We performed a transplantation experiment in which mesocosms with intact vegetation were transplanted southward from north Sweden to north-east Germany along a transect of four bog sites, in which both temperature and N deposition increased. In addition, we monitored undisturbed vegetation in control plots at the four sites of the latitudinal gradient. Four growing seasons after transplantation, ericaceous dwarf shrubs had become much more abundant when transplanted to the warmest site which also had highest N deposition. As a result ericoid aboveground biomass in the transplanted mesocosms increased most at the southernmost site, this site also had highest ericoid biomass in the undisturbed vegetation. The two dominant Sphagnum species showed opposing responses when transplanted southward; Sphagnum balticum height increment decreased, whereas S. fuscum height increment increased when transplanted southward. Sphagnum production did not differ significantly among the transplanted mesocosms, but was lowest in the southernmost control plots. The dwarf shrub expansion and increased N concentrations in plant tissues we observed, point in the direction of a positive feedback toward vascular plant-dominance suppressing peat-forming Sphagnum in the long term. However, our data also indicate that precipitation and phosphorus availability influence the competitive balance between Sphagnum, dwarf shrubs and graminoids. [ABSTRACT FROM AUTHOR]

Arctic vegetation is often highly heterogeneous, consisting of mosaics of vegetation patches. Vegetation transition zones at the boundaries between patches can therefore make up a significant proportion of the landscape, yet performance of plants in transition zones, compared with their main patches, has not been previously investigated. Not only does this limit our understanding of plant productivity in highly heterogeneous landscapes, this knowledge is also needed to improve our understanding of the controls on Arctic ecosystem productivity, and improve modelling uncertainty in estimates of landscape C fluxes. We investigated changes in annual growth and photosynthetic capacity ( Amax) of two widely distributed dwarf shrubs ( Empetrum hermaphroditum and Vaccinium uliginosum) in these species’ own patches where they dominate, in transition zones at their patch edges and vegetation beyond these in vegetation where the species had lowest abundance. Maximum shoot growth occurred not in the study species’ own patches but in patches where both species mixed with a taller dwarf shrub Betula nana. Here shoot growth was 23 and 25% higher for E. hermaphroditum and V. uliginosum, respectively, compared to within their own patches. However, Amax was maintained at similar levels at all sites, with a slight tendency toward increased rates in vegetation towards more nutrient-rich, wetter areas compared to the species’ own patches, despite these more nutrient-rich areas having greater shading. There was only a very minor tendency towards decreased Amax in vegetation towards drier, more exposed areas compared to the species’ own patches. We show that, despite large changes in abundance and growth, Amax is not highly variable at small scales, meaning that variation in Amax is unlikely to be a large source of error when modelling whole-landscape C fluxes using measurements made within patches. [ABSTRACT FROM AUTHOR]

The snow cover extent is an important factor for the structure and composition of arctic and alpine tundra communities. Over the last few decades, snowmelt in many arctic and alpine regions has advanced, causing the growing season to start earlier and last longer. In a field experiment in subarctic tundra in Interior Alaska, I manipulated the timing of snowmelt and measured the response in mortality, phenology, growth, and reproduction of the eight dominant plant species. I then tested whether the phenological development of these species was controlled by snowmelt date or by temperature (in particular growing degree days, GDD). In order to expand our understanding of plant sensitivity to snowmelt timing, I explored whether the response patterns can be generalized with regard to the temporal niche of each species. Differences in the phenology between treatments were only found for the first stages of the phenological development (=phenophases). The earlier the temporal niche (i.e., the sooner after snowmelt a species develops) the more its phenology was sensitive to snowmelt. Later phenophases were mostly controlled by GDD, especially in late-developing species. In no species did an earlier snowmelt and a longer growing season directly enhance plant fitness or fecundity, in spite of the changes in the timing of plant development. In conclusion, the temporal niche of a species’ phenological development could be a predictor of its response to snowmelt timing. However, only the first phenophases were susceptible to changes in snowmelt, and no short-term effects on plant fitness were found. [ABSTRACT FROM AUTHOR]

Abstract  Detailed pollen analysis and pine megafossils from the immediate area of Rødalen in Central Norway have revealed new knowledge of Holocene alpine environments. A period of about 1,000 years characterised by pioneer herbs, dwarf-shrubs (Betula nana, Empetrum) and Juniperus followed the Holocene climatic amelioration. Local birch forest became established around 10.3 ka b.p., ca 150 years earlier than the local pine rise. Pine dominated at 1,100 m a.s.l. from 9.9 to 8.5 ka b.p., followed by birch forests until 1.3 ka b.p. when deforestation occurred. Slightly after 6 ka b.p., pine forests disappeared from the valley floor (930 m a.s.l.), an area that today is dominated by birch forest. Three short-lasting vegetational set-backs at ca 10.7, 10.5 and 10.3 ka b.p. may indicate climate oscillations. A temporary reduction of local forests reflects the Erdalen 2/9.7 ka b.p. event. The influence of the 8.2 event, superimposed on a cooling trend, lasted ca 400 years and involved a two-step vegetational regression: (1) A strong reduction of pine forests due to cooling and (2) reduction of alder due to cold and drought. Winter stress preventing pine regeneration may have caused scarcity of pine megafossils from the latter period. In the early Holocene, vegetation in the present alpine region was not in equilibrium with temperature development. It is suggested that the birch forest establishment lagged by about 1,000 years due to drought, whereas winter stress may have delayed the establishment of pine even longer. [ABSTRACT FROM AUTHOR]

Here we test the hypotheses that 19 years of simulated pollutant N deposition increases both losses of carbon (C) and the ability of plants to access P from organic material in upland heathland. The grass, Dactylis glomerata, and the dwarf shrub, Calluna vulgaris, were grown in soil containing microbial-derived organic matter labelled with 14C and 33P. We found that both soil and root-surface phosphatase activity increased significantly in response to N deposition. We also found a significant positive relationship between root-surface phosphatase activity and 33P uptake for Calluna, but a negative relationship for Dactylis. Efflux of 14C from the microbial-derived organic matter was strongly dependent on an interaction among plant presence, plant species and N deposition. Our results show that mineralisation of C and P, and subsequent plant uptake of P from organic sources is decoupled. In our experimental conditions, stimulation of P turnover coupled with subsequent plant uptake through up-regulation of root phosphatases is little affected by N addition. However, our data indicate that root-surface phosphatases are likely to be more important for uptake of P derived from organic sources for Calluna than for Dactylis. [ABSTRACT FROM AUTHOR]

Plant diversity is hypothesised to increase soil stability by increasing the diversity of root types. To test this hypothesis, we took soil cores from machine-graded ski slopes and from the adjacent undisturbed vegetation as a control. We quantified aggregate stability as an indicator for soil stability in relation to (1) abiotic soil properties, (2) above-ground vegetation characteristics and (3) root parameters. From the three groups of variables, the number of plant species, root density (RD) and sand content showed the highest correlation with soil aggregate stability and explained 54% of its variance. In variance partitioning, the number of plant species was the most relevant factor explaining 19% of the variance in aggregate stability. Further, it explained another 11% through shared effects with RD and sand content. An additional 8% was explained through the shared influence with sand content. Plant species showing the highest correlation with overall diversity were from different functional groups (grasses, forbs and shrubs), meaning that beneficial effects can not only be assigned to one specific functional group, but to the combination of several groups. Our data demonstrate the positive effect of plant diversity on aggregate stability. We suggest that high plant diversity is one of the most relevant factors for enhancing soil stability at disturbed sites at high elevation. [ABSTRACT FROM AUTHOR]

Climate warming is likely to increase nutrient mineralization rates in bog ecosystems which may change the plant species composition. We examined the competitive relationships between two graminoid species, Eriophorum vaginatum and Rhynchospora alba, and two ericoid species, Calluna vulgaris and Vaccinium oxycoccus, at different nutrient supply rates. In a greenhouse, the plants were grown in monocultures and mixtures at four nutrient treatments: control, high N, high P, and high N + P. The results show that the ericoids responded more strongly to the nutrient treatments than the graminoids. The dwarf shrubs showed higher growth rates and reduced root:shoot ratio at high N + P supply. When grown in mixture the ericoids increased their growth, while graminoids decreased in biomass or showed signs of nutrient limitation compared to their monoculture plants. This suggests that under increased nutrient availability, bogs are more likely to turn into dwarf shrub dominated ecosystems and not grassland. [ABSTRACT FROM AUTHOR]

Abstract  Typologically identical (dwarf birch-herb-dwarf shrub-moss) open and closed larch forests growing on the same altitudinal transect have proved to differ in the structural-functional organization of lower vegetation layers. Coverage, general species composition, and species richness of the herb-dwarf shrub layer are higher in the open forest than in the closed forest. Correlations between individual species of vascular plants weaken upon transition from the open to the closed forest. Conversely, the coverage of the lichen-moss layer increases in the closed forest, which contributes to its role as a factor of selection of vascular plant species against the background of the prevailing influence of the tree layer. [ABSTRACT FROM AUTHOR]

It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess initial effects of warming on the CO2 balance of a lichen-rich dwarf shrub tundra, a widespread but little studied ecosystem type in the Arctic. We analyzed whole ecosystem carbon exchange rates as well as nutrient dynamics, microbial and plant community composition and biomass after 2 years of experimental temperature increase. Plant biomass increased significantly with warming, mainly due to the strong response of lichens, the dominant plant group within this ecosystem. Experimental warming also increased soil nitrogen pools and nitrogen turnover rates. Major changes in soil microbial and plant composition, however, were not detected. Although experimental warming increased gross ecosystem productivity, the higher plant biomass did not compensate for the much greater increase in C losses. Ecosystem respiration and net ecosystem CO2 losses were significantly higher in warmed plots compared to control ones. We suggest that this was due to increased soil respiration, since soil carbon pools were lower in warmed soils, at least in the upper horizons. Our study thus supports the general hypothesis that tundra ecosystems turn from a carbon sink to a carbon source when temperatures increase in the short-term. Since lichens, which produce low quality litter, increased their biomass significantly with warming in this specific ecosystem type, CO2 losses may slow down in the long-term. [ABSTRACT FROM AUTHOR]

Abstract  The effect of 15N-labelled litter of different quality (Luzula sylvatica, a grass species, Vaccinium gaultheroides, a deciduous dwarf shrub, and Calluna vulgaris, a hardy dwarf shrub) and the presence of macro-decomposers (Lumbricus rubellus, Lumbricidae, and Enantiulus nanus, Diplopoda) on the growth of Dactylis glomerata (Poaceae), a grass species abundant on alpine pastureland, was investigated. After 4 months, the presence of soil animals significantly increased litter mass loss of L. sylvatica, V. gaultheroides and C. vulgaris by 27%, 11% and 40%, respectively. Soil animals generally reduced microbial biomass but significantly increased it in treatments where either L. sylvatica or C. vulgaris was present. The presence of soil animals significantly increased shoot and root biomass of D. glomerata by 48% and 64%, respectively. L. rubellus increased the transfer of 15N from the litter into plants. We conclude that macro-decomposers increased nutrient mobilization and plant uptake of nutrients mineralized from recalcitrant litter materials. Litter of L. sylvatica contributed most to the 15N uptake by D. glomerata, suggesting that litter quality is crucial for the cycling of nutrients on abandoned alpine pastureland. [ABSTRACT FROM AUTHOR]

Due to economic needs, a process of abandonment of unfavourably situated areas and intensified cultivation on favoured areas has taken place in the alpine region. This abandonment not only means the loss of a cultural landscape based on centuries of care but also interference with an established ecological balance. We wanted to investigate the impact of land-use, such as mowing, fertilisation and irrigation and the effects of abandonment on the O-horizon type, quantity and quality. Therefore, we selected areas with different types of land use but with equivalent site conditions in the Passeier Valley (Bolzano-South Tyrol province) for investigation. The areas studied were as follows: an organically fertilised and irrigated, intensively managed hay meadow mown once a year; an organically fertilised, intensively managed hay meadow mown once a year; a lightly managed hay meadow mown every second year; a lightly managed hay meadow mown every 3–4 years; an area densely covered with dwarf shrubs abandoned 10 years ago; and a reforested area abandoned 30 years ago. These selected areas represent different intensities of land use or stages of succession. On these areas, vegetation, phytomass, litter quantity, humus type, O-horizon quantity, litter decomposition and C and N storage, were analysed in detail. Abandonment causes the percentage of coverage with grasses and herbs to decrease from 100 to 10%, while lignified species increase from 0 to 90%. This leads to growth of the phytomass pools, which in turn causes an increase in the annual litter quantity (from 117 to 525 g m−2). Significant changes in litter quality in the case of reduced use or abandonment increases the litter’s resistance to decomposition, decreasing overall decomposition. Litter quantity and quality then have a significant impact on the O-horizon quantity. This increases strongly with decreasing intensity of land use or longer times since abandonment (115–1,180 g m−2). This leads to a significant increase of C and N storage and a change in O-horizon type ranging from no definite O-horizon or mull O-horizons on regularly used areas to moder on abandoned areas. [ABSTRACT FROM AUTHOR]

Post-fire nutrient flushes are an important precursor to secondary succession in fire-driven boreal forest. We studied the magnitude of changes in post-fire soil nutrient status across a chronosequence of ericaceous shrub-dominated boreal forest stands in eastern Newfoundland, Canada. The chronosequence comprised nine stands burned between 1 and 38 years prior to the study. These sites have resisted tree reestablishment following forest fire-induced mortality of black spruce and a concomitant increase in dominance of the ericaceous dwarf shrub Kalmia angustifolia L. Our objectives were: (1) to identify the factors driving soil nutrient status in these post-fire stands dominated by ericaceous plants, and (2) to test hypotheses that specific relationships exist among environmental factors, dominant vegetation and indicators of soil nutrient status. Macronutrients such as NH, total organic N and mineral soil P concentrations showed non-linear declines with time since fire. These parameters were also negatively associated with cover of ericaceous plants. Potential phytotoxins such as total phenolics and aluminium concentrations increased with increasing cover of K. angustifolia. Variability in net ammonification, total P and total phenolic acids in organic soils were strongly related to ericaceous dominance even when the effect of time since fire was partialled out using regression analysis. These findings suggest a strong capacity for ericaceous vegetation to have top-down effects on soil chemical property particularly in the organic horizon with the increase in its post-fire dominance. [ABSTRACT FROM AUTHOR]

We tested if subalpine heath vegetation in northern Italy recovered after experimental perturbation of soil nutrient availability (fertilization) and species composition (removal of co-dominant dwarf shrubs). Species cover was assessed non-destructively before the start of the treatments (1995), at the end of the treatments (1999) and 4 years after the treatments ended (2003). Shrub removal had rather modest effects on heath vegetation, except for mosses which decreased significantly in removal plots. Fertilization decreased the cover of shrubs, mosses, and some graminoids but increased the cover of Festuca rubra. Fertilization converted heath to grassland, but the response of graminoid species was individualistic. Fertilization decreased vascular species richness and evenness, probably through negative effects of shading and litter accumulation on plant growth or recruitment. The vegetation had not recovered completely 4 years after the perturbations had stopped. This suggests that, in contrast to rapid responses to species removal and fertilization, recovery from these perturbations was rather slow, presumably because recovery was affected by long-term biotic interactions and species controls on ecosystem properties. [ABSTRACT FROM AUTHOR]

Abstract Types of catenae of the moraine landscape of the Kivach Reserve have been described, and five ecotopes have been distinguished in their composition. The analysis of ecological ranges of the main forest-forming species has made it possible to predict the potential composition of a tree synusia that included five to seven species in the greater part of the catenae and three species in depressions with stagnant moistening. The population demographic approach has been used to determine the succession status of communities in the study area. Six variants of phytochores have been distinguished in the herb-dwarf shrub layer; the main ecological and succession factors of distribution have been determined for them. [ABSTRACT FROM AUTHOR]

The increasing tropospheric ozone (O3) concentration constitutes a potential threat to nature. Plants are known to react to O3, but knowledge of the sensitivity and type of responses of different species and plant communities is widely lacking. This review focuses on the ecological effects of O3 on northern wild field layer plant species. Most of the 65 species examined thus far have proven to be quite tolerant of O3. Visible symptoms were observed in 54% of the 61 species studied, and growth reduction in 31% of the 55 species studied for growth. There were no signs to suggest that certain families or vegetation types are more sensitive or tolerant than others. There were, however, clear differences in sensitivity between the different species. It seems that forbs are usually more sensitive than grasses. It should be kept in mind, however, that we still lack knowledge on the responses of many common and abundant key species. The long-term effects are also far from clear. Hardly any field examinations have been carried out on the effects of O3 on plant communities. [ABSTRACT FROM AUTHOR]

Subalpine tundra ecosystems are characterised by a multitude of ecological stresses such as nutrient poor conditions and low pH, and are dominated by plants producing high levels of phenolic compounds. The aim of this study was to assess how alleviation of those stresses affects the reactivity (oxidation and complexation) of water-soluble phenolics in plant tissue, humus and mineral soil. We used a field manipulation experiment that was set up in 1989 in which plots dominated by the ericacious dwarf shrub Empetrum hermaphroditum Hagerup have been subjected to additions of inorganic and organic nitrogen (N), charcoal, and lime. From these plots we collected senescent leaves of E. hermaphroditum, humus, and mineral soil and determined the levels of redox-active phenolics and complexation activity (e.g., complexation towards phenol, L-tryptophan, and proteins) in water extracts of those samples. Addition of charcoal to the soil increased redox-active phenolics in E. hermaphroditum senescent leaves while the other treatments had no significant effect. Most of the treatments did not significantly affect the levels of redox-active phenolics in the humus and mineral soil water extracts. However, inorganic N amendments slightly increased the concentration of redox-active phenolics in humus. There were strong positive effects of addition of inorganic and organic N on the complexation activity towards phenol, L-tryptophan and proteins in humus water extracts. In addition, charcoal amendments increased complexation towards proteins (measured as lipase activity). In general, our results show that environmental manipulation treatments can have differential effects on redox-active phenolics and complexation activity of phenolics present in senescent leaves and humus. This is important knowledge for a better understanding of how environmental changes can affect humification processes and N cycling. [ABSTRACT FROM AUTHOR]

While there is considerable knowledge of the effects of enhanced levels of ultraviolet radiation (UV) on plant species, much less is known of the importance of ambient levels of solar UV, particularly on natural plant communities. Effects of ambient solar UV radiation on a natural sub-Arctic heath community were investigated in a three year UV exclusion experiment in northern Sweden (68° N). UV transparent and UV opaque (excluding < 400 nm) plexiglas screens were placed over vegetation for three years to determine ambient solar UV effects on growth, reproduction and phenology of the three dominant dwarf shrub species, Vaccinium uliginosum, V. vitis-idaea and Empetrum hermaphroditum. Additionally, effects of ambient solar UV radiation on leaf protection from UV-B were assessed through measurements of leaf UV-B absorbing compounds. Flowering and berry production by V. uliginosum were greatly increased (by five and 15 fold) in plots receiving ambient solar UV compared to those where solar UV had been excluded for three years. However, solar UV had no effect on stem growth, senescence and cover of the dwarf shrub species studied. It was therefore concluded that sub-Arctic dwarf shrubs are generally tolerant of ambient solar UV. Counterintuitively, ambient solar UV radiation reduced the levels of UV-B absorbing compounds in both Vaccinium species suggesting a reduction in protection provided. This indicates that measurements of leaf UV-B absorbing compounds do not necessarily provide a good indicator of plant tolerance to UV. [ABSTRACT FROM AUTHOR]

The CO2 exchange of pine (Pinus sylvestris L.) shoots was continuously monitored over several years. The spatial and temporal variability of gas exchange was thoroughly investigated for three forest types. The net uptake of CO2 by current-season shoots in a bilberry pine stand equaled 5.4 g CO2 per g dry wt for the growing season. The net CO2 assimilation by one-year-old shoots over a growing season constituted 9.9 and 2.4 g CO2/(g dry wt year) in the upper and lower crown parts, respectively. The nighttime respiration of the current-season shoots released 0.7 g CO2/(g dry wt year), and the respiration of one-year-old shoots in the upper and lower parts of the canopy released 0.45 and 0.36 g CO2/(g dry wt year), respectively. Recalculation of three-year data per entire crown yielded an annual average carbon assimilation of 1.54 g C/(g dry wt year). Water relations markedly affected CO2 fixation. Nevertheless, the daily average values of photosynthesis in the summer were similar for pine stands with bilberry, heather, and dwarf shrub–polytric as understory dominants. It is shown that the realization of changes in photosynthetic function is related in time to growth processes. [ABSTRACT FROM AUTHOR]

Our purpose was to characterize the relative competitive and phytotoxic potential of two closely related dwarf-shrub species, Empetrum nigrum and E. hermaphroditum, which form clones in a mosaic pattern in post-fire successions of the boreal forest of northern Sweden. We determined morphological and growth parameters of both species, performed bioassays and chemical analysis, and established field experiments to explore possible differing interference effects on trees by the two species. Both Empetrum species had very similar morphological and growth characteristics. E. hermaphroditum exerted considerably greater negative effects than E. nigrum against Pinus sylvestris and Populus tremula seed and seedlings. These negative effects were related to the different substitution of a bibenzyl in the two species. The effect on seed germination of the two bibenzyls isolated from E. nigrum and E. hermaphroditum was compared with that of other simple phenolics; the latter were found to be inactive, indicating a specific phytotoxic component in the bibenzyls. P. sylvestris seeds planted into clones of both species in the field revealed that E. hermaphroditum had much stronger inhibitory effects than did E. nigrum and the addition of activated carbon partially reversed these effects. Seed germination, biomass and survival of P. sylvestris after four seasons were significantly lower in E. hermaphroditum- than in E. nigrum-dominated plots. We conclude that while both Empetrum species are superficially very similar morphologically, they have vastly different effects on tree seed germination, seedling establishment and growth. These effects appear to be due, at least in part, to the different chemical profile of the two species. [ABSTRACT FROM AUTHOR]

Northern Tierra del Fuego is the insular extreme of the Magellanic steppe, a unique example of a cold-temperate oceanic grassland in South America. We surveyed this poorly known region with a landscape-based procedure to classify plant communities and investigate environmental gradients. Sampling sites were selected with the aid of aerial photos, and floristic composition, soil, topography and landform type were recorded in each site. Classification was achieved with Two-Way Indicator Species Analysis and gradients were analyzed with Detrended Canonical Correspondence Analysis. Two broad groups of communities were separated by the presence of typical acidophilous dwarf shrubs: acidophilous/mesotrophic and neutrophilous vegetation. Along the main floristic gradient, ericoid dwarf shrubs were replaced by forbs and grasses as soil acidity decreased. The acidic habitats were on Pleistocene glacial and alluvial deposits, and had coarse texture, poorly decomposed organic matter, and low base status. The eutrophic habitats were on Tertiary rocks of medium to fine texture and had well-decomposed organic matter and high base status. A second axis of variation was associated to latitudinal position and slope aspect, revealing a precipitation/evaporation gradient. Scrubs dominated by midheight shrubs, with species from the southern forests, were at the humid extreme (higher latitudes/south aspects); and short grass steppes, with taxa commonly found further North in the continent, at the xeric end (lower latitudes/north aspects). Although fertility and moisture seem to control the overall floristic gradient, the extreme vegetation types of the fertility gradient, both having a very simple structure, could be attributed to grazing disturbance. Floristics and ecology of the Fuegian steppe resemble to a certain degree some boreal oceanic systems. [ABSTRACT FROM AUTHOR]

An experiment is described which studies the effects of enhanced UV-B radiation (simulating a 15% reduction in the Ozone layer) and elevated atmospheric concentrations of CO2 (600 ppm) on the dwarf shrub layer of a sub-arctic forest heath ecosystem at Abisko, North Sweden. The experimental treatments were first applied in 1993, and have covered most of the snow-free season (late May to early September) 1993–1995. Effects of the treatments on the four dwarf shrub species have been recorded largely using non-destructive measures (Vaccinium uliginosum, Vaccinium myrtillus – deciduous species and Vaccinium vitis-idaea and Empetrum hermaphroditum – evergreen species). Effects of the treatments on stem growth and leaf thickness have so far been small, although CO2 treatments initially stimulated stem extension in Vaccinium myrtillus 1993 and depressed growth in V. vitis idaea in 1994 and E. hermaphroditum during 1995. UV-B treatments stimulated fruit production in V. myrtillus in both 1994 and 1995, but there was no effect on reproductive phenology. There were also marked effects of UV-B treatments on insect herbivory in the deciduous dwarf shrubs; with leaf area loss being greater than the control in the UV-B treatment in V. myrtillus and less in V. uliginosum. The results point to the possibility of important effects of the treatments on physiological and chemical processes within the plants. The ecological results of such effects may not be immediately apparent, but may be far reaching, pointing to the need for long-term in situ experimentation in predicting the effects of these global change variables. [ABSTRACT FROM AUTHOR]