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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]

Fire is a major disturbance in many ecosystems world-wide including the boreal forest, and significant quantities of charcoal can be input to the soil from fire. Some recent studies have provided evidence that wood-derived charcoal produced by fire can significantly stimulate plant growth. However, the mechanisms by which charcoal affects plant growth are poorly understood, and little is known about how charcoal effects on plant growth are influenced by charcoal type, soil type and plant species., Seedlings from four common boreal tree species, two evergreen gymnosperms and two deciduous angiosperms, were grown in each of two soils of contrasting nutrient availability amended with charcoal with each of nine charcoal types (each produced from wood from a different plant species) in a greenhouse experiment. We also measured several functional traits for each of the charcoal types, as well as of the wood used to prepare the charcoal., Charcoal addition had either positive or neutral effects on seedling growth, with great variability among charcoal types. The charcoal types that had the strongest positive effect were those that had the greatest concentrations of phosphate and total phosphorus and, in some cases, were derived from woods that had the highest total phosphorus concentration. Addition of charcoal on average had a stronger positive effect on plant growth on soil with the lowest levels of phosphate and total phosphorus., Generally, charcoal derived from angiosperms stimulated seedling growth more than charcoal from gymnosperms. Further, angiosperm seedlings were on average stimulated more by charcoal addition than were gymnosperm seedlings. These results indicate that charcoal produced by fire could contribute to the initial dominance of angiosperm trees in post-fire succession and suggest a possible feedback whereby charcoal from angiosperm tree species favours growth of angiosperm seedlings., This study highlights a new means by which functional trait variation among tree species could potentially exert 'after-life' effects in forested ecosystems through influencing traits (and notably phosphate concentrations) of the charcoal that they produce following wildfire, with potentially important consequences for plant growth and community and ecosystem properties during post-fire succession. [ABSTRACT FROM AUTHOR]

Aims: Feather mosses form a thick ground layer in boreal forests that can intercept incoming litter fall. This interception may influence the decomposition of incoming litter but this has been little explored. We investigated how the moss layer influences decomposition of intercepted litter along a 362-year fire driven forest chronosequence in northern Sweden across which soil fertility declines. Methods: We placed leaf litter from three plant species into plots in which mosses and dwarf shrubs were either experimentally removed or left intact, at each of ten stands across the chronosequence. After one year we measured litter mass loss, and litter nitrogen and phosphorous. Results: Litter decomposed consistently faster, and had higher nitrogen and phosphorus, in the presence of mosses and at greater depth in the moss layer. Despite an increase in moss depth across the chronosequence we did not find consistent increases in effects of moss removal on litter decomposition or on litter N or P. Conclusions: Our findings identify a clear role of the moss layer in boreal forests in promoting the decomposition of intercepted leaf litter, and highlight that this role is relatively consistent across chronosequence stages that vary greatly in productivity and moss depth. [ABSTRACT FROM AUTHOR]

Aims: In the long term absence of catastrophic disturbance ecosystem retrogression occurs, and this is characterized by reduced soil fertility, and impairment of plant biomass and productivity. The response of plant traits to retrogression remains little explored. We investigated how changes plant traits and litter decomposability shift during retrogression for dominant trees and understory shrubs. Methods: We characterized changes in intraspecific, interspecific and community-averaged values of plant traits and litter decomposability, for six abundant species across thirty lake islands in boreal forest that undergo retrogression with increasing time since fire. Results: For understory shrubs, trait values and litter decomposability often changed as soil fertility declined in a manner reflective of greater conservation (versus acquisition) of nutrients, particularly at the interspecific and whole community levels. Such responses were seldom observed for trees, meaning that trees and shrubs show a decoupled response to declining soil fertility during retrogression. Conclusions: Our results only partially agree with previous studies on temperate and subtropical retrogressive chronosequences. Because traits of only shrubs were responsive, they also highlight that impairment of belowground ecosystem processes during retrogression is primarily driven by changes in the trait spectra of understory vegetation rather than that of the trees. [ABSTRACT FROM AUTHOR]

Background and Aim: Nitrogen (N) and carbon (C) isotopic signatures (δN and δC) serve as powerful tools for understanding temporal changes in ecosystem processes, but how these signatures change across boreal forest chronosequences is poorly understood. Methods: The δN, δC, and C/N ratio of foliage of eight dominant plant species, including trees, understory shrubs, and a moss, as well as humus, were examined across a 361 years fire-driven chronosequence in boreal forest in northern Sweden. Results: The δC and C/N ratio of plants and humus increased along the chronosequence, suggesting increasing plant stress through N limitation. Despite increasing biological N fixation by cyanobacteria associated with feather mosses, δN showed an overall decline, and δN of the feather moss and associated vascular plants diverged over time from that of atmospheric N. Conclusions: Across this chronosequence the N fixed by cyanobacteria is unlikely to be used by mosses and vascular plants without first undergoing mineralization and mycorrhizal transport, which would cause a change in δN signature due to isotopic fractionation. The decreasing trend of δN suggests that as the chronosequence proceeds, the plants may become more dependent on N transferred from mycorrhizal fungi or from N deposition. [ABSTRACT FROM AUTHOR]

Fertilizer experiments aid understanding of the role of nutrient limitation in tundra ecosystems, and of the effects that global change may exert on them through enhancing nutrient availability. However, little is known about whether fertilizer additions influence tundra ecosystem properties directly, or indirectly through altering plant community composition. To separate these direct and indirect effects, we used an ongoing fertilization experiment in subalpine tundra in northern Sweden initiated in 1989. Here, the slow-growing dwarf shrub Empetrum hermaphroditum (hereafter Empetrum) dominates, but fertilization causes its replacement by the fast-growing grass Deschampsiaflexuosa (hereafter Deschampsia)., Therefore, in 1999, we set up three subplots in every plot of the fertilizer experiment subjected to different treatments, i.e., regular removal of Empetrum or of Deschampsia, or no removal. An interactive effect between fertilizer and removal treatments means that fertilization indirectly influences ecological properties through its effects on the dominant species whereas no interactive effect means that fertilization effects are more likely direct. We measured plant community properties four times between 1999 and 2010, and belowground properties in 2010. Fertilization exerted large effects on nearly all variables aboveground (i.e., vascular plant community properties, bryophyte and lichen cover) and belowground (i.e., measures of nutrient availability, mass of humus and major elements per area, microbial community properties). Meanwhile, loss of either Deschampsia or Empetrum reduced total vascular plant cover, with greatest effects in those fertilization treatments where they otherwise had the most mass. Deschampsia removal affected several other plant community properties, but mostly independently of fertilizer treatment; Empetruni removal had little effect on any other plant community variable. Belowground, both removal treatments reduced humus mass per area but had no effect on any other variable. Our finding of few interactive effects of fertilizer and removal treatments aboveground and none belowground means that fertilizer effects on most community and ecosystem properties operate independently of even large shifts in the plant community. These results also point to a decoupling between aboveground and belowground communities in tundra, and therefore offer insights about the mechanistic basis through which global change impacts on soil nutrient availability may transform tundra ecosystems. [ABSTRACT FROM AUTHOR]

In the long-term absence of rejuvenating disturbances, forest succession frequently proceeds from a maximal biomass phase to a retrogressive phase characterized by reduced nutrient availability [notably nitrogen (N) and phosphorus (P)] and net primary productivity. Few studies have considered how retrogression induces changes in ecophysiological responses associated with photosynthetic carbon (C) gain, and only for trees. We tested the hypothesis that retrogression would negatively impact photosynthetic C gain of four contrasting species, and that this impact would be greater for vascular plants (i.e., trees and shrubs) than for non-vascular plants (i.e., mosses). We used a 5,000-year-old chronosequence of forested islands in Sweden, where retrogression occurs in the long-term absence of lightning-ignited wildfires. Despite fundamental differences in plant form and ecological niche among species, vascular plants and mosses showed similar ecophysiological responses to retrogression. The most common effects of retrogression were reductions in photosynthesis and respiration per unit foliar N, increases in foliar N, δC and δN, and decreases in specific leaf areas. In contrast, photosynthesis per unit mass or area generally did not change along the chronosequence, but did vary many-fold between vascular plants and mosses. The consistent increases in foliar N without corresponding increases in mass- or area-based photosynthesis suggest that other factor(s), such as P co-limitation, light conditions or water availability, may co-regulate C gain in retrogressive boreal forests. Against our predictions, traits of mosses associated with C and N were generally highly responsive to retrogression, which has implications for how mosses influence ecosystem processes in boreal forests. [ABSTRACT FROM AUTHOR]

Most theories attempting to explain the coexistence of species in local communities make fundamental assumptions regarding whether neighbors exhibit competitive, neutral, or positive resource-use interactions; however, few long-term data from naturally assembled plant communities exist to test these assumptions. We utilized a 13-year experiment consisting of factorial removal of three shrub species ( Vaccinium myrtillus, V. vitis-idaea, and Empetrum hermaphroditum) and factorial removal of two functional groups (tree roots and feather mosses) to assess how neighbors affect N acquisition and growth of each of the three shrub species. The removal plots were established on each of 30 lake islands in northern Sweden that form a natural gradient of resource availability. We tested the hypotheses that: (1) the presence of functionally similar neighbors would reduce shrub N acquisition through competition for a shared N resource; (2) the removal of functional groups would affect shrub N acquisition by altering the breadth of their niches; and (3) soil fertility would influence the effects of neighbor removals. We found that the removal of functionally similar neighbors (i.e., other shrub species) usually resulted in higher biomass and biomass N, with the strength of these effects varying strongly with site fertility. Shrub species removals never resulted in altered stable N isotope ratios (δ15N), suggesting that the niche breadth of the three shrubs was unaffected by the presence of neighboring shrub species. In the functional group removal experiment, we found positive effects of feather moss removal on V. myrtillus biomass and biomass N, and negative effects on E. hermaphrotium N concentration and V. vitis-idaea biomass and biomass N. Tree root removal also caused a significant shift in foliar δ15N of V. myrtillus and altered the δ15N, biomass, and biomass N of E. hermaphroditum. Collectively, these results show that the resource acquisition and niche breadth of the three shrub species are often affected by neighbors, and further that both the identity of neighbors and site fertility strongly determine whether these interactions are positive, negative, or neutral. These findings have implications for understanding species coexistence and the reciprocal relationships between productivity and species diversity in this ecosystem. [ABSTRACT FROM AUTHOR]

Despite the likely importance of inter-year dynamics of plant production and consumer biota for driving community- and ecosystem-level processes, very few studies have explored how and why these dynamics vary across contrasting ecosystems. We utilized a well-characterized system of 30 lake islands in the boreal forest zone of northern Sweden across which soil fertility and productivity vary considerably, with larger islands being more fertile and productive than smaller ones. In this system we assessed the inter-year dynamics of several measures of plant production and the soil microbial community (primary consumers in the decomposer food web) for each of nine years, and soil microfaunal groups (secondary and tertiary consumers) for each of six of those years. We found that, for measures of plant production and each of the three consumer trophic levels, inter-year dynamics were strongly affected by island size. Further, many variables were strongly affected by island size (and thus bottom-up regulation by soil fertility and resources) in some years, but not in other years, most likely due to inter-year variation in climatic conditions. For each of the plant and microbial variables for which we had nine years of data, we also determined the inter-year coefficient of variation (CV), an inverse measure of stability. We found that CVs of some measures of plant productivity were greater on large islands, whereas those of other measures were greater on smaller islands; CVs of microbial variables were unresponsive to island size. We also found that the effects of island size on the temporal dynamics of some variables were related to inter-year variability of macroclimatic variables. As such, our results show that the inter-year dynamics of both plant productivity and decomposer biota across each of three trophic levels, as well as the inter-year stability of plant productivity, differ greatly across contrasting ecosystems, with potentially important but largely overlooked implications for community and ecosystem processes. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

Many studies at the regional scale have found either negative or hump-shaped relationships between productivity and diversity, and some theories propose that these occur because soil resource heterogeneity is either lower or less important in more productive environments. However, there have been few explicit tests of these theories in natural ecosystems. We evaluated the relationship between soil resource heterogeneity and plant richness within a well characterized system of 30 islands in northern Sweden across which soil fertility and productivity declines, and species richness increases, as a consequence of ecosystem retrogression. On each island we created a spatially explicit grid consisting of 49 sampling points in a 9.5 m quadrat, which we used to quantify spatial heterogeneity of five soil variables (NH4+-N, amino N, PO4−-P, microbial biomass, and decomposition), and plant community composition. Using a hierarchical Bayesian approach, we estimated mean semivariograms of each variable for each island size class to compare three components of spatial heterogeneity: total variability, spatial grain, and patchiness. This analysis showed that variability within islands was usually lowest on small islands, where species richness was highest and productivity lowest; however, NH4+-N and amino N had greater patchiness and spatial grain on small islands. We did not detect any significant across-island correlations between whole-plot plant species richness and either whole-plot standard deviation or coefficient of variation of any soil variable. Using partial Mantel tests, we found that mean correlation coefficients between within-plot plant community composition and the soil variables were never significant for any island size class, and did not differ between island size classes. Our findings do not provide any evidence that soil resource heterogeneity controls the productivity-diversity relationship in this system, and suggests other mechanisms are primarily responsible. [ABSTRACT FROM AUTHOR]

Feather mosses in boreal forests form a dense ground-cover that is an important driver of both nutrient and carbon cycling. While moss growth is highly sensitive to moisture availability, little is known about how moss effects on nutrient and carbon cycling are affected by the dynamics of moisture input to the ecosystem. We experimentally investigated how rainfall regimes affected ecosystem processes driven by the dominant boreal feather moss Pleurozium schreberi by manipulating total moisture amount, frequency of moisture addition and moss presence/absence. Moisture treatments represented the range of rainfall conditions that occur in Swedish boreal forests as well as shifts in rainfall expected through climate change. We found that nitrogen (N) fixation by cyanobacteria in feather mosses (the main biological N input to boreal forests) was strongly influenced by both moisture amount and frequency, and their interaction; increased frequency had greater effects when amounts were higher. Within a given moisture amount, N fixation varied up to seven-fold depending on how that amount was distributed temporally. We also found that mosses promoted vascular litter decomposition rates, concentrations of litter nutrients, and active soil microbial biomass, and reduced N release into soil solution. These effects were usually strongest under low moisture amount and/or frequency, and revealed a buffering effect of mosses on the decomposer subsystem under moisture limitation. These results highlight that both the amount and temporal distribution of rainfall, determine the effect of feather mosses on ecosystem N input and the decomposer subsystem. They also emphasize the role of feather mosses in mediating moisture effects on decomposer processes. Finally, our results suggest that projected shifts in precipitation in the Swedish boreal forest through climate change will result in increased moss growth and N fixation but a reduced dependency of the decomposer subsystem on feather moss cover for moisture retention. [ABSTRACT FROM AUTHOR]

Alpine tundra ecosystems are characterised by low productivity, due in part to low nutrient availability. These ecosystems are often dominated by ‘stress tolerant’ species such as Empetrum hermaphroditum, which contribute to stress by producing and releasing biologically active phenolic compounds into the environment. In a nine-year field experiment in alpine tundra, we investigated changes in growth and the levels (concentrations and contents) of foliar redox-active phenolics of current-year shoots of E. hermaphroditum in response to nine long-term environmental manipulation treatments. The treatments were aimed at reducing ecological stresses commonly present in high-latitude ecosystems, primarily stresses associated with low availability of N and other nutrients. Treatments included additions of various forms of N (single and combined applications of NH4+ and NO3−, inorganic N as a component of a full nutrient treatment, and protein as a source of organic N), and additions of glucose, activated carbon, and lime. Shoot growth and levels of foliar phenolics varied greatly between years, but the variation was not clearly explained by the inter-annual variation in macroclimate. Addition of inorganic N generally stimulated growth (especially stem biomass) and increased levels of leaf phenolics. The responses were, however, slow, and varied both between years and between individual inorganic N treatments. Compared to the other treatments, application of inorganic N as a component of a full nutrient treatment had the most consistent positive effect on shoot growth and phenolic content, but it did not affect the concentration of phenolics, suggesting that the treatment did not affect the net rate of phenolic production per unit shoot biomass. During some years of the experiment, the combined application of NH4+ and NO3− resulted in increased production of phenolics per unit biomass accumulation. In contrast to inorganic N fertilisation, application of organic N generally reduced both shoot biomass and phenolic content. Non-N treatments had no substantial effects on either the growth or levels of foliar phenolics of E. hermaphroditum. The observed long-term responses of E. hermaphroditum to environmental manipulation treatments may be important for evaluating potential effects of variation in phenolics production and interference potential of this species under conditions of environmental change and for predicting long-term responses of nutrient-poor communities to environmental changes. [ABSTRACT FROM AUTHOR]

Picea abies, which is predominantly sexual, has been reported to propagate vegetatively through layering in a cold harsh climate, although this has not been demonstrated genetically. Using 105 amplified fragment length polymorphism markers, we analyzed 117 trees of Norway spruce from seven islands in Lake Hornavan in Lapland, northern Sweden. These islands differ in size, time since last wildfire disturbance, and vegetation successional age. A total of 96 distinct genotypes were identified among the 117 samples, and the average gene diversity was 0.37. Genetic differentiation among islands was high, . Drift, founder effect, small F[SUBst] = 0.19 st population size, infrequent sexual reproduction, and low seedling establishment would have contributed to the high F[SUBst]. Layering was found on five of the seven islands, giving an average clonal composition of 18%. A total of 11 clones, each consisting of two to five closely clustered ramets, were detected. Interestingly, layering was more common on the small islands that have not been disturbed by fire for over 1000 yr than on the larger islands with more recent fire disturbance. Our results indicate that island size and ecological conditions related to fire disturbance history on each island are important for the observed patterns of population structure. [ABSTRACT FROM AUTHOR]

Focuses on the study of forest ecosystem dynamics. The failure of managed coniferous forests to regenerate naturally; The possible role of ground and below ground organisms in the failure to regenerate; Field and laboratory techniques used to study biological processes related to plants; The framework of forest regeneration.

It is well established that application of biochar to soils can promote soil fertility, which ultimately may enhance plant growth. While many mechanisms have been proposed to explain this, one specific mechanism, the "microbial refugia hypothesis," suggests that biochar may provide physical protection for soil microbe from soil microfauna that otherwise exert top‐down control on microbial biomass and activity. We tested the microbial refugia hypothesis by incubating two boreal soils with and without biochar derived from a wood mixture of boreal tree species (Picea abies and Pinus sylvestris), and with and without soil nematodes. We measured phospholipid fatty acids (PLFA) as a relative measure of microbial biomass, and several variables indicative of microbial activity, including extractable nutrient concentrations (NH4+, NO3−, and PO4−), heterotrophic N2‐fixation, and soil respiration. Contrary to our expectations, we found that biochar by itself did not stimulate microbial biomass or activity. Furthermore, we found that nematode addition to soil stimulated rather than depressed the biomass of several bacterial PLFA groups. Finally, interactive effects between the nematode treatment and biochar never worked in a way that supported the microbial refugia hypothesis. Our findings suggest that a typical boreal biochar applied to boreal soils may not have the same stimulatory effect on microbial biomass and activity that has been shown in some other ecosystems, and that enhanced plant growth in response to biochar addition sometimes observed in boreal environments is likely due to other mechanisms, such as direct nutrient supply from biochar or amelioration of soil pH. [ABSTRACT FROM AUTHOR]

Boreal forests are frequently subjected to disturbances, including wildfire and clear‐cutting. While these disturbances can cause soil carbon (C) losses, the long‐term accumulation dynamics of soil C stocks during subsequent stand development is controlled by biological processes related to the balance of net primary production (NPP) and outputs via heterotrophic respiration and leaching, many of which remain poorly understood. We review the biological processes suggested to influence soil C accumulation in boreal forests. Our review indicates that median C accumulation rates following wildfire and clear‐cutting are similar (0.15 and 0.20 Mg ha−1 year−1, respectively), however, variation between studies is extremely high. Further, while many individual studies show linear increases in soil C stocks through time after disturbance, there are indications that C stock recovery is fastest early to mid‐succession (e.g. 15–80 years) and then slows as forests mature (e.g. >100 years). We indicate that the rapid build‐up of soil C in younger stands appears not only driven by higher plant production, but also by a high rate of mycorrhizal hyphal production, and mycorrhizal suppression of saprotrophs. As stands mature, the balance between reductions in plant and mycorrhizal production, increasing plant litter recalcitrance, and ectomycorrhizal decomposers and saprotrophs have been highlighted as key controls on soil C accumulation rates. While some of these controls appear well understood (e.g. temporal patterns in NPP, changes in aboveground litter quality), many others remain research frontiers. Notably, very little data exists describing and comparing successional patterns of root production, mycorrhizal functional traits, mycorrhizal‐saprotroph interactions, or C outputs via heterotrophic respiration and dissolved organic C following different disturbances. We argue that these less frequently described controls require attention, as they will be key not only for understanding ecosystem C balances, but also for representing these dynamics more accurately in soil organic C and Earth system models. [ABSTRACT FROM AUTHOR]

Abstract: When tree seedlings establish beyond the current tree line due to climate warming, they encounter existing vegetation, such as bryophytes that often dominate in arctic and alpine tundra. The stress gradient hypothesis (SGH) predicts that plant interactions in tundra become increasingly negative as climate warms and conditions become less harsh. However, for seedlings, climate warming might not result in lower winter stress, if insulating snow cover is reduced. We aimed to understand if bryophytes facilitate seedling survival in a changing winter climate and if these effects of bryophytes on tree seedlings comply with the SGH along elevational gradients under contrasting snow conditions. In the Swedish subarctic, we transplanted intact bryophyte cores covered by each of three bryophyte species and bryophyte‐free control soil from above the tree line to two field common garden sites, representing current and future tree line air temperature conditions (i.e. current tree line elevation and a lower, warmer, elevation below the tree line). We planted seedlings of Betula pubescens and Pinus sylvestris into these cores and subjected them to experimental manipulation of snow cover during one winter. In agreement with the SGH, milder conditions caused by increased snow cover enhanced the generally negative or neutral effects of bryophytes on seedlings immediately after winter. Furthermore, survival of P. sylvestris seedlings after one full year was higher at lower elevation, especially when snow cover was thinner. However, in contrast with the SGH, impacts of bryophytes on over‐winter survival of seedlings did not differ between elevations, and impacts on survival of B. pubescens seedlings after 1 year was more negative at lower elevation. Bryophyte species differed in their effect on seedling survival after winter, but these differences were not related to their insulating capacity. Synthesis. Our study demonstrates that interactions from bryophytes can modify the impacts of winter climate change on tree seedlings, and vice versa. These responses do not always comply with SGH, but could ultimately have consequences for large‐scale ecological processes such as tree line shifts. These new insights need to be taken into account in predictions of plant species responses to climate change. [ABSTRACT FROM AUTHOR]

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited.Two years after a large wildfire in managed even‐aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality).While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree‐ and soil‐related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum, but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf‐shrub Vaccinium vitis‐idaea and the grass Deschampsia flexuosa. Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil‐related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree‐ and soil‐related fire severity.Synthesis: Our results 2 years postfire suggest that a change in fire regime from a historically low‐severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand‐replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short‐term recovery of stand structure and above‐ and belowground species composition of even‐aged P. sylvestris boreal forests. [ABSTRACT FROM AUTHOR]

Neda Farahbakhshazad, Gregory M. Morrison and Eneas Salati Filho This paper reviews the knowledge on crowberry (Empetrum nigrum ssp. nigrum and ssp. hermaphroditum) dominated ecosystems in the Nordic region. Empetrum leaves and litter have high phenolic content resulting in slow decomposition, and with the formation of an organic top soil, nutrients are kept in an organic nutrient bank in the soil mainly available for plants with ericoid mycorrhiza. Empetrum nigrum ssp. hermaphroditum is a strong nutrient competitor and outcompetes most plants in late successional stages. This is due to chemical interference (allelopathy) and resource competition. Crowberry as an organism is resistant to atmospheric pollution and may even increase in vigor by high atmospheric N deposition in nemoral coastal heaths, but is very sensitive to mechanical disturbances and fire. However, there are indications that the closed nutrient cycle established when Empetrum is dominant may be disturbed after airborne inputs of inorganic N. [ABSTRACT FROM AUTHOR]

Vaccinium myrtillus L. ground vegetation in boreal forests reduces tree seedling survival and growth. We studied below- and above-ground competition and phytotoxicity of V. myrtillus on transplanted Picea abies (L.) Karst. seedlings in a 3-year full factorial field experiment. Exclusion tubes were used to reduce and selectively test for belowground competition by V. myrtillus. Shoots of V. myrtillus were folded back to reduce aboveground competition. Reduced belowground competition by V. myrtillus increased P. abies current-year shoot length, shoot and root biomass, seedling nutrient concentration, and mycorrhizal colonization. Reduced aboveground competition affected P. abies seedling root biomass positively whereas seedling survival, shoot length, and shoot/root ratio were negatively affected. Addition of activated carbon to the soil surface to reduce the effect of possible phytotoxic leachates from V. myrtillis leaves and litter had no effects on P. abies seedling survival and growth. No significant interactions among treatments were found. We conclude that suppressed growth of P. abies seedlings in V. myrtillus sites of northern boreal forests is caused mainly by belowground resource competition. [ABSTRACT FROM AUTHOR]

Ericaceous-dominated ground vegetation in boreal forests strongly suppresses tree seedling establishment and growth. Attempts to control this vegetation have led to the large-scale, and often criticized, use of soil scarification and herbicide treatment to control vegetationafter cutting. We investigated a new site preparation technique by steam treatment to control ground vegetation dominated by Empetrum hermaphroditum Hagerup in a north Swedish boreal site. Sowing experiments were performed between 1990 and 1993 with Pinus sylvestris L. in four treatments: (1) steamed vegetation, (2) activated carbon added to the soil surface of steamed vegetation, (3) untreated vegetation, and(4) activated carbon added to the soil surface of otherwise intact ground vegetation. Activated carbon was added to adsorb germination inhibitors from E. hermaphroditum leaves and litter. Steam treatment killed field- and bottom-layer species during the first 5 years after treatment. Scots pine seedling establishment was much improved for allseed years by steam treatment when activated carbon was added to the soil. Dry weight of 5-year-old seedlings was 260% higher in steam-treated plots than in untreated plots. Seedlings in untreated vegetation were few and had gained little or even lost important macronutrients when compared with the original seed supply. We interpret the increased growth of seedlings in steamed plots mainly as an effect of reduced interference of forest floor vegetation. We suggest that steamtreatment has the potential to be an effective tool to reduce negative influence of competitive ericaceous ground vegetation on tree seedling growth. [ABSTRACT FROM AUTHOR]