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Abstract—The functioning of mycorrhizal associations in forest ecosystems is discussed. Mycorrhizae are involved in supplying plants with nutrients and improve their growth, but they can also inhibit plant development. The level of participation of ecto-ericoid mycorrhizae in the carbon cycle of boreal forests is considered to be very significant. According to isotope indications, the role of mycorrhizae in the nitrogen cycle is high in the tundra and less pronounced in boreal forests. Mycorrhizae are involved in the decomposition of soil OM to obtain available nitrogen, but the enzymatic mechanisms of this process and the pathways for the movement of N and P from fungal cells to plants are largely unknown. Mycorrhizae prevent nitrogen losses from forest soils during leaching. Mycorrhizal networks contribute to the processes of reforestation and structuring of plantations and protect against pathogens and pests. [ABSTRACT FROM AUTHOR]

We used bioproxies from paleosoils buried within two aeolian dunes to test hypotheses concerning the origin of dry sandy boreal forests in Canada. These forests are dominated today by Pinus banksiana Lamb. One hypothesis is that too frequent Holocene stand-replacing fires would have transformed the original vegetation through extirpation of susceptible species to fire in water stress habitat. Alternatively, the ecosystem would have not changed since the dunes stabilized enough to support forest establishment. The vegetation composition and richness were determined by identification of charcoal and macroremains and radiocarbon dating for the chronology. Both sites revealed a similar history covering 6400 years. Half of the charcoal layers were less than 2500 years old in both sites, indicating that they had been subjected to the same fire history. Data indicated a stable plant composition and richness, although the percentage of Pinus decreased slightly over 4000 years (decreasing rate 1% per century). The fungus Cenococcum geophilum was consistently present, with a stochastic abundance. The vegetation grew under natural fire conditions and soil dryness since 6000 years. The ecosystem was probably not stressed by late-Holocene fires or climate changes, as the multi-millennial steady state reveals a resistant and resilient ecosystem. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) derived from plant litter plays an important role in the ecosystem carbon balance and soil biogeochemistry. However, in boreal coniferous forests no integrated understanding exists of how understory vegetation contributes to litter leaching of DOC, nitrogen (N) and phosphorus (P) with different bioavailability at the forest stand level. We characterized water extractable leachates from fresh and decayed litter of dominant canopy and understory sources in a boreal coniferous forest, in order to explore the contribution of understory vegetation as a source of both total and bioavailable forms of DOC, N and P. Recently produced litter from deciduous species (including Vaccinium myrtillus) yielded the highest amounts of DOC. However, this leaching potential decreased exponentially with mass loss through litter decay. The DOC lability generally showed little interspecific variation, although wood derived DOC was more recalcitrant. Lability decreased progressively with litter aging. Water extractable nutrients increased proportionally with DOC, and roughly a quarter (N) or half (P) had directly bioavailable inorganic forms. Scaled to annual litterfall at the forest stand, understory vegetation contributed ~ 80% of the water extractable DOC and nutrients from fresh litter, with > 60% coming from Vaccinium myrtillus alone. However, as litter decomposes, the data suggest a lower leaching potential is maintained with a larger contribution from needle, wood and moss litter. Our study shows that understory vegetation, especially V. myrtillus, is a key driver of litter DOC and nutrient leaching in boreal coniferous forests. [ABSTRACT FROM AUTHOR]

Analyses characterizing canopy gaps are required to improve our understanding of spatial and structural variations in forest canopies and provide insight into ecosystem-level successional processes. Gap size frequency distributions (GSFD) are indicative of ecological processes and disturbance patterns. To date, GSFD in boreal forest ecosystems have not been systematically quantified over large areas using a single consistent data source. Herein we characterized GSFDs across the entirety of the Canadian boreal forest using transects of airborne laser scanning (ALS) data. ALS transects were representatively sampled within eight distinct Canadian boreal ecozones. Gaps were detected and delineated from the ALS-derived canopy height model as contiguous canopy openings ≥8 m2 with canopy heights ≤3 m. Gaps were then stratified by ecozone and forest type (i.e. coniferous, broadleaf, mixedwood, wetland-treed), and combinations thereof, and GSFDs were calculated for each stratum. GSFDs were characterized by the scaling parameter of the power-law probability distribution, lambda (λ) and Kolmogorov-Smirnov tests confirmed that GSFDs for each stratum followed a power-law distribution. Pairwise comparisons between ecozones, forest types, and combinations thereof indicated significant differences between estimates of λ. Scaling parameters were found to be more variable by ecozone (1.96–2.31) than by forest type (2.15–2.21). These results contrast those of similar studies done in tropical forest environments, whereby λ was found to be relatively consistent across a range of site types, geological substrates, and forest types. The geographic range considered herein is much larger than that of previous studies, and broad-scale patterns in climate, landforms, and soils that are reflected in the definition of unique ecozones, likely also influence gap characteristics. [ABSTRACT FROM AUTHOR]

Comparisons between field data and available maps show that 64% of wet areas in the boreal landscape are missing on current maps. Primarily forested wetlands and wet soils near streams and lakes are missing, making them difficult to manage. One solution is to model missing wet areas from high-resolution digital elevation models, using indices such as topographical wetness index and depth to water. However, when working across large areas with gradients in topography, soils and climate, it is not possible to find one method or one threshold that works everywhere. By using soil moisture data from the National Forest Inventory of Sweden as a training dataset, we show that it is possible to combine information from several indices and thresholds, using machine learners, thereby improving the mapping of wet soils (kappa = 0.65). The new maps can be used to better plan roads and generate riparian buffer zones near surface waters. [ABSTRACT FROM AUTHOR]

In a climate change context, the sequestration of atmospheric carbon (C) in forests is key for achieving emission targets. It is thus critical to understand how large-scale disturbances are affecting the overall forest C stocks. C dynamics in North American boreal forest ecosystems are strongly affected by the defoliation and mortality that occurs during a spruce budworm (SBW) outbreak. We used forest inventory geospatial databases, monthly climate data, spatially explicit defoliation sequence data, and the TRIPLEX-Insect model to simulate C dynamics with and without SBW disturbances in stands with different vulnerability to the SBW in the boreal forest of Quebec. Our results showed that SBW defoliation and related mortality decreased the average aboveground biomass and belowground biomass by 5.96% and 6.94% by 2017, respectively. At the same time, 21,046 km2 of forest were converted from a C sink to a source. This study provides the first quantitative analysis of the effect of a SBW outbreak on carbon dynamics for three different boreal stand types (that is, fir, spruce, and mixed fir-spruce) at a regional scale. Our results suggested that younger fir forests lost less C than either fir-spruce or spruce forests during SBW attacks between 2007 and 2017 in Quebec. This highlights the importance of considering species composition when assessing vulnerability or resilience. [ABSTRACT FROM AUTHOR]

Understanding and measuring forest resistance and resilience have emerged as key priorities in ecology and management, particularly to maintain forest functioning. The analysis of the factors involved in a forest's ability to cope with disturbances is key in identifying forest vulnerability to environmental change. In this study, we apply a procedure based on combining pathway analyses of forest composition and structure with quantitative indices of resistance and resilience to disturbances. We applied our approach to boreal forests affected by a major spruce budworm outbreak in the province of Quebec (Canada). We aimed to identify the main patterns of forest dynamics and the environmental factors affecting these responses. To achieve this goal, we developed quantitative metrics of resistance and resilience. We then compared forests with different pre-disturbance conditions and explored the factors influencing their recovery following disturbance. We found that post-outbreak forest dynamics are determined by distinct resistance and resilience patterns according to dominant species and stand composition and structure. Black spruce forests are highly resistant to spruce budworm outbreaks, but this resistance is conditioned by the length of the defoliation period, with long outbreaks having the potential to lead the system to collapse. In contrast, balsam fir forests easily change to a different composition after outbreaks but are highly resilient when mixed with hardwood species. Overall, the severity of the disturbance and the tree species affected are the main drivers contributing to boreal forest resistance and resilience. Our procedure is valuable to understand post-disturbance dynamics of a broad range of communities and to guide management strategies focused on enhancing the resistance and resilience of the system. [ABSTRACT FROM AUTHOR]

Living trees are the main source of biogenic volatile organic compounds (BVOCs) in forest ecosystems, but substantial emissions originate from leaf and wood litter, the rhizosphere and from microorganisms. This review focuses on temperate and boreal forest ecosystems and the roles of BVOCs in ecosystem function, from the leaf to the forest canopy and from the forest soil to the atmosphere level. Moreover, emphasis is given to the question of how BVOCs will help forests adapt to environmental stress, particularly biotic stress related to climate change. Trees use their vascular system and emissions of BVOCs in internal communication, but emitted BVOCs have extended the communication to tree population and whole community levels and beyond. Future forestry practices should consider the importance of BVOCs in attraction and repulsion of attacking bark beetles, but also take an advantage of herbivore-induced BVOCs to improve the efficiency of natural enemies of herbivores. BVOCs are extensively involved in ecosystem services provided by forests including the positive effects on human health. BVOCs have a key role in ozone formation but also in ozone quenching. Oxidation products form secondary organic aerosols that disperse sunlight deeper into the forest canopy, and affect cloud formation and ultimately the climate. We also discuss the technical side of reliable BVOC sampling of forest trees for future interdisciplinary studies that should bridge the gaps between the forest sciences, health sciences, chemical ecology, conservation biology, tree physiology and atmospheric science. [ABSTRACT FROM AUTHOR]

Emulation of natural disturbances is often regarded as a key measure to make forestry biodiversity-oriented. Consequently, extraction of logging residues is assumed to have little negative effect in comparison to extraction of dead wood mainly formed at natural disturbances. This is consistent with the evolutionary species pool hypothesis, which suggests that most species are evolutionary adapted to the naturally most abundant habitats. We tested this hypothesis for dead-wood-dependent macrofungi, lichens, and beetles in a boreal forest landscape in central Sweden, assuming that species are adapted to conditions similar to today's unmanaged forest. No occurrence patterns, for the species groups which we investigated, were consistent with the hypothesis. Overall, stumps and snags had the highest habitat quality (measured as average population density with equal weight given to each species) and fine woody debris the lowest, which was unexpected, since stumps were the rarest dead-wood type in unmanaged forest. We conclude that the evolutionary species pool concept did not explain patterns of species' occurrences, and for two reasons, the concept is not reliable as a general rule of thumb: (1) what constitute habitats harbouring different species communities can only be understood from habitat-specific studies and (2) the suitability of habitats is affected by their biophysical characteristics. Thus, emulation of natural disturbances may promote biodiversity, but empirical studies are needed for each habitat to understand how natural disturbances should be emulated. We also conclude that stump extraction for bioenergy is associated with larger risks for biodiversity than fine woody debris extraction. [ABSTRACT FROM AUTHOR]

Identifying the scales of variation in forest structures and the underlying processes are fundamental for understanding forest dynamics. Here, we studied these scale-dependencies in forest structure in naturally dynamic boreal forests on two continents. We identified the spatial scales at which forest structures varied, and analyzed how the scales of variation and the underlying drivers differed among the regions and at particular scales. We studied three 2 km × 2 km landscapes in northeastern Finland and two in eastern Canada. We estimated canopy cover in contiguous 0.1-ha cells from aerial photographs and used scale-derivative analysis to identify characteristic scales of variation in the canopy cover data. We analyzed the patterns of variation at these scales using Bayesian scale space analysis. We identified structural variation at three spatial scales in each landscape. Among landscapes, the largest scale of variation showed the greatest variability (20.1–321.4 ha), related to topography, soil variability, and long-term disturbance history. Superimposed on this large-scale variation, forest structure varied at similar scales (1.3–2.8 ha) in all landscapes. This variation correlated with recent disturbances, soil variability, and topographic position. We also detected intense variation at the smallest scale analyzed (0.1 ha, grain of our data), partly driven by recent disturbances. The distinct scales of variation indicated hierarchical structure in the landscapes studied. Except for the large-scale variation, these scales were remarkably similar among the landscapes. This suggests that boreal forests may display characteristic scales of variation that occur somewhat independent of the tree species characteristics or the disturbance regime. [ABSTRACT FROM AUTHOR]

Boreal forests store substantial amounts of carbon in vegetation and soil pools. The magnitude of these pools is related to fire regime attributes. Climate change is expected to alter boreal fire regimes, leading to changes in the amount of stored carbon. Quantifying these changes is of importance to understanding and managing global carbon budgets. We investigate how fire return interval (FRI) interacts with seasonal variation in fire intensity and severity to affect carbon stocks and fluxes in the boreal black spruce forests of Québec, Canada. A size-class structured population model of stand dynamics was coupled with an established model of boreal carbon dynamics and linked to a simplified representation of fire regime that simulates the occurrence of fires and their direct effects on canopy tree mortality, surface fuels combustion and regeneration. We simulated carbon stocks and fluxes under seven levels of FRI and two fire seasons: spring and summer. We tested for an effect of these fire regime parameters on equilibrium mean C stocks. All dead organic matter and biomass carbon stocks were sensitive to FRI between 60 and 300 years. These C stocks were lower for summer fires that occurred under shorter FRIs. Net primary production was highest at FRIs between 150 and 300 years. Total C stocks were highest for FRIs from 150 to 700 years, varying little over this range. There was a small but significant difference of C pool sizes between stands with even and uneven tree-diameter distributions. This difference was greatest for FRIs of 150 years or less. Reductions in equilibrium C storage are forecasted for nearly 27% of the study region under expected end-of-century climates. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi are an important component to ecosystem function in the boreal forest. Underlying factors influencing fungal community composition and richness, such as host identity and soil type have been studied, but interactions between these factors have been less explored. Furthermore, mixed-species stands may have additive or synergistic effects on ectomycorrhizal fungi species richness, but this effect is challenging to test on natural sites due to difficulty in finding monospecific and mixed-species stands with similar site conditions and history. Forest reclamation areas can provide an opportunity to explore some of these fundamental questions, as site conditions and history are often known and managed, with the added benefit that knowledge emerging from these studies can be used to evaluate the recovery of degraded forest landscapes. Here, we compared the richness and composition of ectomycorrhizal fungi in young single- and mixed-species stands established on a reclamation area designed to inform strategies to restore upland boreal forests disturbed by oil sands mining. Seedlings of three host tree species (Populus tremuloides, Pinus banksiana, Picea glauca) were planted in single- and mixed-species stands on three different salvaged soils (forest floor material, peat, subsoil). After four growing seasons, there was no difference in total ectomycorrhizal fungi species richness and composition in mixed- versus combined single-species stands indicating that an additive effect of host tree species prevailed early in development. However, there were compositional shifts in fungal communities across both the host tree species and the salvaged soil type, with soil type being the strongest driver. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the potential of different water management options to mitigate sediment and nutrient exports from ditch network maintenance (DNM) areas in boreal peatland forests. Available literature was reviewed, past data reanalyzed, effects of drainage intensity modeled, and major research gaps identified. The results indicate that excess downstream loads may be difficult to prevent. Water protection structures constructed to capture eroded matter are either inefficient (sedimentation ponds) or difficult to apply (wetland buffers). It may be more efficient to decrease erosion, either by limiting peak water velocity (dam structures) or by adjusting ditch depth and spacing to enable satisfactory drainage without exposing the mineral soil below peat. Future research should be directed towards the effects of ditch breaks and adjusted ditch depth and spacing in managing water quality in DNM areas. [ABSTRACT FROM AUTHOR]

The growth of high-latitude temperature-limited boreal forest ecosystems is projected to become more constrained by soil water availability with continued warming. The purpose of this study was to document ongoing shifts in tree growth sensitivity to the evolving local climate in unmanaged black spruce (Picea mariana (Miller) B.S.P.) forests of eastern boreal North America (49°N-52°N, 58°W-82°W) using a comparative study of field and modeled data. We investigated growth relationships to climate (gridded monthly data) from observed (50 site tree-ring width chronologies) and simulated growth data (stand-level forest growth model) over 1908-2013. No clear strengthening of moisture control over tree growth in recent decades was detected. Despite climate warming, photosynthesis (main driver of the forest growth model) and xylem production (main driver of radial growth) have remained temperature-limited. Analyses revealed, however, a weakening of the influence of growing season temperature on growth during the mid- to late twentieth century in the observed data, particularly in high-latitude (> 51.5°N) mountainous sites. This shift was absent from simulated data, which resulted in clear model-data desynchronization. Thorough investigations revealed that desynchronization was mostly linked to the quality of climate data, with precipitation data being of particular concern. The scarce network of weather stations over eastern boreal North America (> 51.5°N) affects the accuracy of estimated local climate variability and critically limits our ability to detect climate change effects on high-latitude ecosystems, especially at high altitudinal sites. Climate estimates from remote sensing could help address some of these issues in the future. [ABSTRACT FROM AUTHOR]

Large herbivores are capable of modifying entire ecosystems with a combination of direct (for example browsing/grazing, trampling, defecation) and indirect (for example affecting plant species composition that then alters soil properties) effects. With many ungulate populations increasing across the northern hemisphere it is important to develop a general theory for how these animals can be expected to impact their habitats. Here we present the results of an 8-year experimental exclusion of moose (Alces alces) from 15 recent boreal forest clear-cut sites in Central Norway. We used standard univariate techniques to describe the treatment effect on multiple forest and soil properties and combined this with a multivariate Bayesian network structure learning approach to objectively assess the potential mechanistic pathways for indirect effects on soils and soil fertility. We found that excluding moose had predictable direct effects, such as increasing the ratio of deciduous to coniferous tree biomass and the canopy cover and decreasing soil bulk density and temperature. However, we found no treatment effects on any measures of soil processes or quality (decomposition, nitrogen availability, C/N ratio, pH, nutrient stocks), and furthermore, we found only limited evidence that the direct effects had cascading (indirect) effects on soils. These findings oppose the commonly held belief that moose exclusion will increase soil fertility, but still highlights the strong ability of moose to directly modify forested ecosystems. [ABSTRACT FROM AUTHOR]

Spatial or temporal forest-peatland transition zones were proposed as potential hot spots of methane (CH4) emissions. Consequently, paludified soils are an important component of boreal landscape biogeochemistry. However, their role in the regional carbon cycle remains unclear. This study presents CH4 fluxes from two forest-peatland transition zones, two wet forest sites and two clear-cut sites which were compared to fluxes of open peatlands and dry forest. The median fluxes measured using the closed-chamber technique varied from − 0.04 to 12.6 mg m−2 h−1 during three climatically different years. The annual mean CH4 emissions of the forest-peatland transition zone were significantly lower than the fluxes of the open peatland sites, 7.9 ± 0.5 and 21.9 ± 1.6 g m−2a−1, respectively. The dry forest site was characterized by a small uptake of CH4 (− 2.3 ± 0.2 g m−2a−1). Although clear-cut forest area drastically increased in European Russia during the last two decades, if water level depths in these forests remains below 10 cm they do not act as CH4 sources. Fluxes of CH4 from the transition zone sites showed a higher response to soil temperature than to water table level. Fluxes of CH4 between the atmosphere and the two investigated peatlands were not significantly different, although a significant difference in water table level could be observed. The meteorological conditions of the investigated summers changed from being hot and dry in 2013 to cold and wet in 2014; the summer of 2015 was characterized as warmer and drier in the first half and colder and wetter in the second half. Significant differences in CH4 fluxes were measured only between 2014 and 2013. Significant differences in CH4 fluxes and in nonlinear regressions showed that the CH4 fluxes of the different site types such as dry forests, transition zones and open peatlands need to be modelled separately on a landscape level. Obviously, underlying processes vary with the ecosystem and (along with regional aspects) have to be understood first before large-scale modelling is possible. [ABSTRACT FROM AUTHOR]

Trace fossils have been found for the first time in the Tavda Formation shallow marine facies, and their possible indicative value has been evaluated. The results of the ichnofossil study suggest that the Tavda Basin had low hydrodynamics. Under these conditions boreal and thetic waters of different characteristics were blended, which caused periodic formation of thermohaline water stratification and anoxic conditions in bottom water levels. Such periodic events conditioned mass extinctions of a wide variety of the Eocene marine biota thus preconditioning the development of freshwater fauna in the upper levels of the Tavda Sea along with saturation of the index beds of the Tavda Formation with micro- and macrofossils. [ABSTRACT FROM AUTHOR]

Quantitative parameters of cenopopulations of Lobaria pulmonaria, an endangered cyanolichen, have been studied in spruce phytocenoses of Karelia recovering after disturbance through the successional stage of aspen stands for a period ranging from 80 to 450 years. The results show that, as the time since disturbance increases, the total number of L. pulmonaria thalli and the number of colonized substrate units increase as well, with no stabilization of these parameters being observed in the series of communities studied. The total area of thalli in the phytocenoses is restored within approximately 200 years after the last disturbance. In old-growth forests (>400 years), L. pulmonaria thalli colonize a broad spectrum of tree species in different life states, including lower branches of young spruce trees. Even if they serve as temporary substrates, this can markedly strengthen the potential of the species for further expansion within the community in case of shortage in the main phorophyte (aspen). Thus, the proportion of regressive populations decreases, while that of colonizing populations increases, which is indicative of successful reproduction of the species. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the applicability of the land degradation neutrality (LDN) concept of the UN Convention to Combat Desertification to the Russian boreal forests. In this regard, it is necessary to adapt three global LDN indicators (land cover, land productivity, and carbon stock) to the assessment of land degradation processes of boreal forests in Russia and around the world. According to the research results, landscapes with different types of forest restoration dynamics can be viewed as an object of forest land dynamic studies. A set of LDN indicators adapted for boreal forests conditions has also been suggested in the course of our research. In order to assess LDN proxies, we calculated the retrospective and projected net carbon balance in the middle taiga zone of the Noshulskoye forest domain (Komi Republic, Russia) using the CBM CFS model. We explored three scenarios of forest net carbon balance under three different felling regimes. The net carbon balance should not be applied as an independent LDN indicator, because it does not take into account changes in species diversity and primary productivity. It is suggested that industrial felling should imitate natural types of restoration dynamics in order to achieve LDN targets. It can be reached through minimization of forest felling at sites with fireless types of succession, which accumulate maximum stocks of dead phytomass matter and serve as forest refuges supporting biodiversity. [ABSTRACT FROM AUTHOR]

An algorithm of regional assessment of the size and structure of the actual (corresponding to the modern state of ecosystems and land use patterns) and potential (for hypothetic natural ecosystems analogous to modern native ecosystems) pools of carbon has been developed and tested. A comparison between actual and potential values of carbon pools makes it possible to assess the integral result of land use in the studied region with multiple changes in the types of land use during the historical period. The calculations are made using a unified cartographic base and take into account the taxonomic position and texture of soil units, the types of modern land use, and the type and age structure of the reconstructed and actual vegetation. The results obtained for the southern taiga and forest-steppe zones of European Russian indicate that the modern actual carbon pool is 24% less than the potential carbon pool in Kostroma oblast (southern taiga zone) and 32% less than the potential carbon pool in Kursk oblast (forest-steppe zone). The actual phytomass reserves in these two regions have decreased by 40 and 75%, respectively, relative the potential phytomass reserves, so the portion of the soil carbon pool in the total carbon pool has increased. It is argues that the use of the territory for forestry and agriculture increases the role of the soil cover in sustaining the carbon budget of the region. [ABSTRACT FROM AUTHOR]

Using tree data from permanent sample plots and climate data from the ClimateWNA model, mixed-effects height to live crown (HTC) models were developed for three boreal tree species in Alberta, Canada: trembling aspen (Populus tremuloides Michx.), lodgepole pine (Pinus contorta var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss). Three model forms, the Wykoff model, a logistic model and an exponential model, were evaluated for each species. Tree height was the most significant predictor of HTC and was used in all models. In addition, we investigated the effects of competition and climatic variables on HTC modelling. Height-diameter ratio and either total stand basal area or basal area of coniferous trees were used as competition measures in the models. Different climate variables were evaluated, and spring degree-days below 0 °C, mean annual precipitation and summer heat-moisture index were incorporated into the aspen, lodgepole pine and white spruce models, respectively. Site index was only significant in lodgepole pine models. Residual variances were modelled as functions of tree height to account for heteroscedasticity still present in the mixed-effects models after the inclusion of random parameters. Based on model fitting and validation results as well as biological realism, the mixed-effects Wykoff models were the best for aspen and white spruce, and the mixed-effects logistic model was the best for lodgepole pine. [ABSTRACT FROM AUTHOR]

The boreal ecoregion supports about one-third of the world’s forest. Over 90% of boreal forest streams are found in headwaters, where terrestrial-aquatic interfaces are dominated by organic matter (OM)-rich riparian zones (RZs). Because these transition zones are key features controlling catchment biogeochemistry, appropriate RZ conceptualizations are needed to sustainably manage surface water quality in the face of a changing climate and increased demands for forest biomass. Here we present a simple, yet comprehensive, conceptualization of RZ function based on hydrological connectivity, biogeochemical processes, and spatial heterogeneity. We consider four dimensions of hydrological connectivity: (1) laterally along hillslopes, (2) longitudinally along the stream, (3) vertically down the riparian profile, and (4) temporally through event-based and seasonal changes in hydrology. Of particular importance is the vertical dimension, characterized by a ‘Dominant Source Layer’ that has the highest contribution to solute and water fluxes to streams. In addition to serving as the primary source of OM to boreal streams, RZs shape water chemistry through two sets of OM-dependent biogeochemical processes: (1) transport and retention of OM-associated material and (2) redox-mediated transformations controlled by RZ water residence time and availability of labile OM. These processes can lead to both retention and release of pollutants. Variations in width, hydrological connectivity, and OM storage drive spatial heterogeneity in RZ biogeochemical function. This conceptualization provides a useful theoretical framework for environmental scientists and ecologically sustainable and economically effective forest management in the boreal region and elsewhere, where forest headwaters are dominated by low-gradient, OM-rich RZs. [ABSTRACT FROM AUTHOR]

The composition of soil water under coniferous forests of Murmansk oblast—an industrially developed region of northern Russia—was investigated. The studied objects were dwarf-shrub-green-moss spruce forests and dwarf-shrub-lichen pine forests on Al-Fe-humus podzols (Albic Rustic Podzols) that are widespread in the boreal zone. The concentrations and removal of organic carbon performing the most important biogeochemical and pedogenic functions were estimated. The results proved significant intra- and inter-biogeocenotic variability in the composition of atmospheric depositions and soil water. Carbon removal with soil water from organic and mineral horizons within elementary biogeoareas (EBGA) under tree crowns was 2-5 and 2-3 times (in some cases, up to 10 times) greater than that in the intercrown areas, respectively. The lowest critical level of mineral nitrogen (0.2 mg/L) was, as a rule, exceeded in tree EBGAs contrary to intercrown areas. Concentrations of sulfates and heavy metals in water of tree EBGA were 3-5 times greater than those in inter-crown areas. Significant inter-biogeocenotic variations related to differences in the height of trees and tree stand density were found. It is argued that adequate characterization of biochemical cycles and assessment of critical levels of components in soil water of forest ecosystems should be performed with due account for the intra- and inter-biogeocenotic variability. [ABSTRACT FROM AUTHOR]

We analysed a dataset composed by the frequency of 79 epiphytic lichens recorded on 243 oaks distributed in 29 oak dominated stands of the Western Carpathians, representing areas with high environmental quality up to disturbed environments. Lichen diversity indices (based on total frequencies and on functional and morphological groups) were used as indicators of the response to air quality and forest management. The level of air quality in these categories was a function of NOx, SO2 and particulate matter. From management viewpoint the units were classified as managed (areas subjected to periodic logging) and semi-natural (which currently have the status of National Nature Reserve and where eventual management practices date back to the history). The results showed that higher environmental levels of pollution were associated to the decrease of fruticose and in general pollution sensitive species, while low environmental levels of pollution were associated to the diffusion of common nitrophilous lichens as well as to a higher share of fruticose and in general pollution sensitive species. As far as forest management is concerned, a higher share of fruticose and sensitive species was associated to semi-natural and natural stands, whereas a higher share of foliose (pioneer and tolerant) species was associated to the managed stands. [ABSTRACT FROM AUTHOR]

Aims: Reclamation following oil sands mining in northeastern Alberta (Canada) creates adverse reforestation soil conditions, including extreme pH values. We elucidated pH tolerance limits of boreal plant species and how pH affects nutrient uptake in these plants. Methods: We measured growth, gas exchange, and foliar nutrient concentration of 15 common northern boreal forest plants after eight weeks exposure to root zone pH ranging from 5.0 to 9.0. Cluster analyses were used to group these species based on their pH responses. Results: Based on their growth and gas exchange responses to pH, the 15 plant species could be divided into five groups, each of which contained species that commonly co-occur in particular boreal forest site types. For the foliar nutrient responses to pH, the 15 species could be grouped into only two categories; both showed decreases in foliar N, P, Fe and Zn concentration with increasing pH, with a more pronounced effect on the group that included trembling aspen, paper birch and chokecherry. Conclusions: The evidence of differential adaptation to pH by habitat type suggests the importance of soil pH as a factor affecting boreal plant species distribution and could be helpful for selection of species suitable for reclamation of sites with altered soil pH. [ABSTRACT FROM AUTHOR]

Ratios between above- and underground phytomass of tree organs were studied for different forest types. The partitioning of phytomass into tree fractions was described using rank distributions characterizing the relationships between the resource volume available for each tree organ and the ranks of biomass fractions. Species-specific parameters of biomass partitioning into tree organs were calculated, and the dependences of these parameters on the forest type and tree size were revealed. Independent verification of the biomass distribution model was performed. [ABSTRACT FROM AUTHOR]

Several species of small birds are resident in boreal forests where environmental temperatures can be −20 to −30 °C, or even lower, in winter. As winter days are short, and food is scarce, winter survival is a challenge for small endothermic animals. A bird of this size will have to gain almost 10% of its lean body mass in fat every day to sustain overnight metabolism. Birds such as parids (titmice and chickadees) can use facultative hypothermia, a process in which body temperature is actively down-regulated to a specific level, to reduce heat loss and thus save energy. During cold winter nights, these birds may decrease body temperature from the normal from 42 ° down to 35 °C, or even lower in some species. However, birds are unable to move in this deep hypothermic state, making it a risky strategy if predators are around. Why, then, do small northern birds enter a potentially dangerous physiological state for a relatively small reduction in energy expenditure? We used stochastic dynamic programming to investigate this. Our model suggests that the use of nocturnal hypothermia at night is paramount in these biomes, as it would increase winter survival for a small northern bird by 58% over a winter of 100 days. Our model also explains the phenomenon known as winter fattening, and its relationship to thermoregulation, in northern birds. [ABSTRACT FROM AUTHOR]

The paper presents results of radiocological monitoring at the site of the Kraton-3 accidental underground nuclear test in Yakutia. The distribution and migration of Cs, Sr, Np, and Pu in the soil and its living cover of the northern taiga are analyzed, and it is demonstrated that the radioecological conditions at the territory are still adverse in spite of the rehabilitation measures. [ABSTRACT FROM AUTHOR]

Background and aims: Fine roots are only a small part of total ecosystem biomass, but substantially contributing to soil carbon accumulation in boreal forests. Wildfires may influence fine root dynamics directly via heating and indirectly via interactions with wildfire-deposited charcoal. We tested if the presence of charcoal in a recently burned larch forest affected fine root vitality. Methods: This study was stratified across vegetation type (understorey and overstorey), soil depth (upper and lower layers), and root diameter classes: fine (≥0.5 mm but <2 mm diameter), and very fine (diameter < 0.5 mm) in a recently surface-burned Gmelin larch ( Larix gmelinii (Rupr.) Rupr .) forest in the Russian Far East. Results: Charcoal content and fine root vitality were positively correlated for overstorey vegetation, but negatively correlated for understorey vegetation. On the other hand, total charcoal content did not significantly correlate with very fine root vitality, biomass or necromass. Conclusions: Our study provides the first field evidence that fine root dynamics are influenced by fire-derived charcoal in frequently burned boreal forest. Furthermore, the effect of charcoal on fine root vitality depends on the vegetation type, root diameter, and soil depth, which indicates the necessity of complicated modeling of soil organic carbon derived from fine roots in post-fire boreal forests. [ABSTRACT FROM AUTHOR]

Specific activities of artificial (Cs, Sr) and natural (К, Th, Ra) radionuclides in background soils of southern and middle taiga of Komi Republic have been estimated with consideration for the landscape-geochemical features of the territory. It has been shown that their accumulation and migration in soils are determined by the following factors: position in relief, texture, and organic matter content. No anomalous zones with increased contents of radionuclides in soils have been revealed. [ABSTRACT FROM AUTHOR]

Two pyrogenic cycles (two succession series) of ecosystems in the boreal forest belt are characterized. One cycle is associated with the subbelt of subgolets (subalpine) spruce and larch forests, and the other, with the subbelt of taiga spruce and larch forests. The bird population at different stages of succession are compared. Quantitative analysis utilizes measures of inclusion and similarity. The avian faunistic and ecological complexes, as well as forest layer aggregations, are considered. As is shown, the ecosystems at the early stage of succession play a significant role in the spread of the Chinese ornithofaunistic complex against the background of prevalence of the Siberian complex. The species involved in both cycles belong to the forest ecological complex. The bird population in the succession systems at later stages and native ecosystems of two subbelts are more similar to one another as compared with the succession systems of the same subbelts at early stages. [ABSTRACT FROM AUTHOR]

Aims: Root fungal relationships in forest understory may be affected by tree harvesting. Deschampsia flexuosa forms a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi functioning in nutrient uptake, and a more loose association with dark septate endophytic (DSE) fungi. We asked how harvesting affects fungal colonisations and whether DSE is more prone to change than AM. Methods: Deschampsia flexuosa plants were sampled close to a control or a cut tree after top-canopy harvesting in a primary successional site. Colonisations were studied using light microscopy. Shoot N%, vegetation cover and soil nutrients were determined. Results: Tree harvesting did not affect vegetation and soil parameters, except potassium (K) increasing near cut trees. AM colonisation did not change, while DSE increased. Shoot N% increased with increasing DSE near cut trees. Hyaline septate (HSE) hyphae and soil K and magnesium (Mg) were positively correlated near control trees. Lichen cover and HSE correlated negatively. Conclusions: DSE colonisation increased but AM did not change after harvesting. Positive correlation of DSE with shoot N% near cut trees may suggest a role for DSE in favouring plant nitrogen uptake after disturbance in an open microsite. HSE may play a role in K and Mg uptake. [ABSTRACT FROM AUTHOR]

Background and aims: Climate warming is expected to accelerate decomposition in boreal forests, but the concomitant effects of tropospheric ozone (O), a phytotoxic greenhouse gas, alone and in combination with warming, are poorly understood. We studied how these two climatic factors affect leaf litter decomposition of two silver birch genotypes. Methods: We used field exposure for growing saplings and native and reciprocal transplant experiments for litter incubation to disentangle environmental and litter quality mediated effects of temperature and O on litter mass loss. We analysed litter C% and N% and microbial biomass (using qPCR) in fresh litter and after 217 and 257 days of incubation. Results: Warming decreased fresh litter C% and N% and bacterial DNA, whereas elevated O increased N% and bacterial and fungal DNA, equally for both genotypes. In contrast, most effects on microbes during litter incubation varied between the two genotypes. Warming effects on microbes were mainly environmental, but despite having effects on litter quality and microbial growth, warming and O both had only weak or no effects on litter mass loss. Conclusions: Litter quality and microbial growth in northern birch stands are likely to change due to warming and O exposures, but effects on litter decomposition rate may remain weak. [ABSTRACT FROM AUTHOR]

New data are presented on unique refugia accounting for the high floristic diversity of dark conifer forests of the Northern Urals, which have some of the highest parameters of species saturation among boreal forests of northern Eurasia. Based on the results of analysis, the most significant biological factors have been revealed and their influence on boreal tall-herb and background plant communities has been evaluated. [ABSTRACT FROM AUTHOR]

Zooplankton abundance and community structures were studied in three west Spitsbergen fjords at the beginning of the warm phase, which seem to have entered in 2006. Sampling was conducted in summer 2007 at stations distributed along transects in Hornsund, Isfjorden and Kongsfjorden. Variations in zooplankton standing stocks and community structures (assessing taxonomic diversity and zoogeographical affiliations) were analysed in relation to the environmental variables using multivariate techniques. The hydrographic conditions in Hornsund were influenced by the cold Arctic Water, whereas those in Isfjorden and especially in Kongsfjorden were, to a greater extent, under the influence of the warm Atlantic Water. High abundances of both meroplankton and holoplankton organisms were observed in Kongsfjorden, with high contributions of boreal and ubiquitous species ( Calanus finmarchicus and Oithona similis, respectively). In Hornsund at the same time, the zooplankton consisted mainly of boreo-Arctic and Arctic species, the abundances of which were comparable along the West Spitsbergen Shelf. Our results indicate that the difference in hydrography had measurable effects on the zooplankton community in the study area. Furthermore, by comparing regions of contrasting oceanographic conditions, we present evidence as to how the zooplankton structure will change in the Arctic ecosystems if the warming trends continue to operate with the same dynamics. The advection of Atlantic waters to the Arctic seas may lead to changes in zooplankton structure, with increased abundance and contributions of boreal and small ubiquitous species. The 'warmer Arctic fjords' scenarios may also induce more rapid development of both holoplankton and meroplankton populations and, consequently, modify the trophic interactions in plankton communities. [ABSTRACT FROM AUTHOR]

Tundra and boreal forests in northern high latitudes contain significant amounts of carbon (C) in the soil, indicating the importance of clarifying controls on soil C dynamics in the region and their feedback effects on climate systems. In northern Alaska, variations in soil C processes are closely associated with variations in soil acidity within ecosystems; however, the reason for this association remains unclear. In this study, we demonstrate that it results from weathering and subsequent changes in soil geochemical characteristics, including minerals and adsorptive organic C. We sampled soils from 12 sites in Alaska along a 600-km transect from the Arctic Ocean to interior Alaska, spanning the biomes of tundra, tundra-boreal forest ecotone, and boreal forest. Mineral soil analyses revealed that soils with low pH have fewer base cations, more aluminum/iron minerals, and lower base saturation, indicating that weathering is a major function of these geochemical characteristics in the broad area over northern Alaska. Adsorbed organic C in soil presented strong correlations with Al and Fe minerals, soil pH, and soil total C and represented approximately 30-55% of total soil C, suggesting that soil C accumulation in the Alaskan ecosystems is strongly controlled by weathering-related changes in geochemical characteristics. An adsorption test supported these observations and illustrated a greater capacity for acidic soil to adsorb organic C. These findings demonstrate that variations in weathering-associated characteristics have a strong influence on the regional variation in C dynamics and biogeochemical consequences in the Alaskan ecosystems. [ABSTRACT FROM AUTHOR]

Creation of canopy gaps can be used as a restoration measure to aid in the diversification of structural variability and tree species composition in forests. However, it is not generally known how the specific properties of gaps influence restoration success. In this study, we examined tree seedling regeneration in 94 small canopy gaps that were established for restoration purposes in two protected Pinus sylvestris (Scots pine)-dominated forests in eastern Finland 10 years earlier. In particular, we assessed the effect of gap size, within-gap position, and soil preparation (exposure of the mineral soil) within the gaps (soil disturbance) on seedling establishment. We found that tree species composition in the sample plots consisted mainly of P. sylvestris (73 %) and Betula spp. (16 %) seedlings. Most Pinus and Betula seedlings were found in the disturbed plots, and only 6 % of the seedlings were found in the undisturbed plots (no soil preparation applied). The mean number of pooled Pinus and Betula seedlings per disturbed plot (40 × 60 cm) was 0.5 and 0.1, respectively. Mean height of the Pinus and Betula seedlings was 9.2 cm and 51.5 cm, respectively, which suggests that seedling development in the disturbed plots was very slow and is probably hindered by an insufficient amount of solar radiation reaching the forest floor, as well as by root competition with the trees that surround the gap. Both factors are affected by gap size, which was probably not large enough (mean diameter ≤23 m) in our study forests to reach a threshold value that meets the requirements of Pinus and Betula seedlings. We conclude that the creation of small canopy gaps does not appear to be an effective method to restore the age class structure and tree species composition in boreal pine-dominated forests. Further studies that manipulate the gap size more widely than this current study are needed. [ABSTRACT FROM AUTHOR]

Data on the input of plant falloff and organic matter decomposition on the surface of the peaty podzolic-gleyic humus-illuvial (Gleyic Podzol) soil under a mature blueberry pine forest in the middle taiga are presented. The fractional composition of the falloff was determined, and constants of decomposition for its components were calculated. The carbon flux to the atmosphere due to the mineralization of plant residues is estimated at 251 g/m. A close positive correlation ( r = 0.71; P < 0.05) was found between the carbon dioxide emission measured using a gas analyzer and the soil temperature at the depth of 10 cm. The CO emission for a growing period calculated from the data on its dependence on soil temperature in different years varied from 243 to 313 g C/m and was related to weather conditions. [ABSTRACT FROM AUTHOR]

Regional estimates of changes in soil organic carbon (SOC) pools during the historical period were obtained according to a unified approach for Kostroma (southern taiga) and Kursk (forest-steppe) oblasts. The potential pools of soil carbon were calculated with due account for the classification position of particular soils, their texture, and the character of natural vegetation. In the estimates of actual SOC pools, land use patterns and the age structure of forest stands were taken into account. It was shown that modern pools of organic carbon in the soils of Kostroma oblast are only 1-2% smaller than the potential pools; for the soils of Kursk oblast, this difference reaches 23-27%. Mean weighted values of the actual SOC contents in these oblasts decreased by 0.1-0.2 and 6.5-7.6 kg C/m in comparison with the potential SOC contents, respectively, which is related to their environmental specificity and to different types of land use at present and in the historical past. [ABSTRACT FROM AUTHOR]

The general patterns of the effect of cuttings on the habitat structure, abundance, territorial distribution, and specific ecological features of 11 small mammalian species are analyzed based on long-term studies (1958-2013) covering the overall area of eastern Fennoscandia. The responses to concentrated cuttings common for most of the examined species include a decrease in total population size, transition to an arrhythmic population dynamics with drastic short-term rises and deep long depressions, formation of unstable mosaic spatial distribution, disturbances of the reproduction rates, and a decrease in reproduction intensity. [ABSTRACT FROM AUTHOR]

Species climate change vulnerability, their predisposition to be adversely affected, has been assessed for a limited portion of biodiversity. Our knowledge of climate change impacts is often based only on exposure, the magnitude of climatic variation in the area occupied by the species, even if species sensitivity, the species ability to tolerate climatic variations determined by traits, plays a key role in determining vulnerability. We analyse the role of species' habitat associations, a proxy for sensitivity, in explaining vulnerability for two poorly-known but species-rich taxa in boreal forest, saproxylic beetles and fungi, using three IPCC emissions scenarios. Towards the end of the 21st century we projected an improvement in habitat quality associated with an increase of deadwood, an important resource for species, as a consequence of increased tree growth under high emissions scenarios. However, climate change will potentially reduce habitat suitability for ~9-43 % of the threatened deadwood-associated species. This loss is likely caused by future increase in timber extraction and decomposition rates causing higher deadwood turnover, which have a strong negative effect on boreal forest biodiversity. Our results are species- and scenario-specific. Diversified forest management and restoration ensuring deadwood resources in the landscape would allow the persistence of species whose capacity of delivering important supporting ecosystem services can be undermined by climate change. [ABSTRACT FROM AUTHOR]

Most studies of stream wood have focused on pieces ≥0.1 m diameter. However, this approach may overlook an important feature of small streams, where wood <0.1 m can constitute the majority of wood pieces. We examined the effect of fine wood (FW) on local drift of stream macroinvertebrates. The study was carried out at seven sites in four boreal forest streams, from early June to mid-August 2011. This was done by anchoring bundles of FW at each site and measuring drift upstream and downstream of each bundle. We hypothesized that FW would increase drift density, biomass and diversity of aquatic invertebrates. Ten weeks after FW addition, aquatic drift density was higher downstream than upstream of FW bundles, while drift biomass and drift diversity did not differ significantly downstream and upstream of FW. [ABSTRACT FROM AUTHOR]

The biodegradation of soil organic nitrogen (SON) into forms available for plant uptake is an important control on nitrogen availability, plant growth, and carbon (C) sequestration in terrestrial ecosystems. Changes in biochemical composition during SON diagenesis were investigated by analyzing hydrolysable amino acids in the organic (L, F, and H) horizons and the surface mineral (B) horizon of soil profiles from the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT). The diagenetic continuum in the soil profiles provides insights about the mechanisms of SON transformations, and comparison of regions along the latitudinal transect provides insight on the effects of climate. The fraction of N accounted for as amino acids decreased with depth in the profile, indicating a preferential loss of amino acids compared to bulk N during diagenesis. The amino acid composition also changed consistently with depth, and was used to construct a degradation index for assessing the extent of SON diagenesis. The compositional changes were similar to those observed in marine and lake sediments, indicating leaching and biodegradation have similar effects on SON composition in all three systems. This was supported by the use of the amino acids hydroxproline and diaminopimelic acid as tracers of plant and bacterial remains, respectively. The contribution of microbial remains increased with depth to >34 % of amino acids and >19 % of total N in the B horizon, consistent with increasing microbial decomposition. The extent of SON diagenesis was similar in the three regions despite a younger mean age of the organic matter at the southernmost site, indicating a higher rate of N turnover with higher temperature and precipitation. The resulting increase in N availability likely contributes to higher productivity and thus the higher litter inputs observed in the southern region, maintaining similar C stocks despite more rapid decomposition. [ABSTRACT FROM AUTHOR]

In the boreal forest of Alaska, increased fire severity associated with climate change is expanding deciduous forest cover in areas previously dominated by black spruce ( Picea mariana). Needle-leaf conifer and broad-leaf deciduous species are commonly associated with differences in tree growth, carbon (C) and nutrient cycling, and C accumulation in soils. Although this suggests that changes in tree species composition in Alaska could impact C and nutrient pools and fluxes, few studies have measured these linkages. We quantified C, nitrogen, phosphorus, and base cation pools and fluxes in three stands of black spruce and Alaska paper birch ( Betula neoalaskana) that established following a single fire event in 1958. Paper birch consistently displayed characteristics of more rapid C and nutrient cycling, including greater aboveground net primary productivity, higher live foliage and litter nutrient concentrations, and larger ammonium and nitrate pools in the soil organic layer (SOL). Ecosystem C stocks (aboveground + SOL + 0-10 cm mineral soil) were similar for the two species; however, in black spruce, 78% of measured C was found in soil pools, primarily in the SOL, whereas aboveground biomass dominated ecosystem C pools in birch forest. Radiocarbon analysis indicated that approximately one-quarter of the black spruce SOL C accumulated prior to the 1958 fire, whereas no pre-fire C was observed in birch soils. Our findings suggest that tree species exert a strong influence over C and nutrient cycling in boreal forest and forest compositional shifts may have long-term implications for ecosystem C and nutrient dynamics. [ABSTRACT FROM AUTHOR]

Forest vegetation composition, including dominant keystone species and floristic diversity, is driven by natural and anthropogenic disturbances. Disentangling these complex interactions to identify the role of species competition, climate and disturbances in boreal forest dynamics is challenging. Here, pollen and charcoal data are used to reconstruct Holocene vegetation and fire history at the local stand-scale within an old-growth Picea abies (Norway spruce) forest hollow in southern Finland. The aim is to reconstruct vegetation history with specific emphasis on the mid-Holocene expansion of Picea and the decline in deciduous species in relation to fire history. Early-Holocene forest development and vegetation dynamics are primarily driven by climatic variations. The spread of Picea at approximately 5,200 cal bp does not coincide with local natural or anthropogenic disturbance or a decline in deciduous species and is consistent with its regional expansion, suggesting climate as the most likely control over the late establishment of this taxon. The mid-Holocene decline in deciduous species corresponds to an increased fire frequency suggesting a higher anthropogenic disturbance (also considered as the primary reason for the loss of floristic diversity in southern Finland). The 'natural' fire frequency in this local stand-scale boreal forest is lower than that observed in the recent past (i.e. the time of significant anthropogenic impact), yet the present-day absence or low frequency of fire remains within the range of natural variability observed during the early- and mid-Holocene. [ABSTRACT FROM AUTHOR]

Disturbance plays an important role in the distributional range of species by affecting their colonization potential and persistence. Short disturbance intervals have been linked to reduced seedbank sizes of some species, but the effects of long intervals are largely unknown. To explore the potential existence of seedbank sizes that may also be limited by long disturbance intervals, we studied an area in boreal eastern North America where time since fire (TSF) coincides with an increase in environmental stress (accumulating organic matter measured as depth of the soil organic layer (SOL)). Along a chronosequence dating back about 710 years, we counted the number of seeds cone of black spruce ( Picea mariana) and then estimated the number of seeds tree and site by upscaling. Younger sites [TSF 60-150 years] with mature first regeneration trees had average-sized seedbanks for black spruce [12.0-17.9 (10) seeds ha], whereas subsequent pulse trees that established in SOL depths greater than 35 cm showed highly reduced seed numbers. Sites with second- to fourth-regeneration pulse individuals [TSF c. 350-710 years] had exceptionally small seedbanks of 0.90 (10) and 0.46 (10) seeds ha, respectively. Radial tree growth rate showed a similarly negative response to SOL depth and could potentially be used as an indicator of seed output in plant species. Because the decline in seedbank size was possibly caused by more general environmental stress factors such as reduced nutrient availability, we suggest exploring whether other examples of ecosystems exist where long time since disturbance may lead to reduced seedbank sizes. [ABSTRACT FROM AUTHOR]

Plants acquire carbon through photosynthesis to sustain biomass production, autotrophic respiration and production of non-structural compounds for multiple purposes. The fraction of photosynthetic production used for biomass production, the biomass production efficiency, is a key determinant of the conversion of solar energy to biomass. In forest ecosystems, biomass production efficiency was suggested to be related to site fertility. Here we present a database of biomass production efficiency from 131 sites compiled from individual studies using harvest, biometric, eddy covariance, or process-based model estimates of production. The database is global, but dominated by data from Europe and North America. We show that instead of site fertility, ecosystem management is the key factor that controls biomass production efficiency in terrestrial ecosystems. In addition, in natural forests, grasslands, tundra, boreal peatlands and marshes, biomass production efficiency is independent of vegetation, environmental and climatic drivers. This similarity of biomass production efficiency across natural ecosystem types suggests that the ratio of biomass production to gross primary productivity is constant across natural ecosystems. We suggest that plant adaptation results in similar growth efficiency in high- and low-fertility natural systems, but that nutrient influxes under managed conditions favour a shift to carbon investment from the belowground flux of non-structural compounds to aboveground biomass. [ABSTRACT FROM AUTHOR]

Mixedwood forests occupy a large extent of boreal regions and have the potential for sequestering large amounts of carbon. In the context of forest ecosystem management, partial cutting prescriptions are increasingly being applied to boreal mixedwood stands. Partial harvesting is expected to maintain carbon pools and dynamics within the limits of those of natural stands. Changes in live tree, deadwood (standing snags, downed logs), forest floor and mineral soil carbon pools were assessed over a 9-year period in a replicated large-scale experiment, which included unharvested controls, two variants of partial harvesting and clear-cuts. We also measured leaf litter and deadwood inputs and decay rates. Carbon flux through leaf litterfall recovered rapidly following partial harvesting. Carbon flux from live trees to deadwood pools was a dominant process in partially harvested stands where snags and downed log carbon pools remained similar to those of natural stands. Hence, the nature of litter inputs diverged strongly among clear-cut and partially harvested treatments. Leaf and wood decay rates were higher in the partial cuts and controls than in clear-cuts. No significant differences in forest floor and mineral soil carbon were observed 9 years after harvesting. Carbon sequestration in live tree biomass was the carbon pool that most strongly differentiated the treatments allowing partial harvesting to maintain forest stands as net carbon sinks. [ABSTRACT FROM AUTHOR]

Tree species influence the litter decomposition process by influencing litter quality and soil microclimate. Furthermore, over the long term, trees could promote soil communities that are particularly capable of degrading the litter they encounter most often. Thus, plant litter could decompose faster when placed in the habitat from which it was derived than in a foreign habitat, which has been termed home field advantage (HFA) of litter decomposition. In mixed-plant species environments however, it is not known whether a specific decomposer community under one tree species is affected by the presence of another tree species in the vicinity. To address this question, we tested if spruce and poplar litters showed HFA in mono-specific and in mixed species plantations under each tree species by reciprocally transplanting litter in the two plantation types. Decomposition rates, as well as the composition and ability of decomposer communities to degrade the different types of litter, were monitored during two years. Only spruce litter exhibited a faster decomposition rate at home. This HFA could be explained by higher abundance of decomposers. Furthermore, cellulose and poplar litter decomposed less or similarly in spruce plantations, suggesting that soil communities of that environment were capable of specifically degrading spruce litter. In mixed plantations, HFA was in the same direction as in mono-specific plantations, but was not as strong, indicating that HFA is sensitive to the surrounding plant community. Furthermore, this 'mixed environment' had synergistic effects on decomposition rates under poplar trees. These 'tree environment-specific' results highlighted the possible importance of spatial distribution of each litter on decomposition rates in mixed stands. Thus, the influence of litter dispersal should be taken into account in future studies. [ABSTRACT FROM AUTHOR]

The position of the southern boundary of reindeer range has been analyzed based on available publications and data of winter censuses over the period from the late 19th century through the early 21st century. Periodic shifts of the boundary to the south and back to the north have been revealed and brought in correlation with the dynamics of reindeer abundance. [ABSTRACT FROM AUTHOR]