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This is the second of a matched pair of articles that present concepts and practices for expanding the territory of narrative therapy to include working with attention and present moment awareness. The first article explored similarities and differences between narrative therapy and attentional practices derived from Buddhist traditions frequently associated in western contexts with the term “mindfulness.” That piece proposed that both narrative and mindfulness support persons in enacting ethical choice, but the process differs in the two traditions. Narrative is preoccupied with stories or discourses, which are externalized, making space for the performance of alternatives. Mindfulness practices key in on attention, supporting persons in relinquishing the grasp on a never-ending flow of mental phenomena. Narrative seeks to liberate our storying capacity; mindfulness seeks to liberate our attention. Both traditions support persons in living in a manner congruent with their values; we have called this ethical intentionality. This companion article offers examples of how these two traditions can be co-mingled in therapeutic practice.

Background and aims Low productivity open lichen (Cladonia spp.) woodlands have been rapidly expanding in the closed-crown feather moss (Pleurozium schreberi (Brid.) Mitt.) boreal forest of eastern Canada. While open-woodland areas are progressing, there is little information on the recoverability of open lichen woodlands back to closed-canopy forests. Methods An experimental set-up using moss transplantation was installed on a poor jack pine (Pinus banksiana Lamb.) stand with a lichen ground cover in 2011. Treatments included: 1) lichen cover removed, 2) lichen cover removed and transplantation of a feather moss cover, 3) lichen control, and 4) a natural jack pine site with feather moss cover (moss control). We extracted tree stem increment cores and collected needles and soil samples for nutrient analysis. Results The transplanted-moss treatment can counteract the adverse effects of lichen on jack pine growth. This treatment enhanced foliar nutrition and soil nutrients, especially ammonium (N-NH4+) and nitrate (N-NO3−). With this treatment, the soil conditions (e.g., soil nutrients, soil moisture) and foliar nutrition were closer to that of moss control. Surprisingly, lichen removal treatment did not improve growth and resulted in poorer jack pine growth and harsher soil conditions. Conclusion Feather moss can establish, survive, and remain healthy in an environment previously occupied by lichen. The replacement of lichen by feather moss establishes soil conditions that appear conducive to better tree growth and have the potential of restoring the productivity of boreal forests in open-canopy lichen woodlands.

The forests of North America have undergone important changes since European settlement, particularly in terms of stand composition and associated changes in soil properties. While soil nutrients availability is known to influence forest productivity, the causes and consequences of its variation through time remain poorly understood. This study investigates the effects of long-term changes in forest composition and soil properties on the radial growth of sugar maple (Acer saccharum Marsh.) and balsam fir (Abies balsamea (L.) Mill.), two important species of northeastern North America’s forests. Using data from 130 plots measured in 1930 and in 2012–2014 and a mixed-effects modelling approach, we studied the links between radial growth, soil nutrients availability, current stand composition, and shifts in vegetation. The radial growth of balsam fir was found to vary with soil available nitrogen and present-day relative basal area of yellow birch in the stand, while that of sugar maple was found to be invariant to soil characteristics, but proportional to present-day spruce (Picea spp.) relative basal area. However, no direct effects of vegetation change on radial growth were detected. Our results suggest that prior stand composition had no influence on radial growth of both studied species, yet vegetation change could indirectly influence balsam fir growth through an improvement of litter quality with an increase in the abundance of yellow birch (Betula alleghaniensis Britton). Moreover, despite clear differences between the studied species, we conclude that maintaining a certain proportion of compositional diversity may enhance radial growth of both balsam fir and sugar maple.

This is the first of a matched pair of articles that present concepts and practices for expanding the territory of narrative therapy to include working with attention and present moment awareness. While the narrative literature richly describes how persons are recruited by normative discourses into problem stories and offers a wide range of practices for developing counter narratives, less has been written about how dominant discourse also captures moment-by-moment attention. The authors share ideas about working with attention in much the same way as working with story. In this first article, the authors identify parallels and differences between narrative therapy and the attentional practices associated with mindfulness before providing a preliminary account of work that draws from both traditions. The practices are depicted in terms of the ethics of daily life, in the sense that enhanced moment-by-moment attention promotes intentional ethical choice.

The pattern of change in carbon (C) accumulation with forest ageing can vary greatly amongst different forest types. Documenting how C accumulates in various forest ecosystems in the absence of logging makes it possible to predict what would be the outcome of extending forest rotations or in dedicating more land to conservation on C storage. This study was conducted in boreal balsam fir (Abies balsamea (L.) Mill.) forests of Quebec, in eastern Canada. We compared carbon stocks in forest pools (aboveground (live) biomass, deadwood, FH horizon and mineral soil) of mature (70 years after harvest) vs old-growth stands (stands with no signs or history of human disturbance). Total ecosystem C stocks were not significantly different between mature and old-growth stands. However, as mature stands transition to old-growth stage, there appears to be a shift of C from live biomass pools towards deadwood and soil FH horizons. Coarse woody debris in old-growth stands were also found to be at more advanced stages of decay. The variability of C stocks was also high amongst old-growth stands; however, there was no obvious difference in structural diversity between mature and old-growth stands. Results suggest that ageing balsam fir stands through the lengthening of forest rotations (e.g. past the maturity age of 70 years) or by placing them under conservation, while not creating an important C sink, still contributes to maintain large forest C stocks across landscapes. Preserving or increasing the presence of old-growth forests is an important aspect of ecosystem-based forest management; our study concludes that it could also be compatible with sustainable forest carbon management.

The main objective of this study was to evaluate the influence of leachates from three typical boreal forest ground layers on young tree growth and to explore the linkages between the chemical composition of the leachates, tree growth, the allocation between belowground and aboveground parts, and ectomycorrhizal colonization. An original 6-month greenhouse experiment was set up to investigate (i) the effects of lichen (Cladonia spp.) and feather moss (Pleurozium schreberii [Brid.] Mitt.) leachates on jack pine (Pinus banksiana Lamb.) growth and (ii) the effects of feather moss and Sphagnum spp. leachates on black spruce (Picea mariana [Mill.] B.S.P.) growth. Belowground growth and root allocation was reduced by lichen leachates in 2-year-old pine seedlings, while the impact was significant on both below- and aboveground growth in 6-month-old pine seedlings. A substance having the same migration time as usnic acid was detected in the lichen leachates by high-performance liquid chromatography. Sphagnum spp. and feather moss leachates were not found to have any effect on black spruce seedling growth, despite a higher supply of dissolved inorganic N in the feather moss leachates compared to the leachates of Sphagnum spp. and the control. These results demonstrate that ground layer composition plays a crucial role in shaping the plant community in boreal ecosystems by influencing the chemical composition of the soil solution. They suggest that chemical interference may be another mechanism by which lichens promote the self-perpetuation of open woodlands in the closed-crown boreal forest.

The increase in open-crown forest stands in the closed-crown boreal forest of Quebec over the last 50 years prompts us to identify and understand the drivers responsible for stand opening. To do so, we studied 37 jack pine plots with varying degrees of canopy opening in the Eastern Canadian boreal forest to answer four questions: (1) Does stand opening result from a deficit in pine regeneration, from poor tree growth, or from both processes simultaneously? (2) In the event that pine stand opening results at least in part from poor tree growth, how early following stand initiation does the tree growth divergence occur between unproductive and productive plots? (3) Is poor tree growth in the unproductive plots related to water stress? Finally, (4) are there predisposing site factors and, if so, what are their contributions versus non-permanent factors such as disturbance history, vegetation, and soil dynamics? In the study area, jack pine stand openings resulted from both a poor regeneration density and weak tree growth. Tree growth divergence between productive and unproductive plots occurred very early during the post-disturbance forest succession and is not likely to result from water limitation during the early development of the trees as revealed by δ13C analysis of tree rings. Low-productivity plots were exclusively found on substrates with low base cation reserves. However, because plots of higher productivity were also found on these substrates, we conclude that stand susceptibility to regeneration failures may be greater on sites with such conditions. Variations in tree cover were mainly related to non-permanent environmental variables, suggesting that restoration of forest productivity is theoretically possible in the low-productivity sites investigated.

The issue of social justice and how it unfolds in the lives of persons seeking counselling has been steadily gaining attention in recent times. This development marks a departure from an in...

This article draws on a case study of a narrative therapy session to explore issues related to relational responsiveness in therapeutic conversations. The central question posed, is “How is it possible to both honor client expertise while also bringing discursive ideas and processes (such as narrative externalizing) to the conversation?” Drawing on Bakhtin and Vygotsky, the authors suggest that externalizing can be understood as a speech genre which furnishes a scaffolding for constructing meaning, and that this practice promotes a move from monologue to dialogue in relation to problem experience. They also caution that this or any practice designed to “promote dialogue” paradoxically does the contrary when the therapist is not responsive to the client. Using segments of a transcribed session and post-session interviews with therapist and client, the authors portray a linguistic shift from oppositional to accommodative metaphors more in keeping with the client’s preferred relationship with her experience. The authors conclude that it is not therapist expertise per se, but the failure to engage in a relationally responsive manner, that constrains the possibility of therapeutic dialogue. This article explores a conversational conundrum experienced by therapeutic practitioners. It hinges on the challenge of both privileging clients’ meaning making while also bringing certain conceptual resources to a dialogue. In a sense, this dilemma pivots on the notion of expertise: how to balance client knowledges with therapist knowledges, how to make room for two traditions (Gadamer, 1975) in the construction of new ways of going forward?

Many jurisdictions have put forward guidelines to identify sites at risks of soil degradation with the extraction of logging residues. Most guidelines are based on expert opinion and use the precautionary principle because of the lack of strong understanding of what makes a site sensitive to intensive biomass removal. Two main approaches are used: 1-identifying thresholds for specific site properties 2- developing nutrient budget indicators to rate the potential for nutrient deficit. Thanks to the development of digital soil mapping, it is becoming easier to develop maps for such indicators. A crucial question is the reliability of the different indicators. One way of evaluating their reliability is to test the coherence between the geographic locations of sites rated as sensitive by different indicators. In this study, we developed maps of key soil properties and of biogeochemical fluxes for the managed forest land of Canada at a resolution of 250 m. We used three site properties (slope, pH and sand content), as well as three nutrient budget indicators (N Budget, Base cation (BC) Budget and N Stability ratio) that were mapped and compared. The results indicated very little overlap between the areas identified as sensitive by the three site property indicators and very little concordance between sites rated as sensitive by site property indicators and those identified as sensitive by nutrient budget indicators while nutrient budget indicators showed coherence among themselves. Because nutrient budget indicators were found to be more dependent on the amount of nutrient extracted in the harvested biomass, than on the rates of nutrient inputs from the soil or the atmosphere, they tended to rate productive sites as sensitive, to the opposite of site property indicators. These results suggest that different indicators are assessing different processes and different aspects of site sensitivity. Because of the lack of coherence amongst the indicators, it is advisable 1) to use indicators based on the results of long-term monitoring plots, 2) to maintain such long-term observations and 3) to leave on the ground a substantial proportion of harvest residues, especially on sites evaluated as sensitive.

Because they generate more wood per area and time, short rotation plantations are likely to play an increasing role in meeting the global increase in the demand for wood fiber. To be successful, high-yield plantations require costly intensive silviculture regimes to ensure the survival and maximize yields. While hybrid poplar (Populus spp.) is frequently used in intensive, short rotation forestry, it is particularly sensitive to competition and resource levels. Mechanical site preparation is thus of great importance to create microsites that provide sufficient light levels and adequate soil water and nutrient availability. We conducted an experiment in Qu&eacute, bec (Canada) to compare two intensive site preparation treatments commonly used to establish hybrid poplar. We compared the effects of double-blade site preparation (V-blade), mounding and a control on hybrid poplar growth and nutritional status four growing seasons after planting on recently harvested forested sites. We also evaluated the effects of site preparation and planted poplar on inorganic soil N. Our results confirmed general positive effects of site preparation on the early growth of hybrid poplar clones. After four growing seasons, survival was higher in the mounding treatment (99%) than in the V-blade (91%) and the control (48%). Saplings planted in the V-blade and in the mounding treatments had mean diameters that were respectively 91% and 155% larger than saplings planted in the control plots. Saplings were 68% taller in the mounding treatment than the control plots, but differences between the V-blade and controls were not significant. We did not detect significant effects of site preparation or the presence of planted hybrid poplar on soil inorganic N. Sapling foliar nutrient concentrations were not influenced by the site preparation treatments. Based on these results, mounding appears to be a good management approach to establish hybrid poplar plantations under the ecological conditions we have studied, as it is less likely to cause erosion because of the localized nature of the treatment. However, these environmental benefits need to be balanced against economic and social considerations.

International audience; Almost half of the total organic carbon (C) in terrestrial ecosystems is stored in forest soils. By altering rates of input or release of C from soils, forest management activities can influence soil C stocks in forests. In this review, we synthesize current evidence regarding the influences of 13 common forest management practices on forest soil C stocks. Afforestation of former croplands generally increases soil C stocks, whereas on former grasslands and peatlands, soil C stocks are unchanged or even reduced following afforestation. The conversion of primary forests to secondary forests generally reduces soil C stocks, particularly if the land is converted to an agricultural land-use prior to reforestation. Harvesting, particularly clear-cut harvesting, generally results in a reduction in soil C stocks, particularly in the forest floor and upper mineral soil. Removal of residues by harvesting whole-trees and stumps negatively affects soil C stocks. Soil disturbance from site preparation decreases soil C stocks, particularly in the organic top soil, however improved growth of tree seedlings may outweigh soil C losses over a rotation. Nitrogen (N) addition has an overall positive effect on soil C stocks across a wide range of forest ecosystems. Likewise, higher stocks and faster accumulation of soil C occur under tree species with N-fixing associates. Stocks and accumulation rates of soil C also differ under different tree species, with coniferous species accumulating more C in the forest floor and broadleaved species tending to store more C in the mineral soil. There is some evidence that increased tree species diversity could positively affect soil C stocks in temperate and subtropical forests, but tree species identity, particularly N-fixing species, seems to have a stronger impact on soil C stocks than tree species diversity. Management of stand density and thinning have small effects on forest soil C stocks. In forests with high populations of ungulate herbivores, reduction in herbivory levels can increase soil C stocks. Removal of plant biomass for fodder and fuel is related to a reduction in the soil C stocks. Fire management practices such as prescribed burning reduce soil C stocks, but less so than wildfires which are more intense. For each practice, we identify existing gaps in knowledge and suggest research to address the gaps.

Summary Background Tranexamic acid reduces surgical bleeding and decreases mortality in patients with traumatic extracranial bleeding. Intracranial bleeding is common after traumatic brain injury (TBI) and can cause brain herniation and death. We aimed to assess the effects of tranexamic acid in patients with TBI. Methods This randomised, placebo-controlled trial was done in 175 hospitals in 29 countries. Adults with TBI who were within 3 h of injury, had a Glasgow Coma Scale (GCS) score of 12 or lower or any intracranial bleeding on CT scan, and no major extracranial bleeding were eligible. The time window for eligibility was originally 8 h but in 2016 the protocol was changed to limit recruitment to patients within 3 h of injury. This change was made blind to the trial data, in response to external evidence suggesting that delayed treatment is unlikely to be effective. We randomly assigned (1:1) patients to receive tranexamic acid (loading dose 1 g over 10 min then infusion of 1 g over 8 h) or matching placebo. Patients were assigned by selecting a numbered treatment pack from a box containing eight packs that were identical apart from the pack number. Patients, caregivers, and those assessing outcomes were masked to allocation. The primary outcome was head injury-related death in hospital within 28 days of injury in patients treated within 3 h of injury. We prespecified a sensitivity analysis that excluded patients with a GCS score of 3 and those with bilateral unreactive pupils at baseline. All analyses were done by intention to treat. This trial was registered with ISRCTN (ISRCTN15088122), ClinicalTrials.gov (NCT01402882), EudraCT (2011-003669-14), and the Pan African Clinical Trial Registry (PACTR20121000441277). Results Between July 20, 2012, and Jan 31, 2019, we randomly allocated 12 737 patients with TBI to receive tranexamic acid (6406 [50·3%] or placebo [6331 [49·7%], of whom 9202 (72·2%) patients were treated within 3 h of injury. Among patients treated within 3 h of injury, the risk of head injury-related death was 18·5% in the tranexamic acid group versus 19·8% in the placebo group (855 vs 892 events; risk ratio [RR] 0·94 [95% CI 0·86–1·02]). In the prespecified sensitivity analysis that excluded patients with a GCS score of 3 or bilateral unreactive pupils at baseline, the risk of head injury-related death was 12·5% in the tranexamic acid group versus 14·0% in the placebo group (485 vs 525 events; RR 0·89 [95% CI 0·80–1·00]). The risk of head injury-related death reduced with tranexamic acid in patients with mild-to-moderate head injury (RR 0·78 [95% CI 0·64–0·95]) but not in patients with severe head injury (0·99 [95% CI 0·91–1·07]; p value for heterogeneity 0·030). Early treatment was more effective than was later treatment in patients with mild and moderate head injury (p=0·005) but time to treatment had no obvious effect in patients with severe head injury (p=0·73). The risk of vascular occlusive events was similar in the tranexamic acid and placebo groups (RR 0·98 (0·74–1·28). The risk of seizures was also similar between groups (1·09 [95% CI 0·90–1·33]). Interpretation Our results show that tranexamic acid is safe in patients with TBI and that treatment within 3 h of injury reduces head injury-related death. Patients should be treated as soon as possible after injury. Funding National Institute for Health Research Health Technology Assessment, JP Moulton Charitable Trust, Department of Health and Social Care, Department for International Development, Global Challenges Research Fund, Medical Research Council, and Wellcome Trust (Joint Global Health Trials scheme). Translations For the Arabic, Chinese, French, Hindi, Japanese, Spanish and Urdu translations of the abstract see Supplementary Material.

Transformative advances in metagenomics are providing an unprecedented ability to characterize the enormous diversity of microorganisms and invertebrates sustaining soil health and water quality. These advances are enabling a better recognition of the ecological linkages between soil and water, and the biodiversity exchanges between these two reservoirs. They are also providing new perspectives for understanding microorganisms and invertebrates as part of interacting communities (i.e. microbiomes and zoobiomes), and considering plants, animals, and humans as holobionts comprised of their own cells as well as diverse microorganisms and invertebrates often acquired from soil and water. The Government of Canada's Genomics Research and Development Initiative (GRDI) launched the Ecobiomics Project to coordinate metagenomics capacity building across federal departments, and to apply metagenomics to better characterize microbial and invertebrate biodiversity for advancing environmental assessment, monitoring, and remediation activities. The Project has adopted standard methods for soil, water, and invertebrate sampling, collection and provenance of metadata, and nucleic acid extraction. High-throughput sequencing is located at a centralized sequencing facility. A centralized Bioinformatics Platform was established to enable a novel government-wide approach to harmonize metagenomics data collection, storage and bioinformatics analyses. Sixteen research projects were initiated under Soil Microbiome, Aquatic Microbiome, and Invertebrate Zoobiome Themes. Genomic observatories were established at long-term environmental monitoring sites for providing more comprehensive biodiversity reference points to assess environmental change.

There is a growing interest in using logging residues as feedstock in the bioeconomy. Quantifying the amount of this resource over large areas has been difficult due to the lack of availability of ...

Forest management strongly influences the carbon (C) budget of boreal forests and their potential to mitigating greenhouse gas emissions. A better quantification of the net changes of carbon pools with time since harvesting is necessary to guide the development of climate-friendly forest management practices. The objective of this study was to assess the evolution of forest C pools, with a special focus on detrital biomass, in an 80-year post-harvesting chronosequence consisting of 36 very homogenous stem-only harvested plots from a humid boreal balsam fir forest of eastern Canada. Dead wood C stocks comprised of snags, stumps, downed woody debris and buried wood averaged 37 Mg C ha−1 and evolved according to an upward-facing «boomerang» shape pattern throughout the chronosequence (rapid decrease in the first years followed by a constant increase until the end of the time horizon). In contrast, soil C stocks (FH and mineral) averaged 156 Mg C ha−1 and remain constant through time. Stand C sequestration increased rapidly in the early stages up to age 50 when it reached about 250 Mg C ha−1, and then continued to accumulate at a slower rate. The temporal trends observed in C pools suggest that C originating from aboveground dead wood (snags, stumps, downed woody debris) is either leaving the system (respired or leached) or transferred into buried wood, and does not appear to influence the C stocks of the fine fraction of the organic and mineral soil horizons. However, the ultimate fate of dead wood C is still poorly understood and further research is needed in this field. We recommend fixing the length of harvest rotation at a minimum of 50 years for this ecosystem to allow the build-up of its dead wood capital, and to promote dead wood retention on site. We also recommend including buried wood in carbon inventories as this pool represents an important share of the detrital C stock in these humid boreal forests.

Forest composition in North America has undergone important changes since the European settlement. The effects of such alterations on soil properties remain largely unknown. This study aims to understand the long-term effects of shifts in forest composition on soil properties. Using data from 130 plots measured over an eighty-year period, the relationships between stand composition (both current and past), parent material and current soil chemical properties were studied with redundancy analyses. Results indicated that the parent material remained the dominant factor explaining soil properties, followed by current tree species composition. No legacy effect of past forest composition was found, but shifts in forest composition explained part of the current soil properties. Specifically, an increase in balsam fir was related to higher C/N ratio in the O-horizon, while an increase in maple species was related to higher net nitrification in both the O and B-horizons, and higher extractable P in the B-horizon. Our results suggest that increasing the maple component at the expense of conifers over several decades may enhance nutrient availability in the O-horizon.

The accumulation of soil carbon (C) is regulated by a complex interplay between abiotic and biotic factors. Our study aimed to identify the main drivers of soil C accumulation in the boreal forest of eastern North America. Ecosystem C pools were measured in 72 sites of fire origin that burned 2-314 years ago over a vast region with a range of ∆ mean annual temperature of 3°C and one of ∆ 500 mm total precipitation. We used a set of multivariate a priori causal hypotheses to test the influence of time since fire (TSF), climate, soil physico-chemistry and bryophyte dominance on forest soil organic C accumulation. Integrating the direct and indirect effects among abiotic and biotic variables explained as much as 50% of the full model variability. The main direct drivers of soil C stocks were: TSF >bryophyte dominance of the FH layer and metal oxide content >pH of the mineral soil. Only climate parameters related to water availability contributed significantly to explaining soil C stock variation. Importantly, climate was found to affect FH layer and mineral soil C stocks indirectly through its effects on bryophyte dominance and organo-metal complexation, respectively. Soil texture had no influence on soil C stocks. Soil C stocks increased both in the FH layer and mineral soil with TSF and this effect was linked to a decrease in pH with TSF in mineral soil. TSF thus appears to be an important factor of soil development and of C sequestration in mineral soil through its influence on soil chemistry. Overall, this work highlights that integrating the complex interplay between the main drivers of soil C stocks into mechanistic models of C dynamics could improve our ability to assess C stocks and better anticipate the response of the boreal forest to global change.

In the boreal forest, open lichen woodlands have been described as an alternative stable state to closed-crown feather moss forest. In this study, we addressed the role of terricolous lichens in stabilizing open woodlands by hindering tree regeneration and/or growth. Based on field and greenhouse experiments, we compared germination and growth of jack pine (Pinus banksiana) on feather mosses (primarily Pleurozium schreberi) and lichens (primarily Cladonia stellaris), using bare mineral soil as a control. Drivers were investigated by (1) manipulating nutrient supply, (2) simulating shade of a closed canopy on the ground layer with the assumption this would mitigate lichen influence on pine growth, and (3) examining pine root ectomycorrhizal colonization and diversity as indicators of pine ability to take up nutrients. Total growth of 6-month-old greenhouse and 2–3-year-old field seedlings, as well as belowground growth of 2-year-old greenhouse seedlings, was significantly greater in moss than in lichen. Seed germination was not affected by ground cover type. Although field phosphorus and base cation availability was greater in mosses than in lichens, fertilization did not entirely compensate for the negative effects of lichens on pine growth in the greenhouse. Ground layer shading had no impact on pine growth. Lichens were associated with reduced abundance and modified composition of the root ectomycorrhizal community. By suggesting that terricolous lichens constitute a less favorable growth substrate than mosses for pine, our results support the hypothesis that lichens contribute to open woodland stability in the potentially closed-crown feather moss forest.

The composition of the bryophyte layer influences boreal forest regeneration and growth through its effect on soil conditions. Canopy openings in boreal spruce stands can favor the expansion of Sphagnum spp. in the understory at the expense of feather mosses. We use an experimental approach in both paludified field and greenhouse fully-randomized conditions to examine the differential effects of these two ground cover types on black spruce germination and growth, specifically the role of nutrient limitation in generating these effects. We also tested the impact of ground cover shading, simulating the effect of a closed forest canopy on the ground layer, with the assumption that the stress induced to mosses, especially to Sphagnum spp., would have a beneficial impact on tree growth. The two moss types had no differential effects on spruce germination and 0–6-month-old seedling growth in the greenhouse. However, the growth of 2-year-old seedlings in the greenhouse was lower in Sphagnum spp. than in feather mosses. This negative effect was removed by fertilization, suggesting that soil nutrient availability could explain the seedling growth difference between moss types. Greenhouse 2-year-old seedlings also allocated a greater proportion of biomass to roots in Sphagnum spp. than in feather mosses. In the field, feather and Sphagnum spp. mosses had no differential effects on 3-year-old seedling growth, and ground cover shading did not have any short-term positive impact on spruce growth. Although they were not validated in the field, the results we obtained in the greenhouse suggest that the replacement of feather mosses by Sphagnum spp. mosses do not only affect spruce growth through the build-up of an organic layer often associated with low soil temperature and excess water, but also through more direct effects on nutrient availability. Therefore, silvicultural treatments that would favor Sphagnum spp. expansion at the expense of feather mosses, such as partial or total harvesting with protection of regeneration and soils, may result in subsequent tree growth problems even in sites with moderate organic layer accumulation.

Wildfire is the primary abiotic disturbance in the boreal forest, and its long-term absence can lead to large changes in ecosystem properties, including the availability and cycling of nutrients. These effects are, however, often confounded with the effects of successional changes in vegetation toward nutrientconservative species. We studied a system of boreal forested lake islands in eastern Canada, where time since last fire ranged from 50 to 1500 years, and where the relative abundance of the most nutrientconservative tree species, black spruce, was largely independent of time since last fire. This allowed us to disentangle the effects of time since fire and the dominant vegetation on ecosystem properties, including nutrient stocks and concentrations. Effects of time since fire independent of vegetation composition mostly involved an increase in the thickness of the organic layer and in nitrogen concentration in both soil and leaves. Domination by black spruce had strong negative effects on nutrient concentrations andwas associated with a shift towardmore fungi and Gram-positive bacteria in the soil microbial community. Path modeling showed that phosphorus concentration was inversely related to organic layer thickness, which was in turn related to both time since fire and black spruce abundance,whilenitrogen was more directly related to time since fire and the composition of the overstory. We conclude that discriminating between the effects of vegetation and time since fire is necessary for better understanding and predicting the long-term changes that occur in forest nutrient availability and ecosystem properties. This work was financed by Wallenberg Scholars award to DAW, and an NSERC discovery grant to YB. We thank all field assistants that made it possible to collect all this data, as well as the Ministe`re du De´veloppement durable, de l’Environnement et de la Lutte contre les changements climatiques du Que´bec for granting access to protected islands.

Anthropogenic N emissions represent a potential threat for forest ecosystems, and environmental indicators that provide insight into the changing forest N cycle are needed. Tree ring N isotopic ratios (δ15N) appear as a contentious choice for this role as the exact mechanisms behind tree-ring δ15N changes seldom benefit from a scrutiny of the soil-to-tree N continuum. This study integrates the results from the analysis of soil chemistry, soil microbiome genomics, and δ15N values of soil N compounds, roots, ectomycorrhizal (EcM) fungi and recent tree rings of thirteen white spruce trees sampled in five stands, from two regions exposed to moderate anthropogenic N emissions (3.9 to 8.1 kg/ha/y) with distinctive δ15N signals. Our results reveal that airborne anthropogenic N with distinct δ15N signals may directly modify the NO3− δ15N values in surface soils, but not the ones of NH4+, the preferred N form of the studied trees. Hence, the tree-ring δ15N values reflect specific soil N conditions and assimilation modes by trees. Along with a wide tree-ring δ15N range, we report differences in: soil nutrient content and N transformation rates; δ15N values of NH4+, total dissolved N (TDN) and EcM mantle enveloping the root tips; and bacterial and fungal community structures. We combine EcM mantle and root δ15N values with fungal identification to infer that hydrophobic EcM fungi transfer N from the dissolved organic N (DON) pool to roots under acidic conditions, and hydrophilic EcM fungi transfer various N forms to roots, which also assimilate N directly under less acidic conditions. Despite the complexities of soil biogeochemical properties and processes identified in the studied sites, in the end, the tree-ring δ15N averages inversely correlate with soil pH and anthropogenic N inputs, confirming white spruce tree-ring δ15N values as a suitable indicator for environmental research on forest N cycling.

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability.

In mixedwood forest, different types of commercial thinning that generate different gap sizes are being tested as alternatives to clearcutting to create forest stands with an irregular structure that would emulate the pre-industrial forests. The main goal of this study was to investigate the soil nitrogen (N) dynamics in response to two partial harvesting treatments, used alone or in combination: commercial thinning creating tree-size canopy gaps and harvest gaps creating 0.05 ha gaps. In a 30 year old balsam fir (Abies balsamea (L.) Mill.) stand, both treatments, alone or in combination, as well as unharvested controls were compared on replicated 0.75 ha plots. The most noticeable changes following treatments were observed in gaps, while commercial thinning did not significantly influence any of the parameters assessed. In gaps, increases in N mineralization rates and mineral N concentrations and proportions (NO3−-N and NH4+-N) relative to dissolved organic N were observed. Our results suggest that these changes are caused by the increase in soil temperature and water content. In these forests, the response threshold of the N cycling regarding the size of the intervention would therefore be located between the removal of one or a few trees (one to three stems, 6–12 m2) and a gap of 500 m2. Other studies conducted in different climate and forest types have shown that this threshold could be of equivalent or of a smaller size. These findings will contribute to optimizing our management strategies regarding partial cuts or small-scale clearcuts.

Strategies for increasing the mobilization of forest biomass supply chains for bioenergy production require continuous assessments of the spatial and temporal availability of biomass feedstock. Using remote sensing products at a 250-m pixel resolution, estimates of theoretical biomass availability from harvest residues and fire-killed trees were computed by combining Canada-wide maps of forest attributes (2001) and of yearly (2002–2011) fires and harvests. At the national scale, biomass availability was estimated at 47 ± 18 M ODT year −1 from fire-killed trees and at 14 ± 2 M ODT year −1 from harvest residues. Mean biomass densities in burned and harvested pixels were estimated at 34 ± 3.0 ODT ha −1 and at 24 ± 1.2 ODT ha −1 , respectively. Mean biomass densities also varied dramatically among ecozones, from 14 ODT ha −1 to 206 ODT ha −1 and from 6 ODT ha −1 to 63 ODT ha −1 for burned and harvested pixels, respectively. Spatial averaging with a 100-km radius window shows distinct hotspots of biomass availability across Canada. The largest hotspots from fire-killed trees reached 3.6 M ODT year −1 in the Boreal Shield and the Boreal Plains ecozones of northern Alberta and Saskatchewan, where fires are large and frequent. The largest hotspots from harvest residues reached 1.2 M ODT year −1 in the Montane Cordillera ecozone of British Columbia. The use of spatially explicit remote sensing products yields estimates of theoretical biomass availability that are methodologically consistent across Canada. Future development should include validations with on-the-ground forest inventories as well as the factoring in of environmental, technical and economic considerations to implement operational biomass supply chains.

Following a wildfire, organic carbon (C) accumulates in boreal-forest soils. The long-term patterns of accumulation as well as the mechanisms responsible for continuous soil C stabilization or sequestration are poorly known. We evaluated post-fire C stock changes in functional reservoirs (bioreactive and recalcitrant) using the proportion of C mineralized in CO2 by microbes in a long-term lab incubation, as well as the proportion of C resistant to acid hydrolysis. We found that all soil C pools increased linearly with the time since fire. The bioreactive and acid-insoluble soil C pools increased at a rate of 0.02 and 0.12 MgC ha−1 yr−1, respectively, and their proportions relative to total soil C stock remained constant with the time since fire (8 % and 46 %, respectively). We quantified direct and indirect causal relationships among variables and C bioreactivity to disentangle the relative contribution of climate, moss dominance, soil particle size distribution and soil chemical properties (pH, exchangeable manganese and aluminum, and metal oxides) to the variation structure of in vitro soil C bioreactivity. Our analyses showed that the chemical properties of podzolic soils that characterize the study area were the best predictors of soil C bioreactivity. For the O layer, pH and exchangeable manganese were the most important (model-averaged estimator for both of 0.34) factors directly related to soil organic C bioreactivity, followed by the time since fire (0.24), moss dominance (0.08), and climate and texture (0 for both). For the mineral soil, exchangeable aluminum was the most important factor (model-averaged estimator of −0.32), followed by metal oxide (−0.27), pH (−0.25), the time since fire (0.05), climate and texture (∼0 for both). Of the four climate factors examined in this study (i.e., mean annual temperature, growing degree-days above 5 ∘C, mean annual precipitation and water balance) only those related to water availability – and not to temperature – had an indirect effect (O layer) or a marginal indirect effect (mineral soil) on soil C bioreactivity. Given that predictions of the impact of climate change on soil C balance are strongly linked to the size and the bioreactivity of soil C pools, our study stresses the need to include the direct effects of soil chemistry and the indirect effects of climate and soil texture on soil organic matter decomposition in Earth system models to forecast the response of boreal soils to global warming.

Following wildfire, organic carbon (C) accumulates in boreal forest soils. The long-term patterns of accumulation as well as the mechanisms responsible for continuous soil C stabilization or sequestration are poorly known. We evaluated post-fire C stock changes in functional reservoirs (bioreactive and recalcitrant) using the proportion of C mineralized in CO2 by microbes in a long-term lab incubation, as well as the proportion of C resistant to acid hydrolysis. We found that all soil C pools increased linearly with time since fire. The bioreactive and acid-insoluble soil C pools increased at a rate of 0.02 MgC ha−1 yr−1 and 0.12 MgC ha−1 yr−1, respectively, and their proportions relative to total soil C stock remained constant with time since fire (8 % and 46 %, respectively). We quantified direct and indirect causal relationships among variables and carbon bioreactivity to disentangle the relative contribution of climate, moss dominance, soil particle size distribution and soil chemical properties (pH, exchangeable Mn and Al, and metal oxides) to the variation structure of in vitro soil carbon bioreactivity. Our analyses showed that the chemical properties of Podzolic soils that characterise the study area were the best predictors of soil carbon bioreactivity. For the FH horizon (O-layer), pH and exchangeable Mn were the most important (model-averaged estimator for both: 0.34) factors directly related to soil organic C bioreactivity, followed by time since fire (0.24), moss dominance (0.08) and climate and texture (0 for both). For the mineral soil, exchangeable aluminum was the most important factor (model-averaged estimator: −0.32), followed by metal oxide (−0.27), pH (−0.25), time since fire (0.05), climate and texture (~ 0 for both). Of the four climate factors examined in this study (i.e., mean annual temperature, growing degree-days above 5 °C, mean annual precipitation and water balance) only those related to water availability, and not to temperature, had indirect effect (FH horizon) or a marginal indirect effect (mineral soil) on soil carbon bioreactivity. Given that predictions of the impact of climate change on soil carbon balance are strongly linked to the size and the bioreactivity of soil C pools, our study stresses the need to include the direct effects of soil chemistry and the indirect effects of climate and soil texture on soil C decomposition in Earth System Models to forecast the response of boreal soils to global warming.

Climate change and global wood products demand raise concerns about boreal forest ecosystem resilience to natural disturbances and harvesting. A chronosequence experiment located in Foret Montmorency, Quebec was used to evaluate the effects of harvesting on carbon (C) recovery trajectories at the stand level over a period of 77 years in balsam fir-white birch stands. Empirical estimates of 19 Foret Montmorency forest carbon pools were compared with those simulated by the Carbon Budget Model (CBM-CFS3) to test model assumptions for predicting carbon dynamics in this forest. The model was initialized using forest inventory data, spatially explicit environmental conditions, and disturbance matrices designed to represent historical spruce budworm epidemics in Foret Montmorency. Over the chronosequence, total ecosystem C increased significantly (p = 0.05) following harvest from 211 Mg in year-zero to 279 ± 8 Mg C ha⁻¹ in year 67 (mean ± SE), suggesting that FM carbon pools were recovering to pre-harvest levels after seven decades. The CBM-CFS3 model predicted total ecosystem C stocks within 10% of the empirical mean at stand maturity; however, several predicted C pools deviated from field observations in both C amounts and trends over time. The greatest differences were in deadwood and soil C pools, suggesting that model initialization of dead organic matter pools did not adequately simulate the 1000-yr history of C-pool transfers and stand dynamics leading up to the harvest. Modifications to CBM-CFS3 initialization assumptions and default decay parameters may more accurately simulate long-term effects of natural disturbances on C pools for this forest region.

International audience; Identifying geochemical paleo‐proxies of vegetation type in watersheds could become a powerful tool for paleoecological studies of ecosystem dynamics, particularly when commonly used proxies, such as pollen grains, are not suitable. In order to identify new paleological proxies to distinguish ecosystem types in lake records, we investigated the differences in the sediment geochemistry of lakes surrounded by two boreal forest ecosystems dominated by the same tree species: closed‐canopy black spruce‐moss forests (MF) and open‐canopy black spruce‐lichen woodlands (LW). This study was designed as a first calibration step between terrestrial modern soils and lacustrine sediments (0–1000 cal yr BP) on six lake watersheds. In a previous study, differences in the physical and geochemical properties of forest soils had been observed between these two modern ecosystems. Here we show that the geochemical properties of the sediments varied between the six lakes studied. While we did not identify geochemical indicators that could solely distinguish both ecosystem types in modern sediments, we observed intriguing differences in concentrations of C:N ratio, carbon isotopic ratio, and aluminum oxide species, and in the stabilization of their geochemical properties with depth. The C accumulation rates at millennial scale were significantly higher in MF watersheds than in LW watersheds. We suggest that these variations could result from organic matter inflows that fluctuate depending on forest density and ground vegetation cover. Further investigations on these highlighted geochemistry markers need to be performed to confirm whether they can be used to detect shifts in vegetation conditions that have occurred in the past.