Pinus Sylvestris Research Articles

Growth of Nordic container forest tree seedlings in some peatless and peat-reduced growing media

AbstractCarbon emissions and environmental concerns have led to the aspiration to reduce peat extraction and its use as a growing medium (GM). In Nordic Forest tree seedling production, Sphagnum peat has been almost exclusively used as a GM in seedling containers due to its good properties and availability. This study examined the feasibility of several peat-reduced and peat-free GM in container tree seedling production of the key tree species in Nordic forestry (Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. Karst.) and silver birch (Betula pendula Roth) as well as Russian larch (Larix archangelica P. Lawson & C. Lawson ex Trautv.) and common alder (Alnus glutinosa (L.) Gaertn.). Pure or mixed GM, consisting of low-humified Sphagnum peat (pure as a control), harvested Sphagnum moss, wood fiber, cow manure digestate from a biogas plant, and a common reed compost were tested. Seedlings were grown in controlled conditions in greenhouse experiments and also in larger-scale commercial tree nurseries. Peat-reduced media containing peat of at least 50 vol% provided growth that is similar to pure Sphagnum peat for the tested species and container types. All the studied alternative media can yield marketable seedlings, although commonly of reduced size and requiring special adjustments in growing management. The studied media have a potential to reduce or replace peat in seedling production, but adjustments of their physical and chemical properties, as well as of seedling fertigation and management procedures, are required. The economic feasibility and environmental sustainability of these GM, as well as the outplanting success of seedlings grown in these media, remain to be studied.

Structural diversity and carbon stock of forest stands: tradeoff as modified by silvicultural thinning

AbstractIn forest management, merging stand structural diversity with carbon storage is essential for resilience and climate mitigation. This study assesses (1) how structural diversity in stands of spruce (Picea abies (L.) H. Karst.), pine (Pinus sylvestris L.), beech (Fagus sylvatica L.), and oak (Quercus robur L. and Quercus petraea (Matt.) Liebl.) in Central Europe varies with age, site quality, and applied thinning grade; (2) these factors' impact on carbon stock; and (3) the link between structural diversity and carbon stock. Analyzing 26 long-term thinning experiments, we used the Gini coefficient of tree heights to measure structural diversity and species-specific biomass functions for carbon stock assessments. Our results show that structural diversity, highest in beech and spruce, decreases with stand age and on richer sites. Thinning enhances structural diversity in spruce and beech but reduces it in pine and oak. Unthinned or only moderately thinned mature spruce and beech stands outperform pine and oak in carbon stock (200–300 vs. 100–150 Mg C ha−1). C- and D&E-grade thinning halves carbon stock. A decrease in vertical layering with increased carbon storage varies across species. Given the same carbon stock, thinning from above maintains structural diversity in spruce and beech, while non-thinning or thinning from below promotes structural diversity in pine and oak. Based on the current silvicultural practice reflected by the NFI data of Germany, we argue that reduced thinning in previously D&E-grade thinned stands may slightly reduce their structural diversity. However, a suspension or reduction of thinning would strongly improve carbon storage (+ 100–200 Mg C ha−1) in the next 3–5 decades. We discussed options for reconciling structural diversity and carbon storage by silvicultural management of the four considered species in Central Europe.

Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin

Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin

Mediterranean pine forest decline: A matter of root-associated microbiota and climate change

Forest ecosystems worldwide currently face worrying episodes of forest decline, which have boosted weakening and mortality of the trees. In the Mediterranean region, especially in the southeast Iberian Peninsula, Pinus sylvestris forests are severely affected by this phenomenon, and it has been commonly attributed to drought events. Remarkably, the role of root microbiota on pine decline has been overlooked and remains unclear. We therefore used metabarcoding to identify the belowground microbial communities of decline-affected and unaffected pine trees. Taxonomic composition of bacterial and fungal rhizosphere communities, and fungal populations dwelling in root endosphere showed different profiles depending on the health status of the trees. The root endosphere of asymptomatic trees was as strongly dominated by ‘Candidatus Phytoplasma pini’ as the root of decline-affected pines, accounting for >99 % of the total bacterial sequences in some samples. Notwithstanding, the titer of this phytopathogen was four-fold higher in symptomatic trees than in symptomless ones. Furthermore, the microbiota inhabiting the root endosphere of decline-affected trees assembled into a less complex and more modularized network. Thus, the observed changes in the microbial communities could be a cause or a consequence of forest decline phenomenon. Moreover, ‘Ca. Phytoplasma pini’ is positively correlated to Pinus sylvestris decline events, either as the primary cause of pine decline or as an opportunistic pathogen exacerbating the process once the tree has been weaken by other factors.

Spatial Pattern Analysis Reveals Intra-specific Competition and Fractal Characteristics of Pinus sylvestris var. mongolica Populations in Xiaotaojia Gulley Watershed

Spatial Pattern Analysis Reveals Intra-specific Competition and Fractal Characteristics of Pinus sylvestris var. mongolica Populations in Xiaotaojia Gulley Watershed

The growth dynamics of East European Scots pine (Pinus sylvestris L.) populations - a Lithuanian field trial

The growth dynamics of East European Scots pine (Pinus sylvestris L.) populations - a Lithuanian field trial

Clonal variation depending on Cu, Fe and Zn element concentrations in seed orchards

In order to increase the existing forest assets and to maintain sustainable forestry, breeding studies are carried out in forestry. One of the most important practices in these breeding studies is seed orchards. The purpose of seed orchards is to obtain better quality seeds per unit area. In this study, plant nutritional elements were used for the first time to determine clonal variation. The antagonism of nutrients and their accumulation rate in clones were investigated. The research was carried out in the Scots pine (Pinus sylvstris) clonal seed orchard in Taşköprü. Needle samples were taken from 8 ramets of 30 clones in the seed orchard in 3 replications and 240 trees were randomly sampled. In addition, soil samples were taken from the seed orchard. The samples taken were first washed in the laboratory and then two different drying processes were applied to the samples. After drying, samples were prepared by the melting method and then Cu, Fe and Zn element concentration analyzes were performed with the ICP-OES device. The results obtained were evaluated by analysis of variance and Tukey test with the help of Minitab 18 package program and differences between clones were tried to be determined depending on element concentrations. In the findings obtained, it was determined that there were significant differences between the clones in terms of the studied elements at the p<0.05 probability level.

Impact of thinning on leaf economics, plant hydraulics, and growth dynamics

Integrating climate change concerns into forest management strategies remains challenging. Among management strategies, thinning has been proven to alter major components underlying the carbon and water cycles over the short term. However, the functional adaptability of managed forests to cope with long-term drought remains unclear. This study aims to quantify the influence of thinning on key plant functional traits for two pine species, and their impacts on the fundamental processes of tree growth and transpiration. We conducted an experimental silvicultural trial with varying thinning intensities in two Pinus sylvestris and Pinus nigra plantations with the following specific objectives: i) to assess the impact of thinning on major traits involved in the leaf economic spectrum (LES), and hydraulic relations, and ii) to understand which of these traits reflect fundamental aspects of plant growth and transpiration, and their relations with environment. We used a combination of dendrochronological (basal area increment, BAI), sapflow (Fd), and tree ring isotope (δ13C) data, along with key functional and physiological traits including photosynthesis (A), leaf mass area (LMA), Huber value (Hv), sapwood density (Wd), and predawn to midday water potential (Ψpd, Ψmd).Our results revealed species-specific responses, with P. nigra exhibiting a conservative growth strategy, whereas P. sylvestris displayed increased growth after thinning. Despite thinning influenced both BAI and wood δ13C with notable species-dependent variations, we evidenced a general convergence in the relationships between LES traits and Hv across species, treatments and seasons (p < 0.01). Despite thinning influenced both BAI and wood δ13C with notable species-dependent variations, we evidenced a general convergence in the relationships between LES traits and Hv across species, treatments and seasons (p < 0.01). BAI responses to thinning translated into predictable changes in key hydraulic traits and adaptive changes in physiological performance. For instance, BAI was inversely related to LMA and Hv. Consistent with LES, variations in LMA influenced A. In turn, seasonal variations in LMA scaled negatively with Ψpd, and Ψmd (p < 0.01). Such a functional adaptation suggests that thinning promotes growth while favouring forest resilience in the long term. This study provides practical implications for the implementation of a trait-based approach into silvicultural frameworks and anticipating the consequences of climate change for managed forest ecosystems.

The economic evaluation of timber obtained from Norway spruce and scots pine grown under different thinning regimes in Lithuania

ABSTRACT In Lithuania, no studies have determined the relationship between the quality and economic benefits of Norway spruce and Scots pine wood based on age, stand density, and various forest management technologies. This study aims to assess and compare the economic benefits of Norway spruce and Scots pine in stands of different initial densities, depending on different forest management measures. This study calculated different pre-commercial thinning intensities 4 times, 3 times, and 2 times and final thinning profitability by stand volume and wood quality parameters modulus of elasticity and bending strength. Moreover, thinning intensities included three initial stand densities of 3000–3100, 2000–2100, and 1000–1100 trees per hectare, and different thinning regimes when the stand was thinned from below at the age of 8–9, 15, 21, and 35 years. The results showed higher profitability in the pre-commercial thinning of low-intensity with higher frequency − 4 thinning operations over the 40 years. However, the high-thinning intensity − 2 thinning operations over 40 years – applied in young Norway spruce and Scots pine stands will reduce wood quality and profitability in the future. The study found that stand thinning of low intensity tends to improve wood quality and the profitability that depends on it. After assessing the wood quality, it turned out that the 40-year-old Scots pine trees were too young to harvest because of low wood quality. However, the timber from Norway spruce trees could be used profitably if there is a market demand.

Irruptions of crossbills Loxia spp. in northern Europe – patterns and correlations with seed production by key and non‐key conifers

Irruptions by boreal seed‐eating and frugivorous birds are assumed to be driven by the production of seeds and fruits, crops of which are highly variable between years. Using data from Sweden, we tested whether irruptions of Common Crossbills Loxia curvirostra were correlated with low Norway Spruce Picea abies seed production in the same year as the irruption and/or high seed production in the year prior to an irruption. Similar tests were made for Parrot Crossbill Loxia pytyopsittacus irruptions in relation to Scots Pine Pinus sylvestris seed production. In northern Europe, these conifers represent the key food species of the two crossbill species, respectively. Despite differing times that seeds take to mature and asynchronous seed production between the two conifer species, including a 3‐year cycle for Norway Spruce, the two crossbill species often irrupted in the same year as one another. Analyses showed that irruptions into Britain and other parts of western Europe by both crossbill species were correlated with low seed production by Norway Spruce in Sweden. Low seed production by Scots Pine had a marginally non‐significant additive effect on both crossbill species. In a second set of analyses, the best‐fitting model was one in which low seed production by both conifers in a given year and high seed production in the previous year were each correlated with large numbers of irrupting Common and Parrot Crossbills. The models indicate that the incidental co‐occurrence of low seed production of Norway Spruce and Scots Pine in a given year, after a year of high seed production, may result in an irruption. The seed production of Norway Spruce and Scots Pine in Sweden was correlated with production by the same species in Finland, indicating widespread synchrony of cropping across northern Europe.

Characterisation of rotary friction welding process and mechanism of heat-treated Scotch pine

Rotary friction welding of wood to heat-treated lumber from Scotch pine is feasible and the strength of the joint exceeds that of glued and hammered joints. This study investigated the rotary friction welding process parameters and its welding mechanism applicable to heat-treated Scotch pine. Untreated Scotch pine served as the control. The one-way test revealed the tenon/bore ratio of 1.5, rotational speed of 2000 to 3500 r/min, and feed rate of 15 to 20 mm/s as the ideal process parameters for heat-treated Scotch pine. Under the same conditions, heat-treated material had weld strength up to 63.2% higher than untreated material. The portion of the weld zone with better weld strength was larger in size, had a full surface, and was darker in color, according to ultra-depth-of-field microscopic examinations. The internal wood components melted and cooled after the welding was finished and re-polymerized to form a tightly wrapped structure, linking the dowel rods to the substrate, according to the results of scanning electron microscopy.

Transcriptome profiles reveal response mechanisms and key role of PsNAC1 in Pinus sylvestris var. mongolica to drought stress

BackgroundDrought stress severely impedes plant growth, and only a limited number of species exhibit long-term resistance to such conditions. Pinus sylvestris var. mongolica, a dominant tree species in arid and semi-arid regions of China, exhibits strong drought resistance and plays a crucial role in the local ecosystem. However, the molecular mechanisms underlying this resistance remain poorly understood.ResultsHere, we conducted transcriptome sequence and physiological indicators analysis of needle samples during drought treatment and rehydration stages. De-novo assembly yielded approximately 114,152 unigenes with an N50 length of 1,363 bp. We identified 6,506 differentially expressed genes (DEGs), with the majority being concentrated in the heavy drought stage (4,529 DEGs). Functional annotation revealed enrichment of drought-related GO terms such as response to water (GO:0009415: enriched 108 genes) and response to water deprivation (GO:0009414: enriched 106 genes), as well as KEGG categories including MAPK signaling pathway (K04733: enriched 35 genes) and monoterpenoid biosynthesis (K21374: enriched 27 genes). Multiple transcription factor families and functional protein families were differentially expressed during drought treatment. Co-expression network analysis identified a potential drought regulatory network between cytochrome P450 genes (Unigene4122_c1_g1) and a core regulatory transcription factor Unigene9098_c3_g1 (PsNAC1) with highly significant expression differences. We validated PsNAC1 overexpression in Arabidopsis and demonstrated enhanced drought resistance.ConclusionsThese findings provide insight into the molecular basis of drought resistance in P. sylvestris var. mongolica and lay the foundation for further exploration of its regulatory network.

Organic soil greenhouse gas flux rates in hemiboreal old-growth Scots pine forests at different groundwater levels

AbstractTree biomass and soils (especially organic soils) are significant carbon pools in forest ecosystems, therefore forest management practices, in order to ensure carbon storage in these pools and to mitigate climate change, are essential in reaching climate neutrality goals set by the European Union. Overall studies have focused on diverse aspects of forest carbon storage and greenhouse gas (GHG) fluxes from mineral soils, and recently also from organic soils. However, the information about old-growth forests and the long-term effects of drainage on GHG fluxes of organic soils is missing. Additionally, a large proportion of Scots pine (Pinus sylvestris L.) forests on organic soils in the hemiboreal region are drained to regulate groundwater level and to improve above-ground carbon storage. The study aims to assess the intra-annual dynamics of soil carbon dioxide (CO2) and methane (CH4) fluxes in hemiboreal old-growth Scots pine stands on organic soils with diverse groundwater levels. Six old-growth stands (130–180 years old) were evaluated. In old-growth forests, the main source of soil CO2 emissions is ground vegetation and tree roots (autotrophic respiration), while heterotrophic respiration contributes to almost half (41%) of the total forest floor ecosystem (soil) respiration. The total forest floor respiration and soil heterotrophic respiration are mainly affected by soil temperature, with minor but statistically significant contribution of groundwater level (model R2 = 0.78 and R2 = 0.56, respectively). The CO2 fluxes have a significant, yet weak positive relationship with groundwater level (RtCO2 R2 = 0.06 RhCO2 R2 = 0.08). In contrast, total soil CH4 uptake or release depends primarily on groundwater level fluctuations, with a minor but significant contribution of soil temperature (model R2 = 0.67). CH4 flux has high variability between stands.

The monoterpenes as a characteristic marker for pine species distinction: a chemotaxonomic study from the Czech Republic

For the purposes of chemotaxonomic distinction of four pine species Pinus nigra, Pinus ponderosa, Pinus rigida and Pinus sylvestris growing in the suburban landscape of the central part of the Czech Republic, resin extracts from tree trunks, needles and female cones were analysed using gas chromatography-mass spectroscopy. Monoterpenes were shown to be the main terpene fraction of the resins of all studied pine species. On average, they made up 80% of the total terpene content. A characteristic monoterpene for distinguishing pine species was β-pinene, with high levels in P. ponderosa, moderate levels in P. rigida and low levels in P. sylvestris and P. nigra. P. sylvestris contained only trace amount of Δ-3-carene (0.6%) in resins from needles and thus belongs to the α-pinene chemotypic variation. Slight seasonal variability in terpene production was found for resins from needles of P. nigra and P. sylvestris. When comparing European populations according to the monoterpene composition of resins from needles, it can be stated that the α-pinene content increased in the order P. ponderosa < P. rigida < P. nigra < P. sylvestris while the β-pinene content changed in the opposite direction. This statement confirms the terpene biosynthesis uniformity of European pines.

Drought Impact on Eco-Physiological Responses and Growth Performance of Healthy and Declining Pinus sylvestris L. Trees Growing in a Dry Area of Southern Poland

In recent years, several drought events hit Poland, affecting its forests. In Opole, Poland, tons of Pinus sylvestris L. deadwood is removed every year due to drought. Understanding the physiological mechanisms underlying tree vulnerability to drought, and tree responses, is important to develop forest management strategies to face the ongoing climate change. This research provides comprehensive local-scale analyses of the sensitivity of healthy and declining trees to drought. We used dendrochronology and stable isotope analysis to compare five healthy and five declining trees. The analysis focused particularly on comparisons of basal area increment (BAI), δ13C, and intrinsic water-use efficiency (iWUE), as well as tree resistance, resilience, and recovery in response to drought events and sensitivity to selected meteorological parameters. We observed a significant reduction in BAI values in declining trees after 2000. Fifteen years later, the reduction was also visible in the iWUE values of these trees. Despite similar δ13C chronology patterns, declining trees showed higher δ13C correlations with meteorological parameters. We have shown that dendrochronology enables early detection of poor forest health conditions. Differences in iWUE chronologies occurring in recent years suggest that trees of both groups have chosen different adaptive strategies to cope with drought stress.

Physiological and psychological recovery in two pure forests: interaction between perception methods and perception durations

The forest experience is good for people’s physical and mental health. However, few studies on the effects of pure forest based on the duration and way of experience on people’s physical and mental recovery. In this study, we took 180 first-year college students as research objects and conducted experiments in Pinus sylvestris and Betula platyphylla and the control group of grass plot. The changes of physiological and psychological indexes of the subjects were compared by two perception methods (onsite perception, video perception) and three perception duration (10 min, 20 min, 30 min). The results indicated that: (1) Differences between the two pure forests were mainly reflected in short-term recovery of diastolic blood pressure (DBP) and long-term recovery of total mood disorder (TMD). (2) Video perception was more conducive to short-term recovery of systolic blood pressure (SBP) and diastolic blood pressure (DBP). (3) Viewing the Pinus sylvestris for 20 min in different ways was the best way to relieve stress. It is suggested that, Pinus sylvestris can be used as the rehabilitation perception material, and reasonable path length or perception time can be selected for landscape construction in future. These results can provide scientific reference for landscape design based on forest health and environmental perception.

Characterization of randomly oriented strand boards manufactured from juvenile wood of underutilized wood species

AbstractThe wood-based panel industry in Europe, which is dominated by the use of Norway spruce, will face new challenges due to environmental changes and the bark-beetle calamity, which started a new era of forestry. To explore the possibility of replacing spruce with other wood species, juvenile wood of nine underutilized wood species (Scots pine, European larch, poplar, willow, alder, birch, European beech, English oak and hornbeam) were used to make randomly oriented strand boards (OSBs). Single-layer OSBs were produced with 3% pMDI resin and 0.5% wax. Standard physical and mechanical properties were measured. The bending strength (MOR) values showed that there was no statistically significant difference between the values for, on the one hand, spruce (34.6 MPa) and, on the other, larch (25.9 MPa), poplar (25.2 MPa), willow (27.8 MPa), alder (34.3 MPa) or birch (27.1 MPa). A similar trend was found for the boards modulus of elasticity (MOE). The highest MOE values of 5,185 MPa and 4,472 MPa were found for spruce and alder, respectively. There was no significant difference between spruce and other wood species in internal bond strength. Boards made from high-density wood species showed better physical performance, whereas those made from low-density wood species (except pine) gave better mechanical properties. Strand-generalized characteristics, such as the slenderness ratio and specific surface, were analyzed for all investigated physical and mechanical properties. European larch, poplar, willow, and alder are potential wood species for manufacturing OSBs in future without mixing species, as they can replace spruce in the wood-based panel industry.

Properties of Forest Tree Branches as an Energy Feedstock in North-Eastern Poland

Tree branches from forest tree harvesting for the timber industry are an important energy feedstock. Solid biofuel in the form of wood chips, produced from branches, is an excellent renewable energy source for generating heat and electricity. However, the properties of wood chips as a solid biofuel produced from forest tree branches can vary greatly depending on the species from which they have been produced. Therefore, this study aimed to assess the thermophysical properties and elemental composition of fresh branches harvested from nine tree species (pedunculate oak, silver birch, European ash, common aspen, grey alder, Norway maple, Scots pine, European larch and Norway spruce) over three consecutive years (2020–2022). The branches of the tree species most commonly found in Polish forests (Scots pine) were characterized by the highest heating value (an average of 20.74 GJ Mg−1 DM), the highest carbon content (an average of 55.03% DM), the lowest ash (an average of 0.60% DM) and nitrogen contents (an average of 0.32% DM), and low sulfur (an average of 0.017% DM) and chlorine contents (an average of 0.014% DM). A cluster analysis showed that the branches of all three coniferous tree species (Scots pine, Norway spruce and European larch) formed one common cluster, indicating similar properties. The branches of the European ash were characterized by the lowest wood moisture content (an average of 37.19% DM) and thus the highest lower heating value (an average of 10.50 GJ Mg−1). During the three years of the study, the chlorine and ash contents of the branches of the tree species under study exhibited the highest variability.

Historical charcoal production as a factor in soil cover heterogeneity in a fluvioglacial landscape − A case study from northern Poland

Although in situ wood thermal processing, as a common practice in European forests in historical times, has been confirmed in many studies, the environmental implications of that process remain poorly explored. In this study, we focused on evaluating the impact of that process on forest vegetation and soil cover heterogeneity in a fluvioglacial landscape dominated by Brunic Arenosols. This study covered three 70–95-year-old stands of Scots pine in northern Poland. Three soil profiles, including from the relict charcoal hearth (RCH), from the surrounding ditch and a control, were examined from each stand, as well as associated vegetation. The studies showed that 19th century charcoal production platforms were overgrown with 20–60% fewer plant species than control stands. The effect on soils varied according to their characteristics. The presence of anthropogenic horizons consisting of a mixture of burnt soil material, ashes, charcoal particles, and other products of wood pyrolysis was the most distinguishing feature of RCH soils classified as Spolic Technosols (Arenic, Dystric, Pyric, Protospodic, Transportic). Typically, these horizons were characterised by lower bulk density, and higher porosity, as well as higher contents of total organic carbon, nitrogen, and exchange cations than the control soils. The differences between the RCH and control soils were highlighted by a comparison between the pools of the components in a soil column (pedon). Clear tendencies were not recorded for pH, the phosphorus content and stocks, the forms of iron and aluminium, the saturation of the soil sorption complex with bases or the trophic index. This may be due to the long-term neutralising effect of forest vegetation, dominated by Scots pine. Moreover, the results of our study may indicate the problem of toxicity of the RCH soils, which should be undertaken, considering the utilitarian importance of the issue.

Wildfire impacts on the carbon budget of a managed Nordic boreal forest

Wildfire is one of the most important disturbances affecting boreal forests. Most previous research on boreal forest fires has occurred in North American forests which have different fire regimes, tree species and are less intensively managed than their Eurasian counterparts. Recent extreme fire years have highlighted the vulnerability of the Nordic boreal forest to climatic shifts that are increasing forest fire frequency and severity. The Ljusdal fire (2018) was one of the largest wildfires in recorded history in Sweden. We established eddy covariance flux towers to track the impacts of this fire on the carbon balance of two Pinus sylvestris sites subject to different fire severities and forest management strategies 1–4 years post-fire. The ‘SLM’ site was a mature stand that experienced low-severity fire (trees survived) followed by salvage-logging and reseeding, whilst the ‘HY’ site was 10 years old when it experienced high-severity fire (all trees killed) then was replanted with seedlings. During the study period, both sites were net carbon sources at the annual scale. It took up to 4 years after the fire until the first day of net CO2 uptake was recorded at each site. We estimated that it will take 13 years (8, 21; mean ± 95 % confidence intervals) after the fire until the sites reach a neutral annual carbon balance. It will take up to 32 years (19, 53) at HY and 46 years (31, 70) at SLM to offset the carbon lost during and after the fire and salvage-logging. In addition, our measurements showed that more carbon was emitted in the first 4 years after the fire compared to the carbon lost from combustion during the fire. Quantifying carbon fluxes during the initial years after fire is therefore crucial for estimating the net impact of wildfire on the carbon budget of boreal forests.