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In Fennoscandia, wildfires are typically low-intensity surface fires that burn vegetation on the forest floor. Multispectral remote sensing, particularly the normalized burn ratio (NBR) index, is widely used to assess burn severity, but its effectiveness in identifying surface fires under dense canopies is less studied. This study examined the characteristics of surface fires across seven one-hectare test sites in Scots pine-dominated boreal forests in Finland. Fire-induced spectral changes, measured as difference normalized burn ratio (dNBR) values from Sentinel-2 data, were compared with structural changes on the forest floor measured using terrestrial laser scanning (TLS). Breakpoint analysis of NBR time series identified most surface fires, with a noticeable decline in NBR values. Fires not identified with the breakpoint analysis had less burned ground vegetation and denser canopy cover. A moderate correlation (r = –0.5) was observed between spectral and volumetric changes, with higher dNBR values corresponding to greater vegetation reduction. However, dense canopies lowered burn severity despite similar ground vegetation volume changes. NBR changes were explained by vegetation volume, canopy cover, and site conditions (R² = 84%). These findings improve understanding of the applicability of multispectral remote sensing in detecting fires, assessing burn area, and estimating burn severity in boreal forests. [ABSTRACT FROM AUTHOR]

This article provides a detailed analysis of the Crocus-ERA5 snow product covering the Northern Hemisphere from 1950 to 2022. It assesses the product's performance in terms of snow depth and extent compared to in situ observations and satellite data. Compared to its predecessor, Crocus-ERA-Interim, Crocus-ERA5 benefits from improved spatial resolution and better atmospheric data assimilation, resulting in more accurate snowpack estimates, especially in spring in Eurasia. The findings show a good match with observations, though biases remain, particularly in boreal forest areas and some Arctic regions, where the model tends to overestimate spring melt. The production of this snow dataset is motivated by its use by the continental cryosphere community, and in particular by the collaboration between the French National Center for Meteorological Research (CNRM) and Environment and Climate Change Canada (ECCC), which has been involved in Arctic snow cover monitoring as part of the 'Terrestrial Snow' section of the Arctic Report Card since 2017. The Crocus-ERA5 product is freely available on a daily basis and at 0.25° resolution over the 1950-07-01 to 2023-06-30 period (Decharme et al., 2024, https://doi.org/10.5281/zenodo.14513248). [ABSTRACT FROM AUTHOR]

Persistent multiyear drought (MYD) events pose a growing threat to nature and humans in a changing climate. We identified and inventoried global MYDs by detecting spatiotemporally contiguous climatic anomalies, showing that MYDs have become drier, hotter, and led to increasingly diminished vegetation greenness. The global terrestrial land affected by MYDs has increased at a rate of 49,279 ± 14,771 square kilometers per year from 1980 to 2018. Temperate grasslands have exhibited the greatest declines in vegetation greenness during MYDs, whereas boreal and tropical forests have had comparably minor responses. With MYDs becoming more common, this global quantitative inventory of the occurrence, severity, trend, and impact of MYDs provides an important benchmark for facilitating more effective and collaborative preparedness toward mitigation of and adaptation to such extreme events. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal (ECM) fungi comprise a large proportion of the living and dead microbial‐derived soil carbon (C) pool in boreal forests. Because soil nitrogen (N) and C cycles are closely interlinked, shifts in N availability and subsequent effects on dead fungal mass (“necromass”) may influence C storage in soils. Several mechanisms could underlie the balance of fungal necromass production and stabilization, including fungal morphological traits and physiological traits and biochemical interactions between roots and ECM fungi. We applied inorganic N (30 kg ha−1 year−1) for 13 years in a boreal forest dominated by Populus tremuloides Michx. and measured total fungal necromass concentrations and total C concentrations in organic and mineral soil. We also measured total fungal biomass concentrations in soil (representing changes in inputs), condensed tannin and chitin concentrations of mycorrhizal roots (representing changes in necromass stabilization), and the potential genetic capacity of the ECM fungal community to produce chitinases (indicating chitin degradation potential) and class II peroxidases (indicating polyphenol degradation potential). We detected little effect of long‐term N addition on soil fungal necromass concentration. Long‐term N addition did not have a detectable effect on soil C concentration, standing fungal biomass, fine root tannin or chitin concentrations. Despite downward trends, there was also no detectable effect of N addition on the potential genetic capacity of the ECM fungal community to produce chitinases or class II peroxidases. Our study indicates that 13 years of inorganic N addition in a deciduous broadleaf‐dominated boreal forest has little detectable effect on soil fungal necromass concentrations or potential underlying mechanisms. However, morphological and physiological traits of the ECM community appear decoupled in response to inorganic N addition, representing key functional responses that warrant further investigation. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

There is a growing interest in applying machine learning methods to predict net ecosystem exchange (NEE) based on site information and climatic variables. We apply four machine learning models (cubist, random forest, averaged neural networks, and linear regression) to predict the NEE of boreal forest ecosystems based on climatic and site variables. We use data sets from two stations in the Finnish boreal forest (southern site Hyytiälä and northern site Värriö) and model NEE during the peak growing season and the whole year. For Hyytiälä, all nonlinear models demonstrated similar results with R2 = 0.88 for the peak growing season and R2 = 0.90 for the whole year. For Värriö, nonlinear models gave R2 = 0.73–0.76 for the peak growing season, whereas random forest and cubist with R2 = 0.74 were somewhat better than averaged neural networks with R2 = 0.70 for the whole year. Using explainable artificial intelligence methods, we show that the most important input variables during the peak season are photosynthetically active radiation, diffuse radiation, and vapor pressure deficit (or air temperature), whereas, on the whole-year scale, vapor pressure deficit (or air temperature) is replaced by soil temperature. When the data sets from both stations were mixed, soil water content, the only variable clearly different between Hyytiälä and Värriö data sets, emerged as one of the most important variables, but its importance diminished when input variables labeling sites were added. In addition, we analyze the dependencies of NEE on input variables against the existing theoretical understanding of NEE drivers. We show that even though the statistical scores of some models can be very good, the results should be treated with caution, especially when applied to upscaling. In the model setup with several interdependent variables ubiquitous in atmospheric measurements, some models display strong opposite dependencies on these variables. This behavior might have adverse consequences if models are applied to the data sets in future climate conditions. Our results highlight the importance of explainable artificial intelligence methods for interpreting outcomes from machine learning models, particularly when a set containing interdependent variables is used as a model input. [ABSTRACT FROM AUTHOR]

Various aerosols, including mineral dust, soot, and biological particles, can act as ice nuclei, initiating the freezing of supercooled cloud droplets. Cloud droplet freezing significantly impacts cloud properties and, consequently, weather and climate. Some biological ice nuclei exhibit exceptionally high nucleation temperatures close to 0 °C. Ice-nucleating macromolecules (INMs) found on pollen are typically not considered among the most active ice nuclei. Still, they can be highly abundant, especially for species such as Betula pendula, a widespread birch tree species in the boreal forest. Recent studies have shown that certain tree-derived INMs exhibit ice nucleation activity above - 10 °C, suggesting they could play a more significant role in atmospheric processes than previously understood. Our study reveals that three distinct INM classes active at - 8.7, - 15.7, and - 17.4 °C are present in B. pendula. Freeze drying and freeze–thaw cycles noticeably alter their ice nucleation capability, and the results of heat treatment, size, and chemical analysis indicate that INM classes correspond to size-varying aggregates, with larger aggregates nucleating ice at higher temperatures, in agreement with previous studies on fungal and bacterial ice nucleators. Our findings suggest that B. pendula INMs are potentially important for atmospheric ice nucleation because of their high prevalence and nucleation temperatures. [ABSTRACT FROM AUTHOR]

Forest wildfires in interior Alaska represent an important black carbon (BC) source for the Arctic and sub-Arctic. However, BC observations in interior Alaska have not been sufficient to constrain the range of existing emissions. Here, we show our observations of BC mass concentrations and carbon monoxide (CO) mixing ratios in the Poker Flat Research Range (65.12° N, 147.43° W), located in central Alaska, from April 2016 to December 2020. The medians, 10th percentile ranges, and 90th percentile ranges of the hourly BC mass concentration and CO mixing ratio throughout the observation period were 13, 2.9, and 56 ng m−3 and 124.7, 98.7, and 148.3 ppb, respectively. Sporadically large peaks in the BC mass concentration and CO mixing ratio were observed at the same time, indicating influences from common sources. These BC peaks coincided with peaks at other comparative sites in Alaska, indicating large BC emissions in interior Alaska. Source estimation by FLEXPART-WRF (Flexible Particle Dispersion–Weather Research and Forecast) confirmed a contribution of boreal forest wildfires in Alaska and western Canada when high BC mass concentrations were observed. For these cases, we found a positive correlation (r=0.44) between the observed BC/ Δ CO ratio and fire radiative power (FRP) observed in Alaska and Canada. This finding implies that the variability of the BC and CO emission ratio is associated with the intensity and time progress of forest wildfires and suggests that the BC emission factor and/or inventory could be potentially improved by FRP. We recommend that FRP be integrated into future bottom-up emission inventories to achieve a better understanding of the dynamics of pollutants from frequently occurring forest wildfires under the rapidly changing climate in the Arctic. [ABSTRACT FROM AUTHOR]

Nordic forests, such as those found in Canada were known to offer opportunities for large and relatively homogeneous harvesting blocks. Increased fragmentation of forests makes operation planning more difficult and affects costs of road building and machinery relocation. Currently, the diversity of systems used for forest operations in eastern Canada represents only a fraction of existing alternatives. It might be that at least one alternative outperforms the systems currently used in the fragmented boreal forest. Hence, a subset of potential systems was identified in a preliminary evaluation of harvest systems in fragmented operations. From this sample, the objective is to develop a mathematical model to identify the harvest system with the lowest wood procurement cost in fragmented boreal forests. The candidate systems were simulated and optimized using a static deterministic approach. According to our results, the best systems in fragmented forests involve fewer machines, hence a lower relocation cost. Two CTL systems outperformed all others. The system using removable crane self-loading trucks for transport and the one using the forwarder for loading both resulted in 4 $/m3 (USD) advantage over the third least expensive system in the most fragmented harvest sites. The proposed model can be directly applied to assess harvest systems in other parts of the world with similar forest fragmentation challenges. [ABSTRACT FROM AUTHOR]

Two radiocarbon-dated pollen and charcoal records from cores collected at Stump Pond and a wetland in suburban Albany County, New York, provide new insights into the environmental history of a unique inland pine barrens that is currently surrounded and threatened by urban development: the Albany Pine Bush (APB). The Stump Pond core shows that the pond formed roughly 13,000 years ago with the recession of glacial Lake Albany. From ca. 13,000 to 11,000 years ago spruce (Picea) and other boreal forest taxa were more common in the region than they are today, but both cores show that pine-oak (Pinus-Quercus) assemblages similar to those of today's APB have been predominant components of the local forests for the last ca. 11,000 years. Abundant charcoal in both cores demonstrates that fire activity was a frequent occurrence in the APB throughout its history, particularly for the last ca. 6400 years. Water tables rose in response to increasingly humid hydroclimates, leading to the establishment of the wetland site ca. 6400 years ago and a greater abundance of ferns and mosses there during the last millennium. More recently, expanding urbanization and its associated impacts demonstrate that human activity has become the primary driver of change in the APB ecosystem. [ABSTRACT FROM AUTHOR]

A new locality of Chilanodon bicallosa is recorded from near the village of Basandaika in the Tomsk District of Tomsk oblast. Lindholmomneme nordenskioldi is distributed northward to the latitude of the village of Parabel in the Parabel District of Tomsk oblast. Noneulota surprisa was found in the vicinity of the village of Yaylyu in the Turochak District of Altai krai. Euomphalia strigella is recorded in the vicinity of the village of Bakchar in the Bakcharskii District of Tomsk oblast. [ABSTRACT FROM AUTHOR]

We study the four plactic-like monoids that arise by taking the meets and joins of stalactic and taiga congruences. We obtain the combinatorial objects associated with the meet monoids, establishing Robinson–Schensted-like correspondences and giving extraction and iterative insertion algorithms for these objects. We then obtain results on the sizes of classes of words equal in plactic-like monoids, show that some of these monoids are syntactic, and characterise their equational theories. [ABSTRACT FROM AUTHOR]

Deciduous fine woody debris (DFWD) is a common deadwood substrate type in boreal conifer-dominated forests, but it is usually present in low volumes, and its importance for deadwood dependent biodiversity is poorly understood. In this study, we investigated how DFWD-associated fungal and beetle diversity depends on local substrate availability and quality, and how species diversity differs between DFWD and coarse deciduous deadwood (birch logs) in boreal mixed spruce-dominated forests in southern Finland. We studied 25 forest plots (each 0.16 ha), measuring and sampling all pieces of DFWD with a diameter of 2–5 cm and minimum length of 50 cm. Wood-inhabiting fungi were surveyed from wood samples by DNA metabarcoding and saproxylic beetles were surveyed by bark sieving. Our results showed a clear positive relationship between DFWD abundance and the diversity of fungi and beetles. Tree species and decay class diversity were not important in explaining fungal and beetle diversity or community composition, possibly due to low degree of variation in DFWD quality among the study plots. DFWD hosted more diverse fungal assemblages than birch logs, including species of conservation concern, while no red-listed beetle species were observed on DFWD. Overall, species assemblages associated with fine and coarse deciduous deadwood were non-nested. Thus, DFWD represents a non-redundant complementary deadwood resource type alongside coarse deciduous deadwood in boreal forests. [ABSTRACT FROM AUTHOR]

Climate warming can alleviate temperature and nutrient constraints on tree growth in boreal regions, potentially enhancing boreal productivity. However, in permafrost environments, warming also disrupts the physical foundation on which trees grow, leading to leaning trees or "drunken" forests. Tree leaning might reduce radial growth, undermining potential benefits of warming. Here, we found widespread radial growth reductions in southern latitude boreal forests since the 1980s. At mid latitudes, radial growth increased from ~1980 to ~2000 but showed recent signs of decline afterward. Increased growth was evident since the 1980 s at higher latitudes, where radial growth appears to be temperature limited. However, recent changes in permafrost stability, and the associated increased frequency of tree leaning events, emerged as a significant stressor, leading to reduced radial growth in boreal trees at the highest latitudes, where permafrost is extensive. We showed that trees growing in unstable permafrost sites allocated more nonstructural carbohydrate reserves to offset leaning which compromised radial growth and potential carbon uptake benefits of warming. This higher allocation of resources in drunken trees is needed to build the high-density reaction wood, rich in lignin, that is required to maintain a vertical position. With continued climate warming, we anticipate widespread reductions in radial growth in boreal forests, leading to lower carbon sequestration. These findings enhance our understanding of how climate warming and indirect effects, such as ground instability caused by warming permafrost, will affect boreal forest productivity in the future. [ABSTRACT FROM AUTHOR]

Across the western North American boreal region, networks of narrow clearings called seismic lines from oil and gas exploration fragment forests. Restoration of seismic lines for habitat recovery of threatened woodland caribou has been prioritized, but there is little guidance on temporal and spatial targets for boreal forest recovery. Between 2016 and 2022, we sampled regenerating trees on 344 seismic lines with limited re‐disturbance across the oil sands region of Alberta, Canada. We modeled growth relationships for regenerating trees, including regeneration lags, using field and geospatial data to predict passive forest recovery on seismic lines. Recovery on seismic lines in peatland and transitional forests could take >30 years, due to longer regeneration lags (8–13 years) and slower‐growing tree species (>25 years to reach 3 m). Recovery in xeric and mesic uplands was nearly half that, due to shorter regeneration lags (3–5 years), faster‐growing species (9–13 years to reach 3 m), and recent wildfires. Over half of seismic lines in upland forests had predicted regeneration lags ≤5 years, including many seismic lines that burned after initial seismic line clearing, indicating regeneration was not delayed. However, all seismic lines in transitional and peatland forests were predicted to have regeneration lags >8 years. Slower recovery on seismic lines is associated with the compounding effects of longer regeneration lags and slower growth rates of dominant tree species. Restoration efforts should prioritize seismic lines where active treatment can significantly reduce regeneration lags and expedite growth. [ABSTRACT FROM AUTHOR]

As the northern high latitude permafrost zone experiences accelerated warming, permafrost has become vulnerable to widespread thaw. Simultaneously, wildfire activity across northern boreal forest and Arctic/subarctic tundra regions impact permafrost stability through the combustion of insulating organic matter, vegetation and post-fire changes in albedo. Efforts to synthesise the impacts of wildfire on permafrost are limited and are typically reliant on antecedent pre-fire conditions. To address this, we created the FireALT dataset by soliciting data contributions that included thaw depth measurements, site conditions, and fire event details with paired measurements at environmentally comparable burned and unburned sites. The solicitation resulted in 52,466 thaw depth measurements from 18 contributors across North America and Russia. Because thaw depths were taken at various times throughout the thawing season, we also estimated end of season active layer thickness (ALT) for each measurement using a modified version of the Stefan equation. Here, we describe our methods for collecting and quality checking the data, estimating ALT, the data structure, strengths and limitations, and future research opportunities. The final dataset includes 47,952 ALT estimates (27,747 burned, 20,205 unburned) with 32 attributes. There are 193 unique paired burned/unburned sites spread across 12 ecozones that span Canada, Russia, and the United States. The data span fire events from 1900 to 2022. Time since fire ranges from zero to 114 years. The FireALT dataset addresses a key challenge: the ability to assess impacts of wildfire on ALT when measurements are taken at various times throughout the thaw season depending on the time of field campaigns (typically June through August) by estimating ALT at the end of season maximum. This dataset can be used to address understudied research areas particularly algorithm development, calibration, and validation for evolving process-based models as well as extrapolating across space and time, which could elucidate permafrost-wildfire interactions under accelerated warming across the high northern latitude permafrost zone. The FireALT dataset is available through the Arctic Data Center. [ABSTRACT FROM AUTHOR]

Research into various bacterial pathogens that can be transmitted between different animals and may have zoonotic potential has led to the discovery of different strains of Bartonella sp. in bats and their associated ectoparasites. Despite their enormous species diversity, only a few studies have focussed on the detection of bacterial pathogens in insectivorous bats of boreal forests and their associated Macronyssidae and Spinturnicidae mites. We collected and molecularly analysed mite samples from forest‐dwelling bat species distributed all along the boreal belt of the Palearctic, from Central Europe to Far East. Ectoparasitic mites were pooled for DNA extraction and DNA amplification polymerase chain reaction (PCRs) were conducted to detect the presence of various bacterial (Anaplasmataceae, Bartonella sp., Rickettsia sp., Mycoplasma sp.) and protozoal (Hepatozoon sp.) pathogens. Bartonella sp. DNA was detected in four different mite species (Macronyssidae: Steatonyssus periblepharus and Spinturnicidae: Spinturnix acuminata, Sp. myoti and Sp. mystacinus), with different prevalences of the targeted gene (gltA, 16‐23S ribosomal RNA intergenic spacer and ftsZ). Larger pools (>5 samples pooled) were more likely to harbour Bartonella sp. DNA, than smaller ones. In addition, cave‐dwelling bat hosts and host generalist mite species are more associated with Bartonella spp. presence. Spinturnicidae mites may transmit several distinct Bartonella strains, which cluster phylogenetically close to Bartonella species known to cause diseases in humans and livestock. Mites with ubiquitous presence may facilitate the long‐term maintenance (and even local recurrence) of Bartonella‐infestations inside local bat populations, thus acting as continuous reservoirs for Bartonella spp in bats. [ABSTRACT FROM AUTHOR]

Information on terrain conditions is a prerequisite for planning environmentally and economically sustainable forest harvesting operations that avoid negative impact on soils. Current soil data are coarse, and collecting such data with traditional methods is expensive. Forest harvesters can be harnessed to estimate the rolling resistance coefficient ( μ RR ), which is a proxy for forest trafficability. Using spatio-temporal data on engine power used, speed travelled, and machine inclination, μ RR can be computed for harvest areas. This study describes an extensive, high-resolution data on μ RR collected in a boreal forest landscape in Southern Finland during the non-frost period of 2021, covering roughly 50 km of harvester routes. We report improvements in removing some of the previous restrictions on calculating μ RR on steeper slopes, enabling the calculation within a - 10 ∘ to + 10 ∘ slope range with a speed range of 0.6–1.2 ms - 1 . We characterise the variation in μ RR both between and within 11 test sites harvested during the April-August period. The site mean μ RR varies from ∼ 0.14 to 0.19 and shows significant differences between the sites. Using simulations of the hydrological state of the soil and open spatial data on forest and topography, we identify features that best explain the extremes of μ RR within the sites. Several wetness-related indices, such as the depth-to-water index with varying thresholds, explain the μ RR extremes, while biomass-related stand attributes indirectly explain these through their linkage to site and soil characteristics. Obtaining μ RR from actual operational data extends the capabilities of large-scale harvester-based data collection and paves the way for building data-driven models for trafficability prediction. [ABSTRACT FROM AUTHOR]

Changes in the chemical composition of the upper soil horizons (Albic Podzol) under lichen pine forests affected by a running surface fire in the middle taiga of the Komi Republic was studied. It was revealed that two days after the fire, the total carbon content in the pyrogenic horizon (Qpyr) increases by 1.3 times compared to the litter of the conventionally background area. During further post-pyrogenic succession, the total carbon content in the upper pyrogenic horizon decreases. Immediately after the fire, an increase in the benzene polycarboxylic acids content in the pyrogenic horizon by 14.5 times compared with the litter of the conventionally background area was revealed. The concentration of polycyclic aromatic hydrocarbons is 7 times higher than their content in the litter of the original forest. In the first 10 days after the fire, a rapid removal of carbon (4 g/m2) and PAHs (11.5 μg/m2) was shown to occur from under the pyrogenic horizon. Increased removal compared to the conventionally background area can be observed in the first three months. During the further evolution, the chemical composition of lysimetric waters approaches conventionally background values, and after two years the concentration of both carbon and PAHs is close to conventionally background values. [ABSTRACT FROM AUTHOR]

Mast seeding, the synchronous and highly variable production of seed crops by perennial plants, is a population‐level phenomenon and has cascading effects in ecosystems. Mast seeding studies are typically conducted at the population/species level. Much less is known about synchrony in mast seeding between species because the necessary long‐term data are rarely available. To investigate synchrony between species within communities, we used long‐term data from seven forest communities in the U.S. Long‐Term Ecological Research (LTER) network, ranging from tropical rainforest to boreal forest. We focus on cross‐species synchrony and (i) quantify synchrony in reproduction overall and within LTER sites, (ii) test for relationships between synchrony with trait and phylogenetic similarity and (iii) investigate how climate conditions at sites are related to levels of synchrony. Overall, reproductive synchrony between woody plant species was greater than expected by chance, but spanned a wide range of values between species. Based on 11 functional and reproductive traits for 103 species (plus phylogenetic relatedness), cross‐species synchrony in reproduction was driven primarily by trait similarity with phylogeny being largely unimportant, and synchrony was higher in sites with greater climatic water deficit. Community‐level synchrony in masting has consequences for understanding forest regeneration dynamics and consumer‐resource interactions. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top‐canopy twigs and breast‐height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra‐seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C‐enriched C‐1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water‐soluble carbohydrates, possibly caused by discrimination against 18O during O2‐based diterpene oxidation and 35%–50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within‐tree and among‐tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long‐term proxy for physiological and environmental changes. Summary Statement: We studied the poorly understood intra‐seasonal dynamics of resin δ13C and δ18O. We found that resin δ13C was c. 2‰ lower than sucrose δ13C, while resin δ18O was c. 20‰ higher than xylem water δ18O in mature Pinus sylvestris. Both resin δ13C and δ18O recorded a signal of soil water potential. [ABSTRACT FROM AUTHOR]

Monitoring aboveground biomass (AGB) is critical for carbon reporting and quantifying ecosystem change. AGB from field data can be scaled to the region using airborne lidar. However, lidar-based AGB products emphasize upland forests, which may not represent the conditions in rapidly changing peatland complexes in the southern Taiga of western Canada. In addition, to ensure that modeled AGB changes do not incorporate systematic error due to differences between older and newer lidar technologies, model transfer tests are required. The aim of this study was to develop one bi-temporal lidar-based AGB model applicable to (1) vegetation structures at varying vertical and horizontal continuity in this region and to (2) data collected with an earlier generation lidar system for which Canada-wide aerial coverage is available. Goodness-of-fit metrics show that AGB can be modeled with moderate (R2 = 48%–58% Taiga Shield, peatlands) to high accuracies (R2 = 83%–89% Taiga Plains, upland/permafrost plateau forests including ecotones) by using the point clouds average height and 90th height percentile within a weighted approach as function of modeled AGB and calibrating the earlier lidar data. These results are important for quantifying climate change effects on forest to peatland ecotones. [ABSTRACT FROM AUTHOR]

Gravel roads are a common feature in developed areas of Canada's Arctic. These roads can be a source of calcareous dust that drifts to roadside lakes, causing significant changes in conductivity, calcium, and pH levels. In this study, we examined if road proximity was associated with differences in water quality and invertebrate communities in lakes along the Dempster and Inuvik-Tuktoyaktuk Highways in the Northwest Territories, Canada. We collected biological and water quality data from 18 lakes selected using a stratified random sampling design, with distance from the road (0–300 m, 300–600 m, and >600 m) and region of study (boreal forest, tundra) as the two factors. We hypothesized that lakes closer to the road would exhibit differences in water quality and invertebrate communities associated with road dust pollution and other stressors caused by roads. We found no clear differences in water quality or invertebrate communities among lakes based on distance from the highways. In addition, while there were differences between regions, these did not appear to be related to the effects of the roadways. Our results suggest that variability in lake morphometry and water quality in this region might be more important than the influence of roads. [ABSTRACT FROM AUTHOR]

Marginal populations of temperate species at the leading edge of their range will likely play a key role at the boreal‐temperate ecotone (BTE) in the face of climate changes. In eastern North America, red maple (Acer rubrum L.) is the most abundant temperate tree species encroaching into the boreal forest. In order to provide useful insights about possible responses to climate change and anticipate the formation of new assemblages, this study relies on long‐term Holocene data from forest soil wood macrofossils (charcoal and ligneous remains) and contemporary stand analyses to assess the postglacial origin and modern‐day dynamics of red maple at its leading edge within the BTE. We sampled the soils of eight marginal red maple stands. Macroscopic charcoal particles and ligneous remains were identified using microanatomical characteristics. Macrofossils of temperate tree species were radiocarbon dated to reconstruct their long‐term stand‐scale history. Contemporary dynamics (<200 years) were assessed by analyzing tree size structure of all stems within 400 m2 plots, minimal stand age from tree‐ring dating, as well as the recent occurrence of fire and logging from published ecoforest data. White pine (Pinus strobus L.), the only other temperate tree species that was identified, was present 6500–4000 years ago, during the mid‐Holocene thermal maximum but decreased during the cooler and fire‐prone late‐Holocene Neoglacial (4000 years ago to present). By contrast, red maple was found at its current northern limit since the last 4000 years. Modern‐day marginal red maple stands are self‐regenerating populations that established following a recent stand‐replacing disturbance (wildfire or clearcut). The present‐day increase of anthropogenic disturbances within the BTE could mirror the Neoglacial increase in fire activity that fostered red maple during the Holocene. We thus predict that red maple is poised to increase in abundance within the BTE, which should facilitate the northward establishment of other temperate deciduous species into the boreal forest prompted by the new conditions brought about by anthropogenic or climate change‐induced disturbances. [ABSTRACT FROM AUTHOR]

In wet regions, temperature increases can prompt increases in vegetation growth. Vegetation responses are determined in part by N and P availability, yet the relative importance of N‐ versus P‐cycling supporting growth is unclear. Prompted by studies demonstrating that warming‐enhanced N cycling supports greater productivity and soil C stocks in warmer forests along a wet boreal forest transect, we tested the hypothesis that enhanced organic matter cycling supports greater P demand in relatively warm forests. We further asked whether evidence from soil and litterfall fluxes indicates increases in P demand are met in these forests or potentially pose a limit on warming‐enhanced productivity. Elevated tree growth and litterfall rates coupled with similar litterfall P concentrations suggest P demand is greater at warmer sites. By assessing multiple soil N and P stocks, inputs, and stoichiometry, we observed three lines of evidence indicating that this greater P demand is met through a combination of plant tissue plasticity and adequate surface soil P supplies. First, warming‐enhanced N‐cycling results in an increase in N:P of surface soils and litterfall inputs indicating a reduction in needle litter P relative to N. Second, organic layer C:P and P stocks were maintained across latitude despite increases in litterfall P inputs in the warmest forests suggesting increased cycling and retention of P by trees. Third, in contrast with soil N, estimates of soil P residence times are not coupled with those of C, and soil C:P does not correlate with tree growth across sites signifying that N, not P, may limit tree growth in these forests. Results here provide evidence that increased productivity with warming and enhanced N cycling in wet boreal forests is not likely to be limited by available P over the decadal timescale represented by the temperature gradient along this climate transect. However, similarities observed between warming‐enhanced N availability in the current study's forests and that in boreal forests receiving high N additions indicate a need to better understand how boreal trees may adapt to shifts away from N limitation. Such new knowledge is needed to improve our understanding of the longevity of this important climate feedback. [ABSTRACT FROM AUTHOR]

Based on long-term observations of the water discharge (WD) from 1878 to 2018, the main trends and patterns of its change in the basin of one of the largest rivers in the east of the East European Plain, the Vyatka River, were revealed using a set of standard statistical procedures and a graphical analysis of the WD probability curves. Three main phases of the annual river WD were identified, corresponding to the periods 1878–1929, 1930–1977, and 1978–2018. The first and third periods were characterized by increased WD (by 22–23%) relative to the medium period, and the differences in the average annual WD characteristics between these periods were statistically significant. It is also noteworthy that the difference in the average annual WD between the first and last periods of increased WD was very small and statistically insignificant. A gradual increase in the share of the so-called normal annual WD and a decrease in the abnormal (including extreme) annual WD were noted from 1878–1929 to 1978–2018 in the predominantly northern half of the river basin. At the same time, in the predominantly southern half of the basin, according to the analysis of only the periods 1930–1977 and 1978–2018, the so-called normal and abnormal WD remained almost unchanged; only a slight increase in positive anomalies of the WD was noted. Increased intra-annual variability in the WD was characteristic of the period of its reduced average annual value. Between the three identified periods, a gradual reduction in the water runoff coefficient was observed during the warm (mainly summer) season in the Vyatka River basin. The specified long-term variability in the water discharge of the Vyatka River was chiefly due to long-term changes in climatic factors, primarily the ratio of the air temperature and precipitation, expressed as the De Martonne aridity index. The duration of the principal cycle of these changes was 82 years. An additional contribution could also have been made by the widespread reduction in cropland in the study region in recent decades. The obtained results can be preliminarily considered representative of the entire southern sector of the boreal forest zone (taiga zone) of the east of the East European Plain. [ABSTRACT FROM AUTHOR]

The presented work was aimed at studying the features of accumulation of radionuclides 210Po and 210Pb, as well as micro- (Cu, Pb, Zn, Ni, Ba, V, Ti, Sr) and macroelements (Mn, Fe, Al) by fruticose epiphytic (Bryoria spp., Usnea spp.) and epigeal (Cladonia spp.) lichens in the middle and northern taiga subzone of the European Northeast (Komi Republic, Russia). Lichens were collected from forests of seven municipalities. Areas with combined radiation and chemical pollution were also included in the study. The relevance of the study is related to the increasing anthropogenic load worldwide, insufficient data on the concentrations of the studied elements in the environment of Komi Republic, their potential toxicity, including high radioactive toxicity of 210Po and 210Pb, as well as the possibility of using these lichens for bioindication of various pollutants, including radioactive ones. It has been established that the accumulation of chemical elements by lichens differs both for areas with different technogenic loads, and for different ecological-substrate groups of lichens. Based on the data from correlation analysis, principal component analysis (PCA), as well as enrichment factors (EF) of lichens with chemical elements, the features of their intake into lichen thalli were studied. It was concluded that in the taiga zone epiphytes may be the preferable bioindicators of elements that enter the Earth's surface with air. Epigeal lichen Cladonia also showed good accumulating ability for 210Po, 210Pb, as well as microelements in areas with their high content in soils. [ABSTRACT FROM AUTHOR]

A whole genome sequence of a new strain of the nitrogen-fixing bacterium Azospirillum doebereinerae, known for its diverse plant growth-promoting bacteria (PGPB), was obtained for the first time. The strain, designated Azospirillum doebereinerae AT, was isolated during a soil analysis in the Chernevaya taiga of Western Siberia, a unique and fertile forest ecosystem known for its diverse plant growth-promoting bacteria (PGPB). The A. doebereinerae genome under study is fully assembled into seven circular molecules, none of which are unequivocally plasmids, with a total length of 6.94 Mb and a G + C content of 68.66%. A detailed phylogenomic analysis confirmed its placement within the genus Azospirillum, specifically closely related to A. doebereinerae GSF71T. Functional annotation revealed genes involved in nitrogen metabolism, highlighting the potential of strain TA as a biofertilizer and plant growth-promoting agent. The findings contribute to our understanding of the genomic diversity and metabolic potential of the Azospirillum genus, and they are of interest for further study in the field of comparative bacterial genomics, given the strain's multi-chromosomal genome structure. [ABSTRACT FROM AUTHOR]

Root and butt rot, caused by Heterobasidion species, poses a significant threat to coniferous forests in the Northern Hemisphere. Innovative and effective strategies are crucial to enhance the control of this disease. This study aimed at identifying a Streptomyces strain, FY4, and evaluating its biocontrol potential against H. annosum and H. parviporum. Strain FY4 was identified as Streptomyces blastmyceticus based on morphological, physiological, and biochemical characteristics, supported by a multigene phylogenetic analysis using the 16S rRNA, atpD, rpoB, and trpB genes. In vitro dual-culture experiments showed that S. blastmyceticus exhibited antagonistic activity against both H. annosum and H. parviporum, with an inhibition zone diameter exceeding 15 mm. Moreover, the fermentation broth of S. blastmyceticus FY4 displayed significant inhibitory effects on the mycelial growth and spore germination of both Heterobasidion species. At a 10% concentration, the fermentation broth inhibited the mycelial growth by over 90% and reduced the spore germination rate by more than 60%. Additionally, the fermentation broth exhibited significant inhibitory effects on the mycelial growth of four common pathogenic fungi—Phytophthora cinnamomi, P. sojae, Rhizoctonia solani, and Verticillium dahlia, with an inhibition rate over 50%. These findings suggest that S. blastmyceticus FY4 produces antifungal substances capable of effectively suppressing infection of Heterobasidion species in conifers. Consequently, strain FY4 holds great promise as a biological control agent for managing root and butt rot caused by these pathogens, as well as potential for controlling other fungal diseases. [ABSTRACT FROM AUTHOR]

Data from the new hyperspectral satellite missions such as EnMAP are anticipated to refine leaf area index (LAI) or canopy closure (CC) monitoring in conifer-dominated forest areas. We compared contemporaneous multispectral and hyperspectral satellite images from Sentinel-2 MSI (S2) and EnMAP and assessed whether hyperspectral images offer added value in estimating LAI, effective LAI (LAIeff), and CC in a European boreal forest area. The estimations were performed using univariate and multivariate generalized additive models. The models utilized field measurements of LAI and CC from 38 forest plots and an extensive set of vegetation indices (VIs) derived from the satellite data. The best univariate models for each of the three response variables had small differences between the two sensors, but in general, EnMAP had more well-performing VIs which was reflected in the better multivariate model performances. The best performing multivariate models with the EnMAP data had ~1–6% lower relative RMSEs than S2. Wavelengths near the green, red-edge, and shortwave infrared regions were frequently utilized in estimating LAI, LAIeff, and CC with EnMAP data. Because EnMAP could estimate LAI better, the results suggest that EnMAP may be more useful than multispectral satellite sensors, such as S2, in monitoring biophysical variables of coniferous-dominated forests. [ABSTRACT FROM AUTHOR]

Structural complexity is an important forest characteristic for habitat assessment, forest management and planning. However, monitoring how forest structural complexity evolves over time in various forest types has not been widely explored. In this study we investigate the feasibility of bi-temporal low-density airborne laser scanning (ALS) for the assessment of changes in light availability conditions within forest canopy, considered to imply changes in forest structural complexity. We used ALS data acquired in 2012 and 2019 to generate canopy vertical profiles by slicing the point clouds into 4 × 4 ×1 m voxels which were then rasterized and reclassified into four light availability categories. To understand structural development over time in different forest types we used field-measured tree heights and tree species information to stratify sample plots in different stand complexity categories. Stands with higher structural complexity represented increased proportions of space occupied by vegetation as well as decreased proportions of empty space below the canopy. The experiments showed the ability of low-density ALS to characterize the dynamics in canopy layering structure, implying changes in forest structural complexity. The presented methodology could potentially be upscaled and applied in the landscape-level monitoring of the development of boreal forest structural characteristics. [ABSTRACT FROM AUTHOR]

In the present paper, we introduce a high-resolution spatiotemporal point cloud time series, acquired using a LiDAR sensor mounted 30 metres above ground on a flux observation tower monitoring a boreal forest. The dataset comprises a 18-month long (April 2020 - September 2021) time series with an average interval of 3.5 days between observations. The data acquisition, transfer, and storage systems established at Hyytiälä (Finland) are named the LiDAR Phenology station (LiPhe). The dataset consists of 103 time points of LiDAR point clouds covering a total of 458 individual trees, comprising three distinct Boreal species. Additional reference information includes the respective location, the species, and the initial height (at the first time point) of each individual tree. The processing scripts are included to outline the workflow used to generate the individual tree point clouds (LiPheKit). The presented dataset offers a comprehensive insight into inter- and intra-species variations of the individual trees regarding their growth strategies, phenological dynamics, and other functioning processes over two growth seasons. [ABSTRACT FROM AUTHOR]

The "Author Index" from the Journal of Gastroenterology & Hepatology is a comprehensive list of authors and their research papers in the field. The index features authors from diverse backgrounds and regions, highlighting a global perspective on gastroenterology and hepatology research. Researchers and professionals can use this document to easily locate specific authors or topics of interest within the field. The document showcases a collaborative and interdisciplinary approach to research, with authors contributing to a wide range of topics in gastroenterology and hepatology. [Extracted from the article]

Irruptive forest insects are a leading biotic disturbance across temperate and boreal forests. Outbreaks of forest insects are becoming more frequent and extensive due to anthropogenic drivers (e.g. climate and land‐use), perhaps increasing the likelihood that forests will experience multiple insect‐caused disturbances.Across the fire‐prone Douglas‐fir forests of western North America, recent outbreaks of the western spruce budworm and Douglas‐fir beetle have impacted large expanses of forests, with a higher degree of overlap than expected in some ecoregions. Outbreaks of both insects are positively related to host availability and exhibit density‐dependent population dynamics that are affected by climate and weather.Here, we leverage data from aerial detection surveys, estimates of host availability, climate and weather, and categorized fire severity to describe the spatial overlap between western spruce budworm and Douglas‐fir beetle and assess: (1) how climate and host availability influence the biogeography of outbreaks; (2) how weather incites outbreaks; and finally, (3) how prior disturbances (fire and biotic) affect the subsequent outbreak likelihood of western spruce budworm and Douglas‐fir beetle.Models demonstrate that western spruce budworm and Douglas‐fir beetle share similar predisposing drivers of outbreaks. Outbreaks of both insects were more likely to occur following warm weather, but only beetle outbreaks were more likely following drought. When controlling for differences in outbreak distribution and inciting factors, results indicate that both prior fire and interspecific disturbance altered the likelihood of subsequent insect‐caused disturbance.Specifically, Douglas‐fir beetle outbreaks were more likely to occur for several years following low severity fire, but less likely otherwise. Prior defoliation, especially longer duration defoliation, increased the likelihood of beetle outbreak within stands and across the landscape. On the contrary, western spruce budworm outbreaks were less likely to occur following fire, while prior beetle activity dampened budworm outbreak likelihood for several years, and then eventually increased outbreak likelihood.Synthesis: Biotic–biotic disturbance interactions have the potential to amplify the incidence of insect‐caused disturbance across subcontinental scales. Our findings highlight the need for future work on mechanistic linkages between biotic disturbance agents as well as the ramifications for forest trajectories and function. [ABSTRACT FROM AUTHOR]

Fire is the major forest disturbance in Siberian larch (Larix spp.) ecosystems, which occupy 20% of the boreal forest biome and are underlain by large, temperature-protected stocks of soil carbon. Fire is necessary for the persistence of larch forests, but fire can also alter forest stand composition and structure, with important implications for permafrost and carbon and albedo climate feedbacks. Long-term records show that burned area has increased in Siberian larch forests over the past several decades, and extreme climate conditions in recent years have led to record burned areas. Such increases in burn area have the potential to restructure larch ecosystems, yet the fire regime in this remote region is not well understood. Here, we investigated how landscape position, geographic climate variation, and interannual climate variability from 2001 to 2020 affected total burn area, the number of fires, and fire size in Siberian larch forests. The number of fires was positively correlated with metrics of drought (for example, vapor pressure deficit), while fire size was negatively correlated with precipitation in the previous year. Spatial variation in fire size was primarily controlled by landscape position, with larger fires occurring in relatively flat, low-elevation areas with high levels of soil organic carbon. Given that climate change is increasing both vapor pressure deficit and precipitation across the region, our results suggest that future climate change could result in more but smaller fires. Additionally, increasing variability in precipitation could lead to unprecedented extremes in fire size, with future burned area dependent on the magnitude and timing of concurrent increases in temperature and precipitation. [ABSTRACT FROM AUTHOR]

Aim: Climate extremes are becoming more frequent under global warming, with substantial repercussions for vegetation growth. The degree to which climate extremes increase the risk of high‐impact events on vegetation growth is of high concern. Location: Northern Hemisphere (north of 30°N). Time Period: From 2001 to 2022. Major Taxa Studied: Plants. Methods: We utilised solar‐induced chlorophyll fluorescence (SIF) and the normalised difference vegetation index (NDVI) as proxies for vegetation growth. We performed event coincidence and sensitivity analyses to attribute satellite‐derived vegetation growth extremes to diverse climate extremes (extreme heat, cold, wet and drought) in the Northern Hemisphere. Results: Our results showed that extreme heat and cold were the main climatic extremes that induced positive and negative vegetation growth extremes north of 30°N, respectively, mainly in cold and humid ecosystems (boreal and temperate forests). Water‐related extreme events accounted for less than one‐third of vegetation extremes. The contribution of drought to positive vegetation growth extreme events (approximately 17%), mainly in cold and humid ecosystems, was even slightly higher than that of extreme wet (approximately 12%), which predominantly impacted relatively warm and arid ecosystems (croplands and temperate grasslands). We further identified potential climatic thresholds that could reverse vegetation growth responses to climate extremes (temperature is 12.5°C and climatic water deficit is ‐60 mm, approximately). We also showed that the past two decades of warming and precipitation changes did not induce a shift in the main climatic drivers of vegetation extremes across northern ecosystems. Main Conclusions: Our results emphasise the crucial role of background hydrothermal conditions in the attribution of vegetation growth extremes to diverse climate extremes across northern ecosystems and have substantial implications for predicting how Northern Hemisphere vegetation will respond to increasing climate extremes in the future. [ABSTRACT FROM AUTHOR]

Radiative transfer models of vegetation play a crucial role in the development of remote sensing methods by providing a theoretical framework to explain how electromagnetic radiation interacts with vegetation in different spectral regions. A limiting factor in model development has been the lack of sufficiently detailed ground reference data on both the structural and spectral characteristics of forests needed for testing and validating the models. In this data description paper, we present a dataset on the structural and spectral properties of 58 stands in temperate, hemiboreal, and boreal European forests. It is specifically designed for the development and validation of radiative transfer models for forests but can also be utilized in other remote sensing studies. It comprises detailed data on forest structure based on forest inventory measurements, terrestrial and airborne laser scanning, and digital hemispherical photography. Furthermore, the data include spectral properties of the same forests at multiple scales: reflectance spectra of tree leaves and needles (based on laboratory measurements), the forest floor (based on in situ measurements), and entire stands (based on airborne measurements), as well as transmittance spectra of tree leaves and needles and entire tree canopies (based on laboratory and in situ measurements, respectively). We anticipate that these data will have wide use in testing and validating radiative transfer models for forests and in the development of remote sensing methods for vegetation. The data can be accessed at Hovi et al. (2024a, 10.23729/9a8d90cd-73e2-438d-9230-94e10e61adc9) (for laboratory and field data) and Hovi et al. (2024b, 10.23729/c6da63dd-f527-4ec9-8401-57c14f77d19f) (for airborne data). [ABSTRACT FROM AUTHOR]

Scavenging is an alternative foraging strategy to predation for many carnivore species, as they shift between predation and scavenging in response to changes in resource availability. The use of carrion may lead to interspecific competition and is thus influenced by a risk–reward trade‐off to balance coexistence with guild‐members, where smaller species are expected to be more vigilant due to their vulnerability to larger competitors. We used cameras to investigate the utilization of viscera from the annual moose Alces alces hunt by four sympatric carnivore species: wolf Canis lupus, wolverine Gulo gulo, red fox Vulpes vulpes and pine marten Martes martes in south–central Scandinavia, in relation to body size and habitat. Red foxes had highest probability of visiting viscera sites in both open and forested habitats. Visits by both red foxes and pine martens were longer in open habitats, while number of visits or activity did not differ between habitats. For pine martens, the probability of visiting viscera sites was twice as high in forest compared to open habitat; consequently, red foxes showed the highest overall use of viscera. Red foxes were most vigilant, especially in open habitat, whereas wolverines and pine martens spent a higher proportion of time feeding. Increased vigilance of red foxes facilitates extended resources use in open habitat, while for pine martens, the risk–reward decision occurs before leaving forest cover and entering open habitats. Viscera were not used to a large extent by wolves or wolverines. Wolves are generally less prone to scavenging and wolverines probably use other food resources, more suitable for caching. Overall, competition did not prevent use of viscera, probably due to small‐scale temporal segregation and limited use by the larger carnivores. Consequently, this pulse of human‐subsidized food resources before winter may have important implications for the smaller facultative scavengers. Keywords: carrion use, interspecific competition, pine marten, red fox, wolf, wolverine [ABSTRACT FROM AUTHOR]

Both topography and wildfire can exert significant influences on ecosystem processes and functions during boreal forest successions. However, their impacts on ecosystem multifunctionality (EMF) remain unclear. A mega-fire burned an area of 8700 hectares in the Great Xing'an Mountains in 2000, creating a wide range of fire severity levels across various topographic positions. This provided a unique opportunity to explore the impacts of mixed-severity fire disturbance in boreal forests. We evaluated the effect pathways of wildfire and topography on aboveground multifunctionality (AEMF), soil multifunctionality (SEMF), and overall multifunctionality (OEMF). We found that high-severity burning resulted in lower AEMF, SEMF, and OEMF relative to low-severity burning. Topographic positions significantly influenced SEMF and OEMF, but not AEMF. Specifically, both lower SEMF and OEMF were observed on south-facing slopes. The structure equation model analysis showed that aspect had exerted strong indirect effects on AEMF, SEMF, and OEMF by affecting soil moisture and regenerated tree density (RTD). Fire severity had indirect negative effects on AEMF and OEMF by reducing RTD and on SEMF by reducing soil bacterial diversity and RTD. Our study elucidates the necessity of considering postfire site environments to better manage forest ecosystems and, in turn, promote the rapid recovery of boreal ecosystem functions. [ABSTRACT FROM AUTHOR]

The boreal forest ecosystems of the northern hemisphere are dominated by conifers, of which Norway spruce (Picea abies [L.] H. Karst.) is one of the most common species. Due to its economic interest to the agroforestry industry, as well as its ecological significance, it is important to understand seasonal growth and biomass production in Norway spruce. Solid evidence that the circadian clock regulates growth in conifers has proved elusive, however, resulting in significant gaps in our knowledge of clock function in these trees. Here, we reassess the impact of the circadian clock on growth in Norway spruce. Using a combination of approaches monitoring the physiology of vegetative growth, transcriptomics and bioinformatics, we determined that the clock could be playing a decisive role in enabling growth, acting in specific developmental processes influenced by season and geographical location to guide bud burst and growth. Thus, the evidence indicates that there is time for spruce. [ABSTRACT FROM AUTHOR]

Intra-annual variations of carbon stable isotope ratios (δ13C) in different tree compartments could represent valuable indicators of plant carbon source–sink dynamics, at weekly time scale. Despite this significance, the absence of a methodological framework for tracking δ13C values in tree rings persists due to the complexity of tree ring development. To fill this knowledge gap, we developed a method to monitor weekly variability of δ13C in the cambium–xylem continuum of black spruce species [ Picea mariana (Mill.) BSP.] during the growing season. We collected and isolated the weekly incremental growth of the cambial region and the developing tree ring from five mature spruce trees over three consecutive growing seasons (2019–21) in Simoncouche and two growing seasons (2020–21) in Bernatchez, both located in the boreal forest of Quebec, Canada. Our method allowed for the creation of intra-annual δ13C series for both the growing cambium (δ13Ccam) and developing xylem cellulose (δ13Cxc) in these two sites. Strong positive correlations were observed between δ13Ccam and δ13Cxc series in almost all study years. These findings suggest that a constant supply of fresh assimilates to the cambium–xylem continuum may be the dominant process feeding secondary growth in the two study sites. On the other hand, rates of carbon isotopic fractionation appeared to be poorly affected by climate variability, at an inter-weekly time scale. Hence, increasing δ13Ccam and δ13Cxc trends highlighted here possibly indicate shifts in carbon allocation strategies, likely fostering frost resistance and reducing water uptake in the late growth season. Additionally, these trends may be related to the black spruce trees' responses to the seasonal decrease in photosynthetically active radiation. Our findings provide new insights into the seasonal carbon dynamics and growth constraints of black spruce in boreal forest ecosystems, offering a novel methodological approach for studying carbon allocation at fine temporal scales. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycles (FTCs) are the major seasonal environment stress in the temperate and boreal forests, inducing hydraulic dysfunction and limiting tree growth and distribution. There are two types of FTCs in the field: FTCs with increasing temperature from winter to spring (spring FTCs); and FTCs with decreasing temperature from autumn to winter (autumn FTCs). While previous studies have evaluated the hydraulic function during the growing season, its seasonal changes and how it adapts to different types of FTCs remain unverified. To fill this knowledge gap, the eight tree species from three wood types (ring- and diffuse-porous, tracheid) were selected in a temperate forest undergoing seasonal FTCs. We measured the branch hydraulic traits in spring, summer, autumn, and early, middle and late winter. Ring-porous trees always showed low native hydraulic conductance (K branch), and high percentage loss of maximum K branch (PLCB) and water potential that loss of 50% maximum K branch (P 50B) in non-growing seasons (except summer). K branch decreased, and PLCB and P 50B increased in diffuse-porous trees after several spring FTCs. In tracheid trees, K branch decreased after spring FTCs while the P 50B did not change. All sampled trees gradually recovered their hydraulic functions from spring to summer. K branch, PLCB and P 50B of diffuse-porous and tracheid trees were relatively constant after autumn FTCs, indicating almost no effect of autumn FTCs on hydraulic functions. These results suggested that hydraulic functions of temperate trees showed significant seasonal changes, and spring FTCs induced more hydraulic damage (except ring-porous trees) than autumn FTCs, which should be determined by the number of FTCs and trees' vitality before FTCs. These findings advance our understanding of seasonal changes in hydraulic functions and how they cope with different types of FTC in temperate forests. [ABSTRACT FROM AUTHOR]

Fires in coniferous forests throughout the northern United States alter ecosystem processes and ecological communities, including the diversity and composition of microbial communities living in the soil. In addition to its influence on ecosystem processes and functions, the soil microbiome can interact with soilborne pathogens to facilitate or suppress plant disease development. Altering the microbiome composition to promote taxa that inhibit pathogenic activity has been suggested as a management strategy for forest diseases, including Armillaria root disease caused by Armillaria solidipes, which causes growth loss and mortality of conifers. These forest ecosystems are experiencing increased wildfire burn severity that could influence A. solidipes activity and interactions of the soil microbiome with Armillaria root disease. In this research, we examine changes to the soil microbiome following three levels of burn severity in a coniferous forest in northern Idaho, United States, where Armillaria root disease is prevalent. We further determine how these changes correspond to the soil microbiomes associated with the pathogen A. solidipes, and a putatively beneficial species, A. altimontana. At 15-months post-fire, we found significant differences in richness and diversity between bacterial communities associated with unburned and burned areas, yet no significant changes to these metrics were found in fungal communities following fire. However, both bacterial and fungal communities showed compositional changes associated with burn severity, including microbial taxa with altered relative abundance. Further, significant differences in the relative abundance of certain microbial taxa in communities associated with the three burn severity levels overlapped with taxa associated with various Armillaria spp. Following severe burn, we observed a decreased relative abundance of beneficial ectomycorrhizal fungi associated with the microbial communities of A. altimontana, which may contribute to the antagonistic activity of this soil microbial community. Additionally, A. solidipes and associated microbial taxa were found to dominate following high-severity burns, suggesting that severe fires provide suitable environmental conditions for these species. Overall, our results suggest that shifts in the soil microbiome and an associated increase in the activity of A. solidipes following high-severity burns in similar conifer forests may result in priority areas for monitoring and proactive management of Armillaria root disease. IMPORTANCE With its influence on ecosystem processes and functions, the soil microbiome can interact with soilborne pathogens to facilitate or suppress plant disease development. These forest ecosystems are experiencing increased wildfire frequency and burn severity that could influence the fungal root pathogen, Armillaria solidipes, and interactions with the soil microbiome. We examined changes to the soil microbiome following three levels of burn severity, and examined how these changes correspond with A. solidipes, and a putatively beneficial species, A. altimontana. Following severe burn, there was a decreased relative abundance of ectomycorrhizal fungi associated A. altimontana. A. solidipes and associated microbial taxa dominated following highseverity burns, suggesting that severe fires provide suitable environmental conditions for these species. Our results suggest that shifts in the soil microbiome and an associated increase in the activity of A. solidipes following high-severity burns in conifer forests may result in priority areas for monitoring and proactive management of Armillaria root disease. [ABSTRACT FROM AUTHOR]

In the context of increasingly frequent and severe climate extremes, an understanding of the impacts of these events on gross primary production (GPP) and thus on land carbon uptake is crucial. However, research utilizing new model outputs to assess the future trends, characteristics, and driving factors of GPP reduction associated with extreme events remains limited. Here, we use model outputs from Phase Six of the Coupled Model Intercomparison Project (CMIP6) to investigate the spatiotemporal patterns of negative GPP extreme events during the 21st century. We find a notable increase in negative GPP extremes globally under the SSP5‐8.5 scenario. They are characterized by longer durations and larger sizes, despite the smaller number of events. Under the SSP1‐2.6 scenario, while the total negative GPP extremes remain relatively stable, hotspots, including tropical forests, southern China, and boreal forest zones, still experience increases in negative extremes. By attributing these GPP extremes to climate conditions, we identified compound hot and dry conditions, which contributed to over 40% of the negative GPP extremes under both scenarios, as the dominant driver, followed by single‐driver dry conditions. Under SSP5‐8.5, the increasing contribution of compound hot and dry conditions leads to greater GPP reductions through prolonged and intensified negative extreme events. Compared with CMIP5 models, CMIP6 models project an asymmetry of negative and positive GPP extreme events that favors more negative extremes across most regions. Our findings highlight the escalating damage from climate extremes on future ecosystem productivity, emphasizing the urgent need for effective mitigation and adaptation actions. Plain Language Summary: In a world facing more frequent and severe climate extremes, an understanding of how these events affect plant growth and the uptake of CO2 by terrestrial ecosystems is crucial. Our study uses outputs from Earth system models in Coupled Model Intercomparison Project (CMIP6) to analyze the future trends and driving forces of negative extreme events in gross primary production (GPP). We found that under a high‐emission scenario (SSP5‐8.5), global GPP loss linked to negative extreme events of increasing severity and duration almost doubled by the end of the 21st century compared with current levels. Under a strong mitigation scenario (SSP1‐2.6), negative GPP extremes increase in regions such as tropical forests, southern China, and boreal forest zones despite a relatively stable global total GPP loss. Compound hot and dry conditions, the main driver of negative GPP extremes, contributed to more than 40% of the GPP extremes under both scenarios. Compared with those in CMIP5, the latest models in CMIP6 project more negative GPP extremes than positive extremes across most regions. These results emphasize the urgent need for action to mitigate and adapt to the escalating damage caused by climate extremes on future ecosystem productivity. Key Points: A notable increase in negative gross primary production (GPP) extremes is found under SSP5‐8.5, characterized by longer durations and greater magnitudes of eventsCompound hot and dry conditions are the dominant driver, contributing to >40% of the negative GPP extremes under both SSP5‐8.5 and SSP1‐2.6Compared with CMIP5, the Coupled Model Intercomparison Project (CMIP6) models project more negative GPP extremes than positive extremes across most regions [ABSTRACT FROM AUTHOR]

Understanding how pollen assemblages represent the local and regional vegetation composition is crucial for palaeoecological research. Here, we analyze 102 surface moss/soil pollen samples collected from four study regions located in various boreal forest vegetation types in Central Siberia. Despite Larix being the most prevalent tree generus in the study area, the proportion of Larix pollen can be as low as 0.6–1.5% (0.4–4.7% on average) even in localities with a high canopy density of the species. No relationship between the quantity of Larix pollen in the spectra and the abundance of Larix in the local vegetation was found. The dominant components of the pollen assemblages are Betula and Alnus fruticosa. The pollen value of Picea is low (2.6–8.2% on average), with higher proportions at sample plots where spruce is abundant in forests. Pinus is a highly prevalent pollen species within its geographical range, comprising up to 40% of pollen assemblages. Outside of the range, the ratio of Pinus pollen was higher in habitats with low canopy density and in treeless ecosystems. The composition of herbaceous pollen and spores is significantly affected by the local plant community, offering more comprehensive insights into past vegetation patterns. [ABSTRACT FROM AUTHOR]

Background. Climate change and continued development in the wildland--urban interface (WUI) have increased risks to property and infrastructure from destructive wildfires. Aims. A better understanding of the factors associated with building survival will promote resilience of WUI communities. Methods. We studied factors associated with the likelihood that a building burned during the 2019 McKinley fire in the Alaska boreal forest, USA. We examined the potential influence of both ecological or socio-economic factors on building loss. Key results. The probability of a building burning was significantly associated (P < 0.001) with a building burning nearby (within 30 m). Having less flammable deciduous cover nearby (within 100 m) improved survival. Buildings with lower value on larger parcels were more likely to burn, as were buildings with larger perimeters. Other important factors associated with burning included the number of buildings both nearby (within 30 m) and within the property parcel boundary. Conclusions. Our results suggest that social and ecological factors contribute to building survival, indicating that a comprehensive social-ecological approach would provide the most effective support to WUI communities with wildfire risks. Implications. A comprehensive approach that integrates social, economic, and ecological factors is important in understanding building loss in WUI wildfires. [ABSTRACT FROM AUTHOR]

Heterobasidion, a significant forest pathogen affecting coniferous forests in the Northern Hemisphere, can infect 27 species of coniferous trees, leading to widespread forest mortality. It has already caused considerable damage to both natural and plantation forests in Europe. As essential components of the global ecosystem, forests are increasingly affected by ongoing environmental changes. The ability to accurately predict and effectively respond to pathogen outbreaks across different habitats is becoming increasingly critical. This study employs an optimized MaxEnt model in conjunction with six Global Climate Models (GCMs) to simulate and predict the potentially suitable distributions and changes of three Heterobasidion species in Europe (Heterobasidion abietinum, Heterobasidion annosum sensu stricto, Heterobasidion parviporum) under current conditions and four future climate scenarios (SSP126, SSP245, SSP370, and SSP585) for the period 2081–2100. The objective of this analysis is to assess the potential effects of climate change on the distribution of Heterobasidion species. The results indicate that the distributions of the three Heterobasidion species are influenced by factors such as temperature and precipitation. By 2081–2100, under most climate scenarios, except for the SSP585 scenario, the distribution areas of the three Heterobasidion species show an expansion trend. Notably, Heterobasidion abietinum showed the most significant expansion of its suitable habitat, while the expansion of low-suitability areas for Heterobasidion parviporum and Heterobasidion annosum sensu stricto was more pronounced. Heterobasidion abietinum is projected to shift southward due to factors such as precipitation, while Heterobasidion parviporum and Heterobasidion annosum sensu stricto are expected to migrate northward, influenced by factors such as temperature and host tree species. [ABSTRACT FROM AUTHOR]

The roles of diurnal temperature in providing heat accumulation and chilling requirements for vegetation spring phenology differ. Although previous studies have established a stronger correlation between leaf onset and diurnal temperature than between leaf onset and average temperature, current research on modeling spring phenology based on diurnal temperature indicators remains limited. In this study, we confirmed the start of the growing season (SOS) sensitivity to diurnal temperature and average temperature in boreal forest. The estimation of SOS was carried out by employing K-Nearest Neighbor Regression (KNR-TDN) model, Random Forest Regression (RFR-TDN) model, eXtreme Gradient Boosting (XGB-TDN) model and Light Gradient Boosting Machine model (LightGBM-TDN) driven by diurnal temperature indicators during 1982–2015, and the SOS was projected from 2015 to 2100 based on the Coupled Model Intercomparison Project Phase 6 (CMIP6) climate scenario datasets. The sensitivity of boreal forest SOS to daytime temperature is greater than that to average temperature and nighttime temperature. The LightGBM-TDN model perform best across all vegetation types, exhibiting the lowest RMSE and bias compared to the KNR-TDN model, RFR-TDN model and XGB-TDN model. By incorporating diurnal temperature indicators instead of relying only on average temperature indicators to simulate spring phenology, an improvement in the accuracy of the model is achieved. Furthermore, the preseason accumulated daytime temperature, daytime temperature and snow cover end date emerged as significant drivers of the SOS simulation in the study area. The simulation results based on LightGBM-TDN model exhibit a trend of advancing SOS followed by stabilization under future climate scenarios. This study underscores the potential of diurnal temperature indicators as a viable alternative to average temperature indicators in driving spring phenology models, offering a promising new method for simulating spring phenology. [ABSTRACT FROM AUTHOR]

American martens (Martes americana) are often targeted by fur trappers across their distributional range; yet, there are few studies to assess the sustainability of harvest. In the absence of reliable information on abundance, data on the demographics of the harvested segment of populations can be used to provide insights on harvest sustainability. In response to concerns by some fur trappers that marten abundance was low in some areas, we collected 2,394 marten carcasses from three regions of Yukon, Canada, to investigate demographic trends in harvested martens among and within eight trapping seasons (1 November to 28 February; 2002/2003 to 2009/2010). We found consistently higher proportions of females in the harvest (42%) than recommended thresholds or previously reported for other localities. Juveniles made up approximately half of the overall harvest, and the proportion of juveniles varied significantly among trapping seasons (range = 2–90%). During trapping seasons with < 50% juveniles in the harvest, demographic harvest indicators showed signs of unsustainable harvest beginning in December. We also observed higher daily harvest rates (i.e., total number of animals harvested) in early winter and lowest harvest rates in February. Our results suggest that martens in a quota-free system were periodically vulnerable to local over-harvest. Much of the Yukon is remote with likely little trapping pressure, effectively providing harvest refugia for martens and allowing for continual over-harvest in areas with significant trapping pressure. As such, identifying and maintaining putative harvest refugia will be key to ensuring marten harvest is sustainable at broader temporal and spatial scales, especially in the absence of annually adjusted quotas. Regardless, ensuring sustainable harvest of this small carnivore in the future will require improvements to monitoring marten and the availability of their cyclic prey, continued stewardship by trappers, and possibly establishing quotas in areas of concern. Mandatory harvest reporting can aid in evaluating harvest sustainability at broad temporal and spatial scales. [ABSTRACT FROM AUTHOR]

At the northern high latitudes, rapid warming, associated changes in the hydrological cycle, and rising atmospheric CO2 concentrations, [CO2], are observed at present. Under rapid environmental changes, it is important to understand the current and future trajectories of the CO2 budget in high-latitude ecosystems. In this study, we present the importance of anomalous wet conditions and rising [CO2] on the long-term CO2 budget based on two decades (2003-2022) of quasicontinuous measurements of CO2 flux at a poorly drained black spruce forest on permafrost peat in interior Alaska. The long-term CO2 budget for the black spruce forest was a small sink of -53 ± 63 g C m-2 y-1. The CO2 sink increased from 49 g C m-2 y-1 for the first decade to 58 g C m-2 y-1 for the second decade. The increased CO2 sink was attributed to an 11.3% increase in gross primary productivity (GPP) among which 9% increase in GPP was explained by a recent increase in precipitation. Furthermore, a 3% increase in GPP in response to a 37-ppm increase in [CO2] was estimated from the data-model fusion. Our study shows that understanding the coupling between hydrological and carbon cycles and the CO2 fertilization effect is important for understanding the current and future carbon budgets of high-latitude ecosystems in permafrost regions. [ABSTRACT FROM AUTHOR]