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The most rapid climate warming is occurring in northern, permafrost environments. Peatlands of these regions are particularly sensitive to climate warming, with the high ground ice content of peat plateaux resulting in the formation of collapse scars as ground temperatures warm.To quantify the rates of permafrost thaw and associated vegetation changes, we sampled the plant and lichen communities in transects spanning actively thawing collapse scar margins at sites from mid‐Boreal to Low Subarctic conditions, within Canada's Northwest Territories. Seventeen transects were sampled in 2007/08 and 14 of these were resampled 10 years later.The rate of lateral permafrost thaw of collapse scar margins ranged from −6 to 63 cm year−1 (mean: 22.0 cm ± 4.7 cm year−1 (SE)); variability was high and no trends with respect to latitude or temperature gradients were detected.Plant communities displayed a clear gradient from lichen‐ and ericaceous shrub‐dominated peat plateaux, to collapse scars primarily characterized by Sphagnum mosses and graminoids. Both space‐for‐time (distance from collapsing margin) and direct measurement of 10‐year changes showed a successional sequence following permafrost thaw; floating mat communities characterized by Sphagnum riparium or S. balticum proceeded to lawn communities of S. angustifolium and, finally, to hummock communities with Mylia anomala or S. fuscum. This successional sequence was associated with increased water table depth and lower soil water content in plant communities farther from the actively collapsing front, illustrating that peat growth above the water table was driving plant community successional changes.The most rapid plant community succession occurred in recently thawed environments as peat growth propelled the ground surface above the water table while the slowest succession occurred in the collapse scar hummock communities located farthest from the actively collapsing peat plateau margin.Synthesis. In just 10 years, significant vegetation change was detected, in association with both permafrost thaw and subsequent plant community succession. These changes occurred across a broad climatic and latitudinal gradient, from mid‐Boreal to Low Subarctic and have implications for wildlife, global C cycle and indigenous communities who depend on this landscape for harvesting, spiritual and cultural practices. [ABSTRACT FROM AUTHOR]

Soil moisture and evapotranspiration (ET) are important components of boreal forest hydrology that affect ecological processes and land‐atmosphere feedbacks. Future trends in soil moisture in particular are uncertain. Therefore, accurate modeling of these dynamics and understanding of concomitant sources of uncertainty are critical. Here, we conduct a global sensitivity analysis, Monte Carlo parameterization, and analysis of parameter uncertainty and its contribution to future soil moisture and ET uncertainty using a physically based ecohydrologic model in multiple boreal forest types. Soil and plant hydraulic parameters and LAI have the largest effects on simulated summer soil moisture at two contrasting sites. In future scenario simulations, the selection of parameters and global climate model (GCM) choice between two GCMs influence projected changes in soil moisture and ET about as much as the projected effects of climate change in the less sensitive GCM with a late‐century, high‐emissions scenario, though the relative effects of parameters, GCM, and climate vary among hydrologic variables and study sites. Saturated volumetric water content and sensitivity of stomatal conductance to vapor pressure deficit have the most statistically significant effects on change in ET and soil moisture, though there is considerable variability between sites and GCMs. The results of this study provide estimates of: (a) parameter importance and statistical significance for soil moisture modeling, (b) parameter values for physically based soil‐vegetation‐atmosphere transfer models in multiple boreal forest types, and (c) the contributions of uncertainty in these parameters to soil moisture and ET uncertainty in future climates. Plain Language Summary: Future changes in soil water content and evapotranspiration (ET) in boreal regions will influence forest dynamics, permafrost thaw rates and have the potential to alter feedbacks between the land surface and the atmosphere, potentially influencing regional climate dynamics. These changes are uncertain and difficult to model because of the complexity of the boreal ecological and hydrological systems. In this study, we conduct experiments with a hydrological model to better understand which parameters most influence soil water content and ET, how much uncertainty these parameters contribute, and how specific parameter values affect whether soils become wetter or drier and by how much. We find that the parameters that control how tightly soils retain water and how much plants close their stomata and hence reduce transpiration in response to dry conditions, have the largest influences. Interactions between parameters are also important. Even when these parameter values are constrained by model performance in comparison with observations, parameter choice can determine whether soils become wetter or drier in future conditions. These findings suggest that modelers should carefully consider how parameter selection influences simulated future hydrologic conditions and highlight specific parameters that are worthy of further attention. Key Points: Modeled summer soil moisture at rooting depth is most sensitive to soil and plant hydraulic parameters and parameter interactions.Parameter uncertainty affects projected change in evapotranspiration and θVWC about as much as climate change or choice between two global climate models.We present parameter values useful for hydrologic modeling in multiple boreal forest types while quantifying the impacts of equifinality. [ABSTRACT FROM AUTHOR]

In the northern hemisphere, terrestrial ecosystems transition from net sources of CO2 to the atmosphere in winter to net ecosystem carbon sinks during spring. The timing (or phase) of this transition, determined by the balance between ecosystem respiration (RECO) and primary production, is key to estimating the amplitude of the terrestrial carbon sink. We diagnose an apparent phase bias in the RECO and net ecosystem exchange (NEE) seasonal cycles estimated by the terrestrial carbon flux (TCF) model framework and investigate its link to soil respiration mechanisms. Satellite observations of vegetation canopy conditions, surface meteorology, and soil moisture from the NASA SMAP Level 4 Soil Moisture product are used to model a daily carbon budget for a global network of eddy covariance flux towers. Proposed modifications to TCF include: the inhibition of foliar respiration in the light (the Kok effect); a seasonally varying litterfall phenology; an O2 diffusion limitation on heterotrophic respiration (RH); and a vertically resolved soil decomposition model. We find that RECO phase bias can result from bias in RECO magnitude and that mechanisms which reduce northern spring RECO, like substrate and O2 diffusion limitations, can mitigate the phase bias. A vertically resolved soil decomposition model mitigates this bias by temporally segmenting and lagging RH. Applying these model enhancements at continuous soil respiration (COSORE) sites verifies their improvement of RECO and NEE skill compared to in situ observations (up to ΔRMSE = −0.76 g C m−2 d−1). Ultimately, these mechanisms can improve prior estimates of NEE for atmospheric inversion studies. Plain Language Summary: In the northern hemisphere, the plants and the soil respond to warming temperatures and increasing day lengths in spring and begin to store more carbon than they release to the atmosphere, on average. The timing of this change is very important for accurately modeling how much carbon is stored or released to the atmosphere. We found that a commonly used model of plants and soil has delayed predictions of the timing of this seasonal cycle of carbon. We studied different potential changes to the model, including changes to: how carbon inputs to the soil from plant roots, dead leaves, and woody debris are added over time; how soil microbes respond to high levels of soil moisture; whether the soil is represented by a single layer or by multiple layers at different depths; and how the release of carbon by plants varies with solar radiation. We found that multiple different changes resulted in similar corrections to the seasonal cycle of carbon so long as they reduced or delayed the amount of carbon released during the spring season. We discuss why that is and how it impacts the model's performance and its importance for other modeling studies. Key Points: A bias in the seasonal cycle of net ecosystem exchange at high northern latitudes is identified in a first‐order soil decomposition modelSoil respiration processes that reduce or delay respiration during spring mitigate this phase bias and improve modeling skillIn situ chamber measurements of soil respiration provide validation and verification of model enhancements [ABSTRACT FROM AUTHOR]

Abstract In the northern hemisphere, terrestrial ecosystems transition from net sources of CO2 to the atmosphere in winter to net ecosystem carbon sinks during spring. The timing (or phase) of this transition, determined by the balance between ecosystem respiration (RECO) and primary production, is key to estimating the amplitude of the terrestrial carbon sink. We diagnose an apparent phase bias in the RECO and net ecosystem exchange (NEE) seasonal cycles estimated by the terrestrial carbon flux (TCF) model framework and investigate its link to soil respiration mechanisms. Satellite observations of vegetation canopy conditions, surface meteorology, and soil moisture from the NASA SMAP Level 4 Soil Moisture product are used to model a daily carbon budget for a global network of eddy covariance flux towers. Proposed modifications to TCF include: the inhibition of foliar respiration in the light (the Kok effect); a seasonally varying litterfall phenology; an O2 diffusion limitation on heterotrophic respiration (RH); and a vertically resolved soil decomposition model. We find that RECO phase bias can result from bias in RECO magnitude and that mechanisms which reduce northern spring RECO, like substrate and O2 diffusion limitations, can mitigate the phase bias. A vertically resolved soil decomposition model mitigates this bias by temporally segmenting and lagging RH. Applying these model enhancements at continuous soil respiration (COSORE) sites verifies their improvement of RECO and NEE skill compared to in situ observations (up to ΔRMSE = −0.76 g C m−2 d−1). Ultimately, these mechanisms can improve prior estimates of NEE for atmospheric inversion studies.

At the global level, interest is growing in extending agricultural activities northwards to increase future food production. Agricultural activities are emerging at the local level in the subarctic and Arctic regions in order to adapt to climate change, mitigate food insecurities, and build up food autonomy. This pilot crop management study was situated in the Hudson Bay Lowlands within an isolated, Indigenous community garden site surrounded by a mature shelterbelt. The study's purpose was to compare kale growing in three types of low-cost garden bed treatments (four plots per treatment) under ambient conditions in a subarctic climate. The 2019 study measured aboveground biomass and total leaf surface area of kale, monitored soil climate conditions of each treatment, and deciphered, with regards to regional suitability, the benefits and drawbacks of each garden bed treatment. Kale cultivated in the standard boxes (0.25 m height raised bed) and hügelkultur-style boxes (0.50 m height raised bed, including a layer of buried woody debris) resulted in 44 - 58% more aboveground mass and 52% more total surface area than were yielded in kale cultivated in the ground treatment (not elevated), but these increases did not represent statistically significant differences among treatments (ANOVA, p = 0.12) because of the large variation likely from a small sample size. The two raised box treatments increased early-season soil temperatures by 0.5°C to 2.5°C and reduced soil moisture by 41% - 53% compared to the ground treatment. We determined that the standard box treatment is best suited for the study site for improving soil climate conditions, protecting against water erosion, and decreasing the need to bend over. [ABSTRACT FROM AUTHOR]

Obligatory mine reclamation efforts in the Athabasca oil sands region require leased land to be returned to pre-disturbance function. This entails the re-establishment of key ecosystem services such as carbon sequestration and water and nutrient cycling. Surface-atmosphere exchanges of energy, heat and moisture are critical to ecohydrological processes and feedbacks that govern ecosystem functionality. Eddy covariance and remote sensing measurements were used to examine the temporal changes in energy partitioning of a reclaimed fen-upland watershed during the initial seven years post-construction (2013–2019). Surface conditions evolved from bare ground to robustly vegetated plant communities, altering albedo, surface roughness and plant-mediated shading. Initially in the fen, due to near-surface water table, high soil moisture content and the low albedo (0.09) of bare, wet peat, energy was predominantly partitioned to latent heat (Q E) and exhibited a high degree of decoupled surface-atmosphere conditions (surface-atmosphere decoupling factor (Ω) of 0.49). As the fen plant community developed and stabilized, Q E remained the dominant energy flux, but a larger proportion of available energy was partitioned to sensible heat flux (Q H). Plant establishment altered the biophysical surface through sheltering and shading affecting ground heat flux and supressing surface evaporative losses. Moreover, plant-mediated water loss through stomatal controls resulted in an increase in surface-atmosphere coupling (Ω = 0.32), particularly during drier periods. In the drier upland, plant emergence and establishment was slower than in the fen. Initially, bare ground in the upland resulted in higher albedo (0.20–0.25), and Q E and Q H were similar. Once understory and tree species matured, Q E increased with seasonal trends that mirrored plant phenology. Unlike the fen, the upland continually exhibited a higher degree of surface-atmosphere coupling (Ω ranging between 0.23 and 0.3). By year seven (2019) energy fluxes and intra- and inter-seasonal trends at the constructed watershed were comparable to natural and post-disturbance boreal landscapes indicating the system is evolving towards a functional, reclaimed ecosystem. [Display omitted] • Surface energy fluxes during the initial seven years following reclamation • During bare ground conditions edaphic and atmospheric controls drove energy fluxes • Plant development altered biophysical surface properties, changing albedo • Energy partitioning shifted and exhibited strong biotic controls • By year seven energy dynamics were comparable to that of natural boreal landscapes [ABSTRACT FROM AUTHOR]

The accurate identification of forest degradation and its driving factors is a prerequisite for implementing high-quality forest management. However, distinguishing degradation patterns is often neglected in large-scale forest quality assessments. The indicators were constructed to identify typical forest degradation patterns using remote sensing indexes, followed by an analysis of the spatiotemporal dynamics of forest degradation and quantification of the contributions from various driving factors. The results indicated that the constructed indicators could effectively distinguish typical forest degradation patterns, with a fire degradation identification accuracy of 90.0% and a fitting accuracy of drought and pest degradation higher than 0.7. The cold temperate conifer forest zone had the largest proportion of fire degradation, accounting for 67.7% of the area, and totals of 99.0% of the subtropical evergreen broadleaf forest zone and 92.8% of the temperate conifer and broadleaf mixed forest zone were moderately to severely affected by drought, with long-term stability. Additionally, 0.1% of the temperate grassland region and 0.1% of the cold temperate conifer forest zone underwent severe pest infestations, with a long-term stable trend. Meteorological factors were the primary contributors to all typical degradation patterns, accounting for 81.35%, 58.70%, and 82.29%, respectively. The research developed an index for assessing forest degradation and explained the importance of natural and anthropogenic factors in forest degradation. The results are beneficial for the scientific management of forest degradation and for improving forest management efficiency. [ABSTRACT FROM AUTHOR]

Carbon cycle perturbations in high-latitude ecosystems associated with rapid warming can have implications for the global climate. Belowground biomass is an important component of the carbon cycle in these ecosystems, with, on average, significantly more vegetation biomass belowground than aboveground. Large quantities of dead root biomass are also in these ecosystems owing to slow decomposition rates. Current understanding of how live and dead root biomass carbon pools vary across high-latitude ecosystems and the environmental conditions associated with this variation is limited due to the labor- and time-intensive nature of data collection. To that end, we examined patterns and factors (abiotic and biotic) associated with the variation in live and dead fine root biomass (FRB) and FRB carbon (C), nitrogen (N) and phosphorus concentrations for 23 sites across a latitudinal gradient in Alaska, spanning both boreal forest and tundra biomes. We found no difference in the live or dead FRB variables between these biomes, despite large differences in predominant vegetation types, except for significantly higher live FRB C:N ratios in boreal sites. Soil C:N ratio, moisture, and temperature, along with moss cover, explained a substantial portion of the dead:live FRB ratio variability across sites. We find all these factors have negative relationships with dead FRB, while having positive or no relationship with live FRB. This work demonstrates that FRB does not necessarily correlate with aboveground vegetation characteristics, and it highlights the need for finer-scale measurements of abiotic and biotic factors to understand FRB landscape variability now and into the future. [ABSTRACT FROM AUTHOR]

Key message: Above 40° N/S, increasing latitude is linked to greater post-fire tree regeneration. However, species dominance shifts from conifers to short-lived deciduous trees, which may negatively impact flora, fauna, and ecosystem services dependent on coniferous forests. These results were primarily driven by studies from North America, highlighting the need for more research that directly measures post-fire forest recovery in other high-latitude regions. Context: As the size and frequency of wildfires increase across many regions, high-latitude forests may be at particular risk for decreases in regeneration and state shifts post-fire. Aims: Through this systematic review, we sought to determine the general relationship between post-fire tree regeneration densities and latitude in forests above 40° N/S. We expected regeneration densities post-fire would decrease with increasing latitude, and that forest regeneration would be negatively impacted by high burn severities, forest management, harsh site conditions, and unprotected microsites. We also anticipated that light-demanding species with adaptations to fire would replace shade-tolerant species that lack such adaptations post-fire. Methods: We conducted a literature search that returned over 4500 articles. We selected those that directly measured post-fire regeneration at or above 40° N/S and retained 93 articles for analysis. Fire characteristics, pre- and post-fire tree species compositions and regeneration densities, and regeneration predictors were then extracted from the retained articles. We fit linear mixed models to post-fire regeneration density with latitude and species traits as explanatory variables and also explored the significance and magnitude of predictors that informed post-fire tree species response. Results: Contrary to our expectations, post-fire regeneration increased significantly with latitude. High burn severities and unprotected microsites had negative impacts on post-fire regeneration; higher elevations and more prolific pre- or post-fire reproduction were positively correlated with post-fire regeneration, while management of any type did not have an impact. Conclusion: Although forests are regenerating after wildfires at the most extreme latitudes included in this study (above 55° N), regeneration is often limited to only a handful of genera: aspen (Populus) and birch (Betula), for example. Regeneration was less abundant at the lower range of our study area. Certain lower latitude forests that occupy marginal habitats are under increasing stress from drier, warmer conditions that are exacerbated by wildfires. Results were largely driven by studies from Canada and the USA and may not be applicable to all high-latitude forests. [ABSTRACT FROM AUTHOR]

Background: Directly after snowmelt, northern grasslands typically have highly flammable fuel-beds consisting of 100% grass litter. With green-up, the addition of high-moisture foliage leads to progressively decreasing fire hazard. Aims: Our aim was to create a fire-danger index for northern grasslands that incorporated grass phenology. Methods: We made use of 25 years of Swedish wildfire data and 56 experimental fires conducted during one full fire-season, merged with established models for moisture content and flame spread rates. Refined data on equilibrium moisture content of grass litter were obtained through laboratory tests. Key results: The RING (Rate of spread In Northern Grasslands) model uses cumulative air temperature as a proxy for growing season progression. Three independent functions account for impact of wind, moisture content and the damping effect of live grass, respectively. The latter results in exponentially decaying rate of spread (ROS) with the progressing season. Following the field experiments, green grass proportion as low as 10–20% (live/dead dry-mass) resulted in model-ROS so reduced that the grassland fire season could effectively be considered over. Conclusions: The model, calculated from standard meteorological data only, matches the experimental results and separately performed validation tests, as well as wildfire dispatch data. Implications: RING has been used in Sweden since 2021 and is likely applicable to other northern regions as well. After snowmelt, northern grasslands typically consist of highly flammable grass litter. We analysed a series of experimental grassland fires, as well as Swedish wildfire dispatch data, to isolate the impeding effect of grass phenology on fire propagation. A complete grassfire danger index is presented, likely applicable to most regions with cold (snow-covered) winters. [ABSTRACT FROM AUTHOR]

The Acadian Forest Region is a temperate‐boreal transitional zone in eastern North America which provides a unique opportunity for understanding the potential effects of climate change on both forest types. Leaf phenology, the timing of leaf life cycle changes, is an important indicator of the biological effects of climate change, which can be observed with stationary timelapse cameras known as phenocams. Using four growing seasons of observations for the species Acer rubrum (red maple), Betula papyrifera (paper/white birch) and Abies balsamea (balsam fir) from the Acadian Phenocam Network as well as multiple growing season observations from the North American PhenoCam Network we parameterized eight leaf emergence and six leaf senescence models for each species which span a range in process and driver representation. With climate models from the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) we simulated future leaf emergence, senescence and season length (senescence minus emergence) for these species at sites within the Acadian Phenocam Network. Model performances were similar across models and leaf emergence model RMSE ranged from about 1 to 2 weeks across species and models, while leaf senescence model RMSE ranged from about 2 to 4 weeks. The simulations suggest that by the late 21st century, leaf senescence may become continuously delayed for boreal species like Betula papyrifera and Abies balsamea, though remain relatively stable for temperate species like Acer rubrum. In contrast, the projected advancement in leaf emergence was similar across boreal and temperate species. This has important implications for carbon uptake, nutrient resorption, ecology and ecotourism for the Acadian Forest Region. More work is needed to improve predictions of leaf phenology for the Acadian Forest Region, especially with respect to senescence. Phenocams have the potential to rapidly advance process‐based model development and predictions of leaf phenology in the context of climate change. [ABSTRACT FROM AUTHOR]

Canada's boreal forests and tundra ecosystems are responding to unprecedented climate change with implications for the global carbon (C) cycle and global climate. However, our ability to model the response of Canada's terrestrial ecosystems to climate change is limited and there has been no comprehensive, process‐based assessment of Canada's terrestrial C cycle. We tailor the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC) to Canada and evaluate its C cycling performance against independent reference data. We utilize skill scores to assess model performance against reference data alongside benchmark scores that quantify the level of agreement between the reference data sets to aid in interpretation. Our results demonstrate CLASSIC's sensitivity to prescribed vegetation cover. They also show that the addition of five region‐specific Plant functional types (PFTs) improves CLASSIC's skill at simulating the Canadian C cycle. CLASSIC performs well when tailored to Canada, falls within the range of the reference data sets, and meets or exceeds the benchmark scores for most C cycling processes. New region‐specific land cover products, well‐informed PFT parameterizations, and more detailed reference data sets will facilitate improvements to the representation of the terrestrial C cycle in regional and global land surface models. Incorporating a parameterization for boreal disturbance processes and explicitly representing peatlands and permafrost soils will improve CLASSIC's future performance in Canada and other boreal regions. This is an important step toward a comprehensive process‐based assessment of Canada's terrestrial C cycle and evaluating Canada's net C balance under climate change. Plain Language Summary: Canada plays an important role in the global carbon cycle. Its boreal forests and tundra are responding to climate change. There has not been a comprehensive modeling assessment of Canada's land carbon cycle. We modify our model to better represent the distribution of plants in Canada and to include five new plant‐type representations. We then compare results from our model and other independent observation‐based data sets. Our modifications produced model results that agreed better with the independent data sets. This is an important step toward a comprehensive modeling assessment of Canada's land carbon cycle. Key Points: Using region‐specific prescribed vegetation cover and adding five region‐specific Plant functional types reduced model biases against reference dataCanadian Land Surface Scheme Including Biogeochemical Cycle's performance when tailored to the Canada domain is similar to that for comparisons between independent reference data setsFuture work should focus on boreal disturbance (i.e., fire, insect damage, and harvest), peatlands, and permafrost in Canada and other boreal regions [ABSTRACT FROM AUTHOR]

Natural recovery is a restoration technique that relies on natural ecological processes to reestablish native ecosystems. This "minimal intervention" approach is typically more cost‐effective, less labor intensive, and can result in more diverse communities than more intensive restoration techniques. The purpose of this study was to determine if boreal forest vegetation can reestablish naturally after pipeline construction, and whether a site can be identified as similar to adjacent undisturbed areas within 10 years of pipeline construction. Four naturally recovered pipeline segments (1, 3, 5, and 10 years postreclamation) in west‐central Alberta were assessed. Plots were established on and off each pipeline segment right‐of‐way (ROW) in upland, transitional, and wetland habitats. Vegetation percent cover, vigor, and tree seedling density data were used to determine characteristic and indicator species, regulated weeds and agronomic species, richness, diversity, evenness, and tree establishment for each pipeline segment, habitat type, and site type (on‐ vs. off‐ROW). Threshold values for species richness and community diversity were determined using data collected from sites off‐ROW. Sites which fell within established thresholds were identified as on a trajectory toward restoration within 10 years postconstruction. Metrics for the older pipeline segments, including species richness, diversity, evenness, and seedling count were typically closer to threshold values, and sometimes exceeded them. Only the youngest pipeline segment had tree establishment values below calculated thresholds. This study is the first to provide empirical evidence and a method for identifying successful restoration trajectories for natural recovery of pipeline ROWs in boreal forest. [ABSTRACT FROM AUTHOR]

The Peace River region is one of the northern agricultural frontiers in Canada, undergoing farmland expansion as well as intensification with input-intensive industrial agriculture. The cropping systems evolved with the rotations between annual grain and perennial forage crops as a prudent adaptation to fragile, crust-forming, runoff-prone, poorly developed, platy-structured acidic Luvisolic soils. In recent years, there is a decline in the acreage of perennial forage seed crops leading to simplified low-diversity cropping systems with heavy reliance on external inputs. The production systems have been prone to the rapid evolution of herbicide-resistant weeds, and outbreaks of crop diseases and insect pests in the face of global warming. A number of studies conducted in the Peace River region and other parts of North America have shown multiple benefits of integrating perennial forage crops in the cropping systems. By virtue of high root-to-shoot ratio and perennial growth, forage seed crops can provide multiple ecological services in the fragile Luvisolic soil through increased soil organic matter, carbon sequestration, soil biological diversity, soil structural improvement, nutrient mobilization, crop protection and environmental health, thereby creating conducive effects to the resilient performance of the cropping systems. This review discusses the merits of crop rotations in general and those of perennial forage seed crops in particular in the face of changing climate, with special reference to studies conducted in the Prairies and Peace region of western Canada. Research opportunities are highlighted to elucidate multidimensional ecosystem services from diversified cropping sequences integrating perennial forage seed crops. Au Canada, la région de la rivière de la Paix marque une des limites les plus nordiques de l'agriculture. Les terres arables continuent de s'y étendre et l'agriculture industrielle s'y intensifie grâce à l'usage massif d'intrants. Les systèmes culturaux ont évolué et la prudence a voulu qu'on adopte des assolements annuels de céréales et de plantes fourragères vivaces en raison de la fragilité du sol, constitué de luvisols acides, mal développés, à structure lamellaire, qui forment des croûtes et sont sensibles au ruissellement. Depuis quelques années cependant, on assiste à une diminution de la superficie consacrée à la production de graines de plantes fourragères vivaces et à l'avènement de systèmes culturaux plus simples, moins diversifiés, qui reposent lourdement sur l'apport externe d'intrants. Avec le réchauffement climatique, pareils systèmes favorisent l'apparition rapide d'adventices résistantes aux herbicides, mais aussi de maladies et d'infestations de ravageurs. Plusieurs études réalisées dans la région de la rivière de la Paix et ailleurs en Amérique du Nord ont illustré les nombreux avantages de l'intégration de plantes fourragères vivaces aux systèmes culturaux. En raison de leur rapport racines:pousses élevé et de leur caractère vivace, les cultures grainières de plantes fourragères pourraient améliorer de diverses manières l'écologie fragile des luvisols (hausse de la quantité de matière organique, séquestration du carbone, diversité de la biologie du sol, amélioration de la structure du sol, mobilisation des éléments nutritifs, protection des cultures, vitalité de l'environnement), ce qui rendrait les cultures plus résilientes. Les auteurs examinent les avantages de l'assolement en général et des assolements de culture grainière de plantes fourragères en particulier face au changement climatique, en faisant spécialement référence aux études réalisées dans les Prairies et la région de la rivière de la Paix, dans l'Ouest canadien. Ils signalent les possibilités de recherche qui permettraient d'élucider les services multidimensionnels à l'écosystème attribuables à la diversité des séquences culturales qui intègrent la production des graines de plantes fourragères vivaces. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Motivation: The subdivision of the Earth's terrestrial surface into different biomes, ecozones, bio‐climatic realms or other large ecological land units is an essential reference for global biogeographical and ecological studies. Various classification schemes exist. These differ significantly in terms of the considered criteria for classification and the underlying methodology of class assignments. Evident divergences between global biome concepts are elusive, weakening hereon based analyses and assumptions. Compilation and standardization are essential for obtaining a framework that enables the comparison of different products. To address this need, we created a catalogue of standardized categorial biome maps comprising 31 different global products based on various methodological approaches. These products were processed individually to facilitate their use in large‐scale biogeographical and ecological analyses. Main types of variables contained: We provide a unified RasterStack containing 31 terrestrial biome and land‐cover classifications in different layers. Additional ancillary and processing information is allocated. Spatial location and grain: Global, 10 km × 10 km grain size in equal‐area Mollweide projection. Major taxa and level of measurement: Biomes, ecozones, bio‐climatic zones, and ecological land units. Software format: GeoTiff. [ABSTRACT FROM AUTHOR]

For remote communities in the discontinuous permafrost zone, access to permafrost distribution maps for hazard assessment is limited and more general products are often inadequate for use in local‐scale planning. In this study we apply established analytical methods to illustrate a time‐ and cost‐efficient method for conducting community‐scale permafrost mapping in the community of Whatì, Northwest Territories, Canada. We ran a binary logistic regression (BLR) using a combination of field data, digital surface model‐derived variables, and remotely sensed products. Independent variables included vegetation, topographic position index, and elevation bands. The dependent variable was sourced from 139 physical checks of near‐surface permafrost presence/absence sampled across the variable boreal–wetland environment. Vegetation is the strongest predictor of near‐surface permafrost in the regression. The regression predicts that 50.0% (minimum confidence: 36%) of the vegetated area is underlain by near‐surface permafrost with a spatial accuracy of 72.8%. Analysis of data recorded across various burnt and not‐burnt environments indicated that recent burn scenarios have significantly influenced the distribution of near‐surface permafrost in the community. A spatial burn analysis predicted up to an 18.3% reduction in near‐surface permafrost coverage, in a maximum burn scenario without factoring in the influence of climate change. The study highlights the potential that in an ecosystem with virtually homogeneous air temperature, ecosystem structure and disturbance history drive short‐term changes in permafrost distribution and evolution. Thus, at the community level these factors should be considered as seriously as changes to air temperature as climate changes. [ABSTRACT FROM AUTHOR]

Seismic lines are linear clearings created for oil and gas exploration. Regeneration on seismic lines in Alberta's boreal forest is limited by slow natural recovery, making them persistent features on the landscape and prompting interest in line restoration through vegetation reestablishment. The goal of this study was to establish an effective woody vegetation sampling method for monitoring seismic line regeneration in boreal mixedwood forests. Data collected in belt transects and circular plots were similar, and doubling the area sampled did not impact the results. Based on ease of implementation, a 30 m × 2 m belt transect in the center of a seismic line is the recommended sampling method. However, if woody understory vegetation is also being measured, dividing the belt transect into smaller areas is recommended as a single belt transect yielded less accurate height data than circular plots. Plots were also measured along seismic lines' edge and inner areas to determine if vegetation recovery differs across the width of the line. While all tree responses did not differ between the plot locations, woody understory vegetation was more abundant when measured along the inner seismic line locations. Therefore, if woody understory recovery is the focus of the sampling program, using plots placed across the seismic line width is recommended to prevent overestimation. These recommendations are intended for measuring woody vegetation recovery on 5 m wide seismic lines in upland mixedwood forests in the boreal forest; implementation in other environments or for other response variables requires additional testing. [ABSTRACT FROM AUTHOR]

Permafrost formation and degradation creates a highly patchy mosaic of boreal peatland ecosystems in Alaska driven by climate, fire, and ecological changes. To assess the biophysical factors affecting permafrost dynamics, we monitored permafrost and ecological conditions in central Alaska from 2005 to 2021 by measuring weather, land cover, topography, thaw depths, hydrology, soil properties, soil thermal regimes, and vegetation cover between burned (1990 fire) and unburned terrain. Climate data show large variations among years with occasional, extremely warm–wet summers and cold–snowless winters that affect permafrost stability. Microtopography and thaw depth surveys revealed both permafrost degradation and aggradation. Thaw depths were deeper in post-fire scrub compared to unburned black spruce and increased moderately during the last year, but analysis of historical imagery (1954–2019) revealed no increase in thermokarst rates due to fire. Recent permafrost formation was observed in older bogs due to an extremely cold–snowless winter in 2007. Soil sampling found peat extended to depths of 1.5–2.8 m with basal radiocarbon dates of ~5–7 ka bp, newly accumulating post-thermokarst peat, and evidence of repeated episodes of permafrost formation and degradation. Soil surface temperatures in post-fire scrub bogs were ~1 °C warmer than in undisturbed black spruce bogs, and thermokarst bogs and lakes were 3–5 °C warmer than black spruce bogs. Vegetation showed modest change after fire and large transformations after thermokarst. We conclude that extreme seasonal weather, ecological succession, fire, and a legacy of earlier geomorphic processes all affect the repeated formation and degradation of permafrost, and thus create a highly patchy mosaic of ecotypes resulting from widely varying ecological trajectories within boreal peatland ecosystems. [ABSTRACT FROM AUTHOR]

As climate warms, tree density at the taiga–tundra ecotone (TTE) is expected to increase, which may intensify competition for belowground resources in this nitrogen (N)‐limited environment. To determine the impacts of increased tree density on N cycling and productivity, we examined edaphic properties indicative of soil N availability along with aboveground and belowground tree‐level traits and stand characteristics related to carbon (C) and N cycling across a tree density gradient of monodominant larch (Larix cajanderi) at the TTE in far northeastern Siberia. We found no consistent evidence from soil, tree, or stand‐level N cycling characteristics of lower N availability or greater intraspecific competition for N with increased density. Active layer thickness declined, but resin‐sorbed N and soil organic layer thickness did not covary with increased tree density. There was, however, greater allocation belowground to stand‐level coarse and fine roots with increased tree density, an allocation pattern suggestive of limited soil resources. Foliar traits related to C (%C, δ13C, and resorption) were responsive to density indicating the importance of non‐nutrient resources, like light, to foliar stoichiometry. As tree density increased and individual trees had lower productivity, tree‐level N and biomass pools aboveground and belowground declined tracking decreases in N uptake, N resorption, N use efficiency, and allocation to slow cycling tissues like wood. At the stand level, our findings show high N turnover with increased N acquisition, allocation to short‐lived tissues with relatively high N content and reduced N residence time, and greater stand productivity as tree density increased. Yet, these positive relationships were curtailed at the highest tree densities. Our observations of shifts in biomass, C and N allocation, and loss aboveground, along with greater root density with increased tree density, could have strong impacts on C and N cycling and should be represented in models of TTE dynamics and feedbacks to climate. [ABSTRACT FROM AUTHOR]

The Arctic–Boreal Region (ABR) has a large impact on global vegetation–atmosphere interactions and is experiencing markedly greater warming than the rest of the planet, a trend that is projected to continue with anticipated future emissions of CO2. The ABR is a significant source of uncertainty in estimates of carbon uptake in terrestrial biosphere models such that reducing this uncertainty is critical for more accurately estimating global carbon cycling and understanding the response of the region to global change. Process representation and parameterization associated with gross primary productivity (GPP) drives a large amount of this model uncertainty, particularly within the next 50 years, where the response of existing vegetation to climate change will dominate estimates of GPP for the region. Here we review our current understanding and model representation of GPP in northern latitudes, focusing on vegetation composition, phenology, and physiology, and consider how climate change alters these three components. We highlight challenges in the ABR for predicting GPP, but also focus on the unique opportunities for advancing knowledge and model representation, particularly through the combination of remote sensing and traditional boots‐on‐the‐ground science. [ABSTRACT FROM AUTHOR]

Climate warming in the North could lead to lichen decline within critical woodland caribou habitat. We used repeat measurements of sixty-nine plots over ten years (2007-2008 and 2017-2018) to assess lichen biomass changes under a warming climate along a latitudinal/climatic gradient in northwestern Canada. We compared lichen biomass on sensitive landscape features, including peat plateaux (permafrost-containing bogs), areas of permafrost thaw within the peat plateaux (collapse scars), and low-productivity upland forests occurring on mineral soils. Field-based measures of lichen cover and height were coupled with samples of lichen biomass to develop biomass prediction equations. The optimal model incorporated both cover and height, with landscape feature as a covariate. Although height significantly improved the equation fit, models were successfully developed with cover alone. Modeled lichen biomass differed significantly between landscape features, declining from peat plateau (502 g m-2) to upland forest (54.0 g m-2) and collapse scar (0.690 g m-2) environments. In the absence of permafrost collapse at any monitoring location, lichen biomass declined significantly over the ten years for peat plateaux (-75.6 g m-2) and upland forests (-17.5 g m-2). These results will be important for quantifying landscape-level lichen biomass changes under climate warming in boreal and subarctic environments. [ABSTRACT FROM AUTHOR]

Bryophytes are largely responsible for globally significant carbon accumulation in peatland ecosystems. This accumulation is primarily caused by the slow decomposition of these mosses, which can be attributed to a combination of intrinsic (chemical) characteristics of decaying mosses and extrinsic (environmental) influences. Here we investigated the importance of intrinsic and extrinsic drivers of moss decomposition in peatlands and hypothesized that the early stages of decay will be driven primarily by intrinsic characteristics, while extrinsic drivers will become more important in the later phases of decomposition. We tested this hypothesis by placing litterbags of three moss types (Sphagnum divinum, Sphagnum angustifolium/fallax and Polytrichum sp.) into hummock and hollow microtopographies in a bog and a lawn microtopography in a nearby poor fen in northern Minnesota, USA. Decomposition was measured over a 5‐year period and confirmed our hypothesis; while intrinsic and extrinsic variables were both important in driving decay rates over time, decay in the first year was primarily predicted by litter type, while extrinsic influences (e.g. peat temperature, moisture, nutrient limitation) that varied at peatland and microtopographic scales became more important by year 5. Though the nutrient (i.e. nitrogen [N] and phosphorus [P]) content of decaying mosses did not explain the variation in decay rates among litter types, analysis of N:P in moss litter suggested that litter‐decaying microorganisms became increasingly P‐limited over time. The majority of litter decomposition studies in peatlands are generally of short duration (< 3 years). Our study suggests that longer‐term studies are needed to reveal the roles of multiple drivers of moss decay. Improving the mechanistic understanding of decomposition processes in peatlands will be critical to developing more robust representations of peatlands and their ecosystem processes in carbon and climate models. [ABSTRACT FROM AUTHOR]

The impacts of global environmental change on productivity in northern latitudes will be contingent on nitrogen (N) availability. In circumpolar boreal ecosystems, nonvascular plants (i.e., bryophytes) and associated N2‐fixing diazotrophs provide one of the largest known N inputs but are rarely accounted for in Earth system models. Instead, most models link N2‐fixation with the functioning of vascular plants. Neglecting nonvascular N2‐fixation may be contributing toward high uncertainty that currently hinders model predictions in northern latitudes, where nonvascular N2‐fixing plants are more common. Adequately accounting for nonvascular N2‐fixation and its drivers could subsequently improve predictions of future N availability and ultimately, productivity, in northern latitudes. Here, we review empirical evidence of boreal nonvascular N2‐fixation responses to global change factors (elevated CO2, N deposition, warming, precipitation, and shading by vascular plants), and compare empirical findings with model predictions of N2‐fixation using nine Earth system models. The majority of empirical studies found positive effects of CO2, warming, precipitation, or light on nonvascular N2‐fixation, but N deposition strongly downregulated N2‐fixation in most empirical studies. Furthermore, we found that the responses of N2‐fixation to elevated CO2 were generally consistent between models and very limited empirical data. In contrast, empirical‐model comparisons suggest that all models we assessed, and particularly those that scale N2‐fixation with net primary productivity or evapotranspiration, may be overestimating N2‐fixation under increasing N deposition. Overestimations could generate erroneous predictions of future N stocks in boreal ecosystems unless models adequately account for the drivers of nonvascular N2‐fixation. Based on our comparisons, we recommend that models explicitly treat nonvascular N2‐fixation and that field studies include more targeted measurements to improve model structures and parameterization. [ABSTRACT FROM AUTHOR]

In Canada, fire behaviour is modelled based on a fuel classification system of 16 fuel types. Average fuel loads are used to represent a wide range of variability within each fuel type, which can lead to inaccurate predictions of fire behaviour. Dead and down woody debris (DWD) is a major component of surface fuels affecting surface fuel consumption, potential crown fire initiation, and resulting crown fuel consumption and overall head fire intensity. This study compiled a national database of DWD fuel loads and analysed it for predictive driving variables. The database included DWD fuel loads for all dominant Canadian forest types at three size classes: fine (<1 cm), medium (1–7 cm) and coarse (>7 cm). Predictive models for DWD fuel load by size classes individually and collectively for various forest types and ecozones were analysed. Bioclimatic regime, age, spatial position, drainage, and structural components including diameter at breast height and stem density were significant variables. This study provides tools to improve our understanding of the spatial distribution of DWD across Canada, which will enhance our ability to represent its contribution within fire behaviour and fire effects models. This study looks to identify the variables that characterise fuel loads of dead and down woody debris across Canadian forests, using a compilation of datasets. These data were used to examine the geographic variability in woody debris fuel loads across the country and to determine which factors most significantly influence fuel loading. [ABSTRACT FROM AUTHOR]

Plant isotopic baselines are critical for accurately reconstructing ancient diets and environments and for using stable isotopes to monitor ecosystem conservation. This study examines the stable carbon and nitrogen isotope compositions (δ13C, δ15N) of terrestrial C3 plants in Elk Island National Park (EINP), Alberta, Canada, with a focus on plants consumed by grazers. EINP is located in a boreal mixed woodland ecozone close to the transition area between historic wood and plains bison habitats, and is currently home to separate herds of wood and plains bison. For this study, 165 C3 plant samples (grasses, sedges, forbs, shrubs, and horsetail) were collected from three habitat types (open, closed, and wet) during two seasons (summer and fall). There were no statistically significant differences in the δ13C or δ15N values of grasses, sedges, shrubs and forbs. On the other hand, plant δ13C and δ15N values varied among habitats and plant parts, and the values increased from summer to fall. These results have several implications for interpreting herbivore tissue isotopic compositions: (1) consuming different proportions of grasses, sedges, shrubs, and forbs might not result in isotopic niche partitioning, (2) feeding in different microhabitats or selecting different parts of the same types of plants could result in isotopic niche partitioning, and (3) seasonal isotopic changes in herbivore tissues could reflect seasonal isotopic changes in dietary plants rather than (or in addition to) changes in animal diet or physiology. In addition, the positively skewed plant δ15N distributions highlight the need for researchers to carefully evaluate the characteristics of their distributions prior to reporting data (e.g., means, standard deviations) or applying statistical models (e.g., parametric tests that assume normality). Overall, this study reiterates the importance of accessing ecosystem-specific isotopic baselines for addressing research questions in archaeology, paleontology, and ecology [ABSTRACT FROM AUTHOR]