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Peatlands in the Canadian boreal forest are being negatively impacted by anthropogenic climate change, the effects of which are expected to worsen. Peatland types and sub‐classes vary in their ecohydrological characteristics and are expected to have different responses to climate change. Large‐scale modelling frameworks such as the Canadian Model for Peatlands, the Canadian Fire Behaviour Prediction System and the Canadian Land Data Assimilation System require peatland maps including information on sub‐types and vegetation as critical inputs. Additionally, peatland class and vegetation height are critical variables for wildlife habitat management and are related to the carbon cycle and wildfire fuel loading. This research aimed to create a map of peatland sub‐classes (bog, poor fen, rich fen permafrost peat complex) for the Canadian boreal forest and create an inventory of peatland vegetation height characteristics using ICESat‐2. A three‐stage hierarchical classification framework was developed to map peatland sub‐classes within the Canadian boreal forest circa 2020. Training and validation data consisted of peatland locations derived from various sources (field data, aerial photo interpretation, measurements documented in literature). A combination of multispectral data, L‐band SAR backscatter and C‐Band interferometric SAR coherence, forest structure and ancillary variables was used as model predictors. Ancillary data were used to mask agricultural areas and urban regions and account for regions that may exhibit permafrost. In the first stage of the classification, wetlands, uplands and water were classified with 86.5% accuracy. In the second stage, within the wetland areas only, peatland and mineral wetlands were differentiated with 93.3% accuracy. In the third stage, constrained to only the peatland areas, bogs, rich fens, poor fens and permafrost peat complexes were classified with 71.5% accuracy. Then, ICESat‐2 ATL08 spaceborne lidar data were used to describe regional variations in peatland vegetation height characteristics and regional and class‐wise variations based on a boreal forest wide sample. This research introduced a comprehensive large‐scale peatland sub‐class mapping framework for the Canadian boreal forest, presenting the first moderate resolution map of its kind. [ABSTRACT FROM AUTHOR]

Recently burned boreal forests have lower aboveground fuel loads, generating a negative feedback to subsequent wildfires. Despite this feedback, short‐interval reburns (≤20 years between fires) are possible under extreme weather conditions. Reburns have consequences for ecosystem recovery, leading to enduring vegetation change. In this study, we characterize the strength of the fire‐fuel feedback in recently burned Canadian boreal forests and the weather conditions that overwhelm resistance to fire spread in recently burned areas. We used a dataset of daily fire spread for thousands of large boreal fires, interpolated from remotely sensed thermal anomalies to which we associated local weather from ERA5‐Land for each day of a fire's duration. We classified days with >3 ha of fire growth as spread days and defined burned pixels overlapping a fire perimeter ≤20 years old as short‐interval reburns. Results of a logistic regression showed that the odds of fire spread in recently burned areas were ~50% lower than in long‐interval fires; however, all Canadian boreal ecozones experienced short‐interval reburning (1981–2021), with over 100,000 ha reburning annually. As fire weather conditions intensify, the resistance to fire spread declines, allowing fire to spread in recently burned areas. The weather associated with short‐interval fire spread days was more extreme than the conditions during long‐interval spread, but overall differences were modest (e.g. relative humidity 2.6% lower). The frequency of fire weather conducive to short‐interval fire spread has significantly increased in the western boreal forest due to climate warming and drying (1981–2021). Our results suggest an ongoing degradation of fire‐fuel feedbacks, which is likely to continue with climatic warming and drying. [ABSTRACT FROM AUTHOR]

The impact of root water uptake on duff (both fibric and humic horizons) moisture was investigated at deciduous, mixedwood, and conifer stands in Ontario, Canada. Roots were actively excluded from the duff layer using geotextiles inserted at the duff-mineral soil interface and along the plot edges; liquid and vapour water flow was otherwise not affected by the geotextiles. Root exclusion caused little difference in duff moisture content prior to early June, after which the root exclusion plots remained at 15%-20% volumetric water content, whereas root-intact plots declined to as low as 5% volumetric water content during rain-free periods. Only in the root-intact plots did the duff water content reach sufficiently low levels that duff evaporation was limited by low water content. The net effect of root exclusion was to reduce the cumulative growing season water loss in the duff by 19%-31%, depending on the stand type. Root exclusion also decreased the number of days with a high probability of duff smouldering from as many as 72 [days-year.sup.-1] to as few as 0 [days-year.sup.-1]. This root exclusion experiment provides a model for short-term duff moisture transitions under thinned forests such as those forests under community wildfire protection. Key words: forest floor, evaporation, hydrology, forest thinning, smouldering. L'impact de l'absorption d'eau par les racines sur l'humidite de l'humus (horizons fibrique et humique) a ete etudie dans des peuplements feuillus, mixtes et resineux en Ontario, au Canada. Les racines ont ete activement exclues de la couche d'humus a l'aide de geotextiles inseres a l'interface de l'humus et du sol mineral ainsi qu'en bordure de la parcelle. La circulation de l'eau sous forme de vapeur ou liquide n'a pas ete affectee par le geotextile. L'exclusion des racines a eu peu d'impact sur l'humidite de l'humus avant le debut du mois de juin, apres quoi les parcelles ou les racines etaient exclues ont conserve une humidite volumique de 15 % a 20 % tandis qu'elle a diminue jusqu'a un minimum de 5 % dans les parcelles temoins durant les periodes sans pluie. L'humidite de l'humus a atteint des niveaux suffisamment faibles pour que l'evaporation dans l'humus soit limitee par la faible teneur en eau seulement dans les parcelles temoins. L'effet net de l'exclusion des racines etait de reduire la perte d'eau cumulative de 19 % a 31 % dans l'humus durant la saison de croissance dependamment des types de peuplements. L'exclusion des racines a aussi reduit le nombre de jours durant lesquels il y avait une probabilite elevee de feu couvant dans l'humus d'un maximum de 72 jours par annee a aussi peu que zero. Cette experience d'exclusion des racines fournit un modele d'evolution a court terme de l'humidite de l'humus dans les forets eclaircies comme c'est le cas lorsqu'on a recours a l'eclaircie pour proteger les communautes contre les feux de foret. [Traduit par la Redaction] Mots-cles: couverture morte, evaporation, hydrologie, eclaircie des forets, feu couvant., Introduction The duff layer in boreal forest stands plays an important role in the ignition of lightning-caused wildfire (Wotton and Martell 2005), as well as in the effort required for [...]

Mechanical mastication is becoming a common fuel management treatment to reduce vertical fuel connectivity, as well as crown fire initiation and potential fire-line intensity, but the moisture dynamics of these novel fuel types have been largely unstudied. We recorded concurrent in situ meteorological observations with moisture and temperature profiles (at depths of 5 and 13 cm) for masticated fuel beds in three treatments in a lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) black spruce (Picea mariana (Mill.) B.S.P.) boreal stand located in the Upper Foothills of west-central Alberta. Mulch at the 5 cm depth remained at or near 100% moisture content for a majority of the observation period within the treatment that lacked any residual canopy cover. Only during a 10-day rain-free period was substantial drying observed at a depth of 5 cm. At the interface with the underlying duff layer, mulch remained at upwards of 150% moisture content. Drying was typically Key words: fuel management, fuel treatments, mulching, chipping, moisture modelling. Le dechiquetage mecanique est sur le point de devenir un traitement courant de gestion des combustibles pour reduire la connectivite verticale des combustibles aussi bien que l'initiation des feux de cime et l'intensite potentielle de la ligne de feu, mais la dynamique de la teneur en eau de ces nouveaux types de combustibles a tres peu ete etudiee. Nous avons couple des observations meteorologiques in situ a des profils de teneur en eau et de temperature (a des profondeurs de 5 et 13 cm) pour des lits de combustibles dans trois traitements effectues dans un peuplement de foret boreale compose de pin tordu latifolie (Pinus contorta Dougl. var. latifolia Engelm.) et d'epicea noir (Picea mariana (Mill.) B.S.P.) et situe dans la partie superieure des contreforts des Rocheuses dans le centreouest de l'Alberta. A une profondeur de 5 cm, le paillis a conserve une teneur en eau de ou pres de 100 % pendant la majeure partie de la periode d'observation dans le traitement oU il ne restait aucun couvert residuel. Un assechement substantiel a ete observe a une profondeur de 5 cm seulement au cours d'une periode de 10 jours sans pluie. A l'interface avec la couche d'humus sous-jacente, le paillis a conserve une teneur en eau de plus de 150 %. L'assechement etait typiquement inferieur a 10 % du taux d'evaporation potentielle sauf les jours qui suivaient une pluie alors qu'un assechement equivalant a 25-100 % de l'evaporation potentielle a ete observe. Au chapitre des proprietes thermiques, le paillis avait une diffusivite thermique cinq fois plus elevee que les sols mais inferieure a un amas de combustibles, ce qui indique que les lits de combustibles dechiquetes ont des regimes thermal et hydrique qui ressemblent davantage a ceux des sols qu'a ceux des amas de combustibles et qui sont domines par la diffusion et accentues par une advection mineure. Le faible mouvement de l'eau observe des profondeurs vers la surface a favorise une teneur en eau de surface tres variable qui a cree un paillis de surface dont la temperature etait beaucoup plus elevee que la temperature de l'air durant les periodes de plein ensoleillement. Il a ete demontre que de telles temperatures excessives sont un indicateur efficace du dessechement en surface et de la probabilite elevee d'allumage. [Traduit par la Redaction] Mots-cles : gestion des combustibles, traitements des combustibles, paillage, dechiquetage, modelisation de la teneur en eau., Introduction Fuel management prescriptions are becoming increasingly applied in the wildland-urban interfaces of western Canada, with the goals of reducing fire hazard, moderating fire intensity, and reducing crown fire potential [...]

Biomass burning activities can produce large quantities of smoke and result in adverse air quality conditions in regional environments. In Canada, Environment and Climate Change Canada's (ECCC) operational FireWork air quality forecast system incorporates near-real-time biomass burning emissions to forecast smoke plumes from fire events. The system is based on the ECCC operational Regional Air Quality Deterministic Prediction System (RAQDPS) augmented with near-real-time wildfire emissions using inputs from the Canadian Forest Service's (CFS) Canadian Wildland Fire Information System (CWFIS). Recent improvements to the representation of fire behaviour and fire emissions have been incorporated into the CFS Canadian Forest Fire Emissions Prediction System (CFFEPS). This is a bottom-up system linked to CWFIS in which hourly changes in biomass fuel consumption are parameterized with hourly forecasted meteorology at fire locations. CFFEPS has now also been connected to FireWork. In addition, a plume-rise parameterization based on fire energy thermodynamics is used to define the smoke injection height and the distribution of emissions within a model vertical column. The new system, FireWork-CFFEPS, has been evaluated over North America for July-September 2017 and June-August 2018, both periods when western Canada experienced historical levels of fire activity with poor air quality conditions in several cities as well as other fires affecting northern Canada and Ontario. Forecast results were evaluated against hourly surface measurements for the three pollutant species used to calculate the Canadian Air Quality Health Index (AQHI), namely PM2.5, O3, and NO2, and benchmarked against the operational FireWork system (FireWork-Ops). This comparison shows improved forecast performance and predictive skills for the FireWork-CFFEPS system. Modelled fire plume injection heights from CFFEPS based on fire energy thermodynamics show higher plume injection heights and larger variability. The changes in predicted fire emissions and injection height reduced the consistent over-predictions of PM2.5 and O3 seen in FireWork-Ops. On the other hand, there were minimal fire emission contributions to surface NO2, and results from FireWork-CFFEPS do not degrade NO2 forecast skill compared to the RAQDPS. Model performances statistics are slightly better for Canada than for the U.S., with lower errors and biases. The new system is still unable to capture the hourly variability of the observed values for PM2.5, but it captured the observed hourly variability for O3 concentration adequately. FireWork-CFFEPS also improves upon FireWork-Ops categorical scores for forecasting the occurrence of elevated air pollutant concentrations in terms of false alarm ratio (FAR), and critical success index (CSI). [ABSTRACT FROM AUTHOR]

Wildfires, which constitute the most extensive natural disturbance of the boreal biome, produce a broad range of ecological impacts to vegetation and soils that may influence post-fire vegetation assemblies and seedling recruitment. We inventoried post-fire understory vascular plant communities and tree seedling recruitment in the northwestern Canadian boreal forest and characterized the relative importance of fire effects and fire history, as well as non-fire drivers (i.e., the topoedaphic context and climate), to post-fire vegetation assemblies. Topoedaphic context, pre-fire forest structure and composition, and climate primarily controlled the understory plant communities and shifts in the ranked dominance of tree species (***8% and **13% of variance explained, respectively); however, fire and fire-affected soils were significant secondary drivers of post-fire vegetation. Wildfire had a significant indirect effect on understory vegetation communities through post-fire soil properties (**5%), and fire history and burn severity explained the dominance shifts of tree species (*7%). Fire-related variables were important explanatory variables in classification and regression tree models explaining the dominance shifts of four tree species (R² = 0.43-0.65). The dominance of jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.) increased following fires, whereas that of black spruce (Picea mariana (Mill.) BSP.) and white spruce (Picea glauca (Moench) Voss) declined. The overriding importance of site and climate to post-fire vegetation assemblies may confer some resilience to disturbed forests; however, if projected increases in fire activity in the northwestern boreal forest are borne out, secondary pathways of burn severity, fire frequency, and fire effects on soils are likely to accelerate ongoing climate-driven shifts in species compositions. [ABSTRACT FROM AUTHOR]

The destructive nature of the ~ 590,000 ha Horse River Wildfire in the Western Boreal Plain (WBP), northern Alberta in May of 2016 motivated the investigation of the hydrometeorological conditions that preceded the fire. Historical climate and field hydrometeorological data from a moderate-rich fen watershed were used to identify a) whether the spring 2016 conditions were outside the range of natural variability for WBP climate cycles; b) explain the observed patterns in burn severity across the watershed; and c) identify whether fall and winter moisture signals observed in peatlands and lowland forests in the region are indicative of fire susceptibility. Field hydrometeorological data from the fen watershed confirmed the presence of cumulative moisture deficits prior to the fire. Hydrogeological investigations highlighted the susceptibility of fen and upland areas to water table and soil moisture decline over rain-free periods (including winter), due to the watershed's reliance on supply from localized flow systems originating in topographic highs. Subtle changes in topographic position led to large changes in groundwater connectivity, leading to greater organic soil consumption in wetland margins and at high elevations. The 2016 spring moisture conditions measured prior to the ignition of the fen watershed were not illustrated well by the Drought Code (DC) when standard overwintering procedures were applied. However, close agreement was found when default assumptions were replaced with measured duff soil moisture recharge and incorporated into the overwintering DC procedure. We conclude that accumulated moisture deficits dating back to the summer of 2015 led to the dry conditions that preceded the fire. The infrequent coinciding of several hydrometeorological conditions, including low autumn soil moisture, a modest snowpack, lack of spring precipitation, and high spring air temperatures and winds, ultimately led to the Horse River wildfire spreading widely and causing observed burn patterns. Monitoring soil moisture at different land classes and watersheds would aid management strategies in the production of more accurate overwintered DC calculations, providing fire management agencies early warning signals ahead of severe spring wildfire seasons. [ABSTRACT FROM AUTHOR]