Canadian Boreal Forest Research Articles

New insights into the drivers of moss‐associated nitrogen fixation and cyanobacterial biomass in the eastern Canadian boreal forest

Abstract Moss‐associated cyanobacteria nitrogen (N2‐) fixation can contribute to support moss growth and constitutes a major source of new N in boreal forest ecosystems. The biomass of moss‐colonizing cyanobacteria and their N2‐fixation are usually considered linearly correlated. Yet, recent evidence has shown that cyanobacterial biomass and N2‐fixation can be decoupled, suggesting that they are not necessary affected by the same environmental and ecological drivers. Climate and nutrients were reported as affecting moss‐associated N2‐fixation, with equivocal results, whereas drivers of moss cyanobacterial biomass remain unclear. In addition, these drivers are often determined through manipulative experiments (e.g. fertilization and incubation) and remain to be validated with complementary observational studies to help us better understand future impacts of global change on the moss–cyanobacteria symbiosis. We hypothesized that moss‐associated cyanobacterial biomass is controlled in situ by factors affecting bacterial growth, whereas N2‐fixation is controlled by factors affecting enzymatic reactions. Using random forests, Spearman correlations and linear mixed‐effects models, we determined the main drivers of cyanobacterial biomass and N2‐fixation of two feather moss species, which were collected over 3 years along a 1000‐km latitudinal transect in the eastern Canadian boreal forest. We found that temperature, precipitation and phosphorus were the main positive drivers of moss cyanobacterial biomass and that temperature and molybdenum were the main positive drivers of N2‐fixation. Vanadium was a negative driver of N2‐fixation, suggesting the use of alternative nitrogenases by cyanobacteria. Both cyanobacterial biomass and N2‐fixation were strongly influenced by the moss species and were negatively correlated with moss C:N stoichiometry, highlighting the role of N2‐fixation in moss N enrichment. Synthesis. We identified for the first time some environmental drivers of moss‐associated cyanobacterial biomass and showed that they contrast with the drivers of N2‐fixation, which should be considered in further research and confirmed in other experimental settings. This is an important advance in our knowledge of moss–cyanobacteria associations, which would greatly help in better predicting the impacts of global change on this symbiosis and on nitrogen inputs in boreal forest ecosystems.

USING RADIOCARBON AGES ON ORGANICS AFFECTED BY FRESHWATER—A GEOLOGIC AND ARCHAEOLOGIC UPDATE ON THE FRESHWATER RESERVOIR AGES AND FRESHWATER DIET EFFECT IN MANITOBA, CANADA

ABSTRACTFreshwater reservoir ages and a potential freshwater diet effect are examined for Manitoba (Canada), using paired samples of contemporaneous terrestrial, freshwater, and omnivore-diet species (Homo sapiens, Gavia sp.). The freshwater diet effect (n=4) varies from 220 to 370 14C years. The FRE (n=12) is temporally variable, with a median of 230 14C years and values up to 880 14C years (or more). Understanding the FRE is important for geologists who reconstruct the postglacial history of an area. It is also important for archaeologists who rely on 14C dating to develop cultural histories, as inhabitants of the Canadian boreal forest have relied upon freshwater resources as a part of their diet. An analysis of the δ13C on 93 freshwater mollusk samples from 11 species demonstrates significant variability, which highlights the difficulty in assigning an “assumed” fractionation correction.

Mapping organic layer thickness and fuel load of the boreal forest in Alberta, Canada

Forest organic layers are important soil carbon pools that can, in the absence of disturbance, accumulate to great depths, especially in lowland areas. Across the Canadian boreal forest, fire is the primary disturbance agent, often limiting organic layer accumulation through the direct consumption of these fuels. Organic layer thickness (OLT) and fuel load (OLFL) are common physical attributes used to characterize these layers, especially for wildland fire science. Understanding the drivers and spatial distribution of these attributes is important to improve predictions of fire behaviour, emissions and effects models. We developed maps of OLT and OLFL using machine learning approaches (weighted K-nearest neighbour and random forests) for the forested region of the province of Alberta, Canada (538, 058 km2). The random forests approach was found to be the best approach to model the spatial distribution of these forest floor attributes. A databased of 3, 237 OLT and 594 OLFL plots were used to train the models. The error in our final model, particularly for OLT (5 cm), was relatively close to the variability we would expect to find naturally (3 cm). The dominant tree species was the most important covariate in the models. Age, solar radiation, spatial location, climate variables and surficial geology were also important drivers, although their level of importance varied between tree species and depended on the modelling method that was used.

Organic carbon stocks, quality and prediction in permafrost-affected forest soils in North Canada

High-latitude soils store a large amount of the global soil organic carbon (SOC). The SOC stocks in mineral soils under different permafrost conditions, however, are underrepresented in global carbon databases. We sampled mineral forest soils under continuous and discontinuous to sporadic permafrost conditions on the Canadian Boreal and Taiga Plain. We determined the SOC stocks in the upper 60 cm of 94 soil pits across eleven sites (5–9 pits per site) and SOC quality using 13C isotopic signatures, C:N ratios and composition of aliphatic/aromatic and cellulose/lignin-like compounds obtained from mid-infrared spectra analyses. Lastly, we evaluated the prediction of SOC stocks in these soils using mid-infrared spectra and partial least square regression modelling (PLSR). The SOC stocks were on average four times higher in soils under continuous permafrost conditions (93.7–203.8 Mg SOC ha−1 in 0–45 cm) compared to soils under discontinuous to sporadic permafrost conditions (26.7–60.2 Mg SOC ha−1 in 0–60 cm). In addition, the SOC stocks were larger at moist and wet locations compared to dryer locations and varied significantly between sites, stressing the importance of small-scale geomorphic differences in controlling SOC in boreal mineral forest soils. Continuous permafrost SOC had a lower degree of decomposition compared to soils under discontinuous and sporadic permafrost. This indicates a potentially large proportion of SOC in boreal mineral soils to be vulnerable to warming associate increases in decomposition. The combination of mid-infrared with PLSR was suitable to predict the SOC stocks (R2 > 0.8) with an average uncertainty of 14–23%, which was less than the observed spatial variability of the field replicates (29–41%). Mid-infrared spectroscopy can thus offer an alternative to fill SOC data gaps of high latitude mineral forest soils and reduce uncertainties originating from the limited number of currently available SOC observations of Canadian boreal mineral forest soils.

On the efficiency of indicator species for broad-scale monitoring of bird diversity across climate conditions

Multiple constraints (e.g., time, funding, expertise) can impede the broad-scale monitoring of human-induced loss of biodiversity. Non-random species co-occurrence provides an opportunity to estimate local species richness by tracking only a few species that are indicators of more global assemblages. Despite promising fine-scale studies, it remains unclear whether such indicator species remain effective over broad spatial extents. We assessed the value of indicator species to consistently predict species richness despite variation in short-term (5–9 years) climate conditions. Our study involves 22,041 point-count stations distributed over 1.75 M km2 of Canadian boreal forest, where 197,000 birds from 216 species were detected. Using null model analysis of species co-occurrence followed by regression analysis, we identified the minimum set of indicator species that can predict 70% of spatial variation in local bird richness in each of eight short-term climate regions. We found that indicators were non-random subsets of the species pool, as they were species whose presence explained a relatively high percentage of variations in species richness within the short-term climate region, and those sharing a relatively high number of significant pairwise associations. Although only 11 to 26 indicator species were needed to predict species richness at the regional scale, 57 of the 216 species pool (26%) were necessary to make predictions over the entire study area. This large number reflects regional variations in the best indicator species, and those that remained indicators in several regions were representative of different species assemblages. Our observations thus cast doubts on the use of indicator species as an effective and efficient tool for biodiversity monitoring under changing climate conditions. Broad-scale (spatial or temporal) use of indicators thus comes with the colossal challenge of having to determine under which new conditions a given set of indicators must be replaced by another, and by which one.

The direct and habitat-mediated influence of climate on the biogeography of boreal caribou in Canada

Effective species conservation efforts require insight into whether a species’ extent of occurrence may shift due to changing climate, habitat loss, or both. The extent of occurrence of the threatened boreal population of woodland caribou (Rangifer tarandus caribou; caribou) has contracted due to environmental and anthropogenic disruption, with further contractions predicted as boreal habitat shifts with the changing climate. However, the direct and indirect climate drivers of caribou extent of occurrence have not been explicitly investigated. We estimated and compared the influence of climate and habitat drivers on the occurrence of caribou ranges across the Canadian boreal forest. We fit path models that estimated the direct effects of climate on caribou range occurrence and its indirect effect through climate's influence on caribou habitat (i.e., forest cover, presence of peatland, human disturbance and wildfire). Our analysis suggests that the distribution of caribou ranges is less sensitive to the direct effects of climate than to those of habitat and human disturbance. However, through its relationship to caribou habitat, climate exerts indirect influence over the distribution of caribou. As the climate changes, future distributions of caribou may be more heavily relegated to refuge habitats, particularly peatlands in the western boreal forest. Our biogeographical approach enables more informed decisions for large-scale caribou conservation efforts (e.g. establishment of protected areas, habitat restoration) that account for potential shifts in the distribution of caribou under changing environmental and climatic conditions.

A multi-scale dendroclimatological analysis of four common species in the southern Canadian boreal forest

A comprehensive assessment of the tree growth/climate relationship was undertaken to better understand the potential impacts of climate change on the growth dynamics of four widespread and common boreal tree species, namely jack pine (Pinus banksiana), black spruce (Picea mariana), eastern larch (Larix laricina), and trembling aspen (Populus tremuloides), located at the southern limits of the Canadian boreal forest. Over intra-annual time scales, results show that precipitation is likely the main driver of stem radius change (∆R), with jack pine radius exhibiting the most consistent positive relationship. Precipitation had a stronger relationship with stem radius variation in black spruce and eastern larch during periods when volumetric water content (VWC) in the root zone was below average, pointing to the likelihood that certain species rely more heavily on available moisture in the uppermost layers of the soil column to replenish stem water, especially during extended dry periods. Warm air temperatures had an immediate negative impact on stem water content due to transpiration. This was most marked during periods of reduced moisture availability in the root zone, when trees are more susceptible to net water volume loss. During periods when moisture was not limiting, a positive relationship between lagged air temperature and ∆R was detected. Warm air temperatures may therefore play an important role in stimulating radial growth when moisture requirements are met. At annual temporal resolution, the growth/climate relationship changed over the lifetime of our study species. Over the last several decades, the relationship between precipitation and annual radial tree growth has weakened, while positive relationships between spring and summer air temperature and annual radial tree growth have emerged, likely signaling a decrease in moisture limitations, and a positive response to spring warming. Our findings reveal that boreal forest tree species may benefit from spring and summer warming over the near term, providing there is sufficient moisture to support growth. Over the long term, rates of evapotranspiration are expected to overshadow gains in moisture related to an increase in precipitation. Under these circumstances, we are likely to see reduced growth rates and an increasingly negative response of boreal tree species growth to warm air temperatures.

A review of exotic earthworm observations in the Canadian boreal forest and taiga zones

Over the past few decades there has been increasing concern that boreal forests could convert from a carbon sink to a carbon source, thus accentuating the effects of climate change. Although forest fires are generally regarded as mainly responsible for causing boreal forests to transition to a carbon source, other factors, such as the activity of exotic earthworm species, could also play an important role. Invasive and exotic species of earthworm can affect nutrient cycling, biodiversity, and forest dynamics. In this context, greater knowledge of the distribution of exotic species of earthworm could help researchers to understand the likely changes in the ecosystems that they have colonized. Herein, we report the results of an exhaustive literature review of the presence of exotic species of earthworm in the Canadian boreal forest and taiga zones. We identified 230 sectors containing 14 earthworm species (11 exotic, two native, and one putative native) in six provinces and three territories across Canada’s boreal forest and taiga zone. We also report 23 as-yet unpublished observations from the province of Quebec. We noted the presence of earthworms in environments (acid soils, harsh climate) that were historically considered inadequate for their survival. This suggests that the portion of Canada’s boreal forests suitable for the presence or colonization of exotic species of earthworm is larger than was previously believed. This study represents the first compilation of locations with exotic species of earthworm in this large northern area. Factors that could affect their distribution and potential effects on boreal ecosystems are also discussed. We also report that several earthworm species seem to be overcoming the previously assumed limitations of temperature and soil pH.

Effect of feature standardization on reducing the requirements of field samples for individual tree species classification using ALS data

The objective of this study was to evaluate the effectiveness of three standardization approaches for airborne laser scanning (ALS) feature values used for individual tree species classification. This study is the first effort to assess the transferability of forest tree species classification models derived using monospectral and multispectral ALS data. Three research questions were asked; (1) How do the ALS features differ for the same species in different though comparable ecological regions? (2) How to train a model with one sub-population and apply it in another sub-population? (3) How to fuse models for two areas into a global model? To answer these questions, both 3D and intensity features were extracted from the ALS data from Canadian boreal forests. The ALS feature values were standardized in two different scenarios, disjoint areas, and partially overlapping areas, across three study areas. Feature standardization approaches were used: histogram matching, median-based standardization, and linear regression-based standardization. A linear discriminant analysis (LDA) and random forest (RF) algorithms were employed to classify the study area’s major tree species. The Bhattacharyya distance and overall accuracy (OA) were used to assess the classification model performance before and after the feature standardization. Three major conclusions were drawn. First, the Bhattacharyya distance confirmed that intensity features varied across study areas and among tree species, while 3D features were relatively less variable. Second, for the disjoint areas (York Regional Forest (YRF)) and Petawawa Research Forest (PRF)), the feature standardization procedure consistently improved the OA classification for both local model and global model approaches. The feature standardization improved the OA from 16% to 54% using LDA, and from 20% to 55% using RF in the local model. The improvement was from 58% to 66% using LDA, and from 63% to 70% using RF in the global model. It can be concluded that intensity features (at YRF and PRF) were most prone to differ between areas because of scanners and acquisition settings. If ALS data were available from both areas, intensity features need to be normalized so that the local model can be transferred. Finally, for the partially overlapping areas (the northern and southern parts of Black Brook Forest), this study suggests that normalization of ALS data is not needed because they were captured using quite similar ALS settings.

Short- to medium-term effects of crown and surface fires on soil respiration in a Canadian boreal forest

Fires are an important perturbation for the carbon (C) dynamics of boreal forests, especially when they are stand-replacing. In North American boreal forests, crown fires are predominant and, therefore, the most studied. However, surface fires can also lead to major tree mortality with substantial implications for the C balance. Here, we assess the short- (hours to days) to medium-term (1–3 years) effects of the different fire types (surface vs. crown) on the postfire soil C effluxes in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) forest stands in the Northwest Territories, Canada. We found that while trees were instantly killed by the four crown fires studied, trees also died within 1 year after two of three surface fires studied. Associated with this tree mortality, soil autotrophic respiration decreased after both fire types, although at different timings. The soil heterotrophic respiration was either lower or unchanged when measured 1–3 years after either fire type but was increased when measured immediately after a surface fire, possibly due to the interaction between ash generation and wetting performed to suppress the fire. Our results suggest that both fire types can thus substantially alter C fluxes in the short to medium term, both through changes in vegetation and the soil environment.

Small but visible: Predicting rare bryophyte distribution and richness patterns using remote sensing-based ensembles of small models.

In Canadian boreal forests, bryophytes represent an essential component of biodiversity and play a significant role in ecosystem functioning. Despite their ecological importance and sensitivity to disturbances, bryophytes are overlooked in conservation strategies due to knowledge gaps on their distribution, which is known as the Wallacean shortfall. Rare species deserve priority attention in conservation as they are at a high risk of extinction. This study aims to elaborate predictive models of rare bryophyte species in Canadian boreal forests using remote sensing-derived predictors in an Ensemble of Small Models (ESMs) framework. We hypothesize that high ESMs-based prediction accuracy can be achieved for rare bryophyte species despite their low number of occurrences. We also assess if there is a spatial correspondence between rare and overall bryophyte richness patterns. The study area is located in western Quebec and covers 72,292 km2. We selected 52 bryophyte species with <30 occurrences from a presence-only database (214 species, 389 plots in total). ESMs were built from Random Forest and Maxent techniques using remote sensing-derived predictors related to topography and vegetation. Lee’s L statistic was used to assess and map the spatial relationship between rare and overall bryophyte richness patterns. ESMs yielded poor to excellent prediction accuracy (AUC > 0.5) for 73% of the modeled species, with AUC values > 0.8 for 19 species, which confirmed our hypothesis. In fact, ESMs provided better predictions for the rarest bryophytes. Likewise, our study revealed a spatial concordance between rare and overall bryophyte richness patterns in different regions of the study area, which have important implications for conservation planning. This study demonstrates the potential of remote sensing for assessing and making predictions on inconspicuous and rare species across the landscape and lays the basis for the eventual inclusion of bryophytes into sustainable development planning.

Effects of Forest Fires on Diurnal Land Surface Temperature in Boreal Forests

Wildfires are the most prevalent natural disturbance in Canadian boreal forests, which could cause postfire land surface temperature change (ΔLST) through biophysical processes. Here, we used multiple remote sensing products and spatial GIS analysis methods to investigate the fire-induced daytime and nighttime LST change over Canada’s boreal forest from 2004 to 2017. We further examined the differences of ΔLST among three forest types. We found a pronounced asymmetry in diurnal ΔLST, characterized by daytime warming in contrast to nighttime cooling. The differences in the effects of forest fires on diurnal surface temperature were also exhibited among three forest types. The effect of wildfires on diurnal surface temperature is more significant in evergreen forest areas than in deciduous forest areas. These results also revealed that species composition has a strong influence on the climate effects of fire in boreal regions.

Crown fuel consumption in Canadian boreal forest fires

Predictive crown fuel consumption models were developed using empirical data from experimental burning projects. Crown fuel load for foliage, bark, branchwood and stemwood were calculated for live overstorey and understorey trees in each plot using nationally derived tree biomass algorithms. Standing dead tree branchwood and stemwood biomass were similarly calculated. Crown bulk density values were calculated for all non-stemwood fuel components. Factors that affect the initiation and spread of crown fires (live crown base height, foliar moisture content, surface fuel consumption, critical surface fire spread rate, critical surface fire intensity) and components of the Canadian Forest Fire Weather Index System were not statistically significant variables. Crown bulk density was moderately correlated with crown fuel consumption but was not an influential factor. A new crown fuel consumption model was developed by regression analysis using fuel load of overstorey tree foliage and standing dead tree branchwood, and fire rate of spread through crown fraction burned. A simpler model was developed using only overstorey tree foliage fuel load and fire rate of spread. Both models provide forest and fire management agencies with enhanced ability to determine crown fuel consumption, fire behaviour and carbon emissions in boreal fires using basic forest inventory or biomass/carbon datasets.

Converging and diverging burn rates in North American boreal forests from the Little Ice Age to the present

Warning This article contains terms, descriptions, and opinions used for historical context that may be culturally sensitive for some readers. Background Understanding drivers of boreal forest dynamics supports adaptation strategies in the context of climate change. Aims We aimed to understand how burn rates varied since the early 1700s in North American boreal forests. Methods We used 16 fire-history study sites distributed across such forests and investigated variation in burn rates for the historical period spanning 1700–1990. These were benchmarked against recent burn rates estimated for the modern period spanning 1980–2020 using various data sources. Key results Burn rates during the historical period for most sites showed a declining trend, particularly during the early to mid 1900s. Compared to the historical period, the modern period showed less variable and lower burn rates across sites. Mean burn rates during the modern period presented divergent trends among eastern versus northwestern sites, with increasing trends in mean burn rates in most northwestern North American sites. Conclusions The synchronicity of trends suggests that large spatial patterns of atmospheric conditions drove burn rates in addition to regional changes in land use like fire exclusion and suppression. Implications Low burn rates in eastern Canadian boreal forests may continue unless climate change overrides the capacity to suppress fire.

Evaluation of biological nitrogen fixation in coarse woody debris from Eastern Canadian boreal forests

The contribution of Coarse Woody Debris (CWD) to N inputs in boreal ecosystems has been reported in intensively managed Scandinavian forests in Europe and in Pacific coastal rainforest in North America. These estimates range from 0.085 to 2 kg N ha−1 y−1. Data from Eastern Canadian forests that receive fewer sylvicultural treatments than do Scandinavian forests and are exposed to a drier climate than the Canadian rainforest are scare. We evaluated contributions of CWD to total BNF in two forest sites dominated by balsam fir and black spruce. We also measured the conversion ratio (R ratio = ARA/N2) for the acetylene reduction assay, which is the method most often used to estimate N2-fixation, using parallel 15N2 incubations to account for potential methodological biases. We further tested two factors that can affect the R ratio, hance quality of BNF estimates in deadwood; inhibition of N2-fixing methanotrophs by acetylene and molybdenum limitation of N2-fixation. We report that N2-fixation by CWD in balsam fir and black spruce from eastern boreal forest is low (0.05–0.12 kg N ha−1y−1) compared to other estimates for coniferous forests. We also show that moss-covered CWD can significantly contribute to CWD N2-fixation and that improper validation of the ARA can lead to significant underestimation of N inputs.

Riccardia vitrea (Aneuraceae), a liverwort species new to China and North America

Yin, X.-B., Lamara, M., Liyanage, N. S., Zhu, R.-L. & Fenton, N. J. 2021. Riccardia vitrea (Aneuraceae), a liverwort species new to China and North America. – Herzogia 34: 279 –285. The liverwort species Riccardia vitrea Furuki (Aneuraceae) is reported for the first time for China and North America (Canada). This report is primarily focused on its occurrence in Canada.. Riccardia vitrea is characterized by numerous small oil bodies in both epidermal and inner cells, and by prostrate, wide and poorly developed ultimate pinnules, and is thus easily distinguished from other Canadian species of the genus. This constitutes a significant extension of its known range from East Asia to North America. This species could be overlooked owing to the fact that dry specimens without oil bodies are often used in identification, and it is probably more widespread than currently known in the boreal forests of Canada. Illustrations and descriptions based on the Canadian specimens are provided with a key for Canadian species of the genus.

Post-fire peatland vegetation recovery: a case study in open rich fens of the Canadian boreal forest

Fire plays a major role in the structuring and functioning of boreal ecosystems. As peatlands are important components of boreal forests, the impact of fire upon these wetter ecosystems is increasingly studied, but with the focus on treed peatlands and Sphagnum-dominated bogs so far. Important fires occurring more frequently in the past decade in southern Northwest Territories (Canada) provide the opportunity to assess early post-fire vegetation regeneration in open rich fens (one, two, and five years post-fire) and to better understand early recovery succession. We aimed to (i) evaluate whether and how open rich fens are affected by fire, and (ii) describe short-term vegetation regeneration for both bryophytes and vascular species. A shift was observed between pioneer bryophytes and brown mosses between the second and fifth year post-fire. Vascular plants, especially slow-growing species and the ones reproducing mainly by seeds, recovered partially. The first bryophyte species recovering were pioneer species adapted to colonize burned environments such as Marchantia polymorpha L. or Ceratodon purpureus (Hedw.) Brid. For vascular plant species, the ones previously present and able to regrow rapidly from unburned plant structures (base of tussocks, rhizomes, roots) were represented by species like Betula glandulosa Michx. or Carex aquatilis Wahlenb. The wetter conditions and lower fuel availability of fen depressional biotopes were important factors controlling the resistance and regeneration of species associated with them.

Missing Burns in the High Northern Latitudes: The Case for Regionally Focused Burned Area Products

Global estimates of burned areas, enabled by the wide-open access to the standard data products from the Moderate Resolution Imaging Spectroradiometer (MODIS), are heavily relied on by scientists and managers studying issues related to wildfire occurrence and its worldwide consequences. While these datasets, particularly the MODIS MCD64A1 product, have fundamentally improved our understanding of wildfire regimes at the global scale, their performance may be less reliable in certain regions due to a series of region- or ecosystem-specific challenges. Previous studies have indicated that global burned area products tend to underestimate the extent of the burned area within some parts of the boreal domain. Despite this, global products are still being regularly used by research activities and management efforts in the northern regions, likely due to a lack of understanding of the spatial scale of their Arctic-specific limitations, as well as an absence of more reliable alternative products. In this study, we evaluated the performance of two widely used global burned area products, MCD64A1 and FireCCI51, in the circumpolar boreal forests and tundra between 2001 and 2015. Our two-step evaluation shows that MCD64A1 has high commission and omission errors in mapping burned areas in the boreal forests and tundra regions in North America. The omission error overshadows the commission error, leading to MCD64A1 considerably underestimating burned areas in these high northern latitude domains. Based on our estimation, MCD64A1 missed nearly half the total burned areas in the Alaskan and Canadian boreal forests and the tundra during the 15-year period, amounting to an area (74,768 km2) that is equivalent to the land area of the United States state of South Carolina. While the FireCCI51 product performs much better than MCD64A1 in terms of commission error, we found that it also missed about 40% of burned areas in North America north of 60° N between 2001 and 2015. Our intercomparison of MCD64A1 and FireCCI51 with a regionally adapted MODIS-based Arctic Boreal Burned Area (ABBA) shows that the latter outperforms both MCD64A1 and FireCCI51 by a large margin, particularly in terms of omission error, and thus delivers a considerably more accurate and consistent estimate of fire activity in the high northern latitudes. Considering the fact that boreal forests and tundra represent the largest carbon pool on Earth and that wildfire is the dominant disturbance agent in these ecosystems, our study presents a strong case for regional burned area products like ABBA to be included in future Earth system models as the critical input for understanding wildfires’ impacts on global carbon cycling and energy budget.

Concurrent and rapid recovery of bacteria and protist communities in Canadian boreal forest ecosystems following wildfire

Wildfire plays an important role in restructuring bacterial and protist taxonomic and functional communities in forest ecosystems. Yet, the recovery of bacterial and protist communities following wildfire has not been rigorously investigated across long-term wildfire chronosequences. We compared changes in bacterial and protist alpha diversity, community composition, co-occurrence networks and determinant edaphic factors between burnt and unburnt (reference) soils at 11 different sites representing a 76-year wildfire chronosequence in Canadian boreal forests. The fire increased bacterial and protist alpha diversity and altered community composition (beta diversity) as compared to the site-specific controls during the early recovery stage (<5 years since fire), but had no effect on bacterial and protist communities in the middle (8–20 years) and late (>30 years) recovery stages. Bacterial and protist communities showed similar patterns of change across the wildfire chronosequence. The post-fire recovery of bacterial communities was associated with changes in soil chemical properties (e.g., nutrient status and pH) and vegetation succession. The protist community assembly was co-influenced by changes in bacterial communities and vegetation succession/soil properties. The concurrent recovery of bacterial and protist communities, and their influencing factors of vegetation and soil properties, imply the above- and belowground living communities are strongly linked in wildfire-perturbed forest ecosystems.

Restoration of a boreal peatland impacted by an in‐situ oil sands well‐pad 2: Greenhouse gas exchange dynamics

Across Canada's boreal forest, disturbances from in situ oil sands mining, including well‐pads, significantly impact vast areas of the landscape. The creation of well‐pads requires removal of vegetation and placement of mineral fill, which essentially stops any carbon (C) sequestration on the once peatland ecosystem. It is important that, once no longer in use, these well‐pads are restored as long‐term C (peat) accumulation is what defines peatland ecosystem. However, little is known about the recovery of greenhouse gas exchange post‐restoration of these features. We studied a decommissioned well‐pad located in a treed poor fen that was restored using three soil adjustment treatments (SATs): (1) complete mineral fill removal (Peat‐Dec); (2) partial pad removal and burial under peat layer (BUPL); and (3) mixing mineral and peat by inversion (Mixed‐P‐M). The recreated peat surface was revegetated with donor peatland species using the moss layer transfer technique (MLTT). The objectives of this paper were to (1) quantify plot‐scale seasonal carbon dioxide (CO2) and methane (CH4) exchange of the SATs, 2–4 years post‐restoration compared to reference sites and (2) determine the influence of several environmental variables on CO2 and CH4 exchange. All SATs proved effective in recreating a soil surface needed to support peatland vegetation as shown by similar rates of net ecosystem exchange (NEE). Equally, both types of vegetation reintroduced led this site on a trajectory toward functioning as a net C sink.