Disturbance In Boreal Forest Research Articles

Insights into Boreal Forest Disturbance from Canopy Stability Index

The world’s forests are being increasingly disturbed from exposure to the compounding impacts of land use and climate change, in addition to natural disturbance regimes. Boreal forests have a lower level of deforestation compared to tropical forests, and while they have higher levels of natural disturbances, the accumulated impact of forest management for commodity production coupled with worsening fire weather conditions and other climate-related stressors is resulting in ecosystem degradation and loss of biodiversity. We used satellite-based time-series analysis of two canopy indices—canopy photosynthesis and canopy water stress—to calculate an index that maps the relative stability of forest canopies in the Canadian provinces of Ontario and Quebec. By drawing upon available spatial time-series data on logging, wildfire, and insect infestation impacts, we were able to attribute the causal determinants of areas identified as having unstable forest canopy. The slope of the two indices that comprise the stability index also provided information as to where the forest is recovering from prior disturbances. The stability analyses and associated spatial datasets are available in an interactive web-based mapping app. that can be used to map disturbed forest canopies and the attribution of disturbances to human or natural causes. This information can assist decision-makers in identifying areas that are potentially ecologically degraded and in need of restoration and those stable areas that are a priority for protection.

Spatial scale of stand-replacing forest disturbance influences the amplitude of snowshoe hare population fluctuations in boreal forests of northwest Canada

The natural disturbance model for ecosystem management of timber harvesting promotes the emulation of natural disturbance regimes in the patterns of tree removal. Wildfire is a prominent natural disturbance in boreal forests of western Canada, frequently removing most of the tree canopy from patches of 500–10,000 ha in stand-replacing events. However, fire suppression, coupled with a spatial pattern of timber harvesting dominated by small patch cuts of 10–160 ha, have changed the spatial scale of younger stands away from scales within which boreal organisms evolved. In two regions (Sub-Boreal Spruce biogeoclimatic zone of central British Columbia and Liard Basin of southeast Yukon), we tested the hypothesis that different spatial scales of stand-replacing forest disturbance (wildfire and timber harvesting) result in different amplitudes of change in abundance of snowshoe hare, a keystone boreal forest mammal for which mid-seral stand conditions provide optimal habitat. Landscapes with large patches (>2000 ha) of mid-seral forest following stand-replacing disturbance supported consistently and often significantly more hares, with wider amplitude in cyclic fluctuation, than small patches (20–200 ha) of mid-seral habitat and than mature forest landscapes. Densities of hares high enough to support reproduction by Canada lynx (a specialist hare predator) only occurred in landscapes disturbed at the scale of a moderate to large-sized wildfire (1000 – 10,000 ha). Landscapes unaffected by stand-replacing disturbance for at least 80 years (i.e. mature forests) supported very few hares and without cyclic fluctuations. We recommend that the recent pattern of cutting dominated by small patches (20–200 ha) be shifted to include many larger patches (2000–5000 ha). This can happen with incremental, contiguous patch cutting over a period of years short enough that the completed patch will supply high quality, mid-seral habitat for at least the period of one hare cycle (10 y). In designing relatively large patches, mature green tree retention would be desirable for various values, but would be best as small stands of mature forest dispersed within large patch cuts, similar to the legacy of fire. Silviculture (reforestation and stand tending) should create and sustain a mix of conifer and deciduous regeneration in the mid-seral stands. Emulating spatial patterns of stand-replacing natural disturbance appears necessary to sustain snowshoe hare cycles when most fires are suppressed in intensively managed western Canadian boreal forests.

Wildfire effects on the fate of deposited nitrogen in a boreal larch forest

The effects of nitrogen (N) deposition on forests largely depend on the ecosystem N status and the fates of deposited N. Boreal forests are typically N-limited ecosystems and are considered to be more efficient in retaining deposited N relative to temperate and tropical forests. As a primary disturbance in boreal forests, wildfires may alleviate N limitation in the burned ecosystem and increase mineralization, resulting in the altered outcomes of the N deposition. In order to explore the effects of a severe wildfire on the retention of deposited N, we investigated the fates of newly deposited N in burned and unburned boreal larch forests by applying 15NH4NO3 tracers to the forest floors. Results showed that total ecosystem retention for the deposited N was 60% in the forest recovering from a severe wildfire burned five years ago, significantly lower than in the unburned mature forest (89%). The difference was mainly attributed to the substantially lower retention in vegetation (8.3%) in the burned site than in the unburned forest (32.4%), as tracer recoveries in soil were similar (51.2 and 56.6%, respectively). Although most 15N tracer was immobilized in organic soil in both burned and unburned forests (33 and 47%, respectively), a noticeably higher amount of 15N was found in mineral soil in the burned forest (19%) than in the unburned forest (10%), suggesting mineral soil as a significant sink for N deposition in the burned forest. A higher total 15N retention in the unburned forest implies that more new N input may stimulate C sequestration and promote the productivity of the Eurasian boreal forest under the background of atmospheric N deposition. However, a considerable amount of deposited N may be lost from the disturbed boreal larch forest ecosystem after a severe wildfire.

Characterizing forest recovery following stand-replacing disturbances in boreal forests: contributions of optical time series and airborne laser scanning data

The success and rate of forest regeneration following disturbance has implications for sustainable forest management, climate change mitigation, and biodiversity, among others. Systematic monitoring of forest regeneration over large and often remote areas of the boreal forest is challenging. The use of remotely sensed data to characterize post-disturbance recovery in the boreal forest has been an active research topic for more than 30 years. Innovations in sensors, data policies, curated data archives, and increased computational power have enabled new insights into the characterization of post-disturbance forest recovery, particularly following stand-replacing disturbances. Landsat time series data have emerged as an important data source for post-disturbance forest recovery assessments, with Landsat’s 40-year archive of 30-m resolution data providing consistent observations on an annual time step and enabling retrospective capacity to establish spatially explicit recovery baselines. The application of remote sensing for monitoring post-disturbance forest recovery is a rapidly growing area of research globally; however, despite the large amount of disturbance and the disproportionate effects of climate change in the boreal, the boreal biome is relatively underrepresented in the remote sensing forest recovery literature. Herein, the past and present contributions of optical time series and airborne laser scanning data to the characterization of forest recovery in boreal forests are highlighted, and future research priorities are identified.

Fire and retention island remnants have similar deadwood carbon stock a decade after disturbances in boreal forests of Alberta

In an attempt to reconcile wood extraction and forest biodiversity in managed boreal forests, ecosystem-based forest management (EBM) has become the de facto management approach. Retention forestry represents one prominent way that EBM is implemented in many parts of the world. Retention patches commonly left after harvesting serve as analogues of fire island remnants, which are patches of unburned forests in the burned forest matrix. Although the persistence of retention patches has been questioned, few studies have attempted to quantitatively compare forest attributes in both burned and harvested forests. As part of a larger program examining multiple aspects of ecosystem function in fire and harvest island remnants, we investigated the impact of disturbance type (fire/harvest) and forest edges on C stock in snags and coarse woody debris (CWD) found in island remnants in mixedwood boreal forests of Alberta, Canada. Total C stock (in snags and CWD) was similar between the two disturbance types and edge plots had similar total deadwood C stocks to interiors. The edges of island remnants had about two-fold more snag C stock than their interiors in both disturbance types, but C stock in CWD was unaffected by edge effects and disturbance type. Our results suggest that deadwood C dynamics in island remnants in fire and harvest disturbed boreal forests were similar, thus lending support for the continued implementation of retention forestry in Alberta.

Soil Springtail Communities Are Resilient to Forest Tent Caterpillar Defoliation in Quebec Mixed Hardwood Forests

Outbreaks of defoliator insects are important natural disturbances in boreal forests, but their increasing frequency under warming climate conditions is of concern. Outbreak events can shape ecosystem dynamics with cascading effects through trophic networks. Caterpillar defoliation can alter tree physiology, increase sunlight to the understory, and result in the deposition of large amounts of leaf litter and caterpillar frass to the forest floor. These modifications can thus affect soil organisms through direct (e.g., changes in soil temperature or moisture) or indirect (e.g., changes in detrital and root food webs) mechanisms. We assessed whether a recent (2015 to 2017) outbreak of the forest tent caterpillar (Malacosoma disstria) at the Lake Duparquet Teaching and Research Forest (Abitibi, QC, Canada) affected soil springtail communities, abundant microarthropods in forest soils. In 2018 and 2019, we sampled litter and soil (0–10 cm depth) at eight sites each in aspen-dominated (Populus tremuloides Michx) stands that were undefoliated or had a recent defoliation history. We found no significant difference in springtail abundance (specimens cm−2) or alpha diversity indices between undefoliated sites and those with defoliation history. However, we observed a transient change in springtail community composition 1 year after the outbreak (2018) with the absence of Folsomia nivalis, Anurophorus sp1, and Xenylla christianseni in sites with defoliation history, but no compositional differences were observed in 2019. Certain soil nutrients (P, C, Mg, Mn) were significant predictors of springtail community composition, but soil microbial biomass was not, despite its significant decrease in sites with defoliation history. Our results show that soil springtail communities respond in the short-term to the forest tent caterpillar outbreak with compositional shifts, but seem ultimately resilient to these events.

Wildfires affect tree growth and resilience in Northeastern China natural Dahurian larch forests: A dendrochronological perspective

Wildfires are natural and ubiquitous disturbances in boreal forests. Assessing their impacts on tree growth and resilience are particularly important to recognize the adaptation strategies of fire-tolerant species and forest succession in fire conditions. To date, the growth resilience of fire-tolerant species in boreal forests remains largely unquantified, and the drivers of resilience are poorly understood. Here, we measured the tree-ring widths of 99 fire-scarred trees from three sites in natural Dahurian larch (Larix gmelinii) forests. Three moderate-severity fire events in years 1987, 1990, and 2000 occurring at three sites were detected from the records of local forestry bureau. Based on tree-ring width data, we calculated resilience components (i.e., resistance, recovery, resilience and relative resilience) to quantify the responses of growth resilience in the larch trees to fires and analyzed their drivers at three sites. Results indicated that fires significantly reduced the tree growth. With the increasing tree age, these reductions were more pronounced. As for resilience components, our study showed a limited resistance but high recovery of tree growth against fires, and resistance tended to increase northwards but recovery showed the opposite, suggesting a growth-survival tradeoff was exhibited in Dahurian larch trees. With an increasing tree age, regional resistance and resilience showed a decreasing trend, whereas recovery and relative resilience showed an increasing trend. Resilience components were mainly affected by the climatic factors in spring. An increase in moisture availability enhanced resistance, a reduction in diurnal temperature range enhanced recovery, and an increase in mean temperature enhanced resilience and relative resilience. This study reveals that Dahurian larch could be even less favorable when faced with moderate or severe fire events, but a high capacity of recovery enables this species to adapt to the fire-prone condition. Moreover, this work highlights that the resilience of tree growth should be considered to understand tree behaviors and survival strategies of boreal forests following fires across fire-prone regions under future climate warming.

Long-Term Impacts of Forest Management Practices under Climate Change on Structure, Composition, and Fragmentation of the Canadian Boreal Landscape

Forest harvesting and fire are major disturbances in boreal forests. Forest harvesting has modified stand successional pathways, which has led to compositional changes from the original conifer-dominated forests to predominantly mixed and hardwood forests. Boreal fire regimes are expected to change with future climate change. Using the LANDIS-II spatially explicit landscape model, we evaluated the effects of forest management scenarios and projected fire regimes under climate change in northeastern Canadian boreal forests, and we determined the subsequent alteration in stand- and landscape-level composition, succession, and spatial configuration of boreal forests. We observed that, in contrast to successional pathways that followed fire, successional pathways that followed forest harvesting favored mixed forests with a prevalence of shade-intolerant hardwoods for up to 300 y after harvesting. This trend was exacerbated under climate change scenarios where forests became dominated by hardwood species, particularly in ecoregions where these species were found currently in low abundance. Our results highlight the failure of existing forest management regimes to emulate the effects of natural disturbance regimes on boreal forest composition and configuration. This illustrates the risks to maintaining ecosystem goods and services over the long term and the exacerbation of this trend in the context of future climate change.

Specialist or generalist? It depends. Context-dependent habitat relationships provide insight into forest disturbance effects for a boreal bird species

Understanding how disturbance affects species is a critical component of management in the boreal forest, particularly for disturbance specialist species that often help initiate the succession process through seed dispersal, nutrient cycling, and other means. Unfortunately, emulation of natural disturbance rarely incorporates the disturbance response of those specialist species, which may be potentially sensitive to disturbance characteristics because they are attracted to resources provided by the disturbance itself. Identifying disturbance specialist species and the reasons they occur in post-disturbance habitat is thus a priority for maintaining biodiversity in managed forests. We compared two types of habitat use to fill this information gap for a potential boreal forest disturbance specialist, the Common Nighthawk (Chordeiles minor). The Common Nighthawk is of particular interest to forest managers because this wide-ranging species is declining and listed as of conservation concern in multiple jurisdictions. We used passive acoustic monitoring to survey for nighthawks at 326 locations in the boreal forest of northeastern Alberta, Canada where land use pressure for resource extraction is high. We used an occupancy modelling framework to evaluate two hypotheses for why nighthawks use post-disturbance habitat: nesting or foraging resources. The nesting resource hypothesis was supported by all three lines of evidence that we examined. First, time since disturbance negatively affected territorial habitat use, but not extraterritorial habitat use, confirming that this species is only a disturbance specialist for the territorial component of its home range. Second, territorial habitat use differed between disturbance types, with a higher probability of habitat use for post-harvest and abandoned well sites, which are more likely to have lower amounts of residual vegetation. For our third line of evidence, open pine forest mitigated the effects of time since disturbance for territorial habitat use for all three disturbance types, but especially for postfire areas. We conclude that breeding Common Nighthawks require a combination of open habitat for nesting and wetland areas for foraging and provide industry-specific recommendations for incorporating the Common Nighthawk into boreal forest management plans. Our research emphasizes that understanding the context-dependence of species responses to disturbance provides insights that facilitate effective forest management. We advocate that understanding the behavioural context of habitat use can provide this insight and is often more likely to be aligned with the operational scale of forest management.

Compared to Wildfire, Management Practices Reduced Old-Growth Forest Diversity and Functionality in Primary Boreal Landscapes of Eastern Canada

Large primary forest residuals can still be found in boreal landscapes. Their areas are however shrinking rapidly due to anthropogenic activities, in particular industrial-scale forestry. The impacts of logging activities on primary boreal forests may also strongly differ from those of wildfires, the dominant stand-replacing natural disturbance in these forests. Since industrial-scale forestry is driven by economic motives, there is a risk that stands of higher economic value will be primarily harvested, thus threatening habitats, and functions related to these forests. Hence, the objective of this study was to identify the main attributes differentiating burned and logged stands prior to disturbance in boreal forests. The study territory lies in the coniferous and closed-canopy boreal forest in Québec, Canada, where industrial-scale logging and wildfire are the two main stand-replacing disturbances. Based on Québec government inventories of primary forests, we identified 427 transects containing about 5.5 circular field plots/transect that were burned or logged shortly after being surveyed, between 1985 and 2016. Comparative analysis of the main structural and environmental attributes of these transects highlighted the strong divergence in the impact of fire and harvesting on primary boreal forests. Overall, logging activities mainly harvested forests with the highest economic value, while most burned stands were low to moderately productive or recently disturbed. These results raise concerns about the resistance and resilience of remnant primary forests within managed areas, particularly in a context of disturbance amplification due to climate change. Moreover, the majority of the stands studied were old-growth forests, characterized by a high ecological value but also highly threatened by anthropogenic disturbances. A loss in the diversity and functionality of primary forests, and particularly the old-growth forests, therefore adds to the current issues related to these ecosystems. Since 2013, the study area is under ecosystem-based management, which implies that there have been marked changes in forestry practices. Complementary research will be necessary to assess the capacity of ecosystem-based management to address the challenges identified in our study.

Modeling paludification and fire impacts on the forest productivity of a managed landscape using valuable indicators: the example of the Clay Belt

In areas sensitive to forest management, paludification and successive disturbances in boreal forest can affect forest regeneration negatively, sometimes resulting in stand opening. As these negative effects on forest productivity are not fully considered in strategic management planning, a new landscape dynamics model integrating fire, paludification, forest harvesting, and regeneration failure was used to assess these impacts in a large forest management unit (10 828 km2) of northwestern Québec. Two reforestation scenarios, one based on the accessibility of the areas to be treated and the other aimed at restoring all burned and paludified areas to production were compared with one with no intervention. The success of the scenarios was evaluated using the predicted volume harvested, the proportion of closed or opened stands areas, which is an indicator of productivity, and the cost of reforestation and the royalties associated with harvesting. Harvesting the paludified areas without reforesting would lead to a sharp increase in open stands areas (+17.3%). The strategy of reforesting accessible areas is the most promising for achieving sustainable forest management targets. The monitoring of maximum potential volume and the closed forest area as indicators of landscape productivity provides the ability to anticipate problems earlier than with the conventional forest planning indicators.

Study of lichen recovery after catastrophic disturbances in boreal forests: methodological aspects and evaluated characteristics

Study of lichen recovery after catastrophic disturbances in boreal forests: methodological aspects and evaluated characteristics

Boreal permafrost thaw amplified by fire disturbance and precipitation increases

Permafrost soils store huge amounts of organic carbon, which could be released if climate change promotes thaw. Currently, modelling studies predict that thaw in boreal regions is mainly sensitive to warming, rather than changes in precipitation or vegetation cover. We evaluate this conclusion for North American boreal forests using a detailed process-based model parameterised and validated on field measurements. We show that soil thermal regimes for dominant forest types are controlled strongly by soil moisture and thus the balance between evapotranspiration and precipitation. Under dense canopy cover, high evapotranspiration means a 30% increase in precipitation causes less thaw than a 1 °C increase in temperature. However, disturbance to vegetation promotes greater thaw through reduced evapotranspiration, which results in wetter, more thermally conductive soils. In such disturbed forests, increases in precipitation rival warming as a direct driver of thaw, with a 30% increase in precipitation at current temperatures causing more thaw than 2 °C of warming. We find striking non-linear interactive effects on thaw between rising precipitation and loss of leaf area, which are of concern given projections of greater precipitation and disturbance in boreal forests. Inclusion of robust vegetation-hydrological feedbacks in global models is therefore critical for accurately predicting permafrost dynamics; thaw cannot be considered to be controlled solely by rising temperatures.

A Holocene Perspective of Vegetation Controls on Seasonal Boreal Wildfire Sizes Using Numerical Paleo-Ecology

Wildland fire is the most important disturbance in boreal forests of eastern North America, shaping composition, structure and spatial arrangement of the flora. Although the long-term evolution of frequency and quantity of biomass burnt in these forest are known relatively well from paleoecological studies, we know little about the evolution of fire sizes. Here, we developed a modelling framework that provides insights into processes and changes involved through time in the historical fire-vegetation-climate environment of the coniferous and mixedwood forests of eastern boreal North America, with a particular attention on the metric of fire size. On the one hand, lacustrine charcoal particles sequestered in sediments from mixedwood forest and coniferous forest regions (MF and CF, respectively) were analyzed with the most advanced statistical treatments to reconstruct changes in biomass burning, fire frequency, and their ratio, the fire size (FS index), over the last 7000 BP. On the other hand, a fire propagation model was used to simulate fire sizes in the past using both a reference landscape, whose MF and CF compositions through time were prescribed using pollen reconstructions, and climate inputs provided by the HadCM3BL-M1 snapshot simulations. Lacustrine charcoals showed that Holocene FS indices have not differed significantly between MF and CF due to high variability in fire frequencies. However, biomass burning from MF has always been lower than from CF, such differences being significant since 5000 BP. Beyond the variability, MF’s mean FS index was lower than CF’s one throughout the Holocene, with slight changes in both forests from 7000 to 1000 BP, and simultaneous increases over the last millennium. The fire model showed that MF fires were systematically smaller than CF ones throughout the Holocene, with larger differences in the past than today. The fire model also highlighted that spring fires in both forest types have always been larger than summer fires over the last 7000 years, such results being in agreement with present-day fire statistics. This study illustrates how fire models, built and used for forecast and firefighting today, can be used under past conditions to enhance our understanding in the fire-vegetation-climate nexus.

Vegetation Trajectories and Shortwave Radiative Forcing Following Boreal Forest Disturbance in Eastern Siberia

AbstractMajor boreal forest disturbance and associated carbon emissions have been reported in the coldest region of the Northern Hemisphere. Related biophysical feedbacks to climate remain highly uncertain but might reduce warming effects expected from carbon emissions. This study quantifies albedo change after disturbance, primarily fires, in larch‐dominated forests around Yakutsk as compared to undisturbed areas with natural albedo variability, using satellite‐based time series. The related annual mean shortwave radiative forcing was −6.015 W/m2 for the 13 years following forest disturbance. It was highly negative during snow‐covered months (−3.738 to −13.638 W/m2), but positive (+5.441 W/m2) for the summer months in the first year after disturbance, decreasing afterward and also turning into a negative forcing after 5 years. Forcing by surface shortwave radiation must be considered to assess the impact of boreal forest disturbance on climate and additional feedbacks, such as increased permafrost thaw or transition to alternative ecosystem states.

Forest disturbances affect functional groups of macrofungi in young successional forests – harvests and fire lead to different fungal assemblages

Fungal assemblages after a large-scale disturbance can be diverse and have functionally important roles in forests. However, fungi include several functional groups, and the responses of these groups to different forest disturbances is poorly understood. For example, ectomycorrhizal fungi may facilitate the establishment of a new tree cohort while saprotrophic fungi are able to decompose most of the dead organic material that result from the disturbance event. In this study, we examined how functionally different macrofungi respond to two major disturbances: fire (prescribed burning) and different intensities of timber harvest.We used large-scale field experiment where (1) fire and (2) harvest intensity were manipulated simultaneously in a factorial, replicated design. Three levels of harvests and an unharvested control were included, and sites were either burned or not. Fungi were surveyed before treatments in year 2000 and annually over three years (2001–2003) after the treatments. Fungi species were divided into ectomycorrhizal (ECM), saprophyte (SaM) and wood-associated fungi (WAM). The latter group mostly included Aphylloporoid wood-associated species (AWAM) and agarics. We observed also two biotrophic and one parasitic fungus but these were excluded from the assemblage-level analyses due to their rarity. Both number of sporocarps (fruiting bodies) and their biomass were measured.Fungal groups were affected by harvest and fire but the various fungal groups responded in different ways to the treatments. The ECM species were sensitive to timber harvests and disappeared from all the harvested sites. Fire in the unharvested sites did not negatively affect the ECM fungi. The SaM fungi responded quickly after disturbance, and their assemblage composition changed after fire and harvest. Species richness was reduced but fire promoted several pyrophilous SaM species, leading to major compositional changes in SaM species and the formation of distinct assemblages. The WAM species declined after harvests but fire tended to counteract the negative effects of timber harvesting.The results show that fungal groups respond in different ways to major disturbances in boreal forests. Early successional post-disturbance forests contribute to the maintenance of forest biodiversity, especially the specialist SaM species. However, the type of disturbance (fire or harvest) affect fungi in different ways. Understanding the assemblage dynamics of decomposer and other fungi is crucial when estimating how changes in forest disturbance regimes may affect nutrient and carbon cycling, as well as the maintenance of forest biodiversity.

Insect and storm disturbance in boreal forests — predisposing site factors and impacts on ecosystem carbon

Insect and storm disturbance in boreal forests — predisposing site factors and impacts on ecosystem carbon

Effect of salvage-logging on post-fire tree establishment and ground cover vegetation in semi-natural hemiboreal forests

Fire is a common disturbance in boreal forests causing changes in biological diversity at various spatial scales. In the past 100 years, forest management has limited fire outbreaks, but in the future, the fire-affected forest area is expected to increase in many regions due to climate change. Burned forests are typically salvage-logged, but the effect of this type of management versus natural regeneration on biological diversity is not well understood, particularly the mid-term effect to tree establishment and understory vegetation composition and diversity. Various management methods were used after a large fire in 1992 in a peatland-forest complex and neighbouring managed forests, which created an experimental setup for study of the effect of management after fire in the Sliteres National park, northwestern Latvia. Understory vegetation was described in plots using a design of four forest and three management types: natural regeneration (unmanaged) and managed sites with salvage logging followed by no further human intervention and salvage logging with planting. Post-fire management had different effect in each forest type. Species richness was higher in forest types with salvage logging than in natural regenerated sites on rich wet and rich dry forest types, but not for the poor forest types. Tree regeneration was generally greater in salvage-logged stands, but differed between forest types. Species composition was related to tree regeneration and canopy openness. In contrast to other studies, salvage logging had a positive mid-term effect to ground vegetation diversity and tree establishment in the studied stands, implying potential for concomitant management and conservation of ground cover vegetation in semi-natural stands.

Aerial spraying of bacterial insecticides to control spruce budworm defoliation leads to reduced carbon losses

AbstractSpruce budworm (SBW) outbreaks are a major natural disturbance in boreal forests of eastern North America. During large‐scale infestations, aerial spraying of bacterial insecticides is used to suppress local high‐density SBW populations. While the primary goal of spraying is the protection of wood volume for later harvest, it should also maintain carbon stored in trees. This study provides the first quantitative analysis of the efficacy of aerial spraying against SBW on carbon dynamics in balsam fir, spruce, and mixed fir–spruce forests. In this study, we used the TRIPLEX‐Insect model to simulate carbon dynamics with and without spray applications in 14 sites of the boreal forest located in various regions of Québec. We found that the efficacy of aerial spraying on reducing annual defoliation was greater in the early stage (<5 yr since the outbreak began) of the outbreak than in later (5–10 yr since the outbreak began) stage. Our results showed that more net ecosystem productivity is maintained in balsam fir (the most vulnerable species) than in either spruce or mixed fir–spruce forests following spraying. Also, average losses in aboveground biomass due to the SBW following spraying occurred more slowly than without spraying in balsam fir forests. Our findings suggest that aerial spraying could be used to maintain carbon in conifer forests during SBW disturbances, but that the efficacy of spray programs is affected by host species and stage of the SBW outbreak.

Climate change decreases the cooling effect from postfire albedo in boreal North America.

Fire is a primary disturbance in boreal forests and generates both positive and negative climate forcings. The influence of fire on surface albedo is a predominantly negative forcing in boreal forests, and one of the strongest overall, due to increased snow exposure in the winter and spring months. Albedo forcings are spatially and temporally heterogeneous and depend on a variety of factors related to soils, topography, climate, land cover/vegetation type, successional dynamics, time since fire, season, and fire severity. However, how these variables interact to influence albedo is not well understood, and quantifying these relationships and predicting postfire albedo becomes increasingly important as the climate changes and management frameworks evolve to consider climate impacts. Here we developed a MODIS-derived 'blue sky' albedo product and a novel machine learning modeling framework to predict fire-driven changes in albedo under historical and future climate scenarios across boreal North America. Converted to radiative forcing (RF), we estimated that fires generate an annual mean cooling of -1.77±1.35W/m2 from albedo under historical climate conditions (1971-2000) integrated over 70years postfire. Increasing postfire albedo along a south-north climatic gradient was offset by a nearly opposite gradient in solar insolation, such that large-scale spatial patterns in RF were minimal. Our models suggest that climate change will lead to decreases in mean annual postfire albedo, and hence a decreasing strength of the negative RF, a trend dominated by decreased snow cover in spring months. Considering the range of future climate scenarios and model uncertainties, we estimate that for fires burning in the current era (2016) the cooling effect from long-term postfire albedo will be reduced by 15%-28% due to climate change.