Boreal Forest Research Articles

Production of greenhouse gases by logging residue in boreal clear-cut forests

AbstractForest deadwood is an important carbon reserve, estimated to contain 8% of the total forest carbon. This type of woody debris is recognized as a source of carbon dioxide (CO2), as the carbon is released back into the atmosphere by microbial decomposition. Production of methane (CH4) and nitrous oxide (N2O) has also been reported. In managed forests, logging residues form a major source of fine deadwood, but its role in the greenhouse gas exchange of forest ecosystems is poorly understood. We studied the greenhouse gas production of spruce and birch left-over fine woody debris and estimated the residence time of these residues at 18 spruce-dominated boreal forest sites in Central Finland. The study areas consisted of clear-cut forest stands, totally covering approximately 47 hectares, with logging residue ages varying between 0 and 10 years. The research was carried out over eight months from May to December 2019. We observed that CO2 dominated the greenhouse gas production of the logging residues, with the production being regulated by air temperature, tree species, residue age, and wood moisture. Emission of CO2 continued throughout the research period with a clear seasonal pattern. Production of CH4 and N2O was also observed, but not in climatically-relevant amounts. Deadwood half-life was estimated at 18 years for spruce and 9 years for birch. Our study demonstrates that logging residues form a mid-term carbon reserve and suggests that global warming could reduce the lifetime of the residues as a result of elevated and temperature-dependent CO2 release in the studied Myrtillus type forest stands.

Evaluation and development of surface layer scheme representation of temperature inversions over boreal forests in Arctic wintertime conditions

Abstract. In this study, the Noah land surface model used in conjunction with the Mellor–Yamada–Janjić surface layer scheme (hereafter, Noah-MYJ) and the Noah multiphysics scheme (Noah-MP) from the Weather Research and Forecasting (WRF) 4.5.1 mesoscale model are evaluated with regard to their performance in reproducing positive temperature gradients over forested areas in the Arctic winter. First, simplified versions of the WRF schemes, recoded in Python, are compared with conceptual models of the surface layer in order to gain insight into the dependence of the temperature gradient on the wind speed at the top of the surface layer. It is shown that the WRF schemes place strong limits on the turbulent collapse, leading to lower surface temperature gradient at low wind speeds than in the conceptual models. We implemented modifications to the WRF schemes to correct this effect. The original and modified versions of Noah-MYJ and Noah-MP are then evaluated compared to long-term measurements at the Ameriflux Poker Flat Research Range, a forest site in interior Alaska. Noah-MP is found to perform better than Noah-MYJ because the former is a two-layer model which explicitly takes into account the effect of the forest canopy. Indeed, a non-negligible temperature gradient is maintained below the canopy at high wind speeds, leading to overall larger gradients than in the absence of vegetation. Furthermore, the modified versions are found to perform better than the original versions of each scheme because they better reproduce strong temperature gradients at low wind speeds.

Early expansion of mixed oak stands at 16,800–16,600 cal bp at a northern Italian glacial refugium in the Euganean Hills

AbstractContinuous sedimentary lake records covering the Last Glacial Maximum (LGM) are very rare in Europe. Here, we conducted additional palynological analyses to connect two separate radiocarbon-dated pollen sequences of Lago della Costa (AP2 and AP1) to one complete vegetation history record of the Euganean Hills (“Colli Euganei”, northern Italy) covering the past ca. 32,000 years. Previous studies on autochthonous organic lake sediments revealed that during the Last Glacial Maximum (LGM) Lago della Costa likely acted as a refugium of temperate woody taxa. Based on the new data we present the first continuous record of the vegetation history of the Euganean Hills during the past 32,000 years. Specifically, we investigate the early establishment and mass expansion of deciduous Quercus at the refugial site at ca. 16,800–16,600 cal bp. In the oak forests other temperate taxa (e.g. Corylus avellana, Abies alba, Ulmus, Fraxinus excelsior, Vitis, Hedera, Tilia, Acer, Fagus sylvatica) also established at around this time, i.e. 2,000 years prior to the onset of the Bølling/Allerød interstadial (about 14,700–12,800 cal bp). The comparison of our data with other well-dated records from the river Po catchment and refugial sites elsewhere in Italy and southern Europe suggests expansions of boreal and nemoral forests over wide areas prior to the Bølling/Allerød interstadial, i.e. 2,000 years before comparable large-scale afforestation north of the Alps or ca. 45°N. Pollen-inferred expansions of temperate tree communities (e.g. oak forests) correspond to a climatic warming as reconstructed from quantitative, pollen-independent evidence (e.g. chironomids) from the Apennines, Northern Italy, Southern Switzerland and the Swiss Plateau, suggesting that pre-Bølling afforestation processes south of the Alps were promoted by increasing (summer) temperatures during the Oldest Dryas.

IJCH – COVID-19 in the Arctic: special issue

ABSTRACT The Circumpolar region, comprising the Arctic territories encircling the North Pole, is home to diverse Indigenous cultures facing unique socio-economic challenges. Indigenous communities such as the Inuit, Sámi, Athabaskan, Gwitchin, and Russian Arctic groups exhibit rich traditions and adaptive practices tied to their environments. Environmental diversity, from icy tundra to boreal forests, influences livelihoods and biodiversity, while significant socio-economic disparities persist, impacting access to healthcare, education, and economic opportunities. Against this backdrop, the global COVID-19 pandemic accentuated the intersection of environment, culture, and health in remote Arctic regions, presenting distinct challenges and opportunities. Initiated by a collaborative research project led by Fulbright Arctic Initiative Alumni, this special issue of the International Journal of Circumpolar Health explores the impacts of COVID-19 on Arctic Indigenous and rural communities. Building on previous work and recommendations, the issue features community case studies, highlighting community experiences and collaborative approaches to understand and address the pandemic’s effects. The authors highlight both positive and negative societal outcomes, presenting community-driven models and evidence-based practices to inform pan-Arctic collaboration and decision-making in public health emergencies. Through sharing these insights, the special issue aims to privilege local and Indigenous knowledge systems, elevates community responses to complex and multifaceted challenges, and contributes to the evidence base on global pandemic response.

Late Glacial and Holocene vegetation and lake changes in SW Yakutia, Siberia, inferred from sedaDNA, pollen, and XRF data

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.

Use of linear features by mammal predators and prey in managed boreal forests

In managed boreal forests, logging operations maintain high levels of anthropogenic disturbance in the ecosystem. The establishment of permanent anthropogenic linear features such as logging roads in the landscape may be a major factor in the predator-prey system. Logging roads may potentially improve the numerical and functional response of predators. Using camera traps, our objective was to explain according to local and landscape factors how the number of uses by wolves, black bears, lynx and moose, varies along different natural and anthropogenic linear features during the snow-free season. In western Quebec (Canada), the managed forest south of Val-d’Or encloses an isolated caribou population facing extinction that requires active restoration of their habitat. In this site, we used stratified random selection of gravel forest roads (n = 33), winter forest roads (n = 28) and riparian areas (n = 19) to compare their characteristics and number of uses by the four species. For wolves, black bears, and lynx, positive differences in lateral cover between the surroundings and the linear feature mainly explained their number of uses. Number of uses by wolves and lynx were positively related to use by their respective prey species (moose and snowshoe hare). Gray wolf use was also positively affected by distance to a higher forest road class and negatively affected by distance to the nearest urban area. Gravel forest roads had the highest number of uses by all species, as they showed greater positive differences in lateral cover as compared to the surroundings area due to their limited vegetation growth and by frequent maintenance activities. We recommend that restoration efforts aimed at forest road closures should target roads with a high value of difference in lateral cover, which is particularly the case in most gravel roads. Lower lateral cover on these linear feature as compared to their surroundings area favors the movement of predators and alternative prey. Our results thus suggest that investing in gravel roads restoration can benefit conservation efforts in caribou habitat.

Wolverine density, survival, and population trends in the Canadian boreal forest

AbstractThere is limited information available on wolverine (Gulo gulo) population density and trends in the boreal forest of North America. We estimated wolverine density using spatial capture‐recapture methods across 2 boreal forest study areas in Red Lake, Ontario (26,568 km2) and Rainbow Lake, Alberta (19,084 km2), Canada. We also used radio‐telemetry data to estimate annual survival of adult and sub‐adult wolverines and evaluated population trends with a stage‐based matrix model. We used an array of run poles and live traps to detect wolverines. In Red Lake over 3 winter field seasons (2019–2022), we detected 56 individual wolverines (17 females, 32 males, and 7 unknown sex), and in Rainbow Lake over 2 field seasons (2014–2016), we detected 48 individuals (19 females, 18 males, and 11 of unknown sex). Average densities in Red Lake and Rainbow Lake were 3.64 and 6.74 wolverines/1,000 km2, respectively. Adults and sub‐adults occurred at equal abundance. Spring snow cover, roads, and industrial developments were not associated with spatial patterns of wolverine density. Most deaths occurred near roads; wolverines were killed in fur traps set along roads, by wolves using roads to travel, and by vehicles. The largest source of death was from incidental (n = 6 in Red Lake) or licensed fur trapping (n = 8 in Rainbow Lake) and we report 8 injuries from fur trapping sets. Red Lake survival estimates for adults (0.87) and sub‐adults (0.86) contributed to a stable population trend. Rainbow Lake survival estimates for adults (0.66) and sub‐adults (0.50) contributed to a declining population trend based on a relatively low sample of radio‐days. Red Lake and Rainbow Lake combined survival estimates for adults (0.77) and sub‐adults (0.73) also contributed to a declining population trend. Our survival and population modeling suggests that human‐caused mortality is a significant risk to these populations. Our results can be applied to wolverine status assessments and used as benchmarks for future monitoring. Wolverine population stability or growth might be achieved by reducing incidental trapping deaths or injury and hindering human access to wolverine habitats through decommissioning or limiting development of industrial roads or other anthropogenic linear features.

Fecal DNA metabarcoding helps characterize the Canada jay's diet and confirms its reliance on stored food for winter survival and breeding.

Accurately determining the diet of wild animals can be challenging if food items are small, visible only briefly, or rendered visually unidentifiable in the digestive system. In some food caching species, an additional challenge is determining whether consumed diet items have been previously stored or are fresh. The Canada jay (Perisoreus canadensis) is a generalist resident of North American boreal and subalpine forests with anatomical and behavioural adaptations allowing it to make thousands of arboreal food caches in summer and fall that are presumably responsible for its high winter survival and late winter/early spring breeding. We used DNA fecal metabarcoding to obtain novel information on nestling diets and compiled a dataset of 662 published and unpublished direct observations or stomach contents identifications of natural foods consumed by Canada jays throughout the year. We then used detailed natural history information to make informed decisions on whether each item identified to species in the diets of winter adults and nestlings was best characterized as 'likely cached', 'likely fresh' (i.e., was available as a non-cached item when it appeared in a jay's feces or stomach), or 'either possible'. Of the 87 food items consumed by adults in the winter, 39% were classified as 'likely cached' and 6% were deemed to be 'likely fresh'. For nestlings, 29% of 125 food items identified to species were 'likely cached' and 38% were 'likely fresh'. Our results support both the indispensability of cached food for Canada jay winter survival and previous suggestions that cached food is important for late winter/early spring breeding. Our work highlights the value of combining metabarcoding, stomach contents analysis, and direct observations to determine the cached vs. non-cached origins of consumed food items and the identity of food caches, some of which could be especially vulnerable to degradation through climate change.

Predictive soil health indicators across a boreal forest to agricultural conversion gradient

AbstractA changing climate offers new opportunities to expand agriculture in northern latitudes, and understanding forest‐to‐agriculture land conversion impacts is critical to ensure soil sustainability. Using the Comprehensive Assessment of Soil Health (CASH) framework, we identified a minimum suite of indicators with little collinearity to reliably predict soil impacts during the conversion of boreal forest to agriculture and a time since conversion gradient (forest, <10 years, >10 and <50 years, and >50 years since conversion). We sampled paired forest and agricultural sites and used multiple linear regression to assess 16 indicators and found four‐ and six‐indicator models predicted the CASH score with varying but reasonable accuracy depending on conversion class. Organic matter, water aggregate stability, and pH were consistent predictors across all classes, as well as one or more micronutrients. The CASH framework appears to be more suitable for agricultural soils and as time since conversion proceeds.

Wildfire impacts on the carbon budget of a managed Nordic boreal forest

Wildfire is one of the most important disturbances affecting boreal forests. Most previous research on boreal forest fires has occurred in North American forests which have different fire regimes, tree species and are less intensively managed than their Eurasian counterparts. Recent extreme fire years have highlighted the vulnerability of the Nordic boreal forest to climatic shifts that are increasing forest fire frequency and severity. The Ljusdal fire (2018) was one of the largest wildfires in recorded history in Sweden. We established eddy covariance flux towers to track the impacts of this fire on the carbon balance of two Pinus sylvestris sites subject to different fire severities and forest management strategies 1–4 years post-fire. The ‘SLM’ site was a mature stand that experienced low-severity fire (trees survived) followed by salvage-logging and reseeding, whilst the ‘HY’ site was 10 years old when it experienced high-severity fire (all trees killed) then was replanted with seedlings. During the study period, both sites were net carbon sources at the annual scale. It took up to 4 years after the fire until the first day of net CO2 uptake was recorded at each site. We estimated that it will take 13 years (8, 21; mean ± 95 % confidence intervals) after the fire until the sites reach a neutral annual carbon balance. It will take up to 32 years (19, 53) at HY and 46 years (31, 70) at SLM to offset the carbon lost during and after the fire and salvage-logging. In addition, our measurements showed that more carbon was emitted in the first 4 years after the fire compared to the carbon lost from combustion during the fire. Quantifying carbon fluxes during the initial years after fire is therefore crucial for estimating the net impact of wildfire on the carbon budget of boreal forests.

Monitoring Snow Cover in Typical Forested Areas Using a Multi-Spectral Feature Fusion Approach

Accurate snow cover monitoring is greatly significant for research on the hydrology model and regional climate variation, especially in Northeast China where forests cover almost forty percent of the total area. However, effectively monitoring snow cover under the forest canopy is still challenging with either in situ or remote sensing observations. The global SNOWMAP algorithm pertinent to the fixed normalized difference snow index (NDSI) threshold is, therefore, no longer applicable in a typical forested region of Northeast China. In order to achieve the goal of improving the accuracy of monitoring snow cover in areas with forest, utilizing MOD09GA and MOD13A1 products, a new approach of snow mapping was developed in this study, and it exploits the fusion and coupling of spectral features by integrating and analyzing the normalized difference forest snow index (NDFSI), the normalized difference vegetation index (NDVI), and the NDSI index. Then, Landsat 8 OLI images of high resolution were used to evaluate snow cover mapping precision. The experimental results indicated that the NDFSI index combined with the NDVI index showed great potential for extracting the snow cover distribution in forested regions. Compared with the snow distribution obtained from the Landsat 8 images, the average bias and FAR (false alarm ratio) values of snow cover mapping obtained by this algorithm were 1.23 and 13.54%, which were reduced by 1.98 and 29.36%, respectively. The overall accuracy of 81.31% was reached, which is improved by 20.19%. Thus, the snow classification scheme combining multiple spectral features from MODIS data works effectively in improving the precision of automatic snow cover mapping in typical forested areas of Northeast China, which provides essential support and significant perspectives for the next step of establishing a runoff model and rationally regulating forest water resources.

Large, sustained soil CO2 efflux but rapid recovery of CH4 oxidation in post-harvest and post-fire stands in a mixedwood boreal forest

The net effect of forest disturbances, such as fires and harvesting, on soil greenhouse gas fluxes is determined by their impacts on both biological and physical factors, as well as the temporal dynamics of these effects post-disturbance. Although harvesting and fire may have distinct effects on soil carbon (C) dynamics, the temporal patterns in soil CO2 and CH4 fluxes and the potential differences between types of disturbances, remain poorly characterized in boreal forests. In this study, we measured soil CO2 and CH4 fluxes using a off-axis integrated cavity output spectroscopy system in snow-free seasons over two years in post-harvest and post-fire chronosequence sites within a mixedwood boreal forest in northwestern Ontario, Canada. Soil CO2 efflux showed a post-disturbance peak, with differing dynamics depending on the disturbance type: post-harvest stands exhibited a nearly tenfold increase (from ∼1 to ∼11 μmol CO2.m-2.s−1) from 1 to 9–10 years post-disturbance, followed by a steep decline; post-fire stands showed a more gradual increase, peaking at ∼6–7.2 μmol CO2.m-2.s−1 after ∼12–15 years. The youngest post-harvest stands were net sources of CH4,whereas post-fire stands were never net CH4 sources. In both disturbance types, the strength of the CH4 sink increased with stand age, approaching ∼2.4 nmol.m-2.s−1 by 15 years post-disturbance. Volumetric water content, bulk density, litter depth, and pH were significant predictors of CO2 fluxes; for CH4 fluxes, litter depth, pH, and the interaction of VWC and soil temperature were significant predictors in both disturbance types, with EC also showing a relationship in post-harvest stands. Our findings indicate that while soil CH4 oxidation rapidly recovers following disturbance, both post-harvest and post-fire stands show a multi-decade release of soil CO2 that is too large to be offset by C gains over this period.

Impact of Wildfires on Land Surface Cold Season Climate in the Northern High-Latitudes: A Study on Changes in Vegetation, Snow Dynamics, Albedo, and Radiative Forcing

Anthropogenic climate change is increasing the occurrence of wildfires, especially in northern high latitudes, leading to a shift in land surface climate. This study aims to determine the predominant climatic effects of fires in boreal forests to assess their impact on vegetation composition, surface albedo, and snow dynamics. The influence of fire-induced changes on Earth’s radiative forcing is investigated, while considering variations in burn severity and postfire vegetation structure. Six burn sites are explored in central Alaska’s boreal region, alongside six control sites, by utilizing Moderate Resolution Imaging Spectroradiometer (MODIS)-derived albedo, Leaf Area Index (LAI), snowmelt timing data, AmeriFlux radiation, National Land Cover Database (NLCD) land cover, and Monitoring Trends in Burn Severity (MTBS) data. Key findings reveal significant postfire shifts in land cover at each site, mainly from high- to low-stature vegetation. A continuous increase in postfire surface albedo and negative surface shortwave forcing was noted even after 12 years postfire, particularly during the spring and at high-severity burn areas. Results indicate that the cooling effect from increased albedo during the snow season may surpass the warming effects of earlier snowmelt. The overall climate impact of fires depends on burn severity and vegetation composition.

Anticipating Future Risks of Climate-Driven Wildfires in Boreal Forests

Anticipating Future Risks of Climate-Driven Wildfires in Boreal Forests

Revegetation of disturbed land reclaimed with suboptimal topsoil replacement depth and organic amendments

AbstractSuccessful reclamation and revegetation of disturbed sites depends on the availability of sufficient topsoil. Current regulations in western Canada require the replacement of ≥80% of the original topsoil depth (TRD) to restore pre‐disturbance productivity. However, salvaged topsoil at many legacy and other disturbed sites is often insufficient to achieve the 80% TRD (TRD80). This 5‐year study examined vegetation responses to 50% TRD without organic amendment (TRD50) or amended with either peat (PTRD50) or biochar (BTRD50), relative to the TRD80 treatment, following borrow site reclamation in northeastern Alberta, Canada. Amendments were applied once at rates calculated to bring organic carbon in the topsoil to concentrations approximating those in the TRD80 treatment. Tree and shrub seedling mixes were transplanted following amendment application and vegetation attributes were measured annually thereafter. Results showed that PTRD50 performed as well as TRD80 and outperformed BTRD50 with respect to native species' canopy cover and tree seedling height. Canopy covers of forb and non‐native species decreased significantly whereas those of graminoid and native species increased over time for all treatments. Across treatments, native plant species richness increased by 5% per year while non‐native species richness decreased by 19% per year. Overall, peat showed a satisfactory rate of recovery and a trajectory toward the natural boreal forest, indicating its potential to improve reclamation success at disturbed boreal sites where salvaged soil is insufficient to attain equivalent land capability. This finding will provide an additional tool for regulators seeking to refine land reclamation guidelines for such sites in boreal forest regions.

Restricted plant diversity limits carbon recapture after wildfire in warming boreal forests

Incomplete wildfire combustion in boreal forests leaves behind legacy plant-soil feedbacks known to restrict plant biodiversity. These restrictions can inhibit carbon recapture after fire by limiting ecosystem transition to vegetation growth patterns that are capable of offsetting warmth-enhanced soil decomposition under climate change. Here, we field-surveyed plant regrowth conditions 2 years after 49 separate, naturally-occurring wildfires spanning the near-entire climatic range of boreal Fennoscandia in order to determine the local to regional scale drivers of early vegetation recovery. Minimal conifer reestablishment was found across a broad range of fire severities, though residual organic soil and plant structure was associated with restricted growth of a variety of more warmth-adapted vegetation, such as broadleaf trees. This dual regeneration limitation coincided with greater concentrations of bacterial decomposers in the soil under increased mean annual temperature, potentially enhancing soil carbon release. These results suggest that large portions of the boreal region are currently at risk of extending postfire periods of net emissions of carbon to the atmosphere under limitations in plant biodiversity generated by wildfire and a changing climate.

Cyclic and linear trajectories of ecosystem evolution on sand dunes in Siberian taiga: A comprehensive analysis

Extensive unforested sandy areas on the margins of floodplains and riverbeds, formed by dunes, barchans, and accumulation berms, are a ubiquitous feature across northern Eurasia and Alaska. These dynamic landscapes, which bear witness to the complex Holocene and modern climatic fluctuations, provide a unique opportunity to study ecosystem evolution. Within this heterogeneous assemblage, active dunes, characterized by their very sparse plant communities, contrast sharply with the surrounding taiga (boreal) forests common for the stabilized dunes. This juxtaposition makes these regions to natural laboratories to study vegetation succession and soil development. Through a comprehensive analysis of climate, geomorphology, vegetation, soil properties, and microbiome composition, we elucidate the intricacies of cyclic and linear ecosystem evolution within a representative sandy area located along the lower Nadym River in Siberia, approximately 100 km south of the Arctic Circle. The shift in the Holocene wind regime and the slow development of vegetation under harsh climatic conditions promoted cyclical ecosystem dynamics that precluded the attainment of a steady state. This cyclical trajectory is exemplified by Arenosols, characterized by extremely sparse vegetation and undifferentiated horizons. Conversely, accelerated vegetation growth within wind-protected enclaves on marginally stabilized soils facilitated sand stabilization and subsequent pedogenesis towards Podzols. Based on soil acidification due to litter input (mainly needles, lichens, and mosses) and the succession of microbial communities, we investigated constraints on carbon and nutrient availability during the initial stages of pedogenesis. In summary, the comprehensive study of initial ecosystem development on sand dunes within taiga forests has facilitated the elucidation of both common phases and spatiotemporal dynamics of vegetation and soil succession. This analysis has further clarified the existence of both cyclic and linear trajectories within the successional processes of ecosystem evolution.

Modeling boreal forest soil dynamics with the microbially explicit soil model MIMICS+ (v1.0)

Abstract. Understanding carbon exchange processes between land reservoirs and the atmosphere is essential for predicting carbon–climate feedbacks. Still, considerable uncertainty remains in the representation of the terrestrial carbon cycle in Earth system models. An emerging strategy to constrain these uncertainties is to include the role of different microbial groups explicitly. Following this approach, we extend the framework of the MIcrobial-MIneral Carbon Stabilization (MIMICS) model with additional mycorrhizal groups and a nitrogen cycle that includes a novel representation of inorganic nitrogen sorption to particles via a Langmuir isotherm. MIMICS+ v1.0 is designed to capture and quantify relationships between soil microorganisms and their environment, with a particular emphasis on boreal ecosystems. We evaluated MIMICS+ against podzolic soil profiles in Norwegian forests as well as the conventional Community Land Model (CLM). MIMICS+ matched observed carbon stocks better than CLM and gave a broader range of C:N ratios, more in line with observations. This is mainly explained by a higher directly plant-derived fraction into the soil organic matter (SOM) pools. The model produces microbial biomass estimates in line with numbers reported in the literature. MIMICS+ also showed better representation of climate gradients than CLM, especially in terms of temperature. To investigate responses to changes in nutrient availability, we performed an N enrichment experiment and found that nitrogen sorbed to particles through the sorption algorithm served as a long-term storage of nutrients for the microbes. Furthermore, although the microbial groups responded considerably to the nitrogen enrichment, we only saw minor responses for carbon storage and respiration. Together, our results present MIMICS+ as an attractive tool for further investigations of interactions between microbial functioning and their (changing) environment.

Winter soil temperature varies with canopy cover in Siberian larch forests

In the Arctic, winter soil temperatures exert strong control over mean annual soil temperature and winter CO2 emissions. In tundra ecosystems there is evidence that plant canopy influences on snow accumulation alter winter soil temperatures. By comparison, there has been relatively little research examining the impacts of heterogeneity in boreal forest cover on soil temperatures. Using seven years of data from six sites in northeastern Siberia that vary in stem density we show that snow-depth and forest canopy cover exert equally strong control on cumulative soil freezing degrees days (FDDsoil). Together snow depth and canopy cover explain approximately 75% of the variance in linear models of FDDsoil and freezing n-factors (n f; calculated as the quotient of FDDsoil and FDDair), across sites and years. Including variables related to air temperature, or antecedent soil temperatures does not substantially improve models. The observed increase in FDDsoil with canopy cover suggests that canopy interception of snow or thermal conduction through trees may be important for winter soil temperature dynamics in forested ecosystems underlain by continuous permafrost. Our results imply that changes in Siberian larch forest cover that arise from climate warming or fire regime changes may have important impacts on winter soil temperature dynamics.

Are forest management practices to improve carbon balance compatible with maintaining bird diversity under climate change? A case study in Eastern North America

The combination of climate change and anthropogenic disturbance significantly impacts forest bird assemblages. Assessing the cumulative effects of forest management and climate change on biodiversity and ecosystem services, including carbon sequestration and storage and provisioning of wood products is key to informing forest management and conservation decision making. Specifically, we projected changes in forest composition and structure according to various forest management strategies under a changing climate using LANDIS-II for two case study areas of Quebec (Canada): a hemiboreal (Hereford Forest) and a boreal (Montmorency Forest) area. Then, we assessed projected bird assemblage changes, as well as sensitive and at-risk species. As part of an integrated assessment, we evaluated the best possible management measures aimed at preserving avian diversity and compared them with optimal options for mitigation of carbon emissions to the atmosphere. Forest management and climate change were projected to lead to significant changes in bird assemblages in both types of forest through changes in forest composition. We projected an increase in deciduous vegetation which favored species associated with mixed and deciduous stands to the detriment of species associated with older, coniferous forests. Changes were more pronounced in Hereford Forest than Montmorency Forest. In addition, Hereford’s bird assemblages were mainly affected by climate change, while those in Montmorency Forest were more impacted by forest management. We estimated that 25% of Hereford and 6% of Montmorency species will be sensitive to climate change, with projected abundance changes (positive or negative) exceeding 25%. According to the simulations, a decrease in the level of forest harvesting could benefit bird conservation and contribute to reduction of carbon emissions in the boreal forest area. Conversely, the hemiboreal forest area require trade-offs, as mitigation of carbon emissions is favored by more intensive forest management that stimulates the growth and carbon sequestration of otherwise stagnant stands.