Canadian Boreal Forest Research Articles

Earlier and more variable spring phenology projected for eastern Canadian boreal and temperate forests with climate warming

Climate change affects timing and variability of spring phenology, as well as occurrence of spring frosts, and therefore influences forest structure, function, and management practices. In this study, we evaluated changes in budburst timing, sequential order of budburst, budburst temperatures, and frosts, from 1981–2010 baseline to different future climates (+2, +4, and +6 °C for moderate, high, and extremely high warming) for selected boreal and temperate species in eastern Canada. We used species-specific budburst models that are developed from large-scale forcing experiments.Budburst averaged 10–15 days earlier per 2 °C increase of temperatures, except for temperate yellow birch and eastern white pine that slowed down to 5–7 days in budburst advancement from +4 to +6 °C. Earlier budburst was associated with greater annual and interspecific variations in budburst timing, lower budburst temperatures, more frosts, and less annual variations in sequential order of budburst. Compared to temperate trees, boreal trees had greater budburst advances and annual variations, but less interspecific variations in timing and sequential order of budburst. Early flushing species had greater phenological changes and annual variations, as well as more frosts. Our results suggest that budburst advance that has occurred will continue with greater among years/species variability but is unlikely to converge between boreal and temperate regions in eastern Canada under anticipated levels of climate warming.

Sensitivity analysis of hydrological processes to perturbed climate in a southern boreal forest basin

Hydrological processes over and through frozen and unfrozen ground were simulated in the well instrumented boreal forest basin of White Gull Creek, Saskatchewan, Canada using a model created using the flexible Cold Regions Hydrological Modelling (CRHM) platform. The CRHM-created Boreal Hydrology Model was structured and initially parameterized using decades of process hydrology research in the southern boreal forest with minor parameter calibration, and generally produced quite good performance on simultaneously reproducing the measurements of runoff, snow water equivalent (SWE), soil liquid water content and eddy correlation flux tower observations of evapotranspiration (ET) over two decades. To examine the sensitivity of basin hydrology to perturbed climate inputs, air temperature (T) inputs were set up by linear increments in the reference observation of up to +6 ℃, and precipitation (P) inputs were generated by multiplying the reference observed P from 70% to 130%. The model results showed that the basin hydrological variables showed quite different sensitivities to perturbations of P and T. The volume of annual runoff and the annual runoff coefficient increased more rapidly with rising P, at rates of 31% and 16% per 10% increase in P, but decreased by only 3.8% and 4.7% per 1 ℃ of warming. Annual ET increased rapidly with temperature, by 7% per 1 ℃ of warming and therefore drove the streamflow volumetric changes with warming, but increased only 1% per 10% increase in P. Perturbations of P and T had distinctively different influences on the streamflow regime. Increased P enhanced the intra- and inter-annual variabilities of basin runoff, reduced the relative contribution of winter runoff to annual runoff and increased the relative contribution of summer runoff; whilst rising T resulted in the inverse changes in the streamflow regime. Effects of warming on some hydrological processes could be compensated for to varying degrees by the effects of increases in P. Reductions in the annual runoff volume and runoff coefficient caused by warming up to 6 ℃ could be compensated for by increases of <20% in P. However, the maximum increase in P (+30%) examined could only compensate for the changes in snow processes caused by warming of less than 4 ℃ and snow-cover duration decreases with 1 ℃ warming could not be compensated for by any precipitation increase considered. These results inform the vulnerability of boreal forest hydrology to the first-order changes in P and T and provide guidance for further climate impact assessments for hydrology in the southern boreal forest in Canada.

Factors explaining the composition and diversity of vascular plant understories along a transcontinental gradient in the Canadian boreal forest

AbstractAimImpacts of longitudinal gradients on species distributions have received less attention than latitudinal gradients. In Canada, precipitation varies longitudinally, with direct effects on plant growth and fire regimes. Despite the geographical extent of Canadian boreal forests, vascular plant diversity is relatively limited, with just under 300 species. Understorey communities comprise most of this diversity and play key roles in forests, affecting succession, nutrient cycling and wildlife habitat. Our objective was to evaluate the relative impacts of local and regional environmental conditions on vascular plant community composition and diversity in the boreal forest.LocationSampling took place in 33 trembling aspen (Populus tremuloides) stands along a transcontinental gradient in precipitation and fire regimes in boreal Canada.MethodsWe measured community composition and vegetation diversity indices of the vascular understorey in 400‐m2 plots and measured environmental variables at the local (drainage, nutrient and light availability, site heterogeneity) and regional (annual temperature and precipitation, fire weather index, landscape heterogeneity) scales. Multivariate analyses and hierarchical model selection were used to analyze patterns.ResultsSpecies composition varied longitudinally, with western and eastern species pools. Western indicator species tended to be fire‐adapted pioneer species, while indicator species at eastern sites were fire avoiders and late‐successional species. Species richness and intra‐site beta diversity seemed primarily driven by local variables and did not vary across the country. Species evenness, however, was slightly higher in the western region and decreased under higher precipitation, colder temperatures, and higher landscape‐level heterogeneity.ConclusionOur results suggested that even for similar canopy composition environmental variables play a key role in the establishment of plant communities and structure local plant assemblages by selecting or eliminating species from the regional pool, which was also controlled by fire regimes.

TRIPLEX-Mortality model for simulating drought-induced tree mortality in boreal forests: Model development and evaluation

Globally, increasing drought-induced tree mortality rates under climate change are projected to have far-reaching effects on forest ecosystems. Among these forest systems, the boreal forest is considered a ‘tipping element’ of the Earth's climate system. This forest biome plays a critical role in ecosystem services, structures and functions while being highly sensitive to drought stress. Although process-based models are important tools in ecological research, very few have yet been developed that integrate advanced physiological mechanisms to simulate drought-induced mortality in boreal forests. Accordingly, based on the process-based TRIPLEX model, this study introduces the new TRIPLEX-Mortality submodule for the Canadian boreal forests at the stand level, that for the first time successfully incorporates two advanced drought-induced physiological mortality mechanisms (i.e., hydraulic failure and carbon starvation). To calibrate and validate the model, 73 permanent sample plots (PSPs) were selected across Canada's boreal forests. Results confirm a good agreement between simulated mortality and mortality observations (R2=0.79; P<0.01; IA=0.94), demonstrating good model performance in simulating drought-induced mortality in boreal forests. Sensitivity analysis indicated that parameter sensitivity increased as drought intensified, and the shape parameter (c) for calculating percentage loss of conductivity (PLC) was the most sensitive parameter (average SI = -3.51) to simulate tree mortality. Furthermore, the results of model input sensitivity analysis also showed that the model can capture changes in mortality under different drought scenarios. Consequently, our model is suitable for simulating drought-induced mortality in boreal forests while also providing new insight into improving model simulations for tree mortality and associated carbon dynamics in a progressively warmer and drier world.

New methodology shows short atmospheric lifetimes of oxidized sulfur and nitrogen due to dry deposition

Abstract. The atmospheric lifetimes of pollutants determine their impacts on human health, ecosystems and climate, and yet, pollutant lifetimes due to dry deposition over large regions have not been determined from measurements. Here, a new methodology based on aircraft observations is used to determine the lifetimes of oxidized sulfur and nitrogen due to dry deposition over (3-6)×103 km2 of boreal forest in Canada. Dry deposition fluxes decreased exponentially with distance from the Athabasca oil sands sources, located in northern Alberta, resulting in lifetimes of 2.2–26 h. Fluxes were 2–14 and 1–18 times higher than model estimates for oxidized sulfur and nitrogen, respectively, indicating dry deposition velocities which were 1.2–5.4 times higher than those computed for models. A Monte Carlo analysis with five commonly used inferential dry deposition algorithms indicates that such model underestimates of dry deposition velocity are typical. These findings indicate that deposition to vegetation surfaces is likely underestimated in regional and global chemical transport models regardless of the model algorithm used. The model–observation gaps may be reduced if surface pH and quasi-laminar and aerodynamic resistances in algorithms are optimized as shown in the Monte Carlo analysis. Assessing the air quality and climate impacts of atmospheric pollutants on regional and global scales requires improved measurement-based understanding of atmospheric lifetimes of these pollutants.

Relating pre-fire canopy species, fire season, and proximity to surface waters to burn severity of boreal wildfires in Alberta, Canada

Increased global temperature, drought, and extreme weather have increased the frequency and intensity of wildfires in Canadian Boreal forests. We examined how burn severity was related to canopy species composition and proximity to water in six large boreal forest stands across northern Alberta (two in the Bistcho Lake region, three in Wood Buffalo National Park, and one in the Richardson backcountry) and a smaller stand close to the town of Slave Lake (204–5217 km2). We used Landsat 5, 7, and 8 satellite images that included two phenological stages (spring, summer, or fall), followed by Support Vector Machines (SVM) classification to map the distribution of pre-fire canopy species. To quantify the burn severity of each fire, we used the Landsat images to calculate the differenced Normalized Burn Ratio (dNBR); we then combined dNBR for all affected areas to develop the Standardised Burn Impact Score (SBIS), that quantifies the average impact of each fire based on the size of the burned area and mean burn severity per pixel. In general, pre-fire dominance of coniferous species (jack pine and spruce) led to higher SBIS values while pre-fire dominance of broad-leaved species (aspen, birch, and poplar) led to lower values. Mean burn severity and SBIS values increased when fire events occurred at a distance of 1 km or greater from surface waters (e.g. lakes, rivers, and streams). We further analyzed the influence of fire season on burn duration and the proportion of canopy species being burned in each season. We found that fires that were ignited in spring lasted longer and burned more deciduous stands compared to fires that were ignited in summer. By integrating burn impact over very large temporal and spatial scales, we have confirmed the general influence of pre-fire canopy species on burn severity, and the ameliorating effect of surface waters on fire behavior at the landscape level.

Does the type of silvicultural practice influence spruce budworm defoliation of seedlings?

AbstractSpruce budworm (Choristoneura fumiferana (Clem)) is the main defoliator in the boreal forest of North America, and its outbreaks have major ecological and economic consequences and represent a challenge for forest management. Numerous studies have addressed the effects of this defoliator on mature trees, whereas the effects of spruce budworm on regeneration remain elusive. Furthermore, intensive exploitation practices during the last decades have left a large area of the Canadian boreal forest in an early development stage. In this context, it becomes vital to understand those factors affecting the severity of spruce budworm‐related defoliation on regeneration. Here, we determine the defoliation severity of black spruce and balsam fir seedlings in both mature pure black spruce and black spruce–balsam fir stands subjected to two different silvicultural treatments (clear‐cutting and partial cutting). Defoliation intensity varied between stand types, silvicultural treatments, species, and height classes. Seedlings in black spruce–balsam fir stands experienced twice the defoliation of those in pure black spruce stands (black spruce seedlings 10% vs. 23%; balsam fir seedlings 29% vs. 47%, respectively). Harvesting methods also influenced seedling defoliation. Under clear‐cutting, black spruce seedlings (24%) were three times as defoliated as black spruce seedlings in partial cutting stands (8%), whereas balsam fir seedlings in clear‐cutting plots experienced twice the defoliation (42%) of balsam fir seedlings in partial cutting plots (20%). The level of defoliation also increased with seedling height. This study will help silvicultural strategies adapt to the effects of natural disturbance regimes. As the intensity and severity of defoliator outbreaks are expected to increase under climate change, these results will help guide forest management strategies to select harvesting methods that will limit the effects of defoliation on conifer regeneration.

Multi-year white spruce drought legacies in southern Saskatchewan

In many regions across western Canada’s boreal forest, drought impacts on long-term white spruce (Picea glauca (Moench) Voss) radial growth are poorly understood. This is also the case for white spruce shelterbelt trees south of their natural range in agricultural regions of the Canadian Prairies. Understanding how white spruce has responded to drought in the past will be vital for management purposes for those who rely on shelterbelts and will help develop a better understanding of how white spruce in the Canadian Boreal Forest will be impacted by climate change. Using tree-rings, we tested how radial growth responds to different drought magnitudes, time-steps, and timing in southern Saskatchewan during and after droughts. White spruce radial growth is statistically associated to 3-month June-August and July-September Standardized Precipitation-Evapotranspiration Index (SPEI) values. Drought severity has a greater impact on radial growth compared to timing and time-step during the drought year and the five years after. Three-month, extreme droughts from July-September appear to have the greatest overall negative impact on white spruce growth in southern Saskatchewan. Our results indicate that white spruce has a complex multi-year response to varying drought conditions in southern Saskatchewan although the physiological mechanisms behind radial growth changes are yet unknown. This research augments our current understanding of white spruce’s drought-growth relationship and provides new information useful for understanding how the shelterbelts in southern Saskatchewan and the Canadian Boreal Forest may respond to different characteristics of moisture deficit conditions in the future where longer and more pronounced droughts are projected to occur.

A 249-yr chronosequence of forest plots from eight successive fires in the Eastern Canada boreal mixedwoods.

A combination of wildfires and defoliating insect outbreaks play an important role in the natural successional dynamics of North American boreal mixedwood forests, which, in the long term, change the post-disturbance composition and structure of forest stands. After stand-replacing disturbances (mainly wildfires), early successional hardwoods typically dominate the affected areas. Provided enough time following disturbances, the increasing recruitment of mid- to late-successional softwoods as well as the mortality of hardwoods gradually change forest composition from hardwoods to admixtures of hardwood-conifer species and conifer-dominated stands in mid and late successional stages, respectively. Such mixedwoods are abundant across the southern Canadian boreal forest. In boreal Canada, mixedwoods are the most structurally heterogeneous forest ecosystems, are highly productive, and form an important source of timber supply. Here we present the EASTERN BOREAL MIXEDWOODS CANADA data set, which documents the changes in composition and structure of stands originating from eight different wildfires representing a chronosequence of 249 yr since fire in eastern Canada. This data set has been used in several different projects to study and model the influence of natural (e.g., insect outbreaks) and anthropogenic disturbances (e.g., harvesting) on the dynamics of post-fire stands. The data set covers a high range of variability in stand composition and structure, explained by species establishment, dominance, and mixture. It thus constitutes a useful source of information to trace the dynamics of the main boreal tree species of eastern North America, from their establishment to their replacement at different spatial scales (e.g., from stand to landscape level). Please cite this data paper when the data are used in publications. We also request that researchers and teachers inform us of how they are using the data. We are open to collaborate in developing or co-authoring relevant research projects based on this data set.

Narrow anthropogenic linear corridors increase the abundance, diversity, and movement of bees in boreal forests

Understanding how invertebrates respond to disturbance is important to maintaining biodiversity. In western Canadian boreal forests, anthropogenic linear corridors associated with energy exploration are a pervasive disturbance that affect many species. Trees and large shrubs are removed in a grid of narrow corridors, but the understory vegetation is generally maintained, mimicking early seral conditions. Little is known about how bees, an important group of pollinators, respond to linear corridors, with their response having important implications for plant-pollinator communities. Here, we investigated how bee abundance, diversity, species composition, and movement respond to these anthropogenic linear corridors, locally known as seismic lines. We compared bee abundance and diversity from pan traps on seismic lines (6 – 12 m wide) to traps placed 50 m into the adjacent forest interior, across 12 replicated sites. Malaise traps were used to measure bee movements on seismic lines relative to paired interior forests, but also with respect to flight direction relative to the orientation of seismic lines. Abundance and richness of bees were 3-times and 1.5-times higher, respectively, on seismic lines compared to the forest interior, with significant differences in species composition. Bees were more than twice as abundant and diverse in malaise traps that caught bees flying along seismic lines than any other combination of trap orientation and location. These results demonstrate that narrow anthropogenic linear corridors are locally increasing bee abundance and diversity in boreal forests, as well as use of these lines for movement. These results have major implications for boreal forest plant-pollinator communities.

Influence of environmental factors on autotrophic, soil and ecosystem respirations in Canadian boreal forest

Ecosystem respiration (Reco) and its components, the autotrophic respiration (Ra) and soil respiration (Rs) are the essential indicators of the global carbon cycle. They are represented as functions of either temperature or soil moisture, or a combination of both in the widely-used Earth System Models (ESMs). Thus, it is difficult to evaluate the influence of other environmental factors (such as, precipitation, soil temperature, dissolved oxygen level and oxidation reduction potential (ORP)) on Ra, Rs and Reco. Here we introduced microbially mediated, detailed carbon cycle processes within our mechanistic model to address this issue. Dominance analysis using a multivariate approach was performed to find out the influence of individual environmental factors on Ra, Rs and Reco in the cold climate regions of Athabasca River Basin (ARB), Canada. Contribution of the 6 predictor variables, including air temperature, precipitation, soil temperature, water-filled pore space (WFPS) used as a proxy of soil moisture, dissolved oxygen level, and ORP, on Ra, Rs and Reco were estimated based on the R2 values originated from multiple regression analyses. Our results showed that the prevailing temperature (both air and soil) and dissolved oxygen levels are the major influencing factors on Ra, Rs and Reco. WFPS is found to be the least influential factor on respiration estimation. Output of this study can be used to consider the crucial roles of environmental drivers in Ra, Rs and Reco estimation in the development of future ESMs.

Projecting future aboveground biomass and productivity of managed eastern Canadian mixedwood boreal forest in response to climate change

Eastern Canadian boreal forests are mainly influenced by natural wildfires and forest management activities. To evaluate forest dynamics under possible interactions among fire and timber harvest in a future climate warming scenario (RCP 2.6, RCP 4.5 and RCP 8.5) the forest landscape model Landis II was used to simulate the dynamics of the 78000 km2 of boreal forests in eastern Canada. Forest management intensity scenarios were modeled considering the changes in the annual harvested area (0.5%, 1%, and 2%) and the age that conifers and hardwoods can be harvested (50 and 30 years, 70 and 50 years, and 90 and 70 years). The results of the 300-year model projections implied that both forest management intensity and climatic scenarios explained most of the variability in aboveground biomass, aboveground net primary productivity and forest composition. Forest management seems to be the most important factor that modified the landscape in the southern forests because there were scheduled stands with the age and composition required by each harvesting prescription to deal with the annual allowable cut volume. On the contrary, in the northern forests there was a mixed effect of climate change and forest management because many of the areas suitable for harvesting were previously burned limiting the amount of area available for harvesting. Thus, although it is expected an increase in wildfire area burned due to climate change, the intensification of forest management seems to be the most important driver of the increase of hardwoods and mixed stands and the decrease of conifers stands on the mixedwood boreal landscape, mainly in the southern forests. These results suggest that timber supply would be at risk in the Abitibi Plain, therefore, some strategies should be applied to adapt forest management to climate change.

Short-term effects of wildfire in boreal peatlands: Does fire mitigate the linear footprint of oil and gas exploration?

Exploration practices for oil sands developments in the boreal forest of western Canada create a network of thousands of kilometers of linear features, particularly seismic lines that dissect these forests posing significant environmental challenges. As wildfire is one of the prevalent stand‐replacing natural disturbances in the Canadian boreal forest, it is an important driver of environmental change and stand development that may contribute to the mitigation of such linear industrial footprint. Here, we evaluate the short‐term cumulative (also known as combined) effects of seismic lines and wildfire on biodiversity and site conditions. One year after the Horse River (Fort McMurray, Alberta, Canada) fire event in the spring of 2016, we compared dissected and undisturbed forests in burned and unburned boreal peatlands, assessing changes in overall stand structure and the responses of a variety of organisms. Soil moisture was significantly higher on seismic lines than in the adjacent forest, suggesting why most of the study sites within the fire perimeter showed little evidence of burning at the line in relation to the adjacent forest. Low fire severity on seismic lines seemed an important driver of local species diversity for ants, beetles, spiders, and plants in disturbed peatlands, resulting in similar species composition on seismic lines both within and outside the burned area, but different assemblages in burned and unburned adjacent forests. Our results suggest that fire did not erase seismic lines; rather, wildfire might increase the influence of this footprint on the recovering adjacent forest. Longer‐term monitoring will be necessary to understand how boreal treed peatlands respond to the cumulative effect of wildfire and linear disturbances.

There and back again: Breeding season movement of a female Mallard (Anas platyrhynchos) across the boreal forest and prairie potholes

Understanding how ducks use breeding habitat can help managers ensure conservation efforts are focused on the types, locations, and connectivity of habitat species require. Recent technological advancements have provided high temporal and spatial resolution on animal movements, revealing unexpected patterns in movement and habitat use. As part of a larger study, we attached a GPS-GSM backpack transmitter to a second-year female Mallard (Anas platyrhynchos) captured in a decoy trap on 28 April 2018 in Alberta, Canada's boreal forest. Following marking, we qualitatively inferred from the duck's movement path that she made at least one nesting attempt; however, we were unable to confirm a nest location. Approximately 30 d after marking, the duck made a long-distance (>200 km) movement west-southwest into the boreal transition zone and then proceeded to make another long-distance movement southeast (>450 km) into the prairie potholes region, where we suspected she made at least one more nesting attempt in early July based on clustered GPS data. After spending just over 30 d in a localized prairie potholes region (all points within ∼1 km radius), she began moving north in early August and by the end of the month had returned to within 4 km of where she was originally marked, and to the same boreal wetland where she first attempted to nest. Overall, the female Mallard traveled >1,000 km within the breeding period and used habitats in 2 disparate biomes for presumed nesting, the prairie potholes and the boreal forest. Herein we provide additional details about our observation and propose some hypotheses to explain the phenomenon.

Trophic consequences of terrestrial eutrophication for a threatened ungulate.

Changes in primary productivity have the potential to substantially alter food webs, with positive outcomes for some species and negative outcomes for others. Understanding the environmental context and species traits that give rise to these divergent outcomes is a major challenge to the generality of both theoretical and applied ecology. In aquatic systems, nutrient-mediated eutrophication has led to major declines in species diversity, motivating us to seek terrestrial analogues using a large-mammal system across 598 000 km2 of the Canadian boreal forest. These forests are undergoing some of the most rapid rates of land-use change on Earth and are home to declining caribou (Rangifer tarandus caribou) populations. Using satellite-derived estimates of primary productivity, coupled with estimates of moose (Alces alces) and wolf (Canis lupus) abundance, we used path analyses to discriminate among hypotheses explaining how habitat alteration can affect caribou population growth. Hypotheses included food limitation, resource dominance by moose over caribou, and apparent competition with predators shared between moose and caribou. Results support apparent competition and yield estimates of wolf densities (1.8 individuals 1000 km−2) above which caribou populations decline. Our multi-trophic analysis provides insight into the cascading effects of habitat alteration from forest cutting that destabilize terrestrial predator–prey dynamics. Finally, the path analysis highlights why conservation actions directed at the proximate cause of caribou decline have been more successful in the near term than those directed further along the trophic chain.

Cumulative effects of natural and anthropogenic disturbances on the forest carbon balance in the oil sands region of Alberta, Canada; a pilot study (1985\u20132012)

BackgroundAssessing cumulative effects of anthropogenic and natural disturbances on forest carbon (C) stocks and fluxes, because of their relevance to climate change, is a requirement of environmental impact assessments (EIAs) in Canada. However, tools have not been developed specifically for these purposes, and in particular for the boreal forest of Canada, so current forest C assessments in EIAs take relatively simple approaches. Here, we demonstrate how an existing tool, the Generic Carbon Budget Model (GCBM), developed for national and international forest C reporting, was used for an assessment of the cumulative effects of anthropogenic and natural disturbances to support EIA requirements. We applied the GCBM to approximately 1.3 million ha of upland forest in a pilot study area of the oil sands region of Alberta that has experienced a large number of anthropogenic (forestry, energy sector) and natural (wildfire, insect) disturbances.ResultsOver the 28 years, 25% of the pilot study area was disturbed. Increasing disturbance emissions, combined with declining net primary productivity and reductions in forest area, changed the study area from a net C sink to a net C source. Forest C stocks changed from 332.2 Mt to 327.5 Mt, declining by 4.7 Mt at an average rate of 0.128 tC ha−1 yr−1. The largest cumulative areas of disturbance were caused by wildfire (139,000 ha), followed by the energy sector (110,000 ha), insects (33,000 ha) and harvesting (31,000 ha) but the largest cumulative disturbance emissions were caused by the energy sector (9.5 Mt C), followed by wildfire (5.5 Mt C), and then harvesting (1.3 Mt C).ConclusionAn existing forest C model was used successfully to provide a rigorous regional cumulative assessment of anthropogenic and natural disturbances on forest C, which meets requirements of EIAs in Canada. The assessment showed the relative importance of disturbances on C emissions in the pilot study area, but their relative importance is expected to change in other parts of the oil sands region because of its diversity in disturbance types, patterns and intensity. Future assessments should include peatland C stocks and fluxes, which could be addressed by using the Canadian Model for Peatlands.

Allometric Equations for Estimating Biomass and Carbon Stocks in Afforested Open Woodlands with Black Spruce and Jack Pine, in the Eastern Canadian Boreal Forest

Allometric equations use easily measurable biometric variables to determine the aboveground and belowground biomasses of trees. Equations produced for estimating the biomass within Canadian forests at a large scale have not yet been validated for eastern Canadian boreal open woodlands (OWs), where trees experience particular environmental conditions. In this study, we harvested 167 trees from seven boreal OWs in Quebec, Canada for biomass and allometric measurements. These data show that Canadian national equations accurately predict the whole aboveground biomass for both black spruce and jack pine trees, but underestimated branches biomass, possibly owing to a particular tree morphology in OWs relative to closed-canopy stands. We therefore developed ad hoc allometric equations based on three power models including diameter at breast height (DBH) alone or in combination with tree height (H) as allometric variables. Our results show that although the inclusion of H in the model yields better fits for most tree compartments in both species, the difference is minor and does not markedly affect biomass C stocks at the stand level. Using these newly developed equations, we found that carbon stocks in afforested OWs varied markedly among sites owing to differences in tree growth and species. Nine years after afforestation, jack pine plantations had accumulated about five times more carbon than black spruce plantations (0.14 vs. 0.80 t C·ha−1), highlighting the much larger potential of jack pine for OW afforestation projects in this environment.

Trace metals as indicators of tree rooting in bituminous soils

AbstractIn some reclamation practices, following bitumen mining in the Canadian Boreal forest, overburden containing low concentrations of hydrocarbons (&lt;8% of bulk soil volume) is buried under suitable soils. Residual hydrocarbons may influence the growth of trees used in afforestation of reclaimed sites, thus determining whether roots interact with buried bitumen is a key to predicting reclamation success. As the organic fraction of bitumen is enriched in vanadium, nickel, molybdenum, and rhenium, dendrochemistry may be a method to determine whether tree roots are interacting with bitumen without disturbing soils. We analyzed trace concentrations of these metals in soil, soil pore water, and tree cores of Pinus banksiana growing on natural bitumen deposits and sites free of bitumen. If roots are present within bitumen and passively uptake trace metals during water transport and wood growth, metals enriched in bitumen should be present in higher concentrations in the woody tissue of trees growing in bituminous soils compared to trees growing in bitumen‐free soils. Concentrations of nickel in trees growing on shallow bitumen deposits were approximately 3× higher than those growing in bitumen‐free soils. The concentration of vanadium (1.33 μg kg−1 in younger wood and 3.21 μg kg−1 in older wood) was also elevated in trees on bituminous sites, though not significantly. Molybdenum concentrations decreased by ~25% in trees growing on bituminous sites, likely an outcome of soil pH. This research supports the use of dendrochemistry to investigate, and potentially monitor, tree rooting at depth in substrates with signature metals.

Sub-Canopy Topography Estimation from TanDEM-X DEM by Fusing ALOS-2 PARSAR-2 InSAR Coherence and GEDI Data

This paper develops a framework for extracting sub-canopy topography from the TanDEM-X digital elevation model (DEM) by fusing ALOS-2 PARSAR-2 interferometric synthetic aperture radar (InSAR) coherence and Global Ecosystem Dynamics Investigation (GEDI) data. The main idea of this method is to estimate the forest height signals caused by the limited penetration of the X-band into the canopy from the TanDEM-X DEM. To achieve this goal, a spaceborne repeat-pass InSAR coherent scattering model is first used to estimate the forest height by the ALOS-2 PARSAR-2 InSAR coherence (APIC), taking the GEDI canopy height as the reference. Then, a linear regression model of the TanDEM-X DEM Vegetation Bias (TDVB) depending on the forest height and the fraction of vegetation cover (FVC) is established and used to estimate the sub-canopy topography. The proposed method was validated by the data of the Amazon rainforest and a boreal forest in Canada. The results showed that the proposed method extracted the sub-canopy topography at the study sites in the tropical forest and boreal forest with the root mean square error of 4.0 m and 6.33 m, respectively, and improved the TanDEM-X DEM accuracy by 75.7% and 39.7%, respectively.

Dominant drivers of plant community assembly vary by soil type and time in reclaimed forests

Information on plant community assembly mechanisms is limited on forest reclamation sites after mining in the Canadian boreal forest. We assessed the change in plant community composition after Year 2 and Year 5 on species-rich forest floor mineral mix (FFMM) and species-poor peat mineral mix (PMM) reclamation soils by examining assembly mechanisms, i.e., seed bank, seed rain, biotic dispersal, vegetative expansion, and competition. Initial plant cover and diversity were greater on FFMM due to non-native species originating from the seed bank, which had 5× more seeds in the FFMM. By Year 5, both soil types had approximately 40% cover and 80 species richness due to the addition of wind and biotic-dispersed species and were characterized by a shift towards native species. Native forbs using vegetative reproduction expanded up to 2 m from FFMM into PMM. At Year 5 competition does not seem to have a large role in the structuring of the vegetation community. Overall, multiple factors were involved in structuring plant communities on reclamation sites, but we observed a general convergence between plant communities on different soil types in a relatively short period of time.