Northwestern Quebec Research Articles

Ecological drivers of post-fire regeneration in a recently managed boreal forest landscape of eastern Canada

Clearcutting practices combined with the predicted increase in fire activity may induce post-fire regeneration failure in boreal forest landscapes. This study aims (1) to evaluate if recently managed landscape by clear cut logging is susceptible to be affected by post-fire regeneration failure; and (2) to explore the ecological drivers of black spruce (Picea mariana (Mill.) BSP) post-fire regeneration. In 2014, we surveyed the regeneration of 36 stands in northwestern Quebec that had burned in a major fire in 2005. Fire severity was evaluated for each site with the differenced Normalized Burn Ratio. Using linear models, we explored the relationship between environmental variables (fire severity, pre-fire stand maturity, nature of the seedbed, and physiographic variables) and black spruce post-fire regeneration. Black spruce post-fire seedling density was highly variable (range: 25–16000seedlings/ha; mean±standard deviation: 4549seedlings/ha±4752) within the studied fire, but did not significantly differ between stands that had been logged 50years prior to fire and those that were mature prior to the 2005 fire. However, post-fire regeneration failure (defined as <40% stocking that corresponds in our study region to a regeneration density <1750seedlings/ha) was observed in 48% of the stands that had been logged, but only in 29% of the stands that were mature prior to the fire. The presence of residual trees left after clearcutting may explain why regeneration level was relatively good (>50%) in stands affected by past logging activities. Our study illustrates how biological legacies, environmental conditions and fire severity determine post-fire recovery and resilience of black spruce-dominated ecosystems of eastern Canada. By identifying the drivers of post-fire regeneration success, our study will help forest managers allocating resources where restoration of productive forest are truly needed.

Comparative evaluation of three sampling methods to estimate detection probability of American red squirrels (Tamiasciurus hudsonicus)

Measuring changes in species distribution and understanding factors influencing site occupancy are recurring goals in wildlife studies. Imperfect detection of species hinders such studies, resulting in the underestimation of the number of sites occupied by the species of interest. American red squirrels (Tamiasciurus hudsonicus) are sampled traditionally with live-traps that require substantial resources to deploy and monitor. Here, we assessed whether auditory methods yield similar detection probabilities. We compared the detection probability of American red squirrels in boreal forest using point counts, playback counts, and live-trapping. Over the summer of 2014, we conducted three trapping sessions in 60 sites within black spruce forests of northwestern Quebec, Canada. We also conducted 10min point counts in the same sites, together with playback counts using recordings of American red squirrel alarm and territorial calls. Using dynamic occupancy models to analyse three primary periods, all composed of three secondary periods, we found that the detection probability of squirrels from point counts was as high as with live-trapping. Our results thus highlight the value of the point count method in measuring American red squirrel occupancy.

Evidence of late glacial paleoseismicity from submarine landslide deposits within Lac Dasserat, northwestern Quebec, Canada

An integrated seismo- and chronostratigraphic investigation at Lac Dasserat, northwestern Quebec, identified 74 separate failures within eight event horizons. Horizons E and B, and H and G have strong or moderately-strong multi-landslide signatures, respectively, composed of 11–23 failures, while horizons F, D, C, and A have minor landslide signatures consisting of a single or pair of deposit(s). Cores collected at six sites recovered glacial Lake Ojibway varve deposits that are interbedded with the event horizons. The correlation of the varves to the regional Timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons. Horizons H, G, E, and B are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence, based on the relative strength of the multi-landslide signatures, the correlation to other disturbed deposits of similar age in the region, and the lack or possibility of alternative aseismic mechanisms. The four interpreted paleoearthquakes occurred between 9770 ± 200 and 8470 ± 200 cal yr BP, when glacial Lake Ojibway was impounded behind the Laurentide Ice Sheet during deglaciation. They probably represent an elevated period of seismicity at deglaciation that was driven by crustal unloading.

Interactions between macroclimate, microclimate, and anthropogenic disturbance affect the distribution of aspen near its northern edge in Quebec: Implications for climate change related range expansions

Policy to address the shifting tree species distributions anticipated in coming decades requires a sound understanding of how forests respond to environmental change. Using a combination of remote sensing, geographic information systems (GIS) analysis, and ground-based techniques, we explored the environmental factors associated with the distribution and abundance of trembling aspen (Populus tremuloides Michx.) across regional gradients near its northern range limit in northwestern Quebec, Canada. Although not regionally abundant, aspen is the main deciduous tree species in this conifer-dominated landscape. Regionally, the ∼51,200-km2 study area has very few settlements or roads, and little industrial resource extraction. Most of the region is inaccessible to humans except by foot or water travel. We utilized Landsat Thematic Mapper images from 2010 and 2011, and a robust collection of ground reference data developed from aerial photography, supported by field verification (vegetation sampling) where access permitted, to construct a thematic map of 11 land cover classes. The map highlights the spatial distribution of aspen, which represents only 0.3% of the study area. Map validation indicated an overall mapping accuracy of 74%, and the aspen predicted class was determined to be over 77% accurate. The regional-scale distribution of aspen stands ⩾0.5ha within the study area shows two patterns: (1) a shift toward greatest abundance on south-facing aspects with increasing latitude; and (2) a highly clustered pattern with a strong signal of concentration in areas of human activity. These patterns suggest that aspen range expansion due to climate warming will vary with topographic and other microclimatic factors (i.e. be a function of climate change interacting with landscapes) and that anthropogenic activities have the potential to influence future aspen abundance independently of climate. Forest management policies concerned with changing forest composition in these northern landscapes should recognize the potentially important role of human activity in driving the abundance of aspen.

Deadwood abundance in post-harvest and post-fire residual patches: An evaluation of patch temporal dynamics in black spruce boreal forest

In managed boreal forests, variable retention harvest is considered by forest managers as a means of mitigating harvest impacts on biodiversity. Variable retention harvest consists of maintaining within a cutblock structural attributes of the original forest stand in intact forest patches that could provide quality habitat (i.e., with large trees and deadwood) for many forest species during forest regeneration. However, retention patch modalities (size, shape, age of the forest) allowing both persistence and sustainable recruitment of deadwood over time remains unknown. The objective of this study is to evaluate the abundance of recent deadwood in post-harvest and post-fire residual patches and to compare their temporal dynamics in black spruce dominated stands located in northwestern Quebec. Abundance of the recent deadwood, estimated as the sum of recent standing deadwood volume and recently fallen deadwood volume was analyzed in 41 post-fire residual patches, and in 45 post-harvest retention patches of varying ages (i.e. exposure time to the disturbed matrix) and in 37 continuous black spruce forest stands (controls). This study shows that post-fire residual patches appear in general more durable than post-harvest retention patches after disturbance. In a management context, our results indicate that: (1) large island patches and large linear separators oriented to escape windthrow usually have deadwood recruitment dynamics similar to that of post-fire patches; (2) retention patches with an initial stand volume greater than 60m3/ha will generate more deadwood volume over time. This suggests that the selection of large retention patches in the shape of an island or a separator, with high volume (between 60 and 300m3/ha) should help increase the persistence of post-harvest retention patches in black spruce forest, and simultaneously ensure quality habitat for several forest species while the adjacent managed forest regenerates.

Plasticity of bud phenology and photosynthetic capacity in hybrid poplar plantations along a latitudinal gradient in northeastern Canada

Intensively managed plantations are being established in a wide range of environmental conditions to satisfy the high demand for wood products and reduce the exploitation pressure on natural forests. In this study, we investigated the plasticity of four hybrid poplar (Populus spp.) clones established in 2005 along a latitudinal gradient in northwestern Quebec, Canada. The effect of latitudinal gradient on maximum rates of electron transfer (Jmax) and carboxylation (Vcmax), dark respiration (Rd), spring and fall bud phenology, net photosynthesis (Pn), specific leaf area (SLA), per mass nitrogen leaf concentration (Nm) were assessed in order to evaluate if clonal plasticity would result in increased overall productivity.Growth season duration between the southernmost to the northernmost sites ranged 21–32 days, and was positively correlated to stem volume and negatively correlated to bud burst and bud set duration. Growth increment (stem volume) along the latitudinal gradient ranged 100–184% between the least and most productive clone. Clone 747215 had the most stable but the slowest growth. Leaf net photosynthesis decreased or did not change northwards except for the most productive clone for which it increased slightly likely due to a significant decrease in SLA. Maximum rates of carboxylation and photosynthesis electron transfer (Vcmax and Jmax) decreased northwards for three of the four clones, suggesting that photosynthesis of trees did not acclimate to lower temperatures from south to north. Plasticity of photosynthetic variables, measured with trait plasticity index was usually greater than that of SLA and Nm.

Bluejoint Is an Effective Bio-Barrier Species on Mine Covers.

Covers with capillary barrier effects (CCBE) are used to prevent acid mine drainage from mine wastes in the short term. However, the long-term efficiency of CCBE can be affected by trees because their roots may reduce the ability of covers to limit oxygen migration and also physically damage the CCBE. Two plant species that are native to boreal Canada, bluejoint () and sheep laurel (, were selected as bio-barrier species (BBS) to test if they reduce the growth and root system architecture of trees established on mine covers (balsam poplar [], willow [ spp], and black spruce []). The experiment was established in 2008 on a mine tailings impoundment located in northwestern Quebec, Canada. Trees were measured for height, diameter, and biomass. Coarse roots were excavated from the plots and digitized in three dimensions. Compared with the control (no BBS), bluejoint strongly decreased tree height and diameter increment, biomass, maximum root depth and radial extension, total root length and volume, and number of second- and third-order tree roots. Height and diameter increment, biomass, maximum root depth and volume, and number of second-order roots of balsam poplar increased with sheep laurel compared with control conditions, whereas willow showed no response to this treatment. Most characteristics of black spruce (except root-to-shoot ratio and number of second-order roots) improved in the presence of sheep laurel compared with the control. Thus, bluejoint was a more efficient BBS than sheep laurel. Bio-barriers comprised of bluejoint can be used as a countermeasure for controlling tree invasion of CCBE.

The influence of climate on pool inception in boreal fens

Fens are one of the two most important peatland types of the boreal biome. The fen surface is often made of contrasted microenvironments, pools and strings, distributed in a geometric arrangement known as patterned fen. The fens are under the influence of varying water regimes causing the formation of pools, a process that we named aqualysis. The term refers to the physical degradation of the vegetation cover under the influence of water ponding. It is proposed here that pool inception is among a set of differential responses of peatland ecosystems to changes in hydrology caused by climate. In this study, we have evaluated the influence of climate on pool inception using the spatiotemporal distribution of trees found dead in pools of four boreal fens of northwestern Quebec. Tree-ring dating of tree mortality allowed the determination of the most recent and synchronized periods of pool formation in the studied fens. Most trees died over the last centuries, particularly after 1750 AD. The demographic pattern of tree establishment and mortality highlights a climatic forcing linked to the Little Ice Age oscillation opposing less humid events facilitating tree colonization succeeded by more humid events causing massive tree death and pool inception. We conclude that peatland aqualysis is among the processes controlled by climate contributing to the dynamics of patterned fens through pool formation.

Transforming Abandoned Farm Fields to Conifer Plantations Reduces Ruffed Grouse Density

Abstract Natural forests likely will be unable to fulfill society’s needs sustainably for wood fiber in the near future. In an attempt to meet increasing demands while protecting intact forests, producers have increasingly considered alternative sources of timber, such as intensively managed plantations. In regions that are economically dependent on forest harvesting, abandoned farm fields are often targeted for conversion to intensive coniferous plantations. These sites are generally in an early successional stage that is dominated by deciduous stands, which provide an important habitat type for several game species, including ruffed grouse (Bonasa umbellus). Therefore, conversion could represent a loss of habitat for this species and several others that are associated with early successional deciduous stages. We conducted grouse drumming surveys in northwestern Quebec, Canada to evaluate the effects of transforming old fields into conifer plantations on ruffed grouse by comparing densities between two habitat types: abandoned farm fields (n = 22) and old fields converted to conifer plantations (n = 19). To correct any audibility bias between habitat types, we located all drumming males that were heard at each site. We then analyzed the number of individuals that were detected in the sites with repeated count models. Our results show that overall drumming males avoided plantations. Overhead cover increased drumming male densities in both habitat types, whereas lateral cover increased drumming grouse densities only in plantations. The density of deciduous stems and fruit-bearing stems also had a tendency to increase drumming male densities, but their effects were marginal. Most ruffed grouse in abandoned farm fields used piles of woody debris on the ground as drumming structures rather than large logs or rock outcrops. Our results suggest that plantations do not have the vegetative cover and quantity of food stems necessary to support high ruffed grouse densities during the drumming season and that conversion of abandoned farm fields to coniferous plantations may exert negative cascading effects for reproduction and population growth.

Using diatom assemblages and sulfur in sediments to uncover the effects of historical mining on Lake Arnoux (Quebec, Canada): a retrospective of economic benefits vs. environmental debt

Monitoring changes in environmental conditions is increasingly important as the Canadian economic infrastructure ramps up exploration and mining development in the more inaccessible northern regions of Canada. Governments are concurrently assessing effects from past mining activities and absorbing the economic cost to society with on-going remediation and monitoring initiatives. The abandoned Aldermac mine in northwestern Quebec, mined from 1932–1943, is an excellent case study for assessing the state of environmental and economic effects of past mining operations. A paleolimnological approach, using diatoms as environmental proxies, was used to evaluate the spatial and temporal impacts on aquatic receiving environments. Based on the inferences drawn from diatom assemblages in Lake Arnoux, prior to mining activity, lake water pH was similar to that of surrounding lakes (circumneutral to weakly acidic). After mining operations terminated, changes in pH and alkalinity in Lake Arnoux coincided with distinct increases in sediment sulphur content. Across a 30- to 40-year span (circa 1940 to 1970s) a significant decline in phytoplankton flora coincided with lake acidification and increased clarity of the water column. This resulted in an increase in the benthic diatom population (>90%), replacing the planktonic diatoms. Observed shifts in environmental proxies are concurrent with one, and possibly two, reported tailings pond breaches at the abandoned mine site. Adverse effects of the abandoned Aldermac mine on nearby ecosystems, combined with pressure from local citizens and environmental groups, forced responsible accountability for site restoration led by the Quebec government. Based on the historical period of economic growth, the financial benefits of the Aldermac mine were significant and justify the current pay-it-backward costs for environmental remediation. However, it has now been documented that the pay-it-backward model is not sustainable in the modern economy.

A GIS-based approach for supporting groundwater protection in eskers: Application to sand and gravel extraction activities in Abitibi-Témiscamingue, Quebec, Canada

Abstract Study region Part of Abitibi-Temiscamingue in northwestern Quebec (25,750 km 2 ), within the Quebec/Ontario Clay Belt, Canada. Study focus The focus is set on the unconfined granular aquifers found in eskers, the latter containing significant groundwater resources, both in terms of water quality and quantity. Yet, these glaciofluvial deposits also constitute the main source of exploitable sand and gravel and are therefore frequently at the roots of land use conflicts. New hydrological insights Methods and indices based on the use of geographic information systems (GIS) were developed in support of land management strategies oriented towards the protection of groundwater resources in eskers of northwestern Quebec. A groundwater resource sensitivity index was defined for each 10 × 10 m parcel of esker on the basis of (1) an evaluation of the aquifer potential based on three geomorphological parameters observable on well-known granular aquifers and (2) estimates of the parameters included in the DRASTIC method. The pressure induced by sand and gravel extraction on the groundwater resources was subsequently evaluated on the basis of (1) the resource sensitivity index, and (2) the spatial density of sand and gravel extraction sites and groundwater wells. These calculations are used to suggest solutions for supporting the sustainable management of sand and gravel extraction activities at the regional scale and for highlighting sectors where field data acquisition is most needed.

Late-stage phases of glacial Lake Ojibway in the central Abitibi region, eastern Canada

The decay of the Laurentide ice sheet southern margin during the last deglaciation led to the development of Lake Ojibway that covered large expanses of northeastern Ontario and northwestern Quebec. The history of Ojibway lake phases is poorly detailed mainly because of the physical configuration of the lake basin and the dominance of fine-grained glaciolacustrine sediments that prevent the formation of well-developed and extensive sandy strandlines. Here we use a complex sequence of relict terraces carved in glaciolacustrine rhythmites to document the evolution of Lake Ojibway in northwestern Quebec. Specifically, lake levels were constrained by measuring the elevation of 154 raised wave-cut scarps present in the eastern Lake Abitibi region. Results provide evidence for four distinct shorelines with elevations of 299, 289, 282, and 272m (±1m) at the latitude of La Sarre. The highest lake level documented appears to be linked to one of the two known (Kinojévis) phases of Lake Ojibway, while the three other lake levels project well below the main outlet system that controlled the elevation of the lake during the deglaciation. The elevation, uplift gradients, and areal extent of these lower shorelines suggest that the two intermediate lake levels likely formed during late stages of the deglaciation, following abrupt drawdowns of the lake's surface. The fourth and lowest shoreline is associated with a postglacial lake that developed after the complete withdrawal of Ojibway water from the region. These low-elevation shorelines bring new evidence for significant changes in the areal extent and depth of Lake Ojibway near the end of the deglaciation. Although the origin of these late-stage phases remains unspecified, the associated drawdowns likely implied routing events into newly deglaciated regions and/or (subglacial) meltwater discharges into the North Atlantic.

Cyclic dynamics of a boreal southern red-backed vole population in northwestern Quebec

In Fennoscandia, red-backed vole populations (Myodes spp.) often show regular fluctuations of abundance of 3- to 5-year periods. In contrast, only a few populations show evidence of cyclic fluctuations in North America. From 2001 to 2009, we livetrapped southern red-backed voles (Myodes gapperi) in 3 mature jack pine and 3 mature black spruce forest stands in the Muskuchii hills region, Quebec, Canada. We found that their density fluctuated (up to 41-fold) with a cyclical pattern and 4-year periods. Our study is the first to demonstrate cyclic dynamics in a southern red-backed vole population found in the boreal forest of North America. Regular pulse of food or heavy predation may be responsible for the fluctuations of southern red-backed voles. Furthermore, vole cycles may help elucidate the factors driving the irruptions of owls in the boreal forest.

Groundwater age investigation of eskers in the Amos region, Quebec, Canada

• Aquifers in eskers are the only source of drinking water at high latitudes. • Ages and flow difficult to quantify because heterogeneity of the medium. • Eskers in Amos contain precious water resources but no age available. • Fast flow dominate esker’s top aquifers, recharged in the last 30 years. • Flow is slow at the base of eskers with occurrence of fossil meltwater. Noble gases, in particular 3 He/ 4 He ( R ) ratios, were measured together with tritium activity in groundwater from eskers and moraines of the Abitibi-Temiscamingue region of northwestern Quebec (eastern Canada). These high-latitude glaciofluvial landforms contain precious freshwater resources that need to be quantified. Here we provide estimates of residence time for groundwater in glaciofluvial sediments forming the Saint-Mathieu–Berry (SMB) and Barraute eskers, the Harricana moraine and in the underlying fractured bedrock aquifer. The 3 He/ 4 He ratios range from 0.224 ± 0.012 to 1.849 ± 0.036Ra, where Ra is the atmospheric 3 He/ 4 He ratio (1.386 × 10 −6 ). These results suggest the occurrence of 3 He produced by decay of tritium and terrigenic 4 He produced by decay of U and Th. Calculated 3 H/ 3 He apparent ages of groundwater from the SMB esker and the Harricana moraine range from 6.6 ± 1.1 a to 32 ± 7.4 a. Terrigenic 4 He ( 4 He terr ) was found in the deeper wells of the SMB esker and in the wells tapping water from the deeper fractured aquifer located below the eskers and moraines and confined by postglacial clays. The amount of 4 He terr ranges from 3.4 × 10 −9 to 2.2 × 10 −6 cm 3 STP g −1 and shows a clear gradient with depth, suggesting addition of a 4 He terr flux entering the bottom of the eskers. Modeled 4 He terr fluxes range from 2.0 × 10 −8 cm 3 STP cm −2 yr −1 at the Harricana moraine to 6.6 × 10 −7 cm 3 STP cm −2 yr −1 in the southern section of the SMB esker. Calculated fluxes are highly variable and 5–165 times lower than the helium continental crustal flux, suggesting local helium sources, with helium being driven upward through preferential pathways such as local faults. Maximum U–Th/ 4 He ages obtained for the groundwater in the fractured bedrock range from 1473 ± 300 a to 137 ± 28 ka, suggesting the occurrence of several generations of fossil meltwater trapped under the clay plain after the last two glaciations.

Valorization of acid mine drainage treatment sludge as remediation component to control acid generation from mine wastes, part 2: Field experimentation

The possibility of using acid mine drainage (AMD) treatment sludge as a cover component to control AMD generation from mine wastes was investigated through laboratory characterization and kinetic column testing (companion paper). The results showed that mixtures of sludge and waste rock, and sludge and tailings, may be integrated in an AMD prevention and control strategy at Doyon mine site (northwestern Quebec, Canada). In order to further investigate these scenarios in realistic climatic conditions, instrumented field test cells were installed on site to evaluate the performance of the mixtures to control AMD generation from tailings and waste rock under natural field conditions. The main findings from two seasons of monitoring are presented in the paper. The waste rock-sludge mixture placed over waste rock was able to reduce the generation of AMD from the waste rock, therefore confirming lab results, and was able to produce a neutral effluent with low concentrations of dissolved metals. The tailings-sludge mixture placed over tailings, with an evaporation protection layer, maintained a high volumetric water content and reduced sulphide oxidation from the tailings as exhibited by a neutral effluent. Monitoring of the field cells will continue to provide valuable information on the possible sludge valorization options.

Effects of topography and thickness of organic layer on productivity of black spruce boreal forests of the Canadian Clay Belt region

Northern Canadian boreal forest has a considerable ecological and economic importance, with the black spruce forest type occupying a large extent of this ecosystem. Organic layer thickness and its relationship to topography are two key factors affecting tree growth and productivity of black spruce boreal forests of the Canadian Clay Belt region. This study linked multi-scale models of organic layer thickness and topography to improve our understanding of how these variables influence forest productivity and its distribution at different spatial scales within the Clay Belt region, northwestern Quebec. Field data were used to calculate site indices, which were used as estimators of forest productivity. Organic layer thickness was determined from field measurements obtained by manual probing, whereas topographic variables were extracted from multi-scale LiDAR-derived digital terrain models (DTM) at four resolutions, i.e., 5-, 10-, 15- and 20-m. Correlations between individual predictors and site index were found to be weak; however, few were significant, viz., organic layer thickness. Regression tree-based models were fitted using two different sets of explanatory variables at the four scales: organic layer thickness and topography (model 1); and topographic variables only (model 2). Organic layer thickness, aspect, and slope were the most important variables explaining forest productivity (63% and 31% total variance explained for models 1 and 2, respectively). Model 1 was found to be scale-independent, since the total explained variance was similar under the four resolutions, whereas with model 2, effects of topography on productivity were greater for coarser scales (highest R2 at 20-m resolution). Both models indicated higher forest productivity on southwest-facing slopes (i.e., >2.2%) with shallow organic layers (<35cm), so then where organic horizons are the deepest the tree productivity is low. In contrast, lowest site indices (expressing low productivity) were found in areas with very deep organic layers (>85cm). The resulting models could be applied at operational scales to predict site index at locations for which organic layer thickness information and DTM exist. Such information could be used to help forest managers in predicting how forest growth will respond to various harvesting activities.

Sapling recruitment and mortality dynamics following partial harvesting in aspen-dominated mixedwoods in eastern Canada

Boreal mixedwood management has shifted from a relatively narrow focus on commercial wood supply to greater consideration of the natural dynamics and multiple ecological services. This recognition has generated interest in ecosystem management approaches that include diversifying and adapting silvicultural practices, including partial harvesting. The effects of partial harvesting on stand dynamics was assessed over a 12-year period in trembling aspen (Populus tremuloides Michx.) dominated stands in northwestern Quebec, Canada. Four treatments were tested: clearcuts (100% basal area (BA) removal); 1/3 partial cut (1/3 PC, 33% BA removal using low thin); 2/3 partial cut (2/3 PC, 61% BA removal using high thin) and controls (0% removal). Aspen sapling recruitment was directly affected by harvesting intensity with 1/3 and 2/3 partial cuts generating 5% and 56%, respectively, of aspen sapling densities in clearcuts. Aspen sapling recruitment increased continuously following clearcut and partial cut treatments with no significant mortality in the sapling layer over the 12-year period. Recruitment of conifer saplings also increased with time and was significantly higher in the two partial cuts than in the clearcut treatment. Twelve years after treatments, mortality of residual aspen stems (⩾10cm DBH) reached 250stemsha−1 12yr−1 in controls, compared to 106, and 170stemsha−1 12yr−1 in 1/3 PC, and 2/3 PC stands, respectively. Initially (1–3years after treatments), higher overstory aspen mortality was associated with the 2/3 PC treatment. Aspen mortality was strongly associated with small-sized merchantable stems (10–19.9cm DBH) regardless of treatment. Both partial harvesting treatments had the effect of maintaining mountain maple (Acer spicatum Lamb.), a shade-tolerant, high woody shrub, at densities similar to those in control stands whereas recruitment of mountain maple saplings was negligible in clearcuts due to high aspen recruitment. Our results indicate that (i) heavy-high partial harvesting promotes sapling recruitment of both aspen and conifers when advance regeneration of the latter is present, (ii) because aspen sucker response can be controlled by varying harvesting intensities and stem selection, it is possible to create a range of mixedwood conditions, depending on whether mixed, structurally complex or more regular aspen-dominated stands are desired, and (iii) on rich mixedwood sites, tall woody shrubs could hinder desirable partial harvesting outcomes.

Long-term dynamics of a palsa in the sporadic permafrost zone of northwestern Quebec (Canada)

In the sporadic permafrost zone of the James Bay region in northwestern Quebec (Canada), permafrost has been showing signs of advanced degradation for the past 50 years. Several palsa peatlands are...

Development and activity of early saproxylic fungal communities in harvested and unmanaged boreal mixedwood stands

Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Quebec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.

Competitive Advantage of Black Spruce Over Balsam Fir in Coniferous Boreal Forests of Eastern North America Revealed by Site Index

The boreal zone of northeastern North America is characterized by mixedwood forests dominated by balsam fir (Abies balsamea (L.) Mill.) in the south and by coniferous forests dominated by black spruce (Picea mariana (Mill) B.S.P.) in the north. Site index values of balsam fir and black spruce were compared in 364 sites spread across the boreal zone of northwestern Quebec to determine if the northward dominance shift from balsam fir to black spruce could be explained by a difference in height growth. Site index of both species decreased along a south‐north gradient, although the trend was only significant for balsam fir on clay deposits. Site index values shifted from being significantly higher for balsam fir in the boreal mixedwood forest, to being slightly (but not significantly) higher for black spruce in the coniferous forest. Mean annual temperature had a significant positive effect on site index for both species, and precipitation of the growing season had a significant negative effect only for balsam fir. The competitive advantage of black spruce over balsam fir in coniferous forests is due to a greater tolerance to cooler temperatures and water-logged soils.