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ABSTRACTIn the boreal forest of eastern North America, the distribution of eastern white cedar (Thuja occidentalis) is characterized by a latitudinal fragmentation gradient from south to north. Marginal populations could be outposts allowing cedar to expand its presence in the north in response to climate change. This study aimed to characterize the spatio-temporal regeneration dynamics of 20 marginal cedar stands in order to evaluate their expansion capacity into adjacent black spruce stands. Cedar recruitment within marginal cedar stands was mainly by layering, which allowed the species to maintain for a long time in the landscape. However, the rate of expansion of marginal stands into adjacent black spruce stands through seed dispersal was very low (0.28 m.year−1) and it was negatively influenced by distance to seed trees. Substrate had no significant effect. Global warming could lead to increased seed production by cedar, which could favour the species’ expansion at its northern distribution limit. However, global warming could also increase the frequency and severity of wildfires, which would have a negative effect on cedar expansion capacity.

ABSTRACTBryophytes and pteridophytes are important contributors to ecosystem services in boreal regions. Abiotic agents are considered their main dispersers, but recent studies suggest that biotic agents including invertebrates, birds and large mammals might also be efficient dispersal agents. Dispersal of cryptogams by ground-dwelling small mammals is often assumed to occur, but has yet to be demonstrated. In this study, we present the first evidence of boreal cryptogam species being dispersed by ground-dwelling small mammals. In 2013 and 2014, we recorded bryophyte cover and fern presence in 35 sites in black spruce forest. We also collected diaspores by brushing the fur of 99 ground-dwelling small mammals live-trapped in the same sites. Diaspores were then germinated on nutrient agar for six months. Viable diaspores of five bryophyte species and one fern species were successfully grown. No association was found between the cryptogam community sampled on site and the diaspore community grown on artificial substrate. Unlike abiotic agents that randomly disperse cryptogams, small mammals are more likely to transport diaspores to suitable substrates where microhabitat requirements for germination are met. Our results highlight the need to consider a broad spectrum of dispersal agents when focusing on the community dynamics of cryptogams.

AbstractThis study aims to demonstrate that contemporary landscape vegetation heterogeneity is controlled by a combination of natural disturbances with other sets of explanatory variables. Integration of these drivers should be considered the key to explaining vegetation changes along ecological gradients characterizing the boreal forest. Forest inventory plots and maps produced from about 1970 to 2000 were used to characterize a large area (175000 km2) according to 3 vegetation themes constituting distinct aspects of forest community composition (tree species, forest types, and potential vegetation—successional stages) and 4 sets of explanatory variables (climate, natural disturbances, physical environment, and human disturbances). Canonical ordinations were performed to define ecological gradients as well as the overlap between vegetation themes and sets of explanatory variables along each gradient. For each vegetation theme, we quantified the relative proportion of vegetation variation explained by unique as well as combined sets of explanatory variables. The landscape vegetation heterogeneity described by species and potential vegetation—successional stage was mostly explained by natural disturbances and climate in association with other sets of explanatory variables. The influence of physical environment was higher for landscape vegetation heterogeneity related to forest types than for the other themes, but this theme also was dominated by natural disturbances and climate. Compared to natural sets of explanatory variables, human disturbances played a secondary but significant role in the 3 vegetation themes. This research contributes to a better understanding of the relationship between vegetation and the factors underlying its development in the boreal forest and represents an important step toward ecosystem-based management.

AbstractTo improve our understanding of climate-driven long-term dynamics of eastern Asian mountain forests, we used field surveys and dendrochronological techniques to examine regeneration density, growth rate of mature trees, and growth sensitivity to climate of 3 common coniferous tree species at their respective altitudinal distribution limits on Changbai Mountain, northeastern China. The studied species were Manchurian fir (Abies nephrolepis, distributed between 780 and 1750 m asl), Korean pine (Pinus koraiensis, 780 and 1300 m asl), and Jezo spruce (Picea jezoensisvar. komarovii, 1000 and 1750 m asl). Regeneration densities did not differ significantly among the elevations except for Jezo spruce, which showed a significantly lower regeneration density at 1000 m asl as compared to 1300 and 1750 m asl. All 3 species showed a significantly higher basal area increment (BAI) at the middle part of their distribution ranges than at their limits. The growth of Manchurian fir and Jezo spruce exhibited higher sensitivity to precipitation than to temperature at their lower distribution limits, and the inverse pattern was observed at the upper limit. In all cases the correlations between growth and the respective climate variable were positive, except for the correlation between Jezo spruce growth and precipitation. Growth of Korean pine was positively correlated with spring temperature and summer moisture at its lower distribution limit and with summer temperature at its upper limit. Our study suggests that elevational limits of forest vegetation were likely constrained by climate factors affecting growth of dominant species rather than those controlling regeneration density.

AbstractUrbanization results in ecosystem fragmentation, habitat loss, and altered environmental conditions that usually favour pioneer and ruderal species. The objective of this study was to evaluate the impact of urban conditions on liana abundance in temperate forests. Fieldwork was conducted in 50 forests of the metropolitan Montréal area (Quebec, Canada) and focused on the 6 most common lianas of the study area, Celastrus scandens, Menispermum canadense, Parthenocissus quinquefolia, Solanum dulcamara, Toxicodendron radicans, and Vitis riparia.Potential drivers of liana distribution at the landscape scale (e.g., surrounding land use, urban heat island) were quantified based on satellite images and land use maps. At the forest scale, we investigated biotic and abiotic variables in 429 sampling plots. We found that at the landscape scale, lianas benefited from urbanization, mainly through warm microclimates created by urban heat islands (UHI) as lianas are not well adapted to cold climates. At the forest scale, lianas were more abundant in disturbed forests and in edge habitats than in less disturbed forest and core habitats. Their fast growth rate enables them to quickly take advantage of high light availability on disturbed sites. Our results suggest that urbanization and ongoing climate changes will lead to an increase in liana abundance in temperate forests.

AbstractTrembling aspen (Populus tremuloides) is widely distributed in North American forests. Increased stand productivity with resource availability has been reported, but the relationship between soil microbial community structure and stand productivity remains unclear. To examine soil microbial composition of 4 aspen stand productivity classes, we assessed soil properties, microbial biomass and respiration, and bacterial and ectomycorrhizal diversity. Most variables showed no significant differences between productivity classes. However, mean values for basal respiration (0.05 to 27.99 μg CO2-C·g−1soil·h−1), bacterial biomass, and metabolic quotient (0.08 to 5.22 CO2-C·mg−1Cmic·h−1) were lowest in low productivity (Class 1) sites. Bacteria to fungi ratios were significantly lower (P= 0.05) in Class 1 compared to other classes. Microbial biomass ranged from 1.39 to 8.11 mg Cmic·g−1soil. Thirty-seven distinct aspen ectomycorrhizas (ECM) were characterized, 21 were considered rare (from ≤3 trees). ECM richness did not differ significantly between classes, although relative abundance for some types did. Canonical correspondence analysis showed productivity class explained most microbial community variation, e.g., ECM fungi (80% explained) and soil bacteria (46%). Despite some differences, we could not identify statistically significant bacterial or ECM assemblages linked to stand productivity. Results may reflect a strong association between microbial processes and the dominant host, aspen. Aspen associated with widely distributed fungi common to all classes, possibly facilitating its survival and growth, including on sites exhibiting low pH and low soil fertility.

AbstractIn boreal mixedwood stands dominated by trembling aspen (Populus tremuloides), forest tent caterpillar (Malacosoma disstria, FTC) outbreaks are recurrent events whose effects on stand dynamics are poorly documented. To describe and characterize the effects of FTC outbreaks, we assessed canopy opening, gap size, and understory tree recruitment in 12 stands dominated by trembling aspen that had experienced different levels of defoliation (in terms of severity and duration) during the last outbreak in northwestern Quebec (1999–2002). The study showed a significant increase in canopy opening and gap size with defoliation intensity. Furthermore, the proportion of large gaps and aspen mortality increased with defoliation intensity. Balsam fir (Abies balsamea) regeneration benefited from changes in canopy structure caused by the FTC, while aspen did not. Forest succession in mixedwood stands that had been defoliated for 1 y was not profoundly affected, while multiple years of defoliation likely caused more rapid canopy transition from aspen to fir. By creating a variety of gaps, FTC outbreaks modify stand structure in ways that differ from succession to coniferous dominance controlled by single-stem exclusion.

AbstractTraditional knowledge has become a topic of considerable interest within the research and development environment. The contribution of traditional knowledge to conservation and management is increasingly recognized, and implementation endeavours are underway in several countries. The current scale of ecosystem degradation underscores the need for restoration interventions. It is increasingly recognized that successful ecological restoration depends on effective coordination of science and traditional ecological knowledge. This paper synthesizes the literature to evaluate the present and potential contribution of traditional knowledge to ecological restoration. Despite a growing number of articles published on traditional knowledge, only a few have addressed its contributions to ecological restoration per se.The main contributions of traditional knowledge to ecological restoration are in construction of reference ecosystems, particularly when historical information is not available; species selection for restoration plantations; site selection for restoration; knowledge about historical land management practices; management of invasive species; and post-restoration monitoring. Traditional knowledge and science are complementary and should be used in conjunction in ecological restoration projects. Incorporation of traditional knowledge can contribute to build a strong partnership for the successful implementation of restoration projects and increase their social acceptability, economical feasibility, and ecological viability.

AbstractForest stands within the Quebec—Ontario paludification-prone Clay Belt are expected to converge to open unproductive black spruce (Picea mariana) stands regardless of initial tree composition with the prolonged absence of fire. We hypothesized that different surface deposits would display different stand transition characteristics, as recent research on the deglaciation history of the regions suggests that certain site conditions could exhibit different susceptibility to paludification. We quantified the rate and age of transitions of different succession stages for various surface deposits using a large spatio-temporal forest database. Our results suggest that a complete convergence to open and less productive black spruce stands can occur, but it may take a long time (i.e., more than 500 y), especially on surface deposits less prone to paludification, such as coarse-textured soils. We also observed that if succession pathways start with open and less productive black spruce stands, their capacity to change to more productive stands is conditioned by the surface deposit. Consequently, based on preferential age of transition, transition rates, and succession pathways, we suggest an increased susceptibility to paludification as one goes from coarse-textured deposits to fine-textured deposits and finally to restructured clay deposits, which are regionally designated as Cochrane Till. In terms of forest management, surface deposit susceptibility to paludification should be taken into account in order to minimize soil organic accumulation and the loss of tree productivity.

AbstractThe influence of site productivity on epiphyte diversity on aspen (Populus tremuloides) trunks was examined in 19 stands from northeastern British Columbia, whose site indices (dominant tree height at 50 y) ranged from 6.7 to 27.9 m. Canopy epiphyte communities responded strongly to gradients in site productivity. Correlations between plot scores along the axes of non-metric multidimensional scaling ordinations and environmental variables indicated that site index, diameter at breast height, tree age, bark cation concentrations (K, Ca, Mg, and Mn), canopy cover, and bark roughness were significant explanatory variables for epiphyte community composition at trunk base and at breast height. Less productive sites (site indices below 17.25) were dominated by crustose lichens. Indicator species in these sites included Caloplaca cerina, C. holocarpa, and Catillaria glauconigrans.Closed-canopy environments in the more productive stands were dominated by mosses. Associated indicator species included Brachytheciumspp., Pylaisiella polyantha, and Eurhynchium pulchellum.Cover of epiphytic species at breast height was higher in stands with low site indices, whereas cover of epiphytic species at trunk base was higher in stands with high site indices. These findings would suggest that management for epiphyte community diversity in aspen dominated landscapes will necessitate the retention of mature aspen stands from across a range of site productivities.

Abstract:The effects of fire severity and initial post-fire tree composition on long-term stand structural development were investigated in the Picea mariana–feathermoss bioclimatic domain of northwestern Québec. Paleoecological methods were used to categorize the severity of the last fire (high or low) and initial tree composition (Picea mariana versus Pinus banksiana). Changes in stand structure were evaluated by quantifying stand structural attributes along three chronosequences. Except for accelerating stand break-up, the post-fire presence of P. banksiana(which is eventually replaced by P. mariana) had little effect on stand structural development. Fire severity had significant effects on the evolution of stand structural attributes, with low severity fires being particularly detrimental for stand productivity. Stands colonizing low severity fires were characterized by low post-fire tree recruitment and growth and remained open throughout succession. In contrast, after high severity fires, dense productive stands were rapidly established regardless of tree composition and gradually became open as succession proceeded. These results suggest that in the prolonged absence of fire, the different stand structural development pathways gradually converge regardless of fire severity or initial composition. We argue that stand structural diversity within the coniferous boreal forest is a result of the severity of the last fire and of processes operating at the stand scale in the absence of fire.

Abstract:Fire regimes in the boreal forest are dominated by crown fires that burn over large areas. However, these fires rarely burn forest stands entirely and with the same intensity throughout, resulting in a mosaic of vegetation burnt to varying degrees of severity. The objectives of this study were to: (1) assess regeneration of tree species six or seven years after fire in relation to crown fire severity in non-salvaged jack pine and black spruce stands, and (2) assess establishment preferences of seedlings on the different types of germination beds created by fire. Logistic regressions indicated that seed trees abundance influenced regeneration success. The relationship between fire severity at the crown level and regeneration success was not significant, although seedling recruitment appeared limited in areas where severity was light to moderate. Poisson regressions showed that seedlings preferentially establish on mineral soil, and that woody debris seem to be a good substrate for germination and survival. Seedlings establish more frequently and grow better where thickness of residual organic matter is lowest. Crown fire severity, combined with severity at ground level may therefore be a good indicator of regeneration success in coniferous stands.

Abstract:In sub-boreal forests of northeastern North America, late-successional stands often contain a fine-scale mixture of several coniferous and hardwood tree species, including an important proportion of relatively shade-intolerant species such as white birch (Betula papyrifera) and yellow birch (B. alleghaniensis). In order to better understand the recruitment of these species, we determined the age at 1 m height of each tree in sample plots located in three stand types representative of different site conditions in a small forest mosaic undisturbed by humans. Three recruitment pulses occurred synchronously in all stand types during the periods 1835-1860, 1910-1930, and 1970-1990, the last two being related to known spruce budworm (Choristoneura fumiferana) outbreaks. These pulsed recruitment episodes were identified for birch species, but also for more shade-tolerant species such as balsam fir (Abies balsamifera) and to a lesser degree white cedar (Thuja occidentalis). White cedar was the only species for which there was some recruitment during the 1940-1960 period, but this was restricted to only one stand type located on mesic sites. These results indicate that when examined over relatively long periods of time, resource availability after canopy disturbances is an important factor for the recruitment above 1 m height for most tree species. In sub-boreal forests, periodic and synchronous mortality of balsam fir can favour the emergence of multi-species, multi-cohort stands, especially where soil conditions are adequate for the recruitment of other tree species.

Abstract:Two sites that burned in 1847 (H) and 1823 (I) in the mixedwood boreal forest in Québec were selected to follow aspen genetic and clonal diversity over time. At each site, three cohorts were identified by core dating, and about 30 trees per cohort were randomly selected to compare tree genotypes using four microsatellite loci. The first cohorts were of post-fire origin (large disturbance), while the second and third cohorts were promoted by gap disturbances. These gaps were created by the natural mortality of post-fire aspen trees and a spruce budworm outbreak that attacked the coniferous species. Expected heterozygosity ranged from 0.37 to 0.72 across cohorts and averaged 0.66 and 0.54 in H and I, respectively. More than 99% and 96% of the genetic variability existed within cohorts, respectively. Genotypic diversity was high in all cohorts, and most genets were unique. Only two clones suckered for three successive cohorts, indicating little selection for specific genets to dominate aspen stands with time. High genetic and clonal diversity changed slightly between post-fire and gap disturbance cohorts. Apical dominance might have favoured the suckering of genets that existed in the post-fire cohorts but that were later eliminated by natural mortality.

Abstract:Soil quality in the boreal mixedwood forest depends to a certain extent on the chemical, biochemical, and microbial properties of the forest floor. Given that forest floors are composed mainly of decomposing plant detritus, forest composition (i.e.,stand type) should play a key role in determining soil quality. Stand age is also expected to control certain forest floor properties, due to the balance in the amount and quality of substrates introduced into, and lost from, the forest floor during stand development. Finally, mineral parent material should also be related to some forest floor properties, by controlling site nutrient capital which may affect litter quality. In order to compare the relative effects of these three factors, forest floor material was collected in the Abitibi region of northwestern Québec, from replicated (n= 3) treatment plots comprising a factorial array of three stand types (spruce/fir, aspen, and paper birch), three stand ages (57, 78-85, and 131 y-old), and two parent materials (clay and till). Forest floor samples were compared on the basis of 18 variables depicting i) chemical properties, ii) base cation status, iii) nitrogen cycling, and iv) microbial properties. All three sampling factors exerted a significant effect on some of the measured forest floor properties, but parent material had a significant effect on twice the number of forest floor properties as did stand type or stand age. Besides exerting an effect on nutrient capital, we propose that parent material also affects cation exchange capacity and unsaturated hydraulic conductivity, which in turn influence litter quality and ecosystem productivity. Our results suggest, therefore, that a detailed classification of mineral parent materials might be a useful basis for interpreting and predicting soil quality in the mixedwood boreal forest.

Abstract:The forest fire regime was characterized for the boreal forest of western Québec using the provincial government’s digital databases (1945-1998). Lightning- and human-caused fires account for 71% and 29% of the total area burned, respectively. With regard to ignition sources, lightning was responsible for 38% of the fires while humans were the ignition agent for 62% of fires. The fire regime parameters (burn rate, fire occurrence, and size) were subjected to a stepwise regression analysis on the basis of regional landscape units. Models indicate that climatic factors, particularly summer precipitation and maximum temperatures, play a primary role in forest fire dynamics, regardless of the ignition source. Fire occurrence models were the most predictable with R2values of 0.79 and 0.60 for lightning fires and human-caused fires, respectively. Models of burned areas reached an R2value of 0.63 for lightning but only 0.22 for human-caused fires; on the other hand, the fire-size model for human-caused fires showed an R2value of 0.57 but only 0.24 for lightning fires. In the case of human-induced fires, the density of the road network and sand deposits were important in fire occurrence and burned areas models. Once characterized, landscape units tend to group together naturally, forming extensive areas in which the fire regime is relatively homogeneous. The results of the regionalization based on lightning fire regimes are discussed from the standpoint of sustainable forest management.

AbstractRocky outcrops represent about 30% of the boreal forest of Abitibi, Québec, Canada. Although these outcrops have similar edaphic and climatic conditions, their vegetation can vary. Some are composed of a closed forest of black spruce (Picea mariana) and eastern white cedar (Thuja occidentalis), while others support open Pinus-dominated stands. A long-term study using palynology and charcoal analysis was used to determine the processes involved in creating the open vegetation observed on one outcrop located at Roquemaure. Changes in the fire regime through time seem to be the explanatory factor. Vegetation on this outcrop started 3,775 calibrated years ago as a closed Picea mariana-dominated stand. Increase in fire frequency ca 1,465 calibrated years ago led to the replacement of the Picea mariana-dominated stand by the more open Pinuswoodland observed today. Changes in climate from wet to dry might explain this increase in fire frequency. Dry soils and exposed bedrock created by climate change and increased fire frequency limited the regeneration of Picea mariana.For future landscape management, long-term studies should be taken into consideration to determine the natural variability of ecosystems.

AbstractA dendrochronological study was performed at six sites dominated by eastern larch, Larix laricinain Québec’s southwestern boreal forest. The objectives were to reconstruct periods of larch sawfly (Pristiphora erichsonii) outbreak in the region and to determine which physical factors (precipitation, temperature, water level or drought) explained the greatest variation in radial growth. From the presence of light latewood rings followed by periods of growth suppression, we identified larch sawfly outbreaks for the years 1895-1912, 1937-1942, and 1955-1962. We suspect that additional outbreaks occurred in the early 1920s, late 1970s and early 1980s as well, but at the same time as spruce budworm outbreaks (Choristoneura fumiferana). Response function analysis demonstrated negative relationships between larch radial growth and May and August precipitation and May and September current year water level, and demonstrated positive relationships with May current year drought index and September previous year drought index. These results suggest that flooding in the early growing season and excessive water levels at the end of the growing season may negatively affect larch radial growth. Our results also indicate an increase in the year-to-year variation in radial growth in larch sites subjected to flooding. This may reflect the increase in the Lake Duparquet water level at spring break up.

AbstractTo better understand the causes of sugar maple (Acer saccharumMarsh.) replacement by beech (Fagus grandifoliaEhrh.) in the Boisé-des-Muir old-growth forest (Québec), we studied, i) the effect of beech litter on soil properties, ii) the effect of low light availability on maple survival, and iii) beech regeneration via root sprouts. Soil properties, understory light, seedling emergence and survival, height growth, and density distribution of maple and beech were compared between the old-growth stand and an adjacent managed stand where the abundance of maple regeneration was high. We did not observe any detrimental effect of beech litter on soil properties and maple early establishment. Overall light availability and maple stocking were lower, and maple density declined more markedly with increasing size in the old-growth stand than in the managed stand. The deficient maple regeneration in the old-growth stand might be related to a lack of microsites where light availability is high enough for maple survival, and not to a lack of initial recruitment in this species. In the old-growth stand, beech was located in more shaded microsites than maple but had a higher growth. Size class distributions of maple and beech suggest that beech had a higher survival rate than maple and that beech sprouts had a higher survival rate than beech seedlings. Beech seems to be better adapted than maple to survive in the deep shade of the old-growth stand. However, we expect that maple will regain its dominance in the understory of the Boisé-des-Muir with increasing stand breakup that is likely to occur in the future.

AbstractGap dynamics theory suggests that spatial and temporal patterns of species recruitment within canopy gaps may be due to differences in shade tolerance. Although this theory has been developed in low latitude forests, we suggest that it is also applicable in boreal forests. This study investigates temporal and spatial patterns of seedling and sapling regeneration in canopy gaps caused by spruce budworm. Tree seedlings, saplings, and shrubs were mapped, measured, and aged in five gaps in a 234-year-old conifer stand in the southern part of the boreal forest. Shade-tolerant fir and cedar seedlings and saplings were found in the southern part of the gaps, whereas intolerant aspen root suckers were associated with the northern part of the gaps. Within gaps, fir seedling and sapling density at the quadrat scale was negatively related to mountain maple cover. A temporal partitioning of seedlings and saplings into pre- and post-gap formation also showed a gradient of species establishment related to shade tolerance. The zone of high light in the northern part of large gaps may permit the maintenance of shade-intolerant species in these forests. However, the small area of this zone and the slowness of gap formation will limit shade-intolerant species abundance.

Abstract:Creek chub, Semotilus atromaculatus(Mitchill), has been introduced in several brook trout, Salvelinus fontinalis(Mitchill), lakes of the Laurentian Shield, Québec, Canada. The objectives of this study were to determine (i) if creek chub parasites colonized the lakes of the Laurentian Shield, (ii) if parasites were exchanged between the two fish species, (iii) the effect of the diet shift of brook trout in the presence of creek chub on its parasite fauna, and (iv) the importance of lake mean depth as a factor responsible for parasite community structure in brook trout. Eleven parasite species were identified from creek chub and fourteen from brook trout. Eight of the eleven parasite species found in creek chub colonized the lakes with creek chub. Two creek chub parasite species were exchanged with brook trout and two brook trout parasite species were exchanged with creek chub. The mean number of brook trout parasites acquired by feeding on benthic intermediate hosts was significantly higher in allopatric brook trout populations than in sympatric creek chub and brook trout populations. Larval stages of most parasite species occurred in low abundance or were absent from brook trout found in deep lakes, indicating that bird and mammal definitive hosts were not common in those lakes. A cluster analysis also showed that lakes with similar fish communities tended to clump together, suggesting that fish community structure clearly influences parasite community structure in brook trout. Brook trout parasite community structure was affected by parasite exchange, by diet shift of brook trout when living in sympatry with creek chub and by inter-lake variation due to depth and other factors.