With an increasing pressure on forested landscapes, conservation areas may fail to maintain biodiversity if they are not supported by the surrounding managed forest matrix. Worldwide, forests are managed by one of two broad approaches—even- and uneven-aged silviculture. In recent decades, there has been rising public pressure against the systematic use of even-aged silviculture (especially clear-cutting) because of its perceived negative esthetic and ecological impacts. This led to an increased interest for uneven-aged silviculture. However, to date, there has been no worldwide ecological comparison of the two approaches, based on multiple indicators. Overall, for the 99 combinations of properties or processes verified (one study may have evaluated more than one property or process), we found nineteen (23) combinations that clearly showed uneven-aged silviculture improved the evaluated metrics compared to even-aged silviculture, eleven (16) combinations that showed the opposite, and 60 combinations that were equivocal. Furthermore, many studies were based on a limited study design without either a timescale (44 of the 76) or spatial (54 of the 76) scale consideration. Current views that uneven-aged silviculture is better suited than even-aged silviculture for maintaining ecological diversity and processes are not substantiated by our analyses. Our review, by studying a large range of indicators and many different taxonomic groups, also clearly demonstrates that no single approach can be relied on and that both approaches are needed to ensure a greater number of positive impacts. Moreover, the review clearly highlights the importance of maintaining protected areas as some taxonomic groups were found to be negatively affected no matter the management approach used. Finally, our review points to a lack of knowledge for determining the use of even- or uneven-aged silviculture in terms of both their respective proportion in the landscape and their spatial agency.

Because of their scarcity, protected areas alone cannot maintain biodiversity. Therefore, it is necessary to create conditions appropriate for plants and wildlife in managed landscapes. We compared the effects of different intensities of forest management on functional responses of vascular understory plants using the fourth-corner method. We analysed functional community composition along a management gradient that spanned semi-natural forests to extensively managed forests (naturally regenerated cuts) to intensively managed forests (planted forests) in Canada. Results showed trait filtering along the gradient of forest management intensity. In natural and extensively managed forests, where forest retention was high in time and space, persistence traits (e.g. perennial geophytes or chamaephytes, non-leafy stem foliage structure) were maintained. At the opposite end of the gradient, in intensively managed plantations where forest retention elements (e.g. amount of dead wood) were reduced, trait filtering led to species associated with colonization, such as tall species with limited lateral extension. These results suggest that intensive forestry conducted over a large extent may change the functional composition of understory plants.

Tree plantations are commonly used to restore abandoned agricultural fields with varying degrees of success. Agricultural soils differ from forest soils in nutrient availability and microbial communities. The objective of this study was to test the effect of adding small amounts of forest soil on the survival, growth and rates of mycorrhizal fungal colonization of trees planted in an abandoned agricultural field over the crucial first three growing seasons. Seedlings of two arbuscular mycorrhizal (AM) and two ectomycorrhizal (EM) tree species were planted in an abandoned agricultural field. Soil inocula were taken from four forest stands, each dominated by one of the planted species. Half of the soil samples were sterilized before inoculation to distinguish microbial from nutrient effects. The effect of the quantity of soil inoculum added was tested using 300 and 1500 ml of forest soil. Tree mortality was low and did not vary between treatments. The growth of EM tree species responded, positively or negatively, to forest soil inoculation. A negative feedback was detected on the growth of red oak seedlings inoculated with red oak soil. Seedlings inoculated with EM sterilized soils were smaller than control seedlings, presumably due to lower nutrient availability of EM forest soils compared to agricultural field soil. The majority of the effects, either positive or negative, were observed the first year. After three seasons of growth, only yellow birch seedlings that had received 1500 ml of non-sterilized red oak soil still benefited from soil inoculation. More research is needed in nutrient-limited soils to determine whether inoculation would have greater or longer term benefits on tree survival and growth. © 2016

We studied three hybrid poplar plantations in Quebec (Canada) established on sites with varying soil and environmental characteristics to investigate the effects of logging residues on the water potential, carbon isotope ratio and foliar nutrients of planted trees. On each site, four treatments representing different residue loads, as well as treatments aimed at manipulating specific factors of the environment (Herbicide, Geotextile) were applied to test their effects on seedling water potential, carbon isotope ratio and foliar nutrients. Along with analyses of variance, we used structural equation modelling to infer causal relationships of logging residues on height, basal diameter and foliar nutrition of trees through their effects on soil temperature, soil water content and competing vegetation cover. Logging residues decreased soil temperature at all sites and woody plants cover at one site out of three. Height, basal diameter and unit leaf mass were strongly related to each other. Foliar ?13C, N concentration and unit leaf mass increased with decreasing cover of woody plants suggesting an important role of competition for resources. Overall, logging residues had no direct influence on hybrid poplar dimensions after two growing seasons: their effects on the microenvironment of this resource demanding tree species were either cancelling out each other, or were not significant enough to have a significant impact on the growth drivers measured. For example, presence of logging residues might reduce soil temperature, impeding overall seedling performance. Our study highlights the fact that any given silvicultural method aimed at manipulating logging residues has a complex influence involving the interaction of multiple environmental drivers and that the net effect on tree productivity will depend on species and site specific conditions.

A climate warming of 2–5°C by the end of the century will impact the likelihood of seed germination of sugar maple (Acer saccharum), a dominant tree species which possesses a restricted temperature range to ensure successful reproduction. We hypothesize that seed origin affects germination due to the species’ local adaptation to temperature. We tested this by experimentally investigating the effect of incubation temperature andtemperatureshifting on sugarmaple seed germination fromseven different seed sources representing the current species range. Survival analysis showed that seeds from the northern range had the highest germination percentage, while the southern range had the lowest. The mean germination percentage under constant temperatures was best when temperatures were ?5°C, whereas germination percentages plummeted at temperatures ?11°C (5.8%). Cool shifting increased germination by 19.1% over constant temperature treatments and by 29.3% over warm shifting treatments. Both shifting treatments caused earlier germination relative to the constant temperature treatments. A climate warming of up to +5°C is shown to severely reduce germination of seeds from the southern range. However, under a more pronounced warming of 7°C, seed germination at the northern range become more affected and now comparable to those found from the southern range. This study states that the high seed germination percentage found in sugarmaple at the northern range makes it fairly resilient to the warmest projected temperature increase for the next century. These findings provide forestmanagerswith the necessary information to make accurate projections when considering strategies for future regeneration while also considering climate warming.

Les forêts nord-américaines dominées par l’érable à sucre (ERS, Acer saccharum Marsh.) sont de plus en plus influencées par des modifications des conditions environnementales d’origine anthropique. Pour remédier à cette situation, des traitements sylvicoles adaptés sont nécessaires. Même s’il est généralement accepté que la santé de l’ERS est liée à la fertilité du sol et qu’il y a une littérature abondante sur la dynamique de la régénération des peuplements composés d’ERS et de hêtre à grandes feuilles (HEG, Fagus grandifolia Ehrh.) en fonction de la disponibilité de lumière, l’interaction entre ces deux facteurs a rarement été étudiée. Notre objectif principal était donc de vérifier le rôle potentiel d’une interaction entre la lumière et le sol sur la dynamique des peuplements composés d’ERS et de HEG. Nous avons utilisé un dispositif factoriel à trois facteurs (intensité de récolte, chaulage et élimination des gaules de hêtre) pour tester cette interaction. Nos résultats montrent que la croissance radiale des arbres et des gaules d’ERS et de HEG était positivement influencée par l’ouverture du couvert, mais pas par le chaulage. Le chaulage n’a pas favorisé les semis de HEG, mais il a favorisé ceux d’ERS dans des situations spécifiques d’ouverture du couvert, ce qui confirme, bien que partiellement, l’hypothèse de l’interaction entre la lumière et le sol. Globalement, le chaulage a eu des effets très limités sur la dynamique des peuplements composés d’ERS et de HEG comparativement aux traitements d’ouverture du couvert et d’élimination des gaules de HEG. Nous ne préconisons pas l’utilisation généralisée du chaulage puisque les autres stratégies sylvicoles testées ont produit des résultats plus prometteurs pour favoriser l’ERS aux dépens du HEG. [Traduit par la Rédaction]

We quantified the effects of different loads of forest logging residues on the microenvironment (soil temperature, soil volumetric water content, competing vegetation cover, and available nutrients) of planted hybrid poplars one year after planting, and assessed the corresponding seedling growth until the third growing season. In four experimental plantations across Quebec (Canada), we used a factorial design of four residue loads that were applied at the tree-level over three planted species: hybrid poplars ( Populus spp.), black spruce ( Picea mariana (Mill.) BSP), and either jack pine ( Pinus banksiana Lamb.) or white spruce ( Picea glauca (Moench) Voss), depending upon the site. Logging residues linearly decreased competing vegetation cover on two of four sites and reduced fluctuations in soil temperature on all sites. Logging residues also decreased summer soil temperatures at all sites through a negative quadratic effect. On one site, the frequency of freeze-thaw cycles increased under logging residues, while logging residues increased soil water content on another site, for certain measurement events. Logging residues did not affect available nutrients. Seedlings showed no consistent growth response to logging residues for three years after planting, except for a beneficial effect of logging residues on hybrid poplar growth on one site. Because logging residues affected seedling microclimate and competing vegetation, their maintenance and on-site spatial arrangement on site could be used to manipulate the growing conditions for planted trees.

In their Review “The consequence of tree pests and diseases for ecosystem services” (15 November 2013, p. 823), I. L. Boyd et al. discuss the effects of pests on forest ecosystem services. However, urban forests garnered little attention. With increasing global trade, urban trees are among the first affected by newly introduced pests. Low tree diversity combined with low tree density in cities limits the potential for compensatory responses of ecosystems, unlike the model presented by Boyd et al. Decades ago, diseased elms were felled en masse in cities in eastern North America; many of the same cities are bracing yet again for extensive canopy loss, this time due to emerald ash borer (1). Boyd et al. suggest that cultural services are affected, but a more complete portfolio includes services important to city dwellers, such as air pollution removal and climate regulation (2, 3). As Boyd et al. suggest, planting more species and species selection will reduce losses to new tree pests. However, few species tolerate urban conditions, leading to overuse of those that do. Greater genetic diversity within species is particularly important to address enhanced pest risks in urban areas (4). Chemical treatments of urban trees can prolong their service life while also controlling pest spread (1). Outbreak-related tree removals cost millions. A greater investment in better infrastructure and soil [e.g., (5)] would be a cost-effective way to reduce stress and permit more species to be planted.

Partial harvesting during the snow-free season disturbs the forest floor and modifies seedbed characteristics. Quantitative information is lacking about the distribution of changes in seedbed proportions between areas located in and outside skid trails, and about how long these changes persist after harvest. These effects could interact with species’ seedbed requirements and seed input and influence spatio-temporal patterns of seedling establishment in forests, which would have important implications for regeneration dynamics. The objectives of this study were to determine how selection cutting affects seedbed proportions in and outside skid trails in northern hardwood stands, how these seedbed proportions vary over time following harvest, and how seedbed proportions in selection cuts compare with unharvested stand conditions. We sampled 12 sugar maple-dominated stands in southeastern Quebec, Canada. Two had not been harvested in the recent decades, while 10 had been harvested through selection cutting, 1–3 years earlier. A total of 3600 quadrats were sampled to determine the proportions of 8 seedbed types and whether or not a quadrat was located in a skid trail. This was the case for 24.1% of the quadrats in selection cuts. Outside skid trails, seedbed proportions in selection cuts did not vary from those in unharvested stands. In these stands, leaf litter was the most abundant substrate, covering 87.3% of the forest floor, followed by rotten wood (4.9%) and fresh wood (3.0%). Humus, rocks and live tree bases occupied 1–2% the forest floor, while mineral soil and moss covered less than 1%. In selection cuts, proportions of rotten wood and live tree bases were lower in skid trails than outside, and this difference persisted 13 years after harvest. In 1- and 2-year-old cuts, the proportion of litter was lower in skid trails than outside, but not later on. The proportions of mineral soil and disturbed humus increased sharply in the skid trails after harvest (17.1-fold and 2.7-fold increases, respectively), but these effects lasted only 3 years for mineral soil and 1 year for humus. Power functions were used to model variation in litter, mineral soil and disturbed humus proportions as a function of time since harvest. We discuss the implications for regeneration dynamics of the marked, but short term increase in mineral soil and disturbed humus availability. Spatially explicit models that can simulate the mid- to long-term availability of substrates in both time and space would be useful for assessing the long-term implications of harvesting on seedbed proportions and regeneration patterns.

Partial cutting has been proposed as a means to better conserve biodiversity in managed forest landscapes. However, partial cutting encompasses many forms of silviculture; some with implicit goals of maintaining biodiversity such as multicohort harvesting or others which may specifically focus on regeneration of stands but may still provide some additional benefits for biodiversity such as shelterwood harvesting. Here we compared ground beetle assemblages of clear cuts, shelterwoods, multicohort harvested stands and uncut stands collected using pitfall traps both 2 and 3-years post-harvest. We hypothesized that partial cutting treatments would maintain assemblages that were more similar to uncut stands than to clear cuts. We further hypothesized that among partial cuts the multicohort harvested stands, with relatively high levels of retention (66%), would maintain beetle assemblages that were more similar to uncut stands than would shelterwoods, which had lower levels of retention (50%). We collected 6692 individuals, representing 42 species. Catch rates of beetles were similar among all harvested treatments (shelterwood, multicohort and clear cuts) and lower than uncut stands. Species richness and composition was similar between shelterwood and multicohort stands. Both partial cut treatments fell between clear cuts and uncut stands in terms of species richness and compositional similarity. Compositional differences between uncut stands and partial cut stands were defined primarily by reduced abundances of forest associated species such as Agonum retractum (LeConte), Synuchus impunctatus (Say) and four Pterostichus species within partial cuts. Within partial cuts, beetle assemblages differed between machine corridors with 0% retention and adjacent partial cut strips (50% retention) and uncut vegetation corridors (100%). We conclude that both shelterwoods and multicohort harvesting stands provide at least initially similar benefits for biodiversity compared to clear cutting although neither maintains assemblages consistent with those found in uncut stands. We expect that these similarities will end once trees are removed from shelterwoods. The reductions in abundances within partial cuts may extend the time necessary for individual populations to increase to pre-harvest levels in partial cuts. For land-managers, similar initial responses of beetle assemblages in multicohort and shelterwood harvests may permit some flexibility for conservation planning whereby final removal of seed trees within shelterwoods could be delayed depending on the status of recovering beetle populations.

L’aménagement forestier contribue à simplifier la structure et la composition forestière. En conséquence, le maintien de la complexité structurelle est de plus en plus cité comme objectif de l’aménagement durable des forêts. Différentes initiatives proposent d’utiliser les coupes partielles de manière à augmenter la complexité des forêts. En utilisant la longueur de la description des patrons forestiers comme un nouvel indicateur de complexité des forêts, nous avons comparé les effets de deux intensités de coupes partielles sur la complexité des patrons forestiers, aux complexités mesurées dans des forêts fermées. Nos résultats montrent que les coupes partielles permettent d’augmenter la complexité des patrons forestiers par rapport aux forêts matures et secondaires.

Les conditions lumineuses jouent un rôle important dans la dynamique forestière et sont directement affectée par les interventions sylvicoles. L'objectif de cette étude était de déterminer comment les conditions lumineuses du sous-bois d'un peuplement boréal mixte sont affectées par des variations dans l'intensité et le patron spatial de récolte. À l'aide du modèle de simulation SORTIE-ND, nous avons simulé neuf traitements de coupe partielle en combinant trois taux de prélèvement (30 %, 45 % et 60 % de la surface terrière) et trois patrons de récolte (uniforme, par bandes étroites et par trouées). Nos résultats démontrent que la récolte n'augmente pas nécessai-rement la transmission de la lumière en sous-étage d'une façon proportionnelle au taux de prélèvement, le patron spatial de récolte jouant un rôle déterminant. De façon générale, on observe que, pour un même niveau de prélè-vement, un patron de récolte plus agrégé génère des conditions lumineuses plus élevées.

In the context of partial harvesting, adequately managing post-harvest light conditions are essential to obtain a desired composition of tree species regeneration. The objective of this study was to determine how varying the intensity and spatial pattern of harvest would affect understory light conditions in boreal mixedwood stands of northwestern Quebec using the spatially explicit SORTIE-ND light model. The model was evaluated based on comparisons of observed and predicted light levels in both mapped and un-mapped plots. In mapped plots, reasonably accurate predictions of the overall variation in light levels were obtained, but predictions tended to lack spatial precision. In un-mapped plots, SORTIE-ND accurately predicted stand-level mean GLI (Gap Light Index) under a range of harvest intensities. The model was then used to simulate nine silvicultural treatments based on combinations of three intensities of overstory removal (30%, 45% and 60% of basal area) and three harvest patterns (uniform, narrow strips, large gaps). Simulations showed that increasing overstory removal had less impact on light conditions with uniform harvests, and a more marked effect with more aggregated harvest patterns. Whatever the harvest intensity, uniform cuts almost never created high light conditions (GLI > 50%). Gap cuts, on the other hand, resulted in up to 40% of microsites receiving GLI > 50%. Our results suggest that either a 30% strip or gap cut or a 45–60% uniform partial harvest could be used to accelerate the transition from an aspen dominated composition to a mixedwood stand because both types of cut generate the greatest proportion of moderately low light levels (e.g., 15–40% GLI). These light levels tend to favour an accelerated growth response among shade-tolerant conifers, while preventing excessive recruitment of shade-intolerant species. A better understanding of how spatial patterns of harvest interact with tree removal intensity to affect understory light conditions can provide opportunities for designing silvicultural prescriptions that are tailored to species’ traits and better suited to meet a variety of management objectives.

Forest management has been criticised in the last 20 years for its negative impact on the native species, structures and functions of the forest. Of many possible alternatives proposed to minimize these effects, the functional zoning (or TRIAD) approach is gaining popularity in North America. The goal of this approach is to minimize the negative environmental impacts of forestry while maintain timber supply by dividing the forest into three broad land-use zones: (1) conservation, (2) ecosystem management, and (3) wood production. In this study, we used a spatially explicit landscape model to simulate the effects of fire and six different forest management scenarios on a boreal mixedwood forest management unit in central Quebec. The management scenarios examined included the current practices scenario, a scenario proposed by the provincial government, and four TRIAD scenarios varying in the amount of forest allocated to each of the three zones. For each scenario, we examined the harvest volume, percentage old-growth forest or old forest managed to favour old-growth attributes, and effective mesh size of forest patches by 20-year age classes. With more area set aside for conservation and high-retention partial cut harvesting techniques designed to maintain the attributes of old-growth stands, all TRIAD scenarios resulted in higher percentages of stands with old-growth attributes than the current practices scenario and the government proposed scenario, and two of the four TRIAD scenarios also resulted in higher harvest volume over the long term. All forest management scenarios resulted in significantly lower effective mesh size than the fire-only scenario, but this difference was not as pronounced for the four TRIAD scenarios as for the current practice and government proposed scenarios. We conclude that the TRIAD approach has the potential to minimize some of the negative impacts of forestry on the landscape, while maintaining timber supply over the long term.

The TRIAD approach to forest management involves dividing the forest into 3 zones, each with its own management objectives, but with the overall goal of increasing the ecological and economic sustainability of the forest. For the past 5 years, we have been experimenting with TRIAD zoning in central Quebec, incorporating social interests into the original concept of TRIAD management. Results generally indicate that this approach is economically viable, socially acceptable, and preferable ecologically in this area. Although much remains to be done, thus far the consensus among the various project participants is that this approach may be a good fit for the public forest of Canada.

Dans le cadre d’un aménagement forestier TRIADE, la forêt est divisée en trois zones ayant chacune ses propres objectifs d’aménagement. L’objectif global est cependant toujours l’atteinte d’une gestion durable au niveau écologique et économique. Depuis 5 ans, nous expérimentons avec le concept de zonage TRIADE au centre du Québec, incorporant les intérêts sociaux dans le concept original de la TRIADE. Nos résultats indiquent que cette approche est viable au niveau économique, acceptable au niveau social et préférable au niveau écologique. Il nous reste beaucoup à faire, mais le consensus général des nombreux participants est que cette approche pourrait nous aider à mieux gérer les forêts publiques du Canada.

Definitions of what constitutes an ‘old-growth’ forest are manifold and often ambiguous. This chapter starts with a review of existing concepts and critically examines their usefulness in the context of ecosystem functioning and forest conservation. Using examples from all major forests biomes, the merits and limitations of structural, successional and biogeochemical definitions are discussed. Second, the plethora of related terms (primary, pristine, intact, virgin, etc.) is screened. A semantic meta-analysis based on entries in the Web of Science reveals that the usage of terminology in the literature depends strongly on the time period, discipline, and scientific community. Third, a model is presented that combines literature data on natural disturbance intervals and maximum longevities of pioneer trees to estimate the landscape fraction covered by old-growth forests (using the successional definition) without human impact. This fraction varies and is about 90%, 50% and 20% in tropical, temperate and boreal forest, respectively. Finally, detection and mapping methods of old-growth forests are discussed and a pragmatic approach to defining old-growth forest is advocated.

Questions: What climate variables best explain fire occurrence and area burned in the Great Lakes-St Lawrence forest of Canada? How will climate change influence these climate variables and thereby affect the occurrence of fire and area burned in a deciduous forest landscape in Témiscamingue, Québec, Canada?

Location: West central Québec and the Great Lakes-St Lawrence forest of Canada.

Methods: We first used an information-theoretic framework to evaluate the relative role of different weather variables in explaining occurrence and area burned of large fires (>200 ha, 1959-1999) across the Great Lakes-St Lawrence forest region. Second, we examined how these weather variables varied historically in Témiscamingue and, third, how they may change between the present and 2100 according to different scenarios of climate change based on two Global Circulation Models.

Results: Mean monthly temperature maxima during the fire season (Apr-Oct) and weighted sequences of dry spells best explained fire occurrence and area burned. Between 1910 and 2004, mean monthly temperature maxima in Témiscamingue showed no apparent temporal trend, while dry spell sequences decreased in frequency and length. All future scenarios show an increase in mean monthly temperature maxima, and one model scenario forecasts an increase in dry spell sequences, resulting in a slight increase in forecasted annual area burned.

Conclusion: Despite the forecasted increase in fire activity, effects of climate change on fire will not likely affect forest structure and composition as much as natural succession or harvesting and other disturbances, principally because of the large relative difference in area affected by these processes.

Tree mortality is a major force driving forest dynamics. To foresters, however, tree mortality is often considered a loss in productivity. To reduce tree mortality, silvicultural systems, such as selection cuts, aim at removing trees that are more likely to die. In order to identify trees with higher risks of mortality, field classifications are employed that assess vigour based on external characteristics of trees. We used a novel longitudinal approach for estimating survival probabilities based on ring-width measurements, initially developed by Bigler and Bugmann [Bigler, C., Bugmann, H., 2004. Predicting the time of tree death using dendrochronological data. Ecol. Appl. 14 (3), 902 914], to parameterize a survival probability model for sugar maple (Acer saccharum Marsh.) and to test whether field-assessed tree vigour classes are corroborated by survival probabilities determined from radial growth history. Data from 56 dead and 321 live sugar maples were collected in stands in western Quebec (Canada) that had undergone a selection cut H"10 years prior to sampling. Our results showed that tree vigour established from external defects and pathological symptoms, using the classification of Boulet [Boulet, B., 2005. Défauts externes et indices de la carie des arbres: guide d interprétation. Publication du Québec, Sainte-Foy, Quebec. 291 pp.], is partially corroborated by growth-driven survival probabilities. Moribund trees had lower survival probabilities than vigorous trees over several years in the period prior to vigour assessment. Intermediate vigour classes showed less obvious tendencies, but this may be due to the growth-independent nature of some defects used for their classification. Although the timing of tree death may not be correctly predicted by the vigour classification (i.e., our results suggest that time of death generally was overestimated), its general agreement with survival probabilities determined from growth series make it a useful tool for tree selection in sugar maple stands under selection management.<b> &#169; Elsevier B.V. All rights reserved.</b>

Single-tree selection cutting is sometimes believed to be similar to the natural gap disturbance regime of hardwood forests, but few studies have specifically compared the compositional and structural characteristics of old-growth hardwood stands, undergoing natural gap dynamics and hardwood stands previously subjected to partial cuts. This study characterized and compared the composition (saplings and trees) and structure (gaps, foliage distribution, tree diameter and density, snags and coarse woody debris) of old-growth stands (OG), 12-year-old selection cuts (SC), and 28–33-year-old diameter-limit cuts (DLC) in sugar maple (Acer saccharum)-dominated northern hardwood stands.

Results showed marked structural differences between OG and harvested stands, with stronger differences between DLC and OG than between SC and OG. The synchronized formation of numerous canopy openings in harvested stands induced a massive post-harvest recruitment of advance regeneration in both SC and DLC that created a dense foliage layer in the understory. Large living trees (dbh > 39.1 cm) and defective trees were less numerous in SC than OG, which can have a detrimental impact on species dependent on these structural elements, and on the future availability and characteristics of coarse woody debris. Relatively few compositional differences were noticed among stand types, although a greater proportion of mid-tolerant species was found in the post-harvest recruitment cohorts of harvested stands compared to OG, and a lower proportion of beech (Fagus grandifolia Ehrh.) saplings was observed in DLC compared to OG and SC.

We argue that even if selection cutting is closer to the natural disturbance regime of hardwood forests than diameter-limit cutting, and therefore representing progress toward the development and implementation of a natural-disturbance-based management, a recurring application of selection cutting might lead to a homogenization of forest structure and composition, a reduction of key structural features and a reduction in biological diversity at both the stand and landscape scales. Some management recommendations are proposed. © 2005 Elsevier B.V. All rights reserved.

Canopy gaps play an important role in the dynamics of old-growth forests, although it is not well known how gap dynamics differ among regions. To further our understanding of natural gap dynamics in mixedwood forests, this study compares mixed stands located in eastern (Gaspésie region) and western (Témiscamingue region) Quebec. We tested whether the gap fraction in mixedwood stands was similar in these two regions. Data from field transects were used to characterize current canopy gaps, and aerial photos were used to contrast gap characteristics before and after the most recent spruce budworm (Choristoneura fumiferana Clem.) outbreak, which occurred from 1973 to 1991 in Gaspésie and from 1972 to 1984 in Témiscamingue. The current gap fraction was found to differ between the two regions: it varied from 2% to 48% with an average of 25.6% for the Gaspésie region and from 24% to 52% with an average of 36.6% for the Témiscamingue region. While the last spruce budworm outbreak coincided with a significant increase in canopy openings in the Témiscamingue region (p = 0.047), no such effect was observed in Gaspésie. These results suggest that the temporal pattern of small-scale disturbances can vary among regions, even when similar forest types are compared.

On sait que les trouées de canopée sont importantes pour la dynamique des peuplements de fin de succession, mais nous disposons de peu d'informations sur la variabilité inter-régionale. Dans le but d'améliorer nos connaissances sur la création des trouées en forêt mixte, cette étude compare des peuplements mélangés de l'est (Gaspésie) et l'ouest (Témiscamingue) du Québec. Nous avons vérifié si le pourcentage d'ouverture de la forêt, pour un même type de forêt, est similaire dans ces deux régions. Des données provenant de transects établis sur le terrain on permis de caractériser les ouvertures actuelles, et des photographies aériennes ont été utilisées pour comparer la proportion de trouées avant et après la dernière épidémie de tordeuse des bourgeons de l'épinette (Choristoneura fumiferana Clem.), qui a eu lieu entre 1973 et 1991 en Gaspésie et de 1972 à 1984 au Témiscamingue. Les résultats obtenus indiquent que le degré d'ouverture de la canopée diffère entre les deux régions : en Gaspésie, le pourcentage d'ouverture de la forêt varie de 2 à 48 % avec une moyenne de 25,6 % alors qu'au Témiscamingue il varie de 24 à 52 % avec une moyenne de 36,6 %. Alors que la dernière épidémie de tordeuse des bourgeons de l'épinette a coïncidé avec une augmentation significative des ouvertures de canopée dans le Témiscamingue (p = 0,047), un tel effet n'a pas été observé en Gaspésie. Ces résultats suggèrent que le taux de création de petites ouvertures peut varier entre les régions, même lorsque des types forestiers similaires sont comparés. ©2005 NRC Canada

1 We investigated recovery following small-scale disturbance, i.e. selection cutting, by determining how understorey light profiles vary over time in temperate deciduous forests in Quebec (Canada).

2 We measured light availability (% PPFD, photosynthetic photon flux density) 0.2, 1, 2 and 5 m above the forest floor, as well as the density of saplings < 5 m in height, in seven Acer saccharum-Betula alleghaniensis-Fagus grandifolia stands that had been subjected to selection cutting 1-13 years before the study, and in adjacent uncut plots.

3 In the most recent cut (1 year old), mean % PPFD was 3.5 to 5 times higher (depending on height) than in the uncut plot. Light availability rapidly decreased over time following selection cutting, especially near the forest floor. By about 13 years after cutting, light availability was similar to levels observed in the uncut plots.

4 Light profiles were used to assess the temporal pattern of recovery of the understorey after selection cutting, and four recovery phases could be identified. Uncut stands were characterized by profiles with low light near the forest floor and with a rather slow increase in light with increasing height, and recent cuts (1-4 years old) were characterized by J-shaped light profiles with relatively high % PPFD at all heights. Intermediate-age cuts (7-8 years old) were characterized by reverse J-shaped profiles that had a high % PPFD (13-46%) at 5 m, and very dark conditions (< 2%) near the forest floor, and were associated with high abundance of saplings. The relative frequency of the various profiles found in older cuts (11-13 years old) was generally similar to that observed in the uncut stands, except that the reverse J-shaped profiles were slightly more frequent.

5 As the microsuccession that follows canopy disturbance is very much influenced by local understorey structure and composition, forestry practices should consider such microscale forest characteristics in their harvest planning to regenerate the desired tree species.

Temporal, spatial, and structural patterns of adult trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) mortality were studied in intact 150-year-old stands in the southwestern boreal forest of Quebec. For both species, mortality decreases (number of dead trees/total number of trees) with distance from the lake edge until 100–150 m, from which point it slightly increases. Strong peaks in mortality were found for 40- to 60-year-old aspen mainly between 1974 and 1992. Such mortality in relatively young aspen is likely related to competition for light from the dominant canopy trees. Also, the recruitment of this young aspen cohort is presumably the result of a stand breakup that occurred when the initial aspen-dominated stand was between 90 and 110 years old. For spruce, strong peaks in mortality were found in 110- to 150-year-old trees and they occurred mainly after 1980. No clear explanation could be found for these peaks, but we suggest that they may be related to senescence or weakening of the trees following the last spruce budworm outbreak. Suppressed and codominant aspen had a much higher mortality ratio than spruce in the same height class, while more surprisingly, no difference in mortality rate was found between dominant trees of the two species. Most spruce trees were found as standing dead, which leads us to reject the hypothesis that windthrow is an important cause of mortality for spruce in our forests.

Les patrons de mortalité temporel, spatial et structurel ont été établis pour le peuplier faux-tremble (Populus tremuloides Michx.) et l'épinette blanche (Picea glauca (Moench) Voss) adultes dans des forêts de 150 ans situées dans le sud-ouest de la forêt boréale du Québec. Chez les deux espèces, on observe une diminution de la mortalité (nombre d'arbres morts / nombre d'arbes total) du bord du lac jusqu'à 100–150 m et une faible augmentation par la suite. La mortalité était importante chez les peupliers de 40 à 60 ans et s'était produite entre les années 1974 et 1992. Cette mortalité chez les jeunes peupliers est probablement reliée à la compétition pour la lumière venant des arbres dominants. Le recrutement de cette jeune cohorte de peuplier est présumé être le résultat d'une ouverture assez soudaine du peuplement mature de peuplier entre les années 90 et 110 ans. Chez l'épinette blanche, une mortalité importante fut observée pour les arbres âgés entre 110 et 150 ans et s'est produite surtout après 1980. Nous croyons que cette mortalité est induite par la sénescence des arbres, ou en raison de leur affaiblissement suite à l'épidémie de la tordeuse des bourgeons de l'épinette. Les peupliers supprimés et codominants avaient un taux de mortalité beaucoup plus élevé que les épinettes, mais il n'y avait pas de différence entre les arbres dominants des deux espèces. La plupart des épinettes étaient morts debout, ce qui rejette l'hypothèse voulant que le vent soit une cause importante de mortalité chez l'épinette.©2004 NRC Canada

The SAFE (sylviculture et aménagement forestiers écosystémique) project was set up in 1998 in the Lake Duparquet Research and Teaching Forest to test stand-level silvicultural treatments designed to reflect different aspects of natural forest dynamics. In the winter of 1998–1999, four levels of forest harvesting, including a no-harvest and a clearcut treatment, were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands according to a complete block design with three replications. Two partial cut treatments removed 33% and 61% of the stand basal area. During the first growing season, harvesting induced a large increase in indigenous understorey biomass that paralleled changes in the canopy opening. Aspen sucker density increased from 4916 stems/ha in the control to 28 751 and 63 333 stems/ha in the one-third and two-thirds harvesting treatments and 102 916 stems/ha in the clearcut. Most changes in nutrient cycling occurred in the second year and included an increase in forest floor organic C, total N, and base cation availability and a decrease in microbial C/N ratio. These changes may have occurred in response to reduced vegetation uptake and woody debris abundance.

Le projet SAFE (sylviculture et aménagement forestiers écosystémique) a débuté en 1998 dans la Forêt d'enseignement et de recherche du lac Duparquet afin de tester différents traitements sylvicoles inspirés de la dynamique naturelle des peuplements. Quatre intensités de récolte, incluant la coupe totale, la récolte de 33 et 61% de la surface terrière totale et un traitement témoin non coupé, ont été appliquées à des peuplements équiennes de tremble (Populus tremuloides Michx.) au cours de l'hiver 1998–1999, selon un plan en block complet avec trois répétitions. La végétation de sous bois a répondu par une augmentation de sa biomasse proportionnelle à l'ouverture du couvert. Au cours de la première année, la densité des drageons de tremble était de 4916 tiges/ha dans le traitement témoin, 28 751 et 63 333 tiges/ha dans les coupes partielles et 102 916 tiges/ha dans la coupe totale. La plupart des changements observés dans le cycle des nutriments sont survenus dans la couverture morte pendant la deuxième année suivant la coupe. Parmi ceux-ci figurent une augmentation du C organique, du N total et des cations basiques échangeables et une diminution du ratio C/N de la biomasse microbienne. La diminution du prélèvement par les plantes et les changements dans l'abondance des débris ligneux expliqueraient ces changements.©2004 NRC Canada

This study is a component of the Sylviculture et aménagement forestier écosystémique project, which examines ecosystem-based forest management strategies in mixedwood boreal forests. Four harvesting treatments, one no-harvest, one clearcut, and two partial cuts (33% and 61% of basal area removed), were applied to even-aged aspen stands according to a complete block design. Mountain maple (Acer spicatum Lamb.) and balsam fir (Abies balsamea (L.) Mill.) early response was examined to understand how they react to and interact with canopy opening. Only in clearcuts was maple's response (increase in growth and density) sustained and significant. Balsam fir suffered from a very slight "growth shock" 1 year after harvesting in both clear-cut and two-thirds partial-cut treatments, but growth and vigour increased with canopy opening during the next 2 years. The first year following harvesting, balsam fir growth was negatively affected by understorey aspen and mountain maple. Our results show that the two-thirds partial harvesting treatment could speed up the conversion of pure aspen stands toward mixedwood.

Cette étude s'insère dans le cadre du projet Sylviculture et aménagement forestier écosystémique qui examine les stratégies d'aménagement forestier écosystémique en forêt boréale mixte. Quatre traitements de coupe, incluant un témoin, la coupe totale et deux coupes partielles (33 % et 61 % de la surface terrière), ont été appliqués à des peuplements de tremble selon un dispositif en blocs complets. La réponse de l'érable à épis (Acer spicatum Lamb.) et du sapin baumier (Abies balsamea (L.) Mill.) a été étudiée afin de comprendre comment ces deux espèces réagissent et interagissent suite à l'ouverture du couvert. L'érable à épis n'a répondu de manière soutenue et significative (augmentation en croissance et densité) qu'à la coupe totale. Le sapin a subi un très léger « choc de croissance » l'année suivant la coupe totale et la coupe partielle deux-tiers, mais les deux années suivantes, la croissance et la vigueur de la régénération de sapin ont augmenté avec l'ouverture de la canopée. La croissance du sapin n'a été négativement affectée par la densité des rejets de tremble et d'érable à épis que la première année après la coupe. Nos résultats indiquent que la coupe partielle deux-tiers accélérerait la succession des peuplements de tremble vers une composition plus mélangée.©2004 NRC Canada

The effects of different harvest intensities, including uncut, 1/3 and 2/3 partial cuts, clearcuts with and without slash, were investigated on the germination and cumulative survivorship of white spruce and balsam fir over 2 consecutive years. We also investigated the regenerative capacity of both species on three different seedbeds across all harvest intensities. The seedbeds included were mineral, humus, and organic soil. At the germination stage, both species were strongly affected by seedbed type (p < 0.032). The germination rates of fir seeds in partial cuts were significantly greater than clearcut treatments, but spruce remained unaffected at this stage by harvest intensity. The addition of slash improved the germination rates of fir relative to the clear-cut plots without slash. The germination rates the following year were reduced on mineral soil for spruce. The cumulative survivorship at the end of the third summer still showed a significant seedbed response for both species (p < 0.007) and a significant harvest response for fir (p < 0.005). The cumulative survivorship of the second fir cohort was no longer affected by either harvest or seedbed type. Spruce, however, was still affected by seedbed type (p=0.006). The data from this study provide us with a more detailed description of the fate of cohorts recruited following a harvest operation. Still, what remains to be studied is the fate of these cohorts over the next 5–10 years.

Les effets de différentes intensités de récolte sur la germination et la survie cumulative de l'épinette blanche et du sapin baumier, incluant l'absence de coupe, la coupe partielle d'un tiers ou des deux tiers du peuplement et la coupe totale avec ou sans rémanents, ont été étudiés pendant 2 années consécutives. Nous avons aussi étudié la capacité de régénération des deux espèces sur trois lits de germination à toutes les intensités de récolte. Les trois lits de germination retenus incluaient le sol minéral, l'humus et le sol organique. Au stade de la germination, les deux espèces étaient fortement affectées (p < 0,032) par la nature du lit de germination. Le taux de germination des graines de sapin était significativement plus élevé dans les coupes partielles que dans la coupe totale mais à ce stade l'épinette n'était pas affectée par l'intensité de la récolte. L'addition de rémanents a amélioré le taux de germination du sapin comparativement aux parcelles de coupe totale sans rémanents. La deuxième année, le taux de germination de l'épinette chutait sur le sol minéral. Le taux cumulatif de survie à la fin du troisième été était toujours significativement influencé par le lit de germination chez les deux espèces (p < 0,007) et par l'intensité de la récolte dans le cas du sapin (p < 0,005). Le taux cumulatif de survie de la seconde cohorte de sapin n'était plus affecté ni par le type de récolte ni par la nature du lit de germination (p=0,006). Les résultats de cette étude nous fournissent une description plus détaillée du sort des cohortes recrutées après une opération de récolte. Il reste tout de même à étudier le sort de ces cohortes au cours des 5–10 prochaines années.©2004 NRC Canada

We used a micrometeorological dispersal model to simulate seed and seedling distributions derived from subcanopy balsam fir (Abies balsamea (L.) Mill.) source trees in a trembling aspen (Populus tremuloides Michx.) dominated forest. Our first objective was to determine the effect of substituting basal area for cone production as a proxy for seed output. The results showed that the r² from the regression of predicted versus observed densities increased by similar to5% for seeds and similar to15% for seedling simulations. Our second objective was to determine the effects of changing the median horizontal wind speed. The median speed in this forest environment varies according to the proportion of leaves abscised. For values of the median expected wind speed between the extremes of leafless and full-canopy forests, the r² of predicted versus observed varied between 0.35 and 0.49 for seeds and between 0.33 and 0.62 for seedling simulations. We demonstrated that the simple one-dimensional model can have added precision if the dispersal parameters are chosen so as to allow more fine-scale variation.©2002 NRC Canada