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Personne :
Achim, Alexis

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Achim

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Alexis

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Université Laval. Département des sciences du bois et de la forêt

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ncf11852316

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Voici les éléments 1 - 10 sur 54
  • PublicationAccès libre
    Quantifying the probability of decline in quality : implications for selection management in northern hardwood forests
    (MDPI, 2023-01-31) Moreau, Guillaume; Cecil-Cockwell, Malcolm J. L.; Achim, Alexis; Bédard, Steve; Guillemette, François; Caspersen, John Peter
    Northern hardwoods are susceptible to a wide range of defects that can reduce the amount of sound wood with desirable qualities, such as the clear sapwood of sugar maple trees. Yet, the rate at which trees decline in quality due to the development of such defects has never been quantified in northern hardwood forests due to a dearth of repeat inventories that record the appearance of defects over time. As a result, it remains uncertain whether, and how, selection management reduces the probability of decline in quality. In this study, we quantify the rate at which trees decline in quality due to the development of defects, and we test several hypotheses regarding the influence of selection management on quality. Our results show that (1) the probability of decline in quality increases as trees grow larger; (2) crown dieback also increases the probability of decline in quality; (3) the probability of decline in quality is slightly lower in managed stands than in unmanaged stands, and (4) the probability of decline in quality increases with the mean annual temperature of the site. Finally, we combined our estimates of the probability of decline in quality with previous estimates of the probability of mortality to assess the overall risk associated with retaining trees of different species, sizes, and vigour profiles. The resulting metric can inform efforts to improve the management of northern hardwood forests by providing an integrated estimate of the risk that the value of a tree will be reduced, or eliminated, due to mortality or decline in quality.
  • PublicationAccès libre
    Primary and secondary branch growth in black spruce and balsam fir after Careful Logging around small Merchantable Stems (CLASS).
    (Multidisciplinary Digital Publishing Institute (MDPI), 2019-06-12) Lemay, Audrey; Achim, Alexis; Krause, Cornelia
    Careful logging around small merchantable stems (CLASS) is a partial cutting treatment that consists of the harvest of 70%–90% of the merchantable volume of an irregular coniferous stand. In this treatment, regeneration, saplings and small merchantable stems (DBH < 15 cm) are preserved and can continue to grow and develop into the dominant layer of the new stand. The aim of this project was to examine the effects of CLASS on the primary and secondary growth of branches, as well as on branch diameter in black spruce and balsam fir trees in the boreal forest of Quebec, Canada. Primary and secondary growth were measured on five branches per tree while branch diameter was analysed from 15 whorls distributed within the crown of the 48 black spruce and 48 balsam fir trees sampled. Branch primary and secondary growth significantly increased after CLASS in the lower part of the crown in both species, and both types of growth increased proportionally. These findings suggest that CLASS may delay crown recession as the lower branches tend to survive and grow for a longer period. However, although radial growth increased in the years post-CLASS, this did not significantly influence the final branch diameter and should not lead to lumber downgrade.
  • PublicationAccès libre
    Assessing the potential impact of a biorefinery product from sawmill residues on the profitability of a hardwood value chain
    (National Research Council of Canada, 2018-05-15) Beaudoin, Daniel; Achim, Alexis; Hassegawa, Mariana; Gélinas, Nancy
    Due to the high amount of low-quality hardwoods harvested during selection cuts, the forest industry has been facing a decline in profit margins. One possible solution for utilizing the low-quality raw material is the production of extracts. The objective of this work was to estimate to what extent the inclusion of betulin in the traditional wood products portfolio could extend the profitability of a hardwood value chain. The profitability of a selection cut was assessed from the sawmill perspective, followed by an evaluation of the potential financial gain of producing betulin. Finally, the inclusion of betulin in a value chain was assessed. Results showed that the profitability of selection cuts was very low in some forest stands. The sensitivity analysis demonstrated that, among selected costs and revenues, profit was more sensitive to variations in the value of coproducts. If a fraction of coproducts volume was used to extract betulin, it would be sufficient to generate enough revenue to offset the total costs; however, a major constraint was the small size of the current betulin market, with annual sales not exceeding 1000 kg. Despite that, results demonstrate the potentially strong contribution of high value added extracts to the profitability of the forest value chain.
  • PublicationRestreint
    Comparison of carbon balance and climate change mitigation potential of forest management strategies in the boreal forest of Quebec (Canada).
    (Institute of Chartered Foresters, 2019-03-04) Paradis, Laurence; Achim, Alexis; Thiffault, Évelyne
    Management of the world’s forests can play a role for climate change mitigation by increasing CO2 storage in vegetation biomass and harvested wood products, and by displacing CO2-intensive materials such as steel or concrete. This study aimed to determine how management of boreal forest stands could contribute to climate change mitigation in the context of ecosystem-based management. The study was based on the comparison of different strategies applied to a balsam fir-white birch stand in the Eastern boreal forest of Quebec (Canada). Five scenarios were simulated over a 199-year period at the stand level: a reference scenario involving clearcut at 50-year intervals, and four alternative scenarios clearcut with longer rotation length (70 and 80 years), partial cut, and a no harvest scenario. The study included an appropriate sensitivity analysis of the results. Overall, scenarios with longer clearcut rotations and, to a lesser extent, partial cut resulted in a higher potential to mitigate climate change. The substitution effect of wood products was revealed as a key aspect, suggesting that wood product manufacturing and utilization on the markets, and not only forest management, need to be carefully considered.
  • PublicationAccès libre
    Correction, update, and enhancement of vectorial forestry road maps using ALS data, a pathfinder, and seven metrics
    (Elsevier, 2022-09-21) Roussel, Jean-Romain; Bourdon, Jean-François; Morley, Ilythia D.; Coops, Nicholas C.; Achim, Alexis
    Accurate information about forestry roads is a key aspect of forest management in terms of economy (e.g. accessibility, cost, optimal path) and ecology (e.g. wildfire and wildlife protection). In Canada, and in fact, globally, most provincial, state or territory governments maintain vectorial information on the forestry roads under their jurisdiction. However, official maps are not always accurate, may lack road attributes of interest and are not always up-to-date. Airborne Laser Scanning (ALS) has become an established technology to accurately characterize and map broad territories by providing high density 3D point-clouds with, at least, 3 or 4 measurements per square meter. This paper addresses the problem of the automatic updating, fixing, and enhancement of vectorial forestry road maps over large landscapes (¿10000 km2). For this purpose, we developed a production ready, documented and open-source software. From metrics derived from the point-cloud the method produces a raster of road probability. It then uses an existing, inaccurate, map of the road network to define approximate start and end points for each road. Then, a pathfinder retrieves the accurate road shape by computing the least cost path between the two points on the probability raster. Using the accurate road position given by the algorithm, road width and road state are then estimated based the on characteristics of the point-cloud. We demonstrate that our algorithm retrieves the centrelines of roads in a natively vectorial form with an error below 3 m in 95% of the roads using a fully automatic method. The accuracy of the road location allows us to derive other accurate measurements, including the state of the roads.
  • PublicationRestreint
    Deciphering the black spruce response to climate variation across eastern Canada using a meta-analysis approach
    (New York, NY : Elsevier, 2022-06-20) Chagnon, Catherine; Wotherspoon, Amy R.; Achim, Alexis
    Boreal forests are experiencing climate change more rapidly than other biomes, which is likely to impact their future management. Understanding how tree growth responds to regional and seasonal variation in climate is essential to anticipate future management of boreal forests. We compiled and summarized black spruce climate-growth relationships from 11 dendroclimatology studies in boreal forests of Northeastern North America. Using a statistical synthesis of 113 sites and 2,995 black spruce trees, latitudinal trends were found to affect the growth response to monthly climate variables. Below 50°N, a high portion of sites showed a negative growth response to summer temperatures, whereas these were positive between 50°N and 54°N. Growth response to previous summer precipitation was consistently positive across latitudinal range. This shift from negative to positive growth response to summer temperatures observed between 50 and 51°N was confirmed through meta-analysis and was found to be associated with a mean annual temperature of ∼ 0 °C. This threshold is likely representative of the limit at which black spruce growth shifts from being moisture- to temperature-limited. By directly relating growth-climate relationships to mean annual temperature and precipitation at a given site, our meta-analysis allows readers to easily grasp the current growth response of black spruce to climate variation. Combined with climate projections, our results may also be used to facilitate the estimation of black spruce growth trends through time, and thus inform the implementation of adaptative silvicultural measures.
  • PublicationAccès libre
    Broad-scale wood degradation dynamics in the face of climate change : a meta-analysis
    (Blackwell, 2022-05-13) Chagnon, Catherine; Moreau, Guillaume; Bombardier-Cauffopé, Christine; Barrette, Julie; Havreljuk, Filip; Achim, Alexis
    In the context of global change, a better understanding of the dynamics of wood degradation, and how they relate to tree attributes and climatic conditions, is necessary to improve broad-scale assessments of the contributions of deadwood to various ecological processes, and ultimately, for the development of adaptive post-disturbance management strategies. The objective of this meta-analysis was to review the effects of tree attributes and local climatic conditions on the time since death of coarse woody debris ranging in decomposition states. Results from our meta-analysis showed that projected warming will likely accelerate wood decomposition and significantly decrease the residence time in decay stages. By promoting such a decrease in residence time, further climate warming is very likely to alter the dynamics of deadwood, which in turn may affect saproxylic biodiversity by decreasing the temporal availability of specific habitats. Moreover, while coarse woody debris has been recognized as a key resource for bioenergy at the global scale, the acceleration of decay-stages transition dynamics indicates that the temporal window during which dead trees are available as feedstock for value-added products will shrink. Consequently, future planning and implementation of salvage harvesting will need to occur within a short period following disturbance, especially in warmer regions dominated by hardwood species. Another important contribution of this work was the development of a harmonized classification system that relies on the correspondence between the visual criteria used to characterize deadwood decomposition stages in locally developed systems the literature. This system could be used in future investigations to facilitate direct comparisons between studies. Our literature survey also highlights that most of the information on wood decay dynamics comes from temperate and boreal forests, whereas data from subtropical, equatorial and subarctic forests are scarce. Such data are urgently needed to allow broader-scale conclusions on global wood degradation dynamics.
  • PublicationRestreint
    Fire as a driver of wood mechanical traits in the boreal forest
    (Elsevier, 2020-08-04) Waldron, Kaysandra; Auty, David; Tong, Tessie; Ward, Charles; Pothier, David; Paes Torquato, Luciane; Achim, Alexis
    In boreal forests where the fire return interval is long, the high structural variability of stands may affect wood traits. Here, we build on earlier work that revealed a difference in wood mechanical traits of black spruce between regular (regenerated from fire in the last 200 years) and irregular (undisturbed by fire for at least 200 years) stands. This study aimed to identify the ecological drivers of this variation in wood traits. To do so, we first sought to corroborate existing results on the effects of stand structure induced by the time since the last stand-replacing fire (TSLF) on wood mechanical stiffness in the eastern boreal forest of Canada. Results confirmed that black spruce from regular stands tend to produce wood with higher modulus of elasticity (MOE) than those from irregular stands. For both regular and irregular stands, we compared a set of linear models that were defined a priori to determine the structural and site productivity variables having the largest influence on MOE. The ‘growth efficiency index’ (aboveground woody biomass production per unit leaf area) was the best predictor of MOE variation among regular stands. For irregular stands, the model with TSLF as the sole explanatory variable was a better predictor of MOE than any other candidate model. However, we did not find strong evidence of a direct relationship between TSLF and wood traits, since our best models explained a relatively small proportion of the variance. Our results suggest that differences in wood traits could be attributable to the seed or layer origin of the trees and/or to the length of time trees remain in the understory. We propose that intensive wood production strategies focus on stands of the first post-fire cohort.
  • PublicationRestreint
    Comparison of wood density in roots and stems of black spruce before and after commercial thinning.
    (Elsevier, 2017-11-02) Lemay, Audrey; Achim, Alexis; Krause, Cornelia
    Roots play an important physiological and mechanical role in the survival and growth of a tree, but also in the success of silvicultural treatments. Studies comparing the xylem in roots and stems have shown that conifer tracheids tend to be wider and longer in roots, which renders root wood less dense and more susceptible to cavitation and embolism. The increased radial growth often observed after thinning may induce changes in wood anatomy that could alter wood properties, such as wood density, in the stem and roots. The aim of this study was to compare growth, wood density and tracheid dimensions between the stem and roots of black spruce trees growing in the boreal forest. We also evaluated whether these wood properties were altered by the application of a commercial thinning treatment. Six black spruce trees were harvested in four commercially thinned stands. Samples were collected from the stem and two locations of each root. Radial growth, wood density and tracheid dimensions were measured on each sample. Results show that all wood density components, especially earlywood density, were higher in the roots than in the stem in black spruce. This denser wood in roots might provide increased safety against cavitation in a part of the xylem where hydraulic stresses are higher. After thinning, growth was increased in the stem and particularly in roots, resulting in slight wood density decreases, which should not influence the vulnerability of roots to cavitation or wood quality in the stem. These results lead us to suppose that the hydraulic network of the black spruce root system may not be so vulnerable to cavitation.
  • PublicationRestreint
    Use of northern hardwoods in glued-laminated timber : a study of bondline shear strength and resistance to moisture
    (Springer, 2020-07-25) Morin-Bernard, Alexandre; Dagenais, Christian; Achim, Alexis; Blanchet, Pierre
    The growing demand for engineered wood products in the construction sector has resulted in the diversification of the product offer. Used marginally in structural products in North America, northern hardwoods are now attracting a growing interest from industry and policy makers because of their outstanding strength as well as their high availability and distinctive appearance. Currently, there is no standard in Canada governing the use of hardwoods in the manufacturing of glued-laminated timber. As part of a larger project aiming to assemble the basic knowledge that would lead to such standard, the specific objective of this study was to assess the shear strength in dry and wet conditions of assemblies made from different hardwood species and structural adhesives. Results suggest that a mean shear strength as high as 20.5 MPa for white oak, 18.8 MPa for white ash and respectively 18.2 MPa and 17.4 MPa for yellow birch and paper birch can be obtained in dry conditions. The choice of adhesive did not affect the dry shear strength of these specimens, but differences were observed in wet conditions. Specimens bonded with melamine-formaldehyde adhesive had generally the highest wet shear strength and wood failure values. These results also highlight the important influence of wood density on the percentage of failure that occurs in wood and, to a lesser extent, on shear strength. Further investigations on finger joint strength and full-size bending tests will allow confirming the potential for the investigated species to be used in glued-laminated timber.