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 27
  • Publication
    Restreint
    Wood degradation after windthrow in a northern environment
    (Forest Products Society, 2010-01-31) Ruel, Jean-Claude; Cloutier, Alain; Espinoza-Herrera, Raul; Achim, Alexis; Brossier, Benoît
    Severe windthrows often require salvage operations that can lead to increased costs. Given these extra costs, it is of paramount importance to make sure that wood degradation does not become so advanced that significant value loss is incurred. The rate at which wood deteriorates is a function of many factors, including species and climate. The study was conducted in a northern area affected by two partial windthrows. Logs from the damaged area were collected for two species, balsam fir (Abies balsamea) and black spruce (Picea mariana). Logs were classified into one of three degradation classes based on visual assessments. A sample of logs from standing trees was also collected. In total, 167 logs were sampled. Each log was sawn and one piece of lumber was selected from each to determine the bending strength and stiffness and the visual grade. The time since tree death, as determined from dendrochronology, ranged from 1 to 31 years. The visual grade of the lumber was not affected after 1 year but severe downgrades were observed after 4 years. Moisture content decreased rapidly for both species during the first year and continued to decrease until 4 years after mortality. No clear decrease in bending stiffness was identified even though such a tendency was noticed for older black spruce windthrows. Bending strength became variable after 4 years for balsam fir and was reduced after 4 years for black spruce. Windthrows older than 7 years will produce low visual grade timber of reduced bending strength and possibly of lower bending stiffness.
  • Publication
    Restreint
    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.
  • Publication
    Restreint
    Influence of shifts over an 80-year period in forest composition on soil properties.
    (Springer Nature, 2018-09-27) Gauthray-Guyénet, Vincent; Paré, David.; Schneider, Robert; Achim, Alexis; Sirois, Luc; Loi, Cédric
    Background and aims: Forest composition in North America has undergone important changes since the European settlement. The effects of such alterations on soil properties remain largely unknown. This study aims to understand the long-term effects of shifts in forest composition on soil properties. Methods: Using data from 130 plots measured over an eighty-year period, the relationships between stand composition (both current and past), parent material and current soil chemical properties were studied with redundancy analyses. Results: Results indicated that the parent material remained the dominant factor explaining soil properties, followed by current tree species composition. No legacy effect of past forest composition was found, but shifts in forest composition explained part of the current soil properties. Specifically, an increase in balsam fir was related to higher C/N ratio in the O-horizon, while an increase in maple species was related to higher net nitrification in both the O and B-horizons, and higher extractable P in the B-horizon. Conclusion: Our results suggest that increasing the maple component at the expense of conifers over several decades may enhance nutrient availability in the O-horizon.
  • Publication
    Restreint
    Untapped volume of surplus forest growth as feedstock for bioenergy
    (Pergamon, 2018-12-08) Durocher, Claude; Achim, Alexis; Thiffault, Évelyne; Auty, David; Barrette, Julie.
    In Canada, the annual allowable cut (AAC) sets the harvest limit of roundwood and aims to maintain the longterm productive capacity of the forest while taking into account other values such as biodiversity and needs of stakeholders. Current harvest levels in the province of Quebec, which feed an industrial network dominated by the production of lumber, panels and pulp, average only 55% of the AAC, which may cause a gradual depletion of the forest resource if stands that have the highest value are preferably selected. In this context, using surplus forest growth consisting of low quality trees and less desirable stands as bioenergy feedstock could help improve both silvicultural practices and wood value chain profitability. The aim of this study was to identify biophysical and socio-economic factors that affect the proportion of the AAC that is harvested in Quebec's 74 management units. Results from the analysis of AAC and harvesting data for the period 2008–2013 showed the harvested proportion of the AAC was particularly low for hardwood species, with the proportions for poplar, birch and maple ranging between 19 and 38%. The distance to the nearest pulp or particle board mill was confirmed as the prime factor determining the harvest/AAC ratio for deciduous species. For softwoods, the presence of deciduous stands in a given region affected the harvest/AAC ratio. Low quality hardwoods could be used as an important source of feedstock for the bioenergy sector. Developing a synergy between conventional and bioenergy products could facilitate the application of sound silvicultural practices and increase profitability along the entire wood value chain.
  • Publication
    Accès libre
    Fuel properties of sugar maple and yellow birch wood in relation with tree vigor
    (North Carolina State University, 2016-05-01) Cloutier, Alain; Stevanovic-Janezic, Tatjana; Achim, Alexis; Nguyen, Quy Nam
    The fuel properties of wood obtained from sugar maple (SM) and yellow birch (YB) of temperate hardwood stands located in the Province of Québec, Canada were studied to see how tree vigor affects the chemical composition and calorific value of the wood. This study focused on the physical and chemical properties of wood with the aim of using the material for the production of solid biofuels. Specific items measured included the wood’s calorific values, and the levels of extractives, ash, and lignin. Changes in chemical composition were found among tree vigor classes. The low vigor trees had higher extractives, ash, and lignin contents than the vigorous trees. Total extractives ranged between 4.88 and 7.32% in SM, and between 3.35 and 5.12% in YB. Klason lignin ranged between 21.46 and 23.53% in SM, and between 18.60 and 21.51% in YB. Ash content ranged between 0.38 and 0.97% in SM, and between 0.26 and 0.47% in YB. The combined effects of higher lignin content that could contribute to a better self-bonding of particles and of higher extractives content that could facilitate the pelletization process makes the low vigor trees more suitable for conversion into solid biofuels. The higher amounts of extractives and lignin present in the low vigor sugar maple and yellow birch trees could also have a positive role in maintaining the high calorific values of this wood despite higher ash content.
  • Publication
    Restreint
    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.
  • Publication
    Accès 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.
  • Publication
    Accès 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.
  • Publication
    Restreint
    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.
  • Publication
    Accès libre
    American beech in value-added hardwood products: Assessing consumer preferences
    (Dept. of Wood and Paper Science College of Natural Resources North Carolina State University, 2018-08-01) Durocher, Claude; Bernard, Anne; Achim, Alexis; Gélinas, Nancy; Duchateau, Emmanuel
    The depleted state of the northern hardwood forests of Quebec, Canada has forced the hardwood flooring industry to adapt its production. American beech (Fagus grandifolia), a traditionally less desired species, is now increasingly being included in wood supplies to sawmills in western Quebec, where forest managers hope this resource can be valued before the onset of significant mortality and wood degradation from the beech bark disease. This study aimed: 1) to assess the preferences of consumers towards American beech flooring products compared to well known species traditionally used in this market; and 2) to compare results obtained in face-to-face surveys with web-based surveys of consumer preferences. Results from both survey types revealed that the finishing colour was the most important factor affecting the decision of respondents, followed by species and price. American beech ranked third in species preferences, just above birch. Divulgating species names only affected (positively) the perception of respondents towards oak. It was concluded that American beech could be included in the current wood flooring market, probably among cheaper options such as birch. The similarity of results from face-to-face and online surveys suggests that general trends in consumer preferences could be rapidly and cheaply assessed using the latter option