Le 25 Novembre 2020  

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Ahmed Koubaa est titulaire d’un Baccalauréat en sciences et technologies du bois (université Laval 1989), d’une maîtrise en sciences du bois (université Laval 1991) et d’un doctorat en génie papetier (université du Québec à Trois-Rivières 1996). De 1996 à 1997, il a travaillé comme chercheur postdoctoral au centre de recherche en biologie forestière et au département de sciences du bois (université Laval).

Ahmed Koubaa

Il a travaillé également comme chercheur à Forintek Canada de 1997 à 2000. De 2000 à 2004, il a travaillé au Service de Recherche et d’expertise en transformation du bois de l’Est (SEREX) de Québec à titre de chercheur. En mai 2004, il s’est joint les rangs de l’UQAT à titre de professeur chercheur. Les travaux du Dr Koubaa portent sur la caractérisation, la valorisation et la transformation du bois. Il s’intéresse particulièrement à l’étude des variations de la qualité du bois tant phénotypiques et génétiques qu’avec les traitements sylvicoles et les pratiques d’aménagement forestier intensif. Une bonne partie de ses recherches porte sur la valorisation du bois et de la fibre issus des essences indigènes sous utilisées ou encore issues des programmes de ligniculture. Il travaille particulièrement au développement de nouvelles technologies pour la production de biomatériaux. Il est membre régulier de la chaire AFD et du centre de recherche sur le bois (CRB, université Laval). Il est professeur associé au département des sciences du bois et de la forêt de l’université Laval et est titulaire de la chaire de recherche du Canada en valorisation, caractérisation et transformation du bois.

Axes de Recherche

  • Caractérisation de la qualité du bois des essences à croissance rapide;
  • Valorisation du bois des essences à croissance rapide pour des applications à haute valeur ajoutée ;
  • Étude des variations génétiques, phénotypiques et en fonction des traitements sylvicoles des propriétés de la fibre et du bois;
  • Développement de nouvelles technologies de production de biomatériaux à base de bois et des polymères.

étudiant(e)s de maîtrise et doctorat recherchés

Je recrute régulièrement de nouveaux étudiants de maîtrise et de doctorat pour travailler sur des projets touchant la caractérisation, la valorisation et la transformation du bois. Veuillez consulter la section Offre d'emploi et bourses pour connaître les projets disponibles me concernant.

Publications récentes

  • BOUAFIF, H., KOUBAA, A., PERRÉ, P., CLOUTIER, A., RIEDL, B. 2008. Analysis of Among-Species Variability in Wood Fiber Surface Using DRIFTS and XPS: Effects on Esterification Efficiency. Journal of Wood Chemistry and Technology. 28: 296–315.

  • DING, W., KOUBAA, A., CHAALA, A., BELEM, T., AND KRAUSE, C. 2008. Relationship between wood porosity, wood density and methyl methacrylate impregnation rate. Wood Material Science and Engineering. 3(1):62-70.

  • NGUEHO YEMELE, M. C., BLANCHET, P., CLOUTIER, A., AND KOUBAA, A. 2008. Effects of bark content and particle geometry on the physical and mechanical properties of particleboard made from black spruce and trembling aspen bark. Forest Prod. J. 58(11):48–56.

  • NGUEHO YEMELE, M. C., CLOUTIER, A., DIOUF, P.N., KOUBAA, A., BLANCHET, P., AND STEVANOVIC, T. 2008. Physical and mechanical properties of particleboard made from extracted black spruce and trembling aspen bark. Forest Prod. J. 58(10):38-46.

  • NGUEHO YEMELE, M.C., KOUBAA, A., DIOUF, P. N., BLANCHET, P., CLOUTIER, A. AND STEVANOVIC, T. 2008. Effects of hot water treatment of black spruce and trembling aspen bark raw material on the physical and mechanical properties of bark particleboard. Wood and Fiber Science 40(3):339-351.

  • Koubaa, A., N. Isabel, S.Y. Zhang, J. Beaulieu et J. Bousquet. 2005. “Transition from juvenile to mature wood in black spruce (Picea Mariana (Mill.) B.S.P.)”. Wood and Fiber Sci. 37(3): 445-455.
  • Zhang, S.Y. Yu, Qibin, G. Chauret. et A. Koubaa. 2003. “Selection for both growth and wood properties in hAKrid poplar clones”. Forest Science. 49(6):901-908.
  • Koubaa, A. S.Y. Zhang, et S. Makni. 2002. Defining the transition from earlywood to latewood in black spruce based on intra-ring wood density profiles from X-ray densitometry. Ann. For. Sci. 59:511-518.
  • Koubaa, A. S.Y. Zhang, N. Isabel, J. beaulieu, et J. Bousquet. 2000. "Phenotypic correlations between juvenile-mature wood density and growth in black spruce". Wood Fiber Sci 32(1):61-71.

Résumés

TRANSITION FROM JUVENILE TO MATURE WOOD IN PICEA MARIANA (MILL.) B.S.P.
Ahmed Koubaa, Nathalie Isabel, S. Y. Zhang, Jean Beaulieu, and Jean Bousquet

The radial patterns of several intra-ring traits in increment cores of black spruce (Picea mariana (Mill.) B.S.P.) plantation trees were modeled with polynomials to characterize trends and to estimate the transition age from juvenile to mature wood. Wood density, ring width, latewood density, and latewood proportion were obtained by X-ray densitometry. Average radial trends were similar to those reported earlier in Picea species. For all traits measured, significant differences were found among diameter classes. Thus, the juvenile wood production period varies with growth rate. In addition, transition age for a given diameter class varied depending on which trait was used to estimate it. Hence, transition age needs to be more precisely defined and related to biological processes.

Selection for Both Growth and Wood Properties in HAKrid Poplar Clones
S.Y. Zhang; Q. Yu; G. Chauret; A. Koubaa

To better understand the genetic control of growth and wood properties in hAKrid poplar (Populus spp.), genetic relationships of selected wood properties with growth traits were examined in a 3-yr-old clonal trial located in Windsor and St-Ours, southern Quebec, Canada. In total, 371 trees from 21 hAKrid poplar clones were sampled at the two locations. Clonal effects are stronger than growth traits effects on wood density and initial moisture content. The estimated clonal repeatability for wood density (0.92) and initial moisture content (0.80) across the two sites are thus considerably higher than for dbh (0.64) and tree height (0.72). Neither wood density nor mean fiber length were found to significantly correlate with growth traits. This suggests that in the hAKrid poplar clones selection for growth traits will not result in a significant reduction in the wood quality traits. Selection for stem dry fiber weight appears to be an optimal selection strategy, as it will lead to the highest genetic gain in stem dry fiber yield, or maximum fiber production while wood density is improved. FOR. SCI. 49(6):901–908.

Defining the transition from earlywood to latewood in black spruce based on intra-ring wood density profiles from X-ray densitometry
Ahmed Koubaa, S.Y. Tony Zhang and Sami Makni

Defining the transition from earlywood to latewood in annual rings is an important task since the accuracy of measuring wood density and ring width components depends on the definition. Mork's index has long been used as an anatomical definition of the transition from earlywood to latewood. This definition is arbitrary and extremely difficult to apply to X-ray densitometry. For X-ray densitometry, a threshold density of between 0.40 to 0.55 g cm -3, depending on species, has been chosen to differentiate between earlywood and latewood density, but this method has shortfall. Therefore, new methods need to be developed and integrated into the computational programs used to generate X-ray densitometry data. In this study, we presented a mathematical method. We modelled the intra-ring wood density profiles in 100 plantation-grown black spruce (Picea mariana (Mill.) B.S.P.) trees using high order polynomials. The correlation between the predicted and the measured densities is very high and highly significant. Based on this model, we define the transition from earlywood to latewood as the inflexion point. Results indicate that wood density at the earlywood-latewood transition point varies from juvenile to mature wood. This method could be easily integrated into any X-ray densitometry program and allows to compare individual rings in a consistent manner.

Définition de la transition du bois initial au bois final chez l'épinette noire à partir des profiles de densité intra cernes obtenus par densimétrie aux rayons X. La précision de l'estimation des densités et des largeurs du bois initial et du bois final dans un cerne annuel dépend de la définition de la transition du bois initial au bois final. L'indice de Mork a longuement servi pour donner une définition anatomique à cette transition. Cette définition est arbitraire et difficile à appliquer en densimétrie aux rayons X. En général, un seuil de densité variant entre 0,40 à 0,55, dépendamment de l'essence, sert à différencier le bois initial du bois final. Cette méthode a certaines limites et d'autres méthodes doivent être développées et intégrées aux programmes de densimétrie aux rayons X. Nous avons utilisé une approche mathématique pour modéliser les profiles de densité intra cernes dans 100 arbres d'épinette noire (Picea mariana (Mill.) B.S.P.). Le point d'inflexion de polynômes aux degrés élevés a servi pour définir la transition du bois initial au bois final. Les corrélations entre les densités mesurées et prédites sont élevées et significatifs. La transition du bois initial au bois final varie entre le bois juvénile et le bois adulte. Cette méthode est facile à intégrer dans les programmes de densimétrie aux rayons X et permet d'obtenir des comparaisons consistantes entre cernes annuels.

PHENOTYPIC CORRELATIONS BETWEEN JUVENILE-MATURE WOOD DENSITY AND GROWTH IN BLACK SPRUCE
Ahmed Koubaa, S. Y. Zhang, Nathalie Isabel, Jean Beaulieu, and Jean Bousquet

Phenotypic correlations between juvenile-mature wood density and growth were examined based on increment core samples from two plantations, a provenance test and a commercial plantation, of black spruce [Picea mariana (Mill.) B.S.P.]. The ring density components are significantly correlated to their respective ring width components: earlywood and ring densities are negatively correlated to ring and earlywood widths, respectively, while ring and latewood densities are positively correlated to latewood width. These hold true in both juvenile and mature wood. However, the correlation between ring width and ring density decreases with increasing age. This suggests that the correlation between wood density and growth rate tends to lessen as the tree ages. For each character, the correlation between juvenile and mature wood is significant but moderate. Thus, juvenile wood characters are only indicative of mature wood ones. On the other hand, trees with 12 growth rings from the pith were good predictors of wwood density and radial growth of the whole tree. Individual growth rings from the juvenile-mature wood transition zone can be used to predict to some extent the wood density of either mature wood or the whole tree.

Étudiants sous la direction ou la co-direction de Ahmed Koubba:

Maîtrise

Doctorat

Post-Doctorat

Samia Belkhir

Weidan Ding

Hadhemi Kasraoui

Mina Ourais

Imene Slama

Adil Zerhouni

Houcine Bouafif

Besma Bouslilmi

Azmul Huda

Sébastien Migneault

Joël Soucy

David (Young-In) Park

Étudiants diplômés sous la direction ou la co-direction de Ahmed Koubba:

Maîtrise

Doctorat

 

Lise Harrisson (2006)

Sébastien Migneault (2007)

Joël Soucy (2006)