Tree classification systems are generally designed to predict the supply of high-quality logs for the wood processing industries and to mark defective trees for removal with the aim of improving both the vigor and quality of future stands. Although these two objectives are generally inversely related, their joint consideration could enable the development of robust criteria for improved tree selection in partial cuttings of northern hardwood stands by targeting low-vigor (LV) trees of high quality (HQ). In this study, we used a copula approach to model the joint probability distribution of trees characterized by both vigor and quality, which accounts for the statistical dependence between the different classes of both classification systems. The relationships between the probability of occurrence of a tree in each joint category and tree diameter at breast height (DBH) were quite similar among the three studied species: yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.), and American beech (Fagus grandifolia Ehrh.). In particular, the probability of occurrence of LV-HQ trees was characterized by a parabolic curve with a maximum value attained at the mid-DBH range, whereas that of LV and low-quality (LQ) trees increased with increasing DBH. This suggests that instead of harvesting large and mostly LV-LQ trees, partial cutting should target smaller LV-HQ trees, so that the volume of harvested HQ trees would increase without compromising the silvicultural objective of improving the vigor of future stands.Résumé : Les systèmes de classification des arbres sont généralement conçus pour prévoir l'approvisionnement en bois de haute qualité des industries de transformation et pour marquer les arbres défectueux à prélever dans le but d'augmenter la vigueur et la qualité des futurs peuplements. Bien que ces deux objectifs soient généralement contradictoires, leur prise en compte simultanée pourrait permettre de définir des critères robustes visant à améliorer la sélection des arbres à prélever lors de coupes partielles dans des peuplements de feuillus nordiques en ciblant les arbres de faible vigueur (FV) et de haute qualité (HQ). Dans cette étude, nous avons utilisé une approche par copule pour modéliser la distribution de la probabilité conjointe des arbres caractérisés par leur vigueur et leur qualité qui tient compte de la dépendance statistique entre les classes des deux systèmes de classification. La relation entre la probabilité qu'un arbre se situe dans chaque catégorie conjointe et son diamètre à hauteur de poitrine (DHP) était assez similaire pour les trois espèces étudiées : le bouleau jaune (Betula alleghaniensis Britt.), l'érable à sucre (Acer saccharum Marsh.) et le hêtre à grandes feuilles (Fagus grandifolia Ehrh.). De façon particulière, la probabilité d'occurrence des arbres FV-HQ était caractérisée par une courbe parabolique dont la valeur maximale était atteinte près du milieu de la gamme des DHP, alors que celle des arbres FV et de faible qualité augmentait avec le DHP. Ces...

Past silvicultural treatments have resulted in the high-grading mixed temperate forests of Qué bec, Canada. Despite recognition of this issue, the low occurrence of yellow birch (Betula alleghaniensis Britton) within current stands raises questions about the potential of the species to grow and eventually constitute a high-quality forest resource. The objective of this study was to assess this potential using tree characteristics, forest structure and additional site and climatic conditions as predictors. A total of 145 trees were sampled in two areas located in the same bioclimatic zone. Lower-Saguenay-Charlevoix was chosen as an area where a restoration plan could be implemented, whereas Portneuf was selected as a reference. We used nonlinear mixed models to investigate which environmental factors are likely to influence the radial growth and stem quality of yellow birch sample trees. Our results suggest that topographic and climatic conditions, as well as the competitive environment of the trees, are important factors to consider in the evaluation of yellow birch production. Despite the limited occurrence of yellow birch, the potential for growth and quality was high in the Lower-Saguenay-Charlevoix area. For equivalent topographic, climatic, and competitive environment conditions, there was no significant difference in either radial growth or stem quality with Portneuf. We suggest that the economic interest of producing high quality timber should be used to justify the implementation of a restoration strategy in the Lower-Saguenay-Charlevoix area. OPEN ACCESSForests 2013, 4 767