No abstract

-This study proposes a generalized linear mixed model to predict individual tree mortality in northern hardwood stands under uneven-aged management. The model is based on a complementary log-log (CLL) link function, and was calibrated using permanent-plot data. Tree vigor, stem product, diameter at breast height and stand basal area were tested as explanatory variables. A plot and an interval random effect were specified to account for spatial correlations. When compared with the traditional logit link function, the CLL facilitates the inclusion of the time factor. In this case study, there was an important variability of mortality predictions between the plots and the intervals for a given plot. The interval random effect is thought to be associated with catastrophic mortality. Since both tree vigor and stem product proved to be significant mortality predictors, we recommend that these variables be evaluated to increase the accuracy of mortality models. mortality / generalized linear mixed model / random effects / hardwoods / single-tree selection cutting Résumé -Prévision de la mortalité des tiges individuelles dans les peuplements de feuillus nobles sous aménagement inéquienne dans le sud du Québec, Canada. Cette étude présente un modèle linéaire mixte généralisé pour la prévision de la mortalité dans les peuplements de feuillus nobles sous aménagement. Le modèle utilise une fonction de lien log-log complémentaire (LLC) et a été étalonné à l'aide de données de placettes permanentes. La vigueur de l'arbre, le produit, le diamètre à hauteur de poitrine et la surface terrière ont été testés comme variables explicatives. Des effets aléatoires de placette et d'intervalle ont été spécifiés dans le modèle afin de tenir compte des corrélations spatiales. Comparée au traditionnel logit, la fonction de lien LLC facilite l'inclusion du facteur temps. Dans ce cas d'étude, il existait une importante variabilité des prévisions entre les placettes et les intervalles de temps d'une même placette. On présume que l'effet aléatoire d'intervalle représente la mortalité catastrophique. Puisque la vigueur et le produit des tiges se sont avérés être des variables significatives, il est recommandé de les évaluer afin d'améliorer la précision des modèles de mortalité. mortalité / modèle linéaire mixte généralisé / effets aléatoires / feuillus nobles / jardinage par pied d'arbre

Balsam fir (Abies balsamea (L.) Mill.) forests are inherently vulnerable to windthrow, especially when silvicultural treatments are applied. During recent years, it has become possible to model windthrow risk based on a good understanding of windthrow mechanics. In the present paper, the British ForestGales model has been adapted for balsam fir with data from a winching study in Quebec, Canada. This model calculates the threshold wind speed required to break or overturn the average tree in a stand and then calculates the probability of exceeding the threshold value. Modifications of the equations predicting crown characteristics and overturning resistance were introduced. The effects of age, site quality, wind exposure, thinning and the creation of new edges were assessed. The estimated critical wind speed for overturning and breakage decreases with age but the probability of damage remains low on sheltered sites. The creation of a new edge leads to an increased probability of damage, especially on exposed, highly productive sites. Thinning alone also increases the probability of damage and the magnitude of the increase varies with age and thinning intensity. On highly productive sheltered sites, the effect of thinning becomes especially important when thinning exceeds 35% of the number of stems or when stand age is greater than 70 years for a 35% thinning intensity. Thinning of new edges was also found to further increase the risk of windthrow on the most sheltered, high quality sites.Les peupements de sapin baumier (Abies balsamea (L.) Mill.) sont, de f a~o n inhkente, vulnCrables au chablis, en particulier lorsque des traitements sylvicoles y sont appliques. Au cours des dernicres annCes, il est devenu possible de modCliser le risque de chablis sur la base d'une saine comprChension de la mCcanique du chablis. Dans le prCsent article, le modkle Britannique ForestGales a Ct C adaptC pour le sapin baumier h partir d'une Ctude de treuillage rCalisCe au QuCbec. Ce modkle calcule la vitesse nkcessaire la rupture ou au deracinement de la tige moyenne d'un peuplement puis estime la probabilite que cette valeur soit dCpasde. Des modifications ont Ct C apportCes aux Cquations prkdisant les caracttristiques de la cime et la rksistance au renversement. La simulation a port6 sur l'effet de l'bge, de la qualit6 de station, de l'exposition au vent, de l'tclaircie et de la crkation de nouvelles lisikres. Selon les simulations, la vitesse critique pour le bris ou le dkracinement diminue avec l'bge mais la probabilitt demeure faible pour les sites abritCs.

Information on eastern Canadian tree species vulnerability to windthrow is scarce. Some statements on relative species vulnerability have been made but they rely on empirical observations, which are often difficult to generalize. In this context, a study was conducted to compare the overturning resistance of balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss) on a mesic site. To establish which tree characteristics would best explain the critical turning moment, simple linear regressions were calculated using tree dendrometric data. The best regressions were obtained with stem weight. With this variable, resistance to overturning did not differ between the two species. Only regressions involving total height showed a significantly greater resistance for white spruce. This difference can be explained by a difference between the species in height–diameter relationships. For a similar height, spruce has a greater diameter, involving a higher stem weight and thus a greater resistance. Decay did not play a major role in our experiment as trees with external defects were excluded. Our results suggest that to minimize losses from windthrow, silvi cultural treatments on mesic sites should try to increase the proportion of trees of either species with the lowest height/diameter ratio.

In this study, a diameter increment model was calibrated for individual trees in hardwood stands in Quebec, Canada. Two random effects, a first one for the plot and a second one for the time interval nested in the plot, and a covariance structure were included in the model to account for spatial and serial correlations. The diameter at breast height, species group, vigor and product classes, and basal area were the explanatory variables that were tested in this analysis. The adequacy of the covariance features (random effects and covariance structure) were tested through empirical correlations calculated from normalized residuals. A cross-validation was also carried out to evaluate the model. The normalized residuals showed no departure from the assumption of independently and normally distributed error terms with homogeneous variances. Consequently, the statistical inferences could be considered as valid. The results showed that the average diameter increment pattern differs among the species. Although tree product and vigor were significant explanatory variables, their effects were relatively small. On the other hand, basal area had a large and significant negative effect on diameter increment. Our study demonstrates that empirical correlations calculated from normalized residuals can be used as an additional tool to test the adequacy of the covariance features in a mixed-effects model.