Regional variation in wood discoloration in paper birch trees

Wood discoloration was investigated in 721 paper birch (Betula papyrifera Marsh.) trees from 146 sites across the managed forest of Quebec, Canada. Discoloration was present at breast height in 85% of trees, but its impact was limited in terms of tree basal area and volume, with proportions of 6.4% and 3.6%, respectively. These two measures were strongly correlated. Discoloration changed wood appearance but had no effect on microfibril angle and modulus of elasticity. Discolored wood was nevertheless denser, probably due to the accumulation of colored extractives. Predictive models were also developed and applied to 415 711 paper birch trees from 51689 inventory plots across the province to study regional variation. Higher proportions of discolored basal area were obtained in the southwestern areas of the province where the climate is warmer and drier. In these areas, paper birch trees are larger and, likely, support bigger branches which can cause larger columns of discoloration when broken. Lower proportions were found in eastern regions where snowfall is more abundant. Smaller, more flexible branches in trees growing in these areas could explain this result. This study confirms the feasibility of large-scale mapping of wood discoloration in standing trees based on forest inventory and climate data. Key words: paper birch, wood discoloration, wood properties, regional variation, climate. La coloration du bois a ete etudiee chez 721 tiges de bouleau blanc (Betula papyrifera Marsh.) provenant de 146 sites repartis a travers la foret amenagee du Quebec, au Canada. La coloration etait presente chez 85 % des arbres mais son impact etait faible : elle occupait seulement 6,4 % de la surface terriere et 3,6 % du volume des tiges. Ces deux variables etaient etroitement correlees. La coloration a modifie l'apparence du bois mais n'a eu aucun effet sur l'angle des microfibrilles ni sur le module d'elasticite. Le bois colore est neanmoins plus dense, vraisemblablement a cause de l'accumulation de matieres extractibles colorees. Des modeles de prediction ont egalement ete elabores et appliques a 415 711 tiges de bouleau blanc provenant de 51689 parcelles d'inventaire reparties a travers la province pour etudier la variation regionale. De plus grandes proportions de surface terriere de bois colore ont ete obtenues dans les regions du sud-ouest de la province oU le climat est plus chaud et plus sec. Dans ces regions, les tiges de bouleau blanc sont plus grosses et supportent probablement de plus grosses branches qui peuvent causer de plus grandes colonnes de coloration lorsqu'elles cassent. De plus faibles proportions de coloration ont ete trouvees dans les regions de l'est oU les chutes de neige sont plus abondantes. Le fait que les arbres croissant dans ces regions aient des branches plus petites et plus flexibles pourrait expliquer ce resultat. Cette etude confirme que la cartographie de la coloration a grande echelle dans les arbres sur pied est realisable a partir de donnees d'inventaire forestier et du climat. [Traduit par la Redaction] Mots-cles: bouleau blanc, coloration du bois, proprietes du bois, variation regionale, climat.
Introduction Paper birch (Betula papyrifera Marsh.) is one of the most abundant hardwood species in Canada with a natural range from eastern to western coast (Safford et al. 1990). In [...]