Effects of release from suppression on wood functional characteristics in young Douglas-fir and western hemlock

Little is known of wood properties in trees that were initially suppressed and subsequently released from suppression. The purpose of this study was to assess differences in growth ring width, specific conductivity (Ks), tracheid dimensions, moisture content, and wood density in suppressed Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg. ) trees and trees released from suppression averaging 12- 18 years of age. Growth ring width was 370% higher for Douglas-fir and 300% higher for western hemlock trees released from suppression, and Ks was 182% higher for Douglas-fir and 42% higher for western hemlock trees released from suppression. Earlywood width was approximately four times greater after release in both species, whereas the relative increase in latewood width was much greater in Douglas-fir. Tracheids were 25% wider and 11% longer in released Douglas-fir trees. In western hemlock, released trees had 19% wider tracheids that were approximately the same length as those in suppressed trees. Moisture content was 66% greater in released Douglas-fir and 41% greater in released western hemlock. Wood density decreased by 21% in Douglas-fir trees and by 11% in western hemlock trees released from suppression. However, wood density of released trees did not differ from average reported values, implying that wood from released trees may be suitable for many of its traditional applications. Resume : On connait peu de choses des proprietes du bois dans les arbres initialement supprimes et degages par la suite. Le but de cette etude consistait a evaluer les differences dans la largeur des cernes annuels, la conductivite speci- fique (Ks), la dimension des tracheides, le contenu en eau et la densite du bois entre des tiges supprimees et des tiges degagees de douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco) ainsi que de pruche occidentale (Tsuga hete- rophylla (Raf.) Sarg. ) ayant en moyenne 12-18 ans. La largeur des cernes annuels etait 370 % plus grande chez les ti- ges de douglas de Menzies et 300 % plus grande chez les tiges de pruche occidentale degagees et Ks etait 182 % plus elevee chez les tiges de douglas de Menzies et 42 % plus elevee chez les tiges de pruche occidentale qui avaient ete degagees. La largeur du bois initial etait approximativement quatre fois plus grande apres le degagement chez les deux especes tandis que l'augmentation relative de la largeur du bois final etait beaucoup plus forte chez le douglas de Men- zies. Les tracheides etaient 25 % plus larges et 11 % plus longues chez les tiges degagees de douglas de Menzies. Chez la pruche occidentale, les tracheides des tiges degagees etaient 19 % plus larges et avaient approximativement la meme longueur que chez les tiges supprimees. Le contenu en eau des tiges degagees etait 66 % plus eleve chez le douglas de Menzies et 41 % plus eleve chez la pruche occidentale. La densite du bois des tiges degagees a diminue de 21 % chez le douglas de Menzies et de 11 % chez la pruche occidentale. Cependant, la densite du bois des tiges dega- gees ne differait pas des valeurs moyenne deja rapportees, ce qui implique que le bois des tiges degagees peut convenir a plusieurs des usages traditionnels.