Wood moisture content variation in white spruce defoliated by spruce budworm

Abstract

Mature and over mature white spruce [Picea glauca (Moench) Voss] repeatedly defoliated by spruce budworm (Choristoneura fumiferana Clem.) in eastern Manitoba, were investigated for variation in moisture content (MC) which is known to influence pulping quality. In the fall of 1991, 100 trees in the Abitibi-Price Inc. Forest Management Licence area were selected randomly in two size classes and four defoliation classes. Heartwood and sapwood MC (% dry weight) was measured in 5-cm thick disks cut at 2.5 to 5.0 m intervals for small and large trees, respectively. Living trees with more sapwood than heartwood had a mean MC of 117%, and those with more heartwood than sapwood had a mean MC of 77%. Both of these groups contained sufficient overall moisture (> 45%) for pulping. The repeated defoliation did not affect the overall MC in live trees. Mean MC of trees killed by spruce budworm defoliation was 42% but this level varied with diameter and height above ground: > 45% in stems greater than 36 cm diameter inside bark, 30–60% in sections 17–36 cm, and < 45% in sections less than 17 cm. A minimum DBH of 30 cm is suggested as a criterion for accepting dead trees. Key words: insect defoliation impact, wood moisture content, sapwood, heartwood, dead tree fibre, Manitoba