An estimate of timber degrade in Sitka spruce due to bark stripping by deer in a Scottish plantation

Abstract

Trees monitored for bark stripping over the previous 20 years were examined for timber defects by felling, then observing stain and rot in the split butt logs and strength testing wood samples. Logs (52 bark stripped, 28 controls) came from eight sites that had tree crops 28–39 years old; the logs were stratified for wound size (180 cm2), large wounds being rare. Many wounded logs had no stain or rot, but six of the 33 better-quality sawlogs were judged to be usable only for pulp. Modulus of elasticity and modulus of rupture were affected only at wounds and only in the sapwood there; at this position, mean stiffness and strength were both significantly reduced compared with control logs, with lowest means for logs with large wounds. Large wounds suffered a much greater incidence of stain and rot than small wounds, but their rarity meant that the calculated financial loss caused by the bark stripping estimated to be incurred over the whole rotation up to felling was only 3 per cent of the crop value