Compression wood in Scots pine and Norway spruce -Distribution in relation to external geometry and the impact on dimensional stability in sawn wood

Warensjö, M. 2003. Compression wood in Scots pine and Norway spruce-Distribution in relation to external geometry and the impact on dimensional stability in sawn wood. With the aid of compression wood the conifer trees are able to maintain their predetermined growth form. Compression wood is formed as soon as the tree is displaced from its normal vertical position. Trees with expressed curvature do often contain large amounts of compression wood. Straight trees or trees that are leaning can also contain substantial amounts of compression wood. This thesis gives a summary and discussion of results from five studies concerned with: the distribution of compression wood in relation to external stem and log geometry and the impact of the compression wood distribution on deformations of sawn timber. Moreover the straightening process of trees is discussed. In order to study the distribution of compression wood in stems and logs, 63 trees of Norway spruce and Scots pine representing different age and curvature categories were sliced into 621 discs. In order to study the impact of compression wood on deformations of sawn timber, 146 logs of Scots pine and Norway spruce were processed into studs and battens. Before crosscutting, the external geometry of stems and logs were assessed. A 3D-logscanner was used for the assessment of logs. Deformations such as bow, spring and twist were measured on studs and battens at green condition, at 18% moisture content and at 12% moisture content. Compression wood content in thin cross sections of discs, studs and battens were analysed using transmitted light and image analysis. The analyses showed that a majority of all discs and cross sections contained compression wood. In all studies, the pith eccentricity was significantly correlated to the discs´compression wood content. For the 6-year-old Scots pine trees, the compression wood content was significantly correlated to the size of basal sweep but not to out-of-roundness. For the 22-year-old Scots pine trees, the compression wood content was not correlated to either bow height or size of basal sweep. For the 60-year-old Norway spruce trees, the compression wood content was significantly correlated to compression wood content in log ends, pith eccentricity and bow height. For sawn timber, the compression wood content and its position were significantly correlated to bow and spring but not twist. Twist was significantly correlated to grain angle measured on tangential faces of studs and spiral grain angle measured under bark on the surface …