Edinburgh Napier University

  Inherent in the structure of timber are features affecting dimensional stability, stiffness and strength. These include knots, compression wood and spiral grain. Physical characteristics such as log shape, density, rate of growth,
presence of juvenile wood and microfibril angle also affect these properties and, in turn, utilisation. In this thesis, the relationships between tree, log and board variables to the properties of stiffness and distortion of British-grown
Sitka spruce (Picea sitchensis) are examined. The research‟s main aim was to identify variables which could potentially be used to sort timber.
Different behaviour in terms of the relationship between stiffness and variables such as density, knot content, log taper, tree height and axial position were noted between groups of upper log and butt log material, and between the four stands and two sites studied. Relationships between
stiffness and these variables were generally weak, notably for density.
Overall, variables based on radial position within the stem were not found to be useful sorting parameters. No relationship between batten stiffness and compression wood content or slope of grain was observed. The relatively low
stiffness of butt wood material was associated with high microfibril angle.
Batten twist was found to be a function of spiral grain angle and distance from pith. However, practical difficulties with the use of slope of grain measurements to sort timber were noted. Although severe forms of compression wood were seen to be associated with stem-form correction, relatively straight logs and those which were round, or without pith
eccentricity, were also observed to contain compression wood and hence yield timber which distorted on drying.
In particular, this work demonstrates the effect of sorting timber using combined variables (e.g. log shape and knot content). These findings may be of use to foresters, sawmillers and developers of timber scanning technologies.