Effect of Initial Spacing and Thinning on Some Wood Properties ofEucalyptus grandis

SYNOPSIS A study was made of the effect of thinning intensity on wood density and some wood anatomical properties and their within-tree variation patterns, as well as the extent to which the development of growth-stress splits in logs and sawn boards is affected. Material used for this study was obtained from an Eucalyptus grandis CCT trial. Three trees were selected from each of 12 plots representing a series of thinning treatments. Density variation patterns in Eucalyptus grandis trees are significantly affected by the degree of suppression, having a pronounced inverse effect on wood uniformity. The density of suppressed trees increases rapidly with increasing distance from the pith, showing no tendency to level off towards the bark. On the other hand, the wood of trees growing more freely reaches maximum density levels fairly early in life, resulting in a stem with a large proportion of mature wood of relatively uniform density. Fibre lengths and their length distribution are not significantly affected by thinning, but it can be expected that the less the tree is suppressed, the larger the proportion of thick-walled fibres that will be produced owing to the good positive correlation that exists between wood density and fibre wall thickness. Vessel and ray sizes and their proportions are not greatly affected by thinning intensity, while vessel proportion tends to increase with increasing thinning intensity.