Longitudinal shrinkage behaviour of compression wood in radiata pine

The behaviour of longitudinal shrinkage was investigated in the corewood of a swept, 17-year-old New Zealand radiata pine stem. Wood categories in terms of normal wood, mild compression wood and severe compression wood were identified microscopically using autofluorescence of lignin. Average longitudinal shrinkage was collated according to corewood location and wood category within corewood in the leaning and the vertical parts of the stem, and then maximum radial difference of longitudinal shrinkage within growth ring was examined. The results show that the average longitudinal shrinkage is significant (2.4%) in the corewood of the leaning part of the stem. Among wood categories, severer compression wood displays the highest (2.9%) average longitudinal shrinkage. In the context of this study, growth rings may consist of one of three types of wood: (1) only normal wood; (2) a single compression wood type; and (3) mixed-type wood. Where multiple compression woods co-existed with normal wood, the maximum radial difference of longitudinal shrinkage within the growth ring was found to be 4.0%. A strong correlation (R ² = 0.90) between average MFA and average longitudinal shrinkage suggests a significant influence of the average MFA on average longitudinal shrinkage across the three growth ring types.