The effect of specimen geometry on wood shrinkage and collapse in Eucalyptus grandis

Eucalyptus is the most widely planted hardwood genus globally and an important source of industrial roundwood. In many Eucalyptus species, a substantial proportion of shrinkage arises from cell collapse occurring above the fibre saturation point (FSP). Shrinkage and collapse are commonly evaluated using increment cores or small specimens prepared as wedges or strips, yet the influence of specimen geometry on measured responses remains poorly understood. This study investigated the effect of specimen geometry on shrinkage and collapse behaviour in Eucalyptus grandis . Specimens from five trees were dried from the green state to an operational fibre saturation point and subsequently to oven-dry condition. Collapse-induced shrinkage was defined as shrinkage occurring above FSP, while normal cell-wall shrinkage occurred below FSP. The effects of longitudinal length, tangential length and specimen shape (wedge versus strip) were evaluated. Mean radial shrinkage and radial collapse did not differ significantly between wedge- and strip-shaped specimens. Tangential collapse was greater in wedges based on specimen means, although this difference was not significant when analysed using tree means. Longitudinal length had a significant but non-linear influence on collapse and total shrinkage, with 70 mm specimens generally showing the highest collapse, 45 mm specimens the lowest, and 20 mm specimens intermediate values. Tangential length had no significant effect over the tested range. Wedge and strip specimens also exhibited contrasting pith-to-bark trends in tangential collapse, indicating that specimen shape influenced pith-to-bark collapse profiles. These findings demonstrate that specimen geometry is not a neutral sampling consideration and can influence measured collapse behaviour in Eucalyptus grandis . Longitudinal length and specimen shape should therefore be standardised and reported explicitly when comparing results among studies or using laboratory specimens in breeding and screening programmes.