Farm Forestry New ZealandImproved Drying of Eucalyptus nitens: Screening standing trees and drying thin boards
By Rosie Sargent and Doug Gaunt, June 2018.
Download SWP-T055 (pdf)
Executive summary
Following on from work in 2016/17, a model was created to predict the propensity for checking and collapse in E. nitens standing trees. This model was validated by measuring 100 trees, then selecting 10 that were expected to produce checking and collapse (‘bad’ logs) and 10 that were not (‘good’ logs). Two thicknesses of boards were cut from these logs (10mm and 30mm) and these were dried using two methods; air drying and kiln drying at 50°C. Following drying, levels of checking and collapse were assessed.
Air dried boards show much lower levels of degrade compared to kiln dried boards, however around 50% of kiln dried boards had no degrade, or acceptably low levels of degrade. For each drying method, the 10mm boards showed slightly less degrade than 30m boards, but this difference was not significant. The majority of the degrade was in the form of collapse but a small proportion (10-20%) of the 30mm boards had within ring checking.
No significant difference in levels of degrade were seen between boards cut from the ‘good’ and ‘bad’ logs. As with previous studies, some logs consistently produced boards with low levels of degrade, and some logs consistently produced boards with high levels of degrade, irrespective of drying method. This suggests that the underlying mechanisms causing checking and collapse propensity are not well correlated to the tree properties that were measured in this study. These mechanisms are currently not well understood. If these mechanisms become better understood in future, there may be scope to revisit this screening work using non-destructive measurements that better target the wood properties responsible for checking and collapse.
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