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Summary
Processing young, small-diameter eucalypt logs into veneer is a burgeoning industry across southern China. However, plantations supplying these logs are mostly managed on silvicultural regimes which are appropriate for pulpwood and little information is available on alternative regimes for eucalypt plantations with respect to veneer yields and quality. Log size along with a range of tree and log traits were assessed on 12-year-old eucalypts in six spacing treatments, ranging from 666 to 2 222 trees ha−1, in a field trial in southern China. Logs harvested from these were rotary peeled for veneer; recovery percentages plus a range of quality and value traits were assessed on the outturn. Log volumes, small-end diameters and individual log values varied significantly between spacing treatments, but total veneer recoveries (as a percentage of log volume) and veneer values per unit volume did not. The spacing treatment providing the highest veneer value per unit area was that with the highest stocking; 2 222 trees ha−1. Although the second logs (up from the butt log) had significantly lower average volume than butt logs, and they had significantly higher average value per unit volume because of higher average total veneer recovery (68.7%) compared with the butt logs (59.7%). A number of external log features were significantly correlated with veneer value per unit volume and total veneer-recovery percentage. In declining order of importance these were taper, sweep, number of visible epicormic stubs, number of bumps and visible branch stubs, and longitudinal growth strain in the outer-wood. Branch-related defects were the most important grade-limiting defect, limiting veneer sheet quality to D-grade for most sheets. Considerable improvement in veneer sheet quality may have been achieved by pruning either just before or after branch death. Mill-door prices for logs were calculated after accounting for processing costs obtained from the mill and averaged RMB774 m−3 (about A$126 m−3). Had the trees been pruned, simulations indicated that prices/values could be lifted by RMB60–128 m−3 (A$10–21 m−3) and RMB393–461 m−3 (A$63–74 m−3) for production of higher-quality structural veneer and appearance-grade face veneer, respectively. It appears feasible that improvement in mill-door log values is possible with production of appearance-grade face veneer, but this will require some improvement in log quality through silvicultural intervention with pruning. It will also require improvement in processing methods and reduction in the impact of log end-splitting on veneer quality.
Acknowledgements
This project was funded jointly by the China Eucalypt Research Centre (CERC), the Guangxi Forest Research Institute, CSIRO, Australia, and the Australian Centre for International Agricultural Research (ACIAR). The processing was conducted at the Dongmen Veneer Mill and considerable support was generously provided by Dongmen Forest Farm. Richard Northway (formerly CSIRO, Australia), Changrong Li, Tengzhou Long, Xincui Zai and Zhaoyuan Zhang (Guangxi Forest Research Institute), along with Bing Wu and Donglin Chen (Dongmen Forest Farm) greatly assisted the project during log harvesting, processing and data collection.