Designing silvicultural regimes with a structural log index

Authors: Euan Mason
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2012, Issue N.Z.J.For. 57(2) 2012, pp 13-18, Aug 2012
Publisher: New Zealand Institute of Forestry

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Abstract: We need a structural log index (SLI), similar to Jim Park’s pruned log index (PLI) in order to improve estimates of value in the log market, identify existing stands of high quality structural wood, and allow silviculturalists to plan structural regimes effectively. Key components of a structural log index are potential conversion of logs to boards, stiffness, and stability during drying. We can use conversion potential from the PLI for the SLI and existing models of branching plus branch index (BIX) can be employed so that large-scale geometry is represented. In addition we need estimates of gradients in cellulose microfibril angle (MFA) across log radii because MFA influences stiffness and MFA gradients affect stability during drying. Gradients can be estimated from standing trees using an ultrasonic velocity (USV) core scanner we have developed at the School of Forestry, University of Canterbury, and a USV disc scanner can provide higher resolution maps of gradients if required. Spiral grain also needs to be included, and our recent results show that this is likely to be relatively unaffected by silviculture but may be critically influenced by genotype. Three datasets from sawing studies are available for us to test formulations of the SLI, but no one dataset covers all the required variables and so a new sawing study will be required after a pilot study with existing data. Recent research results support these ideas, and developing the SLI will involve balancing complexity with utility.

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