Sitka Spruce Segregation and Cutting

Summary Description:

This project had four key aims and objectives:

1. Investigate the potential causes of error when using acoustic instruments to measure stiffness of standing trees and logs, examining effects such season, dominance class and silviculture.

2. Compare the accuracy of standing tree instruments to predict log velocity with other indicators such as live crown ratio and slenderness.

3. Simulate a standing tree acoustic measurement, examine the wave propagation behaviour and compare results with fundamental theories presented in the wood science literature and qualitatively examine the possible interaction with variation in density of the outer part of a tree.

4. Determine if alternative cutting patterns based on log acoustics could be a viable way of maintaining the viability of sawmilling in the face of declining timber quality.

Project Outcomes:

Acoustic, or stress wave tools are increasingly used in the forest and timber industries and offer great potential for improving the processing and growing of timber.  Recent research mapping the properties of the British spruce resource has given reason to be concerned about the trend in quality over time; particular in respect of stiffness, which is the property that determines structural grade for British spruce.  If the competitiveness of the UK sawmilling industry is to be maintained, there will likely need to be changes in the way logs are sorted and processed.  Acoustic tools offer potential for this, as well as in improving silviculture.

Measurements of stiffness on standing trees using time-of-flight acoustic velocity tools need to be treated with caution as this research shows that current assumptions about the behaviour of a sound wave in a tree are too simplistic, particularly for the kind of silviculture we have in the UK.  More research is needed into wave behaviour in a tree to be able to use these tools to their full potential.  This research has shed light on the problem of why sometimes these standing tree tools work well and sometimes they do not.

Devices that measure log stiffness through acoustic resonance tools work well, but simply diverting low stiffness logs to non-structural applications is unlikely to be an economically viable option now or in the future.  Even low stiffness logs contain timber that will meet the strength grade.  This research shows that by processing lower stiffness logs differently it would be possible to reduce strength grader failure rates.  The economics of this depend on market values and production costs.