Non-destructive Methods and Process Capability Analysis to Assess Conformance of Douglas Fir Stands to Customer Quality Specifications*

Largest branch diameter in the breast-height region (LLBH) and acoustic velocity on lower bole were measured on trees in a 20-year-old Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) experiment comparing seven density management/fertiliser regimes. The less dense regimes tended to have larger mean branch diameter at breast height, with fertiliser increasing the mean even further. However, except for the densest regimes, the difference between a density regime and its counterpart with fertiliser was not statistically significant. The densest regime had significantly higher mean acoustic velocity than the other regimes, which were all the same except for one with very low velocity attributed to abnormal wood formed after damage by black bears. Although statistical significance may be lacking with respect to mean properties, subtle differences in their distributions may be important to timber sellers where purchasers often pay premiums for stands with higher percentages of trees that meet their process and customer needs. A statistical * Based on a paper presented as part of Session 16 – Wood Quality from Intensive Management, during the XXII IUFRO World Congress 2005, Brisbane † Corresponding author: [email protected] Briggs et al. — Conformance of Douglas fir stands to specifications 171 quality control procedure, process capability analysis, was used to assess the conformance of each regime to specifications for largest branch diameter at breast height and acoustic velocity. Conformance of largest branch diameter to a 35-mm maximum ranged from 84% to 100%, with fertiliser reducing conformance by 10–15%. Conformance of acoustic velocity to a 3.5 km/sec minimum ranged from 15% to 85%, with negligible difference between a thinned regime and its counterpart with fertiliser. Joint conformance ranged from 10% to 85%, with generally lower conformance associated with fertiliser. There is potential for using statistical quality control techniques to assist with timber marketing, harvest planning, and monitoring stand development.