Pre-sorting of Norway spruce structural timber using acoustic measurements combined with site-, tree- and log characteristics

This study assesses whether acoustic velocity alone or in combination with information about the timber obtained in the forest or on the log-yard can be used for pre-sorting of Norway spruce (Picea abies [L.] Karst) structural timber. The study is based on 1235 boards from 205 trees sampled from 14 sites in Norway. In addition to various site-, tree- and log variables, acoustic velocity was obtained by Fibre-gen tools, the ST300 on standing trees and the HM200 on logs. Both ST300 and HM200 explained parts of the variability of the indicating property measured by Dynagrade strength grading machine, but the accuracy was better for HM200 than for ST300. The model with ST300 was substantially improved by introducing forest data, i.e., height to diameter ratio, age and relative longitudinal position in the tree while the improvement by combining HM200 with log data, i.e., log tapering, was minor. Grade yield after pre-sorting based on the developed models was simulated, and the results showed a possibility of increasing the C30 yield. The results show that acoustic velocity could be used either as an inventory tool, to give information about the available material from a site, or as a pre-sorting tool before sawing the logs to certain products.