Economic value of optical and X-ray CT scanning in bucking of Scots pine

In the Nordic countries, trees are typically bucked into logs using harvesters that measure only a two-dimensional diameter profile of the stem. Because the value of a log can vary significantly depending on its shape and internal defects, bucking decisions can in principle be improved by optical scanning of the three-dimensional stem shape, and detection of knots and other features inside the stem by X-ray computed tomography (CT). The objective of this study was to quantify how much the value recovery at a sawmill could be increased, if bucking decisions took advantage of additional measurement data and a sawing simulator to estimate log values. A simulation study on 1582 Scots pine stems was performed to compare bucking based on a two-dimensional diameter profile with bucking that maximises log value based on either optical scanning alone, or both optical and CT scanning. For log positioning, both the traditional “horns-down” position, and value-maximising rotation based on CT scanning were considered. The results show that bucking based on optical scanning alone can potentially increase the value of sawn timber by up to 5%, and CT scanning before bucking provides little additional value for a sawmill using a CT scanner to optimise log rotation.