Timber Measurement and Conversion Factors: A Comparison Between Harvester, Optoelectronic Log-By-Log, Section-Wise Manual and Photo-Optical Measurements As Well As Log Truck Load Scans For Volume Assessment

From an economic standpoint, accurate timber measurement is of utmost importance. Besides being used for billing purposes, an accurate assessment of the quality and quantity of wood, along with predicting product yields, holds significance for optimizing the timber supply chain. In Germany, different timber measurement systems are used depending on the assortments or products. Whereas high quality timber is often measured at the sawmill gate logwise, the volume of timber assortments destined to the wood panel or pulp industry is mostly estimated in wood piles manually or photo-optically at the forest road side. Through conversion factors, which relate the gross and net volumes, net timber volume can thereby be estimated quickly based on the measured gross volume of the pile. However, the commonly used conversion factors for Scots pine in Germany are not based on scientific findings and are therefore controversially discussed. This study therefore aimed to evaluate the accuracy of conversion factors by comparing different measurement systems i) harvester measurement, ii) optoelectronic log-by-log measurement at sawmill gate, iii) section-wise manual wood pile measurement, iv) photo-optical wood pile measurement and v) log truck load scan measurements for five different assortments including OSB, MDF, LAK, LAS 3 m-length, and LAS 5 m-length. The analysis was conducted using 56 wood piles in Northeastern Germany, a region where Scots pine is the dominant tree species with a proportion of 70 % of the forest area. The total gross volume of these wood piles was approximately 4,000 m³ (st). The average of the resulting conversion factors ranged between 0.57 and 0.62 for higher quality assortments, varying from a minimum of 0.51 to a maximum of 0.66. The results revealed significant differences in both net timber volume measurements and gross wood pile volume measurements, across all assortments. Notably, a significant difference was observed between harvester and log-by-log measurements, especially for the 3 m-length assortments. Concerning the truck load scans for gross volume estimation of industrial timber assortments, the comparison with the section-wise manual wood pile measurement highlighted noticeable differences.