Prediction of density and mechanical properties of Scots pine ( Pinus sylvestris L.) using ultrasonic time-of-flight and drilling resistance measurements methods

Scots pine is one of the main wood species in European Russia, widely used for the production of construction materials. Nondestructive prediction of its technical quality is an important topic for breeding programs, tree assessment, sawn timber manufacturing, and structural health monitoring of wooden constructions. Straight-grained, defect-free specimens (n = 176) were collected from two boards and used for ultrasound velocity measurements with Pulsar 2.2 (Interpribor, Chelyabinsk, Russia) and Pundit PL-200 (Proceq SA, Schwerzenbach, Switzerland), as well as for drilling resistance (DR) measurements using the IML-RESI PD 400 (IML System GmbH, Wiesloch, Germany). Standard tests were also conducted to evaluate density, stiffness, and strength properties of the wood. Statistically equivalent models predicting MOE and MOR in static bending from dynamic MOE measured in the longitudinal direction demonstrated the highest predictive power for both ultrasonic instruments used (R² = 0.91, 0.88). Ultrasound measurements in the radial and tangential directions showed limited practical relevance due to negligible or weak relationships between ultrasound velocity or dynamic MOE and the estimated wood properties. The combined use of DR measurements and acoustic time-of-flight methods holds significant practical potential for nondestructive construction of tomograms that visualise the distribution of elastic and strength properties radially and vertically within the tree.