Ring width distribution as a valuable anatomical trait for predicting bending strength and rigidity in European oak wood beams

Ring width variability affects the elasticity and strength of wood members. This study was conducted to determine which dispersion statistics of annual ring width distributions measured in cross section in European oak (Quercus robur L.) wood beams are useful as covariates in models for predicting modulus of elasticity (MOE) and modulus of rupture (MOR). For this purpose, 21 European oak trees growing in north-western Spain were felled, logged, and sawn. The planks obtained were air-dried and surfaced into beams (50 mm x 100 mm x 2000 mm), which were visually graded according to the UNE 56544:2022 standard. MOE, MOR, moisture content and density (determined according to EN 408:2010 standard) and abundance of sapwood and ring widths were determined in 30 beams apt for structural purposes. MOE was significantly related to standard deviation, variance and interquartile range of the ring width distribution in the beam. MOE was also related to mean ring width (r = -0.52, p < 0.01) and maximum ring width per beam (r = -0.54, p < 0.01), an easy to measure variable. MOR was also related to ring width distribution parameters, although yielding lower r values. The influence of ring width evenness and maximum ring width can be considered to improve visual strength grading standards for European oak timber.