Growth strain assessment at the periphery of small-diameter trees using the two-grooves method: influence of operating parameters estimated by numerical simulations

The two-grooves method used for estimating the surface locked-in strains on standing stems was studied using a finite-element model simulating the gauge measurement resulting from the groove cutting, having in mind the particular of small diameter trees. The assumed growth stress distribution was described by simple polynomial expressions of the relative radius with the possible existence of a tension wood sector characterized by higher residual stresses in the longitudinal direction. The end effect of the crosscutting vanished for a height/diameter ratio higher than 3 and the simulated gauge measurement reasonably approached the local growth strain average. For very small trees with a diameter of about 2 cm, the distance between gauge end and groove should not exceed 3 mm, a value of up to 5 mm is allowed in case of larger stems, 5–20 cm. For any combination of stem diameter, gauge length, groove distance and depth, and assumptions on the internal stress distributions, the underestimation of the surface growth strain by the gauge can be evaluated using the developed numerical tool.