Non-destructive estimation of wood density in standing Pinus brutia trees using the drilling resistance method: Results and insights

In recent years, the use of drilling resistance method and devices which operate based on the method for non-destructive evaluation of wood has expanded, but research for density evaluation on standing trees remains limited. The study aimed to assess the effectiveness of the method through a device (IML RESI F500-S) in estimating wood density for standing Turkish red pine (Pinus brutia) trees. Increment core samples and measurement data were collected from stands of various ages and types in the Mediterranean region of Türkiye. Wood density data determined by x-ray densitometry were compared with estimates derived from charts of the device. The effect of drilling path direction was investigated on a group. Results showed that linear modelling by using the device data (obtained only by following the device manual) was moderately successful (r2≈0,62) in estimating density for only a sampling group (S1: Consisting of trees at different age, on different diameter etc.; range of density: 0,270 g/cm3; coefficient of variation:11 %). However, the other investigated group (S2), which had lower density variation due to less individual differentiation in terms of age, diameter etc., did not reveal a successful linear model. Solely the results for the subgroup 6th, showing lower density range than S1, demonstrated that even with lower density variation (cv≈7 %), standing tree wood density could be non-destructively estimated by a linear model (r2=0,72) using the device data. However, the data of the group obtained by using increment cores to ensure proper alignment of the drilling. In this case accurate estimation required a drilling path perpendicular to annual rings and passing through the pith, but the current form of the device or such devices are unable to meet the requirement. The drilling resistance method has potential use in tree selection. To improve the device's accuracy, future research should focus on developing techniques or modifications of such device to ensure more consistent and reliable drilling paths for standing trees.