Longitudinal variation in log properties of Pinus radiata in northern Tasmania: predicting log stiffness using resistance drilling

Abstract

This study assessed within and between-stem variation in log dynamic modulus of elasticity (MOE) using 591, 2.5 m logs from 65 Pinus radiata D.Don trees. Trees were sampled across 13 plots (5 individuals per plot), across 7 stands from 7 different forests in northern Tasmania, Australia. The result showed average log MOE was significantly influenced by stand age, stems per hectare, tree height, breast height diameter and dominance index. Within individual stems, we observed a consistent pattern where MOE and acoustic wave velocity increased to a peak between 5 and 15 m above ground before declining. This general increasing then decreasing pattern remained consistent across all stands, with between-site variance appearing predominantly in the y-axis intercept value, effectively representing the log MOE at zero stem height. Resi-predicted basic density showed significant correlation with log MOE, though the strength of this relationship varied markedly depending on sampling position along the stem. Multiple regression and random forest models based on 29 traits extracted from the Resi trace accounted for greater variance in log MOE compared to Resi-predicted basic density alone. Notably, random forest models explained 56% of variation at the individual log level, compared to 30% from basic density alone. This improved substantially when analysed at the mean plot level.