Determination of radial profiles of wood properties using a near infrared scanning system

Abstract

A near infrared (NIR) spectrometer, equipped with a 2-mm diameter fiber optic probe, was used to develop a rapid and automated method for determining the radial profiles of wood properties for six tree species of the boreal forest of eastern Canada. Partial least squares regressions were performed using individual spectra, collected every 5 mm, from the pith to the bark, using 1,538 samples previously scanned by SilviScan to provide reference data. Results obtained for density (r2 of 0.57 to 0.65; SE of 21 to 33 kg/m3), microfibril angle (0.56 to 0.82, 2.3 to 4.8°) and modulus of elasticity (0.71 to 0.85, 1.3 to 1.8 GPa) were suitable for the purpose of this study. This method was then applied to more than 30,000 tree cores and the resulting radial profiles of the properties were consistent with literature. Area-weighted average predictions also gave reliable estimates at the disk scale. NIR-estimated values were strongly correlated to the measured density (r of 0.83 to 0.93) and modulus of elasticity (0.82 to 0.88) and moderately correlated to measured microfibril angle (0.64 to 0.78). Radial profiles of wood properties are needed to characterize the proportions of juvenile and mature wood. The developed method therefore offers interesting opportunities for estimating the quality of wood fiber in trees growing in plantation or natural forest.