Non-destructive evaluation of strength and stiffness of Eucalyptus pellita. A comparison of near infrared spectroscopy and acoustic wave velocity assessment

Abstract

Tree improvement programmes benefit from measured data for multiple phenotypes in order to potentially gain maximum genetic leverage for selection. Diameter at breast height, tree height and tree form have traditionally dominated the measured phenotype due to their ease of measurement, and the fact that logs are traded by volume. More complex traits, including those that potentially offer economic benefit in terms of quality and end-product performance such as strength and stiffness, are more difficult to measure in standing trees and are frequently overlooked. These traits are therefore in need of rapid methods of assessment. Tree improvement of Eucalyptus pellita in Malaysian Borneo for solid wood and veneer product utilisation is one such example of where selection for improved stiffness is desirable. Genetic trials of E. pellita were assessed using acoustic velocity measurements at several intervention points, including the standing tree, fallen stem, logs and boards, along with near infrared spectroscopic measurement of the final test samples. Calibrations were developed for modulus of elasticity (MOE), modulus of rupture (MOR) and compression parallel to the grain, using reference values obtained from 3-point bending of small clearwood test samples obtained from the trees following felling and sawing to ensure back-to-log recovery of the test sample location. Dynamic MOE calculated from the standing tree acoustic velocity showed good correlation with the mean MOE from static bending for the wood in the butt log, representing the location where standing tree acoustic velocity measurements were obtained. The Savitzky-Golay second derivative pre-treatment yields the best performing calibration for the microNIR and MPA on ground wood for MOE (R2Cal = 0.76, r2CV = 0.80, r2Pred = 0.46, RMSEC and RMSECV = 1.4 GPa, RMSEP = 2.3 GPa, LV = 3) for the microNIR and R2Cal = 0.98, r2CV and r2Pred = 0.70, RMSEC = 0.5 GPa, RMSECV and RMSEP =1.5 GPa, LV = 4 for the MPA.