Toward global calibrations for estimating the wood properties of tropical, sub-tropical and temperate pine species

Near infrared (NIR) spectroscopy is increasingly being used to replace traditional methods of wood property assessment and, as a result, multi-site, multi-species (or global) calibrations are of interest to organisations who assess wood properties on a large-scale. In this study, the development of global wood property calibrations for tropical, sub-tropical and temperate pines is explored. In a three-stage process, samples provided by ten forest industry companies and representing 14 pine species (two species had two varieties) and one hybrid, grown on 17 different sites in five countries (Argentina, Brazil, Chile, Colombia and South Africa) were used to develop calibrations for air-dry density, microfibril angle (MFA) and stiffness. Initial calibrations, based on samples from individual co-operators, had variable statistics; for example, R(2) for density ranged from 0.51 to 0.89. In the second stage, multi co-operator calibrations were obtained from two independent data sets that included samples from sites in each country. For the three properties, calibration statistics compared well to those obtained in stage 1, with stiffness having the best fit statistics (R(2)=0.917, RPDc=3.3). MFA and stiffness calibrations showed the presence of nonlinearity in the data. The calibrations performed reasonably well when used to predict the wood properties of the alternate set, with density having the weakest predictions. Stage 3 calibrations were based on all available samples and were similar to those developed in stage 2, demonstrating that it is possible to build multi-site, multi-species calibrations for pines.