Effect of site on within-tree variation of wood properties of eucalypts as determined by NIR spectroscopy and multivariate analysis

The variation in wood properties of trees of Eucalyptus globulus and Eucalyptus nitens grown on a range of sites in Tasmania, Victoria and Western Australia was explored by analysing their near infrared (NIR) spectra using Principal Components Analysis (PCA) and Soft Independent Modelling of Class Analogy (SIMCA). Core orientation (east-west or north-south), variation around breast height and longitudinal variation were examined. PCA models were developed for each set of samples (classes), and the distance between the classes, in terms of standard deviations, were measured using SIMCA. Comparison of models developed from cores with different cardinal directions showed that the models were only a small distance apart (maximum 1.48) indicating that core direction had little influence. Comparison of cores from 6 heights ranging from 0.5 to 1.5 m (0.2 m intervals) had larger model-to-model distances (maximum = 3.21) than the cardinally oriented cores. No consistent pattern of variation was observed between the heights, Models developed using discs from several heights ranging from 0 to 70% of tree height (10% intervals) were compared. Several heights were found to have model-to-model distances greater than 3. E. nitens from a Gippsland site had the largest model-to-model distances (maximum = 28.10) while E. globulus from a Southern Tasmanian site had the smallest (maximum = 4.27). It was found that model-to-model distance tended to increase as height increased to a maximum at 60 or 70% height, particularly in E. nitens.