Radial variation in cellulose content and Kraft pulp yield in Eucalyptus nitens using near-infrared spectral analysis of air-dry wood surfaces

To date, near infrared (NIR) spectroscopy calibrations to predict Kraft pulp yield (KPY) and cellulose content (CC) have been developed using woodmeal samples. Our study, building upon such calibrations for KPY and CC, used NIR spectra collected at 5 mm intervals from the radial longitudinal surface of pith-to-bark breast height strips in 12 Eucalyptus nitens trees to develop calibrations for KPY and CC prediction from wood surface spectra. Both laboratory and portable NIR spectrometer instruments were effective in predicting radial variation, with standard errors of prediction in the vicinity of 1%. Both cellulose and KPY increased from pith to bark, showing a range of 5-8% within individual cores. The range was greater when the radial sampling interval was reduced to 1 mm, allowing the sub-annual variation to be better resolved. Commercially useful calibrations can now be developed quickly from air-dry increment cores and more cheaply than has been previously possible.