Radial variation in Kraft pulp yield and cellulose content in Eucalyptus globulus wood across three contrasting sites predicted by near infrared spectroscopy

There is little published information on the variability of pulp yield within eucalypt stems. This is primarily due to the difficulty in measuring pulp yield in small samples, especially those obtained nondestructively. Thus, information of the effect of site, climate, and silviculture on pulp yield variability is lacking, minimizing its consideration in the economic optimization of pulpwood production. Near infrared spectroscopic measurement of pulp yield directly from intact wood surfaces at a small, radial sampling interval provides forest managers with opportunities to better understand and manage its sources of variability. Calibrations based on solid wood samples were constructed to describe radial variation in Kraft pulp yield and cellulose content using intact wood samples from Eucalyptus globulus Labill. Plantations at three sites with contrasting annual rainfall were studied. Pulp yield and cellulose content were higher at the more productive, wetter sites. Outer wood near the cambium had pulp yield values up to 8% higher than those at the pith. There was no clear intra-annual cycle of variation. The more productive sites exhibited significantly steeper pith-to-bark increases in pulp yield than the driest site. This has implications for optimizing pulp productivity by considering rotation length and site quality.