The influence of irrigation and fertilization on heartwood and sapwood contents in 18-year-old Eucalyptus globulus trees

The quality of wood from 18-year-old Tasmanian bluegum (Eucalyptus globulus Labill.) trees was assessed in relation to heartwood content, accumulation of extractives, and pulp yield using two growth conditions: control (C) and growth optimized by irrigation and fertilization in the first 6 years of growth (IL). Within the tree, heartwood content decreased from the base upwards, representing, on average, 77.7% and 67.6% at the base and 7.0% and 4.8% at 29.3 m height for IL and C trees, respectively. Heartwood volume represented 65.6% and 55.6% of total tree volume for IL and C trees, respectively. Heartwood content was positively correlated with tree growth, while sapwood content remained rather constant, with a radial width of approximately 2 cm. Heartwood contained more extractives than sapwood (5.3% vs. 4.0%) and pulp yield was lower from heartwood than from sapwood (58.0% vs. 56.0%). Pulp yield was negatively correlated with content of extractives. No difference in extractives or pulp yield was found between IL and C trees. The presence of heartwood decreases the quality of raw material for pulping and should be regarded as a stem-quality variable in eucalypt forestry.