Predicting pulp yield and pulp productivity of Eucalyptus dunnii using acoustic techniques

The economics of kraft pulping are influenced by variation in wood density and chemistry, or their product, pulp productivity. The ability to predict basic density, pulp yield or pulp productivity before harvest would provide an economic advantage to the grower or processor. Acoustic velocity in green wood is correlated with both basic density and pulp yield, offering potential for rapid screening. We explored relationships between acoustic velocity, density, pulp yield and fibre length using data from Eucalyptus dunnii plantations in northern NSW, Australia. Acoustic velocity measured on logs accounted for 27% of the variation in pulp yield and 50% of variation in pulp productivity. The strong relationship between fibre length and pulp yield is proposed as a possible causal mechanism. A threshold acoustic velocity of 3.65 km s–1 was defined as the point at which logs would produce at least 250 kg of dry pulp per cubic metre of green wood. Removal of the worst 25% of logs, based on velocity, would give a 2.2% gain in pulp productivity which equates, in turn, to an additional 6.2 kg of pulp produced from every cubic metre of green wood. Keywords: acoustic properties; wood pulps; yields; wood density; fibre length; grading; segregation; Eucalyptus dunnii.