Interdisciplinary approach to the study and management of stem defect in eucalypts

In Australia large areas of forest have been closed to industrial forestry and it is necessary to compensate for lost production. Future wood products will come from intensively managed silvicultural regimes — eucalypt regrowth forest and plantations. Solid-wood regimes involving high-cost operations such as pruning and thinning will be economically sensitive to downgrade due to various types of stem defect — fungal and insect damage, staining, kino veins. In Tasmania, research over the last decade has focused on developing management strategies to minimise stem defect caused by decay fungi in both regrowth and plantation eucalypts. Under plantation conditions neither Eucalyptus nitens (Deane & Maiden) Maiden nor E. globulus Labill. shed branches efficiently. Retention of dead branches leads to defects in wood such as a large knotty core or loose knots, making the stem unsuitable for either veneer or sawlog. Pruning of green branches at canopy closure and in subsequent lifts shortly afterwards solves this problem. However, on the more productive warm and wet sites there is a high level of decay infections in E. nitens and E. globulus via pruning wounds. We are investigating the complex pathological, physiological, genetic, and silvicultural components dictating eucalypt susceptibility to decay infection and its long-term spread into clearwood including: crown characteristics prior to pruning; growth responses to pruning; growth responses to fertiliser; host resistance and antimicrobial defences; and the identity and pathogenicity of decay fungi. An interdisciplinary approach is fundamental to understanding such questions and also to the successful development of site productivity models that include predictions of risk and impact of biotic and abiotic damage