The influence of wound location on decay extent in plantation-grown Eucalyptus globulus and Eucalyptus nitens

Wounding caused by certain silvicultural practices such as pruning and thinning can facilitate the development of wood decay. In plantation trees grown for the purpose of timber production, wood decay commonly develops from dead branches and is usually confined into the mature portion of wood than in the sound sapwood. To better predict the susceptibility (or resistance) of sapwood to decay in different wound locations, this study compared the influence of stem with branch wounding on decay extent in plantation Eucalyptus globulus and Eucalyptus nitens in Tasmania (Australia) after summer wounding and artificial inoculation with two white rot decay fungi. The amount of sapwood discoloration and decay, as well as the amount of total phenols extracted from the reaction zone (a dark colored zone produced by the accumulation of phenolics) were assessed after tree felling (13 months). In both Eucalyptus spp., greater sapwood discoloration and decay developed from stem wounds than branch wounds. Sapwood discoloration and decay extended further in the axial than radial or tangential wood alignments. Fungal isolations showed that wounds challenged with the white rot decay fungi Acanthophysium sparsum and an unidentified white rot fungus always developed significantly greater sapwood discoloration and decay than the control treatment, regardless of wood alignment. In unwounded parts of the tree, total phenols were 4.7- and 6.3-fold higher in the branch sapwood compared to stem sapwood in E. globulus and E. nitens, respectively. The higher inherent level of total phenols in the branch sapwood may partly explain why less dysfunction resulted from the inoculation of branches compared to stems. Overall, E. globulus developed smaller columns of discoloration and decay than E. nitens