Natural durability of mid-rotation plantation Gympie messmate and red mahogany in a 13-year aboveground field test

Abstract

Compared with the same species from native forests, faster growth and earlier harvesting of plantation timber may cause reductions in heartwood extractive levels, density and decay resistance due to the immaturity of wood tissues. The aim of this study was to evaluate the decay resistance of mid-rotation plantation Gympie messmate and red mahogany heartwood in ground proximity and L-joint aboveground field tests at three sites in Queensland, Australia. After 12-13 years in both tests, the inner heartwood of each plantation species generally had more decay than the middle and outer heartwood. Middle heartwood was significantly less durable than outer heartwood for each plantation species in the ground-proximity test at the tropical South Johnstone site. Plantation Gympie messmate outer heartwood performed similarly to native-forest spotted gum, the high-durability reference species. Plantation red mahogany had more decay than Gympie messmate. Given the need for plantation timber to supplement supplies from sustainable native forest resources, substantial research is recommended to fully characterise the durability of key plantation hardwood species, including investigation of protective treatment supplementation and communication of design requirements.