Impact of fungal decay on the structural integrity of wood

Abstract Wood-destroying fungi induce different types of decay, which cause significant reductions in elastomechanical properties of wood when the mass loss is not yet gravimetrically detectable. Particularly difficult to define is incipient decay since the reduction of elastomechanical properties is highly dependent on the heterogeneity of wood species. Early-stage effects of incipient decay on impact behavior remain insufficiently understood. The aim of this study was to clarify how different rot types affect structural integrity in relation to mass loss. Therefore European beech ( Fagus sylvatica ) and Scots pine ( Pinus sylvestris ) sapwood specimens were incubated with white-rot ( Trametes versicolor ), brown-rot ( Coniophora puteana ) or soft-rot fungi. After incubation, moisture content and relative mass loss were measured. Mass loss (ML) increased linearly over time across all fungi-wood combinations, reaching a maximal reduction of 67% in European beech wood and 39% in Scots pine sapwood with Trametes versicolor . For Coniophora puteana , ML in European beech peaked at 26%, while Scots pine sapwood reached 24%. Soft-rot fungi caused the least degradation reaching 9% ML for European beech wood and 4% for Scots pine sapwood after 99 days. High-Energy Multiple Impact (HEMI) – tests were performed to evaluate the effect of mass loss by fungal decay on the structural integrity of wood, expressed as the Resistance to Impact Milling (RIM). The RIM decreased with increasing ML at early-stages proving the high sensitivity of the test to detect incipient decay, especially with brown rot. The reduction of structural integrity was compared with the reduction of different strength properties of wood depending on the mass loss, where RIM values exhibited less variability compared to other strength properties, suggesting higher measurement stability in case of white and brown-rot decay.