Strength loss caused by fungal degradation is an important factor to be considered during tree-stability assessment. Detailed information on the relationship between static mechanical properties in relation to the heterogeneity of density and dynamic mechanical parameters of wood degraded by the soft-rot fungus Kretzschmaria deusta can improve the understanding of its decay process and the interpretation of results obtained from stress-wave-based non-destructive methods used for tree-stability assessment. This research presents density profiles of artificially inoculated samples with K. deusta and static mechanical properties of green beech wood in relation to physical parameters (density, moisture content, vibroacoustic parameters). A statistically relevant difference (p < 0.01) in the variability of density distribution between degraded and intact samples was proved. Relevant correlations were proved among modulus of rupture ( M O R $MOR$ ), mass loss and variability longitudinal density distribution. A strong linear relationship between M O R $MOR$ and static modulus of elasticity ( M O E $MOE$ ) of degraded and intact specimens was presented. A strong relationship was also proved between M O R $MOR$ and dynamic parameters (dynamic modulus of elasticity ( M O E D $MOED$ ) and stress-wave velocity in longitudinal direction ( c l ${c}_{l}$ )). M O E D $MOED$ showed a stronger correlation to M O R $MOR$ than c l ${c}_{l}$ proving the importance of density in assessing strength loss through non-destructive methods.

Wood-decaying fungi are responsible for the degradation of wood and the alteration in its material properties. Fomes fomentarius (L.) Fr. is one of the most common white-rot fungi colonising coarse wood and standing trees. In recent years, according to their genetic, physiological, and morphological differences, Fomes inzengae (Ces. and De Not.) Lécuru was identified as an independent species. This article aimed to compare the impact of the degradation caused by both species on the anatomical, physical, and mechanical properties of beech wood. When comparing the degradation caused by different strains of both species, no statistically significant difference was found in mass loss (ML) or moisture content (MC). A relevant correlation between ML and MC was confirmed for both species. Variabilities in the density distribution of the degraded and intact bending samples were found to be statistically different. No relevant difference was observed in the modulus of rupture (MOR) between the two species after each exposure period. A strong linear relationship between the MOR and the dynamic modulus of elasticity was revealed for both species. Both species showed decay patterns typical for simultaneous white rot and soft rot. According to the presented results, the impact of both species on the investigated material properties of wood cannot be considered significantly different.

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