Degradation of beech wood by Kretzschmaria deusta: its heterogeneity and influence on dynamic and static bending properties

Abstract

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.

Fomes fomentarius and F. inzengae—A Comparison of Their Decay Patterns on Beech Wood

“…Even if no statistically significant difference was found for F. inzengae between the two exposure times, as shown in Figure 4 b, the variability in density distribution tended to decrease with a longer fungal exposure (higher level of degradation). Cristini et al [ 28 ] presented the variability in density distribution for bending samples after 12 weeks of exposure to the soft-rot fungus K. deusta (average between 10% and 15%). The lower variability measured for the Fomes species can be explained by a higher level of degradation caused by both species in comparison to K. deusta , supporting the previous observation that with a more progressed deterioration, variability in density decreased.…”

“…For mechanical testing, small orthotropic bending samples (7 × 7 × 100 mm) of European beech ( F. sylvatica ) were crafted ( Figure 1 a). These specimens were cut according to the methodology presented by Cristini et al [ 28 ]. To obtain oven-dry mass, the samples were completely dried in a kiln for two days at 103 °C and weighed after approaching steady conditions.…”

“…A detailed description of the physical and mechanical measurements is presented by Cristini et al [ 28 ].…”

“…All the small samples were prepared from the centre of each selected specimen. Sample preparation and microscopy setup are described in detail by Cristini et al [ 28 ].…”

“…Deflorio et al [ 27 ] studied the decay development of six different fungal species in the standing trees of four different wood species, revealing different results for nondestructive testing and ML (after tree felling) depending on the time of inoculation. Cristini et al [ 28 ] tested the physical and dynamic/static bending mechanical properties of beech wood artificially inoculated with the soft-rot fungus Kretzschmaria deusta (Hoffm.) P.M.D.…”