A New Decay Parameter Focused on the Arrangement of Cells in Radial Files of Dried Japanese Cedar after Decay from Brown-rot Fungi Fomitopsis palustris

This study describes a new parameter that can show the degree of decay of a sample, although its mass and/or density when it was sound are unknown. Small blocks of Japanese cedar (Cryptomeria japonica) were exposed to Fomitopsis palustris for an increasing time period ranging from one to seven weeks. A microfocus X-ray computed tomography (CT) system was used to observe the cross-section of the dried samples. The tracheids were arranged in linear radial files for sound or minor decayed (less than 5% mass loss) wood, and for decayed wood (more than 5% mass loss) the arrangement was curved. The degree of curvature increased with increasing mass loss of specimens. A two-dimensional fast Fourier transform was performed on each CT image and an amplitude spectrum image was obtained. The spectrum peak width in the R-direction of the decayed samples was wider than that in the sound and minor decayed samples. This main feature was quantified as a new parameter that corresponds to the mass loss (r = 0.82) and shear strength (r = -0.75).