Clarifying the decay process by Inonotus obliquus in Japanese white birch naturally grown in Nikko, Japan

Abstract Decay process of wood of Japanese white birch [Betula platyphylla Sukaczev var. japonica (Miq.) H. Hara] tree by Inonotus obliquus (Fr.) Pilát was clarified by using the regression model in wood color and chemical components as a function of height position (1, 2, 3, and 4 m above the ground), wood type (sound wood and decayed wood), and their interactions, and anatomical observations. The 3 m height position, at which a sclerotium of I. obliquus was found, showed the highest decayed area percentage among four height positions. By the results of two-way analysis of variance, wood type affected all color indice. In addition, all factors (height position, wood type, and their interaction) were significant in all wood chemical components except for Klason lignin and hemicellulose. In the wood of the reaction zone, some substances were formed in the lumens of many vessels and a few wood fibers. Based on the results, we proposed the decay process of I. obliquus in naturally grown Japanese white birch, and the proposed process will contribute to a full understanding of the interactions between I. obliquus and Japanese white birch in the future.