Factors predicting incidence of butt rot and trunk rot in individual stems of main tree species in a cool-temperate natural mixed forest in Japan

Abstract

ABSTRACTWe examined the incidence of heart rot (butt rot and trunk rot) in stems of each main tree species, with regard to the effects of individual and site characteristics, in the northern Japanese natural mixed forest. We addressed the hypotheses that incidences of rot are influenced by species identification, individual size, local vegetation, and topographic conditions. The proportions of tree individuals with heart rot (totally 36.7%) varied with tree species, with trunk rot having a significantly higher incidence in two broadleaved species (Quercus crispula and Betula ermanii) than coniferous species (Abies sachalinensis). However, butt rot incidence was similar among tree species, suggesting that each rot type appeared differently by species. The random forest classifications did not necessarily show high accuracy; it was suggested that heart rot incidence in stems of Acer mono and A. sachalinensis occurs randomly. However, in the models for both rot types of B. ermanii and trunk rot of Q. crispula, we revealed that diameter at breast height was highly important factor. Another important variable was sum of basal area of the neighboring trees, in which the incidence of both rot types tended to increase at low and high tree basal area. In addition, it was appeared that the butt rot incidence in B. ermanii was sensitive to steep slope.