Spatiotemporal factors affecting bark stripping of conifer trees by Asiatic black bears (Ursus thibetanus) in Japan

Abstract

Bark stripping by Asiatic black bears (Ursus thibetanus) has a serious impact on conifer plantations in Japan, resulting in physical damage to the tree trunks and reduction of the value of the timber. The aim of this study was to clarify whether these plantations are more prone to damage by bears at particular times and sites, to more effectively prevent this damaging behavior. The study was conducted at Kusaki University Forest of Tokyo University of Agriculture and Technology in Gunma Prefecture, central Japan. To determine where, when, and how frequently bears strip the bark, we established circular plots in each of 65 stands and felled all trees that had been damaged by bears. In total, we felled 1639 damaged trees, analyzed 1490 samples (Cryptomeria japonica: 1236, Chamaecyparis obtusa: 254) across the 65 study stands, and calculated the timing of bark stripping for each by counting the number of annual growth rings in each tree. Generalized linear mixed models were then used to examine the effects of various spatiotemporal factors on bark stripping. In terms of temporal variation, we found no relationships between the occurrence of bark stripping by bears and the meteorological conditions from the previous November to the previous March. In terms of spatial variation, there was no relationship between the occurrence of bark stripping by bears and the environmental characteristics of the stands. We did, however, find that stands that experienced bear damage in the previous year were more prone to experiencing bear damage in the current year, and furthermore, the rate at which damage of trees spread during the 10years after the first occurrence of a damaged tree was significantly faster in young stands. These findings will allow forest managers to predict the conditions that make conifer stands more prone to bear damage, allowing them to make effective forest management plans. Additionally, to reduce bear damage, foresters should focus on direct protection efforts that they would like to protect from bears.