The Causes of a fatal accident during forestry experience activity involving a falling cryptomeria japonica branch, with reference to forest stand characteristics

Abstract

We report details of a fatal accident in Ogaki, Gifu Prefecture, involving a first-grade girl who was hit directly on the head by a falling tree branch (length 3.5 m; weight 5.4 kg) while participating in a forestry experience program. The branch, from a large Cryptomeria japonica tree, was viable but had many galls, and it fell from a height of 23 m after being broken off by a strong gust of wind (maximum wind speed ca. 10 m/s). The artificial forest where the accident occurred is an isolated one composed of C. japonica and Chamaecyparis obtusa trees, where 68% of the C. japonica trees in the large size class(> DBH 40 cm) are affected by gall disease. The mean density of fallen branches longer than 1.5 m on the forest floor was recorded as 207/ha, and all had fallen within a distance of 5 m from the large trees with gall disease. When a strong wind is blowing, it is considered very dangerous to stay under large C. japonica trees, because any large branch that breaks off from a high point may fall down through the other branches with its broken part directed downwards. This incident underlines the need to pay more attention to the danger of falling branches in areas where trees have gall disease.