2016 Volume 15 Issue 1-2 Pages 31-38
We investigated the distribution of root systems of fallen trees around the slopes of Izu-Oshima Island where landslides occurred because of Typhoon No. 26 (Wipha) on October 16, 2013. We surveyed tree species, tree height, root depth, and root width of fallen trees. Distribution of root systems was different for different tree species. Species of the surveyed fallen trees were Eurya japonica, Ilex crenata var. hachijoensis, Prunus lannesiana var. speciosa, Camellia japonica, etc. Distribution of E. japonica and ,I. crenata var. hachijoensis was high on the slopes. These trees had wide roots in the shallow range under the slope surface. In contrast, P. lannesiana var. speciosa, and C. japonica had relatively wide roots in the deep range under the slope surface. These findings suggested that tree species that took roots in the shallow range under the slope surface could not prevent the occurrence of landslides.