2016 Volume 15 Issue 1-2 Pages 39-47
We investigated the distribution of root systems of wind-fallen trees on the not-landslide slopes near the slopes where landslides occurred by the Typhoon 26 (Wipha) in October 16, 2013, in Izu-oshima Island. Wind-fallen trees were scattered in the study area. We surveyed the species, tree height, root depth, and root width of wind-fallen trees, in order to clarify the difference of root systems between the wind-fallen trees and the not wind-fallen trees around them. Many of the wind-fallen trees were Ilex crenata var. hachijoensis. The wind-fallen tree produced even on the gentle slope and the wind-fallen tree’s roots were distributed in a shallow range than 50cm from the ground. Therefore, it was guessed that trees that roots are distribution in a shallow range were damaged by wind. Tendency of windthrow was often southwest-north direction. For this reason, it was considered that the trees might have fallen by the wind from the southeast before the maximum wind speed at the time of the passage of the typhoon is observed.