Effects of physical tree characteristics and soil shear strength on overturning moment due to
flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants
in Japanese rivers. Tree pulling experiments were conducted, and the resulting damage was examined in
order to assess the effects of physical tree characteristics on the maximum overturning moment (Mmax).
In situ soil shear strength tests were conducted in order to measure soil strength parameters. The effects
of species differences on the Mmax were examined by analysis of the root architecture. S. babylonica has
a heart-root system that produces a greater overturning moment due to the strong root anchorage and the
large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root
system that produces a smaller overturning moment. However, trees with the plate-root system may
withstand overturning better due to an increased root:shoot ratio. Considering the strategy of J.
ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index
(height*Dbh
2) is a better parameter than Dbh
2 because it indirectly involves the difference in
belowground volume and surface area. Different soil cohesion values were found at different
experimental sites, and the average Mmax for overturning each species decreased linearly with increasing
soil cohesion
