2024 Volume 106 Issue 8 Pages 251-256
The landslides (tephra slides) caused by the 2018 Hokkaido Eastern Iburi Earthquake gave rise to many bare slopes. In order to verify forest regeneration through Japanese larch (Larix kaempferi) planting, three test sites were set up on the bare slopes. At test sites Takaoka B and Horonai, where clayey tephra was observed in the topsoil, the soil had lower permeability and was harder than Takaoka A, where a large quantity of residual tephra was present. The low water permeability and hardness were moderate in Takaoka B and severely poor in Horonai. In the third year after Japanese larch was planted in each test site, Takaoka B larch had a significantly smaller tree height, diameter, and height growth than those of Takaoka A. At the same time point, Horonai larch had a significantly smaller tree height, diameter, growth amount, and growth rate than those of Takaoka B. These results indicate that, on bare slopes caused by landslides, firstly, the low water permeability and hardness of clayey tephra are the primary factors that inhibit the initial growth of planted Japanese larch, and secondly, the lower the permeability and harder of clayey tephra, the smaller the initial growth of planted Japanese larch trees.
