2018 Volume 100 Issue 5 Pages 165-173
We evaluated the conditions necessary for the establishment of an avalanche protection forest on a steep slope mounted with wooden anti-glide tripod structures under 2 m of annual maximum snow depth. We investigated five forest stands on slopes of 35° with 450 tripods/ha or 40° with 620 tripods/ha, more than 7 years after the construction of the tripods and planting of sugi (Cryptomeria japonica) seedlings (planting density of 1,020-2,500 seedlings/ha). Survival rates of the tripods decreased to ca. 80 and 40％ after 9 and 12 years, respectively. In contrast, height growth of sugi trees could be termed a middle site quality. In addition, under planting density of 2,500 seedlings/ha, which is a common regime for afforestation, stand densities of erect sugi trees, which had grown up to twice the annual maximum snow depth, were estimated to be 1,000 and 1,500 trees/ha after 9 and 12 years, respectively. It is considered that snow cover can be stabilized in more than 1,000 trees/ha of erect sugi. Thus, these results suggested that, for avalanche protection, sugi forests can be successfully established with wooden tripods on a steep slope, and with planting density above a certain level, under 2 m of annual maximum snow depth.
