[in Japanese]

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[in Japanese]

View full abstract

[in Japanese]

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Although Nepal has been implementing conventional soil bioengineering measures to protect and stabilize bare roadcut slopes, it is still seeking a perennial strategy to combat the instability and destabilization of slopes. A case study was carried out at a Churiya Pass roadcut slope, which had been a serious issue for the Department of Roads(DOR), to protect and stabilize the slope from severe deterioration. The study area lies in the Siwalik region, which is very fragile and has a high erosion capacity. The DOR was unable to solve the problem through conventional soil bioengineering measures, as evidenced by the results of a revegetation project in 1993. This case study was carried out to investigate the adaptability and feasibility of a Rapid Afforestation Seeding(RAS)method by a soil seeder in Nepal. With the use of Japan’s hydro-seeder, soil-seeder technology was implemented to protect and stabilize roadcut slopes perpetually, principally by establishing a woody vegetation colony. Most of the basic materials used in the study were imported from Japan. Only half of the soil and organic matter used for preparing the carrying soil was locally prepared and arranged; it was mixed with carrying soil imported from Japan a 1:1 ratio. Local and imported plant species were used in the study. A year after the vegetation was introduced, the entire degraded study area was covered by the introduced Nepalese as well as Japanese species, showing excellent growth of more than 2 m in height. The established vegetation colony successfully prevented the development and formation of ephemeral gullies that would have resulted from concentrated flows, and protected the roadcut slope from further deterioration from severe erosion. The findings of the study show that a 3-cm growth-foundation layer is ample for growing both native and introduced vegetation in the Siwalik region.

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Land failure must cause severe damage to the soil faunal communities. The recovery of them seems to take long time because the litter layers, which are their habitats, run off, although it’s not verified. So the purpose of this study is to show the recovery process of soil faunal communities in hillside works area, and clarify whether hillside works can recover the original condition of the soil faunal communities. Four study sites were chosen on Mt. Esan, Hokkaido where hillside works were constructed in different years(1989, 1987, 1980 and 1973)to study the chronological fluctuation of the soil faunal communities. The results suggest that land failure make soil faunal communities decrease, but soil fauna gradually recovers as vegetation grows. Soil faunal communities in hillside works area, however, seem to be peculiar compared with other soil faunal communities in ordinary forests. In conclusion, this study indicates there are factors that obstruct the stabilization of soil environment in hillside works area.

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Imperata cylindrica is recognized as a desirable natural green cover on the face of slopes. As this species has been known to have wide intraspecific variation both morphologically and ecologically, the study was carried out to compare clones with suitable characteristics to be a revegetation plant. Twenty-two clones in our collection from various locations and habitats across Japan were used. Plants were grown in pots and 6 characters, leaf number, plant height, plant length/plant height ratio, amount of underground parts, and sprouting/rooting ability and dry tolerance of rhizome fragments, were evaluated. Although there was no clone that showed high values in all characters in evaluation, some clones were found to have suitable characteristics in shoot growth or reproductive ability of rhizomes. The fact suggested a possibility of selection of clones of Imperata cylindrica desirable for the green cover material.

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[in Japanese]

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