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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.

We investigated the effects of 6 kinds of plant mulch added to the surface of coarse sandy pot soil. Soil microbial enzyme activities and some soil properties were measured at regular intervals at depths of 0-5 and 10-15 cm over 8 months. Soil enzyme activities increased rapidly as the mulch decomposed, and varied among different mulch. All treatments were significantly different from the control. Stems and leaves of C. agatiflora greatly enhanced the enzyme activities relative to the other treatments, maintained higher FDA scores even in winter.

Woody vegetation affects the stability of steep mountain slopes mainly by increasing the shear strength of soil via root reinforcement. Plant roots on steep terrain tend to elongate uphill. As the slope angle increases, the root growth uphill is greater. It is assumed that gravitational force may be one of the factors responsible for this orientation of roots. Therefore, we carried out a study of root growth under applied centrifugal force to determine the effects of root gravitropism on steep slopes. Pinus densiflora was sown in plastic pots and placed at different distances from the same center (at different radii) on a continuous rotary circular platform for five months. Two other stationary plots, one in the horizontal plane and the other with an inclined slope of 45°, were set up as control plots. This experiment showed that the direction of root elongation changes extensively with respect to the centrifugal force applied on the plant. The tap-root elongates towards the resultant direction of the sum of gravity and centrifugal force, whereas the lateral roots elongated in the direction opposite that of centrifugal force. The control plots also showed the same tendency i.e. lateral roots elongated in the uphill direction in the inclined plot, and the tap-root developed towards the gravity in the horizontal plot.