Abstract
To evaluate the reinforcement effect that the rhizomes of Sasa nipponica have on a slope for preventing surface failure, we conducted a field survey of the structure of Sasa nipponica populations at 33 sites in an eastern part of Hokkaido. As a result, we confirmed that the leaf area index (LAI) is regarded as the representative indicator of the biomass of the terrene parts of Sasa nipponica. Further survey of the relationship of several factors of the subterranean parts by using LAI revealed that LAI increases with the dry weight of the subterranean parts in both flat ground and slopes. Correlations between LAI and the volume or length of the rhizomes per 1 m2 that were detected in a flat ground could not be detected in a slope. We also found that LAI correlates strongly with the factor for calculating the tensile strength of the rhizomes as a reinforcement effect, that is, the total sectional area of the rhizome per unit sectional width in a slope. From these findings, we devised a general method for evaluating the reinforcement effect of the rhizomes on a slope by using LAI as the indicator of the terrene parts of Sasa nipponica. Moreover, it has been clarified that rhizomes in the forest area of a slope are thicker and extend more easily in the contour direction than rhizomes in the open area.
