HR: 0800h
AN: H51C-0373    [Abstracts]
TI: Evaluation of splash erosion at forest floor in mature Japanese cypress plantations
AU: * Nanko, K
EM: nanko@fr.a.u-tokyo.ac.jp
AF: Graduate School of Agricultural and Life Sciences, the University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan
AU: Mizugaki, S
H51C-0373 AF: Japan Science and Technology Agency, Tennodai 1-1-1, Tsukuba-shi, Ibaraki, 305-8577 Japan
AU: Onda, Y
H51C-0373 AF: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tnnodai 1-1-1, Tsukuba-shi, Ibaraki, 305-8577 Japan
AU: Hiramatsu, S
H51C-0373 AF: Department of Agriculture, Shinshu University, 8304 Minami-minowa, Kami-ina, Nagano, 399-4598 Japan
AB: Poorly managed mature Japanese cypress ( Chamaecyparis obtusa) plantations in Japan have bared floor with little surface cover because cypress litter readily decomposes small pieces and weak penetration of sunlight results in poor growth of forest undergrowth, therefore suffered from surface erosion. In surface erosion process at forest floor, the effect of raindrop-impact-induced erosion would be high because the canopy produces large raindrops and promotes raindrops' erosive potential by increasing their kinetic energy. In this study, we evaluated the effect of slopes and transition of the splash erosion in order to investigate the process of surface erosion at bared forest floor. This study area is a mature Japanese cypress plantation in Taisho town, Shikoku Island, Japan. The splash erosion was observed by 27 splash cups (exposed soil area with 10cm in diameter) at forest slope with the inclination from 9 to 39°, respectively. The splash cups were divided five slope classes; each class value was 12.5, 20.5, 25.5, 29.5, and 37°. The splashed soil was separately collected in three split periods; each period had 86.2, 68.0, and 84.0 mm throughfall precipitation. Raindrop kinetic energy was simultaneously monitored by 2 laser raindrop-sizing instruments. Throughfall had similar drop size distribution and kinetic energy during each period and mean drop kinetic energy was 15.0 J m^-2 mm^-1. The splash rate during all observation period was 14.5, 11.4, 12.2, 9.1, and 4.6 g m^-2 mm^-1 at the each slope class, respectively. The splashed soil was found to reduce as time. Particularly the gentlest slope class had marked decrease for the splash rate; 25.2, 10.4, and 6.9 g m^-2 mm^-1 during 1st, 2nd, and 3rd period, respectively. On the other hand the steepest slope class had little change of the splash rate; 3.3, 6.7, and 4.2 g m^-2 mm^-1 . Some earlier studies using cultivated soil showed the splash rate increased with slopes, but this study showed contrary results. Although soil detach potential is larger at steep slopes than at gentle ones, steep slopes could deposit little soils on the surface of Japanese cypress plantations.
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 1833 Hydroclimatology
DE: 1862 Sediment transport (4558)
DE: 1865 Soils (0486)
SC: Hydrology [H]
MN: Fall Meeting 2005