Abstract
Soil erosion has been progressing over a large area in Doudaira (located in East Tanzawa of Kanagawa Prefecture) due to the sika deer (Cervus nippon) feeding which has in turn resulted in a reduction in the understory of beech (Fagus crenata) forests. Three test plots which have different understory coverage were set in Doudaira and the soil erosion rate from July 2004 to December 2006 was monitored. The results revealed that if the coverage of understory is smaller, the litter depositional volume will be smaller and erosion amount increase. At the 1% coverage of understory plot erosion depth was 2∼10 mm per year. At the study site, litter mostly from overstory beach tree deposited on the forest floor. However, the amount of litter is decreased partly through the processes of decomposition and partly washed away through the process of overland flow. Therefore the amount of litter changes season to season. At the 1% coverage of understory plot, in summer (Jul.∼Sep.) with less litter, infiltration rate decreased and surface flow rate increased rather than in Spring (Apr.∼Jun.) and Autumn (Oct.∼Nov.). Even in the case of equal rainfall amounts, soil erosion progresses more in summer. It is clear that most of the soil erosion occurred in summer, because of abundant rain in this season and decrease of amount of litter.
