Abstract
Hydrometric observation was conducted at the small forested catchments in order to reveal the effects of tree species and forest managements on the short-term runoff characteristics. The litter layer had became very sparse and soil surface was exposed at the cypress and the cedar plot, on the other hand, it was covered by thick litter layer and understory vegetations at the young cypress and the deciduous plot. The root layer (the upper organic soil layer permeated by fine and dense root networks) was formed at the unmanaged coniferous forests, but it was not formed at the managed young cypress and the natural deciduous forests. Responses of surface runoff at the cypress and the cedar plot were distinctly larger than that of the young cypress and the deciduous plot. Surface runoff measured at the cypress and the cedar plot was root flow (shallow preferential flow through the root layer) and it of the young cypress and the deciduous plot was litter flow, because surface runoff occurred at each plot during lower rainfall intensity (<4.0 mm/5 min) than the final infiltration rate of the soils (6.4-26.8 mm/5 min) and the shallow preferential (root flow) actually occurred at the edge of the unmanaged Japanese cypress slope during storms. ‘New water’ of each catchment would be mainly composed of direct precipitation onto the stream channel and surface runoff (root flow or litter flow) occurred nearby the stream channel, because runoff coefficient of ‘New water’ (New/P) was very small (0.2-2.0%) during both the middle typhoon storm and the small autumn rainfall. Consequently, contribution of ‘New water’ to discharge peaks and hydrological response at the unmanaged coniferous catchment (1.29 ha) was relatively larger than the other two catchments due to the root flow (shallow preferential flow pathways developed within the upper organic soil layer).
