Characteristics of soil erosion in a moso-bamboo forest of western Japan: comparison with a broadleaved forest and a coniferous forest.
In Japan, moso-bamboo (Phyllostachys edulis (Carrière) J. Houz.), an invasive species, has spread into and replaced surrounding broadleaved and coniferous forests because of the inactive management of moso-bamboo forests. Some local governments in Japan have speculated about an increase in soil erosion caused by the replacement with moso-bamboo forests. To evaluate the impact of such replacement on soil erosion, the soil erosion rate in a moso-bamboo forest was compared with those in an evergreen broadleaved forest and a coniferous forest. We established three plots (width 1 m, length ca. 2 m) in each forest and measured overland flow and soil erosion in two continuous periods (Period I: July 26, 2012-April 26, 2013; Period II: April 26, 2013-July 17, 2014). In Period I, the soil erosion rate in the moso-bamboo forest (0.08-0.10 g m-2 mm-1) was not significantly higher than that in the broadleaved forest (0.27-0.55 g m-2 mm-1) and the coniferous forest (0.16-0.27 g m-2 mm-1). In Period II, we removed understory vegetation and litter from two of the three plots in each forest. In Period II, the plots with such removal had higher soil erosion rates than the control plots. The soil erosion rate for the removal plots of the moso-bamboo forest was less than half of those of the broadleaved and coniferous forests. Although rock fragment cover on the soil surface and shear strength of the topsoil did not differ significantly among the three forests, root density in the moso-bamboo forest was much greater than those in the broadleaved and coniferous forests. These results suggest that a large amount of roots in moso-bamboo forests could reduce soil erosion there. The findings of this study show that moso-bamboo forests have strong resistance against soil erosion, so the replacement of broadleaved and coniferous forests by moso-bamboo forests would not seem to imply an increase in soil erosion.