岡山地方のはげ山について (5)

はげ山形成作用の機構

抄録

As was previously reported by the author, in this district the common forests were most over-used and denuded, the private forests were best conserved, and the former were used for manure and fuel gathering by poor people who had no private forest. Such human activity as manure and fuel gathering made in excess made the earth surface arid, and the increasing aridity finally made the soil so barren that the vegetation cover repeatedly hewed and scratched became difficult or impossible to survive. The soil in an area showing evidence of deforestation is usually hard and repels water. The hardened and dried soil arrests the growth of vegetation, the protector of the earth surface, and its rejection of water causes the soil erosion in a long time. The degree of soil aridity is well expressed by the production of Armillaria matsudake, the mushroom characteristic to a forest of Pinus densiflora which is the most prevailing tree in a secondary forest of the district. This mushroom likes arid soil and does not come out from humid soil as in a primary thick forest. The poor yield of the mushroom in the devastated area under discussion shows that the soil is too arid even for Arnillaria matsudake.
There are some people who attribute the formation of bare land to the prevalence of granitic rock in the district or to the nature of rock whether it is much or a little resistant to weathering and erosion. But this view must be denyed, because, even if the rock is, not so resistant, soil erosion never goes on unless the vegetation cover has been taken away.