1999 Volume 81 Issue 1 Pages 42-50
In order to predict erodibility of surface soil in Japanese cypress stands by using the quantification theory, categorisa-tion of undergrowth vegetation and construction of an index of susceptibility to soil erosion were made. The undergrowth vegetation of 64 study plots distributed over 17 areas in Kochi Prefecture were grouped into five types on the basis of coverage and life form of the dominant species : "poor vegetation type, " "fern type, " "herb-Chamaephyte type, " "deciduous broad-leaved tree type, " and "evergreen broad-leaved tree type." This grouping is proved to be a sound basis for vegetation categorisation because of the observed differences among the types in protective capacity against soil erosion. "Soil Erosion Susceptibility Index" was defined as the sum of the following three indices of soil erosion, each expressed as a percentage of its maximum value : number of soil poles, area of soil cliffs, and percentage exposed area of fine roots. Combining the two tree types into one category, "tree type, " the "Soil Erosion Susceptibility Index" increased in the following order : "herb-Chamaephyte type" < "fern type" <"tree type" < "poor vegetation type." This order reflects the differences in the characteristics of vegetation among the categories. It was concluded from these results that the "Soil Erosion Susceptibility Index" and the categorisation of undergrowth into the four categories were effective in predicting soil erosion susceptibility.
