Altitudinal zoning of understory vegetation in planted Hinoki cypress (Chamaecyparis obtusa Endl.) forest from the view of surface soil erosion control

Zoning of understory vegetation by temperature was made, and application of it to vegetation control was discussed from the view of protection of surface soil loss by using the data collected from 68 Hinoki cypress plantations distributed over the whole area of Kochi Prefecture, Southwestern Japan. Based on percent coverage, "species coverage index" was determined for every undergrowth species with visual observation. All species were classified into the following six life forms : conifer seedling, evergreen tree, deciduous tree, herb-Chamaephyte, Gleichenia japonica-Dicranopteris linearis (the commonest two species of fern under Hinoki plantations in southwestern Japan, being referred to as "commonest fern" in the following) and dwarf bamboo. "Life form coverage index" was calculated as the total of "species coverage index" of every species belonging to each life form. Three zones were distinguished along the gradient of Kira's Warmth Index. They were separated by breaks of distribution pattern of life form coverage indices of evergreen tree (Coldness Index, -10) and commonest fern (Warmth Index, 105-110) ; Gleichenia japonica-Dicranopteris linearis zone, the warmest zone, being with both evergreen tree and commonest fern, Evergreen oak zone without commonest fern, and Deciduous tree zone without both evergreen tree and commonest fern. Relative frequency of five vegetation types that are known to have different efficiency of erosion control, poor vegetation type, Gleichenia japonica-Dicranopteris linearis type, herb-Chamaephyte type, deciduous tree type and evergreen tree type differed between the zones. The relationship between relative frequency of different vegetation types and stand density (Yield Index) also differed from zone to zone. Based on these results, we concluded the applicability and usability of the zoning to understory vegetation control from the view of protection of surface soil loss.