Estimation of the effects of different forest managements on the characteristics of sediment yield in a mountainous area

为了评估树木根系在大面积土壤加固的效果，我们将一个分布式浅层滑坡模型应用到位于丰余的宇都宫大学森林。总面积为530公顷，其中320公顷为人工柏木林，1998年8月底因暴雨发生浅层滑坡。林龄的面积频率分布向幼龄林转移。根据浅层滑坡实际面积与林分年龄的关系，采用分布式浅层滑坡模型进行反演。反算结果表明，林龄与土壤粘聚力之间存在一定的关系，土壤粘聚力（包括根系）的变化范围约在5.3 ~ 7.6kPa之间，在林龄20年时出现最小值。

In order to evaluate soil reinforcement by tree root system in wide area, we applied a distributed shallow landslide model to Utsunmoiya University forest at Funyu. Total area is 530ha, and 320ha is a artificial forest of Hinoki Cypress, where the shallow landslides occurred by the heavy rainfall at the end of August 1998. The area frequency distribution to stand age was shifted to young stand age. We carried out the back calculation based on the relation between the actual area of shallow landslides and stand age with distributed shallow landslides model. Result of back calculation was showed as the relation between stand age and soil cohesion and the range of soil cohesion (including root system) was approximately between 5.3 to 7.6kPa, and the minimum value at 20 years stand age.