Study on the systematic manegement of plantation forests for water resources.

研究计划包括以下四个课题，以完成研究目标。研究结果总结如下：1)土壤特性和坡面地形对坡面径流过程的影响：利用水头剖面图分析了坡面垂直入渗过程。绘制了吸力场图，分析了饱和通流的特性。利用Richard方程建立了蒸腾作用对坡面径流影响的模拟模型，结果表明，下半坡的蒸腾作用对坡面径流有明显的日波动。(2)森林处理对产水量的影响：所有现有的小流域试验数据都以每10千卡/平方厘米的年净辐射为一组。建立了这10千卡地区森林采伐后年增水量的预测模型。用加权法对成熟树的截留进行了分析。通过测定树干径流、穿透流和林冠滴水的小区试验，评价了修剪间伐对杉木林截留效果的影响。抚育作业对试验流域养分循环和水质的影响：除采伐后几年采伐对复合污染物排放影响较大外，森林流域矿质化合物排放总量与水量高度相关。在古生代土壤中，杉木对镁的吸收是缓慢的，而钾是养分循环中快速旋转的化合物。(4)有利于水资源的森林管理系统：试图根据土壤-植被-径流关系对所谓的“森林均匀径流功能”做出一致的解释。平泉区森林经营是最有利于水资源和水土流失的多层森林经营的典型案例之一。

The research program consists of the following four subjects to accomplish the research objective. The research results are summerized as follows.<I> ) Effect of soil characteristics and slope topography on runoff process on hillslopes: Vertical infiltration was analysed by using hydraulic head profile maps. Suction field maps were drawn to analyse the behavior of saturated throughflow. A simulating model on the effect of transpiration on discharge from a hillslope by using Richard's equation showed that transpiration on the lower half slope gives a distinct diurnal fluctuations on hillslope discharge.<II> ) Effect of forest treatments on water yield: All small watershed experiment data available are grouped with the net radiation of every 10 kcal/ <cm^2> .year. A predicting model of annual water yield increase after forest cutting is presented in these 10 kcal regions. Interception of a matured tree is analysed by a weighing method. The effect of prunning and thinning on interception of Sugi forests is evaluated with plot experiments catching all stemflow, throughflow and canopy drops.<III> ) Effect of tending works on nutrient cycle and water quality in a experimental watershed: Total discharge of mineral compounds from a forested watershed is highly correlated with water discharge amount, except a few years after forest cutting when cutting affects greatly compound discharge. In paleozoic soils, absorption of magnesium by Sugi trees is slow, while kalium is a quickly rotating compound in a nutrient cycle.<IV> ) Forest manegement system favourable for water resources: A consistent explanation is attempted for so-called "forest function of uniforming streamflow" basing on the soil-vegetation-runoff relationship. Forest manegement in Hiizumo district was investigated as one of the representative cases of multi-storied forest manegment which is most favourable for water resources and soil erosion.