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

研究计划包括以下四个主题，以完成研究目标。研究结果总结如下：土壤特征和坡面地形对坡面径流过程的影响：利用水头剖面图分析垂直入渗。绘制了吸力场图，分析了饱和通流的特性。利用理查德方程建立了蒸腾作用对坡面流量影响的模拟模型，结果表明，下半坡的蒸腾作用对坡面流量有明显的日波动。森林处理对产水量的影响：所有现有小流域试验数据按每10千卡/ <cm^2> .年的净辐射分组。建立了10大卡地区森林采伐后年增水量的预测模型。采用称重法对成熟采油树的截留量进行了分析。通过小区试验，对杉木林的茎流、通流和冠层落差进行监测，评价了修剪间伐对杉木林截留的影响。<III>)抚育工程对试验流域养分循环和水质的影响：森林流域矿物化合物总排放量与水量高度相关，但采伐后数年对化合物排放量影响较大。在古生代土壤中，杉树对镁的吸收缓慢，而钾在养分循环中是一种快速旋转的化合物。<IV>)有利于水资源的森林经营制度：基于土壤-植被-径流关系，试图对所谓的“均匀流的森林功能”做出一致的解释。作为最有利于水资源和水土流失的多层森林经营模式的代表案例之一，对平云地区的森林经营模式进行了调查。

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.