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通过定位观测和对比试验，对密云水库上游水源保护林试验示范区土壤水分的动态变化规律进行了初步研究．结果表明，试验区内土壤水分年动态变化主要决定于降雨量的大小和降雨的年内分配，与降水的年动态变化非常一致，与蒸发量的年动态变化相反．１９９６年土壤水分动态可分为：雨季前土壤水分缓慢蒸发期、雨季湿润期、雨季后逐渐降低稳定期；１９９７年的土壤水分动态可分为：雨季前土壤水分蒸发期、雨季湿润期、雨季后期干旱期、冬春土壤水分缓慢升高稳定期．下坡的土壤含水量显著大于上坡的土壤含水量，同一坡向的有林地比无林地的土壤含水量高．不同坡向土壤含水量由大到小的顺序是：有林地西坡、有林地东坡、无林地北坡、无林地南坡．林地涵养水源的效应非常明显
The dynamic changes of soil moisture in the experimental zone of water source protection forests in the upper reaches of Miyun Reservoir were studied by means of positioning observation and comparative experiment. The results show that the annual dynamic change of soil moisture in the experimental area is mainly determined by the amount of rainfall and annual distribution of rainfall, which is in good agreement with the annual dynamic change of precipitation and the opposite with the annual dynamic change of evaporation. The soil moisture dynamics in 1996 can be divided into: slow evaporation of soil moisture before the rainy season, wet season in the rainy season, and gradually decrease in the stable period after the rainy season. The soil moisture dynamics in 1997 can be divided into: evaporation of soil moisture before rainy season, humid season in rainy season, rainy season In the late drought period, the soil moisture in winter and spring slowly increased and stabilized. The soil moisture content of the downhill was significantly higher than that of the uphill soil, and the soil water content of the same aspect forest land was higher than that of the non-forest land. The order of soil moisture in different slopes is as follows: there are west slope of forest land, east slope of forest land, north slope of non-forest land and southern slope of non-forest land. The effect of water conservation in woodland is obvious