Evaluation of forest clear cutting effects on hydrological cycle and material cycle in a watershed

在东京大学千叶大学森林福山实验流域进行了配对流域法实验。流域A和流域B的集水区面积均约为1ha，覆盖了70年树龄的柳杉和黄杉混交林。1999年2 - 4月，B流域所有树木均采用电缆采伐。本试验3年内检测到的采伐对环境因子的影响如下：1)采伐后蒸散量减少，导致B流域径流量增加250 ~ 300 mm/年。2)采伐后几个月开始检测到溪流中硝酸盐氮浓度的升高。硝态氮浓度仍高于对照流域。(3)清淤流域输沙量与对照流域相比变化不显著。④清净小流域下坡土壤水分较为湿润，而山脊浅层土壤水分相对干燥。5)砍伐后的太阳辐射增加了流域土壤温度。(6)伐净流域土壤呼吸明显增加，但其变化程度可以用土壤温度升高来解释。

A paired watershed method experiment has been conducted in Fukuroyama Experimental Watershed in University Forest in Chiba, the University of Tokyo. Watershed A and B are both approximately 1ha in catchment area and have been covered a 70-years-old mixed stand of Cryptomeria japonica and Chamaecyparis obtuse stand. All trees in the watershed B were cut and yarded by cable system from February to April in 1999. Effects of clear-cut on environmental factors detected within three years by this experiment are as follows:1) Increase in discharge water in watershed B is 250-300 mm/yr which caused by decreasing in evapotranspiration after cutting.2) Increase in concentration of nitrate nitrogen in stream water is detected from several months after cutting. Concentration in nitrate nitrogen is still higher than the control watershed.3)Sediment discharge from clear-cut watershed shows no remarkable change compared with the control watershed.4)Soil moisture in lower slope in clear-cut watershed is in wetter condition, however relatively dry in shallow layer in ridge.5)Soil temperature in clear-cut watershed is increased by incoming solar radiation after cutting.6)Soil respiration in clear-cut watershed is apparently increased, however the extent of changes can be explained by increase in soil temperature increase.