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

在东京大学千叶的大学森林中的尾尾山实验流域进行了配对流域法实验。集水区A和B的集水面积均约为1ha，集水区内已覆盖70年生的柳杉和Chamapolis paris obtuse混交林。集水区B内的所有树木均于1999年2月至4月采用缆索系统进行采伐和集材。在3年内，皆伐对环境因子的影响表现为：1）皆伐后流域B的排水量增加250-300 mm/a，这是由于皆伐后蒸散量减少所致; 2）皆伐后几个月内，流域内的硝态氮浓度增加。结果表明：（1）退耕还林后，土壤硝态氮含量仍高于对照流域;（2）退耕还林后，土壤硝态氮含量仍高于对照流域;（3）退耕还林后，流域输沙量与对照流域相比无显著变化;（4）退耕还林后，下坡土壤水分状况较湿润，5）采伐迹地土壤温度随采伐后太阳辐射的增加而升高; 6）采伐迹地土壤呼吸作用随采伐后太阳辐射的增加而增强;切割流域明显增加，但变化的程度可以解释为土壤温度升高的增加。

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.