Soil Water Balance of Protection Forest in the Loess Plateau

The black locust (Robinia pseudoscacia L.) and Chinese pine (Pinus tabulaeformis Carr.) are used as the main arbor species for establishment of protection forest in the loess area of the south western Shanxi Province. Based on the on-site observation, water consumption regularity of evapotranspiration was analyzed. By means of Bow en -ratio energy balance methods and water balance methods, the relationship between water supply and water consumption of black locust and Chinese pine forests was determined. The inter -seasonal and interannual changes are significantly different. The percentages of crow n evaporation by interception, soil evaporation and transpiration to total water consumption in forests are, respectively,14.8%~29.1%, 12.3%~24.6% and 55.2%~63.7%. Total water consumption in the stand is higher in summer than spring and autumn. The result shows that water consumption by evap-otranspiration is relatively higher in June, July and August than other months. Water supply is less than water consumption in April,May and June,and it is more than water consumption in rainfall season. The percentages of transportation,evaporation,interception and runoff to the total precipitation in a year are, respectively,54.8%~108%, 14.6%~21.6%,1.9%~2.5% for black locust stand, 45.4%~113.7%, 22.4%~26.5%and 1.5%~2.3% for Chinese pine stand,50%~68.2%, 4.0%~6.0%and 2.1%~3.5%for grassland (Bothriochaloa chaemum).