Based on theories and methods of hydrology

the main factors of water consumption and supply by stand survey and on-site observationater were obtained. Available water resource and regularity of water supply and consumption in forest soil

the relationship between water supply and water consumption of black locust(Robinia pseudoscacia L.)and Chinese pine (Pinus tabulaeformis Carr.) forests were analyzed

which are used as the main tree species for establishment of protection forest in the loess area of the western Shanxi province. Water supply is less than water consumption in April

May and June

and more than water consumption in rainfall season

in the high-density stand

the available water amount is relative inadequate

serious water deficit always occurs. Deficit amount of northward slope is higher than that in southward slope. According to the determination of soil moisture in deeper soil layer

soil moisture is lower in medium-age forest with high-density in southward slope

so soil is becoming desiccation.Analysis results on correlation between water supply

consumption and forest productivity show that opitimum water balance is the critical factor to improve water potential productivity in forest

which plays important role in management of protection forest in similar types and areas.