Abstract: Macrophanerophytes play an important role in soil and water conservation in the gully region of Loess Plateau. In this study, the moisture dynamics of soils covered with three macrophanerophytes of Populus cathayana, Salix matsudana, and Pinus tabuliformis in Wuzhai, Northwestern Shanxi were investigated by soil drilling and drying methods. Results showed that the soil moisture in the 0-600 cm depth had great differences among the three macrophanerophytes during the early growing season (April to May). The soil moisture of the three macrophanerophytes was in order of: P. cathayana > S. matsudana > P. tabuliformis. Soil moisture in profile of the three macrophanerophytes in 0-600 cm increased initially, then gradually reduced, finally stabilized with increasing the soil depth. The degree of drought of the soil layer among the three macrophanerophytes types was in the order: P. tabuliformis > S. matsudana > P. cathayana. Coefficients of variation of soil moisture contents of the three macrophanerophytes varied in different depth ranges: P. tabuliformis > P. cathayana > S. matsudana in depths of 0-100 cm and 400-500 cm, S. matsudana > P. cathayana > P. tabuliformis in depths of 100-200 cm and 500-600 cm, and P. cathayana > S. matsudana > P. tabuliformis in depths of 200-400 cm. Concerning with the influence of macrophanerophytes on the soil water balance and the regional hydrological cycle, the three macrophanerophytes were unsuitable in the gully region of Loess Plateau.

Key words: water source, community, hydrogen and oxygen isotopes, Beijing mountainous area