| Based on continuous field observation in the small watershed of Xiangshuihe at the south side of Liupan Moutains, China, this paper analyzed the spatio-temporal variation of soil moisture in this area and how it is affected by the environmental factors. The study focused on the spatio-temporal variation of soil moisture under Larixprincipis-rupprechtii, Betula platyphlla, and shrub, and the impacts of such categories of environmental factors as vegetation types, terrain characteristics, meteorological characters (e.g, rainfall), soil physical properties, and the joint effects of all these factors on soil moisture. Main result is as follows:According to the soil moisture dynamics under the three vegetation types, the growing season can be divided into three parts as relatively wetness period, durative consuming period, and recovering period. The situation of soil moisture under Betula is better than the other two types, while temporal undulation of shrub soil moisture is the most significant, indicating a relatively bad spatial stability of soil moisture.Slope aspect has obvious impact to the spatial and temporal of soil moisture. Soil moisture content and its stability of semi-sunny slope are better than that of sunny slope and semi-shady slope. The coefficient of variability (CV) of soil moisture at shady slope was larger than that of sunny slope and semi-sunny slope. There were significant differences in identical soil depth among different slope aspect (p﹤0.01).The result indicated that terrain characteristics influence on spatial distribution of soil moisture was affected by vegetation types and its struction.The trend of soil moisture content showed integral increase from slope top to slope bottom, but the maximum of soil moisture appeared in Mid-slope slope position. The coefficient of variability of soil moisture decreased gradually from slope top to slope bottom. It showed that uniform distribution of soil moisture in down-slope position.Soil moisture content of steeper slope is higher than that gentler slope. The impact of slope in deep layer was larger than thatin surface layer on spatial variation.A negative correlation was observed between soil moisture of three vegetation types and air temperature, while there was a positive correlation between soil moisture and rainfall, and between soil moisture and relative humidity. There were no significant differences between soil moisture and soil temperature, and between soil moisture and solar radiation. There were obvious difference between the mode by which the meteorological factors affect soil moisture under shrub and the other two vegetation types. According to correlation analysis in temporal step of Month, air temperature is the most significant one among in the study area. Soil moisture and its spatial variation of surface layer under Larixprincipis-rupprechtii increased obviously after rainfall of medium intensity or more.From surface to deep soil layers (0~60cm), soil moisture trends decreased gradually under all kinds of vegetation, terrain characteristics, and meteorological situation.There is significant difference between physical properties of soil under different vegetations, and the soil moisture capacity of Betula is higher than other vegetation types. The variation characteristics in soil profiles (0～100cm) indicated a higher bulk density, lower porosity and moisture capacity in deeper soil layer. The result of soil moisture availability analysis of different vegetation types showed that soil moisture was generally enough for plants in Larixprincipis and shrub vegetation types during growing season, while it was in poor availability in Betula vegetation during some periods and in some soil layers. According to correlation analysis between soil moisture and soil physical properties, the physical properties of most significance was wilting water content, field moisture capacity and rock fragment content by discussing, however, the key soil physical properties factors were different in different soil layers.Analyze the main environmental factors by Principal Component Analysis, the results shows that three main factors influenced soil moisture, which was satursted volume content, total porosity, rock fragment content, rainfall, vegetation type, slope aspect and gradient.
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