Soil moisture is a key factor driving a series of hydrological and biological processes.Since the influences of meteorological,topographical,soil and vegetation factors,the soil moisture often shows an obvious difference among slope positions and a spatial scale effect.This should be deeply understood and accurately quantified,to provide a scientific basis for the precise forest management and the representative plot selection in eco-hydrological studies.In this study,a representative slope covered by 34-year-old Larix principis-ruprechtii plantation and with a horizontal length of 425.1 m was selected in the small watershed of Xiangshuihe of Liupan Mountains.A 30 m wide survey transect was set up on the whole slope and it was evenly divided into 16 continuous plots.The soil moisture within 0 ～ 100 cm soil layer was measured from May to October of 2015.The variation of soil moisture with rising slope length (i.e.,the horizontal distance from the slope top) in different months was analyzed.The results showed:(1) there was a remarkable soil moisture variation along the slope.For the whole growing season,the variation of soil moisture with rising slope length showed a trend of firstly a gradual increase,reaching its maximum at the middle-upper slope position (at the horizontal slope length of 109.2 m),and thereafter a gradual decrease,reaching its minimum at the middle-lower slope position (at the horizontal slope length of 350.4 m),and then an increase again.The variation trend of soil moisture in each month was similar to that of the whole growing season.(2) The soil moisture showed a slope scale effect.i.e.,there was a remarkable variation in the moving average of soil moisture with rising slope length.The variation trend of scale effect of soil moisture was similar in each month,but the amount of scale effect was somewhat different.(3) Under the "normal-year" condition of 2015 with relative rich precipitation,the soil water-holding capacity became the dominant factor to determine the spatial variation pattern of soil moisture on the study slope.A significant correlation was observed in each month among the soil moisture,the porosity and water-holding capacity of soil.(4) The best representative slope position for the whole slope average of soil moisture was found at the middle slope position (corresponding to the relative horizontal slope length of 0.57).Therefore,the observed soil moisture at this slope position can be simply viewed as the slope average,or can be used for a more accurate estimation of the slope average of soil moisture using the statistic relation developed in this study.Based on the results of this study,it can be said that the whole slope average of soil moisture can be accurately estimated using the soil moisture at reprehensive slope position.%受气象、地形、土壤、植被因子的影响,土壤水分具有坡面位置变化和空间尺度效应,需对此深入理解和精细刻画,以便为精细化森林管理、坡面生态水文研究中的代表性样地选择和尺度转化提供科学依据.在宁夏六盘山香水河小流域,选择一个设置有空间连续样地的华北落叶松人工林典型坡面,于2015年5-10月利用土钻取土,并烘干测定了0 ～100 cm土层的质量含水量,研究生长季内各月土壤含水量沿坡的时空变化规律.结果表明:(1)土壤含水量存在沿坡变化,在整个生长季表现为随水平坡长增加先逐渐升高,在坡中上部(水平坡长109.2 m)达到最大,之后逐渐降低并在坡中下部(水平坡长350.4 m)达到最小,之后又有所回升.各月的土壤含水量沿坡变化趋势与整个生长季基本一致.(2)土壤含水量存在坡面尺度效应,表现为土壤含水量滑动加权平均值随水平坡长增加有明显变化,整个生长季及各月的土壤质量含水量的坡面尺度效应的变化趋势基本一致,但数值大小有所不同.(3)在研究年份为平水年和降水较多的条件下,土壤持水性能是影响土壤质量含水量沿坡差异格局的主要因素,表现为各月土壤含水量均与土壤孔隙度、持水能力显著相关.(4)对整个坡面平均土壤质量含水量而言,最佳代表性样地位于坡中部相对水平坡长0.57处,可由此样地的土壤含水量测定值代表坡面均值,并可利用本文建立的该样地土壤含水量测定值与坡面均值的关系式精确上推估计坡面均值.
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