华北落叶松林土壤物理性质空间变异与取样量

Spatial heterogeneity and sampling size of soil hydrophysical properties in a Larix principis-rupprechtii plantation

准确刻画森林土壤水文物理性质空间异质性对于深入理解林地的水文、生态过程具有重要意义,而量化其合理取样量有助于提高森林土壤调查的精度。采用经典统计学和地统计学的方法,研究宁夏六盘山华北落叶松林土壤水文物理性质的空间异质性,并利用Monte Carlo模拟重抽样的方法,量化90%和95%置信水平下各指标的合理取样量。结果表明:1)土壤水文物理性质存在空间异质性,土壤含水量、土壤密度和饱和导水率的变异系数分别为0.23、0.11和0.47,块基比分别为0.043、0.119和0.075。2)在90%或95%的置信区间下,将测定误差控制在10%以内,在30 m×30 m的样地内至少需布设土壤含水量、土壤密度和饱和导水率采样点分别为13或18个、4或5个、34或45个;将测定误差控制在5%以内,则至少需布设采样点分别为35或45个、13或15个、70或75个。目前森林土壤水文物理特性取样数量偏少,今后研究中应加大其取样数量,提高估计的精度,在进行森林土壤水文物理特性取样时,充分考虑其空间异质性带来取样数量的变化。

[Background]Accurate description of spatial heterogeneity of hydrophysical properties of forest soil is of great significance for understanding hydrological processes such as stand infiltration and runoff,as well as ecological processes such as tree growth and material cycle.And the accurate acquisition of the optimal sampling size is conducive to improving the measurement accuracy of soil hydrophysical properties,and thus providing scientific basis for forest soil investigation and sampling design in the study area.[Methods]We selected a Larix principis-rupprechtii plantation in the semi-humid area of Liupan Mountains,Ningxia province as the study area.The spatial variability of surface(i.e.0-20 cm soil depth)soil mass moisture content,bulk density and saturated hydraulic conductivity was studied using the methods of classical statistics and geostatistics.And the optimal sampling quantity of each index at 90%and 95%confidence level was quantified using Monte Carlo simulation resampling method.[Results]1)The surface soil hydrophysical properties had obvious spatial heterogeneity,for example,the coefficient of variation of soil mass moisture content and bulk density and saturated hydraulic conductivity were 0.23,0.11 and 0.47,respectively,which belonged to medium variation and had obvious spatial structure.And their ratio of nugget(C0)and sill(C0+C)were 0.043,0.119 and 0.075,respectively,showing a strong spatial correlation and small spatial autocorrelation range.2)Under the confidence interval of 90%or 95%,if the measurement error was controlled within 10%,it was at least 13 or 18 sampling points of soil mass moisture content,4 or 5 sampling points of soil bulk density and 34 or 45 sampling points of soil saturated hydraulic conductivity should be arranged in 0-20 cm soil depth of the sample plot of 30 m×30 m.If the measured error was controlled within 5%,at least 35 or 45 sampling points of soil mass moisture content,13 or 15 sampling points of soil bulk density and 70 or 75 sampling points of soil saturated hydraulic conductivity should be arranged.[Conclusions]Surface soil mass moisture content,bulk density and saturated hydraulic conductivity of the L.principis-rupprechtii plantation in our study site have significant spatial heterogeneity,and the optimal sample size of each index representing the average level of sample plot vary largely.At present,the sampling size of forest soil hydrophysical properties is relatively small,and it is necessary to increase the sampling size in the future research to improve the accuracy of estimation.Besides,the change of sampling quantity of soil hydrophysical properties caused by their spatial heterogeneity should be fully considered in the investigation of forest soil.