六盘山半湿润区华北落叶松林内降雨的空间异质性及合理取样数

Spatial Heterogeneity and Reasonable Sampling Sizes of Rainfall In a Larix gmelinii var.principis-rupprechtii(Mayr)Pilg.Plantation in the Semi-humid Liupan Mountains

[目的]林内降雨的空间变异对林地土壤水分、林下植被生长有重要影响,准确刻画其空间变异特征,并确定其收集器的合理布设数量,有助于准确理解森林对水文的影响。[方法]于2021年6—10月,在六盘山半湿润区香水河小流域的华北落叶松(Larix gmelinii var.principis-rupprechtii(Mayr)Pilg.)纯林样地,利用样地内布设的40个林内降雨收集器收集每场降雨事件的林内降雨量,分析展叶和落叶期林内降雨的空间变异特征,并量化雨量收集器的合理布设数量。[结果](1)整个生长季,林内总降雨量440.0 mm,占同期林外降雨量的77.5%,林内降雨空间变异系数28.23%;展叶和落叶期,林内总降雨量分别为153.8和290.2 mm,占同期林外降雨量的73.0%和80.2%,林内降雨空间变异系数分别为36.0%和18.5%。总体上,林内降雨空间变异随次降雨量、雨强和降雨历时的增加先快速下降后逐渐趋于稳定。(2)整个生长季及展叶和落叶期林内降雨的块基比分别为0.042、0.012和0.275,变程分别为4.8、4.0和6.5 m。(3)在95%置信区间内,若将误差控制在5%内,至少需在展叶和落叶期分别布设17和14个截面积为235.58 cm2的雨量收集器。[结论]受降雨量和冠层结构差异影响,华北落叶松林内降雨空间变异在展叶和落叶期存在差异,不同时期雨量收集器合理布设数与林内降雨空间变异密切相关,要确保整个生长季林内降雨评估的准确性,应重视不同时期雨量收集合理布设数差异的影响。

[Objective]Spatial heterogeneity of rainfall in the forest has an important impact on soil moisture and growth of understory vegetation.Therefore,accurately describing the spatial variability of rainfall in the forest under the forest canopy and determining the reasonable sampling sizes are helpful to accurately understand the impact of forest on hydrology.[Method]A Larix gmelinii var.principis-rupprechtii(Mayr)Pilg.plantation in the Xiangshuihe small watershed of the semi-humid Liupan Mountain was set up to collect the rainfall in the forest for each rainfall event based on 40 deployed collectors during the growing season(June-Oct.)of 2021.The spatial variabilities of rainfall in the forest during the leaf-expanding and leaf-withering periods were analyzed,and the reasonable sampling sizes of collectors were quantified.[Result](1)During the growing season,the total rainfall depth inside the forest was 440.0 mm,accounting for 77.5%of the corresponding gross rainfall,and the coefficient of variation of rainfall in the forest was 28.23%.The total rainfall in the forest was 153.8 and 290.2 mm during the leaf-expanding and leaf-withering periods,accounting for 73.0%and 80.2%of the corresponding gross rainfall,and the coefficient of variation of rainfall in the forest was 36.0%and 18.5%,respectively.In general,the spatial variability of rainfall in the forest first decreased rapidly and then gradually stabilized with the increase of rainfall,rainfall intensity and rainfall duration.(2)The nugget/still(range)of rainfall in the forest was 0.042(4.8 m)in the growing season,0.012(4.0 m)in leaf-expanding period and 0.275(6.5 m)in leaf-withering period,respectively.(3)Within the 95%confidence interval,if the error is controlled within 5%,at least 17 and 14 collectors with a sectional area of 235.58 cm2 should be installed in the leaf-expanding and leaf-withering periods,respectively.[Conclusion]Affected by differences in rainfall and canopy structure,the spatial variability of rainfall in the forest varies between leaf-expanding and leaf-withering periods.The reasonable sampling sizes of collectors in leaf-expanding and leaf-withering periods are closely related to the spatial variability of rainfall in the forest.The impact of the difference in reasonable sampling sizes of collectors in different periods should be paid attention to ensure the accuracy in rainfall in the forest assessment during the whole growing season.