三峡库区马尾松林穿透雨和树干茎流空间变异特征

Spatial Variability of Throughfall and Stemflow in Pinus massoniana Plantation in Three Gorges Reservoir Area

【目的】探讨马尾松林下穿透雨和树干茎流空间分布特征及其影响因素,为准确量化马尾松林下降水分配过程以及水源涵养功能评价提供科学依据。【方法】2017年5—9月,在1个马尾松林下布设16个截面面积为3000 cm^2的雨量收集器来观测穿透雨,选择27株马尾松标准木研究树干茎流的空间变异特征,应用Pearson相关分析研究冠层结构参数与穿透雨、树干茎流之间的关系,并用Monte Carlo抽样方法确定在一定误差范围内估测穿透雨所需雨量收集器的数量。【结果】研究期间林外总降雨量1008.4 mm,林下总穿透雨量和树干茎流量分别为829.8和14.4 mm,各占总降雨量的82.3%和1.4%;树干茎流量和茎流率均随降雨量的增加而增加,但茎流量变异系数随着降雨量增加而减小,且茎流量变异系数达到60%后趋于稳定,树干茎流量与树木的冠幅面积和胸径呈显著正相关(P<0.01);穿透雨率随降雨量增加而增加,穿透雨率达到87%后趋于稳定,用"S"曲线函数可较好地拟合穿透雨率与降雨量的关系(P<0.01);在测定样地中,穿透雨量存在较大的空间异质性,其变异系数随降雨量增加先显著降低而后稳定,两者用倒数函数拟合效果较好(P<0.01);冠层结构是影响穿透雨量空间变异的主要影响因子,但其作用因降雨量的大小而不同;叶面积指数、冠层厚度、测点距树干的距离以及冠层覆盖度均能影响穿透雨的空间分布,其中以叶面积指数对穿透雨量的影响最大;不同雨量级在相同置信区间达到相同的误差水平,所用穿透雨收集器数量不同,随着雨量级增大,用较少雨量收集器就可以达到相同的误差水平,当雨量级在0~10mm时,所用穿透雨收集器数量最多,即95%置信区间下,5%误差范围内,所需最少的穿透雨收集器数量为13个;雨量级在大于40 mm时,达到相同误差水平所用集水槽数量最少,即95%置信区间下,测的穿透雨值在5%误差范围内,所需最少的穿透雨收集器数量为6个。【结论】马尾松林下穿透雨量和树干茎流量空间变异特征同时受降雨特征和冠层结构特征的影响,且穿透雨量和树干茎流量的空间异质性均随着降雨量增大而减小,而后趋于稳定,但树干茎流量的空间变异系数稳定值大于穿透雨,冠层结构决定了林内穿透雨量空间分布的总格局,其中以叶面积指数与穿透雨率相关性最强,而胸径对树干茎流量的影响最为显著;本研究在参考降雨量级0~10 mm时,在95%或90%的置信区间下,若将穿透雨数值控制在5%误差范围内,在50 m×50 m样地内至少需布设13或11个3000 cm^2收集器。

【Objective】Characterization of the spatial distribution of throughfall and stemflow in Pinus massoniana forests and their regulating factors were investigated in order to provide a scientific basis for accurately quantifying the distribution of precipitation in P.massoniana forests and evaluating their water conservation function.【Method】In May 2017,in a P.massoniana forest,we installed 16 throughfall collectors with a cross-sectional area of 3000 cm 2 and selected 27 standard trees of P.massoniana to study the spatial variation of their stemflow.We used Pearson correlation to analyze relationships between canopy structure parameters and spatial variability of throughfall and stemflow and employed Monte Carlo simulations to determine the amount of rainfall collector needed to accurately estimate throughfall within a certain error range.【Result】During the study period the gross rainfall in open field was 1008.4 mm,and the amounts of throughfall and stemflow were 829.8 and 14.4 mm,respectively,accounting for 82.3%and 1.4%of the gross rainfall.Both ratios of stemflow volume and stemflow volume increased with the increase of the gross rainfall,but coefficient of variation of stemflow volume decreased with the increase of the gross rainfall and tended to be stable after 60%.The stemflow volume was positively correlated with crown area and DBH(P<0.01).The throughfall ratio increased with the increase of rainfall,and tended to be stable after throughfall reached 87%,showing a“S”curve(P<0.01).Throughfall showed a large spatial heterogeneity,and the coefficient of variation significantly decreased first and then stabilized with the increase of rainfall.The relationship between coefficient of variation of throughfall and rainfall was fitted by a reciprocal function(P<0.01).Characteristics of the canopy structure were the main factors influencing the spatial variability of throughfall,but their effects varied with rainfall.The leaf area index,the canopy thickness,the distance of the measuring point to the trunk and the canopy coverage all affected the spatial distribution of throughfall,and among them,the leaf area index had the greatest influence.Different rainfall levels reached the same error level in the same confidence interval,and the number of throughfall collectors used was different.With the increase of rainfall level,the same level of error could be achieved with less throughfall collectors.When the rainfall level was 0-10 mm,the number of throughfall collectors used was the largest,i.e.,under the 95%confidence interval and within the 5%error range,the minimum number of throughfall collectors required was 13.When the rainfall level was greater than 40 mm,the number of throughfall collectors used to achieve the same error level was the least,i.e.,under the 95%confidence interval and when the measured throughfall was maintained within the 5%error range,the minimum number of throughfall collectors required was six.【Conclusion】The spatial variability of throughfall and stemflow of P.massoniana were influenced by rainfall and canopy structure.The spatial heterogeneity of throughfall and stemflow decreased with the increase of rainfall,and then tended to be stable.However,the stability coefficient of the stemflow was greater than that of throughfall.The canopy structure determined the overall pattern of the spatial distribution of throughfall,and among them the leaf area index and throughfall ratio had the strongest impacts.DBH had the most significant effect on stemflow.At the reference rainfall level of 0-10 mm and under the confidence interval of 95%or 90%,at least 13 or 11 collectors should be installed with a cross-sectional area of 3000 cm 2 in a 50 m×50 m plot if the value of throughfall was controlled within the range of the 5%error.