六盘山华北落叶松林下穿透雨空间变异特征

摘要

The depth and spatial distribution of throughfall under the forest canopy can affect the hydrological (i.e.,infiltration,runoff and evaporation) and ecological processes (i.e.,tree growth,litter decomposition) of forest ecosystems.Therefore,both the evaluation of forest hydrological impacts and forest ecosystems management require an accurate description of the spatial distribution of throughfall.In order to interpret the spatial heterogeneity of throughfall in the plantation of Larix principis-ruprechtii,a 30 m × 30 m sized stand plot was set up in the Xiangshuihe watershed of the Liupan Mountains.Within this plot,40 throughfall collectors,with a size of 230.58 cm2,were evenly installed.The throughfall depth of 34 rainfall events was measured individually during the growth season (May-Oct.) of 2015.The gross rainfall in open field in the study period was 567.0 mm,and the throughfall depth in the plantation plot was 483.5 mm,accounting for 85.3％ of gross rainfall.As rainfall increased,the throughfall ratio first increased and then tended to stabilize.A considerable spatial variation of throughfall was observed,and the coefficient of variance of throughfall first decreased and then became constant with increase in rainfall.The spatial distribution of throughfall was influenced by the tree characteristics canopy leaf area index and canopy thickness above throughfall collector,and the distance from throughfall collector to the nearest stem,and this influence varied with the depth of rainfall.When the rainfall was less than 10 mm,throughfall showed a significantly negative correlation with the leaf area index;when the rainfall varied within the range of 10-20 mm,throughfall showed a significant positive correlation with the distance to the nearest stem and a significantly negative correlation with canopy thickness.However,when the rainfall was more than 20 mm,throughfall showed no correlation with any of the tree characteristics.Considering that the depth of individual rainfall events is concentrated within 0-10 mm,at least 13 or 9 throughfall collectors with the size used here are required for a plot of 30 m×30 m if the error of measured throughfall should be controlled within 10％ under confidence levels of 95％ or 90％.At least 26 or 23 throughfall collectors are required when the error should be controlled within 5％ under confidence levels of 95％ or 90％.%受林冠截持影响后形成的林下穿透雨的数量和空间分布会影响林地的入渗、产流、蒸发等水文过程和林木生长及枯落物分解等生态过程,因而精细的森林水文功能评价和森林生态系统经营都需要准确描述林下穿透雨的空间变异规律.在宁夏六盘山香水河小流域设立了面积为30 m×30 m的华北落叶松人工林样地,均匀布设了40个截面面积230.58 cm2的雨量收集器,测定了2015年生长季(5-10月)34次降雨事件的穿透雨量.结果表明,研究期间林外总降雨量567.0 mm,林下总穿透雨量483.5 mm,占同期雨量的85.3％.随着次降雨量增加,林内次穿透雨率呈现先快速增加后趋于稳定的变化.穿透雨量在林内存在较大空间变异,其变异程度随次降雨量增加先快速下降后趋于稳定.林下穿透雨空间分布受树木特征(穿透雨收集器上方的林冠叶面积指数和冠层厚度、穿透雨测点离最近树干的距离)的影响,且其影响随次降雨量大小而变,当次降雨量＜10 mm时,穿透雨量与叶面积指数显著负相关;当次降雨量在10-20 mm时,穿透雨量与距最近树干距离显著正相关,与冠层厚度显著负相关;当次降雨量＞20 mm时,穿透雨量与3个树木特征均不显著相关.考虑到研究区次降雨量集中在0-10 mm,在95％或90％的置信区间下,若将测定的次穿透雨数值误差控制在10％以内时,在30 m×30 m样地内至少需布设13或9个本研究所用大小的收集器;满足次穿透雨数值误差在5％以内时,至少需布设26或23个这样的收集器.