单株华北落叶松树冠穿透降雨的空间异质性

The spatial heterogeneity of throughfall under the Larix principis-rupprechtii single tree's canopy

森林与水的关系是生态学和水文学研究的核心问题之一,为了研究降雨通过华北落叶松树木冠层后的空间分异规律,并合理确定准确测定穿透降雨所需的雨量筒数量及位置,2005年生长季在一株样树冠层下按离开树干的位置机械布置了32个雨量筒,测定了11场不同降雨事件的穿透降雨量,并利用传统统计学与地统计学方法分析了叶面积指数和穿透降雨的空间变异性规律。结果表明,树冠的叶面积指数在不同方向上具有空间变异性,随离开树干的距离增大而减小;穿透降雨率与叶面积指数呈负相关性,且随降雨量增大相关性减弱;穿透降雨率半方差函数分析结果表明,基台值C+C0随降雨量增大而减小,C0/(C+C0)随降雨量的增大而增大,分维数D随降雨量的增大而增大,随降雨强度的增大而先增大后减小,这说明较小降雨量时,冠层结构是引起穿透降雨率空间变异的主要因素;降雨量较大时,冠层结构的影响减弱,其空间分布差异主要受随机因素影响;通过Kriging插值法绘制的树冠下穿透降雨空间分布图表明,树冠下存在着穿透降雨的最小区域和有汇集降雨作用的“漏斗”区域,最小区域一般在树干偏东南或南方向,而降雨汇集区域多不固定。在比较了不同雨量筒布设方案的穿透降雨变化后发现,在距离树干1/2冠幅半径的同心环上至少布设内径不小于9cm的5个雨量筒时,测定的穿透降雨量可基本接近整个树冠下的穿透降雨量平均值。

The relation of forests and water resource is one of the key scientific issues in ecology and hydrology. To understand the spatial heterogeneity of throughfall under forest canopy and determine the suitable number and location of rain gauges for measuring throughfall exactly under the canopy, throughfall was measured under Larix principis-rupprechtii single tree＇s canopy during 11 rainfall events, using 32 rain gauges in the growing season （Jun. - Sep. ） of 2005. The spatial heterogeneity of leaf area index （LAI） and throughfall ratio was analyzed by statistical and geostatistical method （Semivariance and Kriging interpolation）. It indicates that leaf area index （LAI） of canopy has strong spatial heterogeneity at different direction and the LAI reduces with increasing distance from trunk. A negative relation exists between the throughfall ratio and LAI, and the correlative coefficient diminishes with the increase of rainfall. The analysis of semivar/ance of throughfall shows that the sill C ＋ CO reduces with increasing rainfall, and the Co/（ C ＋ Co ） and the fractural D increase with increasing rainfall, and D increases firstly and then diminishes with increasing rainfall intensity. These infer that canopy structure is a key factor influencing spatial variation of throughfall ratio when the rainfall is lower; the influence of canopy weakens with increase of rainfall and the distribution of throughfall is random when rainfall is higher. The distribution map of throughfall in different rainfall events produced by Kriging interpolation shows that the lowest region and the highest ＂funnel＂ region of throughfall exist, the lowest region of throughfall is situated in the South or southeast direction of canopy, while and the ＂funnel＂ region alters frequently in different rainfall events. The comparison of different rain gauge arrangements indicates that the throughfall measued from at least 5 rain gauges （ diameter at least 9 cm） at the 1/2 canopy radius can reasonably represent the average throughfall ratio under the Larix principis-rupprechtii canopy.