岷江冷杉针叶林下穿透雨空间分布特征

森林对降水的截留作用、林下穿透雨的水文学及生态学意义一直是生态水文学研究中的热点 ,但是关于林下穿透雨空间分布特征的研究还比较少。在四川西部的卧龙自然保护区研究了岷江冷杉林下穿透雨的空间分布特征。在岷江冷杉针叶林下布设了 8个雨量筒用以测量林下穿透雨 ,对两年共 35次降雨的穿透雨研究结果表明 ,林下各观测点的穿透雨率同林外降雨量之间的关系都可以用逻辑斯谛曲线方程较好地模拟 ,与传统的对数方程模拟相比 ,前者的相关程度显著高于后者 ,而且用逻辑斯谛方程进行模拟时 ,方程中的各参数具有一定的生态学意义。此外 ,研究发现林下各点的穿透雨率具有显著的差异 ,位点 4下的穿透雨存在着明显的聚集效应 ,此处的平均穿透雨率达到了 10 3.2 %。对林下 8个点穿透雨进行聚类分析表明 ,林下位点 4和位点 8的穿透雨特征与其余 6个点的穿透雨特征有显著的差异。对影响岷江冷杉林下穿透雨空间分布的因素分析表明 ,观测点上方的冠层覆盖度、枝叶层厚度与降雨量之间均有一定的负相关关系 ,但其影响未达到显著水平 ;观测点到树干的距离与林下的穿透雨之间的关系可以较好地用二次多项式方程模拟 ,方程的相关程度很高 (R=0 .94 91) ;各观测点正上方的冠层以及枝叶性质也对穿透雨的空间分布特征有一定的

The spatial distribution characteristics of throughfall under Abies faxoniana forest in the Wolong Nature Reserve

Rainfall redistribution by forest canopy has been a study hotspot of ecological hydrology all the while, but studies on the horizontal spatial distribution of the throughfall under the forest canopy have so far been neglected. Examination of the spatial distribution of the throughfall is important to comprehend the eco-hydrological processes and the nutrient cycling in the forest. This study has been conducted in an Abies faxoniana forest in the Wolong nature reserve in the western part of the Sichuan province of China to determine the spatial distribution characteristics of the throughfall and to analyze the factors influencing the differences in spatial distribution. Eight rain gauges for throughfall collection were settled under the forest canopy at fixed positions, and the throughfall was recorded for 35 occasions of rain from July to September in 2001 and from June to August in 2002. The rainfall in this area is mainly comprised of light and moderate rains with a total rainfall of less than 31 mm, with rainfall intensities in most of the cases (about 98.2%) of less than 5 mm/h. The results showed that: the relationship between the throughfall percentage and total rainfall at each sampling site can be modeled more accurately by the Logistic equation than by the often used logarithmic equation, which employs ecologically less relevant parameters than the Logistic equation. The Logistic equation model is also fit for the whole forest. The throughfall percentages at the eight sites under the forest canopy were significantly different. The throughfall percentage at the fourth as well as the eighth sampling site showed different characteristics with the other six sites according to Q-clustering analysis. The throughfall under the fourth site had evident rainfall concentration (average throughfall 103.2%), which might be caused by the lower canopy coverage. The throughfall under the eighth site had a bigger variability than at the other seven sites, which might be caused by a more simple canopy form increasing the possible impact of wind. To assess the impact factors of the spatial distribution characteristics of the throughfall, canopy coverage, canopy depth, texture of leaves and branches above the sampling sites and the distance from the sampling site to the nearest tree trunk were analyzed. The results showed that: the throughfall percentage and the canopy coverage at each site seem to be negatively correlated, but the correlation is not significant (R=0.6996); throughfall percentage and canopy depth seem to be negatively correlated as well, the correlation is however not significant (R=0.4523). The relationship between the throughfall and the distance from the sampling site to the nearest tree trunk could be fitted with a polynomial equation with a high correlation coefficient (R=0.9491). The texture of the leaves and the branches above the sampling sites seemed to have influence on the throughfall percentages, but the influence of this factor is complex and needs to be examined further.