大兴安岭北部兴安落叶松(Larix gmelinii)林下穿透雨空间分布特征

森林冠层对降雨的水量和水质再分配是生态水文学研究的热点问题之一。为了研究兴安落叶松林下穿透雨的空间分布规律,探究森林冠层结构对穿透雨影响的生态机制,利用在兴安落叶松林下布设38个雨量筒,测定19场不同降雨事件的穿透雨数据(2013年7—8月),通过统计学方法分析冠层结构各因子与穿透雨的空间变异性规律,结果表明:观测期间,兴安落叶松林穿透雨量为148.3 mm,占同期大气降雨量的80.62%,穿透雨率随着降雨量的增加呈增加趋势;兴安落叶松林下穿透雨具有较大空间异质性,其变异程度随降雨量的增加而减小,以对数方程拟合较好(P0.01);冠层结构特征是影响穿透雨空间变异的重要因素,冠层复杂程度与穿透雨量呈负相关关系(P0.01);距树干距离、冠层厚度、叶面积指数等因素均可影响穿透雨的空间分布,以距树干距离影响最大,其与穿透雨率呈正相关关系(P0.01),而冠层厚度、叶面积指数则均与穿透雨率呈负相关关系(P0.01),但拟合效果不佳;从影响穿透雨的生态学机制来考虑,在冠层结构特征因子中,冠层厚度是决定穿透雨空间分布的最主要因素。

Characteristics of the spatial distribution of throughfall in a Larix gmelinii forest in the northern Greater Khingan Range, northeast China

In forested ecosystems, complex forest canopies may redistribute and chemically modify the composition of rain water; this field within the study of ecological hydrology has recently attracted a considerable amount of attention. Throughfall is a major part of the rainfall penetrating the forest canopy and redistributes rainfall, and throughfall patterns can affect the distribution of soil water as well as the cycling and use of nutrients. Furthermore, spatial variability in the amount of throughfall can affect the concentration and deposition of solutes and the spatial distribution of nutrients in a forested landscape. Therefore, changes in throughfall beneath the canopy have very important effects on water balance, hydrological processes, and nutrient cycling within forest ecosystems. Many studies have analyzed the effects of the forest canopy on the interception and redistribution of rainfall, and the regularity of throughfall in different forest types; these studies provide a clearer understanding of the hydrological processes involved in rainfall interception and redistribution. However, few studies have addressed the horizontal spatial distribution of throughfall under a forest canopy. An examination of the spatial distribution of throughfall would provide important data to aid comprehension of the eco-hydrological processes and nutrient cycling within a forest. The goal of the present study was to determine the spatial heterogeneity of throughfall under a forest canopy and to explore the ecological mechanisms of the effects of canopy structure in a Larix gmelinii forest on throughfall. Several factors, such as distance (of the sampling site to the trunk), canopy thickness, and leaf area index (LAI), can all influence the spatial distribution of throughfall. Throughfall was measured under a Larix gmelinii forest canopy at three locations-beneath the canopy itself, beneath the canopy edge, and in canopy gaps-during 19 rainfall events, using 38 rain gauges during the period of development of a stable canopy (Jul.-Aug. 2013). The spatial heterogeneity of both forest canopy structure (LAI and canopy thickness) and throughfall were analyzed using statistical methods. The spatial variability of throughfall in the Larix gmelinii forest analyzed here was estimated for different rainfall events. The results indicate that throughfall under a Larix gmelinii forest canopy was 148.33 mm during the observation period, and accounts for 80.62% of the rainfall in an open field. The throughfall ratio increased with increasing amounts of rainfall, and the relationship between these could be described with a power function (P<0.01). The coefficient of variance of throughfall decreased with increasing rainfall amounts, and the relationship between these could be described with a logarithmic function (P<0.01). Structural characteristics of the canopy were found to be the most important factors controlling the spatial variability of throughfall, and the throughfall amount was significantly negatively correlated with the degree of complexity within the canopy structure (P<0.01). The influence of distance was most important, and was significantly positively correlated with the throughfall ratio (r²=0.580, P<0.01). Canopy thickness and LAI were significantly negatively correlated with the throughfall ratio (P<0.01), but exhibited poor fitting results. When considering the ecological mechanism of throughfall, canopy thickness was the most important canopy structure/factor that affects the spatial redistribution of throughfall in a Larix gmelinii forest.