武夷山常绿阔叶林空间结构参数分布特征

基于武夷山9.6hm~2常绿阔叶林动态监测样地调查资料,采用角尺度、大小比数、混交度等空间结构参数分析其群落乔木层内部空间结构特征,阐述群落结构的形成与维持机制。结果表明,该样地乔木层以随机分布为主,聚集分布为辅;树种混交度也极高,具有很强的物种异质性;树种的优劣程度参差不齐,整体处于中庸的生长状态。样地呈强度混交的轻度聚集分布格局。前10位优势树种均呈集聚分布,且它们的树种混交程度都极高。木荷、甜槠等喜阳植物在乔木上层占有一定的生长优势;随着林内微环境的不断改变,赤楠、格药柃等喜阴植物开始在乔木下层广布繁殖,并占据有利地位,这不仅提高了该区域的物种混交程度,还大大增加了该生境中的物种多样性,有助于群落形成较为稳定的动态结构。同时,该样地当前以中、幼龄树木居多,暂未有建群种出现,可能正处于演替中后期。只有角尺度和混交度这两个参数间存在着极显著负相关,说明当一个样地内的树种混交程度越高,物种多样性越大,其空间分布也就越密集,反之亦然。

Spatial distribution characteristics of an evergreen broad-leaved forest in the Wuyi Mountains, Fujian Province, southeastern China

In this study, spatial structure parameters such as uniform angle index, size ratio, and mingling degree which based on the nearest four adjacent tree structure unit were used to analyze the spatial structure characteristics of the evergreen broad-leaved forest community in the Wuyi Mountains; this analysis was based on the examination of the tree layer of a community in a 9.6hm² dynamic forest plot. This analysis method eliminated the influence of the mesoscale effect, unlike traditional analysis patterns. This method was also more convenient, because accurate distribution information could be obtained merely by investigating the angle between adjacent trees. The results showed that the spatial distribution pattern of the tree layer in the forest dynamics plot was largely predominated by random distribution and accompanied by slightly clustered distribution; high species heterogeneity was present in the forest dynamic plot as indicated by the high mingling degree of tree species; and the dominance index of the tree species was uneven as indicated by different size ratios for different tree species. The whole forest was in a moderate state of growth. The spatial structure characteristics of this plot represented a slightly aggregated distribution. Analysis of the three spatial structure parameters of the top 10 dominant tree species in the plot revealed that the dominant species all showed aggregated distribution and had a high mingling degree. For these 10 dominant species, heliophiles such as Schima superba and Castanopsis eyrie had certain growth advantages in the upper tree layer, while sciophiles such as Syzygium buxifolium and Eurya muricata propagated widely in the lower tree layer with the passage of time, and occupied favorable positions, leading to continuous changes in the micro-environment of the plot. This changing structure of the distribution not only improved the mingling degree of species, but also greatly increased species diversity, which contributed to the formation of a more stable dynamic community structure in this region. Moreover, young and mid-aged trees were predominantly distributed in this 9.6hm² evergreen broad-leaved forest; this might suggest that the plot was in the middle or later stages of succession. Finally, only the uniform angle index was significantly and negatively correlated with mingling degree, indicating that the higher the mingling degree of tree species, the greater the species diversity, and therefore the more dense the spatial distribution of tree species. To understand succession in evergreen broad-leaved forests, we should continue to strengthen community investigations and monitoring of this area in future.