贵州赤水常绿阔叶林不同层次树木空间分布格局和竞争的关系

在贵州赤水桫椤国家级自然保护区的亚热带常绿阔叶林中设置0.96 hm~2的固定样地进行调查,将2299株乔木按树高分级(林木下层、中层、上层),进行空间定位并记录胸径和冠幅等个体指标。采用基于个体间距离的对数相关函数(Paircorrelation functions,PCF)和基于个体胸径、冠幅的标记点格局分析(Marked correlation functions,MCF)空间统计方法检测不同高度层内和层间的空间分布格局和潜在的竞争,结果表明:(1)样地内上层树种呈现随机分布,中下层树种在0—6 m的小尺度内呈聚集分布,在层间关系上表现为0—1 m尺度下显著的正相关关系。(2)在群落内上层个体中没有检测到显著的层内竞争,也未发现其与中、下层树种存在层间竞争关系。(3)群落中、下层树种的层内和层间竞争对两者间空间分布格局和个体大小均产生了一定影响,其相邻个体的胸径和冠幅呈现显著负相关关系。这说明在贵州赤水地区常绿阔叶林中群落中不同层次个体处于不同演替阶段,群落内层内和层间竞争对个体较大的林木上层物种的影响已经非常微弱,而主要发生在中、下层树种内,导致了个体较小的中下层更新树种在层间和层内都出现了小尺度下聚集分布格局,这解释了研究地内不同高度级别树种间竞争关系与共存策略,也验证了标记点格局分析方法在检测植物群落竞争中的敏感性。

Spatial patterns and competition among trees of different height classes in Guizhou, Chishui evergreen broadleaved forest

A 0.96 hm² plot was established in a subtropical evergreen broad-leaved forest in the Chishui Alsophila National Nature Reserve, Guizhou province. The 2299 individual trees were stem-mapped and classified into three height classes:lower, intermediate, and upper height class. Diameter at breast height (DBH) and crown width (CW) were recorded as additional measures of individual growth and performance. In this study, the spatial distribution patterns, spatial associations, and competition among different tree height classes were analyzed PCF (Pair-correlation functions) Analysis based on individual distances. MCF (Marked correlation functions) based on individual DBH and CW were used to detect spatial patterns and within and between different size classes. We found that:(1) The upper tree species showed random distributions at almost all scales. The middle and lower tree species clustered on the small scales of 0-6 m, which showed positive associations with each other within a 1 m scale. (2) No intra-class competition of individual trees within the upper height class was detected, nor was there a significant association with other classes. (3) Intra-and interclass competition in the lower and intermediate height classes had some negative influence on the growth and spatial distribution of individuals. This suggested that individuals among different height classes were at different succession stages in the subtropical evergreen broad-leaved forest in Chishui. Intra-and interspecies competition had the least influence on the upper height classes, but significantly influenced the intermediate and lower size classes, resulting in an aggregated distribution of lower and intermediate height individuals at small scales. This study helps explain competition strategies and coexistence between different height classes. Additionally, it verified the high sensitivity of the marked correlation function analysis in the competition detection of a plant community.