尖峰岭热带山地雨林优势树种白颜树空间分布格局

Spatial distribution pattern of the dominant species Gironniera subaequalis in tropical montane rainforest of Jianfengling,Hainan Island,China

优势树种对群落的构建和形成起主要作用。该文以海南岛尖峰岭60 hm2样地内重要值第二大的树种白颜树(Gironniera subaequalis)为研究对象,探索其种群分布格局特征,讨论环境异质性、密度依赖死亡、扩散限制等机制在格局形成过程中所起的作用。将白颜树10 022个植株分为6个径级,分别归属于幼树、中龄树、成年树三个生活史阶段,采用成对相关函数分析各径级的空间分布特征;双变量成对相关函数和标签关联函数分析不同生活史阶段之间的空间关系;Berman检验方法检验3个地形因子分别对幼树、中龄树、成年树分布影响的显著度。结果表明:白颜树种群内I、II、III、IV径级呈现聚集分布,聚集程度随径级的增加减弱;V和VI径级小尺度上均匀分布,大尺度上以随机分布为主。幼树与中龄树空间正关联;幼树与成年树空间负关联;成年树与中龄树在较小的尺度上负关联,大尺度上微弱正关联。但是不同生活史阶段的个体之间彼此分离,个体间无直接的促进作用。地形因子中,坡度、海拔、凹凸度对幼树的分布影响显著;坡度、凹凸度对中龄树的分布影响显著;仅坡度对成年树的分布影响显著。从现有的空间格局可以推断出环境异质性和密度依赖死亡对格局形成起作用,但是种子的扩散限制对空间格局的影响没有明确地表现出来。

Aims Dominant species play a major role in the formation of community. Our objectives were to detect and assess the spatial pattern of Gironniera subaequalis, which is a dominant species with the second largest importance value in the tropical montane rainforest of Jianfengling, and to explore the effects of environmental heterogeneity, density-dependent mortality and dispersal limitation on the formation of its current spatial pattern. Methods 10 022 individuals were categorized into six size classes and three life-history stages, i.e. young trees, middle-aged trees and adult trees, respectively. The spatial pattern of each age class was analyzed by pair-correlation function. The spatial associations between paris of life-history stages were analyzed by bivariate pair-correlation function and mark-connection function. The impacts of topographic factors on the distributions of young trees, middle-aged trees and adult trees were analyzed by Berrnan test. Important findings Results showed that the size classes I, II, III, and IV of G. subaequalis occurred in aggregated distributions. The aggregation intensities declined with increasing size classes. Size classes V and VI exhibited a uniform distribution at the smaller scales and a random distribution mainly at the larger scales. Young trees and middle-aged trees had a positive association; whereas young trees and adult trees had a negative association. Middle-aged trees and adult trees had a negative association at smaller scales and a weakly positive association at larger scales. The individuals of different life-history stages were separated from each other. There were no direct facilitative interactions between pairs of individuals. The tree topographic factors, slope degree, altitude and concave-convex, had significant impacts on the distribution of small trees; slope degree and concave-convex had significant impacts on the distribution of the middle-aged trees; whilst only slope degree had significant impacts on the adults trees. We inferred that the environmental heterogeneity and density-dependent mortality contributed to current spatial pattern of G. subaeoualis, while the effects of disersal limitation were not obvious.