桂西南喀斯特季节性雨林枯立木的空间格局及生境关联性分析

枯立木是森林生态系统物质循环和能量流动的重要组成部分,对森林群落动态和演替具有重要作用。该研究以位于桂西南的弄岗北热带喀斯特季节性雨林15 hm~2森林动态监测样地为平台,以样地中2011年第一次植被调查数据胸径(diameter at breast height,DBH)≥1 cm的枯立木为研究对象,在充分考虑空间自相关的基础上分析其不同径级(小径级,1 cm≤DBH5 cm;中径级,5 cm≤DBH15 cm;大径级,15 cm≤DBH)的空间分布格局、枯立木多度与环境因子的相关性及生境关联性等。结果表明:枯立木所有个体和小径级分别在0~4 m和0~5 m尺度上表现为聚集分布,其它尺度为随机分布;中径级和大径级在0~30 m尺度上均为随机分布。大径级与凹凸度表现为显著负相关,所有个体和小径级与干旱度指数和样方内所有植株个体数为显著正相关,所有个体和小径级与样方内最大胸径和平均胸径呈显著负相关。所有个体和小径级与3种生境类型间的关联性并不显著;中径级与山坡呈正关联性、与山脊呈负关联性、与山谷无显著关联性;大径级与山谷呈正关联性、与山坡无显著关联性、与山脊呈负关联性。在喀斯特季节性雨林中,枯立木空间分布格局总体表现为随机分布,仅小径级在小尺度内聚集分布,而较大径级在样地中表现出一定的生境关联性;树木死亡过程可能是小尺度内密度制约、大尺度内生境过滤和个体自然衰老等生态学过程形成的。

Spatial distribution and habitat-association of snags in the tropical karst seasonal rainforest of Southwest Guangxi, China

Snag is an important component of forest ecosystems, and studying the spatial distribution of snags abundance and its impacting factors will provide insights of the mechanism of tree death and the succession of community. The objective of this study was to understand how snags would vary with environmental factors, and to infer the underlying mechanisms. Our study was based on data from a 15 hm² study plot investigation in tropical karst seasonal rain forest, Southwest Guangxi, China. The snags with DBH(diameter at breast height)larger than 1 cm were classified. And the spatial distribution of snags abundance and its impact factors like spatial and topographic variables were analyzed using point pattern analysis with K2(r)-index and habitat associations analysis with Torus-translation tests. Snags were mostly randomly distributed in the plot, but aggregated at local scales of 0-5 m for small group. Snags and the small group were significantly positively with ACH(altitude above channel)and abundance, but negatively the mean DBH and maximum DBH of each 20 m×20 m quadrat. The large group was only significantly negatively with convexity, while the middle group was no significant correlation with any environmental factors. Density of snags had no habitat association with three habitat types, but the density of larger groups was different significantly associated with three habitat types. The spatial patterns of snags of karst tropical seasonal rainforest had spatio-temporal discrepancy. Snags were randomly distributed in the mass. The spatial patterns of snags might be formed by density dependence at local scales, but habitat filter and intrinsic aging at larger scales.