Abstract: The spatial structure evolution of forests in karst areas is a key scientific issue in global forest research. In order to explore the dynamics of spatial structure in karst evergreen and deciduous broad-leaved forests, a study was conducted in Mulun National Nature Reserve, focusing on a fixed monitoring plot of 2 hm². Based on data from three surveys conducted in 2007, 2012, and 2017, the dynamics of community spatial structure were analyzed using the spatial structure parameters, i. e., angular scale(W_i), mixing degree(M_i), and size ratio(U_i). The results were as follows:(1)The univariate distribution results of spatial structure parameters revealed that the forest structure gradually shifted towards a slightly clumped distribution state as the stand age increased between 2007 and 2017. The mixing degree was at a level of strong mixing and showed a tendency towards extreme mixing. In terms of the size ratio, the stand exhibited a moderate state, shifting towards subdominance as the stand grew.(2)The study of spatial structure for different diameter classes of trees showed that the anglular scale, size ratio, and mixing degree of trees in diameter classes 1-15 cm gradually increased with stand growth. As the diameter class increased, the values of the size ratio showed a decreasing trend while the mixing degree showed an increasing trend.(3)The study of spatial structure for dominant tree species revealed that, during the period from 2007 to 2017, all five dominant tree species groups exhibited a slightly clumped distribution. The size ratio showed a tendency towards subdominance and a moderate distribution state, while the mixing level was at a high degree and gradually shifted towards extreme mixing. In conclusion, the karst evergreen and deciduous broad-leaved forest in Mulun currently exhibits a slightly clumped distribution, a strong degree of mixing, and a tendency towards subdominance. The community is relatively stable, the stand regeneration is in good condition, and the forest is gradually transitioning towards a climax community. The analysis of the dynamic changes in vegetation structure in karst evergreen and deciduous broad-leaved forests is of great significance for predicting the future development and changes of forests.

Key words: angular scale(W_i), mixing degree(M_i), size ratio(U_i), structural characteristics, dynamic change

摘要： 喀斯特地区森林的空间结构演变规律是全球森林研究的关键科学问题之一。为探究喀斯特常绿落叶阔叶林空间结构动态,研究以木论国家级自然保护区内喀斯特常绿落叶阔叶林2 hm²固定监测样地为研究对象,以2007、2012、2017年3次调查数据为基础,利用空间结构参数角尺度(W_i)、混交度(M_i)与大小比数(U_i)对群落空间结构特征动态变化进行分析。结果表明:(1)空间结构参数的一元分布结果表明,2007—2017年林分随着林龄增大逐渐向轻微团状分布状态演变; 混交度处于强度混交水平,呈向极强度混交方向演变的趋势; 从大小比数来看,林分呈中庸状态,随林分增长表现为向亚优势的方向转变。(2)不同径级林木空间结构研究结果表明,径级为1～15 cm的树木角尺度、大小比数、混交度随林分生长逐渐增大; 随径级增大,大小比数取值呈逐渐降低趋势,混交度呈逐渐升高趋势。(3)主要优势树种空间结构研究结果表明,2007—2017年间5个优势树种组均呈现轻微团聚分布; 大小比数呈现亚优势偏向于中庸分布状态,混交水平处于强度混交水平,逐渐向极强度混交方向演变。综上所述,目前木论喀斯特常绿落叶阔叶林林分呈现轻微团聚分布,混交程度较强,林分偏向于亚优势分布状态,群落较稳定,林分更新状况良好,正向顶极群落方向逐渐演替。该研究关于喀斯特常绿落叶阔叶林植被结构动态变化的分析对预测森林未来发展的变化趋势具有重要参考借鉴意义。

关键词: 角尺度(W_i), 混交度(M_i), 大小比数(U_i), 结构特征, 动态变化