桂林岩溶石山常绿落叶阔叶混交林群落结构与物种多样性

Community structure and species diversity of evergreen deciduous broad-leaved mixed forest in Karst hills of Guilin

常绿落叶阔叶混交林是亚热带岩溶石山典型的森林植被类型之一,为了掌握这类森林植被的群落结构和物种多样性的变化特征,在桂林市灵田镇小水村岩溶石山常绿落叶阔叶混交林内设置了1个320 m×60 m的样地,用于分析群落的垂直结构、径级结构和α多样性变化。结果表明:(1)组成群落的木本植物有37科75属96种,密度为6371株/hm^(2)。其中,常绿树53种,落叶树43种。(2)垂直结构可以分为乔木上层、乔木下层和灌木层。其中,乔木上层分布34个物种(常绿18种,落叶16种),优势种为青冈栎(Cyclobalanopsis glauca)和南酸枣(Ziziphus jujuba);乔木下层分布30个物种(常绿17种,落叶13种),优势种为粗糠柴(Mallotus philippensis)和菜豆树(Radermachera sinica);灌木层分布32个物种(常绿18种,落叶14种),优势种为狗牙花(Ervatamia divaricata)和刺叶冬青(Ilex bioritsensis)。(3)在个体水平上,整个样地内所有个体胸径(DBH)呈明显的倒"J"型分布,平均胸径为4.32 cm;以小径级植株数量最多,DBH≤5 cm的个体占总个体数92.36%,而DBH≥20 cm的个体数较少,仅占0.96%;在物种水平上,平均DBH≤5 cm的物种有79种,占总物种数的85.86%,平均DBH≥20 cm的物种数(6种)仅占总物种数的6.52%。(4)每个样方中个体数的均值为262±132,Shannon-Wiener指数均值为2.67±0.26,Simpson指数均值为0.89±0.03,Pielou均匀度指数均值为0.78±0.05。(5)人为干扰和海拔对物种分布影响极显著,土壤厚度、岩石裸露率和坡度对物种分布影响显著。

Evergreen deciduous broad-leaved mixed forests are typical ecosystems in subtropical karst hills. To understand variation in community structure and species diversity within this ecosystem, we established an experimental plot(320 m by 60 m) divided into quadrats(20 m by 20 m) in the karst hills behind Xiaoshui Village, Lingtian Town, Guilin. We analyzed vertical structure spatial variation, size class, and α diversity variation. Our results demonstrated several things:(1) 37 families of woody plants make up this forest community, comprised of 75 genera and 96 species. Of these, 53 species were evergreen and 43 were deciduous. Plant density within the plots averaged 6371 plants/hm^(2).(2) We divided the vertical structure of the community into upper tree layer, lower tree layer, and shrub layer. Among the 34 species(18 evergreen and 16 deciduous) found in the upper tree layer, Cyclobalanopsis glauca and Ziziphus jujube were dominant. 30 species(17 evergreen and 13 deciduous) were found in the lower tree layer, with Mallotus philippensis and Radermachera sinica being dominant. Of the 32 species in the shrub layer(18 evergreen and 14 deciduous), Ervatamia divaricata and Ilex bioritsensis were dominant.(3) The diameter at breast height(DBH) of individual plants throughout the plot averaged 4.32 cm. Plants with small diameters accounted for the highest proportion of total individuals: plants with a DBH≤5 cm accounted for 92.36% of all individuals. Only 118 individuals had a DBH≥20 cm, which accounted for only 0.96% of the total number of individuals. 79 species had an average DBH≤5 cm, accounting for 85.86% of all species. Only 6 species had an average DBH≥20 cm, accounting for 6.52% of total species.(4) The average number of individuals in each quadrat was 262±132. The average Shannon-Wiener index was 2.67±0.26, and the average Simpson index was 0.89±0.03. The mean Pielou Uniformity index was 0.78±0.05. The number of individuals varied significantly between quadrats, while there was no significant variation in the Simpson index or the Pielou evenness index between the plots.(5) CCA ranking revealed that, among environmental factors, elevation and disturbance play a significant role in determining species distribution. Soil thickness, rock exposure, and slope have a less significant impact on species distribution. Consequently, conducting relevant research in this plot will promote a deeper understanding of community assemblage rules and maintenance mechanisms of species diversity during the natural recovery process in subtropical evergreen and deciduous broad-leaved mixed forest.