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

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