Study on species composition and community structure of the Excentrodendron tonkinense (A. Chev.) H. T. Chang & R. H. Miao+Cephalomappa sinensis (Chun & F. C. How) Kosterm. community in Yunnan karst seasonal rainforest

The Excentrodendron tonkinense (A. Chev.) H. T. Chang & R. H. Miao community represents a distinctive and ecologically significant component of the karst seasonal rainforests in southern China and northern Vietnam. Despite its ecological importance, this endemic forest type has experienced widespread degradation due to human activities, and its floristic composition and structural attributes remain poorly documented. A detailed vegetation survey was conducted using standard quadrat sampling within a 4 800 m² plot in Daweishan National Nature Reserve, Yunnan, China. Results showed that: (1) A total of 92 vascular plant species belonging to 78 genera and 45 families were recorded. The seed plant flora exhibited strong tropical affinity, accounting for 73.68%, 94.20%, and 99.05% of families, genera, and species, respectively. Phanerophytes accounted for 79.12% of species. Species diversity indices showed a Shannon Wiener index of 2.84, Simpson index of 0.14, and Pielou index of 0.63. (2) The community exhibited a well-defined stratification with three primary vertical layers: the tree layer contained 1 593 individuals representing 38 species in 32 genera and 18 families; the shrub layer contained 453 individuals representing 29 species in 27 genera and 18 families; and the herb layer contained 357 individuals representing 22 species in 19 genera and 10 families. An additional interlayer contained 232 individuals representing 23 species in 20 genera and 17 families. (3) Comparative analysis of species importance values across layers identified E. tonkinense (Malvaceae) as the dominant constructive species and Cephalomappa sinensis (Chun & F. C. How) Kosterm. (Euphorbiaceae) as the characteristic species, forming the Excentrodendron tonkinense+Cephalomappa sinensis community. (4) The age structure of dominant arboreal taxa displayed an “L” type distribution. These findings characterize a native tropical karst rainforest community with rich and stable species composition, pronounced vertical complexity, and robust regenerative capacity.