Abstract:

Aims: Mid-montane evergreen broadleaf‌ forests constitute an important component of subtropical forest ecosystems in China, yet they remain scientifically understudied. Strikingly, the mid-montane zone of Jiulongshan National Nature Reserve contains a large and exceptionally well-preserved primary evergreen broadleaf‌ forest that is highly representative of eastern subtropical China. 

Methods: Following the protocols of the Chinese Forest Biodiversity Monitoring Network (CForBio), we established a 30-ha forest dynamics plot in this region and conducted the first full census of all woody stems with a diameter at breast height (DBH) ≥ 1 cm. Based on these data, we analyzed species composition, community structure, vegetation formations, and habitat differentiation. 

Results: A total of 179,533 woody individuals were recorded in the plot, belonging to 201 species, 96 genera, and 49 families. Ericaceae, Theaceae, and Fagaceae were the dominant families. Twenty-one species had importance values ≥ 1%, with Rhododendron simiarum, Schima superba, and R. latoucheae as the top three dominant species. The importance values of evergreen broadleaf‌, deciduous broadleaf‌, and coniferous species were 69.49%, 21.75%, and 8.76%, respectively. Vegetation formations were dominated by evergreen broadleaf‌ forest and showed a mosaic distribution with other vegetation types along topographic gradients, indicating stronger transitional characteristics than those of lower-elevation subtropical forests. The mean DBH of all woody individuals was 6.8 cm, and the DBH-class distribution showed a typical inverse J-shape, indicating good regeneration potential. Vertical stratification was pronounced, with the canopy layer dominated by S. superba, Pinus taiwanensis, Cyclobalanopsis multinervis, and C. stewardiana, and the sub-canopy and shrub layers dominated by Ericaceae species, especially R. simiarum and R. latoucheae, reflecting a vertical stratification pattern typical of mid-montane forests. Floristic composition exhibited a clear transitional pattern, with tropical elements dominating at the family level (51.0%) and temperate elements dominating at the genus level (57.3%). Rare species accounted for 51.24% of all species. Multivariate regression tree analysis showed that the plot could be classified into five habitat types. Total phosphorus, available sodium, aspect, and slope were identified as the key environmental factors distinguishing habitat types. Rare species were proportionally more concentrated in the transitional habitat characterized by high phosphorus and steep slopes. 

Conclusion: The Jiulongshan plot well reflects the characteristics of primary montane evergreen broadleaf‌ forest in the mid-subtropics, including high species richness, complex community composition and pronounced vegetation differentiation. This plot provides baseline data and a research platform for long-term monitoring, cross-regional comparison, and related ecological studies.

Key words: mid-montane evergreen ?broadleaf? forest, Zhejiang Jiulongshan, forest dynamics plot, floristic composition, diameter-class structure