Abstract:To understand the changes in species diversity of Emmenopterys henryi community and its driving factors, 35 sample circles with a 15 m radius centered on an E. henryi tree were set up in the Jiulongshan National Nature Reserve, Zhejiang Province. The species and diameter at breast height (DBH) of arbor layer trees (i.e. woody plants with a DBH more than 2.5 cm) within the sample circles were investigated. The relationship between α diversity of arbor layer trees and altitude, and slope aspect, and DBH of E. henryi in each sample circle were analyzed by linear mixed model, and the influences of spatial structure, altitude, and slope aspect, and DBH of E. henryi on β diversity were studied using the mantel test and variation partition analyses. The results showed that the number of species in arbor layer of E. henryi communities was rich, with 145 woody species belonging to 98 genera and 50 families, and dominated by deciduous or semi-evergreen species. The Shannon-Wiener index ranged from 2.37 to 3.40 and the Simpson index from 0.86 to 0.94. The α diversity indices increased at first then decreased with elevation, and neither related to the slope aspect nor DBH of E. henryi. The Sorenson index of community pairs ranged from 0.15 to 0.95 and the contribution of turnover components to the total β diversity of arbor layer was 74.88%. The geographical distance between sample circles was significantly positively correlated with β diversity and its components of arbor layer trees; while the altitude difference between sample circles was significantly positively correlated with β diversity and species-richness difference of arbor layer trees. The DBH difference of E. henryi between sample circles was only positively correlated with species turnover of arbor layer trees. The geographical distance of the sample circles is the likeliest explanation for β diversity and its two components (23%–29%) of arbor layer trees. The altitude difference is also a probable explanation for β diversity of arbor layer trees (16%). Therefore, α diversity of arbor layer trees in the E. henryi community in Jiulongshan was mainly affected by altitude, while β diversity and its two components of arbor layer trees were affected by dispersal limitation, habitat filtering, and interspecific interaction between E. henryi and associated species.