Abstract: Based on the investigation data collected from 84 field plots in the forests at altitude 1630-2430 m in Pangquangou National Nature Reserve of Shanxi, China, the forest communities’ species diversity and its relationships with environmental factors were investigated. With the altitudinal variation of forest communities, i.e., from Larix principis-rupprechtii+shrubs at 1630-2000 m to L principisrupprechtii + Picea sp. +Betulaat 2000-2200 m to L. principisrupprechtiiCarex lanceolataat 2200-2430 m, the richness (R₀) and ShannonWiener index (H) increased first and reached the maximum at medium elevation, and then decreased gradually; while the Simpson index (λ ) and Pielou evenness index (E) exhibited an increasing trend. Elevation had significant negative correlations with R₀ and H (r=-0.541，and -0.377, respectively; P<0.01) but positive correlation with  λ(r=0.495, P<0.01), and slope direction was significantly negatively correlated with R₀ and H (r=-0.365, P<0.01; r=-0.250, P<0.05, respectively) but positively correlated with  λ (r=0.356, P<0.01). Slope grade and soil thickness had no significant relationships with diversity indices. Tree layer coverage had significant positive correlations with R₀ (r=0.238, P<0.05) and H (r=0.217, P<0.05), herb layer coverage had significant correlations with R₀ (r=0.275, P<0.05) and  λ(r=-0.381, P<0.01), while shrub layer coverage had no significant correlations with the diversity indices.

Key words: Gaps, Natural disturbance, Mid-subtropical evergreen broad-leaved forest