Abstract: Based on the field survey, and by using Shannon index and Pianka index, a quantitative analysis was made on the niche characteristics of 26 dominant species, including 6 tree species, 6 shrub species, and 14 herb species, in the forest vegetation in Pangquangou National Nature Reserve in the middle of Lüliang Mountains, west of Shanxi. In the tree layer, Betula platyphylla had the widest niche breadth; in the shrub layer, the niche breadth of Spiraea pubescens was the widest. Among the 26 dominant species, Carex lanceolata in herb layer had the widest niche breadth, suggesting its strong adaptability to environment factors and the advantages in competition with the other species. There was a significant positive correlation between the species niche breadth and the species frequency (P<0.01). The niche overlapping among the 26 dominant species occurred generally, but the overlapping degree was lower, suggesting the less strong competition between species. The correlation between the niche overlapping and niche breadth was not positively significant (P>0.05).

Key words: Pinus thunbergii, tree ring, stable carbon isotope ratio, climate change., intrinsic water use efficiency