[Effects of slope position and aspect on structure and species diversity of shrub community in the Jiajin Mountains, Sichuan Province, China].

We examined the impacts of slope direction and position on the community structure and species diversity of shrub community in Jiajin Mountains. The results showed that a total of 186 vascular plant species belonging to 50 families and 127 genera were recorded in the 24 sample plots. 32 species belonging to 14 families, 22 genera were recorded in the shrubs layer, with most species distributed at lower position of the shady slope. 154 species belonging to 43 families and 109 genera were recorded in the herbaceous layer, with the species number being the lowest on the shady slope. The average height of the shrub layer showed a decreasing order of sunny slope, semi-sunny slope, and shady slope, while an opposite order was observed for the average density. The average height of the herb layer was in the decreasing order of the shady slope, semi-sunny slope, sunny slope, whereas no significant changes were observed for the average density. The slope position had significant effect only on the average height of the herbaceous layer on the sunny slope. The overall level of species diversity in the shrub layer on the shady slope was relatively high, while that in the herbaceous layer was relatively high at the lower position of the sunny slope and at the middle position of the shady slope. Slope aspect had significant effect on species richness index, Shannon diversity index, Simpson dominance index, Pielou evenness index of shrub and herb layers except for Simpson index of herb layer. Slope position did not affect these indices. The interaction effect of slope aspect and position on the diversity index for herb layer was greater than that for the shrub layer. Results from redundancy analysis showed that species diversity was related to sin(aspect), cos(aspect), and community structure.