Time structure and dynamics of the insect communities in bush vegetation restoration areas of Zhifanggou watershed in Loess hilly region

The insects were investigated in Zhifanggou watershed, Ansai County, Shaanxi Province, China. The results showed that the insect species varied spatially in the following order: the natural bush forests, the mixed forests and the simple forests. The individual number of insects in Caragana korshinskii was the highest, followed by mixed forests and Hippaphae rhamnoides, and the change range of the insect individuals in the natural bush forests was the smallest. The species number of insects with seasonal changes and the individual number of insects in various types of vegetation can be described by the Univariate cubic equation. The order of the diversity index of the insect communities in various types of vegetation from May to September was the natural bush forests, the mixed forests and the simple forests. The change ranges of the evenness values of the simple forests and the mixed forests were higher, and that of the natural bush forests was smaller. The reverse trend was assumed between the dominance values and the evenness values in the time course. Moreover, the main factors and temporal patterns of the insect communities in the natural bush forests were more complicated, fluctuative and obvious than those in the mixed forests and the simple forests by using the principal component analysis.