Species diversity and interspecific association in development sequence of Hippophae rhamnoides plantations in loess hilly region
黄土丘陵区沙棘人工林发育过程中物种多样性及种间关联变化

Based on field investigation, this paper analyzed the characteristics of species diversity and interspecific association at different development stages of Hippophcze rhamnoides plantations. The results showed that the species diversities of shrub layer, grass layer, and whole community of H. rharnnoides plantations were all fluctuated in "S" shape. At different development stages, the species richness and diversity were higher in grass layer than in shruh layer. The shrub species diversity was lower on hare land, but increased gradually with development stage. Shrub evenness index was higher in 13-year forest stand, while grass diversity index was higher in 3-year plantation, lower in 8-year plantation, and higher in 25-year plantation. The positive and negative absolute values of interspecific association between H. rharnnoides and other principal species changed in parabola shape, and the notable degree and the interspecific association intensity were weaker in 13-year plantation, showing that the species substitution rate was slower, competition was less, and community composition and its structure were relatively stable. To improve ecological environment, the H. rhamnoides plantations younger than 13 years old should he given priority to protection, while for those of 25 years old, moderate thinning should be made to promote the regeneration.