Plant diversity in various forest community types in the Loess Plateau of western Shanxi Province,northern China.

We investigated the plant diversity and soil chemical properties of Pinus tabuliformis plantation, Robinia pseudoacacia plantation and natural secondary forest, and compared these three types of forest stands in order to reveal the plant diversity characteristics in different types of forest community. The results showed that: 1) there were 40 plant species in the study area, which were composed of 6 shrubs and 34 herbaceous species. The number of species in the three types of forest community was ranked as R.pseudoacacia plantationP.tabuliformis plantationnatural secondary forest. 2) The species richness index, Shannon-Wiener index, Simpson index and species evenness index in the three communities were all higher in the herbaceous layer than in the shrub layer, and higher in the plantations than in the natural forest. The species richness index and Shannon-Wiener index in P.tabuliformis plantation were both higher than those in R.pseudoacacia plantation; however, it was opposite for Simpson index and species evenness index, i.e., they were both higher in R.pseudoacacia plantation. 3) Compared with year 2006, the number of understory plant species in the study area increased in 2012. Such increase in the plantations was more obvious than that in natural secondary forest. 4) In the three types of forest community, the degree of correlation between soil chemical properties and species richness index, Shannon-Wiener index, Simpson index and species evenness index was ranked as soil nutrient organic matter pH value.