Study on Natural Seres of Vegetation and Plant Species Diversity on Returning Land for Farming to Forests and Grassplots in the Hilly-gully Regions of the Loess Plateau

Based on the investigated data of 20 sample plots and 60 quadrats of returning land for farming to forests and grassplots in Wuqi County,Shaanxi Province,in this paper the natural seres of vegetation and the plant species diversity on returning land for farming to forests and grassplots in the hilly-gully regions of the Loess Plateau are analyzed by applying the methods of spatiotemporal inter-substitution.The results show that natural restoration of vegetation on returning land for farming to forests and grassplots in the study area can be divided into four stages,i.e.,the speedy restoration stage(1～4 years),primary succession stage(5～13 years),high-level succession stage(13～20 years) and slow restoration stage(after 20 years).In the 25-year natural succession of vegetation on returning land for farming to forests and grassplots,39 herbaceous species in 31 genera and 11 families have been found.The dominant species change in a sequence of the herbaceous species of Chenopodiaceae,annual herbaceous species,and perennial herbaceous species,and 5 seres including Salsola collina,Artemisia scoparia,Lespedeza davurica,Artemisia vestita and Bothriochloa ischcemum form.During the succession,the Margalef indices and Shannon-Wiener indices are increased in a luctuation way,but the increase trend is not so significant.After about 20 years,all the diversity indices are stabilized.In the process that one plant community is substituted by a higher-level plant community,the Margalef indices and Shannon-Wiener indices are increases at first,and then decreased,but the Pielou indices and Alatalo indices are decreased at first,and then increases.