Species Diversity in the Process of Vegetation Succession in Karst Area in Western Guangxi

The process of natural succession of restoring vegetation in western Guangxi after rocky desertification of Karst area appearing was divided into the herbosa stage,the stage of herbosa-shrub,the stage of vineshrub,the stage of subaltern tree forest and the climax stage.Typical quadrats were set up by using space instead of time.The species composition was analyzed in each stage and the species diversity in the layers of herb,shrub,tree and community at different successional stages was measured by the methods of species abundance,Simpson index,Shannon index and Pielou's evenness index. The results showed that,with the exception of the herb layer,the species abundance in all layers rose steadily when the succession developed from the herbosa stage,and reached the maximum in the stage of subaltern tree forest.In the herb layer,species abundance and Shannon index fluctuated but Simpson index and evenness index decreased gradually,and reached the minimum in the climax stage.Simpson index,Shannon index and Pielou's evenness index first increased,followed by a decline,but the stage at which the index reached its maximum was not consistent.Diversity indices of the herb layer were higher than those of the shrub layer in the stage of herbosa.When the succession entered into the stage of herbosa-shrub,diversity indices of the shrub layer rose and exceeded those of the herb layer.Diversity indices of the tree layer were the lowest from the time when arbor appeared.