Effects of human activities and climate changes on plant diversity in Horqin sandy grassland,Inner Mongolia

To help understand the effects of human activities and climate changes on sandy grassland vegetation in north China,a field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin sand land,Inner Mongolia.The results showed that: 1)The grazing distribution had significant effects on species richness of the grasslands.The richness and diversity decreased with increased grazing intensity,and continuous overgrazing could result in a rapid decrease of the richness and diversity;2)There were large differences of the grazing effects on grassland plant diversity among different life forms and different economic groups.With an increase of grazing intensity,the annual plant diversity and Gramineae diversity increased while perennial plant diversity and Composite and Chenopodiaceae diversity decreased;3)Under different grazing intensities,there were large differences in diversity response to climate changes among different life forms and plant families,but the relativity only reached a significant level between Compositae and precipitation in the heavy grazing sites,and between other families' diversity and temperature in the moderate grazing site;4)In the grassland natural restoration succession process,warm and wet weather was favorable to an increase of richness and diversity,especially of perennial plants in the Compositae and Leguminosae.The warming and drying climate will result in a decrease of richness and diversity,but there will be less effect on Gramineae and Chenopodiaceae than on other plants.