Effect Of Grazing Rates On Plant Diversity And Productivity In Northwest Sichuan Alpine Meadow

To explore the changes of grassland plant diversity and productivity and their ecological process under different grazing rates at a local scale in northwest Sichuan alpine meadow,two-year controlled experiment under different yak(Bos grunniens)grazing rates was conducted to determined the effects of grazing on plant diversity,productivity of grassland,selective feeding of yak and soil available resources.The relationships among plant diversity,productivity,selective feeding of yak and soil available resources(water and nutrients)were analysed to provide theory basis of sustainable utilization of alpine grassland in northwest of Sichuan,Main conclusions were as the following:1.2 years yak grazing made the dominant species of Deschampsia caesp itosa and subdominant species of Festuca ovina decreased significantly(P<0.05),but the dominant position were not changed.In addition,the Shannon-wi ener index and the Simpson index at 0.95 yak/hm2 for 2 years were significa ntly higher than that of control(0 yak/hm2),the species richness,Shannon wi ener index and Simpson index at 2.14 yak/hm2 for 2 years were significantly reduced,but there were no obvious changes about Pielou evenness index(P>0.05).2.In two years,plant community aboveground biomass,belowground biomass and total biomass were significantly reduced with the increase of grazing rates(P<0.05).3.With the increasing of grazing rates,soil water content(0-10 cm)and soil organic matter content(0-20 cm)were significantly reduced(P<0.05),while total nitrogen,total phosphorus,available nitrogen,and available phosph orus content had no significant difference(P>0.05)in different grazing rate s.4.In growing season,yak take in the most same plants,but the selectivi ty of grassland plants of yak reduced at 2.14 yak/hm,with the extension of the growing season,the selective index of main plants species of yak also gr adually reduced.There were significant positive correlations between soil mois ture content,organic matter,available nitrogen content,total phosphorus conte nt with plant productivity at 0.01 level,significant positive correlations betwee n soil moisture content and the plant richness at 0.05 level,and significant ne gative correlations between yak selective feeding plant numbers and grassland plant productivity.Above all,0.95 yak/hm2 grazing rate in northwest Sichuan alpine grassla nd was beneficial to the improvement of the plant diversity,while 2.14 yak/h m2 grazing rate reduced the plant diversity and productivity,it may be the re asons of decrease of the soil moisture content,organic matter content and yak selective feeding under heavy grazing rates(P<0.05).