Effect of Different Grazing Intensity on Above-ground Net primary productivity and Regrowth Biomass in Alpine-cold Grassland around Qinghai Lake

The effect of grazing intensity on above-ground net primary productivity and regrowth biomass was studied in alpine-cold grassland around Qinghai Lake by means of grazing experiment.The results showed as follows.①The total net primary productivity under different grazing intensity was the maximum which was 232.01g/m2 when the grazing intensity was 2.29 sheep per hectare.The net primary productivity of every grazing area was less than that of control area and there was not super-compensatory growth.There was a significant difference between heavy grazing and control area(P0.05).②In grass growing season.the above-ground net primary productivity increased firstly,then decreased with the increasing of grazing intensity,The time of maximun amount of above-ground net primary produtivity was ahead under the condition of very heavy grazing intensity(4.01 sheep per hectare).③The suitable grazing intensity conduced to increase the regrowth biomass of grass and the regrowth biomass of grass was the maximum when the grazing intensity was 2.29 sheep per hectare.