Responses to continual grazing of major functional types of Gramineae in Horqin sandy grassland,Inner Mongolia

Four field plots with different grazing intensities,namely,heavy grazing (6 sheep/hm~2,HG),moderate grazing (4 sheep/hm~2,MG),light grazing (2 sheep/hm~2,LG) and a control (0 sheep/hm~2,CK) were set up on typical Horqin sandy grassland.After four years of continual grazing,the main Gramineae plants were assessed.The average height and coverage of three functional groups,namely,perennial grasses (PG),annual high-quality grasses (AHG),and annual low-quality grasses (ALG) were analyzed.There was little difference between average coverage of Gramineae plants in plots MG,LG and CK,but was markedly lower in HG,indicating greater sensitivity to the disturbance of heavy grazing.With increasing grazing intensity,PG relative coverage gradually decreased,and was only 0.69% with HG.Relative coverage of AHG showed the following differences:MGLGHGCK,indicating grazing disturbance had an enhancing effect.Relative coverage of ALG gradually increased with increase of grazing intensity.Heights of the three functional types of Gramineae all decreased with increase in grazing intensity.Sensitivity of height to grazing intensity for the three types showed the following differences:PGAHGALG.