Impact of enclosure on community characters of sowed Elymus nutans grassland in black soil Land

The thirdyear and seventhyear sowed Elymus nutans grassland in black soil land in the ThreeRiver region were fenced for 3 years, and the community was surveyed during the middle August in each year. The same grassland outside the fence which was grazed in winter was used as the control. The results showed: 1) the species diversity index of fenced grassland was higher than the grazing grassland, and with the increase of sowed age, the diversity index gradually increased; 2) the change of total coverage, coverage and height of dominant species were same, i.e., they decreased with the increase of sowed age and that of fenced grassland was lower than the grazing grassland; 3) The aboveground biomass was consistently decline with the increase of sowed age, and that of fenced grassland was significantly lower than the grazing grassland.