[Effects of different disturbance types on plant species composition and functional group cha racteristics of typical...

The impacts of three kinds of human disturbances, i.e., non-grazing, reseeding and free-grazing, on plant community characters, i.e., species composition, composition of functional groups, species diversity, and aboveground biomass, were studied in a typical steppe in Inner Mongolia, China. The results showed that different disturbances had significant impacts on the structure and diversity of plant functional groups. The number of plant species, aboveground biomass, community diversity, and richness indices were the highest in the non-grazing treatment, with the fi-gures of 22, 171.32 g·m^-2, 1.46 and 5.7, respectively. The importance value (IV), percentage, aboveground biomass, diversity, richness, and evenness indices of shrub and sub-shrub, and perennial grasses were also the highest in the non-grazing treatment. In contrast, the IV, species percentage, aboveground biomass, diversity, and evenness indices of perennial forbs were the lowest in the non-grazing treatment. The aboveground biomass of mesophyte, C3 and C4 plants was the highe-st with the figures of 22.22, 143.35 and 27.97 g·m^-2 respectively in the non-grazing treatment. The aboveground biomass of mesoxerophyte was highest (13.60 g·m^-2), the species percentage of xerophyte was lowest (48.5%) and that of C4 plants was highest (28.8%) in the reseeding treatment. The species percentage of annual or biennial herbs was highest (12.3%), while that of mesophyte and C4 plants was lowest (17.0% and 20.9%) in the free-grazing treatment. The non-grazing treatment showed a beneficial effect for restoration of degraded grassland system.