Abstract: Stellera-dominated degraded grassland is one of the more common categories of degraded grassland in the northern Tibetan Plateau. Protection by grazing exclusion (fencing) is a common measure for the restoration of degraded grasslands. We conducted observations over a three-year period (2010-2012) in both grazed and protected (fenced in 2004) habitats in a Stellera-dominated, degraded grassland, to explore how grazing exclusion impacts on plant community characteristics and productivity of degraded grasslands. It was found that: 1) Grazing exclusion significantly increased the total aboveground biomass in the Stellera-dominated degraded grassland (P<0.05), with the largest increase in 2012. Compared with grazed grassland, the total above-ground biomass in the fenced habitat was increased by 62.4%, 64.3% and 70.2%, respectively, in 2010, 2011, and 2012. 2) Grazing exclusion also increased aboveground biomass of Stellera chamaejasme (P<0.05). Aboveground biomass of S. chamaejasme in grazed plots in 2010, 2011, and 2012 was 43.8%, 55.3% and 89.3% lower, respectively, than that under grazing exclusion (P<0.05). 3) Grazing exclusion was beneficial in that it improved the community species diversity of Stellera-dominated degraded grassland. The species diversity, evenness and species richness indexes all increased significantly as grazing exclusion time increased (P<0.05). 4) The pattern of annual variation in aboveground plant biomass under grazing exclusion was similar to that in grazed plots. In summary, grazing exclusion has no obvious suppression effect on Stellera chamaejasme, so for the restoration of Stellera-dominated degraded grassland, other management measures should be combined.

Key words: Northern Tibetan Plateau, grazing prohibition, Stellera chamaejasme, community characteristics, productivity