Plant Community Structure and Soil Carbon and Nitrogen Status of Degraded Alpine Meadows

This study investigates the plant community structure and soil carbon and nutrient content in Kobresia meadows atop the Qinghai-Tibetan Plateau. Three degrees of degradation of native alpine meadow and a seeded (ploughed) pasture which was established on a heavily degraded meadow were studied using standard plant ecological methods. Degradation was characterized by a shift in species composition from a Kobresia-dominated to a forb-dominated community. Live vegetation covers was reduced by 40% and vegetation height by 80% from a lightly degraded meadow to a heavily degraded meadow. The total aboveground phytomass in the three communities were similar (P>0.05), but aboveground phytomass of sedges, graminoides, and forbs was different among lightly, moderately and heavily degraded meadows (P<0.01). The Shannon's diversity index, species evenness and species richness all decreased with increasing degradation (P<0.01). Significant positive correlations were found between meadow quality cover index and diversity indices. Organic carbon (C) and total nitrogen (N) concentrations in the topsoil (0-10 cm) of lightly degraded meadows were higher (P>0.05) compared to the other meadow types. At 10-20 cm, C and N concentration and soil C stocks in the seeded pasture were significantly lower than in the other meadow types. Total carbon stocks (0-30 cm) were lowest in the seeded pasture most likely as a result of ploughing. In light of these findings, ploughing is not a recommended treatment for meadow rehabilitation.