Changes in vegetation parameters and soil nutrients along degradation and recovery successions on alpine grasslands of the Tibetan plateau

Understanding the changes in vegetation parameters and soil nutrients in the different stages of grasslands degradation and recovery is crucial for assessing and restoring degraded grasslands. Consequently, we determined above-ground vegetation and soil C, N and P concentrations and their stoichiometry in different degradation and recovery stages on the Tibetan Plateau. Four degradation succession stages, GKC: Grass-Kobresia community, KHC: Kobresia humilis community, KPC: Kobresia pygmaea community, and FBC: forbs - black soil beach community, and three recovery succession stages, FG: freely grazed, RG: restricted grazed, and NG: non-grazed, were identified. Above-ground biomass and vegetation coverage decreased with degradation succession and there was a concomitant shift of plant functional groups to more above-ground biomass of forbs and less biomass of grasses and sedges. The highest species diversity emerged in the K. pygmaea succession stage, mainly due to an influx of Compositae. Significant differences in soil total nitrogen (TN), total phosphorus (TP) and soil organic carbon (SOC) concentrations occurred in the 0–10 and 10–20 cm layers among degradation successions. Vegetation cover, above-ground biomass, soil TN and SOC, as well as C:N and C:P ratios increased in non-grazed grasslands when compared to grazed grasslands. Soil TN, TP and SOC concentrations decreased with increasing soil depths across all degradation and recovery successions. In addition, soil nutrients and their stoichiometry were affected by above-ground biomass. We concluded that grazing exclusion could improve the above-ground vegetation and soil nutrients of degraded alpine grasslands, but that the rate of recovery was related to the degree of degradation.