Effects of long-term grazing exclusion on vegetation structure, soil water holding capacity, carbon and nitrogen sequestration capacity in an alpine meadow on the Tibetan Plateau

Grazing exclusion is one of the primary management practices used to restore degraded grasslands on the Tibetan Plateau. However, to date, the effects of long-term grazing exclusion measures on the process of restoring degraded alpine meadows have not been evaluated. In this study, moderately degraded plots, in which the vegetation coverage was approximately 65% and the dominant plant species was Potentilla anserina L, with grazing exclusion for 2 to 23 years, were selected in alpine meadows of Haibei in Qinghai-Tibet Plateau. Plant coverage, plant height, biomass, soil bulk density, saturated water content, soil organic carbon (SOC) and total nitrogen (TN) were evaluated. The results were as follows: (1) With increased grazing exclusion duration, aboveground biomass and total saturated water content at 0-40 cm depth, the average SOC and TN contents in moderately degraded alpine meadows increased as a power function, and the plant height increased as a log function. (2) The average soil bulk density at 0-40 cm depth first decreased and then increased with increasing grazing exclusion duration, and the minimum value of 0.90 g center dot cm(-3) was reached at 15.23 years. The plant coverage, total belowground biomass at 0-40 cm depth, total aboveground and belowground biomass first increased and then decreased, their maximum values (80.49%, 2452.92 g center dot m(-2), 2891.06 g center dot m(-2)) were reached at 9.41, 9.46 and 10.25 years, respectively. Long-term grazing exclusion is apparently harmful for the sustainable restoration of degraded alpine meadows. The optimal duration of grazing exclusion for the restoration of moderately degraded alpine meadows was 10 years. This research suggests that moderate disturbance should be allowed in moderately degraded alpine meadows after 10 years of grazing exclusion.