Effects of Enclosure on Ecological Properties of Degraded Alpine Meadows and Optimal Length of Enclosure on the Qinghai-Tibet Plateau, West China

Vegetation biomass, soil carbon, and water retention capability of degraded alpine meadow are in a state of continuous decline as degradation worsens. One of the effective means of halting and reversing this decline is via meadow enclosure, an important measure to naturally restore the degraded alpine meadow ecosystem. This study aims to assess the impacts of enclosure duration on the quality of alpine meadow on the Qinghai-Tibet Plateau and determine the optimal enclosure length, through field investigation and indoor analysis of 340 samples collected from meadows that have been fenced between 1 and 31 years. The quality of the alpine meadow is judged by aboveground and underground biomass, soil bulk density, soil organic carbon change characteristics, and soil water-holding capacity. Also analyzed in this paper is the evolutionary and synergistic relationship between enclosure length and meadow properties to identify the optimal restoration period of each ecological index whose weight was determined by experts in a questionnaire survey. The results showed that the best enclosure length of degraded alpine meadow was 9.1 years based on the consideration of vegetation and soil qualities. Under long-term enclosure, it took 5.4a and 12.4a for soil organic carbon and saturated water holding capacity to recover to their pre-degradation level, respectively, and the recovery of aboveground biomass required 12a. Aboveground biomass, soil bulk density, soil organic carbon and soil saturated water holding capacity showed a logarithmic relationship with enclosure duration. The soil bulk density of degraded alpine meadow decreased with enclosure length, and was inversely proportional to the soil saturated water holding capacity. Aboveground biomass, soil organic carbon, and soil saturated water holding capacity all increased rapidly immediately after the enclosure but tended to recover slowly with the increase of enclosure length.