2.2 Data compilation
We collected site information and soil data from peer-reviewed literature. Literature searches were performed using the Web of Science, Google Scholar and China National Knowledge Infrastructure with key words relating to grazing exclosure/fencing/exclusion, soil pH, Inner Mongolia, Xinjiang, Qinghai–Tibetan Plateau, temperate grassland/meadow/typical steppe/desert steppe and alpine grassland/meadow/steppe/desert steppe. We selected the papers according to the following criteria: 1) the soil samples and pH data had accurate soil depth; 2) the soil pH value were determined from both GE and free grazing sites, and had to have similar climate and soil conditions; 3) an accurate period of GE had to be recorded; 4) the studies could employ paired sites, chronosequence or retrospective design to analyse the change of soil pH; 5) other interference factors needed to be excluded, such as fertilization and seeding; 6) only field manipulation studies were selected, and model simulation data were not included. If there were several sampling dates in one year, only the growth season (July–August) data were selected because the biomass at this time reaches the maximum for a year and is consistent with most of the previous research. The site information (e.g., location, longitude, latitude, MAP, MAT, dominant species, duration of GE, soil data (e.g., soil sampling depth, pH, SOC and SN concentrations) and biomass (AB and BB) were extracted from the grazed and GE plots. If the exact MAP and MAT data were not available, we extracted the climate data by using the method described above for the field sampling according to their geographical locations. The conversion factor of SOM to SOC is 1.724 (Pribyl, 2010). All data were extracted from tables or figures. Summary information for each site is available in supplementary dataset. The dataset included 63 study sites from 10 provinces (the Xinjiang Uygur Autonomous Region, the Inner Mongolia Autonomous Region, the Ningxia Hui Autonomous Region, the Tibet Autonomous Region, Shaanxi province, Sichuan province, Gansu province, Qinghai province, Shanxi province and Jilin province) reported by 46 peer-reviewed papers published between 2004 and 2019, which together include most of the area of the China’s ‘Returning Grazing Land to Grassland’ project (supplementary dataset).