4.4 Uncertainty analysis
We combined 106 sites ranging from large temperature and precipitation gradients covering the main grassland types in China, which offers relatively accurate estimates on changes of soil pH following GE across grassland ecosystems. However, there remain some uncertainties and limitations. Uneven distribution of data collected in different types of grassland, soil layers and durations of GE may have some bias on our results. In addition, we were unable to evaluate several other potentially important environmental factors, such as grazing intensities before GE (heavy, moderate or light grazing), type of grazing management (seasonal or perennial grazing) and livestock (e.g., cattle, sheep, horse or yak), because most of these factors were not measured in field sampling and the peer-reviewed literature. Despite these uncertainties, the present study did reveal several interesting and informative patterns, which can provide important references for future management of the ecological environment in China’s grassland ecosystems.