The impact of climate change and anthropogenic activities on alpine grassland over the Qinghai-Tibet Plateau

Climate change and anthropogenic activities are two factors that have important effects on the carbon cycle of terrestrial ecosystems, but it is almost impossible to fully separate them at present. This study used process-based terrestrial ecosystem model to stimulate the potential climate-driven alpine grassland net primary production (NPP), and Carnegie-Ames-Stanford Approach based on remote sensing to stimulate actual alpine grassland NPP influenced by both of climate change and anthropogenic activities over the Qinghai-Tibet plateau (QTP) from 1982 to 2011. After the models were systematically calibrated, the simulations were validated with continuous 3-year paired field sample data, which were separately collected in fenced and open grasslands. We then simulated the human-induced NPP, calculated as the difference between potential and actual NPP, to determine the effect of anthropogenic activities on the alpine grassland ecosystem. The simulation results showed that the climate change and anthropogenic activities mainly drove the actual grassland NPP increasing in the first 20-year and the last 10-year respectively, the area percentage of actual grassland NPP change caused by climate change declined from 79.62% in the period of 1982-2001 to 56.59% over the last 10 years; but the percentage change resulting from human activities doubled from 20.16% to 42.98% in the same periods over the QTP. The effect of human activities on the alpine grassland ecosystem obviously intensified in the latter period compared with the former 20 years, so the negative effect caused by climate change to ecosystem could have been relatively mitigated or offset over the QTP in the last ten years.