Quantitatively assessing the effects of climate change and human activities on ecosystem degradation and restoration in southwest China

Identifying the effects of climate change and human activities on the degradation and restoration of terrestrial ecosystems is essential for sustainable management of these ecosystems. However, our knowledge of methodology on this topic is limited. To assess the relative contribution of climate change and human activities, actual and potential net primary productivity (NPP_a and NPP_p respectively), and human appropriation of net primary productivity (HANPP) were calculated and applied to the monitoring of forest, grassland, and cropland ecosystems in Yunnan-Guizhou-Sichuan Provinces, southwest China. We determined annual means of 476 g C m^-2 year^-1 for NPP_a, 1314 g C m^-2 year^-1 for NPP_p, and 849 g C m^-2 year^-1 for HANPP during the period between 2007 and 2016. Furthermore, the area with an increasing NPP_a accounted for 75.12% of the total area of the three ecosystems. Similarly, the areas with increasing NPP_p and HANPP accounted for 77.60 and 57.58% of the study area respectively. Furthermore, we found that ∼57.58% of areas with ecosystem restored was due to climate change, 23.39% due to human activities, and 19.03% due to the combined effects of human activities and climate change. In contrast, climate change and human activities contributed to 19.47 and 76.36%, respectively, of the areas of degraded ecosystem. Only 4.17% of degraded ecosystem could be attributed to the combined influences of climate change and human activities. We conclude that human activities were mainly responsible for ecosystem degradation, whereas climate change benefitted ecosystem restoration in southwest China in the past decade.