What drives the vegetation restoration in Yangtze River basin, China: Climate change or anthropogenic factors?

Knowledge of the vegetation dynamics is critical for addressing the potential challenges and threats facing the land surface ecosystems. Various climatic and anthropogenic factors such as temperature, precipitation, ecological engineering, and population density can affect the vegetation conditions. Yet how vegetation in the Yangtze River basin (YRB) responses to climate change and human activities is not well established. We investigate the spatiotemporal variations of vegetation coverage using Normal Difference Vegetation Index (NDVI) during 1982-2015, and distinguish the effects of climatic and anthropogenic factors on vegetation dynamics. The results show that the growing-season NDVI (GSN) has increased by 0.09% during the 34-year period, the changes indicated a significant upward trend of vegetation with annual change rates of 0.09% GSN year(-1) during 1982-2015.especially after 1994, the vegetation coverage has significantly increased. Temperature is a controlling factor determining the vegetation greenness in YRB, and the response of vegetation to precipitation is relatively lower because of the abundant water. Meanwhile, land use changes caused by ecological restoration project is the major driving factor for improving vegetation conditions in YRB, and the spatial distributions between human-induced GSN increasing trends and areas with increased forest have a strong consistency in the north of YRB. High effectiveness of ecological restoration projects are closely related to the combined effects of topography, climate and human management. The areas in northern part of Hubei and Sichuan are characterized by suitable climate and moderate elevation, leading to a high effectiveness for vegetation restoration. For the Hengduan Mountain area with complex terrain and lower precipitation added with poor traffic accessibility, low or even no effectiveness of project implementations can be observed. Furthermore, the large-scale migration and movement of the labor force in YRB relieve the environmental pressures and improve the vegetation conditions for the region of emigration.