Increasing terrestrial vegetation activity of ecological restoration program in the Beijing–Tianjin Sand Source Region of China

China's capital city, Beijing, has been suffering from sandstorms due to grassland degradation and the large distribution of deserts in western and Northern China, named as the Beijing–Tianjin Sand Source Region (BTSSR). To improve the ecological condition in the BTSSR and to reduce its impacts, the Chinese government has adopted the Beijing–Tianjin Sand Source Control Program since 2001. It is necessary to rigorously evaluate the effectiveness of this 10 years’ program, not only as an essential topic of environmental change in an ecologically vulnerable area, but also as an important aspect of policy efficiency assessments. Toward this aim, this study assessed vegetation changes both temporally and spatially in the areas under the program from 2000 to 2010 with the Moderate-resolution Imaging Spectroradiometer (MODIS) monthly Normalized Difference Vegetation Index (NDVI) data and trend analysis method. The results showed an overall improvement and its spatial variation in vegetation activity. The annual NDVI increased by 0.0121year−1 over 64.33% of the total area, with the greatest increasing trend of NDVI occurring in the spring. However, the change in NDVI varied remarkably in space. This study identified a southwest-to-northeast band in the study area where NDVI decreased notably, while most of the BTSSR experienced a positive trend of NDVI. Although the cause of the increased NDVI in the BTSSR remains uncertain, drought may result in a non-significant increasing trend in vegetation activity and the ecological restoration program may be one of the main driving forces behind the increasing trend in vegetation activity. All of these findings will enrich our knowledge of human activities that impact vegetation in arid and semi-arid environments and will provide a scientific basis for the management of ecological restoration programs.