Positive effects of ecological restoration policies on the vegetation dynamics in a typical ecologically vulnerable area of China

Ecological restoration programmes have been initiated worldwide because of serious environmental degradation. However, the effectiveness of ecological restoration remains contentious because vegetation restoration is impacted by both climate change and human activities. Climate change is an important factor for vegetation restoration, especially in ecologically vulnerable areas. The Zhangjiakou region of northern China is located in a semiarid and subhumid climate region with apparent ecosystem vulnerability. Since the late 1970s, a series of ecological restoration programmes have been carried out in this area to recover the vegetation and ecosystems. Based on remote sensing images and ground-based meteorological data, two vegetation indexes (NDVI and EVI2) and aridity index were calculated to analyse (i) the vegetation dynamics and climate aridity trends in the Zhangjiakou region and (ii) the response of the vegetation dynamics to ecological restoration programmes and climate change between 1987 and 2017. The results indicated that vegetation cover increased with twice abrupt changes in 2002 and 2009, respectively, which simultaneously underwent an increase in aridity. Vegetation cover has increased rapidly since 2003 because of ecological recovery projects and policies. The contributions of climate change and human activities to vegetation cover were12%~ 5.2% and 88% ~ 94.8% during the period 2003–2009, respectively. The contributions of climate change and human activities to vegetation cover were2.1% ~ 2.4% and 97.9% ~ 97.6% during the period 2010–2017, respectively. The ecological restoration projects and policies effectively promoted vegetation cover in the study area.