Abstract:

Since the end of the 20th century,to reverse the trend of ecological degradation,China has implemented a series of national ecological construction projects and vegetation restoration has been the core goal.It is crucial to examine the effectiveness of ecological construction programs in Shaanxi Province,China,on vegetation restoration and clarify the roles of other driving factors.For this purpose,based on a dataset comprising MODIS NDVI data products,meteorological station observations,and socialeconomic statistics,the spatiotemporal changes of vegetation cover in Shaanxi from 2002 to 2016 were analyzed and a paneldata fixed effect model was built for attribution.The results show the following: (1) After the implementation of the Grain for Green Program and Natural Forest Conservation Program,the vegetation cover in Shaanxi showed an overall improving trend,but there were significant temporal fluctuations and spatial heterogeneities.(2) The ecological construction project exerted a significant and positive effect on vegetation restoration while it possessed a time lag.The NDVI value of each county is expected to increase by 0.012 3 after a 1% increase in afforestation rates three years ago,which is equivalent to the effect of increasing annual precipitation levels by 56 mm.(3) The precipitation and temperature increase had significant positive effects on vegetation restoration.The NDVI values for each county are expected to increase by 0.021 6 and 0.043 9 after a 100 mm increase in precipitation and a 1°C increase in temperature,respectively.However,the population and economic growth exerted a significant negative impact.The NDVI value for each county is expected to decrease by 0.033 1 and 0.031 5 after a 1 unit increase in population density and intensity of economic activity.To consolidate the achievements in vegetation restoration,it is necessary to continue increasing investments for ecological construction programs and strengthen supervision,monitoring,and evaluation.At the same time,an ecological migration policy should be actively implemented to relieve the ecological pressure brought about by human activities.The economic structure should also be adjusted and optimized,while the mode of economic growth should be transformed to abandon the extensive mode that exhausts resources and degrades the environment.In addition,unobserved factors that do not change with time,such as topography and geomorphology,have important impacts on vegetation coverage.Therefore,the government should follow the basic characteristics and laws of ecosystem succession and adapt measures to local conditions when designing and implementing ecological construction projects.

Key words: ecological construction, vegetation cover, NDVI, fixed effect model, Shaanxi Province