Ecosystem Functioning of the Loess Plateau in China from Vegetation Restoration Relied Largely on Climate

Climate change and anthropogenic replantation are supposed to greatly change vegetation coverage and ecosystem stability and functions, e.g., net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE). Our study compared WUE of nature- and human-induced forest cover increase on the Loess Plateau since 2000 using satellite-derived Vegetation Continuous Fields (VCF), NPP, ET. This study also applied over 30 years of model-based NPP and meteorological observations to compare the stability and changes brought up by the Grain for Green Project. The result showed that the average forest coverage fraction increased from 7.1% (~4.5 × 104 km2) in 2000 to 11.2% (~7.3 × 104 km2) in 2014. Artificial forest cover increase occupied 76.43% of the significantly increasing tree cover regions. The role of revegetation practice in NPP and ET became gradually more dominant than climate factors in artificial forests from the northern to the southern part of the Loess Plateau. For areas experiencing limited forest coverage increase, artificial forest areas showed higher WUE than natural forest areas under similar mean annual precipitation (MAP). The difference in stability was small between neighboring natural and artificial forest areas. The northwest of the Loess Plateau had an increasing resilience, whereas the south of the Plateau had an increased resistance to precipitation and temperature change. The higher dependency of the northern reforested areas on climate fluctuation indicates a growing threat of water scarcity to the sustainability of anthropogenic reforestation in semi-arid regions.