Trends in satellite-observed vegetation trends and its environmental impacts across the Loess Plateau

Background/Question/Methods Land-use and land-cover change has profound influences on biodiversity and ecosystem processes.  The Loess Plateau of China, where soils are vulnerable to wind and water erosion, has suffered form dramatic environmental devastations due primarily to agricultural activities for decades.  Human activities have dramatically transformed the landscape and influenced the spatial distribution of vegetation.  In recent decades, new policies on land management have also been an important factor for landscape change in the Loess Plateau.  Previous studies in the region have focused mainly on vegetation responses to climate change, and little is known about the mechanisms of land-use and land-cover change that may involve a plethora of natural and anthropogenic factors.  Thus, this research was designed to evaluate the land-cover change dynamics and its environmental effects on the Loess Plateau based on remote sensing data, climate data, and other related field measurements.  The spatiotemporal pattern of NDVI (Normalized Difference Vegetation Index) was computed for each pixel using linear least square regression over the 1982-2003 periods.Results/Conclusions Our results indicate that most of the Loess Plateau (>72%) showed no statistically significant trend in vegetation activity although climate was warming up during the period of analysis (1982–2003).  A quarter of the Loess Plateau, drylands north of the Great Wall, experienced a marked increase in NDVI.  Of the areas where NDVI did change, dramatic vegetation improvement was observed. The NDVI has markedly increased in the Mu Us sandland as a result of the “Forbidden Grazing” policy. Moreover, the antecedent NDVI was found highly negatively correlated to the frequency of sand-storm events of the following year. Agricultural activities (such as irrigation) have significantly contributed to an increase in NDVI in two large irrigation agricultural areas (Qingtongxia and Hetao) along the Yellow River.  This increase is predominantly associated with intensified water consumption, suggesting the Qingtongxia–Hetao areas are human activity hot spots that may have been responsible for the Yellow River drying-up phenomenon. Our findings provide valuable information for local decision-makers and land managers.