Attributing vegetation change in an arid and cold watershed with complex ecosystems in northwest China

Attributing vegetation change in regions with complex ecosystems is fundamental for environmental management. The Manas River Basin in northwest China has a complex mountain-oasis-desert ecosystem sensitive to environmental change because of the arid and cold climate. This study investigated the spatiotemporal variations in vegetation coverage, and further analyzed the attributions in the Manas River basin. In particular, we sepa-rated the contributions of climate change and CO2 fertilization from human activities for each subregion and the whole basin. From 1982 to 2015, the mean annual NDVI values varied with ecosystems, i.e., high in the oasis ecosystem and low in the mountain and desert ecosystems. NDVI significantly increased at a rate of 0.021/10a for the whole study period and for the whole basin, but had spatial and temporal variations. The increase rates of NDVI were larger in the oasis ecosystem than other ecosystems, and they were larger for the period 1982-1997 (0.03/10a) relative to 1998-2015 (0.02/10a). Compared with the period 1982-1997, the vegetation for 1998-2015 was less correlated with climate and more strongly perturbed by human activities. Quantification showed that the anthropogenic contributions of vegetation change were 87% and 88% for the whole basin and the oasis ecosystem, respectively; however, the vegetation change in the mountain and desert ecosystems was overwhelmingly dominated by climate change and CO2 fertilization. The heterogeneity in changes and driving forces of vegetation highlights that the environmental management should be differentiated over space and time for those regions with complex ecosystems.