Relative contribution of climate change and human activities to vegetation degradation and restoration in North Xinjiang, China

Climate change and human activities are the two primary driving factors in the vegetation degradation process, and the assessment of their relative roles in vegetation degradation is important to understand the driving mechanisms of vegetation degradation. In this study, net primary productivity (NPP) was selected as an indicator to distinguish the relative roles of climate change and human activities in vegetation degradation and restoration from 2001 to 2010 in North Xinjiang, China. The potential NPP and the human appropriation of NPP were served as the indicator of the effects of climate change and human activities in vegetation degradation and restoration. The results showed that human activities were the dominant factor that induced vegetation degradation, accounts for 55% (153 720 km2) of the total degradation, whereas 25% (69 336 km2) of the total degradation resulted from climate change; the combination of human activities and climate change was the cause in 20% (55 429 km2) of the total degradation. In contrast, 61% (66 927 km2) of the total vegetation restoration was dominated by human activities and 29% (31 553 km2) was caused by climate change; the areas of vegetation restoration caused by the combination of human activities and climate change were 10 551 km2 (10%). The relative roles of the two factors possessed great spatial heterogeneity in five vegetation types. Climate dominated degradation expansion and human activities dominated vegetation restoration in forest. Both the degradation and restoration were dominated by human activities in grassland. In desert, degradation was dominated by human activities and vegetation restoration by climate. In cropland and crop/natural vegetation mosaic, degradation was dominated by both human activities and climate change and restoration was dominated by human activities. These results demonstrated that human activities played a demonstrably positive role in vegetation restoration, and ecological restoration projects were effective on mitigating vegetation degradation and also promoting restoration in the southern areas of North Xinjiang.