Spatial and temporal patterns of Holocene vegetation and climate changes in arid and semi-arid China

Pollen data from 30 sites in arid and semi-arid regions of China were reviewed to document regional patterns of Holocene vegetation and climate change and to understand the large-scale controls on these changes. Vegetation at most sites in eastern Inner Mongolia switched between forest, forest steppe, and typical steppe, showing maximum moisture conditions before 6 ka (1 ka=1000 cal yr BP) and a dry climate after ∼6 ka. Vegetation in the northwestern Loess Plateau changed between desert steppe, forest steppe and steppe, suggesting wet–dry oscillations, from an initial dry to wet climate at ∼9–4 ka and then back to a dry climate. In the northern Tibetan Plateau, vegetation was characterized by steppe desert, steppe or desert, indicating a wet climate in the early and mid-Holocene until 6–4.5 ka. In western Inner Mongolia and Xinjiang, pollen assemblages show changes between desert, steppe desert and steppe, with a wet period occurring during 8.5–5.5 ka at most sites. All the four regions show a drying trend during the late Holocene. The complex climate patterns suggest that regional climate responses to large-scale climate forcing were controlled by interactions of competing factors, including the monsoons, westerlies and topography-induced regional atmospheric dynamics. The role of human activity in vegetation change requires further investigation.