Vegetation history, climate change and human activities over the last 6200 years on the Liupan Mountains in the southwestern Loess Plateau in central China

Fossil pollen data from Tianchi Lake on the Liupan Mountains in the Loess Plateau in China were used to investigate the interplay of climate change, vegetation history and human activities. The chronology of an 11-m-long sediment core was controlled by 19 accelerator mass spectrometry radiocarbon dates on terrestrial plant macrofossils. The pollen record shows a long-term change from a closed canopy forest to open landscape over the last 6200 years: from mixed deciduous–coniferous forest dominated by Betula, Quercus, Picea and Pinus at 6200–2900 cal yr BP, to transitional steppe forest co-dominated by trees (Betula, Picea and Pinus) and herbs (mostly Artemisia) at 2900–1100 cal yr BP, and to open landscape dominated by Artemisia and Poaceae after 1100 cal yr BP. This general pattern of vegetation change indicates a drying climate trend, consistent with other independent climate records mostly from the monsoon region that show a weakening summer monsoon since the mid-Holocene. The gradual increase in both Poaceae pollen and microscopic charcoal since about 2000 cal yr BP and a sharp increase in Poaceae but a decrease in charcoal at 1000 cal yr BP indicate two phases of human impacts on vegetation. The results from pollen and charcoal analysis, together with archaeological and historical evidence, suggest that human activities over the last 2000 years have significantly accelerated deforestation that was initiated by a drying climate since the mid-Holocene.