Broad-scale valley agriculture reaches back to the Ming Dynasty based on multiproxy records from Guli Lake, northeastern Tibetan Plateau

The northeastern Tibetan Plateau is the region with the longest history of development, most densely populated, and most obvious land use of the Tibetan Plateau. However, there is a lack of accurate knowledge of the timing and intensity of the human impacts on vegetation during the mid-to-late Holocene. In this study, we quantitatively compare the pollen assemblages from farmland with surrounding natural vegetation and results show that agricultural activities lead to an increase of Brassicaceae, cerealia Poaceae, and Hippophae pollen. Vegetation and climate change since 5 cal ka BP for Guli Lake in Hehuang Valley have been reconstructed from pollen and sediment chemistry data; and anthropogenic pollen indicators identified from a sediment core are combined with evidence from archaeological sites and historical documents, revealing that agricultural activity began after 4.8 cal ka BP but initially had a limited impact on vegetation. By 0.5 cal ka BP, the impact of farming activity on the vegetation increased significantly and oil-seed crops were cultivated, but the vegetation was still strongly affected by climate. Due to its superior natural condition, favourable government policy, and advanced agricultural technology, the Hehuang Valley became a pioneer area for agricultural expansion into the high-elevation region of the Tibetan Plateau.