Possible role of the regional NDVI in the expansion of the Chiefdom of Lijiang during the Ming Dynasty as reflected by tree ring

Abstract

Although many studies have linked complex social processes with climate change, few have examined the connections between changes in environmental factors, resources, or energy and the evolution of civilizations on the Tibetan Plateau. The Chiefdom of Lijiang was a powerful chiefdom located on the eastern Tibetan Plateau during the Ming Dynasty; it began expanding after the 1460s. Although many studies have analyzed the political and economic motivations responsible for this expansion, no high-resolution climate records representing this period of the Chiefdom of Lijiang were available until now. Here, we obtain a 621-year reconstruction of the April-July normalized difference vegetation index (NDVI) values derived from moisture-sensitive tree rings from the eastern Tibetan Plateau. Our NDVI reconstruction accounts for 40.4% of the variability in instrumentally measured NDVI values and can effectively represent the historical changes in regional vegetation productivity that occurred on the eastern Tibetan Plateau. In combination with a reconstruction of summer temperatures on the eastern Tibetan Plateau, these results reveal that the regional climate was relatively warm and persistently wet during the period 1466-1630. This period was characterized by long periods of above-mean vegetation productivity on the eastern Tibetan Plateau that coincided with the expansion of the Chiefdom of Lijiang. We therefore propose that the NDVI anomaly and associated favourable political environment may affected the expansion of the Chiefdom of Lijiang. Instrumental climate data and tree rings also reveal that the early 21st-century drought on the eastern Tibetan Plateau was the hottest drought recorded over the past six centuries, in accordance with projections of warming over the Tibetan Plateau. Future climate warming may lead to the occurrence of similar droughts, with potentially severe consequences for modern Asia.