Drivers of prehistoric cultural evolution in the Chengdu Plain: Fire events and environmental changes during the middle and late Holocene

The Chengdu Plain (CDP), located in the upper reaches of the Yangtze River and recognized as one of the cradles of ancient Chinese civilization, is closely associated with the ancient Shu culture. While previous studies have extensively explored the relationship between environmental disasters and cultural evolution in the CDP, the impact of paleofire events remains insufficiently examined. This study provides a comprehensive analysis of charcoal particles across various size (0–30, 30–50, 50–125, and > 125 μm) from sediment samples collected at the Baodun and Majie sites in the CDP. Key findings include: (1) Minimal paleofire activity is evident between 6200 and 5100 cal. a BP, aligning with low levels of human occupation. After 5100 cal. a BP, anthropogenic fire activity notably increased, associated with practices such as slash-and-burn agriculture, pottery production, bronze smelting, ritual activities, warfare, and social conflicts. (2) Large-scale fires corresponded closely with abrupt climatic shifts. An expansion of herbaceous vegetation likely contributed to heightened fire frequencies, particularly of local fires after 4500 cal. a BP, indicating that climatic conditions significantly influenced fire regimes alongside changing vegetation patterns. (3) High charcoal concentrations in the late phases of earlier cultural periods correlate with later settlements located at higher elevations and greater distances from rivers. Shifts in settlement orientation, with eastern-facing settlements showing lower average charcoal concentrations and westward-facing settlements exhibiting increased charcoal deposition, suggest changes in fire exposure related to settlement locating choices. (4) The decline of the Sanxingdui and Jinsha-Shierqiao cultures appears to be primarily driven by natural disasters, rather than solely by climate-induced environmental changes. However, in other periods, a strong correlation between climatic fluctuations and cultural transitions underscores the complex interplay between environmental dynamics and human adaptation strategies.