Abstract:

Fire disturbance is a key driver of ecological succession in grassland ecosystems. As a critical component of the Eurasian steppe, the grassland belt of the western Tianshan Mountains bears the imprint of historical agropastoral interactions and serves as an ideal region for investigating the combined mechanisms of fire disturbance, climate, vegetation, and human activities in the arid and semi-arid zones dominated by westerlies. However, quantitative reconstructions of key fire-regime parameters (e.g., fire frequency, fire return interval, fire episodes, and peak magnitude) over the past 5000 years remain limited across the vast grassland systems of northwest China. To fill this gap, based on four charcoal particle-size categories (10-30 μm, 30-50 μm, 50-100 μm, and >100 μm) from a sediment core in Wenquan County, combined with multi-proxy evidence, the quantitative paleofire evolution patterns across different spatiotemporal scales and their response mechanisms to environmental changes we revealed. The results indicated that (1) Regional fire episodes dominated in Wenquan County, with herbaceous plants serving as the primary fuel source. (2) Paleofire evolution in Wenquan County exhibited four distinct phases: A low-activity phase (5000—4500 cal a BP), a development phase (4500—3700 cal a BP), a decline phase (3700—2600 cal a BP), and a high-frequency fluctuation phase (2600—746 cal a BP). (3) Fire regime in Wenquan County was primarily regulated by moisture-mediated fuel availability, driven by synergistic interactions between increasing humidity, grass productivity, fuel loads, and favorable weather conditions during the fire season. (4) Human activities contributed to frequent fire episodes through periodic slash-and-burn events associated with prehistoric agropastoral expansion, as well as land reclamation and oasis agriculture during historical periods.

Key words: fire-regime, charcoal, climate change, human activities, western Tianshan Mountains