Holocene fire regimes across the Altai-Sayan Mountains and adjacent plains: interaction with climate and vegetation types

Abstract. The Altai-Sayan Mountains and adjacent plains (including the west Siberian Plain, Kazakhstan Hills and Junggar Basin) have experienced accelerated warming in recent decades, raising growing concerns about escalating wildfire risks. However, two key gaps hinder understanding: paleofire dynamics in western Mongolia are understudied and no comprehensive regional synthesis exists for charcoal influx across the Altai-Sayan ecoregion. To address this, we reconstructed the Holocene fire sequence in western Mongolia and analyzed the spatiotemporal variations in charcoal influx across different vegetation zones of the Altai-Sayan Mountains and adjacent plains, as well as their coupling relationships with vegetation structure. The results reveal that Holocene declines in charcoal influx were driven by distinct mechanisms across subregions: above the forest limit in the central Altai Mountains, the decline was primarily controlled by temperature-limited woody biomass availability; in the western Sayan Mountains, it stemmed from the substantial expansion of fire-resistant P. sylvestris. Since ∼ 2 cal. kyr BP, intensified anthropogenic disturbances – pecifically agricultural expansion and pastoral activities – have significantly increased fire frequency in the southeastern, western and northern Altai Mountains, the west Siberian Plain and the forest zones of central Altai Mountains. Conversely, the marked decline in charcoal influx observed in the Khangai Mountains may be closely associated with vegetation fragmentation caused by overgrazing. Our findings provide a long-term perspective on fire-vegetation- climate interactions, offering critical insights for sustainable land management in the Altai-Sayan ecoregion.