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

Abstract. The Altai-Sayan Mountains and adjacent plains have experienced accelerated warming in recent decades, heightening concerns about escalating fire risks. However, critical knowledge gaps persist regarding paleofire dynamics in western Mongolia and comprehensive regional syntheses of biomass burning patterns across the Altai-Sayan ecoregion. Addressing these gaps is essential for understanding vegetation resilience under projected environmental changes and disturbance regimes. This study reconstructs the Holocene fire sequence in the steppe region of western Mongolia and systematically elucidates the spatiotemporal variations in biomass burning across different vegetation zones of the Altai-Sayan Mountains and adjacent plains, as well as their coupling relationships with forest community structure. The results demonstrate that the declining biomass burning since the Holocene has been primarily controlled by temperature-mediated variations in woody biomass above the forest limit in the central Altai Mountains, while in the western Sayan and northern Altai Mountains, it stems from significant reductions in combustible components (Larix, Abies and Picea). Notably, a marked resurgence of biomass burning has been observed since ~4 cal. kyr BP in multiple regions associated with archaeological cultural complexes. This intensification of fire activity during the late Holocene predominantly occurred in two types of previously low-fire-risk areas: 1) regions where excessive moisture and cold climate inhibited sufficient fuel accumulation (e.g., the West Siberian Plain and mountain taiga zones of the Altai Mountains), and 2) arid environments where steppe/desert-steppe vegetation failed to maintain continuous combustible substrates. Since ~2 cal kyr BP, intensified anthropogenic disturbances including agricultural expansion and pastoral activities have significantly increased surface fire frequency in the southeastern/western and northern Altai Mountains, West Siberian Plain, and forest zones of the central Altai Mountains. In contrast, the dramatic decline in biomass burning observed in the Khangai Mountains may be closely linked to vegetation fragmentation induced by overgrazing. This research clarifies the long-term feedback mechanisms between biomass burning processes and forest community structure across different vegetation zones. The findings hold significant scientific value for understanding human-fire-ecosystem interactions in the arid Central Asia, while offering historical references for regional sustainable ecological management.