Convergence and divergence of Holocene fire regimes and vegetation dynamics on hills and in the Clay Belt of northwestern Quebec

The role of topography in long-term climate–fire–vegetation nexuses remains understudied, particularly in the boreal mixedwood lowlands of eastern Canada due to limited accessibility and scarcity of lake-sediment archives on hills. Yet, reconstructing paleoenvironmental conditions on hills is essential to understand long-term boreal landscape dynamics along the entire elevation gradient. We reconstructed fire activity and vegetation dynamics during the Holocene on hills in northwestern Quebec (Canada). To do so, we analyzed sedimentary charcoal particles and pollen grains from two lakes located above 460 m a.s.l. on the Abijévis Hills of Aiguebelle National Park. We then compared our fire and vegetation reconstructions with paleo-records from previous lake-sediment studies conducted on other hills and in the lowlands across the boreal mixedwood forest of the Abitibi Clay Belt region. The earliest pollen-based evidence of vegetation was recorded on hilltops around 9,900 cal. yr BP, when hills formed islands within proglacial Lake Ojibway. Fire activity began a few centuries later, before the drainage of Lake Ojibway, as revealed by increased charcoal accumulation rates. Low tree density and limited fuel availability during the early Holocene open woodland phase constrained fire activity to low levels. Fire occurrence increased after 6,500 cal. yr BP during the mid-Holocene in pine –dominated forests, and during the late Holocene in spruce–moss forests. In the lowlands, fire activity began ca. 8,000 cal. yr BP, after the drainage of Lake Ojibway. Fire frequency remained lower than on hills during the mid-Holocene, before it increased from 5,000 to 1,000 cal. yr BP. Throughout the Holocene, vegetation dynamics diverged between hills and lowlands, except for Pinus strobus , whose long‑term abundance patterns were correlated between both landscapes. Nevertheless, Pinus spp. was consistently more abundant on hills, whereas Cupressaceae and Alnus incana subsp. rugosa were more abundant in the lowlands. We have shown that topography had a predominant role in shaping Holocene fire regimes and vegetation composition in northwestern Quebec’s boreal mixedwood forests. Hills were generally more fire prone, especially between 8,400 and 4,200 cal. yr BP, likely reflecting drier fuel conditions and greater exposure associated with elevated topography. Cooler and drier conditions during the late Holocene reduced the difference in fire regimes between hills and lowlands, as the occurrence of high-severity fires increased in the lowlands. A French abstract is provided in the SI.