Drying Spring Accelerates Transitions Toward Pyrogenic Vegetation in Eastern Boreal North America

The ongoing climate change increases vegetation flammability in the boreal forests of eastern North America, leading to more intense and severe wildfires. Using palaeoecological data-including charcoal, pollen, chironomids and testate amoebae-and climate model simulations of vapour pressure deficit (VPD) and available soil water (ASW), we analysed fire dynamics over the past 8000 years in boreal eastern North America. Over the last 4000 years, and particularly in the last 250 years, increasing spring drought has led to fewer, but more severe fires. This shift in the fire regime has favoured the spread of fire-adapted conifer species, particularly jack pine (Pinus banksiana), across the landscape. We infer that the predicted increase in VPD and decrease in ASW triggered by climate change will alter the fire regime and amplify the transition toward more pyrogenic vegetation within the boreal forest of eastern North America, with ecological and socio-economic consequences.