Regional paleofire regimes affected by non-uniform climate, vegetation and human drivers

English Abstract:

Climate, vegetation and humans act on biomass burning at different spatial and temporal scales. To date, much of our understanding of millennial-scale biomass burning in North America was gained from the analysis of pooled paleofire records at sub-continental to continental scales, which hinders the possibility of fully deciphering the importance of local- to regional-scale factors on fire. In this study, we used a dense network of sedimentary charcoal records from eastern North America to reconstruct a spatially explicit (regional scale) biomass burning history for different regions that were delineated using potential vegetation attributes. This high sampling resolution enabled us to discriminate the influence of climate, vegetation and humans on the Holocene Regional Biomass Burning (RegBB, last 7000 years). We found that a long-term decrease of regional biomass burning since 5000 years before present (BP) in the open coniferous/tundra forests, and dense coniferous forest, were primarily shaped by gradual establishment of less climate-conducive burning conditions (Neoglacial period). In the evergreen/deciduous mixed forests, both climate and vegetation shaped the long-term RegBB trajectories. Therein, an increasing relative proportion of flammable conifers in landscapes 3000 years BP contributed to maintaining RegBB constant despite climatic conditions less favourable for burning. In the temperate forest, the main driver of RegBB was climate and vegetation until the European colonisation, i.e. 300 years BP. This profoundly changed the fire activity in the temperate forest towards an unprecedented rise of RegBB with levels exceeding the Holocene range. Current climate change will likely modify biomass-burning activity in North American ecosystems, with different trajectories according to vegetation zones and dynamics, and human-induced ignitions.