Fire activity in the northern Arctic tundra now exceeds late Holocene levels, driven by increasing dryness and shrub expansion

Abstract

Tundra ecosystems are characterized by small, rare and infrequent fires due to cold, often waterlogged conditions, and limited biomass. However, ongoing climate warming and drying in northern soils and peatlands are contributing to increasingly frequent and extensive wildfires. To place recent fire regimes in the context of long-term variability and to better understand interactions between fire, moisture, and vegetation, we reconstructed wildfire history over the past 3000 years using a network of charcoal, vegetation, and hydrological records in combination with satellite-derived fire datasets from northern Arctic Alaska peatlands. The composite charcoal record shows minimal fire activity from ĝ1/4 1000 BCE to 1000 CE, followed by a modest increase between 1000 and 1200 CE, and then a renewed decline. This long-term pattern shifted abruptly after 1900 CE, reaching its maximum between 1950 and 2015 CE, when fire activity exceeded any levels observed in the preceding three millennia. Individual charcoal records show a spatially heterogeneous pattern in fire occurrence before 1950 CE, and a more homogeneous one thereafter. Our findings suggest that the deepening of water tables and peatland drying associated with permafrost thaw have facilitated woody encroachment, especially by more flammable Ericaceous shrubs. These vegetation changes have increased fuel availability and flammability, ultimately driving the recent surge in wildfire activity, highlighting the growing vulnerability of Arctic tundra ecosystems to fire. We also found that the charcoal source area of our tundra fire reconstruction encompasses broader landscapes over tens of kilometres. Our study emphasizes the significance of long-term, multidisciplinary research in documenting moisture-vegetation-fire feedbacks that influence tundra fire regimes. Ultimately, this long-term fire dynamic study provides critical context for evaluating recent changes and incorporating tundra peatland fire risk into global climate mitigation strategies.