COS 13-4
Spatiotemporal trends in Alaska tundra fires over the Late Quaternary
Wildfires have been rare in the majority of Alaskan tundra during the past 60 years. However, recent burning in areas including Alaska’s North Slope and northwestern Alaska suggest that climate-driven increases in tundra burning may already be occurring. A shift to higher occurrence and increased severity of fires could potentially release large carbon stocks that have been accumulating in these ecosystems for thousands of years. Thus, the impact of climate change in tundra ecosystems will likely be most pronounced in regions historically characterized by infrequent fires, if these regions cross the climatic thresholds for burning in the future. Given the rarity of historic tundra burning, it is difficult to assess the novelty of recent burning in tundra ecosystems. To address this limitation, we place recent fire regimes in the context of past variability based on macroscopic charcoal from lake sediments. We reconstruct fire history from sites on the Alaskan North Slope, Yukon-Kuskokwim (YK) Delta, Ahklun Mountains, and southern Brooks Range to capture a broad range of climate and tundra-vegetation types. The long temporal span of these records (~9,500-35,000 years) allows for interpreting fire trends under varying climate conditions, refining our understanding of climate thresholds that may alter future fire regimes.
Results/Conclusions
Over the past 60 years, fires were more frequent in northwestern Alaska than the tundra regions in this study. Our records suggest that this modern spatial pattern in burning was similar through time, implying spatial differences in climate/vegetation controls have been the maintained for millennia. The most recent fire at our sites occurred between 880 and 12,450 years ago, highlighting the rarity of fires in these tundra regions. Fire reconstructions from southwestern Alaska are consistent with the paucity of modern fires, with the most recent fire ~7000 years ago at the YK Delta site and no burning at the Ahklun Mountain site over the Holocene. Fire frequency increased ~7500 years ago in the Brooks Range following the regional establishment of boreal forest and FRIs as low as ~1100 years/fire characterize the most arid period in the YK Delta record, suggesting tundra regions can support burning given suitable conditions. The North Slope records reveal FRIs of ~3000 and ~6500 years/fire, suggesting that further increases in burning will result in a profound change to the long-term stability of this region. Rare burning at all sites suggests future fires may release soil carbon that has been accumulating in these ecosystems for millennia.