Paleodata-informed modeling of large carbon losses from recent burning of boreal forests

Wildfires play a key role in the boreal forest carbon cycle1,2, and models suggest that accelerated burning will increase boreal C emissions in the coming century3 . However, these predictions may be compromised because brief observational records provide limited constraints to model initial conditions4 . We confronted this limitation by using palaeoenvironmental data to drive simulations of long-term C dynamics in the Alaskan boreal forest. Results show that fire was the dominant control on C cycling over the past millennium, with changes in fire frequency accounting for 84% of C stock variability. A recent rise in fire frequency inferred from the palaeorecord5 led to simulated C losses of 1.4 kg C m−2 (12% of ecosystem C stocks) from 1950 to 2006. In stark contrast, a small net C sink of 0.3 kg C m−2 occurred if the past fire regime was assumed to be similar to the modern regime, as is common in models of C dynamics. Although boreal fire regimes are heterogeneous, recent trends6 and future projections7 point to increasing fire activity in response to climate warming throughout the biome. Thus, predictions8 that terrestrial C sinks of northern high latitudes will mitigate rising atmospheric CO2 may be over-optimistic.
Kelly, R., H. Genet, A.D. McGuire, and F.S. Hu
Nature Climate Change