Simulating the response of natural ecosystems and their fire regimes to climatic variability in Alaska

The dynamic global vegetation model MC1 was used to examine climate, fire, and ecosystems interactions in Alaska under historical (1922-1996) and future (1997-2100) climate conditions. Projections show that by the end of the 21st century, 75%-90% of the area simulated as tundra in 1922 is replaced by boreal and temperate forest. From 1922 to 1996, simulation results show a loss of about 9 g C(.)m(-2.)year(-1) from fire emissions and 360 000 ha burned each year. During the same period 61% of the C gained (1.7 Pg C) is lost to fires (1 Pg C). Under future climate change scenarios, fire emissions increase to 11-12 g C(.)m(-2.)year(-1) and the area burned increases to 411 000 - 481 000 ha(.)year(-1). The carbon gain between 2025 and 2099 is projected at 0.5 Pg C under the warmer CGCM1 climate change scenario and 3.2 Pg C under HADCM2SUL. The loss to fires under CGCM1 is thus greater than the carbon gained in those 75 years, while under HADCM2SUL it represents only about 40% of the carbon gained. Despite increases in fire losses, the model simulates an increase in carbon gains during the 21st century until its last decade, when, under both climate change scenarios, Alaska becomes a net carbon source.