Simulated response of conterminous United States ecosystems to climate change at different levels of fire suppression, CO₂ emission rate, and growth response to CO₂

Abstract

A modeling experiment was designed to investigate the impact of fire management, CO₂ emission rate, and the growth response to CO₂ on the response of ecosystems in the conterminous United States to climate scenarios produced by three different general circulation models (GCMs) as simulated by the MCl Dynamic General Vegetation Model (DGVM). Distinct regional trends in response to projected climatic change were evident across all combinations of the experimental factors. In the eastern half of the United States, the average response to relatively large increases in temperature and decreases in precipitation was an 11-percent loss of total ecosystem carbon. In the West, the response to increases in precipitation and relatively small increases in temperature was a 5-percent increase in total carbon stocks. Simulated fire suppression reduced average carbon losses in the East to about 6 percent, and preserved forests, which were largely converted to woodland and savanna in the absence of fire suppression. Across the West, unsuppressed fire maintained near constant carbon stocks despite increases in vegetation productivity. With fire suppression, western carbon stocks increased by 10 percent, and most shrublands were converted to woodland or even forest. With a relatively high level of growth in response to CO₂, total ecosystem carbon pools at the end of the century were on average about 9 to 10 percent larger in both regions of the United States compared to a low CO₂ response. The Western United States gained enough carbon to counter losses from unsuppressed fire only with the high CO₂ response, especially in conjunction with the higher CO₂ emission rate. In the Eastern United States, fire suppression was sufficient to produce a simulated carbon sink only with both the high CO₂ response and emission rate. Considerable uncertainty exists with respect to the impacts of global warming on the ecosystems of the conterminous United States, some of which resides in the future trajectory of greenhouse gas emissions, in the direct response of vegetation to increasing CO², and in future tradeoffs among different fire management options, as illustrated in this study.

Citation

Lenihan, James M.; Bachelet, Dominique; Neilson, Ronald P.; Drapek, Raymond. 2008. Simulated response of conterminous United States ecosystems to climate change at different levels of fire suppression, CO₂ emission rate, and growth response to CO₂. Global and Planetary Change. 64(1-2): 16-25