Document: RON-3-17-1

Potential impacts of global warming on U.S. ecosystems.

NEILSON, R.P.* ^1,2, D.BACHELET ², J.M.LENIHAN ² and R.J.DRAPEK ²

USDA Forest Service, Corvallis, Oregon, U.S.A. ¹
Oregon State University, Corvallis, Oregon, U.S.A ²

Abstract:
The Kyoto protocol has focused the attention of the public and policy makers on theearth s carbon budget. Previous estimates of the impacts of vegetation change have been limited to equilibrium snapshots and could not capture possible non-linear or threshold effects along its trajectory of change. New vegetation models have been designed to complement equilibrium models and simulate succession through time while estimating year-to-year variability in the carbon budget and responses to infrequent events such as drought and fire. Our objectives were: to use (1) the equilibrium model MAPSS to simulate potential vegetation at the end of the 21st century across a wide gradient oftemperature changes and (2) the dynamic vegetation model MC1 to simulate possible trajectories of vegetation change near the high and low ends of future temperature change. Results show that a moderate increase in temperature produces an increase in vegetation density and carbon sequestration across most of the U.S. with small changes in vegetation types. Large increases in temperature trigger losses of carbon with large shifts in vegetation types. In the western states, particularly southern California, precipitation and thus, vegetation density, increase and forests expand under all but the hottest scenarios. In the eastern U.S., particularly the Southeast, forests expand under the more moderate scenarios, but decline under more severe climate scenarios with catastrophic fires triggering rapid vegetation conversions from forest to savanna. The results suggest that there may be a threshold temperature, below which biosphere growth could slow climate change, but above which biosphere stress could release carbon and accelerate climate change. The threshold could be about mid-way in the range of possible future temperature increases. The timing of these changes is governed by the interannual and interdecadal variability inherent to the climate change scenario.

Keywords: global climate change, biogeography, carbon budget, MAPSS, MC1

This abstract is being presented at: 9:00 AM in session:
Symposium # 20: Global Change in Forests: Interactions Among Biodiversity, Climate and Land Use.