HR: 0800h
AN: B31A-04    [Abstracts]
TI: Three General Circulation Model Projections Effects on Forests in the US Northern Rocky Mountains using Biome-BGC
AU: * Boisvenue, C
EM: celine@ntsg.umt.edu
AF: Numerical Terradynamic Simulation Group, Dept.Ecosystem and Cons.Sc. College of Forestry and Conservation University of Montana , Missoula, MT 59812, United States
AU: Running, S W
EM: swr@ntsg.ume.edu
AF: Numerical Terradynamic Simulation Group, Dept.Ecosystem and Cons.Sc. College of Forestry and Conservation University of Montana , Missoula, MT 59812, United States
AB: Most projected climate scenarios over the next century generally agree that temperature will increase (IPCC, et al. 2007) and although the Intergovernmental Panel for Climate Change (IPCC) Fourth Assessment Report (AR4) confirms an improved understanding of precipitation patterns with projected increases in the amount of precipitation at high-latitudes, General Circulation Model (GCM) precipitation projections are still widely variable. This study explores the effects of three GCM temperature and precipitation projections, on six forested sites in the US Northern Rocky Mountains using the process-based model Biome-BGC. The first GCM projects a warmer and much wetter climate than the present day, the second, a slightly wetter and warmer climate, and the third, a dry/hot climate compared to the present day. Our results show that across most sites and all GCM projections, growing season length increases, the number of days where snow is present on site decreases and the number of water stress days increases between 2005 and 2089. Although productivity measures generally exhibit slow increases across the time series, the driest and hottest GCM projections resulted in five of our six sites becoming carbon sources by the end of the projection period, as opposed to only one site becoming a source with the two other GCM projections. At a relative site scale, total carbon on sites under the drier/hotter model projections, either declines rapidly or shows a much slower rate of accumulation as compared to the two other projections, suggesting a temperature and precipitation tipping point in site carbon accumulation. These results show that despite an apparently unilateral increase in growing season and water stress, and decline in snow water, there are important differences in outcome depending on precipitation level and the amplitude of temperature increases. These may, on one side of the scales, drive forest systems towards rapid declines in productivity and make these systems carbon sources as opposed to carbon sinks.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0495 Water/energy interactions (1878)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly