HR: 0800h
AN: B21B-1025    [Abstracts]
TI: Widespread Dieback of Forests in North America under Rapid Global Warming: Response to the VINCERA Future Climate Scenarios Simulated by the MC1 DGVM
AU: * Lenihan, J
EM: lenihan@fsl.orst.edu
AF: USDA Forest Service, PNW Research Station 3200 SW Jefferson Way, Corvallis, OR 97330 United States
AU: Neilson, R
EM: neilson@fsl.orst.edu
AF: USDA Forest Service, PNW Research Station 3200 SW Jefferson Way, Corvallis, OR 97330 United States
AU: Bachelet, D
EM: bachelet@fsl.orst.edu
AF: Department of Bioengineering, Oregon State University, Corvallis, OR 97330 United States
AU: Drapek, R
EM: drapek@fsl.orst.edu
AF: USDA Forest Service, PNW Research Station 3200 SW Jefferson Way, Corvallis, OR 97330 United States
AB: The VINCERA project is an intercomparison among three dynamic general vegetation models (DGVMs) simulating the response of North American ecosystems to six new future climate scenarios. The scenarios were produced by three general circulation models, each using two different future trace gas emissions scenarios. All of the scenarios are near the warmer end of the Intergovernmental Panel on Climate Change's projected future temperature range. Here we present results from the MC1 DGVM. All major forested ecosystems in North America exhibit carbon sequestration until the late 20th or early 21st century, followed by a drought induced decline and loss of carbon to levels below those at 1900 in the absence of fire suppression. By the end of the 21st century, the entire continent will have lost from 10 to 30 Pg of carbon, depending on the scenario. However, fire suppression can significantly mitigate carbon losses and ecosystem declines, producing a net change in carbon from a loss of about 5 Pg to a gain of about 8 Pg under the different scenarios. Most of the suppression benefits are obtained by forests in the western U.S. Suppression also mitigates carbon losses and conversions to savanna or grassland in the eastern U.S., but forest decline still occurs in the east under all scenarios. Dieback is triggered by two mechanisms. Reduced regional precipitation, variable among the scenarios, is one. The second more pervasive mechanism is the influence of rising temperatures on evapotranspiration. Even with the benefits of enhanced water use efficiency from elevated CO2 and slight increases in precipitation, dramatic increases in temperature can produce widespread forest dieback, and increases in fire severity. The eastern United States appear to be particularly vulnerable, as does the central Canadian boreal forest because of the relative flatness of climate gradients near ecotones. Under some scenarios, dieback is also driven by both increasing temperatures and decreasing precipitation, most notably the southeastern and northwestern United States. Following a period of gradual carbon sequestration, the enhanced evapotranspiration appears to overtake the 'greening' processes producing a rapid dieback. The point of turnaround from greenup to dieback occurs about now for the temperate forests and about a decade from now in the boreal forests, initiating an extended period of rapid losses of ecosystem carbon. These results underscore the critical importance of addressing uncertainties with respect to ecosystem water balance and the direct effects of elevated CO2 concentrations.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0466 Modeling
DE: 0495 Water/energy interactions (1878)
SC: Biogeosciences [B]
MN: Fall Meeting 2005