HR: 0800h
AN: B11D-0761    [Abstracts]
TI: Interactive effects of fire, soil climate, and vegetation on CO₂ fluxes in an upland black spruce forest and peatland in interior Alaska
AU: * O'Donnell, J A
EM: ftjao1@uaf.edu
AF: University of Alaska Fairbanks Department of Biology and Wildlife, 211 Irving I, Fairbanks, AK 99775, United States
AU: Turetsky, M R
EM: mrt@msu.edu
AF: Michigan State University, Department of Plant Biology, East Lansing, MI 48824, United States
AU: Harden, J W
EM: jharden@usgs.gov
AF: USGS, 345 Middlefield Rd. ms 962, Menlo Park, CA 94025, United States
AU: Manies, K L
EM: kmanies@usgs.gov
AF: USGS, 345 Middlefield Rd. ms 962, Menlo Park, CA 94025, United States
AU: Pruett, L E
EM: lpruett@usgs.gov
AF: USGS, 345 Middlefield Rd. ms 962, Menlo Park, CA 94025, United States
AB: Fire is an important control on the carbon (C) balance of the boreal forest. In addition to the immediate release of stored C to the atmosphere through organic matter combustion, fire has the capacity to alter controls on decomposition, through changes in soil climate and substrate quality. Here, we present findings from two complimentary studies that examine how fire modifies the physical properties of soil and how these modifications influence rates of decomposition and C exchange in Alaska's boreal forest. First, we conducted a laboratory study to evaluate the interactive effects of fire, soil temperature, soil moisture, and moss type on CO2 fluxes from organic soils. Second, we conducted intensive field measurements of ecosystem CO₂ fluxes in a 3 year-old burn to evaluate the effect of fire on carbon exchange in an upland forest and peatland in interior Alaska. Incubation CO₂ fluxes showed a significant interaction between burn status (burned, unburned sites), temperature (2 °C vs. 20 °C treatments), and moisture treatment (field moisture vs. saturated). Incubation CO₂ fluxes in the unburned sites increased with temperature by a factor of 5 and 29, whereas incubation CO₂ fluxes in the burned sites only increased by 6 to 8 times. Incubation CO₂ fluxes in the unburned sites increased with moisture content between 19 and 24 times, whereas incubation CO₂ fluxes in the burned sites only increased by a factor of 4. Incubation CO₂ fluxes from unburned Sphagnum samples were nearly 3 times greater than fluxes from burned Sphagnum. In the field At 3 years post-burn, moisture content was higher in the burned upland forest and burned peatland relative the unburned sites. However, soil temperature was not significantly different between burned and unburned sites. Mean rates of net ecosystem exchange (NEE) showed greater rates of CO₂ uptake in the unburned peatland site than in the burned peatland, averaging -1.51 and 0.16 g C m^-2 d^-1, respectively. NEE rates were not significantly different in the two upland forest sites, averaging 0.0005 g C m^-2 d^-1 across sites. Mean rates of ecosystem respiration (ER) were not significantly different between the burned and unburned upland forest sites, averaging 0.9 g C m^-2 d^-1 overall. ER rates were not different between the burned and unburned peatland sites, averaging 1.4 m^-2 d^-1 overall. Soil temperature and moisture content accounted for between 20 to 45 % of the variation in ER rates in unburned upland forest and unburned peatland, and less than 10 % in the two burned sites. These findings, together with the incubation study, suggest that while fire creates soil climate conditions more conducive to rapid decomposition, rates of C release from soils may be constrained following fire by changes in litter quality that slow rates of decomposition.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting