HR: 0800h
AN: B41C-0640    [Abstracts]
TI: Coarse woody debris dynamics: revisiting a boreal black spruce chronosequence
AU: * Bond-Lamberty, B
EM: bpbond@wisc.edu
AF: University of Wisconsin-Madison, Forest Ecology and Management 1630 Linden Drive #120, Madison, WI 53706, United States
AU: Gower, S T
EM: stgower@wisc.edu
AF: University of Wisconsin-Madison, Forest Ecology and Management 1630 Linden Drive #120, Madison, WI 53706, United States
AB: We re-visited a seven-stand boreal chronosequence west of Thompson, Manitoba, Canada, in which coarse woody debris (CWD) and its instantaneous decomposition were measured in 2000. New CWD levels and tree and snag fall rates were measured in 2007, and the resulting data used to evaluate how well CWD changes can be modeled using one- and three-pool decay class models. Thus this study compared three independent measures of decomposition (k): direct measurements of CWD respiration; rates based on a seven-year resampling effort; and rates inferred from the chronosequence progression itself. Measured CWD was between 3.3 and 80.4 Mg ha^-1, with the lowest and highest values in the 77- and 18-year-old stands, respectively. Spatial variability was high, and thus at most stands CWD levels had not changed significantly from 2000 to 2007. Snag fall rate varied by an order of magnitude, from 1.4% yr^-1 in the 43-year-old stand to 10.4% yr^-1 in the 12-year-old stand. A one-pool model based on these inputs underestimated actual 2000-2007 CWD decomposition, implying that fragmentation was at least as important a process as heterotrophic respiration; the mean overall k was 0.08 for most stands. The three-pool model was hampered by limited data on decay class transition rates and performed no better than the one-pool model. Although the computed k values implied a failure in chronosequence site selection for at least one site, the overall CWD trend was consistent with a larger number of sites surveyed in the region.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting