HR: 1330h
AN: B22A-0792    [PDF]
TI: Estimation of leaf-level contribution to total stand net ecosystem exchange along a boreal forest chronosequence
AU: * Litvak, M
EM: mlitvak@mail.utexas.edu
AF: University of Texas, 1 University Station A6700 316 Bio Labs, Austin, TX 78712-0183 United States
AU: Goulden, M
EM: mgoulden@uci.edu
AF: University of California, Irvine, Earth System Science, Irvine, CA 92697-3100 United States
AU: Miller, S
EM: sdmiller@uci.edu
AF: University of California, Irvine, Earth System Science, Irvine, CA 92697-3100 United States
AU: Elliot, J
EM: jrelliot@cnr.colostate.edu
AF: Colorado State University, College of Natural Resources, Fort Collins, CO 80523-1472 United States
AB: Quantifying the role of recovery from fire in stand level carbon dynamics is critical to estimate the current and future contribution of boreal ecosystems to the global carbon cycle. We have been using tower-based eddy covariance to measure net ecosystem exchange (NEE) above 6 black spruce stands that range in age from 5 to 170 years post-burn in central Manitoba since 2001. Here we explore to what extent stand-level patterns in NEE can be explained by changes in leaf-level physiology as community composition and structure vary through succession following wildfire. We combined ecological measures of the dominant plant functional groups in each stand (forbs, deciduous shrubs, deciduous canopy trees, coniferous trees) with leaf-level physiological measurements to calculate the contribution each plant functional group makes to overall stand NEE. From light response curves measured on the dominant canopy and forest floor species in each stand, total leaf area index of each species, above and below canopy PAR, and tower-based eddy covariance measurements we determined the contribution of each functional group to stand NEE in discrete intervals throughout the day. Despite large differences in ecosystem structure, peak summer daytime net CO$_{2}$ uptake rates were surprisingly similar across the chronosequence. Above the 5, 13, 20, 73, 160 year old stands peak values for daytime NEE were -16, -13, -18, -15 and -15 $\mu$ mol m$^{-2}$ s$^{-1}$, respectively. As these boreal stands regenerate, high densities of plant functional groups with high photosynthetic capacities (i.e. fireweed: light-saturated photosynthetic rate (A$_{max}$) = 16.5 $\mu$ mol m$^{-2}$ s$^{-1}$; quantum yield = 0.05) are replaced by plant functional groups with low photosynthetic capacity (black spruce: A$_{max}$ = 4.4 $\mu$ mol m$^{-2}$ s$^{-1}$, quantum yield=0.014). A consequence of this shift in community structure is that the leaf-level contribution to peak daytime NEE remains relatively consistent across the chronosequence.
DE: 0400 Biogeosciences
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 1851 Plant ecology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting