Document: PET-3-34-56

Comparison of biometric and eddy-covariance based estimates of annual Net Ecosystem Production in a northern hardwood forest ecosystem.

CURTIS, P.S.* ^1,2, C.S.VOGEL ², H.PETER SCHMID ³, H.SU ³, B.D.BOVARD ¹ and A.E.HARTLEY ¹

The Ohio State University, Columbus OH 43210 USA ¹
The University of Michigan Biological Station, Pellston MI 49769 USA ²
Indiana University, Bloomington IN 47405 USA ³

Abstract:
Understanding the dynamics of net carbon exchange by forest ecosystems is important for improving models of the global carbon cycle and for verifying changes in forest carbon stores, as required under the terms of the Kyoto Protocol. At the University of Michigan Biological Station we have initiated a long-term program of research into mass and energy exchange by the surrounding mixed hardwood forest using a combination of biometric (e.g., inventory and ecophysiological measurements) and micrometeorological (eddy-covariance) approaches. Results from the first full year of measurements, January 1999 December 1999, show an ecosystem that is either losing significant amounts of C (biometry based) or gaining C (eddy-covariance based). Carbon budget components based on biometric measurements were 3,183 kg C ha^-1 yr^-1 net aboveground production, 1,869 kg C ha^-1 yr^-1 net belowground production, and 11,560 kg C ha^-1 yr^-1 total soil respiration. Based on a soil trenching experiment we estimated soil heterotrophic respiration to be ca. 75% of total soil respiration, or 8,670 kg C ha^-1 yr^-1. This budget indicates a net loss from the ecosystem of ca. 3,618 kg C ha^-1 yr^-1. It is unlikely that unaccounted for C fluxes such as losses by herbivory, volatilization or leaching contributed significantly to the annual net C exchange. Ecosystem cumulative net C exchange based on preliminary eddy-covariance data suggest an annual uptake by this forest of approximately 2,000 kg C ha^-1 yr^-1. The magnitude of belowground C fluxes and local advection of CO₂ are among the key uncertainties affecting these different estimates.

Keywords: carbon budget, net ecosystem productivity, eddy-covariance

This abstract is being presented at: 3:30 PM in session:
CLIMATE CHANGE