Oregon State University

Accounting for canopy coupling improves NEE estimates in dense, tall forests

New framework to compute NEE in dense forestsNew publication: A new paper by Thomas et al. published in Agricultural and Forest Meteorology describes a novel approach of how to improve annual and seasonal estimates of net ecosystem exchange (NEE) of carbon dioxide by analyzing the degree of communication of air between the sub-canopy, canopy, and above-canopy air layers. Particularly dense forests suffer from persistent decoupling between these air layers because of the dense foliage acting as a mechanical barrier, but also because of the low wind speeds suppressing turbulent motions that mix the air. Using year-round observations of the flow, turbulence, and carbon and water fluxes at two levels collected at a Douglas-Fir site in Oregon's Coast Range over a period of 6 years we developed a framework and an associated set of equations to derive biologically meaningful NEE estimates for these dense forests, which are underrepresented in global analysis. The novelty of this framework is to indirectly account for advective losses of ecosystem respiration, which act to overpredict the net carbon uptake, when the layers are decoupled. The NEE estimates from this improved framework reduce the carbon sink strength of this high-leaf area index forest by approximately 50 % compared to estimates from traditional single-level observations and data processing.

The full citation is:

Thomas, C.K., Martin, J.G., Law, B.E., Davis, K., 2013. Toward biologically meaningful net carbon exchange estimates for tall, dense canopies: multi-level eddy covariance observations and canopy coupling regimes in a mature Douglas-fir forest in Oregon. Agric. For. Meteorol. 173, 14–27. DOI:10.1016/j.agrformet.2013.01.001

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