Forest floor CO2 fluxes estimated by eddy covariance and chamber-based model

An intercomparison study of two methods for estimating forest soil CO2 effl ux was conducted during a 3-week period in summer. An empirical model estab lished from nearly 2 years of chamber measurements predicted that the soil CO2 efflux ranged from 1.2 to 1.4 mu mol m(-2) s(-1). This small range was due to the lack of variability in the model parameters (soil temperature an d moisture) during the study period. Eddy covariance measurements showed mo re variability and diurnal dependence. Turbulent fluxes of CO2 during the d ay apparently were influenced by the presence of a moss layer on the forest floor; the combined effects of moss photosynthesis and respiration reduced the turbulent fluxes by an average of 0.6 mu mol m(-2) s(-1) relative to t he modeled soil efflux. At night, the eddy fluxes of CO2 agreed well with t he modeled soil efflux; however, the turbulent fluxes were highly variable (standard deviation exceeding the mean), due to the imperfect sampling cond itions associated with the nocturnal boundary layer. These results illustra te the different processes measured by the two methods, and highlight some of the limitations of the eddy covariance technique for estimating soil CO2 efflux. Finally, they demonstrate the need for more long-term intercompari son studies, covering a broader range in soil temperature and moisture. (C) 2001 Elsevier Science B.V. All rights reserved.