Upscaling Tundra CO2 Exchange from Chamber to Eddy Covariance Tower

Paul C. Stoy* Extrapolating biosphere-atmosphere CO2 flux observations to larger scales in space, part of Mathew Williams† the so-called ‘‘upscaling’’ problem, is a central challenge for surface-atmosphere exchange Jonathan G. Evans‡ research. Upscaling CO2 flux in tundra is complicated by the pronounced spatial variability Ana Prieto-Blanco§ of vegetation cover. We demonstrate that a simple model based on chamber observations with a pan-Arctic parameterization accurately describes up to 75% of the observed temMathias Disney§ poral variability of eddy covariance–measured net ecosystem exchange (NEE) during the Timothy C. Hill# growing season in an Abisko, Sweden, subarctic tundra ecosystem, and differed from NEE Helen C. Ward‡@ observations by less than 4% for the month of June. These results contrast with previous studies that found a 60% discrepancy between upscaled chamber and eddy covariance Thomas J. Wade† and NEE sums. Sampling an aircraft-measured normalized difference vegetation index (NDVI) Lorna E. Street% map for leaf area index (L) estimates using a dynamic flux footprint model explained less *Corresponding author: Department of Land of the variability of NEE across the late June to mid-September period, but resulted in a Resources and Environmental Sciences, lower root mean squared error and better replicated large flux events. Findings suggest Montana State University, Bozeman, Montana that ecosystem structure via L is a critical input for modeling CO2 flux in tundra during 59717, U.S.A. [email protected] the growing season. Future research should focus on quantifying microclimate, namely †School of GeoSciences, University of photosynthetically active radiation and air temperature, as well as ecosystem structure via Edinburgh, Edinburgh, EH9 3JN, U.K. ‡Centre for Ecology & Hydrology, L, to accurately model growing season tundra CO2 flux at chamber and plot scales. Wallingford, OX10 8BB, U.K. §Department of Geography, University College London, Gower Street, London, WC1E 6BT, U.K. #School of Geography & Geosciences, University of Saint Andrews, Saint Andrews, KY16 9AL, U.K. @Department of Geography, King’s College London, London, WC2R 2LS, U.K. %School of Biological Sciences, Bangor University, Bangor, Gwynedd, LL57 2UW, U.K. DOI: http://dx.doi.org/10.1657/1938-4246-45.2.275