Original Article

International Journal of Biometeorology

, Volume 49, Issue 6, pp 377-387

First online:

Predicting the onset of net carbon uptake by deciduous forests with soil temperature and climate data: a synthesis of FLUXNET data

  • Dennis D. BaldocchiAffiliated withEcosystem Science Division, Department of Environmental Science, Policy and Management, University of California Email author 
  • , T. A. BlackAffiliated withFaculty of Agricultural Sciences, University of British Columbia
  • , P. S. CurtisAffiliated withDepartment of Evolution, Ecology & Organismal Biology, Ohio State University
  • , E. FalgeAffiliated withBayreuth University
  • , J. D. FuentesAffiliated withDepartment of Environmental Sciences, University of Virginia
  • , A. GranierAffiliated withINRA
  • , L. GuAffiliated withEnvironmental Science Division, Oak Ridge National Laboratory
  • , A. KnohlAffiliated withMax Planck Institute for BiogeochemistryPresent address: ESPM, University of California
  • , K. PilegaardAffiliated withRISOE
    • , H. P. SchmidAffiliated withDepartment of Geography, Indiana University
    • , R. ValentiniAffiliated withDepartment of Forest Science and Environment, Universita’ di Tuscia
    • , K. WilsonAffiliated withAtmospheric Turbulence and Diffusion Division, NOAA
    • , S. WofsyAffiliated withDepartment of Earth and Planetary Science, Harvard University
    • , L. XuAffiliated withEcosystem Science Division, Department of Environmental Science, Policy and Management, University of CaliforniaPresent address: LICOR
    • , S. YamamotoAffiliated withNational Institute of Advanced Industrial Science and Technology

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We tested the hypothesis that the date of the onset of net carbon uptake by temperate deciduous forest canopies corresponds with the time when the mean daily soil temperature equals the mean annual air temperature. The hypothesis was tested using over 30 site-years of data from 12 field sites where CO2 exchange is being measured continuously with the eddy covariance method. The sites spanned the geographic range of Europe, North America and Asia and spanned a climate space of 16°C in mean annual temperature. The tested phenology rule was robust and worked well over a 75 day range of the initiation of carbon uptake, starting as early as day 88 near Ione, California to as late as day 147 near Takayama, Japan. Overall, we observed that 64% of variance in the timing when net carbon uptake started was explained by the date when soil temperature matched the mean annual air temperature. We also observed a strong correlation between mean annual air temperature and the day that a deciduous forest starts to be a carbon sink. Consequently we are able to provide a simple phenological rule that can be implemented in regional carbon balance models and be assessed with soil and temperature outputs produced by climate and weather models.


Phenology Eddy covariance CO2 exchange Canopy photosynthesis