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Factors controlling CO2 exchange on timescales from hourly to decadal at Harvard Forest
Fire Sciences Laboratory, Rocky Mountain Research Station, USDA Forest Service, Missoula, Montana, USA
Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, Wisconsin, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, Wisconsin, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Atmospheric Sciences Research Center, State University of New York at Albany, Albany, New York, USA
Atmospheric Sciences Research Center, State University of New York at Albany, Albany, New York, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
We analyzed 13 years (1992−2004) of CO2 flux data, biometry, and meteorology from a mixed deciduous forest in central Massachusetts. Annual net uptake of CO2 ranged from 1.0 to 4.7 Mg-C ha−1yr−1, with an average of 2.5 Mg-C ha−1yr−1. Uptake rates increased systematically, nearly doubling over the period despite forest age of 75–110 years; there were parallel increases in midsummer photosynthetic capacity at high light level (21.5−31.5 μmole m−2s−1), woody biomass (101−115 Mg-C ha−1 from 1993−2005, mostly due to growth of one species, red oak), and peak leaf area index (4.5−5.5 from 1998–2005). The long-term trends were interrupted in 1998 by sharp declines in photosynthetic capacity, net ecosystem exchange (NEE) of CO2, and other parameters, with recovery over the next 3 years. The observations were compared to empirical functions giving the mean responses to temperature and light, and to a terrestrial ecosystem model (IBIS2). Variations in gross ecosystem exchange of CO2 (GEE) and NEE on hourly to monthly timescales were represented well as prompt responses to the environment, but interannual variations and long-term trends were not. IBIS2 simulated mean annual NEE, but greatly overpredicted the amplitude of the seasonal cycle and did not predict the decadal trend. The drivers of interannual and decadal changes in NEE are long-term increases in tree biomass, successional change in forest composition, and disturbance events, processes not well represented in current models.
Received 21 August 2006; accepted 17 January 2007; published 9 May 2007.
Citation: (2007), Factors controlling CO2 exchange on timescales from hourly to decadal at Harvard Forest, J. Geophys. Res., 112, G02020, doi:10.1029/2006JG000293.
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