Ecosystem CO2 flux over two growing seasons for a sub-Boreal clearcut 5 and 6 years after harvest

We measured the ecosystem-level growing season CO2 fluxes for a 6-year-old vegetated sub-Boreal clearcut from 24 May to 20 September 2000, and compared the results to CO2 fluxes from the same clearcut in 1999 (27 June–3 September). Two independent approaches were used to measure ecosystem CO2 flux for both years. A Bowen ratio energy balance (BREB) method was contrasted with a second approach using component fluxes. The Component model approach was based on scaling up from regressions relating in situ CO2 flux measurements for conifer seedlings (Picea glauca × engelmannii), as well as representative herbaceous (Chamerion angustifolium), woody (Lonicera involucrata) plant species and soil surface CO2 efflux to microclimate conditions. The BREB method and Component model estimated the clearcut to be a source of CO2 6 years post-harvest (24 May–20 September 2000) in amounts of 142 g C m−2 (1.4 t ha−1) and 103 g C m−2 (1.0 t ha−1), respectively. The positive net ecosystem CO2 fluxes over the growing season resulted from a large soil surface CO2 efflux (686 g C m−2) that surmounted the photosynthetic CO2 uptake for the clearcut. The photosynthetic CO2 uptake partially compensated for the soil surface losses: the conifer seedlings, herbaceous plants and woody shrubs were estimated to uptake −96, −315, −172 g C m−2, respectively.