Fluxes of carbon dioxide and water vapour over Scots pine forest and clearing

The carbon dioxide and water vapour fluxes were measured by the eddy covariance (EC) technique from July to September 2000 at two closely located sites in southern Finland: over a 38-year-old pine forest and over a 5-year-old forest clearing. The night-time respiration was of the same magnitude at both sites. At day-time the pine forest was a strong sink but the clearing close to CO2 balance, indicating that CO2 uptake of ground vegetation over the clearing balanced the release from the soil. The shoot scale gas exchange measurements in combination with process-based modelling were used to evaluate the measured CO2 exchange of the forest ecosystem. The forest CO2 exchange was explained by soil respiration and photosynthesis of forest canopy, while the contribution of understory and ground vegetation CO2 exchange could be neglected. During the study period the forest was a net sink of CO2 and the clearing a source. The daily average uptake of CO2 by the forest was −2.4 and −1.7 g m−2 per day in July–August and September periods, respectively; and average release by the clearing 4.0 and 2.5 g m−2 per day during the same periods. This shows that carbon losses 5 years after clear-cutting are substantial. The evapotranspiration (ET) was higher over the forest compared to clearing as a result of transpiration from the forest canopy. The difference in ET was small during the July–August period when precipitation frequently occurred.