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

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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 CO 2 balance, indicating that CO 2 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 CO 2 exchange of the forest ecosystem. The forest CO 2 exchange was explained by soil respiration and photosynthesis of forest canopy, while the contribution of understory and ground vegetation CO 2 exchange could be neglected. During the study period the forest was a net sink of CO 2 and the clearing a source. The daily average uptake of CO 2 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.