Аннотация:Atmospheric fluxes of CO2 and H2O above a mature spruce stand (Picea abies (L.) Karst.) have been investigated using the eddy- correlation technique. A closed path sensor adapted to the special requirements of long-term studies has been developed and tested. Field measurements have been performed since April 1995. Estimates of fetch showed a very narrow source area dimension under instable stratification (≤ 200 m). Fetch requirements at night are not met in some directions. Energy balance closure was influenced systematically by the wind direction indicating a substantial attenuation of the vertical wind motion by the tower (up to 40 %). Even for optimal flow directions, energy balance closure was about 88%. Intercomparison of the used ultra sonic anemometer (USAT-3) with a GILL - anemometer showed systematically lower values of vertical wind speed fluctuations (13 %). Average CO2-fluxes ranged between -13 at noon to 3 μmol m−2, s−1 at night in summer. In November and December the stand released CO2 on a daily basis. A preliminary estimate of the cumulative net carbon balance over the observed period of 9 months is 4–5 t, C ha−1.