abstractNet ecosystem productivity (NEP) was studied in a bog located in the middle taiga of Siberia using two approaches, the accumulation of peat above the hypocotyl of pine trees, and the eddy covariance flux methodology. NEP was 0.84 tC ha−1 yr−1 using the peat accumulation method; it was 0.43–0.62 tC ha−1 yr−1 using eddy covariance over three growing seasons. These data were compared with NEP of the surrounding forest, which was 0.6 tC+1.1 ha−1 yr−1. The trees growing on the bog reached a total height of about 3 m and an age of 80–120 yr when peat accumulation reached 0.5–0.6 m. At that stage the growth rate of the oldest trees declined. This indicates that there is a maximum age that can be reached by trees growing on hummocks (<150 yr), depending on conditions. The data show that the determination of NEP in bogs by using the peat accumulation above the hypocotyl is a useful method which can be applied on a wide range of bog types, but it may systematically overestimate NEP. The total sink capacity for carbon assimilation of bogs is comparable to that of forest, although methane emissions and losses of dissolved organic carbon must be taken into account when assessing the regional carbon cycle.