Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchange
fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2
exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim
of the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy season
at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up
to −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such high
fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil
nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO2
uptake was high, the annual budget of −229 ± 7 ± 49 g C m−2 y−1 (±random errors ± systematic
errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy
season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no
systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets
indicated that corrections for air density fluctuations were the largest error source (11.3% out of
24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic
carbon pool for the uppermost .20 m. These findings have large implications for the perception of
the carbon sink/source of Sahelian ecosystems and its response to climate change.