CO2 and water vapour fluxes for 2 years above Euroflux forest site

The ‘Le Bray’ site, a 28-year old plantation of maritime pine (Pinus pinaster Ait.) with an understorey of graminae, is part of the European network Euroflux. Carbon dioxide and water vapour fluxes were measured continuously for 2 years above the canopy with an eddy-covariance system. The 2-year accumulated evapotranspiration amounts to 3184±440 MJ m−2 (1331±186 mm of water) compared to 1860 mm rainfall or 6011 MJ m−2 net radiation. The overall gap in the energy balance is 1322 MJ m−2, partly due to the poor estimation of evapotranspiration during rainy periods. The 2-year sum of carbon sequestration is 11.5±0.8 t of carbon per hectare. The 2-year total ecosystem respiration, estimated by adjusting statistically night-time CO2 fluxes against the soil–litter interface temperature for turbulent nights only, is about 33.6±2.0 t of carbon. A fairly good statistical relationship is found by multiple regression between daily gross primary production (GPP) on the one hand, and direct and diffuse absorbed PAR on the other hand. The water use efficiency (defined as the ratio of GPP to evapotranspiration) is inversely related to air saturation deficit.