Annual greenhouse gas fluxes from a temperate deciduous oak forest floor

There is large uncertainty over the net greenhouse gas (GHG) balance of European forest ecosystems because of a lack of knowledge about the factors controlling GHG fluxes and the response to changes in management. We measured GHG fluxes from the forest floor (i.e. including soil, litter, roots and any ground vegetation) between 2007 and 2012 from a managed deciduous oak forest in south-east England to quantify fluxes and to investigate: (i) the seasonal and spatial variations between areas of the forest with different thinning management history, (ii) the relationships between GHG fluxes and environmental variables, and (iii) the contribution of the forest floor CO2 fluxes to the total ecosystem respiration derived from eddy covariance. The annual flux of CH4 was a net oxidation of 276 mg CH4-C m(-2) yr(-1) showing that forests on mineral soils can be appreciable CH4 sinks. There was a large temporal variation in N2O fluxes with both emission and uptake and a net annual efflux of 52 mg N2O-N m(-2) yr(-1). The net annual CO2 efflux was 894 g CO2-C m(-2) yr(-1), which contributed 60 per cent to total ecosystem respiration and dominated the combined global warming potential of all three GHGs. In this oak forest, soil temperature and moisture changes explained 73 per cent of the CO2 efflux variations. CH4 and N2O annual fluxes differed little between areas of the forest that had been thinned between 1990 and 2007, but CO2 effluxes were significantly lower from the least recently thinned area, which had a higher tree and canopy density.