Temporal and spatial variation of soil CO2 efflux in a Canadian boreal forest

The efflux of CO2 from the soil surface is a key component of the carbon balance of any ecosystem. Quantifying this flux and understanding the factors that underlie the temporal and spatial variation in its magnitude are fundamental to our understanding of the behaviour of the ecosystem as a whole and to our ability to predict the likely consequences of climatic change. Forest floor CO2 efflux was measured at 45 locations over 2 y in a Picea mariana stand at the BOREAS Southern old black spruce (OBS) site. Spatial variability was high, and was related empirically to the thickness of the dead moss layer. Short term (hour to hour) variation was well described as a simple exponential function of soil temperature, and was significantly related to atmospheric turbulence. Seasonally, soil CO2 efflux varied between low, but positive, rates before the springtime thaw and after the wintertime freeze, to rates as high as 14 μmol m−2 s−1 in late summer. The total annual carbon efflux from the forest floor for 1996 was estimated to be 8.96 Mg (C) ha−1 with 95% confidence limits of 7.86 Mg (C) ha−1 and 10.26 Mg (C) ha−1. For individual sampling locations, both the total annual carbon efflux and the responsiveness of the efflux to atmospheric turbulence were significantly correlated with the structural properties of the forest floor.