Tree stand volume as a scalar for methane fluxes in forestry-drained peatlands in Finland

Forestry drainage is a method used extensively to grow timber in peat soils in Finland. Following drainage, the developing tree stand influences methane (CH 4 ) emissions by altering plant and microbial communities through water-level drawdown, competition for nutrients and shading. Therefore there should be a close correlation between tree stand volume and CH 4 fluxes in drained peatlands. We used previously published material along with data collected in this research programme to assess the potential of tree stand volume as a tool for estimating CH 4 fluxes for drained peatland forests, and to quantify this relationship under conditions prevailing in Finland. There was a clear negative exponential relationship between tree stand volumes and CH 4 emissions. Sites with small stand volume emitted CH 4 after drainage (up to 4 g CH 4 m -2 a -1 ), while larger stands consumed it (up to 1 g CH 4 m -2 a -1 ); the turning point from source to sink was about 140 m 3 ha -1 . Similar relationships were also found for undrained mires, although not as clearly as for the drained sites. Since drained peatland forests in Finland are generally rather young in drainage age and small in stand volumes, they are still estimated to emit CH 4 to the atmosphere, although the rate has substantially decreased after drainage.