Soil preparation to expedite stand establishment after clearcutting is an extensively applied measure in peatland forest regeneration sites particularly in Fennoscandinavia. Thus far, the impact of preparing peat soil on greenhouse gas fluxes is a chapter unwritten in GHG research on forestry-drained peatlands. Not only is such information vital in order to accurately estimate the GHG balance nationally, it may dictate the very methods used to regenerate forests on peat soils in the future. Over a 22-month period, we studied the impacts of mounding and scalping relative to the control on soil CO2 (heterotrophic peat soil respiration, SRp), CH4, and N2O fluxes along a moisture gradient in a nutrient-poor, clearcut forestry-drained peatland. First, we measured instantaneous gas fluxes (g m(-2) h(-1)) of the microsite types (unprepared, mound, pit, scalp) within a given treatment plot (control, mounding, scalping) in order to estimate their annual rates (g m(-2) a(-1)). Then, we estimated annual flux rates for each treatment comprehensively by considering the surface area-based distribution of microsite types in the corresponding treatment plot, and finally, the overall climatic impact of GHG emissions expressed in terms of CO2 equivalents (100-year GWP) 2-3 years after clearcutting and soil preparation. Compared to the control microsites, instantaneous CO2 emissions from scalps and pits were lower while those from mounds equivalent. However, increased CO2 emissions from the unprepared microsites within prepared plots were observed in respect to those of the control. Comprehensively, the annual CO2 emission rates differed little between treatments, ranging between 929 and 1078 g m(-2) a(-1). Hence, neither mounding nor scalping accelerated annual SRp relative to the control treatment. Annual fluxes of CH4 were dependent on the position of the water table. In our wet block, the mounding treatment led to the greatest annual CH4 emissions (3.62 g m(-2) a(-1)), followed by the control (2.14 g m(-2) a(-1)) and scalping (1.05 g m(-2) a(-1)); in the dry block, however, only the scalping treatment was a net, though minimal, source of CH4 (0.80 g m(-2) a(-1)) while the other two treatments effectively consumed CH4 (mounding -0.16 g m(-2) a(-1); control -0.05 g m(-2) a(-1)). Though annual N2O emission levels were low (0.05-0.08 g m(-2) a(-1)), both soil preparation treatments increased the flux of N2O from peat soil compared to the control. When considering the fluxes of all three greenhouse gases, the cumulative impact of soil preparation (mounding or scalping) on the global warming potential of the nutrient-poor, clearcut peatland forest was negligible in respect to the control.
