Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes

Abstract

During 2010-2013, we investigated the effects of stump harvesting on greenhouse gas (GHG) fluxes of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous ox- ide (N 2 O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO 2 , CH 4 and N 2 O fluxes within treatments and significant effects of stump harvesting on CO 2 and N 2 O fluxes at the dry plots. The CO 2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO 2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N 2 O at this plot. At the wet plots, CO 2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N 2 O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224×10 3 and 1.442×10 3 gm -2 of CO 2 -equivalents at the wet and dry stump harvested plots, respectively, and 1.070×10 3 and 1.696×10 3 gm -2 of CO 2 -equivalents at the wet and dry control plots, respectively. CO 2 fluxes dominated GHG budgets at all plots but N 2 O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO 2 +CH 4 ) budgets were 4.301×10 3 and 4.114×10 3 g m -2 of CO 2 -eqvivalents at the wet and dry stump harvest plots, respectively and 4.107×10 3 and 5.274×10 3 gm -2 of CO 2 -equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO 2 emissions but uncertainties regarding GHG fluxes (especially N 2 O) remain and more long-term measurements are needed before robust conclusions can be drawn.