Methane and nitrous oxide emissions from mature forest stands in the boreal forest, Saskatchewan, Canada

Despite the spatial significance of Canada's boreal forest, there is very little known about CH₄ and N₂O emissions from non-peatlands within it. The primary objective of this project was to study the atmosphere–soil exchange of CH₄ and N₂O at three sites in the boreal forest of central Saskatchewan. In the summers of 2006 and 2007, CH₄ and N₂O emissions were measured along transects in three different mature forest stands (aspen, black spruce and jack pine) using a sealed chamber method. At the aspen site, the gross rates of mineralization and nitrification, and the relative contribution of nitrification and denitrification to N₂O emissions, were also measured using the ¹⁵N isotope dilution technique. Results indicated that the jack pine and black spruce sites were slight sinks of CH₄ (−0.123 g CH₄–C m⁻² yr⁻¹and −0.017 g CH₄–C m⁻² yr⁻¹ respectively in 2006 and −0.095 g CH₄–C m⁻² yr⁻¹and 0.045 g CH₄–C m⁻² yr⁻¹ respectively in 2007), whereas the aspen site was a net source (4.40 g CH₄–C m⁻² yr⁻¹ in 2006 and 19.60 g CH₄–C m⁻² yr⁻¹ in 2007). The high CH₄ emissions at the aspen site occurred at depressions that were water-filled due to above-average precipitation levels in 2005–2007. All three sites had very low cumulative N₂O emissions, ranging from −0.002 to 0.014 g N₂O–N m⁻² yr⁻¹ in both years. The ¹⁵N results indicated that N cycling at the aspen site was very conservative, allowing little N to escape the system as N₂O; the emissions that did occur were due primarily to a nitrification-related process.