A comparison of the net ecosystem exchange of carbon dioxide and evapotranspiration for treed and open portions of a temperate peatland

Net ecosystem exchange of carbon dioxide (NEE) and evapotranspiration (ET) were measured at open and treed portions of a temperate ombrotrophic bog using the eddy covariance technique to examine the potential influence of plant community characteristics on peatland carbon and water vapour exchange. The sites were located 2.7 km from each other within the same peatland complex and thus experienced similar weather. Both sites were characterized by a Sphagnum ground cover and a shrub layer with similar total biomass. However, at the treed bog, 35% of this understory vascular plant layer was made up of Picea mariana (<0.5 m tall) compared to less than 0.2% in the open bog. The treed bog was also characterized by an overstory dominated by a patchy distribution of stunted P. mariana. Over a single year, net CO2 uptake and ET was lower at the treed bog (NEE: −72 g C m−2 year−1 and ET: 449 mm year−1) than at the open bog (NEE: −104 g C m−2 year−1 and ET: 493 mm year−1). Chamber measurements revealed that P. mariana was associated with low rates of net primary productivity (NPP) compared to the relatively more productive ericaceous and deciduous shrubs. Although the presence of a P. mariana overstory increases both the total aboveground biomass and leaf area index in this peatland, P. mariana appears to be important in reducing both ecosystem-scale carbon sequestration and water vapour loss.

• We examine eddy covariance fluxes for a treed and open portion of the same bog.
• The treed site has an overstory of black spruce and twice the vascular leaf area.
• The treed site has lower annual net CO2 sequestration and lower evapotranspiration.
• Chamber measurements show black spruce to have the lowest maximum assimilation rates.
• Peatland plant species composition is important in determining ecosystem functioning.