Ecological and environmental transition across the forested-to-open bog ecotone in a west Siberian peatland

Climate change may cause increasing tree cover in boreal peatlands, and the impacts of this encroachment will be noted first at forested-to-open bog ecotones. We investigate key metrics of ecosystem function in five such ecotones at a peatland complex in Western Siberia. Stratigraphic analysis of three cores from one of these transects shows that the ecotone has been dynamic over time with evidence for recent expansion of forested peatland. We observed that the two alternative states for northern boreal peatlands (forested/open) clearly support distinct plant and microbial communities. These in turn drive and respond to a number of feedback mechanisms. This has led to steep ecological gradients across the ecotones. Tree cover was associated with lower water tables and pH, along with higher bulk density, aquatic carbon concentrations, and electrical conductivity. We propose that the conditions found in the forested peatland of Western Siberia make the carbon sink more vulnerable to warmer and drier conditions

A comparison of the net ecosystem exchange of carbon dioxide and evapotranspiration for treed and open porti

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 2.7km 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 (<0.5m 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 CO 2 uptake and ET was lower at the treed bog (NEE: -72gCm -2year -1 and ET: 449mmyear -1) than at the open bog (NEE: -104gCm -2year -1 and ET: 493mmyear -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