Hydromorphic soils easily unbalance GHG balances from forests: A focus on Europe

In terms of Non-CO2 Greenhouse Gases (GHG), forests are usually considered to be near neutral CO2 equivalent emitters, emitting low amounts of N2O and taking up considerable amounts of CH4. Typically more CO2 is assimilated than returned to the atmosphere by forests. Consequently, forests are regarded as sinks for atmospheric CO2 equivalents. This perspective inherently goes along with the perception that forests are dryland sites, because as wetlands they would have to be considered as CH4 sources too. It is well known that forests can include wetlands. In this presentation, we present the potential bias range for European bottom-up inventories of CH4, when forests and wetlands are considered to be strict opposites in the CH4 cycle. For selected scenarios with different proportions of wet forests on the land surface, we observed that net methane budgets that include methane sinks and sources, approximately double (~4.6 to 6.7 Tg CH4-C instead of 2,8 Tg CH4-C) when wet forests are included. The highest uncertainty appears to be associated with the determination of the area of methane emitting land surfaces. Furthermore, we present similar observations at the landscape scale and N2O was additionally adding to these unbalanced GHG budgets.