Forests on drained agricultural peatland are potentially large sources of greenhouse gases – insights from a full rotation period simulation

Abstract. The CoupModel was used to simulate a Norway spruce forest on fertile drained peat over 60 years, from planting in 1951 until 2011, describing abiotic, biotic and greenhouse gas (GHG) emissions (CO₂ and N₂O). By calibrating the model against tree ring data a “vegetation fitted” model was obtained by which we were able to describe the fluxes and controlling factors over the 60 years. We discuss some conceptual issues relevant to improving the model in order to better understand peat soil simulations. However, the present model was able to describe the most important ecosystem dynamics such as the plant biomass development and GHG emissions. The GHG fluxes are composed of two important quantities, the spruce forest carbon (C) uptake, 413 g C m⁻² yr⁻¹ and the decomposition of peat soil, 399 g C m⁻² yr⁻¹. N₂O emissions contribute to the GHG emissions by up to 0.7 g N m⁻² yr⁻¹, corresponding to 76 g C m⁻² yr⁻¹. The 60-year old spruce forest has an accumulated biomass of 16.0 kg C m⁻² (corresponding to 60 kg CO₂ m⁻²). However, over this period, 26.4 kg C m⁻² (97 kg CO₂eq m⁻²) has been added to the atmosphere, as both CO₂ and N₂O originating from the peat soil and, indirectly, from forest thinning products, which we assume have a short lifetime. We conclude that after harvest at an age of 80 years, most of the stored biomass carbon is liable to be released, the system having captured C only temporarily and with a cost of disappeared peat, adding CO₂ to the atmosphere.