Greenhouse gas budget of a poplar bioenergy plantation in Belgium: CO₂ uptake outweighs CH₄ and N₂O emissions

Abstract

Biomass from short-rotation coppice (SRC) of woody perennials is being increasingly used as a bioenergy source to replace fossil fuels, but accurate assessments of the long-term greenhouse gas (GHG) balance of SRC are lacking. To evaluate its mitigation potential, we monitored the GHG balance of a poplar (<i>Populus</i>) SRC in Flanders, Belgium, over 7 years comprising three rotations (i.e., two 2 year rotations and one 3 year rotation). In the beginning-that is, during the establishment year and during each year immediately following coppicing-the SRC plantation was a net source of GHGs. Later on-that is, during each second or third year after coppicing-the site shifted to a net sink. From the sixth year onward, there was a net cumulative GHG uptake reaching -35.8 Mg CO₂ eq/ha during the seventh year. Over the three rotations, the total CO₂ uptake was -51.2 Mg CO₂/ha, while the emissions of CH₄ and N₂O amounted to 8.9 and 6.5 Mg CO₂ eq/ha, respectively. As the site was non-fertilized, non-irrigated, and only occasionally flooded, CO₂ fluxes dominated the GHG budget. Soil disturbance after land conversion and after coppicing were the main drivers for CO₂ losses. One single N₂O pulse shortly after SRC establishment contributed significantly to the N₂O release. The results prove the potential of SRC biomass plantations to reduce GHG emissions and demonstrate that, for the poplar plantation under study, the high CO₂ uptake outweighs the emissions of non-CO₂ greenhouse gases.