Net ecosystem production and carbon balance of an SRC poplar plantation during its first rotation

To evaluate the potential of woody bioenergy crops as an alternative energy source, there is need for a more comprehensive understanding of their carbon cycling and their allocation patterns throughout the lifespan. We therefore quantified the net ecosystem production (NEP) of a poplar (Populus) short rotation coppice (SRC) culture in Flanders during its second growing season. Eddy covariance (EC) techniques were applied to obtain the annual net ecosystem exchange (NEE) of the plantation. Further, by applying a component-flux-based approach NEP was calculated as the difference between the modelled gross photosynthesis and the respiratory fluxes from foliage, stem and soil obtained via upscaling from chamber measurements. A combination of biomass sampling, inventories and upscaling techniques was used to determine NEP via a pool-change-based approach. Across the three approaches, the net carbon balance ranged from 96 to 199 g m(-2) y(-1) indicating a significant net carbon uptake by the SRC culture. During the establishment year the SRC culture was a net source of carbon to the atmosphere, but already during the second growing season there was a significant net uptake. Both the component-flux-based and pool-change-based approaches resulted in higher values (47-108%) than the EC-estimation of NEE, though the results were comparable considering the considerable and variable uncertainty levels involved in the different approaches. The efficient biomass production with the highest part of the total carbon uptake allocated to the aboveground wood led the poplars to counterbalance the soil carbon losses resulting from land use change in a short period of time. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.