Allocation of five macroelements and quality of fuels derived from Norway spruce wood obtained by thinning operations

The use of forest biomass for energy production is growing in Europe and biomass energy plants market is constantly increasing. However, there is the need to define the environmental sustainability issues dealing with the emerging renewable energy scenario. In particular, the polluting emissions (i.e. PMx, NOx and ozone) caused by the biomass combustion heavily impact on the air quality. In this context, the elemental characterization of the wood and the element allocation in the different tree organs, can provide important information about the quality of the derived wood fuels and give hints about the choice of the most appropriate combustion technique and/or the right wood fuel for a given combustion technique. Moreover, since elements have different concentrations in the different plant tissues, the preventive knowledge of the elements allocation can lead to the identification of the best harvesting strategy aimed at producing wood fuel with the lowest possible ash forming elements and environmental impact. This work focuses on the allocation in three tree compartments (foliage, branches and stem) of five important macroelements (K, Mg, Ca, N and P) in Norway spruce (Picea abies), and points out the possible effects of different harvesting strategies and tree age on the quality of the wood fuels. Results suggest that the Stem Only Harvesting is preferable to Whole Tree Harvesting system in terms of prevention of mineral content loss, as well as is preferable to avoid forest biomass from young trees because of the poorer fuel quality of the wood chips.