Estimation of primary forest harvest residues and potential bioenergy production from fast-growing tree species in NW Spain

Abstract

Around 50% of the wood harvested annually in Spain for industrial purposes is produced in the north-western region of Galicia. In this study, species-specific equations were developed for estimating dry harvest residues (kg) from stem volume (m3) in the fast-growing Pinus pinaster Ait., Pinus radiata D. Don and Eucalyptus spp., which generate around 95% of harvested wood. The presence of heteroscedasticity was taken into account in model fitting. Regional dry harvest residues were estimated using the equations and regional harvested volume records (m3), by assuming a mean harvested tree of diameter at breast height of 45 cm for pines and 25 cm for eucalyptus. A moisture content (M) of 25% was assumed for direct combustion of harvest residues; therefore, wet values were calculated from dry estimates, and a lower heating value (M = 25%) was used. The bioenergy potentially produced from the estimated harvest residues (M = 25%) was 377 ktoe year−1 in the period 2018–2019, equivalent to 4.7% of the total primary energy consumption in Galicia in 2018. Currently 70% of potential bioenergy production is concentrated in a sub-region representing 40% of the whole region. The approach used provides a direct link between regional or local harvested volume (registered or simulated) and accurate estimation of potential bioenergy from direct combustion of harvest residues, thus supporting decision-making related to climate change targets and to decreasing dependence on fossil fuels. However, further research that takes into account environmental, economical and social constraints in removing harvest residues is required.