Evergreen Oak Biomass Residues for Firewood

This chapter presents the assessment of the availability for residential heating of residual biomass from cork and holm oaks in a 12,188 ha agroforest area in Portugal. First, the above-ground biomass of evergreen oaks using very high spatial resolution satellite images was determined, followed by the definition of different scenarios for residues removal from the stands. The useful energy potential of the firewood that can be collected from the study area under the various silviculture scenarios was determined considering different energy conversion technologies: open fireplaces (still popular in Portugal) and more efficient closed burning appliances. Additionally, emissions of airborne pollutants from combusting all the available residual biomass in the study area were determined. Depending on the percentage of residues collected when the trees are pruned and on the conversion technologies used, the energy potential of evergreen oak firewood ranged from 5.0 × 106 MJ year−1 to 7.5 × 107 MJ year−1. Heavier pruning combined with the use of open fireplaces generates less useful heat and much higher emissions of pollutants per unit useful energy produced than lighter pruning combined with a more efficient technology. This case study illustrates the need to promote the transition from inefficient to more efficient and cleaner technologies