Potentials and wood fuel quality of logging residues from indigenous and planted forests in Mozambique

Abstract: Search for complementary and alternative renewable energy sources is imperative to meet the current growing demand for wood fuel and for diversification of electricity supply sources in Mozambique. Logging residues from timber harvesting operations and whole tree biomass from short rotation coppice (SRC) are available options. The overall aim of this thesis work was to increase knowledge of the potentials and fuel quality of woody biomass from natural forests and SRC plantations as a renewable energy source. The aim also included an assessment of climate effects associated with the replacement of fossil fuels by Eucalyptus pellets for energy production. To estimate the biomass of logging residues species-specific above-ground biomass and stem volume equations were developed for four commercial timber species in Mozambique. The indigenous species included Afzelia quanzensis Welm. (Chanfuta), Milletia stuhlmannii Taub. (Jambire) and Pterocarpus angolensis D.C. (Umbila), while the planted species was Eucalyptus grandis W. Hill ex. Maiden (Eucalyptus). Diameter at breast height was the best predictor of biomass, while diameter and height explained the stem volume best. Results on biomass quantification showed that Jambire had the highest dry weight per tree and Umbila had the lowest. The stem had the largest share of the total biomass for Chanfuta, Jambire and Eucalyptus, while branches constituted the major biomass in Umbila. The dry weight proportion of the logging residues relative to the total tree biomass was 77% for Chanfuta, 83% for Umbila, 47% for Jambire and 38% for Eucalyptus. Chemical analyses were carried out to characterize the biomass and evaluate the fuel quality of tree components, stem, branches and leaves. Evaluation parameters, including higher heating value, moisture content, ash content and basic density were used to calculate fuel value index. The stem wood and logging residues of Umbila was ranked as the best fuel with the highest fuel value index, while Eucalyptus ranked lowest. Producing and using wood pellets in a power plant in Mozambique, was more beneficial from a climate perspective than producing it in Mozambique and export to Sweden to be used in a combined heat and power plant. The results indicate that there is a significant amount of biomass with good fuel properties that could be obtained as by-products of logging activities and from SRC for uses such as energy, thus reducing the need for clearing new forests for energy use.