Quantity and Quality of Stem Wood Concerning Biofuel Production from Young Paulownia Species Planted in Tochigi, Japan

Paulownia forestry in Japan has traditionally focused on producing high-value solid wood for traditional household goods. In the present study, to explore the potential of a new Paulownia plantation forestry model aimed at meeting Japan’s increasing demand for biofuels, the volume and weight of stems and the fuel characteristics of wood and bark were investigated for 15 four-year-old Paulownia trees planted in Tochigi, Japan. Fuel characteristics were also examined for nine common Japanese species as a reference. For Paulownia species, the bark had higher extractives, ash, and Klason lignin, lower contents of holocellulose and α-cellulose, and higher gross calorific value than wood. Potassium was the predominant inorganic component in both wood and bark in Paulownia species. Although the gross calorific value per unit volume of Paulownia species was the lowest among the tested nine Japanese species, the estimated annual gross calorific value per unit area was almost the same between Paulownia species and Cryptomeria japonica (the most common plantation softwood species in Japan) when the whole stem was used for biofuel production. Thus, Paulownia species might be used for biofuel production under short rotation cycles, even in lower bulk density of wood. On the other hand, wood from higher stem positions exhibited lower moisture content in Paulownia species. Therefore, drying costs might be reduced by using the lower stem portions for solid wood production, improving the overall economic efficiency of biofuel production.