2.1.3. Paulownia (*Paulownia tomentosa*)

*Paulownia tomentosa* is a large deciduous hardwood and fast growing tree that is native from China [20]. Paulownia species are found naturally growing and under cultivated conditions at several regions of the world. It quickly spreaded to other parts of Asia, being cultivated in particular in Japan and Korea. Presently, it can also be found mainly in central Europe, north and central America, and Australia. Its main uses are industrial applications of the wood, due to its high ignition point, as well as to its dimensional stability and life time maintenance its characteristics [21].

*Paulownia tomentosa* is widely studied and utilized for the rehabilitation of contaminated soils and abandoned agricultural soils with low water needs, adapting itself to a grea<sup>t</sup> variety of climatic conditions and diversity of soils. It helps, too, in soil recuperation and stabilization including erosion control [22]. In Portugal, the Government recommends its afforestation in "Annex II-Non-indigenous species with interest for afforestation" of Decree-Law n. ◦ 565/99, being a non-indigenous species, with non-invasive character [23]. Concerning the growth, it was found that in a period of only 5–7 years after planting 2000 trees/ha under favorable conditions a significant annual production of 150–300 tons of wood was achieved [24]. Due to its high cellulose content, paulownia has shown its feasibility for use in the pulp industry and in lignin applications, combining both delignification and auto hydrolysis processes [25,26]. A wood analysis showed a composition of 50.55% cellulose, 13.6% hemicellulose, 21.36% lignin, 14% extractable and only 0.49% ash [27]. The energetic valorization of paulownia may be through its direct use as solid biomass for the production of heat and electricity or as a raw material to second generation advanced biofuels, such as bioethanol [28,29]. For those reasons, paulownia was included in this list of options for bioenergy in Portugal.
