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The use of biomass for energy purposes is an important European Union policy. In light of the restrictions concerning the use of the full−value wood from forests for energy purposes, short rotation forestry can become an alternative source of woody biomass. In this context, the most promising species is poplar (Populus spp.), productivity of which depends on various aspects such as plant spacing, cutting cycles, fertilization and cultivar characteristics. The aim of this study was to assess the possibility of cultivation of ten selected poplar clones from the section Aigeiros and Tacamahaca in short−rotation coppice in the climatic conditions of Poland. An experiment was set up in the north−eastern part of Poland in the Wichrowo Forest District. Survival, tree stocking, and biomass yield were compared. Productivity of clones was examined in five−year cutting cycle. The highest dry biomass yield (7.8 t/ha/yr) was achieved by the clone 'Hybrida 275'. In contrary, the biomass yield of the worst clone ('AF−8') amounted to 2 t/ha/yr. Some other Italian clones, such as 'AF−6' and 'MON' were not able to adapt to the local conditions at all and were excluded from the experiment. Because of the need to implement the full economic analysis of short rotation poplar plantations, it would be important to study propagation ability of certain currently studied varieties of poplar in subsequent rotations and with different production cycle period length up to the end of biomass production on a given plantation. Resistance to diseases of energy poplar plantations should also be researched.
Knowledge of diameter at the breast height (DBH), tree height and form factor allows to estimate tree volume, which is one of the most important measures in forestry. The paper presents empirical equations for the determination of DBH form factor of different species and hybrids of Populus sp. The study was set up on short−rotation plantation in Wichrowo Forest District (northern Poland). Four poplar hybrids at the age of six were taken into account: P. × generosa × P. trichocarpa, P. trichocarpa, P. maximowiczii × P. trichocarpa, Populus × canadensis. In total, 427 trees were felled and individually measured in one meter sections. The estimation equations are based on the relationships between form factor and one or some independent variables derived from diameter at breast height and height. We used determination coefficient as a goodness−of−fit measure. In addition, standard error of estimates from this dataset was calculated. The standard error values varied from 5.8 to 6.6% depending on the formulae and Populus hybrids. Th e equations proposed in this paper enable the determination of the discussed form factor for varied poplar cultivars and can be treated as a regional equations.
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