Biomass productivity of selected poplar (Populus spp.) cultivars in short rotations in northern Poland§

Abstract

Renewable energy sources such as biomass are an important aspect of the energy policy of the European Union. As the use of ‘full-value wood’ for energy purposes has been restricted, short-rotation forestry may be an alternative source of woody biomass. In Poland, the most promising genus is poplar (Populus spp.). Ten poplar cultivars from the Aigeiros or Tacamahaca sections of the genus Populus were compared in 5- and 6-year rotations for biomass components and yields. Additional aims were to preliminarily (a) identify a suitable rotation length and (b) evaluate the sprouting capacity of various cultivars in the climate of northern Poland. The following variables were measured: diameter at breast height (DBH), height, survival rate, single-tree dry mass, crop biomass production, and sprouting ability. The cultivars ‘NE-42’ and ‘Fritzi Pauley’ showed the best growth characteristics (DBH and height) and highest biomass production (7.6 and 7.7 t ha−1 year−1, and 5.2 and 6.9 t ha−1 year−1, respectively, for cultivars in the 5- and 6-year cycles). These cultivars were also distinguished by a large number of coppice shoots and a high shoot length. Eight cultivars did well enough to produce worthwhile data, and five of these gave higher biomass production (t DM ha−1 year−1) during the 6-year, as opposed to the 5-year cycle. Of the eight cultivars analysed, ‘AF-8’ had the poorest growth parameters and produced two thirds less dry biomass than either the ‘NE-42’ or ‘Fritzi Pauley’ cultivars. Data for two Italian cultivars (‘AF-6’ and ‘MON’) were not analysed because of their cold tenderness and their high mortality. Rotation length is important for biomass production in energy plantations. Most of the tested poplar cultivars gave higher biomass productivity over an initial 6-year cycle than over a 5-year one. Our preliminary results suggest that the ‘NE-42’ and ‘Fritzi Pauley’ cultivars performed best among those tested. Both of these have been tested previously in Poland in medium and long rotations. The data indicate the importance of testing cultivars under local climatic conditions before planting on a commercial scale.