Summary

Populus L. belongs to the family of Salicaceae (Salicaceae Lindl.). This genus includes from about 40 to even 100 species and hundreds of cultivars cultivated on nearly the whole northern hemisphere. Poplars are divided into five sections: Leuce, Aigeiros, Tacamahaca, Leucoides and Turanga, where the former three are of greater significance.

Poplars are only dioecious and wind-pollinated; they require a lot of sunlight and soil with high humidity, although particular species and hybrids tend to vary in this respect. Poplars propagate generatively from seeds and vegetatively too.

These plants which are cultivated to produce biomass on plantations in short rotations have high soil, water and climatic requirements. In order to reach high productivity they require a long vegetation period (minimum 180 days) and high temperature, particularly from June to September when the mean temperature should be 17°C.

In order to gain satisfactory biomass yields and economic effectiveness, poplar plantations in short rotations should be established on fertile soils with good water and air conditions. Sandy soils of low class of bonitation are not suitable for this type of cultivation. The soil reaction should be within the range 6.0--7.5 whereas the optimal level of groundwater is 0.5-2 m.

The planting stock comprises stem cuttings of 20 cm length. They are gained from mother plantations during the winter period, from one-year or two-year shoots. Generally, 5500 to 6600 stem cuttings are planted per 1 ha.

Stem cuttings are planted to the surface of the soil; they may also jut out 2-3 cm over the surface. The distance between the rows is 3 to 3.5 m and the distance between the plants in a row is 0.5 to 0.6 m. The rotation of harvest should occur every 6-7 years and 10 to 12 years in the case of aspen. Nonetheless, balsam poplars and their cross-breeds as well as hybrids with the black poplar may be cultivated in short, 3- 5 year summer rotations, and produce satisfactory yield. In literature, poplar yielding is highly varied (1.6 – 28 t d.m./ha/ year) depending on climatic conditions, the type of the soil habitat, species and clone, crop rotation, the age of the plantation, the level of fertilization and other agrotechnical operations.

In Italy, the poplar clone Populus deltoides L. in a two-year rotation produced the yield of 11.7 t d.m./ha/year. Extending the crop rotation to three and four years had a significant impact on the size of the yield, as it reached 15.0 and 18.4 t d.m./ha/year respectively.

As for the generation of biomass in the form of forest chips, the total costs of poplar production varied and ranged from 10 to 56 euro/t d.m..

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