Energy production of poplar clones and their energy use efficiency

Poplar clones "Robusta" and "I-214" (Populus x euramericana) are characterized by fast growth and high quality biomass production. In this investigation the calorific value of these clones was determined, and modeling of the calorific production of a whole poplar clone stands in relation to stand age and site index was performed. Eleven trees were sampled in four sites in the eastern and seven in the western part of Slovakia. Samples of bark, wood and small-wood with bark were excised from three points along the stem and from two parts of the crown. No significant differences were observed between clones with regard to either the biomass fraction or the excising location. The average calorific capacity of all biomass fractions was approximately 6.86-8.73 GJ m(-3), with the lowest bark values obtained for samples excised from the stem base. The mean annual calorific energy production for site index 20-40 was 320-380 GJ ha(-1) y(-1) after 17-26 years since plantation, with the clone "I-214" culminating 1-2 years earlier than "Robusta". Energy use efficiency of these clones was estimated approximately 0.4-1.6% of the incoming solar radiation.