The Slovakian portion of the Danube inland-delta represents a unique landscape. Branches of the Danube and more or less regular flooding with its alluvial deposit have created the most fertile soils which are partly forested. The greatest portion of the area is the crop land, while the forests are man-made with the poplar clones representing the stand-forming tree species. The present study investigates the influence of 7 predictors composed of the 3 biomass fractions, location on tree and clone factors and the 4 variables of stand index and age of stand and the height and diameter of tree on the calorific values of Robusta and 1-214 (Populus x euramericana) clones in Slovak territory. A statistical significance influence resulted for all predictors except for the clone factor. The average calorific value of all biomass fractions is approximately in the range of 17.8-18.4 MJ kg(-1) and statistical tests showed that wood has the highest calorific values while the thick bark on the lower parts of the stems had the least. (C) 2012 Elsevier Ltd. All rights reserved.