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ŠUMARSKI LIST 1-2/2013 str. 38     <-- 38 -->        PDF

Immediately after felling the whole trees were measured, as well as the bark mass after debarking in moist condition. For the determination of moisture content, wood samples were oven dried at 105 °C to a constant weight. All analyses were done in duplicate and the results were expressed on a dry weight basis.
The specimens were dried at room temperature until moisture content was 8%–10%, and after that the samples were ground into wood flour suitable for pellet pressing. The calorific value was determined for ground air-dried samples. Pellets were made by a special device producing pellets ranging from 0.60 g to 0.85 g. Samples were combusted in C200 IKA Werke calorimeter. There were three replications for each sample.
The renewal of the trial stand in the second cycle was done using regeneration force of shoots from the tree stumps. During the first vegetation period of the regeneration from the stump the shoot reduction was performed by leaving the best developed shoot on each stump.
3. Results and discusion
Rezultati istraživanja i diskusija
3.1. Taxation elements – Taksacijski elementi
Diameters and heights of medium-sized trees, number and volume of trees per hectare for each cycle are given in Table 2.
As far as survival of cuttings is concerned there were no statistically significant differences and the percentage of survival for all clones was 91.6%. The least percentage of survival of 89% was obtained in clone 618, in clone 450 (91%), while in clones 457 and 55/65 this percentage was 93%. At the end of the first two-year cycle the diameters ranged from 2.9 to 3.7 cm, and heights from 5.4 to 6.2 m. In the second cycle significantly higher values of diameters and heights were obtained due to the coppice vigor. Diameters ranged from 3.9 to 5.1 cm, and heights from 6.6 to 7.5 m.
Analysis of variance for diameters showed that there were no statistically significant differences between clones in the first cycle. However, differences in diameters influenced by various stand densities were highly significant. Among clones in the first cycle there were statistically significant differences in heights, influenced by genetic variability of clones, while differences in heights competing for living space (planting distances) were statistically highly significant. Mean variance analysis at the end of the second cycle revealed that differences among diameters as well as among heights were significantly different. In all clones the greatest dimensions were achieved at planting distances of 1.2 × 1.0 m, and the least 1.2 × 0.5 m (Table 3).
The total determined volume of wood, bark, and branches in the first two-year cycle for clones of Eastern cottonwood ranged from 27.391 m3·ha–1 in clone 450 at planting distance 1.2 × 1.0 m, subtreatment (a) to 42.006 m3·ha–1 in clone 618, subtreatment (c) at planting distance of 1.2 × 0.5 m (Table 2).
By renewing the stand using regeneration force of shoots from the tree stumps the produced wood mass in the second two-year cycle ranged from 54.664 m3·ha–1 in clone 55/65 subtreatment (a), to 79.235 m3·ha–1 in clone 450