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ŠUMARSKI LIST 3-4/2012 str. 54     <-- 54 -->        PDF

 values of Laureysens (2005), at 6 years, the DBH averaged over planting densities (500 to 1111 plants ha–1) was from 17 cm to 18 cm, and the tree height averaged over planting densities was 16.60m to 18.08m for examined clones. Wood volume, ranged from 79.2 m3ha–1 (cl. ‘Pannonia’) to 116.7 m3ha–1 (cl. ‘PE 19/66’). Average wood volume of all clones amounted to 96.11 m3ha–1.
After seventh year of growth in the Experimental plot 3, average diameter varied between 23.0 cm and 25.9 cm, and average height was from 17.8 m to 22.1 m. Wood volume, ranged from 97.2 m3ha–1 (cl. ‘182/81’) to 130.6 m3ha–1 (cl. ‘PE 19/66’). Average wood volume of all clones amounted to 113.89 m3ha–1. We can conclude that in both experiments the maximal yield was obtained by the same clone (cl. ‘PE 19/66’), with the annotation that the increasing of around 12 % in the 3rd trial was presumably caused by the differences in soil type. The minimal yield was obtained by the clones ‘182/81’ and ‘Pannonia’, and the differences attain the amount of 20 %. The value of middle average volume increment for all clones is also for around 18 % higher in the 3rd trial.
The values of wood density were used in the calculation of weight of mean trees, i.e. estimated weight produced biomass per unit area of plantation. The values of basic wood densities varied from 320 kgm–3 (min) to 387 kgm–3 (max), and oven dry from 361 kgm–3 (min) to 452 kg m –3 (max). This agrees with the values of the specific gravity of wood, being from 0.30 to 0.36 for several poplar clones (Goyal 1999), as well as with the values from 0.343 to 0.371 for P. balsamifera aged 7 years (Ivkovich 1996). Our previous research produced similar results for P. deltoides wood (aged 4 years) – 456 kgm–3 (clone 457 aged 10 years), i.e. 368 kgm–3 (Klašnja et al. 2003).
Estimated biomass yield – Procijenjen prinos biomase
The weight of the harvested biomass per unit area was calculated based on the data on bulk density of the study clones. The values of average biomass weight after the first and the second year (Fig. 1) behaved similarly to the volume. Namely, the mini­mal values were measured for clone ‘Pannonia’ (1.941 DM tha–1), while the maximal yield was shown by clone ‘B81’ (6.617 DM tha–1).
The minimal values of biomass weight after the second year (Fig.1), were measured for clone 182/81 (11.076 DM tha–1), while the maximal yield was shown by clone B-229 (20.103 DM tha–1).
This agrees with the literature data, because the yields given in the literature for poplars in SRC differ considerably. Mean annual increment (oven dry) lies between 20 tha−1 and 35 tha−1 (Ciria et al. 1995; Scarascia-Mugnozz a et al. 1997), but other publications report mean annual increment in the range of 2 tha−1 to 3 tha−1 (Schneider 1995). Average harvestable yields of poplars from SRC in temperate regions of Central Europe and North America range between 10 tha−1 and 12 tha−1 (Kauter et al. 2003). Riddel‑Black (1998) reported that the yield of six poplar clones (16500 plants ha–1) after the first growing season was 4.88 tha–1to 9.54 tha–1.
Regarding the data for the values of DBH, it can be noticed that the trees in the examined plantation (Experiment plots 2 and 3) haven’t reached the dimensions needed for the mechanical processing, because the diameters are below 25 cm (except the cl. ‘PE 19/66’ in the 3rd trial, with a little bit higher value of diameter – 25.9 cm). Therefore, the wood can be used either as raw material for chemical processing (pulp production, mostly), or for producing thermal energy.
The minimum values of biomass weight per unit area (Experiment plot 2) are estimated for the clones Pannonia (28.500 tha−1) and ‘182/81’ (29.322 tha−1), which fully agrees with the trends in the early stages of growth of examined clones (Experimental plot 1, Fig. 1).