DIGITALNA ARHIVA ŠUMARSKOG LISTA
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subtreatment (c). Within the same planting distances biomass production in the second cycle is larger for 40 % to 60% compared to the first cycle. The results of these studies confirmed the real possibility of renewal of dense poplar stand using regeneration force of shoots from the tree stumps after felling. When establishing the stand of this type special attention should be paid to choice of clone with rapid growth in the juvenile developmental stage and genetic characteristics of stump regeneration after felling, as possibility to regenerate the stands with shoots from the stumps in several cycles. 3.2. Estimated weight of biomass – Procijenjena težina biomase Biomass produced in this type of stands can be used as raw material for panel production and chemical processing (fiber production), but its primary purpose is energy production. Achieved yields of highly productive clones of Eastern cottonwood indicated that the selection of clones during stand establishment should be paid special attention, because it is one of the basic parameters providing maximum biomass production with the same costs of investment in intended poplar stands for bio-energy production. Mass volume of wood is considered the basic parameter of its quality, because several other traits such as structural, physical, and mechanical wood properties are in close correlation with the mass of volume. Clone 618 achieved the minimum value of the wood mass volume (368 kg.m–3) Kopitović and Klašnja (1991), Herpka (1980), while the value for the clone 450 (395 kg·m–3), for clone 457 (420 kg·m3), and wood of clone 55/65 achieved the maximum value (447 kg.m–3) Herpka (1980). Many authors emphasized the significance of the selection for the fiber characteristics and mass volume of poplar wood, hence the quantity of the produced energy Goyal (1999), Ivkovich (1996). Klasnja et al (2003/a, 2003/b, 2005) confirmed these studies and concluded that mass of wood does not changes significantly with aging. The weight of biomass is estimated based on produced volume and value of the mass volume of wood. At the end of the first two-year cycle the weight of biomass ranged from 10.35 t·ha–1 in clone 618 at density of (1.2 × 1.0 m) to 18.68 t·ha–1 in clone 55/65 at density of (1.2 × 0.5 m). During the second cycle the weight of biomass ranged from 22.54 t·ha–1 in clone 618 at density of (1.2 × 1.0 m) to 33.86 t·ha–1 in clone 55/65 at density of (1.2 × 0.5 m) due to the regeneration force of shoots from the tree stumps (Table 4). Beside the influence of the clone selection and the regeneration force of shoots from the tree stumps on the produced weight of biomass, the planting density was also influenced. The best effects are achieved at densities (c) 1.20 × 0.50 m. It can be seen from the Table 4 that in addition to clone selection the stand density (number of plants.ha–1) also exerted a significant influence on yield of biomass. 3.3 Energy value of biomass – Energetska vrijednost biomase In order to estimate the quantity of energy obtained by complete felling of trees after the first and the second two-year cycles, the caloric values of the high heating value were |