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ŠUMARSKI LIST 1-2/2013 str. 36     <-- 36 -->        PDF

1. Introduction
Increased participation of renewable energy sources in the total energetic balance is one of the strategic goals of the ever increasing number of countries. Foundation of energetic plantations for biomass production is in accordance with the world trends, and it is the basis for better usage of renewable energy sources without emitting the additional quantities of carbon dioxide (CO2) the fossil fuels are loaded with.
Biomass is produced through photosynthesis when plants capture atmospheric carbon dioxide (CO2) and release oxigen (O2), which makes it a renewable and environmentally friendly source of energy and gives it considerable advantages over other fuels. According to the reasearch of Zenone et al, (2008) the average annual amount of CO2 consumed by poplar varieties with short rotation at plant density of 12.500 plants.ha–1 ranged from 11.2 to 23.2 t CO2·ha–1·year–1. In the 10-year period, with several short production cycles in dense poplar stands it would amount from 134 to 235 t·CO2·ha–1 (taken over by Pašičko et al, 2009).
Shortage of wood as energy raw material requires control of technological procedures for accelerated wood production as a renewable resource in special types of short-rotation poplar coppice stands.
Due to their autovegetative propagation ability by cuttings, or by regeneration force of shoots from the tree stumps enabling selection of high genetic gain, the strong regeneration force of poplars allows several production cycles with minimal production costs.
Poplars and willows represent the greatest potential for biomass production in short rotation stands in our area. By selecting clones with appropriate characteristics for growing in very dense short rotation stands, it is possible to produce large quantity of biomass (by chipping of whole trees with branches, bark and roots at the end of production cycle), and it does not require production of technical wood of greater dimensions, because technology intended for this purpose uses chipped wood.
The fact that smaller trees are used for biomass production is the main factor that determines the elements of technology of targeted production of wood for energy purposes. Optimal use of genetic poplar potential in production of biomass is influenced by the choice of clone, type of planting material, and density of stand crucial for duration of the production cycle and number of rotations.
Short rotation stands in which felling of trees is performed each year, every second or third year are established with tested genetic material and stand density of ~ 15000 plants ha–1 (Tharakan et. al. 2003).
In regard to the poplar production technology numerous problems remain whose solution would influence the realization of the mentioned goals, and in particular the cost of investment in the process of establishment, development and protection of stand. These problems include the choice of habitat, soil preparation, choice and technology of planting material production, choice of the manner of planting, care measures, and stand protection.
In addition to poplars being the most productive forest tree species in our area, they also have several important characteristics making them fit for short rotation stand establishment such as a large selection of clones, the possibility of restoration by shoots from stumps after multiple cuttings, and uniform quality of planting material. Possibility to produce biomass in poplar stands of different production cycle duration has been studied for long period of time, which was confirmed by numerous literature citations (Marković et al. 1986, Rončević et. al. 2002, 2011, Klašnja et al. 2002, 2003, 2009, Andrašev et al, 2003, Orlović et al, 2004, Kajba et al, 2004).
2. Object of investigation and working method
Objekt istraživanja i metoda rada
2.1. Object of investigation – Objekt istraživanja
Studies were done on the Trial field of the Institute of lowland forestry and environment in the vicinity of Novi Sad (N: 45°1657’’, E: 19°5240’’). Area on which the studies were performed is suited at an altitude of 75 m and was flooded at high water-levels of the Danube until the construction of defensive embankment in 1928. According to the hydrographic position the pilot facility was suited on the medium high mountain terrains of alluvial plains of the Danube basin (Herpka, 1965), where natural conditions for marsh forest prevailed prior to the construction of the defensive embankment. Until the construction of the defensive embankment this soil was formed by the dominant pedological process called fluvial sedimentation (Iva­ni­šević, 1993; Ivanišević, et al. 2000) with significantly lesser accumulation of organic matter (Ivanišević and Mila­nov­skij, 1991), and after the construction of the embankment the prevailing pedological processes were influenced by ground water and plants formation (Pekeč, 2010; Pekeč, et al. 2011a, 2011b). According to the soil classification of Škorić, et al. (1985) this soil belongs to hydromorphic order, the class of undeveloped hydromorphic soils. According to soil systematic classification the soil at the pilot facility belongs to loamy fluvisol type. This soil is layered, very deep, carbonate through entire depth, with alkaline reaction of soil solution, with obvious signs of gleying process, and with physiologically active profile depth (rhizospehere zone) of 180 cm (Ivanišević, 1991, 1995).