Trees growing under the wires and around the pylons carrying power lines (PL) represent a significant threat to the power supply because they can cause power outages and damage. The vegetation in these PL corridors is cleared motor-manually on a regular basis, which represents about 50% of the PL maintenance costs. In Sweden, PL corridors account for 140 000 ha of productive forest land, with an estimated bioenergy potential of 3 TWh/year. The aim of this study was to measure the productivity of a harvester (with an accumulating felling head) and a forwarder, performing PL corridor clearing (with the collection of whole trees for energy use) and to calculate how the cost and economic profitability is dependent on tree height, biomass removal, harvested area, forwarding distance and wood fuel price. The study also compared the economic profitability of the mechanized harvesting system with motor-manual clearing. Experimental units were inventoried along a PL corridor in central Sweden and a time study of one harvester and one forwarder (with a single operator per machine), working in those units, was carried out. The results showed that if the tree height was greater than about 6 m, the mechanized harvesting system became a more cost-efficient alternative, when compared to motor-manual clearing, but it was also found that mechanized clearing is not always the most cost-effective option. Nevertheless, mechanization of PL clearing has a huge potential for expansion, requiring further research in the combined management of the PL corridors and side areas.
Thinning is an essential practice in Mediterranean pine forests management but is rarely applied because of the high harvesting costs. The new market of bioenergy products could give a profit to wood biomass harvesting activities, though the drawbacks of elevated supply chain costs, related to technical problems and lack of knowledge about the wood quality have to be overcome in advance. This study analyzed technical, economic, energy and environmental factors of a pine stand thinning in Central Italy, where collected biomass was directed to energy, in order to give a decisional support to reach economical profitability and environmental sustainability in thinning practices. The introduction of Full Tree System maximized the recovery of available biomass, full tree chipping produced material with Heating Value superior than single tree components. The use of a felling frame in motor-manual felling in comparison with the traditional chainsaw reduced operator effort, increasing the number of felled trees per hour, when the stump diameter remained under 15 cm. The energy wood supply chain is not sustainable from an economic point of view, the profitability could be reached only acting on suggested technical levers and particularly reducing costs of hauling operation. The estimation of output/input energy ratio in the supply chain underlined the feasibility of thinning practices for energy. The assessment of CO2 emissions confirmed the environmental sustainability of biomass supply chain in energy when compared to traditional fossil fuels. Study conclusions provide the guidelines for thinning treatment in Mediterranean pine stands, in order to reach environmental and economic sustainability of these practices
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