engleski

Mechanized wood chips harvesting in the thinning of the forest culture of Weymouth pine (Pinus strobus L.)

Investigated mechanized system consisted of a harvester for felling and processing trees, a forwarder for primary transport of produced roundwood assortments, a forest truck and trailer for long distance transport and a chipper for production of wood chips. Mechanized felling, processing and extraction of produced roundwood assortments were researched in the Forest Administration Gospić, Forest Office Perušić, in a forest culture of Weymouth pine. The average DBH of the investigated trees was 31 cm. Average extraction distance was 450 m. All produced roundwood assortments, with the exception of the saw logs, were transported to a nearby (12.5 km) sawmill and chipped during the unloading. Main aim of the research was to determine the time consumption of the individual work elements in the working process, to design a mathematical model for calculating productivity and to calculate the costs of production. Work of the machines in the wood chips harvesting system was recorded with a digital camera. Division of the work elements and determination of their duration was performed by a subsequent analysis of the recorded video data. Regression analyses were performed in order to determine the dependence of time consumption of felling and time consumption of processing on DBH. Time consumptions of all the other work elements in the system were expressed as average values. By applying the related machine rate the unit costs was calculated on the subsystem level and on the system level. Produced wood chips were sampled and analyzed. Bulk density, moisture content and particle size distribution were determined according to HRN EN standards for solid biofuels. Productivity of the harvester in the thinning of the studied forest culture of Weymouth pine, calculated by a constructed mathematical model, ranges from 14.36 m3/h for DBH 22.5 cm to 26.29 m3/h for DBH 47.5 cm. Standard time, for the studied conditions amounts to 3.04 min/m3 for the harvester, 5.51 min/m3 for the forwarder, 4.89 min/m3 for the forest truck and trailer 1.33 min/m3 for the chipper. Unit cost of the production system is € 18.28/m3. Produced wood chips were classified as particle size distribution class P16B, moisture content class M55+ (64), and bulk density class BD350. Analysis results of the studied wood chips harvesting system in the thinning of the Weymouth pine forest culture allow the evaluation of the application of mechanized harvesting system in similar stand conditions. Valorization should be done in the light of the expected costs of harvesting and the quality and prices of produced wood assortments.

harvesting system; productivity; unit cost; wood chips quality

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