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The purpose of the research was to present problems related to the damage to the stand resulting from the scraping works performed on its surface, mainly with the use of forwarder skidding. The research was conducted in thinned Scots pine stands in the IV and V age class in the Wipsowo Forest District (northern Poland). In the selected stands we carried out the inventory of the stand layers. Based on the obtained data, the level of damage to trees after thinning operations was calculated. Damage resulting from the skidding with forwarder in the individual manipulation plots was at a level of 18.2−18.7% in the method used by the Wipsowo Forest District, while in the method proposed by the author damage level equaled 3.9−9.8%. It was found out that the highest number of damage occurred in the belt up to 5 m from the skidding trail, especially at the width of the trails below 4 m. The damage is most affected by the stand density – the higher it is, the more trees are damaged.
The amount of timber extracted from Polish forests is expected to increase in near future. The most common equipment for timber extraction is an agricultural tractor with a trailer equipped with a hydraulic crane. The research was carried out in the Wymiarki Forest District (Regional Directorate of the State Forests in Zielona Góra) in the third (TP1) and fourth age class (TP2) in Scots pine stands, during extraction of timber from thinning. Extraction was carried out using BELARUS MTZ 1221.2 agricultural tractor with PALMS 120 forest trailer equipped with PALMS 700 hydraulic crane. The scope of the study was to conduct time studies of extraction process and to estimate the extraction productivity as well as time and fuel consumption. Working time was measured by stopwatch, while the forwarding distance was determined with measuring wheel. The exact number of logs in each load was established. Average volume of each log and each load was calculated. The dominant work time category was effective working time 74.78% (TP1) and 73.60% (TP2), while the prevailing work task was loading 56.82% (TP1) and 58.99% (TP2). In older stands, the extraction productivity was higher than in younger ones reaching 11.28 and 9.62 m³/h, respectively. Statistical analysis proved that extraction distance significantly affect productivity and time consumption. With increasing extraction distance productivity decreases and time consumption increases. Fuel consumption was exactly the same in younger and older stands (0.52 l/m³).
Skidding includes timber transport from the place of its harvest to the place of its storage, loading or pre−treatment. This process in the thinned stands can result in serious damage to the remaining trees. The purpose of the described research was to characterize and compare the size and location of damage in the thinned stands after forwarder skidding with the damages resulting from the combined forwarder and tractor ground skidding. These tests also aimed at determining whether the contractor’s experience affects the level of damage. The research was carried out on four study plots located in the Chojnów Forest District (C Poland). Although the works on each plot were performed by different contractor, they had equipment of comparable technical and overall parameters.The height of the damage, the distance of the damaged tree from the skidding trail and the size of the damage were measured. Damage was classified according to the degree of the tissue damage. The most serious damage occurs at a distance of up to 1 m from the skidding trail and at a height of up to 1 m. The most severe damage was over ⅛ of the trunk perimeter. No significant dependence of the size and location of damages on the skidding method was found.The highest fraction of the damaged trees was recorded on the area in the Młochów Forest Range (5.17%) where only the forwarder skidding took place. In the Sierzechów Forest Range (the same method of skidding, but almost twice as dense stand), there was significantly less damage (0.62%). In this case, the share of the damaged trees was the smallest, despite the highest number of trees. The reason for this may be the impact of the human factor on the amount of damage as the most experienced contractor worked on that study plot.
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