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ŠUMARSKI LIST 1-2/2020 str. 41     <-- 41 -->        PDF

It was found that the average productivity of uphill winching was calculated as 12.98 m3/hour. In a previous study where the uphill winching was performed by a farm tractor, it was stated that the average productivity was 5.05 m3/hour for a stand with 0.20 m3 timber volume, winching distance of 30 meters, and ground slope of 45% (Gulci 2014). Therefore, average timber volume transported in each trip dramatically effects the productivity of the winching operation, when distance is constant.
For skidding the average time study data for each work stage is indicated in Table 4. It was found that skidding trees while moving backward to landing was the most time consuming work stage (64%), followed by moving to the prebunching area (23%). In a similar study where farm tractor was used for skidding, it was found that the most time consuming work stage was skidding loaded to landing area (46%), followed by moving to the roadside (Gilanipoor et al. 2012).
The average productivity of skidding trees by farm tractor on skid trail was 14.30 m3/hour. Gulci et al. (2017b) reported that the productivity of farm tractor in skidding whole-tree was 13.50 m3/hour in a stand with average skidding distance of 80 meters and 20% skid trail slope. Thus, slope of the skid trail is one of the main factors that affects productivity. The skidding distance is other important factor on operation time which reflects the overall productivity (Borz et al. 2015; Đuka et al. 2017; Gilanipoor et al. 2012). On the other hand, undoubtedly terrain conditions and operator experiences also influence the productivity of harvesting methods (Mousavi and Naghdi 2014).
The results show that different volume classes have significant (p<0.01) effects on productivity in both working phases (winching and skidding). The average productivity for uphill winching increased from low volume class to medium and high volume classes (Table 5, Table 6). Previous studies conducted on forest operations also indicated that efficiency of the system increases as the timber volume per trip increases (Gulci et al. 2017b; Ozturk and Akay 2007;