The effect of timber harvesting in thinning of pine stands Pinus sylvestris L. on efficiency of extraction using an agricultural tractor with a self-loading trailer

The aim of this study was to compare basic efficiency parameters in forwarding of logs felled using a harvester and chain saws. Logs of 4.0 m in length came from late thinnings of pine stands and they were extracted with an 86 kW agricultural tractor with a self-loading trailer of 9500 kg load capacity. Analyses included the load, extraction distance, organizational structure of oper- ation time, duration of the extraction cycle, as well as productivity in the operation time. It was also verified whether there is a relationship between the distance covered to collect log loads and the duration of the extraction cycle and the duration of the loading operation. These values were recorded during 27 extraction cycles for logs felled using a harvester and 25 extraction cycles for logs felled using chain saws. The extraction distance for logs felled using a harvester was 250 m, while for chain saw-felled logs it was 200 m. The mean load of logs felled using a harvester and those chain saw-felled was comparable (6.2-6.4 m3). The distance covered to collect the load of logs felled using a harvester was statistically significantly shorter than that for chain saw-felled logs. Within the structure of operation work time the greatest share accounted for loading time (almost 50 and 60% for logs felled using a harvester and chain saws, respectively). The duration of the extraction cycle for chain saw-felled logs was almost 33 min. and it was statistically signifi- cantly longer than the duration of the extraction cycle for logs felled using a harvester (24.5 min.). Extraction productivity in the operation time for logs felled using a harvester was over 15 m3<middle dot>h-1 and it was statistically significantly greater than extraction productivity recording for chain saw- felled logs (almost 12 m3<middle dot>h-1). In the case of both log harvesting technologies a weak, statistically non-significant correlation was found between the distance covered to collect the load and the duration of the extraction cycle. A similar situation was observed in the case of the distance and duration of loading for chain saw-felled logs, whereas for logs felled using a harvester no correlation between these variables was recorded.