Investigation of Log Length Accuracy and Harvester Efficiency in Processing of Oak Trees

• Published in: Croatian journal of forest engineering Vol. 39; no. 2; pp. 173 - 181
• Main Authors: Piotr S. Mederski, Zbigniew Karaszewski, Zenon Pilarek, Agnieszka Łacka, Mariusz Bembenek
• Format: Journal Article
• Language: English
• Published: University of Zagreb, Faculty of Forestry 2018
• ISSN: 1845-5719; 1848-9672

Harvester use in broadleaves has recently become more effective economically. However, difficulties with delimbing have shown that not all harvesting heads are suitable and efficient for broadleaved species. The typical obstacles are mainly large tree sizes, bends and forks in the trunks and large branches. For these reasons, it is difficult to obtain specific log lengths according to the settings in the harvester on-board computer. The objective of the research was to determine: 1) the accuracy of the log lengths from the bottom, middle and top parts of oak trees, and 2) harvester efficiency in the utilisation of the trunk for logs. The research was carried out on 61-year-old oaks from which logs with an expected length of 250 cm were processed. To achieve this length, a margin of error was set in the harvester computer with minimum and maximum lengths of 252 and 257 cm. For thinning operations, a Ponsse Ergo harvester with a H7 harvesting head was used. After harvesting, manual log measurements were carried out on 280 logs: 69, 142 and 69, from bottom, middle and top parts of the trees, respectively. The largest share of assortments satisfying the minimum requirement of 250–257 cm was obtained from the middle part of the trees (93%), followed by bottom logs (91%) and top logs (88%). The highest frequency of logs, which were too short, were found to be the top logs (9%), while bottom logs were most often too long (6%); therefore, different length settings should be applied to limit such inaccuracies. Analysis of the last log from the highest part of the tree indicated a strong goodness of fit between the top diameter and the DBH; the mean value of the top diameter was 13.3 cm over bark.