Epsilon Archive for Student Projects

Abstract

The aim for this study where to investigate the frequency of cutting cracks in saw timber harvested in the storm-damaged forests in regions where the storms Hilde and Ivar hit. The idea for this work came from one of the region’s biggest actors, SCA Skog and Jämtlands district. The purpose where to find out how big proportion of the saw timber that contains cutting cracks, their financial cost in lost wood value and also give advice and suggestions on how to work against the frequency of cutting cracks.
For the field-study some guidelines where used to make sure that the samples were taken under the same conditions, they were:
• The field-study must be performed under harvesting of storm-felled forest, which are horizontal/inclined trunks.
• The averaged sized tree will make it possible to harvest saw timber.
• The trunks can’t be root cut.
A methodology called in Swedish “Trissmetoden” was used because it is the most frequent used methodology in earlier performed studies and the only one that can be used I field.
Under the field-study data were collected from 570 saw timber logs, 30 logs from each one of the tested harvesters. Logs of log-types middle- and topplogs of pine and spruce was cheched and were a part of the study. 56 percent of the logs were pinelogs and 44 percent of the cheched logs were sprucelogs. 85,3 percent of the logmaterial had an diameter between 16 cm and 24 in rootdiameter and 74,4 percent had lengths between 37 dm and 49 dm.
In average of the 19 controlled harvesters there were 28 percent cutting cracks and it was a small different between the tree species, spruce had an higher frequency cracked logs but only 2,7 percent higher frequency. The crack frequency increased especially for logs with a diameter ≥30 cm and length ≥49.
A comparison between different harvesting-head manufacturers was made and the two manufacturers that had most tested harvesting-heads were John Deere and Komatsu. John Deere’s harvesting-heads produced timber with fewest cutting-cracks, they had a cut frequency of 18 percent in average and were the best among the manufacturers while Komatsu had 30 percent. Other manufacturers that were included in the study was Logmax, Ponsse and SP.
The average crack for both tree species were 8,4 cm long but the pine had a tendency to crack more. In average did the cutting crack occurred after that 75 percent of the trunks diameter were cut thru.
The wood loss that occurs while harvesting windfalls due to cutting cracks and shortening of the average crack length to get crack free timber were 0,54 percent of the harvested saw timber volume. But with shortening of a length module at 30 cm the wood loss was 2,01 percent of the harvested saw timber volume.