Volume 8, numéro 2, july 1997

EN :

Harvester productivity, extraction rate, selection criteria for harvesting a tree, and logging damage after different thinning types were studied in northern Sweden. Thinning operations were mechanized and carried out according to normal Swedish practice. The treatments were supervised thinning from below, supervised thinning from above, and unsupervised thinning from above. Time consumption per tree and harvester productivity in thinning from below were significantly different from thinning from above. Extraction rate was higher than the desired level in one plot for unsupervised thinning from above. One plot had a thinning ratio high enough to fit the definition for thinning from above, due to trees harvested independently of thinning type. Mean diameter for damaged and suppressed trees harvested was not different between treatments. No differences in the frequency for size and type of logging damage was found between treatments. For thinning from below, damage was located higher up on the stem than for thinning from above. This study concludes that differences in thinning ratio may be reduced when carried out in commercial forestry, due to the harvest of damaged, suppressed, and, to some extent, strip road trees. Harvester productivity increases with increased thinning ratio. To attain the desired stand densities and to keep damage level down, a skilled and motivated harvester operator is needed.

EN :

A study of the effect of slash on forwarder soil compaction was carried out. The level of soil compaction at two soil moisture contents, three slash densities (0, 10, and 20 kg/m2 ), and two levels of traffic (one and five passes) were measured. Results indicated that, on dry, loamy sand soils, the presence of slash did not decrease soil compaction after one forwarder pass, but did provide some protection from subsequent passes. The density of slash (over 10 kg/m2 ) did not affect compaction. On the same soils in a wetter condition, however, slash density at 20 kg/m2 was significantly less than on bare plots. At 10 kg/m2 , the increase in bulk density after five passes was smaller than on the bare plots, but not significantly so.

EN :

The purpose of the study was to determine the competitive strategies of the most successful forest machine contractors. Porter's strategy of focus was applied. Forest contracting businesses were assumed to have three alternative focus strategies, of which two, customer focus and geographic focus, were operationalized and measured. The success of the businesses was measured by financial results and strategic position.

A total of 27 entrepreneurs were personally interviewed. The average age of the entrepreneurs was 46 years, and the length of time as an entrepreneur, 19.5 years. The businesses employed an average of 5.1 permanent staff, and owned an average of 3.9 machines, about 40% of which were harvesters. The profitability of even the best businesses was excellent only during two of five years. Larger companies were in the top 50% of income generators, while smaller businesses were in both the upper and the lower halves.

The businesses in the most successful group had only one customer each, with whom the business was able to achieve a sufficiently high rate of capacity utilization and the operating radius did not grow to be too large. The competitive strategy for the group was customer focus. The question of sufficient solidity would be the criticism levelled at the most successful group. The capital costs were in excess of 30% and indebtedness was more than 50% of turnover. The strategic position for the best business group is judged to be fairly good.

EN :

Time consumption, heart rate, sagittal load moments for the low back, perceived exertion, and tool preferences were measured during motor-manual cleaning with chain saws and cleaning saws in western Norway. While no difference was found in heart rate or perceived cardiovascular exertion, the chain saw was observed to have the lowest time consumption per ha of the two tools. Calculated sagittal load moments and local feeling of strain in the low back were significantly higher for the chain saw than the cleaning saw. The difference in time consumption between the two tools was greatest for the least experienced personnel in steep terrain. However, because of the higher risk for low back pain, the chain saw could only be recommended on relatively steep slopes. The cleaning saw was preferred most often by the most experienced forestry workers in stands of high removal density.

EN :

Two methods of felling were tested in a thinning operation to determine if Scandinavian techniques in manual felling could be applied successfully in combination with a cable yarder for thinning in young stands of western hemlock and Douglas-fir. The study results suggest that manual felling productivity was much lower using the Scandinavian techniques, although subsequent yarding productivity was improved by more than 170% when compared with yarding production after conventional felling operations. Cost estimates developed during the study suggest that productivity improvements in the yarding phase reduced the cost of processed logs delivered to roadside by more than $2.50 per ton for the Scandinavian system.

EN :

This paper describes a prototype computer vision system based on texture analysis that can automatically locate and identify certain classes of defects on freshly harvested tree stems (with bark present) by using digital camera imagery. This system includes two modules: (1) a feature extraction or "computing" module for estimating the oriented texture field from the raw image of the surface of a log; and (2) a scene analysis and detection module for analysing the oriented texture field. Basic principles of the system based on the gradient of the Gaussian filter have been given.

The sample digital images processed in this study are of sections of freshly harvested Radiata pine tree stems with bark still on them. The feasibility of the computer vision system has been very well demonstrated by initial experimental results.

This study has also resulted in a new taxonomy for texture description and identification in the field of forestry. Texture analysis technology has been found to be a potentially powerful approach to determine wood properties, timber and log quality.

The system developed in this study can be widely applied into forest industry activities and research.