Volume 9, numéro 2, july 1998

EN :

When a containerized seedling is pneumatically transported through a pipe or hose it occasionally undergoes oscillating movements, referred to as “wobbling“, with the container being flung from one side of the hose to the other. Data on this phenomenon obtained in a previous feed-time study were further analyzed. In addition, a laboratory study was carried out in which the behaviours of seedling-container dummies of different sizes and shapes were studied at different air velocities in Plexiglas pipes of various diameters. Both the analyses of the frequencies of wobbling from the previous feed-time study and the results from the laboratory test confirmed that there is covariation between the wobbling tendency of a seedling and the shape of its container. Containers with a large butt-end area tend to wobble more. This leads to differentiation of the seedlings into two groups, seedlings with butt-ended and less butt-ended containers. This differentiation was the same whether it was based on feed times from the previous study, frequencies of wobbling from the previous study, or the wobbling behaviour in the recent laboratory test with dummies.

EN :

Data Envelopment Analysis (DEA) models were used to measure the technical efficiency of a sample of logging contractors. DEA is a nonparametric efficiency measurement technique based on linear programming methods. This paper demonstrates how DEA models can be applied in a forest operations context to gain insights on the factors which affect technical efficiency and performance.

Twenty-three fully mechanized loggers were compared in regards to the efficiency with which they converted inputs – dollars of capital, consumables, and labor – into output – tons of wood. Overall, for the period of 1988 to 1994, the logging contractors studied were efficient, but some were considerably less efficient than others. Low capacity utilization had a negative impact on technical efficiency. The scale of an operation also influenced technical efficiency. For the sample, the most productive scale size was estimated to be around 75,000 tons per year.

EN :

In this study the effect on occupational safety and health of increasing mechanization and improved ergonomics in Swedish forestry has been analyzed by using data on accidents and health hazards for chainsaw operators and logging-machine operators. In 1990 the accident frequency rate was 63 and 17 respectively, indicating a risk reduction of 73% by mechanization compared to chainsaw-based methods. There have also been significant improvements within each group. Between 1970 and 1990 the frequency rate for chainsaw operators was reduced by 48%, and for logging-machine operators by 70%, the result of improved ergonomics and safety organization. Health hazards have also been reduced, notably vibration-induced white fingers (VIWF) among chainsaw operators. The increasing number of machine contractors form a potential risk group. Some 50% of logging-machine operators have symptoms of repetitive stress injuries (RSI). Large-scale prevention programs have been initiated, with the emphasis on development of new work organization.

EN :

Mechanical injuries were examined after single-tree selection harvesting in multi-storied stands of Norway spruce. Randomised block studies were used to compare the effect of two operating systems and three harvest intensities upon the injury rate to the residual stand. The average injury rate for mechanised shortwood harvesting was higher than for motor-manual cutting and cable skidding. The largest differences between these two systems were found at high harvest intensities in densely stocked stands. A number of variables were used to quantify this interaction. The variable which best explained the risk for injury in the individual stand was the ratio between removed vertical crown projection and horizontal crown-free projection before harvest. The higher injury rate for mechanised harvesting is attributed to the greater proportion of the stand which is impacted by the handling of trees.

EN :

Adjusting truck tire inflation to changing road and load conditions has been demonstrated to improve road conditions and is thought to decrease truck maintenance costs. Good roads will minimize the future cost of utilizing forest resources.

In this study, the various effects of both low-pressure and high-pressure truck tires on the transportation vehicle were examined in terms of seat vibration. The data collected by the US Army Corps of Engineers, Waterways Experiment Station (WES), for the USDA Forest Service in 1989, were used to perform the analyses. Analysis of the data pertaining to road failure is fairly complete. However, a significant portion of the truck data still needs to be analyzed.

Vibration levels were higher in the truck with high tire-inflation pressure, but the differences in vibration levels between low- and high-pressure trucks were not as high as expected. Although vibration levels were higher in 10 out of 15 road sections in the high-pressure truck, two sections had significantly reversed results.

EN :

This paper presents results from comparative studies of conventional Scandinavian shortwood processing vs a differentiated processing method. The latter signifies processing only sawlogs at the logging site. Pulpwood and forest fuel are transported off the site as undelimbed tree sections. The objective of the studies was to contribute to the development of new methods suitable for integrated harvesting of forest fuel and conventional forest products for industrial use. Study methods include direct measurement of workpiece and output and a precise indirect time measurement and working pattern evaluation, both by using videogrammetry.

Both a motor manual and a mechanized system was studied. For motor manual logging, differentiated processing was found to be recommendable for ergonomical, economical, and efficiency reasons. For the studied mechanized system – single-grip harvester in thinning – the productivity of differentiated processing did not match conventional logging. The main reason for this seems to be that crane handling and not processing is the weak point of the harvester system. According to the study, the amount of crane handling increased when differentiated processing was applied in mechanized logging. The output of forest fuel was markedly lower than that of the motor manual version.

EN :

Timber procurement is part of the flow of wood from forest to production. In the present study, it is referred to as timber flow, which consists of logging, roadside inventory, transportation, and mill inventory functions. Local timber flows should be managed by tactical means of decentralized decision making (DDM), which are facilitated by dynamic models of a decision system. The technique consists of several hierarchical negotiation levels which can solve a local procurement problem by the technique of functionally decentralized decision making (FDDM). Models describing the system are also bigger and more complicated than models which are constructed for geographically decentralized decision making (GDDM). Consequently, the models may cause different dynamic results. Therefore, this study has two main objectives: 1) to introduce a technique of GDDM and 2) to consider the effects of the time-factor using dynamically determined functions of local procurement. Using this application, the system can be controlled for balancing timber flows, because the system's internal adjustment process is defined with higher precision; the extra costs caused by a disturbance can be diminished by adjusting the durations of local timber-flow functions. The implications of these results for improving decision making (DM) of local timber procurement in Finland are discussed.