Volume 11, numéro 2, july 2000

EN :

A new method for measuring the silvicultural result of thinning is presented in the study. The measuring method was based on rectangular sample plots measured parallel to strip roads. An individual sample plot consisted of eight zones, each 30 m2 in area. Due to its considerable importance in Finland, the one-grip harvester operation was the harvesting system examined. The research material was collected from 15 stands amounting to a total area of 14.7 ha.

The post-harvesting inventory provided good information on the removed and standing trees, their size and distribution. The number and distribution of standing and removed trees were according to Finnish thinning instructions, and thinning was typical low thinning, in which smaller trees and trees of low quality are removed. The average tree damage percentage, 4.6, is acceptable. However, the proportion of damage varied from 1.1% to 9.1% with different operators. The damage was highest during the summer. Small, superficial damage was typical. The average strip road width was 4.8 m, the distance between strip roads 19.8 m and the rut depth 0.6 cm.

The economic consequences of the damage was estimated using a calculation model. The model estimates the losses caused by strip roads, tree and soil damage. The economic consequences of harvesting damage during the rotation period was 1158 FIM (1 U$ = 5.60 FIM). Strip roads make a significant contribution to the amount of costs.

Due to the high variation in the harvesting quality, both the continuing supervision of the silvicultural thinning result and the training of machine operators are necessary. Thinning spruce stands during the sap period should be avoided due to the high risk of tree damage, and decay following damage. Generally, it is possible to obtain a good silvicultural thinning result with one-grip harvester operation.

EN :

In forestry, roads are essential structures as they provide access to the forest from the establishment phase to harvesting stage. Thus it is important that roads are properly planned, constructed and maintained in order to ensure easy access, smooth transport of forest products, safety, comfort and economy on vehicle operations. For Tanzania where commercial timber harvesting in plantation forests has just started, appropriate values of parameters for road alignment and gradient, in the context of the country's settings, need to be established.

This study, which was carried out on a gravel secondary access road, established that traffic and water contribute significantly to road deterioration or loss of road surface materials. Road alignment and road gradient were found to influence the rate of soil loss. The study found that the optimal road grade and curve radii which minimized road maintenance cost in this area were grades less than 6% and radii above 100m respectively. Statistical analysis however showed that there was no significant difference between straight sections of the road and the curve sections in terms of loss of surface layer materials.

EN :

Coillte Teoranta (the Irish Forestry Board) harvested approximately 2.0 million m3 in 1994. By the year 2000 this annual harvest is projected to increase to approximately 2.8 million m3 and to 3.7 million m3 by the year 2011. To facilitate the management of these increased timber flows more efficiently and effectively, the Harvest Scheduling System (HSS) was developed.

In order to evaluate the HSS's solutions, five case studies were carried out, two of which are presented in this paper. Initially, the HSS model was solved without any management constraints, resulting in a theoretical maximum net present value (NPV) (case study 1). Subsequently, the effect of imposing national and regional level volume fluctuation constraints was examined (case study 2).

The investigations in the "no constraints" study resulted in a theoretical optimal harvest schedule for Coillte over the period 1998 to 2002. The solution showed great volume fluctuations from year to year, in terms of total volume, species, harvest type and product. It would be impossible to implement such a schedule, due to management, harvesting resources and industry requirements. However, the NPV achieved was used as a base to estimate the cost of applying management constraints in the second case study. This second study also showed that Coillte's production smoothing process results in harvest schedules that are not feasible, as no adjustments for volume are included.

EN :

The optimum solution of locating a forest road network in a given forest area is still difficult to determine due to the complexity and the nature of the problem. Heuristic solutions are estimations of the optimum location but not the optimum one. This paper presents a dynamic programming procedure, integrated with microcomputer-based spatial database and transport network models, which can be used to assist foresters in determining the optimum location for a forest road. This method contributes to the optimum location of an entire road network serving a forest area.

EN :

This paper describes an investigation of fatigue resistance in different steel wire rope constructions used in Norwegian cable logging operations. Test results indicate the following:

A clear difference in fatigue resistance between ropes (approximately 50% decreased endurance for the compacted rope of highest density).

Differences in rope wear for varying angles of deflection.

A correlation between the number of visible broken wires and remaining strength in the rope.

EN :

The aim of this study was to i) develop and examine a methodology to handle spare part utilization data for work machinery for future inclusion into a life cycle assessment study and ii) assess the material consumption per 1000 m3ub harvested and transported to the roadside due to spare part utilization by three types of forest machinery. Thirteen forwarders, 14 single-grip harvesters and 10 two-grip harvesters operating in northern Sweden were followed up by repair records that covered a period from half a year up to 3.5 years. The replaced machine components were sorted in seven material categories - steel and iron, aluminum, other metals (brass, copper), plastics, rubber, glass and batteries. Two scenarios with different assumptions on the consumption of saw chains, guide bars and tires were developed. According to the low scenario about 46 kg of material will be consumed for harvesting and transporting 1000 m3ub to the roadside. The corresponding figure for the high scenario is 58 kg. The total component mass expected to be replaced during the operational lifetime (18000 E15 hours) of the machines was also calculated. According to the low scenario 38-45% of the mass of a machine will be changed during its operational lifetime. The corresponding figure for the high scenario is 50-56%.

EN :

This study determined how much wood was potentially available from short rotation hybrid poplar, and how much was actually recovered when trees were delimbed and debarked with chain flails and chipped. 31 groups of five trees each were measured and then processed.

For trees larger than 50 kg total dry weight, potentially recoverable wood averaged 75% of total weight. Over 95% of this wood was converted into chips. Losses due to breakage by the flails, which show up in the bark discharge, amounted to 0.8 dry kg per tree and were relatively independent of tree size. Chipper reject wood losses averaged 2.3 dry kg per tree, but increased in almost direct proportion to tree size, from 1.2 kg for 50 kg trees, to 3.2 kg for 120 kg trees.

For trees less than 50 kg total dry weight, potentially recoverable wood fraction was highly variable _ from 50 to 75% of total weight. Because of breakage of small stems by the flail, wood recovery was also relatively low, ranging from 40 to 95%. Most of the wood loss for smaller trees showed up in the bark discharge rather than as chipper rejects.

For larger trees, the chipper rejects represent the biggest opportunity for improving the recovery of wood fiber. Sharp chipper knives appear to be important for minimiz ing losses. Beyond that, it is not clear whether wood in the chipper rejects is the result of bole damage by the flail or chipper design characteristics.

EN :

This study investigated the impact of two different timber extraction systems on the natural regeneration in two compartments in the Hyrcanian Forests in northern Iran. These forests consist of mixed uneven-aged stands which are managed under the single tree selection system, with timber extraction taking place by cable system or by skidder. The operations were carried out by standard crews in 2 compartments with very similar terrain and stand conditions. The amount of damage to all stages of the regeneration was significantly higher in the skidding operation than in the cable operation. Based on this preliminary result and on observations of the authors, recommendations for future research and for improved harvest practices were drawn up.