Volume 14, numéro 1, january 2003

EN :

During mechanised forest harvesting, extraction routes may be armoured with a dense carpet of logging residues (slash roads) to reduce soil disturbance associated with heavy machinery. However, guidelines regarding the design of slash roads remain largely qualitative, and their efficacy as a means of ground protection uncertain. Trials were undertaken in north-east England and south-west Scotland to identify the main causes of slash road failure during repeated trafficking. Failure of the slash roads was defined as (a) deflection of logging residues and exposure of the ground surface to harvesting machinery or (b) mixing of logging residues with surface soils. The frequency of slash road failure was directly linked to terrain factors (soil water content, the presence of rocks, tree stumps, furrows and drain channels, or slope). In addition, failure was linked to the design of the slash roads where large diameter logging residues were readily deflected, or at junctions and turning points where 'shearing' of the slash road took place. A simple means of assessing the potential for slash road failure is presented based on terrain characteristics. These guidelines allow harvesting staff to locate extraction routes in order to maximise the structural longevity of the slash road, whilst reducing down-time associated with their repair. In addition, and where standard yield tables apply, a means of predicting the volume of logging residues available at any site is demonstrated, and the implications of this for effective slash road construction are discussed.

EN :

The aim of this study is to investigate the productivity, thinning quotient, reduction in basal area, damage rate, and costs of operation of row and selective thinning in the establishment of a shelterwood in a medium-aged Norway spruce stand. The cutting was performed with a single-grip harvester operating from existing striproads (spacing 15 m) parallel to the tree-rows. Extraction with a forwarder was studied in the same stand.

The two thinnings were more alike than expected. The thinning quotient was 0.9 and the reduction in basal area round 40% in both treatments. The time consumption for harvesting was larger in row than in selective thinning because row thinning was more difficult to perform when the harvester worked from striproads parallel to the tree-rows. No difference in forwarding productivity was found. The damage rate was higher in row than in selective thinning. It is concluded that row thinning from striproads parallel to the tree-rows has a negative influence on both productivity and quality of the work. This type of row thinning is difficult to perform because the tree-rows are difficult to identify and because the trees are more difficult to reach.

The operational aspects should be considered before a thinning method is chosen. Row thinning should preferably be carried out either by driving on removed rows or from striproads perpendicular to the tree-rows.

EN :

Machines with lower investment and operating costs can be one solution in solving the harvesting costs problem of first thinnings. The long-term productivity of thinning harvesters and harvester-forwarders was investigated in a joint project between Finnish research institutions. In the follow-up study, three harvester-forwarders and five thinning harvesters were studied. The total harvested volume was almost 30000 m3.

The work performed by harvester-forwarders includes both cutting and forwarding. The average productivity of a harvester-forwarder varied from 3.81 m3/E15 hours in first thinnings to 7.87 m3/ E15 hours in regeneration cuttings. The productivity was calculated for a 250 m forwarding distance. Average stem size of the stand, removal per hectare, and number of timber assortments were the factors affecting productivity when the forwarding distance was standardized. The productivity of thinning harvesters varied from an average of 6.92 m3/E15 hours in first thinnings to 16.18 m3/E15 hours in clear cuttings. Some of the harvesters were well capable in small dimensioned clear cuttings, the smallest machines being solely designed for thinnings.

Harvesting costs were compared at the harvesting system level. The costs of a medium-sized forwarder were added to the costs of harvesters. Cost data for the widely used medium-sized harvester system were added to the comparisons made for the forwarding distance of 250 metres. The thinning harvester system had the lowest costs for both two and five timber assortments. In the case of five assortments, which is the typical number in thinnings in Finland, the medium-sized harvester system had lower costs than the harvester-forwarder above a stem size of 60 dm3. At an average stem size of 200 dm3 the difference between the harvester systems was minimal. In the case of two assortments, the competitiveness of the harvester-forwarder was better, and below a stem size of 100 dm3 its costs were lower and between 100-200 dm3 at the same level as for the medium-sized harvester system. The thinning harvester system was still the cheapest alternative.

Thinning harvesters and harvester-forwarders are interesting alternatives for thinnings. The high capacity and all the properties of medium-sized harvesters cannot be fully exploited in thinnings. Thus machinery with lower capital costs and reasonable productivity can be competitive. Some of the studied machines can be used effectively in clear cuttings with a reasonable stem size. The harvester-forwarder is an interesting type of machine that is currently undergoing rapid development. The harvester-forwarder is most competitive in small stands with a short forwarding distance.

EN :

A Differential Global Positioning System (DGPS) -supported working procedure was developed for the mulching of access corridors in age class I stands in Germany. In an empirical investigation, this DGPS navigation procedure was compared to the conventional stake orientation procedure. In addition, a work study was carried out for the two procedures, and the accuracy and economic characteristics of both were compared.

The relative proportions of individual work elements within the processes are similar. The productivity is the same. There are ergonomic differences for the driver with the two procedures. During the stake orientation procedure the driver has to twist around in his seat for orientation, during heavy vibration. With DGPS navigation the driver does not need to turn his head. With the stake orientation procedure there is a high risk of injury for the person setting the stakes. DGPS navigation is a one-man working procedure, so nobody has to work in the danger zone.

Stake orientation is characterised by very straight mulching lines. Deviation from the prescribed route increases with increasing distance from the starting point. Obstacles in the area complicate this stiff orientation procedure. DGPS navigation enables the driver to keep to the prescribed line and to adapt vehicle movements dynamically to the obstacles in the area.

The economic characteristics of the two procedures were compared using the cost comparison method. The DGPS navigation procedure was found to be better economically because the work was carried out by one man only.

EN :

The average log size in many parts of the world is getting smaller and it is becoming increasingly time consuming and expensive to individually scale each log. Truck scaling of various forms, including the use of weighbridges, is becoming increasingly popular.

Understanding the factors affecting the accuracy of weighbridge systems is vital if measurement errors are to be minimized. We used a mixture of interviews with weighbridge operators, suppliers and government weights and measures staff in New Zealand along with experiments on a small set of weighbridges to identify, and where possible quantify, the most important factors affecting weighbridge accuracy. In our paper we have broken down the sources of variation into mechanical, environmental, truck, human and system-related. It is difficult to put a figure on the possible magnitude of these combined sources of variation, however, interviews, experiments and calculations show that it could be as much as 4% of the payload weight - although it is likely that some sources of variation will act in opposite directions and cancel each other out.

EN :

This study quantifies the economic effect of optimizing roundwood destinations in North Sweden. The effect of planning horizon and delivery precision on costs and revenues are also quantified. The results show that the effect of optimizing roundwood destination varies with the specific application. When minimizing transport costs for a forest company, the transport output (t-km) was reduced by 8-9%. The reductions of transport costs in this case were often in the range of 4-5% (two-week planning horizons). Longer planning periods gave slightly greater cost reductions. Increased net revenues of roundwood sales by an independent forest owner organization were in the area of 1-4% (two-week planning horizons). In this case, however, transport output was often increased by the optimization. Reduced demands to delivery precision made it possible to achieve greater increases in net revenue. Shorter planning horizons had fewer active supply nodes. This situation requires greater spatial variation in procurement areas in order to fill the demand restrictions per period. Only 15-20% of the annual procurement volume per sawmill came from supply nodes where the mill acted as monopsonist.

EN :

Operational harvest planning in the southern USA has not been widely used in the past due to a lack of state legislation, non-regulatory water quality protection programs, and relatively easy logging conditions. Increased government regulation and market pressures to document sustainable forest management under various certification standards is increasing the need for harvest planning in the region, particularly on private, non-industrial timber sales. We developed an ArcView extension, Setting Analyst (SA), to assist harvest planners. SA can use spatial information obtained from scanned air photos or detailed data from a geographic information system. It models travel patterns of ground-based machines and compares different harvest settings based on projected average skidding distance, costs of skidding and improvements, and site disturbance levels. In its current form, it does not account for slope. SA can model settings with complex features such as stream crossings, restricted areas, and skidding on designated trails. Travel intensity is assessed since it is highly correlated with site disturbance and soil compaction. To assess the utility of SA, we used it to model ten actual harvesting settings and contrasted each with two proposed settings. SA produced sale plans that were very similar to those observed on the ground. Its primary advantage is that it conveniently documents each alternative setting considered for the timber sale. These can be kept on file to demonstrate the level of planning used when forest certification audits are conducted. SA offers the most potential to harvest planners that already use GIS or GPS but desire additional analysis and documentation capabilities.

EN :

Three log grapple tong shapes used in logging operations; horizontal ellipse, circle, and vertical ellipse, were analyzed mathematically and mechanically. The three same tongs as defined were designed and tested to evaluate their performance in terms of grabbing unrestrained log piles. Three operational variables; grabbing force, grabbed log weight, and unit grabbing force were examined using five diameter classes of logs for each set of tongs. Results indicated that the grabbing performance of log grapples with horizontal ellipse tongs is better than the grapples with circular tongs or vertical ellipse tongs.