Volume 13, numéro 2, july 2002

EN :

Recent labour shortages and rapid increases in labour costs in Irish forestry have directed attention to mechanised, containerised tree planting systems as an alternative to the traditional manual planting of bare-rooted stock. The objective of this study was to compare mechanised planting with manual operations, on both reforestation and afforestation sites, using Sitka spruce (Picea sitchensis (Bong.) Carr.) plants in three container types (i.e. hard container, root trainer, fen container). The Bräcke tree planting machine was selected for the study, as it is capable of handling a wide range of site conditions and a variety of plant types and sizes. A qualitative analysis of the collected data showed that, in general, manual planting scored significantly higher than mechanised planting for plant position and planting quality. However, the quality of planting resulting from mechanised operations was well within acceptable operational requirements. On the reforestation site, plant growth after one growing season was investigated. No overall significant differences in height growth and root collar diameter increment were found in the first growing season between mechanised and manual planting operations. Plants grown in `fen containers' had the highest relative increase in height growth and root collar diameter, irrespective of planting method. The results showed that the Bräcke planting machine was capable of planting a range of containerised plants to an acceptable standard on both reforestation and afforestation sites. Further research to optimise the combination of machine, plant size and container type should result in improvements in both the quality and productivity of the planting operations.

EN :

Harvesting very small trees one by one has always been comparatively unproductive. Multiple-tree handling creates opportunities to reduce time per tree and thereby make it profitable to harvest small trees instead of thinning to waste. Multiple tree-handling is achieved by felling more than one tree in one cut or by felling one tree per cut and accumulating trees on the felling head, thereby handling several trees during one crane cycle.

The effect of accumulating trees depends on how much faster each additional tree can be felled (positioning head and cutting off) compared with the previous tree and how much time (per tree) is saved when moving several trees during crane-in (bunching). Felling several trees in one cut reduces time per tree substantially, but is often of limited relevance due to spacing between trees.

Field studies showed significantly lower time consumption when accumulating smaller tree sizes. Reduction of time consumption for crane work was approximately 40 % for the smallest trees. The difference decreased as tree size increased. Time consumption for the first "crane to tree" was a little higher than for the following crane movements to trees to be cut. Time for "crane-in" only slightly increased with the number of trees in the felling head. The time required to fell two or more trees in one cut was not significantly different than for a single tree, giving a substantial reduction in time per tree.

EN :

This article describes the interface between a one-grip harvester and its operator as it relates to motor-sensory and cognitive activities of the operator when carrying out thinning and regeneration harvesting in Sweden. Work tasks are described, as are operator data gathering, cognitive and motor-sensory processes. Descriptions of motor- sensory inputs and control manipulation are based on digital data gathering from machine controls combined with parallel, multi-camera video taping of work activities. Work element descriptions, data gathering and cognitive processes were inferred based on interviews with 20 operators and operator instructors.

Work features found to limit an operator's efficiency were: few breaks in the work; very intensive handling of controls ( 4000 control inputs per hour in our study) due to lack of automatic functions in the boom and harvester head; restricted view from the cab; lack of information about the stand and log; and skewed and twisted work postures.

The main part of the operator's cognitive work was found to be done through automated skills. The experienced operator acts upon the global situation and seldom analyses it explicitly. Their chunks of information (memory aggregates recognized in toto) guide them in what to do, and usually they see only one course of action to follow in a particular situation.

Key future technical development needs and opportunities include additional automation to reduce operator control inputs, developing means of improving visibility such as 3-D laser scanning and additional use of stand inventory and historical data about log properties to improve automation of cross-cutting.

One of the key future research areas regarding training and robotization is to determine the data contained in the `chunks' of information used by operators in making machine location, harvesting and processing decisions.

EN :

The performance of alternative equipment for the whole-tree harvesting of eucalypt stands was evaluated, using data from five different commercial operations. The study covered three machines for felling and bunching, two for extraction (skidding), and two for combined delimbing, debarking and chipping. Productivity and operating cost models were evaluated for each of the machines, in order to estimate the net harvesting costs under varying forest stand and site conditions.

It was found that under easy terrain conditions (flat terrain, dry ground), trees should be felled by three-wheeled feller-bunchers and extracted by front-end loaders, as this combination had the lowest harvesting costs. Due to mobility limitations, this equipment may have to be replaced by tracked feller-bunchers and conventional skidders in steep terrain and/or soft ground

It was estimated that the cost of using the wheeled feller-buncher and the front-end loader system ranged between 16-22$ per oven-dry-ton (odt), depending on tree size. If difficult terrain imposes a shift towards the second, more expensive combination, harvesting cost will increase by about 30% and may exceed 25 $/odt for an average tree weight less than 0.1 odt. Unit costs are inflated by 30% if the hog fuel is considered a by-product and the harvesting cost is charged entirely on the clean chip.

EN :

In the last 25 years, helicopter extraction of timber has developed as an important harvesting alternative in mountainous areas. Typical helicopter operations include the extraction of valuable timber from stands with inadequate road networks, large areas of difficult to reach wind-throw, and sensitive sites where the negative impact on soil and water must be minimized. An empirical study provides information on the effect of silvicultural treatment and pilot experience on the productivity of the K-Max helicopter. The productivity model is a function of the average stem piece size, the horizontal distance between stump and landing, the silvicultural treatment, and the experience of the pilot. The productivity obtained when harvesting from a clear-cut was greater than from the `femel-cut' (patch-cut) extraction site by 0.20 m3/min, or 21% at an average piece size of 1.5 m3. The inexperienced helicopter pilot had timber extraction experience but just 30 flight hours on the K-Max while the experienced pilot had 22,000 K-Max flight hours. The experienced pilot yielded a 0.37 m3/min increase in productivity, which is a 63% increase at an average piece size of 1.5 m3. This indicates that operator experience on a particular machine may be very important when comparing harvesting systems based on time studies.

EN :

The aim of this study was to examine the extent and severity of accidents and long-term health problems, and to evaluate perceptions of health and safety issues among forest harvesting contractors and sub-contractors in Ireland. A postal questionnaire was distributed to 450 forest harvesting (sub)contractors with the co-operation of the Irish Forestry Contractors Association (IFCA) and Coillte Teoranta (the State Forestry Company, referred to as Coillte). The questionnaire was completed and returned by 61 respondents. The majority of these were chainsaw, harvester and forwarder operators. The occurrence of an accident (requiring medical attention) in the last three years was reported by two respondents, while long-term health problems were reported by 23 (40%) of the respondents. Results showed that long-term health problems were not significantly correlated to age or training level. The two work elements in forest harvesting operations that were found to be most hazardous were operating a chainsaw and machine maintenance. When asked about the perceived dangers in the industry and the obstacles to improvements, 59% of the respondents identified harvesting work as dangerous, while 62% described financial pressure as the main barrier to improvements in safety, followed by the pressure of work (39%) and a lack of adequate training (36%). Suggestions on ways to improve the overall health and safety situation within forest harvesting included improved training and safety education (45%) and reduced work pressure (36%).

EN :

Consensus forums are one method of dealing with controversial natural resource issues. Minnesota regulators learned numerous important lessons when they used a consensus-based approach to develop voluntary site-level forest management guidelines. These include: 1) take active steps to facilitate information sharing among team leaders, 2) select team members who can effectively represent their group's perspective, who are solution-oriented, and who can help shape a compromise, 3) be prepared for problems that will arise so that they don't bog down the process, 4) use field tours as a mechanism to educate participants and to test the practicality of proposed guidelines, and 5) build in flexibility to accommodate the range of considerations which affect guideline application.