The Effect of New Silvicultural Trends on Mental Workload of Harvester Operators

Close-to-nature (CTN) forestry offers many advantages, but makes management more complex and generally results in lower harvesting productivity and higher harvesting cost. While the higher harvesting cost of CTN is widely acknowledged, few ever consider the potential impact on operator workload, as the harvesting task becomes more complex. This study aimed to determine the mental workload of harvester operators under two silvicultural regimes: »pure conifer« stand and »mixwood« stand. In total, 13 harvester operators with varying experience levels were monitored for work performance and mental workload when operating a harvester simulator in two virtual stands designed according to the above-mentioned silvicultural regimes. Mental workload was assessed using the NASA Task Load Index (NASA-TLX) interview method and heart rate variability measurements, during two 30-minute test sessions performed in the »pure conifer« and the »mixwood« stand, respectively. As expected, operating in a more diversified »mixwood« stand resulted in a marked productivity loss, estimated between 40 and 57%. The study also confirmed the increased aggravation of mental demand, effort and frustration experienced by the operators when passing from the »pure conifer« stand to the »mixwood« stand. Such increase in mental workload was independent of the age and experience of the operators. Results can be used to paint a more holistic picture of CTN forestry and its implications for harvester operators. Besides increasing the number of subjects being monitored, future studies should focus on live forest operations

Quantitative and qualitative workload assessment in steep terrain forest operations: fostering a safer work environment through yarder automation

Many forestry roles have changed from being manual tasks with a high physical workload to being a machine operator task with a high mental workload. Automation can support a decrease in mental fatigue by removing tasks that are repetitive and monotonous for the operators. Cable yarding presents an ideal opportunity for early adoption of automation technology; specifically the carriage movement along a defined corridor. A Valentini V-850 cable yarder was used in an Italian harvesting setting, in order to gauge the ergonomic benefit of carriage control automation. The study showed that automating yarder carriage movements improved the ergonomic situation of the workers directly involved in the related primary tasks. However, the caveat is that improving one work task may negatively affect the other work tasks, and therefore introducing automation to a worksite must be done after considering all impacts on the whole system. Practitioner summary: Automation decreased the winch operator’s mental workload while improving overall productivity. At the same time, the mental and physiological workload of the operator tasked with bucking were slightly increased. Ideally, winch automation should be coupled with bucking mechanisation to balance the intervention and boost both operator well-being and productivity.publishedVersio

Trends and Perspectives in Coppice Harvesting

Coppice management is applied to many species, in many countries and in many ways, so that several harvesting techniques have been developed depending on specific local conditions. However, all techniques designed for handling coppice stands must be suitable for coping with small stem size and stump crowding, and often with steep and generally difficult terrain. Traditional harvesting systems are labor intensive because they usually include motor-manual felling and processing into one-meter lengths at the stump site, and manual loading of the short logs onto pack animals or tractors. Thus, in industrialized countries, these systems are no longer viable and they are being replaced with mechanized cut-to-length and whole-tree harvesting, depending on site conditions. Mechanization dramatically improves worker safety, and compensates for the reduced availability of rural labor, with their propensity to perform heavy and low-paying jobs. Much progress has already been made, with the massive introduction of modern harvesters, forwarders and tower yarders in coppice harvesting operations. The presence of multiple stems on the same stump offers a serious challenge to the introduction of mechanized felling to coppice harvesting operations, because stump crowding hinders felling head movements. However, new machines have been designed that can handle coppice stumps. Further research should address the relationship between stump damage and regeneration vigor, in order to define new standards for cut quality. Silvicultural practice may need adapting to the new harvesting technology and to the products required by the modern bio-economy

Manipulating Chain Type and Flail Drum Speed for Better Fibre Recovery in Chain-Flail Delimber-Debarker-Chipper Operations

A chain-flail delimber-debarker-chipper (CFDDC) was adapted for treating smaller trees than normal by replacing the standard flails with lighter ones, and by reducing flail drum rotation speed. The machine produced 16 full containers (24 t each) for the standard configuration and 24 full containers for the innovative one. For each container the researchers measured: original tree mass, chip mass, time consumption and fuel use. Results indicated that the innovative setting accrued a 12% improvement on fiber recovery compared with the standard setting (control). At the same time, productivity increased by 20% and fuel consumption was reduced by 30%. Product quality was largely unaffected, with bark content remaining below the 1% threshold specification. If at all, product quality was improved through the reduction of fine particles, possibly derived from less diffused fraying. These results have triggered the real scale adoption of the new setting by contractors who participated in the study. The success of the innovative treatment is likely explained by its better alignment with the weaker structure of small trees from low-yielding stands

Forest Workers and Steep Terrain Winching: the Impact of Environmental and Anthropometric Parameters on Performance

Winching is common in small-scale forest operations, especially on steep slopes, where tractors cannot reach the logs inside the forest. In this case, logs are dragged to the roadside with tractor-mounted winches, for later collection by transportation units. Winching is a heavy task, posing a high physiological stress on winching crew members. The aim of this study was to investigate the relationship between experienced workload, work conditions and operator fitness. The study confirmed the assumption that fit, young operators experience a lower workload than older ones. Workload depends on winching direction, and it is higher when winching downhill than when winching uphill. Results confirmed that gravity is the main factor, and it has a stronger effect than task type and tool weight. Walking uphill with no tools is heavier than walking downhill and carrying a steel cable. As a consequence, tool weight reduction can only palliate the problem, without solving it. Winching crews should be composed of fit, young workers. When the task is assigned to older workers, it is necessary to allow longer rest breaks, accepting a lower productivity

Comparison of Cost Efficiency of Mechanized Fuel Wood Thinning Systems for Hardwood Plantations on Farmland

A harwarder is a machine used for both wood harvesting and extraction. A small and a large harwarder (SH and LH) were time studied whilst thinning hardwood plantations established on agricultural land in Italy. Two treatments were studied: whole tree sections (WT) or firewood logs integrated with tree tops (IH) were harvested and forwarded to the roadside. The selective thinning yielded 45 tonnes of fresh biomass (t) per hectare. The average productivity of the SH and LH with the WT harvesting treatment were 3.46 and 2.77 t per gross productive work hour, respectively. The SH was more efficient for felling and loading, while the LH was more efficient in the terrain transport work. The productivity of both machines was about 15% lower for IH treatment. The harwarder based thinning operation gave a harvesting cost between 18 and ‘ €/t under the conditions studied. Thus, the operational cost per t of the SH was less than for the LH. The harvesting cost decreased with increasing size of harvested trees for both machines. The level of stand damage caused by both harwarders was almost as low as the levels recorded in the literature for motor-manual thinning. The LH was able to handle larger trees than the SH in the studied conditions. The LH gives higher flexibility, since it can be used more efficiently in thinning of larger trees and in larger plantations than in the present study

The Effect of Yarding Technique on Yarding Productivity and Cost: Conventional Single-Hitch Suspension vs. Horizontal Double-Hitch Suspension

Cable yarding is a well establish technology for the extraction of timber in steep terrain. However, it is encumbered with relatively low productivity and high costs, and as such this technology needs to adapt and progress to remain viable. The development of biomass as a valuable byproduct, and the availability of processors to support yarder operations, lend themselves to increasing the level of whole-tree extraction. Double-hitch carriages have been developed to allow for full suspension of whole-tree and tree-length material. This study compared a standard single-hitch to a double-hitch carriage under controlled conditions, namely in the same location using the same yarder with downhill extraction. As expected, the double-hitch carriage took longer to load up (+14%), but was able to achieve similar productivity (10–11 m3 per productive machine hour) through increased inhaul speed (+15%). The importance of this study is that it demonstrates both the physical and economic feasibility of moving to whole-tree extraction using the double-hitch type carriage for longer corridors, for settings with limited deflection, or areas with lower tolerance for soil disturbance

Cable Logging Contract Rates in the Alps: the Effect of Regional Variability and Technical Constraints

A survey of cable logging contracts was conducted in 5 of the 8 Alpine countries, namely: France, Germany, Italy, Slovenia and Switzerland. The goals of the survey were to set a general reference for cable logging rates, to identify eventual differences between countries and to determine the effect of technical work parameters (i.e. piece size, removal per hectare, line length) on actual contract rates. With a total sample size of 566 units, the mean removal and rate were 165 m3 ha–1 and 42.9 € m–3, respectively. Both removal per hectare and contract logging rates varied considerably and the study found significant differences between countries. Switzerland stood out from the group with the highest removal (345 m3 ha–1), but also the highest contract rate (79.5 € m–3). Removal per hectare was lowest in Italy with just 58.3 m3 ha–1, and logging rate lowest in Slovenia at 29.3 € m–3. Logging rates were highly correlated with the average labour rate of each country. Technical factors such as tree size, line length and tract size explained about 40% of the variability in logging rates. Therefore, 60% of the variability is explained by other technical factors not included in our data and by non-technical factors, such as local market dynamics

Evaluation of Different Modes for Yarding Windthrown Timber with a Double-Hitch Carriage

Yarding whole trees is the most efficient way of extracting timber in steep terrain and allows reaping the combined benefits of mechanization and biomass recovery. In downhill yarding, however, whole-tree extraction is associated with a greater risk of loosening rocks or debris by the incoming loads as they bounce around along the extraction corridor. That may also cause damage to the cables and anchors by corresponding shock loads, ultimately endangering the yarder and its crew. To avoid these risks, »double-hitch carriages« can be employed. They combine a conventional motorized dropline carriage with a secondary carriage (»trailer«), equipped with a further, independent dropline winch. Thus, loads can be attached at two points and transported fully suspended above the ground in a horizontal position. Operation of these carriages may not be limited to the »horizontal« mode: the main carriage could also be operated without trailer (»single« mode), or separate loads may be attached to the two droplines (»double« mode), but their impact on the efficiency and economy of yarding operations is yet unknown. Therefore, the present study investigated how these modes affect the productivity and cost of downhill whole tree yarding. To this end, a classic time and motion study was conducted during a salvage logging operation in Northern Italy under a strictly controlled experimental design. Average productivity (18.2±7.2 to 24.5±15.4 m³ PSH0-1 merchantable volume per productive system hour excluding delays) and extraction cost (18 to 20 Euro m-³) did not differ significantly between treatments, while load composition and time consumption by task did. More (2.2±0.5) pieces per load were yarded under the »double«, than under the »single« (1.4±0.5) and »horizontal« (1.1±0.3) treatments. Inhaul speed (3.1±0.6 m s-1) was significantly higher under the »horizontal« treatment, which compensated for increased loading time derived from attaching the load at least at one point outside the corridor. Unloading took significantly longer under the »double« treatment, as loads had to be dropped successively due to the confined conditions on the landing. Though slowest (2.5±0.9 m s-1) during inhaul, the »single« treatment exhibited none of the other treatments disadvantages and larger loads could be accumulated due to partial suspension. From an economic viewpoint, the »horizontal« mode may only be warranted over yarding distances substantially beyond average. On shorter ones, it must be justified by other reasons, such as minimizing product contamination, soil disturbance or excessive strain to the skyline when the terrain profile impedes sufficient ground clearance