Stampfer Karl, PhD. Assoc. Prof.

Winch-assisted forwarders are now commonly accepted as an innovative alternative for extracting wood on challenging terrain. In order to assess safety risks, it is necessary to know the tensile forces in the steel wire rope and their interaction with the machine tilt under real working conditions. In this study, the tensile force and the machine tilt of two winch-assisted forwarders (John Deere 1210E and Komatsu 840TX) were observed for about 15 work hours without delays on two different stands in Austria. The tensile force data and the machine tilt data were separated by work elements. The mean tensile force ranged from 18.1 kN for unloading up to 56.8 kN for loading activities. During the measurements, the cable tensile force exceeded 50% of the minimum breaking strength (MBS) only twice. The maximum observed tensile force was 174.5 kN or 82.7% of the MBS, respectively, which led to a failure of the steel cable. For the machine tilt, a maximum of 80% was measured during loading and driving during loading. John Deere 1210E was operated 31% of the productive work time above the manufacturers tilt limit. For Komatsu 840TX, the manufacturers’ maximum tilt limit was exceeded only twice. The study also showed that peaks with an amplitude of up to 50 kN can occur within a few centiseconds, which highlights the need of high measurement rates, when measuring cable tensile force of winch-assisted machinery. The detailed analysis of the peaks showed that 90% of the pit-to-peak amplitudes ≥20 kN occurred during driving activities. Only 10% of pit-to-peak amplitudes ≥20 kN were measured during loading activities, although loading took about 43.5% of the productive work time. As such, the study results confirm that amplitudes of peaks in tensile force, and hence safety risks, are significantly higher during driving than during loading.

Forest road networks are exposed to damage by traffic, climate, timber harvesting and vegetation. To maintain their functionality, they must be maintained regularly. Periodical maintenance is required when the forest road surface layer is deteriorated and eroded. Well-graded material is required for replacing the forest road surface and often has to be sourced from gravel storage areas, which is costly and requires a large number of truck trips. Therefore, converting non-graded aggregate available on site into well-graded aggregate with a mobile stone crusher is considered a viable alternative.

The present study was carried out during a periodical maintenance treatment at the Bavarian State Forest Enterprise and the effect of employing a mobile stone crusher was evaluated with regard to (1) forest road load bearing capacity development during a one-year period post-treatment, (2) particle size distribution of the surface layer material before and after crushing, and (3) its cost compared to other alternatives. Samples were collected pre- and post-operation for particle size distribution analysis, load bearing capacity was measured repeatedly with a light falling weight deflectometer and compared to an untreated reference section and cost of the treatment was compared to two alternatives.

The mobile stone crusher was capable of reducing the non-graded to well-graded/close-to-well-graded material and particle size distributions aligned well with the recommendations for lime-water bonded surfaces. Load bearing capacity exceeded the threshold of 40 MN m-2 (Evd, elastic modulus dynamic) for primary forest roads at all times. It increased significantly after the treatment and remained on a significantly higher level throughout the following year. Absolute and relative increases were higher than on the untreated reference section. The treatment variant involving a mobile stone crusher and material available on site was substantially cheaper (5.31 € m-1) than to supply non-graded (16.29 € m-1) or well-graded (19.82 € m-1) material by truck. Material and transport costs represented 67% and 82% of the total costs in the latter two cases. It can be concluded that mobile stone crushers are capable of producing at least close-to-well-graded forest road surface aggregate and that forest road load bearing capacity can be significantly and lastingly increased at only a part of the costs of the alternatives. A maximum of cost and resource efficiency and environmental soundness can be attained when enough surface aggregate is available on site. If this is not the case, sourcing non-graded material as local as possible is the next best alternative.

Cross-cutting of a tree into a set of assortments (»bucking pattern«) presents a large potential for optimizing the volume and value recovery; therefore, bucking pattern optimization has been studied extensively in the past. However, it has not seen widespread adoption in chainsaw bucking, where time consuming and costly manual measurement of input parameters is required for taper curve estimation. The present study investigated an alternative approach, where taper curves are fit based on terrestrial laser scanning data (TLS), and how deviations from observed taper curves (REF) affect the result of bucking pattern optimization. In addition, performance of TLS was compared to a traditional, segmental taper curve estimation approach (APP) and an experienced chainsaw operator’s solution (CHA).

A mature Norway Spruce stand was surveyed by stationary terrestrial laser scanning. In TLS, taper curves were fit by a mixed-effects B-spline regression approach to stem diameters extracted from 3D point cloud data. A network analysis technique algorithm was used for bucking pattern optimization during harvesting. Stem diameter profiles and the chainsaw operator’s bucking pattern were obtained by manual measurement. The former was used for post-operation fit of REF taper curves by the same approach as in TLS. APP taper curves were fit based on part of the data. For 35 trees, TLS and APP taper curves were compared to REF on  tree, trunk and crown section level. REF and APP bucking patterns were optimized with the same algorithm as in TLS. For 30 trees, TLS, APP and CHA bucking patterns were compared to REF on operation and tree level.

Taper curves were estimated with high accuracy and precision (underestimated by 0.2 cm on average (SD=1.5 cm); RMSE=1.5 cm) in TLS and the fit outperformed APP. Volume and value recovery were marginally higher in TLS (0.6%; 0.9%) than in REF on operation level, while substantial differences were observed for APP (–6.1%; –4.1%). Except for cumulated nominal length, no significant differences were observed between TLS and REF on tree level, while APP result was inferior throughout. Volume and value recovery in CHA was significantly higher (2.1%; 2.4%), but mainly due to a small disadvantage of the optimization algorithm.

The investigated approach based on terrestrial laser scanning data proved to provide highly accurate and precise estimations of the taper curves. Therefore, it can be considered a further step towards increased accuracy, precision and efficiency of bucking pattern optimization in chainsaw bucking.

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.

The demand for increased efficiency in timber harvesting has traditionally been met by continuous technical improvements in machines and an increase in mechanisation. The use of active and passive sensors on machines enables improvements in aspects such as operational efficiency, fuel consumption and worker safety. Timber harvesting machine manufacturers have used these technologies to improve the maintenance and control of their machines, to select and optimise harvesting techniques and fuel consumption. To a more limited extent, it has also been used to evaluate the time taken to complete tasks. The systematic use of machine sensor data, in a central database or cloud solution is a more recent trend.

Machine data is recorded over long periods of time and at high resolution. This data therefore has considerable potential for scientific investigations. For mechanised timber harvesting operations, this could include a better understanding of the interaction between productivity and operational parameters, which first of all requires an efficient determination of cycle time.

This study was the first to automatically delimitate tower yarder cycle times from machine sensor data. In addition to machine sensor data, cycle times were collected through a traditional manual time and motion study, and cycle times from both studies were compared to a reference cycle time determined from video footage of the yarder in operation.

Based on three days of detailed time study, the total cycle time in the classic manual time (–1.3%) and in the machine sensor data (–1.2%) was only slightly shorter than in the reference study, and the average cycle time did not differ significantly (classic manual time study: –0.08±0.94 min, p=0.997; machine sensor data study: –0.08±0.26 min, p=0.997). However, the accuracy of the machine sensor approach (RMSE=0.92) was more than three times higher than that of the classic manual time study (RMSE=0.27).

With the integration of sensors on forestry machines now being commonplace, this study shows that machine sensor data can be reliably interpreted for time study purposes such as machine or system optimisation. This eliminates the need for manual time study, which can be both cumbersome and dependent on the experience of the observer, and allows long term data sets to be obtained and analysed with comparatively little effort. However, a truly automated time study needs to be supplemented with automated determination of and linkage to other operational parameters, such as yarding and lateral yarding distance or load volume.

Introduction: Cable yarding is a technology that enables efficient and sustainable use of timber resources in mountainous areas. Carriages as an integral component of cable yarding systems have undergone significant development in recent decades. In addition to mechanical and functional developments, carriages are increasingly used as carrier platforms for various sensors. The goal of this study was to assess the accuracy of individual standing tree and stand variable estimates obtained by a mobile laser scanning system mounted on a cable yarder carriage.

Methods: Eight cable corridors were scanned across two forest stands. Four different scan variants were conducted, differing in the movement speed of the carriage and the direction of movement during scanning. An algorithm for tree detection, diameter and height estimation was applied to the 3D datasets and evaluated against manual tree measurements.

Results: The analysis of the 3D scans showed that the individual tree parameters strongly depend on the scan variant and the distance of each individual tree to the skyline. This was due to changing 3D point densities and occlusion effects. It turned out that scan variant 1, in which the scan was performed during slow carriage movement downwards and back upwards again, was advantageous. At a distance of 10 m, which is half of the recommended corridor spacing of 20 m for whole tree cable yarding, 95.44% of the trees in stand 1 and 92.16% of the trees in stand 2 could be detected automatically. The corresponding root mean sqare errors of the diameter at breast height estimatimations were 1.59 cm and 2.23 cm, respectively. The root mean square errors of the height measurements were 2.94 m and 4.63 m.

Conclusions: The results of this study can help to further advance the digitization of cable yarding and timber flow from the standing tree to the sawmill. However, this requires further development steps in cable yarder, carriage, and laserscanner technology. Furthermore, there is also a need for more efficient software routines to take the next steps towards precision forestry.

The Technodiversity project addresses technological diversity by gathering a common basis of technological knowledge and increasing the sensitivity for diversity in forest engineering. It aims to bring together and make generally available the existing knowledge in forest operations that is scattered across various European countries. It will serve as a bridge between different regions of Europe and generations of students, practitioners, scientists and academics. In this article, a small part of the e-learning module (https://technodiversity-moodle.ibe.cnr.it/) is presented in a glossary of some of the terms of forest operations.

Traditional methods of determining cable corridor layouts often rely on less accurate tree maps based on forest density estimates and satellite imagery, which can lead to designs that rely on infeasible corridors, undermining their reliability. In our previous research, we used LiDAR forest maps to calculate highly realistic cable corridors in steep terrain. We then used a multi-objective optimization strategy to determine an optimal combination of possible cable corridors, taking into account costs as well as ergonomic and environmental factors. The optimization process is however not easily accessible to users not familiar with mixed integer linear programming approaches. To make the optimization process more accessible to forestry professionals, we have developed an interactive interface to support the layout planning process. This interface provides an interactive overview, a 3D perspective of the current layout, and detailed information on costs and metrics of the current cable corridor layout, facilitating the comparison and modification of different corridor layouts. The interface was evaluated by three subject-matter experts and their suggestions were incorporated into the presented version. The resulting tool can help experts use optimized cable corridor layouts in the planning process, and represents another step towards the digitalization of forestry.

Sensor technologies for monitoring danger zones during harvesting operations are not yet widely adopted, despite their potential to significantly enhance occupational safety. The objective of this study was to evaluate the performance of an ultra–wideband (UWB) sensor for detecting people in the danger zones of motor–manual harvesting operations. This was done to determine whether the system performance in practical use matches the results of a prior prototype test. The UWB sensor was deployed during three types of forest operations: thinning, clear-cutting, and overstory removal. Danger zones were defined as a circle with a radius of 1.5 times the top height of the stands: 21.00 m danger zone for thinning, 42.00 m for clear-cutting, and 46.50 m for overstory removal. Key metrics analyzed included detection distances, detection rates, interruptions in signal reception, and optimal sensor configuration. The results indicated mean detection distances of 19.80 m (90% Interval: 15.80–21.00 m) for thinning, 36.80 m (90% Interval: 23.70–42.00 m) for clear-cutting, and 39.00 m (90% Interval: 30.60–46.50 m) for overstory removal, with detection rates remaining stable across operations. The sensor system demonstrated its potential as a valuable tool for improving occupational safety.