Steep terrain harvesting can only be implemented by a limited set of operational alternatives; therefore, it is important to be efficient in such conditions, in order to avoid incurring high costs. Harvesting abiotically-disturbed forests (salvage harvests caused by wet snow), which is becoming common these days, can significantly impact the operational efficiency of extraction operations. This study was implemented in order to evaluate the performance of truck-mounted uphill cable yarding operations in salvage logging deployed in coniferous stands. A time study was used to estimate the productivity and yarding costs, and predictive models were developed in order to relate the time consumption and productivity to the relevant operational factors, including the degree of wood damage. The average operational conditions were characterized by an extraction distance of 101 m and a lateral yarding distance of 18 m, resulting in a productivity rate of 20.1 m³ h⁻¹. In response to different kind of delays, the productivity rate decreased to 12.8 m³ h⁻¹. Under the prevailing conditions, lateral yarding accounted for 32% of the gross work cycle time, and for 50% of the delay-free work cycle time of the machine. Decreasing the lateral yarding distance and increasing the payload volume to the maximum capacity of the machine would eventually lead to a yarding productivity of close to 30 m³ per SMH (scheduled machine hour). The calculation of the gross costs of uphill yarding showed that the labor costs (35.7%) were slightly higher than the fixed costs (32.9%), and twice as high compared to the variable costs (17.7%). The remote control of the carriage, mechanical slack-pulling mechanisms, and radio-controlled chokers are just some of the improvements that would have led to increments in operational efficiency.

Cable-based yarding technology has had a long tradition on steep slopes in Europe, and the new implementation of yarding functions in recent decades favored operational efficiency and lower extraction costs. The main goal of this study was to evaluate the performance of the Syncrofalke 3t truck-mounted Processor Tower Yarder (PTY) on steep terrain, in coniferous forests managed with the shelterwood system. In particular, the aim was to determine PTY productivity and costs, with attention to parameters that could increase PTY effectiveness. The study was carried out in the Sredna Gora Mountains, Central Bulgaria, in pure Scots pine stand, with trees of average DBH = 34 cm and height = 22 m. The study was carried out in six corridors with 120 work cycles of tree extraction up the hill, 28° (53%). The mean productivity of PTY was 15.20 m³ per productive machine hour (PMH) and 12.29 m³ per scheduled machine hour (SMH) and was mainly influenced by the productivity of the yarder unit. Under the given conditions, the performance of PTY significantly increased if more than one tree (at least two trees) were attached and extracted per yarder cycle, since the productivity of the processor was approximately twice that of the yarder. The gross costs of the studied PTY were calculated at 297.48 EUR PMH⁻¹ and 16.17 EUR m⁻³. The variable costs (75%) predominate in the net costs distribution, followed by the fixed costs (15%) and the labor costs (10%). The time, productivity and cost results obtained showed the high efficiency and level of integration of PTY operations in order to achieve economic efficiency of logging in montane pine forest managed in a shelterwood system.

Forwarders often load logs organized in large piles by modified farm tractors, skidders, animals, other forwarders, etc., but currently, there are no studies on how the different concentrations of logs affect forwarder performance in terms of time consumption, productivity, and costs in forwarding operations. A study was conducted in three locations situated in Bulgaria (sites A and B) and in southern Italy (site C): in site A the logs were spread in the stand, in site B they were concentrated in large piles at the roadside, whereas in site C the logs were organized at the roadside in piles of medium size. The average forwarder productivity in site A obtained at an average forwarding distance of 1780 m, an average payload volume of 9.83 m3, and an average number of grips of logs with the crane grapple, during loading (22.97) and during unloading (8.97) per cycle, is 10.43 m3·PMH-1 (PMH, productive machine hour) and 9.93 m3·SMH-1 (SMH, scheduled machine hour), respectively. In site B the productivity rate was lower than that registered by the forwarder operated in site A: 9.38 m3·PMH-1 and 8.81 m3·SMH-1, respectively, at an average forwarding distance of 3760 m, average payload volume of 15.04 m3, and a mean number of grips of logs with the crane grapple, during loading and during unloading, of 23.57 and 14.10 per cycle, respectively. With regard to site C, the average machine productivitiy was 12.39 m3·PMH-1 and 11.85 m3·SMH-1, travelling a mean forwarding distance of 1630 m, transporting a mean load volume of 13.63 m3, and performing an average number of grips of logs with the crane grapple, during loading of 26.52 and during unloading of 12.36 per cycle. The ratio between the number of grips of logs with the crane grapple during loading and unloading operations in site A is on average 2.56, but in site B it is significantly smaller – mean of 1.67, due to the larger number of logs in the grapple when loading from large piles. Site C shows a loading and unloading number of grips ratio intermediate between the two Bulgarian sites. This ratio is characterized by the concentration of logs in the stand. Concentration in larger piles results in a larger volume of grappled logs by crane, and hence, lower time for loading of the forwarder and higher productivity. The obtained results show that the dispersion of small piles of logs results in a smaller volume grappled, a greater number of crane cycles and a larger loading distance, which generally, increases loading time. The larger volume of logs in the crane grapple and the shorter loading distance, when the loading operation is carried out from larger piles at the roadside, lead to less loading time. Gross costs for forwarders were 65.14 € PMH-1 at Site A, 72.96 €·PMH-1 at Site B, and 85.58 €·PMH-1 at Site C. When the forwarders were productive, the costs were 6.35 €·m-3 in site A, 7.90 €·m-3 in site B, and 6.90 €·m-3 in site C.

The efficient planning and control of timber harvesting operations is crucial to growth productivity and reducing costs, and different systems or methods are applied to obtain elevated performance. In particular, cable yarding is a highly appreciated and very efficient wood extraction method in areas that are difficult to access with ground-based extraction machines. Combined logging systems are not diffuse and not often implemented. For this reason, the use and the application of innovative methods are limited. However, some combinations have recently been observed in forest operations. This study, conducted in a deciduous stand in Bulgaria, paid attention to the combination of a tractor-mounted tower yarder (Valentini V400) with a clambunk skidder (Timberjack 1010D), aiming to examine the viability and develop the operational efficiency of the two-stage extraction system and to define the time, log volume extracted per unit by the yarder and the clambunk, and the yarding and skidding costs. The researchers carried out a time-motion study and performed a regression analysis to identify those variables that are most likely to affect the duration of work elements and productivity. For cost analysis, the COST model was used. The mean productivity of the tower yarder was 10.34 m³/PMH and 8.11 m³/SMH, while for the clambunk skidder, the productivity was 6.23 m³/PMH and 4.93 m³/SMH. The net costs for the combined logging system were calculated as 120.87 €/PMH and 14.93 €/m³. This study adds new data about the correct use of both machines, supporting their application in beech forests.

Examination of the technical and economic dimensions of skidding operations is imperative for sustainable forest management, offering invaluable insights crucial for the formulation of sustainable forestry strategies. In many countries, the shift from modified agricultural machinery to purpose-built forest machinery has become apparent in forest operations. However, this transition often accompanies a reduction in logging crew size, raising new questions about productivity, costs, and ergonomics of the introduced harvesting systems. This study investigates two skidding systems utilizing the cable-grapple skidder Welte 115/5L, differing in work team size: one with one skidder operator and two chainsaw operators (WT3) and the other with one skidder operator and one chainsaw operator (WT2). Conducted in natural European beech forests in southern Bulgaria, the research focused on the group shelterwood system within the Natura 2000 network. Both WT3 and WT2 exhibited net skidding productivity of 9.96 m³ PMH⁻¹ over a mean skidding distance of 300 m and a mean winching distance of 20 m, outperforming conventional systems in the area. Despite this, there were notable differences in gross skidding productivity (8.64 m³ SMH⁻¹ for WT3 vs. 7.30 m³ SMH⁻¹ for WT2), affecting skidding cost (EUR 5.41 m⁻³ for WT3 vs. EUR 6.62 m⁻³ for WT2) and unit production cost (EUR 9.33 m⁻³ vs. EUR 11.53 m⁻³). This study highlights that the cable-grapple skidder can be effectively employed by smaller teams, providing higher productivity, lower unit cost, and increased flexibility during piling, primarily due to the presence of the knuckle-boom loader. While WT2 experienced more delays and production pressure, the findings suggest that WT3 represents a balanced option for small logging crews, ensuring sustainable forest operations in the face of workforce challenges.

In Europe, long-distance transport of wood from landings to consumers is most often carried out by trucks and trucks with trailers. In forests located mainly in mountainous areas with rugged terrain and frequent curves, the construction of forest roads is complicated and often access for trucks with trailers is difficult or there is not enough space on the landing for maneuvers. In these cases, the truck leaves the trailer next to the public road and without it moves to the landing and loads the wood with Palafinger hydraulic crane model Epsilon Kran GmbH mounted on it, which it transfers to the trailer on the way back. Then, the truck moves to the landing to load itself, returns, hooks up the trailer and transports the wood to the customer. This study, conducted in a coniferous stand in Bulgaria, aimed to determine and develop models for the productivity and costs associated with transporting a truck with a trailer and to evaluate the suitability of this method. To study this very common method of long-distance transport, observations were made of 185 turns of a truck with a trailer operating with coniferous wood in Rila-Rhodope Mountain Massif, Southern Bulgaria. It was found that the duration of the working cycle is affected by the total mileage (average 65.41 km), the volume of the load and the number of logs. The productivity with and without delays, 7.80 and 7.30 m³/h, respectively, is affected by the mileage and the volume of the wood, while the corresponding transportation productivity (177.46 and 167.24 m³ km/h) is affected by the transport distance loaded and the volume of the load. To increase efficiency and reduce the cost of transporting wood over long distances, investments are needed to improve forest roads to eliminate the need to uncouple the trailer.