Based on the knowledge of the dimensional and mass features of a forwarder, a model was developed to assess its mobility during timber forwarding uphill in a safe and eco-efficient way. The model is ...based on knowledge of the position of the forwarder’s centre of gravity, its declared payload and the length of the loaded timber, as well as the gradeability for uphill timber forwarding based on the traction characteristics of the vehicle. The model connects two research approaches, (1) vehicle–terrain approach (distribution of axle loads depending on the longitudinal terrain slope) and (2) wheel–soil approach (estimation of the traction characteristics of the forwarder based on the wheel numeric), concerning previous research: (i) underload on the front axle of the vehicle, (ii) overload on the rear axle of the vehicle, (iii) permissible tire load, (iv) minimal soil bearing capacity, (v) wheel slip. Simulation modelling for the assessment of the forwarders’ mobility range during timber forwarding uphill was conducted on an example of an eight-wheel Komatsu 875 forwarder, with a declared payload of 16,000 kg, equipped with 710/45-26.5 tires, for which the position of the centre of gravity was determined by the method of lifting the axle. The results of the distribution of the adhesion load on the front and rear axles of the forwarder indicated that, during timber forwarding of 16,000 kg and 4.82 m long hardwood logs on a terrain slope below 68%, there is no critical unloading on the front bogie axle, nor overloading on the rear bogie axle, i.e., wheel tire overload that could limit forwarder mobility. For the specified range of longitudinal terrain slope, a minimal cone index of 950 kPa for an exemplary forwarder is an environmental factor and was calculated based on the nominal ground pressure of the reference (heavier loaded) rear wheels of the vehicle. The forwarders’ mobility range was determined by the intersection curves of the gradeability (based on forwarders’ traction characteristics at wheel slip of 25% vs. cone index) and the curve of the minimal soil cone index.
This study compared oak butt-log volume estimations gained through terrestrial measurements in the forest stand with a remote approach using an unmanned aerial system (UAS) and photogrammetric ...post-processing. Terrestrial measurements were conducted in the lowland part of Croatia after a completed motor–manual final felling of a 140-year-old even-aged oak stand. Butt-logs’ volumes were estimated with four methods: the sectioning method and Huber’s, Smailan’s and Riecke–Newton’s methods. Measuring diameters and lengths and estimating volumes remotely were based on orthophotos using four different software: ArcGIS, QGIS, AutoCAD and Pix4D. Riecke–Newton’s method for volume estimation had the smallest relative bias of +1.74%, while for Huber’s method it was −8.07% and with Smailan’s method it was +21.23%. Log volume estimations gained remotely via ArcGIS and QGIS were, in the case of Huber’s method, at +3.63% relative bias, and in the case of Riecke–Newton’s method at +1.39% relative bias. Volume estimation using the sectioning method resulted in a total of 51.334 m3 for the whole sample, while the sectioning method performed with the help of AutoCAD resulted in 55.151 m3, i.e., +7.43% relative bias. Volume estimation of thirty oak butt-logs given by Pix4D software (version 4.8.4) resulted in +9.34% relative bias (56.134 m3). Comparing terrestrial measurements and the volume estimations based on them to those gained remotely showed a very high correlation in all cases. This study showed that using a UAS for log volume estimation surveys has the potential for broader use, especially after final felling in even-aged forests where the remaining trees in the stand would not block photogrammetric analysis.
Rutting measurements are a significant part of scientific research on the impact of forest vehicles on the forest soils and damage to the forest transport infrastructure. Although photogrammetric ...methods of measurement or measurements based on LiDAR (light detection and ranging) data are increasingly being used for rutting measurements, the previous research conducted using these methods indicated the challenge of recording water-filled ruts. For this reason, it is necessary to define a reliable method of rutting field measurement in lowland forest stands characterized by a high level of groundwater that fills the ruts shortly after the passage of forest vehicles. This research analyzed the measurement accuracy using a total station and a GNSS RTK device with a CROPOS correction base in relation to the measuring rod that represented the reference method. Based on recorded and processed data, ruts are displayed in two ways: as net and as gross value of rut depth. The analysis of net rutting revealed a statistically significant difference between the calculated rut depths based on measurements with a GNSS RTK device and other methods. On average, the net rutting measured by the GNSS RTK device was 2.86 cm smaller than that of the reference method. When calculating the gross rutting, which consisted of the net rut depth and the bulge height, no statistically significant difference was found between the measurement methods used. Based on this result, the bulge height was also analyzed, and showed a statistically significant difference between the data recorded by the GNSS RTK device and other methods. It can be concluded that measuring the depth of ruts with a total station gives accurate data and represents the optimal modern field measurement method for the same or similar terrain conditions. In contrast, the GNSS RTK device, which constantly gives higher elevation points, can be used to measure gross rutting.
During the seven-year research period, the average annual removal was by 3274 m3 higher than the average annual removal prescribed by the existing management plan (MP). The main reason lies in the ...high amount of salvage felling volume at 55,238 m3 (38.3%) in both the main and the intermediate felling due to oak dieback. The analysis of forest accessibility took into account the spatial distribution of cutblocks (with ongoing felling operations) and the volume of felled timber for two proposed factors: (1) the position of the cutblock and (2) the position of the removal. Cutblock position factor took into account the spatial position of the felling areas/sites, while removal position factor besides the spatial reference took into account the amount of felled timber (i.e., volume) both concerning forest infrastructure network and forest operations. The analysed relative forest openness by using geo-processing workflows in GIS environment showed four types of opening areas in the studied management unit (MU): single-opened, multiple-opened, unopened and opened areas outside of the management unit. Negative effects of the piece-volume law and low harvesting densities on forest operations are highlighted in this research due to high amount of salvage felling particularly in the intermediate felling by replacing timber volume that should have come from thinnings.
This research was conducted to determine the cause, intensity and location of damage (stem, butt end, root collar, root) and the extent of damage to standing trees during felling and processing by an ...harvester and timber extraction by a forwarder (cut-to-length system). The research was conducted in the central part of the Republic of Croatia in the Management Unit (MU) “Bjelovarska Bilogora” during the thinning of Subcompartment 14b, area of 18.28 ha, in the stand of hornbeam (Carpino betuli—Quercetum roboris fagetosum Rauš 1975), age 70, and of Subcompartment 14c, area of 9.07 ha, in a stand of common beech (Carici pilosae—Fagetum Oberdorfer 1957) aged 79 years. The thinning intensity was 12.13% in Subcompartment 14b and 13.72% in Subcompartment 14c. Field measurements were carried out on sample plots—the first time in 2017 to determine the intensity and characteristics of the damage to standing trees with regard to the cause of the damage (harvester or forwarder), and the second time in 2018 to determine the overall intensity and features of the damage to standing trees after finishing harvesting operations. For all trees remaining in the stand after the harvesting operations, the following were determined: tree species, diameter at breast height (DBH), the position of the tree in the stand depending on the forest traffic infrastructure, and—if damaged—cause of damage, type of damage, the position of damage on the tree, and dimensions of damage. The intensity of the damage was expressed by the ratio of damaged and undamaged trees, with a detailed analysis of bark damage (squeezed-bark damage and peeled-bark injuries). The results of the research indicate the highest prevalence of peeled-bark injuries. In relation to the total number of standing trees, trees with peeled-bark injuries were more represented in Subcompartment 14c (39%) than in Subcompartment 14b (33%). In Subcompartment 14b, the harvester and the forwarder damaged an equal number of trees, while in Subcompartment 14c, the harvester damaged 59% of the damaged trees. In both subcompartments, an average of 83% of (peeled bark) injuries were up to 1.3 m above the ground. In both subcompartments, the most common (67%) were injuries up to 100 cm2 in size, for which many authors claim the tree can heal by itself. Given the increasing use of harvester-forwarder systems in deciduous stands and research results that indicate possible damage to standing trees, it is necessary to pay attention to all phases of planning and execution of timber harvesting operations, thus minimising negative effects.
The use of forestry vehicles in mechanised harvesting systems is still the most effective way of timber procurement, and forestry vehicles need to have high mobility to face various terrain ...conditions. This research gives boundaries of planning timber extraction on sloped terrain with a cable skidder, considering terrain parameters (slope, direction of skidding, cone index), vehicle technical characteristics and load size (5 different loads) relying on sustainability and eco-efficiency. Skidder mobility model was based on connecting two systems: vehicle-terrain (load distribution) and wheel-soil (skidder traction performance) with two mobility parameters: (1) maximal slope during uphill timber extraction by a cable skidder based on its traction performance (gradeability), and (2) maximal slope during downhill timber extraction by a cable skidder when thrust force is equal to zero. Results showed mobility ranges of an empty skidder for slopes between −50% and +80%, skidder with 1 tonne load between −26% and +63%, skidder with 2 tonne load between −30% and +51%, skidder with 3 tonne load between −34% and +39%, skidder with 4 tonne load between −35% and +30% and skidder with 5 tonne load between −41% and +11%.These results serve to improve our understanding of safer, more efficient timber extraction methods on sloped terrain.
This study aims to define a simple and effective method to calculate skidding distances on steep karst terrain, rich in ground obstacles (stoniness and rockiness) to support decision planning of ...secondary and primary forest infrastructure network for timber extraction in productive selective cut forests. Variations between geometrical extraction distances and actual distances were highlighted on the operational planning level (i.e., compartment level) through GIS-related calculation models, focusing on cable skidder timber extraction. Automation in defining geometrical and real extraction distances, as well as relative forest openness were achieved by geo-processing workflows in GIS environment. Due to variation of extraction correction factors at the compartment level from a minimum of 1.19 to a maximum of 5.05 in the same management unit, it can be concluded that planning harvesting operations (timber extraction) at operational level should not include the use of correction factors previously obtained for entire terrain (topographical) categories, sub-categories or even management units.
Skidder mobility during timber extraction is defined by: 1) basic dimensional features of the vehicle, 2) ability to overcome obstacles during movement, 3) traction performance and 4) environmental ...soundness. Traction performance depends on the ground conditions (soil bearing capacity) and the total effect of all forces on the vehicle. In downhill skidding, the skidder is under great influence of parallel component of forces, adhesion weight and longitudinal terrain slope, which combined result in negative traction force, torque and thrust force. When the horizontal component of rope force is equal to zero i.e. the moment when the weight of the load and resistance to traction are in equilibrium, the slope angle a is a function of load mass distribution factor and skidding resistance factor. This is a "turning point" that can be defined as a critical slope because the load starts to push the vehicle downhill, which results in negative horizontal component of rope force. Depending on skidder Ecotrac 120V dimensional features, centre of gravity, load mass distribution factor, skidding resistance factor of previous research, five different loads were analyzed (1 to 5 tonnes) in order to define the critical slope angle for each of them. Critical slope for downhill skidding of 1 tonne timber is on longitudinal slope of -26%, for 2 tonne timber on -30%, 3 tonne timber on -34%, 4 timber on -38% and for 5 tonne timber on -43% of terrain longitudinal slope. Even though skidding bigger load increases vehicle mobility to even greater slope angles, the most important in downhill skidding, is to avoid blocking of the wheels, which will lead to a complete vehicle slippage and the driver must be constantly aware of that fact. The general recommendation should be that skidding small loads (1 to 3 tonnes) downhill is suitable for smaller longitudinal terrain slopes (up to maximum -34%), while the heavier the load, the further down the slope the skidder can go. The load of 5 tonnes "anchors" the skidder better and therefore it can go on terrain slopes up to -43%, during which less traction force is used (torque is used for braking) and skidder pulls the load by its own weight. It can be concluded that extending the operating range of skidder onto steeper slopes with heavier loads has the potential to decrease harvesting costs and increase productivity. Keywords: skidder, downhill timber extraction, rope force, critical slope
Ambrosia bark beetles belong to a group of xylomycetophagous insects from the order Coleoptera, family Curculionidae and are characterized as important pests of oak timber. Galleries they form during ...their life cycle and infect with »ambrosia fungi« significantly decrease the economic value of oak roundwood. A state owned Croatian company »Hrvatske šume« Ltd. manages FSC certificated forests, where pedunculate and sessile oaks account for 22.6% in the annual allowable cut. Methods of oak roundwood protection, that used to be implemented in the past, are now banned in accordance with EU legislation as well as FSC criteria of forest protection. In these forest management conditions, it becomes necessary to introduce new biotechnical methods for oak roundwood protection. Available commercial products, flight barrier traps and synthetic semiochemicals, as well as pretreated insecticide treated polymer nets, were tested as means of integrated oak roundwood protection. Implementation of these products was tested in field conditions. Good knowledge of phenology of ambrosia bark beetles, thorough understanding of timber harvesting operations and field conditions that dominate in even aged oak forests, is crucial if applied methods are to be effective and taken on time. Field experiments conducted in this research showed that early seasonal deployment of semiochemically baited flight barrier traps can reduce the number of bark beetles that infest oak timber. It was also concluded that without additional protection with polymer nets, it is not possible to protect oak timber in compliance with strict FprEN 1316-1: 2012 E standards for oak roundwood classes, which do not allow any timber infestation in the highest quality grades (A and B quality class). Semiochemicals used as repellents during the research were ineffective. In the early months of spring, oak roundwood is at high risk of infestation at the roadside landings, where it is waiting to be transported.
This paper discusses the key issues of forestry workers training in Croatia, especially dealing with the providers of vocational training, their profile, training procedures and measures necessary ...for training improvement. A combined approach of literature review, internet search and questionnaire of training providers was applied in order to collect data on training programs conducted in Croatia. The research was conducted during 2016, and it included 94 legal entities authorized for occupational safety training in the Republic of Croatia, with respect to safe working practice training and vocational training for operating machinery (chainsaw and/or skidder). The analysis used basic descriptive statistics. Research results showed that 30.85% of the analyzed legal entities provide only training for safe working practice, 15.96% provide both trainings--safe work practice and vocational training for operating machinery, 5.32% of the analyzed entities provide only vocational training for operating machinery, 31.91% do not carry out any form of training in forestry, while 15.96% refused to answer questions. On the other hand, 15.56% of the legal entities, which do not carry out any training or did not answer these questions, have on their official website services posted for vocational training in operating machinery (chainsaw and/or skidder). The key findings of the conducted research have pointed out the great heterogeneity amongst providers of forestry workers training, and certain reductions or limitations in the current training programs, both from the aspect of duration of the theoretical and practical training, and the use of non-transparent criteria and standards in the assessment of training. As an example of successful solution in forestry workers training, European Chainsaw Standard model (ECS) is shortly presented in the paper. Discussion and conclusion sections provide an overview of legislative and organizational requirements for the application of previously developed European model (ECS) in developing the certification system for training of for estry workers in Croatia. Keywords: forestry, chainsaw worker, health and safety, vocational training, certification, Croatia
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