The Productivity and the Costs Forwarding Wood of a Farm Tractor with a Trailer in Late Thinning and Cutting in Gaps of Forests

Abstract

The aim of the study was to compare the efficiency and the direct costs of wood forwarding with a farm tractor with a trailer in a gap cutting and in the late thinning of a stand. The forwarding productivity was determined by the timing method. The unit costs of wood harvesting were calculated on the basis of annual own costs. With the same set, short wood harvesting is more productive in a stand with a cut over the entire surface than in group cutting. It resulted from a shorter time of accumulating a larger load and higher driving speeds. Most of the forwarding time is spent on loading, so stacking the logs in an orderly manner, preferably in bundles, can improve performance. Better use of the loading case increases productivity and reduces unit costs. The speed of the forwarding is independent of the cutting category and the volume of the load. The speed of the forwarding is influenced by the arrangement of the remains of branches, soil conditions, the condition of the skidding trails, and the weight of the load. In flat and less demanding terrain, an agricultural tractor with a trailer will be a good alternative to a forwarder.

1. Introduction

Currently, environmental protection is becoming more and more an issue during timber extraction [1]. A forwarder is recommended, preferably a forwarder with wide tires where the weight of the machine and the load are evenly distributed, thus minimizing the impact on the ground. In Poland, small- and medium-sized forwarders are used with forwarding stacked and log timber. There are machines in the world that allow for harvesting of whole trees, but due to the huge size and structure of our stands, it is not possible to use them [2]. Bearing in mind the fragmentation of the skidding areas, Nurek and Gendek [3] point out that the full potential of forwarders are not used. The efficiency drops significantly when, from one small cutting area, the logging wood has to be transported for several kilometers to the second cutting area. In addition, in Poland, sustainable forest management is carried out, where it is forbidden to make clearings larger than 6 ha, and harvesting often takes place in groups, where the clearing area may be only a dozen ares. In such cases, the working time may be less than the transport time of the machine. Compared to forwarders, agricultural tractors are faster and more mobile, which significantly reduces transport costs [4].

Manual and machine logging systems dominate Polish forestry [5], in contrast to Scandinavian countries where nearly 100% of the wood is harvested by machine. However, a clear increase in custom-made machine harvesting has been observed recently in Poland as well as in other Central and Eastern European countries, e.g., in the Czech Republic and Bulgaria [6,7]. Manual and machine logging systems cut, delimb, and manipulate trees by a woodcutter using a saw and forwarding using various logging machines. Due to the growing market demand for short timber, forwarders are increasingly used for logging, but their number is still insufficient. The barrier to increasing the share of these machines for owners of small forestry companies, which dominate in services for state forests in Poland, is the high price of forwarders. Therefore, forwarders working in the forests of Central and Eastern Europe have an average age of 9.9 years. In comparison, it is 6.1 years in Scandinavian countries [8]. A cheaper alternative is forestry trailers equipped with hydraulic cranes. Such trailers can be aggregated with an agricultural tractor. Currently, these sets are the most popular among short wood harvesting machines in Poland [9]. Agricultural tractors offer great versatility because they can work in agriculture and forestry with a large number of machines and can be used with them all year round. The machine can still be fully used at times when the amount of wood being cut is reduced. Equipment purchase costs are recovered faster [10]. When equipped with a few additional elements, they allow for safe work in the forest. A large number of tractors, both used and new are available. The engine power can be selected according to the existing needs, and their price compared to specialized forestry tractors is much lower, e.g., Hejazian et al. [11] report that the contractor, when buying an agricultural tractor with a trailer, can save approximately 44% of costs compared to the price of a small forwarder. The latest review [12] on Cost and Productivity of Ground-Based Timber Harvesting Machines completely omits farm tractors with a trailer. Hence, our work may be a partial supplement to the most recent literature on this subject, and the importance of this study may be great for forestry research and operational practice, as the article deals with a very important part of forest production.

The aim of the study was to compare the productivity and direct costs of harvesting wood with a farm tractor with a trailer equipped with a hydraulic crane for loading/unloading wood in a group felling and in a stand where a late thinning was carried out with an even cut over the entire surface. The following research hypothesis was adopted: with the same means of transport and a similar distance, forwarding productivity depends on the category of cuts and the type of harvesting assortment. In order to achieve the aim of the study, forwarding performed by a set consisting of a Valmet 6300 tractor, a Palms 101 forest trailer, and a Palms 670 crane was investigated.

2. Materials and Methods

The study was carried out on two plots located in adjacent forest divisions; therefore, the topography and the type of ground were similar. The plots were located in the Sieniawa forest district. The tractor with a trailer on both surfaces moved along designated trajectories (lines). The distance between the trajectories (lines) was approximately 15 m. The wood was harvested with chainsaws; it was loaded onto a trailer with a hydraulic crane and was not previously stacked by hand into packages. The skidding of harvested wood was carried out by forestry workers with many years of work experience in the forests. There was no stagnant water nor any puddles on the skidding routes, however small depressions in the ground left by the tractor and trailer were present (Figure 1), which did not have a large effect on the tractor’s pull and resistance. The litter and the top layer of soil were not broken but dented under the weight of the machine. The tractor did not lose traction, and the wide wheels of the trailer spread the pressure well on the ground. Therefore, not all the roots in the top part of the soil were damaged, some were only dented [13].

2.1. The First Plot—Forest Area Number 330a

The stand (8.84 ha) was managed by cutting down trees in gaps. The forest habitat type is a wet forest. The species composition was made up of 70% of Scots pine (Pinus sylvestris L.) and 30% of oak (Quercus sp.). The average age of the stand was 107 years. There were also oaks at the ages of 80 and 50. The average DBH for pine was 43 cm and for oaks, depending on age: 42 cm, 37 cm, and 21 cm. The height for the pine was 27 m and for the oak: 27 m, 25 m, and 18 m, respectively. The crown cover was 0.4; intermittent/loose. The undergrowth consisted of buckthorn (Frangula alnus Mill.) and common hazel (Corylus avellana L.). The terrain was low and flat.

2.2. The Second Plot—Forest Area Number 331a

In the stand (15.85 ha), late thinning was performed, which is a uniform cut across the entire area, leaving fertile trees until the felling age. The forest habitat type is a fresh mixed forest. The species composition was made up of 70% Scots pine (Pinus sylvestris L.) and 30% oak (Quercus sp.). The age of the stand was 77 years. The average DBH was 33 cm for oak and 34 cm for pine. On the other hand, the average height for oak was 26 m and for pine—28 m. The crown cover was 0.8; moderate density. The undergrowth consisted of 80% buckthorn (Frangula alnus Mill.). The terrain was low and flat.

2.3. Characteristics of the Skidding Set

In the study of the skidding productivity, a Valmet 6300 farm tractor was used, which was aggregated with a Palms 101 forestry trailer equipped with a Palms 670 crane (Figure 2, Table 1). This set worked on both research plots, forwarding wood harvested in two lengths: 1.25 m and 2.5 m. The trailer fit well with the length of the harvested assortments in terms of spacing and the number of stanchions.

The tractor was properly prepared for work in the forest. From the bottom, a sheet metal cover was mounted along the entire length, which protected against damage when running over a tall stump. In addition, such a cover allowed the branches to slide through without catching on various elements. A metal cover with holes was mounted on the front of the hood to allow air flow to the radiators and the fan. Two steel cables stretched from the hood to the cabin, effectively protecting the tractor from the impact of branches on the windshield. The cab roof had a frame made of steel tubes. All of these elements minimize the risk of damage to the tractor, and properly selected power for the trailer enables operation even in difficult conditions. Palms is the largest company in Europe that produces forestry trailers and cranes. Forest trailers of this brand are produced in Estonia. In 2019, there were approximately 3000 forest trailers of this manufacturer in Poland [14]. The trailer is coupled to the tractor via a piton-fix hitch. The selection of the appropriate revolutions on the shaft allows the engine revs to be reduced, due to which fuel consumption is reduced, and the hydraulics in the trailer work in the right way. The most economical use of the tractor is when the engine is loaded with a torque in the nominal range [15].

Table 1. Characteristics of the machines in the study [16].

Machine	Valmet 6300	Machine	Palms 101 Forest Trailers
Configuration	4 × 4 wheel drive	Weight/loaded weight	1.2/11.2
Weight (tons)	4.2	Length (mm)	3850 (4250 *)
Power (kW)	66	Width (mm)	2180
Transmission	powershift 12 + 12	Number of stanchions	6 pairs
Max. speed (kmh)	39	Loader	Palms 670
Min. speed (kmh)	0.9	Weight (tons)	1.1
Length (mm)	4440	Crane reach (mm)	6700
Height (mm)	2730	Lifting moment (kNm)	42
Width (mm)	2330	Rotation angle (°)	370

*—the trailer model has been equipped with a special extension adapter.

Table 1. Characteristics of the machines in the study [16].

Machine	Valmet 6300	Machine	Palms 101 Forest Trailers
Configuration	4 × 4 wheel drive	Weight/loaded weight	1.2/11.2
Weight (tons)	4.2	Length (mm)	3850 (4250 *)
Power (kW)	66	Width (mm)	2180
Transmission	powershift 12 + 12	Number of stanchions	6 pairs
Max. speed (kmh)	39	Loader	Palms 670
Min. speed (kmh)	0.9	Weight (tons)	1.1
Length (mm)	4440	Crane reach (mm)	6700
Height (mm)	2730	Lifting moment (kNm)	42
Width (mm)	2330	Rotation angle (°)	370

*—the trailer model has been equipped with a special extension adapter.

A steered drawbar is a very useful element when maneuvering on narrow logging routes. The steering angle of the drawbar is approximately 40°, which is possible due to two cylinders mounted on both sides. This function is driven by the tractor’s hydraulics, so when arriving, e.g., from the harvest site to the storage yard, WOM can be disengaged, and the drawbar steering will still work. The Palms 670 crane has been mounted in the front part of the trailer. The grapple is mounted on a special rotator, which allows it to rotate and makes the manipulation of the raw material easier. Extendable A-type supports ensure good stability of the set during crane operation.

2.4. Field Works, Development of the Results

2.4.1. Determining the Time-Consumption and Productivity of Wood Forwarding

The research took place in April 2021. The weather conditions were favorable. The methodology proposed in the work by Dudek [17] was used when carrying out research activities and developing the results. The productivity of wood forwarding was determined by the timing method.

In the analyzed forwarding cycles, the time of the following transport activities was measured:

• Driving time for the load, i.e., driving from the timber yard to the place of harvesting and more precisely to the first logs on the clearing, from which the operator started loading;
• Loading time, this procedure included several activities, such as unfolding and folding the supports and the crane, loading the raw material, and moving to the next logs;
• Loaded driving time, i.e., driving from the place of harvest to the timber yard;
• Unloading time, this activity included unloading various assortments in appropriate places in the timber yard and folding and unfolding supports and a crane at the timber yard.

Time was measured with a stopwatch on the phone with an accuracy of one second. The distance of the timber yard to the nearest logs at the place of harvest was measured using the Geoportal application. This was done by switching on the GPS location and covering the road that the skidding set travelled. The distance is given in meters. However, the volume of wood transported in each cycle was averaged to the data provided by the manufacturer—the operator loaded the trailer to full capacity each time.

After measuring the time, load volume, and distance, the time consumption of individual activities was calculated. Then, the time consumption of the entire cycle was calculated [17]:

TC = A∙L + B∙Q∙[h]

where:

• TC—time consumption of the entire cycle [h];
• A—unit time consumption of unloaded and loaded driving [h m⁻¹];
• L—forwarding distance [m];
• B—unit time consumption of unloading and loading [h m⁻³];
• Q—volume of a single load [m³];

In the last stage, the hourly productivity of the forwarding was calculated [17]:

Wh = 1/Tc∙Q = Q/Tc [m³ h⁻¹]

15 complete forwarding cycles were measured on both research plots.

2.4.2. Determining the Costs of Short Wood Forwarding

The unit costs of wood forwarding were calculated on the basis of the annual own costs. The unit hourly forwarding cost Kh (€ h⁻¹) was calculated as the quotient of the annual costs Kr (€ year⁻¹) and the number of hours worked in the year Tr (h year⁻¹). Hence, the cost of forwarding 1 m³ of wood was calculated from the ratio of the unit hourly cost of forwarding to the hourly productivity:

K€ m⁻³ = Kh Wh⁻¹ [€ m⁻³]

where:

• K€ m⁻³—cost of forwarding 1 m³ of wood;
• Kh—unit hourly cost of forwarding;
• Wh—hourly productivity of forwarding.

When calculating the annual cost of using the tested forwarding technology, the following cost groups were taken into account:

• Fixed costs: depreciation of forwarding equipment, interest on capital, equipment insurance;
• Variable costs: service wages; fuel, oils, and lubricants; repairs.

The input data for the calculation of the costs of forwarding with the researched technologies (

Table 2. Input data for the calculation of the cost of short wood forwarding.

Parameter for Cost Calculation	Valtra G105 HiTech + Palms 10D with Crane 4.70 *
Purchase price, €	60,737 + 24,946
Depreciation period, years.	8
Value after the depreciation, % of the purchase price	10
The loan interest rate per year, %	8
Equipment insurance, % of the purchase price	2.5
Fuel consumption, dm3 h−1	6
Oil and lubricant consumption, % of the fuel price	10
Fuel price without VAT (22%), € dm−3	1.75
Number of service people	1
Employee wages, € h−1	5.42
Number of working hours per year	1680
Repair cost index, % of depreciation costs	70

*—This is the most similar to the tested set available in the companies’ offer.

) come from own market analyses, environmental interviews, and the specialist literature of the subject [18,19,20,21].

The interest rate on the loan, the minimum wage (in the study it was increased by 25% due to the workload and field data), the fuel price, the exchange rate (1 Euro = 4.61 PLN), and the purchase price of the forwarding resources were assumed at their amounts applicable on 10 June 2022. The cost of the fuel was calculated without VAT. The average annual working time was assumed at the level of 1680 h (8 h × 20 days × 10.5 months) [19,20,21].

Using the output data included in Table 2, the costs of using the tested wood forwarding technology were calculated on an annual basis. Then, the unit cost of forwarding per hour of work was calculated. Knowing the hourly capacity for the distance and the cost of an hour of skidding, the direct expenditure for 1 m³ of wood forwarding at different transport distances was calculated.

3. Results

Testing time-consumption and productivity of wood forwarding.

On the plot with the group felling, the forwarding unit under study transported 1.25 m long pile wood (pine and oak) and 2.5 m long log timber (only oak). The average size of the load to be forwarded here was 5.57 m³, and the average forwarding distance was 271 m. However, on the plot with pre-cutting, 2.5 m long logs (only pine) were obtained. The average size of the forwarded load here was 6.50 m³, and the average forwarding distance was 475 m.

On the basis of the collected data, the unit time consumption of forwarding with a Valmet 6300 tractor and a Palms 101 trailer equipped with a Palms 670 hydraulic crane on the felling and thinning areas was calculated (

Table 3. Time consumption of forwarding with the studied unit.

Area	Time Consumption by Unit
	Unloaded Driving [h m−1]	Loading [h m−3]	Loaded Driving [h m−1]	Unloading [h m−3]
group felling	0.000280	0.094231	0.000342	0.052077
late thinning	0.000247	0.075360	0.000292	0.041606

).

Following these data, the unit time consumption of driving (driving for the load and loaded driving) (A) and loading work (loading and unloading) (B) was calculated for the group felling (1) and the stand with late thinning (2):

A1 = 0.000280 + 0.000342 = 0.000622 h m⁻¹

B1 = 0.094231 + 0.052077 = 0.146308 h m⁻³

A2 = 0.000247 + 0.000292 = 0.000540 h m⁻¹

B2 = 0.075360 + 0.041606 = 0.116965 h m⁻³

The unit time consumption of driving (A) at the distance (L) and loading work (B) at the load (Q) grouped in the above manner allowed for the determination of the cycle time-consumption equation for group felling (Tc1) and late thinning (Tc2):

Tc1 = 0.000622 L + 0.146308 Q1

Tc2 = 0.000540 L + 0.116965 Q2

Using these regression equations, the forwarding productivity of a Valmet 6300 tractor with a Palms 101 trailer equipped with a Palms 670 hydraulic crane was calculated for both types of cuts (

Table 4. Productivity of forwarding with the studied unit [m³ h⁻¹].

Area	Forwarding Distance [m]	Volume of a Single Load [m3]	Time Consumption of the Cycle [h]	Cycle Frequency [Number h−1]	Productivity of Forwarding [m3 h−1]
group felling	100	5.57	0.8772	1.14	6.35
	200		0.9394	1.06	5.93
	300		1.0016	1.00	5.56
	400		1.0639	0.94	5.24
	500		1.1261	0.89	4.95
late thinning	100	6.50	0.8142	1.23	7.98
	200		0.8682	1.15	7.49
	300		0.9222	1.08	7.05
	400		0.9761	1.02	6.66
	500		1.0301	0.97	6.31

).

The obtained tests (Table 4) indicated that the Valmet 6300 forwarding set with the Palms 101 trailer equipped with the Palms 670 hydraulic crane obtained higher performance in the stand with late thinning than in the stand with group felling (Table 4). This result was influenced by a 15% higher load in a thinning stand which resulted from the forwarding of logs with the same length of 2.5 m, and thus better use of the trailer’s load box. The greater productivity achieved in the stand with late thinning was also due to the lower time-consuming nature of the forwarding operations (driving for a load, loading, driving with a load, unloading; Table 3), despite the longer time of driving for a load and with a load in thinning, which resulted from longer haulage distance (Figure 3). Hence, at a forwarding distance of 100–500 m, the forwarding set was more efficient in the stand with thinning by 20%–22% (Table 4).

Analysis of direct costs of forwarding.

The data in Table 2 were used to calculate the costs of short wood forwarding with a farm tractor with a forestry trailer. The unit cost of a machine hour of short wood forwarding was 30.32 € h⁻¹ (

Table 5. Calculation of annual and hourly direct costs of short wood forwarding.

Cost Items	Valtra G105 HiTech + Palms 10D with Crane 4.70 *
	€ year−1	€ h−1
Depreciation	9639	5.74
Loan interest	3893	2.32
Insurance	2142	1.28
I. Fixed costs–total	15,674	9.33
Fuel	17,640	10.50
Oils and lubricants	1764	1.05
Wages	9106	5.42
Repairs	6747	4.02
II. Variable costs–total	35,257	20.99
Forwarding costs total (I + II)	50,931	30.32

*—This is the most similar to the tested set available in the companies’ offer

).

On the other hand,

Table 6. Direct costs [€] of forwarding of 1 m³ of short wood in the distance of 100–500 m.

Category of Use	Forwarding Distance [m]
	100	200	300	400	500
	Forwarding Cost [€ m−3]
Thinning stands	3.80	4.05	4.31	4.56	4.81
Felling stands	4.78	5.12	5.46	5.80	6.13

presents the results of direct costs of skidding of 1 m³ of short wood in the range of 100–500 m (Table 6). Higher direct costs of 1 m³ forwarding were recorded for the stand with group cutting, which was caused by the lower forwarding productivity of the tested set in this stand.

4. Discussion

In the case of the tested set, the operator always loaded the trailer to the maximum, which was a volume of 6.5 m³. However, in the case of a stand with group felling, the set forwarded assortments of various lengths (1.25 m and 2.5 m), which resulted in different load volumes during individual forwarding cycles, and the average obtained from 7 cycles was 5.57 m³. Better use of the trailer’s loading space in thinning stands when forwarding longer assortments was one of the reasons for obtaining higher forwarding productivity and, consequently, lower direct costs of 1 m³ of forwarding. Więsik [22] pointed out that forwarding with a forestry trailer in which the load box is always fully loaded, significantly increases its productivity. Similarly, increasing the intensity of cuts in the utilization rate of the harvesting increases the forwarding productivity [23]. A well-developed forest infrastructure also clearly contributes to the increase in productivity [24]. The observations carried out as a part of this study allow for confirmation of the impact of the quality of maintenance of forwarding routes on higher driving speeds, and thus higher forwarding productivity.

Speeds during unloaded and loaded driving in the area of group felling were 16.6% lower in the first stage of driving and 23.1% lower in the second stage than in thinning with an even cut across the entire surface. Group cutting was performed in the study area, timber forwarding required avoiding damage to plantings of young trees. Well-marked technological routes and their good condition contributed to faster driving during forwarding in thinning stands. In the study by Stempski [25], clear-cut and disordered felling were compared, the results clearly indicated that the clear-cut is more efficient.

The greatest part of the time in the full forwarding cycle, both in felling and thinning stands, was spent on loading. In felling stands, this activity took 53.35% of the cycle time, while in thinning—48.18%. The obtained results are comparable with the results of Naskrent et al. [10], where loading also consumed the largest part of the entire cycle and accounted for approximately 58% of the forwarding cycle time. As noted by Pszenny et al. [26], the most time during the entire working day of a forwarder or tractor with a self-loading trailer is spent on the crane during loading—34.03% of the forwarding machine operation time. In addition, the authors note that during this activity, unfolding and folding the supports takes a large part of the time.

The results of the forwarding productivity can be compared with the results of the work of Dudek [27], for three technologies of short-wood skidding in mountain felling stands. The volume of one-off load for skidding with a 2-horse cart + wagon was 3.38 m³, for farm tractor + wagon it was 4.20 m³, and for skidder + single axle trailer it was 5.60 m³. On the other hand, a single load carried by the set in this study was 5.57 m³. This comparison shows that a skidder with a single axle trailer took the same load as a farm tractor with a forestry trailer. Comparing the performance for a distance of 300 m, the best one was the skidder aggregated with a single axle trailer—6.18 m³ h⁻¹, followed by a tractor with a self-loading forestry trailer 5.56 m³ h⁻¹ (Table 3), followed by the 2-horse cart—4.15 m³ h⁻¹, and the lowest productivity was achieved by a tractor with a cart—3.53 m³ h⁻¹.

The results of the forwarding productivity in late thinning can be compared to the results from the publication of Dudek [28], where the author investigated the productivity of various technologies of short-wood forwarding in late thinning pre-cutting stands. The volume of a single load for a 2 horse-drawn cart + a wagon was 1.54 m³, 3.25 m³ for the MTZ 82 tractor + trailer without drive, and 4.72 m³ for the MTZ 82 farm tractor + trailer with all-wheel drive. On the other hand, for a tractor with a self-loading trailer in this study it was 6.5 m³. In this case, the largest single load in terms of volume was taken by a tractor with a self-loading trailer. Comparing the performance for a distance of 300 m, the best was obtained by the tractor with a self-loading trailer 7.05 m³ h⁻¹ (Table 4), the next was the tractor with trailer with all-wheel drive 5.01 m³ h⁻¹, a two-horse cart with a wagon 3.52 m³ h⁻¹, and a tractor with a trailer without drive 2.72 m³ h⁻¹.

In the two previously mentioned works [27,28], loading and unloading in all cases was done manually. On the other hand, the forwarding set tested in this study—a farm tractor with a self-loading trailer—the loading works were carried out with the use of a hydraulic crane.

Spinelli et al. [4] report the average productivity of tractor-trailer combinations at 6.8 m³ h⁻¹ in mountain forests with an average transport distance of as much as 5.5 km. It should be assumed that only a part of this distance was forwarding wood on the cut area and the vast majority took place on a forest road with good surface, where it was possible to achieve high speeds. By contrast, Spinelli et al. [29] report that a farm tractor with a trailer on a eucalyptus plantation reached productivity of 13.4 m³ h⁻¹, with an average forwarding distance of 174 m. This value is nearly twice as high as that obtained in this study (7.61 m³ h⁻¹ for a distance of 174 m). On the other hand, Mousavi and Nikooy [30] report the efficiency of a combination of a farm tractor with a trailer, operating on a poplar plantation situated on level ground, at the level of 3.59 m³ h⁻¹ for an average hauling distance of 167 m. This value, in turn, is twice as small as that obtained in this study, but in the case of the study by Mousavi and Nikooy [30], loading works were performed manually, and in other cases loading works were done mechanically with the use of a hydraulic crane. Zychowicz and Kasprzyk [31] give, for a distance of 174 m, for a farm tractor with a trailer equipped with a crane, an operating productivity of 4.72 m³ h⁻¹. Kormanek and Fiszer [32] reported a similar value—4.98 m³ h⁻¹—but for a forwarding distance of approximately 500 m, conducted in winter conditions with snow cover.

Comparing the results obtained in this paper in late thinning for a forwarding distance of 300 m (7.05 m³ h⁻¹; Table 4) with the average values obtained by specialized forest tractors of the forwarder type working in late thinning (8.8–15.1 m³ h⁻¹ [7]), it can be noticed that the productivity obtained in this study for a farm tractor with a self-loading trailer is comparable to the lower limit of the range for the forwarding productivity achieved by forwarders. Eriksson and Lindroos [33] report slightly higher results (12.9 m³ h⁻¹), with an average forwarding distance of 420 m for a forwarder. On the other hand, in stands with group felling, the efficiency of forwarding with an agricultural tractor with a trailer (5.56 m³ h⁻¹; Table 4) is approximately three times lower than in clear cut, with the use of forwarders (16.5–17.9 m³ h⁻¹) [7]. In this case, such a large difference could have been caused by a much lower intensity of cuts—the accumulation of loads—in the stands with cutting in gaps.

The hourly cost of forwarding calculated at work was 30.32 €, which is approximately 34% lower than the John Deere (JD) 1010 (40.6 €) forwarder, as much as 146% lower than the John Deere 1110E (74.7 €), and higher by approximately 5% on the small forwarder Novotný LVS 5 (28.4 €) [34]. On the other hand, Barnardi et al. [35] report hourly costs of 48.27 € h⁻¹ for the forwarder JD 1010D, and Proto et al. [36] report 65.8 € h⁻¹ when forwarding on a 26%–29% slope. Leszczyński et al. [23], for the MTZ Belarus 952.2 Farm Tractor with FAO FAR 84, quote an hourly cost of 31.73–37.15 €. In turn, Spinelli and Magagnotti [37] report for the Entracon Loglander LL85 mini forwarder (load capacity 4.5 t) a much higher hourly cost of 47.6 € h⁻¹ than that obtained in this study (57% higher); although, in the same paper, they claim that the working hour of the Valtra 130 farm tractor with the Kronos 100 forestry trailer is even higher—67.7 € h⁻¹. These JD forwarders have a declared load capacity of 11 t; the Novotný LVS 5—5 t; the forest trailer Palms 101 used in the work—10 t; and FAO FAR 84—8 t.

The similar hourly cost of work of a small LVS 5 forwarder with an agricultural tractor with a forestry trailer at a similar purchase cost (LVS 5—84.122 €, Valtra G105 HiTech + Palms 10D with a crane 4.70—currently available versions of the tested set—85.683 €), may result from much higher material costs (10.55 € h⁻¹, Table 5), including fuel in 2022 than in 2004–2020 (4.3 € h⁻¹) [34]. However, when comparing the two works, it can be seen that staff costs in Poland are much lower than in the Czech Republic. The cost of forwarding of 1 m³ of wood, calculated in this study in the range of 100–500 m, was 3.80–4.81 € m⁻³ in thinning stands and 4.78–6.13 € m⁻³ in felling stands with group cutting (Table 6). On the other hand, Dvořák et al. [34] report for the LVS 5 forwarder operating in approximately 40-year-old thinning stands the direct operational costs per 1 m³ of forwarded wood ranged from 3.60 to 7.93 € m⁻³ for an average forwarding distance of 389 m; JD 1010 reached costs ranging from 3.55 to 6.10 € m⁻³ with an average forwarding distance of 321 m; and JD 1110E reached costs from 6.22 to 7.22 € m⁻³ with an average forwarding distance of 526 m. Spinelli and Magagnotti [37] for an average forwarding distance of 400 m, calculated the cost of work for a mini forwarder of 12.4–15.1 € m⁻³ and for a farm tractor with a trailer the cost was 14.9 € m⁻³. These values are 2–3 times higher than those obtained in the study, however, in the study by Spinelli and Magagnotti [37], forwarding was carried out on very small areas (0.21 and 1.29 ha) and in younger stands. In turn, Leszczyński et al. [23], for an agricultural tractor with a trailer that forwarding short wood for an average distance of 700 m, give 7.80–9.13 € m⁻³ depending on the utilization rate (0.8–0.6, respectively). This value is greater by 47% to 72% than that calculated in the study for a distance of 700 m in a thinning stand (5.31 € m⁻³) and by 14% to 34% to that calculated in the study for a distance of 700 m in a felling stand with group cutting (6.81 € m⁻³).

5. Conclusions

With the same forwarding set, Valmet 6300 farm tractor with Palms 101 forestry trailer and Palms 670 crane, short-timber forwarding was more efficient in the stand where late thinning was carried out (even cut over the entire area of 15.85 ha) than in the group felling (cutting on gaps with an area of several to several dozen ares). This result was influenced by a shorter time of accumulating a larger load and higher driving speeds in the stand where the loads were distributed more evenly over the entire cut surface.

Most of the forwarding time is spent on loading, so stacking the logs in an orderly manner, preferably in bundles, can improve forwarding performance.

Forwarding of only longer assortments from the thinning area allows for better use of the load box, which increases the efficiency of forwarding and reduces unit costs.

Forwarding speed is independent of cutting category and load volume. The speed of the forwarding agent is influenced by the arrangement of the remains of the branches, soil conditions, the condition of the skidding trails, and the weight of the load. In the thinning stand, only pine wood was harvested, while from group felling, much heavier oak wood was harvested.

In flat and less demanding terrain, an agricultural tractor with two-axle drive coupled with a forestry trailer will be a good alternative to much more expensive forwarders with a similar payload. Despite the lower forwarding capacity of an agricultural tractor with a trailer than a forwarder, the unit costs of forwarding are comparable in both cases.

According to the authors, the forwarding tractor set will be more suitable than a specialized forwarder forest tractor for harvesting wood with a chainsaw. These are cheaper machines, therefore, even with the lower work efficiency achieved, the costs are still kept at a low level. At the same time, it must be added that the forwarding tractor set can also work with a harvester. In this case, you should take into account that the forwarding tractor set will not keep up with the work. Hence, more agricultural tractors with a trailer would have to cooperate with one harvester than specialized forestry tractors of the forwarder type. In the short and medium term, it should be assumed that in countries, such as Poland, agricultural tractors with forestry trailers will play a dominant role in the forwarding of short-wood.