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.
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).
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):
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):
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).
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).
On the other hand,
Table 6 presents the results of direct costs of skidding of 1 m
3 of short wood in the range of 100–500 m (
Table 6). Higher direct costs of 1 m
3 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 m
3. 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 m
3. 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 m
3 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 m
3, for farm tractor + wagon it was 4.20 m
3, and for skidder + single axle trailer it was 5.60 m
3. On the other hand, a single load carried by the set in this study was 5.57 m
3. 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 m
3 h
−1, followed by a tractor with a self-loading forestry trailer 5.56 m
3 h
−1 (
Table 3), followed by the 2-horse cart—4.15 m
3 h
−1, and the lowest productivity was achieved by a tractor with a cart—3.53 m
3 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 m
3, 3.25 m
3 for the MTZ 82 tractor + trailer without drive, and 4.72 m
3 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 m
3. 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 m
3 h
−1 (
Table 4), the next was the tractor with trailer with all-wheel drive 5.01 m
3 h
−1, a two-horse cart with a wagon 3.52 m
3 h
−1, and a tractor with a trailer without drive 2.72 m
3 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 m
3 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 m
3 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 m
3 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 m
3 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 m
3 h
−1. Kormanek and Fiszer [
32] reported a similar value—4.98 m
3 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 m
3 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 m
3 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 m
3 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 m
3 h
−1;
Table 4) is approximately three times lower than in clear cut, with the use of forwarders (16.5–17.9 m
3 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 m
3 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 m
3 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.