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Re-engineering firewood extraction in traditional Mediterranean coppice stands
Ecological Engineering 38 (2012) 45–50
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Re-engineering firewood extraction in traditional Mediterranean coppice stands Natascia Magagnotti a , Luigi Pari b , Raffaele Spinelli c,∗ a
CNR – IVALSA, Via Biasi 75, I-38010 San Michele all’Adige (TN), Italy CRA ING, Via della Pascolare 16, Monterotondo Scalo (Roma), Italy c CNR – IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy b
a r t i c l e
i n f o
Article history: Received 7 May 2011 Received in revised form 30 August 2011 Accepted 28 October 2011 Available online 25 November 2011 Keywords: Logging Coppice Mules Economics
a b s t r a c t In an attempt to perpetuate traditional forest management, the authors tested a new compact tractor designed to replace pack mules when harvesting firewood from Mediterranean coppice stands. The new machine was capable of replacing a standard eight-mule team, and small enough to use the same infrastructure. The main characteristics of the tractor were its narrow width, a shifting center of gravity and a capacity to unitize loads for more efficient handling. The tests showed that the new tractor can outperform an equivalent mule team under the same working conditions, doing the job without incurring a higher cost. Installing a remote control can enhance operator safety, and bring it to the same good levels achieved with animal extraction. Even if the new machine can fill the technical role of pack mules, it certainly cannot reflect the same cultural and historical value. This research was never spurred by the desire to replace draught animals, but rather by their rapidly declining numbers, and was undertaken with the purpose of preserving traditional coppice management. There is a cultural and ethical obligation to preserve animal logging, which can partly be obtained through optimized deployment, so as to increase animal logger revenues and provide them with a further motivation to stay in business. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Due to a long and intense settlement history, human activity is a characterizing factor of Mediterranean forestry, which is best understood from a “total human ecosystem” perspective (Naveh and Lieberman, 1984). That explains the relative abundance of coppice stands, which are best suited to satisfy the needs of a dense rural population. For centuries, these forests have provided local communities with firewood, posts, tool handles and fencing materials. The rapid industrialization of the region seems to have brought limited changes to the demand for these products, if the annual firewood harvest is estimated to over 5 million cubic meters even in a modern and developed country like Italy (ISTAT, 2006). On the other hand, industrialization has certainly reduced the availability of rural labor, and their propensity to perform heavy and low-paying jobs. Hence the need for re-engineering traditional supply chains, in order to maintain the human, ecological and financial sustainability of Mediterranean forest management (Mitsch and Jørgensen, 2003). While radical modernization is likely to provide the ultimate solution (Spinelli et al., 2009), incremental innovation may be easier to introduce and may offer a practical stop
∗ Corresponding author. Tel.: +39 055 5225641; fax: +39 055 5225643. E-mail addresses: [email protected] (N. Magagnotti), [email protected] (L. Pari), [email protected] (R. Spinelli). 0925-8574/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2011.10.006
gap measure. From this perspective, one may analyze traditional chains, identify weak links and suggest alternatives. One of the most important harvesting systems applied to Mediterranean coppice stands is based on the application of animal power, which has remained very popular until present (Picchio et al., 2009). Trees are normally felled and crosscut into 1-m logs at the stump-site, then loaded onto pack mules and taken to a roadside landing, where the logs are unloaded and stacked manually, ready for collection by transportation vehicles (Spinelli and Baldini, 1987). Mules are best suited to warm climates, and to the steep terrain conditions inevitably associated with Mediterranean forestry, after flat terrain was turned to agriculture or urbanized already in ancient times. Under these conditions, animals can still outperform modern machinery, as recently demonstrated by independent studies in developed Mediterranean countries such as Greece (Gallis, 2004) and Italy (Magagnotti and Spinelli, 2011a). Animal extraction is also light on the environment and produces minimal site impact (Spinelli et al., 2010a). Even when environmentally acceptable and financially viable, animal logging is not sustainable from the social viewpoint. Increasingly few people are willing to accept the strong commitment required by livestock management, and the number of animal logging teams is dwindling in all industrialized countries (Toms et al., 1998). This is enough to define animal extraction as the weak link in the system, and to look for alternatives. Tractors are the obvious replacement, but they are confined to easy terrain or prepared skid trails (Spinelli and Magagnotti, 2011; Zeˆcic´ et al.,
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2005). However, the cost of opening new trails often makes tractor extraction more expensive compared to extraction by animals, further reducing the financial sustainability of mountain operations (Magagnotti and Spinelli, 2011b). Building new trails also generates significant erosion, aesthetic impact (Spinelli and Marchi, 1998) and fire hazard (Curt and Delcros, 2010) and is subject to resource consent procedures, which require additional time and money. Ideally, the mechanical substitute of pack mules should be able to use the same dense infrastructure of narrow paths, designed for animal logging in most coppice forests. These paths are about 1 m wide, and would allow access to very narrow machines only. Over time, several machine manufacturers have presented compact tractors designed for replacing pack animals, and derived from motorized wheelbarrows (Dekking, 1984), recreational vehicles (Savelli et al., 2010; TDB, 2002) or construction equipment (De Lasaux et al., 2009). None has proved a good match for animal power, unless deployed in favorable terrain conditions. Furthermore, none was designed for carrying 1-m long firewood, so that the eventual introduction within traditional operations would require further adaptation of the work technique, and the production of longer log lengths. In turn, that would aggravate manual pre-bunching and loading. The goal of this study was to develop and test a new compact tractor that may effectively replace pack mules under steep terrain conditions, without requiring any major changes of the existing practice. The new machine had to be capable of climbing steep grades and using existing mule paths after minor upgrading, of the type normally exempted from formal resource consent. It also had to be heavier, sturdier and more stable than previous designs. Finally, it had to unitize loads in order to improve subsequent load handling, facilitating transition along the supply chain, which is a typical weakness of animal logging operations (Magagnotti and Spinelli, 2011a).
Table 1 Technical specifications for the compact tractor. Machine Machine Machine Weight Engine Power Hydraulic pump Overall width Length (track base) Height (bonnet) Ground clearance Track width Max. speed
Make Model Type kg Make kW (SAE) type cm cm cm cm cm km h−1
Uemme Messersì 35 BV Crawler tractor 2400 Perkins 26 @ 2200 rpm HP – M4 110 170 133 22 28 ∼12
Note: Data provided by the manufacturer.
and the drying up of state subsidies for stand improvement have slowed down the past trend towards conversion into high forest, and determined a massive revival of coppice management. Hence, the test site can be considered generally representative for Central and Southern Italy, the Mediterranean basin and the Balkan mountain (Vacik et al., 2009). Trees were felled, delimbed and crosscut into 1-m logs by twoman crews, with a main operator felling and processing with a chainsaw, and a helper throwing the logs towards accumulation
2. Materials and methods A new compact tractor has been jointly developed by Uemme and Messersì for the Italian logging companies operating in the Northern Apennine. This machine is specifically designed to replace pack mules, no longer available in the Northern Apennine. The tractor runs on steel tracks, considered more durable than the rubber tracks applied to earlier designs. The tracked carriage is long and relatively narrow, to allow use of narrow mule paths, while maintaining a good longitudinal stability, which is the main handicap of tracked machines when surmounting obstacles (Nåbo and Yamada, 1992). The loading platform also carries the engine and the driver seat, and is connected to the tracked carriage by a double rail, allowing active longitudinal displacement through hydraulic rams. This way, one can shift the center of gravity forward or backward, to balance the tractor when dealing with steep uphill or downhill grades, respectively. The load deck is also equipped with rails, designed to engage sliding load racks. Logs are loaded onto the racks, which can be easily stacked at the landing or transferred onto other vehicles without requiring manual handling. Loading racks are made of welded steel pipe and are quite inexpensive, so that each unit is equipped with enough spare racks to cover a full work day. The tractor also configures as an independent power station, capable of operating complex hydraulic implements, and especially a detachable excavator boom, used for path upgrade. Further detail is shown in Table 1. So far, 6 units have been successfully deployed (see Photos 1 and 2). The study was conducted in a Turkey oak (Quercus cerris L.) forest, in the Northern Apennine (Table 2). The stand was regularly coppiced for firewood production, as most hardwood forests in the Apennine mountain range. The increasing value of firewood
Photo 1. Two compact tractors ready for work, with the empty firewood racks.
Photo 2. Manual loading of the firewood racks, on the cutover.
N. Magagnotti et al. / Ecological Engineering 38 (2012) 45–50 Table 2 Main characteristics of the test site. Municipality Province Altitude, m a.s.l. Slope gradient, % Mean trail gradient, % Trail density, m ha−1 Species Management Treatment Age, years Removal, m3 ha−1 Removal, trees ha−1 Residual density, trees ha−1 Avg. tree DBH, m Avg. stem height, m Avg. stem volume, m3
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Table 3 Costing: assumptions, cost centers and total cost. Premilcuore Forli 695 65 30 45 Quercus cerris L. Coppice Clearcut with standards 20 109 1210 100 0.14 (1.8) 9.8 (1.2) 0.09 (0.01)
Note: Number in parentheses represents the standard deviation from the average.
areas near the paths. Two of the new tractors were used for extraction. Each driver would first place an empty rack on the load deck, then drive to an accumulation area and manually load the rack. Once the rack was full, he would drive back to the roadside and transfer the rack onto a tractor trailer, used for transportation. As in most cases, the road was placed at the bottom of the slope, so that extraction proceeded in a downhill direction, with the unloaded tractors climbing up the slope, and descending with a load. Two drivers were tested, both comparatively young (30–40 years of age) and well acquainted with the new machine and procedure. No attempt was made to normalize individual performances by means of productivity ratings, recognizing that normalization or corrections can introduce new sources of errors and uncontrolled variation in the data material (Gullberg, 1995). The effect of an assistant was included in the study, where observations were divided in two batches, depending on whether drivers were or were not assisted by a second operator at the loading site. Since tractors alternated at the loading site and the assistant would serve both as they showed up, only half of his cost was added to the cost of the single tractor when working in the “assisted” mode. This was the norm, while working alone was the exception. Manual loading imposes a heavy physiological strain on the operators, and the presence of an assistant helps relieving their task, more than it increases production. A time-motion study was carried out to evaluate tractor productivity and to identify those variables that were most likely to affect it, such as extraction distance and slope gradient (Bergstrand, 1991). Each cycle was stop watched individually, separating productive time from delay time (Björheden et al., 1995). Extraction distances were determined with a measuring tape, and slope gradient with an inclinometer. No correction was made for slope gradient, so that these distances represented the actual paths covered by the tractors. Load size was estimated by determining the bulk volume of all loads with a tape measure and the fresh weight of 10 sample loads with a portable scale, in order to obtain a figure for bulk density. This factor was used to convert the bulk volumes of remaining loads into weight values. Data from individual cycle observations were analyzed with regression techniques in order to estimate meaningful relationships between productive time consumption and work conditions, such as extraction distance, slope gradient and load size. Indicator variables were used to mark differences between treatments (Olsen et al., 1998). The tractor rate was calculated with the method described by Miyata (1980), on an estimated annual utilization of 1000 scheduled machine hours (SMH) and a depreciation period of 10 years. The costs of fuel, insurance, repair and service were obtained
Unit
Tractor
Tractor
Mule
Assistant Purchase price, D Economic life, years Resale value, % new Interest rate, % Fuel consumption, l SMH−1 Crew, n Depreciation, D year−1 Annual use, SMH Total fixed cost, D SMH−1 Fuel, D SMH−1 Repair and maintenance, D SMH−1 Fodder, D SMH−1 Vet, D SMH−1 Shoeing, D SMH−1 Daily care, D SMH−1 Personnel cost, D SMH−1 Total variable cost, D SMH−1 Overhead (20%), D SMH−1 Total, D SMH−1
No 38,000 10 30 4 1.5 1 2660 1000 4.7 2.0 2.7 – – – – 15.0 20.3 4.7 29.7
Yes 38,000 10 30 4 1.5 1.5 2660 1000 4.7 2.0 2.7 – – – – 22.5 27.8 6.5 39.0
– 2800 10 20 4 – 0 224 1000 0.4 – – 1.5 0.2 0.4 1.5 – 3.6 0.8 4.8
Note: Cost in Euro (D) as on April 29, 2011 – 1 D = 1.45 US$; SMH = scheduled machine hour, including delays.
directly from the operators. Labor cost was set to 15 D SMH−1 inclusive of indirect salary costs. The calculated operational cost was increased by 20% to account for overhead costs (Hartsough, 2003). The same method was used to calculate the hourly rate of a single mule, later used for comparison purposes. Further detail on cost calculation is shown in Table 3. The study material consisted in 31 tractor turns, necessary for extracting 105 m3 (stacked volume) or 52 t of firewood. Overall, the time study sessions lasted about 20 h. 3. Results Fig. 1 shows the productivity of the tractor as a function of extraction distance. This was estimated using the empirical functions derived from experimental data, and reported at the bottom of the table. Travel speed was low and in the order of 2 km h−1 , which is explained by the need of negotiating a narrow and steep path. It is interesting to notice that the increasing path slope determines an increase of climbing time, and a proportional decrease of descent time. That could define engine power as the main limit, rather than braking power or operator skills. Loading time was somewhat constant, given the almost constant size of firewood loads: the only difference was made by the assistant, whose presence sped up loading, as expected. Unloading time was constant, because it consisted of a single standard process, where the loaded rack was pulled with a winch over the deck rails, and towards an identical set of rails installed on the trailer of a conventional farm tractor, later used for transporting fresh firewood to the storage yard. Fig. 2 translates productivity into cost figures. The productivity increase offered by detaching a loading assistant does not repay the additional cost of the assistant. Hence, deploying single-man crews is preferable from the financial viewpoint. Table 4 offers an attempt at comparing tractor extraction costs with the cost of mule extraction under the same conditions. Mule extraction cost was estimated from the productivity data available in bibliography. References are listed in the table. These data were recorded in different places and years, but they all refer to the hauling of firewood on packsaddles, under conditions that were comparable with those of our study. The hourly cost of each team was recalculated on the assumptions reported in Table 3, in order
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N. Magagnotti et al. / Ecological Engineering 38 (2012) 45–50
Table 4 Comparing mule and tractor extraction: distance, productivity and cost. System
Mules
Compact tractor
Source Citation
Distance m
Mules #
Cost D SMH−1
Productivity t SMH−1
Cost D t−1
Productivity t SMH−1
Cost D t−1
Baldini and Spinelli (1989) Baldini and Spinelli (1989) Verani (1990) Sperandio and Verani (2003) Sperandio and Verani (2003) Gallis (2004) Ghaffaryian et al. (2008) Picchio et al. (2009)
300 640 174 200 450 290 80 200
5 8 5 8 8 6 1 6
42.0 56.4 42.0 56.4 56.4 64.8 22.8 46.8
1.7 1.8 1.6 2.4 1.6 1.8 2.0 1.2
24.3 30.9 27.1 23.5 35.3 36.7 11.5 37.6
2.2 1.6 2.6 2.5 1.9 2.3 3.0 2.5
17.7 24.4 15.0 15.6 20.5 17.0 13.0 15.6
Average
292
6
48.5
1.8
28.4
2.3
17.3
Note: Cost in Euro (D) as on April 29, 2011 – 1 D = 1.45 US$; hourly cost of the mule operation has been calculated by multiplying the number of mules reported in the study by the rate shown in Table 3, and adding 18 D SMH−1 for the driver; the equivalent productivity for the compact tractor has been calculated inserting the distance reported by the respective mule study into the functions in Fig. 1; the cost of extraction with the compact tractor has been calculated assuming work with an assistant (hourly rate = 39 D SMH−1 ).
to obtain a valid rate for the economic conditions of Italy, where the tractor was tested. The hourly cost of one mule was then multiplied by the number of mules in each team, as indicated in the respective reports. The cost of the mule driver was the same as for the tractor driver, i.e. 18 D SMH−1 including indirect salary costs and overheads. Each of the quoted mule studies indicated an extraction distance, which we used to estimate the productivity of the tractor, based on the graph in Fig. 1. We assumed that the tractor worked with an assistant, because this was the standard work mode, although not the most efficient. Even so, the new tractor seems to offer a cheaper alternative to mule logging in all cases, but one.
Fig. 2. Extraction cost as a function of distance and treatment.
4. Discussion
Fig. 1. Extraction productivity as a function of distance and treatment.
The comparisons in Table 4 are only indicative, and must be taken with much caution. First of all, the quoted mule studies were conducted under similar but not identical conditions, which naturally decreases the accuracy of the comparisons themselves. Only one of these studies specifies whether extraction was conducted uphill or downhill, so that this factor is still unverified, although downhill extraction is the common practice. The treatment of delays in the different studies is also of capital importance, and might have introduced significant variability. In fact, one may also wonder if the delay incidence reported in our tractor study can be representative of long term trends, given the short duration of the study and the erratic nature of delays (Spinelli and Visser, 2009). Furthermore, the comparison in Table 4 might be too narrow, as it focuses on pure extraction work, excluding worksite preparation and subsequent load management, which may be different for the two systems. Between 15 and 30 years can elapse between two subsequent harvests, during which the original paths meet with significant decay. Hence, paths generally need to be restored before harvesting, by mending collapsed segments and clearing overgrown tracts. This preliminary operation requires more work in the case of tractor extraction, where restoration also includes a general upgrading. However, one may reasonably assume that the cost will be similar, because mule teams have to work less but need to do it manually, whereas tractor teams can resort to the small excavator arm included with the machine. As to load
N. Magagnotti et al. / Ecological Engineering 38 (2012) 45–50
management, the tractor might be a clear winner, since unitized loads can be handled mechanically and do not require stacking. In contrast, mules drop their load scattered on the ground, which imposes manual re-stacking. At the landing, one operator can restack about 2 t of firewood SMH−1 , at an estimated cost of 9 D t−1 (Sperandio and Verani, 2003). That gives a further advantage to the mechanical alternative. These considerations seem to corroborate the thesis of a general financial superiority of the compact tractor over mule teams. A measure of the exact margin, however, will only be obtained with side-by-side comparative studies. In any case, present results fulfill the goal of this study, which aimed at determining if the new tractor could effectively replace mules in firewood extraction. Results clearly demonstrate its technical and financial capacity to replace mules, because the compact tractor was operated without incurring higher costs. It is also worth noticing that the mule team incurs a higher fixed cost than the tractor. Animals require daily maintenance, whether they work or not, and therefore all costs incurred by the animal operator can be considered as fixed. Hence, the fixed cost of one mule reaches 4800 D year−1 , whereas that of the tractor is 4700 D year−1 . In fact, the tractor replaces about 8 mules, so that the we are matching 4700 D year−1 with 38400 D year−1 . While decreasing annual use will determine an increase of extraction cost for both methods, such increase will be lower for the compact tractor, which is especially suited to part-time use. Even with the new machine, traditional firewood harvesting requires considerable physical effort. The new tractor is loaded manually, and its introduction does not much alleviate the driver’s task. That explains the general use of an assistant, despite the higher profitability of one-man crews. Theoretically, the new machine could be equipped with a small detachable loader, to be left at the loading site and alternately coupled to the machine being loaded at the moment. However, this would require cutting longer logs than traditional 1-m lengths, thus introducing a major disruption of the traditional system and imposing a higher strain on cutters, who would need to handle much heavier logs. If one was to redesign the whole system, then radical innovation could offer better returns, as when shifting to modern cable yarding. This is already the case in parts of Central (Spinelli et al., 2010b) and Southern Italy (Zimbalatti and Proto, 2009). While it does not alleviate the physical burden of drivers, introducing the new tractor may increase their risk for injury, as drivers must sit on the machine and could be harmed in the event of a roll-over. The tractor is indeed very stable and is equipped with a roll-over protection structure, but it is no match for the mules, which can be steered with voice commands, keeping at a safe distance whenever required (Snoeck, 2000). In this respect, balance could be restored by equipping the tractor with a simple remote control, which would be neither difficult nor particularly expensive.
5. Conclusion Even if the new machine can fill the technical role of pack mules, it certainly cannot reflect the same cultural and historical value. Draught animals are an important component of the mountain landscape and culture. Their rapid extinction presents a serious cultural threat, which should be faced by supporting the few teams still willing to use them. Our research was never spurred by the desire to replace draught animals, but rather by the urgent need to do so, in order to save at least the cultural ecosystem offered by traditional coppice management. Animal logging systems offer an ecological alternative to tractors, and depend much less on fossil energy inputs (Rydberg and Jansén, 2002). There is a cultural and
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ethical obligation to preserve them, which can partly be obtained through optimized deployment, so as to offer a financial incentive to the use of animals. Recent studies indicate that horse skidding could be integrated with tractor skidding in order to reduce total extraction cost (Magagnotti and Spinelli, 2011a). There would be an ample scope for determining when and how mule extraction could compete with tractor extraction, and for devising improved harness and/or techniques. A solution might be searched in the integration of animal and mechanical power, which would allow making the most efficient use of the few remaining operations. A similar and converse effect could be obtained in developing countries, where integration would allow making the most efficient use of the few available machines. Efficient use of draught animals may also help increasing animal logger revenues, thus providing a further motivation to stay in business.
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Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Re-engineering firewood extraction in traditional Mediterranean coppice stands Natascia Magagnotti a , Luigi Pari b , Raffaele Spinelli c,∗ a
CNR – IVALSA, Via Biasi 75, I-38010 San Michele all’Adige (TN), Italy CRA ING, Via della Pascolare 16, Monterotondo Scalo (Roma), Italy c CNR – IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy b
a r t i c l e
i n f o
Article history: Received 7 May 2011 Received in revised form 30 August 2011 Accepted 28 October 2011 Available online 25 November 2011 Keywords: Logging Coppice Mules Economics
a b s t r a c t In an attempt to perpetuate traditional forest management, the authors tested a new compact tractor designed to replace pack mules when harvesting firewood from Mediterranean coppice stands. The new machine was capable of replacing a standard eight-mule team, and small enough to use the same infrastructure. The main characteristics of the tractor were its narrow width, a shifting center of gravity and a capacity to unitize loads for more efficient handling. The tests showed that the new tractor can outperform an equivalent mule team under the same working conditions, doing the job without incurring a higher cost. Installing a remote control can enhance operator safety, and bring it to the same good levels achieved with animal extraction. Even if the new machine can fill the technical role of pack mules, it certainly cannot reflect the same cultural and historical value. This research was never spurred by the desire to replace draught animals, but rather by their rapidly declining numbers, and was undertaken with the purpose of preserving traditional coppice management. There is a cultural and ethical obligation to preserve animal logging, which can partly be obtained through optimized deployment, so as to increase animal logger revenues and provide them with a further motivation to stay in business. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Due to a long and intense settlement history, human activity is a characterizing factor of Mediterranean forestry, which is best understood from a “total human ecosystem” perspective (Naveh and Lieberman, 1984). That explains the relative abundance of coppice stands, which are best suited to satisfy the needs of a dense rural population. For centuries, these forests have provided local communities with firewood, posts, tool handles and fencing materials. The rapid industrialization of the region seems to have brought limited changes to the demand for these products, if the annual firewood harvest is estimated to over 5 million cubic meters even in a modern and developed country like Italy (ISTAT, 2006). On the other hand, industrialization has certainly reduced the availability of rural labor, and their propensity to perform heavy and low-paying jobs. Hence the need for re-engineering traditional supply chains, in order to maintain the human, ecological and financial sustainability of Mediterranean forest management (Mitsch and Jørgensen, 2003). While radical modernization is likely to provide the ultimate solution (Spinelli et al., 2009), incremental innovation may be easier to introduce and may offer a practical stop
∗ Corresponding author. Tel.: +39 055 5225641; fax: +39 055 5225643. E-mail addresses: [email protected] (N. Magagnotti), [email protected] (L. Pari), [email protected] (R. Spinelli). 0925-8574/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2011.10.006
gap measure. From this perspective, one may analyze traditional chains, identify weak links and suggest alternatives. One of the most important harvesting systems applied to Mediterranean coppice stands is based on the application of animal power, which has remained very popular until present (Picchio et al., 2009). Trees are normally felled and crosscut into 1-m logs at the stump-site, then loaded onto pack mules and taken to a roadside landing, where the logs are unloaded and stacked manually, ready for collection by transportation vehicles (Spinelli and Baldini, 1987). Mules are best suited to warm climates, and to the steep terrain conditions inevitably associated with Mediterranean forestry, after flat terrain was turned to agriculture or urbanized already in ancient times. Under these conditions, animals can still outperform modern machinery, as recently demonstrated by independent studies in developed Mediterranean countries such as Greece (Gallis, 2004) and Italy (Magagnotti and Spinelli, 2011a). Animal extraction is also light on the environment and produces minimal site impact (Spinelli et al., 2010a). Even when environmentally acceptable and financially viable, animal logging is not sustainable from the social viewpoint. Increasingly few people are willing to accept the strong commitment required by livestock management, and the number of animal logging teams is dwindling in all industrialized countries (Toms et al., 1998). This is enough to define animal extraction as the weak link in the system, and to look for alternatives. Tractors are the obvious replacement, but they are confined to easy terrain or prepared skid trails (Spinelli and Magagnotti, 2011; Zeˆcic´ et al.,
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2005). However, the cost of opening new trails often makes tractor extraction more expensive compared to extraction by animals, further reducing the financial sustainability of mountain operations (Magagnotti and Spinelli, 2011b). Building new trails also generates significant erosion, aesthetic impact (Spinelli and Marchi, 1998) and fire hazard (Curt and Delcros, 2010) and is subject to resource consent procedures, which require additional time and money. Ideally, the mechanical substitute of pack mules should be able to use the same dense infrastructure of narrow paths, designed for animal logging in most coppice forests. These paths are about 1 m wide, and would allow access to very narrow machines only. Over time, several machine manufacturers have presented compact tractors designed for replacing pack animals, and derived from motorized wheelbarrows (Dekking, 1984), recreational vehicles (Savelli et al., 2010; TDB, 2002) or construction equipment (De Lasaux et al., 2009). None has proved a good match for animal power, unless deployed in favorable terrain conditions. Furthermore, none was designed for carrying 1-m long firewood, so that the eventual introduction within traditional operations would require further adaptation of the work technique, and the production of longer log lengths. In turn, that would aggravate manual pre-bunching and loading. The goal of this study was to develop and test a new compact tractor that may effectively replace pack mules under steep terrain conditions, without requiring any major changes of the existing practice. The new machine had to be capable of climbing steep grades and using existing mule paths after minor upgrading, of the type normally exempted from formal resource consent. It also had to be heavier, sturdier and more stable than previous designs. Finally, it had to unitize loads in order to improve subsequent load handling, facilitating transition along the supply chain, which is a typical weakness of animal logging operations (Magagnotti and Spinelli, 2011a).
Table 1 Technical specifications for the compact tractor. Machine Machine Machine Weight Engine Power Hydraulic pump Overall width Length (track base) Height (bonnet) Ground clearance Track width Max. speed
Make Model Type kg Make kW (SAE) type cm cm cm cm cm km h−1
Uemme Messersì 35 BV Crawler tractor 2400 Perkins 26 @ 2200 rpm HP – M4 110 170 133 22 28 ∼12
Note: Data provided by the manufacturer.
and the drying up of state subsidies for stand improvement have slowed down the past trend towards conversion into high forest, and determined a massive revival of coppice management. Hence, the test site can be considered generally representative for Central and Southern Italy, the Mediterranean basin and the Balkan mountain (Vacik et al., 2009). Trees were felled, delimbed and crosscut into 1-m logs by twoman crews, with a main operator felling and processing with a chainsaw, and a helper throwing the logs towards accumulation
2. Materials and methods A new compact tractor has been jointly developed by Uemme and Messersì for the Italian logging companies operating in the Northern Apennine. This machine is specifically designed to replace pack mules, no longer available in the Northern Apennine. The tractor runs on steel tracks, considered more durable than the rubber tracks applied to earlier designs. The tracked carriage is long and relatively narrow, to allow use of narrow mule paths, while maintaining a good longitudinal stability, which is the main handicap of tracked machines when surmounting obstacles (Nåbo and Yamada, 1992). The loading platform also carries the engine and the driver seat, and is connected to the tracked carriage by a double rail, allowing active longitudinal displacement through hydraulic rams. This way, one can shift the center of gravity forward or backward, to balance the tractor when dealing with steep uphill or downhill grades, respectively. The load deck is also equipped with rails, designed to engage sliding load racks. Logs are loaded onto the racks, which can be easily stacked at the landing or transferred onto other vehicles without requiring manual handling. Loading racks are made of welded steel pipe and are quite inexpensive, so that each unit is equipped with enough spare racks to cover a full work day. The tractor also configures as an independent power station, capable of operating complex hydraulic implements, and especially a detachable excavator boom, used for path upgrade. Further detail is shown in Table 1. So far, 6 units have been successfully deployed (see Photos 1 and 2). The study was conducted in a Turkey oak (Quercus cerris L.) forest, in the Northern Apennine (Table 2). The stand was regularly coppiced for firewood production, as most hardwood forests in the Apennine mountain range. The increasing value of firewood
Photo 1. Two compact tractors ready for work, with the empty firewood racks.
Photo 2. Manual loading of the firewood racks, on the cutover.
N. Magagnotti et al. / Ecological Engineering 38 (2012) 45–50 Table 2 Main characteristics of the test site. Municipality Province Altitude, m a.s.l. Slope gradient, % Mean trail gradient, % Trail density, m ha−1 Species Management Treatment Age, years Removal, m3 ha−1 Removal, trees ha−1 Residual density, trees ha−1 Avg. tree DBH, m Avg. stem height, m Avg. stem volume, m3
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Table 3 Costing: assumptions, cost centers and total cost. Premilcuore Forli 695 65 30 45 Quercus cerris L. Coppice Clearcut with standards 20 109 1210 100 0.14 (1.8) 9.8 (1.2) 0.09 (0.01)
Note: Number in parentheses represents the standard deviation from the average.
areas near the paths. Two of the new tractors were used for extraction. Each driver would first place an empty rack on the load deck, then drive to an accumulation area and manually load the rack. Once the rack was full, he would drive back to the roadside and transfer the rack onto a tractor trailer, used for transportation. As in most cases, the road was placed at the bottom of the slope, so that extraction proceeded in a downhill direction, with the unloaded tractors climbing up the slope, and descending with a load. Two drivers were tested, both comparatively young (30–40 years of age) and well acquainted with the new machine and procedure. No attempt was made to normalize individual performances by means of productivity ratings, recognizing that normalization or corrections can introduce new sources of errors and uncontrolled variation in the data material (Gullberg, 1995). The effect of an assistant was included in the study, where observations were divided in two batches, depending on whether drivers were or were not assisted by a second operator at the loading site. Since tractors alternated at the loading site and the assistant would serve both as they showed up, only half of his cost was added to the cost of the single tractor when working in the “assisted” mode. This was the norm, while working alone was the exception. Manual loading imposes a heavy physiological strain on the operators, and the presence of an assistant helps relieving their task, more than it increases production. A time-motion study was carried out to evaluate tractor productivity and to identify those variables that were most likely to affect it, such as extraction distance and slope gradient (Bergstrand, 1991). Each cycle was stop watched individually, separating productive time from delay time (Björheden et al., 1995). Extraction distances were determined with a measuring tape, and slope gradient with an inclinometer. No correction was made for slope gradient, so that these distances represented the actual paths covered by the tractors. Load size was estimated by determining the bulk volume of all loads with a tape measure and the fresh weight of 10 sample loads with a portable scale, in order to obtain a figure for bulk density. This factor was used to convert the bulk volumes of remaining loads into weight values. Data from individual cycle observations were analyzed with regression techniques in order to estimate meaningful relationships between productive time consumption and work conditions, such as extraction distance, slope gradient and load size. Indicator variables were used to mark differences between treatments (Olsen et al., 1998). The tractor rate was calculated with the method described by Miyata (1980), on an estimated annual utilization of 1000 scheduled machine hours (SMH) and a depreciation period of 10 years. The costs of fuel, insurance, repair and service were obtained
Unit
Tractor
Tractor
Mule
Assistant Purchase price, D Economic life, years Resale value, % new Interest rate, % Fuel consumption, l SMH−1 Crew, n Depreciation, D year−1 Annual use, SMH Total fixed cost, D SMH−1 Fuel, D SMH−1 Repair and maintenance, D SMH−1 Fodder, D SMH−1 Vet, D SMH−1 Shoeing, D SMH−1 Daily care, D SMH−1 Personnel cost, D SMH−1 Total variable cost, D SMH−1 Overhead (20%), D SMH−1 Total, D SMH−1
No 38,000 10 30 4 1.5 1 2660 1000 4.7 2.0 2.7 – – – – 15.0 20.3 4.7 29.7
Yes 38,000 10 30 4 1.5 1.5 2660 1000 4.7 2.0 2.7 – – – – 22.5 27.8 6.5 39.0
– 2800 10 20 4 – 0 224 1000 0.4 – – 1.5 0.2 0.4 1.5 – 3.6 0.8 4.8
Note: Cost in Euro (D) as on April 29, 2011 – 1 D = 1.45 US$; SMH = scheduled machine hour, including delays.
directly from the operators. Labor cost was set to 15 D SMH−1 inclusive of indirect salary costs. The calculated operational cost was increased by 20% to account for overhead costs (Hartsough, 2003). The same method was used to calculate the hourly rate of a single mule, later used for comparison purposes. Further detail on cost calculation is shown in Table 3. The study material consisted in 31 tractor turns, necessary for extracting 105 m3 (stacked volume) or 52 t of firewood. Overall, the time study sessions lasted about 20 h. 3. Results Fig. 1 shows the productivity of the tractor as a function of extraction distance. This was estimated using the empirical functions derived from experimental data, and reported at the bottom of the table. Travel speed was low and in the order of 2 km h−1 , which is explained by the need of negotiating a narrow and steep path. It is interesting to notice that the increasing path slope determines an increase of climbing time, and a proportional decrease of descent time. That could define engine power as the main limit, rather than braking power or operator skills. Loading time was somewhat constant, given the almost constant size of firewood loads: the only difference was made by the assistant, whose presence sped up loading, as expected. Unloading time was constant, because it consisted of a single standard process, where the loaded rack was pulled with a winch over the deck rails, and towards an identical set of rails installed on the trailer of a conventional farm tractor, later used for transporting fresh firewood to the storage yard. Fig. 2 translates productivity into cost figures. The productivity increase offered by detaching a loading assistant does not repay the additional cost of the assistant. Hence, deploying single-man crews is preferable from the financial viewpoint. Table 4 offers an attempt at comparing tractor extraction costs with the cost of mule extraction under the same conditions. Mule extraction cost was estimated from the productivity data available in bibliography. References are listed in the table. These data were recorded in different places and years, but they all refer to the hauling of firewood on packsaddles, under conditions that were comparable with those of our study. The hourly cost of each team was recalculated on the assumptions reported in Table 3, in order
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Table 4 Comparing mule and tractor extraction: distance, productivity and cost. System
Mules
Compact tractor
Source Citation
Distance m
Mules #
Cost D SMH−1
Productivity t SMH−1
Cost D t−1
Productivity t SMH−1
Cost D t−1
Baldini and Spinelli (1989) Baldini and Spinelli (1989) Verani (1990) Sperandio and Verani (2003) Sperandio and Verani (2003) Gallis (2004) Ghaffaryian et al. (2008) Picchio et al. (2009)
300 640 174 200 450 290 80 200
5 8 5 8 8 6 1 6
42.0 56.4 42.0 56.4 56.4 64.8 22.8 46.8
1.7 1.8 1.6 2.4 1.6 1.8 2.0 1.2
24.3 30.9 27.1 23.5 35.3 36.7 11.5 37.6
2.2 1.6 2.6 2.5 1.9 2.3 3.0 2.5
17.7 24.4 15.0 15.6 20.5 17.0 13.0 15.6
Average
292
6
48.5
1.8
28.4
2.3
17.3
Note: Cost in Euro (D) as on April 29, 2011 – 1 D = 1.45 US$; hourly cost of the mule operation has been calculated by multiplying the number of mules reported in the study by the rate shown in Table 3, and adding 18 D SMH−1 for the driver; the equivalent productivity for the compact tractor has been calculated inserting the distance reported by the respective mule study into the functions in Fig. 1; the cost of extraction with the compact tractor has been calculated assuming work with an assistant (hourly rate = 39 D SMH−1 ).
to obtain a valid rate for the economic conditions of Italy, where the tractor was tested. The hourly cost of one mule was then multiplied by the number of mules in each team, as indicated in the respective reports. The cost of the mule driver was the same as for the tractor driver, i.e. 18 D SMH−1 including indirect salary costs and overheads. Each of the quoted mule studies indicated an extraction distance, which we used to estimate the productivity of the tractor, based on the graph in Fig. 1. We assumed that the tractor worked with an assistant, because this was the standard work mode, although not the most efficient. Even so, the new tractor seems to offer a cheaper alternative to mule logging in all cases, but one.
Fig. 2. Extraction cost as a function of distance and treatment.
4. Discussion
Fig. 1. Extraction productivity as a function of distance and treatment.
The comparisons in Table 4 are only indicative, and must be taken with much caution. First of all, the quoted mule studies were conducted under similar but not identical conditions, which naturally decreases the accuracy of the comparisons themselves. Only one of these studies specifies whether extraction was conducted uphill or downhill, so that this factor is still unverified, although downhill extraction is the common practice. The treatment of delays in the different studies is also of capital importance, and might have introduced significant variability. In fact, one may also wonder if the delay incidence reported in our tractor study can be representative of long term trends, given the short duration of the study and the erratic nature of delays (Spinelli and Visser, 2009). Furthermore, the comparison in Table 4 might be too narrow, as it focuses on pure extraction work, excluding worksite preparation and subsequent load management, which may be different for the two systems. Between 15 and 30 years can elapse between two subsequent harvests, during which the original paths meet with significant decay. Hence, paths generally need to be restored before harvesting, by mending collapsed segments and clearing overgrown tracts. This preliminary operation requires more work in the case of tractor extraction, where restoration also includes a general upgrading. However, one may reasonably assume that the cost will be similar, because mule teams have to work less but need to do it manually, whereas tractor teams can resort to the small excavator arm included with the machine. As to load
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management, the tractor might be a clear winner, since unitized loads can be handled mechanically and do not require stacking. In contrast, mules drop their load scattered on the ground, which imposes manual re-stacking. At the landing, one operator can restack about 2 t of firewood SMH−1 , at an estimated cost of 9 D t−1 (Sperandio and Verani, 2003). That gives a further advantage to the mechanical alternative. These considerations seem to corroborate the thesis of a general financial superiority of the compact tractor over mule teams. A measure of the exact margin, however, will only be obtained with side-by-side comparative studies. In any case, present results fulfill the goal of this study, which aimed at determining if the new tractor could effectively replace mules in firewood extraction. Results clearly demonstrate its technical and financial capacity to replace mules, because the compact tractor was operated without incurring higher costs. It is also worth noticing that the mule team incurs a higher fixed cost than the tractor. Animals require daily maintenance, whether they work or not, and therefore all costs incurred by the animal operator can be considered as fixed. Hence, the fixed cost of one mule reaches 4800 D year−1 , whereas that of the tractor is 4700 D year−1 . In fact, the tractor replaces about 8 mules, so that the we are matching 4700 D year−1 with 38400 D year−1 . While decreasing annual use will determine an increase of extraction cost for both methods, such increase will be lower for the compact tractor, which is especially suited to part-time use. Even with the new machine, traditional firewood harvesting requires considerable physical effort. The new tractor is loaded manually, and its introduction does not much alleviate the driver’s task. That explains the general use of an assistant, despite the higher profitability of one-man crews. Theoretically, the new machine could be equipped with a small detachable loader, to be left at the loading site and alternately coupled to the machine being loaded at the moment. However, this would require cutting longer logs than traditional 1-m lengths, thus introducing a major disruption of the traditional system and imposing a higher strain on cutters, who would need to handle much heavier logs. If one was to redesign the whole system, then radical innovation could offer better returns, as when shifting to modern cable yarding. This is already the case in parts of Central (Spinelli et al., 2010b) and Southern Italy (Zimbalatti and Proto, 2009). While it does not alleviate the physical burden of drivers, introducing the new tractor may increase their risk for injury, as drivers must sit on the machine and could be harmed in the event of a roll-over. The tractor is indeed very stable and is equipped with a roll-over protection structure, but it is no match for the mules, which can be steered with voice commands, keeping at a safe distance whenever required (Snoeck, 2000). In this respect, balance could be restored by equipping the tractor with a simple remote control, which would be neither difficult nor particularly expensive.
5. Conclusion Even if the new machine can fill the technical role of pack mules, it certainly cannot reflect the same cultural and historical value. Draught animals are an important component of the mountain landscape and culture. Their rapid extinction presents a serious cultural threat, which should be faced by supporting the few teams still willing to use them. Our research was never spurred by the desire to replace draught animals, but rather by the urgent need to do so, in order to save at least the cultural ecosystem offered by traditional coppice management. Animal logging systems offer an ecological alternative to tractors, and depend much less on fossil energy inputs (Rydberg and Jansén, 2002). There is a cultural and
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ethical obligation to preserve them, which can partly be obtained through optimized deployment, so as to offer a financial incentive to the use of animals. Recent studies indicate that horse skidding could be integrated with tractor skidding in order to reduce total extraction cost (Magagnotti and Spinelli, 2011a). There would be an ample scope for determining when and how mule extraction could compete with tractor extraction, and for devising improved harness and/or techniques. A solution might be searched in the integration of animal and mechanical power, which would allow making the most efficient use of the few remaining operations. A similar and converse effect could be obtained in developing countries, where integration would allow making the most efficient use of the few available machines. Efficient use of draught animals may also help increasing animal logger revenues, thus providing a further motivation to stay in business.
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