Analysis of Operational Efficiencies and Costs for Extracting Thinned Woods in Small-Scale Forestry, Nasunogahara Area, Tochigi Prefecture, Japan ^†

Abstract

In this study, two operational methodologies to extract thinned woods were investigated in the Nasunogahara area, Tochigi Prefecture, Japan. Methodology one included manual extraction and light truck transportation. Methodology two included mini-forwarder forwarding and four-ton truck transportation. Furthermore, a newly introduced chipper was investigated. As a result, costs of manual extractions within 10 m and 20 m were JPY942/m³ and JPY1040/m³, respectively. On the other hand, the forwarding cost of the mini-forwarder was JPY499/m³, which was significantly lower than the cost of manual extractions. Transportation costs with light trucks and four-ton trucks were JPY7224/m³ and JPY1298/m³, respectively, with 28 km transportation distances. Chipping operation costs were JPY1036/m³ and JPY1160/m³ with three and two persons, respectively. Finally, the total costs of methodologies one and two from extraction within 20 m to chipping were estimated as JPY9300/m³ and JPY2833/m³, respectively, with 28 km transportation distances and three-person chipping operations (EUR1 = JPY126, as of 12 August 2020).

1. Introduction

In July 2011, the Feed-in Tariff (FIT) Scheme for Renewable Energy Use was introduced in Japan, in accordance with new legislation entitled the Act on the Purchase of Renewable Energy-Sourced Electricity by Electric Utilities. Under the FIT program, electricity generated from woody biomass must be procured at a fixed price (without tax) for over 20 years for (a) unused materials such as thinned wood and logging residue (at JPY32/kWh), (b) general materials such as sawmill residue (at JPY24/kWh), and (c) recycled materials such as construction waste wood (at JPY13/kWh) [1]. Incentives have promoted the use of power generated from unused materials.

The price of JPY32/kWh for unused materials was determined based on a model plant featuring 5 MW of direct combustion with an initial cost of JPY410,000/kW, annual operating cost of JPY27,000/kW, and an internal rate of return of 8%. The annual consumption of fuel wood chips was 60,000 ton/year, collected within 50 km, with a price of JPY12,000/ton consisting of 34% (JPY4080/ton) extraction, 25% (JPY3000/ton) transportation, 16% (JPY1920/ton) chipping, and 25% (JPY3000/ton) chip transportation. However, forest ownership in Japan is characterized by a large number of small, fragmented, and scattered forest owners [2]. Therefore, it is difficult to supply the amount of 60,000 ton/year stably from such small, fragmented, and scattered forests.

To promote the use of thinned wood and logging residue from these forests, the price of JPY40/kWh for unused materials with less than 2 MW of direct combustion was set, starting in April 2015. The price of JPY40/kWh was determined based on a model plant featuring 1.5 MW of direct combustion, with an initial cost of JPY620,000/kW, annual operating cost of JPY64,000/kW, and an internal rate of return of 8%. The annual consumption of fuel wood chips was 20,000 ton/year, collected within 30 km, with a price of JPY9000/ton excluding chip transportation, because a small-scale power generation plant could chip small amount volumes necessary for its own plant on its own place.

An agrarian organization in the Nasunogahara area in Tochigi Prefecture was willing to conduct thinning operations and extract thinned woods for a small-scale woody biomass power generation in cooperation with the forest owners’ cooperative. This would nurture river resources as well as maintain forests for soil and water conservation. Forest ownership in the region studied is also characterized by a large number of small, fragmented, and scattered forest owners. Therefore, it is difficult to aggregate forestry operation sites in this region even though private forests are located on relatively gentle slope areas and forest road networks are well established. Thus, the optimal method to extract logging residues from such small, fragmented and scattered forests should be examined separately from the mechanized operational systems used for aggregated forestry operation sites.

In many regions of the world, small-scale harvesting machines have been used in forestry where terrain conditions and size of forest operations are not limiting [3]. In some European counties, farm tractors are commonly used for various forest harvesting tasks, including felling, processing, extraction and transportation in small-scale logging systems. A standard winch and a sulky can be fitted to any tractor at relatively low cost and can be used for part-time forest operations [4]. This simple technology has a strong potential for effective deployment in farm forestry in developing countries. On the other hand, various animal species (oxen, horses, buffaloes and mules) have been used for skidding operations. Oxen are commonly used for skidding in Turkey [5]. Furthermore, over 80% of extraction operations in Turkish forests are conducted with manpower such as skidding or sliding, but these methods have technical, ergonomic and environmental problems. To overcome these problems, manual extractions with plastic chutes have been examined [6]. In Japan, mini-forwarders are commonly used for forwarding operations by small-scale private forest owners and logging companies [7]. Furthermore, light trucks with a 350 kg loading capacity are also commonly used for commuting to the forests and transporting small-sized logs.

Niyodo, a local community in the Kochi area of southwestern Japan, has started a government-subsidized woody biomass utilization project. The project collects logging residues for a processing plant using three methodologies: (1) a large-scale methodology operated by a logging contractor, (2) a medium-scale methodology operated by a forest owners’ cooperative, and (3) a small-scale methodology operated by an individual forest owner. Although the largest expected source of logging residues was the large-scale methodology, the small-scale methodology procurement was, in fact, the largest [8]. Therefore, a small-scale methodology used by individual forest owners with mini-forwarders and light trucks would be important for extracting logging residues from such small, fragmented and scattered forests all over Japan as well as in some other regions of the world with manual logging.

In this study, two operational methodologies to extract thinned woods were investigated in Nasunogahara area, Tochigi Prefecture, Japan. Methodology one included manual extraction and light truck transportation. Methodology two included mini-forwarder forwarding and four-ton truck transportation. Furthermore, a newly introduced chipper was investigated.

2. Materials and Methods

The study was conducted using the following steps: (1) small-scale methodologies operated by an individual forest owner and a private logging contractor were investigated (Figure 1), (2) cycle times were analyzed, (3) equations to estimate productivities and costs were established, and (4) costs of the small-scale methodologies––manual extraction and a light truck operated by an individual forest owner as well as a mini-forwarder and a four-ton truck operated by a private logging contractor––were estimated and compared. This study assumed that a private logging contractor was professional, whereas an individual forest owner was amateur and had recently commenced forestry operations from logging residue extraction.

The study site was a 29-year-old Japanese cedar (Cryptomeria japonica) and 23-year-old Japanese cypress (Chamaecyparis obtusa) plantation. The Japanese cedar plantation had the following characteristics: an area of 0.23 ha with average slope angle of 7 degrees; stand density: 1700 stem/ha; average diameter at breast height (DBH): 19.5 cm; average tree height: 16.0 m; average stem volume: 0.24 m³/stem. The Japanese cypress plantation had the following characteristics: an area of 0.62 ha with average slope angle of 8 degrees; stand density: 1600 stem/ha; average diameter at breast height (DBH): 17.3 cm; average tree height: 13.6 m; average stem volume: 0.17 m³/stem. Precommercial thinning operations were conducted by a forest owners’ cooperative. Thinned woods were left in the forest.

Thinned woods were manually extracted and transported with a light truck (loading capacity of 0.35 t) by individual forest owners, and extracted with a mini-forwarder (Chikusui Canycom Yamabiko BFY1001, 7.4 kW engine horsepower) and transported with a truck (loading capacity of 4 t) by a private logging contractor. Time study was conducted to analyze cycle times and productivities. Manual extractions were conducted by three persons within 10 and 20 m. Mini-forwarder extractions were conducted within 20 m. Chipping was conducted using Dynamic VP3000, 83 kW engine horsepower with three and two persons (Figure 2).

The productivities, P (m³/h), were estimated with average cycle time, T (s/cycle), and average volume, V (m³/cycle):

$$P=\frac{3600\times V}{T},$$

(1)

The direct operational expenses, OE (JPY/m³), were estimated using productivities and hourly operational expenses consisting of labor expenses, OL (JPY/h), and machinery expenses, OM (JPY/h):

$$OE=\frac{OL+OM}{P},$$

(2)

Labor expenses, OL (JPY/h), were set at JPY1300/h. Machinery expenses, OM (JPY/h), consisted of maintenance, management, depreciation, and fuel and oil expenses: JPY570/h for a light truck, JPY572/h for a mini-forwarder, JPY1320/h for a four-ton truck and JPY3155/h for a chipper [9,10].

3. Results

Productivities of manual extractions for Japanese cedar were 3.53 m³/h, with an average log volume of 0.018 m³/log within 10 m, and 2.01 m³/h, with an average log volume of 0.017 m³/log within 20 m. For Japanese cypress, productivities of manual extractions were 5.15 m³/h, with the average log volume of 0.019 m³/log within 10 m, and 5.80 m³/h, with the average log volume of 0.022 m³/log within 20 m. Productivities for Japanese cypress were higher than those for Japanese cedar. In Japanese cypress, productivities within 20 m were also higher than those within 10 m. One of the reasons for these was the higher average log volume.

The average cycle time and volume with a mini-forwarder were 792 s/cycle and 0.84 m³/cycle, respectively. Therefore, productivity was estimated at 3.75 m³/h. The average productivity of manual extractions within 20 m was estimated at 1.25 m³/person/h, whereas that within 10 m was estimated at 1.38 m³/person/h; thus, the productivity of a mini-forwarder was higher. The direct operational expenses of manual extractions were estimated at JPY942/m³ and JPY1040/m³ within 10 m and 20 m, respectively. On the other hand, the direct operational expense of a mini-forwarder was JPY499/m³ within 20 m. Using a mini-forwarder reduced the direct operational expenses of extractions.

The average cycle time and volume of loading/unloading with 2 persons and a light truck were 795 s/cycle and 0.644 m³/cycle, respectively, with an average log volume of 0.028 m³/log for Japanese cedar. Therefore, productivity was estimated at 2.92 m³/h. The average cycle time and volume of loading/unloading with a light truck were 816 s/cycle and 0.552 m³/cycle, respectively, with an average log volume of 0.023 m³/log for Japanese cypress. Therefore, productivity was estimated at 2.42 m³/h. The productivity for Japanese cedar was higher than that for Japanese cypress because of the higher average log volume.

The average cycle time and volume of loading/unloading with a four-ton truck were 2160 s/cycle and 4.950 m³/cycle, respectively. Therefore, productivity was estimated at 8.25 m³/h. As the average productivity of loading/unloading with a light truck was estimated at 1.34 m³/person/h, the productivity of loading/unloading with a four-ton truck was higher.

The cycle time, T (s/cycle), of transportation was related to transportation distance, L (km/cycle), travel velocities, V (km/h), and the loading and unloading time, tf (s/cycle).

$$T=tf+7200 L/V,$$

(3)

Travel velocities were assumed to be 30 km/h. As the loading and unloading time was 1612 s/cycle for a light truck with one person and 2160 s/cycle for a four-ton truck, the cycle times were as follows:

$$\mathrm{Light}\mathrm{truck}:T=1612+240 L,$$

(4)

$$4\mathrm{ton}\mathrm{truck}:T=2160+240 L,$$

(5)

As the average volumes were 0.598 m³/cycle for a light truck and 4.950 m³/cycle for a four-ton truck, productivities were as follows:

$$\mathrm{Light}\mathrm{truck}:P=2153/\left(1612+240 L\right),$$

(6)

$$4\mathrm{ton}\mathrm{truck}:P=17,820/\left(2160+240 L\right),$$

(7)

The direct operational expenses were as follows:

$$\mathrm{Light}\mathrm{truck}:OE=1400+208 L,$$

(8)

$$4\mathrm{ton}\mathrm{truck}:OE=318+35 L,$$

(9)

Transportation costs with a light truck and a four-ton truck were estimated at JPY7224/m³ and JPY1298/m³, with 28 km transportation distances from the test site to a planned woody biomass power generation plant.

Chipping operations were conducted with 82 logs for three persons and 124 logs for two persons. Average small-end diameters were 11 cm and 11 cm, average log lengths were 2.1 m and 1.7 m, and average log volumes were 0.022 m³/log and 0.021 m³/log for three and two persons, respectively. Therefore, chipping volumes were 1.763 m³ and 2.639 m³ for three and two persons, respectively. As chipping times were 932 s and 1221 s for three and two persons, respectively, productivities were 6.81 m³/h (2.27 m³/person/h) and 4.96 m³/h (2.48 m³/person/h), respectively. Therefore, chipping operation costs were JPY1036/m³ and JPY1160/m³ with three and two persons, respectively.

Total cost with manual extraction within 20 m for 28 km transportation with a light truck and chipping for three persons was estimated at JPY9300/m³ (Figure 3), whereas that with a mini-forwarder, four-ton truck and three-person chipping was JPY2833/m³ (Figure 4). As the price of fuel wood chips, JPY9000/ton for a small-scale power generation plant, was converted to JPY6120/m³ with a bulk density of 0.68 ton/m³ [11], thinned woods could be utilized within 13 km transportation distances, even with manual extractions and a light truck.

4. Discussion

Logging by chainsaw felling and chainsaw or processor processing followed by forwarding is widely used at small and large sites in the mountainous forests of Japan. However, a grapple equipped with a forwarder is usually small, and the forwarder’s operational efficiency for loading and unloading is low. An arm roll forwarder was developed to overcome this problem [12,13,14,15]. An arm roll forwarder can only load a steel container that has been fully loaded with logs by processor beforehand, and it can only unload such a container afterward. Therefore, such a forwarder can shorten the loading time and improve loading operational efficiency significantly.

In addition to the investigation of an arm roll forwarder with 3 m logs [15], an arm roll forwarder with 2 m logs and biomass containers as well as an arm roll truck were investigated (Figure 5). As a result, total costs of an arm roll forwarder for use between 610–780 m forwarding distances, an arm roll truck with 28 km transportation distances, and three-person chipping were estimated at JPY5206/ton and JPY8040/ton for 2 m logs and biomass containers, respectively (Figure 6 and Figure 7). Therefore, thinned woods and logging residues could be used as fuel wood chips for a small-scale woody biomass power generation plant. However, forwarding distances were longer at this site. If a grapple loader could just load thinned woods without forwarding, total costs were reduced to JPY4603/ton. As the total cost with a mini-forwarder, a four-ton truck, and three-person chipping was estimated at JPY4166/ton with a bulk density of 0.68 ton/m³, the small-scale systems could be effective for harvesting small areas.