Comparison of harvesting productivity, cost, and residual stand damages between single-tree selection thinning and mechanized line thinning using a small-scale grapple-saw

Figures & data

Figure 1. Location of study site in South Korea.

Table 1. Description of the study site.

Parameter	Description
Location	Mt. 99-31, Bupyeong-ri, Jinjeop-eup, Namyangju-si, Gyeonggi-do, South Korea (experimental forest of NIFoS)
Latitude (WGS84)	37°45′01.85”
Longitude (WGS84)	127°11′42.47”
Elevation above sea level (m)	101
Forest type	Plantation
Species	Abies holophylla
Thinning type	SST	MLT1	MLT2
		(Fourth double row thinned)	(Third row thinned)
Slope (%, avg.)	30.4	27.4	29.9
Area (ha)	0.45	0.29	0.08
Tree volume (m^3/tree)	0.23	0.20	0.25
Stand density (trees/ha)	1,055	1,224	1,475
Removal (trees/ha)	404	489	491
Rate of removal (%)	38	40	33
Height (m,avg./min.–max.)	16/4–22	16/5–18	16/6–19
DBH (cm,avg./min.–max.)	18/4–36	18/5–28	20/8–29

Figure 2. Study site and thinning treatments of SST and MLT systems.

Table 2. Descriptions of SST and MLT systems.

	Operation
Thinning	Felling	Extracting	Processing
SST
(uphill and downhill)	Chainsaw	Tractor equipped a winch	Excavator-based wood grapple loader and chainsaw
MLT1 and MLT2
(downhill)	Excavator-based grapple-saw

Table 3. SST and MLT machine specifications.

Machine	Model	Specifications
Chainsaw	STIHL MS261	Weight (kg)	5.3
		Displacement (cc)	50.2
		Guide bar length (cm)	40
		Fuel tank capacity (ℓ)	0.5
		Oil tank capacity (ℓ)	0.25
Tractor equipped a winch	TAJFUN EGV 65A	Weight (kg)	515
		Size (L × W × H, cm)	168 × 69 × 231
		Required tractor capacity (hp)	50–90
		Pulling power (kN)	64.5
		Brake power (kN)	80.1
Base machine for wood grapple loader and grapple-saw	DOOSAN DX55MT-5K	Weight (kg)	6,010
		Size (L × W × H, cm)	594 × 196 × 258
		Engine power (hp)	52.9
		Boom length (cm)	300
		Arm length (cm)	160
		Bucket capacity (m^3)	0.18
		Fuel tank capacity (ℓ)	115
		Max. pressure (kgf/cm^2)	240
		Max. oil flow (ℓ/min)	116
Grapple-saw head	GS350 OAK	Weight (kg)	245
		Max. felling capacity (cm)	35
		Max. felling force (kN)	85
		Max. pressure (kgf/cm^2)	250
		Required oil flow (ℓ/min)	35–65

Table 4. Classification of residual stand damage.

Items	Descriptions
Type	Scar: removal of the bark and cambial layer (width: >10.16 cm)
	Gouge: wood fibers removed from the scar
Shape^1	Square, narrow rectangular, wide rectangular, irregular
Location		North: 315°– 45°,
		East: 45°– 135°,
		South: 135°– 225°,
		West: 225°– 315°
Height (m)		Height of scars from ground level
Length and width (cm)		Scar length and width

Table 5. Cost factors and assumptions used for machine cost calculation using the KWF method.

Cost factor		Unit^c	Machine
			Chainsaw	Tractor-winch		Wood grapple loader	Grapple-saw
				Tractor	Winch		Excavator	Grapple-saw
Purchase price	(P)	$	772	77,154	18,860	49,464	46,292	18,860
endurance period^d	(N)	years	1	10	12	8	8	8
Economic life	(H)	hr	1,392	13,920	16,704	11,136	11,136	11,136
Annual operating time^a	(J)	hr/year	1,392	1,392	1,392	1,392	1,392	1,392
Fuel consumption	(c)	ℓ/hr	1.04	1.35	–	4.50	5.50	–
Fuel price^e	(p)	$/ℓ	1.28	1.16	–	1.16	1.16	–
Repair and maintenance	(r)	%	60	80	80	80	80	90
Coefficient of lubricant	(l)	%	40	40	40	40	40	40
Interest rate	(i)	%/year	10	10	10	10	10	10
Machine cost
Depreciation^f	P/H or P/(N·H)	$/hr	0.19	5.54	1.13	4.44	4.16	1.69
Interest	0.5·P·i·0.01/J	$/hr	0.03	2.77	0.68	1.78	1.66	0.68
Repair and maintenance	P/H·r or P·r/(N·H)	$/hr	0.11	4.43	0.90	3.55	3.33	1.52
Fuel cost	c·p·(1 + l)	$/hr	1.86	2.19	0.00	7.30	9.43	–
Other costs (Insurance, storage fee etc.)	–	$/hr	0.03	0.78	0.16	0.62	0.58	0.25
Sub total		$/hr	2.21	15.71	2.87	17.69	19.15	4.15
Labor cost^b (50% inclusion incidental expense)		$/hr	32.03	60.28		36.08	36.08	–
Total machine cost		$/hr	34.24	75.99	2.87	53.78	55.24	4.15
				78.86			59.39

^a174 day × 8 h = 1392 h (KFS, 2012).

^bStandard of labor cost: feller ($99.47), machine operator ($160.37), worker ($107.52) (Construction Association of Korea 2019).

^cExchange rate of 2019: KRW 1166.5–$1.

^eEndurance period (Miyata 1980; Woo et al. 1997; Brinker et al. 2002; Ministry of Government Legislation, 2018).

^eGasoline: $1.28, diesel: $1.16 in July 2019, South Korea (Korea National Oil Corporation, 2020).

^fDepreciation was divided corresponding to the annual use of machines by KWF method. as followed; J ≥ H/N, D = P/H or J < H/N, D = P/(J·N).

Table 6. Productivity and cost of SST and MLT systems.

Thinning method		Operation	Productivity (m^3/SMH)	Utilization (%)	Machine cost ($/SMH)	Cost ($/m^3)
SST (uphill and downhill)		Felling	2.0	76.5	34.2	16.8
						(21.6%)
		Extracting (Skidding)	2.0	47.0	78.9	38.8
						(50.0%)
		Processing	5.5	–	122.2	22.04
						(28.4%)
		Total				77.6
						(100.0%)
MLT1 (downhill)	Fourth double row thinned	Felling	10.9	92.2	60.0	5.5
						(37.3%)
		Extracting (Shovel logging)	18.5	92.4	60.0	3.2
						(21.8%)
		Processing	9.9	80.1	60.0	6.1
						(40.8%)
		Total				14.8
						(100.0%)
MLT2 (downhill)	Third row thinned	Felling	11.2	91.9	60.5	5.4
						(23.7%)
		Extracting (Shovel logging)	6.1	94.2	60.5	9.9
						(43.6%)
		Processing	8.1	94.1	60.5	7.5
						(32.7%)
		Total				22.8
						(100.0%)

Figure 3. Cost comparison between SST and MLT systems.

Table 7. Productivity and cost of felling and processing operations using a small-scale grapple-saw and small harvester.

Study	Machine	Productivity (m^3/PMH)	Machine cost ($/SMH)	Cost ($/m^3)
Mederski et al. (2018)	Vimek 404 T5^a(small harvester)	4.3	83.0^c	24.9
This study (MLT1)	DOOSAN DX55MT-5K^b(small-scale grapple-saw)	6.0	60.0	11.5

^a Price: $ 273,164, engine power: 60 hp, Keto Forest Silver head (felling capacity: 30 cm), utilization: 77.5%.

^b Price: $ 65,152, engine power: 53 hp, GS350 OAK head (felling capacity: 35 cm), utilization 85.9%.

^c Machine cost of Vimek 404 T5 was re-calculated by KWF.

Table 8. Kruskal-Wallis H test of residual stand damage between SST and MLT systems.

Group	Kruskal-Wallis H test
	N	Avg. Rank
		Height	Length	Width
SST (uphill and downhill)	11	25.27	19.00	23.00
MLT1 (downhill)	27	31.91	31.52	27.59
MLT2 (downhill)	16	21.59	26.56	30.44
Total	54	–	–	–
p-Value	–	0.100	0.080	0.473

Table 9. Description of residual stand damage by SST and MLT systems.

Thinning method	Residual stand (trees)	Residual stand damage (trees)	Percentage of residual stand damage (%)	Area of residual stand damage
				(cm^2)	(cm^2/tree)^a
SST	293	10	3.4	1,778.9	177.9
MLT1	272	13	4.8	8,683.1	667.9
MLT2	52	11	21.2	7,089.0	644.5

^aSST: Scar (59.2 cm²/tree), Gouge (6.7 cm²/tree), MLT1: Scar (571.9 cm²/tree), Gouge (96.1 cm²/tree).

Figure 4. Percentage of total stand damages as related to (a) type, (b) location, (c) height, and (d) shape for SST and MLT systems.

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