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Research Paper

Assessing the cost of stump-site debarking in eucalyptplantations

Natascia Magagnotti a, Carla Nati b, Luigi Pari c, Raffaele Spinelli b,*, Rien Visser d

aCNR, Timber and Tree Institute, Via Biasi 75, I-38010 San Michele all’Adige (TN), ItalybCNR, Timber and Tree Institute, Via Madonna del Piano, Pal. F, I-50019 Sesto Fiorentino (FI), ItalycCRA ING, Via della Pascolare 16, Monterotondo Scalo (Roma), Italyd Forest Engineering, Canterbury University, Private Bag 4800, Christchurch, New Zealand

a r t i c l e i n f o

Article history:

Received 9 May 2011

Received in revised form

30 August 2011

Accepted 21 September 2011

Published online 22 October 2011

* Corresponding author. Tel.: þ39 055 522564E-mail addresses: magagnotti@ivalsa.cnr

cnr.it (R. Spinelli), rien.visser@canterbury.ac1537-5110/$ e see front matter ª 2011 IAgrEdoi:10.1016/j.biosystemseng.2011.09.009

Mechanised cut-to-length (CTL) harvesting is commonly deployed in eucalypt plantations

and is based on the application of specialised machinery for felling, delimbing, debarking

and crosscutting trees directly at the stump site. Debarked logs are then moved to the

roadside with dedicated forwarders for loading onto transportation vehicles. This study

determined the cost of stump-site debarking, which was calculated between 1.7 and

6.7 Vm�3, depending mainly on tree size. Avoiding stump-site debarking would allow

reducing the overall stump-to-road harvesting cost between 11 and 17%, while making

bark biomass available for energy or biochemical conversion. The figures obtained from

this study are specifically valid for European pulpwood plantations and winter harvest

conditions, but the underlying principles may hold a general significance. Further studies

should determine the cost of off-site debarking, and the effects of bark removal on soil

fertility.

ª 2011 IAgrE. Published by Elsevier Ltd. All rights reserved.

1. Introduction Plantation forestry is stemming the trend towards net

The world-wide total area of eucalypt plantations has

expanded to 19 million ha (Flynn, 2010), fulfilling predictions

made over 10 years earlier (Brown, 2000). Large plantations

have been established in South America, China and South

East Asia, and their importance to total wood supply is likely

to keep increasing (Whiteman & Brown, 1999). Most foresta-

tion projects are the result of industrial endeavour, spear-

headed by large private companies, but their results may go

beyond pure financial profit and touch the spheres of nature

conservation (Sedjo & Botkin, 1997) and rural development

(Lockie, 2003).

1; fax: þ39 055 5225643..it (N. Magagnotti), nati@i.nz (R. Visser).. Published by Elsevier Lt

deforestation (Mather, 2007), and may even play a significant

role in promoting regeneration of the native tree species, thus

facilitating natural forest succession (Selwyn & Ganesan,

2009). At the same time, plantation forestry can be a suitable

solution for many small family farms, unable to cope with the

high labour requirement of traditional land tenure systems

(Riveiro, Alvarez, Pereira, & Miranda, 2005).

Growing competition in commercial wood supply creates

demands for increasedmanagement efficiency, particularly in

harvesting, which accounts for a large proportion of the total

financial and energy inputs of plantation forestry (Romanelli

& Milan, 2010). Mechanised cut-to-length (CTL) harvesting is

valsa.cnr.it (C. Nati), luigi.pari@entecra.it (L. Pari), spinelli@ivalsa.

d. All rights reserved.

Table 1 e Site and study description.

Site Montalvo, Portugal

Coordinates Easting 8�16014.0300WCoordinates Northing 39�30’36.1300NElevation m asl 135

Species Eucalyptus globulus

Age Years 14

Management Coppice, clearcut

Rotation Second

Treatment Not debarked Debarked

Density trees ha�1 1280 1328

Stocking m3merch [ub] ha�1 115 117

Surface ha 0.68 0.66

Slope gradient % 22.7 23.6

Volume m3merch [ub] 78.4 77.2

Trees no. 870 877

Avg. DBH cm 12.8 12.6

Avg. height m 17.7 17.6

Avg. volume M3merch [ub] 0.090 0.088

Logs no. tree�1 5.4 5.1

Harvesting PMH 8.9 11.0

Productivity trees PMH�1 97.8 79.7

Productivity M3 PMH�1 8.8 7.0

Forwarding PMH 8.1 8.1

Productivity trees PMH�1 107.4 108.3

Productivity M3 PMH�1 9.7 9.5

Note: PMH¼ Productive machine hour, excluding delays;

merch.¼merchantable.

b i o s y s t em s e n g i n e e r i n g 1 1 0 ( 2 0 1 1 ) 4 4 3e4 4 9444

often deployed in eucalypt plantations, and is based on the

application of specialised machinery for felling, delimbing,

debarking and crosscutting trees directly at the stump site

(Spinelli, Owende, & Ward, 2002). Trees are debarked at this

stage in order to avoid the accumulation of bark residue at the

field edge or at the processing plant, and also because some

plants may lack capable log debarking facilities (Gavrilescu,

2008). Furthermore, bark bond strength may increase with

decreasing moisture content, which makes it preferable to

debark as soon as possible after felling, and before logs get too

dry (Moore & McMahon, 1986).

The increasing demand for wood biomass is also stimu-

lating a keen interest in the recovery of all forest residues,

including bark and tree stumps (Palander, Vesa, Tokola,

Pihlaja, & Ovaskainen, 2009). In this light, stump-site debark-

ing represents a waste of a potentially useful material, or an

additional cost is incurred if the residue is retrieved from the

field. If residue must be recovered, there are better ways than

retrieving it from the stump site (Talbot & Suadicani, 2005),

including the use of a delimberedebarkerechipper stationed

at the roadside landing, where loads are transferred to the

transportation vehicles (Spinelli, Ward, & Owende, 2009).

New trends in plantation management may offer another

reason for postponing debarking. Many companies are

exploring the potential of eucalypt plantations for use as

structural timber (Washusen et al., 2009), following the same

policy already applied to poplar plantations (Spinelli,

Hartsough, & Moore, 2008). In this case, delaying debarking

may slow down moisture losses and help contain the devel-

opment of drying checks, which are only partly related to poor

genetics (Blackburn et al., 2010). At the same time, a substan-

tial production of sawlogsmay favour CTL harvesting, which is

gentler on the stems and is known to cause less product

damage (Favreau, 1998, p. 2). However, an informed decision

can only be taken after evaluating the savings potentially

accrued when on-site debarking is avoided, and balancing

these savings against the cost of debarking at the plant. The

goal of this study was to determine the first element of this

approach and provide an accurate estimate for the cost of on-

site debarking with a specialised harvester commonly used for

the task. Future studies will address the second element:

namely the cost of using debarking at the plant.

2. Materials and method

The study was conducted on a 1.3 ha test site, located near

Montalvo, in Portugal. The plantation consisted of 14-year-old

Eucalyptus globulus, and was managed for pulp production by

clearcutting (Table 1). The area was divided into 6 subplots,

randomly assigned to the two treatments: harvesting with

and without debarking. A John Deere 1270 (www.deere.com/

forestry) dedicated harvester was used to fell trees and

process them into 2.4 m logs to a minimum small end diam-

eter of 70 mm (Fig. 1). The harvester head mounted special

steel rollers with spiral cutting edges, specifically designed for

debarking. These were replaced with conventional rubber-

and-chain rollers when debarking was to be avoided.

Debarking required between one and four passes through the

harvester head. Processing without debarking generally

required one pass, and if large branches were encountered,

occasionally two. Logs were extracted to the roadside with

a John Deere 1210 forwarder. Debarked logs and logs with bark

were kept separate during the whole process (Fig. 2).

Both machines were operated by experienced profes-

sionals, who had run them for at least 3 years. No attemptwas

made to normalise individual performances by means of

productivity ratings (Scott, 1973), recognising that all kinds of

corrections can introduce new sources of errors and uncon-

trolled variations in the data (Gullberg, 1995). However, the

skills of operators studied were considered representative of

the region and were very similar, ensuring that the repre-

sentative character of the study was not invalidated. In any

case, operator skills have a stronger impact on the perfor-

mance of machines used for thinning than in clearcutting

(Karha, Jouhiaho, Mutikainen, & Mattila, 2003).

The diameter at breast height (DBH) of each harvest trees

was measured and associated to the respective processing

time, without interfering with the work process. DBH records

were translated into volume records using a proprietary

double-entry volume table developed by the plantation owner

for commercial purposes. The table returned volume under

bark in cubic metres (m3 [ub]). A height-diameter curve for the

test site was developed using 53 sample trees, evenly distrib-

uted within all diameter classes. Individual trees were

assigned a form index denoting the density and dimension of

their limbs, and any presence of sweep or other malforma-

tions. Form index values were assessed visually, and ranged

from 1 to 5: index 1 described straight stems with few small

limbs, whereas index 5 indicated crooked, forked or generally

malformed trees. A full description of the five index classes

was reported in Spinelli et al. (2002).

Fig. 1 e The harvester at work, with the rubber-and-chain rollers.

b i o s y s t em s e ng i n e e r i n g 1 1 0 ( 2 0 1 1 ) 4 4 3e4 4 9 445

A time-motion study, designed to evaluate machine

productivitywhile separating specific process steps (Bergstrand,

1991) was carried out. Each complete work cycle represented

a replication and was timed individually, using Husky Hunter

hand-held field computers (Husky Computers Ltd, 1991, p. 444)

running the dedicated Siwork3 time study software (Kofman,

1995, p. 37). A cycle was defined as the time to process a single

Fig. 2 e Stacked debarked (right) and

tree for the harvester, or to haul a single load for the forwarder.

Productive time and delay time (Bjorheden, Apel, Shiba, &

Thompson, 1995, p. 16) were recorded separately, and delay

time was then removed. This avoided the typically erratic

occurrence that could blur the eventual relationship between

cycle time and significant independent variables (Spinelli &

Visser, 2008). If included, delays would have added 10% and

not debarked (left) eucalypt logs.

Table 2 e Costing: assumptions, cost items and total cost.

Machine Type Harvester Forwarder

Machine Model JD 1270 C JD 1210

Purchase price Euro 385,000 235,000

Economic life Years 8 8

Resale value % new 25 30

Interest rate % 10 10

Fuel consumption l PMH�1 14 12

Crew n 1 1

Depreciation V year�1 36,094 20,563

Annual use PMHyear�1 1400 1600

Total fixed cost V PMH�1 48.0 25.1

Fuel V PMH�1 18.2 15.6

Repair and maintenance V PMH�1 8.5 4.2

Personnel cost V PMH�1 25.0 25.0

Total variable cost V PMH�1 57.2 49.5

Overhead (20%) V PMH�1 21.0 14.9

Total cost (machine rate) V PMH�1 126.1 89.5

Note: PMH¼ Productive machine hour, excluding delays.

0

5

10

15

20

25

30

0 0.1 0.2 0.3 0.4 0.5

Tree Volume (m3 [ub])

Pro

du

ctiv

ity

(m

3 [

ub

] P

MH

-1)

Undebarked

Debarked

Fig. 3 e Harvesting productivity as a function of tree size

and treatment.

b i o s y s t em s e n g i n e e r i n g 1 1 0 ( 2 0 1 1 ) 4 4 3e4 4 9446

20% to the timeconsumptionof theharvester and the forwarder,

respectively.

Data were analysed with t-test and regression techniques

in order to check the statistical significance of eventual

differences between treatments. Indicator variableswere used

to represent different treatments when exploring the rela-

tionship between productivity and tree size (Olsen, Hossain,

& Miller, 1998, p. 31). All data sets were at first checked for

normality, in order to select the appropriate analytical

procedures.

Machine costs were calculated with the method described

by Miyata (1980, p. 14), using the assumptions shown in

Table 2. Economic life, annual use and resale value were ob-

tained from a recent survey (Spinelli, Magagnotti, & Picchi,

2011). Labour cost was set to 25 V per productive machine

hour (PMH), inclusive of indirect salary costs. The costs of fuel,

insurance, repair and service were obtained directly from the

operators. The calculated operational cost was increased by

20% in order to include administration costs (Hartsough,

2003).

Eucalypt plantations are often managed as coppice, and

their successful regeneration depends on the good health of

Table 3 e Felling and processing.

Treatment Debarked Not debarked Diff. Significance

Time element Mean SD Mean SD % p value

Moving 4.3 18.0 5.3 27.5 23.3 0.3969

Felling 15.2 5.7 16.0 6.9 5.3 0.0114

Processing 48.6 15.6 33.4 14.9 �31.3 <0.0001

Other 6.9 6.9 6.5 4.7 �5.8 0.1820

Total time 75.0 27.0 61.2 33.8 �18.4 <0.0001

Note: Time elements in min� 10�2; SD¼ standard deviation;

Diff.¼ difference in % for the not debarked treatment vs. the

debarked treatment (e.g. processing time is reduced by 31.3% when

passing from the debarked to the not debarked treatment).

tree stumps and on the absence of harvesting damage.

Hence, the conditions of cut stumps were evaluated by

inspecting 360 specimens, distributed within 15 ten-stump

blocks per treatment. Stump height from ground level was

measured using a carpenter ruler on both the uphill and the

downhill side. Stump damage was visually assessed and

attributed to one of the following damage classes: no

damage, superficial damage, split, crushed (Spinelli, Cuchet,

& Roux, 2007).

Treatment type was expected to alter the release of har-

vesting residue on the terrain, and potentially impact soil

disturbance levels. These were determined through visual

inspection, carried over the whole surface of the test site on

a 3� 2 m grid. The disturbance type within a square metre

around each grid intersection point was recorded using

a classification adapted from McMahon (1995, p. 16). This

system is widely used in scientific studies (Deconchat, 2001;

Gondard, Romane, Aronson, & Shater, 2003) and has been

adopted as part of the harmonised European protocol for work

studies in forestry (Visser, 1997).

Overall, the test was conducted over 1.34 ha, from which

1747 trees were harvested, yielding 155 m3 ub of pulpwood.

The time study sessions covered a total of 41 observation

hours, corresponding to 36 PMHs.

0

2

4

6

8

10

12

0 100 200 300 400 500

Extraction distance (m)

Pro

du

ctiv

ity

(m

3

[u

b] P

MH

-1

) Undebarked

Debarked

Fig. 4 e Forwarding productivity as a function of distance

and treatment.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 0.1 0.2 0.3 0.4 0.5

Tree volume (m3 [ub])

Harvestin

g co

st (€ m

-3 [u

b])

Undebarked

Debarked

Fig. 5 e Stump-to-roadside cost as a function of tree

volume and treatment.

b i o s y s t em s e ng i n e e r i n g 1 1 0 ( 2 0 1 1 ) 4 4 3e4 4 9 447

3. Results

Analysis of time element duration showed that debarking

caused a statistically significant increase in processing time,

whereas no large and significant differences were recorded for

the other time elements (Table 3). This appears to confirm that

debarking is the cause for the significant productivity differ-

ence recorded between the two treatments, all along the

explored range of tree size values (Fig. 3). In contrast, treat-

ment had little effect on forwarding productivity, which was

affected primarily by load size and extraction distance (Fig. 4).

As expected, harvesting productivity increased with tree size,

while forwarding productivity decreased with extraction

distance.

The machine rates shown in Table 2 were used to estimate

the impact of stump-site debarking on harvesting and

extraction cost. Results are shown in Fig. 5, and have been

calculated all along the tree size range, assuming a tree form

index 2 and a 300 m extraction distance, with the forwarder

unloading on a stack rather than directly onto a truck. Over-

all, stump-site debarking incurs a cost between 1.7 and

6.7 Vm�3 [ub]. Thus, avoiding stump-site debarking reduced

the overall stump-to-road harvesting cost between 11 and 17%.

Stumps were cut close to the ground (average 70 mm on

the uphill side) and the large majority showed a clean cut,

with no damage. Only 2e4% of the stumps presented severe

damage, such as splitting or crushing. No significant differ-

ence was found between treatments (Table 4).

Table 4 e Survey of stump conditions after harvest.

Parameter Treatment Debarke

Mean

Stump height Upslope (mm) 219.9

Stump height Downslope (mm) 79.8

No damage % 71.1

Superficial damage % 26.7

Split % 1.1

Crushed % 1.1

The treatment with no debarking caused substantially less

soil disturbance than the other (Table 5). The incidence of the

undisturbed soil surface was twice as high (41% vs. 19%) with

no debarking, but that mainly depended on slash accumula-

tion e which was predictably much higher when debarking

was used (58% vs. 39%). Rutting was also higher with

debarking, but its incidence was very small in both treatments

(1.3% and 0.6% for debarking and no debarking respectively),

despite the heavy rain during the days just before the tests.

4. Discussion

The estimated general productivity levels closely matched the

results of previous studies, especially for felling and process-

ing. In this study, harvester productivity spanned 5 and

25 m3 [ub] PMH�1 depending on tree size, and this compares

well with the 5e14 m3 [ub] PMH�1 found by Spinelli et al. (2002)

for less efficient excavator based units, or the 7.8 and

10.7 t PMH�1 found by Hartsough and Cooper (1999) and

Perinot and Rivals (2001, p. 4), respectively. With its

8e10 m3 [ub] PMH�1, the forwarder used in this study was

much less productive than those used in conifer clearfells,

which can move 12e20 m3 [ub] PMH�1 (Tiernan et al., 2004).

That is likely to be because larger pieces are handled in conifer

clearfells. However, specific studies conducted on eucalypt

clearfell operations have also shown higher productivities

than recorded in this study: 12.5 t PMH�1 (Spinelli, Owende,

Ward, & Tornero, 2003), 13.8 t PMH�1 (Dos Santos, Machado,

& Leite, 1994), 16.2 t PMH�1 (Hartsough & Cooper, 1999). Such

discrepancies could be attributed to the different characteris-

tics of the European plantations compared to those in America

(e.g. Dos Santos et al., 1994; Hartsough & Cooper, 1999), or to

the specific terrain conditions encountered during our tests,

which were conducted on relatively steep and wet ground.

Among the authors quoted above, only Hartsough and

Cooper (1999) compared mechanised harvesting with and

without debarking. Their results indicate that debarking may

cause a higher productivity loss than found in our study. The

difference is dramatic: between 19% and 23% for our study,

and 38%e56% for theirs. There could be many explanations

for such large difference, including machine type, tree char-

acteristics (Eucalyptus viminalis instead of E. globulus) and

seasonal variations in the bark bond strength. However, even

if the figures concerned are quite different, both studies agree

on attributing a significant productivity loss to the debarking

d Not debarked Significance

SD Mean SD p value

71.6 222.0 73.7 0.8071

70.0 88.6 67.7 0.2708

10.5 67.1 14.3 0.4484

10.0 29.2 12.5 0.5945

3.3 1.2 3.4 0.9166

3.3 2.5 5.3 0.4722

Table 5 e Survey of soil disturbance.

Soil condition Debarked Not debarked

Points % Points %

Undisturbed 180 19.3 415 41.4

Litter disturbance 197 21.1 134 13.4

Organic soil exposed 56 6.0 19 1.9

Mineral soil exposed 33 3.5 33 3.3

Rut� 100 mm 10 1.1 6 0.6

Rut> 100 mm 2 0.2 0 0.0

Slash� 300 mm 311 33.4 346 34.5

Slash> 300 mm 143 15.3 50 5.0

Total 932 100.0 1003 100.0

Note: adapted after McMahon (1995).

b i o s y s t em s e n g i n e e r i n g 1 1 0 ( 2 0 1 1 ) 4 4 3e4 4 9448

process. Taken together, these studies draw specific attention

to the role of tree species and seasonal variation, thereby

warning readers against extrapolating the results of this study

to other plantation types, and other seasons than the Euro-

pean Atlantic winter.

This study also appears to show progress in terms of cut

quality, with lower stump heights than reported by Hartsough

and Cooper (1999) and amuch lower incidence of damage (30%

vs. 66%) than reported by Spinelli et al. (2007) for machine-

felled traditional coppice stands. Soil disturbance was also

moderate and, in the case of the treatments not debarked, at

the same levels recently recorded for semi-mechanised

traditional operations (Spinelli, Magagnotti, & Nati, 2010).

Any decision on stump-site debarking should also include

the potential side effects on soil fertility, which were not

included in this study. Short-rotation eucalypt plantations

require many nutrients, whose shortage is considered as the

main cause of growth decline in the second and following

rotations (Nambiar, 2010). Hence, there is interest in returning

to the soil as much organic matter as possible. Whilst bark

represents <10% of the above ground tree mass, it contains

large amounts of nutrients; for this reason several authors

suggest that stump-site debarking could have a major role in

preventing soil nutrient depletion in eucalypt plantations

(Santana, Barros, & Comerford, 2000; Turner & Lambert, 1983).

However, themajority of nutrients is in the leaves, and it is not

certain that bark nutrients would be easily available due to the

very slow decomposition of bark material (Hernandez, Del

Pino, Salvo, & Arrarte, 2009). For this reason it has been sug-

gested that bark should be treated before turning it into an

effective soil conditioner (Yadav, Sharma, & Kothari, 2002).

Specific tests conducted on eucalypts in Brazilian plantations

indicate that bark removal may have minimal effects on soil

fertility, and that the traditional practice of windrowing and

burning the residue is amain cause of nutrient depletion (Lima

et al., 2006). In any case, recent studies indicate that fertilisa-

tion remains the best way to promote fast growth in eucalypt

plantations, evenwhen releasing all residues on site, including

bark (Smith & Du Toit, 2005).

5. Conclusions

Mechanised CTL harvesting is a very effective technique

commonly applied to eucalypt plantations, and it often

integrates stump-site debarking. However, this specific

process incurs a significant cost and prevents the effective

recovery of a potentially valuable secondary product. In the

near future, debarking could bemoved to the processing plant

site, where large-scale industrial technology may further

reduce its cost and allow profitable use of the residue. This

study determined the cost of on-site debarking and offered

a first element to decision making. Selecting the best

debarking strategy will also require information about the

exact cost of debarking at the plant, and about the value of the

biomass recovered in the process. When deciding where to

debark, much attention must be paid to soil fertility issues,

which are especially affected by logging residuemanagement.

Acknowledgements

The authors gratefully acknowledge the organisational

support received from Dr. Jose Luis Carvalho, Enerforest,

Portucel Soporcel SA, Lisbon, Portugal.

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