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Volume 39 No. 2

Including Exogenous Factors in the Evaluation of Harvesting Crew Technical Efficiency using a Multi-Step Data Envelopment Analysis Procedure

volume: 39, issue: 2

The performance of a harvesting crew in terms of its ability to transform inputs into outputs
is influenced by discretionary factors within the unit’s control, such as the selection of machines
and operators. However, factors associated with the operating environment, such as
terrain slope and tree size that are outside the direct control of management, can also influence
harvesting system efficiency. Using data on forest harvesting operations in New Zealand, this
paper applies an established four-stage Data Envelopment Analysis (DEA) procedure to estimate
the managerial efficiency of independent forest harvesting contractors, while taking into
account the influence of the operating environment. The performance of 67 harvesting contractors
is evaluated using seven inputs, one output (system productivity) and three operating
environment factors in an input-oriented, variable return to scale DEA. The results show that
the operating environment including terrain slope, log sorts and piece size influence the efficient
use of inputs by harvesting contractors. A significant difference is observed between the
mean managerial efficiency of the crews before and after controlling for the influence of the
operating environment, the latter being higher by 11%. This study provides evidence that
without accounting for the influence of the operating environment, the resulting DEA efficiency
estimates will be biased; the performance of crews in favourable operating environment
would be overestimated and those in unfavourable environment underestimated.

Productivity, Efficiency and Environmental Effects of Whole-Tree Harvesting in Spanish Coppice Stands Using a Drive-to-Tree Disc Saw Feller-Buncher

volume: 39, issue: 2

Whole tree harvesting was conducted on two coppice stands with different tree composition
(Q. ilex and Q. pyrenaica) in gentle terrain. Felling and bunching were performed by a
drive-to-tree wheeled feller-buncher with disc saw head. Operations were analyzed on 17 plots
25x25 m2 in order to develop productivity models and to assess operational costs. The study
also aimed at determining biomass collection efficiency and evaluating the impact of the new
harvesting method on the soil, the remaining trees and stumps. The treatment consisted in a
strong coppice thinning leaving standards. Productivity ranged from 2.8 to 4.6 odt/pmh in
the Q. ilex coppice, and from 0.9 to 2.6 in the Q. pyrenaica stand. Tree species, dry weight
per tree and percentage of removed basal area were the main independent variables affecting
productivity. Approximately 50% of the standards showed damages. Most wounds were light,
caused by the drive-to-tree work pattern, followed through GPS tracking. Soil damage was
also light; in no plots, deep disturbances were found. However, most of the stumps were damaged.
Forwarding and chipping productivity and cost were also evaluated. The slash left on
the terrain averaged 3.0 and 1.5 odt/ha in Q. ilex and Q. pyrenaica, respectively, including
scrub debris. As a conclusion, while this heavy feller-buncher can be useful in coppice heavy
thinnings with larger trees, it would be a good option to try lighter disc saw felling heads
mounted on the harvester boom tip, which probably would reach better productivity and reduce
the frequency of stand damage.

Investigation of Log Length Accuracy and Harvester Efficiency in Processing of Oak Trees

volume: 39, issue: 2

Harvester use in broadleaves has recently become more effective economically. However, difficulties
with delimbing have shown that not all harvesting heads are suitable and efficient for
broadleaved species. The typical obstacles are mainly large tree sizes, bends and forks in the
trunks and large branches. For these reasons, it is difficult to obtain specific log lengths according
to the settings in the harvester on-board computer. The objective of the research was
to determine: 1) the accuracy of the log lengths from the bottom, middle and top parts of oak
trees, and 2) harvester efficiency in the utilisation of the trunk for logs. The research was carried
out on 61-year-old oaks from which logs with an expected length of 250 cm were processed.
To achieve this length, a margin of error was set in the harvester computer with minimum
and maximum lengths of 252 and 257 cm. For thinning operations, a Ponsse Ergo harvester
with a H7 harvesting head was used. After harvesting, manual log measurements were carried
out on 280 logs: 69, 142 and 69, from bottom, middle and top parts of the trees, respectively.
The largest share of assortments satisfying the minimum requirement of 250–257 cm was
obtained from the middle part of the trees (93%), followed by bottom logs (91%) and top logs
(88%). The highest frequency of logs, which were too short, were found to be the top logs (9%),
while bottom logs were most often too long (6%); therefore, different length settings should be
applied to limit such inaccuracies. Analysis of the last log from the highest part of the tree
indicated a strong goodness of fit between the top diameter and the DBH; the mean value of
the top diameter was 13.3 cm over bark.

Impact of Season and Harvester Engine RPM on Pine Wood Damage from Feed Roller Spikes

volume: 39, issue: 2

Harvesters have become a common solution for wood harvesting in coniferous and broadleaved
stands. Unfortunately, not every customer will accept logs with damage on the lateral surface
of the roundwood caused by feed roller spikes. The extent of the wood damage caused by the spikes
of harvester heads depends mainly on the type of feed rollers and tree species. The objective of the
study was to investigate the external damage to pine (Pinus sylvestris L.) roundwood from
harvester head spikes depending on the season of the year and harvester engine RPM, as well as
the significance and potential consequences of such damage. The scope of the study also included
an analysis of wood damage depth in three stem sections. The experimental plots selected
were all in an 85-year-old pure pine stand. Logging was performed using a Ponsse Beaver harvester
with an H60e harvester head manufactured in 2006. The mean depth of wood damage at
all the points of measurement was 4.1 mm, while the maximum depth of wood damage totalled
5.3 mm. The depth of wood damage depended on the season of the year in which the logging work
was performed, the harvester engine RPM and the stem section from which the log was processed.
The damage was the deepest during summer operations and the shallowest during winter and
springtime. The differences were statistically significant, however, the difference in the depth of
damage was only 1 mm in average. Deeper wood damage was found at a lower engine RPM.
Wood damage depth differed axially, and the least damage was found in the bottom logs.

Tensile Force Monitoring on Large Winch-Assist Forwarders Operating in British Columbia

volume: 39, issue: 2

The forest industry around the world is facing common challenges in accessing wood fiber on
steep terrain. Fully mechanized harvesting systems based on specialized machines, such as
winch-assist forwarders, have been specifically developed for improving the harvesting performances
in steep grounds. While the mechanization process is recognized as a safety benefit,
the use of cables for supporting the machine traction needs a proper investigation. Only a few
studies have analyzed the cable tensile forces of winch-assist forwarders during real operations,
and none of them focused on large machines normally used in North America. Consequently,
a preliminary study focused on tensile force analysis of large winch-assist forwarders was
conducted in three sites in the interior of British Columbia during the fall of 2017.
The results report that in 86% of the cycles, the maximum working load of the cable was less
than one-third of the minimum breaking load. The tensile force analysis showed an expected
pattern of minimum tensile forces while the forwarders were traveling or unloading on the
road site and high tensile forces when operating on steep trails, loading or traveling. Further
analysis found that the maximum cycle tensile forces occurred most frequently when the
machines were moving uphill, independently of whether they were empty or loaded. While the
forwarders were operating on the trails, slope, travel direction, and distance of the machines
from the anchor resulted statistically significant and able to account for 49% of tensile force
variability. However, in the same conditions, the operator settings accounted for 77% of the
tensile force variability, suggesting the human factor as the main variable in cable tensile force
behavior during winch-assist operations.

A Mobile Hydraulic Winch for Use in Small-Scale Forestry

volume: 39, issue: 2

Winches have recently been used to extract timber from forests. Winches are often components
of tractors, but tractors cannot be used on difficult terrain and are generally too expensive for
small forest owners. The current study considers the use of an experimental winch for the
extraction of timber from small plots with difficult terrain. The mobile hydraulic winch used
in this study weighs 50 kg and has a pulling force of up to 53 kN, a 12 V motor, and a 64x224 mm
drum. The associated power unit is a gasoline, single-cylinder, four-stroke, air-cooled KIPOR
KG 390D (400D), 389 cm3 engine, with 7.7 kW of power, and a torque of 22.6 Nm at 2500 rpm.
The engine powers a high-pressure oil pump with an output pressure of 3 MPa and a flow rate
of 60 litres per minute. The input torque of the pump shaft is 25 Nm at 3000 rpm. The hydraulic
winch can be fixed to tree trunks, stumps, or wooden pegs by lashings. The winch was
tested at three locations with different assortments of wood. The results showed that the experimental
winch was practical for timber extraction and that <250 kN of force was needed
for successful extraction. At the test sites, the expense of lumber removal was on average 140%
greater with the winch than with a horse but the advantage of the hydraulic winch is high
pulling force. Because of its small size and low weight, the unit can be easily handled by two
workers, easily moved at short distances in small plots with rough terrain, and easily transported
among plots. With a one-man crew, the percentage of direct costs represented by wages
dropped to 56%, and the percentage represented by fuel increased to 40%.

Productivity and Cost Analysis of Three Timber Extraction Methods on Steep Terrain in Thailand

volume: 39, issue: 2

Steep terrain harvesting in Thailand has low productivity because of the shortage of suitable
logging extraction methods. Common methods involve extraction using manpower on steep
slopes where machines cannot operate. This study compared the utilization of log chutes against
manpower and mule methods with regard to productivity and cost-efficiency in the same logging
compartment in Northern Thailand. The extraction methods were divided into work elements
and data were collected based on described work cycles. The log chutes clearly had the highest
productivity (2.29 m3/h) compared to the other methods. The hourly cost was lowest using
manpower and the highest cost was using the log chute. However, the unit cost indicated the
most economic method was the log chute (THB 72.40/m3) and the least was using mule extraction.
From a logging contractor point of view, the log chute method helps reduce the number of
working days during the harvesting season and provides a higher profit for business.

Production of Wood Chips from Logging Residue under Space-Constrained Conditions

volume: 39, issue: 2

A study was conducted on chip production from logging residue left after a cable yarder operation.
The logistics were managed with tractor and trailer units (shuttles). The study specifically
dealt with a very difficult case of space constrained operations, further expanding the
knowledge about chip supply in extreme work conditions. The focus of the investigation was
also extended to the shuttles. The study tested a production chain, in which only 3 machines
(1 chipper, 2 shuttles) were used to minimize operational costs. The use of 2 shuttles was decisive,
reducing shuttle delays. The chips produced had an average moisture content of 40.2 ±3.1%.
Particle size distribution shows an unfavorable composition. The content of accepts is as low
as 72%, while oversized particles get up to 5.4% and fines rise to a maximum of 24%. The
estimated net productivity of the whole system was 11.5 t PMH-1, corresponding to a gross
productivity of 11.1 t SMH-1. The cost of the whole operation amounted to 21.2 €t-1.

Dynamic Soil Pressures Caused by Travelling Forest Machines

volume: 39, issue: 2

Machines travelling in forest stands cause dynamic loading of soil, the size of which depends
on a multitude of factors such as terrain ruggedness, machine speed, axle load and tyre inflation
pressure. To decide on harvesting and transport machines suitable for specific field conditions,
it is necessary to have at least some awareness about their dynamic effects on the soil,
which sometimes considerably differ from static values measured on standing machines. The
paper deals with the method of determining dynamic ground pressures according to the given
parameters of vehicle weight and speed. At the same time, it compares dynamic pressures
calculated by using this method with actually measured values.

Comparison of Sampling Methods Used to Evaluate Forest Soil Bulk Density

volume: 39, issue: 2

The objective of this study was to compare forest soil bulk density values obtained through
conventional sampling methods such as the volumetric ring (VR: diameter 5 cm, length 10 cm)
and paraffin sealed clod (PSC), with a variation of the VR, where rectangular boxes (RB) of
four different dimensions were used. Sampling transects were established on a machine operating
trail located in a beech (Fagus orientalis Lipsky) stand in Northern Iran. At each
transect, three soil samples were collected at three different locations. Samples from different
methods were spaced by a 50 cm distance to avoid direct interactions. The soil class of our
study area was Combisols according to the WRB classification with a clay texture. Soil bulk
density differed significantly between the three sampling methods. The lowest values were
obtained with the RB (average 1.25 g cm-3), followed by the VR (average 1.40 g cm-3), and
lastly the PSC (average 1.52 g cm-3). The values obtained with four variations of the RB
method ranged from 1.22 to 1.28 g cm-3 and were not found significantly different. When soil
bulk density was calculated after the removal of the weight and volume of roots included in
the samples, the values were determined to be higher than before but with the same range of
magnitude. The lowest coefficient of variation was found for RB4 (CV=2.3%), while the highest
values were observed for VR and RB1 (CV=5.7%).

Root Tensile Force and Resistance of Several Tree and Shrub Species of Hyrcanian Forest, Iran

volume: 39, issue: 2

Shallow landslides are a frequently recurring problem in some parts of Iran, including the
Hyrcanian forest. In addition to traditional civil engineering measures, a potential solution
for this problem is the application of soil bioengineering techniques. The mechanical reinforcement
effect of plant roots is one of the major contributions of vegetation to the mitigation of
shallow landslides. Given the lack of information on the mechanical properties of common
Hyrcanian forest species, the present study assessed the root strength of 10 common species
of this forest. Eight tree species occurring in natural regeneration sites (Carpinus betulus,
Fagus orientalis, Parrotia persica and Quercus castaneifolia) and plantations (Acer velutinum,
Alnus glutinosa, Fraxinus excelsior and Picea abies) and two shrub species
(Crataegus microphylla and Mespilus germanica) were selected. Fresh roots were collected
and mechanical tests were carried out on 487 root samples. The ranges of root diameter,
tensile force, and root resistance were 0.29–5.90 mm, 3.80–487.20 N, and 2.41–224.35 MPa,
respectively. Two different algorithms, including the nonlinear least square method and logtransformation,
were used to obtain power regressions for diameter-force and diameter-resistance
relationships. The results of the two algorithms were compared statistically to choose
the optimal approach for soil bioengineering applications. The nonlinear least square method
resulted in lower Akaike information criteria and higher adjusted R2 values for all species,
which means that this model can more efficiently predict tensile force and resistance based on
root diameter. Log-transformation regressions generally underestimate tensile force and resistance.
Significant differences were found among mean root tensile force (ANCOVA;
F=37.36, p<0.001) and resistance (ANCOVA; F=34.87, p<0.001) of different species. Also,
root diameter was significant as a covariate factor in tensile force (F=1453.77, p<0. 001) and
resistance (F=274.26, p<0.001). Shrub species and trees in natural regeneration sites had
higher tensile force and resistance values, while trees from plantation stands had lower values.
The results of this study contribute to the knowledge on the root force and resistance characteristics
of several shrub and tree species of the Hyrcanian forest and can be used in evaluating
the efficiency of different species for bioengineering purposes.

Pavement Deterioration Modeling for Forest Roads Based on Logistic Regression and Artificial Neural Networks

volume: 39, issue: 2

The accurate prediction of forest road pavement performance is important for efficient management
of surface transportation infrastructure and achieves significant savings through timely
intervention and accurate planning. The aim of this paper was to introduce a methodology
for developing accurate pavement deterioration models to be used primarily for the management
of the forest road infrastructure. For this purpose, 19 explanatory and three corresponding
response variables were measured in 185 segments of 50 km forest roads. Logistic regression
(LR) and artificial neural networks (ANNs) were used to predict forest road pavement
deterioration, Pothole, rutting and protrusion, as a function of pavement condition, environmental
factors, traffic and road qualify. The results showed ANNs and LR models could classify
from 82% to 89% of the current pavement condition correctly. According to the results,
LR model and ANNs predicted rutting, pothole and protrusion with 83.5%, 83.00% and
81.75%, 88.65% and 85.20%, 80.00% accuracy. Equivalent single axle load (ESAL), date of
repair, thickness of pavement and slope were identified as most significant explanatory variables.
Receiver Operating Characteristic Curve (ROC) showed that the results obtained by
ANNs and logistic regression are close to each other.

Current State and Improvement Potential of Forestry Workers Training in Croatia

volume: 39, issue: 2

This paper discusses the key issues of forestry workers training in Croatia, especially dealing
with the providers of vocational training, their profile, training procedures and measures
necessary for training improvement. A combined approach of literature review, internet search
and questionnaire of training providers was applied in order to collect data on training programs
conducted in Croatia. The research was conducted during 2016, and it included 94
legal entities authorized for occupational safety training in the Republic of Croatia, with respect
to safe working practice training and vocational training for operating machinery (chainsaw
and/or skidder). The analysis used basic descriptive statistics.
Research results showed that 30.85% of the analyzed legal entities provide only training for
safe working practice, 15.96% provide both trainings – safe work practice and vocational
training for operating machinery, 5.32% of the analyzed entities provide only vocational
training for operating machinery, 31.91% do not carry out any form of training in forestry,
while 15.96% refused to answer questions. On the other hand, 15.56% of the legal entities,
which do not carry out any training or did not answer these questions, have on their official
website services posted for vocational training in operating machinery (chainsaw and/or skidder).
The key findings of the conducted research have pointed out the great heterogeneity
amongst providers of forestry workers training, and certain reductions or limitations in the
current training programs, both from the aspect of duration of the theoretical and practical
training, and the use of non-transparent criteria and standards in the assessment of training.
As an example of successful solution in forestry workers training, European Chainsaw Standard
model (ECS) is shortly presented in the paper. Discussion and conclusion sections provide
an overview of legislative and organizational requirements for the application of previously
developed European model (ECS) in developing the certification system for training of forestry
workers in Croatia.

Economic Consequences of Different Management Approaches to Even-Aged Silver Fir Forests

volume: 39, issue: 2

Economic analysis of even-aged fir stand management was illustrated using the example of the
forests of the Croatian Dinaric region, as well as their transformation into more stable unevenaged
structures. Two scenarios (even-aged, uneven-aged) were simulated against the backdrop
of the existing forest stand structure of future forest stand management during a 140-year
period using forest growth modeling software MOSES version 3.0 in order to identify economic
differences amongst different scenarios both at stand level and at forest level. The research
included forest management analysis throughout the transformation period and subsequently
the continuation of balanced state forest management. Moreover, the research also
provided the opportunity of forest purchase within the price range from 1000 to 12,500 EUR/ha,
amid assumed fluctuation of selling prices of timber assortments throughout the simulation
period. Discount rates from 1% to 5% were used during the economic analysis. The research
findings showed that, according to harvesting costs, Net Present Value and Internal Rate of
Return, uneven-aged forest management system, including the transformation period, achieved
superior economic results, albeit at discount rates that exceeded 1.24%. The conclusion was
reached that, according to all economic criteria, uneven-aged mixed silver fir-beech management
system is preferred compared with the pure even-aged silver fir management.

The Quality of Fired Aleppo Pine Wood (Pinus Halepensis Mill.) Biomass for Biorefinery Products

volume: 39, issue: 2

Open-air fires or forest fires are becoming a key factor in reducing the forest surface areas and
they are one of the major factors of devastation and degradation of forests and forest land and
their ecosystems in the Mediterranean, mainly in coastal karst. They cause extreme material
and economic damage, and they negatively affect biological and landscape diversity. After the
forest fire, significant quantities of fired trees are left behind, representing a significant amount
of lignocellulosic biomass available for conversion into a variety of biobased products. The
question arises as to what degree they are chemically degraded, or whether they still have the
properties required for further application in mechanical or chemical processing.
The main aim of this paper was to study the group chemical composition as a biomass chemical
property of the Aleppo pine (Pinus halepensis Mill.) sapwood before and after the impact
of low ground fire and high fire of the treetops at tree height of 0, 2 and 4 m. Therefore, the
impact of forest fires on the Allepo pine sapwood group chemical composition was studied in
terms of quality for further application in production of biorefinery products. In addition,
research results on group chemical composition of the same unfired and fired Aleppo pine wood
bark from previous study were used for comparison with sapwood from this study.
The obtained results show that the distribution of the main chemical components of Aleppo pine
unfired wood bark and sapwood is similar to the results of previous studies for different wood
species. That means that the bark contains a significantly higher content of ash, accessory materials
(extractives) and lignins, and a significantly lower content of polysaccharides cellulose and
polyoses (hemicellulose) than sapwood. The bark results from previous studies show a significant
difference in reduced ash, cellulose and lignin content, and in the increased accessory materials
and wood polyoses (hemicellulose) content between the unfired and fired wood. Furthermore, the
content of individual chemical components of fired bark at different forest fires heights of 0, 2 and
4 m for each sample did not differ significantly. Contrary to fired bark, no significant differences
have been observed in the chemical composition of sapwood between unfired and fired wood, not
even resulting from different forest fires heights. It can be concluded that the forest fire did not
have any effect on Aleppo pine sapwood, where the fired wood bark took over all the damage
caused by high temperature during the forest fire. In addition, the fired sapwood still retains the
chemical properties required for further application in biorefinery biobased products.

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Web of Science Impact factor (2017): 1.714
Five-years impact factor: 1.775
Next issue: January 2019

Subject area

Agricultural and Biological Sciences

Category/Quartile

Forestry/Q1