Human Factors in Mechanized
Cut-to-Length Forest Operations
Faculty of Forest Sciences
Department of Forest Biomaterials and Technology
Swedish University of Agricultural Sciences
Acta Universitatis agriculturae Sueciae
I ISBN (print version) 978-91-576-8316-8
ISBN (electronic version) 978-91-576-8317-5
© 2015 Carola Häggström, Umeå
Print: Arkitektkopia, Umeå 2015
Cover: Logging operations with a harvester operator wearing eye-
equipment. (photo: Skogforsk)
Human Factors in Mechanized Cut-to-Length Forest Operations
Although forest operations research has a more than 50-year-long tradition in the field
of human factors, there is a current decline in resources put on continuous and
systematic human factors research. Therefore, the overall aim of this thesis was to
contribute new knowledge on working conditions in mechanized cut-to-length logging
operations and their relationship to system performance. Findings from four different
studies, each using different research methods and approaches, were compiled and
discussed based on their relevance to operator working conditions and logging system
performance in a Nordic context and with a broader international outlook.
A human, technology and organization (HTO) framework was used in Study I to
scrutinize the problems that exist in the interactions between these three aspects. The
body of knowledge on the H, T and O aspects was extended in Studies II, III and IV
based on problem identification Study I.
In study II, it was emphasized that most Swedish logging contractors were relatively
small enterprises working purely with machine operations. Consequently, with the
exception of between harvester and forwarder, task rotation has limited potential to be
implemented within most companies.
In Study III, forwarder crane work was essentially ruled out as a major source of
harmful levels of whole body vibration (WBV). The results also indicated that the
choice of grapple may prove important with respect to avoiding costly growth losses
for the landowner and environmental concerns.
In Study IV, gaze behaviour was investigated in an observational field study. By
comparing operators in first thinning, second thinning and final felling, a task-
dependent information search pattern was identified. Specifically, the information on
the bucking monitor and the tree being felled was less frequently attended to, i.e. less
interesting, during first thinning than during the other operation types.
Taken as a whole, much of the forestry literature focuses on individual aspects of the
work environment, as in studies II-IV, and a systems perspective is less frequently
applied. A hindrance to applying a systems perspective is that it demands
transdisciplinary research teams and interdisciplinary research. However, this should be
seen as an opportunity and not a hindrance to successful future research.
Keywords: contractors, cut-to-length, ergonomics, eye tracking, forwarder, harvester,
logging, mechanized forestry, MTO, whole body vibration
Author’s address: Carola Häggström, SLU, Department of Forest Biomaterials and
Technology, 901 83 Umeå, Sweden
Writing is easy: All you do is sit staring at a blank sheet of paper until drops of
blood form on your forehead.
There are many people who have influenced and helped me to get to this point:
my supervisors, colleges at SLU and Skogforsk, all the people in the FIRST
and SweCog research schools, my friends and my family. However, there are a
few that I wish to explicitly thank.
Åsa Hedenskog and Jocke Ekberg were the two people who influenced me
greatly in making the decision to apply for this PhD position. I would have
never started this journey without your initial support! Jocke, you have been a
friend, an inspiration and a great support. I will never forget that you were the
one to lend me 3000 kr when I needed a locksmith to get back into my
apartment the unfortunate Saturday morning when I was still a student.
Foremost, I wish to thank my supervisors Gun Lidestav and Ola Lindroos.
I’m so grateful that you didn’t lose faith in me and that you stood by my side
and supported me all the way to the finish line. To my co-supervisor Håkan
Alm, thank you for all the advice. I wish I had listened to you more often and
whenever I’m expecting guests I twist my neti pot and think of you.
Thanks to Tomas Nordfjell for all your guidance, support and funny
remarks over the years. Micke Öhman, it was a pleasure working with you but
I had much more fun at our common lunch breaks. You really know how to
make cheeks hurt.
Thanks to Skogforsk, for employing and welcoming me during these years.
To my colleagues and friends at Skogforsk, thank you for all the help,
company and encouragement! Magnus Thor, Björn Löfgren and Rolf
Björheden, your support meant a lot to me. I would like to thank Martin
Englund for a great collaboration, insightful discussions and great company in
the mist. Now as then: we don’t need this bloody mist. Mikael Öhman, thank
you for being the guy who cares about everyone and especially for brightening
my visits to Skogforsk.
To my friends and colleagues in Forest Biomaterials and Technology and in
Forest Resource Management: so many of you have made such an impact on
me, I cannot name you all. I appreciated all the advice you have given me,
especially those that I didn’t take, your concerns really touch me. And if it
hadn’t been for all the laughter we had during breaks, I would have never
finished. Every now and then you need some bullshit! Mona, Mikaela, and
Marianne you are and you have been indispensable. Marjan on such a short
amount of time, I learnt so much from you, both professionally and personal.
Anna and Emanuel, you gave me cycling! Thank you for many fantastic hikes
and journeys which I would not have experienced without you. Jeanette, your
energetic company has been lovely on so many study trips and conferences all
over the world. Mattias, thank you for the support and all the discussions we
had in Sweden and abroad.
Thanks to the SLO foundation that supported this research and for granting
me money to learn to operate the forwarder. To everyone involved in the
Forest Industry Research School on Technology (FIRST): thank you for giving
me this opportunity.
I would also like to thank Olle Hilborn, for your invaluable insights, helpful
discussions and for being a friend.
To all my friends outside university, thanks for staying put when I was too
occupied with work to give you the time you deserve and the time I wanted.
To my family, for your unconditional love, support and acceptance.
Mamma och pappa, för att ni alltid stöttar mig och aldrig tvekar att ge en
hjälpande hand. Christina, Mats, Linnea, Selma och Gustav, min tisdagsfamilj,
tack för all kärlek och omtanke och för att ni gödde mig under mina första år i
Umeå, May 2015
List of Publications 9
1 Introduction 13
1.1 Mechanized CTL operations 16
1.1.1 Harvesting 16
1.1.2 Forwarding 17
1.1.3 The physical environment 18
2 Aim 21
3 Conceptual framework 23
4 Study I – HTO in mechanized CTL forestry 25
4.1 Human: skills and abilities 25
4.2 Technology: tools and prostheses 28
4.2.1 The physical dimension 28
4.2.2 The cognitive dimension 29
4.3 Organization: culture and structures 30
5 Study II - Labour Organization in Swedish forestry 33
5.1 Materials and Methods 33
5.1.1 Data collection 33
5.1.2 Data analysis 34
5.2 Results 34
5.2.1 Forestry contractors’ development and structure 34
5.2.2 Logging contractors 2009 35
6 Study III - Technology and human reactions 37
6.1 Materials and methods 37
6.1.1 Data collection 37
6.1.2 Data processing and analysis 38
6.2 Results 39
7 Study IV - Human behaviour and human–technology interaction 43
7.1 Materials and methods 43
7.1.1 Data collection 43
7.1.2 Data analysis 44
7.2 Results 46
7.2.1 Viewing the canopy 49
7.2.2 Guiding positioning-to-cut and felling 49
7.2.3 Felling the tree 50
7.2.4 Preparing processing 50
7.2.5 Focus on feeding, cutting and sorting 50
7.2.6 Utilization of digital bucking information 51
7.2.7 Finding and choosing the next tree or position for the machine 51
8 Discussion and conclusions 53
8.1 Strengths and limitations 55
8.2 Experiences of using eye tracking 59
8.2.1 Experiences and recommendations in the field 59
8.2.2 Experiences and recommendations for analysis 61
8.3 Future research 62
8.4 Concluding remarks 64
9 References 65
List of Publications
This thesis is based on the work contained in the following papers, referred to
by Roman numerals in the text:
I Carola Häggström & Ola Lindroos. Human, technology, organization and
environment – A systems perspective on human factors in forest
II Carola Häggström, Akie Kawasaki & Gun Lidestav (2013). Profiles of
forestry contractors and development of the forestry-contracting sector in
Sweden. Scandinavian Journal of Forest Research 28(4), 395-404.
III Carola Häggström, Mikael Öhman, Lage Burström, Tomas Nordfjell &
Ola Lindroos (In press). Vibration exposure in forwarder work: effects of
work element and grapple type. Croatian Journal of Forest Engineering.
IV Carola Häggström, Martin Englund Ola Lindroos (accepted with minor
revision). Examining the gaze behaviors of harvester operators: an eye-
tracking study. International Journal of Forest Engineering.
Paper II is reproduced with the permission of the publisher.
The contribution of Carola Häggström to the papers included in this thesis was
I Planned and designed the study in cooperation with main supervisor and
co-author. Carried out the literature search, developed the extended the
framework and wrote the majority of the manuscript.
II Contributed to the study design. Performed the analysis of the material and
wrote the majority of the manuscript.
III Contributed to the study design. Performed the statistical analysis of the
material and wrote the majority of the manuscript.
IV Designed the study jointly with the co-authors and main supervisor.
Performed the majority of the material analysis and wrote the majority of
Area of interest
Human, Technology and Organization
Root mean square
Retrospective think aloud interview
Fourth power vibration dose value
Whole body vibrations
Forest operations research has a more than 50-year tradition in the field of
human factors. The main focus of this research has been on forestry workers’
abilities, physical workloads, work satisfaction and the workers’ exposure to
various environmental stresses, such as noise, vibration and non-ideal lighting
conditions (Gardell, 1976; Teljstedt, 1974; Hellstrøm & Andersen, 1972;
Hansson, 1965). Ager’s (2014) detailed and personal description of this
research and the long-term development of forestry work in Sweden exposes a
current lack of systematic and continuous human factors research in Sweden.
The scientific discipline of human factors is concerned with understanding how
humans relate to the world around in order to optimize human well-being and
performance of the system. Health and safety in forestry has been the subject
of many reviews (e.g. Albizu-Urionabarrenetxea et al., 2013; Jack & Oliver,
2008; Kirk et al., 1997; Slappendel et al., 1993). In the present study, the focus
is on issues related to the forest machine operator’s work environment and the
operational performance. While the specific focus is on operator and
performance, safety and health are recognized as important aspects within this
domain, and those aspects are thus also briefly discussed.
Production performance and resulting economic performance are key
factors in most production systems. However, the term performance has a wide
range of definitions in the literature (see Tangen, 2005) and can be applied to
the entire supply system (Audy et al., 2012; Beamon, 1999), company
(Tangen, 2003) and production unit levels (e.g. Eriksson & Lindroos, 2014).
Naturally, these factors are of great importance within forestry in terms of
competitiveness and value-adding (Rådström, 2014). To date, value adding has
been mainly addressed on the manufacturing side (e.g. saw and pulp mills),
whereas the supply side (logging and hauling) has mainly focused on
competitiveness through improved cost-efficiency. In the face of continuously
increasing (e.g. labour) costs, productivity improvement has been key to
maintaining and even decreasing costs per produced unit (e.g. USD/m3
roundwood). However, lately concern has been raised, for example in Sweden,
that the trend of continuous productivity improvements has stagnated, and even
declined somewhat (Rådström, 2014; Nordfjell et al., 2010). Hereafter, the
term productivity is used in reference to the relation between produced goods
(output) and the resources used (input), whereas performance is used to
encompass productivity and other more qualitative aspects of how well work is
executed. The performance of the logging system is affected by performance
shaping factors (PSFs), commonly categorized as internal PSFs, external PSFs
and stressors (Osvalder & Ulfvengren, 2008). External PSFs for harvesting
can, for example, be divided into physical environment, machine related and
organizational factors. Internal PSFs are related to personality and behaviour
and also the physiological properties of the body. The knowledge and abilities
of colleagues, superiors, and the operators themselves are also important
internal PSFs. Stressors are related to pressure at work, such as work pace and
lack of feedback, and to physiological stressors, such as fatigue, vibration and
The work organization of Swedish forestry workers changed drastically
during the 1980s as machines became commonplace. Large-scale forestry
companies began subsequently to outsource mechanized forestry operations in
order to reduce costs. The first tasks to be outsourced were mechanized
operations in terrain transportation, harvesting, and soil scarification (Lidén,
1995; Lidén, 1994; Bostrand, 1984), later followed by manual and motor-
manual silvicultural activities, mainly planting and pre-commercial thinning
(Eriksson, 1999). However, silvicultural machines, such as planting machines
and pre-commercial thinning machines, are still rare (Ersson, 2014; Ligné,
2004; Lidén, 1995). As a result of the ongoing outsourcing of processes,
forestry contractors now hold a key position in the timber supply chain in many
European countries, as well as in some American, African, and Asian countries
(see Kastenholz et al., 2011; Kawasaki & Kohroki, 2009; Baker & Dale
Greene, 2008; Westermayer, 2006; Bigot et al., 2005; Louw, 2004).
Nevertheless, there is a lack of systematically gathered data on Swedish
Large scale forestry now determines the planning horizon and many of the
preconditions for the contractors’ work (see Eriksson et al. 2015; Vik, 2005). If
the cooperation between client and contractor is dysfunctional it can induce a
negatively charged organisational culture characterised by dissatisfaction,
stress and higher costs for the logging operations (see Vik, 2005; Pontén,
The physical nature of the work also changed fundamentally with
mechanization. Although the physical intensity of the work fell dramatically, it
also became highly repetitive and workers became exposed to associated
stresses for longer durations (Axelsson & Pontén, 1990). Interacting stressors
typically associated with repetitive stress injuries include, for example, whole
body vibrations (WBVs), repetitive hand and arm movements, non-neutral
body postures and manual lifting (Burström et al., 2014; Lis et al., 2007;
Okunribido et al., 2006; Punnett & Wegman, 2004). Consequently, operators
of forestry machines have a high prevalence of musculoskeletal symptoms in
the lower back, neck and shoulders (Jack & Oliver, 2008; Rehn et al., 2002). It
is suggested that the high prevalence of neck pain among forestry machine
operators is associated with exposure to shock-type vibration, although the
association between WBV exposure and neck and arm pain has not yet been
clearly established (Rehn et al., 2009). Shocks may also be more important
than sinusoidal vibration with regard to low back pain (Okunribido et al.,
2006). Reduced WBV should therefore improve the work environment for
forestry machine operators.
Today, the cut-to-length (CTL), or rather bucking-to-value procedure is
fully (machine) automated, but the harvester operator is expected to determine
tree qualities and species and to visually identify stem defects. However, the
increase in work-related data yielded by advanced sensors and computers in
forestry machines provides rapidly increasing opportunities to produce
decision support systems and automate processes. Upcoming decision supports
will most likely utilize graphical user interfaces due to problems in using
tactile or advanced auditory stimuli in vibrating and noisy environments. Thus,
thorough understanding of workers’ visual behaviour will become important
for developing safe, efficient forestry machines and work procedures. Research
is ongoing in areas such as decision support for route planning of logging sites
(Mohtashami et al., 2012), intelligent boom control and automated functions
(Ortiz Morales, 2015; Hansson & Servin, 2010; Löfgren, 2009; Attebrant et al.,
1997), teleoperated forestry vehicles (Milne et al., 2013; Westerberg &
Shiriaev, 2013; Bergkvist et al., 2006), and unmanned self-navigating vehicles
(Ringdahl et al., 2011; Hellström et al., 2009; Vestlund & Hellström, 2006).
Autonomous vehicles are lighter and drive faster, and relieve the operator of
harmful WBV exposure. However, concerns remain regarding the safety and
the cognitive work needed to monitor and control such vehicles (see Sarter et
al., 1997; Bainbridge, 1983). Human factors engineering thus offers a way of
minimizing the risk of unwanted outcomes from product design. Moreover,
poor usability engineering may prove costly for the company producing the
product (Bias & Mayhew, 2005). The cost of customer support for a poor
product may become high, leading, in the worst case, to its failure and
withdrawal from the market. According to Stanton et al. (2001), automation in
aviation has taught us to expect a shortfall in expected benefits; it becomes
more costly, causes equipment to become less reliable, increases the need for
training in skills and maintenance, and may induce human error. With
increasing automation operators receive less on-the-job training in manual
procedures, thus impoverishing the operator’s knowledge and, specifically,
their skilled expertise. Moreover, insufficient operator knowledge and ability to
override the automation when necessary can lead to major consequences in
terms of both safety and performance (Amalberti & Deblon, 1992). These
expected shortfalls can be compared to early mechanization when logging
costs increased and worker health was severely compromised by immature
systems (see Ager, 2014; Axelsson, 1998; Väyrynen, 1984). Thus, the next
generation of automation is likely to introduce a system change comparable to
that brought by the introduction of mechanization to forestry work. As the
nature of the work continues to evolve, old “truths” about safety, health and
performance will need to be re-examined and revised in light of both new and
old methods. Consequently, there is a need to include human factors specialists
in product design and to conduct research that is relevant to practitioners in this
1.1 Mechanized CTL operations
Mechanized CTL harvesting is most often associated with harvester and
forwarder operations, which is also what is considered here. Although the
logging operation is rather straightforward in terms of how the two machine
types are used to do the work of transforming trees to logs placed at roadside,
there is nevertheless some variation in the tasks and decisions that are taken by
the machine operators. In some regions the operator takes the majority of
operative forest management decisions (see Hultåker 2006, Eriksson et al.
2015), whereas in other regions operators are expected to follow detailed
instructions from foresters (e.g. drive on pre-marked strip roads and harvest
pre-marked trees). The former case is most common in the Nordic countries,
and will therefore be the main point of view in this thesis. For a thorough
description of roles and the principal organization of Swedish industrial
forestry, see Hugosson (1999).
The harvester operator is expected to position the machine for harvesting, to
select and reach the tree to be felled, to fell and move it to the chosen location
where it is processed (i.e. delimbed and bucked), and put into log piles where
the logs, sorted by assortment, can be easily collected by the forwarder.
Delimbing is done by feeding the stem through the harvester head. A delimbed
stem section is cross-cut (i.e. bucked) into a log of suitable length before
delimbing the next section and bucking the next log. The bucking is aided by
decision support systems which suggest value-maximizing log lengths and
assortments (Malinen & Palander, 2004; Olsen et al., 1991). This process is
repeated for each tree, with around 100-200 trees cut per hour (Eriksson &
Forest harvesting has been described as joystick-intense, mentally
demanding work in which visual information and supervision are important
(Gellerstedt, 2002; Hansson, 1990). As partly described above, the harvester
operator’s work tasks include, among other things, controlling both the crane
and the machine, evaluating ground conditions, determining tree species and
quality, detecting approaching people, and supervising the equipment. Riding a
bike or driving a car soon becomes an automatic behaviour, and the same
applies to manoeuvring a forestry machine (see skill-based behaviour
Rasmussen, 1983). Many automatic behaviours rely on implicit knowledge,
and thus harvester operators are typically unable to describe the functions of
the joysticks without physical demonstration (see Gellerstedt, 2002).
Nevertheless, visual supervision is involved in the performance of automatic
tasks due to the complexity of coordinating the actions – even when the
operator not is consciously aware of it (Land et al., 1999). Thus, apart from the
traditional methods of cognitive task analysis, eye movement analysis may
prove valuable by facilitating the difficult process of extracting implicit
The forwarder operator is tasked with collecting the pre-sorted logs from the
forest and transporting them to the roadside. Terrain driving is therefore an
essential part of forwarding, whereas driving is only required for short
distances during harvesting, such as when repositioning to reach new trees. As
a consequence, the work pace is normally lower in forwarding compared to
harvesting. In forwarder work, productivity is benefitted by as fast driving as
possible. However, the work also includes the complex logistic problem of
determining how to allocate the correct number and proportion of assortments
in the various loads in order to forward a given stand efficiently.
The work of the forwarder operator also includes many tasks similar to
those of the harvester operator, such as controlling both the crane and the
machine, evaluating ground conditions, detecting approaching people, and
supervising the equipment. An important logistic, problem-solving aspect of
forwarder operation is the ability to identify and separate wood assortments
among logs on the ground as well as in the bunk. Similar to harvesting, crane
work and driving soon become highly automatic for the operator.
Driving in terrain is the major source of WBV during forestry operations,
and the type and amount of vibration transmitted to the driver is mainly
determined by speed and ground roughness in combination with chair and
vehicle design (Rehn et al., 2005a; Hansson, 1990). Much research has
therefore been put into various dampening systems for vehicles, chairs and
cushioning (Baes, 2008; Cation et al., 2008; Sherwin et al., 2004; Mansfield et
al., 2002; Gellerstedt, 1998; Sankar & Afonso, 1993; Boileau & Rakheja,
1990). Nevertheless, WBV persists as a major challenge in forestry, and
knowledge of when and why shocks occur remains scarce. Shock-type
vibrations have been identified while loading the forwarder (Rehn et al.,
2005a), but to my knowledge no previous study has examined WBV exposure
in sufficient detail to differentiate exposure levels during crane work and
1.1.3 The physical environment
The performance of the human operator is affected by the physical
environment. The outdoor setting in which forest operations are conducted
offers limited possibilities to influence the work environment of the operator
compared, for instance, to industrial settings. Forest work is thus affected by
the characteristics of the forest stand in which the work is carried out. For
instance, tree species composition, stem size, distance to roads, stand size,
terrain slope, type of felling (e.g. thinning or final felling) and environmental
concerns delimit and define the boundaries of forestry machine operation (see
e.g. Eriksson & Lindroos, 2014; Hiesl & Benjamin, 2013). Moreover, difficult
terrain, such as poor carrying capacity, slippery ground or steep slopes, hinders
work (see e.g. Kolodny & Kiggundu, 1980; Andersson et al., 1968).
The forest itself can range from natural forest to plantation. Natural forests
vary depending on the local conditions, and plantations also vary greatly in
appearance. Some plantations are similar to prepared agricultural fields (crops),
while others are managed to preserve as much of the forest’s natural features as
possible (Sands, 2013).
Weather is also a key source of variation in work conditions, especially as
the work is often conducted round the clock and year-round. In the Nordics, an
operator might be working in bright daylight at +25°C one day, and a few
months later in pitch dark and snow at -25°C. The weather can impact
performance through, for instance, impaired visibility due to rain, snow or sun
glare, and physical exposure to heat or cold during repair and maintenance
work or when entering or exiting the cabin (Wästerlund, 1998; Gellerstedt,
1993). Maintenance may also expose the worker to harmful oils and solvents
Some environmental conditions may be alterable, if permitted according to
national legislation and certification schemes. For instance, some countries
may permit the levelling of rough terrain, whereas in others a minimum impact
policy may be enforced. However, many environmental aspects, such as
climate and weather, are impossible to alter but their effects can be managed.
Forest work conditions are thus largely determined by environmental factors,
and human operators are required to adapt their choice of technology, work
methods and work organization accordingly.
The overall aim of this thesis was to contribute new knowledge on working
conditions in mechanized cut-to-length logging operations and their
relationship to system performance by examining aspects of the operator, the
machine, and the work organization. Findings from four different studies, each
using different research methods and approaches, were compiled and discussed
based on their relevance to forest machine operators and logging system
performance. Study I, presented in Chapter 4, provides a background to human
factors research applied in Forestry. The study introduces some key problems
identified in the interactions between human, technology and organization
(HTO), and provides an HTO perspective with which to approach studies II–
IV. The following chapters 5-7 address the aspects of HTO. Accordingly,
Chapter 5 aims to elaborate the understanding of the organizational context of
Swedish contract forestry, and especially the structures of logging contractors
(Study II). Chapter 6 addresses specific logging technology (grapples) and
human reactions with respect to vibration and performance (Study III). Chapter
7 addresses aspects of human (visual) behaviour and human–technology
interaction (Study IV). The study concludes with suggestions for future
research and comments on implications for forestry researchers and
Specific aims of papers I-IV:
Paper I: To provide an updated description of human factors research relevant
to the production performance of the harvesting system and to scrutinize
problems that exist in the interactions between human, technology and
Paper II: T
o describe and discuss forestry contractors’ company structure
and development, including an evaluation of who they are, how many
there are, how many workers they employ and who are hiring them.
Paper III: To assess the contributions of specific crane work elements to
overall vibration exposure in small forwarders and possible effects of three
grapple and brake-link combinations on whole body vibration exposure.
Paper IV: Firstly: to obtain information on harvester operators’ visual
behaviour and categorize it in relation to existing literature on natural vision.
Secondly: to evaluate an eye-tracking system as a diagnostic tool in real-world
harvesting work in terms of data quality, precision and accuracy, and the data
analysis process in terms of ease of analysis.
3 Conceptual framework
The International Ergonomics Association (IEA) defines human factors and
ergonomics as: the scientific discipline concerned with the understanding of
interactions among humans and other elements of a system, and the profession
that applies theory, principles, data and methods to design in order to optimize
human well-being and overall system performance (retrieved 2015-02-06,
Human factors and ergonomics are often used as synonyms. However, in
many countries ergonomics is closely associated with physical ergonomics.
Thus, the term human factors is mainly used in this thesis. Similar to the
concept of human factors and ergonomics is HTO (Human, Technology and
Organization; in some literature referred to as MTO). This concept has been
introduced to facilitate a comprehensive socio-technological view (system
thinking) of work in which the three interrelated elements – human, technology
and organization – and their relations are brought into keener focus (Karltun et
al., 2014; Rollenhagen, 2000). While safety has been the main focus of HTO
studies (see Rollenhagen, 2000), HTO has also been successfully applied to
increase efficiency and enhance performance (Karltun et al., 2014). The HTO
framework (Figure 1) and its implications for harvesting system production
performance framed and provided the focus for the present thesis.
Figure 1. The HTO framework showing the interactions between human, technology,
organization and environment (context) affecting system performance (Paper I).
4 Study I – HTO in mechanized CTL
This chapter introduces some key problems identified in the interactions
between human, technology and organization, and their implications for the
production performance of the harvesting system. Moreover, Study I positions
the other three studies within the HTO framework. For this purpose, a selective
literature review was conducted. Most literature for the review was found in
the Web of Knowledge and Google Scholar databases, or as a consequence of
the snowballing approach also applied. In addition, local libraries and papers
encountered during previous research projects were also used. Literature
addressing the operation of machines in the harvester-forwarder system was
prioritized. Moreover, mainly papers published in English or Swedish were
A literature search was conducted using various terms closely related to
human factors (e.g. ergonomics, human engineering, human factors
engineering, usability engineering, and user-centred design, Beith, 1999), as
well as variations of following terms: Human-Machine-Interaction/interface
(HMI), Human-Computer-Interaction/interface (HCI), organization, cognitive,
cognition, (Hu)man-Technology-Organization (HTO), sociotechnical system
and system perspective in relation to forestry, forestry machines, harvester,
harvesting and logging.
4.1 Human: skills and abilities
It has been argued that operator performance is becoming a bottleneck for
increased productivity (e.g. Westerberg & Shiriaev, 2013; Löfgren, 2009;
Gellerstedt, 2002; Gellerstedt, 1997). The importance of specific human
abilities to forestry work performance has been (somewhat moderately)
researched for over 60 years (Ager, 2014; Andersson et al., 1968; Hansson,
1965). Concentration, decision making, memory, motivation, motor
coordination, pattern recognition, planning capacity, logic reasoning, and
spatial perception are abilities that have been described as important for
successful harvesting work (Tervo et al., 2010; Ovaskainen & Heikkilä, 2007;
Parise, 2004; Gellerstedt, 2002; Andersson et al., 1968). However, the
importance and validity of ability testing for identifying skilled or talented
operators has yet to be proven (see the results of Ovaskainen & Heikkilä, 2007;
Garland, 1990; Andersson et al., 1968). In addition to the challenge of finding
and testing relevant performance indicator(s), selection processes involve an
abundance of applicants. However, in many areas of the world it can be
challenging to find even the minimum number of forest workers required and
future labour shortages are expected (Bernasconi & Schroff, 2011; Baker &
Dale Greene, 2008; Egan & Taggart, 2004). Thus, training and usable, user-
friendly, machines are and will be crucial in the future, and will require
adaption to general, as opposed to narrowly selected, users.
Moreover, in order to keep existing machine operators and attract new ones
the work must be considered attractive (see Kolstrup, 2012; Kolstrup et al.,
2008; Lewark & Kastenholz, 2007; Åteg et al., 2004). In a small Swedish
study, most machine operators stayed within the profession (Bergquist, 2009).
However, the general perception both in Sweden and internationally is that it
has become difficult to attract new forestry workers (see Ager, 2014; Lewark
& Kastenholz, 2007; Egan & Taggart, 2004).
Operator skill clearly has an important impact on operational outcome.
However, exactly what skills constitutes this impact is less obvious and less
investigated. Various skills have been reported to affect system performance,
including technical, maintenance, planning (of how and in what order a stand is
harvested and extracted), cooperative, know-how, and automated machine
control skills (e.g. Tervo et al., 2010; Gellerstedt, 2002; Kolodny & Kiggundu,
1980). In order to measure skill, the concept has been operationalized as, for
example, the number of simultaneous lever or joystick movements (see Tervo
et al., 2010; Parise, 2004; Andersson et al., 1968) and the proportion of time
spent on various work phases (Palander et al., 2012; Tervo et al., 2010; Parise,
2004). Productivity is also a measure of skill. When there is a discrepancy
between operator skill and ability and the conditions and demands of the work
task, the workload becomes high. Measures of heart rate variability as an
indicator of mental workload have been presented in a few studies on harvester
operators (Tynkkynen, 2001; Yamada, 1998; Gellerstedt, 1997; Inoue, 1996),
but the measure was excluded from the study of Nåbo (1990) due to
immaturity of the technology as a measure of mental workload. Moreover,
these studies did not use workload measures as a means to evaluate attempts to
reduce (or increase) the workload of a task in the context of given forestry
work. Thus, it is difficult to evaluate the magnitude or effect of those measures.
Neck and shoulder pains among operators are most likely due to a combination
of the mental and physical aspects of the work, physical properties of the
operator, task demand, organizational pressure, vibration and cab design
(Burström et al., 2014; Jack & Oliver, 2008; Østensvik et al., 2008; Lis et al.,
2007; Okunribido et al., 2006; Punnett & Wegman, 2004; Rehn et al., 2002;
Hagen et al., 1998; Eriksson, 1995; Bostrand, 1984). These injuries (repetitive
stress injuries) furthermore tend to be costly to the employer (as well as the
employee and society) due to the high amount of sick leave compared to
accidents or acute injuries (Eriksson, 1995). All injuries and ill-health are
nonetheless costly to the employer (Bohlin & Hultåker, 2006), and a health and
performance guideline have been therefore developed (see Gellerstedt et al.,
One way of working with the human aspect of these parameters (i.e. skills
and abilities) is through education and training. Several studies have shown
that working methods and techniques matter (e.g. Alam et al., 2014;
Ovaskainen et al., 2004) and training has been considered crucial for
successful, healthy and safe machine operators (Gellerstedt & Dahlin, 1999;
Kirk et al., 1997; Axelsson & Pontén, 1990; Väyrynen, 1984). Moreover,
machine operators show continuous productivity improvement for many years
after the start of their professional work. For example, it has been suggested
that is takes up to five years to reach full potential as a harvester operator
(Gellerstedt, 2002), an assumption which is supported by the findings of a
three-year study of harvester operator productivity (Purfürst 2010). In the latter
study, there was great variation in the number of years of experience and/or
specialized machine education among the operators. Half of the studied
population initially had, on average, eight months of significant productivity
increase (Purfürst, 2010). Furthermore, highly experienced hauling operators
have shown continuous productivity improvements over the course of a three-
year study period (Björheden, 2001). Thus, the general assumption is that there
is much to gain from more and/or better education and training. Nevertheless,
education and training systems vary greatly between countries (Bernasconi &
Schroff, 2011; Bigot et al., 2005; Vik, 2005; Gellerstedt & Dahlin, 1999). In
Finland, effort has been made to develop simulator-based training (Ranta,
2009) and computerized skill evaluation and feedback systems (Palmroth,
2011; Tervo et al., 2010). Simulators have also been successfully used for
training harvester operators in Canada for almost 20 years (Lapointe & Robert,
2000). The benefits of using simulators are that they are cheaper than real
machines, and training can be standardized, custom-made and performed
without concern about environmental disturbance or personal safety. However,
the results from Purfürst and Erler (2006) serve as a reminder that simulators
are not universal tools and that training tasks must be carefully designed (see
Ranta, 2009; Lapointe & Robert, 2000).
Nevertheless, the right abilities, skills, techniques and training alone are not
sufficient for ensuring high performance of the logging system. The operator is
affected by and interacts with the machines and technologies, the work
organization, and the environment surrounding the system.
4.2 Technology: tools and prostheses
This section focuses on the effects of human–technology interaction in
mechanized forest operations. The focus is on two dimensions in which
machines and technology act as extensions (see tools or prosthesis, Duchowski,
2003) for the human body: the physical dimension, and the cognitive
4.2.1 The physical dimension
As the operator becomes proficient in using the machine to perform specific
work tasks, controlling the crane becomes automatic (Gellerstedt, 2002;
Rasmussen, 1983) and little conscious attention is required. Nevertheless, the
interface through which this interaction occurs may affect performance by
having an impact on the speed of operation and learning and the amount of sick
leave (see Murphy & Oliver, 2008; Gellerstedt, 2002; Attebrant et al., 1997;
Grevsten & Sjögren, 1996; Hagberg & Lidén, 1991). It is also possible that the
interface may affect work precision, and thus the speed and quality of work
(see Hansson, 1990).
Exposure to environmental stresses, such as particles, noise and WBVs, are
potential health hazards and thus may induce sick leave, sickness presenteeism
and rehabilitation costs. They may also affect stress and cognitive
performance, and thus affect system performance and productivity. Much
effort has been invested in researching WBV, its physical effects, and ways to
minimize exposure (e.g. Paper II, Gerasimov & Sokolov, 2009; Baes, 2008;
Cation et al., 2008; Burström et al., 2006; Rehn et al., 2005a; Rehn et al.,
2005b; Sherwin et al., 2004; Mansfield et al., 2002; Gellerstedt, 1998; Sankar
& Afonso, 1993; Boileau & Rakheja, 1990). The effect of WBV on
performance in complex tasks is difficult to assess; however, studies have
shown that performance in motor tasks, especially accuracy-based tasks (which
are typical to crane work in forest machines) and perceptual tasks with high
demand on oculomotor control, is impaired by WBV (Conway et al., 2006;
Wertheim, 1998). However, there seems to be little or no effect on cognitive
performance in general (Wertheim, 1998), nor in combination with noise tested
at levels typical to forwarder work (Ljungberg & Neely, 2007).
4.2.2 The cognitive dimension
Cognitive work in mechanized forestry has been generally described by
qualitative approaches (Zylberstein, 1992), but attempts have also been made
to quantify the cognitive work (e.g. Ovaskainen & Heikkilä, 2007; Tynkkynen,
2001), and some studies have combined the two approaches (Gellerstedt, 2002;
Gellerstedt, 1997; Nåbo, 1990). Early attempts to increase the performance of
the man-machine system have altered decision and information processes in a
way that can most easily be described with the concept of function allocation,
or Fitts’ list (1951). The automation of log length and diameter measurement
has increased the speed and quality of work (Malinen & Palander, 2004; Olsen
et al., 1991). Intelligent boom control involving various automated functions
has been tested or implemented (Ortiz Morales, 2015; Hansson & Servin,
2010; Löfgren, 2009; Attebrant et al., 1997). Despite some interesting concepts
(e.g. Brander & Eriksson, 2004), the full effect of implementation of automated
boom control systems is yet to be evaluated.
As shown in Paper IV, forestry machine work depends heavily on visual
cues and information. Hence, poor visibility may degrade cognitive
performance severely. Early research, which focused on artificial lighting and
dazzling reflexes, found that brighter and better lighting conditions correlated
with higher performance (Teljstedt, 1974), but similar lighting conditions were
nevertheless found 25 years later (Nordén & Thor, 2000). Research, in for
instance Sweden, has indicated performance variations with different colour
temperatures of lights with the same lux during work in dark environments
(Poom et al., 2007). Operator line of view may be restricted by the crane, cabin
walls or protective grills, etc. (Gellerstedt, 1998; Nåbo, 1990), which may
result in musculoskeletal injury and accidents if the operator has to alter their
position to see properly (Eger et al., 2010; Thomas et al., 1994; Hansson,
1990). Despite lack of research, it seems reasonable to assume that restricted
visibility affects performance negatively by either lowering productivity or
decreasing the quality of work in terms of product quality or safety. Recent
developments have resulted in rotating and levelling cabins, first among
harvesters and lately also among forwarders, where the cabin automatically
compensates for unevenness and rotates so that the harvester head or grapple is
kept directly ahead of the operator. In addition, in many machines, visibility
restrictions have also been partly compensated for by introducing a filmed
view of the outdoor environment. Due to these solutions, it is possible for the
operator to see what is going on in front of machine and behind it without
changing position or stretching. Information presentation and visibility are
fundamental to the implementation of teleoperated or autonomous vehicles.
Viewing angle and abstraction level have been shown to affect operator
performance (Westerberg & Shiriaev, 2013).
Several design propositions have been developed to ease the use of bucking
related information (Lopez, 2009; Norén et al., 2008; Järrendal & Tinggård
Dillekås, 2007; Lundin et al., 2005; Forsberg, 2002). These developments have
been driven by the discovery that the majority of interfaces on the market were
violating design principles. However, there are no indications that current
designs significantly degrade bucking performance (Study IV). Nevertheless,
with the addition of advanced automation and further decision support (e.g.
route planning in logging sites and teleoperation of machines, Westerberg &
Shiriaev, 2013; Mohtashami et al., 2012) there will be a need for new
interfaces and interactive techniques (Wickens & Hollands, 1999; Sanders &
4.3 Organization: culture and structures
Work organization (and its human–technology interactions) was acknowledged
as a major influence on forestry work during early mechanization (cf.
Bostrand, 1984; Kolodny & Kiggundu, 1980; Gardell, 1976) and, following a
period of research focus on technological solutions and physical problems,
received increased attention again during the 2000s. Work organization is a
wide concept dealing with subjects such as work schedules, job design (tasks,
skill and effort required, and degree of worker control), relationships with
supervisors and co-workers, job security, carrier opportunities, management
style, and organizational climate, culture, communications, and payment
systems. Research on the effects of shift schedule in forestry has shown
somewhat contradictory results, thus it seems that there is no single optimal
way of arranging work schedules. In Sweden, from the 1980s to the end of the
90s some schedules were designed to include more variation and pauses in the
work, and the results were promising in terms of both health and productivity
(see Ager, 2014; Synwoldt & Gellerstedt, 2003). Many, but not all, contractors
that tried these so-called “overlapping” shifts but went back to working straight
shifts (eight hours straight per operator) after a few years on the basis that the
overlapping shift was not economically feasible (Ager, 2014; Persson et al.,
2003). In general, daytime work is found to be most productive, but it is
difficult to determine whether this is due to natural variation in cardiac rhythm,
better visibility during daylight or other benefits of single shift work (Gallis,
2013; Lebel et al., 2010; Mitchell et al., 2008; Nicholls et al., 2004; Persson et
al., 2003; Synwoldt & Gellerstedt, 2003; Pontén, 2000). Nevertheless, there
might also be benefits to shift work, such as higher redundancy and flexibility
of the organization (Hultåker, 2006) and lower fixed machine costs (Mitchell et
al., 2008). The general conclusion, though, is that operator performance
degrade after 9-10 hours of daily work including regular pauses (Gallis, 2013;
Passicot & Murphy, 2013; Murphy & Vanderburg, 2007; Nicholls et al., 2004).
Task variation, breaks and control over work tasks are related to beneficial
health effects (Hanse & Winkel, 2008), and have been found to be beneficial
for productivity and machine uptime in a small South African case study
(Steyn et al., 2011). However, past experience has shown that it can be difficult
to find additional tasks for machine operators (Persson et al., 2003) and such
measures are probably not sufficient to solve neck and shoulder associated
problems (Persson et al., 2003). Moreover, frequent changes between, for
example, harvester and forwarder operations may degrade performance
initially on either machine (Hultåker, 2006). Night shifts may, for example,
also induce higher insurance costs (Mitchell et al., 2008).
The importance of human skill has been discussed, and to facilitate
continuous learning and training there has to be a well-functioning learning
culture within the organization. For learning organizations, it is important that
there are systems for knowledge exchange within and between organizations,
that new knowledge is accepted and implemented, and that errors are seen as
opportunities to learn and not as something to be hidden (Jacobsen & Thorsvik,
2002). One study on Croatian private forestry contractors (Landekić et al.,
2013) showed that as little as 50% of employees had received formalized job
training. Moreover, few Polish operators had received any training in working
techniques despite a willingness to participate (Nowacka, 2012). The problem
of lack of training has also been acknowledged by Vik and Veiersted (2005). In
Europe in general, contractors performing forestry services see little or no use
in providing formalized training for their workers (Lewark et al., 2010), which
is viewed with scepticism with regard to training outcome, relevance to work,
and return on investment. Some of this scepticism is likely also due to the fact
that many forest workers consider education and formalized training merely as
a way of gaining theoretical knowledge, while long-term practical experience
is considered to be the most important way of gaining competence (Hugosson,
1999). Thus, theoretical knowledge is not fully trusted. Nevertheless, learning
does not only happen in formalized settings. A culture that embraces
knowledge exchange and transfer within the organization has been put forward
as being important for the organization’s problem solving skills and knowledge
production (Hugosson, 1999). Moreover, knowledge exchange provides
opportunities for learning from co-workers’ experiences and thus ensuring that
important knowledge does not leave the company with exchange of personnel.
Internal knowledge exchange typically functions best in smaller organizations
(Jacobsen & Thorsvik, 2002), which most forestry contractors in Sweden count
as (Study II). Nevertheless, knowledge exchange between organizations is
likely to be especially important for enterprises with few employees where the
shared body of knowledge is consequently less. Contractor associations, other
contractors, machine manufacturers, research institutes, clients, seminars and
workshops, forestry fairs and exhibitions, and magazines have been identified
as important sources for interorganizational knowledge exchange among
European forestry contractors (Lewark et al., 2010; Kutzschenbach, 2006). It
was also found that information exchange between those sources was mostly
5 Study II - Labour Organization in
This chapter elaborates on the organizational context of Swedish contract
forestry, and especially the structures of CTL logging contractors. The
organizational context (O) is studied in isolation, without acknowledging
human (H) or technology (T) interactions. Study II thus in many ways sets the
scene for studies of HTO components in Swedish logging operations.
5.1 Materials and Methods
5.1.1 Data collection
Study II was based on the Swedish Forest Agency’s annual written
questionnaire to Swedish forestry contractors. When possible, comparisons
were made with previous results based on the same survey for the years 1993-
1998 (Ejermo, 2001) to obtain trends and growth rates.
A stratified random sample of forestry contractors was drawn from
Statistics Sweden’s Business Register (CFAR) to estimate the numbers of
contractors, clients, machines, work hours, working owners, and their
employees for the years 2006-2009. The combined group of working owners
and employees will henceforth be referred to as workers. Four strata were
constructed according to the stated number of employees: one-person
enterprise = 0, small-sized enterprise = 1-4, medium-sized enterprise = 5-9,
large-sized enterprise = 10 or more. Responses were received from 700 to 770
forestry contractors, corresponding to ca. 20% of the estimated total population
of Swedish forestry contractors. The total response rate varied from 53% to
A survey was also conducted to determine the number of machine operators
employed by the four biggest large-scale forestry companies (i.e. companies
with at least ten employees in forestry or companies with at least 5,000
hectares of forest land, Swedish Statistical Yearbook of Forestry 2011) in 2009.
5.1.2 Data analysis
Answers to the questionnaire were weighted by the actual sampling fraction for
each stratum to obtain estimates of the total population. Combined ratio
estimates were calculated to estimate ratios of the following variables: work
hours, numbers of clients, workers, and machines per company or per worker
(See paper II or Cochran (1977) for equations).
The data analysis was conducted for the entire population of logging and
silviculture contractors, but also for logging contractors separately. To be
categorized as a predominantly logging contractor, the enterprise had to spend
at least 30% less time on tasks typical to silviculture contractors. Typical
logging tasks were: mechanized harvesting, mechanized forwarding, operation
of a chipper, motor-manual thinning, and motor-manual final felling. Typical
silvicultural tasks were: mechanized soil scarification, planting, and pre-
commercial thinning. About 10% of all contractors, corresponding to 10% of
total forestry work hours, did not fit into either group according to the above
Using a benchmark of 25% of one person’s yearly working time in Sweden,
we defined occasional contractors as enterprises with less than 455 hours per
year in forestry work and typical contractors as enterprises working more than
455 hours per year. Thus, forestry work was not necessarily the main
occupation of occasional contractors.
5.2.1 Forestry contractors’ development and structure
From 1993 to 2009, the estimated number of contractors in Swedish forestry
increased by 80% (Figure 2). In 2009, there were 2,488 typical contractors
primarily focused on forestry work in Sweden and 1,074 occasional
contractors. Logging remained the main task of Swedish contractors in 2009;
27% of all work was allocated to mechanized harvesting and 25% to
forwarding. Taken together, motor-manual thinning and final felling comprised
no more than 3% of all work. However, the amount of time spent on
silvicultural activities had increased since 1998 (Figure 2), and it became clear
from the data that most contractors focused on either silvicultural services or
In 2009, most contractors (2,358 companies, 65%) were machine owners. The
number of purpose-built forestry machines remained relatively constant
between 1993 and 1998 but increased by almost 50% by 2009, at 5,960
machines in total. Machines for silvicultural work (mainly soil scarifiers)
increased the most (ca. 120%), although there were only 466 machines in total
by 2009. The vast majority of machines were harvesters (2,201) and forwarders
(2,501), machine which had increased by 51% and 39%, respectively. In
addition, there was a large growth (323%, 724 pieces by 2009) in the number
of other than purpose-built forestry machines.
Figure 2. Number of forestry contractors in Sweden 1993-2009. Data for 1993-1998 adapted
from Ejermo (2001); dotted lines represent changes between estimates for 1998 and 2006. The
estimates for 2006-2009 have a relative standard error of less than 25%.
5.2.2 Logging contractors 2009
In 2009, there were 2,219 logging contractors in Sweden and they employed
6,337 workers. Less than 2% of workers were women (Table 1). Logging
contractors carried out almost all work in mechanized harvesting and
mechanized forwarding but less than half (47% in 2009) of motor-manual
felling. In accordance with the high degree of mechanized work, only 13% of
logging contractors were purely manual or motor-manual (did not own any
machines, Table 1). Twenty-two percent of logging contractors worked less
than 455 hours per year (occasional contractors) and 78% were typical
contractors with more work hours (Table 1). Ninety-nine percent of logging
contractor work was carried out by typical contractors. Average working time
per worker and year was 1,334 hours for workers in typical logging enterprises,
in 2009. Average working time increased with increasing company size.
Typical logging contractors were mainly contracted by large-scale forestry
companies (51% of the work), but other, mainly private, forest owners were the
most important clients for occasional logging contractors (79% of the work).
On average, logging contractors worked for five clients, but 38% were
contracted by only one client.
Large-scale forestry companies themselves employed 541 machine
operators, which accounted for 8.5% of all logging workers in Sweden in 2009.
Overall, most work (42% of total work hours) was performed by workers in
small-sized enterprises, i.e. enterprises with an average of three workers, while
one-person logging enterprises with an average of 1.3 workers accounted for
only 14% of total logging contractor work. Large-sized logging enterprises,
with on average 11 workers per enterprise, accounted for 15% of logging
contractors’ total work in 2009.
Table 1. Estimated properties of logging contractors in 2009.
Typical (> 455h a year)
Occasional (< 455h a year)
Worker per Special Machine
Note. Special Machine = machine purpose-built for forestry work; No machine = number of contractors who
do not own any machine.
6 Study III - Technology and human
This chapter addresses technological aspects and human reactions.
Specifically, the aim is to assess the contribution of crane work to overall
vibration exposure in small forwarders, and the possible effects of three
grapple and brake-link combinations on whole body vibration exposure and
performance. Study III thus addresses the T and H-T aspects of the HTO
6.1 Materials and methods
6.1.1 Data collection
Repeated field measurements of cabin WBV in a Vimek 608.2 BioCombi
forwarder (Vimek AB, Vindeln, Sweden) were acquired while a single
operator was forwarding standardized wood piles on a standardized track using
three types of crane equipment. Each monitored work cycle (observation)
corresponded to one round on the standardized track, beginning with loading
the empty bunk and ending when the last log was unloaded. Through time
studies, each work cycle was split into work elements (WEs) and WBVs were
analysed within and over WEs. Thus, the design consisted of two fixed factors
(crane equipment and WE) within five sets of repetitions (blocks). Collisions
between the grapple or lifted logs, and trees or the base machine were also
counted, as were the alignments of end surfaces of the logs. Fuel consumption
was measured for each work cycle, and forwarding productivity (seconds per
work cycle) was calculated from time study data. The three types of crane
equipment were randomly assigned within blocks to minimize possibilities of
order and carry-over effects confounding the results.
Figure 3. The three studied grapples from left to right: a Vimek standard grapple with no brake-
link (standard grapple); a Vimek standard grapple with Vimek dynamic brake-link (brake-link
grapple); and a Vimek tilt grapple with a Vimek dynamic brake-link (braked tilt grapple).
The three studied types of crane equipment were (Figure 3): (a) a Vimek
standard grapple (standard grapple); (b) a Vimek standard grapple with Vimek
dynamic brake-link (brake-link grapple); and (c) a Vimek tilt grapple with a
Vimek dynamic brake-link (braked tilt grapple). The gripping area was the
same for all grapples (0.16 m2) and the mass of a single pile was not a limiting
factor for the crane or any of the studied grapples.
Vibrations were measured in three orthogonal axes according to ISO 2631-1
(ISO, 1997) using a MTi-G triaxial accelerometer (Xsens, Enschede,
Netherlands) placed on the floor close to the centre of the cabin, in front of the
chair. The placement ensured that the operator’s weight, height and the chair’s
dampening would not affect the measurement. Samples were taken at a
frequency of 100 Hz during each approximately 40-minute work cycle using a
XKF Scenario “2.7 Automotive unit” (Xsens, Enschede, Netherlands).
The field study was conducted during October 7-22, 2013, with one trial
(work cycle) per day for the first block, and subsequently two trials per day.
One designated researcher filmed all the trials and made all the measurements.
6.1.2 Data processing and analysis
All data processing was performed off-line using a commercial software
package (MATLAB R2014a 8.3, MathWorks Inc., Natick, USA) with the
Continuous Sound and Vibration Analysis program (Zechmann, 2013). The
acceleration data were converted from the recorded time domain to frequency
domain with a frequency range up to 50 Hz. In the analyses, 1/3 octave band
(a)(a) (b) (c)
values were calculated from 0.1 to 50 Hz. The resulting data were then used to
calculate frequency-weighted root mean square (r.m.s.) acceleration and fourth
power vibration dose value (VDV) values with respect to health effects on a
seated driver in accordance with ISO 2631-1 (ISO, 1997). VDV and r.m.s.
values were calculated with respect to the three orthogonal axes (x, y and z),
and the sum vector (v). The crest factor and the 8-hour equivalent, A(8), were
calculated for all orthogonal axes over each measurement period.
Data were analysed using Minitab 16 (Minitab Ltd, State College, PA,
USA). Analysis of variance (ANOVA) was used to analyse the fixed effects of
WE and crane equipment type, and the fixed interaction between them, on the
vibration measurement. The ANOVA models also included the random block
effect. A general linear model (GLM) was applied when analysing the
ANOVA models and Tukey’s Honest Significant Difference (HSD) test of
means was used for pairwise comparisons. Moreover, the fixed effects of crane
equipment type on the number of collisions, and alignments, were analysed
with a GLM including block as a random factor. In all analyses the
significance level was set to 5%.
The frequency distributions were similar for all crane equipment types; i.e.
low-frequency vibrations were more intense during driving than during crane
work, with no visible differences in frequency spectra over the vertical (z)
direction between driving and crane work, but accelerations in the horizontal
directions (x and y) were highest in the frequency range 1.25-4 Hz during
crane work and 0.25-5 Hz during driving.
Driving had higher vibration magnitudes than crane work (Table 2).
However, on average, more than four times as much time was spent on crane
work than on driving. Thus, for the time weighted r.m.s. value, A(8), the
relationship was reversed (Table 2). A high crest factor in the x-direction
(mean 12, max 15) indicated occurrences of shocks during crane work.
Nevertheless, other indicators of shock occurrences (VDVx, and VDVy) were
higher during driving than during crane work. In contrast, VDVz was higher
during crane work than during driving. Consequently, the overall vector
(VDVv) was not affected by WE.
Crane activities significantly affected all vibration measures, but the
interaction between crane activities and crane equipment was non-significant.
Crane in and release & reorganize were the most time consuming crane
activities and the WEs with the highest average vector vibrations. However,
they differed in that crane in had high values in the y-direction while release &
reorganize had high values in the x-direction (Table 2). Since no effect of crane
equipment type on any vibration measurements was found during crane work
(Table 2) it can be concluded that the studied crane working techniques and
crane equipment types were found to have little or no effect on daily WBV
exposure with respect to seated health.
Figure 4. Average numbers of collisions – with residual trees (Trees), the Machine, or both
(T&M) – and alignments of end surfaces of the logs per work cycle with each type of crane
equipment. Means within categories with different letters are significantly different (Turkey’s
HSD, p < 0.05).
Significant differences were found between crane equipment types in the
frequency of collision with residual trees. Fewest trees were hit when using the
braked tilt grapple and most trees were hit when using the standard grapple
(Figure 4). However, applying collisions and alignments as covariates in the
ANOVA did not reveal any significant relationship between collisions or
alignments and vibration levels in any direction, nor for the sum vector for any
of the vibration measurements.
Preliminary data indicate that work with the braked tilt grapple resulted in
about 15% higher fuel consumption than the other grapples, while productivity
was 3-5% higher. However, the differences were not significant according to
the preliminary analyses (Öhman & Häggström, unpublished manuscript).
Table 2. Frequency-weighted acceleration in the three orthogonal axes (x, y and z), the sum vector (v) and the A(8) value for indicated work elements according
to “health” in ISO 2631-1. Measurements were taken at the feet.
Type of work
Release & Reorganize
Note: Mean values within columns and type of work with different superscript letters (A-B for the full work cycle and a-d for crane activities) are significantly different (p < 0.05,
Turkey’s HSD). WE = Work Element; SD = Standard Deviation.
1 Crane Work includes all crane activities pooled
7 Study IV - Human behaviour and
This chapter addresses aspects of human (visual) behaviour and human–
technology interaction, i.e. the H and H-T aspects of the HTO framework.
Specifically, the visual behaviour of CTL harvester operators during real-life
harvesting operations is examined. The study had two main objectives: firstly,
to obtain and categorize information on harvester operators’ visual behaviour;
secondly, to evaluate an eye-tracking system as a diagnostic tool in real-world
harvesting work in terms of the quality, precision and accuracy of data it can
provide, and the process of data analysis, in terms of ease of analysis
7.1 Materials and methods
7.1.1 Data collection
The eye movements of six harvester operators were tracked during separate
CTL harvesting sessions in which two operators were engaged in first thinning,
two in second thinning and two in final felling operations in central Sweden
during autumn 2012. Four of the operators had sight impairment, including
astigmatism in one case, although none had strabismus (eye misalignment).
Eye movement data were recorded with Tobii Glasses (Tobii Technology
AB, Sweden), which utilize a monocular right eye pupil-centre and corneal
reflection technique to record eye movements and scene video as seen by the
wearer at 30 Hz with overlaid gaze cursor. The glasses are light head-mounted
eye-trackers that allowed the operators to move freely during the study (Figure
5). The harvesting operations were simultaneously recorded with an ultra-wide
angle lens GoPro camera (GoPro, Inc., California, USA) positioned at the side
window and directed towards the front windshield to capture both the forest
scene and the machine work.
To capture the harvester operators’ natural work behaviour, they were
instructed to work as normal in the stand they were scheduled to work in that
day using the machine they usually operated. In each session eye-tracking and
GoPro video data were collected for about 10 to 15 minutes of work, during
which a researcher was riding in the cabin with the operator. Each of these
naturalistic observational sessions was followed by a retrospective think-aloud
(RTA) interview during which the operators viewed the eye-tracking-video
with gaze cursor overlay and were asked to explain their actions, what they had
looked at, or describe their reasoning in a review of the work and decision
Figure 5. Eye-tracking equipment (Tobii Glasses) in use during the study.
7.1.2 Data analysis
Machine work was coded manually using the ELAN video transcription
software (Max Planck Institute for Psycholinguistics, Netherlands). Both the
GoPro recordings and eye-tracking videos were imported to ELAN and synced
to more precisely determine the time that the operators allocated to five
standard harvester WEs: crane work, positioning-to-cut and felling, processing,
release of the top, and driving; and also miscellaneous work. Cues to define
exact start times for cutting each tree and log (when the saw symbol appeared
on the harvester’s computer screen, or when the saw or
Table 3. Areas of interest (AOIs) analysed in the study.
The harvester head. When possible also categorized by the specific
sections: saw unit, upper delimbing knives, multi
equipment, and rotator and backside.
The part of the harvester head where the saw is located.
Upper delimbing knives
The parts of the harvester head where the upper delimbing knives are
The part of the harvester head where the multi-tree handling
equipment, or the rotator, is located during all elements but processing.
Rotator and backside
The backside of the harvester head and the centre part of the feeding
rolls while upright. The backside and the part of the harvester head
where the ro
tator is located while tilted down and during processing.
The bucking monitor. Dwell times on this AOI include the saccade
from the previously dwelled AOI and the saccade to the next dwelled
The forest, individual trees and g
round. When possible also
categorized by the specific sections: canopy, standing tree, falling tree,
upcoming processing site, pile, between pile and delimbed stem
The canopy, as seen in upward gazes, including head movements
he canopy without any hits.
Individual standing trees gazed at close to the machine.
The top and stem of the falling tree, including gazes in its felling
An area where the harvester head
and tree are to be positioned to
process the tree. Fixations on this area are by definition look
The ground or pile where the processed logs will be put.
Between pile and
Area between the piles and delimbed stem.
A tree gripped with the harvester head, either a delimbed or
unprocessed part of the stem. When possible also categorized by the
specific sections: delimbed stem and unprocessed tree.
A part of a tree that has been fed through the
harvester head but not yet
cut and put in a pile
A part of a fell-cut tree that has not yet been delimbed or released from
the harvester head.
Gaze that cannot be classified in any of the above categories.
saw sound became perceptible in the videos) were identified in a separate time
study. The gaze recordings from the Tobii Glasses were examined frame by
frame using the video player functionality in Tobii Studio (Tobii Technology
The number, duration and order of dwells in each operator’s recording were
coded for each area of interest (AOI) in all WEs. A dwell was defined as a gaze
in an AOI lasting at least 100 ms from entry to exit. An exit was defined as a
hit outside that AOI. The 16 AOIs were constructed based on RTA data,
interviews with six exceptionally skilled operators in 2011 and on results
presented by Gellerstedt (2002). Different sets of AOIs were analysed for the
entire work cycle, positioning-to-cut and felling, and for processing. Dwell
time, dwell frequency (dwells/s), and one-way transitions between AOIs
(transition matrices) were then calculated. RTA data were analysed and the
purpose of the dwell, or the attribute of interest during the dwell, was
categorized by AOI.
The operators conducted the work by continuously manoeuvring the joysticks
without visual supervision. Their eyes dwelled on the harvester head and
various aspects of the forest most of the time (82%, Figure 6f). Dwells on the
forest (in its broadest sense) often served a general purpose of getting an
overview and organizing the work, whereas dwells on the harvester head were
of a more specific monitoring and guiding character (Table 7).
During crane work, the harvester head was in focus most of the time (45%
of total dwell time, presented in circles in Figure 6a) and the canopy was the
third most attended area (8% of total dwell time, presented in circles in Figure
6a). Most transitions in dwells went from the harvester head towards the forest
(29.5% of total transitions, represented by arrows in the direction of transition
in Figure 6a), and the operators very rarely looked at the canopy directly after
looking at the harvester head (1.4% of total transitions, represented by arrows
in the direction of transition in Figure 6a). Thus, a high proportion of gazes at
the canopy must have come from the harvester head via the forest (see Figure
Figure 6. Percentages of transitions from one area of interest (AOI) to another. Transitions with
frequencies ≥ 1% of the total number of transitions are shown for all WEs (in panels a-e) except
for the total work cycle (in panel f), which shows all shifts between AOIs with frequencies ≥
0.2% of the total number. Numbers in circles indicate percentages of the total dwell time allocated
to the designated AOIs. N/A = dwells not defined.
Table 4. Attributes of information searched for and purposes of gaze towards areas of interest
(AOIs) according to the retrospective think aloud (RTA) interviews with the operators. Detailed
information carried by features, or objects, within the AOIs are also listed.
Damaged trees or trees
otherwise not fit for
Landmarks and terrain
features that signal good
Getting a general overview.
Identifying where the trees are.
Identifying which trees should be felled.
Deciding how to organize work, e.g. where to drive
and where to put piles.
Deciding which directions to fell trees and where
they will land.
Deciding which tree to handle next.
Deciding whether thinning can be finished from the
current machine position: do
more trees need to be
thinned and how far can the machinery reach?
Ensuring the crane and harvester head is not
touching any trees in the stand.
Straight or curved stem.
Small or dry crowns.
If trees are straight or
Identifying trees to remove.
Looking for tree damage.
Ensuring the crane does not touch the trees.
Deciding or identifying where to place logs.
Determining if piles are present for placing the
Shifting between delimbed stems and piles to
check that logs are put in the right piles (involving
gaze shifts between piles, stems and sometimes the
Finding a suitable place to process a tree.
e to feed trees.
Ensuring that nothing is hit while processing (e.g.
Deciding whether to put a log in an old pile or
make a new one (involves gaze shifts between the
upcoming processing site and the pile).
The side of remaining
trees that the
canopy/crown ended up
The felling direction.
Avoiding trees getting stuck in another tree.
Checking if a tree got stuck.
Searching for an opening in which to fell.
Checking that the felling direction is the same as
Deciding where the stem is fed and checking that
nothing gets hit (e.g. trees and the machine).
Damage, e.g. broken tops
(Remaining) length and
Checking if the stem is large enough for log
Checking if it is possible to make another log.
Positions of hoses.
Searching for the exact point to fell-cut.
Ensuring that there are no rocks or other things that
may damage the saw during felling.
Monitoring when the cut is complete.
Monitoring to ensure that the saw does not cut too
little or too deep.
Considering increasing or decreasing the length of
Checking that the right species is
Ensuring that the machine
-measures are correct.
Checking whether the length has to be adjusted.
Obtaining support for sorting logs into piles.
Ensuring that no error messages have come up
before working at maximum crane reac
NOTE: The table presents a collection of all comments made about the AOIs during the unstructured RTA that
could be categorized within the given categories. Thus, this is not a complete list of purposes or information-
carrying areas that are attended during forest harvesting. Neither is there any intention to produce a complete
overlap between the detailed information-carrying areas described within each AOI and the presented purposes
for dwelling on them.
7.2.1 Viewing the canopy
Dwells on the canopy were associated with activities including planning the
felling and making decisions about which trees to remove (Table 4). The
canopy was mainly dwelled on during driving, crane work and release of the
top (Figure 6). The operators’ gaze dwelled on the canopy once or twice per
felled tree. The longest and most frequent dwells occurred during second
7.2.2 Guiding positioning-to-cut and felling
When positioning-to-cut and felling the tree, the operators made long dwells on
the harvester head. The long dwell times were composed of several dwells on
different parts of the harvester head, especially the saw unit. Accordingly, they
looked at the harvester head to find exact felling-cut points and to ensure that
the saw was not damaged during operation (Table 4). During no other WE was
the proportion of dwell time on the harvester head as high (Figure 6).
7.2.3 Felling the tree
During felling, operators looked most often at, or beneath, the tree being felled.
A marked exception, however, was during first thinning, where the operators’
looked at only about 70% of the trees being felled. The main reason for
watching the falling trees was to ensure that nothing went wrong (Table 4).
However, instead of following the falling trees all the way until they hit the
ground, the operators’ eyes moved on to other objects.
7.2.4 Preparing processing
Often, while the tree was still falling, the operators’ eyes made look-ahead
fixations towards where the log was to be fed, i.e. the upcoming processing site
and sometimes towards the processed wood pile, forest, and standing trees
around this site. Many dwells on this site followed a dwell on a tree being
felled or the saw unit of the harvester head. During felling, most dwells on the
upcoming processing site were followed by a transition to the pile or saw unit
of the harvester head, whereas during processing most dwells on this AOI were
followed by transitions to the delimbed stem. Almost one third of the dwell
time during processing that was spent looking at the forest (see Figure 6) could
be classified as look-ahead dwells towards the upcoming processing site.
Figure 7. Typical dwell sequences during the processing WE, showing transition frequencies and
dwell time proportions. Percentages of total transitions are marked along the arrows in the
direction of the transition. Numbers in circles show percentages of the total dwell time during
processing that were allocated to the designated AOIs.
7.2.5 Focus on feeding, cutting and sorting
While processing, the operators maintained a strong visual focus on feeding,
cutting and sorting the logs (Figure 7a). During processing, the operators had
the highest proportions of gazes (in terms of dwell frequencies and total time)
(d) Monitor usage during processing
Pile and between
pile and stem
directed towards the gripped tree, pile and bucking monitor (Figure 6). Many
dwells on the harvester head were for the purpose of acquiring information
about the saw and cutting process (Table 4). Consequently, most hits (58%)
just before (0-233 ms prior to) cutting were focused on the saw unit of the
harvester head. This was 23 percentage points more than the processing WE
7.2.6 Utilization of digital bucking information
The bucking monitor was looked at very rarely and almost only during
processing. Even then, the monitor was observed for just 6% of the WE time,
often just before the log was cut or the suggested cutting position was manually
changed. Most (95%) transitions to and from the monitor were to or from the
area of the pile, delimbed stem or saw unit of the harvester head (Figure 7b).
Nevertheless, there were large between-operator differences in dwells on the
bucking monitor. Moreover, 64% of all dwells on the bucking monitor were
attributable to one operator and only 6% of the total number of dwells on the
bucking monitor occurred during first thinning. One operator in first thinning
and one in second thinning dwelled on the bucking monitor only once during
the recorded sessions. Besides that single dwell, the monitor was not even
visible in the eye-tracking video of the operator in first thinning; however, the
tracking was interrupted during seven downward nods of the head that brought
the bucking monitor back to clear visibility in the video. However, operators’
gaze generally dwelt on the bucking monitor longer and more frequently
during second thinning and final felling than during first thinning.
7.2.7 Finding and choosing the next tree or position for the machine
The tasks of identifying, locating and/or choosing the next tree to cut (or save)
or a new position for the machine can only be done while looking at aspects of
the forest. This visual behaviour often occurred already before the top of the
prior log was released from the harvester head, i.e. there were sharp increases
in both the frequency and time of dwell on the forest and canopy, accompanied
by sharp falls in frequency and time of dwell on the pile and the gripped tree,
relative to those in the prior WE, processing (Figure 6c-d). However, the
operators also sometimes planned ahead, thus reducing the need to search for
the next tree after each tree is processed. For example, one operator first
showed a high level of situational awareness when shifting focus to a car
passing on the nearby road exactly when the last cut in processing was
initiated, the operator then showed foresightedness when the next saccade went
directly to the next tree to cut with no sign of visual searching in the forest.
Moreover, to resume the work process the operator apparently had no need to
refocus on the harvester head or the unprocessed top that had been released
without visual supervision. The harvester head was not dwelt upon again until
it approached the next tree to be cut.
In general, it can be assumed that information specific to driving, strip road
preparation and tree selection were gathered during driving (Table 4). This was
done while the operators made long and frequent dwells on the forest and
canopy (Figure 6e), the average dwell duration on the forest was, for example,
higher during driving than during any other WE.
8 Discussion and conclusions
The overall aim of this thesis was to contribute new knowledge on working
conditions in mechanized logging operations and their relationship to system
performance by examining aspects of the operator, the machine, and the work
organization. An HTO framework was used in Study I to scrutinize the
problems existing in the interactions between the human operator, the
technology and the work organization, while at the same time taking into
consideration the context in which the work is performed. Studies II, III and IV
were used to extend the body of knowledge on aspects of the concepts H, T
and O. In each of these studies, different methods and measuring techniques
In Study II we found that more than 90% of logging workers were
employed by contractors. The previous established understanding that Swedish
logging contractors are mainly small enterprises, i.e. three employees on
average, was also confirmed. Furthermore, despite the fact that the share of
larger enterprises has increased in recent years, only a few employ more than
10 persons including the working owner. When working in a small enterprise
with few colleagues, information exchange tends to be informal but rather
effective (Jacobsen & Thorsvik, 2002). However, the body of knowledge and
experience within the company may not be sufficient for ensuring safe
practices and improving knowledge of new technologies, work methods or
practices. Consequently, the “network” of inter-organizational knowledge
exchange, as discussed in Study I, is important for company development.
However, for this sharing to be efficient it is important to have national, and
perhaps international, organizations that the contractors can draw on. Trust
between actors is important for the shared information to be trusted. Trust is
also important when there is an interest in having contractors share their
knowledge and experiences with others.
In Study II, it was also emphasized that most logging contractors were
working purely with machine operations. Thus, efforts to improve health and
performance through increased task rotation, as discussed in Study I, have
limited possibilities to be implemented within most companies, apart from
rotating between harvester and forwarder work.
In Study III, crane work was basically ruled out as a major source of WBV
at levels harmful to the human body. However, it should be emphasized that
this was a small study with only one operator and one machine. More
important results of this study were the positive effects on residual trees in the
stand through the use of an active brake-link with the possibility of precise
tilting of the grapple and the gripped logs. Avoiding damage to the residual
stand is a high priority in terms of both environmental concerns and avoiding
costly growth losses for the landowner (e.g. Sirén et al., 2013). The differences
in collision frequency between crane equipment types observed in this study
would therefore be of interest when selecting thinning equipment to minimize
damage to residual trees. Moreover, the results of Study III suggest smoother
operation of the grapple, and thus a more relaxed and comfortable work
environment for the operator. Cranes with automated or semi-automated
controls have also achieved smoother trajectories of the crane and less
unwanted movements of the grapple (Hansson & Servin, 2010). Such systems
may therefore prove especially valuable for novices in crane operations, both
by helping them reach higher performance faster and by reducing equipment
damage through improved controllability, as indicated in Study III. Possible
hindrances to implementation of the technology studied in Study III include
increased fuel consumption during usage (Öhman & Häggström, unpublished
manuscript) and purchase price.
The results from Study III are in accordance with the results of several other
studies on vibration exposure during driving versus crane work (e.g. Rehn et
al., 2005a; Hansson, 1990). Efforts to reduce WBV exposure should thus aim
at minimizing exposure to WBVs during driving. This can be achieved
organizationally by reducing the number of machine hours and by refusing to
work in the most severe terrains conditions. WBV reduction can also be
achieved technologically by adding stability and better dampening systems, but
also by reducing the maximum driving speed. However, the latter suggestion
may induce other risks related to machine manoeuvrability, and thus a negative
knock-on effect on productivity.
Nevertheless, if attempting to reduce operators’ exposure to crane work
induced WBVs, i.e. for comfort or fatigue reasons, the results from Study III
imply that technological modifications that increase the stability of the base
machine should be considered as a first option. This is based on the plausible
assumption that the predominant vibrations in the z-direction in Study III, i.e.
up and down (Table 2), reflect the tilting of the machine while handling logs.
The recommendation is also supported by findings that WBVs are negatively
correlated with machine weight (Rehn et al., 2005a). However, for
environmental reasons, improved stability of the base machine should not be
achieved by adding weight to the machine. Lightweight machines minimize
damage to forest soils, which ideally should remain unaffected by forest
operations. This trade-off exemplifies the challenges involved in designing
efficient work conditions adapted to the worker under tight constraints on how
the work environment can be modified or influenced by the work. Other
measures to reduce crane work induced vibrations include improved hydraulics
and crane control systems, which offer the potential to make operations
smoother and more comfortable for the operator (Hansson & Servin, 2010).
From the performance perspective, a highly interesting finding relates to the
utilization of bucking data from the onboard monitor, as revealed by the gaze
behaviour investigation in Study IV. It was shown that bucking information is
utilized and important, as the information was used by all operators at some
point. There were also indications of task dependency in gaze allocation, i.e.
the information on the bucking monitor and information from areas
surrounding the falling tree were less frequently attended to, i.e. less
interesting, during first thinning than during second thinning and final felling.
Thus, the gaze analysis indicates an information search pattern that is felling
type and/or stand dependent, i.e. the number of assortments and/or tree sizes
determines the perceived information need. The presentation and design of
bucking information may, at best, have a very slight impact on operator
performance due to the sparse amount of time spent observing it. However,
there will be a need for new interactive techniques (see Westerberg & Shiriaev,
2013) when, for example, adding advanced automation and decision support
(e.g. route planning in logging sites, Mohtashami et al., 2012). By providing an
understanding of monitor usage, Study IV may have an impact on the design
process of adaptive displays or other future interactive systems.
8.1 Strengths and limitations
The HTO framework stresses the need to scrutinize problems that exist in the
interactions between H, T and O, while also taking into consideration the
context in which the work is performed. Individual studies II, III and IV each
had a narrow focus on either human, technology or organization aspects.
However, in line with a hermeneutic research paradigm (see e.g. Johansson,
2000), this is typical when applying a systems perspective; one must shift
between the narrow view and the wider scope in order to understand all aspects
and draw the pieces of the puzzle together.
The main strength of this thesis is the use of several different methods and
techniques to examine the research questions. Large samples and more general
analysis, as in Study II, as well as small samples and more detailed analysis, as
in studies III and IV, were used. In Study I the data was mainly qualitative, in
studies II and III it was purely quantitative, and Study IV combined the two
approaches. The information obtained from the qualitative material in Study IV
was essential for interpreting the findings from the quantitative material.
The combination of structured literature search and snowballing approach
in Study I enabled identification of papers highly relevant to the situation of
workers in mechanized forestry but published under other topics and in non-
forestry journals. Those papers would have been missed if solely applying a
One limitation of Study I is that many (potentially) interesting studies and
research reports from, for instance, the organizations SCION (New Zeeland)
and FERIC (Canada) are missing due to their online unavailability. Apart from
the apparent problem of missing data, this may have affected the view of the
system. It has been noted that European researchers have different research
traditions to their American colleagues; they have, for example, treated the
harvester and forwarder as separate research subjects, whereas American
researchers have mainly investigated the harvester and forwarder as a complete
harvesting system (Nurminen et al., 2006). Thus, the European research
tradition may have had a greater influence on the results, in which the harvester
and the forwarder are described as separate, but interrelated, subsystems.
Moreover, due to the focus on mechanized CTL operations with a harvester-
forwarder system, Nordic literature is overrepresented in the literature list.
A strength of Study II is the large sample on which it was based, i.e. an
estimated 20% of the total population replied. This has an positive effect on the
findings' accuracy and external validity. Moreover, the large sample size
allowed segmentation, thus conclusions could be confidently drawn about the
logging contractors subgroup, which was the main interest when initiating the
When interpreting Study II, it should be taken into consideration that the
results based on the strata (one-man, small-sized, medium-sized, and large-
sized enterprises) are not exactly the same as results for enterprises with 0, 1-4,
5-8, or 9 or more employees. However, the chosen method was used to enable
population total estimates and comparisons with the 1993-1998 data sets. The
average number of workers for each stratum was also consistent with the
categorization. It should also be noted that the register from which the
population was drawn has some inconsistencies, but consistencies between
repeated measures indicate the reliability of our results, even in instances with
high relative standard error. Moreover, the study covered about 20% of the
estimated population of Swedish contractors, which must be regarded as a
substantial part of the population.
Study III was conducted as a field experiment on small samples in a
standardized but natural environment, from which generalizations should be
made with care. During the experiment, standardization of the track and efforts
to eliminate unwanted sources of vibration, i.e. ground roughness, helped
isolate the effects of the studied factors. However, the recorded vibration
values in Study III are only valid under the prevailing conditions during the
study. Nevertheless, there are no (obvious) indications that the obtained
relationship between grapple type and vibration should be falsified under other
conditions or in other machines. Moreover, the vibration exposure during
driving would become higher in a more uneven terrain, thus reducing the
impact of crane induced vibrations.
It should also be noted that the upper frequency limit in this study was 50
Hz compared to the standard 100 Hz, thus the results should be interpreted
cautiously. Nevertheless, inspection of the frequency spectra reviled that the
highest vibration magnitudes were below 50 Hz. Thus, the limitations in
measuring technology should not have had a major impact on the calculated
exposure and the relative levels are fully comparable.
Study IV was conducted as a naturalistic observational study to gain insight
into harvester operators’ gaze behaviour and perceived information need. The
approach was chosen due to the immaturity of gaze tracking as a research
method and the, to date, scare knowledge on eye movements in forestry
operations. To the best of our knowledge, a portable eye-tracker has never
before been used to study eye movements during work in a forestry machine.
Thus, the approach provided possibilities to explore and evaluate gaze
behaviour, the AOIs, and the eye-tracking technology. This revealed aspects of
the work that could be interesting to test experimentally in forthcoming studies,
e.g. if there are differences on a population level in dwell patterns during
different operation types when felling, and if those differences are due to the
bucking prescriptions or the size of the tree.
In study IV, it was difficult to obtain usable high quality data. Six
recordings were used in Study IV, but four more recordings were conducted in
relation to this research; two of those were tracked during special forest
conditions and were therefore not included in this study, the other two had too
low proportions of gaze samples (59-71%) in combination with severe
problems with exposure in the video and were therefore excluded from
analysis. Parts of the analysed data of the two operators with the lowest
proportions of gaze samples seemed to contain some systematic errors. Firstly,
a systematic displacement in the estimated point of gaze, i.e. a minor offset in
the scan path, was visible in parts of two recordings. A more thorough
procedure for calibration testing may have spotted and corrected this problem
already in the field. Nevertheless, in general, the operators themselves did not
observe any displacement while watching the eye-tracking video and only one
of them expressed a vague statement about possibilities of a minor
misplacement. Moreover, the given displacement was negligible with respect
to the AOI-analysis since the offset could be compensated for.
Secondly, we also encountered difficulties in tracking the gaze when
driving, which may be due to vibration as well as rapid head movements and
changes in illumination due to these head movements. The usability of eye-
tracking equipment in natural settings are well known to be limited by, for
example, pupil position in the eye outline, head movement, vibration,
illumination, monocular vs. binocular tracking, physical properties of the
tracked eye and the number of cameras in the (fixed) eye-tracking system
(Holmqvist et al., 2011; Morimoto & Mimica, 2005). Moreover, variation in
illumination, causing the pupil to constrict and dilate, is also likely to have a
negative effect on the accuracy of the eye-tracker (Wyatt, 2010). Thus, it is
likely that the gaze allocation on the forest is somewhat overestimated
compared to the gaze on, for example, specific trees or the harvester head. In
general, when interpreting Study IV, it should taken into consideration that the
quality of the scene video reduced the number of dwells that could be assigned
to the more detailed AOIs. Additionally, the measure of dwell time on the AOI
bucking monitor reflects the time that the eyes were directed away from the
ongoing tree processing. Thus, it included saccades or fixations shorter than
100 ms to and from the monitor which, in turn, may have contributed to minor
underestimation of dwell time on the forest.
We assumed natural vision to be a mainly top-down and goal-directed and
less influenced by bottom-up saliency (see Orquin & Mueller Loose, 2013;
Tatler et al., 2011; Ballard & Hayhoe, 2009; Land, 2009), and used the
measures as approximations of overt attention and of the nature of information
acquisition during harvesting. However, we did not study attention and
information acquisition per se, but eye movements and introspective reports on
information acquisition. We cannot rule out that some objects were attended to
in the periphery; partly because the study was conducted with experienced
operators in a well acquainted task (see Strasburger et al., 2011). Moreover, it
is possible that operators were not processing information from the focused
AOI, but instead thinking about something else. However, during the short and
intensely active time that the operators were studied (ca. 15 min) it is unlikely
that they would have lost focus on the task.
8.2 Experiences of using eye tracking
This section discusses and provides recommendations for eye tracking research
based on experiences of using eye tracking in a naturalistic observational field
study. The discussion covers both data gathering experiences from the field
and experiences of data processing and analysis.
8.2.1 Experiences and recommendations in the field
When planning the field study, it is important to acknowledge that not all
humans are suitable subjects for eye-tracking, since features of the participant,
like eye colour, eyelid droop, astigmatism etc., and artefacts such as glasses
and mascara affect the tracking quality (Holmqvist et al., 2011). The studies
with the two operators wearing glasses under the eye-tracking glasses resulted
in the poorest data quality, while the operator wearing contact lenses
underneath the eye-tracking glasses achieved data in line with the three
operators without sight impairment. Glasses with correction for astigmatism
did not provide worse data than glasses without. Thus, it is important to
determine whether participants have sight impairment, use contact lenses,
glasses or mascara, or have a distinctly dominant eye. However, confirmed
sight impairment does not necessarily mean that the person must be excluded
from the study.
When conducting the study, one should always try to keep the illumination
fixed (Holmqvist et al., 2011). However, as shown in Study IV, this is
impossible in outdoor environments. Changes in illumination, between, for
example, the harvester head and the canopy, were of such a magnitude that
tracking was often lost completely for some time. Nevertheless, good planning
based on the sun’s position with regard to the operator’s line of sight, i.e. the
intended AOIs, can reduce illumination variation.
Reliable calibration is essential for the validity and generalization of the
results. Therefore, it is important not to rely solely on built-in calibration. For
example, the Tobii eye-tracker calibrates at focal points of one metre from the
eye; this is therefore where precision is highest, and deviations will occur when
the focus shifts from this point. In thinning, work is often performed at a boom
length of 10 m. Thus, asking the participant to look at various objects in the
environment (preferably intended AOIs) provides important validation of the
calibration and makes it possible to adjust the gaze position after recordings.
Moreover, vibrations and head and body movement decrease the data precision
and increase the likelihood that the eye tracker moves out of position
(Holmqvist et al., 2011). Since harvester operators move their head in a
vibrating environment, recalibration with the AOIs should be done at least
twice during recordings; before and after the study. In addition, to help ensure
usable data it is also recommendable to check the calibration against objects in
the natural environment at half time as a safeguard against the glasses moving
out of position during recording. In studies with a high demand on precision
and accuracy, calibration should be done in both bright and dim conditions to
enable correction for pupil size (Drewes et al., 2012).
In Study IV, a monocular tracker was used. However, for future studies use
of a binocular tracker for “eye tracking in the wild” is recommended so that
both eyes are tracked. Binocular recordings should give better data and
problems in tracking should be more easily detected than with monocular
recordings. This recommendation is based partly on the observation that the
operators’ gaze naturally shifted right-left as well as up-down between the
corners of the eyes during the work. This could happen, for example, when
logs were processed close to the ground below the cabin on the right- or left-
hand side of the machine. Since only the right eye was tracked, tracking was
sometimes lost and, when processing took place on the left-hand side, the
estimated focus was sometimes on an object with no obvious information
Reflective interviews with video recordings have previously been
successfully utilized in the study of safety critical logging work (Parker, 2010). The
glasses provided a non-obtrusive way of studying real-world operations while
adding a dimension of data compared to the study of Parker (2010). Non
obtrusive studies of behaviour in natural settings, is essential for ecological validity and
robust extrapolation of results to real situations (Dicks et al., 2010; Parker, 2010; Klein,
As previously stated, the qualitative material from the RTA interviews was
essential for interpreting and explaining the tracking data. However,
interviewees quite often had difficulty verbalizing what they were doing, and
difficulty understanding what information we wanted them to provide. Due to
the cyclic nature of the task, the interviewees often felt that there was nothing
new to tell after the first few fellings had been described. Thus, it is important
to prepare the interviews thoroughly and to continuously motivate the
interviewee to give more detailed explanations of their dwell patterns and the
task. Since the interviewees are the only ones with introspective access to the
intentions and purposes of their dwells, they are a valuable asset in detecting
and ruling out irregularities and problems in tracking precision. Thus, it can be
beneficial to let them view the full recording during the interview. Based on
the experience from Study IV, it is also recommended that critical sequences
are identified and “walked through” at a very low playback speed so that the
interviewee has time to reflect and formulate a response without feeling time
pressured by immediate introduction of the next event.
8.2.2 Experiences and recommendations for analysis
When planning and conducting the analysis of collected eye-tracking material,
resource availability should be a key determinant. Frame-by-frame analysis is
highly time demanding (Study IV, Holmqvist et al., 2011; Land & McLeod,
2000), and the expected gains should be carefully weighed against effort and
resource demands. Thus, if conducting frame-by-frame analysis the focus
should be on narrowly defined (spatially and/or temporally) parts of the work
(recordings). The results of Study IV give a guide as to how and what AOIs
can be constructed in this domain, and during what tasks tracking is likely to
provide better or lower data quality and, thus, help determine whether eye-
tracking is a viable means to answer the research questions. To give an
example: from our experience, detailed objects could not be identified correctly
either on the bucking monitor (i.e. the exact information consulted from the
monitor) or in the forest (i.e. stumps and piles on previous strip roads). This
was due partly to tracking precision and accuracy, and partly to video quality
and limitations in obtaining 3D information from 2D representations. Thus,
research questions on, for instance, strategies for keeping strip roads parallel
and at the right distance from each other are likely to fail to be answered.
Nevertheless, detailed quantitative gaze analysis of the recordings may not
always be necessary. If aiming for the “whys”, analysis of RTA data may
provide sufficient, and better, results. Moreover, eye-tracking data should not
only be used for answering research questions. An interesting topic for further
research is how the video material (i.e. the visualization of gaze behaviour) can
be used for instructional purposes.
In Study IV, dwell measures was used as a proxy for gaze allocation.
However, we also considered extracting blink data, which is sometimes used as
a proxy for mental demand, but we could neither find a satisfactory algorithm
that worked when the pupil changed due to changes in light conditions, nor
when the same phenomenon produced a loss in tracking due to reasons other
than blinking. Thus, further research and development is needed before eye
tracking equipment can be used to study the mental work loads of harvester
operators in real operations.
Last, but not least, is the issue of validity. Due to the relatively low
precision of the eye movement data, it was important to investigate and
validate the data set not only by statistical means but also with complementary
interview data and scan path evaluation (evaluation of the path of eye
movements). Thus, it is important that the researcher evaluating the data is
familiar with the conducted task in order to be able to recognize erroneous
8.3 Future research
Future studies to address the design and evaluation of operator learning and
education are warranted according to Study I. Study IV presented a method for
gathering information on gaze behaviour, which can be used to examine and
explain good work practices applied by skilled workers. Indeed, knowledge of
expert performance and dwell patterns in forestry work may provide valuable
insights and material that could be used in teaching or be refined to
recommended practices. Eye-tracking may be used to facilitate learning of
challenging harvester work by teaching the visual gaze behaviour of skilled
operators and providing explanations for information gathering behaviour that
is not instantly apparent to novices. Indeed, many studies have shown that task-
dependent gaze behaviour can be taught (Diaz et al., 2013; Hayhoe &
Rothkopf, 2011; Kandil et al., 2009). However, controversy remains over
whether learned gaze behaviour equates with acquired knowledge and the
ability to understand the importance of the objects attended and, thus, whether
the new behaviour actually improves task performance and situational
awareness. Can operators learn where to look, without knowing why? For the
novice, learning the behaviour of an expert without acquiring sufficient
knowledge of the reasons behind that behaviour could result in a deterioration
in situational awareness and, thus, in performance. Eye-tracking may thus
prove a valuable tool to improve education and enhance forestry machine
operator learning. It is left to future research to determine whether eye-tracking
recordings should be used in educational settings to modify operator behaviour
by having them mimic visual gaze patterns derived from eye tracking, or
whether the technology should be used for extracting operators’ implicit
knowledge and then applying that knowledge in the development of operator
training. It would also be warranted to investigate whether value could be
added by combining these two approaches.
Maintenance, which plays a crucial role in the work and performance of the
harvester-forwarder system, was not included within the scope of this thesis.
While maintenance improvements are acknowledged for their potential
financial benefits (Bohlin & Hultåker, 2006), the work itself is generally
considered unsafe (e.g. Väyrynen, 1984). Therefore, there are many work
environment aspects related to maintenance that deserve further study. To date,
there has been little focus on the possibilities of computer-assisted maintenance
and repair work. Considering the hours spent on maintenance, a small
improvement in time to complete maintenance would greatly benefit the
contractor. Better knowledge and support during maintenance and repair
should reduce work methods based on trial and error. This can save time, but
also improve safety by reducing unnecessary climbing on the machine and
other unsafe work practices involved in locating and repairing faults. On the
negative side, the potential for faster and safer maintenance work also brings
the potential for longer hours in the machine, and thus increased risk of
musculoskeletal problems. On the other hand, reductions in maintenance time
provide opportunities to invest more time in preventive measures or other
constructive tasks such as harvest planning.
It has been stated that the main health and safety problem of today is not
lack of knowledge, but putting existing knowledge into practice (Lewark &
Kastenholz, 2007). Based on my experience, this is true in many, but not all,
cases. The present thesis has shown that although much work has already been
implemented, the problem of musculoskeletal pain is multifaceted, and that
some promising solutions, such as introducing mini-levers (Murphy & Oliver,
2008; Attebrant et al., 1997; Hagberg & Lidén, 1991) and better dampening of
machines, have not been sufficient. Other solutions have failed in practice due
to a failure to comprehensively consider the impacts of the change on the
organization and the operator, such as introducing new work schedules with
less machine time (see. Persson et al., 2003; Synwoldt & Gellerstedt, 2003;
Ager). Moreover, automation and decision support systems are rapidly growing
research areas in which new knowledge is being constantly produced.
Automation in forestry is likely to have a system change affect comparable to
that brought by the introduction of mechanization to the harvesting system (see
Ager, 2014). Therefore, in order to be prepared, there is a need for continuous
research into methods, interfaces, forms of interaction, safety and health and
the automation technology itself. It is difficult to predict the future, but the
consequences of not trying may be devastating for performance as well as
safety in mechanized forestry (see Sarter et al., 1997; Bainbridge, 1983).
8.4 Concluding remarks
The right abilities, skills, techniques and training of operators are not alone
sufficient for ensuring high performance of the logging system. Neither are the
most advanced and fastest machines. The operator is affected by and interacts
with the machines and technologies, the work organization and the
environment surrounding the system. Knowledge of all of these parts and their
interactions is crucial for successful development of future logging systems.
Future forest operations researchers therefore need to be team players and
interact to share specialized knowledge on each of these aspects as well as the
tools and methods to study them. Given the challenges and current
developments indicated above, such research teams may include practitioners
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