Volume 39 No. 1
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Volume 39 No. 1

Productivity Model for Cut-to-Length Harvester Operation in South African Eucalyptus Pulpwood Plantations

volume: 39, issue: 1

There has been a concerted shift from traditional motor-manual and semi-mechanised timber
harvesting systems to mechanised cut-to length (CTL) operations in South Africa. This is
particularly true in Eucalyptus pulpwood felling and processing, South Africa’s largest commercial
wood resources used in the pulp and paper industry. Mechanisation improvements
are typically driven by increasing safety regulations, product quality and productivity concerns
related to traditional harvesting systems. The objective of this study is to develop productivity
models for mechanised Eucalyptus pulpwood CTL felling and processing operations by combining
the results of a number of individual studies done over a period of 24 months in the summer
rainfall areas of South Africa. The study takes into account species, machine type (purpose
built vs. excavator based), silvicultural practices (planted vs. coppiced) and slope. The pooled
data revealed general productivity ranges from 5.16 m3 PMH-1 to 27.49 m3 PMH-1.


Productivity of Cut-to-Length Harvesting by Operators’ Age and Experience

volume: 39, issue: 1

In the study, the relationship between operators’ age, experience and mechanized cut-to-length
(CTL) harvesting productivity was examined. The data were five-year follow-up data from 28
operators and 38 CTL harvesters collected from southern Finland. Productivities were converted
to relative productivities and average productivity models were created. Case specific
productivities were compared to modelled values, and productivity ratio models including
separate lower and upper quartile models were produced.
The relative productivity of operators at the age of 45 years in clear cuttings was 17.8%
higher and in thinnings 14.9% higher than that of operators at the age of 25 years. The relative
lower quartile productivity increased from operators aged 25 to operators aged 45 years by
38.6% in clear cuttings and 29.4% in thinnings. The relative productivity of operators having
experience of 20 years was 23.6% higher in clear cuttings and 16.2% higher in thinnings than
that of operators having experience of 3 years. Operators’ experience of 20 years produced
43.1% better lower quartile relative productivity in clear cuttings and 29.1% in thinnings
compared to 3 years’ experience. The relative upper quartile productivity was 5.7% higher in
clear cuttings for operators aged 45 years than for operators aged 25 years, but otherwise, there
was no statistical correlation between upper quartile productivity and age or experience.
As a conclusion, CTL harvester operators’ average productivity increases slowly after the
initial learning phase up to 15 years of experience. The peak productivity was uncorrelated to
age or experience, but the experience raised the bottom productivity values.

Effects of Short-Term Storage Method on Moisture Loss and Weight Change in Beech Timber

volume: 39, issue: 1

Productivity and Costs of Harwarder Systems in Industrial Roundwood Thinnings

volume: 39, issue: 1

In several studies, the harwarder has proven to be a more cost-effective wood harvesting system
than the traditional two-machine (harvester-forwarder) system, especially when the average
stem size of the marked stand is relatively small, the removals per hectare/stand low (i.e. the
harvesting site small), and the forwarding distance short. One of the strengths of a harwarder
is considered to be the lower relocation costs compared to the two-machine system. The time
consumption of harwarder relocations have not, however, been reported in the previous harwarder
studies. Metsäteho Oy conducted a follow-up study of harwarders in industrial roundwood
harvesting, and also investigated the relocations of harwarders. A total of five – three
Ponsse Wisent Dual and two Valmet 801 Combi – harwarders were examined in the follow-up
study. The amount of harvested industrial roundwood in the study totalled nearly 30,000 m3.
The cost calculations showed that the harwarder system is more competitive than the twomachine
system when the average stem size of the marked stand is relatively low, i.e. less than
110–170 dm3. Furthermore, harwarders were the most competitive at low-removal harvesting
sites. The proportion of the total working time of harwarders used in relocations between harvesting
sites was 2.5%, and the effective relocation time was, on the average, 1.3 hours/relocation.
The study results underlined that it makes sense to harvest relatively small-removal and
small-diameter thinning stands marked for harvesting with a harwarder while, conversely, it
is more worthwhile to harvest sites with larger removals and trees using a two-machine harvester-
forwarder system, thereby raising the profitability of forest machine business.

Planning Forest Road Network in Natural Forest Areas: a Case Study in Northern Bosnia and Herzegovina

volume: 39, issue: 1

Natural forests are one of the three types of forest management in terms of origin. These forests
are of seed origin and they regenerate naturally. Therefore, natural forests are the most important
forest category from the point of view of timber production, as well as its quality and
biodiversity. The natural forests accessibility and overall forest accessibility are insufficient
for sustainable forest management. This is the reason for dealing with planning of forest roads,
actually planning of forest accessibility and designing of forest roads in this forest category.
This task requires quantity and quality analysis of the current forest road network, determination
of optimal density of forest roads, determination of suitability of forest area for the construction
of forest roads and designing of forest roads in the end. Planning of forest roads is
carried out at strategic level. Analytic Hierarchy Process (AHP) allows the selection and
evaluation of influential factors related to planning of forest roads. The tools of Geographic
Information System (GIS) allow a complete spatial and statistical analysis and management
of data collected from the forest management plans or data surveyed in the field and obtained
by means of »Digital Terrain Model« (DTM) and AHP method. Planning of forest roads will
be done in the Management Unit (MU) »Prosara«, located in the northern part of Bosnia and
Herzegovina (BIH). The current density of forest roads is 7.3 m/ha in natural forests of this
management unit. The optimal density of forest roads should be 17 m/ha. The length of new
forest roads designed in the MU »Prosara« is 21 km, and forest accessibility has increased to
13.5 m/ha.

Study of Forest Road Effect on Tree Community and Stand Structure in Three Italian and Iranian Temperate Forests

volume: 39, issue: 1

Roads are built in forests for two main reasons, but always in function of management of forest
ecosystems, and these reasons are to provide access to the forest area for transportation
mobility and wood extraction. This creates a relatively even network in the forest. This topic
has received much attention in recent years due to its function and effect on forested rural
landscapes and the related environment. Forest road network is important for various types
of functional use, such as the interface between forested lands and roads. The aim of this study
is to assess the effects of road existence and use on the occurrence of tree dieback and on the
composition of the tree community in three forest areas (two in Italy and one in Iran). The
effort to determine the dynamics of the effects caused by road use was done by examining the
changes in stand structure and abundance of species. As demonstrated by the results, the
edges (20 m) of the forest road network are a fine mosaic composed of different trees (qualitative
and quantitative), coupled with the moderate presence of dead trees. In the three areas, from
the road edges to the interior forest, a similar taxonomic composition of forest community was
found. The first main difference was related to the abundance of less shadow tolerant species
along the road. The second main difference was related to the tree biodiversity indices that are
higher along the road. The main similarities are in the structure of live and dead trees.

Middle-Term Сhanges in Topsoils Properties on Skidding Trails and Cutting Strips after Long-Gradual Cutting: a Case Study in the Boreal Forest of the North-East of Russia

volume: 39, issue: 1

In this work, physical and chemical properties of the upper horizons of podzolic light loamy
soil were investigated 21–23 years after forest cutting. This was after the first shift of long-term,
gradual felling was carried out by tree-length logging in wintertime in mixed conifer stands
of the Middle Taiga of the Arkhangelsk Region in Russia. The increased density of the forest
litter composition was observed. This was especially the case on skidding trails. On the forest
floor of skidding trails subjected to a greater stress caused by timber skidding, lower total
porosity and aeration porosity was observed, in comparison with the cutting strip and natural
forest. It was established that timber skidding during wintertime does not affect the density of
podzolic horizon composition. An inverse pattern was observed here: the total porosity and
the aeration porosity became higher and were close to the optimum values for plant growth
(54.16–52.99% and 15.72–19.97%). In the podzolic horizon on skid roads, comparison to the
natural forest showed a significant reduction of phosphorus mobile forms and an increase in
the amount of absorbed bases, which is the result of grassy vegetation overgrowth and natural
birch regeneration. On skidding trails and cutting strips, the organic matter content and total
nitrogen significantly increased, which is related to a change of light intensity, the composition
of living ground cover and vigorous decompositions of the organic horizon and woody residues.
In cutting areas, a system mosaic of soil cover developed, which differed according to favourable
conditions for tree species regeneration, compared to the control stands.

Tractive Performance of Tyres in Forest Conditions – Impact Assessment of Ground and Tyres Parameters

volume: 39, issue: 1

This article deals with the assessment of traction properties of tyres on forest grounds. The
research was carried out on skid trails located in pine stands. The tested grounds were different
due to the cover of the soil and its mechanical properties. The study also deals with the
evaluation of ways to improve traction by reducing the inflation pressure and using the tyre
chain. The research was carried out using a specialized traction test stand for two tyres (9.5–24
and 400/55–22.5) different in width and tread pattern. The studies showed significant effect
of ground conditions on traction. As a result of changes in the ground conditions, the values
of drawbar force, rolling resistance and tractive efficiency were altered by 25%, 23% and 6%,
respectively. The higher values of the drawbar force and tractive efficiency on all tested trails
were obtained for 400/55–22.5 tyre. Both the use of tyre chains and the reduction of inflation
pressure resulted in the increase in drawbar force and tractive efficiency. A better way to improve
traction properties was the reduction of the tyre inflation pressure, which caused the
increase in drawbar force and tractive efficiency. The use of tyre chains caused an increase in
drawbar force over the entire slip range, while an increase in tractive efficiency has only been
shown for the slip larger than 15%.

Trailer Overturning during Wood Transportation: an Experimental Investigation of Effects of Trailer Joint Point and Frame Structure

volume: 39, issue: 1

Trailers may increase the risk of tractor overturn during wood transportation in dangerous
conditions. In this work, tests were carried to simulate a trailer rollover using three two wheel
tractors and a crawler tractor and three trailers (two single-axle and one two-axle), all of their
combinations moving downhill along the path on a short dirt road. The trailers were always
loaded with the same load of logs cut at a length of about 1.5 m and put transversely to the
longitudinal axis of the trailer. During each test, the following parameters were measured: the
lateral dragging of the rear wheels/crawler of the tractor, the ground detachment of the rear
upstream wheel/crawler and both the longitudinal and transversal strains (released over the
tractor hooking system) produced by the trailer overturn. The study highlighted that the biaxle
trailer structure with a turntable steering had the best performances compared to the
single-axle in terms of safety during trailer overturning. Independently of the trailer type
considered in this work, a tied load is more dangerous than a load restrained only by steel
struts, because during the overturn the load forms a single unit with the trailer mass, which
increases the transversal and longitudinal strain.

Analysis of Hazardous Emissions of Hand-Operated Forestry Machines Fuelled with Standard Mix or Alkylate Gasoline

volume: 39, issue: 1

In addition to safety, small hand-operated forestry machines can be criticised for affecting the
operators’ health, especially because of high levels of exhaust gas emissions, noise and vibrations.
In this study, gas emissions, noise and hand-arm vibrations (HAV) levels have been measured
on chainsaws, hedge cutters and blowers fuelled with two different types of fuel: a commercial
RON 95 gasoline with the addition of 2% of synthetic oil suitable for two-stroke engines and,
as an alternative, a specific advanced mixture available on the market, based on alkylate gasoline.
For two different running conditions, i.e. with the engine at idle speed and when executing a
typical working routine (maximum speed with load), tests were carried out for:
Þ gas emissions, using a gas analyser, for measuring the volatile organic compounds (VOC)
Þ noise, using a sound level meter, to record the levels at both of the operator’s ears
Þ HAV, using a tri-axial accelerometer fixed on the handgrip(s) of the machines.
The results demonstrated that, when using the alkylate fuel, the VOC emissions were reduced,
in the considered machines, from 23 to over 77%, while for noise and HAV, the differences in
level were not statistically significant. The present study confirms that the reduction in the
amount of emissions can be remarkably improved by adopting advanced fuels that lead to a
more efficient combustion process.

Accuracy Assessment of Digital Terrain Models of Lowland Pedunculate Oak Forests Derived from Airborne Laser Scanning and Photogrammetry

volume: 39, issue: 1

Digital terrain models (DTMs) present important data source for different applications in
environmental disciplines including forestry. At regional level, DTMs are commonly created
using airborne digital photogrammetry or airborne laser scanning (ALS) technology. This
study aims to evaluate the vertical accuracy of DTMs of different spatial resolutions derived
from high-density ALS data and existing photogrammetric (PHM) data in the dense lowland
even-aged pedunculate oak forests located in the Pokupsko basin in Central Croatia. As expected,
the assessment of DTMs’ vertical accuracy using 22 ground checkpoints shows higher
accuracy for ALS-derived than for PHM-derived DTMs. Concerning the different resolutions
of ALS-derived (0.5 m, 1 m, 2 m, 5 m) and PHM-derived DTMs (0.5 m, 1 m, 2 m, 5 m,
8 m) compared in this research, the ALS-derived DTM with the finest resolution of 0.5 m
shows the highest accuracy. The root mean square error (RMSE) and mean error (ME) values
for ALS-derived DTMs range from 0.14 m to 0.15 m and from 0.09 to 0.12 m, respectively,
and the values decrease with decreasing spatial resolution. For the PHM-derived DTMs, the
RMSE and ME values are almost identical regardless of resolution and they are 0.35 m and
0.17 m, respectively. The findings suggest that the 8 m spatial resolution is optimal for a
given photogrammetric data, and no finer than 8 m spatial resolution is required. This research
also reveals that the national digital photogrammetric data in the study area contain certain
errors (outliers) specific to the terrain type, which could considerably affect the DTM accuracy.
Thus, preliminary evaluation of photogrammetric data should be done to eliminate possible
outliers prior to the DTM generation in lowland forests with flat terrain. In the absence
of ALS data, the finding in this research could be of interests to countries, which still rely on
similar photogrammetric data for DTM generation.

Determination of Service Life of Sintered Powder Metallurgy Gears in Regard to Tooth Bending Fatigue

volume: 39, issue: 1

The aim of this study is to check the possibility of replacing the pinion gear made of structural
steel with the one made of sintered material. The pinion is part of the gear pair mounted
in front of the gearbox of the skidder Ecotrac 55V to increase the speed and lower torque. In
larger series, powder metallurgy (PM) gears are used as a cost-effective alternative for wrought
metal gears in a number of industries including the one producing forest products. The present
paper discusses the computational and experimental approach for determining the service
life of sintered PM gears in regard to tooth bending fatigue. The proposed computational
model is based on the stress-life approach, where the stress field in a gear tooth root is determined
numerically using finite element method. The needed material data have been taken
from the authors’ previous work. Due to the scattering nature of fatigue, the statistic approach
has also been considered by presentation of computational results. The experimental procedure
was done on a custom made back-to-back gear testing rig. The comparison between computational
and experimental results has shown that the proposed computational approach is an
appropriate calculation method for estimating the service life of sintered gears regarding tooth
root strength. Namely, it has been shown that, in case of proper heat treatment of tested gears,
tooth breakage occurred in the interval with 95% probability of failure, which has been determined
using the proposed computational model.

Research Trends in European Forest Fuel Supply Chains: A Review of the Last Ten Years (2007–2016) – Part Two: Comminution, Transport & Logistics

volume: 39, issue: 1

Within the fuel wood supply chain, comminution and transport have been identified as processes
with the highest costs, energy consumption and emissions. The coordination of comminution
and transport aimed at avoiding operational delays is also complex. Nevertheless,
the use of forest biomass helps to reduce the effects of climate change and produces an additional
income, especially in rural areas. About 20 years ago, at the beginning of the industrial
forest fuel utilisation, the focus of the research was on developing and analysing adequate
supply chains and machines. Nowadays, as state-of-the-art systems have been established, the
focus is on improving the efficiency of the processes and the quality of the products. This paper
provides a review of research trends of the last ten years focusing on comminution and transport
of forest biomass in Europe.
Comminution should become more efficient by analysing the effects of wood characteristics on
chipper performance and product quality, by tailoring chipper configuration according to those
findings and by introducing mechanical devices for improving the quality of chips. Transport
processes have the potential to become more efficient if the configuration of trucks is adapted
according to operational and legal requirements, and when considering moisture content
management. Finally, economic and environmental assessment of supply chains was made by
several studies. Future research is expected to focus on customizing the product quality according
to user’s requirements and on optimising the coordination of chipper and truck by
simulation and automatization tools.


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

Subject area

Agricultural and Biological Sciences