Harvesting systems and technologies

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 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.

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%.

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

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

volume: 39, issue: 2

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

Dynamic Soil Pressures Caused by Travelling Forest Machines

volume: 39, issue: 2

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


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

Subject area

Agricultural and Biological Sciences