Forest harvesting involves felling trees, extracting logs from the felling site to a landing area, and processing trees into commercial products. It is a critical part of forest management, influencing sustainability, profits, and future forest health. Careful planning is required to consider factors like tree characteristics, environmental impacts, equipment capabilities, and business needs. The basic steps in timber harvesting are harvest planning, felling, processing trees, extracting logs, stacking logs, transporting logs, and site rehabilitation. Extraction methods include manual, animal, chute systems, and ground-based skidding machines. Proper equipment selection depends on terrain, soils, weather, silvicultural systems, and other factors.

1. Forest Harvesting and Engineering
FOR 327

2. What does forest harvesting
involve?
• Forest harvesting involves:
—tree felling
—delivery to processing
points
• Components:
—road construction
—Tree felling
—log transportation

3. Why is harvesting critical in forest enterprise
• Could influence the sustainability of
the forest enterprise regarding:
–Profit or loss
–Soil productivity
–Health of the next crop

4. Planning Harvesting Operations

5. What needs to be considered
• Type and age of the trees to be harvested
• Type, age species of forest to be harvested
• Other products obtained from the forest
—Ecosystem services e.g. catchment and climate change
issues
—Residues
—Non timber forest products
• Structures within the harvesting area (houses, power lines,
roads and railway lines)
• Environmental aspects

6. Harvesting manager key decisions
• What?
• Why?
• How?
• When?

7. Basic steps in timber harvesting
• Timber harvesting involves the following basic steps:
— Harvest planning.
— Felling.
— Conversion (debarking, cross cutting and infield stacking).
— Timber extraction ( skidding, forwarding and cable yarding).
— Stacking at landing depot.
— Loading and offloading.
— Timber transport.
— Slash disposal and site rehabilitation.

8. Planning Harvesting operations
• Three levels of planning are involved:
— Strategic plan
— Tactical plan
— Operational plan

9. Strategic plan
• Planning is at a higher level
• Considers all available resources including:
— timber, manpower, contractors, management structure, equipment and road networks
• It also takes into consideration:
• political, social, cultural and economical factors that influence the environment in which
harvesting will take place

10. Tactical plan
• Done to allow a working plan unit to balance the compartments, road network, the
transport methods and harvesting systems with the physical environment and
silvicultural requirements, over an immediate period of 3 – 5 years.
• The objective is to ensure:
—a sustained timber supply
—optimum utilization and allocation of equipment
• Tactical plan considers the following:
— harvest volumes,
—silvicultural requirements,
—costs,
—environmental issues.

11. Tactical plan
• The planning process depends on:
—Reliable maps
—Well-defined operating objectives
—Reconnaissance trips
—Careful system choices

12. Tactical plan
—Thorough paper planning and field verification
—Thorough review of implications (impact appraisal)
—Readiness to change the plan if necessary
—Effective communications between planners and executers
—Market conditions
—Accurate yield regulation

13. Operational plan
• Operational planning is when decisions taken during tactical planning
are converted into harvesting or road construction plans.
• Apart from timber harvesting, there are plans for road construction
and road maintenance that take place.
• For the sake of this course we will dwell much on operational plan
centered on timber harvesting

14. Timber harvesting plan should include:
• A large-scale contour map (preferably 1:2500) showing the following:
—Compartment boundaries
—special management zones (indigenous forests, historic and archaeological sites,
buffer strips and riparian zones)
—detailed functional terrain classification
—haulage roads, extraction routes
—landings and depot locations
—streams and streams crossing locations
—drainage structures and felling direction

15. Timber harvesting plan should include…..
—Order of harvesting operations.
—Harvesting systems (i.e. method of felling, extraction, conversion and
transport) matched to the terrain and balanced.
—Equipment and manpower requirements.
—Direction of timber flow and transportation.
—Harvest and transport scheduling.
—Change of responsibility (harvest done by owner or contractor).

16. Timber harvesting plan should include…...
—Special protection measures to be taken when opening up the
plantation.
—Management prescriptions to protect specific values and designated
special management zones.
—Detailed production and cost calculations.

17. Harvesting systems
• Refers to tools, equipment and machinery used to
harvest an area.
• The use of human labour and animals is also
included.
• For instance,
—A grip harvester can fell, delimb, and buck with some
attachment.
—A forwarder can be used for loading, extraction and
offloading.
—A chainsaw can fell, delimb and buck.
—A skidder can extract.
• In Malawi, three harvesting systems are
commonly used depending on the level of
technologies used.

18. Manual skid systems
• This operation is completely manual.
—Felling is done by an axe or a bow saw.
—Delimbing is done by an axe while cross cutting is done by a bow saw.
—Extraction is manually done.
• This is a single man operation.
• It is commonly done in first thinning, which may be used for pulp
production.
• Short wood method is deployed.

19. Motor – manual skid systems
• Chainsaws are used in thinning and
clear-felling operations in conjunction
with skidders or cable yarders.
• Motor - moter systems have higher
economies of scale than manual
systems.
• Harvesting methods other than short
wood are commonly practiced.

20. Mechanized skid systems
• Mechanized harvesting systems have not yet been introduced in
Malawi.
• Felling machines such as feller bunchers and harvesters have become
the standard equipment in the harvesting operations in South Africa
and most developed countries.
• In any case, these harvesting systems are by far the most competitive
in terms of operational efficiency.

21. Motor manual animal skid systems
• Chainsaws are used to fell, delimb and cross cut.
• An axe may also be used to delimb.
• Extraction is wholly done by animals (e.g. mules, horses, oxen, etc).
• It is commonly in second and third thinning.
• Short wood methods are mostly used.
• Animal skidding is common in Malawi for small scale harvesting
activities.

22. Equipment selection: why is it important?
• Each cut block has a set of management objectives that likely
include aspects of safety, profitability, forest health, water
quality and environmental concerns.
• The consequences of improper equipment selection may range
from unsafe working conditions to unacceptable costs.
• Making sound choices aims to reduce the risk stipulated above.

23. Factors affecting choice of equipment
a) Terrain:
• while cable and aerial systems allow for remote access. The factors to
consider include slope, ground profile, streams, wetlands, gullies and
roughness.
• These factors affect the ability of the equipment to travel over the
ground to reach the operating sites.
• Driving access is required to all parts of the cut block for ground-
based equipment,
• Ground based systems may cause more soil disturbance than cable or
aerial systems, especially on steep slopes or rough ground.

24. b) Soil
• Soil characteristics to consider include texture, moisture
content, and seasonal impact
• These factors affect the bearing strength of the soil, and its
ability to withstand machine traffic without degradation
• Fine textured and moist soils are more sensitive to machine
traffic than course textured or dry soils.
• Frozen or deep snow conditions allow ground-based machines
to access ground that may not support traffic during non-frozen
conditions

25. c) Timber characteristics
• The following timber characteristics can influence equipment
selection: tree size, volume per hectare, and timber quality
• There are two primary concerns, however:
Physical ability of the equipment to handle the trees without causing unsafe
working conditions or causing damage to the equipment, site, or timber; and
Harvesting economics for both per tree and per cut block costs. Small trees are
less economical to harvest than large trees, and small cut blocks are less
economical than large cut blocks.

26. e) Business requirements
• Timber must be harvested safely and economically for the licensee
and its contractor to remain in business.
• Business requirements, as opposed to site characteristics, may
impose conditions on the harvesting operations.
• These business requirements may include the operating season,
timber flow, mill’s log specifications, amount of timber available,
unique operating methods, labour availability, and equipment
availability, service, and transportation.

27. f) Weather and climate
• Extreme weather such as rain or wind can affect the severity of soil
disturbance.
• Saturated soils are more susceptible than dry soils to damage from
machine traffic.
• Wind is especially problematic for manual and motor manual felling
equipment.
• Deep snow can provide a protective ground covering for machines to
travel on but it can also impair machine’s mobility because of ground
slipperiness

28. g) Silvicultural systems
• The silvicultural system is significant because some machines can
maneuver better than others between the standing trees and extract
logs from a partial cut without damaging the residual stand or
affecting future growth potential.
• Machine size and flexibility are important issues to consider in
relation to silvicultural systems.

29. h) Legislation, regulation, or permit
requirements
• Some of the operating parameters in the cut block result from
legislative requirements or permit conditions required by
government.
• For example, utilization standards may include acceptable limits for
stump heights and levels of breakage.
• Soil disturbance guidelines can limit the number of roads, trails, and
other access structures that are allowed to be constructed on various
sites, and thus affecting the candidature of the equipment.

30. Success in harvesting operations
• Criteria for measuring success of harvesting system is
categorized into operation and environment
• The operational criteria include such factors as safety,
profitability, and log quality
• Environmental criteria include water quality, soil disturbance,
and residual stand protection
• The contractor may rank profitability before the environment
while the forester may reverse their importance.
• In today’s corporate and situation, the two criteria must be
balanced for sustainable gains.

31. Harvesting operations
Tree felling
• The first operation after wood procurement and in wood supply chain
• It is the process by which a tree is severed from its root system
• It can be done manually (by use of axes or chainsaws), motor –
manually, (by use of portable motorised tools i.e. power saws) or
mechanically (by use of feller bunchers or harvesters).
• Success depends on the felling techniques, felling direction, and
felling patterns among other things

32. Felling techniques
• It is recommended that the felling distance should be at least twice
the height of the tree to avoid accidents in the cut block.
• It is also imperative that felling facilitates subsequent operations and
processing.

33. Felling direction
• A tree should be felled in the most convenient direction; and the
direction of fall should in any was be controlled for the following
reasons:
• Safety
• To minimise residual and / or product damage
• To facilitate extraction

34. Factors to determine felling direction
• Slope: fell along the contour.
• Lean: trees tend to fall in the direction of lean.
• Obstacles: adjacency to trees, buildings, powers lines, etc. will
determine the direction of fall.
• Shape of crown: as for lean. The weight of the crown will likely dictate
the direction of fall.
• Wind direction: very important factor.

35. Before felling
• Remove branches on the base.
• Clear bushes around.
• Decide on direction of fall.
• Prepare an escape route, 45 degrees from the direction of fall.

37. Types of cuts
• Fore-cut (undercut) – horizontal
• Wedge cut – slanting at 45 degrees to the fore-cut
• Felling cut (back cut) – horizontal

39. Tree processing
• It is the conversion of the whole tree into commercial assortments
(saw logs, peeler logs, pulp logs, firewood, poles) for further
processing.
• Tree preparation includes delimbing, cross cutting and debarking.
• The aim is to deliver to the mill the most valuable part of the tree.
• By-products are normally left in-situ to decompose.

40. Delimbing/ debranching
• In spite of advancements in the harvesting technology, delimbing or
snedding or debranching requires a relatively high manual input.
• Mechanized operations are, however, in place to overcome the short
falls associated with chainsaws.
• Debranching machines include delimbers, chain flails and harvesters.
• In Malawi, mechanized delimbing is not yet in use.
• Manual (axes and machetes) and
• motor manual systems, depending on industrial scale, are present in
our forests.

41. The following tips apply:
• Cut limbs flash to the log (stem)
• Always start from the butt end
• Cut following the branch angle
• For branches, under the stem, roll or turn over the stem
• Stand on the opposite side to the cutting side.

42. Debarking
• This is the removal of bark.
• Debarking normally takes place at the mill.
• Debarkers are used to remove the bark.
• However, manual debarking is commonly done at the cut over, using
debarking spuds and axes in Eucalyptus poles.
• In some countries, bark is used as a nursery-growing medium.

43. Crosscutting
• Is done to provide assortments of the required lengths.
• The operation is commonly done at the landing side.
• Usually an over measure allowance is given (possibly 4 cm).
• The stem is assessed and marked so as to achieve maximum
productivity during conversion.
• During cross cutting, the following factors are considered:
• Taper, crookedness of the stem, whorls or monopodial knots in case of
Araucaria and Pinus pseudostrobus, and folked or multiple leaders.
• In hardwoods, some branches may be utilized.

44. • Crosscutting operations can also be shifted away from the
plantation to a central merchandising yard.
• Production rates at the central place of operations are normally
better than roadside operations for the following reasons:
• Typical delay times associated with roadside merchandising (waiting
for skidder, etc) are eliminated.
• Better underfoot conditions for chainsaw operators.
• Timber is raised off the ground.
• Less non-production time due to sharpening of chainsaws.
• More effective supervision is possible.
• Less congestion of people and machines.
• Walking distances are reduced.

46. EXTRACTION
• Is the process of moving trees or logs from the felling site by the most
convenient, economical and environmentally acceptable means to a
landing where the timber will be processed into logs or consolidated
into larger loads of transport to the final processing plant or user
(Dykstra & Heinrich, 1996).
• This is also known as primary transport. Primary transport can be
accomplished
• by aerial, cable or ground based harvesting systems

48. Ground based extraction
• Ground based extraction is commonly accomplished by making
use of skidding machines, forwarders, chutes, animals or
manual labor.
• The type of equipment required depends on the extraction
method to be employed and the machine to be used.
• The equipment travels from the landing or roadside to the
stump and returns with a payload of logs.
• The process requires that roads are located within an
acceptable skidding distance of the felling site.
• The terrain of the site must not be too deep or broken and the
site must have good soil bearing capacity

49. a. Manual extraction
• Involves the carrying, rolling or sliding of timber from a stump to a
strip road or forest road manually.
• In small diameter saw logs, and fuel wood and pole vending manual
extraction is common in Malawi.

50. b. Animal extraction (slipping)
• The use of draught animals is considered
to be environmentally friendly
• Animals used as draught power include
cattle, yaks, buffaloes, elephants, horses,
mules, donkeys, camels and Llamas
• Donkeys and oxen are mostly used in
southern Africa.

51. A comparison between donkey and oxen:
• Donkeys move faster than oxen
• A Donkey can haul slightly heavier loads than an oxen
• Donkeys require less rest than oxen
• Can work on steeper slopes than oxen
• Donkeys can be spanned singly
• Less susceptible to disease than horses / oxen
• Have longer service life than oxen.

52. c. Chute extraction
• A chute is a channel system which has been
developed to transport timber by guiding it down a
slope to roadside or a landing, from where it is
easily accessible to other means of transport
• A chute line consists of round or half pipes joined
end to end, forming a continuous channel
• The logs are fed into the chute manually and, by
force of gravity, side down the chute to a
designated landing
• Chutes may be constructed from steel, timber or
plastics.

53. The use of chutes has the following advantages:
• Low capital investment
• Relatively simple concept
• Minimal maintenance required
• Low environmental impact
• Minimum damage to remaining trees if used in a thinning
operation
• Improved productivity if compared to manual extraction

54. Potential disadvantages include:
• Logs are presented in untidy fashion at roadside.
• The exit of logs can be very dangerous.

55. d. Skidding machines
• Skidding is the process where the timber is attached to an extraction
unit, lifted at one end, and dragged along the ground to the landing
site
• “Skidding” normally refers to the dragging of timber with machines,
while the term “slipping” refers to extraction by animals
•
• There are no strict requirements for forestry equipment since there is
such a diverse number of extraction methods and machines to
choose from

56. • However, in the optimum case, forestry
equipment for skidding operations include
the following:
• Winch, grapple or clambunk, for holding
and pulling the timber
• Front mounted blade for stacking tree
lengths and small grading operations
• Safety cabin and safety equipment of the
operator
• Protection plates and gear to protect the
vehicle
d. Skidding machines

57. Agricultural tractors
• Tractors are characterized by the following:
• High clearance (from 38 – 50 cm) above ground
• Have power take off (PTO) shields for driving
winches, mills, etc.
• Have 3 – point systems
• A trailer can be towed for skidding
• Can be used for ploughing
• Have good speed, around 30 km/hr.

58. Skidding methods with Agricultural tractors
• Direct skidding – makes use of an angle iron –
“A frame” mounted on a 3 – point system.
• It can be lifted hydraulically.
• One of the angle iron pieces has grooves or
slots.
• The system works together with a chain, which
is used for choking the butt ends of the logs.

59. Skidding methods with Agricultural tractors
• Winch skidding – Makes use wire ropes
of diameter 8 - 11 mm, 40 – 550 m long
• Can pull loads of 3000 to 8000 kg
• The winching speed varies from 0.3 – 61
m/s
• Other fittings do allow for grapple
skidding.

60. Skidders
• Skidders are mainly used by large harvesting contractors and bigger
timber companies
• The purchase cost and the machine cost per hour is relatively high
Skidders have higher work performance
This is, however, achieved under the following conditions:
• High annual utilization is reached.
• Efficient planning and organization of the operation occurs.
• Operation is optimum in terms of wood size and terrain conditions.

61. Skidders
• Skidders have high ground clearance of about 45.7 cm from the
ground
• They are highly powerful machines
• Can be fitted with high floatation tires for less pressure on the ground
• They have bulldozer blades fitted at the front for log piling, clearing
the surroundings and maintaining machine stability.

62. Wheeled skidders (articulated units)
• Three wheeled skidder configurations,
based on the extraction machine fitted to
the machine are cable, grapple and
clambunk
• Articulated steering (also known as frame
steering) is accomplished by bending the
vehicle about a pivotal point with
hydraulic cylinders
• Articulated skidders are the most
commonly used machines in southern
Africa

63. Cable skidders
• Timber is attached, means of a light chokers, a main cable attached,
single or double drum, winch at the rear of the skidder.
• Double drum winches are ideal for skidding small diameter long
lengths.
• By winching in the main cable, trees are drawn together with their
forward ends (top – butt-end) raised off the ground, under the
integral fairlead arch at the rear of the tractor.

64. Cable skidders have the following features:
• Flexibility - can be used in a wide variety of terrains.
• Relatively inexpensive compared to forwarders, grapple and clambunk
skidders of similar engine power.
• Loading and unloading times are very long.
• The operator must dismount 2-3 times per load or have one or more
assistants.
• Load is dragged through sand and mud, creating problems at the landing
site and the sawmill.
• Operator training is easier than for clambunk skidders, grapple skidders
and forwarders.
• Usually travel faster than forwarders.

65. Cable skidders have the following features
• Performance is better than grapple and clambunk skidders on wet
ground (load can be dropped and re-winched).
• Pay load / operating weight = 0.30 – 0.6
• Better stability on side slopes and rough terrain
• Generally versatile in their mode of operation.

66. Grapple skidders
• Grapple skidders have the following features:
• Suitable for larger and bunched timber
• Operator needs not dismount during each load
• No extra assistants (chokermen) and loose accessories (chokers,
tag lines, wire ropes, etc) required.

67. Grapple skidders
• Same dirt problems as cable skidders
• The load location, far behind the rear axle, creates a very
unfavourable load distribution, which greatly reduces the potential
load capacity and skidder life
• Pay load / operating weight = 0.15 – 0.25
• Self-loading.

68. Clambunk skidders have the following
features
• Large payloads (5 – 15 m3 of tree length or full trees) make longer
forwarding distances economical.
• Payload / operating weight = 0.60 – 0.70.
• Self loading.
• Carries 60 – 80% of the load, thus delivering (on average) cleaner
wood.

69. Clambunk skidders have the following
features
• Long loading times (5 – 15 minutes)
• More complexes loader and loading operations (longer training
required and lower reliability)
• High purchase costs
• High ground pressure at the front wheels.

70. Tracked skidders and Forwarders
• Tracked skidders and forwarders have the
following features:
• Low centre of gravity.
• Steel road wheels on torsion arms that move
and down in relation to the ground underneath.
• Driven from the front, compared to the rear
driven crawler tractor, resulting in less stress on
the ground.
• Very mobile, can turn 3600 times in virtually its
own length

71. Introduction to forest Engineering

72. Values
• The environmental and commercial values of natural renewable
resources should be balanced to ensure optimum utilisation and
sustained yiield of timber
• Development of appropriate management guidelines aimed at
balancing the environment and commercial values is therefore very
important
• The guidelines development process should ensure that the following
aspects are covered:

73. Steps in guideline development
• Outline what you are are trying to protect
• Determine the step that you need to follow to ensure efficient
protection of the aspects you want to protect
• Usually site and social considerations are the two key aspects that are
considered when deciding what to protect
• As regards how to protect site aspects, site classification, roads,
extraction routes, depots, landings and general timber harvesting
aspects are considered

74. Site considerations
• Soil quality and quantity
• Nutrient status
• Forest health
• Water quality and quantity
• Stream habitat
• Channel stability
• Biodiversity

75. Social considerations
• Economics
• Cultural values
• Occupational health
• Safety
• Legislation
• Recreation
• Public perceptions
• Research values

76. How to protect the site aspects
• Soil and water
identify and map all the special management zones in your forest entity
including hydrologically and highly erodible soils
classify vehicles and choose systems to suit the terrain, soil sensitivity,
growing stock and weather conditions
Appropriately design and maintain forest roads
use designated extraction routes
use of geo-fabrics or branches when sensitive areas need to be traversed

77. How to protect the site aspects
• Soil and water
avoid areas with wetness hazard
rehabilitate compacted areas
 institute soil erosion and soil compaction reduction measures
situate extraction routes, landings and depots outside of wetland areas
Machine-terrain matching
• Once all measures are established, monitor to ensure success

78. • Encourage self improvement amongst the labour force
• Provide training and retaining
• Adhere to safe working procedures
• Evaluate ergonomic status of equipment
• Maximize profits by optimising value recovery through the application
of sound harvesting practices and considering other important values
How to protect social aspects

79. Introduction to Forest Road Construction

80. Why are forest roads important?
• Road construction in a forest setup are very complex engineering
structures
engineering design
field layout
construction
maintainance
• Forest roads are not only important for extraction of wood, but also
provide access to forest for management, development, conservation,
and protection purposes
• Road infrastructure development is thus complex

81. General perception of society about forest roads?
• Overall, the improved road network developed primarily for the forest
interprise may be a key element in the economic development of an
area
• However, forest roads also have potential for disrupting ecosystem
services e.g. Disruption of hydrology by diverting subsurface flows to
surface flows and hence increasing runoff
• Roads can also alter wildlife both terrestrial and aquatic
• Can also open up forest areas to illegal harvesting

82. What do foresters say
• Properly designed, constructed and maintained roads provide convenient, low-cost
access to forest products and serve the needs for forest management conservation and
protection
• Revenue generated from a forest enterprise provides much needed resources to
enhance long term sustainable forest amangement
• Roads do create a highly visible impact on the landscape, but they probably are not a
direct cause of forest loss; rather they are the agent of change
• The overharvesting of high-valued species, excessive damange to the residual stands,
overharvesting of fuelwood, illegal logging
• The challenge is therefore to find appropriate ways to plan, locate, design, and maintain
the roads to maximize the benefits while controlling direct envirnmental impacts

83. Characteristics of forest roads
• Unlike public roads, forest roads serve special purpose of offering
efficient access for heavy vehicles associated with timber production
• The experience low traffic volumes
• Frequent access to long heavy trucks
• Usually traversed by loaded tracks travelling mostly in one direction
• Characteristics of different road sections depends on its function in
the road system
• At its extreme points, the forest road is an extension of a harvesting
system

84. Key aspects to consider when planning roads
• Design vehicle
• The design vehicle is a frequent user of a
given road and dictates the minimum
required turning radius
• In forestry, log-transporting trucks
normally determines the design of a
road
• Always aim to find the design which
results in lowest total cost of design,
construction, and maintainance while
providing for safe operation and
environment protection

85. Road Standards
Terminology:
• Travel way
• Shoulder
• Subgrade
• Surface course
• Roadside ditch
• Intercept

86. • Travel way: This refers to the road surface design width designated for
vehicle travel, both travel lanes of a double-lane road, or a single-lane
width on a single-lane road
• Shoulder: The designated road shoulder width specified in a design, or any
width in excess of the travel way width available as a usable shoulder
adjacent to the travel way
• Subgrade: The road surfacing foundation
• Base course: The layer of material above the subgrade that supports the
weight of a traffic. On roads with only one layer on top of the subgrade, the
layer has a dual function; providing for vehicle support and the vehicle
running surface

87. • Surface course: The top layer of the travel way that provides a
running surface for vehicles
• Roadside ditch: The ditch constructed at the bottom of a back slope
parallel to the road subgrade for the purpose of keeping water out of
the subbase or improved soil layer, collecting road-surface and cut-
bank runoff water
• Intercept or catchwater ditch: A ditch located above a cut bank to
collect runoff water and divert it from cut banks that will erode
• Subdrains: Any form of drain placed within the subgrade or under a
roadside ditch for the purpose of collecting and removing
underground water
• Cross slope: A general term for either the crown or the
superelevation (degree of banking) of travel ways and/or shoulders

88. Forest road classification
• Access roads: these are permanent transport links between the forests and
public roads. They are usually all weather roads
• Main forest roads: These constitute branch roads, forest truck roads and
they form the basic forest road network. They usually require higher-
standard construction
• Secondary forest roads: These constitute feeder roads used for connecting
lines in the forest from the landings to the main roads
• Terrain truck roads: roads that are specially built for all-wheel-drive, off-
rod truck use and are low standard
• Skid roads: these are temporary earth roads between the trees for skidding
and forwarding from felling site to landing constructed along a secondary
forest road

89. Economic basis for forest road construction
• In order to determine the most economical alignment, standard, and
density of the road system, it is necessary to be able calculate the
cost of the vehicles which use the roads and the cost of the roads
themselves
• The optimal design is one that minimises the combination of logging,
transport, construction, and maintenance costs while providing for
safe operation and controlling environmental impacts

90. Determination of truck costs
• The operating cost of a truck is the sum of several components:
Depreciation
Interest on average investment
Insurance
Annual taxes
Operating labour
Fuel
Oil and lubricants
Servicing and repairs
Tyres

91. Determination of road construction and
maintenance costs
• Understanding road construction and maintenance costs is important
to evaluate roading strategies including:
Alternative choices of road location
Tradeoffs between harvesting costs and roading costs
Choices of road standards
Choice of transport mode
Selection of dryseason and wet season harvesting areas

92. Selection of road spacing
• A harvesting manager is responsible for calculating both skidding
costs and road construction costs
• Placing roads too close together, although good for production, is not
good for overall costs
• No discussion of log skidding is complete without an introduction to
the spacing of roads to minimize the sum of road and skidding costs
• When using a specific skidding or forwarding machine, there is a road
density ( metres per hectare) or spacing which will result in the
lowest combined cost of constructing roads and skidding/forwarding

93. Optimum road spacing
• Road spacing is the more practical guide for a forest engineer laying out a
road network in a forest
• ORS = k*
40𝑅𝐿
𝑞𝑐𝑡(1+𝑝)
• Where ORS is expressed in metres; R is the cost per kilometre of
constructing and mainting a road; L is the average skidder or forwarder
load in cubic metres, q is the quantity of wood harvested expressed in
cubic metres per hectare; c is the operating cost per minute of skidder or
forwarder including operator, t is the time in minutes for the skidder or
forwarder to travel 1 m loaded and return 1 m empty, k is a correction
factor, with a normal value between 1.0 and 0

94. Optimum road density
• Having determined the ORS, the ORD can be found with the formula
• ORD =
10000
𝑂𝑅𝑆
• Where ORD is in metres per hectare and ORS is in metres

95. Example
• What is the optimal road spacing if the road construction cost is
$10,000 per kilometre, the average skidder load is 4 m3, the volume
to be harvested is 30 m3/ha, the operating cost is $0.80 per minute,
and the skidder travels 5 km/hr unloaded and 3 km/hr loaded?
Skidding is equidistant from each side and a correction factor of 0.2 is
used to account for delays.

96. Route selection
• Step 1: Examination of general information from maps, aerial
reconnaissance, and aerial photographs to select a proposed route
corridor
• Step 2: Draw up preliminary alignments using information collected
• Step 3: Detailed ground reconnaissance to locate preliminary
alignment possibilities
• Step 4: Establish the final alignment by correcting the prelimanry one
using information gained by the ground reconnaissance
• Step 5: Mark out and stake the selected alignment with regard to the
actual ground conditions to guide construction

97. Compass-Step-Method

98. What it is used for
• Design tool for forest roads
• Ensuring a uniform gradient
• Joins positive cardinal points and stays clear of negative cardinal
points
• Also by other names
• Assumption is made that all preparatory planning has been done

99. 1st Steps
• Maps
• Scale (1: 5000 or 1: 10 000)
• Showing contours (5 or 10 m)
• Cardinal points
• Positive (e.g. Start and Finish )
• Negative (e.g. SMZ’s)
• Corridors marked out

100. Zero-line
• If a gradient is considered:
• 1st step is to place a zero-line
• Depicts a desired gradient
• Is not the same as a smooth axis
• Fixes the course of the proposed road
• Use maps, air photos etc. to recognize any major obstructions
• Test various options

101. Gradient
• Decide on the gradient required
• Terrain
• Transport Equipment
• Environment
• Erosion
• Usually between 2 and 12 %

102. What is not desired
• A gradient that is not constant
A
B
Usually 2-12%

103. Trigonometry Revision
Hypotenuse (h)
Opposite (o)
Adjacent (a)
Sin α = o/h
Tan α = o/a
Cos α = a/h
α Always the
contour
interval

104. Formulas
Where D = horizontal distance between given cardinal (+ ve) points, and the
min and max gradients (%) are given.

105. Recording Sheet

106. Table for 5 and 10 meter contours
Slope Divider/Compass width (m)
Percent Degrees 5m contours 10m contours
1 0.6 500.0 1000.0
2 1.1 250.0 500.0
3 1.7 166.7 333.3
4 2.3 125.0 250.0
5 2.9 100.0 200.0
6 3.4 83.3 166.7
7 4.0 71.4 142.9
8 4.6 62.5 125.0
9 5.1 55.6 111.1
10 5.7 50.0 100.0
11 6.3 45.5 90.9
12 6.8 41.7 83.3
13 7.4 38.5 76.9
14 8.0 35.7 71.4
15 8.5 33.3 66.7
16 9.1 31.3 62.5

107. Shown graphically

108. Around Weza Sawmill Complex

109. Zoomed in
Contour intervals=10m

110. Cardinal points
Contour intervals=10m
Finish
Start

111. Distance
Contour intervals=10m
Finish
Start
675m

112. Difference in elevation
Contour intervals=10m
Finish
Start
1080
950

113. Calculations
• Gradient = 130*100/675= 19.3 %
• Dmax=130*100/2=6500m
• Dmin=130*100/12=1083m

114. Therefore
• Use the compass-step-method to plot the zero-line
• Thereafter smooth the axis and design the curves (prefer level areas )
• Gives a good approximation
• Walk the course on the ground, if one meets with any obstruction,
then redraw on the map using a different gradient, and walk again.

115. Demonstration

116. Road Building Materials
• Surface layer: As a rule it is made of bituminous binder to which the
wheels adhere well
• Base layer: The road base should be 10 -20 cm in thickness. It should be
resistant to all vertical and lateral forces exerted upon it and be dense and
cohesive
• Subbase: The subbase, which is thicker than the road base, and which has
to resist moderate vertical forces, is generally made from a cohesionless
material
• It is also possible to place a lower layer between the subbase and the natural earth
to stop water rising by capillarity from a water table and drain away water infiltrating
from above
• In practice, this succession of three layers of material is not found in forest
roads which have been made of compacted soils

117. Road drainage structures
• Water is the principal destructive agent of the road
• When constructing roads, ensure that there is a crown in the road of
3 -4 cm / m to eliminate standing water which causes the road to
break up under heavy roads
• Ditches are used to collect water falling on the road and carry it
toward the streams or rivers

118. Road drainage structures
• Side ditches
• Drainage outlets
• Catchwater or intercepting ditches
• Culvert under the roadway
• Dips or rolling grades

119. Road drainage structures
• Side ditches
• These collect water which falls on the road as well as reduce the
water table in the vicinity of the ditch
• The camber of the road is designed for runoff of water toward the
side ditches

120. Road drainage structures
• Drainage Outlets
• These carry water in the side ditches toward the natural drainage
channels
• The more drainage outlets the better, particulary if the road gradient
is steep
• To avoid the silting up of an outlet, it should have a steeper sloe than
the adjoining side ditch
• Construction is carried out at the same time as that of the ditches

121. Road drainage structures
• Catchwater Ditches
• These are made above a cut to stop the water before it reaches the
face of the cut slope and to lead it to a drainage channel, preventing
it from reaching the road
• The size depends on the steepness of the slope situated above it
• It should not be constructed too close to the top of the cut slope to
prevent possible seepage

122. Road drainage structures
• Culverts
• Carry water across the road in order to drain a side ditch
• When there is no culvert, the water must pass over the road during
storms
• The road then acts as spillway, sometimes leading to a rut in the road
• Culverts can be built of different materials of varying durability
according to the length of time it is expected that the road will be sue
and the materials available
• Hollow logs, rejected sawmill planks, salvaged metal pipes, or pipes
made from cement, steel, or plastic

123. Road drainage structures
• Dips or rolling grades
• Where cross-drain culverts are not possible, dips are used
• Drainage dips work well for taking surface runoff of outsloped roads
without a ditch
• A surface of crushed rock should be placed on the dip and mound for
soils and conditions where rutting may occur

124. Forest Road Maintenance
• The purpose of road maintenance is to:
• protect the road sturcture
• permit safe travel
• maintain truck transport productivity
• minimize the adverse impacts to water quality, fish habitat, wildlife etc
• The appropriate maintenance cycle depends on the level of traffi,
season of use, grade, alignment and surfacing type

125. Forest Road Maintenance
• The maintainance levels are measured by visual inspection of the
drainage systems and road surface and road roughness
measurements
• The key factor to road performance is maintenance of drainage
system
• This consists of maintaining and restoing the road crown and surface,
ditch, and culvert cleaning
• Other road maintenance activities include clearing bush on the right
of way to improve sight distance, applying dust abatement, and
resurfacing

126. Forest Road Maintenance
• The basis for the development of a road maintenance plan is a
thorough understanding of the road system, its characteristics and
needs
• This involves establishing and maintaining an inventory of the road
system
• Inventory provides information necessary for identifying and
prioritizing required maintenance
• In addition, the inventory also provides the basis for development of
road improvement plans

127. Aspects of Forest Ergonomics during Forest
Harvesting Operations

128. ERGONOMICS
• The word ergonomics is derived from the Greek words ‘ergon’ (work)
and ‘nomos’ (law).
• A concise definition would be that ergonomics aims to design
appliances, technical systems and tasks in such a way as to improve
human safety, health, comfort and performance.
• The formal definition of ergonomics, approved by the International
Ergonomics Association (IEA) is as follows:

129. Definition of ergonomics
• Ergonomics (or human factors) is the scientific discipline concerned
with understanding of interactions among humans and other
elements of a system, and the profession that applies theory,
principle, data and methods to design, in order to optimize human
well-being and over system performance.

130. • In the design of work and every day life situations, the focus of
ergonomics is man.
• Unsafe, unhealthy, uncomfortable or inefficient situations at work or
in everyday life are avoided by taking account of the physical and
psychological capabilities and limitations of humans.
• A large number of factors play a role in ergonomics; these include
body posture and movement (sitting, standing, lifting, pulling and
pushing), environmental factors (noise, vibration, illumination,
climate, chemical substances), information and operation
(information gained visually or through other senses, controls,
relation between displays and control), as well as work organization
(appropriate tasks, interesting jobs).

131. Application of ergonomics
• Ergonomics differs from other fields by its interdisciplinary
approach and applied nature.
• The interdisciplinary character of the ergonomic means
that it relates to many different human facets.
• As a consequence of its applied nature, the ergonomic
approach results in the adaptation of a workplace or
environment to fit people, rather than the other way
round.

132. Social significance of ergonomics
• Ergonomics can contribute to the solution of a large number of social problems related to safety,
health, comfort and efficiency.
• Daily occurrences such as accidents at work, in traffic and at home, as well as disasters involving
cranes aeroplanes and nuclear power stations can often be attributed to human error.
• From the analysis of these failures it appears that the cause is often a poor and inadequate
relationship between operators and their task.
• The probability of accidents can be reduced by taking better account of human capabilities and
limitations when designing work and everyday life environments.

133. • Many work and everyday life situations are hazardous to health.
• These conditions can be partly ascribed to poor design of equipment, technical
systems and tasks.
• Here, too, ergonomics can help reduce the problems by improving the working
conditions.
• Finally, ergonomics can contribute to the prevention of inconveniences and also,
to some considerable degree, can help to improve performance.
• Some ergonomic knowledge has been compiled into official standards whose
objective is to stimulate the application of ergonomics.
• For instance, a range of ergonomic subjects is covered by the Organisation for
International Standardisation (ISO).
• In addition, there are specific ergonomic standards, which are applied in individual
companies and in industrial sectors.

134. POSTURE AND MOVEMENT
• Posture and movement play a central role in ergonomics.
• The body’s muscles, ligaments and joints are involved in
adopting a posture, carrying out a movement and applying
a force.
• A number of principles of importance to the ergonomics of
posture and movement derive from a range of specialists
fields, namely biomechanics, physiology and
anthropometrics.

135. Factors of biomechanical background:
• Joints must be in a neutral position.
• Keep the work close to the body.
• Avoid bending forward.
• A twisted trunk strains the back.
• Sudden movements and forces produce peak stress.
• Alternate posture as well as movements.
• Limit the duration of any continuous muscular effort.
• Prevent muscular exhaustion.
• More frequent short breaks are better than a single long one.

136. Factors of physiological background
• Estimates are made of the energy demands of the heart and lungs resulting from
muscular effort during movements.
• General body fatigue can develop from carrying out physical tasks over a long
period.
• The limiting factor here is the amount of energy, which the heart and lungs can
supply to the muscles to allow postures to be adopted or movements to be
carried out.
• Below are some of the factors:
• Limit the energy expenditure in a task.
• Rest is necessary after heavy tasks.

137. Factors of anthropometric background
• Anthropometry is concerned with the size and proportions of the
human body.
• A few anthropometric principles of importance to the ergonomics of
posture and movements are:
• Take account of differences in body size i.e. height and fatness.
• Use the anthropometric tables appropriate for specific populations.
• The heights of the work surface, seat and feet must be compatible.