The
harvester is a type of heavy vehicle employed in
cut-to-length loggingCut-to-length logging is a mechanized harvesting system in which trees are delimbed and cut to length directly at the stump. CTL is typically a two-man, two-machine operation with a harvester felling, delimbing, and bucking trees and a forwarder transporting the logs from the felling to a landing...
operations for felling,
delimbingLimbing in logging is the process of removing branches from the stem of a felled tree. Options for cutting off the branches include chain saws, harvesters, stroke delimbers and other options...
and
buckingthumb|right|Bucker measuring and swamping or knot bumpingthumb|right|Oregon Bucker - Making the CutBucking is the process of cutting a felled and delimbed tree into logs...
trees. A harvester is typically employed together with a
forwarderA forwarder is a vehicle that carries logs from the stump to a roadside landing. Unlike a skidder, a forwarder carries logs clear of the ground, which can reduce soil impacts but tends to limit the size of the logs it can move...
that hauls the
logLog may refer to:*Chip log, a device used in navigation to estimate the speed of a vessel through water.*Data log, a record of sequential data*Laplacian of Gaussian*Log , an architectural magazine...
s to a roadside landing.
Harvesters were mainly developed in
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
and
FinlandFinland , officially the Republic of Finland
, is a Nordic country and democracy situated in the Fennoscandian region of northern Europe. It borders Sweden on the west, Russia on the east, and Norway on the north, while Estonia lies to its south across the Gulf of Finland...
and today do practically all of the commercial felling in these countries. The first single grip harvester head was introduced in the early eighties by Swedish company SP Maskiner.
The
harvester is a type of heavy vehicle employed in
cut-to-length loggingCut-to-length logging is a mechanized harvesting system in which trees are delimbed and cut to length directly at the stump. CTL is typically a two-man, two-machine operation with a harvester felling, delimbing, and bucking trees and a forwarder transporting the logs from the felling to a landing...
operations for felling,
delimbingLimbing in logging is the process of removing branches from the stem of a felled tree. Options for cutting off the branches include chain saws, harvesters, stroke delimbers and other options...
and
buckingthumb|right|Bucker measuring and swamping or knot bumpingthumb|right|Oregon Bucker - Making the CutBucking is the process of cutting a felled and delimbed tree into logs...
trees. A harvester is typically employed together with a
forwarderA forwarder is a vehicle that carries logs from the stump to a roadside landing. Unlike a skidder, a forwarder carries logs clear of the ground, which can reduce soil impacts but tends to limit the size of the logs it can move...
that hauls the
logLog may refer to:*Chip log, a device used in navigation to estimate the speed of a vessel through water.*Data log, a record of sequential data*Laplacian of Gaussian*Log , an architectural magazine...
s to a roadside landing.
History
Harvesters were mainly developed in
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
and
FinlandFinland , officially the Republic of Finland
, is a Nordic country and democracy situated in the Fennoscandian region of northern Europe. It borders Sweden on the west, Russia on the east, and Norway on the north, while Estonia lies to its south across the Gulf of Finland...
and today do practically all of the commercial felling in these countries. The first single grip harvester head was introduced in the early eighties by Swedish company SP Maskiner. Their use has become widespread throughout the rest of Northern Europe, particularly in the
harvestingLogging is the process in which certain trees are cut down for forest management and timber.In forestry the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard. In common usage...
of
plantationA plantation is a large farm or estate, usually in a tropical or subtropical country, where crops are grown for sale in distant markets, rather than for local consumption. The term plantation is informal and not precisely defined....
forests.
Uses
Harvesters are employed effectively in level to moderately steep terrain for clearcutting areas of forest. For very steep hills or for removing individual trees, humans working with chain saws are still preferred in some countries. In northern Europe small and manoeuvrable harvesters are used for
thinningThinning is a term used in agricultural sciences to mean the removal of some plants, or parts of plants, to make room for the growth of others.- Forestry :...
operations, manual felling is typically only used in extreme conditions, where tree size exceeds the capacity of the harvester head or by self-employed forest owners.
The principle aimed for in mechanised logging is "no feet on the forest floor", and the harvester and forwarder allow this to be achieved. Keeping humans inside the driving cab of the machine provides a safer and more comfortable working environment for industrial scale logging.
The leading manufacturers of harvesters are
TimberjackTimberjack was a manufacturer of forestry machinery for both cut-to-length and whole tree logging who have been a subsidiary of John Deere since 2000. Timberjack was owned by the Eaton Corporation in the 1960s, 1970s and early 1980s...
(owned by
John DeereDeere & Company, usually known by its brand name John Deere , is an American corporation based in Moline, Illinois, and the leading manufacturer of agricultural machinery in the world. In 2008, it was listed as 102nd in the Fortune 500 ranking...
),
ValmetValmet Oy was a Finnish state-owned company. Valmet was formed in 1951, when the state of Finland decided to group their various factories working on war reparations to the Soviet Union under one company...
(owned by Komatsu) and Ponsse.
Harvesters are built on a robust all terrain vehicle, either
wheelA wheel is a circular device that is capable of rotating on its axis, facilitating movement or transportation whilst supporting a load , or performing labour in machines. Common examples are found in transport applications. A wheel, together with an axle overcomes friction by facilitating motion by...
ed or
trackedContinuous tracks are large tracks used on the so-called caterpillar tanks, construction equipment and certain other off-road vehicles. Unlike the Kégresse tracks which use a flexible belt, most continuous tracks are made of a number of rigid units that are joined to each other...
. The vehicle may be articulated to provide tight turning capability around obstacles. A
diesel engineA diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression...
provides power for both the vehicle and the harvesting mechanism through
hydraulic driveHydraulic machinery are machines and tools which use fluid power to do work. Heavy equipment is a common example.In this type of machine, high-pressure liquid — called hydraulic fluid — is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders...
. An extensible, articulated boom, similar to that on an
excavatorAn excavator is a heavy equipment consisting of an articulated arm , bucket and cab mounted on a pivot atop an undercarriage with tracks or wheels...
, reaches out from the vehicle to carry the
harvester head. Some harvesters are adaptations of excavators with a new harvester head, while others are purpose-built vehicles.
"Combi" machines are available which combine the felling capability of a harvester with the load-carrying capability of a forwarder, allowing a single operator and machine to fell, process and transport trees. These novel type of vehicles are only competitive in operations with short distances to the landing.
Felling head
A typical harvester head may consist of (from bottom to top, with head in vertical position)
- a chain saw to cut the tree at its base, and also cut it to length. The saw is hydraulically powered, rather than using the 2-stroke engine
A two-stroke engine is a combustion engine that completes the thermodynamic cycle in two movements of the piston compared to twice that number for a four-stroke engine. This increased efficiency is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to...
of a portable version. It has a more robust chain, and a higher power output than any saw that can be carried by a human.
- two or more curved delimbing knives which reach around the trunk to remove branches.
- two feed rollers to grasp the tree. The wheels pivot apart to allow the tree to be embraced by the harvester head, and pivot together to hug the tree tightly. The wheels are driven in rotation to force the cut tree stem through the delimbing knives.
- diameter sensors to calculate the volume of timber harvested in conjunction with
- a measuring wheel which measures the length of the stem as it is fed through the head.
All of this can be controlled by one operator sitting in the cab of the vehicle. A control
computerA computer is a machine that manipulates data according to a set of instructions.Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century . These were the size of a large room, consuming as...
can simplify mechanical movements and can keep records of the length and diameter of trees cut. Length is computed by either counting the rotations of the gripping wheels or, more commonly, utilising the measuring wheel. Diameter is computed from the pivot angle of the gripping wheels or delimbing knives when hugging the tree. Length measurement also can be used for automated cutting of the tree into predefined lengths. Computer software can predict the volume of each stem based on analysing stems harvested previously. This information when used in conjunction with price lists for each specific log specification enables the optimisation of log recovery from the stem.
Harvesters are routinely available for cutting trees up to 900 mm in diameter, built on vehicles weighing up to 20 t, with a boom reaching up to 10 m radius. Larger, heavier vehicles do more damage to the forest floor, but a longer reach helps by allowing more trees to be harvested with fewer vehicle movements.
The approximate equivalent type of vehicle in full-tree logging systems are feller-bunchers.
External links