Harvester (forestry)
A harvester is a type of heavy forestry vehicle employed in cut-to-length logging
Cut-to-length logging
Cut-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, delimbing
*An extension or projecting part of a tree.When the tree is lying on the ground, branches may be storing enormous potential energy through mechanical strain. When a branch is cut, often with a chain saw, this energy can be released suddenly and the branch can jump dangerously. In addition, a branch...

 and bucking
Log bucking
thumb|right|Bucker measuring and swamping or knot bumpingthumb|right|Bucker - Making the CutBucking is the process of cutting a felled and delimbed tree into logs...

 trees. A forest harvester is typically employed together with a forwarder
A forwarder is a forestry vehicle that carries felled 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 logs
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.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...

 to a roadside landing.


Forest harvesters were mainly developed in Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 and Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

 and today do practically all of the commercial felling in these countries. The first fully mobile timber "harvester", the PIKA model 75, was introduced in 1973 by Finnish systems engineer Sakari Pinomäki
Sakari Pinomaki
Sakari Pinomäki was a Finnish systems engineer, who pioneered the mechanized forestry industry. He was the founder of PIKA Forest Machines which produced the first purpose-built forest machine in 1964 in Ylöjärvi, Finland.-History:...

 and his company PIKA Forest Machines. The first single grip harvester head was introduced in the early 1980s by Swedish company SP Maskiner. Their use has become widespread throughout the rest of Northern Europe, particularly in the harvesting
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.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...

 of plantation
A plantation is a long artificially established forest, farm or estate, where crops are grown for sale, often in distant markets rather than for local on-site consumption...


Before modern harvesters were developed in Finland and Sweden, two inventors from Texas developed a crude tracked unit that sheared off trees at the base up to 30 inches in diameter was developed in the US called The Mammoth Tree Shears. The operator after shearing off the tree could with the movement of his controls cause it to fall either to the right of left. Unlike a harvester, it did not delimb the tree after felling it.


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 thinning
Thinning 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 small woodlot 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 Timberjack
Timberjack 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.-History:Timberjack was owned by the Eaton Corporation in the 1960s, 1970s and early 1980s...

 (owned by John Deere
Deere & Company
Deere & 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 2010, it was listed as 107th in the Fortune 500 ranking...

), Valmet
' was a Finnish state-owned conglomerate. 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 wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

ed or tracked
Caterpillar track
Continuous tracks or caterpillar tracks are a system of vehicle propulsion in which modular metal plates linked into a continuous band are driven by two or more wheels...

. The vehicle may be articulated to provide tight turning capability around obstacles. A diesel engine
Diesel engine
A 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...

 provides power for both the vehicle and the harvesting mechanism through hydraulic drive
Hydraulic machinery
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...

. An extensible, articulated boom, similar to that on an excavator
Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform . The house sits atop an undercarriage with tracks or wheels. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the...

, 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 consists 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
    Two-stroke cycle
    A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft...

     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 computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 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, using 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

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