The following points highlight the four main equipments that are used for logging. The equipments are:- 1. Felling Equipments 2. Extraction Equipments 3. Processing Equipments 4. Loading Equipments.
1. Felling Equipments:
Where harvesting is done manually most of the operations are done by the axe, saws and billhooks. Modern logging equipments have now replaced them because of their high efficiency and are widely utilized in commercial forestry.
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i. Chain Saw:
Chain saws are the most commonly used equipment for felling and delimbing. It is powered by diesel, hydraulic or electric motor and has a saw with a loop of chain that is pulled around a bar which rotates at a high speed. The chain contains cutting teeth that are capable of sawing wood. A chainsaw can be used to fell and process trees.
Chains come in a variety of pitches (the distance between the rivets in the chain), gauges and cutter teeth and a range of power sizes and bar lengths. Though the operations are faster while using chain saws, proper safety measures have to be ensured due to the inherent dangers associated with the working. The greatest advantage of chain saws is that felling is generally not limited by slope or soil conditions.
ii. Harvester:
“Harvester” is a commonly used term in forestry. It refers to a machine that fells, delimbs and bucks trees into logs. It is the first of a pair of machines, the second being a forwarder, that jointly makes the mechanized “cut-to-length” (CTL) system. It is a 4 or 6 wheeled articulated machine used to fell trees, remove branches and cut the logs to required lengths which help to maximize the value of the end product.
It is a heavy machine powered by diesel engine and is usually fitted with a hydraulic loader onto which a harvester head is mounted. A harvester head consists of a hydraulically powered chain saw, two or more curved de limbing knives which reach around the trunk to remove branches, feed rollers to grasp the tree and to move the tree through the head, diameter sensors to calculate the volume of timber harvested and a measuring wheel to measure the length of the stem as it is fed through the harvesting head.
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The whole harvesting process is controlled by an on-board computer and an operator sitting in the cab of the vehicle. Harvesters are mostly employed for cut-to-length logging operations, for felling, delimbing and bucking trees.
The standard cut-to-length logging system consists of a harvester, forwarder and self- loading trucks. This system contains relatively few types or number of equipment, but the harvester and forwarder are very expensive to purchase and operate. A forest harvester is mostly used along with a forwarder that hauls the logs to a point from where it is finally transported outside the forests.
The major limitation of harvesters is that it can be employed effectively only on level grounds and moderately steep terrains and not on very steep terrains and undulating surfaces. They are most effective for clear felling of even aged uniform stands and is seldom used for selective felling and in mixed stands. They operate best in forests consisting of single stem soft wood species such as conifers, aspen and birch. They are not suitable for hardwood species with multiple merchantable stems.
Harvesters may be tracked or wheeled. Tracked harvesters can operate on slopes up to 55 per cent and wheeled harvesters are generally limited to less than 40 per cent slope. For very steep hills and for felling individual trees chain saws are more preferred. Operating on steep slopes is risky and may cause roll over of the machine.
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For productivity reasons, harvesters are being widely used and prototype machines like walking harvesters or steep terrain harvesters are put to use in steep unfriendly terrains. The size of the tree that can be felled and processed is also limited by the capacity of the cutting head and the weight of the machine. Harvesters are not very effective to fell and process large trees with multiple merchantable stem.
iii. Feller Buncher:
It is a motorized vehicle which runs on tracks or wheels, with an attachment that can rapidly cut and gather several trees before felling them. It is a type of harvester with a cutting head that can hold more than a single tree at a time. The cutting head is not only used for cutting but also for holding and placing the stems on the ground but feller bunchers cannot do any kind of processing.
A feller buncher consists of a standard heavy equipment base with a tree-grabbing device furnished with a chain-saw or circular saw or shear (shear is a device designed to cut small trees off at the base). The machine keeps the cut trees on a stack facilitating the further removal of the loads by a skidder or forwarder or other means of transport. The feller buncher may be ‘drive to tree buncher’ or ‘swing boom buncher.’
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A ‘drive to tree feller buncher’ is a machine with the cutting head mounted directly to the carrier rather than on a hydraulic boom. And as the name indicates the whole machine drives up to each tree to cut it. Where as a ‘swing boom feller buncher’ has the cutting head mounted on a boom and the machine does not have to drive to each tree.
2. Extraction Equipments:
Pulling or extracting the tree from the forest area to a landing or storage area is referred to as extraction. Any harvesting system that uses an extraction machine that drives into the forest or enters the forest on ground is referred to as ground-based harvesting. When the tree is dragged out of the forest it is called skidding, when they are carried out on a trailer it is called forwarding. Skidders, Forwarders, agricultural tractors and animal power are all ground-based extraction methods. Aerial logging and yarders (cable logging) are other methods of extraction practiced in specific locations where ground based extractions are nearly impossible.
i. Skidder:
Specialized machines used for dragging the wood out of the forest area to the storage areas or road side are called Skidders. Wheeled skidders and tracked skidders can be used as per the terrain. Tracked skidders have slow ground speeds and should be limited to shorter extraction distances typically less than 500 feet. The wheeled skidders are capable of faster speeds and can extract material up to 1,000 feet.
Very large grapple skidders, also called grapple forwarders, are also available that can extract material to greater distances. Cable skidder uses a main winch cable and choker set to assemble and hold a load. In Grapple skidder, a set of bottom-opening jaws assembles and holds the load. A cable skidder has skid line with chokers attached.
The grapple skidder is capable of picking up more than one stem at a time and the main advantage over a cable-skidder is that the operator need not get out of the cab to accumulate the lot. It greatly increases productivity and safety, but is limited to sites where it can be drawn to the stump site.
A clam-bunk skidder is also a type of skidder used in logging. It has top-opening hydraulic jaws to hold a load of trunks for extraction. The advantage over a grapple skidder is typically a larger load and improved traction. But the disadvantage is that it needs to be loaded.
Other commonly used machinery includes the shovel, a tractor and bulldozers. A shovel is a tracked excavator with a grapple on the arm for moving logs or trees from the woods to either directly to the landing or road, or it can also be used to shovel to a skid road, whereby it will pre-bunch the trees for more efficient extraction.
ii. Forwarder:
They are extraction machines that remove material from the forests. They are basically tractors pulling a wagon load of wood. The cab may be fixed or capable of rotating on the chassis. Many forwarders have a boom mounted grapple for loading and unloading material. Compared to skidders, forwarders cost more to purchase. But the ability of forwarders to accumulate large loads makes the cost of forwarding per unit of extraction distance covered a lesser issue when compared to skidding.
iii. Skyline and Cable Logging (Yarder):
Skyline and cable logging operations are preferred when logs or trees have to be extracted from steep terrains. In such systems, a skyline or wire rope or cable, which aids to pull the stems from the forest to a landing, is suspended across the slope with a yarder (basic component of the cable yarder system) at one end and a tail tree or tail holder at the other end. The yarders may be mobile yarder or a stationary yarder.
The yarder helps to keep the cable off the ground and helps to lift the logs off the ground. Carriers or wagons facilitate the transport of materials. The yarder has mechanical or hydraulic winches or drums which facilitate the movement of the carriages and the main line along the skyline cable. The drum stores the main line cable. The logs are set and hooked by the chocker setter standing on the ground and the lots are pulled up and dropped at the landing.
An operator from a cab controls the yarder with the help of electronic switches and hydraulic levers. Where there are possibilities of using other machines to fell, bunch or process the trees, a cable yarder with a grapple is used. Loader booms and processing heads mounted on cable yarders are also in use.
Yarders may have either a swinging boom or a fixed boom. Most swinging booms have a limited height of 30 feet to 60 feet. Fixed boom yarders have towers as tall as 100 feet. Swinging booms permit a wider skyline corridor and thereby reduce the number of yarder moves. For increasing the productivity of cable operations, automated yarders are being used.
Automated yarding systems make use of a computer to control the inhaul and outhaul of the carriage. Outhaul is either to the last location it stopped or to a pre-set distance and inhaul is automatically set to stop 10 or 20 m from the yarder for safety reasons. Automating the movement of the carriage frees up both the yarder operator and the choker-setters to carry out their tasks while the carriage is in motion.
iv. Aerial Logging with Helicopter:
Helicopter can be used to extract trees in steep, remote areas and in areas that lack road infrastructure. Since the early 1950’s, helicopter yarding is in practice due to its ability to avoid many of the obstacles that are encountered in the ground based and skyline systems, including site sensitivity, urgency to remove or deliver the product, lack of access and slope of the terrain. The use of helicopters in forestry still continues to expand in many countries. Helicopter operations have high operational costs as well as high initial costs. Though the cost involved is huge, it is highly productive.
Advantages of aerial logging using helicopters are:
i. Avoid road constructions and road transport.
ii. Applicable in any kind of terrain.
iii. It will reduce the impact on soil, vegetation and regeneration because the logs are lifted vertically.
iv. It is able to extract large volumes of logs within short period of time.
3. Processing Equipments:
Once the tree is extracted to the landing, it is processed before loading onto the truck. Processing may be done on the stump site or at the landing. This process typically involves delimbing, topping the tree and bucking (cutting the stem into logs). These tasks can be carried out by chainsaw or delimbers. If the desired product is logs, then processing is done with delimbers. If the wood is to be used for paper and pulp, a wood chipper may be used. To remove the tree residues, mulchers and grinders are used.
i. Delimber:
Delimbing and topping are the processes of removing the limbs (branches) and cutting the top of the tree from the stem. Delimbing can be done by chainsaw or mechanically using delimbers. There are different kinds of delimbers available. A stroke boom delimber consists of two grapples: a front grapple and a rear grapple and saw mounted on base machine. It is capable of delimbing and bucking the tree trunk.
The tree trunk is normally grasped near the middle of the stem. The butt of the tree is placed in the rear grapple. The grapple arms functions as delimbing knives. The front grapple moves along the stem to remove limbs while the rear grapple holds the tree stem in position. The trunk is topped and bucked into log lengths by the saw on the boom.
The rear saw is also used to trim the butt end of the tree and also to make bucking cuts. Delimbers are generally used with a whole tree harvesting system such as a feller buncher/skidder system. They are good at processing trees into sorted piles, but are not capable of loading trucks.
Gate, flail and pull-through delimbers are the other different types of delimbers available based on methods employed for removing limbs from the boles of trees. These are relatively low cost methods for delimbing. Gate delimbers are welded structures consisting of steel tubing welded in a grid pattern. Gate delimbers may have an integrated support structure, or consist of a simple flat grid that is tied to standing trees.
A grapple skidder backs a load of trees through the gate, breaking the limbs off the bole in the grid. Pull-through delimbers lack feeding mechanism or measuring abilities. A pull through delimber can either be a stand-alone unit, or it can be mounted onto a trailer as and when required.
The tree has to be picked up and placed in the pull-through delimber. The delimber has three knives at the point where the loader pulls the stem through, removing the limbs from the tree. Most pull-through delimbers also have a topping saw in them which cuts off the top.
Flail delimber consists of chains mounted on rotating drums. The chains break the limbs off stems of the trunk fed through them. They may be self-feeding or may require a loader to pull the stems through the delimber. When a bunch of stems are pulled through the delimber, the chains not only beat and break off the limbs, but also effectively remove most of the bark.
Most efficient for relatively small trees from dense stands with small limbs and where the primary product is ‘clean’ chips (chips going to be used for making pulp and paper). Delimbers are used where full trees are being delivered to the delimber.
The form of the trees, single bole trees, and the size of the tree that can fit through the throat of the delimber or grids in the gate generally limit their use to few specific species only. Flail delimbers are not limited by tree size, but also by the size of the branches.
ii. Chipper:
A chipper is a machine that is used to produce high quality chips for the pulp and paper industry. The machines are large and highly productive and are capable of reducing trees to wood chips. Chippers differ from grinders in that they produce uniform sized chips depending on the equipment settings. Common features include a feed mechanism, a set of rotating knives, which may be either drum or disc mounted, an anvil and a discharge chute.
Chip size is determined by the distance from the anvil to the knives, the distance between the knives on the drum or disc, the feed speed and the speed the drum or disc rotates. The feed mechanism is usually a set of feed rollers at the throat of the chipper. Some chippers may have conveyor belts or trailers to assist in feeding the chipper.
Chippers may be either trailer mounted or self-propelled. Self-propelled chippers are usually track mounted. Some chippers are also equipped with a loading arm and grapple for self-loading. Some chippers have integrated delimbing/debarking functions. These are used to produce clean chips that may be used for fuel or pulpwood.
iii. Mulcher (Masticator or Brushcutter):
Mulchers are equipments used to cut, chop or grind vegetation and left over residues after harvesting into smaller pieces that are usually left on-site as mulch or waste materials. It is as a part of alternative to chemical treatment of residues, for aesthetic treatments, right-of- way maintenance and site rehabilitation. Mulchers are mounted on a variety of chasses including skid steers, excavators, farm tractors, four wheel drive loaders and bulldozers.
Mulchers mounted on the chasses are pushed through the stand. As the stems are felled, the stems fall in front of the machine and are shredded into smaller bits as the machine drives over them. The biggest safety concern with mulchers is flying objects thrown by the head.
Most mulching occurs at ground level, so the chance of picking up rocks or other debris is high. Most mulchers have shrouds that direct the material towards the ground. Another safety concern is cutting the standing trees. There are also equipments called tub grinders which grind the debris and divert it for other purposes like fuel.
4. Loading Equipments:
Once bucking of the logs is over they have to be loaded. The logs have to be sorted as per sizes or as to where they need to be delivered and stacked into piles. When the sorted lot is ready, they can be loaded onto the truck and transported to their final storage depots or sawmills or processing units. Sorting and stacking is done in order to make the loading out onto logging trucks and transport easier.
i. Log Loader:
There are also a number of ingenious methods using pulleys to manually load trucks. However, nowadays the stacking and loading are done with the help of ‘loaders’. There are different types of loaders used in the harvesting process like the knuckle boom loaders, trailer mounted knuckle boom loaders, tracked loaders, shovel type loaders, etc. Knuckle boom loaders are machines with specially designed booms for handling logs.
They are hydraulically operated loading boom whose mechanical action imitates the human arm. They may be also track based, wheel based, or trailer mounted. They are versatile implements and a knuckle boom loader mounted on a semi-trailer can be used for any or all of the following functions viz. delimbing, bucking, sorting, and/or loading. Knuckle boom loaders are often used where they are needed only at the landings and the tree size is not too large.
Truck mounted loaders are boom type loaders mounted directly on the log truck. Truck mounted loaders are only used to load small wood and have the disadvantage that it can handle logs only as much the truck can carry. There are also number of grapples like the bunching grapples, pulp wood grapples, log grapples, butt and top grapples, etc. that can be used for loading the logs depending on size and length of the lot.
Bunching grapples have tongs for picking up and handling multiple stems. The alternative is a log grapple that has single tines. Shovel loaders are used where piece sizes and volumes are too large for knuckle boom loaders.
Trucks and trailers or tractors are the most common vehicles that are used to transport logs. The vehicle selection depends on the size of logs being transported, the condition of the roads and regional preferences. Trucking delivers the logs from the landing to the saw mill for further processing. The trucks used to transport are different from those used for transport of other goods and have special features that aid the movement of long logs.
Full-length logs and poles are transported by log trailers attached to the trucks to their final destination points. The trailers may be for a fixed length log trailers or for flexible lengths. Straight trucks with a single log bunk or more than one log bunks are also used depending on the size of the lot.