As timber harvesting , forest harvesting or harvester (English harvester ) is called special harvesting machines.
The machines fix the trees, cut them down and can delimb the trunks and put them down for transport with the forwarder . If the branches are also chopped up into wood chips at the same time , it is called a wood chip harvester . As heavy forest machines, they require a narrower meshed back lane network than traditional processing and make it possible to carry out some work steps such as assigning the wood sections to so-called assortments immediately on the spot. They have changed and accelerated forest management worldwide. In Germany they were used for the first time on a large scale to process the wind throws caused by the hurricane lows “ Vivian ” (February 26, 1990), “ Wiebke ” (March 1, 1990) and “ Kyrill ” (January 18, 2007); Since then, the share of wood harvesters in the logging volume has increased steadily, which also appears to be sensible because of the reduced risk of accidents.
Today, the following types of harvesters are predominantly used (commonly referred to as a processor according to the definition of a machine that carries out several work steps; in the order of their frequency):
- Wheeled wood harvester with two to four axles
- Excavator , with harvester head and crawler tracks
- Walking harvester, also with a wood harvester head and feet or stilts and rarely too
- Push wood harvester with rear wheels that can be moved in the direction of travel
In forestry , wood harvesters are mainly used for softwood. In the case of hardwood, the delimbing quality is unsatisfactory. There are special versions for use in weak, medium or strong wood.
The machines usually have a crane arm ten to fifteen meters long, at the end of which the felling head (processor) is freely moveable. The felling head is equipped with feed wheels (rollers), measuring unit, hydraulically driven chainsaw and delimbing knives. Instead of a chainsaw, a circular saw blade is also installed in rare cases. Some machines are equipped with cabs that can be tilted according to the slope, with others the entire machine can be brought into the horizontal despite the slope of the terrain. An air conditioning system is installed, and often automatic preheating of the hydraulic oil and the cabin before work begins. Wheeled wood harvesters have low-pressure, low- profile tires with a tire width of up to 70 cm for use that is gentle on the soil. If it is wet or snowy, chains or metal straps can also be attached. Despite this equipment, considerable damage cannot be ruled out on soft soils. In some cases, lanes with a depth of up to 70 cm are reported.
The Kuratorium für Waldarbeit und Forsttechnik (KWF) divides harvesters into three classes according to their output in kilowatts (kW):
- Small harvester: up to 70 kW (95 HP): optimal tree diameter approx. 15 cm
- Medium harvesters: 70 kW to 140 kW: optimal tree diameter approx. 20 cm
- Large harvesters: over 140 kW (190 PS): optimal tree diameter approx. 30 cm.
Harvesters that are classified as "small" according to this classification can hardly be found today. Most of the common types of harvesters are "medium" or "large". Machines that are frequently used in practice, such as the John Deere 1270, Ponsse Ergo or Valmet 911, all have more than 140 kW of power and are therefore classified as large harvesters.
The power is only transmitted hydraulically, all functions are controlled electrically or with hydraulic pilot control. The very extensive hydraulic system must be filled with biodegradable oils according to the latest PEFC and FSC standards. A vacuum pump reduces oil leakage during repairs; In addition, the crane is equipped with a shut-off valve or stopcock, which closes the flow of oil to the unit and thus holds back the oil in the event of an accident. Excavator wood harvesters mainly have chains that are flattened on the side and rounded webs to reduce damage to the soil or to the forest. Damage to forest stands usually occurs in the form of subterranean root cracks as a result of shear forces . Rotating movements on forest roads cause damage to the surface layer.
Due to the low ground pressure (to avoid soil compaction ), the main areas of application of the excavator wood harvester are on the one hand wet soils and on the other hand steep slopes of up to around 50% because of its better climbing ability compared to the wheeled wood harvester. However, the caterpillar or chain drives have the disadvantage that they can be damaged by stumps or other sharp objects. When moving the excavator wood harvester, the low drive speed (around 5 km / h) and the risk of damage to asphalt roads (use of a low-loader required) are disadvantageous. The machines are equipped with around 15 work lights all around , which also allow you to work at night.
The timber harvesters are now equipped with GPS , mobile communication and an on-board computer that supports timber management and variety formation . The processed wood can be saved and wood lists can be printed out. The accuracy of the measured wood mass is largely dependent on the sensor system used, the felled tree species, the correct consideration of the necessary bark removal and, last but not least, regular, documented calibration . Measurement deviations from the factory measurement or manual wood recording are the rule. In the case of well-adjusted systems, the deviations are an acceptable 2 to 4% above the factory input dimension, but larger deviations are not uncommon. For this reason, in addition to determining the number of pieces, it makes sense to measure the dimensions of the felled wood on the forest road.
Originally, wood harvesters were used in thinning weak coniferous wood stocks , but now also in the stem wood harvest (mostly coniferous wood, sometimes also in hardwood beech stocks ). The strongest felling heads can handle trunks with a diameter of up to 70 cm at breast height (BHD). Harvesters can process between five and thirty solid cubic meters (fm) of wood per hour, which depends mainly on the thickness of the wood harvested.
Special tracked wood harvesters (e.g. Valmet 911.1 X3M ) are used in more steeply sloping terrain . Another special development is the six-legged walking wood harvester, which was developed in Finland for thinning stands on waterlogged or boggy soils. However, this machine turned out to be unsuitable for use on steep slopes.
When processing storm wood , the use of these machines significantly reduces the risk of accidents, as the dangerous tension in the thrown trees is released outside of the human hazard area. In Switzerland, large caterpillar harvesters were used for the first time to cut open old head trees and to cut entire trees at heights of 3 to 5 meters. Due to the capping, one expects to come to new head trees in 15 to 20 years, which are very cave-rich as a culture.
Due to the increasing importance of bioenergy, well-known forest machine manufacturers have developed combinations of harvesters and mobile chippers , so-called wood chip harvesters . With this type of machine, residual wood and crown cuttings are processed into wood chips in the same work step during the wood harvest. Another combination comes from the Finnish manufacturer Pinox. Here, with an additional unit, mainly crown sections are pressed into bundles suitable for transport, which are also used to generate energy.
In Scandinavia (especially Sweden and Finland ) these machines have been used since the early 1980s. In the meantime, almost the entire timber harvest is carried out in a highly mechanized manner. In Central Europe, these machines process between 30 and 50 percent of the logging volume - with a very strong upward trend. In Germany they were used for the first time on a large scale to deal with the otherwise unmanageable wind throws caused by the hurricane lows “ Vivian ” (February 26, 1990), “ Wiebke ” (March 1, 1990) and “ Kyrill ” (January 18, 2007); since then, the share of harvesters in the logging volume has increased steadily. Lesser numbers of wood harvesters are also used in North America. Because of the wood's dimensions, so-called felling collectors (Feller Buncher) are used there, with their significantly larger felling heads able to fell trees up to a BHD of one meter. Another area of application are tropical plantations, where they are used to harvest pine ( Pinus radiata ) and eucalyptus stands . The dimensions of the tree and the fact that the area is fully driven allow work rates of up to 50 cubic meters per hour.
The harvester falls, delimburs and divides the wood. Then it is placed in Rauhbeugen on the return path . Transport to the next truck drivable forest road, the wooden back is the following forwarder (Forwarder) or with a skyline crane done. Except in storm wood, the harvester works from alleys that he creates himself when he first thins a stand and that the forwarder then drives on. The same logging lanes are used again and again for each subsequent thinning every 5 to 10 years . With a crane reach of up to 10 m, areas with aisle spacing of 20 m can be processed. If further aisle spacing is required or if you are working on a steep slope, it is done manually, i.e. with a chainsaw .
On level terrain, the harvester lays the stripped branches as cushion on the tramline. This also reduces the ground pressure of the moving machine. The processed logs are placed on the side, differentiated according to assortment. A color coding of the assortments according to buyer is possible, also to mark assortments that are difficult to distinguish from one another. The special design of the wood chip harvester also processes the stripped branches , as described above . The branches and treetops can also be chopped up into wood chips and transported away with the following mobile small chopping machines or a combination of forwarders and large chippers.
Effects on forest work
Since harvesters in the previous use stocks are more productive and more cost-effective than motor-manual procedures, their use in Germany is constantly increasing.
In end-use stocks or in stocks with rejuvenating parts that can be taken over, felling with forest workers is often equal to the use of the processor after weighing all the facts.
Currently, 30 to 40 percent of the timber harvest in Germany is carried out with full harvesters. Harvesters reduce the risk of accidents, which is very high when harvesting wood with a chainsaw, and help reduce occupational diseases. The use of full harvesters leads to downsizing in forest operations and to a changed qualification structure in forest work . Many companies handle all or part of the logging through forest contractors. The requirement for logging entrepreneurs to offer inexpensive timber harvesting also in existing stocks will have a structural change in this occupational field.
When using trained and experienced machine operators, the use is gentle on the inventory and comparable to manual reconditioning. Logging contractors and machine operators should not try to achieve a better operating result at the expense of the remaining inventory because of cost pressures. The forest owner should note that timber harvesting costs that are set too low contradict an economic approach if one takes into account the enormous damage a full harvester can cause with pure piecework thinking. Therefore, the training of machine operators should not be limited to the machine, but must also include forest maintenance and economic aspects.
Forest owners whose main occupation is not forestry can reduce the time burden caused by the timber harvest and thus have the opportunity to take more care of management, maintenance, mixed growth regulation or other forestry tasks.
It is reported (Rheinauewald Baden-Württemberg 2015/2016) that trees affected by "ash dieback" (hose fungus infestation) can be very dangerous for the woodcutter, as rotten roots may no longer provide the trees with adequate support. Such trees can fall over without warning if they are felled, injuring or killing the logger. In those areas, the ash is currently only felled with full harvesters on the instructions of the forest administration.
Damage from the use of heavy machinery is the subject of long-term studies. Problems can arise from soil compaction and root damage, especially in unstable locations. Until reliable results of the long-term studies are available, it is advisable to continue to select the spacing of the maintenance lines at critical locations and to deliver it by motor or to give preference to other wood harvesting methods (cable crane, e.g. also in flat terrain). Possible restrictions with regard to the timber harvesting methods in biotopes or nature and other protected areas are pointed out in individual cases.
The brushwood is deposited in the maintenance line and thus remains in the stock. Further balancing will be necessary in order to determine damage (soil, pressure) and benefits (shelter for small animals in brushwood, mushrooms, etc.). With regard to fuel consumption, the total consumption per cubic meter of harvest must be compared manually (chain saw, sanding of the wood with winch and tractor to the road) with the consumption of the harvester per cubic meter of harvest. The latter can produce roughly ten to twenty times the harvesting capacity compared to manual wood harvesting.
The discussions on the environmental impact are ongoing and need to be followed up. Scientific procedures require objectivity on all sides.
- Arne Bergmann: Customer-oriented raw wood supply with fully mechanized wood harvest. A system for the optimal division of sawed sections with on-board computers on full harvesters. Dissertation. University of Göttingen, Göttingen 1997, .
- Christoph Hoß: Human- friendly design of harvester use. Cuvillier, Göttingen 1994, ISBN 3-89588-039-6 (Dissertation University of Göttingen 1994).
- Reinhard Pausch: A system approach to investigate the relationships between forest structure, work volumes and costs of technical and biological production in forest areas in eastern and northern Bavarian low mountain PDF; 325 pages; 3.1 MB ). , dissertation TU Munich 2002, (
- Background information on waldwissen.net on the use of forest harvesters in the forest ( Memento from January 30, 2012 in the Internet Archive )
- Information on probably the largest harvester in Europe (PDF; 369 kB)
- Harvesters and forwarders - what is it? In: forstcast.net (video)
- Work safety accident series in autumn. The agricultural and forestry trade association, December 9, 2010
- Logging - Harvester. Retrieved December 12, 2016 .
- various harvesters (wood harvesters)
- Push harvester Highlander ( Memento from May 19, 2010 in the Internet Archive )
- Ecological assessment of wood chips