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| Forestry for Biomass > Harvesting > Extraction
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| Extraction
Extraction is the process of transporting cut timber from the place where it was growing to a point where it can can be removed from site. There are a wide range of different methods of timber extraction and they vary in their strengths and weaknesses, and in the sites where they are most appropriate. Unless the site is particularly valunerable to damage, machinery will nearly always be used to extract timber. On the most valunerable sites, or when extracting the very smallest products (like coppice poles) extraction may be carried out using horses. there is more information about using horses for forestry work on the British Horse Loggers Association website.
Extraction machinery
Forest machinery developments have been rapid over the last decade, with a diverse range of available machines that are highly efficient and affordable.
Forwarders
Purpose built or agricultural tractor-trailer units equipped with a loading crane. They come in a range sizes and extract converted products by lifting them entirely clear of the ground. Variations include All Terrain Vehicle (ATV) based units and mini/midi tractor variants.
| Purpose Built Forwarders |
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Availability | Widely available. |
Costs | High capital and transport costs, can achieve low unit costs on large scale operations. |
Terrain ability | Slopes up to 50%. |
Potential site impact | Ground damage generally less than with skidding or cable crane systems. In the right conditions (soil type, weather conditions, availability of brash mat), large forwarders will require fewer passes to remove produce, reducing ground impact. |
Potential crop impact | Potential damage to standing trees / root systems. |
Access and transportation | Requires low loader transportation. |
Other operational considerations | Particularly suited to extraction distances greater than 500 m. Particularly suited to larger operations where greater load capacity increases efficiency. Generally suitable for a range of products, although it might not always be able to accommodate whole tree or pole length systems depending on bunk. On wet and sensitive soil sites, careful planning and maintenance of extraction routes are critical to avoid site damage. |
Ergonomics | Generally good ergonomics. |
| Farm Forwarders |
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Availability | Widely available. |
Costs | Mid-range capital cost, versatile; can achieve lower unit cost than purpose built machines on small operations. |
Terrain ability | Slopes up to 30%. Obstacles and rough terrain might cause problems, less so for power drive trailers. |
Potential site impact | Ground damage generally less than with skidding or cablecrane systems. On wet and sensitive soil sites, careful planning and maintenance of extraction routes are critical to avoid site damage. |
Potential crop impact | Potential damage to standing trees / root systems. |
Access and transportation | Easy access. |
Other operational considerations | Suited to extraction distances over 500 m. Can accommodate a range of products, including small whole tree systems with adaptations of equipment and work methods. Not suited to pole systems. Can be used for other agricultural activities. |
Ergonomics | Non purpose built equipment is likely to required additional guarding/protection for forestry work. |
| Mini Forwarders |
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Availability | Not widespread. |
Costs | Relatively high capital cost, with higher unit costs than large machines on larger operations or longer extraction distances. For smaller operations or shorter extraction distances, can compete with larger purpose built machines. |
Terrain ability | Slopes up to 30% to 50% dependent on machine design. Obstacles and rough terrain might be a problem because of relatively low ground clearance. Good manoeuvrability. |
Potential site impact | Low ground impact. |
Potential crop impact | Low crop impact. |
Access and transportation | Easy access and transportation. |
Other operational considerations | Best suited to extraction distances shorter than 250m. Low load capacity, most suited to small operations. |
Ergonomics | Some machines are not equipped with adequate protection for forestry work. |
| ATC Forwarders |
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Availability | Not widespread. |
Costs | Capital costs vary, with generally low cost of attachments. Unit costs are generally high. |
Terrain ability | Slopes up to 25%. Site roughness can cause problems. Good manoeuvrability, but brash and waste on the ground can impede travelling. |
Potential site impact | High traction force and low weight can cause ground damage if not properly used. |
Potential crop impact | Low crop impact. |
Access and transportation | Easy access and transportation. |
Other operational considerations | Best suited to extraction distances shorter than 200m. Low load capacity, most suited to small operations. |
Ergonomics | Some manual handling is required. Some machines are not equipped with FOPS or ROPS protection. |
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Skidders
Purpose built tractors, which extract by lifting one end of full-length trees clear of the ground and pulling them to roadside. Variations include All terrain vehicle (ATV) based units and mini/midi tractor variants.
| Farm Skidders |
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Availability | Widespread. |
Costs | Relatively low capital cost, but only gives competitive unit costs over short extraction distances. |
Terrain ability | Not suited to wet sites or slopes > 30%. Good manoeuvrability in crops. |
Potential site impact | High ground damage risk on sensitive sites. |
Potential crop impact | High crop damage risk. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Not suited to shortwood systems. Best suited to extraction distances of less than 150 m. Requires conversion space at roadside. Can be used for other agricultural activities. Generally low load capacity. |
Ergonomics | Some manual handling is required. |
| Purpose Built Skidders |
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Availability | Widespread. |
Costs | Relatively low capital cost, but only gives competitive unit costs over short extraction distances. |
Terrain ability | Not suited to wet sites or slopes > 30%. Good manoeuvrability in crops. |
Potential site impact | High ground damage risk on sensitive sites. |
Potential crop impact | High crop damage risk than other systems. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Not suited to shortwood systems. Best suited to extraction distances of less than 250 m. Requires conversion space at roadside. Can be used for other agricultural activities. Generally low load capacity (up to around 5 m3.Careful planning of extraction routes is essential to avoid site and crop damage. |
Ergonomics | Some manual handling is required. |
| Small Tracked Skidders |
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Availability | Not widespread. |
Costs | Relatively low capital cost, achieving low unit costs over shorter extraction distances. |
Terrain ability | The tracks improve traction on slopes and make the crossing of narrow ditches possible, however stability is more affected by slope than with wheeled vehicles. |
Potential site impact | Lower ground pressure than many other tractors, but high ground damage risk on sensitive sites. Track damage sensitivity on rough sites. |
Potential crop impact | High crop damage risk. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Not suited to shortwood systems. Best suited to extraction distances of less than 150 m. Generally low load capacity. |
Ergonomics | Some manual handling is required. |
| Skid Arch Sulky |
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Availability | Not widespread. |
Costs | Capital costs vary, with generally low cost of attachments. Unit costs generally high. |
Terrain ability | Good manoeuvrability, but trailed load constraint turning. Ability to cope with some steep ground. Terrain roughness can be an issue. Brash and waste on the ground can impede travelling. |
Potential site impact | Low risk from the arch itself but high traction force and low weight from ATC can cause ground damage if not properly used. |
Potential crop impact | High crop damage risk. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Best suited to extraction distances of less than 150 m. Low load capacity, most suited to small operations. |
Ergonomics | Some manual handling is required. |
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Other tractor based systems
These include: Tractor cradles: a purpose made frame or box unit which mounts on an agricultural tractor 3-point linkage system. Produce is manually loaded into the cradle.
Tractor-mounted hydratongs: a tractor-based unit equipped with hydraulically operated tongs, which extracts by lifting one end of full-length trees clear of the ground and pulling them to roadside.
Tractor and wire loader: drum winch based system using an adjustable ‘A’ shaped frame, that can be mounted on a tractor.
| Tractor and cradle |
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Availability | Widespread. |
Costs | Low capital cost. |
Terrain ability | Allows access to difficult sites. Manoeuvrable within crops. Slopes of less than 25%. |
Potential site impact | High ground damage risk on sensitive sites. |
Potential crop impact | May cause standing tree/root damage. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Best suited to extraction distances of less than 150 m. Can be used for other agricultural activities. Low load capacity, only suited to small jobs. Only suitable for early thinning operations and shortwood system producing short lengths. |
Ergonomics | Manual handling requirement precludes the production of large products. |
| Tractor and hydratongs |
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Availability | Not very widespread. |
Costs | Low capital cost. Can achieve lower unit costs over short extraction distances. |
Terrain ability | Manoeuvrable within crops. Maximum slope 25%. |
Potential site impact | High potential for site damage, especially on sensitive sites. |
Potential crop impact | May cause standing tree/root damage. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Can be used for other agricultural activities. Low load capacity, only suited to small operations. Best suited to extraction distances of less than 150 m. Only suitable for thinnings operations. Best suited to whole tree or long pole systems, with downhill extraction. |
Ergonomics | No data. |
| Wire loader |
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Availability | Not very widespread. |
Costs | Low capital cost, but generally high unit costs. |
Terrain ability | Generally has lower flotation capacity than purpose built machines. |
Potential site impact | Moderate ground impact potential. |
Potential crop impact | May cause standing tree/root damage. |
Access and transportation | Easy transportation and access. |
Other operational considerations | Allows access to difficult sites. Able to work with very widely-spaced racks. Low load capacity, only suited to small operations. Best suited to extraction distances of less than 500 m. Shorter product length will improve efficiency. Careful route planning and products presentation essential to avoid high unit costs. |
Ergonomics | Manual handling required. |
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Cableway / Cable Crane systems
Ropeway systems where timber is extracted by means of moving cables, powered by a static tractor or lorry powered winch. The timber load can be carried wholly or partially clear of the ground. Examples include skyline and high lead systems.
| High lead systems |
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Availability | No Data. |
Costs | Low capital cost, with competitive unit costs over shorter extraction distances. |
Terrain ability | Suitable for use on steep banks and wet soils. |
Potential site impact | Low ground impact and site disturbance. |
Potential crop impact | Some potential for stem damage. |
Access and transportation | Allows access to difficult sites. |
Other operational considerations | Best suited to extraction distances of up to 150 m, depending on concavity of terrain. Best suited to small thinnings or shorter extraction distances, and high product density. Low load capacity. Substantial setup time, but lower than other cable systems. Stacking space required at roadside. May require secondary extraction. |
Ergonomics | Some manual handling involved. |
| Gravity systems |
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Availability | No data. |
Costs | Low capital cost, but competitive unit costs over shorter extraction distances. |
Terrain ability | Suitable for steep banks. |
Potential site impact | Low ground impact and site disturbance. |
Potential crop impact | Some stem damage risk. |
Access and transportation | Allows access to difficult sites. |
Other operational considerations | Best suited to extraction distances of up to 300m. Best suited to small thinnings or shorter extraction distances, and high product density. Low load capacity. Substantial setup time, but lower than other cable systems. Stacking space required at roadside. May require secondary extraction. |
Ergonomics | Some manual handling involved. |
| Skyline systems |
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Availability | No data. |
Costs | High capital cost and high unit costs, generally only used on sites where other methods are not an option. |
Terrain ability | Allows access to difficult sites, suitable for use on steep banks and wet soils. |
Potential site impact | Low ground impact. |
Potential crop impact | Some stem damage risk. |
Access and transportation | Allows access to difficult sites. |
Other operational considerations | Best suited to extraction distances >300 m. Best suited for high product density due to high unit cost. Low load capacity. Substantial setup time. |
Ergonomics | Some manual handling involved. High level of skill required. |
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Terrain Chippers
These are purpose built or agricultural tractor units, in a range of size, comprising of a bulk container or trailer unit, a loading crane and a chipper unit. Produce is normally processed directly into the container or trailer.
| Terrain chippers |
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Availability | No data. |
Costs | Capital cost moderate, depending on components used, to high for purpose-built units. |
Terrain ability | Limited manoeuvrability. Suitable only for slopes of less than 25%. |
Potential site impact | Can cause site damage on sensitive sites; route planning, construction and maintenance are essential to avoid damage. |
Potential crop impact | Some damage possible. |
Access and transportation | From easy for small units to difficult for larger purpose built units. |
Other operational considerations | Best suited to extraction distances of less than 250 m. Low load capacity. Best suited for high product density. Presentation of produce to be chipped is critical to the efficiency of the operation. |
Ergonomics | Some manual handling involved with man-fed units. |
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Funded by
Forestry for Woodfuel and Timber
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