Extraction

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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 vulnerable to damage, machinery will nearly always be used to extract timber. On the most vulnerable 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.

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.

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.

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.

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.

Forwarders

Purpose built forwarders
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
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
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
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

Skidders

Farm skidders
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
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	Higher 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
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
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

Other tractor systems

Tractor and cradle
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 hydrotongs
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
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

Cable systems

High lead systems
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
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
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

Terrain chippers

Terrain chippers
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