Extraction is the process of transporting cut timber from the place where it was growing to a point where it 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.
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 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.
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.
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.
These are purpose built, or agricultural tractor units, in a range of size, comprising 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, 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
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 cable crane 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 250 m. 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 200 m. 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
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
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
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
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 hydra-tongs
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
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
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 300 m. 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
These are purpose built, or agricultural tractor units, in a range of size, comprising 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
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
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