Timber harvesting in farm forestry
Harvesting is the cutting and extraction of timber to roadside, usually during thinning or clearfelling.
Thinning is the removal of inferior trees, increasing the quality and size of those remaining. It is generally undertaken 2 to 5 times over a forest rotation.
In conifers, first thinning usually removes lines of trees within the crop as well as selected inferior trees in between these lines. This provides access for subsequent selective thinnings.
Thinnings in broadleaf plantations involve the periodic selective removal of competing trees to favour higher quality stems.
Clearfelling is the harvesting of all marketable trees at the end of a forest rotation, generally between age 30 and 50 in conifer forests and later for broadleaves.
Continuous Cover Forestry is an alternative approach to clearfelling where some trees may be periodically removed but the canopy is continually maintained.
Harvesting operations may involve the felling of selected trees, the removal of branches, cross-cutting of stems into size categories, stacking along tracks in the forest and extraction to roadside.
Up to the early 1990s felling was carried out mainly using chainsaws. Manual felling is still an option in smaller plantations or where machine access is limited.
Tractor-mounted timber processors are used to a limited extent in Ireland and may have applications in small harvests. Some systems require trees to be manually cut before being fed by winch or crane to the processing unit. Processors can debranch, cross-cut and stack timber assortments in the forest.
Most felling now involves the use of specialised harvesting heads, either fitted to standard excavators or purpose built ‘harvesters’.
Achieving economies of scale
Harvesting contractors require significant timber volumes in felling areas to justify transfer of these specialised machines. Sufficient volumes as well as good economies of scale can be achieved with co-operation between neighbouring forest owners and co-ordination of harvesting activity within local or regional areas.
Timber extraction options
Horses were commonly used in the past to extract timber to roadside. This option may still be suitable in small scale forestry or in environmentally sensitive forests areas.
Quad-based extraction systems may be an option for small scale operations where soil conditions are good.
Tractor ‘skidders’ provide further extraction options. The timber is winched to the metal plate mounted on the back of a tractor and skidded on the ground to roadside.
Tractor forwarders with grapple loaders are used to a limited extent in Ireland where soil and ground conditions are favourable.
Cable extraction systems are expensive but may have applications in environmentally sensitive forest areas.
Specialised forwarding machines are the most common extraction system in Ireland. Similar to harvesters, forwarders can be fitted with tracks or chains and can remove on average 9-12 tonnes per journey.
Crucial to the cost-effectiveness of a forwarder is the distance it has to travel to the collection point. The increased cost of forwarding may significantly affect thinning costs beyond an optimal extraction distance of 250-300 metres.
Alternative harvesting systems
Forestry thinnings or residues may be chipped on site for wood energy using tractor mounted chippers or specialised chipping machines.
Timber can be converted to firewood using one of a wide range of processing machines.
Trees harvested in the forest can also be sawn and planked on site using a mobile sawmill.
Planning of harvesting operations
Advanced planning in conjunction with a professional forester is essential and generally involves:
- Assessment of standing timber
- Provision of access and loading areas
- Securing of a market
- Application for a felling licence
- Co-operation/co-ordination of harvesting with other forest owners
- Preparation of a harvesting plan to minimise environmental disturbance