A harvesting system is a succession of operations to fell, process and extract timber products to an loading area. The choice of a given system will depend on a combination of factors including: terrain conditions, access, crop characteristics, products assortment, availability of equipment and labour, operational costs, scale of the operations, long term objectives for the stand (see Managing Harvesting).
Pole length (or tree) system
In this system the tree is felled and delimbed, and extracted to roadside by a skidder or cable-crane system. The pole is then generally cross-cut into various products, sorted and stacked for collection, although it can sometimes be transported to the sawmill to optimise conversion. A variation of this system is the part-pole length system, where the stem is cut into sawlog lengths at stump.
This system only uses the stem wood and results in crown and branch wood residues, and is generally best suited to trees with a volume greater than 0.1 m3. Bear in mind that, particularly with broadleaved species, the branchwood can form a very significant proportion of the tree which could also be processed into fuel.
From an operational point of view, this system generally require ample conversion and stacking space at roadside; and in the case of skidder extraction, there may be a high risk of damage to soil and crops depending on conditions.
In this system the tree is felled, de-limbed and crosscut into the different product specifications at stump, and only marketable products are then extracted, generally by forwarder. The smaller the number of products, the more efficient the system. Stem, crown and branchwood are used generally down to a specific diameter size, and unmarketable products are left on site.
In this system, the whole tree is extracted and processed into marketable products, either by whole tree chipping, integrated harvesting combining conventional roundwood products and chipping of residues, or residue harvesting taking place separately from conversion to conventional roundwood products.
In this system little or no residues are left on site; the suitability of such systems depending on site type must be evaluated. There is guidance on site selection for brash removal downloadable here.
Products are accumulated prior to chipping either by forwarding or skidding, and a terrain chipper then processes the material into a trailer or bin which can be extracted to roadside. This system might also result in very little residues left on site and its suitability for a given site should also be evaluated. There is guidance on site selection for brash removal downloadable here.