Woody biomass from purpose-grown energy crops offers the opportunity to positively affect logistics costs in several ways. One of the most obvious is the opportunity to reduce transportation costs by geographically concentrating the source of the material, in the form of plantations, close to the consuming facility. Secondly, and even more impactful, would be the higher productivity of the energy plantations versus wood derived from natural stands. Producing more biomass per acre means less acres required to sustain operations, resulting in shorter haul distances for the woody biomass fuel or feedstock. Therefore, it can be seen that highly-productive energy plantations, grown in close proximity to the consuming bioenergy facility, offer an excellent opportunity to minimize the logistical complexity and cost of sourcing the woody fuel or feedstock.

Dedicated woody energy crops currently represent only a minor source of biomass for energy, although it is expected that energy plantations will become an increasingly impor­tant source in the future. Harvesting systems for woody biomass from energy plantations remain somewhat developmental and will need to be adapted to the specifics of the regime being considered. Specifically, the number of stems, spacing and tree size are important determinants of feasible harvesting solutions, production, and costs.

Short-rotation woody energy crops from genera such as the willows (Salix sp.), pines (Pinus sp.), poplar (Populus sp.) and Eucalyptus (Eucalyptus sp.) provide important SRWC crops. SWRC crops differ from pulp or sawlog stand thinnings and logging residues as biomass sources in that the sole purpose of intensive energy crop plantations is biomass production. By contrast, thinning materials and logging residues from silvicultural treat­ments in forestry are a secondary product, after sawlogs or pulp. Poplar energy wood crop rotations are short, from 7 to 15 years [1], and stands are established primarily through cuttings. Willow rotations may be even shorter (3-4 years). Because poplar and willows can also be regenerated well in coppice systems, coppice regeneration systems can also be deployed for both crops. Coppice systems are those in which stump sprouts or “suckers” re-sprout from stumps to establish the new stand of woody crop following harvest.

The systematic row-crop spatial location and small diameter of short rotation woody energy crops are conducive to agriculture-style harvesting with short-rotation woody har­vesters. These purpose-built machines are forage harvesters with harvesting heads that can handle woody stems, typically less than 5 inches (12.7 cm) in diameter at breast height (DBH). A major advantage of using short rotation woody harvesters is that the resulting material delivered to roadside is a chip that is ready for transport without further prepro­cessing, that is, a single pass system. A further advantage of short rotation woody crop harvesters over the equivalent, conventional timber harvesting equipment (e. g., small exca­vators with harvester heads), is that they are able to conduct continuous travel harvesting, rather than stop-and-go felling of individual stems [2].

Although dedicated SRWC harvesters are the most promising emerging modern equip­ment for woody energy crops, a variety of conventional logging equipment has been evalu­ated in the context of woody biomass. Feller-bunchers and single-grip harvesters designed for sawlog production have been evaluated, as have a variety of forwarding systems. Mobile harvester-chipper-forwarders with knuckleboom harvester arms, chipper-forwarders, slash forwarders, slash compactors, and slash bundlers all have potential use with short-rotation crops. However, these systems tend to have either lower overall hourly production or higher hourly logging costs compared to modified swath harvesters because they require multi­stage processing. The many harvester-chipper-forwarders now available for woody biomass tend to be designed for larger diameter stems than are achieved in short rotation crops, and are better designed for intermediate thinning treatments in stands being grown for pulp or sawlog production. Unlike SWRC harvesters that have evolved from forage harvesters, the harvester-chipper-forwarder style machines tend to be designed for single approach harvest. That is, they have a harvester head mounted on a knuckleboom arm that is used to fell one or more stems, and the stems or bunch of stems are fed into the conveyor-feed mouth of an internal chipper. They are not able to perform continuous travel harvesting, but instead must stop intermittently.