The fibre length of the cellulose fibres is the most important parameter of the pulpwood and determines what it may be used for. The first separation is into softwood and hardwood, that have long and short fibres respectively. In paper production fibres from softwood gives tensile strength and fibres from hardwood gives opacity.
In the logging of mixed forest stands, the better trees are usually used for sawlogs for lumber production, while the inferior trees and components are harvested for pulpwood production. Pulpwood usually derives from four types of woody materials in a mixed logging operation:
Natural forest stands may also be harvested solely for pulpwood where, for various reasons, the value of the trees as sawlogs is low. This may be due to the predominant species in the forest stand (for example, some aspen forests in northern North America), or to the relative proximity of the nearest sawmill or pulp mill.
Pulpwood is also harvested from plantations/tree farms established for the specific purpose of growing pulpwood, with little or minimal sawlog production. Monocultures of species intended specifically for pulpwood include loblolly/slash pine in the southern USA; various species of eucalyptus (most commonly Eucalyptus globulus and Eucalyptus grandis) in Latin America, Iberian Peninsula, Australia, south-east Asia and southern Africa and acacia (most commonly Acacia mangium) in south-east Asia and southern Africa.
Salvage cuts after forest fires, tornadoes, hurricanes, or other natural disasters are often used for pulpwood. An alternative source of wood for use in kraft pulping is recovered lumber from demolition, industrial processing of wood and wooden pallets.
Saw residuals are used as pulp wood. The most important of these are the side cuttings from lumber edgers. This gives wood with almost only sapwood and no hearthwood. The sapwood is easier to pulp. due to a more open structure and less content of extractives than the hearthwood. The fibre length of sapwood is generally longer than the fibre length of hearthwood. The sapwood is also normally lighter and that is an advantage when producing mechanical pulp as less bleaching is needed.
Earlier sawdust had some limited use in paper production. It gives very short fibres that are suitable as part of the furnish for paper tissue and writing papers. Saw blades have become thinner and with smaller teeth making the sawdust too small as fibre source.
|colspan=6||Chemical composition of pulpwood (%)|