New Zealand forests contain a large resource of woody biomass that has potential to be used for bioenergy. Most of this biomass will arise from the 1.7 million hectares of pine plantation forests currently spread throughout the country.
Woody residues result largely from harvesting operations, and occur at two general locations: within the forest or on central landings (skid sites).
When large trees are felled, they frequently break when they hit the ground. This breakage typically occurs at around two-thirds to three-quarters of the tree height. Often these broken sections are small and of low value so they are not extracted to the landings. Instead they are left on the cutover, along with the branches, to rot away.
On central landings (skid sites) tree-length material is cut into logs. Off-cuts from the base, tip and midsections of trees become waste material that averages 6-6% of the extracted volume. A variable amount of branch material is also produced. Because these landings are centralised processing sites, they make it relatively easy to recover significant volumes of wood residues.
Currently in New Zealand there are only a few industrial sites where the use of forest residues as fuel occurs. These industries are generally associated with forestry and forest products processing. They have existing plant for burning wood processing residues to produce heat, and have access to good transportation networks through the forest.
Systems are already in place to utilise logging residues from landings. Such systems consist of either processing at landings, or at centralised processing facilities. When using centralised processing, 10-15% may be added to the delivered cost due to extra transport and handling requirements.
How much residue is available from forests?
Systems already in place to harvest logging residues currently yield about 250,000 tonnes of residue per annum. Most of this residue is used to fuel energy plant for wood processing facilities.
This volume represents approximately 27% of the existing available resource from skid sites, or 7% of the total residues available from forest harvesting operations. In future, the volumes of residues potentially available from forest harvesting will increase significantly.
For more information on harvesting residues please see the attached Logging Residues Report (2 parts)