Wood residue results as a by product of tree felling and timber processing and can be used by industry to produce energy for their activities and operations.
Wood residue can be collected and used from in-forest cutover, log landing or wood processing sites. Most of New Zealand’s wood residue arises from the 1.7 million hectares of pine plantation forests currently spread throughout the country.
The use of wood residue as an energy source has expanded in the New Zealand wood processing industry in recent years. Sites that use wood energy have an existing plant for burning wood residue to produce heat, and have access to good transportation networks through the forest.
Types of wood residue
Wood residue comes in a variety of forms including:
- Wood chips which are made from wood off cuts and are fairly regular in size once screened
- Hogged wood which has been mechanically broken down and is usually lower quality
- Sawdust and shavings in very small sized wood particles
Wood residue location
There are three main locations where wood residue can be found:
In-forest cutover sites
When large trees are felled in the forest, 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 moved to log landings and are instead left to rot away. However, this left-over tree material has the potential to be used as fuel.
Log landing sites
On log landings (skid sites) in forests tree-length material is cut into logs. Off-cuts from the base, tip and midsections of trees become waste material (averaging 4-6% of the wood volume) and branch material is also leftover. Because log landings are centralised sites, they make it relatively easy to recover significant volumes of wood residue which can then be used as fuel.
Wood processing sites
When logs are processed into lumber in sawmills, wood residue is leftover in the form of planer shavings, sawdust and ‘slabwood’. This residue can also be used as fuel.
Wood residue availability
Systems already in place to harvest wood residue currently yield about 250,000 tonnes of residue per annum. Most of this residue is used to create energy for wood processing facilities.
This volume represents approximately 27% of the existing available resource from log landings, or 7% of the total residue available from in-forest cutover operations.
Pros and cons of using wood residue
Once a plant is set up, wood residue provides a cheap form of energy. Wood energy can be produced from a range of sources, requires limited processing and can often be sourced locally. The use of wood residue also minimises wastage and therefore reduces the impact of the forestry industry on the environment. However, wood residue requires a larger area for storage per unit of energy produced than other fuel sources.