Logging residues are branches and discarded stem wood that collect on the landing site during harvesting. They accumulate at landings at a rate of about 4 to 6% of the volume of logs extracted through the landing.
In many cases this residue is pushed aside and left to rot. Depending on the landing this can create problems for the logging system and the future management of the site.
Problems include:
- reduced landing area
- reduced planting area
- slips
- fire
These problems can be expensive to mitigate. It would be better to manage the residue to avoid these costs and risks.
The best management option is, where possible, to use the residue for some productive purpose. The most common current method is to extract the residue and use it for fuel to produce heat. There are operations collecting landing residues in Northland, Central North Island, Hawke’s Bay, Nelson and Canterbury. It is estimated that the total volume being removed is around 200,000 to 250,000 tonnes per annum, or about 27% of the total estimated volume of landing residues available.
Increased landing space
Removing residues will increase the workable area of the landing, improving the ability of the crew to operate and increasing the storage space for logs.
Improved planting area
Removing residues can increase the area available for planting and reduce weed infestations. In some cases, the planting area around the landing becomes covered by residue as the logging crew pushes it off the landing using bulldozers. These areas become a source of weed infestation often with the most vigorous and least desirable weeds (blackberry, gorse, broom, buddleia, pampas, tutu).
Reduced risk of slips
Removing residues can reduce the risk of slips and resulting environmental damage. Residue cannot be left perched on steep slopes where there is a possibility that it collapses and causes a large debris flow into waterways or onto neighbouring land. The residue has to be either retrieved, burned, or a have a bench cut around the landing. All these practices have associated costs.
Reduced risk of fire
Removing residues can reduce the risk of fire by removing the fuel source. Fire is a significant risk particularly on super-skids. Super-skids are a central processing area for a number of harvesting areas. Accumulation of residue can be in the order of 20,000 to 30,000 m3 of bulk volume and can therefore be a serious issue. In some cases, the residue is pushed into an adjacent gully, and covered with dirt as more and more residue is pushed out. There are numerous cases of these very large piles (which often contain a lot of bark as well as stem wood and branches) catching fire and smouldering for weeks. These fires are difficult and expensive to extinguish, with fire suppression costs in the tens of thousands of dollars.