Timber Harvesting Systems
When it is time for a harvest to be carried out, a forester’s job is to implement the silvicultural treatment which will best work towards the landowner’s long term goals for their woodlot. One portion of this is the selection of which trees are to be harvested. However, those decisions cannot be disentangled from decisions around what types of equipment will carry out the harvesting.
There are three primary types of harvesting utilized in Maine. Which is most suitable for a given harvest depends on variety of factors including terrain, forest type, timing of harvest, and landowner goals.
Whole tree harvesting is the most commonly utilized method of harvest in this region. With this system, a feller-buncher fells trees, which are then dragged out of the woods whole by a skidder. At the landing, a stationary slasher/delimber machine processes the log-length sections of the tree into sawlogs and pulpwood, while the remaining tops and branches are run through a chipper and turned into biomass.
This is an efficient harvesting system that is adaptable to most situations. Everything from large sawtimber to small, suppressed, or undesirable trees can be harvested quickly and fully utilized from butt to top. Whole trees being dragged out of the woods scarify the soil in skid trails, which can aid in the establishment of desirable white pine seedlings. However, it has limitations in some specific situations. A skidder dragging a whole tree including its top results in skid trails that are relatively wide, and makes wide turns. This can make it more difficult than with other systems to preserve desirable regeneration and residual trees. Impact on soils in less-than-ideal conditions can be greater than with other systems. Additionally, a larger open log landing area is required. These factors are mitigated when trails are laid out carefully by a forester who can designate “bumper trees” which protect regeneration and desirable residual trees from damage (see article on timber harvest layout).
A feller-buncher harvester
A Cut-to-Length harvesting system utilizes a harvesting machine which after felling a tree, can process it on the spot into sawlogs and lengths of pulpwood, which are then carried, rather than dragged, out of the woods by a forwarder. The forwarder carrying logs is more maneuverable than a skidder dragging a whole tree, and can make tighter turns to avoid desirable regeneration and crop trees. It also can have as lesser impact on soils in wet conditions. Because the trees are processed by the harvester in the woods, rather than by a slasher on the landing, a smaller landing area can be utilized.
Cut-to-length harvesting generally involves leaving the “slash” (tops and branches that cannot be made into sawlogs or pulpwood) on the ground in the woods, rather than hauling it out to be chipped into biomass. This is not inherently negative – wood on the forest floor will decompose and return its nutrients to the soil. However, it may not be desirable in some situations based on landowner’s aesthetic preferences. This also can make cut-to-length harvesting unsuitable for situations in which a large portion of the trees are low-quality and branchy enough that much of their volume is only merchantable as biomass.
A Cut-to-Length Harvester processing felled trees into logs, and a forwarder carrying logs out of the woods.
Today, most timber harvesting in Maine is carried out by one of the above mechanical harvesting systems. However, there are still chainsaw and cable skidder loggers operating on a smaller scale. With this system, a logger fells and limbs trees by hand with a chainsaw, and then manually attaches logs to a skidder via cables to drag them out of the woods. This system is significantly slower than mechanized harvesting systems, and the time and labor-intensive progress makes harvesting the lowest quality trees, or harvesting large areas within a given timeframe, unviable. However, the relatively low overhead cost to the logger of equipment, and of transporting that equipment to a job site, means that it can still be a preferred harvesting method in some niche situations, such as when a harvest involves removing relatively low volumes of good quality sawtimber.
See this Northern Woodlands article for further reading on these harvesting systems and their history: https://northernwoodlands.org/articles/article/three-logging-systems-matching-equipment-to-the-job