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Forest Harvesting

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Forestry Processes
A crawler tractor is used for skidding logs.
Forest harvesting
refers to the total process of cutting down trees and delivering them to a mill. It may also refer to the removal of dead or damaged trees from an area.[1] The term logging, on the contrary, is used in reference to the cutting down of trees.[2] However, it may also be used interchangeably to mean the same thing as harvesting.

There are many considerations and steps involved in harvesting a forest crop. This includes everything from developing a detailed harvesting plan and geologically surveying the harvested area so logging roads can be built, to determining the method of felling and corresponding forestry equipment to be used in harvesting operations.[3]

Contents

[edit] Process

[edit] Engineering a Harvest Plan

The first phase in executing a harvesting operation is devising a harvesting plan. Forest engineers are individuals who specialize in drafting harvest plans. Their knowledge in multiple disciplines such as surveying, geology, and soil science enable them to develop a harvesting plan that weighs out equally significant economical and environmental objectives. They are not only familiar with the surrounding forest landscape, but with the type of forestry equipment and method best applied to a particular harvesting operation. Part of their job is to also figure out where logging roads should be built and whether or not later on these roads will be turned into public access roads or highways.[4] Forest engineers must also collaborate closely with the government, industrial foresters and consultants, and other specialists. Together they work as a team to generate a plan that reveals the timber plot to be harvested and the proposed rate of cutting.

[edit] Logging Road Construction

Approximately 9,321 miles (15,000 km) of logging roads are constructed in Canada each year.[5] Each road built requires surveying and planning to build. The single most important factors to consider when building roads used for logging is minimizing soil erosion and ground damage on the forest site and protecting nearby water sources. One practice addressing these concerns is to rehabilitate temporary logging roads after harvesting for replanting. This is quite a common practice in British Columbia’s logging industry.[6] The type of equipment used to build logging roads varies according to the terrain. For example, bulldozers are typically used in dry, sandy conditions and backhoes in the wetland areas such as the boreal forests along B.C.’s coast.

[edit] Logging

Logging describes the actual cutting and extraction of trees from a forest using a particular harvesting method or system. The primary harvesting methods used in logging are:

[edit] Felling

Chainsaws are the most common pieces of equipment used to cut down trees. Fellers (or fallers) are workers who fall the tree by making an undercut in the bottom of the tree and then place a wedge in the undercut to control the direction in which the tree falls. Felling is a very skilled and highly dangerous occupation.

Mechanized felling machines such as feller bunchers cut down trees using chainsaws or circular saws up to 262 feet (80 m) in diameter mounted on a boom arm that is attached to a tractor or excavator.[7] Multi-functional tree harvester machines are used in smaller tree stands and cut, delimb, and top trees before transporting them to the roadside. They may perform all or a combination of these functions. Mechanized felling is much safer than chainsaw felling.

Trees are felled one of three different ways:

[edit] Skidding

After a tree is felled and delimbed, the process of transporting it from the stump to a landing site where it is loaded onto a truck and taken to a mill is called skidding or ground skidding.[8] Skidding involves the terrain or ground transport of logs using skidders. Articulated-center steering wheel skidders developed in Canada during the 1950s are the most common type of skidder used in logging operations today.[9] Major improvements have been made to skidding equipment over the last several years, with the addition of new features such as four-wheel drive, excess horsepower, and hydraulic steering, making maneuvering through almost any forest area, including steep slopes, possible.[10] One of the drawbacks of this increased power and capacity is that it leads to the likelihood of greater soil erosion. A skidder removing logs from the forest naturally creates skid trails. Skidders also drive directly over streams and dry channels and this is thought to have contributed to the decline in forest soil integrity.[11]

An alternative to conventional skidding is forwarding. Forwarders are a combination of a mechanized arm upon a wheeled or tracked frame. Forwarding differs from skidding in that logs are carried out of the forest as opposed to being dragged. As a process, forwarding is considered to be a gentler or low-impact form of skidding. Crawler tractors also exist as a low-tech alternative for skidding on steep ground in addition to horse-drawn skidding.[12]

Cypress 7280 Grapple Yarder

[edit] Yarding

Yarding also involves dragging logs from stump to roadside, except cables and yarders (also called winches) are used. These systems are able to fully or partially lift logs off the ground into the air during transit to the landing site. Another primary difference from skidding is that equipment used in yarding sits stationary upon the ground.[13]

High-lead yarding, in which logs are lifted off the ground at one end and then dragged across the ground, is the most common method of yarding. Skyline yarding involves lifting the log up through the air. Helicopter logging involves the use of helicopters in yarding logs from the forest to the landing site. Average yarding systems can cover a distance of 984 feet (300 m) up to 2,297 feet (700 m).[14]

[edit] Processing and Sorting

Processing and sorting involves removing limbs and the tops of trees and cutting them into merchantable log lengths. Each log is then sorted according to grade and species before being delivered to a mill. The goal of processing and sorting is to recover the maximum value from each tree. Delimbing and bucking can be carried out at the stump or at the landing using equipment. Bucking, also referred to as crosscutting, is the cutting of felled trees into logs.[15] Once logs have been delimbed and bucked, they are sorted at the landing. Log stackers, front end loaders, log loaders, and cranes are common types of equipment used in processing and sorting, which includes loading logs onto a log truck or trailer for transport to a mill.

[edit] Log Transporting

In Canada, the chief method of transporting logs from a landing site to a mill is by log trucks. Pulpwood is hauled crossways on flat-deck semi-trailers. Longer logs in B.C. and Alberta are hauled on what are called pole trailers. Water transport exists as a second means of moving logs. In B.C., for example, it is common to transport logs by truck from a landing site to water. In the water, the logs are then arranged into large rafts or booms that get pulled tug to a mill. B.C.’s forestry industry also uses tug-pulled barges to move logs, pulp, pulp chips, lumber, and other products. Water transport exists as a cost-effective means for moving large amounts of wood.[16]

[edit] Equipment Used

[edit] References

  1. Glossary of Forestry Terms. Boreal Forest.org. 2008-11-05.
  2. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  3. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  4. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  5. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  6. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  7. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  8. Erosion control when skidding logs. Best Management Practices During a Timber Harvest. Cornell Cooperative Extension Forestry. 2008-11-05.
  9. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.
  10. Erosion control when skidding logs. Best Management Practices During a Timber Harvest. Cornell Cooperative Extension Forestry. 2008-11-05.
  11. Erosion control when skidding logs. Best Management Practices During a Timber Harvest. Cornell Cooperative Extension Forestry. 2008-11-05.
  12. Erosion control when skidding logs. Best Management Practices During a Timber Harvest. 2008-11-05.
  13. Glossary. FAO Corporate Document Repository. Forestry Dept. 2008-11-05.
  14. Erosion control when skidding logs. Best Management Practices During a Timber Harvest. Cornell Cooperative Extension Forestry. 2008-11-05.
  15. Limbing and Bucking. U.S. Department of Labour. 2008-11-05.
  16. Forest Harvesting. The Canadian Encyclopedia. 2008-11-05.