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Danger Tree Mitigation Guidelines for Managers

Mechanical Felling

Felling danger trees with mechanical logging equipment is a commonly used method. Managers may select this method after considering operational costs, terrain types, and machine availability.

Some benefits of mechanical felling are:

  • Equipment has protective features to increase operator safety and shield the operator from inclement weather.
  • Equipment can have climate-controlled cabs that minimize operator fatigue.
  • Equipment, operators, and work crews typically are available year round.
  • Equipment capability can increase productivity and efficiency.
    • Felled trees can be stacked for removal.
    • When equipped with lights, working at night is an option.

The Forest Service has a limited inventory of mechanical logging equipment and typically uses contracting for mechanical felling of danger trees. The availability of mechanical equipment may depend on proximity to the worksite of a forest products mill, a road construction company, or a land development contractor. Demand for raw materials drives timber sale bids even if contractors are near the worksite. A timber sale may not be an option if markets for house logs, saw logs, woodchips, or solid biofuels do not exist. In this case, a stewardship contract or a labor intensive service contract (LISC) may be an option.

Mechanical logging equipment ranges from small machines, such as skid steers with small mulcher (masticator) heads, to large machines capable of felling 32-inch diameter at breast height (d.b.h.) trees with a single cut. However, the majority of mechanical equipment is designed for 8- to 28-inch d.b.h. trees.

Because most mechanical logging equipment is privately owned, equipment modification is common. Equipment can be configured with many different attachments.

One type of machine used for felling is the feller-buncher. A feller-buncher can be equipped with different cutting heads:

  • Continuous high-speed disc saws (also known as hotsaws) can fell multiple stems (trees) at a time.
  • Buncher heads can build multistem bundles with accumulatsor arms.

Another machine used for felling is the harvester (figure 8). A harvester can be equipped with a boom-mounted bar saw head (also known as a processor head) to fell, delimb, and buck trees. This cutting head can be used in vertical and horizontal positions, which allows cutting severely leaning or "jackstrawed" trees.

Image of a harvester felling and delimbing a tree.
Figure 8—A harvester felling and delimbing a tree.

Mechanical felling is especially useful when the timber can be sold. Feller-bunchers can transport and deck trees but harvesters require an additional piece of equipment for transporting the materials. According to "Mechanized Equipment for Fire and Fuels Operations: 2009 edition" (MEFFO), feller-bunchers and harvesters are the two most common types of felling machines used for mitigating danger trees

Conventional felling machines are classified by carrier type (tracked or wheeled) and cutting attachment type (swing boom or frame mounted). Some machines have self-leveling cabs. These features determine felling machines' stability and maneuverability.

Tracked machines with a cutting head (hotsaw or bar saw) attached to a knuckle or telescoping boom are common in the West (figure 9).

Image of a feller-brancher grasping and cutting multiple trees.
Figure 9—A feller-buncher grasping and cutting multiple trees.

Swing booms typically have a 360-degree swing that allows a machine to approach a danger tree from any angle. The boom can reach from 22 to 37 feet (figure 10). Boom length is important when a machine is operating in sensitive areas where soil disturbance is a concern. A longer boom can treat a larger area with less machine movement.

Image of a feller-buncher extending its boom to reach a tree.
Figure 10—A feller-buncher extending its boom to reach a tree.

The most common tracked machine (feller-buncher) in the West has a 12-foot-wide excavator-style carriage and a swing boom with a 25-foot reach. Tracked feller-bunchers (figure 11) are designed to travel off road and some allow the operator to level the cab on steep slopes of up to 55-percent.

Image of a pair of feller-bunchers felling and stacking trees.
Figure 11—A pair of feller-bunchers felling and stacking trees.

Some site factors may limit machine mobility. These factors include:

  • Slope
  • Boulders
  • Amount, type, and height of surface rock, cobble, or scree
  • Density and orientation of trees on the ground
  • Large, old-growth stumps
  • Rough, broken ground
  • Surface depressions
  • Unstable or boggy soils
  • Frozen ground, ice, and snow

Equipment, such as bulldozers (with blades) and excavators (with buckets), can mitigate isolated trees by using techniques such as pushing, toppling, and grubbing.

The choice of equipment and mitigation technique depends on the logistics of the project (figure 12), alternate technique costs, and the desired end result. Criteria for mechanical equipment selection can be found in the "Logistics" section on page 12.

Image of a mountain pine beetle-infested landscape in the West.
Figure 12—A mountain pine beetle-infested landscape in the West. Consider the logistical
factors when selecting danger tree mitigation methods in this type of area.

Mechanical mulching can be used where removal of the material is not needed or when there is no market for the raw material. Suitable material is small-diameter trees (less than 12-inch d.b.h. and more commonly less than 8-inch d.b.h.).

Crushing may be a useful technique for large stands of dead, small-diameter trees (less than 12-inch d.b.h.). Trees are crushed by driving over them, usually with a large dozer, or by pulling a weighted drum (figure 13) with a blade to push over and chop the trees. Trees on sites with relatively gentle slopes (less than 25 percent), small-sized rock, and few obstacles are suitable for crushing. Crushing is effective when the entire stand is planned for removal. When residual stem spacing is a concern, crushing is not recommended.

Danger trees also may be eliminated by pushing them over with a blade (figure 14) or boom, or by pulling them over with a cable attached to a winch or large-tracked machine. Grubbing removes trees by pulling up their root system and is not commonly practiced in shallow soils.

Top image of a dozer pulling a crushing drum and a bottom image of the resulting landscape from pulling the crushing drum over it.
Figure 13—A bulldozer pulling a crushing drum (top) and the end
result (bottom).

Image of a bulldozer pushing over a large danger tree.
Figure 14—A bulldozer pushing over a large danger tree.

Safety Issues

OSHA 29 CFR Part 1910.266(f) lists the general machine safety and operational requirements for mechanical logging operations. For more information, consult with your local timber staff or refer to OSHA's Web site at Click on the "Regulations" tab at the top of the page, then click on the link for "1910.266-Logging operations."

OSHA requires that most "industrial forestry machines" meet the Society of Automotive Engineering (SAE) safety standards covering machine structures and materials. Safety features include operator protective structures (OPS), falling object protective structures (FOPS), and rollover protective structures (ROPS).

These protective structures do not guarantee complete protection. For example, not all FOPS are reinforced to withstand the impact of a large-diameter tree. Additional safety requirements, such as reinforced cabs, may need to be included in danger tree contracts, depending on the size of the trees at the worksite.

Managers who are planning danger tree mitigation may need to identify and include contract clauses requiring the protection of seen and unseen site improvements, such as powerlines, shallow or aboveground pipelines, fences, irrigation ditches, paved roads, and private property. For contract clause information specific to your area, talk to your contracting officer's representative (COR) or timber staff. Mechanical mitigation methods usually are the safest option in these situations because the equipment can control a tree's direction of fall.

Combining hand crews and equipment on a worksite is covered by Federal OSHA regulations that require crewmembers to maintain a safe distance from the equipment and falling trees. Equipment operators may have difficulty keeping track of the hand crews. Hand crews working in the same area as equipment must understand the dangers associated with each particular machine. Refer to the MEFFO 2009 guidebook for safety information on specific types of equipment.

When any type of equipment is used, fire precautions must be taken. Metal tracks, tire chains, or moving saw parts may produce sparks when they strike rocks. Friction or sparks can ignite woody debris lodged in saw guards. Hydraulic oil and debris can build up in the belly pan of some machinery and must be monitored. Contracts or permits issued for mechanical danger tree mitigation may require standard fire suppression equipment and specify operational fire control measures.


The MEFFO 2009 guidebook has detailed information for equipment selection and ordering. The following criteria should be used:

  • Scope of job
  • Worksite location and accessibility
  • Size of trees (include number and density of danger trees, as well as residual trees that need to be protected)
  • Types of terrain and vegetation
  • Project timeline and budget
  • Operating season(s)
  • Desired end result
  • Proximity to private land (consider public safety and the protection of structures)
  • Size of affected areas and potentially affected areas
  • Required rehabilitation
  • Availability of equipment
  • Options for moving equipment to and from the worksite
  • Site security for equipment left onsite

Mechanical equipment and operators typically are available during any season, but may be limited by weather conditions or agency requirements. Worksite proximity to a forest products mill is a consideration if raw materials will be sold. Costs may increase substantially if raw materials must be transported long distances. Decking and storing the timber onsite may be a temporary alternative if transportation costs exceed the timber's value due to market downturns. If decking is used, associated risks to public safety and the potential fire hazard must be addressed.

Refer to the forest plan for the area where danger tree mitigation will occur. This plan typically outlines the limitations on use of heavy equipment and defines the applicable best management practices. Most equipment use limitations can be amended through National Environmental Policy Act (NEPA) analysis for a specific project, except in wilderness areas or other areas where equipment use is prohibited.

Contact your forest's timber staff if you have questions about or require mechanical logging in your area. If necessary, you can contact your regional mechanical logging specialist.

Expected Production Rates and Estimated Costs

Mulching machines typically can mulch 2 to 4 acres per day (see table 3). Some machines can both fell and mulch trees in a single operation. Mulching costs range from $300 to $800 per acre. Mulching production and cost variables include the type of mulching equipment, the stand density, tree size, tree species, site conditions, and the desired size and distribution of the mulch. Mulching heads are available in a variety of sizes. The equipment size determines capability and production rates (figure 15).

Crushing machines typically can crush 2 to 4 acres per day. Crushing costs usually range from $150 to $200 per acre. Crushing production and cost variables include terrain type, tree size, tree species, and stand density.

Image of a tracked machine with a mulching head attachment mulching the landscape.
Figure 15—A tracked machine with a mulching head attachment.

Bulldozers and excavators (used for pushing, toppling, and grubbing individual trees) generally are less expensive than other mechanical felling equipment because they are more widely available. Costs (including an operator) vary based on site access, machine size, tree size, tree species, tree age, tree condition, rooting pattern and mass, and other subsurface variables. Because these techniques can cause site disturbance, the need for site rehabilitation should be considered.

Felling machines typically can fell 100 to 300 trees per hour. Depending on the type of felling machine, a tree may be moved, decked, or mulched after it has been felled. Felling machine costs (including an operator) range from $3,000 to $5,000 per day with a production rate of about 3 to 4 acres per day based on commercial silvicultural regeneration prescriptions. Costs and production will vary depending on slope, tree size, tree species, tree distribution, residual stem spacing, ground conditions, job size, site access, and transportation of the felling machine to and from the worksite.