Mulchers

(Also referred to as Masticators or Brushcutters)

Description

Mulchers cut and chop or grind vegetation into particles that are usually left on-site as mulch. The primary purpose of mulching is to lower the vertical height of fuels, shift fuel volume into the 1 and 10 hour size classes, as an alternative to chemical treatment of competitive species, for aesthetic treatments, right-of-way maintenance, and range rehabilitation.

Mechanical Configurations

Mulchers are mounted on a variety of chasses including skid steers, excavators, farm tractors, four wheel drive loaders, and dozers. They may also be purpose built machines based on any one of those machine forms.

Mulchers come in two basic forms, vertical shaft and horizontal shaft. A horizontal shaft mulcher is basically a chipping drum mounted on a carrier. The drum is continuously spinning as the machine moves through the stand. Some mulchers have push bars to push the severed trees away from the machine, but other than that there is no control over the direction of fall.

Most vertical head mulchers resemble robust lawnmowers, but some resemble chipping discs.

Mulchers mounted on skid steers, tractors, four wheel drive loaders, and dozers are pushed through the stand. As they sever the stems, the stems fall in front of the machine and are shredded as the machine drives over them.

Mulchers mounted on excavators and wheel loaders are capable of mulching standing trees. This provides more control over the process and prevents running the head into the dirt.

Operational Considerations

Physical Limitations

Tree Size: Vertical shaft mulchers are limited in the size of tree they can fell. The size they can handle varies with individual models, but a general rule is a maximum of between 6- and 8-inch material. Horizontal shaft mulchers can handle much larger material, up to 30 inches, but felling trees of this size may pose a risk to the equipment or operator.

Slope: Slope limitations follow the general guidelines for the type of carrier being used. See the chassis page for more information on slope limitations.

Ground Conditions: Rocky ground will wear out the teeth faster and may pose a fire hazard. Uneven ground makes control of the head difficult and may result in poorly processed material.

Safety Concerns

The biggest safety concern with mulchers is flying objects thrown by the head. Most mulching occurs at ground level, so the chance of picking up rocks or other debris is high. Most mulchers have shrouds that direct the material towards the ground. When the mulching head is lifted into the air however, the shroud may become ineffective. It is important that adequate FOPS are mounted on the carrier to protect the operator from flying debris. See the section about chassis configuration for a more thorough discussion of cab safety features.

Another safety concern is cutting standing trees. Mulchers capable of lifting the head and cutting trees from the top down are a safer option when larger standing trees need to be mulched.

Treatment Options

Excavator mounted mulchers can be used on steeper slopes, greater than 30%, or where it is important to minimize soil compaction. The excavator does not need to travel everywhere it is mulching, which is an advantage over the other machine forms. The disadvantage is that the width of the mulching head is at most half the width of the other machine forms’ heads. This means that more passes must be made to mulch a given area. This style of mulcher is safer where larger standing trees are being mulched.

Mulchers mounted on a wheel loader style chassis have a boom which enables them to cut standing trees when necessary.

Deciding which mulcher should be used is a matter of the number and size of standing trees need to be cut and the slope. Mulching of larger pieces, greater than 3 inches in diameter, should be minimized to retain coarse woody debris and to optimize efficiency.

There are certain treatment factors that can affect the cost of treatments. These factors may be controlled by the prescription. Some key things to consider are:

Minimize the amount of volume treated

• Leaving 3 inch and larger stems permits coarse woody debris to be retained on site and helps to optimize efficiency.
• Mulchers should not be used as felling machines.
• For big machines, mulching is typically ineffective at 25 tons per acre or greater.
• When planning a mulching operation, specify the largest acceptable resulting fuel sizes.

Minimize constraints on travel

• Avoid treatment areas narrower than 66 feet wide.
• Avoid operating in dense residual stands greater than 100 trees per acre.
• Minimize areas of steep slope (20 percent or greater) or broken terrain.
• Do not apply soil disturbance constraints unless necessary.

Provide adequate access for service

• Equipment requires road access for fueling and maintenance.

System Interactions

As a system, mulching may be used to clean up a stand following conventional timber or felling operations. Mulchers are capable of reducing limbs, tops, and cull material to shredded particles on the forest floor that can better hold runoff and degrade more quickly back into the soil. This also decreases the fuel ladders created by small standing trees with high limbs that are left after conventional operations.

Mulching may also be considered a complete system with felling and processing being completed in one step, but of course with no extraction or utilization of the processed material. This type of system is useful for decreasing fuel loading on a site and reducing competition to the desired species on the site.

Research

• Title: Fuels planning: science synthesis and integration; economic uses fact sheet 01: mastication treatments and costs
  Author: USDA Forest Service, Rocky Mountain Research Station
  Date: 2004
  Description: Mastication, or mulching, is a mechanical fuel treatment that changes the structure and size of fuels in the stand. This fact sheet describes the kinds of equipment available, where mastication should be used, and treatment factors affecting cost.
• Title: Mastication: A fuel reduction and site preparation alternative
  Author: Halbrook, Jeff; Han, Han-Sup; Graham, Russell T.; Jain, Theresa B.; Denner, Robert
  Date: 2006
  Description: During the fall of 2005, a study was conducted at Priest River Experimental Forest (PREF) in northern Idaho to investigate the economics of mastication used to treat activity and standing live fuels. In this study, a rotary head masticator was used to crush and chop activity fuels within harvest units on 37.07 acres. Production averaged 0.57 acres/hour (range 0.21-0.89 ac/hr). Costs average $530 per acre (range $335-$1395 per acre). Additionally, eleven fireline segments totaling 2326 feet were constructed through activity fuels using the same mastication machine. On average, 18 ft of fuelbreak was created through mastication (range 16-23 feet) combined with 4 ft of fireline (range 3-5 feet) with 100 percent mineral soil exposure constructed down the center of the trail. Total debris (including activity fuels) ranged from 26-61 tons per acre with production averaging 6.9 feet per minute (range 3.1-9.1 feet). This manuscript, concentrates on cost-analysis concerning mastication and it has shown that stand and site characteristics such as slope, residual tree density, and total acreage can significantly affect the time required to treat these areas. This research as it progresses will provide data on cost-benefit analyses comparing mastication, prescribed fire, and grapple piling/burning site preparation and fuel treatment alternatives.
• Title: Midstory reduction treatments with a Woodgator T-5
  Author: Mitchell, Dana; Rummer, Bob
  Date: 2001
  Description: Many stands in the Southern U.S. have developed an increased amount of non-commercial midstory and understory components. Managers may not be able to prescribe burn these stands, due to smoke management concerns or risk of fire climbing into the crowns of the overstory trees. A variety of machines have been designed to mulch, shred, or chop standing vegetation to clear rights-of-way, prepare fire breaks, clean real estate tracts, and site prepare planting sites. These machines also can be used for mid-story reduction treatments as a substitute for prescribed fire.
• Title: Midstory reduction treatments with a Shinn SC-1
  Author: Mitchell, Dana; Rummer, Bob
  Date: 1999
  Description: Fire control and exclusion have led to an increase in the non-commercial midstory and understory components of forest stands on the Croatan National Forest near the coast of North Carolina. The growth of this vegetation has created a fire risk in the wildland-urban interface. The use of a mechanical fuel management treatment is being explored in areas where fire cannot be safely implemented.

Products and Markets

Markets for chipped material exist, but the ability to extract the material from the stand is difficult. Most mulching is performed with the intent of leaving the material on the ground.

References

• USDA Forest Service, RMRS. Fuels planning: science synthesis and integration; economic uses fact sheet 01: mastication treatments and costs. 2004.