Mechanical Methods

Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.

In many situations, hand labor is unavailable or cost prohibitive and more horsepower is needed. Developed for forestry and land clearing operations, mechanical methods use machines to clear large or dense infestations. Skid-steer loaders, mulchers, and tractors and bulldozers having special attachments have been used to reduce invasive woody plants. These methods can complement and increase the efficiency of herbicide treatments. Mechanical methods include root-raking attachments on bulldozers for preparing land for construction, landscaping, and other development. Heavy machinery root raking has eliminated privet thickets and kudzu patches (the uprooted plants are subsequently piled up and burned). Land clearing methods have also been used in large restoration projects when infestations are extensive and dense, followed by herbicide applications to resprouts and seedlings followed by revegetation with desirable plants. Some equipment, with appropriate attachments, can prepare the site for seeding and tree planting. Most important is using the appropriate size equipment to meet job requirements and minimize damage to soils and streams. Equipment and attachments include:

Skid-steer loaders (modified for kudzu removal)
Four-wheel drive tractors with brush mower, mulcher, harrow, seeder, seed drill, and tree planting attachments
Mulchers (masticators)
Bulldozers with sheer blade, root rake, ripper, harrow, combination plow, tree planter, fire plow, and grubber attachments

Timely followup with other control methods is essential, because disturbance of the soil creates favorable conditions for regrowth from seeds and root fragments. Mechanical removal with larger equipment may not be appropriate in natural areas unless the situation for restoration is critical because of special habitat and restoration plan requirements.

Skid-Steer Loaders

Paul David Blakely of the Coalition to Control Kudzu without Chemicals, a nonprofit volunteer organization in Spartanburg, SC, has developed attachments and techniques that equip skid-steer loaders for kudzu removal (http://kokudzu.com/SkidSteer- Loader.html). Tracks attached to the tires of the loader help traction and access to difficult terrain. Additional and wider spaced pronged forks added to the skid loader are inserted beneath the mat of vines, lifted up, and tilted back to pull vines and even kudzu root crowns for removal. Forward motion of the machine can roll the mass of vines into a pile. Other attachments and techniques have been developed by Blakely and the coalition for a range of conditions and treatment objectives. Skid loaders are easily transported, highly maneuverable, and capable of lift and tilt, which gives this machine, if equipped with appropriate attachments, potential for other invasive plant removal tasks in dense infestations.

Four-Wheel-Drive Tractors

For decades, right-of-way and forestry managers have used specially equipped fourwheel drive tractors to apply an array of vegetation management treatments. The advantages of a tractor (over heavier machinery) include good traction for pulling implements in steep terrain and moderately wet soils, versatility of power takeoff (rear power shaft) to drive implements, convenient transportability, and low operation costs. A tractor must have a substantial cab guard to prevent penetration of stray tree limbs into the operator’s cab area and keep the operator safe in the event of rollover and other accidents.

Depending on its size and configuration, a tractor can have a wide range of implements. A tractor can pull mowers and push mulcher attachments that reduce the height of herbaceous and woody invasive plants, prevent seed production, open up access for herbicide applicators, and otherwise prepare sites for further treatment. Tractors can pull plows and harrows that prepare soil, and seeders, seed drills, and fertilizer spreaders that can establish and promote growth of desirable plants. It can pull planting machinery for reforestation to plant pine and hardwood seedlings, and possibly native grass plugs. Tractors are often used to mount or pull herbicide sprayers. With this versatility the four-wheel-drive tractor is gaining favor as one of the most valuable pieces of machinery for integrated treatments aimed at restoration.

Four-wheel-drive tractor with a boomless sprayer.

Mulchers and Mulching Attachments

Mulchers and mulching tractor attachments are increasingly preferred for reducing both standing invasive and native woody plants in dense infestations. Mulching machines are best for nonselective situations where the cost of selective control is prohibitive. Mulching machines are land clearing tools that can cut through dense stands of nonnative plants, reducing them to small pieces of woody debris. A one-operator machine can frequently cover 2 to 4 acres a day depending upon the terrain, vegetation type, and job requirements. Mulchers are designed as a single machine, while mulching attachments can be mounted on many types of equipment, tracked or wheeled, and even on the end of an articulated swing boom. The boom mount results in less trafficking damage to the soil because front-mounted mulchers must travel back and forth across the treatment area. The two basic types of mulching designs are vertical shaft and horizontal shaft. Either type can be equipped with pivoting flail-type cutters or rigidly mounted cutting teeth. Cutter types vary in the size of their shredded output, with smaller and faster rotating teeth producing the smallest size.

After a mulched area has dried and regrowth occurs, prescribed burning can be used to reduce the surface mass, while herbicides can be more efficiently applied to the resprouts. Klepac and others (2007) reported on a trial of mulching dense Chinese privet followed by Garlon 3A herbicide applications to the stumps. Subsequent applications of foliar sprays to resprouts were required because stumps were often hidden by debris, with a total cost of $737 per acre. Mulching is currently a fairly expensive operation, but costs should decrease as the number of competing contractors increases.

Bulldozers

Bulldozers (or tracked tractors) are made in a range of sizes, and the larger ones have played roles in forestry operations for decades. Highly developed bulldozer attachments equip them for residual tree sheering and piling after timber harvest, soil preparation, tree planting, and fire line plowing. These same operations have found use in large-scale invasive plant reclamation projects tackling extensive woody infestation, although smaller tractors and implements are used. The amount of soil disturbance and compaction is considerable with bulldozers, varying by equipment size, soil moisture, number of passes, stand density, and tree/shrub size, but often less than with wheeled tractors. The ground pressure of tracks is less than with wheeled equipment.

Attachments for bulldozers are described below:

Sheer blades are usually mounted at an angle to forward travel with a lower jutting serrated dozer blade that fells trees when pushed against them.
Brush rakes and root rakes are blades with extending lower teeth that dislodge surface roots and stumps of smaller trees. Brush rakes have been used in restoration to clear dense large privet stands in preparation for other treatments before native tree and grass planting.
Rippers are thick steel shanks mounted on the sides of bulldozers to penetrate and loosen the soil and subsoil with forward motion along an intended tree planting row. This treatment is done before tree planting to facilitate root penetration and growth where there are plowpans or hardpans in the soil. However, the benefits for pine establishment in the South have been reported to be minimal, except on particularly rocky soils.
Disk harrows are gangs of disks often pulled in tandem across a harvested or cleared site to loosen surface soils and incorporate organic debris for more rapid decomposition and to facilitate planting. *Combination plows are pulled behind the tractor and can have a ripping shank, colter, wing plow, and/or offset disk harrows on the same implement depending upon the soil conditions. Soils are both loosened and piled within an intended tree or shrub planting row to benefit early survival and growth.
Bedding plows are most useful in seasonally wet coastal sites for raising tree planting rows to prevent water logging and to concentrate scarce soil nutrients.
Tree planters are pulled behind a tracked or wheeled tractor with implements that form a planting slit and then close it after the operator riding in the planter inserts a tree seedling or seedling plug. Native plant seedlings can potentially be planted with this machine for restoration.
Fire plows are pulled behind a tracked or wheeled tractor that clears and parts surface soils in a wide path (several feet across) to a depth of about 6 inches. This fire line of bare soil can be used to set a backfire in preparation for prescribed burning or stopping wildfires.
Grubbers are sharp, U-shaped blades mounted on the front of crawler tractors, wheel loaders, excavators, or farm tractors to uproot individual trees or large shrubs. Other units clamp onto the tree and pull the tree from the soil. The size and type of tractor depends on the size of trees to be grubbed and the terrain. Units are commercially available, but many are fabricated in welding shops. Farm tractors with small, three-point hitch grubbers are popular for use on limited acreages of previously cleared areas. Grubbing is not practical in rocky soil or when tree densities are greater than 250 per acre over extensive acreages. With care, selectivity is afforded with this method, while soil disturbance is great.

If not planned and enacted with care, mechanical root raking and disking can intensify and spread infestations of invasive plants that have runners by chopping the runners into resprouting segments. All mechanical equipment used in treating invasive plant infestation can transport seeds, roots, rhizomes, and spores to other sites. Equipment inspection and cleaning is essential to stop subsequent invasive plant spread.