HAROLD T. WIEDEMANN, Texas Agricultural Experiment Station, Vernon, TX 76385
Abstract: Brush sculpting is the selective application of control treatments to prepare brush-infested rangelands for multiple use. Mechanical treatments are discussed which can be used effectively for selective thinning or selective clearing to accomplish multiple use goals. Information is presented on mechanical techniques to achieve good plant kills, and numerous machines are described for individual tree or broadcast treatments including performance examples.
Brush sculpting is the selective application of control treatments to prepare brush-infested rangelands for multiple use including wildlife habitat, watershed management, traditional livestock production, and recreational enterprises. Mechanical treatments have several advantages because they are positive and immediate, but they are often misused because of the old paradigm, “wipe the slate clean.” A knowledge of the regrowth characteristics of targeted brush species is vital to assure that the correct machine is used in the proper manner. In every case, a well thought out brush management plan reflecting your short- and long-term goals should be in place before attempting brush control. Brush contractors, county agents, Extensions specialists and NRCS technicians are good sources for assistant in planning. Mechanical treatments can be individual tree (e.g., selective thinning) or broadcast application (e.g., selective clearing). The purpose of this paper is to acquaint the reader with some of the equipment available and proper application.
Individual tree treatment is accomplished by grubbing or clipping and is an ideal method to sculpt brush-infested land. Sculpting can involve such practices as leaving islands of brush with connecting strips to provide cover for wildlife habitat and a protected pathway to move from site to site while cleared areas provide plants for grazing, or just general thinning of the brush infestation.
Mechanical grubbing is the severing of tree roots below ground by a sharp, U-shaped blade mounted on a tractor (Fig. 1a). Tractors can be farm-type (Fig. 1b), crawlers, or wheel (Fig. 1c) or track loaders depending on the size of tree to be grubbed and type of terrain.
Table 1 describes the best technique to achieve good plant kills when grubbing various brush species in Texas.
Low-energy grubbing is the use of a small tractor on small trees and this can be effective and cost efficient if tree densities are not too high (Wiedemann et al. 1977). These tractors usually have hydraulically assisted blades that enhance the output by tearing roots loose as the blade is rotated. Table 2 lists the performance of a 65-hp crawler tractor with a hydraulic assisted blade (Fig. 1a) grubbing seven different brush species. Performance curves are shown in Figure 2. Grubbing rates vary due to tree size, density, distribution, soil moisture and type of terrain. Grubbing is best suited to tree infestation of 20 to 250 trees per acre. Brush species such as Ashe (blueberry) juniper which do not sprout from the roots can be clipped above ground. This is accomplished by a small loader with hydraulic shears.
With the advent of foam filling of off-road tires, the use of rubber-tired equipment on thorn-infested rangeland is now practical (Wiedemann and Cross 1982). Rubber-tired loaders are especially useful for grubbing (Fig. 1c) because they can travel on roads between sites, and the bucket can be useful for many material handling jobs. Crawler tractors have to be hauled with large trucks between sites. Performance of a wheeled loader in mesquite regrowth 10 years following rootplowing is shown in Figure 3. Farm tractors with front-end loaders are useful for grubbing juvenile trees (Fig. 1b) and performance in small junipers is shown in Figure 3. A popular method for grubbing limited acreage of small trees is to use a 3-point hitch grubber on the rear of the tractor. Some grubber styles require the tractor to drive over the tree first while others back the tractor to the tree and use the 3-point hitch to lift the tree from the soil. Grubbing by backing into the tree averaged 155 mesquites/hour (McFarland and Ueckert 1982) while grubbing with front-mounted units on a crawler averaged 288 mesquite/hour and 432 small junipers/hour (Wiedemann et al. 1977 and Wiedemann and Cross 1981).
Selective clearing is the application of equipment that treats everything in a swath and is termed “broadcast treatment.” Selective clearing implies that selected areas are cleared leaving a mosaic pattern or strips of brush which can follow the contour of the land. The cleared areas should be seeded with native or introduced grasses and/or shrubs that meet multi-use goals. Treatments can involve removing all above ground growth, severing all roots at a given depth or removing root systems from the soil. Clearing usually involves a combination of methods. The main types of machines and their application are discussed in this section including new developments.
Chains. Ship anchor chain pulled between two crawler tractors is widely used for tree felling because it can open up an area quickly and is low cost. Chains vary in length from 200 to 400 feet, weight from 40 to 75 pounds per foot and are pulled in a U-shape. It is used in dense to moderate stands of trees (trunk diameters greater than 3 inches) and is most effective in uprooting when soil moisture is high. It is not effective on shrubs or small trees with limber stems. Effectiveness is short lived because of regrowth and chaining should be used in combination with other treatments for maximum effectiveness. In north Texas, mesquite is chained 2 to 3 years following aerial spraying while in south Texas, dense stands of mixed brush are chained and stacked prior to subsequent treatments (Fisher et al. 1973).
In moderate to dense stands of junipers an elevated chaining technique reduced pulling requirements by 67% to 84% compared to ground level chaining in north Texas and southern Oklahoma (Wiedemann and Cross 1996b). This one-way chaining method is followed by prescribed burning to achieve 98% plant kill in Ashe juniper, but redberry juniper, a sprouting species, is still under study. Elevating the chain is accomplished by attaching a rotating ball in the center of the chain pulled by two crawler tractors. A four-foot diameter ball worked best in junipers 9- to 18-foot tall while a six-foot ball performed better in trees 16- to 22-foot tall (Wiedemann and Cross 1996a).
Rootplows. A rootplow is a heavy-duty, V-shaped, horizontal blade, 10- to 16-feet wide that is pulled by a large crawler tractor at a depth of 12 to 14 inches (Fig. 1d). This operation severs roots, preventing regrowth of nearly all brush species except those with shallow root systems such as whitebrush and pricklypear. Three to five fins, 20 to 30 inches long, mounted at a 28 degree angle on the cutting blade help loosen the soil surface and destroy many of the shallow-rooted species that might
otherwise survive. Rootplowing with fins kills 80 to 99% of many-stemmed mesquite in moderate to dense stands in the Rolling Plains (Jaynes et al. 1968). Chaining following rootplowing smooths the rough soil surface left by the plow, and help to prevent injury to horses, livestock and wildlife crossing the area.
Rootplows were developed to clear dense stands of mesquite and other hard-to-kill brush species in preparation for seeding grasses or crops (Fisher et al. 1973). Rootplowing generally destroys a high percentage of perennial grasses, and reseeding is advisable unless a good supply of seed is present in the soil. The highest survival of grasses occurs from rootplowing and seeding in the winter or early spring. Success of the operation depends on favorable rainfall in the spring months. Sculpting dense brush infested areas by selective plowing and seeding with plants favorable for wildlife habitat, grazing animals and watershed management could enhance the multi-use value of depleted rangeland on fertile soils.
Stacker rakes. Stacker rakes use large, heavy-duty tines which slide on the soil surface while raking moderate to dense stands of brush following chaining (Fig. 1f). These 14- to 19-foot wide rakes use a 6-inch plate welded to the lower end of the tines to uproot or shear off plants during the piling of brush debris. They are used as an initial treatment to control pricklypear and small woody plants. When used alone, a follow up treatment is necessary to control deep-rooted species. Stackers are front mounted on crawler tractors or wheeled loaders. Stacker rakes without the shear plate are sometimes called brush rakes and are more apt to be used to pile large trees following chaining or grubbing when there is an absence of undergrowth.
Root rakes. Root rakes, sometimes called wheel rakes, are used to penetrate into the soil 6-10 inches to remove and pile roots and stumps following rootplowing (Fig. 1g). These 18- to 24-feet wide rakes are pulled behind large crawler tractors. Root raking is an excellent method to clean the land and prepare a seedbed for grasses or crops. Following root raking, rubber-tired farm tractors can be used for tilling and seeding.
Roller choppers. Large drums, 30 to 40 inches in diameter, are equipped with longitudinal blades to chop brush debris as they are pulled by crawler tractors. They are between 8- to 15-feet wide and can be pulled singularly, two in tandem or in a gang of three. Roller choppers are relatively trouble-free in operation, but do use springs in the drawbar to reduce vibration on the pulling tractor. Chopping removes only the top growth of brush and remaining stems produce a flush of regrowth. This is desirable for some browsing animals, and on selected brush species such as shin oak or guajillo. Chopping Bigelow shin oak averaged 5.3 acres per hour using a 15-foot wide unit filled with water (Wiedemann et al. 1980). Chopper are also used for seedbed preparation on log-littered sites following rootplowing.
A recent advancement in roller choppers is the use of small blades welded to the drums in a cylindrical pattern, and these units are called renovators/aerators (Fig. 1h) (Lawson 1994). The advantages of the renovators are that the small blades chop debris, form basins in the soil which harvest rainfall, and the cylindrical pattern prevents the vibration associated with roller choppers. Renovators are used in sparse to moderate shrub-infested rangeland or pastures to improve water harvesting and to remove top-growth of shrubs. Seedbed preparation is enhanced by the basins.
Disks. Disks used on rangeland are the heavy-duty offset style. Blade diameters range from 24 to 36 inches and units are 8 to 12 feet in width. Disks with 36-inch blades are used for brush control on undisturbed soil while units with blade diameters less the 30 inches are used for seedbed preparation following rootplowing. Whitebrush was controlled by disking in the fall (13% mortality) and then re-disking in the spring after the root crowns had sprouted (91% mortality) (Wiedemann and Cross 1980). Disking was followed by seeding to oats in the fall and buffelgrass in the spring. Seedbed prepared by disking (24-in. blade) consistently produced better grass stands than roller chopping or chaining on rootplowed sites at nine location in the Edwards Plateau and Rolling Plains (Wiedemann et al. 1979). If excessive timber prevents the use of a disk, then a disk chain can be used (see section on disk-chain-diker).
Shredders. Brush shredders are patterned after pasture and crop shredders but are much heavier duty. Width is normally seven feet but selected units are 15 feet. Brush shredding is prone to mechanical failures and usually requires extensive modification of the farm tractor which pulls the unit. Modifications include foam filling of the tires or other approaches to prevent flats and mounting front and belly-pan guards and a rear guard to protect the back of the operator from flying debris. Shredding brush leaves an aesthetically pleasing, level plant height between 3 to 6 inches depending on shredder adjustment. Regrowth is extensive following shredding. Downtime was 64% when shredding Bigelow shin oak with a 7-foot shredder in the Edwards Plateau (Wiedemann et al. 1980).
Disk-chain-diker. A new development for seedbed preparation on debris-littered land is the disk-chain-diker (Fig. 1e). It was designed to follow rootplowing, but it can also be use on undisturbed sites when shrubs are less than 8-feet tall. It tills, smooths the land and forms small basins all in one pass and is energy efficient (Wiedemann and Cross 1994). A disk chain is an anchor chain with disk blades welded to alternate chain links. Disking action occurs when the chain, with swivels attached to each end, rotates as it is pulled diagonally. A flexing roller holds the disk-chain gangs in place. The chain diker, which is attached to the rear of the roller, uses special shaped blades welded to opposing sides of each link of a large anchor chain. As it is pulled over tilled land, the chain rotates and the blades leave a broadcast pattern of diamond-shaped basins 4-inches deep. Pulling requirements depend on the size of each component; a standard size unit requires 515 pounds of force per blade and the usual size is 20 blades. A 20-blade unit is 35-feet wide and requires a 165 to 200 hp crawler tractor for pulling. A detail explanation of the unit is covered by Wiedemann and Cross (1990).
In seeding studies over a 3-year period, grass densities were increased 92% by the disk chain compared to seedbeds prepared by smooth chaining in clay loam soil. There was no significant differences in grass densities between seedbeds prepared by disk chaining or offset disking, but both were significantly higher than chaining alone (Wiedemann and Cross 1990). Basin prepared by the chain diker increase grass stands three fold when rainfall was 37% below normal compared to no basins, but there was no difference in the two when rainfall was 25% below normal in a 25-inch annually rainfall zone. Chain diking reduced runoff by 40% compared to non-diked treatments over a three year period on a slope of 0.3% (Wiedemann and Clark 1996).
Regrowth machines. Regrowth plows are designed to be in area where brush regrowth is present following clearing with conventional rootplows (Fig. 1i). They resemble conventional rootplows but have been downsized to fit D-6 crawlers, rubber-tracked Challengers or large farm tractors (Holt 1997). These 10-foot wide units use quick hitches and can plow to a depth of 12 inches.
A regrowth root rake has been designed to operate in concert with the regrowth plow. These 14-foot wide units remove roots from the soil that might otherwise sprout and pile them along with any above ground brush debris (Holt 1997). They use the same quick hitch as the regrowth plows.
Table 1. Mechanical techniques to prevent regrowth of nine different brush species.1
|Mesquite||Sever taproot below basal crown (below bud zone), 6 to 14 inch depth, depends on size of tree|
|Redberry juniper||Sever taproot below basal crown, 6 to 12 inch depth, depends on size of tree|
|Blueberry (Ashe) juniper||Sever trunk above or below ground level, does not sprout from roots|
|Algerita||Remove basal crown and buried stems under entire canopy area, 4 to 6 inches depth|
|Huisache||Sever taproot below basal crown, 6 to 12 inch depth, depends on size of tree|
|Twisted acacia||Sprouts from roots, remove as many as possible.|
|Blackbrush||Sever taproot below second lateral, 6 to 12 inches deep, depends on size of tree|
|Whitebrush||Remove basal crown, depth of 4 to 6 inches|
|Catclaw||Sever taproot below first lateral and remove all buried stem with adventitious roots|
1Based on grubbing studies listed in Table 2.
Table 2. Performance of the low-energy grubber in Figure 1 operating in six different brush species at maximum output. Normal field efficiency is 70 to 85%.1
|Species||% Plant kill||Trees/acre||Dollars/acre2|
|Mesquite||80||20 to 100||3.00 to 12.00|
|Juniper||98||30 to 175||4.50 to 27.00|
|Huisache||75||75 to 225||9.50 to 30.00|
|Algerita||93||15 to 80||5.50 to 16.50|
|Twisted acacia||0||30 to 250||3.50 to 16.00|
|Blackbrush||86||20 to 130||6.50 to 19.00|
|Catclaw||85||50 to 150||8.50 to 20.50|
1Adapted from Wiedemann et al. (1977), Wiedemann and Cross (1981),Wiedemann (1982), Cross and Wiedemann (1983, 1985, 1997).
2Based on a contractor’s cost of $45/hr to operate on a ranch site.
Figure 1 (a-d). Types of machinery used to control brush. See text for descriptions.
Figure 1 (e-i). Types of machinery used to control brush. See text for descriptions.
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Updated: Mar. 18, 1997