by ARTHUR W. SAMPSON, Professor of Forestry Emeritus, and ARNOLD M. SCHULTZ, Associate Specialist, School of Forestry, University of California
This article represents the second section of a paper which has been prepared at the request of FAO. The first section appeared in Unasylva, Vol. 10, No. 1, together with a list of species mentioned and literature cited; the further sections will appear in succeeding issues of Unasylva. The whole series, when completed, will be made available under a separate cover.
Equipment for Mechanical Brush Clearing
LARGE-SCALE efforts to control undesirable woody species has awaited mass production of machinery to do the job effectively and economically. Our modern age of large-scale operations tends to overlook, however, that many small-scale efforts, using homemade hand tools, might do the same job more effectively and more economically. Time and personal convenience are the main differences between the two. Both types of equipment are discussed in this section.
The equipment is briefly described and illustrated with photographs or drawings wherever possible. The comparative advantages and limitations of each piece are enumerated and, so far as possible, the approximate costs per acre for certain stipulated conditions are cited. Except when specifically discussed, it will be assumed that for larger vegetation, heavier pieces of equipment would be used.
TRACTOR-POWERED MACHINERY
Bulldozers
The bulldozer is the standard machine for the removal of brush and trees. It is a tractor equipped with a heavy pusher blade in front, which can be raised or lowered by hydraulic or cable control (Figure 8). The blade has a high concave moldboard with its bottom edge fitted with a steel-hardened, knife-like member which projects out ahead of the blade. The manner in which the blade is hinged to the pusher arms and lift rods differs in the many commercial models. Although the dozer blade is usually associated with a crawler-type tractor, blades fitting most wheel-tractors are available (24). 1
1 The references to literature cited were given in Unasylva Vol. 10, No. 1, with the first part of this paper.
When clearing brush the bulldozer is used in two ways. One procedure is to hold the blade to the soil surface or a little below it, thus uprooting most of the larger stems while breaking off the smaller, brittle material. The brush is either left lying or pushed into piles or windrows. This method results in much soil disturbance. The grassy cover is frequently broken, huge holes are left where tree roots have been excavated, soil is pushed up in heaps around brush piles, and much of the land is temporarily bared of litter. On erodible sites in particular, such practice should be avoided. The other procedure is to "walk over" or mash the brush with the blade held from a few inches to a foot above the ground. The litter is left in place and is scattered uniformly over the soil surface. Where the brush is brittle, the tractor tracks tend to mulch the brush stems even more. This method does not work well in young brush which springs back to its original position after the dozer has passed over or in stands having numerous large trees which must be cut by some other method or else uprooted. If the land is burned after bulldozing, it is advantageous to have the ashes scattered evenly over the area. Mashing followed by burning is a common practice on rangelands in California and elsewhere.
For reasons already discussed, only approximate cost figures can be given for bulldozing. Several examples follow. In Texas, in 1946, bulldozing of heavy stands of brush, not including piling or windrowing, cost from $8.50 per hour for light tractors to $15.00 for heavy tractors. On a per-acre basis, this is from $11.00 to $14.00 $27.50 to $35.00 per ha.) depending on the brush (19). Heavy bulldozers are more expensive to operate by the hour than light ones but may be much cheaper by the acre since they are more efficient. In California, in 1955, the average cost per acre in brush which can be knocked down and pushed into windrows in one continuous forward movement is about $10.00 ($25.00 per ha.) (6). For heavier and denser brush the estimate per acre is from $10.00 to $20.00 ($25.00 to $50.00 per ha.) and in full density stands, where much backing and turning is required, the costs may run from $20.00 to $50.00 per acre ($50.00 to $125.00 per ha.).
Brush piling equipment
After the brush has been mashed or cut by bulldozers or tree dozers, specially designed rakes may be used for piling. Such brush rakes or bull rakes lift up the brush, allowing the soil to fall down through the teeth of the rake. The soil which still clings to the roots can be knocked loose by lifting and dropping the load several times in rapid succession. When the brush is to be burned, a good method, facilitated by the rakes, is to pile brush as it is being burned. In this way, more of the coarse stems are consumed than if all the piling or windrowing is done first and then burned.
Buck rake (Figure 9). A modification of the hay buck rake is made, attachable either to wheel or crawler-type tractors. The teeth of the rake are made of 2-inch (5 cm.) pipe which will bend without breaking when a stump or stone is struck. Overloading on a tooth will cause it to bend down without breaking, and the neighboring teeth take up part of the load.
Rakes attached to wheel tractors generally do not have enough clearance below the rear end of the frame when brush is moved across fields with high stumps and snags. When lifted high, a 1,000 pound (455 kg.) weight of brush will give the tractor poor balance while in motion. Crawler tractor equipment is generally more efficient on rough brush lands.
Brush rake (Figure 10). The brush rake or "stacker" consists of a concave moldboard, similar to that of a bulldozer, a top guard to prevent limbs from damaging the radiator of the tractor, and teeth extending below the moldboard and slightly forward. The teeth are fitted with skid shoes. Gathering springs on either side of the rake increase the load carrying capacity. Since the teeth are shorter than those of the buck rake and not held horizontally, the brush can only be pushed forward and not lifted. However, there is enough clearance between the teeth and under the moldboard to permit dirt-free piling.
Grubbing equipment
A number of devices which can be bolted to the dozer blade or attached to the tool bar or pusher arms in place of the ordinary concave blade serve to perform specialized tasks in brush clearance. When attached, these pieces inherit the stability and strength of the bulldozer] and also its mobility. Grubbing of roots and stumps, often 18 inches (45 cm.) or more underground, exerts much more strain on machinery than surface equipment receives. For this reason these grubbing implements are simple, massive pieces which do not break readily. A few of the grubbing implements to be described are pulled behind the tractor.
Tree dozer (Figure 11). The tree dozer has a huge push-bar or bumper extending far out in front of a V-shaped blade. After a tree has been pushed over with this bar, exposing the roots, the blade is lowered and the roots are freed from the ground with the sharp cutting edge on the bottom of the blade. The bumper or "knock-down beam" of some models is controlled independently from the cutter blade or plow below (Figure 12).
Tree cutter (Figure 13). The tree cutter is useful where stems are large and where stumps cut flush with the soil surface are not objectionable. Trees up to 20 inches (50 cm.) in diameter can be cut. If there are no larger than 12-inch (30 cm.) trees or shrubs in the stand, a 10-foot (3 m.) swath - the width of the blade - can be cut with the tractor in third gear, without any backing or turning. The tension bar at the top extends forward beyond the cutting blade. It bends the tree, putting the fibers under tension. The blade at the bottom, which is mounted on heavy duty standards, then slices through the trunk.
Root cutter (Figure 14). This consists of a short blade set between two heavy steel supports. These supports slope back toward the front of the tractor so that the blade makes first contact with the root or stump. The blade digs deeply enough to cut below the bud zone. Since the entire attachment can be lifted by hydraulic control just like a bulldozer blade, brush plants or whole trees can be lifted right out of the ground after the roots are cut.
Pull-type root cutter (Figure 15). This operates on the same principle as the previous root cutter except that it is pulled behind the tractor. It cuts 12 to 18 inches (30 to 50 cm.) below the soil surface. The blade is V-shaped, which makes it easier to pull through the subsoil. The width of cut is about 11 feet. The blade can be raised or lowered either with hydraulic or cable lift. The rig shown in the photo plows approximately 2 acres (0.8 ha.) per hour at $10.00 per acre (S25.00 per ha.).
Stumpers. Two types of implements are known as stumpers. The detachable stumper in Figure 16 is attached to the front of a dozer frame. It is cast from one piece of steel. The four teeth are hard-faced and provide a biting width of 30 inches (75 cm.). The stumper is driven into a stump where the teeth hold it fast. Then, by forward motion combined with hydraulic lifting, the stump is uprooted. The pull stumper (Figure 17) attaches to the rear of the tractor and is operated by cable control. The tooth is also one-piece cast steel, securely fastened to a heavy duty frame. It can be used to cut lateral roots 3 feet (90 cm.) deep as well as for pulling stumps.
Stinger (Figure 18). The stinger blade is a modified stumper. It is a narrow plate attached to the center or one side of the dozer blade. It extends below the blade about 12 inches (30 cm.) and slightly ahead of it. The stinger digs out small trees and shrubs which cannot be forced out by the bulldozer or tree dozer. The single tooth concentrates the full power of the tractor on a narrow front.
Juniper bit (Figure 19). This eight-toothed, heavily reinforced bit was especially designed for lifting large shrubs, such as juniper, out of the soil in one operation. It is bolted securely to one side of the moldboard and to the cutting blade of the dozer. The other side is used as a regular bulldozer for pushing down smaller brush.
Root rake (Figure 20). The root rake or grubber blade has 6 to 8 teeth extending forward and below the cutting blade of a dozer. This implement is used most effectively for "combing" roots out of the soil after the larger trees have been cut down and uprooted, It can also be used for piling. Rakes work best in dry or sandy soils. Sticky soils may clog up ahead of the teeth. The photograph was used to illustrate the fact that none of the "heavy duty" implements are rock-proof.
One of the chief advantages of the various forms of toothed attachments over the regular bulldozer blade is that they actually move little soil. In order to give the same grubbing action at a depth of 12 inches (30 cm.), the solid dozer blade would gouge out a foot of soil which would be carried along for some distance by the moldboard. In the root rake, stinger, and horizontally held blades, the soil can sift around the teeth or over the blade and no soil movement occurs.
The effect on the soil is similar to that of a subsoil tiller used on agricultural lands. Frequently the soil is so loose that it is a poor seedbed for grasses unless it is packed or rolled.
Grubbing devices are used when sprouting species are involved and where it is desired that no obstacles remain in the soil which would be harmful to future farming practices. In such cases, two or more kinds of equipment may be used in the same brush-clearing operation. For example, in Texas shrublands, a common practice is to clear the brush in four steps:
1. knocking brush down with bulldozer or tree dozer;2. piling with bull rake;
3. root plowing - cuts the roots at 12 to 18 inches (30 to 50 cm.) under ground and elevates them to the surface;
4. root piling.
Approximate time and costs for each part of the complete operation in 1946 were:
1. 4/5 to 1 acre per hour, $11.00 to $14.00 per acre (0.32 to 0.4 ha. per hour, $24.50 to $35.00 per ha.);2. 1 ¼ , to 1 ½ acres per hour, $6.00 to $8.00 per acre (0.5 to 0.6 ha. per hour, $15.00 to $20.00 per ha.);
3. ¾ to 1 ¼ acres per hour, $11.00 to $13.00 per acre (0.3 to 0.5 ha. per hour, $27.50 to $32.50 per ha.);
4. 2 acres per hour, $11.00 to $13.00 per acre, totaling $35.00 to $45.00 (0.8 ha. per hour, $27.50 to $32.50 per ha.) for the whole procedure (19).
Disc harrows
A number of types of disc harrows (also called disc plows or simply discs) have been developed especially for brush control work. Their construction is based largely on the principles of the standard farm disc. The disc harrow is designed to accomplish three purposes in brush control: kill the plants, mulch the stems, and prepare a seedbed. The implement is essentially a series of concave discs with sharpened edges so placed that a cutting and loosening action is obtained. It may or may not be mounted on wheels.
Although the standard disc plow will be described first, the most effective variations of the implement for brush clearing are the offset disc harrow, the wheatland-type plow, and the brushland plow (40). Another variation - the eccentric disc plow or range pitter - can be used for brushlands but was built primarily for another purpose.
Standard disc plow (Figure 21). This plow has a single gang of disks, up to six in number, each with its own bearing. The discs are set obliquely to the vertical, and usually some adjustment of the angle can be made for different plowing conditions. The frames are mounted on wheels which makes it possible to adjust the depth of plowing.
The disc plow is not very effective in stands of dense brush but is useful for plowing heavily sodded meadows which have species with thick, tough taproots. It works much like a moldboard plow but will scour better in heavy clay soils and can penetrate soils which are too hard or dry for the moldboard plow.
This implement is costly to operate. The width of cut is relatively narrow - 54 inches (135 cm.) for a six-gang plow - and takes at least a 60 to 70 horsepower tractor to pull it. The plow cannot be used on land with large imbedded rocks.
Offset disc harrow (Figure 22). The offset disc is so named because it can be set to run either to the right or left of the center line of the tractor which pulls it. It is a two-way disc which has no wheels, hence the entire weight of the implement rests on the blades. Two gangs, each mounted on separate frames, are situated one ahead of the other. The front gang throws the soil in one direction, the rear in the other. Depending on the kind of brush or soil involved, added weight and durability are incorporated in the construction by using heavier frames. The United States Forest Service has developed several models of the offset disc harrow for sagebrush control work in the western United States. They differ chiefly in the weight of the frame. One model has scalloped edges on the disc blades (Figure 1).
The offset disc harrow is effective in removing sagebrush and other low-growing, brittle forms of brush.
The implement can be weighted down with rocks if the soil is too firm, but this puts much strain on the frame and discs so that excessive breakage is imminent. Breakage is also high on rocky areas, causing chipping of blades and broken arbor bolts. Depth of penetration is difficult to regulate. Power requirements vary with the soil, size of brush, and weight of the implement. An extra heavy duty 10-foot (3 m.) model needs an 80-horsepower tractor; a 6-foot (1.8 m.) light duty harrow can be pulled with a 20 horsepower tractor on level ground. Other advantages of the lighter equipment are lower cost of construction and easier transportability.
The offset characteristic is of no special advantage on brushlands except where it is desired to disc under low hanging branches of trees. Usually it is hitched to the center of the drawbar.
Wheatland-type plow (Figure 23). This is a single gang, one-way plow. It consists of a series of vertical discs spaced along a common axle, all of which revolve as a unit. The axle is at an angle of from 35 to 50 degrees with the line of travel. The implement is mounted on three wheels, which allows leveling and depth adjustments to be made.
In brush eradication the wheatland-type plow is best suited for use on relatively rock-free ground. Kills on sagebrush in western United States have been as high as 95 percent. It will kill 5 to 10 percent more sagebrush than the heavy duty offset disc harrow. The adjustable plowing depth makes it convenient to use in areas where brush density or soil compactness varies from place to place. But because of the number of adjustments and the lighter frame, the implement is easily broken and more care is required than with the offset disc.
A 40-horsepower tractor will pull a 9-foot (270 cm.) plow on level ground. The machine as now built weighs about 300 pounds per foot (100 lb. per m.) of cutting width. A seeder box attachment is available.
Eccentric disc plow (Figure 24). This plow also has a single one-way gang. Every other disc is mounted about 2 inches (5 cm.) off center on the axle or gang bolt. These eccentric discs are spirally arranged so that every fourth eccentric disc is cutting at its full depth at any one time. The discs in between have true centers. This arrangement decreases the machine's effectiveness in brush removal but leaves the soil pitted with 3-inch holes - from 6,000 to 7,000 per acre. These pits hold excess surface water following rainfall which in turn is beneficial to the growth of rangeland vegetation (3). The wheatland-type plow can be converted into an eccentric disc by placing every other disc 2 inches (5 cm.) off center.
FIGURE 27. "A"-rail: this type of rail throws the brush into windrows around the end of the side members. Railing equipment is not sold commercially but can easily be made in any farm shop from available materials. Designs and specifications for the "A"-rail and the Supp rail shown in Figure 28 can be obtained from the U.S. Forest Service, Washington 25, D.C. (U.S. Forest Service)
Brushland plow (Figure 25). The brushland plow was designed especially for rough, rocky land. The principles of plowing are the same as those for the previous types of disc harrows. Here, however, the discs are mounted in pairs. Each pair is held in the ground by spring tension. Thus, when a rock, stump, or heavy root obstructs the way, the pair of obstructed discs can raise up while the others continue to operate.
The discs of a pair are of two sizes. The forward disc is 28 inches (70 cm.) in diameter and the rear one, 24 inches (60 cm.). With two different peripheries, the discs have a slicing action as they roll forward and hence are more likely to cut the brush roots instead of rolling over them. When a pair of discs are raised, the blades become straightly aligned, which results in more of a rolling action over rocks than scraping. As a consequence, there is less strain in the edges and disc arms.
The brushland plow is made with a heavy steel frame and weighs about 3 tons. It has a 10-foot powered cutting width and can be pulled with a 40-horsepower crawler-type tractor on fairly level ground. Its advantages over other types of equipment are the low maintenance and breakage costs even when used on rocky land. In the sagebrush country, kills of 100 percent have been obtained on areas with few rocks and 90 percent or more on rocky areas.
The machine as now constructed costs about twice as much as the offset disc harrow or the wheatland-type plow of the same cutting width. Because of its weight, it is difficult to transport. A detailed account of the construction and limitations of the brushland plow can be found in (8).
Harrows
Pipe harrow (Figure 26). The pipe harrow or Dixie drag was built for the removal of mature sagebrush on very rocky land. It consists of a series of pipes beset with steel spikes, dragged behind a horizontal spreader bar. Each pipe is swiveled so that it rotates freely and cleans itself of stems and clods. It bounces over the rocks, spins, rips out brush plants, gouges into the soil, and covers seed where enough soil is present. In the process it removes from 50 to 70 percent of the sagebrush. The rockier the ground - up to a point - the better it works and cleans itself.
The pipe harrow does not approach the various disc harrows in effectiveness, either as to kill of brush or to seedbed preparation. As stated, however, it is specifically designed for use on land too rocky for these latter implements to work without excessive breakage. The pipe harrow is a sturdy implement. Breakage is uncommon but the spike teeth and the swivels wear out in time. A 14-foot (425 cm.) unit can be pulled by a 50-horsepower tractor. If two harrows are used side by side, they can be pulled with an 80-horsepower tractor, although a heavier one is more efficient. On side slopes, the harrow should be equipped with troughs to keep them from jumping across one another.
Other harrows. The spring-toothed, spike-toothed, and rotary harrows are useful in covering seed after brush clearing and broadcast seeding of range lands but are of little value in the clearing operation itself.
Rails and cables
One of the oldest methods of removing brush on a large scale is that of dragging heavy objects such as railroad rails, cables, or chains behind tractors. Rails are especially effective in stands of the brittle-stemmed brush, such as big sagebrush in the western United States. Chains and cables can be used to advantage for considerably larger plants.
Many variations of design for rails have been used, with different degrees of success. After tests made on sagebrush by the United States Forest Service, two designs are especially recommended (40).
"A"-rail (Figure 27). As the name indicates, the "A"-rail has an A-shaped frame made of welded railroad rails which is pulled with the apex forward. Not evident in the photograph are two rolling coulters attached to the side rails at or near the position of the extremities of the crossbeam. These cut through debris which tends to accumulate in the angles made by the crossbeam and complement the rail in rolling over the vegetal material instead of dragging it along.
Supp rail (Figure 28). The Supp is a straight rail made out of three sections aligned side by side and perpendicular to the line of travel. Flexible couplings connect the sections. It is necessary to attach drag rails or posts to the ends of each of the sections. This gives the front rails more weight and keeps the entire implement from bouncing around, and it is kept aligned more easily. Recommendations are that these be at least 10 feet (3 m.) long, as compared with the 33-foot (10 m.) combined width of the front rails.
Under normal conditions rails require from 1.6 to 2 horsepower for each foot of width. The designs shown in Figures 27 and 28 are made for a 40-horsepower crawler tractor.
Where the brush stand is mature and brittle and the ground fairly even, rails are excellent for removing the brush cover but they do not prepare a good seed bed for sewing grasses and, unless the soil is already loose, seed coverage by railing is not adequate. Large areas can be railed in a day at low costs. Host grasses are not damaged unless they are prominently pedestaled perennials. Much broken debris is left scattered uniformly over the ground to protect the soil from water and wind erosion. Rails are not effective in young, springy brush and on areas having many boulders and rock outcrops.
Breakage most commonly occurs where the rail sections have been welded together. These places should be strongly reinforced when the rail is reconstructed. It is better to use new railroad rails than used ones which may break because of crystallization. One advantage of rails over other kinds of brush-clearing equipment that should not be overlooked is that they can be constructed in any well-equipped machine shop. The railroad rails can be obtained anywhere.
Chains and cables (Figure 29). In cabling, a long heavy cable or chain trails in a loop behind two tractors traveling along a parallel course. The cable is suspended near the middle of its loop on one or more heavy doughnut-shaped weights. This keeps the cable on the ground over its entire length. Two 155-horsepower tractors traveling 100 feet (30 m.) apart can pull 300 feet (70 m.) of 1 ½-inch (3.75 cm.) cable or 2-inch (5 cm.) chain with weights, and cover about 100 acres (40 ha.) a day. Cabling should be done in two directions: on the first trip the brush is bent over in the direction of travel and on the return trip it is uprooted.
This method has been found to be more effective on larger plants, such as juniper and mesquite which attain 20 feet (6 m.) or more in height, than on smaller flexible shrubs. Cabling is not efficient unless the area is large and the terrain is fairly level. (lost per acre for cabling alone is less than that of a bulldozer, in spite of the need for two tractors. However, the range is messed Up with the many large uprooted plants which must be removed with rakes, bulldozers, or fire before full use can be made of the area.
Brush choppers and beaters
A varied array of ingenious machinery has been designed to reduce brush and trees from the status of a formidable thicket to a level, uniform cover of mulch. The mechanical principles of these devices differ considerably but the result of their work is much the same. Brush stems and tree trunks are finely chopped up and deposited on the soil surface. There is no grubbing action, and except where plants are uprooted as they are pushed over by the frames of the machinery, the soil is little disturbed. The chopped material can be burned or left in place as a mulch.
Many small equipment companies manufacture brush choppers which are sold locally, these being designed especially for the kinds of brush of the immediate vicinity.
Chain beater. This implement was designed for use in brashy forms of brush such as sage, creosote bush, or shinnery oak (12). It works somewhat like a hammer mill. A series of weighted chains are driven by a horizontal shaft which revolves at high speed. The shaft is mounted on a frame supported by two wheels. The chains are slightly over 2 feet (60 cm.) in length, spaced 3 inches (7.5 cm.) apart, and are attached to the quarter dines around the shaft so that the weight is evenly distributed. Welded to the extremities of the chains are heavy iron beater heads. These clear the ground by several inches. The chain shaft is driven by the power take-off of a tractor and is geared to make about 380 revolutions per minute when the tractor is at full throttle. This optimum speed is primarily determined by the accuracy of balance for the machine. Shorter chain lengths will permit higher gear ratios. When an obstacle is struck, the chain wraps itself around the shaft and then unwraps again.
An effective variation of the chain beater is the rotobeater, described and illustrated in Figure 30 (a and b).
Bushwhacker (Figure 31). The bushwhacker is a huge machine consisting of a standard crawler tractor on which is mounted a rectangular steel frame. This frame is pivoted at the approximate longitudinal center of the tractor on a heavy steel shaft running through the tractor chassis. A flail-type disintegrator is built into the front of the frame and is powered by a 175-horsepower Diesel engine mounted at the rear. The disintegrator is further supported by a pair of gauge wheels which move solely in a vertical plane. By raising or lowering these wheels hydraulically, the height of cut is regulated, from 1 inch (2.5 cm.) below ground level to 17 inches (42.5 cm.) above. This amount of clearance is necessary when in operation to avoid rocks and to level large trees. The whole unit, including the gauge wheels, can be raised higher to knock down trees and for traveling by pivoting the frame on its center mounting (24).
The flails in the disintegrator head are made of hardened steel castings and are attached to a drum by 1 1/8-inch round links. Twenty flails are staggered on the drum to present a continuous cutting edge 6 feet wide. The flail heads are 6 ½ inches (16 cm.) wide, weigh 19 ½ pounds (9 kg.), and travel around the drum at a speed of 11,550 feet (5,150 m.) per minute. Since the flails are attached to the drive shaft with links, there is a certain amount of resilience which reduces damage from rocks.
The bushwhacker moves into the standing brush or small trees, a deflector bar bends them over, and the flails rupture all the woody fibres that they contact.
The shredded material is then spread out evenly in the back by means of a skirt. This skirt also keeps limbs and large chunks of wood from escaping the flails.
The limitations of the bushwhacker are stem diameters and ground conditions. Practical ranges for hardwoods are 5 to 6 inches (12.5 to 15 cm.) in diameter and for soft woods, 5 to 8 inches (12.5 to 20 cm.). Rough, rocky terrain minimizes the mechanical effectiveness. Presence of loose rocks and boulders necessitates raising of the general cutting height, which in turn leaves much unshredded debris on the ground. In medium to heavy brush density, the machine moves forward in low gear at about 1 ½ miles (2.4 km.) per hour. At this rate it will clear an acre in one hour of continuous operation. Cost of operation per hour is not known; in arriving at an estimate in comparison with bulldozing, for example, it must be remembered that two Diesel engines are in use. The machine is expensive and small jobs or occasional use would not justify its purchase. However, when much work is to be done, the cost per acre is low considering its high efficiency in brush clearing and disposal in the same operation.
Gyro-brush cutter (Figure 32). This cutter has two heavy blades which are actually one solid iron bar about 1/2 inch (1.25 cm.) thick and 4 inches (10 cm.) wide attached to gears at the center. The blades rotate in a horizontal plane at high speed. Clearance above ground is adjustable up to 14 inches (35 cm.). The machine is supported on two wheels but the blades are propelled by the power take-off of the tractor. Total weight is approximately 1,400 pounds (685 kg.). The gyro cutter works on the same principle as a rotary lawn mower. When a rock is struck a pin is sheered in the clutch and this is easily replaced. The chief draw back with this machine is the relatively low clearance. It works best in low, brashy brush where the stems seldom exceed 1 ½ inches (3.75 cm.) in diameter.
Giant stalk cutter (Figure 33). The basic unit of the stalk cutter is a hollow steel cylinder around which are set 8 full-length sharp blades. A medium sized unit weighs 4,200 pounds (1,905 kg.) empty and 6,000 pounds (2,720 kg.) when the cylinder is filled with water. Large stalk cutters weighing 28,000 pounds (12,700 kg.) have been built. An articulated yoke gives the implement flexibility and permits its use on rough terrain. A simple coupling system allows for the use of two or more of the cylinder units side by side or in tandem. Several designs are commercially available.
Stems up to 2 inches (5 cm.) in diameter can be cut. It is a highly effective follow-up tool for breaking down small trees or brush which have been killed with chemicals for sprout control. The machine is also useful for preparing firelines.
Wood chippers (Figure 34). Several portable wood chippers or grinders are available. They are stationary when in operation and this decreases their usefulness in brush clearing work. They consist of a drum with blades turning at 1,000 to 3,000 revolutions per minute, and will take material up to 6 inches (15 cm.) in diameter, or 2,000 to 3,000 pounds (907 to 1,360 kg.) of brush per hour. The chips are blown out of a pipe either into a truck or onto the ground. Chippers are generally with a 20 or 30-horsepower engine attached to the unit but may be driven by the power take-off of a tractor. Their use is mostly confined to slash and brush removal in forests for fire hazard reduction, but not infrequently the purpose is to provide chips for logging roads and skid trails to prevent erosion.
Power saws and mowers
Tractor power saw (Figure 35). A number of manufacturers make saw attachments for tractors. The saws are either driven from the power take-off or the belt pulley of the tractor. In most cases the saws can be used for cutting- brush and trees while the tractor is in motion but when large trees are encountered, the tractor must be stopped and the saw swung into the tree gradually. The tractor should be fitted with a guard to prevent limbs from crashing down on the operator.
It takes a skillful operator to make the sawing method efficient. It is difficult to keep the saw blade from striking the ground or recutting high stumps. Often the saw operator "saws" himself into a "corner" from which it is hard to extricate himself. For this reason it is advantageous to operate a buck rake along with the saw. As the brush and trees are cut, the buck rake picks them up and removes them. This gives the saw operator more visibility as well as maneuverability. In tests performed in Oklahoma, this two-machine method was used on a tract containing 8,470 brush stems up to 2 inches (5 cm.) in diameter and 133 trees up to 8 inches (20 cm.) in diameter. The operation required 2 ½ hours per acre (6 ¼ hours per ha.).
One of the disadvantages in the use of saws is the large amount of time spent in keeping the blades sharpened. The closer to the ground surface the stems are cut, the more quickly the blades get dull. Contact with soil, especially sandy soil, small rocks, and gritty particles in the bark wear the saw teeth down rapidly. As soon as unreasonable force is required to feed the saw into the stems, the blade is too dull to use. When the blade is only slightly dulled - ordinarily after every two or three hours of use in hardwoods - it should be touched up since this takes but a few minutes. But when allowed to get quite dull, more time is required for sharpening; in the meantime, the output of work has been decreased. Up to 80 percent of the efficiency of circular saws can be lost through dull blades. On large-scale or contract operations it is more efficient to have several blades which are changed in the field. Thus the tractor operator's time is not lost to saw sharpening.
Brush mower (Figure 36). Heavy duty power mowers, which are made like ordinary hay mowers except for heavier construction, can be used on many of the smaller forms of brush. An experienced operator can guide a power-driven mower through dense brush with stems up to 1 ½ inches (3.76 cm.) in diameter, providing the plants are growing vigorously. Larger stems must be cut one at a time or the forward movement of the tractor must be stopped to permit the sickle to hit the stems several times without much pressure from the cutter bar. It is better, however, to remove the larger stems another way than by sawing before the mower goes over the area. Many of the larger stemmed plants have a smaller cross-section a few inches up from the base; therefore if the cutter bar is raised on the shoes to a suitable height an advantage is gained, although stubble height will be greater. The tractor should be run in low gear and not throttled down, so that the sickle, which drives from the power take-off, runs fast in comparison to the forward motion.
Best results for brush mowing have been obtained with the 5-foot (1.5 m.) cutter bar, with stub guards instead of the standard length guards (see photograph), and with extra hold-down chips to keep the sickle from buckling. The sickle should have heavy duty, serrated sections. The amount of power transmitted to the cutter bar can be increased by keeping the slip clutch and safety release on the mower frame tighter than it is ordinarily set for mowing grass.
The economy in using this method for clearing brush is found in the fact that most farmers or ranchers already have a mower. With a few minor changes, it can be converted to a brush mower. The cost of buying and equipping an extra cutter bar with heavy sickle sections, stub guards, and the additional hold-down clips is only about $35.00 (Oklahoma, 1947). No other machine can be purchased for that price (12).
All of the things done by the various implements described in the previous section can also be done with a few simple hand tools: the saw, axe, machete, mattock, or pick. By comparison, their shortcomings are obvious, yet they have certain advantages. They are easy to obtain and inexpensive; they are simple to operate and, if broken, there need be little concern about replaceable parts. Such tools are most efficient where the number of plants to be removed per acre is very small. Examples are fields being invaded by scattered brush seedlings, open savanna where the woody plants are widely spaced, or coniferous forest where a small proportion of the trees are undesirable hardwood.
Between these simple tools and the tractor-powered machines are a number of engine-driven devices which can be carried and operated by one or two men. These include the chain saw (Figure 37), portable circular saw (Figure 38), tree girdler (Figure 39), and scythette. Other equipment of this nature is described in later sections on controlled burning and chemical brush control. (To be continued)
