FM 5-164

CHAPTER 3

CLEARING METHODS AND TECHNIQUES

Section I. BASIC CONSIDERATIONS

3-1. GeneralBefore selecting the equipment and personnel neededto complete a land clearing project, and prior to anyestimation of the time required, certain factors mustbe considered. These factors include the reason for orpurpose of clearing the land, the size and shape ofthe area, the location of the project, the timeavailable to accomplish the work, and the terrain(see app F for information on terrain intelligenceconsiderations).3-2. Purpose of ClearingThe stated or implied purpose for accomplishing agiven land clearing mission has considerable bearingon the specifications or standards to be attained. Intactical land clearing, the primary objective is toenable tactical units and weapons to destroy theenemy, to force him out of the region, and to makekey areas unable to be defended. Accordingly,tactical land clearing is highly selective and usuallyaimed at denying cover to the enemy for a limitedperiod. In construction clearing, normally thepurpose is is remove all the surface and subsurfacevegetation to facilitate a construction project.Sometimes the long and short range use of the landby other than military forces is a factor which shouldbe considered in selecting the clearing method used.The specifications must define the purpose ofclearing and the finished conditions clearly. Careshould be taken to specify only those conditions thatare absolutely essential, because considerable extratime and effort may be expended on work that isunnecessary. Details on specification writing andclearing requirements are contained in the chapterson tactical and construction clearing.3-3 Scope of the ProjectThe size of the area will obviously have a directbearing on the amount of equipment which should beemployed m the area. The shape and topography of

the area must also be considered. Long narrow stripsor areas adjacent to roads require different cuttingand disposal techniques than larger rectangularareas. Small areas such as landing zones and firesupport bases are special cases and will be discussedin chapter 4.3-4. Location of the AreaThe proximity of the area to be cleared to the landclearing unite base area must be considered, not onlyfor the transportation required at the beginning andcompletion of the project but for resupply andmaintenance support throughout the project. Thelocation of the nearest maintenance service facility towhich deadlined equipment can be evacuated and thelocation of the parts supply unit have considerableimpact on the time required to get inoperativeequipment repaired and back to work.3-5. Time AvailableAnother important consideration is the timeschedule for completing the project. Frequently thisis dictated by other considerations such as con-current tactical combat operations in or near the areato be cleared at the time that clearing equipment canbe released from other tasks. Weather has a markedeffect on the time available. When a low-lying areamust be completed prior to the rainy season or anapproaching storm, the duration of the project maydetermine its success or failure.3-6. Other FactorsConsideration of enemy activity within the area to becleared and the enemy capabilities can be significantfactors in planning an operation. These aspects werediscussed in chapter 2. The condition of the clearingequipment, the maintenance posture andcapabilities, and the status of training of the per-sonnel will also have to be considered when planningthe operation. Maintenance will be discussedelsewhere in the manual.

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Section II. METHODS AND EQUIPMENT FOR INITIAL FELLING

3-7. IntroductionThere are several methods for initial felling andmany types of equipment which can be used witheach method. This section includes a discussion ofthe mechanical methods and related equipmentwhich are currently available within the Army in-ventory, as well as a limited discussion of severalspecial purpose items of land clearing equipmentwhich can be procured for use for specific operationsor types of vegetation. The use of explosives, handclearing, and burning will also be discussed. Theselection of the methods and equipment, and theadvantages and disadvantages of each, aredependent upon many variables which must beconsidered individually for each clearing situation.3-8. Uprooting VegetationSeveral types of equipment are used in this methodof clearing. These include bulldozer blades, rakes,knockdown beams, root plows, spade plows, andanchor chains drawn between two large crawlertractors.

a. Bulldozer Blades. Until recently, the mostcommon method of clearing land was by utilizing thecrawler tractor with its ordinary straight or angling

bulldozer blade (fig 3-1). Even though 30 to 40percent more land can be cleared utilizing specializedland clearing tools, the bulldozer can be efficientlyused in small and intermediate sized areas where it isreadily available and specialized land clearingequipment is not. When larger trees which cannot bepushed over are encountered they must be dug out ofthe ground, a time-consuming operation (fig 3-2).Small trees and bushes are often so flexible that theybend over as the dozer blade passes over them, andmay not be removed unless the roots are alsoremoved. Since a ball of dirt is often left on the rootsof the tree when it is uprooted, subsequent disposal,especially by burning, is made more difficult. Arecent improvement of the straight bulldozer bladehas been the development of the hydraulically ac-tuated tilt cylinder. This allows the operator, fromthe seat of the tractor, to tilt one comer of the bladeto facilitate cutting of lateral tree roots for easierfelling. The bulldozer is not the best tool for pilingfelled vegetation because it takes too much soil intothe windrow with the cut vegetation, which retardsthe burning process.

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b. Rakes. Rakes of various specialized types can Rakes are used very successfully and are recom-be mounted on or in place of a bulldozer blade and mended for repiling burned or burning material,utilized for clearing of both trees and rocks (fig 3-3). since the ash residue and soil can sift through theRakes have the advantage of allowing most of the teeth and cleaner, hotter burns can be achieved.soil to pass between the teeth as they are pushed More discussion on the use of rakes in burning isthrough the soil. They can be used for uprooting included in Paragraphs 3-21 through 3-26.vegetation and piling rocks, stumps, and cutvegetation into windrows. Rakes work exceptionallywell in sandy soils and in rocky soils that woulddamage a shearing blade. Rakes do not work well inwet cohesive soils because of the clogging of the soilbetween the rake teeth. When this occurs, the rake isin effect converted to a bulldozer blade with all theinherent disadvantages. Many different types ofrakes are manufactured for track-type tractors. Eachsize, weight, and strength has a particular ap-plication, and care must be exercised to insure thateach type is used only for the purpose for which itwas designed. Listed below are some of these rakesand their application.

Rake ApplicationMulti-application rake All heavy duty land clearning

(fig. 3-3) including tree and rock

Rock rake . . . . . . . . . . .

Blade rake (fig 3-4) . . . . . . .

Brush and cleanup rake(fig 3-5).

removal.Clearing and grubbing boulders,

spreading rock riprap, andgrubbing and piling stumpsand debris.

Light grubbing, piling, andraking .

Final cleanup after initialclearing.

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c. Knockdown Beams. Both bulldozers and rakesdepend on the brute force of the tractor to uproot thevegetation. This same principle applies, in part, tothe knockdown beam (fig 3-6), which is a structureextending above and forward of the tractor to givethe tractor added leverage in pushing over largertrees. They are ideal when used in combination withsome device for cutting the roots around larger treessuch as a rooter, allowing the trees to be pushed overwith greater ease. Knockdown beams can also beused in conjunction with anchor chaining by liftingthe chain higher on larger trees for increasedleverage and pushing against the larger trees toassist the chain. The effectiveness of this tool isimpaired if the trees are too large, taproots arepresent, or traction is poor. Knockdown beams areuneconomical for use on small diameter trees orbrush. This makes the knockdown beam a highlyspecialized tool with limited application to specificland clearing situations.

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d. Root Plow and Grubber. The root plow is a tool ring, killing brush that would normally resprout iffor removing vegetation by cutting it below the soil cut at ground level. The disadvantages of the rootsurface (fig 3-7). It is designed for killing brush and plow are that the size of vegetation it can cut islight vegetation by undercutting it at or below the limited and that it does not work well in sandy orcrown or bud ring at depths from 20 to 50 cen- rocky soil. The grubber is a smaller version of thetimeters (8 to 20 inches). Large roots are forced to root plow and is normally mounted on a wheeledthe surface by the fins on the horizontal blade (fig 3- tractor to clear small clumps of brush. It has the8). Root plows are available for mounting on tractor same advantages and disadvantages as the roottrunnions or tool bars. The advantage of the root plow, but can move quickly from one clump toplow is that it cuts the vegetation below the bud another.

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e. Spade Plow. A relatively recent development isa universal land clearing tool called the spade plow

(fig 3-9), which is capable of removing entire trees,including roots. The spade plow is a combinationrake and root plow, which also incorporates ahorizontal knockdown beam to increase leverage foruprooting larger trees. The heavy duty cutting blademounted between the teeth on the lower part of thespade plow shears light vegetation at or belowground level, while the knockdown beam pushes overand uproots the larger trees. It has the advantage ofbeing applicable to many uses without changingattachments, and is especially effective in stackingand piling debris for disposal in soil-free windrows.The cutting blade may also be used to cut strips ofturf for covering (sodding) bare areas. Soddingcontrols erosion, provides soil stability (includingdust control), and serves as camouflage material.The disadvantages are that it is limited to mediumsized trees and it will not perform well in heavily wetsoils.

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f. Anchor Chains and Large Crawler Tractors.Chaining is a highly effective method of fellingvegetation in some large-scale clearing operations(fig 3-10). Experience has shown that chaining canbe used in all sizes of vegetation. The upper limit invegetation size and density will vary with the sizetractors used, the tractive conditions, and the widthof swath chained. The terrain should be level togently sloping without large gullies, stone out-cropping, or other obstructions preventing freepassage and maneuverability of the tractors andchain. There should be sufficient straight length ofpass to minimize turning around with the chain, atime-consuming operation. Short range two-wayradios with headsets facilitate communicationbetween the two tractor operators. A third tractormay often follow the chain to lift it over obstructionsand to assist the chain when occasional oversizedtrees are encountered. The tractor operator shouldfollow at a safe distance to preclude injury to thetractor operator or damage to the tractor in case oftree backlash. Chain size and length depend upontractor size and the vegetation to be cleared. As arule of thumb, the length of the chain should be threetimes the operating distance between the tractors,and two-and-a-half times the height of the tallesttree. If the tractors operate 61 meters (200 feet)

apart, the chain should be 183 meters (600 feet) long.Swivel-eye-and-socket links can be installed alongthe chain if twisting is a problem. These swivelsshould be placed one at each end and two within thelength of the chain at the point where the loop startsto form. The diameter of the steel in the chain linkshould be sufficient to provide the strength andweight to operate safely even after considerablewear. The following chain sizes have been usedsuccessfully:Tractor size Link steel diameter Approx. wt/ft

180 hp 5.1 cm (2 in) 17.0 kg (37.5 lb)270–385 hp 6.4cm (2.5 in) 27.2 kg (60.0 lb)

385 hp 7.6cm (3 in) 39.7 kg (87.5 lb)One or more metal balls–solid steel, hollow steel, orhollow steel filled with concrete-may be used togive the chain greater weight and impact (fig 3-11).These balls are connected at or near the middle of thechain with universal connectors. When more thanone bell is used, they should be equally distributed inthe central half of the chain. These balls help thechain conform to the terrain on gentle to moderatelysteep grades. They are especially useful when thechain is used to clear and span narrow, wet valleys.Balls are not needed on level terrain where the size ofthe vegetation does not require the added weight.

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Typical sizes and weights of balls in use are asfollows:Diameter Type material Approximate weight.9m (3 ft) Cast iron 2950 kg (6,500 lb)

1.1m(3½ ft) do 4540 kg (10 ,000 lb)1.2m(4ft) do 6810 kg (15,000 lb)1.2m (4 ft.) Concrete filled 2500 kg (5,500 lb)

steel shell1.5m(5ft) do 4540 kg (10,000 lb)1.8m (6 ft) do 7490 kg (16,500 lb)3.0m (10 ft) do 6810 kg (15.000 lb)

The chain is dragged behind two crawler tractors (fig3-10). The outside tractor travels along the edge ofthe uncleared area and the inside tractor travelsthrough the uncleared area avoiding any largevegetation. The distance between the tractors willvary with the size of the tractors, the traction, andthe size of the vegetation. The width of the swathshould be narrow enough that the tractors can travelalmost continuously in a forward direction. A rule of

thumb that is used to determine if chaining is moreeconomical than having the tractors operate in-dividually is as follows: if the two tractors canmaintain a constant forward motion clearing a swaththat is seven times their blade width or greater,chaining is the best technique. The width of theswath may be 12 times the blade width. However, athird tractor is needed to follow to assist the chain.Figure 3-12 shows a third tractor with a bulldozerblade following the chain to assist in uprootinglarger vegetation. Two passes in opposite directionsmay be required to uproot areas with smallerdiameter vegetation which only bends over on thefirst pass. Chaining proved to be extremely effectivein clearing rubber plantations in Vietnam whereuniform diameter trees and little or no undergrowthwere encountered. Chaining has also proved to be asatisfactory technique when clearing bamboohedgerows in some geographical areas of Vietnam.

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3-9. Cutting or Shearing VegetationThis method varies from uprooting the vegetation inthat the growth is cut off at or slightly above groundlevel, leaving the stumps in the ground to decay or tobe removed later. The tools used for this type ofclearing probably vary more than any other method(TM 5-342). They range from a hand axe or macheteat one extreme, to a large crawler tractor equippedwith a shearing blade on the other. This technique isespecially effective in large vegetation where thebrute force of the tractor is insufficient to uproot thevegetation without digging around it. In areas ofheavy rainfall, cutting the vegetation at ground leveldoes not cause the large holes in the soil thatuprooting does, therefore the natural drainage of thearea is not inhibited.

a. Handtools. Handtools such as axes, brush-hooks, machetes, grubbing hoes, and pick-mattocksare generally adequate for small areas and areasinaccessible to heavy equipment. They may also be

suitable when ample manual labor is available andtime is not critical.

b. Chain and Crosscut Saws. In larger diametervegetation, chain saws or crosscut saws are moresuitable for use than axes or similar tools. Crosscutarid chain saws are available in most engineer units(fig 3-13, 3-14). Chain saws are available in lengthsfrom 2 to 5 feet and are either electric, pneumatic, orgasoline-engine driven. Sawing a tree is ac-complished by a single cut, or on larger trees by aseries of cuts. The first step in cutting a tree is todetermine the direction of fall. A tree should not befelled so as to become lodged in the branches ofanother tree. Once the direction of fall is determined,the next step is to clear away brush and low-hangingbranches which will interfere with the use of the axeor saw. The first cut made on a large tree is theundercut which is made on the side toward which thetree is to fall. The undercut is made using two cuts,one horizontal and one at 45 degrees, to a depth of

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about one-fourth of the diameter of the tree (fig 3-15,3-16). The backcut should then be made from theopposite side of the tree approximately 2 incheshigher than the bottom of the undercut. The cutshould be kept parallel with the undercut until only 2or 3 inches of holding wood is left. If the tree has notfallen by this time, it should be tipped by driving oneor two felling wedges behind the saw. Extreme careshould be taken to insure that the saw is not caughtat the hinge when the tree starts to fall. The sawshould be pulled back toward the wedge, or com-pletely out of the cut if possible, as soon as the treestarts to fall. If a cut tree lodges in a standing one, adangerous condition can exist. Providing the tree isnot too tightly lodged, it may be loosened by pryingthe butt off the ground or by pulling it withequipment. Perhaps the most dangerous practice ofall is to cut the tree in which the first one is lodged. Ifthis is done it is difficult to judge the stresses in-

volved, or the direction the two trees will fall. If thissituation exists, cutting the standing tree withexplosives is the safest procedure. Additional handfelling techniques and precautions are found in TM5-342.

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heavy-duty operation. These mowers have short,heavier sickle bars equipped with stub guards andextra holddown clips. The tractor is run in low gearto give a high sickle speed in comparison with theforward speed. This equipment is usually mosteconomical in intermediate sized, level areas of lightand secondary growth.

e. Shearing Blades. Perhaps the most efficientland clearing tool for medium and large vegetation inintermediate to large sized areas is a shearing blademounted on a track-type tractor. The shearing bladeprovides a sharp cutting edge. It is usually equippedwith a stinger or wedge-like projection which maycause trees to be spilt in one or more successivepasses before they can be felled with the cuttingedge. Larger trees can be felled by the shearing blademounted on a tractor. Shearing blades have anadvantage over bulldozer blades in that they areeasier to operate. Shearing blades are equipped witha flat soleplate mounted horizontally on the bottomof the blade which allows the blade to float on top ofthe ground without digging in. This permits fasteroperation with less operator fatigue, since theoperator does not have to constantly manipulate thecontrols to keep the blade at ground level. Throughthe technique of shearing the vegetation at groundlevel and splitting the trees, disposal of thevegetation by burning is much faster and more

c. Tractor or Wheel-Mounted Circular and ChainSaws. Greater production in larger diametervegetation can be obtained using large horizontallymounted circular or chain saws. These saws aregenerally powered by a small four-stroke gasolineengine or the power takeoff of a small wheeledtractor. Trees up to 1.25 meters (50 inches) indiameter can be felled using the circular saw, whilethe chain saw is capable of felling trees 1.8m (72inches) in diameter. Their use is not recommended onsteep slopes.

d. Sickle Mowers. Light brush, with a stem di-ameter of less than 3.8 centimeters (1.5 inches), canbe cut with agricultural tractor mowers adapted for

complete, because the tree has been split and there isno rootball of soil on the butt of the logs. Vegetationis most easily sheared at or slightly below groundlevel since the shearing blade cuts the tree at itsmost firmly fixed point. On most species of trees thiscut also occurs at or below the crown, the pointwhere the root structure starts to form. The rootwood fibers are not as strong as the stem, thus thetree shears easily at this point. There are two basictypes of shearing blades, the angle blade and the Vtype blade. The angle-type blade in use by themilitary is the Rome K/G blade (fig 3- 17). This bladehas an angle of 30 degrees, has the sharp projecting“stinger” mounted on the leading left side, and canbe operated either by cable or hydraulically. TheRome K/G blade is available to fit most sizes oftrack-type tractors. The replaceable cutting edgesand ”stinger” should be resharpened with a portablegrinder daily. More discussion of blade maintenanceprocedures is found in appendix D. A guide barmounted on top of the blade is used to help controlthe direction the trees fall. The cut growth willnormally fall forward and to the right of theoperator. This type of blade is a versatile attachmentwhich can cut, pile, and stump. It can be used on anyterrain on which bulldozers can operate, and givenenough time utilizing the stinger to split the tree itcan fell any size tree (fig 3-18). The V blade (fig 3-19)

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is also available for all track-type tractors. It isequipped with a heavy-duty “splitter,” mounted inthe center, angled, serrated cutting blades, andbrush rack. The V is in two sections which bolttogether so it can be disassembled for easier trans-port. The V blade has the disadvantage in densegrowth that the trees fall to both the left and right ofthe tractor, thus felling trees into uncut forest. It is ahigh production land clearing tool which is veryeffective in sparse to medium density growth or forcutting trails one blade-width wide in dense growth.Unlike the angle blade, the V blade cannot pile orditch. It extends forward further and is heavier so

FM 5-164

the center of gravity of the tractor-blade com-bination is moved forward. This makes it moredifficult to operate when working on steep slopes andin soft underfoot conditions. The use of shearingblades of either type should be limited to heaviertype clay and loam soils, relatively free of rocks andstones which can cause severe damage to the cuttingedge. Under extremely sandy conditions a rake orother tool is more efficient than the shearing bladesbecause the vegetation is readily uprooted and is notfixed firmly enough in the soil to be cut by a shearingblade.

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3-10. Tree Clearing With Explosives modified. Large-diameter trees may be cut withTrees may be cut with explosive charges. In- either external or internal charges. Externally ap-formation on explosives, determination of charge plied charges may be placed rapidly and easily;size, and methods of placing charges is contained in internally applied charges require less explosive butFM 5-25. Tree clearing operations are generally require the use of drilling equipment and con-influenced by the time available, the equipment and siderably more time and skill to prepare.explosives available, and the size and type of trees a. External Charges. The use of convenientlyinvolved. Explosives application technique is packaged block explosives such as TNT, tetrytol,determined by the diameter of the main stem trunk, composition C4, and dynamite is popular due to theirthe altitude of the tree (if directional felling is a ease of handling and simplicity of operation. Theseconsideration), and the root habit. Initial sizing of are fastened to the tree trunk at the desired point ofthe explosive charge is determined by formula (table cut. A formula based on the effectiveness of the3-1) and based solely on tree diameter; actual on-site particular explosive used in relation to that of TNTexperience will allow these initial values to be (table 3-2) may be used to provide charge size.

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(1) Direction of fall is dependent upon chain saw or axe) and then placing block or plasticplacement of the charges. Unless influenced byinitial attitude or a strong wind, the tree will falltoward the side on which the charge is placed. Theuse of a small “kicker” charge of approximately 1pound will provide a positive fall in the properdirection. Such a charge is placed about two thirds ofthe way from the ground to the top of the tree and onthe opposite side of the main charge and desireddirection of fall, as shown in figure 3-20.

(2) Though appropriate Army manuals do notplace a limitation on tree size for the prior formulatechniques, reliability decreases markedly for treesover 18 inches in diameter. Large trees may often behandled more easily by cutting a notch (using a

explosive within the notch. Tamping with sandbags,mud, or other material is also a good practice andwill increase the effectiveness of any explosivecharge.

(3) The characteristics of paste explosive, asemifluid, extremely oily explosive, with a con-sistency of light grease, permits the ready ap-plication of the explosive around a tree trunk such asthe “ring charge” configuration. The highly plasticproperties of the material insure its emplacement inclose contact with the often irregular surfaces of treetrunks. This close placement may be achieved byhand molding. Adequate configuration and taperingof the upper and lower edges improves the efficiency

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of the explosion. Ring charges are effective forcompletely severing trees up to 30 inches in diameter(a), (fig 3-21).

(4) Directional control by paste explosive maybe best achieved with concentrated rectangularcharges applied to the trunk as in (b), figure 3-21.Table 3-1 provides formulas for an estimate of pasteexplosive quantities required.

(5) Shaped charges may be utilized and aremore efficient than conventional block explosives.Shaped charges may be field improvised by loadingcoffee cans or other containers with C4 and formingit around a conical or wedge-shaped (linear) mold inone end. Fusing and detonation are from the rear.They have about the same effectiveness as pasteexplosives.

b. Internal Charges. Trees may be felled with lessexplosive by use of internal charges placed inboreholes. If necessary, calculation of the explosivequantity required may be made by use of the relatedformula (table 3-1); any common explosive may beused since the relative effectiveness factor is notsignificant. The charge is placed in a borehole drilledparallel to the greatest cross-sectional dimensions ofthe trunk and tightly tamped with moist soil; if thetrunk is nearly circular, two nonintersecting holesmay be drilled at right angles to each other, tamped,and fired simultaneously as illustrated in figure 3-22.Priming and detonation are conventional.

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3-11. Leveling Scrub Growth and Light Vegetation a. Rotary Mowers.Mowing equipment, rolling choppers, and tractor-drawn anchor chains are an extremely fast and ef-fective means of clearing and leveling scrub growthand other light vegetation. In primary rain forestareas, this technique is limited to secondary growthand underbrush while larger vegetation must beremoved by another means. Since most of thevegetation is not uprooted and is often chopped up,it is normally not piled for disposal, but may beburned in place after drying is completed or left inplace to decay.

Heavy duty rotary mowerspulled by tractors can be used for vegetation up to 10centimeters (4 inches) in diameter (fig 3-23). Theyhave one or more revolving blades, rotating around avertical shaft and powered by the tractor powertakeoff, which sever the vegetation at or near groundlevel and shred it into small pieces. Rotary mowersshould not be used on steep slopes or where rocksand stones are present.

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b. FlaIl-Type Rotary Cutters. Flail-type rotarycutters are also drawn by a tractor and have cuttingknives or chains which rotate around a horizontalshaft to knock down or shred small brush at or nearground level. These cutters are available in a widerange of sizes and widths as power takeoff at-tachments for both wheeled and track-type tractors.Their application is limited to small and mediumsized brush in intermediate size areas.

c. Rolling Choppers. In larger sizes of small tomedium diameter brush and secondary growth, thefastest method of clearing is with a rolling chopper

(fig 3-24). The rolling chopper is a drum with cuttingblades. Cutting blades are attached by welding orbolting to the drum, which may be filled with waterto increase its weight. These blades are 15 to 25cm (6to 10 inches) wide and cut, fracture, and shatter thevegetation. The effectiveness of the cutting action isdetermined by the firmness of the soil, the weight ofthe drum, and the speed at which the drum is rolled.Increasing the speed at which the drum is rolledimproves its effectiveness so that towed choppersshould be pulled in second or third gear. Rollingchoppers are manufactured in several widths andweights per length of cut. They also may be con-nected in dual, tandem, and triple arrangements inaddition to the single drum. A unique rollingchopper (fig 3-25), called the Marden Duplex, hastwo drums connected with a draglink on one side ofthe frame so the drums are towed at a 20 to 30 degreeangle to each other and to the forward direction ofthe tractor. This angle produces a dragging androlling reaction on the drums and prevents the reardrum from following the same cut pattern as thefront drum. The Marden cutter also uses a “hi-lo -blade” concept by alternately mounting 6- and 8-inch width blades to produce greater choppingimpact on the vegetation. Rolling choppers do notcut grass or other light vegetation, thus allowing thespread of native grasses which prevent soil erosion ordust problems in areas cleared by this method. Themain disadvantage of rolling choppers is that theyare limited in use to vegetation of 6 to 8 inches indiameter and smaller.

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d. Anchor Chains and Large Crawler Tractors. Insmall vegetation the use of anchor chains and largecrawler tractors can be the most efficient methodavailable for knocking vegetation to the ground. Inlarger vegetation, the growth is uprooted rather thanbent over and knocked down. The equipment andtechniques are the same as those described inparagraph 3-8.3-12. Tilling Vegation Into the SoilMany thousands of acres can be cleared every yearsimply by the use of agricultural tillage implementspulled behind a tractor. These implements act to cutand chop the vegation into the upper 15 to 25 cen-timeters (6 to 10 inches) of the soil. This method islimited to vegation that does not exceed 7.5 to 10centimeters (3 to 4 inches) in diameter. To use thistechnique, the soil surface should be free of largestumps protruding above the ground, large treestems lying on the surface, and stones or stoneoutcrops which may damage or otherwise limit theeffectiveness of the implement in chopping thewoody vegation.

a. Moldboard Plows. Pull-type, semimounted, or

fully mounted moldboard plows drawn by wheel ortrack-type tractors can be used to turn over and,cover small brush if the soil is not excessively hard,sticky, or rocky. For all but the lightest plowing,plows with heavy duty frames must be used. Plowsare available in a wide range of sizes from many farmequipment manufacturers. Moldboard plowing of anarea requires considerable effort and should be doneonly in those areas where long-term totally clearedconditions are required. Moldboard plows arenorm ally used only for agricultural clearing pur-poses.

b. Disk Plows. Tractor-drawn disk plows canalso be used effectively in covering small brush.They can be used on soil that is dry, hard, sticky, orrocky where moldboard plows are unable to work.Disk plowing does not normally cover the brush asthoroughly as moldboard plows. Variations of thestandard disk plow have been developed whichincorporate a “stump jump action”, where each diskis independently spring-loaded to permit it to rideover fixed obstructions which may be encountered.Disk plows should be used only where complete long-term clearing is required. Dust and erosion controlprocedures must be instituted in areas cleared withdisk plows.

c. Offset and Gang Disk Harrows. For slightlylarger brush and secondary growth up to 4 inches,heavy-duty offset and gang harrows, pulled bytrack-type tractors equipped with bulldozer bladesor clearing rakes, are effective clearing tools (fig 3-26). The vegetation is bent over by the blade or rakeand then is cut and chopped into the topsoil by theharrow. Offset and gang harrows do not invert thesoil layer or the vegetative matter, but will chop upthe material and mix it with the soil. Large soundstumps and fallen trees inhibit the use of harrowsand even heavy-duty harrows may be damaged ifcare is not taken to avoid these obstacles. Harrowsare extremely useful in clearing secondary growth inareas which have been previously cleared, if the treestems have decayed or have been removed and thestumps were cut flush with the ground. Use of aharrow to clear growth requires more effort than useof a rolling chopper but the vegetative regrowth isretarded for a longer time. The disadvantages of theharrow are the limited size vegetation that it can cutand the fact that the soil must be firm or the harrowwill bog down. The soil in the area cleared by aharrow is disturbed so that it can become a dust orerosion problem if preventive measures are nottaken. Areas cleared by a harrow are normallyimmediately ready for agricultural planting.

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3-13. BurningBurning can be used as an initial clearing method,but it is very difficult to get a complete burn orcontrol it in most types of vegetation without ex-tensive preparation. If herbicides are permitted to beused prior to initiating the burn, more completeresults can be obtained. National policy will governthe use of herbicides in a theater of operations.Commanders will receive specific guidance for their

use together with the necessary authority to employherbicides through command channels. Manytropical jungles are impossible to burn even withextensive defoliation. Burning can be used ef-fectively in many areas as a method for disposal ofvegetation previously cut, knocked down, oruprooted, which has been left in place or windrowed.Further discussion of burning as a method ofdisposal is included in paragraphs 3-21 through 3-26.

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3-14. Combinations of Felling EquipmentOn many land clearing jobs more than one type ofequipment may be used in combination to achievethe fastest and most efficient results. A commoncombination in many military operations is thepower chainsaw, explosives, and the shearing blade.Extremely large vegetation, over 36 inches, and thatwhich is located on extremely steep slopes, over 25percent, often cannot efficiently be felled with ashearing blade. Therefore, it is often moreeconomical to cut this vegetation by hand usingexplosives or power chainsaws. The combination ofthe knockdown beam and the anchor chain can beused in large vegetation, or in rocky areas where thechain may become snagged on a very large tree or arocky outcrop. The knockdown beam followingbehind the chain can assist in knocking down thelarge tree or lift the chain over the rocks. On ex-tremely steep slopes, two track-type tractors

equipped with bulldozer or shearing blades can beconnected back to back with a cable and winch toprevent them from overturning as they clear steephillsides using the “yo-yo” technique: One tractorremains on top of the slope for stability as the othermoves down the slope clearing the vegetation as itgoes. In areas where several different types ofvegetation occur, various combinations may be usedto efficiently clear the area. A summary of methodsand equipment used for initial felling listed by size ofvegetation and size of area is included in the tables 3-3, 3-4, and 3-5. The most economical size area foreach type of equipment will vary with theavailability of the equipment or hand labor. When noequipment is listed in the tables for a certain sizearea using a particular method, it is normally noteconomical to use that method. However, heavyequipment listed under large areas can be used forsmaller areas with less economical results.

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Section III. REMOVAL OF SUBSURFACE VEGETATION AND STUMPS

3-15. Factors to ConsiderMany specifications require that a minimum ofsubsurface growth and stumps are to be left afterclearing. When clearing equipment or loggingoperations sever the vegetation at or near groundlevel, a second operation to remove this subsurfacematerial is necessary. If it is known that the stumpsand roots must be removed prior to starting theproject, serious consideration should be given touprooting the vegetation as the initial fellingtechnique. By uprooting the trees initially, theadded leverage of the height and weight of the tree

will assist in removing the roots, and thus willrequire less effort than removing the stumpseparately as a second operation.3-16. Cutting BladeThe Rome K/G blade cart be used to grub the stumpeither after cutting the tree at ground level orwithout first cutting down the tree. After tilting theblade forward, the initial pass is made just to theright of the tree or stump severing the roots 1 to 2feet below ground level (fig 3-27). The second pass ismade with the stinger to the left of the tree or stump,

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severing additional roots and uprooting it. This in this manner, additional sharpening of the cuttingmethod does not remove all the subsurface growth, edge and stinger will be necessary, especially inbut in most cases only roots 1 inch in diameter and abrasive soils.smaller remain in the soil. If the cutting blade is used

3-17. Stumpers of the tractor directly on the stump and splits it,Both detachable and pull stumpers may be available digging under it and lifting it out of the ground. Theas specialized items for stump removal. The pull stumper is a cast steel tooth and frame which isdetachable stumper is a one-piece casting which connected to the rear of the tractor (fig 3-29). A rearmounts to a track-type tractor C frame in place of cable control unit is required to raise and lower thethe blade (fig 3-28). For larger or tougher stumps, a stumper. One additional feature of the pull stumperdetachable splitter is available to use in conjunction is that it can be used to cut the side roots of largewith the stumper. This tool concentrates the power trees and stumps prior to their removal.

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3-18. RooterThe rooter with one or more teeth removed can beused in a manner very similar to a pull stumper, butthe shank penetration and lift is not as great as withthe pull stumper.3-19. WinchesAnother method of stump or tree removal is to pullthem by means of a winch and a chain or cable at-tached around the trunk. This line is normally achoker type which tightens its grip as the pull in-creases. This method of removal is preferred whenthe ground is too rough or soft to allow the tractorto get at the stumps directly, or more force isnecessary than the traction will permit. Speciallydesigned clearing units consisting of a small wheeled

tractor equipped with a special winch that candevelop a 100,000 pound line pull are used to pullover and uproot trees and stumps. Winches mountedon medium to heavy tractor-dozer units can developa line pull of 51,000 to 74,000 pounds. The effectiveforce on the stump or tree can be increased by in-stalling one or more blocks to improve themechanical advantage (fig 3-30). For detailed in-formation on the methods of rigging see TM 5-725.This method can be used for trees and stumps up to24 inches in diameter. Clearing done by pulling withwinch units is extremely slow and requires skilledpersonnel to do the proper rigging. For most efficientresults their use should be limited to those stumpsand trees that cannot be removed through othermeans.

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3-20. Removal of Stumps With ExplosivesTree stump removal by explosives may be necessaryin the course of initial helicopter landing zoneconstruction, expansion and improvements of suchsites, and during the course of construction of fieldfortifications and artillery positions.

a. The type and condition of root system and thenature of the soil affect the placement, size, andeffectiveness of explosive charges. While most treeshave lateral roots lying near the surface, somespecies also have one or more main taproots ex-tending downward. An old dead stump in a moistheavy clay or loam soil normally requires less ex-plosive than a new “green” stump in dry loose soilswith a high sand content. Dynamite is the preferredexplosive, but any conventional explosive may beused.

(1) A rule of thumb is to use one pound ofdynamite per foot of stump diamter (as measured 12-18 in. above the ground) for dead stumps and twicethis amount for live or green stumps. Table 3-8 in-dicates recommended charge sizes that have beenfound satisfactory under varying conditions, but it isadvisable to plan for several trial shots.

(2) The proper placement of charges requiresjudgement and experience, particularly whenremoving lateral-rooted stumps. If a single charge isused, it should be placed under the center ofresistance of the root system. Multiple chargeswould likewise be distributed in the most effectivemanner. The depth and size of the hole will vary withthe size of the stump; holes may be dug with adriving bar and sledge or a soil auger.

(3) Taprooted stumps can best be blasted bydrilling into the taproot with an auger at an angle ofabout 450 to a point just beyond the center of themot. External placement of charges requires lesseffort but more explosives. In this case, one or moreholes are dug 2 to 3 feet below the surface and ad-jacent to the root (fig 3-31). In all cases, the holesshould allow sufficient room for at least 8 inches ofstemming with packed soil. Particularly largestumps with a heavy root system may be blastedwith a single charge by first “springing theborehole.” This requires the use of about ½ pound ofdynamite to be inserted in the hole to form a cavitylarge enough to contain the required explosives.When the soil has cooled sufficiently, the hole maybe loaded, tamped, and fired.

b. Proper loading of a hole requires that the holebe checked, for obstructions prior to loading, the

charges be tamped firmly together by use of awooden tamping stick, and the hole be stemmed withfirm, moist earth. If several charges are to be used inone hole and no water is present, the cartridgewrappers should be slipped open and pressed firmlytogether to insure effective detonation. The finalcartridge, which is to be primed, is not slipped openexcept as necessary for priming. The charges may beprimed and detonated by several conventionalmethods, but aboveground systems, such as the useof detonating cord to connect the subsurfacedynamite to aboveground electric or nonelectricblasting caps, are preferred. If a time fuse andnonelectric blasting cap system is necessary, eachcharge should be dualprimed to insure detonation.

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Section IV. DISPOSAL OF DEBRIS

3-21. GeneralOnce the vegetation has been felled, it must usuallybe disposed of in some manner. Since disposal of thevegetation is often as time-consuming as the initialfelling, care should be taken to specify only thatdegree of disposal absolutely essential to accomplishthe purpose of the clearing project. The method ofdisposal will be influenced by a number of variables,including type and size of vegetation, specifications,minfall, and terrain.3-22. Left in PlaceSmall vegetation that is chopped up during initial

clearing is normally left in place to decay, be burned,or be incorporated into the topsoil. When deter-mining disposition to be made of larger vegetation,both the long and short term use of the land areimportant considerate ions. If clearing is for tacticalpurposes only, the large vegetation may be left inplace; however, secondary growth may have to becleared later, and the task will be extremely difficultif the large tree stems remain in place. If at allpossible, the large vegetation should not be left inplace and should be disposed of in some manner.

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3-23. Burned in PlaceBurning vegetation in place after it has been felledcan be an effective means of disposal when con-ditions permit. These conditions include fuel forburning in the form of grasses, small limbs, orbrush, and a dry enough climate to allow burning. Aperiod of a few days to several weeks may benecessary for proper drying of the felled vegetation.Heavy jungle brush with many large trunks maytake 1 ½ to 2 months or longer to dry sufficientlybefore burning. Complete burning of large diametervegetation is normally not possible without addingadditional fuel in the form of POL, dry grass, orbrush. If time permits, an effective means has beenthe plant grass in the felled area, and to delayburning until the grass has grown and dried suf-ficiently to serve as a fuel. Chemical spraying of thevegetation with herbicides prior to felling willsometimes accelerate the drying process and insurethat the small vegetation is dry before burning. Inorder to effectively control an in-place burn, it isnecessary to establish fire lines or belts around theboundaries of the area to be burned. In rain forestareas, these belts are normally unfelled vegetation.In dry areas extreme caution should be used whenburning, especially in heavy winds. Escape routes

cut in the area are essential for the safety of theburners. To ignite the area, the burners should movethrough the area with kerosene soaked cloth stripswhich are thrown into the felled vegetation startingat the up slope or downwind side of the area andsetting closely spaced fires along the line. In largervegetation, it will be necessary to prune, stack, andreburn according to the clearing specifications, toaccomplish complete disposal.3-24. PilingIf vegetation is not disposed of in place, it is nor-mally piled, then burned or left to decay. Lightvegetation, including shrubs and tree branches, maybe shredded with a shredding machine. Heavyvegetation (timber) may be piled with a grapple (fig3-32). The equipment used for piling is oftendetermined by what equipment was used for felling.The angled shearing blade and clearing rakespreviously discussed are quite suitable for piling. Insmall areas of light vegetation, piling can be done byhand. If rain is not expected the cut vegetationshould not be piled until it has dried, then it shouldbe piled and burned immediately. If the clearing isdone during a period of heavy rain, the vegetationshould be piled immediately after felling and allowedto dry in the windrow.

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a. Cutting Blades. One advantage of the angled action of the blade on its sole plate permits the bladeshearing blade is its multiple application as both a to carry the vegetation to the pile with very little dirtfelling and piling tool (fig 3-33). The “stinger” can be to produce a cleaner, better burning windrow.used to partially lift the vegetation, and the floating

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b. Clearing Rakes and the Spade Plow. Thesetools can also be used for both felling and piling.They are especially effective in removing surfaceroots while piling. Excess soil passes between theteeth of these tools and very little is carried to thewindrow except in wet or cohesive soils which stickbetween the teeth causing unsatisfactory results.3-25. LoggingOften the area to be cleared contains valuable treeswhich can be marketed as saw timber, pulpwood,firewood, or charcoal. If logging is to be done, itshould be conducted before or after the clearingoperation. The two jobs cannot be done efficientlytogether. Normally most trees sheared or uprootedare not suitable for saw timber because they are splitas they are felled. Thus, if saw timber is desired, itmust be removed prior to clearing. In many areas,most of the vegetation can be disposed of forpulpwood or firewood and often will be removed bylumber companies or indigenous personnel with noexpenditure of effort by the clearing unit.3-26. Removal of DebrisWhen swamps or low-lying areas are located in thearea cleared, it is sometimes desirable to pile brush

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in these areas. The main problem with this method ofdisposal is that the natural drainage can be impeded.Vegetation is often piled in well-placed windrows andleft to decay. In level areas the windrows may beparallel, but in hilly areas the windrows should beleft on the contour to facilitate piling and to helpcontrol erosion. If the vegetation is to be burned inwindrows, they must be piled as compactly aspossible, parallel to the prevailing winds and with aminimum of soil mixed with the vegetation (fig 3-34). The vegetation should be allowed to dry untilthe bark on the larger tree cracks and the foliage hasdried and begun to fall. If the vegetation is ex-tremely difficult to burn, it may be necessary to aidthe burning with forced air and fuel or a combinationof both. Brush burners equipped with 4-cycleengines, airplane-type propellers, and self -primingpumps can be obtained (fig 3-35). They supply air ata high velocity with a continuous fuel spray forstarting and maintaining fires. After the initial burn,repiling should start just as soon as the heat hassubsided enough to permit a crawler tractor with ablower-type fan to approach the fire withoutdamage. piles should be stoked and the fire keptalive until all the woody material is completely

FM 5-164consumed by the flames. Windrows should be cut diameter material. The best tools for repiling areinto segments as soon as possible, making round tractor mounted rakes. Rakes move the vegetationpiles of burning debris which will maintain the readily and allow the dirt and ashes to sift throughhigher temperature necessary to consume the larger the teeth.

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Section V. PRODUCTION ESTIMATE

3-27. GeneralIt is extremely difficult to establish specific rules ofthumb or other guides for selecting land clearingequipment, and determining at what rate each typeof equipment can clear land. There are simply toomany variables involved. Factors such as type ofvegetation, terrain, climate, and underfoot con-ditions, coupled with the purpose for clearing,quantity to be chard, and equipment capabilitiesand limitations directly influence the selection ofequipment and the production rate for any specificclearing job. A number of steps should be followed inanalyzing and planning a land clearing operation.This analysis, combined with good judgment andcommon sense, can result in a reasonable estimate ofproduction rate and time required.3-28. Project Analysis

a. The first step is a thorough study of the projectrequirements and specifications. This should in-clude–

(1) Specific area to be cleared.(2) Time available.(3) Type of vegetation and degree of clearing

required.(4) Climate, rainfall, and topography data.(5) Support operations.(6) Security considerations.

b. After a thorough study of the projectrequirements, the sources of information, such asmap and terrain analysis discussed in appendix F,should be researched. The next step is a personalreconnaissance of the area to determine all of thecharacteristic of the area which will affect theoperation. General topography and soil conditionsshould be determined. Note the size and number ofproblem areas, such as steep slopes, rocks, orswamps, which would significantly affect productionor require special techniques. These should be ex-pressed as a percentage of the whole area. The studyof the vegetation should include two or preferablythree tree counts for each general type of vegetationwithin the area to be cleared. These tree countsshould be recorded as follows:

(1) For secondary growth and undergrowth lessthan 30 centimeters (12 inches) in diameter, notewhether sparse, semidense, or dense.

(2) For trees 30 centimeters (12 inches) andabove in diameter at breast height or above but-tresses, record separately the average number peracre in each of the following size ranges:

30 to 60 centimeters (1 to 2 feet) diameter60 to 90 centimeters (2 to 3 feet) diameter

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90 to 120 centimeters (3 to 4 feet) diameter120 to 180 centimeters (4 to 6 feet) diameter(3) Record the diameter of each tree above 180

centimeters (6 feet) in diameter in each plot andexpress an average number per acre. A more detaileddescription of the tree count procedure, and ad-ditional factors in making the analysis of thevegetation, are contained in paragraph F-9, ap-pendix F. Tabulate the data obtained from thisreconnaissance on a form similar to table 3-7, for usein determining production rate.

c. The degree (scope, quality, and relative per-manency) of clearing to be accomplished is usuallydictated by the purpose or objective of the clearingoperation. However, long-range implications shouldalways be considered since it frequently is possible to

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employ alternative techniques that can also fulfilllong term requirements with little or no additionaleffort. This is especially true when consideringclearing subsurface vegetation and piling the cutvegetation. After determining what items ofequipment are capable of accomplishing the requiredclearing, production rates for each type should bedetermined. The following tasks include those whichmay be required to accomplish the clearing ob-jective:

(1)(2)(3)(4)(5)(6)(7)(8)(9)

Hand clearing.Shearing.Chaining.Spade plow.Rolling chopper.Harrowing.Piling.Grubbing.Burning.

(10) Shredding.Figure 3-36 shows the area conversion factors fromEnglish to metric system for convenient use incalculating production rates.

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3-29 Hand FellingWithout prior experience it is difficult to determinethe ability of indigenous personnel to clear land. Foraverage work output per man-hour, table 3-8 can beused as a guide. This data should be supplementedby records maintained by the unit wherever possibleto obtain a more accurate estimate. The man-hoursshown are for personnel directly engaged in theclearing task and do not allow for maintenance andother overhead personnel.

3-30. Equipment Fellinga. Constant Speed Operations. The production

rate of any clearing operation which is accomplishedby a tractor moving at a relatively constant speedcan be calculated by use of the American Society ofAgricultural Engineers formula.

Speed (mph x width of cut (ft) = acre/hr10

Speed (kph) x width of cut (m) x .825 = hectaes/hr10

This formula allows for 82.5 percent efficiency. Thisreduction is to allow for losses due to turning, etc.Figure 3-37 is a nomogram for calculating thisformula. It can be used in estimating the productionrate for roller chopping, harrowing, plowing,mowing, or any other relatively constant-speedoperation. This formula can also be used for a roughestimation of chaining production. The width of cutwould be the distance between the tractors. Since thewidth and the forward speed vary, an average must

be used for estimating. The speed used in the for-mula must be the actual speed of the tractor. Thismust be measured, but since 88 ft/min. equals 1mph, the lapsed time to travel 88 feet can easily beconverted to mph. Several readings using a stopwatch should be made for accurate speed deter-mination.

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b. Shearing Blade. A formula for estimatingcutting time per acre in minutes for tractorsequipped with shearing blades has been developed.The formula incorporates many of the terrain andvegetation factors which affect land clearingproduction. It is based on a number of years ex-perience in clearing all types of vegetation. Theapproximate number of tractor-hours per acre can becalculated by applying the factors shown below,together with the data obtained from the areareconnaissance, using the formula:

T = X[A(B) + M1N 1 + M2N 2 + M3N 3+M4N4 + DF]

where,T = time per acre in minutes.X = factors affecting total time.A = factors affecting base time.B = base time for each tractor per acre.M = minutes per tree in each diameter range.N= number of trees per acre in each diameter

range obtained from a tree count.D = sum of diameter in feet of all trees above 6’

in diameter obtained from a tree count.F = minutes per foot of diameter for trees above

6’ in diameter.Values for use in this formula are obtained from table3-9.

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Soft underfoot conditions, rocky terrain, and slopessteeper than 10 percent will reduce tractor efficiency.These factors are too variable to give specificreduction factors. This formula was developed foruse with the Rome K/G blade, but it will also applyto V blades attached to the same sized tractors.

c. Spade Plow. During the previous discussion ofthe spade plow, it was noted that this attachmentcould perform several operations. Table 3-9 has been

developed for use with this attachment. Theproduction rates shown in table 3-10 are based ongood underfoot conditions, no heavy vines, andterrain slopes less than 10 percent. The productionrate must be decreased if these adverse conditionsexist in the cut area. The amount of time per acre isreduced if some of the operations such as rootplowing (5) and/or raking (3) do not have to beperformed.

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d. Bulldozer. The bulldozer is readily available inmost engineer units and can be used whenspecialized land clearing tools are not available. Thefollowing are average

Brush and small trees(6" or smaller).

Medium trees (7"–12") . . .Large trees (12"–30) . . .

clearing rates for dozers.

TractorUnder 180 hp Over 180 hp1,000 sq m/hr 1.200 sq m/hr

3-9 min/tree 2-6 min/tree5-20 min/tree 5-20 min/tree

These clearing rates include removal of entire treeand stump and piling the trees in windrows.

3-31. Quick EstimatesTable 3-11 has been assembled for use in makingquick estimates for area clearing and should be usedonly when a detailed reconnaissance and tree countare not possible. The production rates presented arefor average areas, and adverse conditions can reducethese rates significantly. If quick estimates for stripclearing are required, multiply the time required perunit in table 3-11 by 1.6.

3-32. GrubbingWhen the job requires grubbing and piling ofstumps, it is most efficient to accomplish this as apart of the initial felling operation. Grubbing isincluded in the production rates listed in paragraphs3-30 and 3-31 for all types of equipment except theshearing blade. If grubbing is to be done using theangle shearing blade, it is most efficient to ac-complish it as part of the initial felling operation(para 3-30b and table 3-9, also para 3-31, table 3-11).In this case the total time calculated by the cuttingformula is increased by 25 percent (X = 1.25). Ifgrubbing is to be done after initially cutting thevegetation at ground level, the total time is in-creased by 50 percent (X = 1.5).3-33. PilingThe production rate for piling is calculated in amanner very similar to the way the cutting rate wascalculated. This formula is used for estimating pilingtime per acre in minutes for a tractor equipped with a3-44

piling tool. To estimate tractor hours per acre on aspecific land clearing job, apply the factors shownbelow, together with data obtained from the jobcruise in the field, using the formula—

T = B+ M1N1 + M2N2 + M3N3+M4N4 + DFwhere,

T = Time per acre in minutes.B = Base time for each tractor per acre.M = Minutes per tree in each diameter range.N = Number of trees per acre in each diameter

range obtained from field cruise.D = Sum of diameter in feet of all trees per acre

above 6 ft in diameter at ground level ob-tained from field cruise.

F = Minutes per foot of diameter for treesabove 6 ft in diameter.

Values for use in this formula are obtained from table3-12. All the rates are based on a single tractoroperation. Where three or more tractors are workingtogether in a fleet operation, production will increase

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by 25 percent depending on the size and number of Equipment ours per acretrees per acre. For quick estimates for piling use thefollowing data: Equipment Unit Light Medium Heavy

Medium tractor Acre .5 .8 1.2

3-34. BurningWhen burning the cut vegetation in windrows,tractor time must be allowed for tending the firesand repiling the vegetation to insure a completeburn. Thirty minutes to 1 hour tractor time per acreis normally required to accomplish this task. Notractor time is required for burning in place, exceptwhen firebreaks must be constructed.3-35. Special AreasIn addition to the production rate for normal clearingoperation, the time required to clear special problemareas such as steep slopes, swamps, rocky areas, andstreambanks must be calculated separately. Sincethe time required to clear these areas is even morevariable than for normal clearing, personal judgmentand experience may be the only basis for making anestimate.3-36. Tree Blowdown

different situation from that of a natural storm. Thearea damaged by either a nuclear air burst or asurface burst varies according to the size of theweapon (bomb). The degrees of damage may be oneor more of the following: total damage (90 percent ormore, usually at or near ground zero), severe,moderate, and light. The damage becomesprogressively lighter outward from ground zero. Inaddition to the tree blowdown caused by an airburst, a surface burst also produces a radioactivecrater, induced radiation (mainly neutrons), andfallout. Blowdown clearance in a radiologicallycontaminated area requires more time and equip-ment because of the radioactivity. The machinerymust be equipped with protective features whichshield (at least partially) the operator from theharmful radiation. (For further information on treeblowdown in a nuclear environment, see TM 5-220).

Tme blowdown caused by a nuclear burst produces a

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