FM 5-144

By Order of the Secretary of the Army:

Official:

CREIGHTON W. ABRAMS,General, United States Army,Chief of Staff.

VERNE L. BOWERSMajor General, United States Army,The Adjutant General.

Distribution:Active Army, ARNG, USAR: To be distributed in accordance with DA Form 12-

11A requirements for Engineer Construction and Construction-Support Units (Qty rqrblock no. 33).

✩ U.S. GOVERNMENT PRINTING OFFICE : 1991 0- 281-486 (43323)

✩ U.S. GOVERNMENT PRINTING OFFICE:1994-300-421/01217

Field Manual

No. 5-164

* FM 5-164

HEADQUARTERSDEPARTMENT OF THE ARMY

Washington, D. C., 30 August 1974

FM 5-164

CHAPTER 1

INTRODUCTION

1-1. PurposeThe purpose of this manual is to provide com-manders and their staffs with information and datawhich can guide them in their conduct of tacticalclearing operations. It provides a consolidation ofthe latest information and guidance to personnelresponsible for planning land clearing operations andfor utilizing and supervising engineer units engagedi n such operations. Additionally, the manualprovides information about equipment and methodsused by civilian land clearing agencies that are alsoapplicable to military clearing operations.1-2. ScopeThis manual contains information on how toevaluate clearing requirements, determine theamount of effort required, select the most efficientmeans to clear the vegetation, and support andsecure land clearing units. The necessity for soundprior planning is emphasized throughout thismanual because it is a major lesson to be learnedfrom the clearing operations conducted up to now.Good planning will insure that the specifications areconsistent with the purpose for clearing, which isessential to avoid wasted effort resulting fromclearing too thoroughly in one area and notthoroughly enough in another. Clearing foragricultural or forestry purposes specifically is notincluded. However, the potential civic actionbenefits to be derived from a clearing project, suchas making more agricultural areas available andproviding felled vegetation for lumber, shouldalways be considered, due to the favorite social andeconomic impact on the local populace.1-3. ApplicationIn addition to information specifically pertinent to

tactical land clearing, this manual contains a varietyof data and information having application to landclearing in general. These are included becausetactical land clearing operations can utilize most ofthe engineering considerations and techniquesdiscussed therein. At the same time, it should bekept in mind that tactical land clearing operationsare a distinctive, separate, and highly specializedtype of combat operation normally conducted bycombined arms groupings supported by TOEengineer land clearing companies (or composite orprovisional engineer land clearing battalions) andother engineer units as may be appropriate. Landclearing on a relatively small scale may be conductedin mid-intensity or higher level warfare by anyengineer unit equipped with land clearing plows andrelated equipment. However, large-scale landclearing operations in a counterinsurgency en-vironment or in low-intensity warfare where enemyforces make extensive use of heavily forested areasfor their bases and operations will normally be ac-complished with the support of specialized engineerland clearing units as indicated above.1-4. ChangesUsers of this publication are encouraged to submitrecommended changes and comments to improve thepublication. Comments should be keyed to thespecific page, paragraph, and line of the text inwhich the change is recommended. Reasons will beprovided for each comment to insure understandingand complete evaluation. Comments should beprepared using DA Form 2028 (RecommendedChanges to Publications and Blank Forms) andforwarded direct to the Commandant, US ArmyEngineer School, Fort Belvoir, Virginia 22060.

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CHAPTER 2

TACTICAL LAND CLEARING OPERATIONS

Section I. CONCEPT AND PLANNING

2-1. Purpose of Tactical Land Clearing Operationsa. A tactical land clearing operation is a combined

arms operation having the objective of destroying,disrupting, or neutralizing enemy forces andfacilities in a counterinsurgency environment inwhich enemy activities and unite are using heavilyforested areas for cover and concealment. Landclearing and other related combat support functionsperformed by engineers are primarily intended toenhance and complement the mobility, firepower,surveillance, and target acquisition capabilities of allelements in the combined arms grouping. A tacticalclearing operation usually includes some or all of thefollowing subsidiary objectives:

(1) Deny the enemy cover and concealment.(2) Channelize the enemy’s infiltration and

movement.(3) Deny the enemy concealed base areas.(4) Deny the enemy ambush sites adjacent to

land lines of communication.(5) Provide aerial and antipersonnel radar

observation lanes.(6) Provide observation and fields of fire for

perimeter defense of friendly installations.(7) Enable friendly forces access to and control

of key terrain features. Provide off-road cross-country tactical vehicle mobility to friendly units.One land clearing operation can be planned to ac-complish several of the objectives listed above.Tactical counterguerrilla operations in heavilyforested areas sometimes succeed in driving theenemy from jungle areas, but have not been suc-cessful in keeping him out. Land clearing, by fellingand disposing of the vegetation in these criticalareas, can effectively deny the enemy their use.

b. A secondary benefit from a tactical landclearing operation is that it often enhances theeconomic status of the area. Consistent with thetactical situation, marketable timber felled duringclearing can be left for the local lumbering industry.Clearing also converts dense jungle areas intopotentially useful agricultural areas. If foodproduction or lumber is critical to the economicdevelopment and stabilization of an area, landclearing can be accomplished primarily for thesecivic action benefits.

2-2. Responsibilitiesa. Tactical land clearing missions should be

conducted by combat units and/or combined armsgroupings of battalion-size or larger. Engineer landclearing units and other engineer units, as may beappropriate, are attached or placed in support of thecombat unit commander. The commander of thecombat unit or combined arms group is responsiblefor the conduct of the land clearing operation. Theland clearing requirements, in support of the tacticalobjectives, are identified, developed, end establishedby each tactical commander for his area ofresponsibility. Due to the highly specialized natureof tactical land clearing operations and the extensivecommitment of engineer resources usually involved,the advice and assistance of the staff engineer of thetactical commander concerned is of particular im-portance in formulating the tactical land clearingplan. In order to make a sound land clearingestimate and plan, specific quantitative descriptionsof the vegetation on the site to be cleared arerequired. Timely arrangements are made to integrateand coordinate the application of land clearingresources available from or being employed byhigher and collateral commends. Coordinativedetails and supporting arrangements are included inthe tactical land clearing plan. Factors such as treecount, tree size, wood density, root system, vines,and undergrowth significantly affect production inland clearing operations. Allocation of land clearingresources, and details of timing and phasing forexecution of the operation, should be clearly definedwith due consideration to the effect of terrain,weather, and enemy activity on the capabilities andlimitations of land clearing resources. Terrain andweather conditions, such as large swampy areas andmonsoons, must be considered when allocating landclearing resources. Because tactical lend clearing isoften conducted in strongly held enemy territory, theland clearing force must contain sufficient tacticaltroops to provide protection for the land clearingunit. The enemy recognizes the effect of land clearingupon his operations and may be willing to sacrificehis own resources in attempts to disable or destroyland clearing equipment.

b. The tactical land clearing plan must also

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consider the long range requirements for continueddenial of the area through a program of regrowthcontrol and secondary clearing. Tactical clearingshould be coordinated closely with the civil affairsstaff to maximize its benefit in the stabilization ofthe area and minimize the adverse effects of landclearing operations on the local populace.2-3. Unit Capabilities

a. Troop units participating in tactical landclearing operations must be mounted in trackedvehicles to facilitate movement and observation, andto enable delivery of large volumes of firepower onthe enemy. TOE or provisionally organized engineerland clearing companies and battalions should beemployed as primary land clearing elements. TheTOE engineer land clearing company is discussedmore fully in the next subparagraph. Other engineerunits, which may also be equipped with land clearingplows and related equipment, can be used to ac-complish supporting and complementary clearingtasks as well as to provide other forms of engineersupport for the tactical clearing force.

b. Due to the requirement for the clearing of vastareas to deny the enemy sanctuaries in counter-guerrilla operations in a heavily forested or jungleenvironment, a highly specialized land clearingcompany has been organized. The missions of thiscompany, now organized under TOE 5-87, are to—

(1) Destroy or clear extensive dense vegetationin critical areas for the purpose of denying their useby the enemy as bases of operation, supply bases,marshaling areas, ambush sites, and cover andconcealment.

(2) Clear dense vegetation from areas adjacentto friendly installations for the purpose of improvinginstallations security by providing observation andfields of fire, and reducing ambush probability alongland lines of communications.

c. This engineer land clearing company normally isassigned to a corps with reassignment or attachmentto an engineer combat brigade or engineer combatgroup. The major items of equipment of the engineerkind clearing company include 30 medium (180 hp)tracked tractors equipped with angled shearblades,12 full-tracked 6-ton carriers, disk harrows, chain

saws, air compressors, welding shop, generators,and various cargo and utility trucks. In addition,this unit can provide its own direct support (DS)maintenance and maintain a mission load of repairparts for the following mission essential itemsorganic to the company:

(1) Chain saws.(2) Air compressors.(3) Grinding machines.(4) Disk harrows.(5) Tracked tractors and attachments.

d. Additional capabilities of this company areshown in TM 5-142 and in TOE 5-87. The engineerland clearing company is internally self-supporting,but is designed to operate as part of a larger force ortask grouping which provides for external support.It consists of a company headquarters, trans-portation and maintenance platoon, and threeidentical land clearing platoons (fig 2-1). Thiscompany may be employed to accomplish a varietyof land clearing operations to include large areaclearing missions requiring the total company effort(30 tractors), missions requiring a platoon size effort(10 tractors), and missions requiring effort of asingle section (5 tractors). The company may beattached to or placed in support of engineer bat-talions engaged in land clearing or other engineeroperations. The company may also be employedindependent of other engineer units as an attached-orsupporting component of the tactical force involved.Additionally, two or more companies may beprovisionally organized into a land clearing battalionand employed as outlined above or independently.Preservation of land clearing unit integrity is ofparticular importance to facilitate control andsupport of land clearing plows as well as to deriveincreased efficiency and production inherent in enmasse employment of the unit. If the company isfragmented into smaller organizational elements, itshould only be for short periods of time and underexceptional conditions because the maintenanceplatoon operates most efficiently as a single elementand prolonged fragmentation will result in loss of adesirable maintenance posture.

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2-4. Planning an Operation tractor can easily become damaged. If the vegetationThe major steps in planning a land clearingoperation are as follows:

a. Establish clearing specifications, priorities,timing, and phasing as may be appropriate forsubordinate tasks and units.

b. Provide for security of the land clearing unit.c. Provide for support requirements.

2-5. Clearing Specificationsa. After the reason for clearing a particular area

has been determined, the specifications defining therequired results must be established. Clearing in-volves the expenditure of a considerable amount ofeffort. Care should be exercised so that thespecifications require only the amount of clearingnecessary to accomplish the objective.

b. One of the first considerations is the length oftime that the area must remain clear of vegetation. Ifthe future use of the area indicates that long termclearing is required and regrowth is to be controlledusing either herbicides or mechanical means, thearea must be cleared more thoroughly than if it is notbe re-entered. If regrowth is to be mechanicallycontrolled, all stumps must be cut to no more than12 inches above the ground. Higher stumps willinterfere with tractors returning to the area forregrowth control and if they inadvertently straddle ahigh stump, the belly pan and undercarriage of the

is in excess of 12 inches in diameter, it should bewinrowed and burned after the initial clearing, ifregrowth is to be controlled mechanically. Wind-owing patterns and techniques are discussed inparagraph 2-9 e. Isolated large trees, 3 feet or more indiameter, can be left standing because they provideless cover to the enemy in a vertical position.Cutting these large trees even with a shearing bladeis a time-consuming process because of the extrasplitting effort required.

c. An approved overlay defining the specific areato be cleared must be provided to the land clearingunit commander and all interested parties prior tothe start of the operation. This is necessary topreclude confusion in reporting progress or whenreferring to cut areas. Any changes or deviationsshould be made only after careful analysis, andapproval by proper authority.2-6. Security of the Land Clearing UnitSecurity of land clearing personnel and equipment isextremely critical to the success of a land clearingoperation. The land clearing unit has too littleorganic capability to furnish its own security eitherin the cut area or in the night defensive positions.Provision of adequate security is the responsibilityof the tactical commander responsible for the con-duct of the land clearing operation.

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a. The enemy recognizes the effect of land clearingon his operations and is willing to assume great risksto harass or prevent the operation. The security forcemust be aggressive, alert, and responsive at alltimes. The amount of security forces necsssary willvary according to the enemy situation. The tacticalor security element commander and the land clearingunit commander must coordinate their activitiesvery closely in the cut area. The land clearing unitcommander must advise the tactical unit on thedeployment of his troops to obtain maximumsecurity with minimum interference with the clearing

operation. Special consideration should be given tothe enemy’s capability to place mines andbooby traps in the cut area. All clearing tractors areextremely vulnerable to mining activity. The enemymay also attempt to ambush or attack the clearingunit in the cut or on the march between the cut andthe night defensive position (NDP).

b. The night defensive position for a land clearingcompany serves as both a secure night bivouacposition and a maintenance base during both nightand day. An example of a typical NDP is shown infigure 2-2.

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(1) This circular area of 200 meters minimumdiameter is constructed in a doughnut configuration,leaving a ring of jungle between the outer defensiveberm and the center area. Mines and boobytrapsmay dictate complete clearing; if not, the ring ofjungle provides concealment for maintenance andmess areas, and for mortar positions. The entrancesto the center are constructed to preclude directobservation from the out side. Maintenance andother activities can be conducted using lights duringthe hours of darkness, with the concealmentprovided by the opaque ring of jungle. The main-tenance activities of a land clearing unit in the fieldwill often require night work, so an NDP similar tothis is absolutely essential if the maximum numberof operational tractors are to be kept in the cut on thefollowing day.

(2) The NDP should be located on well drainedterrain near the road net if land resupply is an-ticipated. Its location on well drained terrain isespecially essential during the monsoon or rainyseason. If drainage is not adequate during the rainyseason the NDP can become a quagmire as thetractors disturb the soil in the center and make ituntrafficable. When this occurs maintenance ac-tivities are severly hampered.

(3) The NDP should be located not more than 4km from the cut area. Four km is normally themaximum distance the tractors should “walk” to thecut area.

c. When the NDP is to be moved as the clearingprogresses, adequate time must be allowed to insurethat a new NDP can be completed prior to nightfall.New NDP’s should be occupied or secured im-mediately in order to prevent covert mining byenemy elements. To the maximum extent possible,security forces must relieve the land clearing unit ofthe burden of perimeter security in the NDP.Conversely, fields of fire, access routes, weapon andSTANO sites for the security element will be clearedby the land clearing unit under the direction of thetactical commander during the initial construction ofthe NDP.

d. During operations in the cut area the landclearing company is spread over a wide area andcontinually on the move. It is important that thesecurity elements be mobile and responsive to keepup with the continually shifting operations and tomove rapidly in response to an ambush or attack.The composition and strength of security elements isestablished by the tactical commander conductingthe clearing operation. The mobile form of securityand firepower required in tactical land clearing canbeet be provided only by mechanized infantry, ar-mored cavalry, and armored units. The size of theforce required will be governed by the tactical

situation. An armored cavalry troop reinforced by atank platoon has effectively secured one landclearing platoon. Infantry foot troops can be used assecurity when the land clearing element is engaged ina long strip clearing operation and there are suf-ficient troops to outpost and secure the perimeter ofthe area being cleared.

e. Security vehicles and personnel should notapproach land clearing tractors closer than 30 meterswhile they are moving. This will preclude accidentalinjury to personnel and damage to vehicles in theevent a tractor detonates a mine or booby trap.Falling trees can also severely damage unprotectedequipment and injure careless personnel. Theclearing tractor operator’s visibility is severelyrestricted by the protective cab so personnel mustuse extreme caution when approaching movingtractors under any circumstance. When movingbetween the cut and the NDP a good tactic is to havethe column led by a radio equipped tractor with abulldozer blade, followed by a tank. The bulldozerblade can clear a path for the clearing tractors andAPC’s and will also detonate any mines encountered.The convoy should not use the same route to andfrom the cut, in order to minimize enemy mine ef-fectiveness. No equipment should move between thecut and NDP at night or without proper securityescort. It may be necessary to set up a convoy fromthe cut to the NDP at midday in addition to themorning and afternoon convoys to evacuateinoperative tractors for maintenance and repair.

f. In order to discourage ambushes, minelayingparties, and other enemy activity in the cut area,harassing and interdictory fires should be directed atavenues of approach and into the area to be clearedthe following day. Artillery preparation of thecutting area prior to the start of work is advisable.These fires should be scheduled early enough to becompleted prior to the arrival of the clearing unit inthe morning so the start of work is not delayed.Ambush patrols and reconnaissance by fire can alsoassist in locating enemy elements and discouragesnipers and rocket propelled grenade attacks. Themost likely avenues of approach, streams, trails,etc., to the cut area should be cleared first to im-prove friendly surveillance capabilities and denycovert enemy access to the cut area.

g. When required by tactical circumstances,enemy activity, or the land clearing plan, teams ofland clearing and security force elements may bediverted from general clearing operations topenetrate into or isolate a known or suspected enemyposition. The tractors lead by clearing only theundergrowth and small trees and avoiding largetrees or impediments that would delay progress.Speed is the key to such operations and knocking

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down large trees not only takes time, but also im-pedes the progress of tactical vehicles through thecut area. By moving through the undergrowth only,a task force can proceed far faster than enemy footsoldiers can possibly move. The success of suchoperations depends heavily on the availability of acommand and control helicopter, communicantionswith all tractor operators as well as the combat force,and immediate fire support, either from air oratrillery. Since there may be little or no time for priorplanning in such operations, land clearing unitsshould be trained in rapid response missions and,whenever possible, the combined arms forces con-ducting land clearing operations should rehearse.

h. Security forces must be informed that im-mobilized equipment means trouble and that theyshould investigate immediately. The operators willstop their tractors only if they have experiencedmechanical difficulties that prevent them frommoving to a secured area, if in contact with theenemy, or if they have discovered a dud round, mine,or boobytraps. The dud rounds, mines, andboobytraps should be marked immediately toprevent equipment or personnel casualties. Whenoperations are conducted in an area of high mine andboobytrap density, engineer demolition teams andEOD personnel should be attached to the landclearing unit to dispose of them. Land clearingtractor operators are constantly exposed to sniperfire, ground attack, and mines, and are usually thefirst to find enemy bunkers or tunnels hidden by theheavy vegetation.

i. Voice communication between operators isimpractical bacause of the noise of the tractor. Tosignal “danger withdraw” to other operators andalert the security forces, each operator should begiven a supply of colored smoke grenades for usewhen danger threatens. Tractor operators can beequipped with AN/PRR-9 radio receivers andtransmitters to maintain control of operations andcontact between operators. Experience has shownthis practice can improve morale and also reducepersonnel and equipment casualties. The AN/PRC-25, with headsets, can also be used and has beenfound in some instances to be more efficient.2-7. Support Requirements

a. Aviation Support. Reconnaissance is anessential factor in area clearing operations. It isextremely difficult for the clearing unit commanderto control his unit, make sound plans, or make anaccurate assessment of the clearing to be ac-complished in a hostile area without daily aerialreconnaissance. The minimum required aviationsupport is two helicopter sorties daily, one for 2hours at the start of work in the morning and one foran hour at the end of the workday. Aerial

photograph flights of the cut area before, during,and after the clearing operations are beneficial inaccurately determining the quantity of clearingaccomplished. In remote areas where logistical trainscan reach the land clearing unit only with greatdifficulty, aviation support is required for supply ofrat ions, POL, repair parts, ammunition, and othersupplies. Utility helicopter support for high priorityadministrative and maintenance items is alsoessential and should be integrated with recon-naissance missions. Time sharing of a helicopter isnot normally satisfactory because the dailyreconnaissance flights must be accomplished on timeor the entire land clearing effort is delayed.

b. Engineer Support. The tactical commander isresponsible for providing combat engineer supportfor the tactical clearing operation. In terrain that isinterlaced with streams, canals, or steep-sidedgullies it is necessary to provide bridging to cross theland clearing tractors or security force vehicles.Supporting engineer troops are necessary to installbridging across these obstacles. The armored vehiclelaunched bridge (AVLB) is extremely effective forthis purpose. It can be used several times in a cutarea with little expenditure of manpower and time. Itmay also be necessary to install rafts, floats, or moreextensive bridging to complete the cut area. Combatengineers may also be required to conduct daily minesweeps of the cut area and routes to and from the cutarea. If the clearing plan or specifications indicatelarger vegetation or that on steep slopes, vegetationis to be felled using chain saws or explosives, combatengineers and demolitions specialists would have tobe used to accomplish this work. These engineerswill also detonate any mines, boobytraps, or dudrounds found in the cut area. Another piece ofengineer equipment that can add support to landclearing operations is the combat engineer vehicle(CEV). The versatility of the CEV makes it useful inthat it has light dozing capabilities, liftingcapabilities with its hydraulic boom, and can provideadditional security with its armament of a 165-mmdemolition cannon, M73-7.62-mm coaxialmachinegun, and M85 0.50-caliber machinegun. Inaddition, a mine roller can be mounted on the front ofthe vehicle to facilitate detonation of pressuresensitive mines in its path.

C. Logistics Requirements. A land clearingcompany, even more so than other engineer units,bears a particularly heavy logistical burden. Thetractors may consume up to 1800 gallons of dieselfuel daily. An average of 800 pounds of repair partsis necessary each day. This figure will vary widelywhen major components such as tractor engines tiretransported. Over 2000 gallons of water is thenormal daily consumption for equipment, mess, and

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personnel. When clearing heavy vegetation utilizingexplosives, 1000 pounds of C-4 may be requireddaily. The parent engineer organization through itssupport channels is normally capable of coordinatingall the necessary logistical and maintenance support.However, additional transportation either by air orby ground may be required. Since land clearingtractors whould not be directed from their primarytasks for extraction of disabled vehicles, a heavy

recovery vehicle should be furnished by the tacticalcommander for this purpose. Recovery operationsare discussed in detail in appendix C. For the pur-pose of tactical movement a land clearing company isonly 30 percent mobile in organic vehicles. In orderto make a one-lift tactical movement it must besupplemented by twenty-two 10-ton tractors and 25-ton semitrailer low-beds.

Section II. CLEARING PROCEDURES

2-8. Types of CutTactical land clearing is normally accomplishedusing one of three basic techniques depending uponthe size and shape of the area and type of vegetationto be cleared.

a. Area Clearing. This technique is used whenclearing large areas of heavy vegetation. Wheneverpossible, the land clearing company commanderselects three areas, each generally 70 to 125 acres(300,000 to 500,000 square meters), one area for eachplatoon of 10 clearing tractors. These areas aredefined by a clearing a “trace” counterclockwisearound the perimeter. Each area is to be completelycleared during 1 day’s operation. One, figure 2-3illustrates a typical three-platoon area clearinglayout. Often three-platoon areas are not feasible,

because of a shortage of control aircraft or tractors.Also, in heavy vegetation and difficult terrain, ittakes the full attention of the OIC in a helicopter toguide a single trace. Two, figure 2-3 shows the use oftractors protected by APCs (or infantry) in securinga strip clearing operation. Three, figure 2-3 showsthe use of tractors and APC’s to allow mobile defenseduring a land clearing. The security forces arefragmented between each separate cut area whenthree-platoon areas are established and in an ex-tremely hostile area this can seriously reduce theireffectiveness. Consequenty, tactical land clearingoperations are often conducted in company mass.Figure 2-4 shows area clearing with tactical securityforces deployed.

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b. Strip Clearing. This technique is used whenclearing along roads and trails or when clearingsurveillance lanes. One technique for strip clearing isto divide the land clearing company into two teams.The teams operate on opposite sides of the road,progressing at the same rate on both sides. If thestrip is to be cleared is wide enough, clearing may beaccomplished using an elongated rectangular pat-tern. When strip clearing along roads, another ef-ficient technique is to cut from the road outwardrat her than following rectangular traces on each sideof the road. The tractors move in echelon left side ofthe mad, the lead tractor moving along the roadshoulder. At midday the tractors cross the road andreturn down the other side of the road. Securityforces have the advantage of interior lines and maymove on roads and/or cleared areas to maintainpositions of direct observation and protection overtractors and other elements of the land clearingforce. When cutting a rectangular trace, the securityforce is stationed around a perimeter. Enemy forcesare often trapped with the trace and the security

force cannot fire heavy caliber weapons withoutendangering friendly troops on the opposite side ofthe cut. When the clearing tractors must cross themad, care should be exercised to insure thatdrainage ditches and mad shoulders are notdamaged.

c. Orchard and Plantation Clearing. The mostefficient technique used in felling uniformly sizedtrees found in orchards and plantations is by use ofan anchor chain pulled between two tractors. Theproduction rate using this technique is considerablyhigher than shearing this type of vegetation. Thistechnique is described in detail in paragraph 3-8 f.2-9. Area Clearing Operations

a. Daily Work Area. The first step in organizingthe cut area is to establish the daily work area. In ahostile environment alternates are also selected andthese areas are shifted to keep the enemy from an-ticipating the location of the next day’s cut. Thecomplete area outlined should be cut in 1 day,because uncut islands of jungle openly invite the

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enemy to employ mines or ambushes the followingday. Areas which are difficult to clear and those inwhich the vegetation conceals a gully, stream, orother hazard, should be cleared first. By clearingthese hazardous areas with the most experiencedoperators, the remainder of the area can be clearedby less experienced operators with little or no delay.These areas are often also the most likely avenues ofapproach for the enemy to move into the area toharass the operation. The tactical commander whohas the overall responsibility for the operation, inconjunction with the land clearing unit commander,should select these areas and give them priorityduring the first part of the operation. When cuttingheavy vegetation, the most efficient procedure is tobypass the large trees and engage only the un-dergrowth and smaller trees that can be pusheddown in a single pass. A special team of skilledoperators should be assigned to follow up and thinout the large trees as desired. If large trees areengaged in the initial pass, many tractors must sitidle while one operator works on a tree that he isunable to see clearly. Damage which may affect bothtractor and operator under these circumstances canalso be severe because of falling trees.

b. Maintenance Area. Upon arrival at the cuttingarea for the day, a secure area should be establishedfor use as the onsite maintenance and assembly areafor disabled tractors. An air compressor, watertrailer, and contact maintenance vehicle will nor-mally be placed in this secure area.

c. Trace Cutting. The initial trace of the perimeterfor the day’s cutting operation will be made im-mediatley after arriving at the cutting area. A leadclearing tractor will cut this trace counterclockwisearound the perimeter, as shown in figure 2-3.Security is normally provided by combat unitsand/or combined arms elements; however, this is notshown in figure 1, 2-3. This lead tractor operator caneasily become lost when cutting heavy vegetationbecause of limited visibility due to the undergrowthand trees falling back over the cab. When no trail orexisting terrain feature exists to define the perimeterof the cutting area, the lead tractor should be guidedby radio from an observation helicopter. In areaswhich contain streams, gullies, or other hazards,continuous aerial observation and control of theclearing tractors may be necessary. A lensaticcompass can be used to assist the lead tractoroperator in maintaining a course, but this is not aseffective as radio control by an aerial observer, andnormally would be used only in strip clearing. Whencutting the initial trace, the security vehicles oftenare unable to follow in the path of the tractorsbecause of the fallen trees. It is therefore essentialthat the lead tractor is equipped with a bulldozer

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blade that can clear the path for security elements.Only in very high jungle are security vehicles able todo without this assistance. Often, a pioneer road isnecessary. If it appears that the cut originallyoutlined for the day’s work is to be finished early, thecommanding officer of the land clearing unit mustnotify the tactical commander a minimum of 1 hourprior to completion, to permit a timely arrangementfor shifting security forces and the provision of aerialreconnaissance support for continuing clearingoperations at the next scheduled cut or alternate cut.Cutting operations should be suspended at the closeof each work day to allow sufficient time for thetractors to return to the NDP and have a minimumof 2 hours of daylight for maintenance of the trac-tors.

d. Bulldozer Support. When clearing in terrainwhich contains obstacles such as small gullies,streams, tunnels, or bunkers, some of the landclearing tractors should be equipped with bulldozerblades. These bulldozers should be used to do theearthmoving required to destroy the enemy in-stallations, to construct pioneer roads in the cut forsecurity vehicles, to build causeways across streams,and to fill gullies. They are absolutely essential forconstruction of fortifications in the night defensivepositions. Do not attempt to use bulldozers inechelon with clearing blades when clearing largetrees because they cannot maintain the cutting rate.The clearing blade should not be used for earth-moving purposes because it is less efficient andbecomes dull so it will not cut trees effectively.

e. Cut and Piling Patterns. Clearing with anangled shear blade is conducted by the tractors of aland clearing platoon moving in echelon from theoutside of the rectangular area toward the center in acounterclockwise direction. The cut sheds off thetraining (right) end of the blade and leaves the uncutarea free of fallen debris. If the cut material will notshed, the operator should make a sharp right turn,followed by a sharp left turn and resume the originalline of travel. The areas must be more carefully laidout if the vegetation is to be windrowed after felling.Piling is most efficient if windrows are oriented 90°to direction of cut. After the boundaries have beenestablished by the initial trace, spoil areas fordisposal and windrows are selected on the basis ofthe following factors: shortest haul, downgradeslope, and general accessibility. Care must be takenwhen locating windrows so as not to disrupt thenatural drainage of the area. Vegetation windrowscan form ideal concealment for the enemy if im-properly oriented. Windrows should be placedperpendicular to the friendly perimeter so that bothsides of the windrow can be observed. The windrowsshould also be perpendicular to the centerline of a

FM 5-164mad or trail that is used by friendly forces. All forward almost continuously, the most efficientwindrows restrict offroad manueverability of tactical production is obtained by laying out long areas 200elements so they should be burned or disposed of as to 400 feet wide, clearing and piling the vegetation asquickly as possible. When the diameter and density shown in figures 2-5 and 2-6.of the vegetation is such that the tractor can move

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These methods are the best for most relatively levelareas. On steep slopes, rapid production is obtainedby working in a semicircular pattern from left toright, pushing the vegetation downslope (fig 2-7). Ifthe terrain is steep the windrows should be piled onthe contours and the tractor should work from the. .uphill side. On level terrain, if the vegetation isdense and small as in light brush, highest production

increasing rectangle, with the trailing edge of theblade working against the uncut material, theoperator can prevent the cut material from sliding offthe blade and allow the cut material to accumulateon the blade. When the blade is filled, the operatorstops the tractor, deposits the cut material, forminga windrow, then turns to the left twice to the startingpoint and repeats the operation, as shown in figure 2-

can be obtained by cutting and windrowingsimultaneously. By working counterclockwise in

8.

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This technique reduces the time spent backing up. but when clearing, the tractors should be a minimumAll of these methods of piling are 20 to 30 percent of 30 meters apart to preclude felling trees on eachfaster with three to five tractors working abreast. other, colliding due to limited visibility, or in-The tractors should work close together when piling creasing casualties due to a mine or boobytrap. Seethe vegetation to obtain this increased efficiency, figure 2-9 for a typical fleet operation.

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f. Chopping and Disking Patterns. There are two rolling chopper or disk harrow, as shown in figures 2-basic patterns used when clearing growth with a10 and 2-11.

Variations of these two basic methods are made to fitthe topography or shape of the area being cleared.When cutting poles, bamboo, or large saplings, thereccommended procedure is to cut in the same

direction as the previous pass using increasing ordecreasing rectangles.2-10. Strip Clearing OperationsThe first phase of a typical route or strip clearing

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operation is to establish an NDP about 4 kilometersbeyond the last cleared area, as illustrated in figure2-12.

The land clearing unit then clears back toward theNDP and about 4 kilometers beyond. A new NDP isthen established 8 kilometers farther down the road.Along roads or major trails the vegetation is cleared200 meters wide on each side of the road. If the stripclearing is to establish observation and recon-naissance lanes, these cleared strips are from 200 to500 meters wide. Fallen trees are normally piledwhen clearing is adjscent to major roads. Thewindrows are piled perpendicular to the road so theycannot be used as cover by the enemy (fig. 2-13). Theend of the windrow adjscent to the uncut vegetationshould not extend to the forest, but should stop 10 to15 meters short to allow reconnaissance and securityvehicles to pass around the end of the windrowsadjscent to the uncut forest.

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2-11. Clearing Cultivated AreasCultivated areas such as rubber plantations and fruitorchards are most efficiently cleared by chaining.The organization of the area is dependent upon thesize and shape of the plantation. When chaining isused as a clearing technique it is preferable toorganize the pattern of the cut so the tractors canmake as long a pass in one direction as possiblebecause turning or reversing direction with a chainresults in considerable lost time. A pattern similar tothat used in chopping or disking (fig. 2-10 and 2-11)should be used.2-12. Clearing RatesThe following are average estimates for a clearingoperation of one land clearing company with 25operational medium clearing tractors for various

types of cuts under optimum conditions of securityand level, dry terrain, excluding windrowing.

a. Area Clearing.(1) Light (less than 12

inches diameter)(2) Medium (12 to 20 in-

ches diameter)(3) Heavy (greater than 20

inches diameter)b. Strip Clearing.

(1)

(2)

(3)

Light (less thaninches diameter)Medium (12 to 20ches diameter)

12

in-

Heavy (greater than 20inches diameter)

400 acres/day

250 acres/day

100 acres/day

250 acres/day

150 acres/day

100 acres/day

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c. Cultivated Rubber Using One Land Clearing (3) Heavy (greater than 12 100 acres/dayPlatoon With Three Anchor Chains.(1) Light (less than 6

inches)400 acres/day These production rates are subject to considerable

inches)(2) Medium (less than 12

variance due to tactical and terrain conditions and250 acres/day should be used for general planning estimates only.

inches)

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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)

3-14

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

3-36

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

3-38

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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CHAPTER 4

LANDING ZONE, REMOTE SITE AND

CONSTRUCTION CLEARING

Section 1. LANDING ZONE AND REMOTE SITE CLEARING

4-1. Landing Zone Clearinga. General. Landing zone (LZ) clearing is

necessary to support airmobile operations in forestedareas. Initially it may be only a one-helicopter LZcleared from the jungle using demolitions and chainsaws, but it can be developed into a large combatbase in successive stages. When an infantry bat-talion is conducting an airmobile combat assault intoa heavily forested area, the engineer platoon is oftenthe first airlift into the landing zone, depending onwhether or not security is already on the ground.Their mission is to initially clear the landing zone toallow one helicopter to land and then to bring in moreequipment to improve and expand the landing zone.

b. Landing Zone Cutting Team.(1) If an initial clear area is available, an

engineer landing zone cutting team can establish anLZ by descending into the site with its jungle cuttingequipment from a hovering Chinook (CH-47)helicopter (fig 4-1), after the area has been securedby ground forces. This team must be extremely welltrained and each mission well planned. A recon-naissance of the proposed LZ should be made by anengineer officer or NCO if time permits. As a resultof this reconnaissance, the tools and equipmentnecessary to be taken to the LZ may be selected inorder to provide the best tools for the specific type ofvegetation to be cut. For example, bamboo is mosteffectively leveled with bangalore torpedoes. Typicalitems of equipment taken into the LZ are am-munition, machetes, brush hooks, chain saws, two-man crosscut saws, axes, potable water, C-rations,premixed gasoline for chain saws, oil for chain sawlubrication, demolition bags, C-4 plastic explosive,bangalor torpedoes, detonating cord, sharpeningequipment for tools, mechanics tools for chain sawrepair, and chain saw repair parts. This equipment is

prepacked in two sling loads, and a third load forresupply containing additional explosives isprepacked for on-call delivery. Immediately uponarrival at the mission site, the team leader coor-dinates with the tactical commander on the groundto establish work priorities and to explain demolitionsafety and procedures.

(2) A second method of inserting a platoon orsquad sized engineer landing zone cutting team intoan area is by rappelling from a hovering utility ortroop carrier. The team must have had prior trainingin rappelling practice in actually using helicopters.The rappel from the helicopter is made using a rope,and a “Swiss” seat- O -ring arrangement. Gloves areworn to avoid rope burns and only essentialequipment is taken on the initial insertion. Thisconsists of weapons and ammunition, chain saws,demolition bags, C-4 plastic, explosive, machetes,premixed gasoline, oil, C-rations, and water. After aone-s hip LZ has been cut, more equipment and menare inserted. There must always be close coor-dination between the team leader, the helicopterpilot, the pilots of any gunships accompanying themission, and the ground security forces. In com-paring this method of insertion with the methodusing a Chinook (CH-47) and a rope ladder there arecertain advantages. The insertion by rappel is afaster method and gets the team on the groundfaster. This is important when rappelling underhostile fire into a "hot” LZ. Also, there is less chanceof single ropes getting entangled in trees as com-pared to a rope ladder. This becomes significantwhen establishing an LZ in double or triple canopyjungle or very thick forest. The advantage of usingthe Chinook is that it can carry more troops on asingle sortie.

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c. Demolition Techniques. Demolitions used inlanding zone clearing are C-4, TNT, detonating cord,and bangalore torpedoes. The C-4 and detonatingcord are used for felling trees and are the two itemsthat account for the bulk of the demolitions. WhenC-4 is not available, TNT is an acceptable, yet lessdesirable, substitute. Because external charges areused, the approximate weight of C-4 is only 70percent of the weight of TNT required to accomplishthe same task, so there is less to transport. Also, C-4is faster and easier to place than TNT and can bemolded around trees for more effective results.Charges are placed approximetely 4 to 5 feet abovethe ground where the tree has thinned down to thenominal diameter and not at the tapered root sectionor buttress. The remaining stumps are removed orcut down with chain saws or other techniques wheretheir presence will interfere with intended usage orexpansion of the LZ. In dense forest, up to 100 treesare prepared at one time and are detonatedsimultaneously using a detonating cord ring main.Nonelectric caps are preferred over electric caps toeliminate the potential hazard of radio signalsdetonating an electric cap prematurely. However, ifhelicopters are resupplying an LZ while it is stillbeing expanded and improved, the explosives createa precarious situation for the incoming helicopters.Even with good communications there are oftenproblems. For this reason electric caps may bepreferred because the exact instant of detonation canbe controlled using electric caps and a blastingmachine. The quantity of C-4 and detonating cordrequired for clearing a landing zone varies with thetype and density of vegetation and with the size ofthe area required. A “rule-of-thumb” which relatesthe number of pounds of C-4 to feet of detonatingcord has been developed. For dense vegetation(triple canopy, average tree diameter between 12 and36 inches), 1 foot of cord is required per pound ofexplosive; for light vegetation, 2 feet of cord perpound of explosive. Bangalore torpedoes are usedextensively to clear dense bamboo growth. Theshrapnel from the torpedo casing is extremely ef-fective in leveling bamboo with stalk diameters up to6 inches. The pattern used is to place bangaloretorpedoes in parallel lines spaced at 10-foot intervalsthroughout the area of bamboo.

d. Employment of Large Clearing Munitions. Oneeffective innovation for the crest ion of helicopterlanding zones (HLZ) has been the use of largeaerially delivered munitions to knock down trees andother vegetation and thereby create an initialopening suitable for creating a landing zone for useby helicopters. The technique of using a single largeconventional explosive charge for clearing HLZ in

dense forested areas has been found to be highlysatisfactory.

(1) Landing zones may be classified accordingto the ability of a given helicopter to utilize the site.Full touch zones (FTZ) permit a complete landing,skid touch zones (STZ) require that the helicoptersupport most of its weight by the rotor, and non-touch zones (NTZ) allow no more than a hover.Because of the uncertainty associated with the initialsize and postblowdown condition of the clearing, all“bombed” sites should be tentatively classified forplanning purposes as nontouch zones.

(2) An M121 (T56E4) concussion-type bomb of3.6 metric tons (10,000 lb) explosive charge was usedpreviously during tests. Another weapon of 6.6metric tons (15,000) is presently available and one of4.5 metric tons. (12, 195 lb) is under development.The M 12 l-type has been dropped from C-130 andCH-54 aircraft; a good view of the assembly may beseen in figure 4-2. A fuse extender mounted on thebomb nose is designed to detonate the munitionabout one meter above ground, thereby achievingmaximum vegetation blowdown while minimizingundesirable soil cratering. A stabilizing parachute,tail fuse, and metal shroud placed around the tip ofthe fuse extender are designed to insure that thebomb penetrates the vegetative canopy anddetonates as planned.

(3) Soil cratering effects appear to be nominal.At one test site the maximum depth and diameterwere approximately 64 centimeters and 14 meters,respectively; but beyond about 5 meters fromground zero (GZ) cratering was insignificant. Atanother test site cratering was also nonexistent orinsignificant. Consequently, soil cratering has beenassumed to be of no consequence to helicopteroperations when these large munitions are employed.

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New fusing procedures also help by initiatingdetonation from both ends of the explosive charge,thereby minimizing cratering effects whilemaximizing blowdown forces exerted outward.

(4) Tree blowdown is characterized by the upperportion of the tree generally being separated andcarried away from the lower portion by the shockwave. The break is seldom clean and wood splintersprotrude above and below the point where failurebegins. In the area within a 5 meter radius of groundzero tree failure occurs close to the roots. The stemsand crowns of the trees are destroyed and carried outof the area by the blast, giving the ground a cleanappearance. At greater distances, out to a radius ofabout 25 meters, lass vegetation is removed. Treefailure occurs at greater heights, producing tallerremnants. Also, debris (branches, leaves) ac-

cumulates on the ground between the remnamts,producing a littered appearance. Thus, stump heightincreases with increasing distance from ground zero.and the amount of debris littering the ground in-creases also. Experience with air-delivered clearingmunitions indicates that engineer troops must oftenenlarge and clean up this blowdown area to make itfully usable for helicopter operations.

(5) Figure 4-3 shows an aerial view of theclearing effects produced in a test which may helpthe reader visualize the effects of clearing munitionson forested areas. This test detonation producedalmost total removal of vegetation out to a distanceof 10 to 20 meters from GZ and significant damageup to distances of 40 to 60 meters. Table 4-1 presentssome of the limited results available from tests whichwere conducted.

4-4

(6) It is clear that several munitions might beemployed to create a larger HLZ capable of ac-commodating several aircraft or of improving theapproach and departure zones for one site. In suchcases, these devices should be detonated no morethan 24 meters apart. Accurate placement becomesessential and may not be attainable by drops similarto the past operational tests where CH-54 and C-130.aircraft flew at altitudes 1850 meters or higher abovethe terrain and at relatively high air speeds.

e. Chain Saws. Chain saws are used for cuttingdown standing timber up to 16 inches in diameter,but the major portion of their job in clearing alanding zone is to cut timber previously felled bydemolitions. Fallen timber is sawed into lengthswhich permit manual clearing of the area. Timbermay also be cut into lengths for later use in fieldfortifications, gun pads, or other facilities in the LZ.Chain saws are totally ineffective in cutting bamboo.The pulp clogs the chain assembly and it must bedisassembled and cleared after only one cut.Shrapnel from preparation fires causes chain sawmaintenance problems because hidden pieces of steelcause broken and dull chains.4-2. Fire Support Base Clearing

a. General. Often in the sequence of an airmobileoperation, a landing zone is developed into a firesupport base (FSB) by enlarging it to accept theunit’s mortars and eventually support artillery.

b. Layout and Planning. The siting of theheaviest artillery should be given first priority in thelayout of an FSB. It must be reasonably level andfree of stumps, and require a minimum of clearingin the principal direction of fire. The engineershould coordinate closely with the artillery com-mander because often a small shift in gun positionscan significantly increase or decrease the amount ofclearing required to eliminate the tree mask. Theengineer should be prepared to build and assist inbuilding overhead cover and bunkers for all per-sonnel, ammunition, and equipment on the firesupport base. The same equipment as used to cut anLZ should be taken as well as shaped and crateringcharges to blow holes for underground bunkers.

c. Airborne Equipment. Clearing an FSB in aheavily forested area at a site inaccessible by surface

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movement using manual techniques is difficult andslow. When available, lightweight sectionalizedairmobile crawler tractors equipped with landclearing or bulldozer blades should be deployed tothe FSB site by heavy-lift into two sections. Itrequires two sorties by a CH-54 to accomplish thelift. Another tractor that can be helilifted into thebase is the “mini-dozer” or 10,000-pound airmobile(MIL-T-52510/MD) tractor. It can be helilifted intothe base in one piece using one sortie. Thecapabilities of these small tractors should not beoverestimated, but they can speed up the con-struction of the FSB significantly. They can levelbamboo, cut small trees, move large fallen timber,and dig emplacements as well as do rough gradingand leveling of the FSB site. As can be seen in table3-9, the production rate of this light tractor with ashearing blade decreases rapidly in vegetation above12 inches in diameter, so explosives or chain sawsshould be used for the larger vegetation.4-3. Base Camp ClearingNormally, large base camps are developed alongmajor lines of communication (LOC) and are clearedduring the initial construction of the LOC or like areaclearing as described in chapter 2. The majorproblems encountered at these fixed installations arethe initial clearing and maintenance of fields of fire.Because long term clearing is required, the mostcomplete job possible must be done initially,especially in the belts where barbed wire, mines, ortrip flares are to be installed. Weeds and brushgrowing up through these obstacles are almostimpossible to clear without completely removing andreinstalling the obstacles. If these areas are disked orthoroughly cleared with a rolling chopper prior toinstalling the obstacle the problem will be reduced.Herbicides can also be used to retard regrowth.When totally clearing or disking slopes greater than10 percent, erosion control measures must be taken.Dust control and a reseeding program must beestablished in cleared areas near airfields andheliports. Complete clearing to bare soil should beavoided around these facilities. The maintenance offields of fire is best accomplished with a mower oncea good stand of grass has been established.

Section II. CONSTRUCTION CLEARING

4-4. Introduction disposing of all the material cleared. Grubbing is theLand clearing as a construction operation consists of uprooting and removing of roots and stumps.clearing a designated area of all trees, brush, other Stripping is the removal of the organic topsoil andvegetation, and rubbish; removing surface boulders sod. Clearing operations to facilitate constructionand other material embedded in the ground; and work normally include clearing and grubbing and

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may include stripping, whereas tactical landclearing, described in chapter 2, usually onlyrequires felling of the vegetation. Although the areacleared for construction is usually smaller than thatrequired for tactical purposes, the specifications aremuch more stringent so the amount of effort ex-pended per acre is considerably greater.4-5. RequirementsThe constructing agency or unit is responsible fordetermining the clearing requirements that are partof the construction mission. Often in tactical supportconstruction missions, tactical clearing adjacent tothe construction project will be accomplished inconjunction with the construct ion clearing. This isespecially true for tactical road construction where astrip 200 to 500 meters wide is cleared to tacticalclearing specifications while the center area wherethe road is to be built is cleared, grubbed, andstripped at the same time to facilitate construction.4-6. SpecificationsBecause of the effort required and the erosion and

duet control problems created by total clearing, onlythe minimum amount of clearing, consistent with thetactical and construction requirements, should beaccomplished. Removal of the sod cover, especiallyaround airfields, should be avoided wheneverpossible. Clearing, grubbing, and stripping arerequired in all cut or borrow pit areas, and in fillareas of less than 4 foot depth. In fill areas greaterthan 4 feet, normally just surface vegetation iscleared. If the specifications permit and deep fills areto be constructed, significant time and effort can besaved by shearing the vegetation in these fill areas atground level and grubbing only in the cut andtransition areas. Clear areas and approach zonesadjacent to runways and heliports normally do notrequire that subsurface vegetation be removed (ofteneven piling is unnecessary — see fig. 4-4). Rights-of-way for powerlines and pipelines also require onlysurface clearing.

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4-7. TechniquesThe basic patterns of movement and organization ofthe clearing area used for construction clearing arethe same as those described in chapter 2 for area orstrip clearing. Because the areas are small comparedto those in tactical clearing the bulldozer is often themost practical and available tool. It can be im-mediately used for earthwork without changing theblade. A motor grader or scraper can be used forclearing and stripping of light vegetation less than 2inches thick. It may also be used for stripping turffor sodding bare areas. When the stumps are to beremoved, the tree should be uprooted initially ratherthan cut so that the added leverage of the standingtree can assist in removing the roots. The bulldozer,spade plow, tilted Rome K/G blade, and knockdownbeam are the attachments most frequently used inconstruction clearing and grubbing. When clearingin a rainy climate, all holes in the soil formed byuprooting the trees should be filled immediately afterfelling the tree to prevent saturation of the sub-grade. Phased development of the drainage systemin the early stages of clearing, grubbing, andstripping is essential to insure uninterrupted con-struction. For disposal of cleared materials, wasteareas or burning methods are used, depending on thetype of construction, location, and amount of time.Generally, the material is pushed and skidded off the

construction site and into the surrounding timber tospeed disposal and to keep the area cleared forequipment operation. In all cases, the disposalshould be done as rapidly as possible by assigningspecific units of equipment to accomplish thisoperation concurrently with the clearing andgrubbing. The type of disposal method selectedshould be consistent with the methods ofcamouflage, salvage, and drainage used for theclearing operation. In forward combat areas wherethe saving of time is essential, the quickest and mostconvenient method of disposal of all materials is topile or dump the materials adjacent to the work area.A study of the construction plans will show where thedebris can be piled without interfering with drainageor possible work areas. In the construction of themain project, it may become necessary to clear aportion of adjacent land for use in disposing of thecleared material. This clearing for disposal of debrisshould be located as close to the main project aspossible to shorten the hauling distance. Timberuseful for logs, piles, and lumber is trimmed andstockpiled for future use in bridge, culvert, andother types of construction. This type of timber ispushed or skidded into a salvage area from which itcan be later removed to a sawmill with little dif-ficulty.

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APPENDIX A

REFERENCES

A-1. Army Regulations (AR)115-11

A-2. Field Manuals (FM)3-33-123-225-155-255-345-14220-2221-2621-41

30-10A-3. Technical Manuals (TM)

5-2205-330

5-331A

5-331B

5-331C

5-331E

5-3335-3425-4615-7255-3830-236-12

5-3830-237-12

30-24530-245A

30-246

Army Topography.

Tactical Employment of Herbicides.Operational Aspects of Radiological Defense.Fallout Prediction.Field Fortifications.Explosives and Demolitions.Engineer Field Data.Nondivisional Engineer Combat Units.Vehicle Recovery Operations.Map Reading.Soldiers Handbook for Defense Against Chemical and Biological

Operations and Nuclear Warfare.Military Geographic Intelligence (Terrain).

Passage of Obstacles Other than Minefields.Planning and Design of Roads, Airbases, and Heliports in the Theater of

Operations.Utilization of Engineer Construction Equipment-VOL A: Earthmoving,

Compaction, Grading and Ditching Equipment.Utilization of Engineer Construction Equipment-VOL B: Lifting, Land-

ing and Hauling Equipment.Utilization of Engineer Construction Equipment-VOL C: Rock Crushers,

Air Compressors and Pneumatic Tools.Utilization of Engineer Construction Equipment-VOL E: Engineer

Special Purpose and Expedient Equipment.Pits and Quarries.Logging and Sawmill Operation.Engineer Handtools.Rigging.Operator’s and Organizational Maintenance Manual Including Repair

Parts and Special Tool List: Treedozer, Tractor Mounting: ForMounting on Tractor, Caterpillar Model D7E or Allis-Chalmers ModelHD16: (Rome Plow Model KG7EM) FSN 3830-933-5458.

Operator and Organizational Maintenance Manual Including Repair Partsand Special Tools List For: Treedozer, Tractor Mounting, for Mountingon Tractor, Caterpillar Model D7E (Rome Plow Model, KG7ED) FSN3830-935-7981.

Image Interpretation Handbook, (NAVAIR 10-35-685; AFM 200-50).Image Interpretation Handbook, Vol. 2 (U) (NAVAIR 10-35-685; AFM

200-50).Tactical Interpretation of Air Photos (NAVAER 10-35-613).

A-4. Table of Organization and Equipment (TOE)5-87 Engineer Land Clearing Company.

A-5. Films (TF)5-4624 Large Scale Land Clearing Operations,

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APPENDIX B

OPERATOR AND EQUIPMENT PROTECTIVE DEVICES

B-1. Equipment ProtectionIn large vegetation, a land clearing tractor is con-stantly subject to being struck by falling trees.Hydraulic control mechanisms are vulnerable tosevere impact loads so the lift cylinder lines and tiltcylinder lines on bulldozer blades must be wellprotected (fig B-1 and B-3). In addition, heavyradiator grill guards are necessary to prevent treebranches or bamboo from puncturing the radiator.The heavy duty louvered radiator grill guard shownin figure B-1 provides protection for the standardgrill and radiator without impeding the airflow. Grillguards of perforated steel plate or cutout steel plateas shown in figure B-2 can be used as expedients, butthese devices severely impede the airflow throughthe radiator which may cause overheating. Because

the debris in the form of leaves, twigs, and brush isthrown into the air around the engine and radiator, ablower type fan is essential to keep the front of theradiator clear. Perforated engine side panels withhinged inspection and cleanout doors, shown infigure B-3, must be installed to prevent leaves andtwigs from collecting around the engine and on theback of the radiator core. An air breather extension,in the form of a remote air intake, pipes clean air tothe engine from inside the cab and will preventfalling leaves and debris from clogging the airbreather filter element, shown in figure B-4. Heavyduty crankcase guards or belly pans must also beinstalled on a land clearing tractor to preventdamage from stumps.

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B-2. Operator ProtectionWhen clearing all but the lightest vegetation, landclearing tractors and operators must be wellprotected. A heavy duty cab guard is essential. Theoriginal Army cab guard for use on land clearingtractors (fig B-5) proved to be inadequate for thesevere operating conditions found to exist in theheavy monsoon forests of Vietnam. An extra heavyduty jungle clearing cab (fig B-6) was developed foruse in these extreme conditions. The cab is con-structed with high strength fabricated arches and ismounted directly to the frame of the tractor. Itcontains a water tank built into the top of the cab,equipped with a water pump and a hose for use in

extinguishing bellypan fires and for emergencyradiator water supply. The cabs have deflector barsextending forward to the grill to protect the enginecompartment. Heavy screening is installed aroundthe cab to protect the operator from brush. In someareas it may also be necessary to install insectscreening on the inside of the cab to protect theoperator from the painful and harmful stings ofinsects, such as bees and hornets. Operators shouldbe equipped with seatbelts when operating in ex-tremely rough terrain. The extra heavy cab is strongenough to protect the operator if the tractor rollsover.

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APPENDIX C

RECOVERY OPERATIONS

C-1. GeneralLand clearing tractors because of the limitedvisibility due to underbrush and soft underfootconditions can frequently become high centered onstumps, logs, rocks, dry ridges, or mire. In thisposition, the tractor is helpless because both tracksare held clear of the ground and cannot get enoughtraction to move the tractor. Underground for-

tifications often cave in under the weight of thetractor, high centering it, (fig C-1). Sometimes thestinger can become so firmly stuck in a sound treethat raising and lowering the blade will not free itand the tractor has insufficient traction to backaway. All of these situations require some means ofrecovery utilizing either the tractor mounted winchor a recovery vehicle.

C-2. Recovery Procedures estimate of the situation, which can seldom be ac-a. Track Spinning. Once the tracks start to spin complished from the operator’s seat. Because of the

the operator should immediately stop and make an relatively low ground clearance of a tracked tractor

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and the ability of the trackstracks when the tractor iscenter the tractor in one ortracks. This will increase

to dig in, spinning thenot moving can hightwo revolutions of thethe recovery problem

considerably. By stopping to make an estimate ofthe situation, the operator can often extricate hisown tractor.

b. Winch. The best way to recover the tractor iswith its own winch. The winch is most effective whenthe pull is on the bare drum of the winch as shown infigure C-2, since the leverage is decreased as suc-cessive layers of cable are wound on the drum. Forthis reason it is desirable to unreel all or most of thecable from the winch when it is used to pull heavyloads. Another advantage is gained by using alonger cable, because its natural elasticity or stretchprevents it from breaking as readily under a suddenload. Ideally, the winch cable should be anchored insuch a manner that a line drawn through the cablewill continue through the centerline of the tractor. Ifthe cable is very far off this line, it will lead to oneside of the winch drum, pile up, and becomedamaged. The cable should not be used with morethan 20 deflection from the drum centerline. Whenno natural anchor is available another suitablevehicle or prepared holdfast must be used to securethe cable.

C. Expedient Recovery. If no other vehicle ornatural anchor for the winch cable is available, anexpedient method may be used. If the tractor is highcentered, a log can be attached to both tracks at oneend of the vehicle (fig C-3). If no log is available, achain or cable can be used. Secure the log, then applypower gradually to both tracks; the log will strikethe obstacle and move the vehicle. Care must betaken to remove the log when it reaches the rear orfront of the tracks.

d. Recovery Vehicle. When the tractor cannot freeitself, a recovery vehicle is required. In land clearingoperations it is preferable that a VTR or otherservice vehicle with crew be used for recovering thetractor, so that all the other clearing tractors cancontinue productive work. Perhaps the mostcommon error made in attempting to recover a miredtractor is underestimating the force required. Manycables and chains have been broken trying to jerk thetractor loose using the draw bar pull of anothertractor. A tracked tractor has almost twice thepounds pull with a single winch line than it has onthe drawbar. Also traction has much less effect onthe winch capability. A winch line can be riggedalmost as quickly as a chain and even if slight un-derestimate is made, the winch can still accomplishthe recovery. Besides single line pulling, additionalblocks can still accomplish the recovery. Besidessingle line pulling, additional blocks can be installedincreasing the mechanical advantage of the winch.Figures C-4, C-5, C-6, and C-7 show several ways torig a winch line for recovering mired vehicles. TM 5-725 and FM 20-22 show additional rigging andrecovery techniques. Winch lines must be attachedto the tractor only at those points designed towithstand the load. The drawbar and the pull hookare designed for this purpose. Lifting eyes aredesigned for vertical loads so should be used withcare for horizontal pull. Push arms, track frames,and tilt braces may look solid, but can be severelydamaged when heavy loads are applied.

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C-3

APPENDIX D

MAINTENANCE OF LAND CLEARING EQUIPMENT

D-1. GeneralLand clearing, as with any equipment operation, isdependent upon sound maintenance practices andprocedures to insure that the equipment is availableto accomplish the work. The maintenance postureand capability of a land clearing unit often determinethe success or failure of the mission. Commandemphasis at all levels is required to insure thatadequate time is provided for equipment main-tenance and that maintenance activities areorganized and supervised just as efficiently as theclearing operation itself. Land clearing provides themost abusive conditions under which a trackedtractor must operate, so without the most carefullyplanned and stringently enforced maintenanceprogram the deadline rate will soar. There are twoessentials to a successful maintenance programduring land clearing operations. First, maintenanceservices must be available in the cut (para 2-9 b). A300-amp welder and an air compressor each mountedin a 6-ton tracked cargo carrier should be stationedin the cut along with maintenance personnel. Thissaves time in returning the tractors to service duringthe day. Second, tractors should receive a periodicstanddown in the field for complete preventivemaintenance services. The recommended frequencyis every 10th day of operation. This means that acompany will leave three tractors in the night-defensive position each day for this servicing. Wherepossible, maintenance schedules can be adjusted sothat 10-day services are performed on temporarilydeadlined tractors. Special care must be taken whenselecting the maintenance area in the field so that itwill remain firm under continued tractor traffic. Incases of extremely muddy conditions, an AVLB hasbeen launched to use as a maintenance hardstand inthe NDP. Corduroy log areas have also been con-structed for use as hardstands, because it is im-possible to maintain a tractor which is mired almostto its belly pan in mud. In a tactical situation it isoften not possible to accomplish maintenance atnight in the NDP. Even when night maintenance ispossible, it is essential that a minimum of 2 hoursper day during daylight be devoted to maintenanceof the land clearing tractors and blades. Even moretime is required when night maintenance is notpossible. After approximately 45 days operation inthe field, each land clearing element requires aminimum of 15 days standdown for maintenance

which should be conducted at the unit’s home base.Special attention must be paid to the supply of repairparts for the equipment. Demand data from previousoperations is the best source of information todetermine the repair parts required to provide readyavailability of high usage repair parts. In addition toa valid prescribed load list (PLL) taken to the field,provisions must be made for aerial resupply of repairparts.D-2. Chain Saws and HandtoolsThe maintenance of chain saws and handtools isdescribed in detail in TM 5-461 and the toolroomkeeper should have a copy of this TM available.Special attention must be paid to safety procedureswhich are described in TM 5-461. A sharp tool usedproperly and safely is the most efficient tool. If chainsaws are to be used in a remote area, a chain sawmechanic should be designated and a basic load ofrepair parts must be taken to the area. In areaswhere artillery preparatory fires are used ex-tensively, a high rate of chain failure can be an-ticipated.D-3. Land Clearing TractorsThe most serious maintenance problem encounteredwith land clearing tractors is overheating. Becausethe tractor is almost constantly in motion and debrisis continually in the air around the engine com-partment, the cooling system is subjected toclogging and damage. The radiator grill guards andthe engine side guards will help solve some of theseproblems, but cleaning the cooling system is stillrequired. When operating under these extremeconditions, the coolant level must be checked often,the radiator should be flushed, and rust inhibitoradded to prevent loss of efficiency caused by scalingand rust. When small leaves and sticks are forcedagainst the radiator by the fan, they not only clogthe radiator, but they bend the fins, permanentlyrestricting the airflow. An air compressor is used toblow out the debris which is clogging the radiator.Air alone will sometimes not be enough, so a steamcleaner or air and water mixture should be usedfrequently to thoroughly remove dirt and smallparticles from the radiator, The belly pans oftenbecome full of debris and restrict airflow around thecrankcase, also contributing to the overheatingproblem. This debris should be cleaned out as oftenas possible or soaked with water to prevent fire. The

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remote air intake will reduce the air filter cleaningrequirements, but frequent cleaning and inspectionof the air filter is still required. Lubrication and otheroperator and organizational maintenance proceduresoutlined in the technical manual for the tractorshould be followed in detail.D-4. Land Clearing BladesThe clearing blades, like axes, are used for cuttingand must be sharpened or they will become so dullthat the tree will be uprooted and not easily shearedoff. The blade must be sharpened daily, whenclearing in normal conditions, and may requiresharpening more often in sandy, abrasive soils orwhen cutting roots below ground level. A pneumatic,electric, or gasoline portable grinder may be used to

sharpen the cutting edge, web, and stinger. Whensharpening the cutting edge and web, it is importantto maintain the proper shape. Too much angle on theedge limits the shearing action and too small anangle risks having the edge “roll over” or “curl” (figD-1). The keenness of the point of the stinger is notas important as the sharpness of the cutting edge.The primary concern when sharpening the stinger isthat the fillet between the point and the web must bemaintained to avoid the possibility of developingcrocks. TM 5-3830-236-12 and TM 5-3830-237-12,the operator’s and organizational maintenancemanuals for the treedozer, Rome K/G blade,describe additional maintenance procedures to befollowed when maintaining the blade.

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D-3

F M 5 - 1 6 4

APPENDIX E

CONVERSION TABLES

LengthMetric to English

1 millimeter (mm) =1 centimeter (cm) =1 meter (m) =l m =1 kilometer (km) =1 km =

0.04 inch (0.03937 inch) 10.3937 inch 13.281 feet 11.094 yards0.621 statute mile0.5396 nautical mile

English to Metric

yard = 91.44 centimetersfoot = 30.48 centimetersinch = 2.54 centimeters

Area

1 sq. centimeter (sq cm or cm2 ) = 0.155 sq inch 1 sq inch = 6.45 sq centimeters1 sq meter = 10.76 sq ft 1 sq foot = 0.0929 sq meter1 sq meter = 1.196 sq yards 1 sq yard = 0.836 sq meter1 hectare (ha) = 2.47 acres 1 acre = 0.405 hectare1 sq. kilometer = 0.386 sq miles 1 sq mile = 2.59 sq kilometers

Capacity or Volume

1 cubic centimeter (cc) = 0.27 fluid dram 1 cubic inch = 16.3872 cubic centimeters1 liter (1) = 1.06 liquid quarts 1 cubic foot = 0.0283 cubic meter

1 cubic yard = 0.7646 cubic meter1 fluid ounce = 29.5735 milliliters1 pint = 0.4732 liter1 quart = 0.9436 liter1 gallon = 3.7853

Mass or Weight

1 gram (g or gm) = 0.04 ounce (avdp) 1 ounce = 28.3495 grams1 kilogram (kg) = 2.20 pounds (avdp) 1 pound (avdp) = 0.4536 kilogram1 metric ton (Mt or t) = 10000 kilograms 1 hundredweight (cwt) = 45.3592 kilograms

= 2204.62 pounds (avdp)= 1.10 tons

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APPENDIX F

TERRAIN INTELLIGENCE CONSIDERATIONS

Section I. SOURCES OF INFORMATION

F-1. General Informationa. Maps. Maps are a basic source of terrain in-

formation. The classification of US maps by typeand scale is explained in AR 115-11. Special mapsand overlays may be prepared for a specific purpose,or to show only particular characteristics of theterrain. Currently, no maps are being specificallyproduced for land clearing operations; however,several of the following special maps are availableand contain data useful in planning a land clearingoperation.

(1) Agricultural (soil) maps are prepared toshow the potential of a soil for crop production.Engineering soil maps indicate the\qualities of soilfor construction and vehicle cross-country mobility.Agricultural maps have to be interpreted with careto convert them to engineering use.

(2) Geologic maps show the distribution ofvarious kinds of rock formations. Most geologicmaps ignore the soils on top of the rock and thus areof limited use in tactical land clearing, except inareas of shallow soil with many outcrops.

(3) Lines-of-communication maps include thosethat show railway systems, highway route in-formation, navigable waterways, and the routes andstops of airlines.

(4) Relief maps show differences in elevation bythe use of various tints and shading patterns. Theseare valuable in dramatizing areas of steep slopes andrugged topography.

(5) Pictomaps are maps on which thephotographic imagery of a standard photomosaichas been converted to interpretable colors andsymbols. Natural vegetation and cultural featuresare ideally portrayal on a pictomap. Because apictomap is normally more recent than the standardtopomap, it is a good source of more current in-formation.

(6) Other special maps show the distribution ofmajor vegetation, water supply sources anddistribution systems, cross-country movement, and

similar detailed information that can be presentedmost effectively in graphic form. These special mapsare the most useful in planning a land clearingoperation, although they are not always available inlarge scale or for the area of the operation.

b. Intelligence Reports. Several Department ofDefense intelligence agencies have preparedstrategic studies which provide detailed terraininformation concerning major geographic areas. Thestudies of particular interest to the units engaged inland clearing include–

(1) Terrain studies contain area intelligencedepicted on medium and small-scale maps withaccompanying text and graphic material.

(2) Lines of communication (LOC) are studies,prepared on either medium-scale maps or single,small-scale foldup sheets, which cent an an analysisof transportation facilities with information onrailroads, inland waterways, highways, airfields,pipelines, ports, and beaches.

(3) Special reports on military geography aredesigned primarily for strategic planning and aregenerally directed toward analysis of a major aspectof military geography such as cross-countrymovement, amphibious operations, and airborneoperations. With the major use of land clearing as atactical tool, these studies may also be conductedspecifically for tactical land clearing. However, thecross-country movement and soil trafficabilitystudies available include many of the factors whichcan be correlated with land clearing operations.

(4) Engineer reconnaissance reports summarizedata obtained by reconnaissance, and are a goodsource of terrain information. They are of particularvalue in providing current, detailed informationabout the lines of communicant ions and availability ofany natural construction materials.

(5) Other reports and documents. Table F-1 is asummary of Army reports which contain terraininformation, and are of value in planning a landclearing operation.

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c. Books and Periodicals. Valuable information ofuse in land clearing may be found in books andperiodicals. These include scientific and tradejournals, economic atlases, tourist guides, andsimilar publications. Unpublished records coveringmeteorological, hydrological, and similar scientificdata prepared by Government agencies, engineeringfirms, manufacturers of land clearing equipment,private societies, and individuals contribute valuableinformation. Another source is United Nationsinformation on agricultural development potential inforested areas. Extremely valuable data regardingforest vegetation, when desired, may be found inreports prepared by the agricultural, forestry, andconservation agencies of the local government.

d. Other Sources. Captured enemy documents,and interrogation of prisoners of war and refugees,will sometimes give additional up-to-date in-format ion valuable in land clearing planning. Enemymaps and terrain studies are especially valuable.Local government agencies, civilian constructioncontractors, and timber cultivation and harvesting

organizations may also be able to provide in-formation.F-2. Specific Area Information

a. Photographs and Remote-sensor Imagery.Aerial and ground photographs provide an accuratevisual record of the terrain and vegetation. Theyfurnish information that is not readily available orimmediately apparent by ground reconnaissance, orby visual observation from the air, especially ofenemy-held areas. Remote-sensor imagery includesinfrared photography and side-looking airborneradar. General information on aerial photographyusage is given in FM 21-26 and FM 30-10 anddetailed usage is given in TM 30-245, TM 30-245A,and TM 30-246. Properly interpreted, black andwhite, color, and infrared aerial and groundphotography and airborne radar will furnish detailedinformation on the following:

(1) Surface configuration. The physical land-forms of the earth’s surface can be determined. Thisincludes shape, slopes, forest cover, land-use pattern, and obstacle spacing and height.

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(2) Surface imposition. General classes of soil(e.g., coarse-grained versus fine-grained) and rockcan usually be distinguished.

(3) Hydrologic geometry. Both surface andsubsurface drainage characteristics can usually bederived from aerial photographs. Infrared colorphotography is especially useful in determiningdrainage conditions. Swamps and standing water arereadily apparent on color infrared aerialphotographs.

(4) Vegetation. Typical characteristics of thevegetative cover including general type, density,and uniformity can usually be determined. It isessential that at least some ground reconnaissanceinformation be available if reliable interpretations offorest characteristics are to be obtained, especially intropical regions.

(5) Roads and trails. Well traveled roads andtrails can usually be detected and delineated fromaerial imagery. However, lightly traveled trailsthrough closed-canopy forests are very difficult todelineate. Color aerial photography will sometimesreveal the presence of trails located beneath thecanopy of forests where other types of photographyfail.

(6) Suitability of terrain for land clearing,construction, and cross-country movement can bedetermined. Photography and photomaps can beused advantageously in studying areas to determinethe feasibility and difficulty of conducting landclearing operations, based on the evaluation of relief,slopes, drainage, soils, and vegetation.

(7) Limitations. The amount of information thatcan be derived from interpretation of photography islimited by adverse weather and dense closed-canopyvegetation on the terrain. It is important in all casesthat the information obtained from the aerialphotographs be correlated with information fromother sources, such as maps, intelligence reports,and personal reconnaissance.

b. Local Populace. In addition to the generalinformation available from local books, periodicals,and Government reports which were previouslydiscussed, much unpublished detailed information isavailable from inhabitants of the area. Arearesidents, and lumbering and land clearing con-tractors, can provide valuable information aboutprevious and current endeavors in lumbering,conservation, and agriculture in their area, whichcan assist the estimator in determining the requiredland clearing effort.

c. Reconnaissance. The most direct and accuratemethod of obtaining specific information about anarea to be cleared is to make a personal aerial and/orground reconnaissance. Aerial reconnaissance byfixed wing or preferably rotary wing aircraft willverify aerial photograph information on theuniformity of the vegetation and point out poten-tial troublesome areas. Through the aerial recon-naissance the areas can be selected for detailedground reconnaissance. A ground reconnaissance isthe best way to verify the photo-interpretationresults and it is also the only way specific in-formation on trafficability, soil conditions, andvegetation can be obtained. Thus, ground recon-naissance is almost essential to provide “groundtruth” (i.e., the detailed data on which to basephoto-interpretation). Before making a personalreconnaissance, all available intelligence sourcesshould be thoroughly researched for pertinent in-formation. At this time voids in area intelligence aswell as aspects to be checked should be noted. Thisreduces the amount of information that has to beobtained through ground reconnaissance, and limitsthe time required to be spent on the ground in theoften hostile area. The detailed information on theterrain and vegetation necessary to plan a landclearing operation is discussed in the followingsections of this chapter.

Section II. TERRAIN ANALYSIS

F-3. Weather and Climate of wind markedly reduce the drying rates of cutUsually all phases of land clearing from cutting toburning or removal of felled vegetation are concernedto some degree with temperature, humidity, wind,and the amount of rain that falls during a clearingoperation. Heavy or prolonged rainfall may result inpoor trafficability conditions. In climates ofseasonable rainfall, many areas are accessible onlyduring the dry season, and clearing plans should bemade to take advantage of the dry season to clearlow-lying areas. Rain, high humidities, and absence

vegetation; thus periods of dry weather, lowhumidities, and some wind are desireable forpreparing vegetation for burning. A small amount ofrain during clearing operations may cool the air andput an end to dust and enhance the efficiency of landclearing equipment and personnel.F-4. Topography

a. Slopes. Slope has a significant effect on mostequipment. Medium tractors can operate with littleor no loss in production on slopes up to 15 percent

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with good soil trafficability conditions. Themaximum slope on which a medium tractor cannormally operate is 25 percent, but this slope causesa loss in production of up to 50 percent. On slopessteeper than 25 percent or under poor trafficabilityconditions, the “yo-yo” technique is often the onlymethod possible. In the” yo-yo” method, one tractorgoes up and down a steep slope, while being partiallysupported by the winch cable of another tractor atthe top of the slope. This technique is very slow andshould be used only when other methods are notpossible. The production rate for the “yo-yo”technique is about 10 percent of that on level terrain.

b. Ditches and Streams. Whether wet or dry,streams or drainage ditches delay the land clearingequipment even if the bypasses can be madedatively easily. Selected consolidated crossingfords or causeways are essential for multiple tractoroperations. The time lost from the cutting operationis a minimum of 5 minutes per ditch or streamcrossing per tractor plus the time necessary toconstruct the crossing.

c. Water Table. Areas with a high water table,such as in swamps or along streams, present specialdifficulty in land clearing despite otherwise favorablesoil conditions. The water table can often beestimated by noting the water level in bomb andartillery shell craters (fig. F-1). Usually, however, ahole must be dug and observed over a period ofseveral minutes (or even hours), and the level towhich the water rises in it is noted. Infrared aerialphotographs, if available, are often useful, becausewater strongly absorbs infrared energy, andtherefore areas of wet soil (and water) show on suchimagery as dark patches.

F-5. Trafficabilitya. Soils. Soil characteristics affect land clearing

operations chiefly in two ways:(1) They control the ease with which trees may

be uprooted.

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(2) They affect soil trafficability (i.e., the ease ofmovement of men and machines). General traf-ficability conditions can be crudely estimated by askilled interpreter who is familiar with the area andwho has access to aerial photographs, soils in-formation, and weather data for the several daysimmediately preceding the time of the operation. Itis usually adequate to identify trafficability con-ditions in the following terms. Good trafficabilityexists when the vehicle can make almost limitlesspasses in the same track without significant loss ofspeed or pulling capacity. Soft conditions exist whenmore than two passes in the same track result insevere impairment of machine performance. Poorconditions exist when the first pass is precarious ordifficult. Impassable conditions exist when thevehicle would be immobilized on the first pass.

b. Rock and Stony Outcrops. If embedded rocks orstony outcropping are present in the area to be

cleared, equipment which shears the vegetation atground level may be severely damaged when theblade or other parts of the machine strike the rocks.In such situations, maintenance is usually costly andtime-consuming.

c. Duff. Duff (branches and logs lying on theground, and stumps) may constitute a significantobstacle to free movement of both men andmachines, thus making clearing much more difficult.In addition, the total volume of wood which must bemoved may be much greater than anticipated, sincethe duff can rarely be seen on aerial photographs.Significant amounts of duff are most common inareas of secondary growth where primary growthwas not disposed of properly. Large logs and stumpsmay remain relatively solid in the tropics for periodsof 2 to 5 years; in temperate and cold regions theperiod may be much longer (fig. F-2).

F-6. Manmade Features is important to insure that adequate access to thea. Road Net. One of the most important factors area is provided by a road or waterway capable of

which must be considered in planning a clearing sustaining the movement of the equipment which isoperation is the adequacy of the access to the area. It going to be used. However, clearing of distant areas

F-6

inaccessible by surface movement may be ac-complished with airmobile equipment and teams(chap 2).

b. Structures. Buildings, bunkers, and tunnelcomplexes are often found in the area to be cleared,especially in a hostile area. If these structures are tobe destroyed as a part of the clearing operation,consideration must be given as to what equipmentand technique should be used. In many cases theequipment used to clear the vegetation will not bethe best choice for use in destroying structures.

c. Airfields and Landing Zones. Due to the weightand bulk of most land clearing equipment, it is

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normally not airlifted to forward airfields or landingzones. Certain airmobile equipment is used inclearing, but normally these operations are limited inscope and are discussed in detail in chapter 4. Anairfield or landing zone is required for support air-craft and airlift of repair parts and supplies to theunit.

d. Obstacles. Intelligence on the presence offriendly or enemy minefield, boobytraps, explosiveduds, and other obstacles in areas to be cleared isespecially important. Consideration should be givento the use of obstacle reconnaissance and reductionteams to precede land clearing formations.

Section III. VEGETATION ANALYSIS

F-7. Types of Vegetative CoverThe type, density, and distribution of vegetation iscontrolled by climate, soil type, water supply, andthe activities of man. For the purpose of planninglend clearing operations, plants may be grouped intothree general types, on the basis of distinctivecharacteristics requiring separate considerationbecause of their effect on land clearing operations.These three types are: trees (woody plants more than3 meters in height); shrubs (woody plants 3 metersor less in height); and herbs and grasses (nonwoodyplants of all kinds). Grasses and herbs will not beconsidered in this manual.

a. Trees. Trees occur in a variety of patterns andassociations. Trees tend to occur in four generalpatterns or distributions: forests, in which the treesare irregularly placed and so close together that thecrowns touch or intermingle; woodlands, in whichthe trees are irregularly placed but the crowns onlyoccasionally touch; savannas, in which the trees areirregulary placed and so widely spaced that thecrowns rarely if ever touch); and orchards in whichthe trees are regularly spaced in rows or grids. Theterm forest is usually reserved for an extensive area;smaller areas may be termed woods, groves, orwoodlots. On military maps, any perennialvegetation high enough to conceal troops or thickenough to be a significant obstacle is classified as aforest, woods, or brushwood. Trees are usuallyclassified as needle leaf (such as pines, spruces, andlarches) or broadleaf (such as maples, oaks, or figs)and evergreen (i.e., they retain their leaves all year)or deciduous (i. e., they are leafless part of the year).These distinctions are not usually of significance toclearing operations.

b. Shrubs. Shrubs grow in patterns similar totrees. Shrub (or scrub) forests are ones in which theplants are irregularly arranged but so closely spacedthat the crowns touch or intermingle; shrub (or

scrub ) savannas are ones in which the plants areirregularly placed but spaced so far apart that thecrowns rarely touch; and shrub plantations are onesin which the plants are placed in rows or grids.Shrubs commonly comprise the undergrowth in treestands of all kinds, but in arid and semiarid regionsshrubs like cactus, sagebrush, mesquite, acacia, andeuphorbia may be the dominant vegetation.F-8. Types of Vegetation StructuresVegetation structures composed of trees and shrubshave been classified in a large number of ways, noneof which are usually suitable for purposes ofvegetation clearing. Accordingly, a specialclassification system, specifically adapted to theproblems of land clearing, is used as the basis for thediscussions which follow.

a. Swamp Forests. These forests grow insituations in which the soil is perennially saturated(or nearly SO), and in which there is usually standingwater for at least part of the year. Trafficabilityconditions are generally poor to impassable. Thetotal variation in height ranges from 10 to 50 meters,stem diameters range from 50 centimeters to 2meters or more, and the density varies from 10 to 225stems per hectare. Root systems tend to be relativelyshallow, but in many places the bases of the stemsare modified into plank buttresses (i.e., Pterocarpussp. ), greatly enlarged bases (e. g., baldcypress), ormultiple stems (e.g., Ficus sp. ). There is rarely asignificant understory or shrub layer. On air photos,these forests may usually be recognized by thedatively uniform sizes of the tree crowns, and bytheir topographic position; they occur only in placessubject to persistent flooding. A special variety ofswamp forest is the mangrove forest, specificallyconsisting of those species (of Rhizophora andAvicennia) which are characterized by stilt roots (figF-3 ). Stilting is widely variable, ranging from a fewcentimeters to 3 meters high. In extreme cases, the

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stilt roots form an almost impenetrable tangle. Sincethe wood is very tough and resistant, clearing suchforests is a major engineering task. On air photos,mangrove forests usually present a remarkableuniform appearance because the individual treecrowns can rarely be distinguished. They grow onlyin tropical and subtropical regions, and only alongcoastlines and in estuaries within the range of tidalinfluence.

b. Moist Forests. These forests exist where thesoil is perennially moist, and may sometimes beinundated and/or saturated for short periods.Trafficability may range from good to poor, with theusual conditions being good to soft. Moist forests areusually structurally complex, with trees of manydifferent sizes and species (although exceptions dooccur). Tropical moist forests are usually charac-terized in the same stand by stems of widely dif-ferent sizes, with the trees arranged in “layers” or“stories. ” The largest trees (i.e., the first story) maybe as much as 80 meters tall. The stem diametersrange from 1 to 3 meters, and the density may veryfrom less than one to 10 stems per hectare. The

intermediate or “canopy” trees range from 20 to 50meters tall, with trunks 30 centimeters to 1.5 metersin diameter, and the density ranges from 35 to 400stems per hectare.. Small second-story and third-story trees also are frequent, ranging in height from5 to 20 meters, and exhibiting stem diametersranging from 5 to 25 centimeters and densitiesranging from 15 to 900 stems per hectare. Shrublayers are usually sparse and discontinuous. Lianas(woody vines) vary from almost absent to very nu-merous; where they are numerous, they make it al-most impossible to fell a single canopy tree, since itscrown will be laced to its neighbors by many lianas.On air photos, tropical moist forests can usually berecognized by the presence of emergents; their verylarge crowns project in hemispherical masses abovethe general canopy level (fig F-4 and F-5). Tem-perate moist forests are also exceedingly variable.Many temperate moist forests are “species poor”(i.e., they are dominated by one to several species),in which cases the trees tend to be of roughly thesame height and stem diameter. Depending uponsite characteristics, species, and climate, the heightof such “species poor” stands may range from 10 toabout 40 meters (and in extreme cases, nearly 100meters), stem diameters normally vary from 15centimeters to 3 meters (and in extreme cases up toabout 8 meters), and densities may range from 10 to225 stems per hectare. In these stands, smallerunderstory trees are very widely spaced, and theshrub layer is very sparse. However, some temperatemoist forests are “species rich” (i.e., are charac-terized by many species), in which case they tend tostrongly resemble tropical moist forests, thoughthey are usually composed of somewhat shorter trees(10 to 40 meters high). On air photos, the “speciespoor” forest tends to appear as aggregations ofcrowns of approximately equivalent size and height;the “species rich” varieties exhibit greatervariability in crown size and crown height.

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c. Seasonally Dry Forests. These forests (whichare often called “monsoon forests“ in the tropics)grow in situations in which there is a pronouncedwater shortage during at least part of the year, eventhough the soil may be saturated during anotherseason (fig F-6). Trafficability conditions range fromgood during the dry season to poor or even im-passable during the wet season. Seasonally dryforests may also be “species poor” or “species rich”.The “species poor” types are generally characterizedat one site by relatively uniform sizes and spacings,with heights at different localities ranging from 8 to25 meters, stem diameters ranging between 10 and80 centimeters, and densities ranging from 10 to 225stems per hectare. Smaller understory trees arerelatively sparse, and are sometimes thorny. Shrubs

may be sparse or even absent. The “species rich”types are characterized at any one site by a widerange of heights and stem diameters. These foreststend to look irregular and unkempt; stem diametersmay range from 3 centimeters to 80 centimeters andheights from 5 to 25 meters. The densities of thelargest trees may range from 10 to 100 stems perhectare, intermediate tree sizes from four to 900 perhectare, and small trees from 16 to 3600 per hectare.Shrubs are common. On air photos, the “speciespoor” stands exhibit a relatively regular pattern ofcrowns of roughly similar size and height. The“species rich” types usually look very ragged andirregular, with a wide variety of crown sizes andmarked differences in crown height.

d. Woodlands. These tree stands grow in during the wet season. Woodlands usually consist ofsituations where the lack of moisture occurs over a only a few species, and thus exhibit remarkablerelatively long period of the year, even though the uniformity of size and spacings at any one site. Atsoil may be saturated for periods of several days different localities, stem diameters may range fromintermittently during the dry season. Trafficability 10 to 70 centimeters, heights from 7 to 25 meters,conditions are usually good for most of the year, but and densities may range from four to 36 stems permay become soft to impassable for moderate periods hectare. Smaller trees are uncommon, and shrubs areF-l0

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usually sparse to absent. On air photos, these standsare characterized by regularly shaped crowns spacedin such a way that the crowns commonly do nottouch, but in which the distance between crowns israrely more than one-half an average crowndiameter.

e. Tree Savannas. These tree stands grow insituations where the moisture shortage is long andvery severe, even though the soil may be saturatedfor brief periods during the short rainy season.Trafficability conditions are uniformly good duringthe long dry season, but may range from soft to

impassable for short periods during the rainy season.The trees tend to be quite uniform in size in any onelocality, though they may vary considerably amonglocalities. The total range in height extends from 3 to100 meters, stem diameters range from 8 to 50centimeters, and the density may range from 16stems per hectare to one stem per 3 or 4 hectares.Shrubs are sparse. Both trees and shrubs arecommonly thorny. On air photos, these stands maybe readily recognized by the wide spacing of the trees(fig F-7).

f. Shrub Forests. These vegetation stands usuallyoccur in regions in which the climates are similar tothose which produce tree savannas. The reasons forthe occurrences of shrub forests in some localitiesand savannas in others is not certainly known, butthere is some indication that shrub forests are morecommon on slopes (especially with sandy or stonysoils), whereas tree savannas are more common onflat surfaces with clay soils. Trafficability isuniformly good during the dry season, but mayrange from good to poor for short periods during thewet season. Shrub forests tend to be quite irregular,with significant variations of plant size and meanspacing occuring within a few tens of meters. Shrubheights range from 1.5 to 3 meters, stem diametersrange from 1 to 5 centimeters (many shrubs exhibitmultiple stems), and densities range from 300 to as

many as 14,000 plants per hectare. In most of thestands, many of the shrubs are thorny. The rootsystems are commonly deep and extensive. On airphotos, their stands can usually be recognized by theextreme irregularity of crown sizes and crownheights, and by their “patchiness” (i.e., markedchanges in texture within short distances).

g. Shrub Savannas. These stands usually occur inregions characterized by extreme aridity, with rainfalling only rarely and erratically. Trafficability isalmost uniformly good. Shrub heights range from 1to 3 meters, stem diameters range from 1 to 5centimeters (many shrubs exhibit multiple stems),and densities range from one to 400 plants perhectare. Root systems are usually widespread andvery deep. In some localities a large proportion of theplants are thorny. Shrub savannas are common on

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arid plains and mountains, with the densest con-centrations of plants along washes and othersituations where soil moisture tends to collect orpersist. On air photos, these stands may be readilyrecognized by the isolation and low stature of theindividual plants.

h. Tree Orchards and Plantations. These standsmay occur in almost any climatic area, but eachclimatic region is normally restricted to a relativelyfew species. Trafficability conditons may be ex-tremely variable, depending upon the climaticregion; in continuously wet climates, traffic abilitymay range from soft to poor or impassable; inclimates having dry seasons, trafficability is nor-mally good to soft during the dry season. The trees

in these stands are normally (but not invariably)arranged in rows or on a grid. In any one locality thetrees tend to be very similar in size, but there may bea good deal of variation among localities. Trees mayrange in height from 4 to 30 meters, stem diametersrange from 10 to 40 centimeters, and mean densityfrom 10 to 400 per hectare. These stands are usuallykept free of shrubs and lianas, but (especially in thetropics) poorly tended orchards or plantationsrapidly develop very dense stands (3,000 to 40,000stems per hectare) of small trees (stem diameters 1 to3 centimeters, heights 3 to 6 meters) or shrubs. Treeplantations and orchards can usually be readilyrecognized on aerial photographs by the row or gridarrangement of the tree crowns (fig F-8).

i. Shrub Orchards and Plantations. These stands planted more or less randomly among the shrubs.may occur in either temperate or tropic climates, but The shade trees vary in height from 5 to 20 meters,they are especially common in the tropics, where in stem diameter from 5 to 35 centimeters, and incoffee, cacao, and tea are grown. Trafficability may density from complete absence to as many as 36Cbe quite variable, depending upon the climatic area stems per hectare. The shrubs, which commonly are(h above). The shrubs in these stands are often characterized by multiple stems, range in heightarranged in rows or grids, but this practice is by no from 1 to 3 meters, in stem diameter from 1 to 15means as common as in tree plantations and or- centimeters, and the density may range from 350 tochards. In addition, shade trees are commonly 3,000 plants per hectare. These stands are readily

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identified on air photos if the shrubs are planted in aregular pattern but if the planting is irregular, and ifthe shade trees are numerous, the general ap-pearance is one of a very ragged and unkempt lowforest resembling shrub forest, as described in fabove.F-9. Objective Analysis of VegetationThe descriptions of the types of forests and othervegetation outlined in paragraphs F-7 and F-8 arethose commonly used in intelligence reports and arevaluable as far as they go. However, specificquantitative descriptions of the vegetation on thesite to be cleared are required.

a. Tree Count. All of these variables must bedetermined by “tree count.” Methods of treecounting vary (TM 5-342), depending upon theextent of the area to be cleared. In small areas a 100percent count is made, but in larger areas severalrepresentative samples are selected and counted andthe result is then applied to the whole area. Normallya “tree count” is made by measuring a straight lineat least 100 meters long or 363 feet long (fig F-9).The actual tree count is made by three men, onerecorder walking along the line and two counters,

one on each side of the line. Each counter measuresthe number and diameter of all the trees on his sideon the line to a lateral distance of 5 meters, metricsystem, or 15 feet, English system. As the countersprogress along the line, they call out to the recorderthe vegetation they encounter and he records it inthe following categories:

Less than 12 inches diameter (undergrowth)12 to 24 inches diameter24 to 36 inches diameter36 to 48 inches diameter48 to 72 inches diameterOver 72 inches diameter

As trees are counted, they are measured. Thediameter is found by measuring the trees at 4 ½ feet(1.22 meters) (A, fig F-10) above the ground. If abuttress (B, fig F-10) is present, it should be notedand the measurement is then made at the top of thebuttress (C, fig F-10) where the trunk begins to runstraight and true.The tree count should be made two, or preferablythree, times for each distinct type of vegetation inthe area. The number of trees of each size per unitarea may then be estimated from the averages ob-tained in the tree count sample.

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b. Wood Density and Undergrowth. The wooddensity (hard or softwood) and root system (tap orlateral roots), plus a description of any undergrowthor vines should be determined. The wood density ismore easily obtained by striking the tree with an axeor machete and recording the result. For the sake ofstandardization, undergrowth, vegetation under 12inches in diameter, can be described as —

Dense–unable to see a man standing 20 feet(6.1 meters) away.

Semidense-barely able to see a man standing20 feet (6.1 meters) away.

Sparse– able to clearly see a man standing 20feet (6.1 meters) away.Notations should also be made of the presence ofhigh climbing vines which bind the treetops togetherand which would complicate the felling operations.There are more detailed methods of analyzingvegetative cover than that described above whichcan be found in any good forestry textbook, butthese methods are normally more complex thanrequired for most land clearing estimates. The

greater the amount of care that is taken in selectingthe representative samples, the more accurate will bethe results of the analysis. Areas containing ex-tensive undergrowth adjacent to roads, rivers, andclearings should be avoided in sampling unless theyform a significant part of the area to be cleared.

c. Secondary Growth. The above techniqueapplies principally to virgin forests and to oldersecondary growth. In young secondary growth, lessthan 20 years, additional factors become significant.These include the amount of partly decayedvegetation on the forest floor, the number andsoundness of fallen trees, logs, and stumps, and thenumber of stems in the following diametercategories:

Less than 3 inches diameter3 to 6 inches diameter6 to 12 inches diameter

An actual count of these sizes may not be feasible inmany cases, but a percentage estimate of each size isrequired to make a complete analysis of thesecondary growth.

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Index 1

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Index 2

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Index 3