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Tree stumps

K.W. Wilson

K.W. WILSON wrote this article originally for the use of farmers and private forest owners in the UK. It was prepared, with the drawings, for the Department of the Environment by the Forestry Commission, UK, and issued as Arboricultural Leaflet No. 7 in 1982.

Figure 1. Trench digging sequence around tree with high stump being pulled in direction shown.

Figure 2. Tractor with front-mounted blade (left) tilts and partially uproots tree by applying pressure at high point on the trunk, and (right) completes severance and removal by applying lift and lateral pressure at root level.

Tree stumps may present a hazard to vehicles and pedestrians. On development sites and on farms, stumps may impede cultivation or development of the site. Removal of tree stumps will, therefore, assist the development of a site and reduce the nuisance of regrowth from stumps and growth of suckers from the roots. Blockage of drains and any effect on foundations may be alleviated by removal of tree stumps while a potential source of fungal infection (especially honey fungus - Armillaria mellea) will be destroyed.

This article describes the principal methods of stump destruction applicable to both town and country sites.

Root systems

The size and form of stumps vary with species and age of tree and are influenced by soil type. Broad-leaved species tend to develop deeper root systems than conifers because they appear to have greater ability to penetrate tenacious clayey soils. As a result, stumps of broad-leaved trees may be more difficult to extract than those of conifers. However, the latter may make large downward-spreading root systems on deep, sandy loams. The main barriers to downward rooting of all species are permanent wetness, soil compaction, stoniness and the presence of hard surfacing over the soil. Feeder roots exploit preferentially moist, fertile areas of a soil, particularly those containing organic matter. Uneven and asymmetrical root systems may develop where root spread has been restricted by wall or building foundations or has been facilitated into uncompacted or disturbed soils arising from site work. The presence of other woody plants nearby may also influence the root spread.

Preparation for removal

The commonly used terms "stump removal" and "root removal" are misleading because it is rarely possible to remove the whole underground portion of a tree. A larger proportion of roots may often be destroyed along with the stump if removal is begun while the tree trunk is still attached.

It is essential to locate below-ground services, especially gas, water and electricity. It is also important to ensure that large lateral roots have not penetrated soil in the vicinity of foundations. Where stumps are located on boundaries, ownership must be ascertained and a way-leave negotiated where access to the adjoining area is necessary. Where removal operations will affect the normal use of highways and footpaths, the local highway authority and police should be informed so that adequate provision for and supervision of the public's safety are assured.

Once a stump has been extracted from the soil, the mass of woody material needs to be destroyed. Generally, stumps and root wood burn less well than trunks and branches, but if sufficient heat can be produced by burning branches and other debris, stumps may be burned. Alternatively, the stump may have to be carted from the site and dumped. Some local authorities will accept this type of material at their dumps while others are loath to do so. Before commencing work, therefore, the methods of disposal must be decided if the stump is not to remain for many years as an eyesore or obstacle and source of fungal infection for other plants.

The cost of the techniques described in this article varies with location, hazards, quantity of work involved and condition of the stumps. Careful consideration must be given, therefore, to all aspects of the operation, including a detailed written specification if contractors, who should be fully insured, are to be employed.

Figure 3. Methods of attaching cable or chain to tree. (A) Cable stranglehold, incorrect, leads to permanent Linking and damage to cable strands; (B) Too close fitting, incorrect, of chain places excessive strain on shackles (C) Correct- cable or chain wrapped twice around stem and linked to shackle at angle of less than 60°.

Figure 4. Notching of low stump to secure chain. Chain and hood, stranglehold for direct pull (left). Attachment for tipping action (right).

Methods of removal

Digging. Digging out small stumps by hand is often laborious and larger stumps usually require a machine of some kind. In either case the working method should be the same.

When a length of stem has been retained above ground level, it is often unnecessary to dig completely around the stump. Digging should follow the sequence shown in Figure 1. The trenches 1-3 should be cut in numerical order and any roots encountered should be severed. If pressure applied at the top of the stem fails to dislodge the stump, the fourth trench should be excavated.

If the tree has been felled at ground level it will be necessary to excavate all round the stump before lifting it out of the ground.

It may not be necessary to remove all of the stump and, in this case, after partial excavation by hand the stump height can be reduced by sawing. However, the bar and chain of a chainsaw may be easily damaged by contact with the soil and stones. Where the gradient of the ground around the tree is too great for a machine, hand digging may be relatively easy because of the smaller volume of soil to be removed.

Many machines are suitable for digging out stumps but perhaps the most commonly used are the tracked tractor with "4-in-one" bucket, JCB and Hy-Mac types. Stumps may be removed with a powered fore-end loader mounted on an agricultural tractor. However, most of these machines are more appropriate to farms, forests or large building sites where there are large numbers of stumps and plenty of room to manoeuvre. Heavy plant often uproots stumps quickly and efficiently, but is expensive to transport to the site, and the hourly hire charge is high. Machines should be used only where there is an adequate programme of work to justify the cost of transportation, or where the equipment is already on site for some other purpose. When a front-mounted blade or bucket is available, the blade or bucket should be raised and placed against any remaining length of stem (see Fig. 2). As pressure is applied to the stump, the operator raises the blade or bucket further, imparting a lifting action to the tree. This also increases the downward pressure of the vehicle on the ground, thereby increasing the grip. When the stem is permanently tilted and the roots in the front slightly out of the ground, the operator may back the tractor, insert the blade or bucket under the roots and then push/lift with the blade/bucket overturning the tree.

Stump removal by digging involves considerable soil movement and disposal of the stump may be a problem. However, the larger machines are usually able to manoeuvre even heavy and bulky stumps around the site.

Lifting and jacking. Before a stump can be levered or jacked out of the ground, the soil must be excavated from around the main root buttresses. Small stumps may then be prized out with a crowbar. For larger stumps, manually operated hydraulic jacks may be justified. These jacks should be placed on a firm, solid base and each buttress should be eased in rotation applying chocks and wedges to prevent the stump settling back into the ground and possibly trapping the operator. Use of either a crowbar or a hydraulic jack is a dangerous operation because the partially loosened stump may turn or topple as pressure is applied to another buttress.

Figure 5. Correct (left), incorrect (right) attachment of chain to a shackle.

Hydraulically operated attachments are available which can be fitted to the three-point linkage of standard wheeled tractors. These devices depend upon the lift the tractor hydraulics can apply against stabilizing pads placed on the ground. Stumps to be extracted must retain at least 45 cm of stem for the hydraulically operated jaws to grip. Once the stump has been extracted, the machine and tractor can move the stump around the site for disposal. The maximum size of stumps these machines can handle is dictated by the width of the hydraulic jaws (40 cm in currently available machines). These machines are ideally suited for clearing orchards and plantations where experience has shown them to have ample lifting power.

Figure 6. Ground anchors. Picket type (above). Screw type (below).

Winching. A method frequently used for extracting tree stumps is to pull them by means of a line secured around the trunk and attached to a winch or drawbar of a tractor. It is extremely difficult to estimate the force required to winch stumps out of the ground. Caution must be exercised when selecting equipment for winching to ensure that each item in the system is capable of withstanding a safe working load in excess of the anticipated load to be applied to the stump. In addition, each item of equipment, such as wire ropes, shackles, chain and wire-rope slings, pulley blocks and ground anchors, must be strong enough to withstand the force the pulling device is designed to apply. The equipment should be stamped or labelled with its safe working load, and be covered by test certificates issued at the time of purchase. It should be maintained in good condition and be regularly inspected by a qualified mechanical engineer to ensure that it still conforms to the safe working load stamped on each item.

Figure 7. Two layers of colliery belting protect anchor tree from damage by sling (above). Sling attachment below root buttress (below).

Most wear and tear normally occurs at the point of attachment of the pull-line to the stump. A choker system using either a chain or a cable sling should be employed. Under no circumstances should a winch cable be used as a strangle around the stump (see Fig. 3A) because this will cause permanent kinking of the cable, thus seriously reducing its safe working load. A chain is preferable as a choker because it is more resistant to abuse, gives better grip on a stump, is safer to handle and easier to transport. However, chain is much heavier than cable for the same strength and in the larger sizes a chain is too weighty to be practical. The chain or cable sling should be sufficiently long to allow for correct attachment to the pull-line. Unnecessary extra loading will be placed on a chain or sling which fits closely round the stem (see Fig. 3B). A longer chain or sling passing round the stump twice may provide adequate grip without causing overloading (see Fig. 3C). Several methods of attachment are possible but each has the limitation that the chain or cable may slip off a stump as extraction proceeds. This risk may be reduced by cutting around the stump a groove with an axe or chain-saw into which the chain or sling will fit (see Fig. 4). Alternatively, the chain or sling may be attached around the major roots on the opposite side of the stump to the direction of pull (see Fig. 10) The chain or sling should be attached to the pull-line with a screw shackle which should be closed with the correct pin. In order to avoid the shackle jamming after it has been loaded, the load should be applied as shown in Figure 5 and the pin should not be secured home completely-a half-turn anti clockwise after screwing home the pin is normally sufficient to prevent the pin from jamming.

Winches may need an anchor attachment. Ground anchors of the picket type or the screw type should be used (see Fig. 6). They need to be very large or used in multiples to withstand the pull of 5 tons or more which can be exerted by a tree winch.

The picket type of anchor is a long, flat, metal plate with two rows of holes through which pickets are driven, usually at various angles to the upright. The plate has an eye or chain link at both ends and the winch is shackled to one of these. The other eye can be used to attach additional picket plates. Picket anchors can be set up fairly quickly except on stony, compact dry soils and shallow soils over rock.

Figure 8. Use of anchor trees and pulley systems to (A) double (B) treble (C) quadruple the winch pull on the load tree. Arrangement at (D) alters pulling direction to loosen tree without changing winch position.

Screw anchors may be hard work to install, particularly on stony compacted soils. They must be screwed into the ground with a minimum of disturbance to the soil if they are to grip properly. The anchors need to be screwed in flush with the ground at an angle in line with the pull.

Alternatively, if anchorage cannot be achieved, a tree may form a suitable anchor point provided it is sufficiently robust to withstand the expected pull required for removing the stump. Unless expendable, anchor trees must be protected from damage by slings with at least two layers of colliery belting or, as a last resort, billets of timber. Additional strength may be achieved by placing the anchor sling below a root although this will inevitably damage the root bark (see Fig. 7).

When greater pulling force is needed, a system of pulleys can be adopted. Pulley blocks must be of the correct size and strength for use with the winch cable, i.e. the groove and diameter of the pulley wheel must be matched to the cable size. For safety in use, pulley blocks should be fitted with eyes rather than hooks which may become detached accidentally.

Figure 9. Use of snatch-block to shorten a cable or to join cables.

Vehicle-mounted winches must be anchored to prevent the vehicle sliding over the ground. The types of anchor mentioned above may be appropriate or the winch may be fitted with spades which are forced into the ground as the pull of the winch increases. Various combinations of pulley blocks and ground anchors increase the force applied to the stump by using double, triple or quadruple purchase (Figs. 8A-C). As these compound pulley systems increase the force on the stump, they multiply the loading on the equipment in use. The slings, shackles and pulley blocks must be strong enough to withstand the extra loading.

It is sometimes desirable to use anchored pulley blocks to vary the direction of pull so that stumps may be gradually loosened by pulling alternately in different directions. One can then move the rope from pulley block to pulley block without needing to move the winch (see Fig. 8D).

When there is a need either for a temporary attachment to a cable or to shorten a cable, snatch-blocks may be used (see Fig. 9). Additional lift may be gained by using a notched pole or "stumping trestle" (see Fig. 10).

Before pulling starts it is advantageous to trench around all or part of the stump so that the major roots can be cut and the stump overturned. The amount of digging required will depend upon the species of tree, the size of stump and the nature of the soil in which the tree was growing. Shallow spreading root systems may require little digging (see Fig. 10 - above), but cutting lateral roots should reduce the risk of damage to the adjoining land by the tearing out of roots. Even after digging all round a stump there may be deep roots preventing the stump from being extracted. It may be necessary to dig a hole into which the stump can be pulled (see Fig. 10 - below).

Wheeled tractors lack the necessary stability, weight, power and wheel grip to pull out stumps or to pull over large trees. The use of wheel weights, wide wheel setting, double wheels and cage wheels alone rarely provides sufficient grip and stability to pull stumps. Running wheeled tractors forward in a series of jerks in an attempt to loosen trees or stumps is dangerous to the operator and damaging to the tractor. Therefore the larger sizes of tracked tractors should be used whenever possible.

Figure 10. Use of notched pole (above) or stumping trestle (below) to impart lift to pulling action.

It is also important to understand that the cable and anchor employed with a tractor-mounted winch will tend to take a straight line between the work and anchor. In making a high pull, the tightening cable may lift the tractor and turn it over sideways, as shown in Figure 11A. In Figure 11B the downward pull may burst the tyres, unless the axle housing is supported with chocks (see Fig. 11).

Another problem with mechanically driven tractor-mounted winches arises from the lack of a reverse gear. If the operator misjudges the load or position of the vehicle, it may be very difficult and dangerous to release the tension in the pull or anchor lines so that the winch may be repositioned.

When pulling has lifted the stump and parts of the root plate, the operator must remember that continued pull may overturn the stump. As the stump may fall or roll into any position, the area around the stump is potentially very dangerous.

Pulling whole trees. It has already been mentioned that an early decision to grub the roots of a tree may permit the use of the tree's height. Provided there is adequate space and the tree is not rotted, cracked or split, the greater leverage obtained with a winch rope attached to a point high up the stem may remove many of the roots. If space is limited or the crown is unbalanced, so that the tree has a tendency to fall in the wrong direction, preparatory pruning may be needed.

Similarly, trenching around the base of the tree reduces the resistance of the stump to pulling. When using a high attachment point, the pulling angle should not exceed 30°. If space is restricted or a greater angle of pull is required, the use of a pulley block may permit a change of direction (see Fig. 12).

In all situations, placing a log against the base of the tree to be pulled should assist in the extraction of a maximum amount of roots and aid removal of the soil.

Stump chipping. Stump chipping is particularly suitable for individual stumps in gardens and, generally, in urban areas. It will not result in complete removal of all the roots but the longer part will be lost and so the possibility of fungal infection reduced. Manual chipping would be very strenuous, dangerous and is generally impracticable. Several machines capable of chipping tree stumps have been developed and they vary from trailed, self-powered machines to tractor-mounted Pro-driven machines. The main component is a heavy-duty rotating steel disc with toughened teeth attached. As the rotating disc is passed across the stump, the teeth chip away the wood and the level of the cutters may be progressively lowered to a maximum depth of 60 cm. The stump is reduced in this way to a pile of chips which can then be barrowed from the site. Backfilling with imported soil will be needed to reinstate the site.

The use of a stump chipper is frequently restricted by the width of access to the tree stump. The smallest machine requires a minimum 2-m-wide access. Owners of these machines are rarely prepared to operate on stumps in stony ground near buildings or cars. Underground services may be less of a problem with stump chipping than with other methods of extraction.

Explosives. Explosives are very useful for removing tree stumps in rural areas well away from buildings, roads and services.

Explosives work particularly well in heavy-textured, moist soils where removal of large stumps by machine could result in massive soil disturbance. For woodland clearance it may be desirable to use explosives to uproot and shatter large stumps. A tracked tractor mounted with a toothed rake could uproot the scrub and heap the combined debris for burning. The aim with explosives is to lift the stump out of the ground by placing charges underneath the stump and under the major lateral roots. A charge may also be inserted in a hole drilled into the centre of a large stump and this is fired simultaneously with the main charge to shatter the stump. The amount of explosive used and its location will depend on the diameter and condition of the stump, the rooting habit of the species involved and soil type.

Figure 11. Dangerous tractor winching positions. (A) With stump above anchor tree, tractor loses traction and may overturn. (B) Winching from a higher level, rear tyres are under high pressure. To prevent damage, chock axles (C).

Stringent regulations control the purchase, storage and use of explosives and specialist contractors should be employed for stump removal by explosives. Services in the vicinity of the stump to be removed may restrict the use of explosives although there are reports of the successful use of explosives 5 m from drains without any damage resulting. Careful site protection and checks to ensure all charges have exploded are essential.

Chemical treatment. Dead stumps are easier to remove than live ones because the decomposition of the finer roots and the weakening of larger ones decrease the amount of soil held by the root system. Softwoods in well drained soils may show weakening within a few months, while rot-resistant stumps in very wet ground may remain firmly held for many years. Dead stumps contain lighter wood and hold less soil than live ones. Killing tree stumps may, therefore, be advantageous if time permits before extraction is needed.

Several chemicals are available to kill tree stumps. These include sodium chlorate, sodium nitrate, ammonium sulphamate, and 2,4,5-T; the latter is often combined with 2,4-D and marketed under the name "Brush killer".

The first three chemicals may be applied as thick water-based pastes into a frill girdle cut in the bark all round the stump or inserted into holes drilled into the stump and subsequently covered to prevent dilution of the chemical. A plastic container should be used since these inorganic salts corrode metal. A mixture of 2,4,5-T/2,4-D in a solvent of paraffin or diesel may be sprayed over coppice regrowth and also applied to the bark of stumps up to 15 cm in diameter. Larger stumps should be frill-girdled to ensure adequate contact of the chemical with the stump or alternatively more than one application may be required. The greatest care should be taken with the storage and use of chemicals and the operators should also be properly protected.

There are several proprietary chemical products which manufacturers claim "will remove stumps effortlessly" by burning or rotting. Advertisements usually omit to state how long this process will be; it may take up to 10 or 15 years depending upon the species of tree and presence or absence of decay. Two systems are offered, both requiring deep holes to be drilled in the stumps, which is arduous and time-consuming work. These systems provide compounds to "aid burning" or compounds to "aid rotting".

The instructions usually state: "The substance should be applied in solution to the cut stump in holes bored for the purpose. The stump should be left for a period of six weeks to absorb the substance. It should then be fired with the aid of paraffin whereupon it will burn out to the tips of the roots."

Figure 12. Where space is restricted a pulley block on a convenient tree is helpful. A log can act as a fulcrum to aid removal of roots.

Analysis of some of the substances failed to reveal chemicals associated with improved burning. Other compounds contained sodium and/or potassium nitrate which are oxidizing agents. If applied to the stump immediately after the tree is felled these chemicals will be absorbed into the stump and could assist burning when the wood has dried. Experience has shown that unless well rotted, stumps rarely burn even after very prolonged heating of the stump by means of a paraffin flame gun. This is particularly true of large broad-leaf stumps of species such as elm and oak which contain heart wood. Burning is not recommended for stumps in soils with a high organic matter content because the fire could smoulder and spread through the ground, damaging other plants and property.

The stump and roots of trees, especially broad-leaved species, rot away very slowly because the process is dependent upon bacterial or fungal agents. Analysis of "stump rotting" substances revealed only chemicals capable of killing the stumps which could render the stump a more easily colonized medium. However, before decay could begin, the dead stump would have to become colonized by fungi or bacteria capable of decaying timber. Even then, large stumps may remain sound for up to 20 years.

Some people have suggested that poisoned stumps may be more readily colonized by fungi than untreated stumps. However, as one of the most common fungi invading poisoned stumps appears to be honey fungus (Armillaria mellea) which could subsequently spread to other woody plants, poisoning of stumps could place other plants at risk of infection.

At the present time stump removal is undertaken for aesthetic considerations or to facilitate the use of a site. A decision about the most appropriate method of removal must be made during the planning for felling trees and site clearance. But it must be remembered that killing stumps with chemicals can be a successful alternative to mechanical removal. However, the wood will persist for a number of years until it has been rotted away by decay organisms.

In the future, technology may develop to such an extent that stump extraction will be an initial step to utilization of wood hitherto left in the ground. Even when such stump harvesting becomes feasible, the operation is likely to be restricted to woodland situations.

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