Pulling

Equipment with cables, winches, and pulley systems can be used to drag the stump out of the ground. Both vibratory and steady pull systems are available. Deeply soaking the soil with water hours before can greatly reduce extraction power requirements. A cable, chain, or grapple is affixed to the stump and a winch is used to pull the stump. Either straight horizontal pulling, or using a lifting stand or tripod to elevate the chain or cable (adding a vertical component to pulling) can be used, although the power requirements are similar.

Usually a soil saw, trencher, or other means of excavation or root severing are used to reduce the force needed for extraction. Great forces can be generated in stump pulling and it is critical all load bearing components of any set of cables, chains, pulleys, anchor lines, or connectors be designed for the forces generated plus a safety factor. Figure 1 was developed from reanalyzing a number of studies dealing with the pounds of force needed to extract stumps of a given diameter. Figure 1 provides a rough estimate of forces and their variation caused by different stump and soil conditions. Because of the power requirements involved, most pulling systems require large equipment and a large setup area. Customized smaller pulling systems can be designed for unique situations.

For effective pulling of stumps, the mechanics of how a stump is locked into the soil should be reviewed. Trees can have many small diameter roots or a few large diameter roots -- highly branched woody roots or long unbranched roots -- large angles between roots or roots closely packed together. Rooting systems are highly variable in life, and so stumps structure is highly variable in death. The most critical feature of a stump being pulled (to minimize force exerted) are the large diameter roots on the same side as the pulling action – toward the winch cable.

The more roots branch on the pulling side of the stump, the less stiff the stump / soil system and the nearer to the stump will be the extraction fulcrum. Root branching points close to the stump will be the location of bending and breaking failures. Root branch points are places where large changes (abrupt reductions) in root stiffness occur. A stump with a few large diameter, unbranched roots on the pulling side will be very stiff and hard to pull. Stiffness and pulling force required will fall dramatically as the angle between neighboring large roots on the pulling side reach and exceed 60o of horizontal separation.



Figure 1: Rough estimate of pounds of force, and force variability, required to extract a stump of a given diameter. Note every stump has different soil-root mechanical interactions, different levels of damage and decay, and different site constraints. These differences lead to great variability in extraction force. This figure was generated by reanalyzing a number of studies in order to provide a basic level of information regarding extraction forces. This figure was derived from information presented in Biller & Baumgras (1987) and Golob et.al. (1976).

Along with the stiffness of the roots, decreasing the holding interface between soil and root surface is critical for pulling. Saturating the soil with water before pulling will decrease soil strength and root holding capacity by as much as four times (4X). Under saturated soil conditions, roots are more likely to slip rather than break. Use a trencher or soil saw to loosen the stump by severing roots, reducing root length, and reducing root holding capacity. For extracting the main stump mass only, roots should be severed close (no more than stump diameter) from the stump on the pull side. Roots on the opposite side of the pulling force can be severed between two and four times (2-4X) stump diameter measured from the stump center. In essence, you are trying to roll the stump up and out of the ground while minimizing force expended.

Stump Removal Methods (see full text)
Author: Dr. Kim D. Coder - Copyright June 2003
Published by: Warnell School, School of Forest Resources University of Georgia.
Used with Permission.
Reproduction in any form and/or redistribution by any means is a violation of copyright laws.

Decisions, Decisions
Stumps can be eliminated from the landscape in a number of ways. A major decision point is whether to completely extract and remove the stump, or leave some portion or all of the stump in-place in the soil. One low impact alternative includes cutting the stump low and level so a mower or other vehicle can drive over. Another low impact alternative is leaving a high stump for use as a weathered planter, temporary seat or table.
If a stump will be removed from a landscape, the next decision point is whether to extract the stump whole or in large pieces, or to break the stump apart into small pieces where it sits. In-place stump removal usually does not pose an equipment intensive demand on landowners, nor risk extensive landscape disruption as extraction. Stump extraction usually requires plenty of space because of the power requirement of the equipment used and the physical size of the stump to be transported off-site.

What is Best?
Stump removal processes can be generically described as: dig, push up or yank stump out of the ground; break the stump up into various sized pieces; burn what wood you can; accelerate the chemical (~25% faster) or ecological (~50% faster) degradation and decay process; or, do nothing.

Ecological Values
Stumps are a food source and a habitat which is difficult to find in many community landscapes. The creatures which inhabit and use the decaying stump change as the stump changes. Energy concentration in a decaying stump represents a rare and essential resource to a number of animals and micro / meso-organisms. If a stump can be simply left in-place and not disturbed, interesting things can happen, especially when the stump is surrounded by a healthy soil. The pieces and chips of a stump can also be used to enrich the site and provide unique, wood centered habitats.

Soil Subsidence
However a stump is removed from a site, the space it occupied will be left behind -- the stump hole excavation (calera) and root channels of various sizes and lengths. As soil subsides, new mineral soil will need to be applied to the site. Small layers of soil can be applied and then washed into the soil openings or depressions. Be careful to not use water or tamping to compact new soil into old positions. Because the stump and roots will take many years to finally decay away, many years of vigilance will be needed to fill-in areas. Stump and root decay near structures or pavements may require soil stabilization to prevent damage. If roots or stumps were pushing damaging structures when alive, wood decay will lead to additional damage. After you have declared victory on a stump and walked away, periodic visits to minimize liability risks and repair unexpected problems will still be required.

Future Site Use
The site which remains after stump removal will be dominated by decay processes for a number of years. Once the decay process is functioning well, a new tree can be planted near the site. Planting should be completed outside the area impacted byb the removal treatment. The cause of death, or need for removal of the original tree, needs to be considered in both species and site selection for a new tree. The same resource limitations (including pest problems) can impact the new tree as they constrained the old tree, unless changes are made. Planting back into the identical location as the original tree is possible if the old stump is broken and shattered enough to allow the new tree to colonize the native soil. New soil can be used for fill in the stump excavation or caldera, but multiple openings or connections to the surrounding native soil through the old stump site are essential. Usually several years are allowed to pass, with rapid decay progression, before a new tree is planted in the same location. Do not plant in only the wood chips from a stump pushed back into the caldera, as resource fluctuations can be severe for a new tree, as will access to the new roots by pests.

Conclusions
There are many ways to deal with stumps in a landscape. The techniques involved are centered around soil weakening or loosening, excavation, extraction, and/or reduction. Reducing the stump through grinding or chipping is the most prevalent technique used in a well managed, modern landscape operation. Other means of mechanical or natural reduction can be used. For most landscape systems and objectives, quickly recycling the resources and space occupied by a dead stump is critical.

Stump Removal Methods (see full text)
Author: Dr. Kim D. Coder - Copyright June 2003
Published by: Warnell School, School of Forest Resources University of Georgia.
Used with Permission.
Reproduction in any form and/or redistribution by any means is a violation of copyright laws.