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.
Decisions, Decisions
What is Best?
Ecological Values
Soil Subsidence
Future Site Use
Conclusions
