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.
Pounds of Force
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.
Root Branching Points
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.