A pulling test is an investigation during which the reaction of the tree to a tensile load, introduced into the crown via a rope, is measured. The pulling test is the only method of tree assessment that allows conclusions to be drawn about both the fracture resistance of the stem and the stability of the roots. Unless one is prepared to wait for a suitable wind event, an assessment of the stability of a tree is only possible using the pulling test method.
The pulling test method is a closed evaluation procedure with a final safety assessment. The procedure consists of the following evaluation steps:
1. measurement of the tree reaction to a tensile load
2. extrapolation of the the reaction to a theoretical failure load
3. wind load estimation through the analysis of wind structure and tree shape
4. calculation of safety factors for stability and fracture safety