Tree stability testing

Trees, as they age, naturally develop defects. Often these are of little significance in terms of tree safety. However, some defects, particularly those associated with the main trunk and structural roots, have the potential to cause a whole tree to fail. Although infrequent in the urban environment, it is the failure of a whole tree that has the potential to cause greatest damage and harm to people and property.

Until relatively recently, assessing the likelihood of whole tree failure has been largely restricted to establishing the extent of hollowing within the trunk, and methods for evaluating the stability of the root plate have been crude. Although the hollowing of a tree can lead to its structural failure, it is becoming more widely accepted that hollowness, in particular the thickness of the remaining wall of the trunk, is far from a reliable criterion on which to assess the likelihood of tree failure.

The development of a system known as ‘static load testing’, ‘the static integrated method’ or ‘tree pulling’ enables a far more objective assessment of tree stability than has been achieved by previous methods. Static load testing is a procedure whereby the tree is subjected to a pulling force, during which measurements of compression, tension and tilting are taken from the stem and root plate. Evaluation of this data, combined with other parameters, such as crown volume and exposure to wind, provides a factor of safety. Trees with a factor of safety greater than 1.5 would normally be considered able to withstand those wind conditions that could be expected in that particular location. Trees with a factor of safety less than 1.5 would normally require further action such as crown reduction or felling.

Working in conjunction with Treework Environmental Practice, we are able to offer static load testing to our clients. It is important to state that due to the time and resources required to conduct these tests, they are most appropriate for the assessment of large, mature trees with either high visual amenity and/or considerable historical, cultural or ecological value.

Contact us for more information or to discuss your requirements

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