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The Quantified Tree Risk Assessment (QTRA) system, developed by Mike Ellison at Cheshire Woodlands, applies accepted risk management principles to tree safety management. Development of the QTRA system has moved the language of tree safety management forward but represents a paradigm shift for tree managers in both the public and private sectors.
Tree safety management is a matter of limiting the risk of harm from tree failure while maintaining the benefits provided by trees. Although it may seem counter-intuitive, the condition of trees should not be the first consideration. We first consider the usage of the land upon which trees are growing. This will inform how we go about the process of assessing trees.
This system redirects the management of tree safety away from labelling trees as either ‘safe’ or ‘unsafe’, which requires definitive statements of tree safety from either tree surveyors or tree managers. Instead, QTRA quantifies the risk of significant harm from tree failure in a way that enables tree managers to balance safety with tree value and operate to predetermined risk thresholds.
By taking a QTRA approach to tree risk, it’s common that fewer resources are used on assessing and managing tree risk while the benefits from tree populations are maximised. Furthermore, in the event of a ‘tolerable’ or ‘acceptable’ tree risk being realised, there is proof that reasonable action has been taken in the way of risk management.