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A REVIEW OF TREE RISK ASSESSMENT USING MINIMALLY INVASIVE TECHNOLOGIES AND TWO CASE STUDIES

Abstract Tree risk assessment has evolved greatly in recent years, from ground-based visual hazard inspections, through invasive drilling and resistograph tests, to sophisticated and minimally-invasive methods. In this paper, we trace the evolution of tree risk assessment over time, and examine how the latest technologies can be combined with engineering- based computer modelling to develop quantitative risk assessments and effective prescriptions for tree risk mitigation. We focus closely on two such technologies: sonic tomography and static load analysis. Through two case studies we present alternative ways for arborists to quantify the resistance to stem failure and uprooting of suspected risk trees, and therefore derive accurate assessments of risk with a high degree of confidence and minimal damage to the subject tree. These methods require the use of specialized and sophisticated tools, and may be out of reach for some arborists. We therefore also present the “practitioner's” method—a simplified approach to risk assessment which incorporates many of the principles of the more advanced methods.