Tree Risk Assessment
International Society Of Arboriculture
The benefits that trees provide to people living and working in the urban environment range from ecological and monetary to aesthetic and sociological. These benefits increase as the age and size of trees increase. However, as a tree gets older and larger, it is also more likely to shed branches or develop decay as other conditions that can increase the likelihood for failure. Tree Owners have the duty/obligation to maintain their trees to minimize the chance of injury and property damage.
Trees can pose a variety of risks categorized into 2 groups: conflicts and failures.
Conflicts are between trees and society. Problematic flowers, fruit, roots or branches are most common. Branches may rub against structures, roots may heave sidewalks, flowers attract insects and fruit may be a nuisance.
Failures arise when stresses due to forces acting on a tree exceed the strength of tree structure as the tree-soil connection that supports the tree.
Decide on scope of work; ID trees, level of assessment, method of reporting, timetable.
Assess the site for factors that could contribute to or mitigate risk.
Evaluate structure and site conditions, potential loads on the tree and tree adaption to weakness.
Assess likelihood that the tree or parts could strike people or damage property.
Evaluate target value and potential damage to estimate consequences of failure.
Evaluate assessed risks for client tolerance.
Report of findings with recommended mitigation techniques.
Hazard tree assessment (done in the past) has no set format and generally there was little training for assessors. In 2013 The International Society of Arboriculture started a new qualification for tree risk assessment. Now internationally all tree risk assessments are done in the same manner. There will be individual variation but all tree risk assessments are done the same way and results should be similar between individual assessors.