Mike Galvin: Hi! I am Mike Galvin with the Tree Care Industry Association. And today, we are going to talk about tree risk and how to assess and manage it.
Tree risk equals probability times consequences. And what we mean by that is how likely is an event to happen and then what are the consequences if it does in fact happen? If we look at a tree and the tree has a defect, we look at how likely that defect is to cause a failure in the tree, and then if that failure happens, what will it land on? Is it a piece of property, is it a person, is it a vehicle, is it a home?
To assess the risk of a tree or trees on your property, the first thing you should is retain a professional certified arborist. A professional certified arborist is familiar with the processes to systematically evaluate the trees for risk. This should be done according to the American National Standards Institute A300 Standards for tree risk assessment.
According to the ANSI Standards for tree care, there are three levels of tree risk assessment. A level-1 assessment is a limited visual observation from a specific vantage point. It may be an aerial patrol, it may be a drive-by windshield survey, it could be a foot patrol, observation based on photographs, etcetera. The key is that a limited view of the tree in question.
A level-2 inspection is a 360 degree ground-based visual observation of the subject tree or trees. This includes looking at the roots, the trunk, and the crown, for open and obvious structural defects.
A level-3 tree risk assessment is anything in advance of a level-2 tree risk assessment and can include advanced diagnostic procedures such as root collar excavations, aerial inspections on extraction of materials from the tree for processing of samples. When we think of tree risk assessment, we think about potential targets. To do this, we look at the tree and we imagine a circle around the tree with the distance of the circle being as far as the tree is tall. Look on the ground what falls within the circle.
These are things that could be impacted in the event of a tree failure. If they are persons or property, it's something to be concerned about. There are two types of reports you can receive as a client; either a written report or an oral report. They should include recommendations for mitigation of risk. In any tree risk situation there are three primary options. One is removing the risk by removing the tree, one is reducing the risk by treating the tree, and the other is reducing the risk by treating the site. Sometimes these are used in concert with each other and are not mutually exclusive in order to manage risk at a level acceptable to you.
While risk assessment is the responsibility of the arborist, risk treatment is the responsibility of the tree owner. Make sure you communicate with your arborist on how risk-averse you are, and make sure you follow up on any monitoring, a subsequent activity required to keep the risk managed in a manner that's acceptable to you.
Trees with defects can pose risks to persons and property. By retaining a qualified professional arborist who is knowledgeable, and the American National Standards Institute A300 Standards for tree risk assessment, you can properly manage your tree and landscape resources.