Tree Risk Assessment – Qualification, Recognition & Levels

Trees are very vital to every life on Earth. They provide shelter and food to so many creatures, including humans. They can also be used to make furniture and other important woodwork such as fences & doors.

As helpful as trees are, they can also be a big risk to life and property when they are dead, rotten, or leaning. At this point, a tree risk assessment will become very important.

This is what I’ll be discussing in this article, so stay with me!

What Is A Risk Tree Or Hazard Tree?

What professional arborists call a “risk tree” or a “hazard tree” is one that carries a considerable amount of risk to persons or property, which surpasses the risk tolerance of the landowner or property manager.

What this means is that a tree might be considered “dangerous” by one property owner, but safe to another property owner.

So a tree labeled as “hazardous” is relative, making it a subjective concept that is used when making decisions regarding tree risk management on a specific property.

Recognizing A Tree Risk

As far as tree care circles are concerned, the term “risk tree” or “hazard tree” is used to describe a tree that carries a certain threat to persons or property, and requires immediate removal or preventive actions to reduce the threat the tree poses.

When a homeowner consults with an arborist to determine if a tree poses any danger, it means they have certain concerns about the safety of persons and property around the location of the tree.

Just in case you’re wondering what sort of risk a hazard tree poses, well it’s the possibility of the tree or its branches falling, as well as the consequences of such failings.

Assessing Tree Risk Levels

To determine the level of risk a tree poses to property, it is important to have a proper tree risk assessment carried out by a qualified arborist.

A qualified arborist is one who has received specialized training and passed the necessary exams and issued a certificate by the International Society Of Arboriculture (ISA).

For a tree to be labeled as a risk, it has to meet at least one of two criteria.

  • The tree itself or a part of it must have a high potential of failing due to structural defect (decay or diseased)
  • One or more targets must be present (persons, homes, vehicles, etc)

Targets are defined as people or property that can be damaged due to the failure of a tree.

In a case where there are no targets around the surroundings of the tree, then the tree will not be considered to be a hazard, regardless of whether it is in sound condition or not.

On the other hand, if the tree has a high potential of failing, and there are targets around which could be damaged by the tree’s failure, then the tree will be considered to be a hazard.

In the process of tree risk assessment, a few questions have to be answered. These include –

  • What is the possibility of the tree or parts of it failing?
  • What are the possibilities that the failure of the tree will hit a target?
  • What are the possible implications of the failing tree hitting the target?

The structural defect of a tree will determine the possibility of the tree falling. For instance, a tree branch filled with large amounts of rot is more likely to fall than a branch of the same size with little or no decay.

The conditions of the tree’s surroundings can also increase the possibility of tree failure. For example, if a tree is located in an open area where it is exposed to strong winds, it is more likely to fail than a tree of the same size in an area protected from strong winds.

If a decayed tree branch is hanging over a target (a roof for instance), then there is a 100% possibility of impacting the target. On the other hand, if a decayed limb of the same size is hanging over a rural road that doesn’t have up to 8 cars driving through per day, then the possibility of hitting a car will be very low.

If the same sized limb hangs over a car park where cars are parked 35% of the time in a day, then the possibility of the tree limb failure impacting a car will be 35%.

Another factor to consider is the severity of the consequences of the branch impacting the target.

If a decayed branch falls and hits the roof of a house, then the severity of the damage will amount to the money needed to pay for repairs. If the same branch falls and hits a person, the severity could be serious injuries or even death.

All these variables are taken into consideration when tree risk assessment is being carried out.

In the process of determining what a hazard tree is, the property owner and a qualified arborist must have a detailed discussion regarding the level of risk a potentially failing tree poses to persons or property.

The arborist carrying out the assessment must explain the level of risk the tree poses, and the property owner must express his/her risk tolerance.

When this discussion is concluded, it is at that point that they will determine if the tree is a “hazard tree” or not.

A tree that carries a certain risk level could be considered a hazard on one property, and a tree carrying the same risk level can be considered to be non-hazardous on another property.

The property owner and the arborist also have to consider that while a tree may not be deemed as hazardous to the owner’s property, it could be a hazard to targets outside the property.

Failure to acknowledge this could cause “accidents” outside the tree owner’s property and it could lead to lawsuits filed by injured persons.

Tree Risk Assessment Qualification

The person best suited to assess tree risk is a qualified arborist.

To ensure that arborists are qualified for tree risk assessment, the ISA created the Tree Risk Assessment Qualification (TRAQ).

TRAQ is meant to improve the safety of people and property utilizing a standard process that is used to assess tree risk.

The findings from a tree risk assessment can give tree owners and risk managers vital information needed to make calculated decisions aimed at reducing or averting possible calamities.

With the right training, arborists will be taught specific strategies that they would use to identify tree risks and offer practical solutions.

A qualified professional will be able to do the following –

  • Show proficiency with the fundamentals of tree risk assessment as described by the ISA best risk management practices
  • Understand the fundamentals of advanced diagnostic methods for tree risk assessment
  • Gather and process necessary information required to perform a proper tree risk assessment
  • Make calculated assessments and provide practical solutions to reduce or eliminate risks posed by hazard trees


When you feel the need to have your tree risk assessed, you must call on qualified arborists to carry out the assessment. These arborists must be TRAQ certified.

For an arborist to be eligible for the course, they must have received one or more of the following certifications.

  • ISA Certified Arborist or ISA Board Certified Master Arborist
  • ISA Tree Risk Assessment Qualified
  • An urban forestry degree, Arboriculture degree, traditional forestry degree, or horticulture degree from a college
  • A national certification or certificate in arboriculture
  • ASCA Registered Consulting Arborist (RCA) status
  • Licensing or Certification from an approved state/province program
  • SAF Certified Forester

Domestic Instances When A Tree Can Be Considered To Be Hazardous

A dead or decayed tree sitting in the heart of the forest will not be considered to be hazardous mainly because it poses no threat to human life or property. However, the case may not be the same domestically.

Below are some instances where a tree can be considered to be a risk around your home.

The tree is leaning towards your home: A tree can lean for several reasons. It could be that it is dead or rotten from the root system and it has become too weak to support the full structure of the tree. It may also be tilted as a result of a storm.

Either way, a tree in this scenario will be considered a hazard, as it can fall at any time and cause damage to the structure of your home.

Weak branches: If the tree in your yard has decayed or dead branches, then it should also be considered to be a hazard, especially if the branch hangs over your roof or the garden area where your kids play.

Branches crossing in-between power lines: If the tree’s branches have encroached into high-tension electric cables, then it is also a hazard.

The pressure from the branches can cause the cable to snap and drop into your yard or your neighbor’s yard. This could lead to electrocution.


Only a certified arborist is qualified to carry out a tree risk assessment. The arborist and the property owner have to discuss the potential risks as well as risk tolerance to come to a conclusion and take steps to mitigate the risk.

Stay safe!

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