Understanding Tree Risk Assessment: Points from a Recent ISA Publication

Trees add beauty, shade, and value to our homes, but they can also pose risks. Knowing when a tree might become a hazard is crucial for protecting your property and loved ones. Alexander Martin’s article, Assessing Likelihood of Failure: Results of a Survey of 702 Tree Risk Assessors, published in ISA Arborist News (April 2026), offers valuable insights into how professionals evaluate tree risk. This post breaks down the key points from Martin’s survey, focusing on what homeowners need to know about tree risk assessment and how to act on it.

Visible signs of distress on a maple tree in Shady Grove, showing a prominent trunk crack and significant wounds at both the base and upper section, indicating potential risk factors for tree health and stability.

Why Tree Risk Assessment Matters for Homeowners

Many homeowners underestimate the importance of regular tree risk assessments. Trees can develop hidden weaknesses over time due to disease, decay, or environmental stress. When these weaknesses go unnoticed, branches or entire trees may fail unexpectedly, causing property damage or injury.

Martin’s survey of over 700 tree risk assessors highlights that early detection of risk factors can prevent accidents. Assessors use a combination of visual signs and experience to estimate the likelihood of failure. For homeowners, understanding these signs can help decide when to call a professional.

Common Indicators of Tree Failure

The survey identified several key indicators that assessors look for when judging tree stability. Homeowners can watch for these signs around their property:

• Cracks or splits in the trunk or major branches

These can indicate structural weakness. Even small cracks can grow and lead to failure.

• Decay or hollow areas inside the trunk

Decayed areas and cavities weaken the tree. Decay often starts inside and may not be obvious without close inspection.

• Leaning trees or uneven canopy

A sudden lean or imbalance in the tree’s crown can signal root problems or internal decay.

• Dead or hanging branches

Deadwood is more likely to break free from the tree. Hanging branches (aka hangers) may dislodge during storms or high winds.

• Root damage or soil heaving near the base

Roots support the tree. Damage from construction, erosion, or pests can destabilize them. Some tree diseases, such as Armillaria root rot, attack the roots causing them to fail sooner than expected.

Martin’s findings show that assessors weigh these signs differently depending on the tree species, size, location, and environmental conditions. For example, a crack on a mature oak next to a structure is typically more concerning than on a young maple in an open area.

How Tree Risk Assessors Estimate Likelihood of Failure

The survey revealed that assessors combine visual inspection with knowledge of tree biology and site conditions. They consider:

• Tree species and age

Some species are more prone to failure (e.g. Bradford Pear). Older trees may have more internal decay.

• Environmental factors

Wind exposure, soil type, and recent weather events affect stability. Trees with shallow roots are more likely to uproot when exposed to significant rains followed by severe winds.

• Tree history

Previous damage, pruning, or disease history informs risk. Previously topped trees are almost always higher risk than properly pruned trees.

Assessors use ISA Tree Risk Assessment Qualification matrices to determine risk levels. The first matrix determines the likelihood of failure and impact. Results from the likelihood matrix are evaluated against the consequences of failure in the second matrix. The overall risk rating is determined from this assessment and falls into one of four categories

1. Low

2. Moderate

3. High

4. Extreme

ISA TRAQ Matrices - The top matrix result feeds the bottom matrix to determine the overall risk rating

Once the overall risk rating is determined the arborist provides a summary report and recommendations, but the owner is responsible for making the decisions on treatment. Ultimately, a tradeoff between budget and risk inform the decision.

What Homeowners Can Do to Manage Tree Risk

Understanding risk factors is the first step. Homeowners should:

• Schedule regular tree inspections

Especially after storms or if you notice any warning signs.

• Hire arborists for assessments

Professionals have the training and tools to detect hidden problems.

• Maintain tree health

Proper watering, mulching, and pruning reduce stress and decay.

• Address issues promptly

Removing dead branches or treating disease early can prevent failure.

• Consider tree removal when necessary

If a tree poses a high risk and cannot be safely managed, removal may be the safest option.

When to Contact Antrim Tree Service

If you notice any signs of tree risk or simply want peace of mind, contact Antrim Tree Service for a free on-site assessment. Their arborists will evaluate your trees carefully and provide clear recommendations tailored to your property. They are also cognizant of financial constraints and can provide the best solution for your budget.

Taking action early can save you from costly damage and keep your home safe. Antrim Tree Service combines expert knowledge with a friendly approach to help homeowners protect their trees and property.

Trees are living assets that require care and attention. Alexander Martin’s survey underscores the value of professional risk assessment and the key signs homeowners should watch for. By staying informed and proactive, you can enjoy the benefits of your trees while minimizing risks.

References

1. Dunster JA, Smiley ET, Matheny N, Lilly S. 2017. Tree Risk Assessment Manual. 2nd Ed. Champaign (IL, USA): International Society of Arboriculture. 196 p.

2. Martin, Alexander. Assessing Likelihood of Failure Results of a Survey of 702 Tree Risk Assessors. ISA Arborist News, Volume 35, Number 2. April 2026.