Arb Innovators are now Quantified Tree Risk Assessment (QTRA) Registered Users

Arb Innovators consultants are now trained and registered to use QTRA — Quantified Tree Risk Assessment — alongside our existing use of VALID, as Tree Risk Validators.

Tree risk assessment is rarely as simple as deciding whether a tree presents an acceptable risk.

Trees are living structures. They change, their surroundings change, and the consequences associated with failure can vary considerably depending on where a tree is growing and how the surrounding area is used.

That is why we believe good tree risk management needs more than one tool.

We are therefore pleased to add QTRA Registered User status to our existing tree risk assessment services.

What is QTRA Tree Risk Assessment?

QTRA, or Quantified Tree Risk Assessment, is a structured method for assessing and expressing the risk of harm from falling trees and branches.

Rather than considering the condition of the tree in isolation, QTRA considers three components:

• Target — what could be affected by a tree or branch failure and the likelihood of the target being present.

• Size — the size of the tree or branch that could fail.

• Probability of Failure — the estimated probability of the tree or branch failing within the coming year.

  
  

These components are combined to produce a numerical Risk of Harm.

What does being a QTRA Registered User mean?

QTRA is intended to be applied by people who have undertaken specific training in the method.

The Registered User programme covers the principles of probabilistic tree safety management and the correct application of QTRA.

It is worth making an important distinction here.

QTRA training is not a replacement for arboricultural knowledge or tree stability assessment.

The system provides the framework for quantifying and communicating risk. The quality of the assessment still depends on the arborist correctly understanding the tree, its condition, likely failure modes and the environment in which it is growing.

That distinction matters to us.

A risk calculation is only useful when the information going into it is sound.

QTRA and VALID Tree Risk

Our consultants are already VALID Tree Risk Validators, so why add another tree risk assessment system?

There is considerable overlap between the two approaches, but we don't see this as an either/or decision.

Instead, having experience with both systems gives us greater flexibility when designing a tree risk management strategy or undertaking individual tree assessments.

Different clients have different requirements. Some may already operate a QTRA-based tree risk management system. Others may use VALID.

And in some situations, the most appropriate approach may simply be a well-designed arboricultural inspection programme supported by clear inspection frequencies, escalation procedures and detailed assessment where required.

The method should serve the tree management strategy — not dictate it, allowing us to look beyond individual tree inspections and consider how risk is managed across an entire estate or tree population.

For organisations responsible for hundreds or thousands of trees, that distinction is important. Inspecting every tree with the same level of detail and at the same frequency is rarely the most efficient use of resources.

Understanding where the consequences are greatest, where more detailed assessment is justified, and where intervention is genuinely proportionate can produce a much more effective tree risk management system.

The calculation isn't the assessment

There is also a wider point here.

Tree risk assessment can become overly focused on systems, scores and numbers.

But no methodology removes the need for professional judgement.

The starting point is still understanding the tree.

What defects or features are present?

What biological processes are occurring?

How significant are they?

What parts of the tree could realistically fail?

What would they hit?

How frequently is that area occupied?

And, importantly, what are the consequences of intervening?

Systems such as QTRA and VALID help structure those decisions and make them easier to communicate and record.

They don't replace the arborist making them.

Supporting defensible and proportionate tree management

Our aim is not simply to identify defects and recommend tree work.

It is to help clients understand and manage tree risk proportionately.

That means recognising genuine risks while avoiding unnecessary intervention simply because a tree is large, old, decayed or structurally unusual.

It also means being able to explain why a decision has been made.

Adding QTRA to our existing VALID Tree Risk capability gives us another established framework through which we can assess, quantify and communicate tree-related risk.

And ultimately, that gives our clients more options when deciding how best to manage their trees.

For advice on tree risk management, estate-wide tree surveys or detailed assessment of individual trees, contact Arb Innovators to discuss your site and the most appropriate approach.