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About Us


ARBEVENTS is the Australian based events division of Arbor West Pty Ltd. Our seminars and workshops are designed to provide increased industry knowledge, expertise and employment opportunities. 

Our Presenters - Is it VALID? Defects, Decay, & Decisions


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David Evans

David is the Director of VALID - a non-profit social enterprise delivering training and guidance in tree risk-benefit assessment and management.  Before creating VALID, David was one of the lead Quantified Tree Risk Assessment (QTRA) trainers for the previous 10 years, and an invaluable contributor to its past development.

David is currently dipping his toes back into the academic stream by undertaking a PhD into Tree Risk-Benefit Assessment.  He has presented at many international conferences, and introduced the VALID Approach to Likelihood of Failure at a ‘sold out’ Tree Academy Workshop, at the ISA’s conference in Fort Worth this year.  Most recently, David delivered the key concepts of VALID Tree Risk at the UK’s Arboricultural Association’s 50th anniversary conference in September, to considerable acclaim.

“David Evans provided a masterclass on how to deliver an engaging presentation with unique content….  It was the last talk, so those who left early really missed out”

Jeremy Barrell – Barrell Tree Consultancy, UK

"VALID has changed the way I look at tree risk assessment."

Jeff Opar - ISA Tree Academy Workshop, Fort Worth

“Excellent work, thoroughly impressed, a very well presented presentation for once!"

Stefan Kowalczyk – Tree Officer, Winchester City Council, UK

“An innovative and useful advance in tree risk assessment. The opportunity for discussion and debate during the Likelihood of Failure Club practical sessions were especially valuable”

Tim Scott-Ellis - Evolve Tree Consultancy, UK

Paul Muir

Paul is a Senior Arboricultural Consultant, at Treework Environmental Practice, UK. Paul has been a full member of the SAG Baumstatik Group of European consultants specialising in Tree Statics since 2010, and Treework Environmental Practice have been associates since 2005. He has undertaken Static Load Tests to assess the structural condition of more than 200 trees throughout the UK and Europe.

Paul has presented the principles of Tree Statics, and demonstrated the Static Load Test, at events throughout the UK, Europe, and Asia.

"A real step-up in how to apply engineering principles when assessing trees"

Jon Kiely - Aspect Tree Consultancy, UK

Claire Harbinson

Claire is a Senior Arboricultural Consultant with Treework Environmental Practice, UK, and assists with static load tests.  Claire has carried out novel research on the structure and anatomy of branches and forks, leading to a seminal (and controversial) co-authored paper on the biomechanics of branch attachments.

Day Plan

08.30 – 9.00
Registration and Refreshments
09.00 – 9.40
Estimating Likelihood of Failure – The VALID Approach (David Evans)

How the VALID Tool helps you estimate likelihood of failure

  • Not too wide, not too narrow – Goldilocks Ranges
  • Benchmarking, confidence, & uncertainty
  • The VALID decision-making tool, and how to use it
09.40 – 10.20
Tree Failure - Safety Factor v Strength Loss (Paul Muir)
What you need to know about applying the ‘Safety Factor’ in trees, and the critical limitations of strength
loss formulae, such as the t/R ratio
  • Safety Factors and trees – The essentials
  • Engineering principles – wind load, stem geometry, and wood strength
  • How much strength loss (by decay or root severance) is too much
10.20 – 10.30
Q&A David Evans and Paul Muir
10.30 – 11.00
Break and Refreshments
11.00 – 11.40
The Static Load Test – Reducing Uncertainty by Measurement (Paul Muir)
How the Static Load Test assesses the structural integrity and stability of a tree, with case studies.
  • The Static Load Test model
  • Applying the Static Load Test
  • Case studies and lessons learned
11.40 – 12.20
Tree Safety in Numbers and Words (David Evans)
  • Quantitative v Qualitative tree risk assessment
  • Risk concepts, measuring uncertainty, and good forecasting
  • VALID tree risk-benefit assessment and management
12.20 – 12.30
Q&A David Evans and Paul Muir
12.30 – 13.30
13.30 – 17.00 
15.00 – 15.30
Split Sessions (1.5hrs - 30 Delegates per session)
Break and Refreshments
Including demonstrations of TreeCalc software to calculate safety factors using basic field data.
Static Load Test – Practical Demonstration (Paul Muir & Claire Harbinson)
Claire will be setting up a Static Load Test on a tree in the morning, and be on hand to field questions with
Paul in the afternoon.  The test data collected will be used to calculate safety factors at various measured
positions on the tree.  This will present an opportunity for you to consider and discuss the reasons for
differences in safety factors in relation to defects, stem diameter, and load.  You will be encouraged to
compare your assessment of the likelihood of failure of the subject tree by considering both safety factors
and strength loss.
Likelihood of Failure Club (David Evans)
Likelihood of Failure Club rules.  You will be given the VALID Tool voting cards, shown a tree part, and 
invited to form an independent opinion about the likelihood of failure without any discussion.  Votes will
then be taken for a ‘benchmark’, and Likelihood of Failure range.  After the opening opinions have been
declared, those of you who have voted for the same Likelihood of Failure range will form teams and use
the VALID Tool to explain the reasoning for the estimate.  Each team then tries to persuade those who
have voted for a different range why they should join them, and vice versa.  After a healthy round of
discussion and deliberation, a final round of voting allows anyone to change their mind if another team
makes a more convincing case with better evidence.

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