MIS501 Tree Risk Assessment

MIS501 Tree Risk Assessment

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MIS501 Tree Risk Assessment

Minimum Industry Standard series

Members Price is for Members of The New Zealand Arboricultural Association (NZARB).

The vision of NZ Arb is to represent the arboriculture community and make it the primary organisation for tree care and to maintain relevancy to the Association’s members, so if you are in the NZ tree care industry please consider joining NZARB by clicking the link above if you are not already a member.


This book is one in a series of Minimum Industry Standards produced by Arboriculture Australia Ltd and the New Zealand Arboricultural Association in consultation with the national arboriculture community in both countries. These industry peer-reviewed documents provide a ‘body of knowledge’ which is shared by practitioners and can be used as the basis for training, dissemination of skills and professional development.

This book covers the basics of tree climbing equipment and tree access using a variety of tree climbing skills and techniques. Many other techniques, climbing systems and climbing equipment configurations are possible which are not discussed in this document. Nevertheless, the skills and techniques presented in this document form a solid foundation on which practitioners can build.



1: Introduction to tree risk assessment

  • 1.1: What is risk?
  • 1.1.1: Context of tree risk
  • 1.1.2: Applying tree risk assessments

1.2: Tree risk terminology

  • 1.2.1: Risk factors
  • 1.2.2: Probability and likelihood

1.3: Risk thresholds

  • 1.3.1: Baseline risks of trees and risk thresholds

2: Risk assessment methodologies

  • 2.1: Quantitative tree risk assessment
  • 2.2: Qualitative tree risk assessment
  • 2.3: Comparative tree risk assessment

3: Components of tree risk assessment

3.1: Target assessment

  • 3.1.1: Types of target
  • 3.1.2: The target zone
  • 3.1.3: Target occupancy
  • 3.1.4: Specifying targets
  • 3.1.5: Specifying the target zone
  • 3.1.6: Multiple probable targets

3.2: Tree failure assessment

  • 3.2.1: Factors for risk assessment
  • 3.2.2: The likelihood of failure
  • 3.2.3: Trees with multiple factors
  • 3.2.4: Cognitive biases affecting assessment of likelihood

3.3: Impact assessment

  • 3.3.1: Likelihood of impact
  • 3.3.2: Likely consequence
  • 3.3.3: Range of consequences

4: Tree risk assessment professional requirements

  • 4.1: Context of assessment
  • 4.1.1: Limits of assessment
  • 4.1.2: Levels of tree assessment
  • Level 1 (limited visual) assessment
  • Level 2 (visual) assessment
  • Level 3 (advanced) assessment

4.2: Providing advice on risk

  • 4.2.1: Benchmarking risk
  • 4.2.2: Providing advice on risk controls (mitigation)
  • 4.2.3: Determining and communicating residual risk
  • 4.2.4: Value and benefit(s) of the tree(s)
  • 4.2.5: Priority and timeframe for implementing control measures
  • 4.2.6: Recommending other works
  • 4.2.7: Reinspection of tree
  • 4.2.8: Auditing of controls

4.3: Competency to perform tree risk assessment

  • 4.3.1: Benchmarking and auditing assessments of risk
  • 4.3.2: Maintaining industry currency