Ch 12 - Tree Risk Assessment - AgriLife

Identify TargetStatic, mobile, movable

Occupancy rate: constant-Rare

Assess Target(s)

Target Assessment

Targets and Consequences of Failure

Consequences: function of target value and potential harm.

Four categories: Severe Significant Minor Negligible

Depending on Tree Part Being Assessed, Size Matters

Property Damage and Event Disruption

Site Assessment:Factors to Consider

Previous failures Terrain Wind pattern Soil characteristics Drainage Land disturbances Restricted growth conditions Land-use history

Previous FailuresPrevious failures can indicate high potential for future failures.

All trees pruned in the same manner

Consider Site History: Sidewalks

Site History: Construction

Site History: other root issues

If 1 tree is planted with circling roots, chances are…

Tree Decay• White rot• Brown rot• Soft rot• Sapwood & heartwood rot

White Rot Fungi Primarily decays lignin

Decayed wood appears white after darker colored lignin is removed

Armillaria spp. and Ganoderma spp.

Brown Rot Fungi Conifers primarily

Primarily decays the cellulose, leaving behind stiff lignin

Reduces bending strength

Tree Wood DecayHeartwood Rot Sapwood Rot

Indicators of Decay..

Now that you’ve done a tree assessment… It’s time to mitigate

MitigationTarget Based

Relocation Restricting access Can be temporary

or permanent

Tree Based Prune Cable/brace Removal Modify site

Wildlife Trees

Cabling and Bracing

Residual RiskThere will always be some level of risk remaining after mitigation.

Dependent on owners risk threshold

Remember, you can not make a tree safe, only mitigate the risk.

Target Based MitigationRelocation Exclusion

Conclusion You can not make a tree safe, only

mitigate risk If a tree has failed, it is likely to fail again Risk: likelihood of failure and

consequences of impact

Thank You