Tree Hazard Inspections

Introduction

Trees add to our enjoyment of the outdoors.  They contribute to the value of our properties and help us recover from our illnesses.   Trees also have liabilities associated with them.  They can cause injury to property and individuals.  The key to reducing the liabilities is to recognize when a tree becomes hazardous and take actions to correct these hazards.

A "Hazard Tree" is a tree that has a structural defect that is likely to fail in whole or in part.  This "Hazard Tree" also must be within a location where it can hit a target.  This target could be a structure or person.

Why Tree Hazard Inspections are Needed

Reduce Tree Liabilities:  The inspection and assessment of trees forces the tree owner to evaluate the amount of liability that they are willing to assume.  All trees have some liability associated with them.  This liability can be as low as a vehicle or person running into the tree or could be as high as a limb or the whole tree falling and damaging a structure or injuring a person.  Routine inspections and hazard assessments forces the tree owner to determine if the tree is structurally sound and the likelihood of a failure of a part of the tree.  These inspections also exhibits that the tree owner is actively managing their trees and thereby reduces their liability if a failure does occur.

Schedule Tree Work:  While inspecting the trees for hazards, the inspector also notes any tree maintenance needs.  This inspection can determine the timing and priority of the worked needed.  The schedule of the work should be influenced by the tree's needs, the activities around the tree, the season of the year, the accepted amount of liability and the budget of the tree owner.

Document Tree Structure/Health over Time:  The inspection should be documented in writing.  This written documentation should be saved over time to evaluate how the tree's condition has changed.  This documentation could be critical if litigation over a tree problems occurs. 

Improve Tree Health and Structure:  The tree problems found during these inspections can help to improve the tree's health and condition.  The recommended maintenance needs could prolong the life of the tree and make it more aesthetically pleasing.

Inventory Trees:  The hazard assessment and inspection can also help the tree owner inventory their trees.  This inventory can determine the average age and condition, the diversity of species, the location of the trees and other tree and site information.  This information can be inputted into a tree inventory program such as: Canopy from Natural Path Forestry.

How Inspections are Completed

Use Standard Form or Method:  The International Society of Arboriculture publishes "A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas, Second Edition" by Nelda Mathey and James R. Clark.  Within this book, there is a form that guides the inspector to evaluate each part of the tree, the site around the tree and possible targets.  This two page form is a valuable tool for the inspection and documentation of the tree's condition.

Use Same Procedure for ALL Trees:  When inspecting trees, the same procedure should be used to inspect all trees.  Using the same procedure helps the inspector cover all aspects of the tree in a very consistent manner and reduces the chances of skipping a portion of the inspection.  Most inspectors start at the top of the tree and move to the roots or start at the roots and move up the tree.   Following the form that is being used is the best procedure.

Tools:  When inspecting trees, certain tools are needed.  These tools include: a soil probe, sounding hammer or other instrument to determine the "soundness" of the trunk, increment bore, binoculars, diameter tape, dendrology book (for species identification), pest identification book, clip board, and inspection forms.

Climbing or Aerial Inspections:  While most tree hazard assessments are conducted from the ground, there are times when an aerial inspection is necessary.  Aerial inspections should be done when adequate information can not be gathered from the ground.  When conducting aerial inspections, all safety considerations recommended by the American National Standards Institute Standards for Tree Care Operations - ANSI Z133.1-1994.

Who Inspects Trees

Familiar with procedures and equipment:  The inspector should know how to inspect each aspect of the tree and how to use the equipment.

Competent in assessing trees:  The inspector should be competent in assessing and inspecting trees.  He should know tree biology, physiology and dendrology.  A good sign of a competent inspector is a person who is a Certified Arborist.  The International Society of Arboriculture requires education, experience and a written test before designating an individual as a Certified Arborist.

Understand tree structure and decay process:  The inspector should know how trees grow in nature and how decay travels through a tree.  He should further understand how certain man-caused events and activities affect the natural patterns of tree growth and structure.

Anticipate situations:  The inspector should know his surroundings and how trees grow in his area.  

Knowledgeable about past failures:  The inspector should know the history of tree care and activities in the area.  He should know how the tree species within the inspection area have been affected by various activities.

Know soil and weather conditions:  The inspectors should know the soil types and the prevailing weather conditions in the inspection area.  he should know the soil and weather requirements of the various tree species.  He should know how the various tree species are affected by weather phenomenon.  

Archiving Inspections

Write down all evaluations:  All tree inspections should be recorded in writing or on computers.  These records will assist the tree owners if failures occur.

Evaluations show history of tree health and structure:  The evaluation of past inspections can show how a tree has changed in its health and structure.

Written evaluations are beneficial in liability claims and court cases.  These written evaluations are very beneficial if a failure occurs and a claim is filed against the tree owner.  

TRiM Program:  The TRiM Software Program is a vital tool for recording and archiving tree inspections.  The program uses the inspection form from the The International Society of Arboriculture's  "A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas, Second Edition" by Nelda Mathey and James R. Clark.  

Conclusions

Inspections trees on a regular basis:  Trees should be inspected regularly.  These inspections should occur both with leaves off and leaves on.  Further inspections should be conducted after major weather occurrences.  As a minimum, trees should be inspected every five years.

Inspect trees in a systematic manner: Trees should be inspected in systematic order so that each tree is inspected similarly.  This will insure that each aspect of each tree is inspected and assessed.

Use competent, well trained inspectors:  Trees should be inspected by competent inspectors.  These inspectors should know the trees, the soil and weather within the inspection area.  A Certified Arborist designation should be a minimum requirement for the inspectors.

Archive the inspections:  Once the inspection is completed, the data should be stored in writing or on a computer.  This archive may be needed if a liability claim is filed after a tree or limb failure.

For Further Information

Contact Dr. Kim Coder or the University of Georgia's Extension Service's Web Page on Tree Risk Management and Hazard Assessment or The International Society of Arboriculture's Recognizing Tree Hazard Web Page or the Minnesota Department of Natural Resource's How to Recognize Tree Hazards Web Page.

Latest Update 10/7/99