hazard trees isa cert revised 0308

Tree Assessment and Tree Assessment and Risk ManagementRisk Management

Certified Arborist Training

TREES HAVE VALUE!!

Benefits of Urban Trees:

Energy Savings

Property Value

Shade

Air Quality

Aesthetics

Quality of Life

Urban Wildlife

Tree AssessmentTree Assessmentand Risk Managementand Risk Management

The value comes at a “price”, however.

There are risks associated when trees are in areas used by people and their “things” (targets).

Risk assessment includes the potential of a tree to fall, the environment that may contribute to its failure, and the potential target.

Evaluating trees for their potential to fail is a component of risk management.


TREES HAVE VALUE!!

TORT LAW – A “tort” is a civil wrong; more commonly stated, a non-criminal harm (wrong) done to persons or property. Tort can result from an intentional act (assault, battery, libel) OR may be unintentional (e.g., negligence)

NEGLIGENCE – A person is negligent when he or she fails to act as a reasonably prudent person under the circumstances.

Ignorance or stupidity are not excuses for dangerous or inappropriate behavior.


RISK AND LIABILITY

Evidence of Negligence

Appropriate professional practice?

Existing laws, regulations, codes of professional conduct, and standards of behavior apply to individual circumstances.

Testimony from experts or fellow professionals.

Customary practices may be used as evidence of proper or due care, just as deviation from recognized standards may demonstrate negligence.


RISK AND LIABILITY

“Duty of Care” (Reasonable Person)

The current trend in the United States is that the landowner will be held to a “duty of care”, determined by the principles of negligence. A landowner is not only held to the duty of common prudence in maintaining trees on his property, but is also held to an even greater duty of inspection to discover possible defects of a tree in order to prevent it from falling and injuring others. If risk can’t be eliminated, it should be mitigated so that acceptable level of risk is achieved.

Some state have “recreational user statutes” that may exempt a landowner from liability.


RISK AND LIABILITY

Degree of Care Owed to Classes of Visitors

• INVITEE: This is the highest standard imposed on landowners by law. A landowner must make reasonable inspections of the premises to discover dangerous conditions and repair or warn of such dangers.

• LICENSEE: The duty here is limited to acting with ordinary care and to warn of dangerous concealed conditions that the landowner knows about.

• TRESPASSER: This is the lowest duty of care owed by a landowner. The only duty here is to not intentionally harm or set traps; there is no duty to warn of hazards.


RISK AND LIABILITY

Basic Tree Biology

90-95% of a Tree’s Root System is located in the Top 3 Feet of Soil!

3 ft 1 ft

Even though the tree may be left standing (for now) major trauma to these roots will kill the tree!

Roots can grow to twice the height!


50% of a Tree’s Root System is located in the Top 1 Foot of Soil!!!!

These are mostly the absorbing roots that provide WATER and NUTRIENTS

Critical Root Zone (CRZ)

The CRZ is typically the minimum area required to maintain the tree’s health and structural integrity.

The CRZ encompasses all tree roots out to at least the drip line of a tree.


Basic Tree Biology

As a general rule, the Critical Root Zone should extend at least to the drip line of a tree.

If the CRZ cannot be protected…

Disturbance may come as close as 5X the diameter of the protected tree on ONLY ONE SIDE!!

5X…then protect the rest!!


Trees grow as if they are actually trees within a tree. Each year’s growth covers and surrounds the previous year’s tissue.

If a wound occurs, the tree responds by trying to wall off, or compartmentalize, the wounded area. The tissue from each new year of growth will cover the old wound and remain unaffected, as long as rot or decay does not move into the new tissue. If compartmentalization is effective, the new tissue remains healthy and the old wound is “walled off” or sealed behind the new tissue. (e.g., a hollow tree with sound wood around the hollow.)


Tree Wounding

A tree with structural defects likely to cause failure of all or part of the tree, which could strike a target.


Hazard Tree

Approaching the inspection:

Past history of the tree

Assess current health

Owners motives?

Litigation potential? 90% of all defects can be identified by a novice!!


Inspections

Performing the inspection:

Professional conduct

Use scientific methodology

Will a written report be required?

Will the report be a “note” on scrap paper or a five-page report with photos, etc.


Inspections

Hazard Tree Report Forms

There are several… Most are very detailed and require calculation of a “Hazard Rating” or Hazard Potential.


Inspections

Tree Risk AssessmentTree Risk Assessment

Hazard Tree Report Forms

There are several… Most are very detailed and require calculation of a “Hazard Rating”

Failure + Size + Target = Hazard Potential of part Rating Rating Each part of the formula is assigned a value of 1 through 4.

The total Hazard Rating can range from 3 to 12.


Inspections

Failure + Size + Target = Hazard Potential of part Rating Rating

1 = Low (Minor defects)

2 = Medium (Small to medium cavities within safe limits)

3 = High (Significant defects, serious stem decay)

4 = Severe (Cavity at or beyond safe limits, multiple defects, large dead branches or trees)



1 = <6” diameter

2 = 6-18” diameter

3 = 18-30” diameter

4 = >30” diameter



1 = Occasional Use (alley)

2 = Intermittent Use (side street)

3 = Frequent Use (main road)

4 = Constant Use (house)


What is the Hazard Tree Rating for this tree?


Tools of the Trade…..

Rubber mallet

Drill (standard or resistograph)

Increment borer

Binoculars

Ruler

Common sense


Inspections

Dead wood

Cracks

Weak branch unions

Decay

Cankers , conks , fruiting bodies

Root problems

Poor tree architecture (structural defects)


Hazard Types

NOT NEGOTIABLE!

Dead wood is unpredictable and should be removed as soon as possible.

Dead wood is brittle.

Dead Wood


A separation of the wood, a fissure or deep split in the bark and wood.


Cracks

HIGH FAILURE POTENTIAL

A crack goes completely through the stem or branch.

Stem has two cracks on the same segment with a cavity or extensive decay.

Stem has crack with another defect (lean, weak branch, etc.).

MODERATE FAILURE POTENTIAL

Hardwood stem has one crack that has inrolled bark and the internal cylinder of wood is gone or decayed.


Cracks

A fork in the stem or union of two or more main branches.

Co-dominant stems…

U-SHAPED V-SHAPED


Weak Branch Unions

HIGH FAILURE POTENTIAL

A weak branch union that is also cracked or decayed.

A weak union in a tree’s hot spot.


Weak Branch Unions

MODERATE FAILURE POTENTIAL

A weak union with included bark at the branch bark ridge


Weak Branch Unions

Wood that is rotted or missing (visible cavities).

Decay always results in less structural strength and stability.


Decay

Injury occurs.Fungi enters the wound and begins to discolor the wood as rot begins.

As years pass, the rot column grows in height, but is also covered by new layers of wood from each years new “ring” (tree in a tree).

The process continues.After many years of growth, the result is a visible trunk wound with an internal rot column behind it.


Decay

Internal Hollow

Exposed Cavity


If shell thickness is less than 1/3 of the stem radius, then the tree is unsafe.


An area of dead bark and cambium anywhere on the tree, often affecting the wood beneath it.


Cankers

Problems serious enough to warrant correction are partial windthrow (leaning with mounding, missing roots, and extensive root rot.

Problems may be hidden underground.


Root Problems

Check for fruiting bodies at the base of a tree that may indicate serious root rot.

This may be the end result!!


Root Problems

Soil Compaction

Grade Changes

Trenching and Excavating


Root Problems

No root flare (lack of taper)

Wilted/scorched leaves

Drooping branches

Early fall color

Premature leaf drop

Water/sucker sprouts

Flowing out of season

Abnormal die-back

Stunted annual growth


Construction damage results in:

Lack of taper

Splits

Scaffold branches with poor attachment


Poor Tree Architecture

TOPPING CREATES WOUNDS THAT LAST A LIFETIME!


Prevention and Correction (Mitigation)

FLUSH CUTS LAST A LIFETIME TOO!



MOWER DAMAGE



Consider fencing off hazard trees if removal is not a “popular” option.


Prevention and Correction(Mitigation)

Performing an INVENTORY of trees on property you manage can be the best preventive step you can take!!



Inventories can provide you with data about the number of hazard trees you have.

Maintenance Needs FrequencyPercent of Total Tree

Population

Corrective Prune 164 8%Crown Reduction High 20 1%Crown Restoration High 55 3%Crown Restoration Low 2 0%Crown Cleaning High 213 11%Crown Cleaning Low 23 1%Hazard Limb High 66 3%Hazard Limb Low 11 1%Hazard Tree 269 14%Raising/Lifting 260 13%Recommended Removal 112 6%Safety Prune Walk/Street 1 0%Safety Prune Utility 1 0%TOTAL 1197 61%



Hazard Tree Web Page: www.na.fs.fed.us/spfo/hazard/index.htm

Evaluation of Hazard Trees In Urban Areas is available through the International Society of Arboriculture at www.isa-arbor.com


Additional Sources of Information:

hazard trees isa cert revised 0308

Education

risk assessment

hollow tree

protected tree

risk managementrisk

liabilitybasic tree

risk managementtrees

risk management50

risk managementthe value