Chapter 12: Tree Assessment and Risk Management

Question 1

risk management

Answer 1

systematic application of management policies, procedures, and practices for identifying, evaluating, treating, monitoring, and communicating risk; goal of balancing risk levels against other factors such as available time and money

Question 2

risk assessment

Answer 2

process of evaluating what unexpected things could happen, how likely they are to happen, and what the likely outcomes are; in tree management, the systematic process to determine the level of risk posed by a tree, tree part, or group of trees; process of evaluating the likelihood that part or all of a tree will fail and cause damage and/or injury; identifies risk levels and recommends action

Question 3

What factors does tree risk assessment consider?

Answer 3

the potential for tree failure, the environment that may contribute to failure, and what would be damaged and/or injured - the target

Question 4

failure potential

Answer 4

in tree risk assessment, the professional assessment of the likelihood for a tree to fail within a defined period of time; likelihood that an entire tree or part of a tree will break a fall within a given time period

Question 5

What to consider when evaluating a tree’s failure potential?

Answer 5

species, growth habit, defects, quality of branch attachments, condition of the root system, lean, and the history of the tree and site

Question 6

load

Answer 6

general term used to indicate the magnitude of a force, bending moment, torque, pressure, etc. applied to a substance or material; or cargo, weight to be borne or conveyed

Question 7

When does failure occur?

Answer 7

when the load experienced exceeds the structural capacity of a tree or part of tree or due to environmental conditions, such as storms with winds, snow, ice loading, lightning, and rainfall

Question 8

What factors should be considered when assessing tree stability at a site?

Answer 8

1. ) construction, grade changes, and trenching within the root zone
2. ) removal of adjacent trees that previously served as a wind buffer
3. ) replacement of sidewalks and root loss (root pruning)
4. ) failure of nearby trees caused by root disease
5. ) change in wind dynamics due to new structures on the site

Question 9

target

Answer 9

a person, object, or structure that could be harmed (damaged or injured) by a tree or tree part in the event of a failure; location of target pruning; people and/or property that could be damaged or injured if the tree failed

Question 10

structural defects

Answer 10

any naturally occurring or secondary conditions such as cavities, poor branch attachments, cracks, or decayed wood in the trunk, crown, or roots of a tree that my contribute to structural failure

Question 11

What must you be familiar with to discern the difference between a minor defect and a significant weakness that could result in tree failure?

Answer 11

1. ) tree species and typical modes of failure
2. ) normal growth traits
3. ) structure and form
4. ) signs of decay

Question 12

tree health vs. tree structure

Answer 12

not the same thing; a few thin layers of active xylem or phloem can keep a tree alive but structural soundness requires more wood volume; green, full-crowned, and essentially healthy trees can still fail due to structural defects

Question 13

visual tree assessment

Answer 13

VTA; method of assessing the structural integrity of trees using external symptoms of mechanical stress (such as bulges, reactive growth, etc.) and defects (cracks, cavities, etc.); minimum standard for tree risk assessment observing conditions and characteristics 360 degrees around the tree

Question 14

Steps in VTA

Answer 14

1. ) look for dieback, gaps, or discoloration in the crown
2. ) take note of any lean
3. ) look for branches that extend beyond the rest of the crown
4. ) examine the trunk taper
5. ) inspect the trunk, the root collar, and the root zone

Question 15

reaction wood

Answer 15

wood formed in leaning or crooked stems or on lower or upper sides of branches as the means of counteracting the effects of gravity; supports the tree in a leaning position

Question 16

taper

Answer 16

change in diameter over the length of trunks, branches, and roots; a diameter that gradually decreases from the base to the tip; allows distribution of load such as the weight of the canopy and wind, along the length of the stem

Question 17

What trees tend to have bad taper?

Answer 17

trees growing in closely set stands of trees; trees growing in the open tend to have good taper; stem is more likely to break where the stress is greatest

Question 18

What general characteristics should be analyzed on individual parts of the tree for defects?

Answer 18

1. ) the trunk flare - look for visible flare with solid, well-developed roots exhibiting no decay; lack of a trunk flare, discolored or loose bark, wounds, seams, and indentations created by circling roots are all defect indicators
2. ) the trunk - look for wounds, cracks, decay, sloughing bark, codominant stems, and included bark
3. ) major branches attachments - branches should be smaller (50% or less) than the trunk in diameter and spaced vertically along the trunk

Question 19

codominant stems

Answer 19

forked stems nearly the same size in diameter, arising from a common junction and lacking a normal branch union

Question 20

included bark

Answer 20

bark that becomes embedded in a crotch (union) between branch and trunk or between codominant stems; causes a weak structure

Question 21

wood decay

Answer 21

a disease caused by certain fungi, which may or may not form conks or mushrooms

Question 22

conk

Answer 22

fruiting body or nonfruiting body (sterile conk) of a fungus; often associated with decay

Question 23

fruiting body

Answer 23

reproductive structure of a fungus; the presence of certain species may indicate decay in a tree

Question 24

bracket

Answer 24

British English term for the fruiting body of a decay fungus

Question 25

Types of fungal reproductive structures

Answer 25

conks, brackets, and mushrooms

Question 26

What do fungal reproductive structures on a tree indicate?

Answer 26

internal decay; however a tree can have decay without the presence of conks or mushrooms on the outside

Question 27

Types of fungal decay

Answer 27

white rot, brown rot, and soft rot; each characterized by the wood cellular and/or intercellular components that they remove

Question 28

white rot

Answer 28

fungal decay of wood in which both cellulose and lignin are broken down; primarily decay the lignin within and between the cell walls in the wood; reduces wood stiffness; decayed wood appears white after the darker-colored lignin is decayed

Question 29

Examples of white rot fungi?

Answer 29

Armillaria spp. and Ganoderma spp.

Question 30

brown rot

Answer 30

fungal wood rot characterized by the breakdown of cellulose; most common on conifer trees (less common on deciduous trees); primarily decays the cellulose leaving behind the stiff lignin, thereby reducing the bending strength of the tree; makes the wood brittle and the decayed wood is dry and crumbles easily; remaining lignin is dark or brown in color after the cellulose is decayed

Question 31

Examples of brown rot fungi?

Answer 31

Laetiporus and Phaeolus

Question 32

soft rot

Answer 32

decay of plant tissues characterized by the breakdown of tissues within the cell walls; first degrades the cellulose portion of the wood

Question 33

Example of soft rot fungi?

Answer 33

Kretzchmaria

Question 34

How do trees react to white rot?

Answer 34

adapt to the loss of wood strength by laying down more new wood around the decayed area, which compensates for the strength loss in the existing wood

Question 35

branch rot

Answer 35

branch decay located on large branches

Question 36

trunk rot

Answer 36

decay located in the upper trunk

Question 37

basal rot

Answer 37

decay of the lower trunk, trunk flare, or buttress roots; butt rot; decay at the base of the tree

Question 38

structural root decay

Answer 38

develops from the bottom upward; visible symptoms of this rot may or may not develop in the crown

Question 39

root rot

Answer 39

decay located in the roots

Question 40

heartwood rot

Answer 40

any of several types of fungal decay of tree heartwood, often beginning with infected wounds in the living portions of wood tissue; heart rot; decay that starts in the heartwood (center) of the tree

Question 41

sapwood rot

Answer 41

decay located in the sapwood; bark and/or cambium may be damaged or dead; signs of this classification of rot are usually numerous, but small, fruiting bodies along the bark's surface are common; decay progresses from the outside of the branch toward the center

Question 42

positive indicators of decay

Answer 42

means decay is present; presence of fruiting bodies (brackets, mushrooms, or conks) on the wood, open cavities, and visible decayed wood

Question 43

potential indicators of decay

Answer 43

symptoms or signs that decay may be present that that further investigation is warranted; cracks, seams, bulges, and wounds from old pruning cuts, especially topping cuts

Question 44

insects that indicate decay

Answer 44

carpenter ants are usually associated with decayed wood within the tree and bees will make hives in tree cavities

Question 45

birds that indicate decay

Answer 45

cavity-nesting birds will nest in hollows or dig out decayed wood to create a hollow

Question 46

What are trees fundamental strategies to react to decay?

Answer 46

compartmentalization - to contain the progress of decay; | growth - to outgrow it

Question 47

root collar excavation

Answer 47

process of removing soil to expose and assess the root collar (root crown) of a tree

Question 48

air excavation device

Answer 48

air excavator; devise that directs a jet of highly compressed air to excavate soil; used within the root zone of trees to avoid or minimize damage to the roots, or near underground structures such as pipes and wires to avoid or minimize damage to them

Question 49

aerial lift device

Answer 49

mobile elevated work platform; to inspect the upper crown, probe cavities, and look for cracks and defects not visible from the ground

Question 50

resonance testing

Answer 50

nondestructive means of determining the soundness or structural integrity of an object or material by determining the rate at which sound waves travel through it

Question 51

Ways to detect extent of decay?

Answer 51

resonance testing, sounding with a hard plastic or other suitable mallet, inserting a measuring stick or probe in a cavity; drilling and using sound/resistance and color, texture, and odor of extracted wood as an indicator

Question 52

cavity

Answer 52

open or closed hollow within a tree stem, usually associated with decay

Question 53

increment borer

Answer 53

device used to take core samples from trees to determine age or detect problems, such as decay; bore into trunk or root tissue and extract a core of wood for further examination

Question 54

decay detection devices

Answer 54

any device used to assess the presence (and often extent) of hidden internal decay

Question 55

resistance recording drills

Answer 55

small, rotating needle pushed into the wood to record the resistance to wood penetration along the drilling path (decayed wood is softer and generates less resistance)

Question 56

acoustic measurement devices

Answer 56

measure the time it takes for sound to travel between various points around the cross section of a tree; less invasive than drilling devises (sound waves pass through decayed wood slower than through sound wood)

Question 57

tomogram

Answer 57

image generated by tomography; created by sending waves through an object; a computer then produces images of cross sections of the object by using information about how the waves change; color-coded "picture" of the inside of the tree at that section showing areas of decayed and sound wood

Question 58

Types of decay-detecting equipment

Answer 58

resistance measuring devices, tomography, x-rays, and radar

Question 59

What kind of variables influence the stability of trees with decay?

Answer 59

tree and pathogen species; tree age and health; canopy architecture, height, and weight distribution; exposure to wind, snow and ice; wood strength and toughness; root structure; and soil conditions

Question 60

systematic procedure for assessment process

Answer 60

observations, measurements, and recommendations should be documented; good to include digital images as well; good to use an assessment form for consistency and thoroughness

Question 61

What should your assessment form include?

Answer 61

tree genus, species, and common name; size, location, and general description; surroundings and description of any potential targets; environment of the tree such as prevailing winds, microclimates, surrounding trees, and other plants; history of the tree including maintenance and management practices

Question 62

Who decides what level of risk is appropriate?

Answer 62

the property owner or manager

Question 63

mitigation

Answer 63

in tree risk management, reducing, alleviating, or minimizing risk or harm (damage or injury); process of reducing failure potential

Question 64

What is the primary recommendation that can reduce the likelihood of failure?

Answer 64

pruning to remove dead, broken, or high-risk branches or reduction pruning to even remove entire stems; other options are tree support systems, target removal, fencing off the area/posting signs

Question 65

What are good management practices to which trees with cavities may respond favorably and improve in condition?

Answer 65

ensuring good soil health, moisture, and aeration, and applying organic mulch; if the tree has good vitality it may maintain structural integrity by producing new wood around an injury so filling cavities or attempting to remove decay is not usually a good idea

Question 66

duty of care

Answer 66

legal obligation that requires an individual to use a reasonable standard of care when performing tasks that may potentially harm others; emphasizes the importance of documenting any potential hazards and risk levels discovered when assessing a tree, even if it is not for risk assessment

Question 67

liability

Answer 67

something for which one is responsible; legal responsibility

Question 68

negligence

Answer 68

failure to exercise due care; occurs when the arborist has the obligation or responsibility with regard to the tree (duty) and fails to act responsibly in providing the service (breach of duty) and injury or damage occurs (harm) because of the arborist's action(s) or lack of action (causality)

Question 69

breach of duty

Answer 69

the failure to act reasonably under the circumstances

Question 70

standard of care

Answer 70

degree of care that a reasonable person should exercise in performing duty of care; a measurement used to assess whether an individual acted in a reasonable manner; degree of care that a reasonably prudent person should exercise in the same or similar circumstances; determined by courts

Question 71

causation in fact

Answer 71

in determining legal liability, the test of the proximate cause and foreseeability of the consequences; damage, injury, and/or death can be traced back to the defendant's action (or lack of it)

Question 72

proximate cause

Answer 72

legal term that describes an act or omission that can be attributed as cause of loss and/or injury; injury was reasonably foreseeable

Question 73

act of God

Answer 73

an occurrence due to natural causes that could not have been prevented by ordinary skill and foresight; defense used when trees fell/broke and caused damage, but is not always accepted, especially if the failure is a result of human intervention