Field Guide for 

Danger Tree 

Identification and 

Response

United States

Department of

Agriculture

Forest Service

Pacific 

Northwest 

Region

United States

Department of

Interior

Bureau of

Land Management

Oregon 

OSHA

Associated Oregon

Loggers, Inc.
Inside Front Cover
1

Field Guide for Danger Tree 

Identification and Response

Richard Toupin

Regional Logging Engineer,

Gregory Filip

Regional Forest Pathologist,

Thomas Erkert

Transportation Group Leader

Pacific Northwest Region

USDA Forest Service

• Michael Barger

Logging Specialist

Salem District

USDI Bureau of Land Management

•

2008

Acknowledgements

We thank the following people who contributed to revising this guide: 

Diane Hildebrand, Donald Goheen, Craig Schmitt, Kristen Chadwick, Angel 

Saavedra, and Katrina Mallams.

Graphic Design: Michael Hamel (FS)

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, disability, and where applicable, sex, 

marital status, familial status, parental status, religion, sexual orientation, genetic information, 

political beliefs, reprisal, or because all or part of an individual’s income is derived from any 

public assistance program. (Not all prohibited bases apply to all programs.) Persons with 

disabilities who require alternative means for communication of program information (Braille, 

large print, audiotape, etc.) should contract USDA’s TARGET Center at 202-720-2600 (voice 

and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 

1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call 800-795-3272 

(voice) or 202-720-6382 (TDD). USDA is an equal opportunity provider and employer. 

R6-NR-FP-PR-01-08
2
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Table of Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Regulatory Basis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

 Employer Responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Qualified Person. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Conifer Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Douglas-fir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

True firs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Hemlocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Spruces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Larches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Pines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Cedars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Process for Tree Evaluation and Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Step 1 – Identify tree defects and determine the tree’s potential to fail. . . . . . . . . . . . . . . 11

 Low failure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Likely failure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Imminent failure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Wind or snow loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Step 2 – Determine the type of work activity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Activity - Traffic on roads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

 Activity – Non-motorized, non-tree contact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

 Activity – Motorized or tree contact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Step 3 - Determine the potential failure zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Total Tree Failure - Potential Failure Zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

 Tree Part Failure – Potential Failure Zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Step 4 – Determine if the tree poses a danger to people. . . . . . . . . . . . . . . . . . . . . . . . . 22

 Example 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

 Example 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 Example 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Step 5 – Action if tree is a danger to people. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Literature Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Appendix A Forest Service road maintenance levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Appendix B Defect and Disease Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Root and butt rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

• General symptoms and indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

• Laminated root rot caused by Phellinus weirii. . . . . . . . . . . . . . . . . . . . . . . . . . 35

• Armillaria root disease caused by Armillaria ostoyae. . . . . . . . . . . . . . . . . . . . . 36

• Annosus root disease caused by Heterobasidion annosum. . . . . . . . . . . . . . . 37

• Black stain root disease caused by Leptographium wageneri. . . . . . . . . . . . . . 37

• Tomentosus root rot caused by Inonotus tomentosus. . . . . . . . . . . . . . . . . . . . 38

• Schweinitzii root and butt rot caused by Phaeolus schweinitzii. . . . . . . . . . . . . 38

• Ganoderma butt rot caused by Ganoderma tsugae (the varnish conk) or 

 G. applanatum (the artist’s conk). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Heart and sap rot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

• General symptoms and indicators of heart rot. . . . . . . . . . . . . . . . . . . . . . . . . . 40

• Rust red stringy rot caused by Echinodontium tinctorium (Indian paint fungus) 41

• Red ring rot or white speck caused by Phellinus pini (ring-scale fungus). . . . . 41

• Brown trunk rot caused by Fomitopsis officinalis (quinine conk or the 

 chalky fungus).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

• Incense-cedar pecky rot caused by Oligiporus amarus. . . . . . . . . . . . . . . . . . . 43

• Hardwood trunk rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

• General symptoms and indicators of sap rots. . . . . . . . . . . . . . . . . . . . . . . . . . 44

Undermined or severed roots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Leaning, root-sprung, broken, or uprooted trees supported by other trees. . . . . . . . . . . 45

Cracks and structural defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Dead tops and large dead branches, detached tops, limbs, and loose bark. . . . . . . . . . 47

Forked or multiple tops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4

Dwarf-mistletoe brooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Fungal cankers, bole wounds, and mistletoe bole swellings. . . . . . . . . . . . . . . . . . . . . . 49

Fire damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Height-to-diameter ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Insect-caused damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Multiple defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Table 1 Important tree diseases and their chief hosts.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 2 General guidelines for danger tree indicators.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 3 Road treatment priority. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 4 Forest Service road maintenance levels.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Table 5 Indicators for SW & Central Oregon.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 6 Indicators for Eastern Washington.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Table 7 Indicators for Western Oregon & Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 8 Indicators for NE Oregon & SE Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 1 Total tree failure, no slope or lean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 2 Total tree failure, slope, lean.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 3 Tree part failure, no slope or lean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 4 Tree part failure, slope, lean.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 5 Crown decline from root disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 6 Basal resinosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 7 Armillaria root disease mushrooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 8 Windthrow & wind shatter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figure 9 Dead and dying trees caused by root disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figure 10 Bark beetles often attack trees stressed by root disease. . . . . . . . . . . . . . . . . . . . . 53

Figure 11 Laminated decay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 12 Windthrow of live infected trees, laminated root rot. . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 13 Armillaria mycelial fans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 14 Annosus root disease conks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Figure 15 Annosus root disease pustules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Figure 16 Annosus root disease windthrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Figure 17 Tomentosus caused windthrow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 18 Tomentosus root rot mushrooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 19 Brown cubical butt rot old conk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 20 Brown cubical butt rot fresh conk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Figure 21 Brown cubical butt rot butt swelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Figure 22 Conks are good heart rot indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Figure 23 Rust red stringy rot conks, Indian paint fungus. . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Figure 24 Red ring rot conk, Phellinus pini. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Figure 25 Red ring rot punk knot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Figure 26 Brown trunk rot quinine conk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 27 Incense cedar pecky rot conk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 28 Phellinus tremulae conk on decayed aspen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 29 Sap rot conks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 30 Red belt conk, Fomitopsis pinicola. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 31 New lean, soil cracking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 32 Corrected old lean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Figure 33 Crack from lightning strike. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Figure 34 Crack from wind damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Figure 35 Frost crack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 36 Dead top. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 37 Comandra rust killed top in pine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 38 Dwarf mistletoe brooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 39 Atropellis canker on lodgepole. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 40 Dwarf mistletoe bole swelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 41 Fir engraver galleries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Figure 42 Balsam woolly adelgid damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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Introduction

Tree stability is determined by its location and the presence 

of defects, insects, disease, work activities, and weather 

conditions. If a tree is unstable, it may fail either partially or 

totally. If a tree fails, it is a danger to anyone who may be 

struck by it.

Guidebook objectives:

• To provide information to employers and managers that 

will help keep workers and others safe from exposure to 

tree dangers.

• To provide information to qualified people that will enable 

them to do the following:

♦ Recognize tree conditions and determine tree failure 

potential.

♦ Determine a tree’s potential failure zone.

♦ Understand how a work activity could induce a tree to 

fail, given failure potentials based on its condition

♦ Determine if a tree presents a danger to people as a 

result of

◊ Condition and failure potential

◊ Work activity

◊ Exposure

◊ Whether or not the work activity is within the tree’s 

potential failure zone

In this guide, general tree identification is discussed. 

Common diseases and defects that cause trees to fail are 

presented, along with how to identify them. Potential failure 

zones are described. Possible activities around trees are 

grouped into three classifications according to how they may 

induce tree failure. There is a discussion on how to determine 

if the tree is a danger to people, including examples. Finally, 

there is a discussion of what to do if there is a danger.
6

In this guide, a danger tree or a hazard tree is any tree or 

its parts that will fail because of a defect, and cause injury or 

death to people.

These guidelines are intended for use with any forest activity, 

at any location, including roads through forested areas, and 

are based on native tree species in Oregon and Washington. 

They are not intended to be used in developed recreation 

sites, although many of the procedures were adapted from 

guidelines for developed recreation sites (1).

Regulatory Basis

Oregon and Washington, as well as the Federal Occupational 

Safety & Health Administration (OSHA), have administrative 

rules about danger trees. The Oregon rules are called 

Oregon Occupational Safety and Health Code Division 7 

Forest Activities and apply to all types of forest activities (2). 

For Washington, the rules are titled Safety Standards for 

Logging Operations Chapter 296- 54 WAC (3). The rules in 

both states apply to non-federal employers with employees 

operating on private or public land.

Federal OSHA regulations regarding requirements for 

protecting employees in the course of their work apply 

to federal agencies. The OSHA “General Duty” standard 

(29 CFR 960.8) requires agencies to, “...furnish to each 

employee employment and a place of employment which 

are free from recognized hazards that are causing or are 

likely to cause death or serious physical harm” (4). Trees 

with characteristics that indicate instability are considered 

recognized hazards. Federal agencies are required to identify 

trees that pose a danger to employees and establish means 

of protecting employees from that danger.

Federal OSHA rules regarding logging operations (29 CFR 

1910.266) address specific means of protecting employees 

who are working in logging activities (5). They apply to 

federal employees.
7

The health and safety of Forest Service employees is 

addressed by the Health and Safety Code Handbook (6). 

Section 21.14 focuses on the identification of dangers to 

employees. It discusses the correction of dangers and what 

to do if they cannot be corrected.

The Bureau of Land Management addresses the health and 

safety of employees in BLM Manual 2-1, Safety and Health 

Management; and Handbook 2-2, Safety and Health for Field 

Operations (7, 8).

Chapter 2 of the BLM Manual 2-1, Safety and Health 

Management, describes the risk and management process 

that provides management with a systematic method for 

identifying and managing the risks associated with any BLM 

operation. Chapter 5 further discusses workplace and hazard 

assessments (7).

BLM handbook 2-2, Safety and Health for Field Operations, 

reviews the risk management process (29.1), and also 

provides additional information regarding the hazards of 

field activities (3.1). It also outlines prevention and mitigation 

methods (10.2). Section 23.3 specifically discusses the 

potential hazards of forestry activities. Safety and health 

requirements for contractor employees (field work) are 

discussed in section 20 (8).

The Region 6 Danger Tree Roadside Policy in the Forest 

Service Manual FSM 7700 – Transportation System, Chapter 

30 – Operations and Maintenance, contains regulations about 

danger-tree identification and mitigation specific to USDA 

Forest Service roads in Oregon and Washington. 

These rules contain language about danger trees. They are 

the overriding authority on the topic and should be referred 

to for a full understanding of the rules and standards.This 

document, titled Field Guide for Danger Tree Identification 

and Response 2008, is designed to implement the applicable 

rules. It does not replace the rules or standards.
8

Responsibilities

Employer Responsibilities

The employer has the responsibility to identify and mitigate 

dangers to workers from danger trees.

The Oregon Division 7 Forest Activities Standards requires 

an evaluation by employers of any tree or snag (dead tree) 

within reach of a work area to determine if it poses a danger 

to personnel. If a tree or snag poses a danger, it must be 

felled, or the work arranged to minimize danger to workers 

(2).

The Washington rule 296-54-507 (7), defines management’s 

responsibility. Danger trees within reach of landings, roads, 

rigging, buildings or work areas shall be either felled before 

regular operations begin, or work arranged so that employees 

are not exposed to dangers involved (3).

Before work starts, and as often as necessary, a qualified 

person must evaluate danger trees within reach of a work 

area to determine if they pose a danger to personnel. If they 

pose a danger they must be felled, or the work must be 

arranged to minimize danger to workers.

Qualified Person

When an employer or manager is faced with danger trees, 

there should be people available with sufficient knowledge, 

training and experience, to follow a process for dealing with 

them.

A qualified person is defined as a person who has 

knowledge, training, and experience in identifying danger 

trees, their potential failure zones, and measures to eliminate 

the danger.
9

Conifer Identification

When assessing danger trees, it is important to be able to 

identify tree species. Diseases and defects that result in tree 

failure are more serious in certain tree species. The following 

is a brief description of the major native conifer species 

groups in Oregon and Washington forests.

Douglas-fir

Needles are about 1 in. long with a blunt tip and spirally 

arranged around the twig, but may be two-ranked in the 

shade. They are green above with two white bands beneath. 

Cones are 3-4 in. long with pitch and have forked bracts that 

are longer than the scales. The cones hang down from the 

twig. The bark has resin blisters when young, but is deeply 

furrowed and reddish-brown when old. Older inner bark is a 

mottled brown and yellow color similar to bacon.

True firs

Needles are 1-2 in. long and either spirally arranged or flat 

on the twig. Cones are 2-9 in. long and are perched upright 

on the twig. Bark when young has resin blisters. Older bark is 

gray to brown, and when cut, the older inner bark is purple in 

color.

Hemlocks

Needles are less than 1 in. long and in groups that appear to 

be either star-like or tend to stick out of the sides of the twig. 

Terminal branch tips have a natural bend. Cones hang down, 

are 1-3 in. long, and are cylindrical or egg-shaped. Bark is 

gray to brown with either narrow or flattened ridges.

Spruces

Needles are 1 in. long and sharp to touch. Cones are 1-4 in. 

long, hang down, and have thin scales with jagged edges. 

Bark is thin, gray-brown, and scaly.
10

Larches

Needles are 1-2 in. long on woody pegs in clusters of 20-40. 

They fall off in the winter. Cones are 1-2 in. long with papery 

bracts that are longer than the scales. Bark is reddish-orange 

and flakes off in irregularly shaped pieces.

Pines

Needles are 1-10 in. long and are in bundles of 2, 3, or 5 

needles. Cones are 1-20 in. long with thick scales. Bark is 

gray to reddish brown and either furrowed or scaly.

Cedars

Needles are scale-like and flat on the twig. Cones are 1⁄2 to 1 

in. long and are either round or long and thin. Bark is stringy 

or flaky and gray to brown.

Table 1 Important tree diseases and their chief hosts.

Douglas 

fir

True 

fir Hemlock Spruce Pine Larch Cedar Hardwoods

Resinous X X X X

Root & Butt Rots

Laminated X X X X

Armillaria X X X X X X

Annosus X X X X X

Schweinitzii X X X X

Tomentosus X

Black stain X X

Ganoderma X X X X X X X

Heart Rots

Rust-red stringy X X

Red ring X X X X X X

Brown trunk X X X X

Cedar pecky X

Sap rot X X X X X X X

Dwarf mistletoe X X X X X

Fungal cankers X X X X
11

Process for Tree Evaluation and

Action

These are the steps the qualified person should take when 

dealing with potential danger trees:

1. Identify tree defects and determine the tree’s 

potential to fail.

2. Determine the type of work activity.

3. Determine the potential failure zones.

4. Determine if the tree poses a danger to people and 

document the assessment.

5. Determine what action to take if the tree is a danger 

to people.

Step 1 – Identify tree defects and determine the tree’s 

potential to fail

There are three levels of failure potential: low, likely, and 

imminent.

Low failure potential

Defective or rotten trees, snags, or their parts, have a low 

failure potential if they require considerable effort to make 

then fail during project implementation. They have a low 

probability of failure within 10 years of rating.

Likely failure potential

Defective or rotten trees, snags, or their parts, have a likely 

failure potential if they require some effort to make then 

fail during project implementation. They will have a high 

probability of failure within 3-5 years of rating.

Imminent failure potential

Defective or rotten trees, snags, or their parts, have an 

imminent failure potential if they require little effort to make 

then fail during project implementation. They will have a high 

probability of failure within one year of rating.
12

Failure potential is a function of tree condition. Trees with 

likely or imminent failure potentials may be classed as danger 

trees depending on the work activity, and whether the work 

activity is within the tree’s potential failure zone. In order to 

define the potential failure zones, it is necessary to determine

which tree part is likely to fail: entire tree, tree top, branches, 

or bark.

Trees with the following conditions may have either a low, 

likely, or imminent potential to fail. For example, some dead 

tops, dead trees, and fire-damaged or killed trees may be 

less stable than others. Trees with these conditions require 

an evaluation to determine which class to place them in. The 

following are general guidelines for danger-tree indicators. 

Refer to Appendix B for danger tree indicators that are 

specific for each geographic area in Oregon and Washington. 

Table 2 General guidelines for danger tree indicators.

Failure

Indicator

Failure Potential (FP)

Imminent Likely Low

Old dead trees

>5 years

All species except 

cedar or larch

Cedar or larch None

Recent dead 

trees < 5 yrs 

None if no other 

indicators are present

All species except 

cedar or larch

Cedar or larch

Recent dead 

trees in root 

disease pockets 

Trees in laminated root 

rot or annosus root 

disease pockets

Trees in other root 

disease pockets 

Cedar

Live trees in root 

disease pockets

Trees with fading 

crowns and adjacent to 

live windthrown trees 

with root decay

Healthy appearing 

trees with adjacent 

windthrown liveinfected trees of the 

same species; trees 

with fading crowns with 

no windthrown trees 

present

Trees with fading 

crowns and black stain 

root disease

Butt rot Trees with ≥1 basal 

conks and extensive 

decay

Trees with ≥1 basal 

conks and moderate 

decay

None

Bole wounds, 

mistletoe 

cankers, or 

fungal cankers

True fir, hemlock, 

spruce, or hardwoods 

with < 50% crosssection of bole with 

sound wood; pine, 

cedar, larch, or Dougfir with <25% crosssection of bole with 

sound wood

True fir, hemlock, 

spruce or hardwoods 

with 50-75% crosssection of bole with 

sound wood; pine, 

cedar, larch, or Doug-fir 

with 25 to 50% crosssection of bole with 

sound wood

True fir, hemlock, 

spruce or hardwoods 

with >75% crosssection of bole with 

sound wood; pine, 

cedar, larch, or Dougfir with >50% crosssection of bole with 

sound wood

Leaning and/or 

root-sprung trees

Trees with recent (<5yr) 

lean (>15°) or old 

uncorrected lean with 

cracked or mounded 

soil or root damage

Trees with recent lean 

or old uncorrected lean 

without cracked or 

mounded soil or root 

damage

Trees with old corrected 

lean
13

Failure

Indicator

Failure Potential (FP)

Imminent Likely Low

Undermined or 

severed root 

systems

Trees with <50% 

of structural roots 

remaining in the ground

Trees with 50-75% 

of structural roots 

remaining in the ground

Trees with >75% 

of structural roots 

remaining in the ground

Fire-damaged 

trees

Boles with <50% 

cross-section with 

sound wood or more 

than 1 quadrant (1/4 

of the circumference) 

of damaged structural 

roots.

Boles with 50-75% 

cross-section with 

sound wood or one 

quadrant of damaged 

structural roots except 

cedar, larch, ponderosa 

pine, or sugar pine 

which are low FP

Cedar, larch, ponderosa 

pine, or sugar pine with 

>50% cross-section of 

bole with sound wood; 

other species with 

>75% cross-section of 

bole with sound wood

Dead tops 

or dead large 

branches (>5 in. 

dia.)

True fir, hemlock 

or hardwoods with 

significant decay (bark 

absent or conks), top or 

branch is imminent FP, 

not the whole tree

True fir, hemlock or 

hardwoods with little 

or no decay; Doug-fir, 

spruce, or pine tops 

not rust-killed, with 

significant decay.

Cedar, larch, or rustkilled tops on pine

Dwarf-mistletoe 

brooms

None Trees with dead 

brooms ≥10 ft in 

diameter (broom is 

likely FP, not the whole 

tree)

Trees with live brooms; 

dead brooms <10 ft in 

diameter

Bole conks See area tables in 

Appendix B, tables 5 - 8

Trees with ≥1 conks 

except larch or cedar

Larch or cedar with ≥1 

conks

Black 

cottonwood 

branches 

None Live, large branches on 

mature trees if previous 

breakage is apparent

Live, large branches 

without previous 

breakage in the tree 

Forked or 

multiple tops

None Tops with embedded 

bark, cracks, conks, or 

decay (top is likely FP, 

not the whole tree)

Tops without embedded 

bark, cracks, conks, or 

decay; U-shaped tops

Frost cracks None Trees with weeping, 

gaping cracks or are 

associated with ≥1 

conks

Trees with tight cracks 

and no conks

Bole damage or 

cracks

Trees with bole cracks 

showing movement and 

decay

Trees with bole cracks 

without movement or 

decay

Trees with tight cracks, 

not open 

Detached tops, 

limbs, or loose 

bark

All species (parts are 

imminent FP, not the 

whole tree)

None None

Broken or 

uprooted trees 

supported by 

other trees

Trees or parts that are 

not held securely

Trees or parts that are 

held securely

None

Height-diameter 

ratio (H:D)

Trees with >100 H:D Trees with 80-100 H:D Trees with <80 H:D

Balsam woolly 

adelgid

None Infested subalpine fir 

with ≤10% live crown

Infested subalpine fir 

with >10% live crown

Multiple 

indicators

Two or more likely 

FP indicators that 

combine to increase 

FP to imminent (i.e. live 

spruce with recent lean 

without soil damage but 

bole conks are present)

Two or more low FP 

indicators that combine 

to increase FP to likely 

(i.e. live but fire-damaged 

fir with 85% cross-section 

of bole with sound wood 

but with an old corrected 

lean)

Two or more low FP 

indicators that do not 

combine to increase 

FP to likely (i.e. pine 

with 85% of structural 

roots remaining and live 

mistletoe branches)
14

Wind or snow loading

Wind or snow loading may increase the chances that a tree 

with decay or defect will fail. It is prudent to assume that as 

wind or snow loading increases, the potential for a tree to fail 

also increases.

Step 2 – Determine the type of work activity

No worker exposure in the potential failure zone of danger 

tree is allowed by state safety laws.

There are three categories of work activities.

• Traffic on roads.

• Activities that do not impact the tree such as walking or 

conducting non-motorized activities that do not involve 

tree contact.

• Motorized activities near the tree or activities that may 

cause the tree to be contacted.

Road traffic may or may not influence tree failure. This 

category is included because trees may fail and fall on 

vehicles or people congregated along roads, or they may fail 

and fall on roads and be driven into at a later time.

Walking by a tree or other non-motorized, non-tree contact 

activities are not likely to induce the tree to fail. The tree may 

fail due to either its condition or weather influences. Activities 

involving non-motorized, non-tree contact include planting 

and surveys.

Motorized activities or non-motorized activities that may 

contact the tree include road maintenance activities such as 

running a grader, culvert work, road construction, logging 

including timber falling, site preparation, road reconstruction, 

trail construction, and helicopter operations. All of these 

activities may induce tree failure.
15

Activity - Traffic on roads

Oregon OSHA Division 7, 437-007-0500 Roads (6). On those 

portions of roads under the direct control of the employer: (a) 

all danger trees that can fall or slide onto the roadways must 

be felled (2)

Washington 296-54-527 Truck roads (3) safe roadways. The 

following applies to roads under the control of the employer. 

All danger trees shall be felled a safe distance back from the 

roadway (3)

There are many miles of roads that may have danger trees 

adjacent to them. It is not possible to correct the dangertree problem immediately, so it is necessary to prioritize the 

danger tree treatment workload. The treatment priority should 

be highest where people are most likely to be impacted by 

danger trees. Consideration of exposure level and traffic 

frequency provides a way to prioritize the workload.

There are three types of exposure: intermittent, short 

duration, and long duration. Intermittent exposure includes 

traffic driving by a defective tree. Short duration exposure 

includes people either stopping next to a defective tree, or 

stopping at an intersection that is next to a defective tree for 

up to 15 minutes. Long duration exposure includes people 

exposed to defective trees while parked at a trailhead, 

repairing a road, or working on a log landing.

Another aspect of exposure along roads is traffic frequency. 

Roads that have a higher traffic frequency expose more 

people to a danger tree than roads with a lower traffic 

frequency.

The longer people are exposed to a tree, the more 

opportunity there is for the failed tree to impact them. If 

exposure duration and traffic frequency are reduced, the 

opportunity for the tree to impact people is also reduced. 

The qualified person should consider traffic frequency and 

exposure duration when determining whether a tree posses a 

danger to people.
16

Table 3 Road treatment priority

Road Exposure 

Duration

Failure 

Potential

Road 

Segment 

Priority

Priority 

Within 

Road

Areas where people stop and 

congregate such as interior roads of 

developed recreation sites, parking 

areas, active projects/contracts along 

the road where work is stationary such 

as culvert replacement and bridge 

construction.

Intersections along operational 

maintenance level 3-5 roads, scenic 

vistas, geologic points of interest, 

where people are encouraged to stop. 

Refer to Appendix A for a description of 

maintenance levels.

Areas along roads with higher 

traffic volumes such as operational 

maintenance level 3-5 roads not within 

intersections. Limited sight distance 

areas should be evaluated closely, as 

trees that have failed and are in the 

traveled way in these areas may be a 

surprise to drivers.

Haul routes

Long

Short

Intermittent 

but high

frequency

Imminent High

Highest

Lowest

Areas where people stop and 

congregate such as interior roads of 

developed recreation sites, parking 

areas, active projects/contracts along 

the road where work is stationary such 

as culvert replacement and bridge 

construction.

Intersections along operational 

maintenance level 3-5 roads, scenic 

vistas, geologic points of interest, where 

people are encouraged to stop.

Areas along roads with higher 

traffic volumes such as operational 

maintenance level 3-5 roads not within 

intersections. Limited sight distance 

areas should be evaluated closely, as 

trees that have failed and are in the 

traveled way in these areas may be a 

surprise to drivers.

Haul routes

Long

Short

Intermittent

but high

frequency

Likely Medium

Highest

Lowest

Areas with low traffic volumes such as 

operational maintenance level 2 roads.

All Imminent 

or likely

Low

For specific direction, refer to policy about danger trees along

roads. When developing the road treatment priority, consider 

trees in the following situations. 
17

Activity – Non-motorized, non-tree contact 

These are activities that involve walking near trees without 

touching them. They are also non-motorized. The premise 

behind this activity type is that trees are less likely to fail 

if they are not contacted, and workers are more likely to 

recognize tree dangers if they are not focused on operating 

vehicles or machinery. Examples include tree planting, 

inventory (any type), surveying, walking to a jobsite along a 

trail, and designating timber.

With this type of activity, it is important to recognize trees 

that have an imminent failure potential. These trees may fail 

at any time so they are a danger to people regardless of the 

activity type. Because these trees expose people to dangers, 

only qualified employees under the direct supervision of the 

employer should enter the tree’s potential failure zone.

There will also be trees that have a likely potential to fail. 

In order to determine if the tree is a danger to people, the 

qualified person needs to evaluate the tree condition, activity, 

and whether or not the person will be within the potential 

failure zone. If the qualified person determines that the likely

failure potential tree does not represent a danger, people 

should work through the potential failure zone quickly so as 

to minimize exposure time and avoid tree contact. If the tree 

does represent a danger, it should be removed or the work 

activity should be excluded from within the potential failure 

zone. 

Activity – Motorized or tree contact

Motorized activities, or those activities that may contact the 

tree, include road construction, logging, timber falling, tree 

climbing, site preparation, trail construction, and helicopter 

operations. The premise behind this activity type is that 

vibration due to machine operation, air movement in the case 

of a helicopter, or tree contact by a person, machine, log, or 

operating line may induce tree failure. As a result of noise or 

worker focus on the job task, the person might not recognize 

the danger or notice the failure beginning to take place, and 

miss the opportunity to escape.
18

Step 3 - Determine the potential failure zone

The potential failure zone is the area that could be reached 

by any part of a failed tree.When a tree fails, the tree or its 

parts may strike other trees and cause them to fail as well. 

The parts may slide or roll. When a tree is being felled, it may 

strike other trees or debris on the ground and fling material a 

considerable distance. This is especially true in dead timber. 

The qualified person needs to be aware of these situations 

when determining the potential failure zones.

Total Tree Failure - Potential Failure Zone

The failure zone is 

defined as the area on 

the ground that could 

be reached by any 

portion of the tree that 

may collapse. When 

determining the failure 

zone, the following 

conditions must be 

evaluated:

• Ground slope.

• Direction of lean.

• Height of the tree.

Figure 1.

Total tree 

failure, no 

slope, no lean.
19

 Level or sloped ground; no discernible lean

The failure zone is a circle around the tree with a radius of at 

least 11⁄2 times the total tree height. On sloped ground, the 

failure zone downhill of the tree may have to be extended 

whatever distance is necessary to protect people.

 Level or sloped ground; lean in any direction

The failure zone is an area at least 11⁄2 times the tree height 

beginning at the tree base then extending towards the 

direction of the lean and out 90 degrees on either side of the 

tree from the lean direction.

The area behind the lean is not within the failure zone. Be 

aware that if equipment, lines, moving logs, or falling timber 

contacts a likely or imminent failure potential tree, the contact 

could force a backlash opposite to the lean, and create 

an additional danger during the time of impact beyond the 

potential failure zone.

On sloped 

ground 

where the 

dislodged 

section 

may roll 

downhill, 

the potential 

failure zone 

must be 

extended 

on the 

downhill 

side for 

whatever 

distance is 

necessary 

to protect 

people.

Figure 2.

Total tree 

failure, slope, 

lean.
20

Tree Part Failure – Potential Failure Zone

The area on-the-ground that could be reached by a dislodged 

top, branch, slab, or chunk is called the potential failure zone 

for a part failure. When determining the zone, evaluate the 

following conditions:

• Ground slope.

• Amount and 

direction of lean.

• Length of the part 

that could dislodge.

 Level or sloped 

ground; no 

discernable lean

Determine the length 

of the part that could 

dislodge. The failure 

zone forms a circle 

around the tree with a 

radius equal to at least 

11⁄2 times the length of 

the dislodged part. On 

sloped ground where 

the dislodged part may 

slide or roll down hill, 

the failure zone must be 

extended on the downhill side for whatever 

distance is necessary to 

protect people.

Figure 3. 

Top failure, 

no slope, 

no lean.
21

 Level or sloped ground; lean in any direction

Determine the length of the part that could dislodge. 

Determine the amount of lean (horizontal distance from 

where the part could dislodge relative to the base). The 

failure zone is the distance determined by adding 11⁄2 times 

the length of the dislodged part to the lean amount. This 

distance would be applied to an area beginning at the tree 

base then extending towards the direction of the lean and out 

90 degrees on either side of the tree from the lean direction.

The area behind the lean is not within the failure zone. Be 

aware, however, that if equipment, lines, moving logs, or 

falling timber contacts a likely or imminent failure potential 

tree, the contact could force a backlash opposite to the lean 

and create an additional danger during the time of impact 

beyond the potential failure zone. On sloped ground where 

the dislodged part may slide or roll downhill, the potential 

failure zone is extended on the downhill side for whatever 

distance is necessary to protect people.

Figure 4.

Top failure, 

slope, lean.
22

Step 4 – Determine if the tree poses a danger to people

Not all trees with a likely or imminent potential to fail will be 

danger trees. For instance, if the work activity is outside of 

the potential failure zone, the tree is not a danger tree. If 

the work activity is mechanized, the tree has a likely failure 

potential, and the work is within the failure potential zone, the 

tree could be considered a danger tree. The following should 

be considered when determining if a tree poses a danger to 

people:

• Evaluate the tree and determine its condition and failure 

potential.

• Determine if the activity is likely to cause the tree to fail.

• Identify the potential failure zone and if the work activity is 

within the failure zone.

• Make a judgment about whether or not the tree is a 

danger to people and document the assessment.

• If the tree is a danger, remove the danger by taking the 

tree down, or arrange the activity so that people are not in 

the potential failure zone.

The following three examples illustrate the process a qualified 

person should follow when evaluating trees:

Example 1

Part 1. Assume there is a skyline logging operation. You 

as the qualified person notice that behind the landing, the 

standing trees look abnormally faded. There is a history of 

dying trees in the area combined with some live trees with 

sparse crowns. There is some basal resin and bark staining 

on them. There has been some windthrow. When you chop 

at the root collar and pull the bark away, you discover white 

latex-like mycelial fans. 

You conclude that the trees have Armillaria root disease and 

have a likely failure potential. Next, you determine that the 

landing is within the potential failure zone of the trees. The 

activity is motorized, and while it is not likely that anything 
23

will strike the trees, wind and vibration may induce them 

to fail. You recognize that the landing crew will be within 

the potential failure zone of the trees for a long time. Your 

conclusion is that the trees pose a danger to workers and 

need to be felled or the landing moved.

Part 2. Assume there is a tree planting operation in the unit 

logged near the landing previously discussed. You, as the 

qualified person, notice that around the unit boundary, many 

of the standing trees look abnormally faded. You don’t notice 

any windthrow. There are mushrooms around the base of 

several of the trees. There is some basal resin and bark 

staining on them. When you chop at the root collar and pull 

the bark away you discover white latex-like mycelial fans.

You conclude that the trees have Armillaria root disease 

and have a likely potential to fail. Next, you determine that 

the planting job site is within the potential failure zone of the 

root diseased trees. The activity is tree planting, and it is not 

likely that anything will strike the trees and cause them to fail. 

Your conclusion is that the Armillaria root diseased trees do 

not pose a danger to workers, so the area around them can 

be planted. You require that the planting crew work rapidly 

through the area and avoid the area on a windy day.

Example 2

Assume that you are evaluating trees along a haul-route 

road. You notice two very similar white fir trees in two 

locations. These trees have one Indian paint fungus conk on 

the bole. You conclude the trees have some heart rot and 

have a likely potential for failure. One tree is on the far side 

of a curve at the bottom of a long steep grade. The other is 

along a straight stretch of road. Exposure will be intermittent. 

Next, you determine the potential failure zone and realize that 

the portion of the road traveled is within the potential failure 

zone. You think that when the trees fail they may not actually 

hit any traffic, but that traffic may run into them, especially the 

one on the curve.

You conclude that the trees pose a danger to people and 

need to be taken down.
24

Example 3

You are evaluating a tree-planting job. The unit being planted 

has many dead trees and a few large live trees left. You 

notice that the bark looks loose on most of the dead trees. 

One of the green trees has a recent lean, and you suspect it 

is root sprung since there is evidence of recent soil cracking 

at the base. You also notice that there are some dead trees 

that are hung up in some other trees. On the other side of the 

unit, there are a few live trees standing straight with heart-rot 

conks on the bole.

You conclude that the leaning root sprung trees, the trees 

that are hung up, and the trees with the loose bark have 

an imminent potential to fail. Because these trees have an 

imminent failure potential, and their potential failure zones 

include the area to be planted, you conclude that the trees 

are a danger to employees. The areas cannot be safely 

planted without removing the danger by taking the trees 

down.

The straight green trees with heart rot are different. While 

they have a likely potential for failure, the exposure under 

them will be short duration, and the activity is not likely to 

cause the trees to fail since there will be no vibration or tree 

contact. You decide to let a crew plant under them if they 

move through rapidly and do not linger under the trees.

Step 5 – Action if tree is a danger to people

As a qualified person, when you examine trees, it is important 

to record your work because you might be expected to justify 

your results.

People are not to be exposed to danger trees. If after 

considering the tree condition and activity, and recording your 

observations, it is determined that the tree poses a danger to 

people, the tree either needs to be taken down or the work 

arranged so that people are not exposed to the danger.
25

Literature Cited

1. Harvey, R. D. Jr., and P. F. Hessburg Sr. 1992. LongRange Planning for Developed Sites in the Pacific 

Northwest: The Context of Hazard Tree Management. 

USDA Forest Service, Pacific Northwest Region, 

FPMTP039-92, Portland, OR. 120p.

2. Oregon OSHA. Division 7 Forest Activities 2003. 437-

007-0225( ).

3. Washington Safety Standards for Logging Operations 

997. Chapter 296-54-WAC.

4. 29 CFR 960.8 General Duty Clause.

5. 1910 OSHA Guide. Federal OSHA 1995. 9 0.266 Logging 

Operations.

6. Health and Safety Code Handbook 1999. Forest Service. 

FSH 6709. . WO Amendment 6709 -99- .

7. BLM Manual 2-1, Safety and Health Management.

8. BLM Handbook 2-2, Safety and Health for Field 

Operations.

9. Goheen, E.M., and E.A. Willhite 2006. Field guide to 

the common diseases and insect pests of Oregon and 

Washington conifers. USDA Forest Service, Pacific 

Northwest Region, R6-NR-FID-PR-01-06, Portland, OR. 

325p.

Citation example: (9, Pg 15) means page 15 in Goheen and 

Willhite.
26

Appendix A Forest Service road maintenance levels

Table 4 Forest Service road maintenance levels.

Maintenance Level

Parameters 1 2 3 4 5

Traffic type Open for nonmotorized uses. 

Closed to vehicles 

licensed to be on 

the public road 

system.

Administrative, 

permitted dispersed 

recreation, 

specialized 

commercial haul. 

Maintained for high 

clearance vehicles.

All National Forest 

traffic, general use, 

commercial haul, 

maintained for 

passenger cars.

Appendix B Defect and Disease Identification

It is important to be able to identify diseases and defects that 

affect tree stability. Detailed information about disease and 

defect identification in Oregon and Washington forests can be 

found in the Field guide to the common diseases and insect 

pests of Oregon and Washington conifers by Goheen and 

Willhite (9).

Tree condition and visible indicators often determine failure 

potential. There are several factors that should be included in 

that evaluation. Following are tables of significant indicators 

specific to different areas in Oregon and Washington.
27

Table 5 Indicators for SW & Central Oregon.

Failure Indicator Imminent Likely Low

Old dead trees All species but cedar 

and larch

Cedar and larch None

Recent dead trees

(<5 years)

None All species except 

cedar and larch 

Cedar and larch

Recent dead host 

trees in root-disease 

pockets

Laminated root rot or 

annosus root disease 

pockets 

Other kinds of root 

disease pockets 

Resistant or immune 

tree species in root 

disease pockets

Live host trees 

in root-disease 

pockets

Symptomatic with 

adjacent windthrown 

infected trees

Non-symptomatic 

trees with adjacent 

windthrown 

infected trees, and 

symptomatic trees 

without windthrown 

trees 

Immune or resistant 

tree species in 

pockets; nonsymptomatic hosts 

with no adjacent 

windthrow

Butt rot Schweinitzii or 

Tomentosus conks 

and extensive decay

Schweinitzii or 

Tomentosus conks 

and moderate decay

Little or no butt rot

Bole wounds, 

mistletoe cankers, 

or fungal cankers

Hemlock, true fir, or 

hardwoods with <50% 

cross-section of bole 

with sound wood

Hemlock, true fir, or 

hardwoods with 50 to 

75% cross-section of 

bole with sound wood; 

Douglas-fir, pines, 

larch, cedar, or spruce 

with <50%.

Hemlock, true fir or 

hardwoods with >75% 

bole cross-section with 

sound wood; Douglasfir, pine, larch, or cedar 

with >50% 

Leaning and/or rootsprung trees Recent (<5yr) 

lean (>15o

) or old 

uncorrected lean with 

disturbed soil or root 

damage

Recent lean or old 

uncorrected lean 

without disturbed soil 

or root damage.

Corrected old lean 

Undermined or 

severed roots 

<50% of the structural 

roots remaining in the 

ground. 

50 to 75% of the 

structural roots 

remaining in the 

ground

>75% of structural 

roots remaining in 

ground

Fire-damaged trees Any tree species with 

<50% cross-section 

with sound wood in 

bole or more than one 

quadrant of damaged 

structural roots 

50 to 75% crosssection of bole with 

sound wood, or one 

quadrant of damaged 

structural roots except 

cedar, ponderosa pine, 

sugar pine, and larch

Cedar, ponderosa 

pine, sugar pine, and 

larch with >50% and 

other species with 

>75% of bole crosssection sound 

Dead tops or large 

dead branches (≥5” 

diameter)

True fir, hemlock, 

or hardwoods with 

significant decay

True fir, hemlock or 

hardwoods with little 

decay; Douglas-fir, 

spruce, or pine with 

substantial decay 

Cedar, larch or 

Douglas-fir, and pine 

tops killed slowly by 

rust that show little 

evidence of decay

Dead Douglas-fir 

mistletoe brooms

None Douglas-fir with large, 

dead brooms ≥10ft 

diameter.

Douglas-fir with dead 

brooms <10ft diameter 

Quinine conks Trees with ≥ 1 conks None None
28

Failure Indicator Imminent Likely Low

Other conks ≥1 conk and extensive 

decay based on tree 

species and type and 

extent of rot

True fir, hemlock, or 

hardwoods with ≥1 

conk and little decay 

evident; Douglas-fir, 

pine, spruce, cedar, or 

larch with ≥5 conks; ≥1 

conks ≥8 in. diameter

Douglas-fir, pine, 

spruce, cedar, or 

larch with <5 conks; 

true firs, hemlocks, 

or hardwoods with no 

conks

Black cottonwood 

branches 

Live or dead branches 

with evidence of 

substantial decay

Live, large branches 

on mature trees with 

evidence of breakage

Live branches without 

decay or breakage

Forked or multiple 

tops 

None Tops with embedded 

bark, cracks, decay, 

or conks

U-shaped forks - no 

embedded bark, 

cracks, decay, or 

conks

Frost cracks None Gaping, weeping 

cracks or ≥1 conks 

associated with crack 

Cracks tight with 

no sign of decay or 

weeping

Bole damage or 

cracks

Damage, or cracks 

with independent 

movement and/or 

substantial decay

Damage or cracks 

without movement or 

with moderate decay.

Damage or cracks with 

insignificant decay or 

no decay; callus has 

formed

Detached tops, 

limbs, or loose bark

All species None None

Broken or uprooted 

trees supported by 

other trees

Trees not held 

securely; failure 

potential determined 

by type of support. 

Trees held securely; 

failure potential 

determined by amount 

and type of support.

Trees not broken or 

uprooted

Height:diameter 

ratio (H:D) 

>100% H:D ratio 80-100% H:D ratio <80% H:D ratio

Multiple Indicators Two or more likely FP 

indicators if synergistic 

effects 

Multiple FP indicators 

if no synergistic effects 

Lacks multiple 

indicators
29

Table 6 Indicators for Eastern Washington.

Failure Indicator Imminent FP Likely FP

Old dead trees All species with evidence of 

obvious decay except cedar, 

larch, or fire-killed subalpine fir 

or spruce

Cedar, larch, or fire-killed 

subalpine fir or spruce

Recent dead trees

(<5 years)

None All species except cedar or larch 

Recent dead or live 

trees in root-disease 

pockets

Symptomatic trees in any root 

disease pocket with adjacent live 

windthrown trees with root disease

Symptomatic trees in any root 

disease pocket without live 

windthrown trees with root disease

Butt rot None Trees with Schweinitzii conks and 

decay with sound-rind thickness 

≤15% of bole dia; >15% would be 

low FP; spruce with Tomentosus 

conks and decay

Bole wounds, 

mistletoe cankers, or 

fungal cankers

None Hemlock, true fir, or hardwoods 

with 50-75% cross-section of bole 

with sound wood

Leaning and/or rootsprung trees Trees with recent (<5yr) lean 

(>15o

) or old uncorrected lean with 

cracked or mounded soil and/or 

root damage

Trees with recent lean or old 

uncorrected lean without cracked 

or mounded soil or root damage.

Undermined or 

severed roots

Trees with <50% of the structural 

roots remaining in the ground. 

Trees with 50 to 75% of the 

structural roots remaining in the 

ground

Fire-damaged trees Boles with <50% cross-section 

with sound wood or more than 

one quadrant of damaged 

structural roots

Boles with 50 to 66% crosssection with sound wood, or one 

quadrant of damaged structural 

roots

Dead tops or large 

dead branches (≥5” 

dia)

None True fir, hemlock, hardwoods, 

or ponderosa pine without rust 

disease (top or branch is likely FP, 

not the whole tree)

Dwarf mistletoe 

brooms

None None (low FP)

Quinine conks None Trees with ≥1 conks

Red ring rot (white 

speck) conks

None Douglas-fir, pine, spruce, cedar, or 

larch with ≥5 conks separated by 

≥15 ft; ≥1 conks ≥4 in. diam.

Other conks None True fir, hemlock, or hardwoods 

with ≥1 conks

Black cottonwood 

branches 

None Live, large branches on mature 

trees if previous breakage is 

apparent 

Forked or multiple 

tops 

None Tops with embedded bark, cracks, 

decay, or conks (top is likely FP, 

not the whole tree)

Frost cracks None Trees with gaping, weeping cracks 

or are associated with ≥1 conks
30

Failure Indicator Imminent FP Likely FP

Bole damage or 

cracks

Trees with substantial damage, 

including cracks with independent 

movement and decay

Trees with damage/cracks without 

movement or significant decay.

Detached tops, limbs, 

or loose bark

All species (parts are imminent 

FP, not the whole tree)

None

Broken or uprooted 

trees supported by 

other trees

Trees or parts that are not held 

securely; failure potential is 

determined by amount and type 

of support. 

Trees or parts that are held 

securely; failure potential is 

determined by amount and type 

of support.

Height:diameter ratio Trees with >100% H:D ratio Trees with 80-100% H:D ratio

Balsam woolly 

adelgid

None Infested subalpine fir with ≤10% 

live crown 

Multiple Indicators Two or more likely FP indicators 

that combine to increase FP to 

Imminent

Two or more low FP indicators 

that combine to increase FP to 

Likely
31

Table 7 Indicators for Western Oregon & Washington

Failure Indicator Imminent FP Likely FP

Old dead trees All species except cedar or larch Cedar or larch

Recent dead trees 

(<5 years)

None All species except cedar or larch 

Recent dead trees in 

root-disease pockets

Dead trees within 30 ft of live 

windthrown trees with decayed 

roots

All species

Live trees in rootdisease pocketsTrees with fading crowns within 

30ft. of live windthrown trees with 

decayed roots

Trees with fading crowns in any 

root rot pocket except black stain 

which has low FP until death; 

non-symptomatic trees within 30ft.

of live windthrown trees of same 

species with decayed roots

Butt rot Trees with basal conks and bole 

cracks

Trees with Schweinitzii or 

Tomentosus conks and evidence 

of decay (swollen butt)

Bole wounds, 

mistletoe cankers, or 

fungal cankers

Hemlock, true fir, or hardwoods 

with <50% cross-section of bole 

with sound wood; Douglas-fir, 

pines, larch, cedar, or spruce with 

<25% cross-section of bole with 

sound wood

Hemlock, true fir, or hardwoods 

with 50 to 75% cross-sectional 

area of sound stem wood; 

Douglas-fir, pines, larch, cedar, 

or spruce with 25 to 50% crosssection of bole with sound wood

Leaning and/or rootsprung trees Trees with recent (<5yr) lean 

(>15o

) or old uncorrected lean with 

cracked or mounded soil and/or 

root damage

Trees with recent lean or old 

uncorrected leans without cracked 

or mounded soil or root damage.

Undermined or 

severed root systems

Trees with <50% of the structural 

roots remaining in the ground. 

Trees with 50 to 75% of the 

structural roots remaining in the 

ground

Fire-damaged trees Boles with <50% cross-section 

with sound wood or more than 

one quadrant of damaged 

structural roots

Boles with 50 to 75% crosssection with sound wood, or one 

quadrant of damaged structural 

roots except cedar, ponderosa 

pine, sugar pine, and larch which 

are Low FP

Dead tops or large 

dead branches (≥5 

in. dia.)

Dead with conks and significant 

decay (top or branch is imminent 

FP, not the whole tree)

Recently dead true fir, hemlock 

or hardwoods; older Douglasfir, spruce, or pine without rust 

disease 

Dwarf mistletoe 

brooms

None Douglas-fir with large, dead 

brooms (broom is likely FP, not the 

whole tree) 

Quinine conks None Trees with one or more conks

Other conks None True fir, hemlock, or hardwoods 

with ≥1 conks; Douglas-fir, pine, 

spruce, cedar, or larch with ≥5 

conks

Black cottonwood 

branches 

None Live, very large branches where 

previous breakage is apparent
32

Failure Indicator Imminent FP Likely FP

Forked or multiple 

tops 

None Multiple tops in true firs, hemlock, 

or hardwoods; any species with 

tight V-forks and embedded bark 

≥3 ft long or cracks (top is likely 

FP, not the whole tree)

Frost cracks None Trees with gaping, weeping cracks 

or cracks are associated with ≥1 

conks 

Bole damage or 

cracks

Trees with bole cracks showing 

movement 

Trees with damage/cracks without 

movement or significant decay.

Detached tops, limbs, 

or loose bark

All species (parts are imminent 

FP, not the whole tree)

None

Broken or uprooted 

trees supported by 

other trees

Trees or parts that are not held 

securely; failure potential is 

determined by amount and type 

of support 

Trees or parts that are held 

securely; failure potential is 

determined by amount and type 

of support

Height:diameter ratio 

(H:D)

None Trees with >100% H:D ratio 

Balsam woolly 

adelgid

None Infested subalpine fir with ≤10% 

live crown 

Multiple Indicators Two or more likely FP indicators 

that combine to increase FP to 

imminent

Two or more low FP indicators 

that combine to increase FP to 

likely
33

Table 8 Indicators for NE Oregon & SE Washington

Failure Indicator Imminent FP Likely FP

Dead Trees PP<16”≥5y; ≥16”≥10y; WL≥20y; 

DF; LP≥5y; GF,SAF,ES, 

hardwoods≥3yr

PP<16”<5y; ≥16”<10y; WL 

5-19y; LP, DF<5y; GF,SAF,ES, 

hardwoods<3yr

Recent dead trees in 

root disease pockets

DF, GF, or SAF in laminated root 

rot pockets; host trees in any 

root rot pocket with adjacent 

windthrown live trees with root 

disease

Host trees in any root disease 

pockets other than laminated root 

rot without adjacent windthrown 

live trees with root disease

Live trees in root 

disease pockets

DF, GF in laminated root rot 

pockets

GF, SAF in annosus root rot 

pockets; both with crown/root 

collar symptoms/ and adjacent live 

windthown trees with root disease

Host trees in any root disease 

pocket without crown or root collar 

symptoms but with adjacent live 

windthrow trees with root disease

Butt rot DF, WL with Schweinitzii conks 

and extensive decay; ES with 

Tomentosus with extensive butt 

rot associated with any indicators

DF, WL with Schweinitzii conks 

and moderate decay; ES with 

Tomentosus with moderate butt 

rot associated with any indicators

Bole wounds, 

mistletoe cankers, or 

fungal cankers

GF, SAF, spruce, hardwoods with 

<50% cross-section of bole with 

sound wood; DF, pines, or WL 

with <25% cross-section of bole 

with sound wood.

GF, SAF, spruce, hardwoods with 

50 to 75% cross-sectional area of 

sound stem wood; DF, pines, or 

WL with 25-50% cross-section of 

bole with sound wood.

Leaning and/or rootsprung trees Trees with recent (<5y) lean 

(>15o

), or old uncorrected lean 

with cracked or mounded soil and/

or root damage

Trees with recent lean or old 

uncorrected lean without cracked 

or mounded soil or root damage.

Undermined or 

severed root systems

Trees with <50% of the structural 

roots remaining in the ground

Trees with 50 to 75% of the 

structural roots remaining in the 

ground.

Fire-damaged trees Boles with <50% cross-section 

with sound wood, or more than 

one quadrant of damaged 

structural roots.

Boles with 50 to 75% crosssection with sound wood, or one 

quadrant of damaged structural 

roots except PP and WL, which 

are Low FP

Dead tops or large 

dead branches (≥5 

in. dia)

True firs or hardwoods with 

significant decay (top or branch 

is imminent FP, not the whole tree)

True firs or hardwoods with no 

decay or minor decay. Also DF, 

ES, or pines with tops not rustkilled 

Dwarf mistletoe 

brooms

None PP or DF with large, dead brooms 

≥10ft dia. (broom is likely FP, not 

the whole tree)

Quinine conks Trees with ≥1conks None

Indian paint fungus 

conks

Trees with large single or smaller 

multiple conks and at least one 

additional indicator of associated 

defect with indications of 

extensive decay

Trees with large single or smaller 

multiple conks without additional 

indicators. Tight dry frost cracks 

are not indicators.

Red ring rot (white 

speck) conks

None DF, pines, ES, or WL with 5 or 

more red ring rot (white speck) 

conks
34

The following is a discussion of each disease, defect, 

and failure indicator:

Root and butt rots

Root and butt rots also called root diseases may cause 

a tree to fail if disturbed. Sites with root and butt rots will 

have danger-tree problems for decades unless treated, 

because these diseases remain on the site for long periods 

and spread slowly among root systems. There are several 

important root and butt rots: laminated root rot, Armillaria 

root disease, annosus root disease, black stain root disease, 

tomentosus root rot, Schweinitzii root and butt rot, and 

Ganoderma butt rot.

Failure Indicator Imminent FP Likely FP

Saprot (pouch) conks Dead trees with >15% decayed 

rind; pouch conks & Indian paint 

conks on recent dead GF

Trees with conks on one or more 

panels associated with beetle strip 

attacks

Hardwood conks None Hardwoods with any conks or 

evidence of ganoderma root rot

Black cottonwood 

branches

None Live, large branches on mature 

trees if previous breakage is 

apparent

Forked or multiple 

tops 

None Tops with embedded bark, cracks, 

decay, or conks (top is likely FP, 

not the whole tree)

GF with frost cracks 

(no conks)

None Fir with gaping, weeping cracks 

without Indian paint or other conks 

Bole damage or 

cracks

Trees with substantial damage, 

including open cracks with 

independent. movement and 

decay

Trees with damage/cracks without 

movement or significant decay.

Detached tops, limbs, 

or loose bark

All species (parts are imminent 

FP, not the whole tree)

None

Broken or uprooted 

trees supported by 

other trees

Trees or parts that are not held 

securely; FP is determined by 

amount and type of support. 

Trees or parts that are held 

securely; FP is determined by 

amount and type of support.

Height:diameter ratio 

(H:D)

Trees with >100% H:D ratio Trees with 80 to 100% H:D ratio

Balsam woolly 

adelgid

None Infested subalpine fir with ≤10% 

live crown

Multiple Indicators Two or more likely FP indicators 

that combine to increase FP to 

Imminent 

Two or more low FP indicators 

that combine to increase FP to 

Likely

PP=ponderosa pine, LP=lodgepole pine, DF=Douglas-fir, GF=grand fir; 

SAF=subalpine fir, WL=western larch; ES=Engelmann spruce, FP=Failure

potential
35

• General symptoms and indicators

♦ Decline of the entire live crown is characterized by 

fading foliage, dying branches, premature shedding of 

older needles, and terminal and lateral shoot-growth 

reduction (Figure 5).

♦ Distress cone crops sometimes are present.

♦ Butt rot occurs often without crown symptoms.

♦ Basal resin flow and bark staining may be present 

(Figure 6). 

♦ Mushrooms or conks often occur on the roots or at the 

root collar of infected trees (Figure 7).

♦ Windthrow or wind shatter of surrounding trees may 

be present (Figure 8).

♦ Groups or pockets of trees are affected usually with 

dead and dying trees of various sizes and levels of 

decay on the site (Figure 9). 

♦ Bark beetles attack trees stressed by root disease 

(Figure 10).

♦ The incidence of root and butt rots generally increases 

with the number of harvest entries.

• Laminated root rot caused by Phellinus weirii

♦ Laminated root rot is the most dangerous root disease 

regarding tree failure.

♦ The disease can readily affect even the healthiest 

trees in the stand and often causes green trees to fail 

due to extensively decayed root systems.

♦ Primary hosts are Douglas-fir, white and grand fir, and 

mountain hemlock.

♦ It is distinguished from the other root diseases by the 

presence of red setal hyphae in the decayed wood or 

in mycelium that look like tiny reddish whiskers when 

viewed with a hand lens.

♦ Decayed wood is laminated with pitting on both sides 

of the laminations (Figure 11).
36

♦ Mycelium on the surface of infected roots called 

ectotrophic mycelium can be found on live and 

recently killed trees.

♦ Conks are difficult to find and occur infrequently on the 

undersides of infected roots or logs.

♦ Live infected trees are frequently windthrown with 

exposed decayed roots (Figure 12).

♦ Root disease pockets can be small to several acres in 

size characterized by abundant windthrow with almost 

no roots (root balls).

♦ Trees adjacent to an infection center may not show 

symptoms of infection making them difficult to rate for 

failure potential.

♦ Symptoms may not occur until much of the root 

system is colonized and dead. 

♦ Trees at the edges of pockets are often infected 

without symptoms. 

• Armillaria root disease caused by Armillaria ostoyae

♦ Armillaria root disease affects many tree species. 

However, it is found primarily on weakened and 

stressed true firs and Douglas-fir.

♦ Root decay may be extensive; trees with this root 

disease should not be considered wind firm whether 

they are live or dead. 

♦ Unlike laminated root rot, Armillaria-killed trees most 

often die standing (Figure 9).

♦ Trees adjacent to an infection center may not show 

symptoms of infection.

♦ Infected trees may have copius resin flow or resin 

soaking of the butt (Figure 6).

♦ White latex-like mycelial fans are found under the bark 

in infected roots and at the root collar (Figure 13).

♦ Rhizomorphs or fungal “shoestrings” resemble 

small black roots but instead are packed with white 

mycelium.
37

♦ Honey-colored mushrooms may be found at the base 

of infected trees in the fall (Figure 7). 

♦ Advanced decay is yellow, stringy, and water soaked.

• Annosus root disease caused by Heterobasidion 

annosum

♦ Annosus root disease is especially dangerous in grand 

fir and white fir.

♦ It is the one of the most difficult root diseases to 

identify.

♦ Infected trees may exhibit symptoms of root disease or 

they may not have symptoms if the decay is confined 

to the butt and lower bole (common in hemlock and 

spruce).

♦ Conks may be found above ground in old stumps or 

in root crotches of living trees, or below ground on 

portions of roots in the duff layer or upper reaches of 

the soil (Figure 14). 

♦ Conks may appear as small pustules on roots (Figure 

15).

♦ Butt decay predisposes trees to windthrow and 

breakage (Figure 16).

♦ Incipient decay is a light-brown to reddish stain in the 

outer heartwood.

♦ Advanced decay is white and stringy to laminated. 

Elongated pits occur only on one side of the 

laminations with no setal hyphae.

• Black stain root disease caused by Leptographium 

wageneri

♦ Black stain root disease causes a vascular wilt and not 

decay. 

♦ Trees die standing and rarely fail until after they die. 

♦ Characteristic sign is a brown to purplish-black stain in 

older sapwood that fades in dead trees.
38

♦ Black stain kills all ages of pine on the eastside and 

young Douglas-fir on the westside. 

♦ Black stain is often associated with soil disturbance 

along roads and with soil compaction.

♦ The disease is spread by root grafts and by root 

feeding insects that are attracted to stressed trees. 

• Tomentosus root rot caused by Inonotus tomentosus

♦ Tomentosus root rot is most commonly found in 

Engelmann spruce (Figure 17).

♦ It typically does not cause extensive damage but is 

locally important in the Cascades and Blue Mountains.

♦ This disease may be completely hidden in trees which 

still have extensive butt rot.

♦ Trees with crown symptoms are not common, making 

the disease difficult to detect.

♦ Mushrooms are small, cinnamon-colored, leathery, 

and may appear in the fall near the base of defective 

trees (Figure 18). 

♦ When infected trees are mature, they are more likely 

to be severely rotted in the roots and butt.

♦ Advanced decay is a white pocket rot.

• Schweinitzii root and butt rot caused by Phaeolus 

schweinitzii

♦ Schweinitzii root and butt rot affects many tree 

species. However, it is found primarily on large old 

Douglas fir. 

♦ The fungus is also called the velvet-top fungus or the 

cow-pie fungus because of its distinctive conks 

(Figure 19)

♦ Fresh fruiting bodies are velvety to the touch and have 

a brightly colored yellow margin but die, turn brown, 

and last for about two years (Figure 20). 
39

♦ Trees with butt rot may have fruiting bodies growing on 

or near the butt.

♦ On the westside of the Cascade Range, significant 

butt decay is indicated by a large fruiting body or 

swollen butts. 

♦ Elsewhere, the disease may be as common, but it 

is often present without indicators, especially on dry 

sites. It is discovered less often until significant wind 

events and tree failure have occurred.

♦ While conks may be absent, trees with extensive 

decay may have pronounced butt swell (Figure 21).

♦ Decay of the butt extending as much as 30 feet occurs 

when trees are >150 years old.

♦ Trees with extensive butt rot often fail under high wind 

conditions leaving a characteristic barber chair and 

shattered butt.

♦ Once trees with fruiting bodies have been identified, 

or butt swell recognized, those susceptible trees 

immediately adjacent to them also should be 

evaluated. 

♦ Tree mortality is unusual unless associated with 

Armillaria root disease.

• Ganoderma butt rot caused by Ganoderma tsugae (the 

varnish conk) or G. applanatum (the artist’s conk)

♦ Ganoderma butt rot affects many conifer and 

hardwood species but is more common in hardwoods.

♦ It occurs in wounded live trees and dead or broken 

trees.

♦ The artist’s conk has a dark upper surface and a white 

underside that stains brown when marked.

♦ The varnish conk has a shiny brown upper surface, 

white underside, and often with a stem or stalk.

♦ The decay associated with both conks is a white 

spongy rot with black flecks.
40

Heart and sap rot

Heart and sap rots also known as stem decays may 

compromise bole integrity leading to tree failure

• General symptoms and indicators of heart rot

♦ Old injuries to a tree may have resulted in internal 

decay. 

♦ Larger wounds, wounds that are in contact with the 

ground, and older wounds are associated with a 

greater amount of decay.

♦ Resinous tree species are less prone to decay than 

non-resinous species (see Table 1).

♦ Heart rots are most abundant in mature and old 

growth trees, regardless of their size.

♦ Some defect may be hidden or inaccessible to the 

qualified person. 

♦ Trees with wounds opening to the outside have a 

much greater potential for failure than trees having 

equivalent rinds of sound wood but no open wounds.

♦ Heart rot fungi generally need an opening to the 

heartwood to invade the host. Entry points can be old 

wounds, branch stubs, or fire scars. 

♦ When heart rot is extensive within the bole of a tree, 

it may be indicated by conks, punk knots, or other 

indicators (Figure 22).

♦ Cavity excavation by woodpeckers may indicate heart 

rot in the tree.

♦ The presence of carpenter ant or termite activity can 

indicate heart rot, especially in wounded trees.

♦ Heart rots will sometimes be present when there are 

few or no external indicators making identification 

difficult.

♦ Trees with split boles or open or bleeding frost cracks 

are likely to have extensive decay.
41

There are several important heart rots in Oregon and 

Washington: rust red stringy rot, red ring rot, brown trunk rot, 

incense cedar pecky rot, and hardwood trunk rots.

• Rust red stringy rot caused by Echinodontium tinctorium 

(Indian paint fungus)

♦ This is the most damaging heart rot of mature true firs 

and hemlocks.

♦ Trees with a single conk have as much as 40 feet of 

continuous decay.

♦ When decay is advanced, large, hoof-shaped conks 

with a spiny lower surface are produced (Figure 23). 

♦ Conks have a fissured upper surface, and they are 

rough, dull black, hard and woody.

♦ The interior of the conk and the point of attachment to 

the tree or branch stub are rusty red to bright orange 

red.

♦ Conks appear on the bole at the site of old branches 

and stubs. 

♦ Conks with bleeding frost cracks or open cracks 

indicate extensive decay.

♦ Decay is a rust red stringy rot that may result in nearly 

hollow stems.

• Red ring rot or white speck caused by Phellinus pini 

(ring-scale fungus)

♦ This is the most common heart rot of Pacific Northwest 

conifers affecting Douglas-fir, pines, larch, hemlocks, 

true firs, and spruce.

♦ Conks are hoof-shaped with cinnamon-brown to tan 

pore surfaces. Pores are irregular rather than round, 

and the interior of the conk has the same cinnamon 

brown coloration as the pore surface. 

♦ Conks form at branch stubs or over old knots. Several 

conks in close proximity or numerous conks indicate 

significant decay (Figure 24). 
42

♦ Punk knots are common on severely decayed trees 

(Figure 25). They are evidence that a conk is about to 

form at an old branch stub, or that a conk was once 

present at the site but has since fallen off. Punk knots 

and conks indicate the same amount of decay.

♦ Unlike other rots, wood decayed by this fungus 

maintains some strength against failure.

♦ When trees have many large conks, damage to the 

heartwood is extensive and tree failure is likely. 

♦ With few or single conks, affected trees may have 

adequate strength to withstand high wind forces, and 

tree failure is unlikely.

♦ Large conks indicate more decay; smaller conks 

usually indicate less decay, unless the apparent small 

conks are remnants of larger conks that have fallen 

off. 

♦ Decay is a white pocket rot that is in rings separated 

by sound wood until decay is advanced.

♦ On hemlocks especially, but occasionally on other 

species, conks may be abundant on the undersides of 

branches (limb conk and butterfly conk).

• Brown trunk rot caused by Fomitopsis officinalis (quinine 

conk or the chalky fungus).

♦ Several conifer species are affected, and damage is 

severe stem decay.

♦ The fungus enters through trunk wounds or basal fire 

scars.

♦ Conks are rare but unmistakable. They are hard, 

perennial, hoof shaped to pendulous, and often quite 

large (Figure 26).

♦ Conks have a chalky white to grayish upper surface. 

Pores are round and the under surface of the conk is 

chalky white.

♦ The interior of most conks is soft and crumbly.

♦ Conks develop at branch stubs, over old wounds, or at 

old top breaks.
43

♦ Punk knots may occur at large, older branch stubs that 

have usually rotted and fallen off. Punk knots are often 

seen weeping a yellowish-brown material that stains 

the bark.

♦ A single conk indicates severe stem decay.

♦ Decay is a dry brown-cubical rot with thick white 

mycelial sheets in the decay shrinkage cracks.

• Incense-cedar pecky rot caused by Oligiporus amarus

♦ This heart rot is very common in mature incensecedar, especially trees greater than 40 inches dbh, 

and trees with basal wounds or old dead limbs.

♦ Tree failure is not common even with advanced decay.

♦ Decay is not limited to the butt log; it may occur along 

the entire merchantable length of the bole.

♦ In severely damaged trees, most of the heartwood is 

decayed. 

♦ Conks are common , and incense cedar maintains low 

failure potential unless there are other indications of 

extensive decay. 

♦ Conks are annual and fruit at knots in summer or 

autumn.

♦ Conks are hoof shaped to half bell shaped, tan to buff 

colored on the upper surface, bright sulfur yellow on 

the underside with small tubes that exude clear drops 

of a yellow liquid (Figure 27).

♦ Insects, birds, and squirrels destroy conks, leaving a 

shot-hole cup that is apparent at and below the knot 

where a conk was attached.

♦ Large open knots or open branch stubs indicate decay.

♦ Woodpecker activity indicates old conk locations and 

decayed trees.

• Hardwood trunk rots

♦ Several heart rots affect hardwoods, the most common 

being caused by Phellinus igniarius, Phellinus 
44

tremulae, and Ganoderma applanatum (the artist’s 

conk). Also causes butt rot. See Ganderma butt rot. 

♦ Conks of Ganoderma applanatum are perennial, 

leathery to woody, and might have a stalk. 

♦ The upper surface is smooth with pronounced 

grooves, dull and often dusty, and gray-brown to dark 

brown. 

♦ The conk undersurface is white, creamy, or light brown 

when fresh and turns brown when bruised.

♦ Conks of Phellinus igniarius or tremulae are hoofshaped, gray to black on top with conspicuous cracks 

when old (Figure 28).

• General symptoms and indicators of sap rots

♦ Sap rots are defects unique to the sapwood.

♦ Most sap-rotting fungi cause rapid decay of dead 

sapwood only.

♦ When these fungi have fully decayed all the available 

dead sapwood, they have completed their job.

♦ Sap rotting fungi compete poorly with other fungi that 

decay heartwood, and they are seldom found past the 

heartwood/sapwood interface.

♦ Sap rots can completely decay tree tops that are often 

all sapwood.

♦ In living trees, sap rots occur on tissue killed by other 

agents, usually bark beetles, mechanical damage, or 

weather damage.

♦ On dead trees, especially those killed by root 

diseases, fire, and/or bark beetles, sap rot is sure to 

occur, and the rate of sapwood decay can be rapid.

♦ On some true firs and often hemlocks, sapwood is fully 

rotted within 2 years.

♦ On other conifers, it may take as many as 3 to 5 years 

for sap rotting fungi to decay all of the available dead 

sapwood.
45

♦ A common sap rotting fungus is the pouch fungus 

(Cryptoporus volvatus). When its many little white or 

gray conks appear completely around the stem, the 

sapwood is fully rotted (Figure 29).

♦ Spores of the pouch fungus are spread by all major 

species of tree-killing bark beetles.

♦ Another common sap rot is caused by the red belt 

conk (Fomitopsis pinicola) (Figure 30). This is the 

most common decay fungus of dead wood and slash 

in Oregon and Washington. 

♦ Hardwoods also have sap rot, and damage may be 

significant on live trees. As with conifers, sap rotting of 

hardwoods can occur in dead portions of living trees.

♦ On many poplars, maples, and alders, sapwood is 

decayed very rapidly once it is dead, and there may be 

few obvious external indicators.

Undermined or severed roots

A compromised root system makes a tree more likely to fall.

• Root disturbance is often seen as undermined or severed 

roots.

• Undermined roots are often associated with roads or are 

adjacent to streams or rivers.

• The result of extreme undermining is tree failure from 

insufficient anchorage.

• Loosened, cracked, broken or severed roots predispose 

trees to failure in the event of high winds.

• High winds, saturated soils, and soil disturbances often 

lead to loosening, cracking, or breaking of roots.

Leaning, root-sprung, broken, or uprooted trees 

supported by other trees

• Root sprung trees are likely to fall because the roots are 

compromised by being partially pulled out of the ground. 

• Root sprung trees are dangerous and are seen as failures 

in progress.
46

• Trees with recent leans (<5 years) may have soil and litter 

not in contact with the base of the tree on the side away 

from the lean resulting in a conspicuous gap (Figure 31). 

• Recent lean may indicate rooting problems that may 

cause the tree to fall. 

• Cracks, mounds, or ridges of recently heaved soil may be 

adjacent to major lateral roots of leaning trees.

• Leaning trees should be examined for evidence of root 

and butt rot.

• Tree leans are recent, old, corrected, or uncorrected. 

• Recently leaning trees are tilted over their entire length 

(uncorrected lean). Since there is no evidence of 

subsequent reinforcement of the root system, trees with 

recent leans with soil lifting and cracking often fail.

• Corrected leaning trees are those that are leaned over but 

have subsequently grown a vertical top in the time since 

the lean occurred. Over time, these trees develop tension 

and compression wood at stress points to aid in their 

support. They also often develop a reinforced root system 

(Figure 32). 

• Live or dead broken or uprooted trees supported by other 

trees have a failure potential that is determined by their 

amount of support.

Cracks and structural defects

• Cracks and structural defects in the main stem may cause 

a tree or its parts to fail.

• Dangerous cracks show movement of the wood on either 

side of the crack.

• Open cracks may be associated with substantial decay.

• Cracks and defects with significant decay are more likely 

to fail.

• Cracks form by tension and compression failure when 

trees with extensive heart rot bend back and forth under 

the stress of high winds. The result is a vertical crack in 

the bole between the ground and where the heart rot is 

greatest.
47

• Cracks may be formed by lightning strikes (Figure 33). 

Damage from lightning can be highly variable, ranging 

from shallow spiraling furrows that just penetrate the bark, 

to cracks that may be several inches wide and penetrate 

deep into the wood. 

• Under the influence of frequent high winds, trees often 

develop shake or separations in the lowest section of 

the butt (Figure 34). The twisting action of the wind first 

causes separations to develop along the growth rings.

• Frost cracks are formed by the action of extreme cold 

(Figures 35). Frost cracks, appear on bark as raised 

nearly vertical callus lines which extend to the ground 

where frosty air is coldest. These cracks begin at the tree 

base, usually from an old wound, and seldom go higher 

than 5 feet up the bole.

• Healed frost cracks that are not weeping, seldom result in 

tree failure. 

Dead tops and large dead branches, detached tops, 

limbs, and loose bark 

• Dead tops can result from insect attack, dwarf mistletoe, 

or rust fungi.

• Dead tops and large branches (≥5 in. large-end diameter) 

with evidence of decay may break apart and fail (Figure 

36).

• Dead tops and branches of cedar or larch rarely fail.

• Pine tops and branches killed by rust fungi such as white 

pine blister rust or comandra rust have extensive resin 

soaking, are very decay resistant, and do not often fail 

(Figure 37).

• Dead tops and branches killed by insects differ from rustkilled tops and branches because they are killed all at 

once rather than progressively, contain sap rot fungi, and 

are more likely to decay and fail than rust-killed tops or 

branches.

• Dead tops and branches of Douglas-fir, spruce, larch, or 

pine are resinous and more resistant to failure.
48

• Dead tops and branches of true firs, hemlock, or 

hardwoods are non-resinous, are highly susceptible to 

attack by decay fungi, and are more likely to fail than 

other tree species.

• Dead tops without bark are more likely to fail than newly 

killed tops.

• Detached tops, limbs, or loose bark often fall and are 

extremely dangerous. 

• Live, large branches on mature cottonwoods can fail 

especially if previous breakage has occurred.

Forked or multiple tops

• Live trees with forked tops or multiple (candelabra) tops 

can fail at the base of the top.

• Forked tops with crotches that are tightly V-shaped can 

split and break from the green weight of foliage, heavy 

snow loads, wind, or internal decay.

• This also occurs in hardwoods with large, spreading 

crowns.

• Trees with deformed tops should be examined for cracks, 

splits, embedded bark, and callus ridges that indicate 

weakening and predisposition to failure or infection by 

decay fungi.

• Mushrooms or conks associated with deformed tops 

indicate internal decay.

• Forked tops that are U-shaped rarely fail.

Dwarf-mistletoe brooms 

• Dwarf mistletoes are parasitic plants that cause branches 

of some tree species to become misshapen. These 

deformed branches are called witches-brooms (Figure 

38).

• Large dead dwarf mistletoe brooms on Douglas-fir and 

sometimes on ponderosa pine can become weighted with 

snow and ice and fail.

• Dead brooms >10 ft. in diameter often fail.
49

• Smaller dead brooms and live brooms are less likely to 

fail.

Fungal cankers, bole wounds, and mistletoe bole 

swellings

• Fungal cankers frequently occur on the boles of pine 

species, especially ponderosa and lodgepole pines 

(Figure 39). Western gall rust, comandra rust, and white 

pine blister rust cause cankers.

• Wounds on tree boles provide openings for decay fungi 

and often indicate internal decay depending on tree 

species.

• Canker fungi cause top kill, branch death, and stem 

malformation.

• Stem malformations increase stem breakage and can be 

decayed by other fungi.

• Dwarf mistletoe bole swellings are caused by mistletoe 

infection of the bole (Figure 40). Swellings are especially 

common on grand and white fir, western and mountain 

hemlock, and occasionally western larch.

• Dwarf mistletoe bole swellings can become decayed and 

result in tree failure.

• True fir, hemlock, spruce, or hardwoods with cankers, 

wounds or swellings are more likely to fail than the 

resinous species.

• Douglas-fir, cedar, pine, and larch are less likely to fail 

because of resin-impregnated or decay-resistant wood.

• Resinous wood around cankers, wounds, and bole 

swellings usually remains sound.

• Failure level does not significantly increase until the face 

of the canker is deeply sunken, and the cross section of 

the bole with sound wood is small.

Fire damage

• Tree boles or limbs may be so badly burned that portions 

of them are missing which may cause the bole or limb to 

break and fall.
50

• Root systems may be damaged by fire, and the entire tree 

may fall.

• Before burning, the tree may have had conks that indicate 

severe decay. They may have burned off, eliminating the 

indicators of root disease or heart rot. Therefore, the tree 

may be more unstable than the visible indicators suggest.

• Likelihood of failure is determined by tree species 

(resinous or non-resinous), the amount of sound wood 

remaining, and time since tree death.

• Large pines, larch, or Douglas-fir with old basal fire 

scars may have compensated for any defect or decay by 

increasing their butt diameter; such trees rarely fail.

• Fire damaged trees may still have green crowns but dead 

cambiums at their base, essentially a dead tree.

• Long lasting and smoldering fires at the bases of large 

pines usually kill the fine roots and eventually the tree.

Height-to-diameter ratio

• Live trees with a high height-to-diameter ratio may fail 

depending on the ratio.

• These trees can break or bend permanently usually 

from snow or ice loading in the winter, especially if dwarf 

mistletoe brooms are present.

• To calculate height-to-diameter ratio, estimate the total 

tree height in feet and divide by the diameter at breast 

height (dbh) measured to the nearest foot. For example, 

a tree 100 ft. tall and 1 ft. dbh would have a height-todiameter ratio of 100.

Insect-caused damage

• Forest insects can weaken roots, stems, tops, or 

branches and result in fungal decay and physical 

degradation.

• Insects interact with fungal pathogens to cause damage 

or directly kill trees or their parts.

• Bark beetles are the most important insects that result in 

tree mortality. Chief beetles are the Douglas-fir beetle, fir 
51

engraver, spruce beetle, mountain pine beetle, western 

pine beetle, and pine engraver.

• Bark beetles frequently attack trees that are stressed from 

root disease, bole damage, defoliation, or drought.

• Symptoms of bark beetle attack are boring dust, pitch 

streams, galleries under the bark, fading or red crowns, 

dead tops, or group mortality (Figure 41).

• Wood borers are similar to bark beetles but prefer even 

weaker trees than bark beetles.

• Bark beetles and wood borers introduce saprot fungi after 

trees are killed.

• Carpenter ants and termites can severely weaken trees 

that are already decayed.

• The balsam woolly adelgid causes widespread mortality 

of subalpine fir and, in some cases, pacific silver fir and 

westside grand fir. Tree failure eventually may occur 

in infested live trees with little green crown remaining 

(Figure 42).

• Defoliating insects such as the western spruce budworm 

and the Douglas-fir tussock moth can kill tops or entire 

trees.

Multiple defects

The potential for tree failure increases dramatically with the 

combined effects of multiple defects such as heart rot and 

cankers, or stem injury, root rot and lean, split crotches and 

heart rot, and wind shake and butt rot. 
52

Figure 6 Basal resinosis

Figure 7 Armillaria 

root disease 

mushrooms

Figure 5 Crown decline from root 

disease
53

Figure 10 Bark beetles often attack 

trees stressed by root disease

Figure 9 Dead and dying trees caused 

by root disease

Figure 8 

Wind throw & 

wind shatter
54

Figure 12 Wind throw of live infected trees caused by 

laminated root rot

Figure 11 Decay associated with laminated root rot

Figure 13 Armillaria mycelial fans
55

Figure 14 Annosus root disease conks

Figure 15 Annosus root disease 

pustules

Figure 16 Annosus root disease wind throw
56

Figure 17 Tomentosus caused wind 

throw

Figure 18 

Tomentosus root rot 

mushrooms

Figure 19 Brown 

cubical butt rot old 

conk
57

Figure 20 Brown cubical butt rot fresh conk

Figure 21 Butt swell caused by brown cubical butt rot

Figure 22 Conks are good heart rot indicators
58

Figure 23 Rust red 

stringy rot conks, 

Indian Paint fungus

Figure 24 Red ring 

rot conks, Phellinus 

pini

Figure 25 Red ring rot punk knot
59

Figure 26 Brown trunk rot quinine conk

Figure 27 Incense cedar pecky rot conk

Figure 28 Phellinus tremulae conk on decayed aspen
60

Figure 29 Sap rot conks, Cryptoporus 

volvatus

Figure 30 Red belt 

conk, Fomitopsis 

pinicola

Figure 31 New lean, 

soil cracking
61

Figure 32 Corrected old lean

Figure 34 Crack from wind damage

Figure 33 Crack from lightning strike
62

Figure 35 Frost crack

Figure 36 Dead top

Figure 37 

Comandra rust 

killed top in pine
63

Figure 38 Dwarf mistletoe brooms

Figure 39 Atropellis canker on 

lodgepole

Figure 40 Dwarf mistletoe bole 

swelling
64

Figure 41 Fir engraver galleries

Figure 42 Balsam woolly adelgid 

damage
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