United States Department of Agriculture

for the greatest good

Field Guide for Danger-Tree 

Identifi cation and Response 

along Forest Roads and 

Work Sites in Oregon and 

Washington 

2016
Acknowledgements

We thank Rick Toupin, Tom Erkert, Craig Schmitt, Diane Hildebrand, Katy 

Mallams, and Don Goheen for their contributions in writing the 2008 

danger-tree guide that served as a template for this guidebook. We also 

thank Kim Mellen-McLain, Rochelle Desser, Robyn Darbyshire, Michael 

Tippie, and Ryan Blaedow for reviews. All figures were by the authors 

and other USFS personnel except where indicated.

Front cover photo: Danger trees killed in the B&B fire of 2003 along US 

Highway 20 just east of Santiam Pass, Oregon. Most danger trees were 

later removed in a joint effort between the USDA Forest Service and the 

Oregon Department of Transportation.
1

Field Guide for Danger-Tree Identification 

and Response along Forest Roads and 

Work Sites in Oregon and Washington

Gregory Filip, USFS Regional forest pathologist, Portland, OR

Michael Barger, USFS Regional logging engineer, Portland, OR

Joshua Bronson, USFS Service-center pathologist, Central Point, OR

Kristen Chadwick, USFS Service-center pathologist, Sandy, OR

Rick Collins, USFS Transportation group leader, Portland, OR

Betsy Goodrich, USFS Service-center pathologist, Wenatchee, WA

Holly Kearns, USFS Service-center pathologist, Sandy, OR

Michael McWilliams, USFS Service-center pathologist, La Grande, OR

Brent Oblinger, USFS Service-center pathologist, Bend, OR

Daniel Omdal, WDNR State forest pathologist, Olympia, WA

Amy Ramsey, WDNR State forest pathologist, Olympia, WA

Angel Saavedra, USFS Forest pathologist, Boise, ID

R6-NR-TP-021-2016 USDA Forest Service, Forest Health Protection,

 Pacific Northwest Region, Portland, OR
2
3

Table of Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Guidebook objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Policy and regulatory basis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Employer responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Agency responsibilities for National Forest System roads. . . . . . . . . . . . . . 13

Who is a qualified person. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Culturally modified trees/heritage trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Wildlife habitat trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

A process for danger-tree evaluation and action. . . . . . . . . . . . . . . . . . . . . . 16

How to survey for danger trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Step 1 – Determine tree-species groups, defects, and failure potential 20

Important tree-species groups in Oregon and Washington. . . . . . . . . . . . 20

Tree-failure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Step 2 – Determine the type of activity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Traffic on roads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Non-motorized, non-tree-contact activities. . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Motorized or tree-contact activities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Prioritizing roads for survey and treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Step 3 - Determine the tree’s potential-failure zone. . . . . . . . . . . . . . . . . . . . 38

Step 4 – Determine if the tree poses a danger. . . . . . . . . . . . . . . . . . . . . . . . . 43

Large areas of recently killed trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Step 5 - Document the danger-tree assessment. . . . . . . . . . . . . . . . . . . . . . . 49

Step 6 – Determine what action to take if the tree is a danger. . . . . . . . . . 52

NEPA considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Tree defect and disease identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Dead trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Root defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Root diseases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Undermined or severed roots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Lower-trunk (butt) defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Butt rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Fire-caused damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Bole (trunk) defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Wounded live trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Fungal and mistletoe cankers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Burls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Cracks and structural defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Heart rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Sap rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Crown defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Dead tops and branches; detached tops, limbs, and bark. . . . . . . . . . . . . . 96
4

Forked or multiple tops or trunks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Dwarf mistletoe brooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Whole-tree defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Wind or snow-loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Broken or uprooted trees supported by other trees. . . . . . . . . . . . . . . . . . . 99

Leaning and/or root-sprung trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Height-to-diameter ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Insect-caused damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Multiple defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Literature cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

For assistance on Oregon and Washington federal lands. . . . . . . . . . . . . 119

For assistance on Oregon and Washington state and private lands. . . 120

List of Tables

Table 1 Failure indicators for imminent, likely, and low-failure potentials 

for trees along forest roads and work sites in Oregon and 

Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 2 USDA Forest Service road-maintenance levels and survey

priority with level-5 roads receiving the highest priority. . . . . . . 35

Table 3 Road-treatment priority for danger trees. . . . . . . . . . . . . . . . . . . . . . 36

Table 4 How to determine if a tree with imminent or likely failure 

potential is a danger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Table 5 Important tree diseases and their chief conifer hosts in Oregon 

and Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Table 6 Important tree diseases and their chief hardwood hosts in 

Oregon and Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Table 7 Minimum sound-rind thickness at various diameters inside the 

bark of conifers measured at the defect for trees without open 

wounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Table 8 Minimum sound-rind thickness at various diameters inside the 

bark of conifers measured at the defect for trees with open 

wounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

List of Figures

Fig 1 - If culturally modified trees, such as shown here, are danger trees, 

they can be treated effectively by cutting the trunk above the 

carvings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Fig 2 - Danger trees along roads may be valuable wildlife habitat but are 

often only a minor part of the overall habitat. Cavities, as in this 

madrone, often provide habitat for several wildlife species. . . . 16
5

Fig 3 - The inner bark of Douglas-fir resembles the color of bacon. . . . . . 22

Fig 4 - The inner bark of most true firs is usually purple in color. . . . . . . . 25

Fig 5 - A road segment with a parking lot that should receive high 

priority for treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Fig 6 - Substantial lean is is greater than or equal to 15 degrees. . . . . . . . 39

Fig 7 – Potential-failure zone for total tree failure with no slope 

or lean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Fig 8 - Potential-failure zone for total tree failure with slope and 

lean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Fig 9 - Potential-failure zone for top failure with no slope or 

lean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Fig 10 - Potential-failure zone for top failure with slope and 

lean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Fig 11 - Trees with likely failure potential can be dangers if exposure 

duration is short or long, as when people have stopped to 

read this roadside sign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Fig 12 - Dead and dying trees are often caused by root disease. . . . . . . . 60

Fig 13 - Windthrow is often associated with root disease. . . . . . . . . . . . . . . 60

Fig 14 - Resin flow at the root collar often is associated with Armillaria 

root disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Fig 15 - Mycelial fans of the fungus, Armillaria ostoyae, under the bark

of an infected Douglas-fir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Fig 16 - White, stringy decay associated with Heterobasidion root 

disease in a hemlock stump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Fig 17 – Conks associated with Heterobasidion root disease. . . . . . . . . . . 63

Fig 18 - Laminated decay caused by Phellinus sulphurascens. . . . . . . . . . . 64

Fig 19 - Setal hyphae, the red-brown, fuzzy material shown here, are 

diagnostic for laminated root rot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Fig 20 - Undermined roots, as seen here, can result in tree failure. . . . . . 65

Fig 21 - Ganoderma root and butt rot is associated with the artist’s

conk, as seen on this infected stump. . . . . . . . . . . . . . . . . . . . . . . . . . 67

Fig 22 - Older conks of Phaeolus schweinitzii often resemble “cow pies” 68

Fig 23 - Butt swell of Douglas-fir is often associated with root and butt 

decay caused by Phaeolus schweinitzii. . . . . . . . . . . . . . . . . . . . . . . . 68

Fig 24 – Wind-shattered spruce caused by Onnia tomentosa. . . . . . . . . . . 69

Fig 25 - Mushrooms of the causal fungus, Onnia tomentosa. . . . . . . . . . . . 69

Fig 26 - Fire-damaged trees have failure potentials that depend on the 

amount of sound wood remaining. This pine has imminentfailure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Fig 27 - Tree bole with an open wound exposing the sapwood. . . . . . . . . 71

Fig 28 - Various bole cross-sectional areas showing percentage of sound 

wood remaining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6

Fig 29 – Atropellis canker is a common disease of lodgepole pine that 

can result in tree failure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Fig 30 - Dead tops of ponderosa pine, caused by Comandra blister rust, 

are often resin-soaked, decay-resistant, and therefore of lowfailure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Fig 31 - Dwarf mistletoe-bole infections are especially common on 

grand and white fir, hemlock, and larch. . . . . . . . . . . . . . . . . . . . . . . 77

Fig 32 - True mistletoe-bole and branch infections can cause cankers 

and decay in oaks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Fig 33 - Ramorum canker, as seen here, is an introduced disease that 

commonly kills tanoak in southwest Oregon. . . . . . . . . . . . . . . . . . 78

Fig 34 - Lodgepole pine boles with western gall rust can fail if the crosssectional area of sound wood falls below a critical threshold as 

in this tree on the right. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Fig 35 – Tree tops killed by white pine blister rust are often resin-soaked 

with little decay and have low-failure potential. . . . . . . . . . . . . . . . 80

Fig 36 - Burls are often large, woody growths of unknown cause that 

sometimes resemble conks but indicate low-failure potential. . 81

Fig 37 - Frost cracks often indicate low-failure potential unless they are 

weeping, as shown here, then failure potential is likely. . . . . . . . 82

Fig 38 - Heart rots compromise tree stability by reducing the amount 

of sound rind as seen here in this wounded spruce that had a 

Fomitopsis pinicola conk at its base. . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Fig 39 - Conk of Phellinus tremulae indicates internal decay in 

this aspen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Fig 40 - Advanced decay caused by Laricifomes officinalis is a browncubical rot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Fig 41 - Quinine conks of Laricifomes officinalis indicate considerable 

stem decay as seen in Fig 40. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Fig 42 - Conk of Phellinus igniarius on a decayed hardwood. . . . . . . . . . . . 87

Fig 43 – Conk of Oligoporus amarus on this incense-cedar indicates 

internal decay but low-failure potential. . . . . . . . . . . . . . . . . . . . . . . 88

Fig 44 – Cavity (at arrow) created by birds indicates heart rot in this 

western redcedar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Fig 45 - Conks of P. pini often indicate only low-failure potential. . . . . . . . 91

Fig 46 - Wood decay caused by P. pini, commonly called whitespeck, 

is relatively sound compared to wood decay caused by other 

fungi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Fig 47 - Conks of the Indian paint fungus are common on true firs and 

hemlocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Fig 48 - Decay caused by the Indian paint fungus can result in tree 

failure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7

Fig 49 – This conk of Fomitopsis pinicola is very common on dead wood 

and may also be on found on wounded, live trees. . . . . . . . . . . . . 94

Fig 50 - These pouch fungus conks may indicate considerable sap rot. . 95

Fig 51 - Dead tops can be caused by many agents including dwarf 

mistletoe as shown here. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Fig 52 - Forked tops shown on this hardwood that are weeping and 

cracked (left) and this cedar with open cracks (middle) have 

imminent-failure potential The ponderosa pine (right) with 

only embedded bark has likely failure potential. . . . . . . . . . . . . . . 97

Fig 53 – Example of embedded bark as seen just below the forked 

stem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Fig 54- Live, dwarf-mistletoe brooms, even large ones as shown here on 

Douglas-fir, have low-failure potential. . . . . . . . . . . . . . . . . . . . . . . . 98

Fig 55 - New cracks in the soil around leaning trees indicate imminentfailure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Fig 56 - Old leans with righted or corrected tops have low-failure 

potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Fig 57 - Trees with high height-to-diameter ratios (skinny trees), such as 

these lodgepole pines, are more prone to stem breakage from 

snow, ice, or wind. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Fig 58 - Bark beetle attack is often indicated by pitch flow as seen 

on this infested pine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Fig 59 – Multiple, likely failure indicators can imply imminent-failure 

potential, such as this maple with hollow, leaning stems. . . . . 103
8
9

Introduction 

Working around, walking in, or driving through forested areas exposes 

people to potentially dangerous (hazardous) trees. This guide presents 

a framework for identifying risk of tree failure and making decisions 

in areas where dangerous trees pose a threat to individuals along 

forest roads or work sites. A tree’s stability and structural integrity 

can be influenced by its location and the extent of structural defects, 

mechanical damage, insect attack, and disease, as well as work activities 

and weather conditions. If a tree is unstable or its structural integrity 

compromised, total or partial failure may occur. During failure events, 

falling trees or parts may pose a danger to people or vehicles that may 

be struck by them.

In this guide, we outline steps to identify danger trees and provide a 

method for documenting survey results and recommended treatments. 

This guide is for forest-resource managers, road-maintenance engineers, 

fire-management teams, and pest-management specialists who deal 

with roads and work sites in forested areas and need to identify and 

mitigate danger trees. It is a revision of a similar guide: Field guide 

for danger tree identification and response, 2008 (10). This guide is not 

intended for developed sites in forested areas; instead, refer to Field 

guide for hazard-tree identification and mitigation on developed sites in 

Oregon and Washington forests, 2014 (1).

Guidebook Objectives:

• To provide information to employers and managers that will 

protect workers and the public from tree-related dangers

• To provide information to “qualified people” that will enable them 

to properly perform the following:

o Recognize tree-species groups and defects to determine 

tree-failure potential

o Determine a tree’s potential-failure zone

o Understand how an activity could induce a tree to fail

o Determine how to prioritize survey and treatment areas

o Document danger-tree evaluations

o Determine if a tree presents a danger as a result of tree 

condition, failure potential, potential-failure zone, activity, 

and exposure duration
10

In this guide, general tree identifi cation is discussed. Common diseases 

and defects that contribute to tree failure are presented along with 

how to identify them. Delineating potential-failure zones is described. 

Possible activities around trees are grouped into three classifi cations 

according to how they may induce tree failure. There is a discussion 

on how to decide if the tree is a danger, including examples and how 

to document danger-tree evaluations. Traffi c frequency and exposure 

duration should be considered when determining whether a tree 

poses a danger to people or vehicles. Finally, there is a discussion of 

appropriate actions necessary to mitigate the threat posed by danger 

trees.

In this guide, a danger tree or hazard tree is any tree or its parts that 

will fail because of damage, defect, or disease and cause injury or death 

to people or property. 

Policy and 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 operating on private or public land.

Danger-tree workshop, 2006, on the Rogue River-Siskiyou National Forest
11

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 danger.

Federal OSHA rules regarding logging operations (29 CFR 1910.266) 

address specifi c means of protecting employees who are engaged in 

logging activities (5). They apply to federal employees.

The health and safety of USDA Forest Service (USFS) employees is 

addressed by the Health and Safety Code Handbook (6). Section 21.14 

focuses on the identifi cation of dangers to employees. It discusses the 

correction of dangers and what to do if they cannot be corrected.

The Bureau of Land Management (BLM) 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).

Both moving and parked vehicles can serve as targets.
12

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 fi eld activities (3.1). It also outlines 

prevention and mitigation methods (10.2). Section 23.3 specifi cally 

discusses the potential hazards of forestry activities. Safety and health 

requirements for contractor employees (fi eld work) are discussed in 

section 20 (8).

The Forest Service Handbook (FSM) 7709.59, Chapter 40 contains policy 

information and responsibilities related to danger-tree hazards along 

National Forest System roads. The Region 6 supplement to this FSM has 

more detailed policy information and responsibilities related to danger 

trees along National Forest System roads in Region 6 (11). 

Although neither a regulation nor a policy, Region 6 of the USFS has 

a Memorandum of Understanding with the Oregon Department of 

Transportation (ODOT) and the Washington State Department of 

Transportation (WSDOT) regarding transportation activities, including 

danger-tree removal, of mutual interest involving highways on, or 

accessing lands managed by the USFS (14, 15).

Roadside danger trees, early 1900s
13

These policies, regulations, and 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 policies, regulations, and rules 

related to danger trees. This document, titled Field Guide for Danger-Tree 

Identification and Response along Roads and in Work Sites in Oregon and 

Washington Forests, is designed to implement the applicable policies, 

regulations, and rules. It does not replace them.

Employer Responsibilities

The employer has the responsibility to identify and mitigate dangers 

to personnel from danger trees. The Oregon OSHA 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 (3) 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. When trees pose a danger they must be 

felled, or the work must be arranged to minimize danger to workers.

Agency Responsibilities for National 

Forest System Roads

National Forest System roads are managed for safe passage by road 

users, including appropriate management of roadside vegetation that 

involves considerations such as motorist sight distance, clear visibility of 

road signs, and identification and mitigation of danger trees per section 

41.7, paragraph 2 of FSH 7709.59 and related Region 6 supplements.

Who is a Qualified Person?

When an employer or manager is faced with potentially dangerous 

trees, a qualified person with sufficient knowledge, training, and 
14

experience must be available to follow the appropriate process for 

identifying and mitigating the hazard.

A qualifi ed person is defi ned as a person who has knowledge, training, 

and experience in identifying danger trees, their potential-failure zones, 

and the appropriate measures to mitigate the danger. A qualifi ed 

person has successfully completed a workshop on implementing this 

fi eld guide.

Culturally Modifi ed Trees/Heritage Trees

Culturally modifi ed trees (heritage trees) are archeological sites that 

are important to Native American tribes and the general public (Fig. 

1). A tree with any human-caused marking or object over 50-years old 

is considered to be a culturally modifi ed tree. Examples of culturally 

modifi ed trees include: (1) peeled, cedar trees in riparian zones, (2) trail 

blazes on trees, (3) bearing trees, (4) salt ground and stock driveway 

signs on trees, (5) arborglyphs (carved tree initials), (6) marten set 

traps (carved holes in trunks), and (6) trees with old insulators or 

wires. Culturally modifi ed trees may be cultural resources. Removal 

or alterations to a culturally modifi ed tree is subject to review and 

Measuring danger-tree heights, Okanogan-Wenatchee National Forest. 

When working along roads, warning signs should be posted and brightorange or re ective clothing worn.
15

consultation with the 

Forest Heritage Program 

Manager per  36 CFR 

800 of the National 

Historic Preservation Act 

(NHPA) and E.O. 13175   

(Consultation with Tribes).

If a culturally modified 

tree is deemed a danger, 

that danger will need to 

be mitigated. Culturally 

modified trees deemed 

as danger trees, however, 

must be mapped 

and photographed 

before treatment. If a 

culturally modified tree is 

determined to be a danger 

tree, plot its location on 

a map or obtain its GPS 

coordinates and photograph the tree and associated object. Preferably, 

a local USFS archeologist should be contacted before a tree is treated. 

If this is not possible, the recommend treatment is to fell the tree at 

a place on the trunk above the cultural marking or object, if possible. 

If not done so before treatment, notify the archeologist soon after 

treatment, because additional documentation or other mitigation 

may be necessary. Safety is always the first priority, and always notify 

a resource expert if mitigation is recommended. There are also NEPA 

considerations (p. 52) that must be evaluated before mitigation.

Wildlife Habitat Trees

Dead trees or live, defective trees often are valuable habitat for wildlife 

such as cavity-nesting birds and mammals. When these trees are 

dangers and require mitigation, compliance with the Endangered 

Species Act is required. USFS wildlife biologists are required to report to 

the US Fish and Wildlife Service if wildlife habitat trees are to be felled 

on National Forest lands. Wildlife biologists should be consulted about 

recommended treatments before surveys begin and implementation 

occurs. There are also NEPA considerations (p. 52) that must be 

evaluated before mitigation.

Fig. 1 - If culturally modified trees, such as 

shown here, are danger trees, they can be treated 

effectively by cutting the trunk above the carvings.
16

Generally, roadside and work site snags, or live, defective trees are a 

relatively minor part of wildlife habitat compared to the habitat in the 

surrounding landscape (Fig. 2). R6-USDA Forest Service policy states: 

“close the facility or parts of the facility if danger trees cannot be felled. 

Danger trees must be felled if the facility or parts of the facility cannot 

be closed. Inquire if a local, programmatic, biologic opinion exists that 

covers this activity.” (11)

A Process for Danger-Tree Evaluation and 

Action

There are six steps the qualifi ed person should take when dealing with 

potential danger trees:

1. Determine tree-species groups, defects, and failure potential.

2. Determine the type of activity.

3. Determine the tree’s potential-failure zone.

4. Determine if the tree poses a danger. 

5. Document the danger-tree assessment.

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

How to Survey for Danger Trees

To identify tree species, defects, failure potential, and danger 

trees, a systematic survey is needed. Forest work sites are 

generally small compared to roadside areas, so surveys 

Fig. 2 - Danger trees along roads may be valuable wildlife habitat but are often only a 

minor part of the overall habitat. Cavities, as in this madrone, often provide habitat for 

several wildlife species.
17

usually can be done on the entire work site and every tree evaluated. 

For roadside surveys, many miles of roads may have danger trees, so it 

is necessary to prioritize 1) which roads are to be surveyed and 2) the 

danger-tree treatment workload (see p. 35-37, Tables 2 and 3). During 

the survey, pay particular attention to areas along roads where people 

stop, such as roadside vistas or informational signs that are within 

striking distance of defective trees.

Once the road system has been prioritized, the survey is best done on 

the ground in a strip along both sides of the road. The width of each 

survey strip should be 1 1⁄2 times the length of the tallest tree that could 

strike the road. Surveys from a slow-moving vehicle may identify the 

obvious danger trees next to the road, such as dead trees, but often will 

miss the more subtle indicators on live trees that suggest imminentfailure potential, such as cow-pie conks (Schweinitzii, p. 67), quinine 

conks (p. 86), or windthrow 50 ft. from the road that may indicate 

Heterobasidion root disease (p. 62) in the surrounding live trees. 

High-priority trees should be marked for removal during the survey 

and addressed as soon as possible. Close the aff ected road segment 

if high-priority danger trees cannot be mitigated in a timely matter. If 

treatment is delayed and marked trees are involved in an accident, 

defending such inaction in court is usually unsuccessful.

To be eff ective, danger-tree surveys should be done outside 

of vehicles, as is being done here on the Wallowa-Whitman 

National Forest.
18

Danger-tree evaluations should be performed by two or more surveyors 

at the same time. Begin the survey by one person evaluating each tree 

from a distance to allow comparison of the vigor and overall appearance 

of trees relative to their nearest neighbors. The view from a distance 

allows the examiners to detect dead trees, branches or tops and livecrown symptoms of root disease that can include reduced lateral branch 

and terminal growth, thinning crowns, chlorosis, and distress-cone 

crops. Evidence of defoliator activity, mistletoe infection (p. 76), stem 

conks, and bark beetle attack often are detected initially from a distance 

and involves inspecting multiple trees from different vantage points.

 

While one person is examining each tree from a distance, a second 

person should examine the area in the vicinity of each tree for obvious 

and subtle evidence of past and current pathogen and insect attack, 

or other damaging agents. Stand-level clues may be easily overlooked 

while driving without careful evaluation and consideration. Nearby 

stumps and old roots should be examined for evidence of advanced 

decay and conks of root and butt pathogens. Broken-out tops lying 

on the ground, and windthrown or wind-shattered trees should be 

examined to determine the causal agents. Conks, mushrooms, and other 

fruiting bodies on and around trees should be identified since these are 

primary indicators of decay. Their identification often leads to detection 

and correct diagnosis of disease 

in adjacent, apparently healthy 

trees. If signs and symptoms 

indicate decay and a potential 

hazard, trees should be 

examined more thoroughly 

to determine the extent that 

the disease has compromised 

structural integrity. 

Systematic tree examination 

begins around the base of the 

tree, then proceeds to the butt, 

bole, limbs, and top. All sides of 

each tree should be examined 

carefully. If basal resinosis, 

crown symptoms, conks, or 

evidence of decay indicates 

a root disease problem, 

examination of several roots 

with a drill, ax, or pulaski is 

Conks on the boles of decayed 

trees, such as this quinine conk 

on larch, are generally easy to see 

when surveying.
19

warranted. Lightly tapping suspect trees with an axe or rubber mallet 

may detect decay columns, hollows, and dead sapwood under the bark. 

This is only practical for trees with relatively thin bark. Trees that sound 

hollow can then be examined in more detail with drills or increment 

borers, but this should only be done for trees where the exposure 

duration for people or property is >15 minutes (p. 46); for example, a 

bus stop or scenic vista. Binoculars may be necessary to inspect tops 

and upper boles of suspect or symptomatic trees.

If root disease symptoms are evident or suspect due to proximity to 

confi rmed infection centers, the root collar, butt, and major lateral roots 

of suspected trees should be inspected for fruiting bodies, ectotrophic 

mycelium, mycelial fans under the bark, stain or decay in the wood, or 

other signs of the causal agent. A pulaski can be used to uncover roots 

(out to a distance of one yard, if needed) and to remove bark for further 

examination. At least two major roots should be examined for root 

disease if preliminary evidence suggests that it may be present. The 

roots that are most likely infected should be checked fi rst. These include 

those closest to infected (hollow) stumps, windthrown trees, or obvious 

root disease centers. If a large area of root disease is suspected, consult 

a forest pathologist for a positive identifi cation.

Root disease centers are di cult to diagnose without examining the 

roots of symptomatic trees or adjacent, windthrown trees.
20

The bole above the lower butt is 

the next logical section to examine. 

From this point upward, visually 

examine the bole and branches to 

detect and estimate the extent of 

defect. Again, signs of past injury 

or fungal fruiting bodies should 

be the target of observation. By 

the time old-growth trees exhibit 

fruiting bodies of stem-decay fungi, 

decay levels are often substantial. 

Fruiting bodies generally develop 

at the site of old, branch stubs 

or wounds. Absence of conks, 

however, does not necessarily 

mean that a tree is free from decay. 

Tree tops and branches should 

be examined thoroughly. Freehanging branches should be 

evaluated and treated as needed. 

Dead tops and branches should be 

examined for decay and instability 

as indicated by conks, cracked wood, exposed decay, woodpecker 

activity, or nesting cavities. Binoculars are useful for this assessment. 

Step 1 – Determine Tree-Species Groups, 

Defects, and Failure Potential

Important Tree-Species Groups in Oregon and 

Washington

When determining potential-danger trees, it is important to be able 

to identify the most common tree-species groups along forest roads 

and work sites in Oregon and Washington. Diseases and defects that 

result in tree failure are more serious in certain tree-species groups. The 

following is a brief description of the major, native, tree-species groups 

in Oregon and Washington forests:

Alders (Alnus spp.)

Four species occur in the Pacifi c Northwest (red, white, thinleaf, and 

Sitka). Leaves are 11⁄2-6 in. long, alternate, simple, unlobed, narrow to 

elliptical, and fi nely toothed to coarsely double-toothed. Fruits are conePouch-fungus conks on this dead 

Douglas-fi r may indicate imminentfailure potential if associated with 

other indicators such as heartrot 

conks.
21

like clusters, 1/3-1 in. long and on stalks. Bark is thin, smooth and patchy 

white and gray. 

Aspen (Populus tremuloides)

There is only one species of aspen in the Pacific Northwest (quaking 

aspen). Leaves are 1-3 in. long, alternate, simple, unlobed, and nearly 

circular to heart-shaped with a pointed tip, straight base, and finely 

toothed margins. Fruits are capsules, 1⁄4 in. long, in hanging clusters that 

split open at maturity to release tiny, white-hairy seeds. Bark is white to 

yellow-white, thin, and smooth when young with black, warty patches 

with age.

Cedars (Calocedrus, Chamaecyparis, Thuja spp.)

Four species occur in the Pacific Northwest (western red, incense, PortOrford, and Alaska yellow). Needles are scale-like and appressed to 

the twig. Cones are 1⁄2-1 in. long and are either round or long and thin. 

Bark is stringy or flaky and gray to brown. Incense cedar occurs only in 

Oregon. Port-Orford-cedar occurs naturally only in SW Oregon. Alaska 

yellow cedar grows only at high elevation. True cedars (Cedrus spp.) are 

not native to the Pacific Northwest.

Cottonwood (Populus balsamifera ssp. trichocarpa)

There is only one cottonwood species native to the Pacific Northwest 

(black cottonwood). Leaves are 3-6 in. long, alternate, simple, unlobed, 

Western white pine with branch killing from blister rust
22

and arrowhead-shaped with pointed tips and fine, blunt teeth along 

the margins. Fruits are 1⁄4 in. long, round capsules that split in three at 

maturity to release tiny, white-hairy seeds in late spring. Bark is gray 

with corky ridges and deep furrows in older trees.

Douglas-fir 

(Pseudotsuga 

menziesii)

One species occurs in 

the Pacific Northwest. 

Needles are about 

1 in. long with a 

blunt tip and spirally 

arranged around the 

twig but may be tworanked in the shade. 

Buds are sharppointed. Cones are 

3-4 in. long with 

3-pronged bracts 

that are longer than 

the scales. The cones 

hang down from the 

twig. Bark has resin 

blisters when young, but deeply furrowed and reddish-brown when old. 

When cut, the older, inner bark is a mottled-brown and yellow color 

that resembles bacon (Fig. 3).

Hemlocks (Tsuga spp.)

Two species occur in the Pacific Northwest (western and mountain). 

Needles are under 1 in. long and in groups that appear to be either starlike (mountain hemlock) or tend to stick out of the sides of the twig 

(western hemlock). 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.

Junipers (Juniperus spp.)

Three species occur in the Pacific Northwest (Rocky Mountain, western, 

and common). Needles are either scale-like or awl-like. Cones are 

semi-fleshy, bluish, or reddish-brown called “juniper berries”. Bark is 

gray-brown to reddish-brown and broken into narrow, flat, interlacing 

ridges. Native junipers occur only east of the Cascade crest.

Fig. 3 - The inner bark of Douglas-fir resembles the color 

of bacon.
23

Larches (Larix spp.)

Two species occur in the Pacific Northwest (western and subalpine). 

Needles are 1-2 in. long and borne 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. Subalpine larch occurs naturally only in 

Washington and at high elevations.

Madrone (Arbutus menziesii)

One species occurs in the Pacific Northwest (Pacific madrone). Leaves are 

3-6 in. long, simple, evergreen, and elliptical with a bluntly pointed tip. 

Fruits are clustered, and berries are round and orange-red or yellow. Bark 

is very distinctive with newer bark being chartreuse in color and aging 

to gray, lilac, or pink, and finally to red or orange.

Maples (Acer spp.)

Three species occur in the Pacific Northwest (bigleaf, vine, and Rocky 

Mountain). Leaves are 2-12 in. long, opposite, simple, and lobed. Fruits 

are paired, winged samaras, 3⁄4-11⁄2 in. long. Bark is gray and becomes 

fissured with age. 

Myrtle or Bay (Laurel) (Umbellularia californica)

One species occurs in the Pacific Northwest in SW Oregon (Oregon 

myrtle or California bay). Leaves are 2-5 in. long, lanced-shaped or 

narrowly elliptic with pointed tips and untoothed margins. Leaves are 

stiff, leathery, shiny, and dark yellow-green above and paler beneath 

and smell like camphor when crushed. Fruits are 3⁄4-1 in. long, round, 

hard, and an olive-like drupe that is green ripening to dark-purplish 

brown. Bark is brown, thin, and breaks into plates that shed with age. 

Oaks (Quercus spp.)

Three species occur in the Pacific Northwest (Oregon white, canyon live, 

and California black). Leaves are 1-8 in. long, alternate, and simple. Fruits 

are acorns, 1⁄2-11⁄2 in. long, ovoid to oblong, and enclosed within a cup 

with scales. Bark is thick and somewhat scaly. Oregon white oak is the 

most abundant oak species in the Pacific Northwest. Canyon live oak 

and black oak occur naturally only in SW Oregon.

Pines (Pinus spp.)

Seven species occur in the Pacific Northwest (ponderosa, Jeffrey, 

lodgepole, knobcone, western white, sugar, and whitebark). Needles are 

1-10 in. long and are in bundles of 2, 3, or 5 needles. Ponderosa pine 

has 3 needles per bundle, whereas western white pine has 5 needles 
24

per bundle that have white lines on 2 of 3 sides of the needle. Sugar 

pine also has five needles per bundle that have white lines on all three 

sides of the needle. Cones are 1-20 in. long with thick scales. Bark is gray 

to reddish brown and either furrowed or scaly. Jeffrey, knobcone, and 

sugar pines occur naturally only in Oregon.

Redwood (Sequoia sempervirens)

One species occurs in the Pacific Northwest (coast redwood). Needles 

are 1⁄4-1 in. long, most are flat-pointed, dark-green above with two white 

bands beneath and arranged in two rows. Cones are 3⁄4-1 in. long, brown, 

ovoid and hang from the ends of green twigs. Bark is thick, fibrous, 

and reddish-brown. Redwood occurs naturally only in SW Oregon, but 

ornamental trees occur throughout western Oregon and Washington.

Spruces (Picea spp.)

Three species occur in the Pacific Northwest (Sitka, Engelmann, and 

Brewer). 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. Engelmann spruce occurs only east of the 

Cascade crest. Sitka spruce occurs naturally only along the Pacific coast 

and Puget Sound. Brewer spruce occurs naturally only in SW Oregon.

Tanoak (Notholithocarpus densiflorus)

One species of tanoak occurs in the Pacific Northwest and is confined 

naturally to SW Oregon. Leaves are 2-5 in. long, elliptic with margins untoothed or with one tooth per side vein and edges that often curl under. 

Leaves are stiff, leathery, evergreen, shiny, dark green with a thin coat of 

wool above and waxy-coated with a dense coat of wool beneath. Fruits 

are a single or double acorn, 3⁄4-1 in. long and 1⁄2-1 in. wide, ovoid, glossy, 

or pointed maturing to yellow-brown and in a shallow cup densely 

covered with bristles. Bark on young trees is mottled-gray and smooth 

that forms plates when older. 

True firs (Abies spp.)

Six species occur in the Pacific Northwest (grand, white, Pacific silver, 

subalpine, noble, and Shasta red). 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 plasters. Older 

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

color (Fig. 4) except for white fir which has inner bark like Douglas-fir 

(like bacon). Shasta red fir and white fir (A. concolor) occur naturally only 

in Oregon.
25

Tree-Failure Potential

Failure potential is defined as the likelihood that a tree or its parts will 

fail during a certain time period. For roadside and work site danger 

trees, there are three levels of failure potential: low, likely, and imminent. 

They are defined as follows:

Low-failure potential 

Trees or their parts are defective or decayed, but it would take considerable 

effort to make them fail. These trees or parts have a low probability of 

failure within 10 years.

Likely failure potential 

Trees or their parts are defective or decayed, but it would take moderate 

effort to make them fail. These trees or parts have a high probability of 

failure within 3 to 5 years.

Imminent-failure potential 

Trees or their parts are so defective or decayed that it would take little effort 

to make them fail. These trees or parts have a high probability of failure 

within one year.

Fig. 4 - The inner bark of most true firs is usually purple in color.
26

Failure potential is a function of tree condition. Trees with likely or 

imminent potential to fail may be classed as danger trees depending on 

the activity and whether the activity is within the tree’s potential-failure 

zone (p. 46). In order to defi ne the potential-failure zones, it is necessary 

to determine which tree part is likely to fail: entire tree, top, branch, or 

bark.

Trees with disease or defect require an evaluation to assign a potentialfailure rating to them. The following are indicators for trees with 

imminent, likely, or low-failure potential (Table 1).

Fire-damaged trees and vehicle loss, Willamette National Forest
27

Table 1. Failure indicators for imminent, likely, and low-failure potentials for trees along forest roads and work sites in Oregon and Washington. 

Failure Indicator

Failure Potential

Imminent Likely Low

Dead Trees

Old dead trees (>5 years) No foliage or fine branches; bark is absent or falling off

All tree species except cedar, 

juniper, larch, or large (>20 in. 

dbh) Douglas-fir 

Cedar, juniper, larch, or large 

Douglas-fir with no other visible 

indicators 

None

Recent dead trees (<5 years) All or some foliage; fine branches; bark mostly intact

All trees <10 in. dbh All trees >10 in.dbh except 

cedar, juniper, larch, or large 

Douglas-fir

Cedar, juniper, larch, or large 

Douglas-fir

Recent dead trees in root disease centers (p. 59-66)

All tree species except cedar Cedar None

Roots

Live trees in laminated root rot centers (p. 64 )Phellinus sulphurascens

Trees with signs or symptoms (ectotrophic mycelium or laminated decay; foliage thinning or yellowing)

Douglas-fir, mountain hemlock, or true firs without signs or symptoms and <25ft. from an infected tree or stump 

Douglas-fir, mountain hemlock, or true firs without signs or symptoms and >25ft. from an infected tree or stump; All other species without signs or symptoms

Live trees in Armillaria or Heterobasidion root disease centers Armillaria spp. (p. 60) Heterobasidionspp. (p. 62)

Trees with signs or symptoms (mycelial fans, resinosis, staining, conks, or wounds with decay; foliage thinning or yellowing) andadjacent (<50 ft.) to windthrown trees with root disease

Trees with signs or symptoms but not adjacent to windthrown trees with root disease

Trees without signs or symptoms 

Live trees in black stain or PortOrford-cedar root disease centersLeptographium wageneri (p. 62) Phytophthora lateralis (p. 65)

None None All trees

Live trees with undermined or severed roots (p. 66)

Trees with <50% of the structural roots remaining in the ground 

Trees with 50 to 75% of the structural roots remaining in the ground

Trees with >75% of the structural roots remaining in the ground
28

Failure Indicator

Failure Potential

Imminent Likely Low

Butt

Butt rot (p. 66-69 ) Schweinitzii (cowpie conk) Tomentosus (spruce rot conk) Ganoderma (artist’s and varnish conks)

Trees with >1 conk(s) associated with open cracks or exposed decay 

Trees with >1 conk(s) not associated with open cracks or exposed decay

Trees with butt swell but no conks

Living, fire-damaged trees for recent (<5yr) fire damage;use bole-wounds for old fire damage (p. 70)

True fir, hemlock, spruce, or hardwoods with >50% of the bole cross-sectional area burned and consumed, or more than one quadrant of burned and consumed structural roots Douglas-fir, pine, cedar, juniper, or larch with >75% of the bole cross-sectional area burned and consumed, or more than one quadrant of burned and consumed structural roots

True fir, hemlock, spruce, or hardwoods with 25 to 50%of the bole cross-sectional area burned and consumed, or one quadrant of burned and consumed structural rootsDouglas-fir, pine, cedar, juniper, or larch with 50 to 75% of the bole cross-sectional area burned and consumed, or one quadrant of burned and consumed structural roots

True fir, hemlock, spruce, or hardwoods with <25% of the bole cross-sectional area burned and consumed, and no burned and consumed structural rootsDouglas-fir, pine, cedar, juniper, or larch with <50% of the bole cross-sectional area burned and consumed, and no burned and consumed structural roots

Bole/Stem

Bole wounds mistletoe cankers, fungal cankers, or old fire wounds (>5 years) (p. 71-80)

True fir, hemlock, spruce, or hardwoods with <50% crosssection of bole with sound woodDouglas-fir, pine, cedar, juniper, or larch with <25% cross-section with sound wood

True fir, hemlock, spruce, or hardwoods with 50 to 75%cross-section of bole with sound woodDouglas-fir, pine, cedar, juniper, or larch with 25 to 50% crosssection with sound wood

True fir, hemlock, spruce, or hardwoods with >75% crosssection of bole with sound woodDouglas-fir, pine, cedar, juniper, or larch with >50% cross-section with sound wood

Frost cracks (p. 82) None Trees with weeping cracks Trees without weeping cracks Bole cracks (p. 82) Trees with open splits or cracks 

with independent movement or exposed rot 

Trees with open splits or cracks without movement or exposed decay 

Trees with sealed cracks

Burls (p. 82) None None All trees
29

Failure Indicator

Failure Potential

Imminent Likely Low

Conks

Quinine conks (p. 86) Laricifomes officinalis

Trees with ≥1 conk(s) None None

Indian paint fungus conks (p. 92)Echinodontium tinctorium

Trees with multiple, large (>6 in. wide) conks;Single, large conk or multiple, small conks associated withopen cracks or exposed rot

Trees with single, large conk or multiple, small conks not associated with open cracks or exposed rot

Trees with a single, small conk

Red ring rot conks, white speck(p. 90)Porodaedalea pini

Trees with >1 conk(s) associated with extensive advanced decay1 such as open cracks or exposed rot

True fir, hemlock, spruce, or hardwoods with >1 conk(s) not associated with extensive advanced decay;Douglas-fir, pine, cedar, juniper, or larch with >3 large conks (>6 in. wide) within a 3-ft.-long trunk cylinder

Douglas-fir, pine, cedar, juniper, or larch with >3 large conks not within a 3-ft.-long trunk cylinder; <2 large conks within a 3-ft.-long trunk cylinder;any number or location of small conks

Other heart-rot conks (p. 84-93) Trees with >1 conk(s) associated 

with open cracks or exposed rot

Trees with >1 conk(s) not associated with open cracks or exposed rot

None

Sap-rot conks Cryptoporus volvatus (pouch conk) (p. 95)Fomitopsis pinicola (red-belt conk) (p.94)

Dead trees with >1 red-belt conk(s)

Live trees with >1 red-belt conk(s) usually associated with bole wounds 

Live trees with >1 pouch conk(s); check for extent of dead bark and sound wood
30

Failure Indicator

Failure Potential

Imminent Likely Low

Tops and BranchesForked or multiple tops or stems (p. 97)

Trees with any fork associated with open cracks, decay, or conks*(tops are imminent FP, not the whole tree unless fork is at the base)

Trees with V-shaped forks with embedded bark but not associated with open cracks, decay, or conks*(tops are likely FP, not the whole tree unless fork is at the base)

Trees with U-shaped forks and no open cracks, decay, or conks*; V-shaped forks with noembedded bark, open cracks, decay, or conks*(tops are low FP, not the whole tree unless fork is at the base)

Dead tops or branches (>3 in. diameter) (p. 96)

True fir, hemlock, spruce, or hardwoods >5 years dead or with red-belt conks(tops and branches are imminent FP, not the whole tree)

True fir, hemlock, spruce, or hardwoods <5 years dead;Douglas-fir >5 years dead (tops and branches are likely FP, not the whole tree)

Cedar, larch, juniper, or pine; Douglas-fir <5 years dead(tops and branches are low FP, not the whole tree)

*Any conk except for red ring rot conks (P. pini) on forked Douglas-fir, pine, cedar, juniper, or larch.

Tops and Branches

Detached tops, branches (>3 in. diameter), or bark (>1 ft.2) (p. 96)

All detached parts(parts are imminent FP, not the whole tree)

Live and attached tops or branches but cracked or split (parts are likely FP, not the whole tree)

None

Dwarf mistletoe brooms (p. 98) None

Trees with large (>10ft. in diameter) dead brooms (broom is likely FP, not the whole tree)

Trees with small, dead brooms or live brooms(broom is low FP, not the whole tree)

Cottonwood branches (p. 97)

Trees with large (>3 in. diam.) dead branches (branches are imminent FP, not the whole tree)

Trees with large, live branches with evidence of decay or past breakage (branches are likely FP, not the whole tree)

Trees with large, live branches with no evidence of decay or past breakage 
31

Failure Indicator

Failure Potential

Imminent Likely Low

Whole Tree

Broken or uprooted trees supported by other trees (p. 99)

All None None

Leaning and/or root-sprung trees (p. 99)

Trees with recent (<5yr) leans >15 degrees or old, uncorrected leans with freshly disturbed soil or root damage

Trees with recent leans >15 degrees or old, uncorrected leans without freshly disturbed soil or root damage

Trees with old, corrected leans 

Height to diameter ratio (p. 100) Trees with >100 H:D ratio2 Trees with 80 to100 H:D ratio Trees with <80 H:D ratioMultiple indicators (p. 113)

Two or more likely-FP indicators with synergistic effects: one condition (indicator) worsens the other (i.e. recently killed true fir with a large, Indian paint fungus conk)

Two or more low-FP indicators with synergistic effects (i.e. 15% severed roots and an old, corrected lean); two or more likely-FP indicators without synergistic effects (i.e. true fir with a weeping frost crack and a recently killed top)

Two or more low-FP indicators without synergistic effects (i.e. top-killed cedar with two P. piniconks on the live bole)

1Firm wood with white speck or firm wood with red discoloration is not considered advanced decay from P. pini. Advanced decay is very soft and crumbly. 2To caluclate H:D ratio, divide the total tree height in feet by the diameter breast height (dbh) in feet.

> means is greater than; < means is less than
32

Step 2 – Determine the Type of Activity

Exposure to danger trees is prohibited by state safety laws. Not all 

activities expose people to the same risks. Some activities can induce 

tree failure, such as operating heavy machinery around an unstable tree. 

Some activities have an increased risk due to the length of exposure to 

a tree with defects. The type of activity is extremely important when 

determining if a tree is a danger to people or property.

There are three categories of activities:

1. Traffi c on roads

2. Non-motorized activities that do not touch the tree 

3. Motorized activities near the tree or activities that may cause 

the tree to be contacted 

Road traffi c may or may not infl uence 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.

Non-motorized activities such as walking by a tree or other non-tree 

contact activities are not likely to induce a tree to fail. A tree may fail due 

to either its condition or weather. Activities involving non-motorized, 

non-tree contact include planting trees, standing near a sign, walking 

on a trail, or 

doing resource 

surveys.

Motorized 

activities or 

non-motorized 

activities that 

may contact the 

tree or otherwise 

infl uence its 

integrity, include 

operating a 

grader, culvert 

work, measuring 

tree diameters, 

examining 

dead roots, tree 

Wounded Douglas-fi r, like this one on the Rogue RiverSiskiyou National Forest, may indicate internal decay. 

The amount of sound wood remaining will determine 

tree-failure potential.
33

falling, road or trail construction, and helicopter operations. All of these 

activities may induce a tree to fail.

 

1) 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 roadways must be felled. 

Washington 296-54-531 Truck roads (3)(a) 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 three types of exposure: intermittent, short duration, and long 

duration. Intermittent exposure includes traffic driving by a defective 

tree. Short-duration exposure includes 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 exposure 

to defective trees while parked at a trailhead, repairing a road, or 

working on a log landing for more than 15 minutes.

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 that people or property are exposed to a danger tree, the 

greater the opportunity for the failed tree to impact them. If exposure 

duration and traffic frequency are reduced, the opportunity for the 

tree to impact people or property is also reduced. The qualified 

person should consider traffic frequency and exposure duration when 

determining whether a tree poses a danger. For specific direction, refer 

to agency policy about danger trees along roads (11). 

2) Non-motorized, non-tree-contact activities

Non-motorized, non-tree contact activities involve walking or 

conducting activities near trees without touching them. The premise 

behind these activity types is that trees are much less likely to fail if they 

are not contacted, and people are more likely to recognize tree dangers 

if they are not focused on operating vehicles or machinery. Examples 

include tree planting, noxious-weed control, surveying, walking along a 

trail, or standing at a bus stop.
34

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

an imminent-failure potential. Since these trees may fail at any time, 

they pose a danger regardless of the activity type. Because these trees 

expose people to dangers, only qualifi ed 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, the qualifi ed person needs to evaluate 

the tree condition, type of activity, and whether or not the person will 

be within the potential-failure zone. If the qualifi ed person determines 

that a tree with likely failure-potential does not represent a danger, 

people should work or walk through the potential-failure zone quickly 

so as to minimize exposure time and avoid tree contact. If the tree is a 

danger, it should be removed or the activity should be excluded from 

within the potential-failure zone. 

3) Motorized or tree-contact activities

Motorized activities and those activities that may contact the tree 

include riparian restoration, logging (all types), increment coring, tree 

falling, tree climbing, site preparation, road or trail construction, and 

Motorized activity can cause trees or parts to fail, as with this tree-falling 

activity near Ashford, WA.
35

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.

Prioritizing Roads for Survey and Treatment 

There are many miles of roads that may have danger trees adjacent to 

them. It is not possible to correct all danger-tree problems on a National 

or State Forest within a few months or even years, so it is necessary to 

prioritize the danger-tree survey and treatment workload. The priority 

for which roads should be surveyed is based on the frequency of road 

usage and maintenance level (Table 2). Maintenance-level 5, 4, and 3 

roads, in that order, should be surveyed first; maintenance-level 2 and 1 

roads should be surveyed last. 

The treatment priority within a surveyed road segment should be highest 

where people or vehicles are most likely to be impacted by danger trees 

(Fig. 5). Consideration of exposure level and traffic frequency provides a 

way to prioritize the danger-tree workload (Table 3).

Table 2. USDA Forest Service road-maintenance levels and survey 

priority with level-5 roads receiving the highest priority.

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 highclearance vehicles

All National Forest 

traffic, general use, 

commercial haul, 

maintained for 

passenger cars

 

A maintenance level-3 road with danger trees, 

Gifford Pinchot National Forest.
36

Table 3. Road-treatment priority for danger trees

Facility

Exposure 

Duration

Failure 

Potential

Road 

Segment 

Priority

Priority 

Within 

Road 

System

Areas where 

people stop and 

congregate such 

as parking areas 

or 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 high 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
37

Facility

Exposure 

Duration

Failure 

Potential

Road 

Segment 

Priority

Priority 

Within 

Road 

System

Areas where 

people stop and 

congregate such 

as parking areas 

or 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 high 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

 
38

Step 3 - Determine the Tree’s PotentialFailure Zone

The potential-failure zone is the area on the ground that could be 

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

parts may slide or roll. When a tree fails, it may strike other trees or 

debris on the ground and propel material a considerable distance. This 

is especially true for dead trees, tops, or branches. The qualifi ed person 

needs to be aware of these situations when determining the potentialfailure zones.

Total Tree Failure – Potential-Failure Zone 

When determining the potential-failure zone for total tree failure, the 

following conditions must be evaluated: (1) ground slope angle, (2) 

direction of lean (>15 degrees), and (3) tree height. 

Leans <15 degrees are too diffi cult to accurately predict the natural fall 

direction (Fig. 6). Such leaning trees should be assumed to fall in any 

direction. 

Fig. 5 - A road segment with a parking lot that should receive high priority for treatment. 

Note several trees with imminent-failure potential that are dangers as well as those with 

likely failure potential that also are danger trees in this case with short or long exposure 

durations.
39

Fig. 6 - Substantial lean is greater than or equal to15 degrees.

Fig. 7 – Potential-failure 

zone for total tree failure 

with no slope or lean.
40

Level or sloped ground with no lean 

On level ground, the potential-failure zone is a circle around the tree 

with a radius equal to 1 1⁄2 times the total tree height (Fig. 7). On sloped 

ground, the failure zone downhill from the tree should be extended 

whatever distance is necessary to protect people from sliding or rolling 

trees (Fig. 8). 

Level or sloped ground with lean in any 

direction

The potential-failure zone has a radius equal to 1 1⁄2 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 (Fig. 8).

The area behind the lean is not within the full-failure zone. Be aware, 

however, that if equipment, lines, moving logs, falling trees, or severe 

winds contact a likely or imminent-failure potential tree, the contact 

could force a backlash opposite to the lean and extend the potentialfailure zone about 1⁄2 times the 

tree height.

On sloped ground, where the 

dislodged section may roll 

downhill, the potential-failure 

zone should be extended 

on the downhill side for 

whatever distance is 

necessary to protect 

people.

could force a backlash opposite to the lean and extend the potentialfailure zone about 1⁄2 times the 

tree height.

On sloped ground, where the 

dislodged section may roll 

downhill, the potential-failure 

zone should be extended 

on the downhill side for 

whatever distance is 

necessary to protect 

people.

Fig. 8 – Potentialfailure zone for total 

tree failure with slope 

and lean.
41

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 angle

• Amount and direction of lean >15 degrees

• Length of the part that could dislodge

Level or sloped ground with no lean 

Determine the length of the part that could dislodge. On level ground, 

the potential-failure zone forms a circle around the tree with a radius 

equal to at least 11⁄2 times the length of the dislodged part (Fig. 9). This 

extra area accounts for parts that 

may slide along branches should 

they fail. On sloped ground where 

the dislodged part may slide or roll 

downhill, the failure zone should be 

extended on the down-hill side for 

whatever distance is necessary to 

protect people. 

Fig. 9 – Potential-failure zone for top failure 

with no slope or lean.
42

Level or sloped ground with 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 potential-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 potential-failure zone. Be 

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

or severe winds contact a likely or imminent-failure potential tree, 

the contact could force a backlash opposite to the lean and extend 

the potential-failure zone about the length of dislodged part. On 

sloped ground where the dislodged part may slide or roll downhill, 

the potentialfailure zone is 

extended on the 

downhill side for 

whatever distance 

is necessary to 

protect people 

(Fig. 10).

Fig. 10 - Potentialfailure zone for top 

failure with slope and 

lean.
43

Step 4 – Determine if the Tree Poses a 

Danger

A tree is identifi ed as a danger tree based on failure potential, type of 

activity, exposure duration, and the potential-failure zone. Not all trees 

with a likely or imminent potential to fail are danger trees (Table 4 and 

Fig. 11). For instance, if the activity is outside of the potential-failure 

zone, the tree is not considered a danger. If the activity is mechanized 

with short or long exposure, the tree has likely failure potential, and 

the work is within the potential-failure zone, the tree is a danger. The 

following should be considered in determining if the tree poses a 

danger:

• Evaluate the tree and determine its condition and failure 

potential.

• Identify the potential-failure zone and determine if the activity is 

within the failure zone.

• Determine the exposure duration (intermittent, short, or long).

All trees or parts with imminent-failure potential are a danger if they 

will strike a road or target (Table 4 and Fig. 11). Trees or parts with 

likely failure potential that will strike a road or target may be a danger 

Danger trees along a summer-home road, Mt. Hood National Forest. Pull-outs 

and parking spurs should have a higher priority for survey and treatment.
44

depending on the exposure duration. If the exposure duration is 

intermittent, such as a drive-by or walk-by, the tree or part is not 

considered a danger. If the exposure duration is short (<15 min.) or long 

(>15 min.), then the tree is a danger and should be treated (Table 4 and 

Fig. 11).

Large Areas of Recently Killed Trees

Severe wildfi res or beetle epidemics can kill trees over hundreds of acres 

within a short time period. Because most of the trees are recently killed 

(<5 years), they have a likely failure potential unless they are small trees 

<10 in. dbh; are cedar, juniper, larch, or large Douglas-fi r; or they have 

root disease or certain defects (Table 1). For most recently killed trees, 

exposure duration along roads mainly is intermittent (drive-by traffi c) 

and therefore the trees are not a danger. However, due to the large 

number of recently killed trees in these situations, there is a higher risk 

of tree failures occurring, because stands are often more open following 

large disturbances, and trees may be more prone to windthrow or windshatter. After fi ve years, most of these trees (except cedar, juniper, larch, 

or large Douglas-fi r) will have imminent-failure potential and therefore 

will become danger trees. The challenge is deciding when to treat 

such trees that are not now a danger but will become danger trees in 

fi ve years. Waiting fi ve years for thousands of trees to become dangers 

presents at least three problems for forestland managers: 1) some trees 

Fire-killed trees were felled along this road on the Okanogan-Wenatchee 

National Forest.
45

may fail before they have been dead for fi ve years, 2) older, dead trees 

have less commercial value because of decay and defect than recently 

killed trees, and 3) older, dead trees are more dangerous to fell because 

of increased decay and defect.

Most USDA Forest Service managers have dealt with this dilemma 

by felling all of the recently killed trees and danger trees within 

striking distance of a road system after a thorough consultation with 

an evaluation team of natural-resource experts, approval from the 

appropriate line offi cers, and addressing all NEPA considerations (p. 

52). In some cases, line offi cers have decided to remove live trees that 

have a very low-probability of survival post-fi re (e.g., trees with ≥ 90% 

crown scorch or consumption) within striking distance of roads that 

would most likely become dangers in the future. This usually requires 

a diff erent level of NEPA than a road maintenance CE (p. 52-55). Roads 

should be closed following large disturbances if the risk of danger 

trees to human safety is unacceptable prior to mitigation. Creative 

fi nancing is usually needed to fund these large projects if there is little 

or no income generated from the felled trees. Burned Area Emergency 

Response (BAER) funds have been used to treat fi re-killed trees along 

roads as recommended in the Region 6 transportation policy (11). 

Guidelines have been published to determine the survival probability of 

fi re-injured, living conifers in northeastern Oregon and elsewhere with 

probable applicability to other areas in Oregon and Washington (12, 13).

These fi re-killed trees were removed using Burned Area Emergency Response 

(BAER) funds on the Okanogan-Wenatchee National Forest.
46

Table 4. How to determine if a tree with imminent or likely failure 

potential is a danger.

Treefailure 

potential 

is:

Road or activity is: Tree is:

Imminent Within the potential-failure zone A danger

Likely Within the potential-failure zone

• and duration of exposure is 

intermittent (i.e. walk-by or drive-by)

Not a 

danger

• and duration of exposure is short or 

long (i.e. bus stop or log landing)

May be a 

danger

Fig. 11 –Trees with likely failure potential and within striking distance can be dangers if 

exposure duration is short or long, as when people have stopped to read this roadside 

sign. 
47

The following three examples illustrate the process a qualified person 

should take when evaluating potential-danger trees:

Example 1

Scenario 1. Assume there is a skyline logging operation. You as the 

qualified person notice that behind the landing, the standing trees look 

abnormally yellow (chlorotic). There is a history of dying trees in the area 

combined with some live trees with sparse crowns. You don’t notice 

any windthrow but do observe basal resin and bark staining in a few 

standing trees. When you chop at the root collar and pull the bark away, 

you discover white, latex-like, mycelial fans. 

You conclude that the live but chlorotic trees have Armillaria root 

disease (p. 60) 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 any machinery 

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 and need to be felled or the landing moved.

Scenario 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 

chlorotic. You don’t notice any windthrow but do notice several honeycolored mushrooms around the base of several of the trees along with 

basal resin and bark staining. When you chop at the root collar and pull 

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

You conclude that the live 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 any equipment will strike the 

trees and cause them to fail. Your conclusion is that the Armillaria rootdiseased 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 you are evaluating trees along a haul-route road. You notice 

two very similar white fir trees in two separate locations. Each tree 

has several, large, Indian paint fungus conks on the bole (p. 92). You 
48

conclude the trees have substantial heart rot and have an imminentpotential 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 consider that when the trees fail they may 

not actually hit any traffi c, but that traffi c may run into them, especially 

the one on the curve. You conclude that the trees pose a danger and 

need to be removed.

Example 3

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

has many dead and a few large, live trees scattered about. You notice 

that the bark appears 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 around the tree base. You also notice 

that some leaning, dead trees are hung up in the crown of other trees. 

On the other side of the unit, there are a few live trees standing straight 

with heart-rot conks on their boles.

You conclude that the leaning, root-sprung trees, the trees that are 

hung up, and the trees with the loose bark have imminent-failure 

White fi r killed by Armillaria root disease on the Fremont-Winema National 

Forest. Most of the dead trees here are danger trees, regardless of activity 

type or exposure duration. 
49

potential. 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. The areas within the failure zones 

cannot be safely planted without removing the danger by felling the 

trees. The danger trees need to be felled, or the planting crews need to 

avoid planting in the tree-failure zones.

The straight, green trees with heart rot are determined to have a likely 

potential for failure. The exposure under them will be of intermittent 

duration, and the activity around them 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 avoid 

contacting the trees.

Step 5 - Document the Danger-Tree 

Assessment

A record that an inspection was performed along a forest road or work 

site is necessary to provide evidence that a survey was completed. 

Documenting trees with imminent or likely failure potential can provide 

evidence that a tree was examined and a decision made to mitigate 

or not mitigate the hazard. A map of the approximate location of the 

danger trees is always helpful. A tree-record form (pp. 50-51) must be 

completed for trees with imminent or likely failure potential. Healthyappearing trees with low-failure potential may be inspected but 

are rarely recorded. A tree-record form that lists trees with elevated 

hazard and their recommended treatment is given to the line offi cer 

or supervisor. Documenting the major defects at each road segment 

or work site makes 

future surveys 

more effi cient 

and is a record 

of performance 

in the event of 

litigation. From a 

legal standpoint, 

if a survey is not 

documented, 

then it was never 

completed.

Documenting danger trees, Okanogan-Wenatchee 

National Forest
50

Road Danger-Tree Evaluation Form

Road: Qualified Person: Mtce Level (1-5) Date:

For individual or groups of trees Exposure (Intermittent, short duration, long duration) and descriptionTree or Group Number 

Mile Post or Coordin ates

Side of Road or Azimuth

Distance From Road(ft)

Tree Species

DBH (in)

Tree Height (ft)

Tree Condition, Defect or 

Disease

Failure Potential (I)mminent, (L)ikely or (Low)

Potential Failure Zone Intersects RoadYes or No

Tree is a DangerYes or No

Recommended Action

Notes:
51

Work Site Danger-Tree Evaluation Form

Work Activity Qualified Person: Date:

Exposure (Intermittent, short duration, long duration) and descriptionTree Number 

Tree Species

DBH(in)

Tree Height (ft) Tree Condition, Defect or Disease

Failure Potential (I)mminent, (L)ikely or (Low)

Potential Failure Zone Intersects RoadYes or No

Tree is a DangerYes or No

Recommended Action

Notes:
52

Step 6 – Determine What Action to Take if 

the Tree is a Danger

Our objective is to minimize exposure to danger trees. If after 

considering the tree condition and activity and recording your 

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

either be felled or the activity arranged so that the danger is mitigated. 

If culturally modifi ed or wildlife trees are involved, archeologists or 

wildlife biologists must be informed of the intended action. Present 

your observations and recommendations to your supervisor. Decisions 

to mitigate danger trees are the responsibility of the supervisor or line 

offi cer. As a qualifi ed person, you have completed your responsibilities. 

Methods of mitigating danger trees are discussed in Danger tree 

mitigation guidelines for managers, 2011 (16).

NEPA (National Environmental Policy Act) 

Considerations

The following section outlines some considerations for implementing 

the National Environmental Policy Act (NEPA) for danger-tree 

management. Coordinate with local NEPA, Endangered Species Act 

(ESA) and Cultural Resource specialists for more information. 

Danger-tree mitigation on the Mt. Hood National Forest. The felled trees were 

used for stream-enhancement projects.
53

In general, NEPA applies to all decisions made by the USDA Forest 

Service that could affect the human environment. However, the level 

of documentation required varies depending on the scope and scale of 

a proposed action. Complexity and documentation requirements are 

proportional to the size of a project’s footprint and the duration of the 

project’s potential effects.

Emergency Situations

36 CFR 220.4 notes that a responsible official may take actions necessary 

to control the immediate impacts of the emergency and are urgently 

needed to mitigate harm to life, property, or important natural or 

cultural resources. This may require action (e.g., felling a danger tree) 

before ordinary NEPA documentation requirements can be met. Any 

foreseeable adverse environmental effects would be mitigated to the 

extent practical.

Unless there is a determination that an emergency exists, danger-tree 

management requires environmental review and documentation prior 

to action on the ground. 

Connected Actions

Danger-tree management may be connected to other actions proposed 

by the Forest Service, such as vegetation management. Connected 

actions would ordinarily be considered together in a single NEPA 

analysis. In such cases, danger-tree management would be listed as 

a mitigation measure or connected action. Danger-tree mitigation 

should extend through the life of the connected project. Adaptivemanagement criteria may be analyzed to ensure that foreseeable 

danger trees are addressed through the life of a project. If danger 

trees are to be sold after felling, the sale of forest products would be a 

connected action. 

Categorical Exclusions

The primary NEPA documents are Environmental Assessments (EA) 

and Environmental Impact Statements (EIS). However, some routine 

actions taken by the Forest Service may be “categorically excluded” from 

documentation in an EA or EIS. Categorical exclusion refers to categories 

of actions that the Forest Service has determined would not individually 

or cumulatively have a significant effect on the human environment. As 

long as there is an applicable category, and there are no extraordinary 

resource conditions, the project may be categorically excluded from 

documentation in an EA or EIS. 
54

Danger-tree management could fall under the following categories of 

actions that can be taken with little documentation. These categories do 

not require preparation of any decision documentation (e.g., decision 

memo). However, some public involvement is usually required and high 

public interest could infl uence the level of documentation required and 

a responsible offi cial could elect to prepare a decision memo for the 

following categories: 

• 36 CFR 220.6(d)(3) Repair and maintenance of administrative 

sites. 

• 36 CFR 220.6(d)(4) Repair and maintenance of roads, trails and 

landline boundaries. 

• 36 CFR 220.6(d)(5) Repair and maintenance of recreation sites and 

facilities 

Extraordinary resource conditions that might warrant further analysis 

and documentation in an EA or an EIS are:

(1) Federally listed, threatened, or endangered species or designated 

critical habitat, species proposed for Federal listing or proposed 

critical habitat, or Forest Service sensitive species;

(2) Flood plains, wetlands, or municipal watersheds;

(3) Congressionally designated areas, such as wilderness, wilderness 

study areas, or national recreation areas;

(4) Inventoried roadless areas or potential wilderness areas;

(5) Research natural areas;

(6) American Indian and Alaska Native religious or cultural sites, and

(7) Archaeological sites, or historic properties or areas. 

In riparian 

areas, waterquality bestmanagement 

practices (BMP) 

and monitoring 

may be required 

for mitigating 

danger trees.
55

The mere presence of one or more of these resource conditions 

does not preclude use of a categorical exclusion (CE). In considering 

extraordinary circumstances, the degree of the potential effects on the 

listed resources (or uncertainty) influences whether the project may be 

categorically excluded. 

Danger-tree mitigation could be connected to other actions that may 

be categorically excluded and also require documentation in a decision 

memo. Some examples include: 

• 36 CFR 220.6(e)(1) Construction or Reconstruction of Trails36 CFR 

220.6(e)(2) Additional construction or reconstruction of existing 

telephone or utility lines in a designated corridor

• 36 CFR 220.6(e)(6) Timber stand and/or wildlife habitat 

improvement activities that do not include the use of herbicides 

or do not require more than 1 mile of low standard road 

construction.

• 36 CFR 220.6(e)(11) Post-fire rehabilitation activities, not to 

exceed 4,200 acres (such as tree planting, fence replacement, 

habitat restoration, heritage site restoration, repair of roads 

and trails, and repair of damage to minor facilities such as 

campgrounds), to repair or improve lands unlikely to recover to a 

management approved condition from wildland fire damage, or 

to repair or replace minor facilities damaged by fire.

• 36 CFR 220.6(e)(12) Harvest of live trees not to exceed 70 acres, 

requiring no more than 1⁄2 mile of temporary road construction.

• 36 CFR 220.6(3)(13) Salvage of dead and/or dying trees not to 

exceed 250 acres, requiring no more than 1⁄2 mile of temporary 

road construction. 

• 36 CFR 220.6(e)(14) Commercial and non-commercial sanitation 

harvest of trees to control insects or disease not to exceed 

250 acres, requiring no more than 1⁄2 mile of temporary road 

construction, including removal of infested/infected trees 

and adjacent live uninfested/uninfected trees as determined 

necessary to control the spread of insects or disease. 

Relationship to Endangered Species Act 

The degree of potential effects to federally listed, threatened, or 

endangered species or designated critical habitat, species proposed for 

Federal listing or proposed critical habitat, or Forest Service sensitive 

species influences whether a project may be categorically excluded 

from documentation in an EA or EIS. It also influences ESA Section 7 
56

Consultation requirements. Actions that may aff ect federally listed, 

threatened, or endangered species or designated critical habitat, 

species proposed for Federal listing or proposed critical habitat require 

consultation with either the US Fish and Wildlife Service (most fi sh, 

wildlife, plants) or the National Marine Fisheries Service (anadromous 

fi sh). 

Consultation is not required if a local biologist fi nds a project would 

have no eff ect on any federally listed, threatened, or endangered 

species or designated critical habitat, or any species proposed for 

Federal listing or proposed critical habitat.

The level of consultation is infl uenced by the degree of impact. For 

projects that may aff ect but are not likely to adversely aff ect federally 

listed, threatened, or endangered species or designated critical habitat, 

or species proposed for Federal listing or proposed critical habitat, 

informal consultation can be conducted relatively quickly. For projects 

that may have an adverse eff ect, regulatory agencies must issue a 

biological opinion. 

In some cases, programmatic consultation has been conducted which 

would negate the need for consultation on an individual project. 

Riparian Areas

If danger trees are to be removed within a riparian area, water-quality 

best-management practices (BMP) and monitoring may be required. 

Some water courses are listed as water-quality limited and may have 

special mitigation 

requirements. 

Other areas 

are considered 

key watersheds 

or priority 

watersheds, which 

may infl uence 

project design or 

documentation 

requirements. 

Scenic roadside overlooks, such as this one near Mt. 

St. Helens, may require special consideration when 

treating danger trees. 
57

Effects on Heritage Resources

Consultation with State Historic Preservation Offices (SHPO) and/or 

consultation with tribal governments may be required. In some cases, 

there has been programmatic consultation with SHPO which negates 

the need for consultation on an individual project. 

Land and Resource Management Plans and Special 

Management Areas

Some places may require special consideration, for instance, older 

forest-management areas, wild and scenic river corridors, research 

natural areas, botanical areas, and scenic overlooks. 

Tree Defect and Disease Identification

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

tree-failure potential (Tables 5 and 6). Detailed information about 

disease and defect identification in Oregon and Washington forests can 

be found in Field guide to the common diseases and insect pests of Oregon 

and Washington conifers (9). 

Table 5. Important tree diseases and their chief conifer host-species 

groups (resinous and non-resinous) associated with danger trees in 

Oregon and Washington 

Douglas 

fir

True 

fir

Hemlock Spruce Pine Larch Cedar Juniper

Resinous X partial X X

Root Rots

Armillaria X X X X X

Black stain X X

Heterobasidion X X X

Laminated X X X

P.O. cedar X

Butt Rots

Ganoderma X

Schweinitzii X X X X

Tomentosa X

Heart Rots

Brown top X

Brown trunk X X X X

Cedar pecky X

Heterobasidion X X
58

Douglas 

fir

True 

fir

Hemlock Spruce Pine Larch Cedar Juniper

Heart Rots

Pencil X

Juniper pocket X

Red ring X X X X X X X

Rust-red stringy X X

Sap rots

Brown 

crumbly

X X X X X X

Gray-brown X X X X X X

Cankers

Atropellis X

Comandra rust X

Cytospora X

Mistletoe X X X X X X

Red ring rot X

Western 

gall rust

X

White pine 

blister rust

X

Table 6. Important tree diseases and their chief hardwood hostspecies groups associated with danger trees in Oregon and 

Washington 

Alder Aspen Cottonwood Maple Madrone Myrtle Oak Tanoak

Root Rots

Armillaria X X X X X X X X

Heterobasidion X

Butt Rots

Ganoderma X X X X

Heart Rots

Aspen trunk X

Hardwood 

trunk

X X X X

Sap rots

Brown 

crumbly

X X X X X X X X

Cankers

Cytospora X

Mistletoe X

Nectria X

Ramorum X
59

Tree condition and visible indicators often determine failure potential. 

There are several factors that should be included in that evaluation. 

Following is a presentation of significant disease and defect indicators in 

Oregon and Washington. 

Dead Trees

Tree-failure potential increases proportionately with the number of 

years a tree has been dead as sap-rotting fungi decay the roots, boles, 

and tops of dead trees. This decay process is slower for resinous species 

such as Douglas-fir, pine, and larch, because resin (pitch) inhibits fungal 

growth and insect attack (Table 5). Decay is also slower in cedar and 

juniper that have decay-inhibiting compounds in their wood. Decay 

is much faster in the sapwood than in the heartwood of dead trees. 

Heartwood also has compounds that inhibit decay by some sap-rotting 

fungi. Smaller dead trees, tops, and branches with proportionately 

more sapwood decay faster than larger dead trees or tree parts with 

proportionately more heartwood. This information is based on observed 

fall-down rates and decay of dead trees and tops by species and size 

classes (17, 18).

Recently killed trees often retain all or some of their foliage and fine 

branches (Table 1). Bark remains mostly intact except maybe for thinbarked species such as lodgepole pine. Trees that have been dead five 

or more years, usually have no foliage or fine branches. Bark is often 

absent or beginning to slough off.

For a recently (<5 years) fire-damaged tree, where green needles may 

still be present, inspect the cambium at the root collar to determine if it 

is alive or dead. For most species, a tree is considered dead, even if the 

crown is green, when at least three of the four quadrants around the 

base of the root collar have cambium, inner bark, or phloem that are 

discolored and dead. Large ponderosa pines are considered dead only 

after all four quadrants of the cambium and inner bark are dead (12).

Root Defects

Root Diseases

Root diseases or root rots often cause a tree to fail. Sites with root rots 

will have danger-tree problems for decades unless properly treated, 

because these diseases can remain on the site for hundreds of years and 

spread slowly through the forest. Root diseases are difficult to diagnose, 

and a forest pathologist may need to be consulted.
60

• General symptoms and indicators:

o Decline of the entire live crown is characterized by 

yellowing foliage, dying branches, premature shedding 

of older needles, and terminal and lateral shoot-growth 

reduction (Fig. 12).

o Distress-cone crops may be present.

o Basal resin fl ow (Fig. 14) or bark staining may be present. 

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

root collar of infected trees (Fig. 17).

o Windthrow of surrounding trees generally is present (Fig. 

13).

o Groups or pockets of trees are often aff ected with dead 

and dying trees of various sizes and levels of decay on the 

site.

o Bark beetles often attack trees stressed by root disease.

Important root diseases commonly associated with danger trees 

include:

• Armillaria root disease caused by Armillaria spp. 

o Armillaria root disease is caused by several species of 

Armillaria, but Armillaria ostoyae is the most damaging.

Fig. 12 – Dead and dying trees often are 

caused by root disease.

Fig. 13 - Windthrow is often associated with 

root disease.
61

o Armillaria affects many tree species (Tables 5 and 6) and is 

often found on weakened and stressed trees.

o Root decay may be extensive; trees with Armillaria root 

disease should not be considered wind firm. 

o Unlike laminated root rot, Armillaria-killed trees most 

often die standing.

o Trees adjacent to a disease center may not show 

symptoms of infection.

o Infected trees may have abundant resin flow or bark 

staining at the root collar (Fig. 14).

o White, latex-like, mycelial fans often are found under the 

bark of infected roots and at the root collar (Fig. 15).

o Rhizomorphs or fungal “shoestrings” that resemble small, 

black roots, may be present under the bark or on infected 

roots.

o Honey-colored mushrooms may be found at the base of 

infected trees in the fall. 

o Advanced decay is yellow, stringy, and water-soaked.

o Tree-failure 

potential 

varies with 

the presence 

of disease 

signs and 

symptoms 

and evidence 

of adjacent, 

windthrown 

trees with 

root disease 

(Table 1).

 

 

Fig. 14 - Resin flow at the root 

collar often is associated with 

Armillaria root disease. 
62

• Black stain root disease caused by Leptographium wageneri

o Black stain root disease kills all ages of pine east of 

the Cascade crest and young Douglas-fi r west of the 

Cascades. 

o The disease causes a vascular wilt and is not a wood 

decayer. 

o Trees rarely fail until after they die. 

o A characteristic sign at the tree base is a brown to 

purplish-black stain in older sapwood that fades with 

time in dead trees.

o Black stain root disease often is associated with soil 

disturbance along roads and with soil compaction.

o The disease is spread by root grafts and root-feeding 

insects that are attracted to stressed trees. 

o Live trees in black stain root disease centers have lowfailure potential; dead trees have imminent-failure 

potential (Table 1).

• Heterobasidion root disease caused by Heterobasidion spp.

o Heterobasidion root disease, formally called annosus root 

disease caused by H. annosum, is especially damaging to 

grand fi r, white fi r, and hemlock.

Fig. 15 - Mycelial fans of the fungus, Armillaria ostoyae, under the bark of an 

infected Douglas-fi r.
63

o Two species of Heterobasidion are now recognized: H. 

occidentale on true fi rs and hemlocks and H. irregulare on 

pines.

o It is one of the most diffi cult root diseases to identify.

o Infected trees may exhibit symptoms of root disease or 

they may not have symptoms if the decay is confi ned 

to the butt and lower bole (common in hemlock and 

spruce).

o Conks are perennial with woody or leathery, dark- to 

chestnut-brown, upper surfaces; white, pore-less 

margins; and creamy-white undersurfaces with small, 

round, regular pores (Fig. 17). Conks may appear as small 

pustules on roots.

o 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. 

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

outer heartwood.

o Advanced decay is white and stringy (Fig. 16) to 

laminated in true fi r. Elongated pits occur only on one 

side of the laminations. Setal hyphae are not present in 

the infected wood. 

o Black fl ecks the size of rice grains may be observed in the 

advanced decay.

o In western hemlock, a water-soaked pattern occurs with 

the advanced decay.

Fig. 16 - White, stringy 

decay associated 

with Heterobasidion root 

disease in a hemlock stump.

Fig. 17 – Conks associated with Heterobasidion root disease
64

o Root and butt decay predispose trees to windthrow and 

stem breakage.

o Failure potential varies with the presence of disease 

signs and symptoms and evidence of adjacent, 

windthrown trees with root disease (Table 1).

• Laminated root rot caused by Phellinus sulphurascens

o The pathogen was formerly called Phellinus weirii which 

now is the name of the causal agent of laminated root rot 

of cedars.

o Primary hosts are Douglas-fi r, white/grand fi r, and 

mountain hemlock.

o Laminated root rot is the most dangerous root disease 

associated with tree failure in the Pacifi c Northwest.

o The disease can readily aff ect even the healthiest trees 

in the stand and often causes green trees to fail due to 

extensively decayed root systems (Fig. 13).

o Laminated root rot is distinguished from other root 

diseases by the presence of red, setal hyphae in the 

decayed wood or in mycelium that, with a hand lens, look 

like tiny, reddish whiskers (Fig. 19).

Fig. 18 - Laminated decay caused by 

Phellinus sulphurascens

Fig. 19 - Setal hyphae, the red-brown, 

fuzzy material shown here, are 

diagnostic for laminated root rot.
65

o Decayed wood is laminated with pitting on both sides of 

the laminations (Fig. 18).

o Mycelium on the surface of infected roots, called 

ectotrophic mycelium, can be found on live and recently 

killed trees.

o Conks are diffi cult to fi nd and occur infrequently on the 

undersides of infected roots or logs.

o Root disease pockets can be small to several acres in size 

characterized by abundant windthrow with almost no 

roots (root balls) (Fig. 13).

o Trees adjacent to an infection center may not show 

symptoms of infection, making them diffi cult to rate for 

failure potential.

o Failure potential varies depending on tree species and 

distance from adjacent, infected trees or stumps (Table 1).

• Port-Orford-cedar root disease caused by Phytophthora lateralis 

o This is an introduced disease and has caused widespread 

mortality of Port-Orford-cedar (POC) throughout its 

native and ornamental range.

o The disease typically causes a cinnamon-colored stain in 

the inner bark of roots and lower stems.

o The disease is common along roads, watercourses, and in 

poorly drained areas.

o Live trees in POC root disease centers have low-failure 

potential; dead trees have likely failure potential (Table 1).

Fig. 20 - Undermined 

and severed roots, as 

seen here, can result 

in tree failure.
66

Undermined or Severed Roots 

• Root disturbance often is seen as undermined or severed roots 

(Fig. 20). 

• A compromised root system predisposes a tree to fall. 

• Undermined roots often are associated with roads or are adjacent 

to streams or rivers. 

• The result of extreme undermining is tree failure from insufficient 

anchorage.

• Failure potential varies with the amount of structural roots 

remaining in the ground (Table 1).

Lower-Trunk (Butt) Defects

Butt Rots

Butt rots often result in tree failures. Sites with butt rots may have 

danger-tree problems for decades unless treated, because, like root 

disease, butt rots may persist in infected trees for decades. Butt rots are 

difficult to diagnose, and a forest pathologist may need to be consulted.

• General symptoms and indicators:

o Butt rot often occurs without causing crown symptoms.

o Mushrooms or conks may occur on the roots, at the root 

collar, or at the base of infected trees (Fig. 21).

o Windthrow or wind-shatter of surrounding trees is 

generally present.

o Groups or pockets of trees may be affected but usually 

only individual trees are decayed.

o The incidence of butt rot sometimes increases with the 

amount of tree wounding.

Important butt rots commonly associated with danger trees include:

o Ganoderma root and butt rot is caused by Ganoderma 

tsugae (lacquer fungus or varnish conk) or G. applanatum 

(artist’s conk)

o Ganoderma root and butt rot affects many conifer and 

hardwood species but is more common in hardwoods, 

especially Oregon myrtle.
67

o The rot occurs in wounded, live trees and dead or broken 

trees.

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

underside that stains brown when marked (Fig. 21).

o The varnish conk has a shiny, brown, upper surface; white 

underside; and often a stem or stalk.

o The decay associated with both conks is a white, spongy 

rot with black fl ecks.

o Failure potential varies with the amount of butt decay 

and the presence of disease signs and symptoms (Table 

1).

• Schweinitzii root and butt rot caused by Phaeolus schweinitzii 

(velvet-top or cow-pie fungus).

o This root and butt rot aff ects many tree species. However, 

it is found primarily on large, old Douglas-fi r and Sitka 

spruce. 

o Fresh fruiting bodies are velvety to the touch and have 

a brightly colored, yellow margin. As they age, they 

become brittle and turn dark brown (Fig. 22). 

Fig. 21 - Ganoderma root and butt rot is associated with the artist’s conk, as seen on 

this infected stump.
68

o Trees with rot may have fruiting bodies growing on or 

near the butt. 

o While conks may be absent, trees with extensive decay 

may have pronounced butt swell (Fig. 23).

o On the westside of the Cascade Range, butt decay may 

be indicated by fruiting bodies or swollen butts, but these 

indicators are not reliable to determine the amount of 

decay. Use these indicators to look for other indicators of 

severe decay such as open cracks or exposed rot (Table 1).

o On the eastside of the Cascade Range, Schweinitzii root 

and butt rot may be common, but it is often present 

without indicators, especially on dry sites. As such, it is 

discovered less often until signifi cant wind events and 

tree failures have occurred or cause the trunk to crack.

o Decay of the butt extending as much as 30 feet up the 

bole occurs when trees are >50- years old. 

o Trees with extensive butt rot often fail under high-wind 

conditions, leaving a characteristic barber-chair and 

shattered butt.

o Once trees with fruiting bodies have been identifi ed 

or butt swell recognized, those susceptible trees 

immediately adjacent to them also should be evaluated. 

o Tree mortality is unusual unless associated with Armillaria 

root disease.

o Failure potential varies with the amount of butt 

decay and the presence of disease signs and symptoms 

(Table 1).

Fig. 22 - Older conks of Phaeolus 

schweinitzii often resemble “cow pies”.

Fig. 23 - Butt swell of Douglas-fi r often 

is associated with root and butt decay 

caused by Phaeolus schweinitzii.
69

• Tomentosus root and butt rot caused by Onnia tomentosa

o The fungus that causes the disease was formerly named 

Inonotus tomentosus.

o Tomentosus root and butt rot is found most commonly in 

Engelmann spruce (Fig. 24).

o It typically does not cause extensive damage but is locally 

important in the Cascade and Blue Mountains.

o This disease may be diffi cult to detect, even in trees with 

extensive butt rot.

o Trees with crown symptoms rarely occur and make the 

disease diffi cult to detect.

o Mushrooms are small, cinnamon-colored, leathery, and 

may appear in the fall near the base of infected trees (Fig. 

25). 

o When infected trees are mature, they are more likely to be 

severely rotted in the roots and butt.

o Advanced 

decay is a white 

pocket rot.

o Failure 

potential 

varies with the 

amount of butt 

decay and the 

presence of 

disease signs 

and symptoms 

(Table 1). Fig.24 – Wind-shattered spruce caused by 

Onnia tomentosa.

Fig. 25 - Mushrooms of the causal fungus, Onnia 

tomentosa.
70

Fire-Caused Damage

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

of them are missing which may cause the tree or limb to break 

and fall (Fig. 26).

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

fall.

• Before burning, a tree may have had signs or symptoms, such 

as conks, frost-crack weeping, basal resinosis, or dead tops that 

may have burned, thus eliminating the indicators of root disease, 

heart rot, or previous dead tops. Therefore, the tree may be more 

unstable than the visible indicators suggest.

• Large pines, larch, or Douglas-fi r with old, basal, fi re 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 (12).

• Long-lasting and smoldering fi res at the bases of large pines 

usually kill the fi ne roots and eventually the entire tree.

• Failure potential is determined by tree species (resinous or nonresinous), the amount of sound-wood remaining, and time since 

tree death (Table 1).

Fig. 26 - Fire-damaged trees have failure potentials that depend on the amount of 

sound wood remaining. This pine has imminent-failure potential.
71

Bole (Trunk) Defects

Wounded Live Trees

Tree wounds are injuries that break the bark of the bole or branch (Fig. 

27). Wounds occurring on live tree roots and root collars can result in 

root disease. Tree wounds are caused by a variety of factors: vehicles, 

people, falling trees or rocks, weather, fire, animals, or insect attack. New 

wounds on living tree boles, especially large, deep wounds, can be entry 

points for stem decay or canker-causing fungi. Wounds on true firs can 

activate dormant spores of decay fungi, such as the Indian paint fungus 

(p. 92). Wounds on non-resinous tree species (Table 1) generally result 

in more decay than do wounds on resinous species. Fresh wounds on 

Douglas-fir or ponderosa pine often are covered with resin.

After a live tree is wounded, the wood-infecting microorganisms may 

be confined to compartments within the tree through a process called 

compartmentalization (19). New wood formed annually after the wound 

occurs is relatively free of decay-causing micro-organisms, unless 

another wound occurs. The infected wood within the compartments 

may eventually become a decayed or hollow cylinder surrounded by 

healthy-appearing wood. This healthy-appearing wood is referred to as 

the sound rind, and its thickness determines the failure potential of the 

affected tree (see appendix, p. 115). A wounded tree with a sound-rind 

thickness <20% of the tree’s diameter inside bark has imminent-failure 

potential. Over time, the tree may seal the wound with new wood 

resulting in a scar. The rate of wound sealing is a function of tree-growth 

rate and vigor. The decay process in live trees generally is very slow, 

and it may take decades for freshly 

wounded trees to form decay columns 

that result in a minimum sound-rind 

thickness (p. 115, 117).

 

Sound-rind thickness measurements 

are routinely taken on danger trees in 

developed sites to determine failure 

potential but are not commonly 

taken during roadside or work site 

evaluations. Determining sound-rind 

thickness of potential danger trees 

should be done, if necessary, at places 

Fig. 27 - Tree bole with an open wound exposing 

the sapwood.
72

along roads or at work sites where people congregate for >15 minutes 

(i.e. scenic vistas, school-bus stops, log landings, buildings, etc.). Soundrind thickness usually is measured with an increment borer or electric 

drill at three or more places on the trunk and averaged. Refer to the 

Appendix, p.115, 117, for sound-rind-thickness tables for wounded and 

unwounded trees. Trees with sound-rind thickness below minimum 

values have imminent-failure potential.

Fungal and Mistletoe Cankers

Fungal cankers frequently occur on the boles of pine species, especially 

ponderosa and lodgepole pines. 

• General symptoms and indicators:

o Canker fungi cause top-kill, branch death, and stem 

malformation (Fig. 29).

o Stem malformations increase stem breakage and can be 

decayed by other fungi.

o Mistletoe cankers are caused by dwarf or true mistletoe 

infection of the bole (Fig. 31). Cankers are especially 

common on grand and white fir, western and mountain 

hemlock, white oak, and occasionally western larch.

o Mistletoe cankers can become decayed and result in tree 

failure.

o Non-resinous tree species, such as true fir, hemlock, 

spruce, or hardwoods with cankers or wounds, are more 

likely to fail than resinous species.

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

because of resin-impregnated or decay-resistant wood.

o Resinous wood around bole cankers and wounds usually 

remains sound.

o Failure potential does not significantly increase until the 

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

of the bole with sound wood is below a critical threshold 

(Fig. 28, Table 1).

 
73

Fig. 28 - Various bole 

cross-sectional areas 

showing percentage of 

sound-wood remaining. 

For non-resinous species, 

<50% of the bole with 

sound wood would have 

imminent-failure potential 

(Table 1).
74

Important cankers associated with danger trees in Oregon and 

Washington include:

• Atropellis canker caused by either Atropellis piniphila or A. 

pinicola

o This canker frequently appears on the boles of pines, 

especially lodgepole pine. 

o Resinous wood around these cankers usually remains 

sound, and failure potential does not significantly 

increase until cankers become old, long, and wide, and 

the face of the canker is deeply sunken relative to what 

would have been the normal bole circumference at that 

point (Fig. 29). 

o When the cankers result in <25% cross-section of the 

bole with sound wood, failure potential is imminent 

(Table 1). 

o Tree failure is most likely to occur in heavily infected 

stands where trees have multiple cankers or two or more 

cankers at the same height. 

Fig. 29 - Atropellis canker is a common 

disease of lodgepole pine that can result 

in tree failure.
75

• Comandra blister rust caused by Cronartium comandrae

o Occurs on ponderosa pine and occasionally lodgepole 

pine in Oregon and Washington. 

o Mortality can occur, especially in young, infected trees. 

o Large, infected pines often have dead tops that 

progressively die back from the top of the tree (Fig. 30). 

o Infected and dead tops are relatively decay resistant 

because of the copious resin associated with infection. 

o These dead tops have low-failure potential, even after 

several years, and rarely fail.

o All dead tops should be examined carefully for open 

cracks, conks, cavities, or other defects that indicate 

higher failure potential.

Fig. 30 - Dead tops 

of ponderosa pine, 

caused by Comandra 

blister rust, are often 

resin-soaked, decayresistant, and therefore 

of low-failure potential.
76

• Cytospora canker caused by Cytospora chrysosperma on 

hardwoods and C. abietis on true firs

o Cankers occur on boles, branches, and twigs and form 

elongated areas of dead wood within well-defined 

borders. 

o Several years after infection, dead bark lifts away from the 

bole and sloughs off.

o When the canker results in <50% cross-section of the bole 

with sound wood, failure potential is imminent (Table 1). 

• Mistletoe cankers caused by dwarf mistletoe (Arceuthobium 

spp.) infection, and true mistletoe (Phoradendron spp.) infection 

o Dwarf mistletoe-bole infections are especially common 

on grand/white fir, western hemlock, and western 

larch (Fig. 31). 

o True mistletoe-bole and branch infections are common 

on oaks (Fig. 32), incense-cedars, and junipers. 

o While bark and cambium tissues are still alive in the area 

of the initial swelling, boles and branches are not often 

significantly weakened, and failure potential is very low. 

o In time, however, the cambium and overlying bark in 

the oldest part of the swelling die and form a canker 

that is subsequently decayed by opportunistic fungi and 

attacked by wood borers. 

o Any of the fungi that function as wound parasites can 

decay mistletoe-induced bole cankers.

o Failure potential varies depending on tree species and 

the amount of sound-wood remaining at the canker 

(Table 1).

• Nectria canker caused by Nectria cinnabarina 

o Nectria canker occurs on many hardwood species. 

o Sunken cankers are associated with wounds or develop at 

the base of dying branches. 

o Cankers can girdle and kill stems, and when bark dies, it 

appears dry and cracked with age.

o When the cankers result in <50% cross-section of the 

bole with sound wood, failure potential is imminent 

(Table 1). 
77

• Ramorum canker caused by Phytophthora ramorum

o The causal agent, a fungus-like water mold, was 

introduced into southern Oregon around 2000. 

o Ramorum canker is also called sudden oak death. 

o This disease causes significant mortality of tanoaks in 

Oregon; Oregon white oak is not affected.

o Ramorum canker is mentioned in the context of danger 

trees not so much for the bole canker that it causes, but 

because of the relatively rapid death of its principal host 

in Oregon, tanoak (Fig. 33). 

o Although other tree species can serve as foliar hosts 

in the PNW: maple, madrone, myrtle, redwood, and 

Douglas-fir, none of these species has had bole cankers or 

have been killed, as yet, by the causal agent in Oregon or 

Washington. 

o Infected trees are rapidly colonized by decay fungi, and 

trunk failures can occur even before trees die.

o Recently infected and dead tanoaks have imminentfailure potential. 

Fig. 31 - Dwarf mistletoe-bole infections are 

especially common on grand and white fir, 

hemlock, and larch.

Fig. 32 - True mistletoe-bole and branch infections 

can cause cankers and decay in oaks.
78

• Red ring rot canker caused by Porodaedalea cancriformans 

o The former name of the causal fungus was Phellinus 

cancriformans.

o This disease occurs in southwestern and west-central 

Oregon on true firs (Table 5). 

o The conks of the fungus are small and numerous with 

their upper surfaces being rough, dark, and furrowed 

(butterfly conks). 

o The conks closely resemble P. pini conks (p. 90) but are 

smaller and occur in groups. 

o The conks grow from a sunken area on the trunk with 

decayed wood beneath (a canker). 

o Substantial amounts of stem breakage are associated 

with this fungus.

o When cankers result in <50% cross-section of the bole with 

sound wood, failure potential is imminent (Table 1). 

• Western gall rust caused by Endocronartium harknessii 

o This rust is common on lodgepole and knobcone pines. 

Fig. 33 - Ramorum canker, as seen here, is an introduced disease that kills tanoak in 

southwest Oregon.
79

o The disease can be found on ponderosa pine, especially 

near water courses. 

o The disease causes branch flagging, bole breakage, 

topkill, and mortality of young trees. 

o The galls are small to large, round to pear-shaped 

swellings on branches and boles. 

o “Hip cankers” result when the main stem flattens and 

broadens as it grows around bole infections (Fig. 34). 

o When stem failures occur, they typically happen directly 

above the canker near the intersection of the deformed 

wood and normal wood (Fig. 34).

o Trees with galls on the main stem or “hip cankers” develop 

progressively and increase the tree’s failure potential as 

the percentage of sound wood in the bole decreases. 

o When the cankers result in <25% cross-section of the bole 

with sound wood, failure potential is imminent (Table 1). 

Fig. 34 - Lodgepole pine with western gall rust can break if the stem cross-sectional area 

of sound wood falls below a critical threshold, as in this tree on the right.
80

• White pine blister rust caused by Cronartium ribicola 

o This rust is found throughout the range of 5-needle 

pines in Oregon and Washington. 

o The causal fungus causes branch fl agging, top-kill, and 

death usually of pines <8 in. dbh (Fig. 35). 

o Mountain pine beetles often attack larger and older, 

infected trees. 

o After needle infection in the spring, spindle-shaped 

swellings form on branches. Bright, yellow-orange 

pustules (aecia) with aeciospores are produced from 

raised blisters on the bark. 

o Cankers result in dead, roughened bark that has margins 

that appear greenish-yellow to orange. 

o Heavy pitch fl ow often occurs with bole cankers. 

o Infected, dead tops and branches are relatively decay 

resistant because of the copious resin associated with 

infection. 

o Blister-rust-killed tops and branches have low-failure 

potential, even after several years and rarely break and 

fall.

o All dead tops should be examined carefully for open 

cracks, conks, cavities, 

or other defects that 

indicate higher failure 

potential.

Fig. 35 - Tree tops killed by white 

pine blister rust are often resinsoaked with little decay and have 

low-failure potential.
81

Burls

• Burls are abnormal swellings on stems and branches (Fig. 36). 

• Usually, burls are composed of sound wood and indicate lowfailure potential. (Table 1). 

• Burls vary in size up to several feet in diameter. 

• Their cause is mostly unknown, but burls are common among 

high-elevation lodgepole pine and subalpine fir or low-elevation 

maples and other hardwoods. 

• When high in the tree or covered with moss or lichens, burls 

sometimes resemble conks and therefore require careful 

examination with binoculars.

Fig. 36 - Burls are often large, woody growths of unknown cause 

that sometimes resemble conks but indicate low-failure potential.
82

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 and have imminent-failure potential (Table 1).

• 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.

• Cracks may be formed by lightning strikes. 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. 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 

(Fig. 37). 

• Frost cracks appear on bark 

as raised, nearly vertical, 

callus lines that extend to 

the ground where frosty air 

is coldest. 

• Frost 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 and have lowfailure potential (Table 1).

• Frost cracks that are weeping 

have likely failure potential 

(Fig. 37).

Fig. 37 - Frost cracks often indicate lowfailure potential, unless they are weeping, 

as shown here, then failure potential is 

likely.
83

Heart Rots 

Heart rots, also known as stem decays, occur in living trees and may 

compromise bole integrity leading to tree failure.

• General symptoms and indicators of heart rot

o Old injuries to a tree may have resulted in internal decay. 

o Larger wounds, wounds that are in contact with the 

ground, and older wounds are often associated with a 

greater amount of decay.

o Resinous tree species are less prone to decay than nonresinous species (Table 5).

o Heart rots are most abundant in mature and old-growth 

trees, regardless of their size.

o 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.

o 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. 

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

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

indicators (Fig. 38).

Fig. 38 - Heart rots compromise tree stability by reducing the amount of sound rind, as 

seen here in this wounded spruce that had a Fomitopsis pinicola conk at its base. 
84

o Cavity excavation by woodpeckers may indicate heart rot 

in the tree (Fig. 44).

o The presence of carpenter ant or termite activity can 

indicate heart rot, especially in wounded trees.

o Heart rots may be present when there are few or no 

external indicators, making identification difficult.

o Trees with split boles or open or bleeding, frost cracks are 

likely to have extensive decay (Fig. 37).

Important heart rots associated with danger trees in Oregon and 

Washington include:

• Aspen trunk rot caused by Phellinus tremulae

o This heart rot is found only in quaking aspen, but a 

related heart rot, hardwood trunk rot (p. 87), affects many 

hardwood species.

o Conks are perennial, hard, woody, and generally 

triangular-shaped (Fig. 39).

o Incipient decay has a yellow-white zone in the heartwood 

and is usually surrounded by a yellow-green to brown 

margin.

o Advanced decay is soft and yellow-white with fine, black, 

zone lines.

o Failure potential varies depending on the presence of 

conks and evidence of extensive decay such as open 

cracks or exposed rot (Table 1).

• Brown top rot caused by Fomitopsis cajanderi (rose-colored conk)

o This heart rot affects most conifers and causes a browncubical heart rot in living trees, especially Douglas-fir.

o It is found often in trees with substantial top damage.

o Conks are perennial, woody, bracket-like to hoof-shaped 

with pink to rose-colored undersurfaces and inner tissue. 

The upper surface is brown to black and usually cracked 

and rough.

o Early wood decay is a faint brownish or a yellow-brown 

stain, sometimes with greenish-black zone lines.

o Advanced decay is yellow to reddish-brown, soft, and 

with irregular cubes. Thin, mycelial felts may be present in 

cracks between the cubes.

• A • C
85

o The amount of decay is proportional to the diameter of 

the broken stem.

o Failure potential varies depending on the presence of 

conks and evidence of extensive decay such as open 

cracks or exposed rot (Table 1).

Fig. 39 - Conk of Phellinus tremulae indicates internal decay in this aspen.

Fig. 40 - Advanced decay caused by Laricifomes offi cinalis is a brown-cubical rot. 
86

• Brown trunk rot caused by Laricifomes officinalis (quinine conk or 

the chalky fungus).

o Several conifer species are affected, and infection often 

results in severe stem decay.

o The fungus, formerly called Fomitopsis officinalis, enters 

through trunk wounds or basal, fire scars.

o Conks are rare but unmistakable. They are hard, perennial, 

hoof-shaped to pendulous, and often quite large (1 to 2 

ft. long) (Fig. 41).

o Conks have a chalky white to grayish-upper surface. 

Pores are round, and the under surface of the conk is 

chalky white.

o The interior of most conks is soft and crumbly.

Fig. 41 - Quinine conk of Laricifomes officinalis indicates 

considerable stem decay, as seen in Fig. 40. 
87

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

old, top breaks.

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

have usually rotted and fallen off. Punk knots often exude 

a yellowish-brown material that stains the bark.

o A single conk indicates severe stem decay.

o Decay is a dry, brown-cubical rot with thick, white, 

mycelial sheets in the decay shrinkage cracks (Fig. 40).

o Trees with one or more conks have imminent-failure 

potential (Table 1).

• Hardwood trunk rot caused by Phellinus igniarius (false-tinder 

fungus)

o This rot occurs in many hardwood species (Table 6).

o Conks are perennial, woody, and generally hoof-shaped.

o The upper surface of the conk is gray-black to black and 

rough when old (Fig. 42). The under surface is brown with 

small, regular pores.

o Early decay has a yellow-white zone in the heartwood 

and is usually surrounded by a yellow-green margin.

o Advanced decay is soft and yellow-white with fine, black, 

zone lines.

o Failure potential varies depending on the presence of 

conks and evidence of extensive decay, such as open 

cracks or exposed rot (Table 1).

Fig. 42. Conk of Phellinus igniarius on a decayed hardwood.
88

• Heterobasidion stem decay caused by Heterobasidion 

occidentale 

o The fungus that causes Heterobasidion root disease (p. 

62) also can cause decay in the trunks of infected trees, 

especially true fi rs and hemlocks.

o In western Washington and Oregon, the fungus more 

commonly causes a butt decay rather than causing root 

disease centers.

o Infection occurs by airborne spores through trunk 

wounds.

o Butt and stem decay predispose trees to windthrow and 

stem breakage.

o Failure potential varies depending on the amount of 

sound-wood remaining at the site of the wound (Table 1). 

• Incense-cedar pecky rot caused by Oligoporus amarus

o This heart rot is very common in mature incense-cedar, 

especially trees >40-inches dbh, and trees with basal 

wounds or old, dead limbs.

Fig. 43 – A conk of Oligoporus amarus on this incense-cedar indicates internal decay but 

low-failure potential.
89

o Tree failure is not common even with advanced decay.

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

the entire length of the bole.

o In severely damaged trees, most of the heartwood is 

decayed. 

o Conks occur rarely and indicate a decayed tree. Conks are 

annual and fruit at knots in summer or autumn.

o Conks are hoof-shaped to half-bell shaped, tan to buffcolored on the upper surface, bright sulfur-yellow on the 

underside with small tubes that exude clear drops of a 

yellow liquid (Fig. 43).

o Insects, birds, and squirrels destroy conks, leaving a “shothole cup” that is apparent at and below the knot where a 

conk was attached.

o Large, open knots or branch stubs indicate decay.

o Woodpecker activity indicates old, conk locations and 

decayed trees.

o Unless there are other failure indicators, living trees with 

conks have low-failure potential.

• Juniper pocket rot caused by Pyrofomes demidoffii 

o This heart rot only affects juniper and is the major cause 

of decay in living junipers, especially old trees.

o The upper surface of the woody, hoof-shaped conk 

is dark brown to black. The lower pore surface is light 

brown.

o Advanced decay has numerous, large pockets that are 

lined with yellow-white fibers that join to form a stringy 

rot.

o Failure potential varies depending on the presence of 

open cracks and exposed decay in the bole (Table 1).

• Redcedar pencil rot caused by Postia sericiomollis

o This heart rot only affects western redcedar, and the 

decay is usually confined to the lowest 40 feet of the 

trunk.

o Conks are annual, thin, flat, white crusts that are not 

common.
90

o Advanced decay is a brown-cubical, pocket rot that 

appears as long, thin pencils of brown-cubical decay.

o Decayed trees are often used by cavity-nesting birds, and 

the cavities are a good indicator of advanced decay (Fig. 

44).

o Failure potential varies depending on the amount of 

sound-wood remaining near the open cavity (Table 1).

• Red ring rot or white speck caused by Porodaedalia pini (ringscale fungus)

o The causal fungus was formerly known as Phellinus pini.

o Red ring rot is the most common heart rot of Pacifi c 

Northwest conifers aff ecting Douglas-fi rs, pines, 

larches, hemlocks, true fi rs, and spruces.

o Conks are hoof-shaped with cinnamon-brown to tan, 

pore surfaces (Fig. 45). Pores are irregularly shaped, and 

the interior of the conk has the same cinnamon-brown 

coloration as the pore surface. 

o Conks form at branch stubs or over old knots.

o On hemlocks especially, but occasionally on other 

Fig. 44 – Cavity (at arrow) created by birds indicates heart rot in this western redcedar.
91

species, conks may be abundant on the undersides of 

branches (“limb conk” or “butterfl y conk”).

o Punk knots are common on severely decayed trees 

and 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 . 

o Punk knots and conks indicate the same amount of decay.

o Decay is a white pocket rot that may occur in rings 

separated by sound wood until decay is advanced.

o Unlike other rots, wood decayed by this fungus, often 

called whitespeck, initially maintains some strength 

against failure (Fig. 46).

o Large (>6 in. wide) conks indicate more decay; smaller 

conks usually indicate less decay, unless the apparent 

small conks are remnants of larger conks that have fallen 

off . 

o When trees have many large conks in close proximity, 

damage to the heartwood is extensive and failure 

potential is likely (Table 1). 

o With few or single conks, failure potential is low.

o Failure potential also varies with tree species and visual 

evidence of advanced decay.

Fig. 45 - Conk of P. pini often indicates only lowfailure potential.

Fig. 46 - Wood decay caused by P. pini, 

commonly called whitespeck, is relatively 

sound compared to wood decay caused by 

other fungi.
92

• Rust red stringy rot caused by Echinodontium tinctorium (Indian 

paint fungus).

o This is the most damaging heart rot of mature true fi rs 

and hemlocks east of the Cascade crest.

o It occurs less frequently in western hemlock west of the 

Cascades.

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

continuous decay.

o When decay is advanced, large hoof-shaped conks with a 

spiny, lower surface are produced (Fig. 47). 

o Conks have a fi ssured, upper surface, and are rough, dull 

black, hard and woody.

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

the tree or branch stub are rusty-red to bright orange-red.

o Conks appear on the bole at the site of old branches and 

stubs. 

o Conks with weeping, frost cracks or open cracks indicate 

extensive decay.

o Decay is a rust-red-stringy decay that may result in hollow 

stems (Fig. 48).

o Failure potential varies with evidence of advanced decay 

and the size and number of conks on the bole (Table 1).

Fig. 47 - Conks of the Indian paint fungus are common on true fi rs and 

hemlocks.
93

Sap Rots 

• General symptoms and indicators of sap rots.

o Most sap-rotting fungi cause rapid decay of dead 

sapwood only.

o When these fungi have fully decayed all the available 

sapwood, they have completed their job.

o Sap-rotting fungi compete poorly with other fungi and 

are seldom found past the heartwood/sapwood interface.

o Sap rots can completely decay tree tops that are often all 

sapwood.

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

agents, usually bark beetles, mechanical damage, or 

weather damage.

o On dead trees, especially those killed by root diseases, 

fi re, and/or bark beetles, sap rot is sure to occur, and the 

rate of sapwood decay can be rapid.

o On some true fi rs and often hemlocks, sapwood is fully 

rotted within 2 years.

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

sap-rotting fungi to decay all of the available sapwood.

Fig. 48 - Decay caused by the Indian paint fungus can result in tree 

failure.
94

o On living hardwoods, damage may be signifi cant. For 

example, on many poplars, maples, and alders, sapwood 

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

few obvious external indicators.

• Brown crumbly rot caused by Fomitopsis pinicola (red-belt conk) 

o This is the most common sap rot of dead wood and slash 

in Oregon and Washington 

o The fungus commonly causes a sap rot of trees and 

occasionally a heart rot of living trees, especially those 

with trunk wounds (Fig. 38).

o Conks are leathery to woody, perennial, and bracketshaped (Fig. 49).

o When young, conks are white and round. 

o As the conk matures, the upper surface turns darkgray to black, the lower surface remains white, and a 

conspicuous, reddish margin develops between the two 

surfaces.

o Advanced decay is light reddish-brown and forms a 

crumbly mass of rough, small cubes with mycelial felts 

between the shrinkage cracks.

o Live trees with conks and wounds usually have likely 

failure potential, but failure potential can be imminent 

depending on tree species and the amount of sound 

wood remaining at the wound.

o Dead trees with conks have imminent-failure potential 

(Table 1).

Fig. 49 – This conk of Fomitopsis pinicola is very common on 

dead wood and may also be found on wounded, live trees.
95

• Gray-brown sap rot caused by Cryptoporus volvatus (pouch 

fungus)

o This is common sap rot of conifers killed by bark beetles 

or fi re. 

o Conks are annual, leathery, and produced on trees the 

fi rst year after tree death.

o Fresh conks are small, round, initially soft and fl eshy, 

yellow-brown to golden-brown with pore surfaces 

covered with a hard membrane (Fig. 50).

o Conks bleach to dirty-white after one year. 

o When many, little, white or gray conks appear completely 

around the stem, the sapwood may be fully rotted. 

o Spores of the pouch fungus are spread by all major 

species of tree-killing bark beetles.

o Advanced decay has gray areas that develop in the 

sapwood beneath the conks.

o Live trees with conks and wounds have low-failure 

potential. 

o Dead trees with conks have likely to imminent-failure 

potential, depending on how long the tree has been 

dead (Table 1) .

Fig. 50 - These pouch fungus conks can indicate considerable sap rot. Note the creamcolored new conks on the left and the dirty-white old conks on the right
96

Crown Defects

Dead tops and branches; detached tops, limbs, and bark 

• Dead tops and branches can be caused by several agents 

including insects, dwarf mistletoe, rust fungi, animals, or weather.

• Dead tops and large branches (>3 in., large-end diameter) with 

evidence of decay are dangerous tree parts because they may 

break apart, fail, and cause extensive damage to structures and 

people (Fig. 51).

• Dead tops and branches of cedar, juniper, 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.

• Dead tops and branches killed by insects differ from rust-killed 

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, larch, or pine are 

resinous and more 

resistant to failure.

• Dead tops and branches 

of true fir, hemlock, 

spruce, 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 recently killed tops.

• The failure potential 

of dead tops depends 

on tree species and the 

amount of wood decay, 

which is a function of 

time since death (Table 

1). Fig. 51 - Dead tops can be caused by many 

agents including dwarf mistletoe, as shown 

here.
97

• Detached tops, limbs, or bark (>1 ft2) often fall; are extremely 

dangerous; and have imminent-failure potential.

• Live, large branches on mature cottonwoods can fail especially if 

previous breakage has occurred.

• Cottonwood failure potential varies with the amount of visible 

branch decay and breakage (Table 1).

Forked or Multiple Tops or Trunks 

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

tops can fail at the base of the fork. 

• 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 forked tops or trunks should be examined for open 

cracks, embedded bark (Fig. 53), and mushrooms or conks that 

indicate weakening and predisposition to failure or infection by 

decay fungi (Fig. 52). 

• Stem breakage often occurs in ponderosa pine at V-shaped forks 

with embedded bark.

• After breakage the remaining stem also may fail depending 

on the amount of sound-wood remaining at its base (see bole 

wounds, Table 1).

Fig. 52 - Forked tops shown on this hardwood that are weeping and cracked (left) and 

this cedar with open cracks (middle) have imminent-failure potential. The ponderosa pine 

(right) with only embedded bark has likely failure potential.
98

• Failure potential 

varies with these 

factors (Table 1).

• Forked tops that 

are U-shaped are 

less prone to fail 

than V-shaped 

forks and therefore 

have low-failure 

potential, unless 

other indicators 

are present.

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 

(Fig. 54).

• Large (>10 ft. in diameter), 

dead, dwarf mistletoe 

brooms, especially on 

Douglas-fir, can become 

weighted with snow and ice 

and fail.

• Such brooms have likely 

failure potential.

• Live brooms and small, dead 

brooms have low-failure 

potential (Table 1).

 

Fig. 53 – An example of embedded bark as seen just 

below the forked stem.

Fig. 54 - Live, dwarf-mistletoe brooms, 

even large ones as shown here on 

Douglas-fir, have low-failure potential.
99

Whole-Tree Defects

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 or its parts to fail also increases.

Broken or uprooted trees supported by other trees

• Damaged roots and heart rots 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.

• All live or dead, broken or uprooted trees supported by other 

trees have imminent-failure potential (Table 1). 

Leaning and/or root-sprung 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.”

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

• Trees with recent (<5 years) leans >15 degrees 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 (Fig. 55). 

• 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 >15 degrees should be examined for evidence of 

root and butt rot. 

• 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 have imminent-failure potential (Table 1).

• Recently leaning trees without soil lifting and cracking have 

likely failure potential.
100

• Corrected leaning trees are those that are leaned over but have 

subsequently grown a vertical top in the time since the lean 

occurred (Fig. 56). 

• Over time, trees with corrected leans develop tension and 

compression wood at stress points to aid in their support. They 

also often develop a reinforced root system.

• Trees with corrected leans have low-failure potential (Table 1).

Height-to-diameter ratios

• Live trees with a high height-to-diameter ratio (skinny trees) may 

fail depending on the ratio (Fig. 57).

• 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 heightto-diameter ratio of 100.

• Trees with a height to diameter ratio >100 have imminentfailure potential (Table 1).

Fig. 55 - New cracks in the soil around leaning trees 

indicate imminent-failure potential.

Fig. 56 - Old leans with righted 

or corrected tops have lowfailure potential.
101

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. 

• Bark beetles most commonly associated with danger trees in 

the Pacific Northwest include the Douglas-fir beetle, fir engraver, 

spruce beetle, mountain pine beetle, western pine beetle, and 

pine engraver. 

Fig. 57 - Trees with high height-to-diameter ratios (skinny trees), 

such as these lodgepole pines, are more prone to stem breakage 

from snow, ice, or wind.
102

• Bark beetles frequently attack trees that are stressed from root 

disease, bole damage, defoliation, or drought.

• Symptoms of bark beetle attack include boring dust, pitch 

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

or group mortality (Fig. 58).

• Wood borers are similar to bark beetles but prefer even weaker 

trees than bark beetles.

• Bark beetles and wood borers introduce sap-rot fungi into dying 

and dead trees.

• 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. 

• Defoliating insects, such as the western spruce budworm and the 

Douglas-fir tussock moth, can kill tops or entire trees.

. 

 

Fig. 58 - Bark beetle attack is 

often indicated by pitch flow 

and boring dust as seen on 

this infested pine
103

Multiple Defects

• Trees are often encountered with two or more (multiple) defects. 

• The potential for tree failure may increase dramatically with the 

combined effects of multiple defects. 

• In the case of multiple indicators, one condition (indicator) often 

worsens another; they interact synergistically. Multiple indicators 

are in contact with each other.

• Examples of multiple defects that indicate increased potential for 

failure include:

o Heart rot and cankers, stem injury, or sap rot

o Root rot and lean

o Cracked forks and heart rot

o Recently killed tree and butt rot

o Leaning trees with hollow stems (Fig. 59)

 

Fig. 59 – Multiple, 

likely failure 

indicators can imply 

imminent-failure 

potential, such as this 

maple with hollow, 

leaning stems.
104
105

Literature Cited

1. Filip, G.M., J. Biro, K.L. Chadwick, D.J. Goheen, E.M. Goheen, J.S. 

Hadfield, A. Kanaskie, H.S.J. Kearns, H.M. Maffei, K.M. Mallams, D.W. 

Omdal, A.L. Saavedra, and C.L. Schmitt. 2014. Field guide for hazardtree identification and mitigation on developed sites in Oregon and 

Washington forests. USDA Forest Service, Pacific Northwest Region, 

R6-NR-TP-021-2014, Portland, OR. 120 p.

2. Oregon OSHA. Division 7 Forest Activities 2003. 437-007-0225( ).

3. Washington Safety Standards for Logging Operations 2007. 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.

10. Toupin, R., G. Filip, T. Erkert, and M. Barger. 2008. Field guide for 

danger tree identification and response. USDA Forest Service, 

Pacific Northwest Region, R6-NR-FP-PR-01-08, Portland, OR. 64 p.

11. USDA Forest Service Manual, Transportation System, 2007. R6-

Supplement 7730-2007-2, FSM 7700, Chapter 30 – Operations and 

Maintenance. Portland, OR. 13 p.

12. Scott, D.W., C.L. Schmitt, and L.H. Spiegel. 2002. Factors affecting 

survival of fire injured trees: a rating system for determining 

relative probability of survival of conifers in the Blue and Wallowa 

Mountains. USDA For. Serv., For. Health Protection, BMPMSC-03-01, 

La Grande, OR. 86 p.

13. Smith, S.L. and D.R. Cluck. 2011. Marking guidelines for fire-injured 

trees in California. Report # RO-11-01, USDA For. Serv., Forest Health 

Protection, Pacific Southwest Region, Susanville, CA. 15 p.
106

14. Memorandum of Understanding between State of Oregon, 

Department of Transportation and USDA Forest Service, Pacifi c 

Northwest Region. 2008. FS Agreement No. NFS 08-RU-11062751-

019, ODOT Misc. Contracts & Agreements No. 24808. Portland, OR. 

13p. 

15. Memorandum of Understanding between State of Washington, 

Department of Transportation and USDA Forest Service, Pacifi c 

Northwest Region. 2008. FS Agreement No. NFS 13-RU-11060051-

01, WSDOT Misc. Contracts & Agreements No. GCB 1336, Portland, 

OR. 22 p.

16. Hoff man, D. 2011. Danger tree mitigation guidelines for managers. 

2011. USDA For. Serv., Technology and Development Program, 

TE02P16 Technical Services, Missoula, MT. 22 p.

17. Parish, R., J.A. Antos, P.K. Ott, and C.M. Di Lucca. 2010. Snag 

longevity of Douglas-fi r, western hemlock, and western redcedar 

from permanent sample plots in coastal British Columbia. For. Ecol. 

& Manage. 259:633-640.

18. Dunn, C.J. and J.D. Bailey. 2012. Temporal dynamics and decay of 

course wood in early seral habitats of dry-mixed conifer forests in 

Oregon’s Eastern Cascades. For. Ecol. & Manage. 276:71-81.

19. Shortle, W.C. and K.R. Dudzik. 2012. Wood decay in living and dead 

trees: a pictorial overview. USDA For. Serv., Gen. Tech. Rept, NRS-97, 

Newtown Square, PA. 26 p.

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

2006.

Danger-tree workshop, 2006, Wallowa-Whitman National Forest
107

Glossary

Abiotic - non-living parts of the ecosystem such as soil particles, 

bedrock, fire, air, or water

Advanced decay – the later stages of decay often characterized by a 

dry, crumbling or wet, wood structure

Aecium (pl. aecia) - specialized spore-producing structure formed on 

trees infected with rust fungi

Aeciospore - type of spore produced in an aecium that typically infects 

alternate hosts

Alternate leaves – arrangement of leaves in which they emerge from 

the stem one at a time, as contrasted with opposite leaves that emerge 

from the stem in opposing pairs

Azimuth – a compass reading in degrees ranging from 0o (north) to 

359o 

Bark beetles – a group of forest insects whose adults and larvae make 

galleries in the cambial region of living or felled trees; a subfamily of 

the Curculionidae

Basal wound - a wound at the base of a tree

Biotic - pertaining to the living parts of the ecosystem such as animals, 

plants, fungi, or insects

Bole - a trunk or main stem of a tree; seedlings and saplings have stems 

rather than boles

Boring dust – a mixture of fecal matter and wood debris resulting from 

chewing and tunneling by bark beetles and wood borers; also called 

frass

Branch flagging – a disease symptom where some of the foliage on 

branches, particularly older foliage, is dead or dying

Branch stub - the remnant of a tree branch after it breaks off near the 

trunk; often an entrance point for decay fungi or a site where fungal 

conks form

Branch whorl – a circle of branches developed from one node on a tree

Broom or witches’ broom - an abnormal clustering of branches 

associated with infection by a dwarf mistletoe, rust fungus, genetic 

aberration, or other insect or disease

Butt - the base of a bole to a height of 8 feet

Butt log - the first log above the stump
108

Butt rot - decay developing in and sometimes confined to the butt; 

originating at basal wounds or coming up through roots

Callus - tissue produced at wound sites in response to injury that may 

or may not overgrow an injured area

Cambium - a layer of living cells between the wood (xylem) and inner 

bark (phloem) of a tree

Canker - a lesion on a stem, branch, or root; typically longer than wide; 

the cambium and cortex of which have been killed

Canopy - the more or less continuous cover of branches and foliage 

formed collectively by the crowns of adjacent trees

Causal agent - a biotic or abiotic entity that causes a deviation from 

the normal form or function of a tree; can be biotic entities such as fungi 

or insects or abiotic entities such as wind or fire

Check - a longitudinal fissure in wood resulting from stresses that 

caused wood fibers to separate along the grain

Chlorosis/Chlorotic - an abnormal yellowing of foliage

Compression strength - a measure of resistance of a body to 

compressive loading; the force at which failure occurs under a 

compressive load

Conk - a shelf-like reproductive structure of the type formed by many 

wood-decay fungi; also called a sporophore or fruiting body

Crook - an abrupt bend in a tree or log

Crotch - that part of the tree where the main stem or larger branches 

fork

Crown - the upper part of any tree carrying the main branches and 

foliage

Cubical decay – decayed wood that breaks into distinct cubes

Dbh - the diameter of a tree at breast height; breast height is defined at 

4.5 feet above the ground on the uphill side of any tree.

Decay - degradation or decomposition of wood by fungi and other 

microorganisms resulting in the progressive loss of integrity and 

strength of affected parts; can be incipient or advanced

Decay column – generally a large section of the tree bole that is 

internally decayed in the shape of a cylinder or column with tapered 

ends; a product of compartmentalization

Danger tree or hazard tree - any tree or its parts that will fail because 

of a damage, defect, or disease and cause injury or death to people or 

property 
109

Defect - any feature, fault, or flaw that lowers the strength, integrity, or 

utility of an affected part

Delaminate - to separate into sheets as with the pages of a book; wood 

delaminates at the growth rings; characteristic of decay caused by 

Phellinus sulphurascens and other decay fungi

Disease – a prolonged disturbance of the normal form or function of a 

tree or its parts; usually caused by organisms such as fungi, mistletoes, 

or abiotic agents (air pollutants) but not insects 

Disease center - a group of dead and dying trees that have developed 

progressively over time; caused by root pathogens such as Armillaria 

spp. or Phellinus sulphurascens; also called a mortality center or infection 

center

Distress- (stress-) cone crop – abundant, small cones that are often 

produced on root diseased trees

Drupe – a type of fruit consisting of an outer skin, a usually pulpy or 

succulent layer, and a hard or woody inner shell usually enclosing a 

single seed.

Dwarf mistletoe - a parasitic flowering plant with stems and seeds that 

develops extensive absorption systems in the sapwood of conifers and 

derives most of its water and nourishment from the host

Ectotrophic mycelium - fungal material, usually white to creamcolored, found on the outside of the root bark that is formed by 

certain root pathogens (i.e. Phellinus sulphurascens and Heterobasidion 

occidentale)

Embedded (included) bark – the inner and outer bark that forms 

between the expanding cylinder of the branch and the trunk or 

between two trunks. As the branch and trunk cylinders expand, the 

inturned bark becomes a wedge between the two cylinders that greatly 

weakens the fork.

Exudate - matter that has oozed out of a stem, branch, or root that may 

be a symptom of a defect or infection such as root-collar exudates 

caused by Armillaria spp.

Failure - partial or total breakage or collapse of a tree or tree part

Frost crack - splitting of the outer bark and sapwood that occurs in the 

trunks of trees subjected to extreme cold; such fissures follow the grain 

and are usually superficial; they originate from old, mechanical wounds; 

often called bleeding or weeping cracks if copious exudates are present

Fruiting body - conk, mushroom, or other fungal, reproductive 

structure that produces spores
110

Fungus (pl. fungi) - a group of organisms lacking chlorophyll (therefore 

it does not photosynthesize), having cell walls with both cellulose and 

chitin, having a vegetative body composed of hyphae, and reproducing 

by spores

Gall - a pronounced swelling or tumor-like body produced on trees 

parasitized by certain fungi or bacteria, or infested by gall-forming 

insects

Gallery - a tunnel formed by the feeding of insect larvae or adults, 

particularly by bark beetles

GPS – Global Positioning System is a space-based satellite-navigation 

system that provides location and time information in all weather 

conditions, anywhere on or near the Earth where there is an 

unobstructed line of sight to four or more GPS satellites.

Haul route – a road that is used to transport logs or other forest 

products

Hazard - the recognized potential that a tree or tree part may fail and 

cause injury or damage by striking a target

Hazard tree or danger tree – any tree or its parts that will fail because 

of a damage, defect, or disease and cause injury or death to people or 

property 

Heart rot - decay usually restricted to the heartwood in living trees

Heartwood - the inner, nonliving part of a tree stem that is altered to 

a protective state as a result of normal, genetically controlled aging 

processes as cells die; provides mechanical support

Hypha (pl. hyphae) - single, microscopic, thread-like filament made up 

of fungal cells

Incipient stain/decay - early stages of decay often characterized by 

discoloration of the wood

Increment borer - an auger-like instrument with a hollow bit and an 

extractor used to remove thin radial cylinders of wood (increment cores) 

from trees having annual-growth rings to determine tree age or detect 

the presence of wood decay or stain

Infection – the act of a pathogen establishing itself on or within a host

Lichen – a type of organism composed of an alga and a fungus that 

grow in symbiotic association often on tree boles and branches, and can 

hide conks, burls, or cavities.

Live-crown ratio - the ratio of live-crown length to total tree height; 

usually expressed as a percentage
111

Mycelial fan - a mass of hyphae that grows under the bark of infected 

roots and butts and has a “fan-like” appearance. Mycelial fans, especially 

of Armillaria spp., are usually thick enough to peel off like latex paint 

and are white to cream-colored when fresh and turn brown when old.

Mycelial felt - a dense and expansive mycelium that takes the form of a 

thick sheet

Mycelium (pl. mycelia) - a mass of hyphae or fungal filaments

Mushroom - the reproductive fruiting body of any fleshy fungus, 

usually produced annually. Spores are produced from mushrooms.

Necrosis - death of a plant or a plant part; usually referring to localized 

death of living tissues of a host

Old-growth (forest) – usually a late-successional stage of forest 

development that contains large and old live and dead trees 

(overmature trees), multiple canopies, and down logs

Opposite leaves – leaves that form on the same side of a stem (node), 

as contrasted with alternate leaves that form on different sides of a 

stem

Parasite - an organism that grows part or all of its life on or within 

another organism of a different species and derives all or part of its food 

from it

Pathogen - a fungus, bacterium, virus, or other infective agent capable 

of causing disease in a particular host or range of hosts

Pitch tubes or streams – a tubular mass of resin, boring dust, and 

frass that forms on the surface of the bark at the entrance holes of bark 

beetles

Pore - a small hole in the undersurface of a fungal fruiting body from 

which spores emanate

Pulaski - a chopping and trenching tool that combines a single-bittedax blade with a narrow trenching blade resembling an adz hoe; named 

for the USDA Forest Service ranger who invented the tool for firefighting 

and saved numerous lives during the 1910 fire in Idaho.

Punk knot or swollen knot - a protruding and unhealed knot of a tree 

with heart rot, the surface is not encased fully in the bark, and the knot 

interior contains highly decayed wood that resembles the interior of the 

conk of the causal fungus

Pustules – very small (<1/2 in. wide) fruiting bodies that form on the 

roots of infected trees, especially Heterobasidion spp. on saplings or 

seedlings
112

Qualified person - a person who has knowledge, training, and 

experience in identifying danger trees, their potential-failure zones, and 

the appropriate measures to eliminate the danger

Resin - secretions of certain trees, especially conifers, that are oxidation 

or polymerization products of terpenes, consisting of mixtures of 

aromatic acids and esters; generally associated with tree resistance to 

fungi and insects; also called pitch

Resinosis - the reaction of a tree to invasion by certain pathogens and 

insects or to abiotic injuries that results in the copious flow of resin

over the outer bark in the area of injury, or resin-soaking within the 

outer bark, or in resin accumulation under the bark

Rhizomorph - a thread-like or cord-like fungal structure made up of 

strands of hyphae that are covered with a protective rind; rhizomorphs 

look like roots, but they are an extension of a fungus that infects live 

or dead host parts (usually roots or wood); may occur with infection by 

several species of fungi including Armillaria spp.

Rind - the shell of solid (undecayed) sapwood surrounding a decay

column in a tree. A rind may be broken and not continuous because of 

a wound or canker.

Risk - the proximity to actual damage and loss; the real possibility or 

chance of damage and loss

Root collar or root crown - where the root system joins the bole of the 

tree

Root graft - the growing together of two or more roots in such a way 

that their cambium, xylem, and phloem eventually fuse, and materials, 

including fungi, pass from one root to another

Rust or rust fungus – term used for a particular group of diseases or 

the fungi that cause them; most rusts require at least two host species 

to complete their life cycles; an example is white pine blister rust on 

white pine and Ribes spp.

Samara – an indehiscent, usually one-seeded, winged fruit

Saprophyte - an organism that lives on dead, organic matter

Sap rot - wood decay that is characteristically confined to the sapwood

Sapwood - the outer layers of a stem, which in a live tree are composed 

of living cells (xylem) that conduct water up the tree

Scar – a wound that shows some evidence of callus tissue (sealing)

Setal hypha (pl. hyphae) - a thick-walled, reddish-brown hypha that 

tapers to a point; it is sub-microscopic and only found in advanced 

decay associated with laminated root rot or cultures of Porodaedalia pini
113

Shake - a physical defect of trees caused by exposure to high winds; the 

defect appears in its most advanced stages as deep longitudinal fissures 

that follow the grain of the butt log and are associated with separations 

of the growth rings deep in the heartwood. More commonly, growthring separations occur without the external fissures.

Sign - the manifestation of disease by the presence of structures of the 

causal agent (conks, mushrooms, setal hyphae, mycelial fans or

felts, rhizomorphs)

Simple leaves – one leaf per stem or petiole as opposed to compound 

leaves which have more than one leaf per petiole

Skyline logging – a type of forest harvesting with a cableway stretched 

tautly between two points, such as a yarder tower and a stump anchor, 

and used as a track for a block or skyline carriage

Snag - a standing, dead tree often classified by different stages of decay

Sound-rind thickness – width of the shell of solid (undecayed) 

sapwood surrounding a decay column; because the width varies in 

thickness, it is usually measured at three or more points on the trunk 

and averaged to get a value. It does not include the bark.

Spore - a microscopic reproductive propagule of fungi (and other 

cryptogams)

Sporophore - conk, mushroom, or other fungal reproductive structure 

that produces spores

Stem - the main trunk or central stalk of a plant; also called a bole in 

trees

Structural roots - major tree roots that significantly add to the support 

of a standing tree

Symptom (symptomatic) - the outward manifestations of disease in a 

host such as chlorotic foliage, dead branches or tops, or dead trees

Target - person or object within striking distance of a tree or its parts

Topkill – death of the upper crown of a tree; usually caused by insects, 

pathogens, animals, or weather

Undermined roots - roots that are no longer firmly anchored due to 

soil removal or loss, beneath and/or around them

Vascular wilt – symptom of a lack of water in the plant vascular system 

whereby foliage loses its turgidity and droops (wilts)

Wetwood - a water-soaked area in the heartwood of a tree that is a 

symptom of infection by certain fungi (particularly yeasts) and bacteria
114

Windshake - a separation along the grain in a tree stem caused by wind 

stress

Windthrow – a tree that has fallen to the ground, usually at the roots 

or butt, due to excessive wind or perhaps without wind because of 

decayed roots or butt

Wind-shatter - a tree that has fallen to the ground as a result of a break 

above the butt due to excessive wind or perhaps without wind because 

of a decayed stem

Wound - an injury that usually breaks the bark of branches, stems, or 

roots of a tree and serves as a possible entry point for many species of 

fungi. Old wounds may become sealed with new bark and eventually 

become hidden. Scars are wounds that have sealed and have callus 

tissue.

Zone line - a narrow, dark-brown or black line in decayed wood, 

generally resulting from the interaction of diff erent strains of fungi or 

the host reaction
115

Appendix

Table 7. Minimum sound-rind thickness1 at various diameters inside 

the bark of conifers measured at the defect for trees without open 

wounds. Trees with sound-rind thickness below minimum values 

have imminent-failure potential.

Tree diam.

(in.)

Rind thickness2

(in.)

Tree diam.

(in.)

Rind thickness2

(in.)

4 0.5 44 6.5

6 1.0 46 7.0

8 1.0 48 7.0

10 1.5 50 7.5

12 2.0 52 8.0

14 2.0 54 8.0

16 2.5 56 8.5

18 2.5 58 8.5

20 3.0 60 9.0

22 3.5 62 9.5

24 3.5 64 9.5

26 4.0 66 10.0

28 4.0 68 10.0

30 4.5 70 10.5

32 5.0 72 11.0

34 5.0 74 11.0

36 5.5 76 11.5

38 5.5 78 12.0

40 6.0 80 12.0

42 6.5 82 12.5

1 Modified from Wagener (1963) by expanding the range of diameters covered

2

 Minimum sound-rind thickness is 0.15 x diameter and rounded to the nearest 0.5 in.
116

Sound-rind thickness in this decayed hemlock stump does not include the 

bark.

Danger-tree policy-review fi eld trip, 2007, Umatilla NF 
117

Table 8. Minimum sound-rind thickness1 at various diameters inside 

the bark of conifers measured at the defect for trees with open 

wounds. Trees with sound-rind thickness below minimum values 

have imminent-failure potential.

Tree diam.

(in.)

Rind thickness2

(in.)

Tree diam.

(in.)

Rind thickness2

(in.)

4 0.5 44 8.5

6 1.0 46 8.5

8 1.5 48 9.0

10 2.0 50 9.5

12 2.0 52 10.0

14 2.5 54 10.5

16 3.0 56 10.5

18 3.5 58 11.0

20 4.0 60 11.5

22 4.0 62 12.0

24 4.5 64 12.0

26 5.0 66 12.5

28 5.5 68 13.0

30 6.0 70 13.5

32 6.0 72 13.5

34 6.5 74 14.0

36 7.0 76 14.5

38 7.0 78 15.0

40 7.5 80 15.0

42 8.0 82 15.5

1

 Modified from Smiley and Fraedrich (1992)

2

 Minimum sound-rind thickness is 0.19 x diameter and rounded to the nearest 0.5 in.
118

An open canker on this aspen probably indicates a thin, sound rind and 

imminent-failure potential.

Danger-tree workshop, 2006, Deschutes National Forest 
119

For assistance on Oregon 

and Washington federal 

lands:

http://www.fs.fed.us/r6/nr/fid/

staffweb/regoff.shtml

Pacific Northwest Regional Office

Forest Health Protection

USDA Forest Service

1220 S.W. Third Avenue

Portland, OR 97204

503-808-2997

Blue Mountains Forest Insect and 

Disease Service Center

USDA Forest Service

Forest Sciences Laboratory

1401 Gekeler Lane

LaGrande, OR 97850

541-962-6544

Southwest Oregon Forest Insect 

and Disease Service Center

USDA Forest Service

J. Herbert Stone Nursery

2606 Old Stage Road

Central Point, OR 97502

541-858-6126 or 6124

Wenatchee Forest Insect and 

Disease Service Center

USDA Forest Service

Forestry Sciences Laboratory

1133 N. Western Avenue

Wenatchee, WA 98801

509-664-9223 or 9215

Central Oregon Forest Insect and 

Disease Service Center

USDA Forest Service

Deschutes National Forest 

Headquarters

63095 Deschutes Market Road

Bend, OR 97701

541-383-5591 or 5788

Westside Forest Insect and 

Disease Service Center

USDA Forest Service

Mt. Hood National Forest 

Headquarters

16400 Champion Way

Sandy, OR 97055

503-668-1475 or 1474
120

For assistance on Oregon and Washington state and 

private lands:

Washington Department of Natural Resources

Resource Protection Division

Natural Resources Building, Fourth Floor

1111 Washington Street, SE

Olympia, WA 98501

390-902-1692 or 1309

Oregon Department of Forestry

Forest Health Management

Insects and Diseases

2600 State Street

Salem, OR 97310

503-945-7397

http://www.oregon.gov/odf/privateforests/ pages/fh.aspx

Danger-tree 

workshop, 

2009, 

FremontWinema 

National 

Forest

 

2006 workshop 

near Lakeview, 

OR

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