Field Guide for Hazard-Tree 

Identification and

Mitigation on Developed 

Sites in Oregon and 

Washington Forests 

2014

for the greatest good
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Front cover photo: This Douglas-fir was felled because of high-failure 

potential due to laminated root rot.
1

Field Guide for Hazard-Tree Identification 

and Mitigation on Developed Sites in 

Oregon and Washington Forests

Gregory M. Filip

Regional Forest Pathologist

USDA Forest Service

Portland, Oregon

Jocelyn Biro

Regional Developed Recreation 

and Fee Program Manager

USDA Forest Service

Portland, Oregon

Kristen L. Chadwick

Service-Center Pathologist

USDA Forest Service

Sandy, Oregon

Donald J. Goheen

Service-Center Pathologist/

Entomologist (retired)

USDA Forest Service

Central Point, Oregon

Ellen M. Goheen

Service-Center Pathologist

USDA Forest Service

Central Point, Oregon

James S. Hadfield

Service-Center Pathologist 

(retired)

USDA Forest Service

Wenatchee, Washington

Alan Kanaskie

State Forest Pathologist

Oregon Department of Forestry

Salem, Oregon

Holly S.J. Kearns

Service-Center Pathologist

USDA Forest Service

Sandy, Oregon

Helen M. Maffei

Service-Center Pathologist

USDA Forest Service

Bend, Oregon

Katrina M. Mallams

Service-Center Pathologist 

(retired)

USDA Forest Service

Central Point, Oregon

Daniel W. Omdal

State Forest Pathologist

Washington Department of 

Natural Resources

Olympia, Washington

Angel L. Saavedra

Service Center-Pathologist

USDA Forest Service

Wenatchee, Washington

Craig L. Schmitt

Service-Center Pathologist 

(retired)

USDA Forest Service

La Grande, Oregon

R6-NR-TP-021-2013 USDA Forest Service, Forest Health Protection,

 Pacific Northwest Region, Portland, OR
2

Acknowledgements

The authors thank Bob Harvey and Paul Hessburg for the 1992 guide 

that served as a template for this guidebook. We thank Robert Fimbel, 

Washington State Parks Dept., for his review. We also thank Michael Hamel 

for editing and formatting. All figures were by the authors and other USFS 

personnel except where indicated.

Suttle Lake, Deschutes National Forest
3

Table of Contents

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

Chapter 1. Vegetation-Management Planning and Mitigating 

Tree Hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1. Hazard-tree mitigation as a part of vegetation management. . . 11

2. What constitutes a hazard?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Hazardous trees and associated liabilities. . . . . . . . . . . . . . . . . . . . . . 13

4. Goal of hazard-tree management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Chapter 2. Components of Hazard-Tree Analysis. . . . . . . . . . . . . . . . . . . . . . . 15

1. A process for hazard-tree evaluation and action. . . . . . . . . . . . . . . . 15

2. What is failure potential?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3. Rating failure potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4. Potential for striking a target and damage potential. . . . . . . . . . . . 22

5. Determining the potential-failure zone. . . . . . . . . . . . . . . . . . . . . . . . 22

6. Rating damage potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

7. A standard for hazard rating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8. How often should hazard rating be done?. . . . . . . . . . . . . . . . . . . . . 27

9. Where and how to collect survey information. . . . . . . . . . . . . . . . . . 28

10. Documentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Chapter 3. Identification of Diseases and Defects that Result

in Hazardous Trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

1. Dead Trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2. Wounded Trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3. Root and butt diseases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4. Other root problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5. Leaning, Root-sprung, Broken, or Uprooted Trees Supported 

 by Other Trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6. Heart Rots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

7. Sap rots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

8. Fungal cankers and stem rusts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

9. Other bole defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

10. Defective branches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

11. Dead or broken tops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

12. Burls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

13. Fire-caused damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

14. High height-to-diameter ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

15. Insect-caused damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

16. Multiple defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4

Chapter 4. Hazard-Tree Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

1. Evaluations Prior to Site Development. . . . . . . . . . . . . . . . . . . . . . . . . 95

2. Management of Existing Sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

References and background material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

For assistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5

List of Tables

Table 1. Failure indicators for high, medium, low and very low failure 

potentials for trees in developed sites in Oregon and 

Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 2. Treatment priorities by hazard class. . . . . . . . . . . . . . . . . . . . . . . . 26

Table 3A. Minimum sound-rind thickness at various diameters inside 

the bark of conifers without open wounds. . . . . . . . . . . . . . 30

Table 3B. Minimum sound-rind thickness at various diameters inside 

the bark of conifers with open wounds. . . . . . . . . . . . . . . . . . 31

Table 4. Distribution of failures by position of defect and tree species 

in Pacific Northwest recreation sites. . . . . . . . . . . . . . . . . . . . . 35

Table 5. Resinous and non-resinous tree species groups in 

development sites in Oregon and Washington. . . . . . . . . . 39

Table 6. Root and butt diseases in Oregon and Washington; 

frequency of occurrence by host species. . . . . . . . . . . . . . . . 41

Table 7. Heart rots in Oregon and Washington; frequency of 

occurrence by host species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Table 8. Sap rots affecting trees in Oregon and Washington. . . . . . . . . 76

Table 9. Fungal cankers and stem rusts in Oregon and Washington; 

frequency of occurrence by host species. . . . . . . . . . . . . . . . 78

Table 10. Tree damage and treatment options for developed sites in 

Oregon and Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Appendix. Cull rules used to identify the extent of red ring rot in 

Douglas-fir west of the Cascade Crest in Oregon and 

Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Cull rules used to identify the extent of red ring rot in oldgrowth (>125 years) western hemlock and true firs west of 

the Cascade Crest in Oregon and Washington. . . . . . . . . 111

Cull rules used to identify the extent of red ring rot in 

Douglas-fir, ponderosa pine, and western larch east of the 

Cascade Crest in Oregon and Washington. . . . . . . . . . . . . 111

Cull rules used to identify the extent of red ring rot in true fir, 

hemlock, and spruce east of the Cascade Crest in Oregon 

and Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Cull rules used to identify the extent of red ring rot in western 

white pine and sugar pine east of the Cascade Crest in 

Oregon and Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Cull rules for white and Shasta red fir in southwest Oregon 

used to estimate defect extent caused by the Indian paint 

fungus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Cull rules used to estimate defect extent caused by the 

Indian paint fungus for all species in Oregon and 

Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
6

 Signs and symptoms of damaging agents in Oregon and 

Washington. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Equipment recommended for hazard-tree evaluations. . . 115

Hazard-Tree Data Forms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

List of Figures

Fig. 1 – Potential-failure zone for total tree failure with 

no slope or lean ≥15o. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Fig. 2 – Potential-failure zone for total tree failure on sloped ground 23

Fig. 3 – Potential-failure zone for total tree failure with lean ≥15o. . . . 23

Fig. 4 – Potential-failure zone for top failure with no slope 

or lean ≥15o. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Fig. 5 – Potential-failure zone for top failure on sloped ground. . . . . . 24

Fig. 6 – Potential-failure zone for top failure with lean ≥15o. . . . . . . . . 25

Fig. 7 – Hazard-tree rating or hazard class is on a scale of 2 to 8.. . . . . 26

Fig. 8 – Battery-powered drills can be used to check for sound-rind 

thickness.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Fig. 9 - Various bole cross-sectional areas showing percentage of 

sound wood remaining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Fig. 10 – Crown decline can be a symptom of root disease. . . . . . . . . . . 44

Fig. 11 – Basal resinosis is often associated with Armillaria root 

disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Fig. 12 – Bark staining is sometimes associated with Armillaria root 

disease.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Fig. 13 – Windthrow can be associated with root disease. . . . . . . . . . . . . 44

Fig. 14 – Dead and dying trees often are caused by root disease. . . . . . 44

Fig. 15 – Armillaria mushrooms are produced in autumn on infected 

trees.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Fig. 16 – Conks associated with annosus root disease often form in 

hollow stumps.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Fig. 17 – Stain caused by Heterobasidion occidentale in grand fir.. . . . . 48

Fig. 18 – White-stringy decay caused by Heterobasidion occidentale 

in a western hemlock stump.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Fig. 19 - Laminated decay can be caused by 

Heterobasidion occidentale.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Fig. 20 - Armillaria ostoyae often produces mycelial fans under the 

bark of infected trees.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Fig. 21 – Ectotrophic mycelium of Phellinus weirii is produced on 

infected roots of Douglas-fir.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Fig. 22 – Rootballs with missing major roots, as shown here, 

are decayed by Phellinus weirii.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7

Fig. 23 – Setal hyphae, the red-brown fuzzy material shown here, are 

diagnostic for laminated root rot.. . . . . . . . . . . . . . . . . . . . . . . . 54

Fig. 24 – Laminated decay as shown here is caused by Phellinus weirii.54

Fig. 25 – Older mushrooms of Phaeolus schweinitzii often 

resemble “cow-pies.”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Fig. 26 – Butt swell of Douglas-fir is often associated with root 

and butt decay caused by Phaeolus schweinitzii.. . . . . . . . . . . 56

Fig. 27 – Stain in a spruce root often is caused by 

Inonotus tomentosus.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Fig. 28 – Undermined roots, as shown here, can result in tree failure.. 59

Fig. 29 - Newly developed leans lack tops that point upward 

(uncorrected).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Fig. 30 – Cracks in the soil around leaning trees indicate that such 

trees have a high-failure probability.. . . . . . . . . . . . . . . . . . . . . 60

Fig. 31 – Old leans with righted or corrected tops have low-failure 

probability.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Fig. 32 – Tree bole with an open wound where the sapwood is 

exposed.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Fig. 33 – Typical conk of Phellinus tremulae indicates internal decay in 

this aspen.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Fig. 34 – Advanced decay caused by Fomitopsis officinalis is a browncubical rot.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Fig. 35 – Quinine conks of Fomitopsis officinalis are distinctive and 

indicate considerable stem decay.. . . . . . . . . . . . . . . . . . . . . . . 69

Fig. 36 - Conks of Oligoporus amarus on incense-cedar are annual 

and disintegrate relatively rapidly.. . . . . . . . . . . . . . . . . . . . . . . 70

Fig. 37 - Typical conk of Phellinus pini often indicates low-failure 

potential.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Fig. 38 – Wood with decay caused by Phellinus pini, commonly called 

whitespeck, is relatively sound compared to wood decay 

caused by other fungi.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Fig. 39 – Advanced decay caused by Echinodontium tinctorium, the 

Indian paint fungus, can result in tree failure.. . . . . . . . . . . . . 74

Fig. 40 – Conks of the Indian paint fungus are distinctive and 

common on true firs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Fig. 41 – Red-belt conk of Fomitopsis pinicola, the most common 

decayer of dead wood in the Pacific Northwest.. . . . . . . . . . 77

Fig. 42 – Pouch-fungus conks of Cryptoporus volvatus often 

indicate considerable sap rot.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Fig. 43 – Atropellis canker is a common disease of lodgepole pine 

that can result in stem breakage. . . . . . . . . . . . . . . . . . . . . . . . . 80

Fig. 44 – Dead tops of ponderosa pine, caused by Comandra blister 

rust, often are resin-impregnated, decay-resistant, and 

therefore of very low-failure potential. . . . . . . . . . . . . . . . . . . . 81
8

Fig. 45 – Dwarf mistletoe bole infections are especially common on 

grand and white fir, western hemlock, and western larch. 82

Fig. 46 – True mistletoe bole and branch infections can cause cankers 

and subsequent decay in oaks.. . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Fig. 47 – Sooty-bark canker, as seen on this infected aspen, can 

result in tree failure.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Fig. 48 - Lodgepole pine with western gall rust can break if stem 

cross-sectional area of sound wood is too low.. . . . . . . . . . . 84

Fig. 49 – Tops of trees killed by white pine blister rust are often 

resin-soaked with little decay and have very low-failure 

potential.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Fig. 50 – Frost cracks often indicate low-failure potential unless 

they are weeping, as shown here, then failure potential is 

medium to high.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Fig. 51 – Forked tops, such as this hardwood that is weeping and 

cracked (A) and this cedar with open cracks (B), have highfailure potential. The ponderosa pine with only embedded 

bark (C) has medium-failure potential.. . . . . . . . . . . . . . . . . . . 87

Fig. 52 – Douglas-fir dwarf mistletoe brooms that are dead 

and >10ft. in diameter have high-failure potential.. . . . . . . 89

Fig. 53 – Failure potential of trees with dead tops depends on 

whether the tree species is resinous like Douglas-fir or 

non-resinous like white fir.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Fig. 54 – Burls are often large woody growths of unknown cause on 

conifers and hardwoods that resemble conks but indicate 

low-failure potential.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Fig. 55 – Fire-damaged trees have failure potentials that depend 

on the amount of sound wood remaining.. . . . . . . . . . . . . . . 92

Fig. 56 – Bark beetles often kill trees and form pitch tubes on 

attacked pines.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Fig. 57 – Multiple medium-failure indicators can imply high-failure 

potential such as this maple with hollow, leaning stems.. . 94

Cabin on Lake Quinault, 

Olympic National Forest
9

Introduction 

Hazard-tree management requires unique skills that combine science 

and intuition. It requires observation, knowledge of the site, experience 

with tree defects and decays, thorough investigation, and adequate 

documentation. This guide is intended to aid users in hazard-tree 

identification, evaluation, and mitigation with an emphasis on native 

forest trees of the Pacific Northwest.

This guide is for forest-resource managers, recreation staff, pestmanagement specialists, concessionaires, consultants, and arborists 

who deal with developed sites in forested areas and need to identify, 

monitor, and mitigate hazard trees. It is a revision of a similar guide: 

“Long-range planning for developed sites in the Pacific Northwest: the 

context of hazard tree management” (Harvey and Hessburg 1992). We 

recommend that this guidebook be used for identifying and mitigating 

hazard trees in and around developed sites such as campgrounds, 

picnic areas, ski areas, boat launches, parking lots, trailhead parking 

areas, buildings, and administrative complexes. These sites should have 

a thorough, systematic survey by knowledgeable inspectors due to 

the long-term exposure and high target values. Such sites should be 

frequently visited and trees of concern documented, treated or retained, 

and periodically monitored. 

Forest trees, especially large ones, greatly add to the beauty and 

enjoyment of developed sites. Pathogens, insects, and weather events, 

however, can cause substantial damage to forest trees in the Pacific 

Northwest. Reducing this damage is an objective of managers for most 

forest sites. On developed sites, tree damage may pose a hazard to the 

safety of people or their property. Developed sites are places where 

people often congregate and are exposed for longer than intermittent 

time periods to potentially failing trees. Camp sites and buildings, where 

breakage from or failure of defective trees could result in damage to 

people or their property, are examples of valuable targets that need to 

be protected. Targets that are exposed during the winter, when storms 

often cause trees or their parts to fail, are particularly vulnerable to 

tree failure and subsequent damage. The longer the exposure to tree 

hazards, the greater the potential for property damage or personal 

injury.

Tree and stand decadence increase with disturbance, advancing age, 

and forest community succession. With increased decadence comes 

an increased presence of defective trees prone to failure. In most 
10

plant-community types, the result of developed-site use and treehazard mitigation has been accelerated succession and increased 

stand decadence over time. Although trees are a renewable resource, 

there has been resistance to removing large, old, defective trees from 

developed sites simply because it takes centuries for them to develop. 

Removal or mortality of early seral species increases the proportion 

of shade-tolerant species such as grand/white fir or hemlock. In 

community types with these species, repeated hazard-tree removals 

have promoted shifts in vegetation toward climax conditions and the 

associated higher susceptibility to insect- and disease-caused damage 

that typify many developed sites today. Other sites, such as those in dry 

ponderosa pine communities, tend to remain in pine dominance, even 

with removals. Trees on these sites are generally more resilient to insects 

and diseases and usually have a relatively low incidence of damaging 

agents that could predispose them to failure. 

This guide will assist you in appropriately inventorying, documenting, 

and treating hazard trees. The objectives of this guide are to present: 

1) The need to develop long-term management plans for developed 

sites 

2) A standard for evaluating tree hazards in developed sites 

3) An up-to-date field aid for accurate identification of diseases, 

defects, and resulting tree-failure potential

4) A standard for recording developed-site evaluations 

Mt. Baker, 

Mt. BakerSnoqualmie 

National Forest
11

Chapter 1 - Vegetation-Management 

Planning and Mitigating Tree Hazards 

To maintain a balance of benefits in the long term, managers of 

developed sites must contend with several forest-disturbance agents. 

The most obvious effects that these agents have on developed sites 

occur through their influence on forest health and succession. Insects, 

diseases, and abiotic factors such as wind, drought, and snow cause 

the deterioration and demise of trees. When removing hazard trees, we 

may need to consider and plan for replacement vegetation to achieve 

the desired future condition of the site and the associated vegetation. 

This, of course, needs to be tailored to the plant community of the site 

and the silvics of the desired tree species. This constitutes the heart of a 

vegetation-management plan, which is advisable for documenting both 

a site-specific and administrative-unit management strategy.

Hazard-Tree Mitigation as a Part of Vegetation 

Management 

Hazard-tree mitigation is one of many management actions 

prescribed in a vegetation-management plan. Appropriate hazard-tree 

management complements other management actions to achieve a 

common set of goals. The primary objective of vegetation-management 

planning is to develop a description of the desired future condition of 

the vegetation and the strategy to achieve that goal. Input by various 

resource specialists should be included.

Older stands with multiple canopy layers generally make highly 

attractive and aesthetically desirable recreation areas. It may take two or 

more centuries to develop stand structures that contribute to the most 

desirable recreation sites. Development and maintenance of desirable 

older stand structures needs to be a planned objective, and achieving 

that goal requires management actions that are dependent on the type 

of plant community and the existing biotic and abiotic disturbance 

agents. In some situations, it may be difficult or impossible to maintain 

old-growth structure and keep the area safe. Thus, for future recreation 

sites it might be more desirable to place them in younger stands 

because they are often hazard free and more easily managed. 

Hazard-tree evaluations, as part of a vegetation-management plan, 

should involve a systematic, peer-accepted evaluation process that 

identifies and mitigates hazards and reduces them to acceptable 
12

levels. The process needs to be repeatable with continuity over 

time as personnel change. Record keeping is important, especially 

documenting trees to be monitored and assuring that hazard trees 

deemed unacceptably dangerous are mitigated. 

Many federally owned developed-recreation sites are being managed 

by private concessionaires, who may be tasked with the identification 

and mitigation of hazard trees on those sites. It therefore becomes 

important that recreation managers work closely with concessionaires 

on hazard-tree documentation, monitoring, and integration with 

vegetation-management plans. 

What Constitutes a Hazard? 

In recreation-resource management, hazard is the exposure to the 

possibility of loss or harm. With reference to trees, it is the recognized 

potential that a tree or tree part may fail and cause injury or damage 

by striking a target. All standing trees within areas occupied by people, 

property, and structures present some level of hazard. Failure potential 

by itself does not constitute a hazard. Hazard exists when a tree of 

sufficient size and mass to cause injury or damage is within striking 

distance of people, property, or structures (targets). Hazard increases 

with increasing tree defect, failure potential, potential for damage, and 

target value. Management actions are taken when the line officer or 

land manager decides to mitigate the hazard when risks (the product of 

damage potential and consequences of damage) are unacceptable. 

Hazard is defined as acceptable (we will not mitigate) when: 

1) All components of hazard have been fully evaluated, and 

2) Failure and/or damage probability is estimated to be low 

Hazard is unacceptable (we will mitigate) when: 

1) The amount of defect indicates failure is likely, 

2) The failure potential and relationship to targets indicates damage 

is likely, and 

3) Targets include people, property, or structures 

Hazard evaluations assess both failure potential and damage potential. 
13

Hazardous Trees and Associated Liabilities 

In this guide, a hazard tree is any tree that is within striking distance 

of a permanent or transitory target of value. Any tree or tree part has 

some level of failure potential. Biotic and abiotic agents can interact to 

increase the likelihood of failure. If visitors wish to recreate in forests, 

they must accept a certain amount of hazard. Land managers and 

evaluators must learn to recognize the signs of increasing hazard so it 

can be minimized. 

Visitors can be grouped into three distinct classes: invited, licensed, 

and trespassing. For lands maintained open to the public, visitors are 

considered invited, and public-land managers are liable to an extent 

for their safety. The USDA Forest Service Manual (FSM 2309, 2330, 6703, 

6730) outlines specific objectives, policies, and responsibilities for 

managers of recreation sites. These include documented hazard-tree 

evaluations by “qualified” people and may include corrective actions or 

treatments. Some liability for injury or loss lies with the landowner or 

agent for the land. In most states, a Recreational Use Statute or similar 

legislation provides protection to landowners by holding them free of 

liability resulting from accidents or deaths occurring on their lands held 

open for public use. This protection does not extend to landowners 

when a fee is levied. In this situation, and when gross negligence, 

intentional wrongdoing, or wanton misconduct is a factor, Federal 

Tort Claims rules apply. Land managers should carefully consider the 

benefits of protection afforded by Recreational Use Statutes before 

applying a user fee. 

Informing the public that dangerous conditions exist does not eliminate 

liability. It is the responsibility of land managers or their agents to 

discover and correct unreasonably dangerous conditions to minimize 

the potential for injury to invited users or damage to personal property. 

Responsibility to actively minimize hazard is roughly proportional to 

the degree of development of an area. Highly developed sites infer a 

greater degree of responsibility than undeveloped areas. It is imperative 

that site managers conduct high-quality, hazard-tree evaluations and, 

as required, treatments that respond specifically to each unacceptable 

hazard. If no fee is levied for recreation-site use, posting signs to expose 

tree hazards and associated risks may reduce liability of the landowner 

or manager. 

The goal in developing recreation sites is to provide facilities that 

visitors will use. Often, large, old-growth trees are the prime attractions, 
14

and those are the very trees that often present the greatest threat 

to public safety. The goal in managing these sites is to maintain the 

old-growth appearance while eliminating unacceptable risk to visitors. 

Similarly, the goal in managing any developed-recreation site is to 

maintain or improve the characteristics of the site that attracted visitors 

initially and that promoted formal development, while eliminating 

unacceptable risk to visitors. 

Goal of Hazard-Tree Management 

Hazard-tree management historically has been used as a short-term 

fix to reduce hazard, but this usually does not, by itself, enhance the 

long-term health or aesthetics of the vegetation in developed sites. 

Vegetation-management plans should contain strategies to meet 

long-term goals or desired future condition of the vegetation. Hazardtree management should be addressed in these plans, and most 

importantly, so should the strategy for developing or maintaining 

healthy, resilient, low-hazard trees. The goal of hazard-tree management 

is to strike a balance between providing healthy trees with low-failure 

potential and forest vegetation that provides an aesthetically pleasing 

and natural environment. Hazard-tree management, although based 

on valid science, is not an exact practice, and mistakes in identifying 

defects and tree-failure potential unfortunately are made. We provide 

this guide as a means to minimize these errors.

South Shore Campground, Deschutes National Forest
15

Chapter 2 - Components of Hazard-Tree 

Analysis 

Hazard-tree analysis involves inspecting and rating trees for 

their potential to fail and strike targets during the time between 

examinations. Since it is not reasonable to eliminate all hazards (i.e. all 

trees) from a developed site, the manager or responsible official must 

decide what constitutes an acceptable level of risk. Trees near targets 

and potential targets should be thoroughly inspected. Hazard-tree 

analysis also involves documentation and record-keeping of trees that 

have some level of defect but will be retained for the short term and 

periodically re-evaluated at some scheduled interval.

A Process for Hazard-Tree Evaluation and Action

There are four steps that the evaluator should take when dealing with 

potential hazard trees in developed sites:

1) Identify tree defects, determine the tree’s potential to fail, and 

assign a numerical score for failure potential.

2) Determine the potential-failure zone and damage potential, and 

assign a numerical score for damage potential.

3) Document the assessment and recommend treatment options 

to the manager or supervisor. 

4) Document the completed action and the date it occurred. 

The degree to which a tree is hazardous depends on two main factors: 

(1) Potential for failure and (2) potential that property damage, injury, or 

death will result from tree failure. Low numerical value for either factor 

implies minimal risk. 

What is Failure Potential? 

Estimating the potential for tree failure may be difficult because of the 

many interacting variables: tree size, age, form, species, condition, and 

location; stand structure; site conditions; and presence and extent of 

tree defects (Table 1). Failure potential is estimated by examining a tree, 

determining the factors and conditions that could contribute to failure 

or weakening, and estimating the likelihood that those factors and 

conditions will simultaneously occur before the next inspection period. 

Tree characteristics to be evaluated include: 
16

Table 1. Failure indicators for high, medium, low, and very low-failure potentials for trees in developed sites in Oregon and Washington 

Failure Indicator High-Failure Potential Medium-Failure Potential Low-Failure Potential Very Low-Failure Potential

Score = 4 Score = 3 Score = 2 Score = 1

Dead trees All None None None

Roots

Live trees in laminated root rot centersPhellinus weirii

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

Douglas-fir, mountain hemlock, or true firs withoutsigns or symptoms and <25ft. from an infected tree or stump (check for butt rot)

Douglas-fir, mountain hemlock, or true firs, withoutsigns or symptoms and >25ft. from an infected tree or stump; Larch, Engelmann spruce, or western hemlockwithout signs or symptoms (check for butt rot)

Pine, Sitka spruce, cedar, or hardwoods withoutsigns or symptoms

Live trees in Armillaria or annosus root disease centersArmillaria spp.Heterobasidion spp.

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

Trees with signs or symptoms but not adjacent to windthrown trees with root disease (check for butt rot)

Susceptible tree species without signs or symptoms (Table 6) (check for butt rot)

Resistant tree species without signs or symptoms (Table 6) 

Live trees in black stain or Port-Orford-cedar root disease centersLeptographium wageneri;Phytophthora lateralis

None None

Trees with signs or symptoms (foliage thinning or yellowing; stained inner bark or sapwood)

Trees without signs or symptoms

Undermined or severed roots 

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

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

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

None
17

Failure Indicator High-Failure Potential Medium-Failure Potential Low-Failure Potential Very Low-Failure Potential

Score = 4 Score = 3 Score = 2 Score = 1

Dead trees All None None None

Butt

Butt rot: Tomentosus, Schweinitzii, Ganoderma, or P. subacida 

Tree with extensive decay: sound-rind thickness <15%of stem diameter1 (Table 

3A) or decay in >50% of the structural roots

Tree butts with moderate decay: sound-rind thickness 15 to 25% of stem diameter or decay in <50% of the structural roots

Trees with little or no decay: sound-rind thickness is >25% of stem diameter and no decay in structural roots

None 

Fire-damaged trees for recent (<5yr) fire damage; use bole wounds for old fire damage

Trees with <50% crosssection of bole with sound wood, or more than one quadrant of damaged structural roots

Trees with 50 to 75% crosssection of bole with sound wood, or one quadrant of damaged structural roots except for cedar, ponderosa pine, sugar pine, and larch

Cedar, ponderosa pine, sugar pine, and larch with >50% cross-section of bole with sound wood; Other species with >75% crosssection of bole with sound wood

Trees with 100% crosssection of bole with sound wood, and no damaged structural roots

Bole

Bole wounds

Trees with sound-rind thickness of <20% of stem diameter1 (Table 3B)

Trees with sound-rind thickness of 20 to 30% of stem diameter

Trees with sound-rind thickness of >30% of stem diameter

None

Mistletoe cankers, fungal cankers

Trees with <50% crosssection of bole with sound wood

Trees with 50 to 75% crosssection of bole with sound wood

Trees with >75% crosssection of bole with sound wood

None

Frost cracks 

Trees with weeping cracks and sound-rind thickness is <20% of stem diameter1

(Table 3B)

Trees with weeping cracks and sound-rind thickness is 20 to 30% of stem diameter

Trees with cracks with no weeping and sound-rind thickness is >30% of stem diameter

None

Bole cracks

Trees with splits or cracks with independent movement, or if decayed, sound-rind thickness is <20% of stem diameter1

(Table 3B)

Trees with splits or cracks without movement, and sound-rind thickness is 20 to 30% of stem diameter

Trees with splits or cracks without movement, and sound-rind thickness is >30% of stem diameter; callus has formed

None
18

Failure Indicator High-Failure Potential Medium-Failure Potential Low-Failure Potential Very Low-Failure Potential

Score = 4 Score = 3 Score = 2 Score = 1

Dead trees All None None None

Conks

Quinine conksFomitopsis officinalis Trees with ≥1 conks None None NoneIndian paint fungus conksEchinodontium tinctorium

Trees with multiple large(>6 in. wide) conks or single large or multiple small conks and at least one additional indicator of associated defect/decay such as open cracks or exposed rot, or sound-rind thickness at conks <15% of stem diameter1 (Table 3A)

Trees with single large (>6 in. wide) or multiple smallconks without additional indicators of associated defect/decay, or sound-rind thickness at conk is 15 to 25% of stem diameter

Trees with a single smallconk, or sound-rind thickness at conk is >25%of stem diameter

None

Red ring rotconksPhellinus pini

Trees with >1 conks andevidence of extensive advanced decay2 such as 

open cracks or exposed rot, or sound-rind thickness at conks is <15% of stem diameter1 (Table 3A)

True fir, hemlock, spruce, or hardwoods with >1 conks without evidence of excessive advanced decay; Douglas-fir, pine, cedar, or larch with >3 large conks (>6 in. wide) within a 3-ft.-long trunk cylinder or sound-rind thickness at conks is 15 to 25% of stem diameter

Douglas-fir, pine, cedar, or larch with >3 large conks not withina 3-ft.-long trunk cylinderor ≤2 large conks within a 3-ft.-long trunk cylinder or any number or location of small conks.or sound-rind thickness at conks is >25% of stem diameter

None

Other heart-rot conks

Trees with >1 conks andevidence of extensive decay such as open cracks or exposed rot, or sound-rind thickness at conks is <15%of stem diameter1 (Table 3A)

Trees with >1 conks; withoutevidence of excessive decay, or sound-rind thickness at conks is 15 to 25% of stem diameter

Trees with ≥1 conks, without evidence of excessive decay and soundrind thickness at conks is >25% of stem diameter

None

Sap-rot conks C. volvatusF. pinicolaT. abietinumC. purpureum

Dead trees with sap-rot conks

Live trees with >2 conks on one or more stem quadrants usually associated with wounds 

Live trees with only 1 or 2 conks; check for extent of dead bark and sound wood

None
19

Failure Indicator High-Failure Potential Medium-Failure Potential Low-Failure Potential Very Low-Failure Potential

Score = 4 Score = 3 Score = 2 Score = 1

Dead trees All None None None

Tops and Branches

Forked or multiple tops or trunks 

Trees with V-shaped forks with embedded bark andopen cracks, decay, or conks

Trees with V-shaped forks with embedded bark but nocracks, decay, or conks

Trees with U-shaped forks or V-shaped forks with noembedded bark, cracks, decay, or conks

None

Dead tops or branches (>3 in. diameter)

True fir, hemlock, spruce, or hardwoods with indicators of significant decay such as open cracks, conks, or exposed rot (tops and branches are high FP, not the whole tree)

True fir, hemlock, spruce, or hardwoods with littledecay;Douglas-fir or pine with significant decay (tops and branches are medium FP, not the whole tree)

Douglas-fir or pine with little decay (tops and branches are low FP, not the whole tree) 

Cedar or larch; Pine tops killed slowly by rust fungi that show resinimpregnation (tops and branches are very low FP, not the whole tree)

Detached tops, branches, (≥3 in. diameter) or loose bark (≥1ft.2

)

All detatched parts (parts are high FP, not the whole tree)

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

None None

Dwarf mistletoe brooms

Douglas-fir with large(>10ft. in diameter) dead brooms (broom is high FP, not the whole tree)

Douglas-fir with small, dead brooms; Other tree species with large, dead brooms (broom is medium FP, not the whole tree)

Douglas-fir with large, livebrooms; Other tree species with small, dead brooms (broom is low FP, not the whole tree)

Douglas-fir with small, live brooms; Other tree species with live brooms (broom is very low FP, not the whole tree)

Black-cottonwood branches 

Trees with large (>3 in. diam.) live or dead branches with evidence of decay and past breakage

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

Trees with large, live branches without decay or breakage

None
20

Failure Indicator High-Failure Potential Medium-Failure Potential Low-Failure Potential Very Low-Failure Potential

Score = 4 Score = 3 Score = 2 Score = 1

Dead trees All None None None

Whole tree

Broken or uprooted trees supported by other trees All None None None

Leaning and/or rootsprung trees 

Trees with recent (<5yr) lean >15 degrees or old uncorrected lean withfreshly disturbed soil or root damage

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

Trees with old corrected lean None

Height:diameter ratio3 Trees with >100% H:D ratio Trees with 80 to100% H:D ratio Trees with 60 to 80% H:D ratio Trees with <60% H:D ratio

Multiple indicators

Two or more medium-FP indicators with synergistic effects: one condition (indicator) worsens the other 

Two or more low-FP indicators with synergistic effects; two or more medium-FP indicators without synergistic effects

Two or more very low-FP indicators with synergistic effects;two or more low-FP indicators without synergistic effects

Two or more very lowFP indicators without synergistic effects

1 To calculate sound-rind thickness as a percentage of stem diameter, divide the sound-rind thickness by the stem diameter and multiply by 100.2Firm 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. Sound-rind thickness should include decay caused by P. pini that is not advanced.

3To calculate H:D ratio, divide the total tree height in feet by the dbh in feet (p. 93).
21

1. Whether the tree is live or dead 

2. Presence of dead, broken, or free-hanging branches 

3. Presence or a recent weakening of co-dominant stems or dead, 

forked, or multiple tops

4. Presence of wounds, injuries, exposed or damaged roots, and 

associated decay or defect

5. Lean of a tree and factors that contributed to the lean 

6. Whether a tree has recently been root-sprung (lateral-root 

anchorage has been compromised) 

7. Whether trees that previously leaned have righted (corrected) 

their tops subsequently and now have acceptable lateral 

anchorage 

8. Presence and extent of lethal or weakening root, stem, or branch 

disease or insect infestation 

9. Presence and extent of damage caused by human activities

Dead trees are important to identify and mitigate in developed sites. 

Tree mortality in Pacific Northwest forests often is a complex process 

involving several related factors. Tree mortality tends to be more 

common in high-elevation forests where stress from weather, insects, 

and disease result in higher rates of mortality and in the drier interior 

forests where mortality from fire, insects, and disease are common. Tree 

mortality may be directly due to biotic or abiotic causes and may be 

affected by previous damage, current condition (vigor), and attack by 

secondary agents such as bark beetles. 

Rating Failure Potential

Failure potential is rated on a scale of 1 to 4 in order of increasing severity: 

POTENTIAL FOR FAILURE

1 = VERY LOW-FAILURE POTENTIAL 

Live trees without visible defects.

2 = LOW-FAILURE POTENTIAL 

Live trees with only minor defects.

3 = MEDIUM-FAILURE POTENTIAL 

Live trees with moderate defects. Decay extent has rendered the tree at 

or near the acceptable sound-rind thickness (p. 30-31).

4 = HIGH-FAILURE POTENTIAL 

All dead trees; live trees that are highly defective. Decay extent in live 

trees has rendered the tree below the acceptable sound-rind thickness.
22

Potential for Striking a Target and Damage Potential

The potential that a tree or tree part will strike a target is determined 

by evaluating where trees or their parts will likely land in the event of a 

failure, and whether those places of impact will be occupied by targets 

at the time. This determination is more straightforward for sites with 

characteristically high and steady occupancy than where intermediate 

or low occupancy occurs. Variables that are evaluated include: 

•	 Location of tent pads, fire rings, barbecue pits, water pumps, 

waste-disposal stations, restrooms, picnic tables, historic 

buildings, information boards, interpretive stations, trailside 

rest stops, scenic-viewing areas, ski-lift lines, children’s play 

areas, parking areas, and other potential targets

•	 Seasonal use patterns 

•	 Day use patterns (day use vs. camping)

Determining the Potential-Failure Zone

The potential-failure zone is the area that could be reached by any 

part of a failed tree. However, when a tree fails, the tree or its parts 

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

slide or roll, especially on moderate to steep slopes. Also, when a 

tree fails, it may strike other trees or debris on the ground and fling 

material a considerable distance. This is especially true among dead 

trees. Determining if targets such as toilets, tent pads, or parking areas 

are within the area where a tree or its parts may fall (Potential-Failure 

Zone) is an important step in determining if the tree or tree part is a 

hazard. Therefore, a tree with defect and no target is not a hazard tree. A 

defective tree, however, whose potential-failure zone intersects a target 

such as a campfire ring is a hazard, and recommendations for mitigation 

should be made.

Total-Tree Failure

The failure zone is defined as the area on the ground that could be 

reached by any portion of the tree that may fail. When determining the 

failure zone, the following conditions must be evaluated:

•	 Ground slope

•	 Direction of lean

•	 Height of the tree
23

The failure zone is a circle around the tree with a radius that is the same 

as the total tree height (Fig. 1). For instance, if a tree is 150 ft. tall, then 

its potential-failure zone has a radius of 150 ft. On sloped ground, the 

failure zone downhill of the tree may have to be extended whatever 

distance is necessary to protect people or property if the tree or part 

slides or bounces (Fig. 2). For trees leaning more than 15 degrees, the 

failure zone is an area the same radius as 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. 3). The 

area behind the lean is not within the normal failure zone, but storms 

with high winds could force a backlash opposite to the lean and create 

an additional danger. 

Fig. 1 – Potential-failure zone for total tree failure with no slope or lean 

1 x height 1 x height

Potential failure zone

height

Fig. 2 – Potential-failure zone for total tree failure on sloped grou

1 x height

height

slide or roll

area

Fig. 1 – Potential-failure zone for total tree 

failure with no slope or lean ≥15 degrees

Fig. 2 – Potential-failure zone for total tree 

failure on sloped ground

Fig. 3 – Potential-failure zone for total-tree 

failure with lean ≥15 degrees 

. 3 – Potential-failure zone for total-tree failure with lean >15 degrees 

1 x height

Potential-failure zone

backlash area
24

Tree-Part Failure

The area that could be reached by a dislodged top, branch, slab, 

or chunk is the potential-failure zone. When determining the zone, 

evaluate the following conditions:

•	 Ground slope

•	 Amount and direction of lean

•	 Length of the part that could be dislodged

On level or sloped ground where the tree has no discernable lean, 

determine the length of the part that could be dislodged. The failure 

zone forms a circle around the tree with a radius equal to the length of 

the defective part (Fig. 4). For instance, if a dead tree top is 10 ft. long, 

then the potential-failure zone has a radius of 10 ft. On sloped ground 

where the dislodged part may slide or roll down hill, the failure zone 

must be extended on the down-hill side, usually about half the radius of 

the potential-failure zone (Fig. 5). Dead tops or branches may fail due to 

high winds that can carry the piece beyond the potential-failure zone.

For tree parts on leaning trees, determine the length of the part that 

could be dislodged. Determine the amount of lean (horizontal distance 

from where the part could be dislodged relative to the base). The failure 

zone is the distance determined by adding the length of the defective 

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 90o on either side of the tree from the lean direction (Fig. 

6).

– Potential-failure zone for top failure with no slope or lean 

1 x length 1 x length

Potential failure 

 zone

top length

Fig. 5 – Potential-failure zone for top failure on sloped ground

1 x length

top length

slide or roll

area

Fig. 4 – Potential-failure zone for top failure 

with no slope or lean ≥15 degrees

Fig. 5 – Potential-failure zone for top failure 

on sloped ground
25

POTENTIAL FOR DAMAGE 

1 = NO DAMAGE

Target impact will involve only very small tree parts, or there is no chance that failed 

parts will cause damage when they impact a target.

2 = MINOR DAMAGE 

Failure of only small tree parts, and impacts in occupied areas are indirect; or failures 

will likely occur when area is unoccupied; damage when it occurs, is to low-value 

targets such as garbage cans, campground signs, or fences. 

3 = MEDIUM DAMAGE 

Failure involves small trees or medium tree parts, and impacts will likely occur in areas 

with targets; impacts will be direct, damage will likely be moderate, target value is 

moderate, such as for water pumps or waste-disposal stations. 

4 = EXTENSIVE DAMAGE

Failure involves medium to large tree parts or entire trees, and impacts will be direct 

in areas with targets; target value is high, and damage to property will likely be severe; 

or serious personal injury or death is the likely result in areas such as tent sites, parking 

spurs, or toilets. 

Fig. 6 – Potential-failure zone for top failure 

with lean ≥15 degrees. 

Rating Damage Potential 

Damage potential is the 

probability, type, and extent of 

damage or injury that may result 

from tree failure. The value of 

a potential target is estimated 

by determining the maximum 

extent of loss in the event that it 

is struck by a failed tree or tree 

part. Financial and emotional 

losses resulting from the death, 

injury, or dismemberment of 

a person are far greater than 

those for the loss of picnic tables, 

buildings, or vehicles. Values are 

expressed in relative terms (low, moderate, and high) and are factors 

considered in evaluating damage potential. For example, if the target is 

a person or their parked vehicle, then the value would be high. A target 

of moderate value may be a building or other developed structure or 

convenience such as a water pump or waste-disposal station. Garbage 

cans, dumpsters, and information boards may be examples of low-value 

targets. Roads, trails, and pathways within the developed site should 

be rated as minor (score=2) or medium (score=3) for damage potential 

depending on their frequency of use.

Damage potential is rated on a scale of 1 to 4 in order of increasing 

severity: 

g. 6 – Potential-failure zone for top failure with lean >15 degrees. 

1 x length

Potential-failure zone

backlash area

top length
26

A Standard for Hazard Rating 

The standard hazard-rating system suggested here incorporates two 

important components (USDA 2011). The first component addresses 

the potential for tree failure within a specified time period. The second 

component of hazard rating addresses damage potential in the event of 

a failure. This portion of the rating must incorporate the likelihood that a 

failed tree or tree part will strike a target, the likelihood of damage, and 

an estimate of target value. The hazard classification for each individual 

tree is determined by combining the values from the Failure Potential 

(1-4) and Damage Potential (1-4) components of the rating system. 

Seven hazard classes ranging from 2 to 8 are possible (Table 2, Fig. 7). 

Table 2. Treatment priorities by hazard class:

Hazard Class Treatment Priority

8 very high

7 high

6 moderate

2-5 low

Fig. 7 – Hazard-tree rating or hazard class is on a scale of 2 to 8. 

1 2 3 4

1 2 3 4 5

2 3 4 5 6

3 4 5 6 7

4 5 6 7 8

Hazard Tree Rating

 Failure Potential Damage Potential
27

As an example, you determine that a tree has low-failure potential with 

a rating of 2. You rate the damage potential as minor with a rating of 

2. The hazard class is therefore 2 + 2 = 4, and the treatment priority is 

therefore low. Another tree has a high-failure potential with a rating of 

4. The damage potential is medium with a rating of 3. The hazard class is 

therefore 4 + 3 = 7 and the treatment priority is therefore high. For sites 

administered by public agencies, the deciding official determines what 

hazard classes are to be treated or monitored. 

How Often Should Hazard Rating be Done? 

Timing and frequency of examinations may vary, but all developed 

sites should be examined for new evidence of hazardous trees at least 

annually. For USDA Forest Service sites, at the National Direction FSM 

2332.1-Public Safety requires annual public safety inspections of these 

sites before the managed-use season, and trees are to be examined 

as part of the annual public safety inspection (Region 6 policy, USDA 

2011). Sites should be examined once the severe weather season(s) 

have passed. This usually occurs in the spring in many parts of the 

Pacific Northwest, because severe weather is most often associated with 

winter storms. Winter storms often bring attention to the most severely 

defective trees or limbs, and the portions of stands with severe root 

disease or stem decay. 

Annual pre-season site reviews should be done systematically, normally 

consist of a walk-through examination, and should be done before 

opening developed sites with seasonal closures. The expertise required 

to do annual inspections is less than for formal hazard-tree evaluations, 

since annual inspection is primarily for obvious winter and storm 

damage. 

A more thorough and formal hazard-tree examination (baseline survey) 

should be conducted at least every five years, where each tree and all 

areas of the developed site are observed for new evidence of hazard or 

defect. More thorough examinations should be done more frequently 

than five years if the site is experiencing a recent disturbance such as 

a bark beetle outbreak, flood, fire, wind event, root disease, or the site 

is in a forest type with a history of many defective trees (i.e. white fir or 

cottonwood).

All trees within striking range of a target, either fixed or transitory, 

should be examined. Evaluations should begin at known or established 

reference points, and all trees in the vicinity of those points be 
28

systematically examined. Ideally, a benchmark or baseline hazard-tree 

evaluation should already be completed for the site, and notes from 

the walk-through examination can be used to modify or upgrade that 

information. If no such baseline evaluation exists for a site, one should 

be conducted. 

The development of a baseline evaluation requires a systematic 

approach that should be organized in planning sessions before going to 

the woods. The approach described here is one that has been used and 

modified over the years. It is divided into four stages: 

1) Identify and gather the necessary equipment (see Appendix) 

2) Determine the information needs and gather those data 

3) Record the information and develop a permanent database 

4) Mitigate the unacceptable hazards 

Where and How to Collect Survey Information 

Where to survey

Walk-through and baseline surveys should begin by obtaining a 

detailed map of the developed site and reviewing any past survey 

information. Trees should be evaluated adjacent to the roads entering 

and exiting the site and all travel loops within the developed portion 

of the site. All trees of a height that if fallen would reach the road 

should be examined. The width of the survey area adjacent to roads 

is equivalent to the height of the tallest trees. Concurrently, all trees 

adjacent to structures, parking areas, restrooms, waste-disposal stations, 

water pumps, picnic tables, or ski lifts must be inspected. The width of 

the survey area around these developments is equal to the height of the 

tallest trees. 

Within developed sites, all trees that could potentially reach tent pads, 

picnic tables, parking areas, ski-lifts, commonly used streamside or 

lakeside fishing spots, fire rings, barbecue pits, and all other recognized 

gathering places or focal points of human activity should be carefully 

evaluated. If these are not known, consult with knowledgeable site 

hosts or maintenance workers prior to establishing the baseline 

evaluation. At all times, examiners should be aware of the tree hazards 

that have potential to impact human targets. These are most important 

to identify and mitigate to protect the safety of visitors. 
29

How to survey

Begin by evaluating trees 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 examiner to detect dead trees or 

tops and live crown symptoms of root disease that can include reduced 

lateral branch and terminal growth, thinning crowns, chlorosis, distress 

cone crops, and dead tops and branches. Evidence of defoliator activity, 

dwarf mistletoe infection, stem conks, and bark beetle attack is often 

initially detected from a distance and involves inspecting multiple trees 

from different vantage points. 

Tree tagging Ideally, each tree with elevated failure potential that 

will be monitored should be tagged with a numbered, aluminum tag 

fixed to the tree with an aluminum nail. Nails should be driven through 

the tag leaving 3/4 to 1 in. of the nail exposed to allow for tree radial 

growth. Tags should be placed near the soil surface of the litter layer, 

if present, so they are hidden from view yet easily found. Normally, 

a cardinal compass direction should be selected, and all tags should 

be placed facing in that direction. This will simplify the process of tag 

relocation. 

Permanent reference points are essential for generating maps and 

for documentation and relocation of individual trees. Locate a large 

object that is a permanent fixture in the site for a reference point. This 

may be a fire pit in a numbered campground site, an outhouse along 

a road, or a lift tower in a ski area. Beginning with the first reference 

point and continuing in order to the last, trees should be evaluated and 

observations recorded. Samples of evaluation forms are located in the 

Appendix.

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 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 that are 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 problems in adjacent, apparently healthy trees. 
30

During tree inspections, examiners should look for signs and symptoms 

of disease and evidence of insect attack. In the event that signs and 

symptoms indicate damage and a potential hazard, trees should be 

examined more thoroughly to determine the extent to which the 

damage has compromised structural integrity. Some defects such 

as frost cracks or broken tops may not demand immediate hazard 

mitigation but suggest the need for periodic re-examination or 

monitoring during annual surveys. 

Systematic tree examination begins at the ground around the base of 

the tree, then proceeds to the butt, bole, limbs, and tree top. All sides 

of each tree should be examined. 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 will be necessary. 

Table 3A - 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 high-failure potential (score=4).

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. 
31

Lightly tapping suspect trees with an axe or rubber mallet can be used 

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

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

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

borers. 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 confirmed infection, the root collar, butt, and major lateral roots 

should be inspected for fruiting bodies, ectotrophic mycelium, mycelial 

fans under the bark, incipient stain or advanced 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 chop into them 

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

Table 3B - 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 high-failure potential (score=4).

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. 
32

disease if preliminary evidence 

suggests that it is present. The 

roots that are most likely infected 

should be checked first. These 

include those closest to infected 

(hollow) stumps, windthrown 

trees, or obvious root-disease 

centers. 

If a tree has conks, wounds, or 

cankers, a cordless electric drill or 

increment borer can be used to 

check for presence and extent of decay associated with these indicators 

(Fig. 8). For soft-wooded species such as cedar, spruce, or alder, coring 

with an increment borer may be more useful than using an electric drill 

for detecting incipient decay. The first place to drill is directly into the 

wound, canker, or flattened area. If decay is found, at least three more 

drillings should be made to the opposite and adjacent sides, to estimate 

the extent of decay. Tree species that display buttressing or fluted butts 

(e.g., western hemlock, western redcedar) may require more sampling 

since the distal portions of fluted areas are often thicker. The thickness 

of the remaining rind of sound wood (Fig. 9) should be recorded by 

averaging all measurements. Refer to Table 3A and 3B for minimum 

sound-rind thickness. When the thickness of the rind of sound wood is 

insufficient for a tree’s diameter, the failure potential is recorded as high 

(score=4). The determination of sound-rind thickness with an increment 

borer should be done only during the baseline survey (p. 27) and then no 

more than every 5 years to minimuze drill wounds.

For trees with open wounds (Fig. 32) (p. 55), minimum sound-rind 

thickness is 25% greater than indicated in Table 3A (0.19 x diam.). For 

example, a suspect tree has a diameter of 32 in. at its base and has a 

large wound near its base. The minimum sound-rind thickness would be 

6.1 in. or 0.19 x diam. (0.19 x 32) because of the wound (Table 3B). After 

Fig. 8 – Battery-powered drills can be used to 

check for sound-rind thickness.

<50% bole cross-section is sound

Fig. 9A

50 to 75% bole cross-section is sound

Fig. 9B

>75% bole cross-section is sound

Fig. 9C

Fig. 9 – Various bole cross-sectional areas showing percentage of sound wood remaining. 
33

increment boring at three points at the base, you determine that the 

average sound-rind thickness is only 4 inches; therefore, the tree has a 

high potential for failure. All of the examples in Fig. 9 where <50% of the 

bole cross-section is sound are below the minimum sound-rind thickness.

The minimum sound-rind thickness applies primarily to conifers but 

less so to hardwood species for the following reasons: 1) the difference 

in basic tree form between hardwoods and conifers, 2) the strong and 

variant influence of leverage on the breakage potential, 3) the high 

mechanical strength of the wood of many hardwood species such as 

oak and maples, and 4) the fact that trunk failures, besides those near 

the groundline, are relatively rare in hardwoods except in weak-wooded 

species such as cottonwood, alder, and aspen. In hardwoods the 

condition of the branches and forks often is more important than the 

condition of the main trunk.

The minimum sound-rind thickness is just one assessment method 

for living trees with internal decay. The values in Table 3A and 3B are 

based on single-stemmed conifers with no lean or other bole defects. 

Also, the guidelines apply to the bole only and not to the roots or root 

collar. Although the presence of bole wounds can be compensated for 

as explained above, other visible and hidden defects associated with 

the decay column should be considered in the assessment (see multiple 

defects, p. 94). Allowing trees to reach a threshold of the minimum soundrind thickness should be done only with evaluation of all other defects.

Drilling all trees is not recommended since it is time consuming and 

usually not warranted, lacking other indicators of internal defect. Trees 

in areas known to have a high incidence of hidden defect, however, may 

warrant close evaluation that may include drilling or sounding. Trees 

with substantial decay usually bear obvious indication of that defect or 

produce a hollow sound when pounded with a mallet or axe. 

Signs of significant woodpecker activity, such as nest-cavity excavation, 

often indicate the presence of advanced decay. Woodpecker activity 

for nest sites should not be confused with sapsucker activity. Sapsucker 

damage often looks alarming but is only superficial. Chopping the bark 

or drilling into the wood can confirm the presence and extent of this 

defect. Be discrete with chopping so as not to suggest to visitors that it 

is an acceptable activity. 

The bole above the lower butt is the next logical section to examine. 

From this point upward, visual examination can be employed to detect 

and estimate the extent of defect. Again, signs of past injury or fungal 

fruiting bodies should be the target of observation. 
34

By the time old-growth trees exhibit fruiting bodies of stem-decay fungi, 

decay levels often are 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. Record the presence 

of all signs of potential defect so that if treatment is not immediately 

warranted, the loss of a conk or misinterpretation of other signs will not 

lead future examiners to believe the stem is sound. 

Tree tops and branches should be examined thoroughly. Free hanging 

and dead branches should be evaluated and dealt with as needed. Dead 

tops should be examined for decay and instability indicated by conks, 

crumbling sapwood, woodpecker activity, or nesting cavities. Binoculars 

are useful for this assessment. 

Recreation site records covering a 10-year period in the Pacific 

Northwest revealed the frequency of tree failure by position of the 

defect on the tree (Table 4). Nearly two-thirds of all recorded failures 

occurred as a result of root or butt defects. Limb failures occurred more 

frequently in hardwoods than in conifers.

Documentation

A record that an inspection was done on a site is necessary to provide 

evidence that a survey was completed. Documenting trees with 

elevated hazard-rating (e.g. ratings of 6, 7, or 8) can provide evidence 

that a tree was examined and a decision made to mitigate the hazard or 

monitor the tree. A tree record form (see Appendix) should be completed 

for trees with elevated hazard-tree ratings of 6, 7, or 8. Healthy-appearing 

trees will be inspected but may not necessarily have an examination 

record filled out. Completing a formal report to the responsible official 

that describes the procedure used, documents the evaluation, and 

includes a record of trees with elevated hazard and recommended 

treatment is advisable. Recording results of evaluated trees in 

developed-site evaluations is necessary for several reasons: 

1. The assessment of current hazards and forest health provides a 

foundation for future vegetation-management activities. 

2. It records the predominant defects in each site making the job of 

future surveys easier.

3. It provides documentation for future hazard management and 

monitoring efforts. 

4. It sets the baseline on which to build other vegetation structures 

and compositions, and planning and investment horizons. 
35

Table 4. Distribution of failures by position of defect and tree 

species in Pacific Northwest recreation sites (Harvey and Hessburg 

1992). 

Tree species

Upper 

bole

(%)

Lower 

bole

(%)

Butt

(%)

Branch

(%)

Root

(%)

Total 

number

Alder 23 11 30 1 35 154

Douglas-fir 17 11 15 3 54 404

Engelmann spruce 0 3 34 0 63 38

Grand fir 12 18 18 0 53 34

Incense-cedar 14 29 8 4 44 111

Larch 8 26 4 4 58 26

Lodgepole pine 13 8 7 3 69 637

Madrone 10 2 28 42 18 321

Maple 13 4 30 9 47 47

Mountain hemlock 12 77 0 0 12 43

Noble fir 37 11 0 0 53 19

Pacific silver fir 5 48 5 0 43 21

Ponderosa pine 42 6 5 0 47 280

Poplar 15 12 19 31 23 26

Red fir 16 30 13 1 40 87

Sitka spruce 18 27 18 0 36 11

Spruce, unidentified 0 53 0 0 47 297

Subalpine fir 55 3 24 0 17 29

Sugar pine 14 25 17 8 36 36

Tanoak 13 24 18 16 28 1614

Western hemlock 4 18 19 1 58 113

Western redcedar 0 15 12 10 63 41

White fir 6 53 15 0 26 34

Average 15 22 15 6 42 4423

5. It is the record of performance in the event of litigation. 
36

A primary benefit of establishing a baseline survey and permanent 

database is that future site re-inspections and hazard monitoring are 

simplified. Hazard and monitoring information can be entered into a 

database and information generated annually, listing the trees indicated 

in prior inspections that are to be monitored in a given year. Files can 

provide the locations of specific trees relative to reference points, 

their species, size, and type of defect, their prior extent of defect, the 

appropriate monitoring interval, prior hazard and risk ratings, 

and recommended treatments. Stem maps can be generated using 

reference points and azimuth/distance information. Maps of virtually 

any specification can be generated: tree-removal maps for 

contractors, annual tree-visitation maps for defect monitoring and 

periodic re-evaluation, and complete developed-site maps for 

long-range planning and visual-perspective projections. Over time, 

annual layers of information may be accumulated and available for 

trend analyses of vegetation, pathogen and insect populations, and 

management activities. 

For trees with disease or defects, a complete tree record should be 

developed at the time of the baseline survey and updated with each reevaluation for developed sites where this is warranted. The tree record 

should contain all the data needed to discover trends for individual 

trees. When observed in aggregate, stand-level trends will become 

obvious. The following information should be recorded (see sample 

forms in Appendix): 

1. Site name

2. Date of survey

3. Name of recorder(s)/examiner(s)

4. Tree tag number

5. Tree species 

6. Tree dbh 

7. Tree height

8. Height to defect(s) or conk(s) (if present) 

9. Symptoms and signs of root or butt disease (resinosis, conks, 

thin crown, cracks) 

10. Thickness of remaining sound wood (rind) 

11. Cause of root or butt disease (Phellinus weirii, Armillaria spp., 

Phaeolus schweinitzii, etc.)
37

12. Stem defects (conks, decay, mechanical injury, fire damage, 

frost crack, dead top, etc.)

13. Stem-disease cause (Phellinus pini, Fomitopsis officinalis, etc.)

14. Failure-potential score and damage-potential score

15. Recommended treatment 

16. Date treatment was accomplished 

Decisions on the soundness of individual trees can be a matter of life 

or death to visitors and public employees. Care should be taken to do 

a thorough job. Adequate time must be allowed to evaluate all trees 

that have potential targets. An evaluation crew of two people is most 

effective and efficient. Ideally, hazard-tree inspections are done when 

weather and lighting conditions are favorable for seeing defects. Trees 

in developed-recreation sites may have great aesthetic and wildlife 

value and are difficult to replace. Removal decisions should be based on 

careful hazard evaluations and should consider other hazard-mitigation 

alternatives, such as seasonal closures, moving the location of potential 

targets, pruning, cabling, bracing, and others (Table 10). Sites that are 

closed for the winter should be evaluated the next spring for any rootsprung trees or recently cracked tree boles that have developed over 

the winter when high winds and snow/ice loading may have occurred.

Western hemlock with annosus rood disease showing advanced decay and the remaining 

sound wood (rind)
38

Determining defects and failure potential on the Mt. Hood National Forest.
39

Chapter 3 - Identification of Diseases and 

Defects that Result in Hazardous Trees 

This section addresses native tree species and their common defects 

beginning with the roots and root collar, progressing to the butt and 

upper bole, and finally the limbs and tops. This is also the progression 

used in evaluating potentially hazardous trees. 

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, pines, and larch, because resin (pitch) inhibits fungal 

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

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. 

For recently fire-damaged trees, where green needles may still be 

present, check the cambium at the root collar to determine if it is alive 

or dead. For most species, a tree is considered dead when at least three 

of the four quadrants from around the base of the root collar have 

cambium, inner bark, or phloem that are discolored and dead. For large 

ponderosa pines, a dead tree has all four quadrants with dead cambium. 

Table 5. Resinous and non-resinous tree species groups in 

developed sites in Oregon and Washington

Species Group Resinous (decay resistant)

True-fir (Abies spp.) No

Hemlock No

Spruce Partially

Douglas-fir Yes

Larch Yes

Pine Yes

Cedar Non-resinous but decay resistant

Hardwoods Non-resinous but some are more 

decay resistant than others
40

Accurate prediction of the failure of dead trees is difficult and uncertain, 

and targets in developed sites are stationary and of high value. 

Therefore, it is USDA Forest Service policy that dead trees of any species, 

size, age, or time since death have a high-failure potential, and the 

hazard should be mitigated in any developed site (Chapter 4 and Table 

1). Dead trees may be retained if their damage potential is very low 

(score 1).

Wounded Trees

Tree wounds are injuries that break the bark of the stem or branch. 

Wounds occurring on tree roots and root collars can result in annosus 

root disease (p. 45), Schweinitzii root and butt rot (p. 55), tomentosus 

root and butt rot (p. 57), or ganoderma root and butt rot (p. 51). Tree 

wounds are caused by a variety of factors: vehicles, people, falling trees, 

weather, fire, animals, or insect attack. A wound is considered open 

if the sapwood is exposed (Fig. 32) or a hollow interior is visible (Fig. 

55). New wounds on living trees can be entry points for stem decay or 

canker-causing fungi, especially in large and deep wounds. Wounds also 

can activate dormant spores of decay fungi, such as the Indian paint 

fungus (p. 74). Wounds on non-resinous tree species (Table 5) 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 tree is wounded, the wood-infecting micro-organisms may be 

confined to compartments within the tree through a process called 

compartmentalization. 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 is referred to as the sound rind, and its 

thickness determines the failure potential of the affected tree (Table 3B). 

A wounded tree with a sound-rind thickness <20% of the tree’s diameter 

inside bark has high-failure potential (Table 1). 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. Once the decay 

process starts in a living tree, however, it cannot be mitigated by wound 

dressings or similar treatments. 
41

Table 6. Root and butt diseases in Oregon and Washington; 

frequency of occurrence by host species where 1=common, 

2=occasional, 3=infrequent, 4=rare, and blank means non-host or 

unknown occurrence

Host species

Annosus root diseaseArmillaria root diseaseBlack stain root diseaseGanoderma root and butt rotLaminated root rot Port-Orford-cedar root diseaseSchweinitzii root and butt rotTomentosus root and butt rotYellow root rot

Alder 4 3 3 3

Aspen 2 3

Ash 3

Birch 3 3 3

Buckthorn 3

Cedar

 Alaska 3 3 3 4 3

 Incense 3 3 4

 Port-Orford 3 3 4 1

 Western red 2 2 3 3 3 3

Cherry 3 3 3

Chinkapin 3 3

Cottonwood 3 2 3 3

Dogwood 3

Douglas-fir

 Coast 3 2 1 3 1 1 4 3

 Inland 3 1 3 3 1 1 4 3

Hemlock

 Mountain 1 2 3 2 1 3 3

 Western 2 2 3 2 2 3 3

Juniper 3 3 4

Larch 3 3 2 1 3

Madrone 2 3 3

Maple 4 3 3 3

Myrtle 3

Oak 4 2 3 3
42

Table 6. Root and butt diseases in Oregon and Washington; 

frequency of occurrence by host species where 1=common, 

2=occasional, 3=infrequent, 4=rare, and blank means non-host or 

unknown occurrence (continued)

Host species

Annosus root diseaseArmillaria root diseaseBlack stain root diseaseGanoderma root and butt rotLaminated root rot Port-Orford-cedar root diseaseSchweinitzii root and butt rotTomentosus root and butt rotYellow root rot

Pine

 Jeffrey 2 2 3 3 3 2 3

 Knobcone 3 3 3 3 3 2 3

 Lodgepole 2 3 3 3 3 2 3 3

 Ponderosa 2 2 2 3 3 2 3

 Sugar 3 2 3 3 3 2

 Western white 3 2 3 3 3 2

 Whitebark 3 3 4 3 3 2

Redwood 3 3 4 3

Spruce

 Brewer 3 2 3 3 2 1 3

 Engelmann 3 2 3 2 2 1 3

 Sitka 3 2 3 3 2 2 3

Tanoak 2

True Fir

 Grand 1 1 3 1 3 3 3

 Noble 2 2 3 2 3 4 3

 Pacific silver 1 2 3 2 3 3 3

 Shasta red 2 2 3 2 3 4 3

 Subalpine 2 2 3 2 3 4 3

 White 1 1 3 1 3 3 3

Willow 3 3 3

Yew 3 4 4 3
43

Root and Butt Diseases 

Historically, root and butt diseases have been associated with 

particularly large numbers of tree failures in Pacific Northwest 

developed sites (Table 4). Some root mortality may be caused by 

adverse changes to the root-system environment such as can occur 

from excesive soil compaction or other disturbance (non-specific 

root decline). Most root diseases, however, are caused by fungi that 

decay roots and butts causing loss of anchorage of affected trees. 

Proper diagnosis is important because tree-failure potential can vary 

considerably depending on which disease is involved. Also, occurrence 

of each disease differs by host (Table 6) and often by geographic 

location. Root and butt diseases can severely weaken infected roots 

and lower stems and cause substantial loss of tree vigor. The most 

conspicuous impacts of such diseases on their hosts are predisposition 

to attack by bark beetles, outright tree death, wind breakage, and 

windthrow.

Unfortunately, root and butt diseases and the defects that they cause 

are often difficult to detect, and detection efforts are time consuming. 

Symptoms can be subtle, and many direct indicators of colonization 

and decay, especially in the early stages of disease, are located either 

underground where they cannot be seen without substantial excavation 

or inside of lower stems where drilling is necessary to evaluate them. 

Because of this, root diseases often go undetected in developed sites 

until wind storms blow over infected trees that reveal decayed roots 

and/or hollow butts. Because many root pathogens can survive for 

decades or centuries in old, infected root residues, it is extremely 

important to document presence of root diseases in developed sites, 

since they will likely continue to be significant tree-hazard concerns in 

those sites far into the future.

Symptoms and signs of root diseases on a host tree include some or all 

of the following (also see the appendix):

1. General decline of the entire live crown characterized by chlorosis 

of foliage, premature shedding of older needles, and terminal 

and, eventually, lateral shoot-growth reduction (Fig. 10)

2. Distress cone or seed crops 

3. Dying branches or thinning crowns from the extremities inward 

in older trees or from the interior crown outward in younger 

hosts 

4. Butt rot, sometimes extending as much as 30 to 35 feet up the 

stem from the base 
44

5. Basal resinosis (Fig. 11), and/or bark staining (Fig. 12)

6. Windthrow or wind-shatter (Fig. 13)

7. Bark beetle attack (Fig. 56)

Fig. 10 – Crown decline can be a symptom of 

root disease. 

Fig. 11 – Basal resinosis is often associated 

with Armillaria root disease.

Fig. 13 – Windthrow can be associated with 

root disease.

Fig. 12 – Bark staining is sometimes 

associated with Armillaria root disease.

Fig. 14 – Dead and dying trees often are 

caused by root disease.
45

8. A progression of dead, 

dying, and declining trees 

in discrete areas or pockets 

within the stand (Fig. 14)

9. Mushrooms or conks of root 

pathogens at root collars 

(Fig. 15) or in stumps

10. Presence of characteristic 

mycelia of the fungal 

pathogens on, in, or under 

the host bark in the roots and root collar area (Figs. 20, 21, and 

23)

Unfortunately, while some trees may exhibit readily visible signs and 

symptoms, many more may be diseased but not yet showing aboveground indication of infections. Root pathogens typically spread 

through a stand at a relatively predictable rate; only a portion of their 

progress at any given time is manifested by above-ground symptoms. 

During extended drought periods, root disease diagnosis becomes 

even more complex. Drought conditions intensify the effect of disease 

damage on tree vigor and further lower host resistance to infection 

and decay. More bark beetle infestation and more tree mortality 

from the combined effects of root diseases and bark beetles acting 

together result during and just after periods of drought. It also is often 

more difficult to confirm the type of root disease associated with tree 

mortality during droughts, since the trees may be attacked by bark 

beetles earlier in the progress of the disease before signs of the root 

pathogen are accessible and apparent.

Major root and butt diseases that contribute to tree hazard in developed 

sites in the Pacific Northwest include the following:

Annosus root disease is caused by two species of fungi, Heterobasidion 

occidentale and H. irregulare. Formerly, these two species were 

considered to be different forms of the same species, H. annosum. These 

two fungi look alike, have the same life cycles, and can cause the same 

kind of disease, but they differ genetically and, most importantly, have 

different host ranges. In the Pacific Northwest, H. occidentale primarily 

infects true firs, hemlocks, and spruces while H. irregulare mainly infects 

pines and junipers. Though one species may occasionally infect stumps 

of the other, cross over to live trees is negligible and not practically 

important from a hazard-evaluation perspective.

Fig. 15 – Armillaria mushrooms are 

produced in autumn on infected trees.
46

Annosus root disease, especially that caused by H. occidentale, often 

is encountered in developed sites and is capable of contributing to 

very substantial tree hazard. Unfortunately, its occurrence appears to 

be increasing in Pacific Northwest developed sites. H. occidentale is 

distributed throughout the forested areas of Washington and Oregon. 

H. irregulare is found primarily in dry areas east of the Cascades in the 

two states.

Both H. occidentale and H. irregulare are spread over long distances by 

windborne spores that land on and infect fresh wounds and newly 

created stumps of host tree species (Table 6). Spread by spores can 

occur over many miles. Once a stump is colonized, the pathogen grows 

into the roots, and the stump becomes an inoculum source. Spread to 

additional host trees occurs when their roots contact these previously 

colonized root systems, and the fungus grows across. Spread across 

root systems requires actual contact; fungal mycelia grow within and 

on the surface of roots but do not grow through soil. Spread across 

root systems occurs at a rate of about one to two feet per year. Fungal 

inoculum in infected stumps and trees can remain viable for decades 

after tree death, being especially long-lived in very large stumps or 

snags.

Annosus root disease can affect hosts in two ways; it can cause a root 

and butt rot that becomes more extensive with time and can eventually 

contribute to windthrow or stem breakage, or it can girdle the host by 

killing the cambium around all or most of the root collar. True firs are 

frequently killed by stem girdling but also may develop root and butt 

decay. Hemlocks and spruces mainly experience root and butt decay. 

Pines and junipers are killed by girdling.

Annosus root disease is often the most difficult of root diseases to 

diagnose. Hazard-tree evaluators are well advised to seek assistance 

from experienced forest pathologists in cases where they suspect 

annosus root disease. Some host trees infected by H. occidentale 

(especially those true firs that are eventually killed by girdling) and H. 

irregulare (pines and junipers) may exhibit crown symptoms similar 

to those caused by other root diseases, including foliage fading and 

thinning, needle chlorosis, growth reduction, and appearance of 

scattered dead branches in the crown in the years before death (Fig. 

14). Others trees show virtually no crown symptoms and appear to 

die without warning. Some infected trees (especially pines) exhibit 

basal resin flow (Fig. 11). Hemlocks and spruces that develop butt and 
47

lower stem decay rarely show crown symptoms. Decay in these species 

tends to develop rather slowly. Significant decay that is capable of 

contributing to tree failure usually does not develop until host trees of 

these species have reached ages of at least 150 years. 

Fruiting bodies of Heterobasidion are perennial conks with woody 

or leathery black to chestnut-brown upper surfaces, white pore-less 

margins and creamy-white undersurfaces with small, round, irregular 

pores (Fig. 16). Conks may be found in old stumps, just above ground 

in root crotches of living, infected trees, and below ground on roots of 

living or dead hosts. Young conks on roots appear as small, white to 

buff pustules. Presence of a conk on a tree or stump proves infection, 

but the opposite is not true; many Heterobasidion-infected trees do not 

produce conks. The presence of a conk on a tree or in a stump indicates 

that adjacent trees of host species also have a high probability of being 

infected as well as the tree or stump where the fruiting body is actually 

found.

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

outer heartwood (Fig. 17). Advanced decay is white and stringy (Fig. 18) 

or laminated with elongated pits on only one side of the laminations 

and no setal hyphae (Fig. 19). Pathologists with laboratory facilities 

can incubate samples of wood with suspicious stain or early decay and 

confirm or disprove the presence of Heterobasidion based on whether or 

not diagnostic microscopic fruiting bodies are formed.

Clearly, hidden infection by Heterobasidion is common. Individual trees 

with wounds may be infected while showing only the most subtle 

of indicators or no apparent indicators at all. Annosus root disease 

can occur in small infection foci centered on old, infected stumps or 

wounded trees or in large infection centers where tree-to-tree spread 

has occurred for many decades. Often, many infected host trees in 

either kind of situation lack indicators.

When annosus root disease is confirmed in a developed site, live trees 

in and around disease centers vary in failure potential depending on 

geographic area, tree species, tree condition and age, and the presence 

of adjacent windthrown trees with evidence of root disease (Table 1). 

Host trees that have already been killed or will likely die soon, as well 

as older host trees with confirmed Heterobasidion-induced butt rot, 

will have the highest failure potential. Because the fungi that cause 

annosus root disease can spread long distances by spores that infect 
48

through wounds and newly cut 

stumps, it is easy to see why 

decay occurrence may indeed be 

increasing in long-established 

developed sites. Major efforts 

should be designed to minimize 

or avoid tree wounding, especially 

of true firs, hemlocks, and 

spruces, in developed sites. Treatment of all freshly cut stump surfaces 

of Heterobasidion hosts with registered boron compounds is highly 

recommended (p. 96). 

Armillaria root disease on conifer hosts is caused by the fungus 

Armillaria ostoyae. On hardwoods it is caused by either A. gallica or A. 

mellea. Though not as damaging as laminated root rot, Armillaria root 

disease has a history of frequently causing tree mortality in developed 

sites in the Pacific Northwest. The fungi that cause Armillaria root 

disease are extremely common and are distributed throughout all 

forested areas in Oregon and Washington. 

Fig. 16 – Conks associated with annosus 

root disease often form in hollow stumps.

Fig. 18 – White-stringy decay caused by 

Heterobasidion occidentale in a western 

hemlock stump.

Fig. 17 – Stain caused by Heterobasidion 

occidentale in grand fir.

Fig. 19 – Laminated decay can be caused by 

Heterobasidion occidentale.
49

The Armillaria species that cause root disease can survive as saprophytes 

in dead host material for at least 50 years. Spread to new hosts involves 

mycelial growth across root contacts or for very short distances in 

soil between old, infected roots and the roots of new hosts, or spread 

to new roots over greater distances through soil via rhizomorphs 

(shoestring-like structures that may extend two feet or more from an 

infected root into the soil). The pathogen then spreads to additional 

new, living hosts by growing across root contacts or through soil 

between them. The pathogen forms gradually expanding infection 

centers that enlarge radially at a rate of one to two feet per year. 

Armillaria species form mushrooms (Fig. 15) that can produce viable 

spores, but the role of spore spread with the disease-causing Armillaria 

species is not believed to be significant.

Armillaria can infect the roots of most Pacific Northwest tree species 

(Table 6). Armillaria species may function either as weak pathogens of 

stressed, low-vigor trees or as aggressive killers of susceptible hosts. 

Armillaria species can be quite variable and affect hosts differentially in 

different areas. As general rules: 

1) Infection of stressed or injured conifers is most likely on highproductivity coastal and Westside sites while aggressive tree 

killing is more common east of the Cascades in Oregon and 

Washington and in the Cascades in Southwest Oregon, 

2) Infection of hardwoods is frequently associated with stress or 

wounding throughout the Pacific Northwest, 

3) In most cases among conifers, the true firs are the most highly 

susceptible hosts of Armillaria root disease, interior Douglasfir is intermediately susceptible, and other conifers are usually 

somewhat tolerant or resistant, 

4) Tree susceptibility to Armillaria root disease can in some cases 

differ markedly by location in ways that are not yet understood; 

for example there are areas in southwestern Oregon, southcentral Washington, and northeastern Washington where 

pines can be severely damaged, and Douglas-fir is the most 

severely damaged host in some localized areas in northeastern 

Washington, 

5) The Armillaria species that cause root diseases often occur in 

combination with other root disease organisms, especially 

Phellinus weirii, Heterobasidion occidentale, Leptographium 

wageneri, or Phaeolus schweinitzii. 

Armillaria species generally kill host trees by colonizing the phloem and 

xylem of the roots and root collar and disrupting movement of water 

and nutrients in the tree. The cambium around the host’s roots and root 
50

collar is killed by the fungus, preventing uptake of water and nutrients. 

Infected trees are frequently predisposed to infestation by bark beetles 

and wood borers. Trees generally die standing. Though roots may 

be decayed to a degree, windthrow of trees prior to death is not as 

common as with other diseases such as laminated root rot and annosus 

root disease. 

Recognizing Armillaria root disease is usually easier than recognizing 

annosus root disease or laminated root rot. Infected trees show typical 

root disease crown symptoms, including crown thinning, foliage 

chlorosis, growth decline, and formation of stress cone crops (Fig. 10). 

Infected trees also often exhibit resin flow or bark staining at and above 

the root collar (Fig. 11) and resin-soaked, decayed wood interspersed 

with straw-colored flecks in the butt and roots. Rhizomorphs may be 

found under the bark of infected trees, and honey-colored mushrooms 

are often formed at the bases of infected trees in autumn (Fig. 15). 

Probably the most certain way to confirm the presence of Armillaria

is to chop into the root collar of a declining or recently dead tree and 

observe the white, latex-like mycelial fans that are produced just under 

the bark (Fig. 20). When these are thick, associated with heavy resin 

flow, and extend above the ground line, they are considered diagnostic 

of Armillaria root disease. In the aggressive tree-killing case, dead and 

dying trees of susceptible host species will be situated in and around 

disease centers that exhibit evidence of progressive tree mortality 

over many years (Fig. 14). Infection centers can be very large. In cases 

where Armillaria is affecting low 

vigor and stressed hosts, infected 

trees may appear as scattered 

individuals or small groups of 

dead and dying trees, often 

clearly associated with such stress 

factors as wounding, compacted 

soils, offsite plantings, drought, 

infection by other disease 

organisms, or fires. 

As with annosus root disease 

or laminated root rot, not all 

Armillaria-infected trees can be 

easily identified. Apparently 

healthy trees of susceptible 

species that are growing close to 

dead or obviously declining trees 

with identifiable Armillaria root 

Fig. 20 – Armillaria ostoyae often produces 

mycelial fans under the bark of infected trees.
51

disease also have a high probability of being infected. The actual extent 

of an Armillaria infection center is larger than indicated by obvious 

indicators. 

When Armillaria root disease is diagnosed in a developed site, trees in 

and around root disease centers vary in failure potential depending on 

tree species and condition and the presence or absence of adjacent 

windthrown trees with root disease (Table 1). Since Armillaria root 

diseased trees are usually killed standing, such dead trees should be 

considered to have the same high-failure potential as any other dead 

trees. Live infected and symptomatic trees that occur on sites where 

trees infected by Armillaria have previously been windthrown may also 

be considered to have high-failure potential in the few cases where 

such a scenario occurs (Table 1).

Black stain root disease is caused by Leptographium wageneri. The 

disease is a vascular wilt that causes tree mortality but not root decay. 

A characteristic sign is a brown to purplish-black stain in older sapwood 

that fades with time in dead trees. The disease is spread from tree-totree across root grafts and contacts by mycelial growth, and mycelia 

also grow very short distances in soil. Long-distance spread is via 

root-feeding bark beetles and weevils that are attracted to stressed 

trees. Black stain root disease kills all ages of ponderosa pines at some 

locations east of the Cascade Crest and young Douglas-fir on the 

westside. Other species besides the pines and Douglas-fir are rarely 

affected (Table 6). Black stain root disease often is associated with 

soil disturbance along roads with soil compaction or large numbers 

of injured host trees. Black stain root disease has been found in a few 

developed sites in the Pacific Northwest but is not nearly as common 

as laminated root rot, Armillaria root disease, or annosus root disease. 

Because black stain root disease does not cause root decay, affected 

trees die standing and then have high-failure potential. Live trees with 

disease signs and symptoms have low-failure potential (Table 1).

Ganoderma root and butt rot or white mottled rot affects many 

conifer and hardwood species (Table 6). It occurs in wounded, live trees 

and dead or broken trees. The decay is caused by two species of fungi: 

Ganoderma tsugae and G. applanatum. Ganoderma tsugae occurs only 

on conifers and forms a distinctive conk that is annual, stalked, eggshelllike, reddish-brown, and shiny as if lacquered or varnished; hence, 

the common name, “lacquer fungus” or “varnish conk.” Ganoderma 

applanatum occurs on dead or partially dead conifers and on live or 

dead hardwoods. It produces conks that are perennial, leathery to 
52

woody, and may or may not be stalked. The conk undersurface is white 

to creamy and is easily bruised; hence, the common name “artist’s conk.” 

Decay associated with both species is a white spongy rot with black 

specks. When Ganoderma root and butt rot is diagnosed in developed 

sites, host trees can have high or medium-failure potential depending 

on the extent of butt decay (Table 1).

Laminated root rot is caused by the fungus Phellinus weirii. A proposed 

new name is Phellinus sulphurascens. It is the most damaging root 

disease of forest trees in Oregon and Washington and one of the most 

hazardous to people and property in developed sites. It is widely 

distributed and common in the forests of Washington, western Oregon, 

and eastern Oregon north of the Crooked River.

The fungus that causes laminated root rot can remain viable and 

infective for more than 50 years after a colonized host has died. The 

roots of old stumps and standing, dead trees function as virulent 

inoculum sources for decades after the trees have been killed or cut. 

The fungus spreads to new hosts via an ectotrophic mycelium (Fig. 

21) that grows onto new host roots when they make direct contact 

with old, infected, residual roots. Subsequently, the pathogen spreads 

to additional living hosts by growing across root contacts and grafts 

between them. Thus the pathogen forms gradually expanding infection 

centers in stands with major host components. The fungus grows across 

roots at a rate of about one to two feet per year. Long-distance spread 

involving spores probably occurs occasionally with P. weirii, but appears 

to be so infrequent that it is not of practical importance.

Phellinus weirii can infect the roots of all Pacific Northwest conifers 

(Table 6). Highly susceptible hosts are true firs, Douglas-fir, and 

mountain hemlock. These tree species are readily infected and their 

roots are extensively decayed by the pathogen. Other conifers can 

tolerate or resist infection and/or damage to various degrees (Table 

6). Though their roots are not as 

severely decayed as are those of 

highly susceptible host trees and 

they are much more tolerant of 

the disease, larches, spruces, and 

western hemlock infected by P. 

weirii may develop substantial 

butt rot over time. Pines and 

cedars are rarely infected and 

almost never killed by P. weirii; 

however, even with these species, 

Fig. 21 – Ectotrophic mycelium of Phellinus 

weirii is produced on infected roots of Douglas-fir.
53

some root colonization can occur, and the pathogen may maintain itself 

on the site. All hardwoods are immune to P. weirii.

The roots of highly susceptible hosts are extensively decayed by P. 

weirii leading to tree death (often as a result of predisposition to bark 

beetle infestation) or windthrow. Windthrow frequently occurs among 

highly susceptible hosts with still-green crowns including some that 

exhibited little if any evidence of crown symptoms prior to falling. This 

makes laminated root rot particularly dangerous when occurring in a 

developed site. More tolerant hosts that develop butt rot may break at 

the butt or lower stem as decay advances with age.

Recognizing laminated root rot is not always easy but skill in doing so 

improves with experience. Many infected hosts, especially of the highly 

susceptible tree species, do show crown symptoms typical of major 

root diseases (Fig. 14), especially when individual root systems have 

half or more of their roots affected. These symptoms include crown 

thinning, foliage chlorosis, growth decline, and formation of stress cone 

crops. Some infected trees exhibit basal resin flow. Phellinus weirii 

occasionally produces flat buff-colored conks, but these are cryptic, 

difficult to find, and uncommon enough that they have little diagnostic 

value. Laminated root rot centers are frequently characterized by an 

abundance of windthrown trees, with only stubs of roots remaining 

(Fig. 22). Laminated decay that separates easily at the growth rings and 

is pitted on both sides of the layers is usually evident in the broken off 

roots (Fig. 24). It can also be detected in excavated roots of standing 

infected trees or in the stumps of infected trees that were previously cut. 

Diagnostic evidence of P. weirii is occurrence of tufts or mats of reddishbrown setal hyphae between the sheets of characteristically decayed 

wood (Fig. 23). Because of their small size, confirming the presence of 

setal hyphae is easiest when the evaluator uses a hand lens. On the 

roots of infected living trees, 

excavation of roots can reveal 

the ectotrophic mycelium of P. 

weirii (Fig. 21) as a grayish-buff, 

crusty sheath of fungal material 

on the surface of the bark that 

cannot be readily rubbed off. 

Close examination shows that 

this ectotrophic mycelium often 

contains tufts of setal hyphae. 

Chopping into roots of infected 

trees can reveal a reddish stain in 

Fig. 22 – Rootballs with missing major roots, 

as shown here, are decayed by Phellinus 

weirii.
54

the wood in advance of the occurrence of the ectotrophic mycelium. 

On the cut surface of the stump of an infected tree, stain will often 

appear in a crescent shape in the wood that is visible for a week or 

two after the tree is cut. Hollows or crescent-shaped areas containing 

advanced decay are also encountered on stumps of some infected trees. 

In long-established recreation sites, a history of frequent removal of 

dead and windthrown trees can mean that finding P. weirii decay in old 

stumps is particularly useful and important because stumps are the only 

indicators left of disease in the particular area. 

Management of laminated root rot centers is important for long-term 

prevention of future hazard trees. This is done by determining the 

boundaries of the root disease center by using crown symptoms and 

root excavations to identify the disease. Include a buffer around the 

disease center that extends at least two trees beyond the last tree 

with confirmed root disease. Many of the trees within this buffer, if of 

susceptible species, probably will be infected and failure prone. It is 

recommended that recreation personnel work with silviculturists or 

pathologists in developing treatment options for developed sites with 

laminated root rot.

When laminated root rot is diagnosed in a developed site, trees in and 

around root disease centers vary in failure potential depending on tree 

condition, size, species, and the location relative to adjacent diseased 

trees. Phellinus weirii-infected trees of highly susceptible host species 

often represent the highest possible failure potential. Given the history 

of damaging failures due to laminated root rot in recreation sites in 

the Pacific Northwest, the often unpredictable nature of these failures, 

and the difficulty frequently associated with detecting the disease and 

determining the actual extents of affected areas, laminated root rot 

should be of particular concern to hazard evaluators and managers of 

developed sites.

Fig. 23 – Setal hyphae, the red-brown, fuzzy 

material shown here, are diagnostic for 

laminated root rot.

Fig. 24 – Laminated decay as shown here is 

caused by Phellinus weirii.
55

Port-Orford-cedar root disease is caused by Phytophthora lateralis. It 

is an introduced pathogen that causes cambial death and subsequent 

tree mortality but not decay. The main host is Port-Orford-cedar, 

although Pacific yew also can be infected on rare occasions (Table 6). 

The diagnostic symptom is a cinnamon-colored stain in the inner bark 

of roots and lower stems. The disease is found mainly in southwest 

Oregon, although it appears in other areas where ornamental PortOrford-cedars are grown. Port-Orford-cedar root disease is common 

along roads, watercourses, and in poorly-drained areas. It has been 

found killing cedar in recreation sites. As with black stain root disease, 

affected trees die standing and then have high-failure potential. Live 

trees with disease signs and symptoms have low-failure potential

(Table 1).

Schweinitzii root and butt rot is caused by Phaeolus schweinitzii. It vies 

with laminated root rot as the most common cause of conifer failure in 

developed sites across Oregon and Washington. On the westside of the 

Cascade Range, significant butt decay may be indicated by occurrence 

of the conspicuous fruiting body, referred to as the “cow-pie fungus” or 

“velvet-top fungus”, and often by a swollen butt on host trees (Fig. 26). 

Fresh conks are velvety to the touch and have brightly colored yellow 

margins. As a conk ages, it dies, turns brown, and lasts about two years 

(Fig. 25). On the eastside of the Cascade Range, infection and decay may 

be as common but are often present without indicators. As such, it is 

less often discovered until significant wind events and tree failures have 

occurred. Tree mortality and windthrow are unusual unless associated 

with Armillaria root disease in eastside forests. 

Decay of the butt extending as much as 30 feet up the tree occurs on 

old trees (>150 years). Butt swell, which develops over many decades, 

is apparent on trees, especially Douglas-fir with extensive butt defect 

(Fig. 26). Trees with butt rot often fail under high-wind conditions 

leaving a characteristic barber chair and shattered butt. Unfortunately, 

the presence of significant decay 

in roots and butts is not always 

indicated by the presence of the 

characteristic conks, even on the 

Westside where they are most 

commonly produced. Also, the 

presence of conks does not always 

indicate significant decay in the 

roots or butts. Therefore, suspect 

trees (those with conks, butt swell, Fig. 25 – Older mushrooms of Phaeolus 

schweinitzii often resemble “cow-pies.”
56

open cracks, or wounds) should 

be drilled near the root collar to 

determine the extent of decay 

and safe sound-rind thickness 

(Tables 3A and B). Since decay is 

commonly found throughout the 

roots and lower bole, decay found 

at the base of the tree by drilling 

should be reason for concern.

The advanced decay is a brown 

cubical rot. The incipient stain, 

while distinctive, is rarely 

observed except on freshly cut log 

ends. The incipient stain is light 

green, occurring immediately 

adjacent to areas of advanced 

decay. Damage most often occurs 

in overmature Douglas-fir and 

Sitka spruce on the westside 

(Table 6). Douglas-fir, western 

larch, ponderosa pine, and lodgepole pine are frequently damaged on 

the eastside. In SW Oregon, Douglas-fir, ponderosa pine and sugar pine 

are frequently decayed. For all but lodgepole pine, the pathological 

rotation age is approximately 150 years. For lodgepole pine, that value 

is a range of years from 100 to 120 depending on site quality, site 

productivity, and growth history. The high end of the range coincides 

with the best lodgepole sites. It is important to remember that for 

lodgepole pine, age becomes a limiting factor in susceptibility to 

mountain pine beetle beginning at about 80 to 100 years. 

Trees are apparently infected by this pathogen at any age. Fresh 

trunk wounds caused by mechanical injury or fire probably are not 

infected directly by spores but instead the wounds exacerbate decay in 

previously infected roots and butts. Many infections, especially on the 

eastside, also occur by mycelial spread from diseased to healthy roots 

through litter and organic residues to root tips. Infections are confined 

to heartwood and are sequestered as relatively innocuous heartwood 

lesions. When trees are immature, smaller roots with heartwood 

are decayed. As trees advance in age, larger roots are decayed with 

increasing deleterious effects on anchorage. 

Fig. 26 – Butt swell of Douglas-fir is often 

associated with root and butt decay caused 

by Phaeolus schweinitzii.
57

When Schweinitzii root and butt rot is encountered in developed 

sites, trees should be carefully and thoroughly evaluated rather than 

automatically removed. This root disease appears to be quite slow 

to weaken trees to hazardous levels. Evaluations should include 

examination for obvious leans, recent root wrenching or partial failure, 

butt swell, shake or cracking of the butt, and evidence of ant or wood 

borer activity in the butt. Additionally, each of the major lateral roots 

should be exposed and drilled within 2 feet or so of the root collar to 

detect any hidden defect in the roots that provide major anchorage. 

If most of the major root anchorage is not decayed, the tree may be 

retained and monitored each year or every other year depending on 

the extent of defect and decay. Trees with seriously compromised 

anchorage and inadequate sound-rind thickness should be removed or 

the hazard otherwise mitigated. 

On mesic and wetter sites where conks are more abundant, a single 

fruiting body indicates that the evaluator should take note and examine 

the defective tree more closely. Once trees with fruiting bodies have 

been examined, those susceptible hosts immediately adjacent to them 

should be evaluated in the same way. 

Tomentosus root and butt rot is caused by Inonotus tomentosus. The 

infection and spread biology of tomentosus root rot is similar to that 

of annosus root disease. Inter-tree spread occurs via an ectotrophic 

mycelium, and spores are involved in infection of new wounds and 

freshly cut stumps. The importance of spores in local spread is poorly 

understood. In developed sites, Engelmann spruce is most often 

affected (Table 6), and damage is manifested typically as windthrow or 

wind shattering of severely butt-rotted, mature trees. Tomentosus root 

and butt rot typically does not cause extensive damage in developed 

sites but is locally important in the Cascade and Blue Mountains. 

This disease may be completely hidden in trees including some with 

extensive butt rot. Trees with crown symptoms are not common, 

making this disease difficult to detect. Also, infection in developed sites 

usually is not in concise disease centers as occurs with laminated root 

rot or Armillaria root disease.

Tomentosus root and butt rot is identified in the field by its 

characteristic fruiting bodies, which are small, yellow to cinnamoncolored, leathery, and may appear in the fall near the bases of defective 

trees. Even when infection and decay are common, fruiting bodies are 

seldom produced in some localities, especially in the Blue Mountains. 

Incipient decay in spruce roots has a distinct pink color that can be 
58

detected by drilling (Fig. 27). Healthy wood is cream-white. Advanced 

decay is a white, pocket rot. Ectotrophic mycelia may occur, but in 

no instance should ectotrophic mycelia alone be used to diagnose a 

specific root disease; three of the root diseases discussed in this guide 

produce surface mycelia, and there is chance of confusion. Other, 

better indicators are available for each root disease (see Appendix), 

and several diagnostic clues should be used for each correct diagnosis. 

Check spruce with potential targets with a drill or borer to detect decay, 

regardless of external indicators.

When tomentosus root and butt rot is encountered in developed sites it 

should be addressed immediately. Resistant and tolerant hosts should 

also be regenerated in tomentosus root and butt rot centers where 

practical (Table 6). When tomentosus root and butt rot is diagnosed in 

developed sites, host trees (usually only spruce) in root disease centers 

can have high or medium-failure potential depending on the extent 

of butt decay (Table 1).

Yellow root rot or stringy butt rot is caused by Perenniporia subacida 

which can cause tree mortality or butt rot in suppressed or stressed 

trees especially Douglas-fir, true firs, and western hemlock as well 

as many hardwood species (Table 6). Affected trees may be easily 

windthrown. The conks are white, crust-like or leathery and flattened 

against the wood or bark on the undersides of roots, logs, fallen trees, 

or exposed roots. Early decay is a light-brown stain that resembles 

wetwood. Advanced decay is composed of irregularly shaped pockets 

of decayed springwood that coalesce into masses of stringy fibers with 

black flecks. Annual rings may separate into a laminated decay. Yellowwhite mycelial mats may form between the laminated sheets of wood. 

Because signs and symptoms are below ground, the disease is difficult 

to detect in live trees. Host trees can have high or medium-failure 

potential depending on the extent of butt decay (Table 1).

Other Root 

Problems

Other important root defects 

include undermined roots that 

result from erosion, seasonally 

high waterline or flooding 

events, and excavation or 

Fig. 27 – Stain in a spruce root often is 

caused by Inonotus tomentosus.
59

Fig. 28 – Undermined roots, as shown here, 

can result in tree failure.

construction activities. Other root problems include severed roots 

that are mechanically induced by various construction, road building, 

and maintenance activities; and loosened, cracked, or broken roots 

which are caused by high winds and typically result in partial failures. 

Tree-failure potential is determined by the amount of structural roots 

remaining in the ground (Table 1).

Undermined roots are often associated with road-building or trailbuilding activities in and around developed sites. Otherwise, they 

frequently are observed at waters’ edge adjacent to lakes, streams, or 

rivers (Fig. 28). When soil is eroded away from tree roots by the action 

of swift current or by waves, anchorage is compromised. Erosion also 

occurs during and after heavy precipitation, when rainfall intensity, 

duration, and accumulation exceeds the soil infiltration rate (capacity 

of the soil to absorb water). The result is high runoff; sheet, rill or gully 

erosion; and often root undermining. Extreme amounts of undermining 

can cause tree failure from insufficient anchorage. 

Severed roots act as entrance points for decay fungi. They are 

commonly associated with utility installations, road building, and trailbuilding activities. Many of the fungi that enter at these points of injury 

will cause root and butt decay that eventually predisposes trees to 

windthrow or other types of failure. Other activities that are associated 

with severed roots are tent-pad construction or ditching to divert runoff 

in areas where tents are routinely pitched, building construction, and 

excavation for placement or repair of water or sewage lines or toilet 

facilities. While severing of roots is not often immediately hazardous, the 

damage is always detrimental in the long term and should be avoided as 

much as possible. In addition to providing anchorage and support, roots 

are essential for water and nutrient uptake. Significant reductions in root 

system uptake and translocation capacity by root severing diminish tree 

vigor and resistance to attacks by bark beetles and root pathogens. 

Loosened, cracked, or broken 

roots predispose trees to 

failure during high winds. Wind 

events, saturated soils, and soil 

disturbances occurring singly 

or in combination, often lead to 

loosening, cracking, or breakage 

of roots. Soil saturation is a 

leading factor in windthrow of 

shallow-rooted species, or of any 
60

Fig. 29 – Newly developed leans lack tops 

that point upward (uncorrected).

Fig. 30 – Cracks in the soil around leaning 

trees indicate that such trees have a highfailure probability.

species growing in high density or in shallow soil. Indicators of root 

damage include: 

•	 Trees with newly developed or newly accentuated leans (Fig.

29); soil and litter are not in contact with the base of the tree on 

the side away from the lean (there is a conspicuous gap) and 

•	 	 Cracks, mounds, or ridges of recently heaved soil adjacent to

major lateral roots (Fig. 30). 

Roots of trees located in heavily used areas frequently become 

exposed to the air and are subsequently damaged. This is particularly 

true in areas where tents are routinely pitched, adjacent to fire rings, 

barbecue pits, picnic tables, or in any area where protruding roots are an 

inconvenience to users, such as in hiking or biking trails. 

Leaning, Root-sprung, Broken, or 

Uprooted Trees Supported by Other Trees

Root-sprung trees are likely to fail because their roots are compromised 

by being partially pulled out of the ground. Such trees are dangerous 

and are seen as failures in progress. Leaning trees (≥15degrees) result 

from root and butt decay, and 

from high winds that cause root 

wrenching. Tree leans are either 

recent or old. All leaning trees 

should be examined for evidence 

of severe root and butt rot. 

Trees with recent lean (<5 years) 

may have soil and litter disturbed 
61

and not in contact with the base 

of the tree on the side away from 

the lean resulting in a conspicuous 

gap (Fig. 30). Cracks, mounds, or 

ridges of recently heaved soil may 

be adjacent to major lateral roots 

of leaning trees. Recently leaning 

trees are tilted over their entire 

length. Since there is no evidence 

of subsequent reinforcement of 

the root system, examiners must 

assume that such partially failed 

trees exhibit a high-potential for 

failure. Hazard associated with 

recently leaning trees should be 

addressed immediately. 

Old, leaning trees are those 

that have been leaning for a 

considerable time and have grown 

a vertical top in the time since the 

lean developed (corrected lean) (Fig. 31). If they don’t fall, leaning trees 

develop tension and compression wood at stress points to aid in their 

support. They also often develop a reinforced root system, where roots 

were wrenched, to compensate for prior damages. Unless these roots 

are disturbed or decay is present, old, corrected, leaning trees have lowfailure potential. Trees that are uprooted or broken but supported by 

other trees have high-failure potential (Table 1).

Heart Rots

Heart rots are most damaging to mature and overmature trees (old 

growth), regardless of tree size. By definition, heart rots are confined 

to the true heartwood. There are some “heart rots” that will affect both 

the sapwood and the heartwood of living trees. The extent of defect 

is best correlated with tree age and not diameter. Most of the damage 

associated with heart rot fungi in most conifer species will occur in trees 

that are more than 150-years old. Especially decay-prone species such 

as western hemlock and grand fir, however, may have substantial decay 

at even younger ages (Table 5). Most fungi that cause stem decay gain 

access through wounds caused by humans, animals, fire, lightning, 

snow, high winds, bark beetles, or other agents. Some fungi commonly 

Fig. 31 – Old leans with righted or corrected 

tops have low-failure probability.
62

enter through branch stubs. Wounds, callus tissue, conks, mushrooms, 

punk knots, swollen knots, old snow breaks, crook, shake, frost cracks, 

wetwood, bole flattening, or depressions are all potential indicators of 

internal defect. 

In most cases, when stem decay is extensive enough within the bole of 

a tree to be hazardous, it can be detected by the occurrence of conks, 

punk knots, and open wounds (Fig. 32). Heart rots, however, may be 

present when there are few or no external indicators. For example, when 

conks have fallen from a defective tree and are not observed on the 

ground, or in dry-habitat types where conks are rarely or not regularly 

produced. Trees without indicators can be evaluated for the presence of 

heart rots by several methods. 

One way to detect a hollow or decay column is by striking the tree trunk 

with a rubber mallet or the butt of an axe. To use this method, though, 

the examiner must develop an ear for recognizing the unique sound of 

a hollow or decay, and thick-bark species are often difficult to sound. 

Additionally, detection of a hollow does not mean that the affected 

tree is a serious hazard to people or property. To evaluate the structural 

integrity of the suspected tree, the examiner must bore into the tree at 

the point of defect, either with an increment borer, or a cordless drill, 

and determine the thickness of the remaining rind of sound wood 

(Tables 3A and B). 

If the suspected defect is well 

above the ground, very valuable 

trees can be climbed and drilled; 

otherwise, most decay and defect 

high in a tree should be assessed 

with binoculars and professional 

judgment rather than by climbing. 

Trees that are large and mature 

or overmature routinely will have 

the greatest amount of stem 

decay. Some of that defect will 

be hidden and inaccessible to 

the examiner by conventional 

means of evaluation. Risks 

associated with defects that have 

been identified but not directly 

evaluated by boring, or those that 

Fig. 32 – Tree bole with an open wound are suspected (based on detection 

where the sapwood is exposed
63

Table 7. Heart rots in Oregon and Washington; frequency of 

occurrence by host species where 1=common, 2=occasional, 

3=infrequent, 4=rare, and blank means non-host or unknown 

occurrence Host species

Ash trunk rotAnnosus stem decayAspen trunk rotBrown cubical rotBrown cubical rot of birchBrown stringy trunk rotBrown top rotBrown trunk rotHardwood trunk rotIncense-cedar pecky rotInonotus trunk rotJuniper pocket rotMaple trunk rotMottled rot - PholiotaRed cedar pencil rotRed heart rot - StereumRed ring rot / white speckRedwood cubical rotRust-red stringy rotWhite spongy trunk rotWhite trunk rotYellow pitted rot

Alder 2 3 3 4 3

Aspen 1 3 2 3 3

Ash 2 3 3

Birch 3 3 1 3 3 3 1

Buckthorn 3 3

Cedar

 Alaska 4

 Incense 2 4

 Port-Orford 4

 Western red 3 1 3

Cherry 3 3 3 3

Chinkapin 3

Cottonwood 3 3 1 3 2 3 3

Dogwood 3

Douglas-fir 3 2 2 4 3 1

Hemlock

 Mountain 1 3 3 2 2 3 3 1 1 3 2

 Western 1 3 3 2 2 3 3 2 2 2 3

Juniper 2 3

Larch 3 3 2 3 1

Madrone 3 4 3

Maple 4 2 2 3 2 2 3 3 3 3

Myrtle 2

Oak 3 2 2 3 2 3 3 3
64

Table 7. Heart rots in Oregon and Washington; frequency of 

occurrence by host species where 1=common, 2=occasional, 

3=infrequent, 4=rare, and blank means non-host or unknown 

occurrence (continued) Host species Ash trunk rot Annosus stem decay Aspen trunk rot Brown cubical rot

Brown cubical rot of birchBrown stringy trunk rotBrown top rotBrown trunk rotHardwood trunk rotIncense-cedar pecky rotInonotus trunk rotJuniper pocket rotMaple trunk rotMottled rot - PholiotaRed cedar pencil rotRed heart rot - StereumRed ring rot / white speckRedwood cubical rotRust-red stringy rotWhite spongy trunk rotWhite trunk rotYellow pitted rot

Pine

 Jeffrey 4 2 3 3 1

 Knobcone 4 4 3 3 1

 Lodgepole 3 3 4 2 3 3 1

 Ponderosa 3 3 4 2 3 3 3 1

 Sugar 3 3 4 2 3 3 1

 Western white 3 3 4 2 3 3 1

 Whitebark 4 4 3 3 1

Redwood 3

Spruce

 Brewer 3 3 3 3 3 2 3

 Engelmann 3 3 4 3 3 3 3 2 3 3

 Sitka 3 3 3 3 3 3 3 2 3

Tanoak

True Fir

 Grand 1 3 4 3 3 2 3 1 1 3 3

 Noble 2 3 4 3 2 3 2 2 3 2

 Pacific silver 1 3 4 3 2 3 2 2 3 2

 Shasta red 2 3 4 3 2 3 2 2 3 2

 Subalpine 2 3 4 3 2 3 2 2 3 2

 White 1 3 4 3 3 2 3 1 1 3 3

Willow 2 3 3 3

Yew 3 2 3
65

clues) but not clearly identified, should be carefully considered. When 

the potential risks are considered unacceptable if hazardous levels 

of decay are known to exist, the potential hazard should be more 

thoroughly investigated or mitigated, but never ignored. 

Failure potential of trees with internal decay is directly related to trunk 

diameter and average thickness of sound wood at the conk or defect.

Because living trees can compartmentalize decay within wood infected 

when stems were wounded, affected trees often have hollows or 

decayed areas within a cylinder (rind) of sound wood that was added 

after wounding (Fig. 9). Conifers can lose approximately 70% of the total 

cross-sectional area to wood decay (which is equivalent to about 1/3 of 

its strength or resistance to failure) without significantly increasing the 

level of hazard, as long as the defect is heart rot uncomplicated by other 

defects. This is equivalent to having a sound rind of 15% of the diameter 

inside bark (Table 3A, Wagener 1963). If the shell of sound wood is 

thinner than the thickness displayed in Table 3A for a comparable trunk 

diameter, failure potential is high. These guidelines are adequately 

buffered for trees with internal decay but no additional defects. 

Trees with wounds or cankers opening to the outside have a much 

greater failure potential than trees having equivalent rinds of sound 

wood but no openings (Fig. 32). A hollow tree with an open wound 

or canker should be considered hazardous if the sound-rind thickness 

at its thinnest point meets or is below the suggested standard for the 

diameter. Minimum sound-rind thickness should be increased by at 

least 25% for hollow trees with open wounds (Table 3B). 

Extra caution should be taken when evaluating trees with multiple 

defects including stem decay, and the sound-rind thickness guidelines 

should be used with caution since they were developed for trees with a 

single defect. For example, forked trees with evidence of heart rot, such 

as a conk directly below the fork, should be evaluated carefully, and the 

evaluator should assume the fork to be unstable.

The rate of radial growth affects future sound-rind thickness. If growth 

rate is rapid, strength loss from advancing decay will be partially offset 

or perhaps even negated by the added strength of new wood. This 

is because decay is often compartmentalized within a column that is 

the size of the tree when it was first wounded; new wood formed after 

wounding usually does not decay unless the tree is wounded again. 

The condition of callus growth around wounds is an indicator of health 

and tree vigor. Vigorous callus activity (abundant new wood and wound 
66

parenchyma produced over wounds), emergence of a new cambial 

region and a thin, healthy, new bark indicate rapid growth. 

Major heart rots that result in tree hazards in developed sites in the 

Pacific Northwest include the following: 

Ash trunk rot is caused by Perenniporia fraxinophilus. Oregon ash is 

the only host species (Table 7). Trees with one or more conks have 

medium-failure potential. Conks are perennial, woody, shelf-shaped 

to hoof-shaped with a rough dark-brown to black upper surface 

and a brownish under surface. Conks can be a width of 1 ft. or more. 

The incipient decay appears first as a brownish discoloration then 

developing white spots with time. Advanced decay is straw-colored to 

white, soft and crumbly, with longitudinal white areas on the radial face. 

Annosus stem decay, common in conifers and some hardwoods (Table 

7), is caused by the same fungi that cause annosus root disease (p. 45). 

Infection occurs by airborne spores through wounds that develop into 

butt or stem rot. Butt and stem decay predisposes trees to windthrow 

and breakage. Tree-failure potential depends on sound-rind thickness.

Some defect rules for estimating extent of Heterobasidion-caused stem 

decay of true firs, hemlocks, and spruces are as follows: 

1) When a Heterobasidion conk is visible near the root collar of a 

tree (not a very common occurrence), the lower 16-foot section 

of the butt log is defective, 

2) Defect extends four feet above and below any stem wound 

with verified annosus decay that is 10-years old or older, 

3) For wounds less than 10-years old, expect internal defect to run 

the length of the wound. 

Aspen trunk rot is caused 

by Phellinus tremulae. A 

single conk generally 

indicates considerable 

internal decay; such trees 

have medium-failure 

potential. Conks of the 

fungus are perennial, hard, 

woody, and generally 

triangular shaped in 

longitudinal section (Fig. 33). 

Conks of P. tremulae have an 

under surface that is brown 

Fig. 33 – Typical conk of Phellinus tremulae

indicates internal decay in this aspen.
67

with small and regular pores. Early decay has a yellow-white zone in the 

heartwood and is usually surrounded by a yellow-green to brown margin. 

Advanced decay is soft and yellow-white with fine, black zone lines. 

Brown cubical rot is caused by Laetiporus conifericola in conifers and L. 

gilbertsonii in hardwoods (both formerly ) (Table 7). Decay 

is usually well advanced before conks develop, so trees with >1 conks 

have high-failure potential. The distinctive conks are known as the 

sulfur fungus or “chicken of the woods.” Conks are annual and orangeyellow with multiple brackets, usually found on the butt and lower bole 

but also commonly occurring on stumps. Older, dead conks may persist 

for a year or two and are bleached chalky-white and brittle. Conks are 

commonly observed on dead trees or tree parts. Early decay is a lightbrown stain. Advanced decay has red-brown cubes with white mycelial 

felts. 

Brown cubical rot of birch, caused by Piptoporus betulinus, is restricted 

to birch. A single conk generally indicates considerable internal decay, 

and such trees have medium-failure potential. Conks are annual and 

leathery with short, thick stalks. The upper surface is light brown turning 

dark brown and scaly with age and a margin that extends below the 

pore surface. The under surface is white becoming light brown and 

tooth-like with age. Decayed wood is yellow-brown and breaks into 

cubes with thin white mycelial fans in the cracks. Advanced decay easily 

crumbles to powder.

Brown stringy trunk rot is caused by Spongipellis delectans and occurs 

in hardwoods (Table 7). A single conk generally indicates considerable 

internal decay, and such trees have medium-failure potential. The 

conk is quite distinctive, annual, and emerges from the butt or bole 

with several shapes but generally is shelf-like. Conks are white- to 

cream-colored, fleshy to leathery with tawny-colored rounded lips. The 

underside has small, uniform pores. Decay is initially streaky brown 

and retains most of its structural strength. As decay advances, it turns 

a uniform brown and the texture becomes stringy but sometimes 

laminated. Decay occurs in pockets of various sizes mostly in the main 

stem, and pockets coalesce as decay progresses. Decay continues after 

the host dies. 

Brown top rot is caused by Fomitopsis cajanderi and occasionally 

damages conifers (Table 7). The fungus causes a brown-cubical heart 

rot in living trees. It is usually found in trees that had past top damage 

resulting from wind or ice and snow loading. Conks sometimes form 

on the lower bole, probably as a result of a very old top-break or 
68

bole wound. Wood strength may be moderately affected before any 

discoloration or texture change becomes evident. A faint brownish or 

yellow-brown stain, sometimes marked by greenish-brown zone lines, 

may be seen in the early decay stages. Advanced decay is yellowish 

to reddish brown, soft, and with irregular cubes. Thin mycelial felts 

that vary from white to faintly rose-colored may develop in the cracks 

between the cubes. 

The amount of decay is proportional to the diameter of the broken stem 

with decay progressing downward into the main stem and eventually 

upward into any new leaders that form after infection. Boles and new 

leaders on trees with one or more conks at the base of a new leader 

have a medium-failure potential. New leaders and boles on trees with 

top-breaks but no conks would have low-failure potential. Such trees, 

however, should be monitored for future conks.

The conks of F. cajanderi are perennial, woody, bracket-like to hoofshaped with pink to rose-colored undersurfaces and inner tissue; hence, 

the common name, “rose-colored conk”. The conk’s upper-surface is 

brown to black and usually cracked and rough. Conks often appear 

stacked in a shelf-like arrangement. Because conks are relatively 

small, those associated with top breaks may need to be viewed with 

binoculars. The conks are very difficult to detect, and even highly 

experienced evaluators easily overlook their presence.

Brown trunk rot is caused by Fomitopsis officinalis, the quinine or 

chalky fungus and occurs in conifers (Table 7). The presence of brown 

trunk rot, as shown by even one conk, indicates high-failure potential 

for host trees. Damage is severe stem decay occurring either as a top 

rot when it has entered a broken top, or as a heart rot of the main stem 

when the site of the old broken top is much lower in the bole and no 

longer visible. This fungus also enters through basal fire scars. The 

advanced decay is a yellowbrown, reddish-brown, 

or purple-brown cubical 

rot (Fig. 34). The decay is 

crumbly with large, brown 

cubical chunks, and mycelial 

felts are conspicuous in 

shrinkage cracks that form 

in the cubical decay. Felts 

may be one-quarter inch 

thick and may extend 

several feet in length in one 

Fig. 34 – Advanced decay caused by Fomitopsis 

officinalis is a brown-cubical rot.
69

continuous sheet. Mycelial felts are 

bitter to the taste and resinous pockets 

or crusts are formed throughout their 

length. The incipient stain is yellowgreen to brownish-green (very similar 

to that of Schweinitzii root and butt 

rot). The coloration of incipient stain in 

ponderosa pine is brown or reddishbrown. 

Conks are not common but 

unmistakable. The conks are usually 

large, white, hoof-shaped to pendulous, 

and are perennial (Fig. 35). They have a 

chalky-white upper surface and a white 

pore surface. The interior of most conks 

is soft and crumbly. Conks develop at 

branch stubs, over old wounds and 

especially at the site of old top breaks. 

Punk knots may be observed at large, older branch stubs that have 

usually rotted and fallen off. Punk knots may have a yellowish-brown 

exudate that stains the bark below. If a conk is located >50 ft. above 

ground, the entire top-half of the tree has decay. If a conk is <50 ft. 

above ground, then the entire tree has decay. Depending on target 

location and value, trees with quinine conks should be mitigated in any 

developed site.

Hardwood trunk rot is caused by Phellinus igniarius, the false-tinder 

fungus and occurs on many hardwood species (Table 7). A single 

conk generally indicates considerable internal decay; such trees have 

medium-failure potential. Conks are perennial, woody, and generally 

hoofed-shaped with the lower surfaces nearly horizontal. The upper 

surface is gray-black to black and rough when old. The under surface is 

brown with small and regular pores. Early decay has a yellow-white zone 

in the heartwood and is usually surrounded by a yellow-green to brown 

margin. Advanced decay is soft and yellow-white with fine black zone 

lines. 

Incense-cedar pecky rot is caused by Oligoporus amarus and is 

common in mature incense-cedar. Unless there are other indicators, 

trees with conks have low-failure potential. Tree failure is not common 

with pecky rot even when decay is extensive. Decay, which is a pocketrot of the heartwood, is not limited to the butt log, and it may occur 

Fig. 35 – Quinine conks of Fomitopsis 

officinalis are distinctive and indicate 

considerable stem decay.
70

along the entire length of the 

bole. The advanced decay is a 

brown cubical rot similar to that 

occurring in western redcedar 

with pencil rot. Conks are 

common but ephemeral. Conks 

are annual, fruiting at knots in 

late summer or autumn. They are 

hoof-shaped to half-bell shaped, 

tan to buff-colored on the upper 

surfaces, bright sulphur yellow 

on the undersides (pore surface) 

with small tubes that exude clear 

drops of a yellow liquid (Fig. 36). As conks age they turn brown and 

hard. Insects, birds, and squirrels destroy conks, leaving “shot-hole cups”, 

which are apparent at and below the knot where conks were attached. 

Presence of a shot-hole cup also indicates decay. Large, open knots or 

open branch stubs are also indicative of extensive decay. Woodpeckers 

like to work around old, punky, open knots, and evidence of old 

woodpecker work also indicates old conk locations and decayed trees. 

Dry sides (p. 72) are not typically associated with this decay of incensecedar. Decay is almost always present in incense-cedar >40 in. dbh with 

basal wounds or old dead limbs. 

Inonotus trunk rot is caused by two species of fungi, either Inonotus 

dryophilus or Inonotus dryadeus, both of which occur on conifers 

and hardwoods. A single conk of either species generally indicates 

considerable internal decay; such trees have medium-failure potential. 

Conks of I. dryophilus have buff to reddish-brown upper and lower 

surfaces. The advanced decay is a white rot of the heartwood of living 

trees with a conspicuous brown mycelium in the decayed wood. Conks 

of Inonotus dryadeus are annual, firm to woody, and exude amber 

colored droplets on the upper surface when young and on the outer 

edge when older; the lower surface is buff colored and becomes dark 

brown and cracked with age. Inonotus dryadeus causes a white rot of 

the heartwood in butts and roots of living trees. 

Juniper pocket rot is caused by Pyrofomes demidoffii and is common 

in mature juniper. Trees with >1 conks have considerable decay but 

rarely fail and therefore have low-failure potential. Trunk conks are 

perennial and hoof-shaped with a brown to black upper surface with a 

buff to black rim. The under-surface is buff-colored with round pores. 

Fig. 36 – Conks of Oligoporus amarus on 

incense-cedar are annual and disintegrate 

relatively rapidly.
71

Early decay is a light-yellow color. Advanced decay is a white rot with 

abundant buff-colored mycelial felts in the decayed wood. 

Maple trunk rot is caused by Oxyporus populinus. This fungus is known 

as the mossy-maple polypore. Conks generally indicate considerable 

internal decay, and such trees have medium-failure potential. Conks 

are usually associated with wounds, scars, or cracks. The conk is 

perennial with multiple shelf-like brackets occurring on the lower butt 

of decayed trees. The lip and the underside of each bracket are white 

while the upper-surface is white to gray. Pores on the under-surface 

are very small. Older conks are distinctive with moss and/or liverworts 

growing on the upper-surface. Decay is a white heart rot. 

Mottled rot is caused by either Pholiota adiposa, the yellow cap fungus, 

or P. limonella, the lemon cap fungus and affects both conifers and 

hardwoods. Failure potential of trees with one or more conks depends 

on the amount of sound-rind thickness (Table 1). The mushrooms 

have gills and are annual, fleshy, yellow on their upper surfaces, and 

sticky when wet. They have a yellow stem and yellowish to brown gills. 

Mushrooms develop singly or in close groups from a common base and 

appear in the fall, usually on host stems. Incipient decay is light yellow 

and is usually confined to small pockets in the heartwood. Advanced 

decay has discolored areas that enlarge and darken to a honey color. 

Brown streaks appear, causing a mottled look that the decay is named 

for. Decayed wood breaks into stringy strands in the last stages after 

separating at the annual rings. Trunks can become completely hollow. 

Most decay is in the lower bole but can extend 45 to 60 ft. above 

ground. Mushrooms are most common on dead trees or on decadent 

trees with areas of dead stem wood. 

Redcedar pencil rot is caused by Postia sericiomollis. It is a severe stem 

decay and butt rot of western redcedar. Failure potential of redcedars 

with pencil rot depends on the amount of sound-rind thickness (Table 

1). In redcedar, decay is usually confined to the butt (first 40 feet) of 

affected trees. Fruiting bodies are annual, thin, flat, white crusts that are 

not common and are of limited use in estimating decay presence. The 

advanced decay is a brown, cubical pocket rot. When decay is minor in 

affected stems, it appears as long, thin “pencils” of brown cubical decay. 

As decay becomes more extensive, this pencil rotting is more abundant, 

and these thin rot columns begin to coalesce. In severely damaged trees, 

most of the heartwood is decayed and pencil rotting is less obvious, but 

it can be observed at the outer margins and upper reaches of decay. 
72

No cull rule is defined for this decay. Decayed trees, however, are often 

used by cavity-nesting birds, and their cavities are a good indicator of 

advanced decay. Trees with significant decay may display a conspicuous 

bole flattening at the butt called a “dry side” or “dry face” that resembles 

a canker. Trees with evidence of a dry side should be sounded with 

an axe or mallet and drilled to determine the extent of decay and the 

sound-rind thickness. Dry sides may extend 40 feet or more up the stem. 

They are normally covered with bark which hides from view an area of 

decayed wood. The perimeter of the dry side is often humped or folded 

as if in reaction to injury. In severe cases, the callus fold on the perimeter 

of a dry side may force the wood of the tree to the outside. Dry sides 

may be confused with irregularities in the butt associated with butt 

swell or fluting. 

Red heart rot is caused by Stereum sanguinolentum and is commonly 

found in conifers. All dead trees with conks have a high-failure 

potential. Fruiting bodies are found on infected wounds of live trees 

and on the bark of dead trees. The conks are numerous, annual, and 

leathery. The upper-surface is gray to light-brown and zoned; the lowersurface is wrinkled, gray to light brown but turning red when bruised 

(common name of bleeding fungus). Incipient decay appears as a redbrown heartwood stain. Advanced decay is light-brown and soft with 

thin mycelial felts that may be present. 

Red ring rot or white speck is caused by Phellinus pini and is the 

most common stem decay of living Pacific Northwest conifers. Failure 

potential of trees with red ring rot depends on tree species, number and 

size of conks per tree, and associated 

indications of extensive decay such as 

open cracks or weeping frost cracks 

(Table 1). Many stands of old-growth 

Douglas-fir, pine, larch, hemlock, or true 

fir exhibit some of this defect. Conks are 

hoof-shaped and are formed at branch 

stubs or knots (Fig. 37). Pore surfaces 

are cinnamon-brown to tan with pores 

that are irregular rather than round. 

The interior of the conk has the same 

cinnamon-brown coloration as the pore 

surface. On hemlocks especially, but 

occasionally on other species, conks 

may be abundant on the undersides of 

branches (limb conk). 

Fig. 37 – Typical conk of Phellinus 

pini often indicates low-failure 

potential.
73

Conks are typically higher on trees in 

older stands. Large conks indicate more 

decay; smaller conks usually indicate 

less decay, unless the apparent small 

conks are remnants of larger conks 

that have fallen off (see Appendix). 

Individual limb conks may be 12 to 18 

in. long with their long axis parallel to 

the limb; conks may extend 2 or 3 in. 

out on either side of a limb. Limbs with 

conks extending up to 2 or 3 feet away 

from the main stem are common in 

some areas. 

Punk knots are common on severely 

decayed trees. They are evidence that 

a conk is about to form at the site of 

an old branch stub, or that a conk was once present at the site but has 

since fallen off. Punk knots and conks indicate the same amount of 

decay. A true punk knot is observed when the cinnamon-brown “punky” 

fungal material that occupies the context of the conk is clearly visible to 

the outside with the naked eye or with the aid of binoculars. Conks are 

formed at branch stubs or over old knots. Often branch stubs, bark flaps, 

burls (Fig. 54), and other features can look like conks or punk knots. 

Close evaluation with binoculars is important to assure the indicator is 

in fact a conk or punk knot. 

The decay caused by P. pini is a white pocket rot (Fig. 38) that occurs in 

rings separated by sound wood until decay becomes very advanced 

(very soft and crumbly). When this decay is encountered in developed 

sites, it must be evaluated carefully. Wood decayed by this pathogen 

maintains some strength against failure. When Douglas-fir, pine, cedar, 

or larch have ≥3 large conks (>6 in. wide) within a 3-ft. trunk cylinder, 

the hazard evaluator can expect that damage to the heartwood 

probably is extensive (Table 1). With many small or separated large 

conks, these resinous tree species may have adequate strength to 

withstand high winds. If an evaluator suspects that a tree is marginally 

safe based on indicators, the evaluation of damage potential, target 

value, and alternative hazard-mitigation strategies must direct the 

course of the hazard-management decision. Where damage potential 

is high, the evaluator should measure the sound-rind thickness at the 

point of greatest defect, usually near the largest conks. This may require 

climbing affected trees to drill near the biggest conks. When boring 

Fig. 38 – Wood with decay caused 

by Phellinus pini, commonly called 

whitespeck, is relatively sound 

compared to wood decay caused by 

other fungi.
74

a tree with P. pini decay, consider firm (not crumbly) wood with white 

speck or red discoloration as sound wood (Table 1). 

In southern Oregon, red ring rot is more severe in older stands, in 

pure stands of host trees, on steep slopes, on shallow soils, and on 

sites dominated by secondary shrub, herb, or forb vegetation (vine 

maple, vanilla-leaf, oxalis, or rose rather than salal, twinflower, or 

rhododendron). 

Redwood cubical rot is caused by Oligoporus sequoiae. The fruiting 

body develops as a thin, white crust composed of fungal strands and 

a spore-producing pore surface. The fruiting bodies rarely exceed 2 

in. long by 1 in. wide and form in fire scars and bark crevices. Incipient 

decay is a dark-brown stain that forms pockets of brown, charcoal-like 

dry rot that shrinks and cracks into cubes when advanced. Redwood is 

a relatively decay-resistant tree species, so failure potential should be 

determined by measuring sound-rind thickness.

Rust-red stringy rot is caused by Echinodontium tinctorium, the Indian 

paint fungus. It is the most damaging stem decay of older true firs 

and hemlocks. The presence 

of rust-red stringy rot as 

indicated by conks results in 

either high- to low-failure 

potential depending on 

number and size of conks 

per tree and associated 

indications of extensive decay 

(Fig. 39) such as open cracks 

or weeping frost cracks (Table 

1). Trees with a single conk 

on average have as much 

as 40 feet of continuous 

decay within the trunk (see 

Appendix). 

Trees can become infected 

at a relatively early age 

through tiny (0.5 mm), dead 

branchlet stubs. Thereafter, 

the fungus becomes dormant 

until re-activated by tree 

wounding. Infected saplings 

Fig. 39 – Advanced decay caused by 

Echinodontium tinctorium, the Indian paint 

fungus, can result in tree failure.

Fig. 40 – Conks of the Indian paint fungus are 

distinctive and common on true firs.
75

and poles are often released from their suppressed condition, and they 

resume vigorous radial growth, often encasing dormant infections in 

heartwood. Following re-activation of the dormant infection by injury 

near the point of original infection, heartwood is decayed. 

Advanced decay is a rust-red stringy rot that may result in nearly hollow 

stems (Fig. 39). When decay is advanced, large, hoof-shaped conks with 

a spiny lower surface are produced. Young conks have mostly a lightcolored pore surface with a dark top. Older conks have a fissured upper 

surface and they are rough, dull black, and woody (Fig. 40). The interior 

of the conk and the cores of infected branch stubs are rusty-red to 

bright orange-red. Conks appear on the bole at the site of old branches. 

Where conks appear at multiple, old branch whorls, greater defect is 

indicated. 

White spongy trunk rot, caused by Fomes fomentarius, produces conks 

that are found on dead trees or dead portions of hardwoods. Trees 

often have multiple conks indicating extensive decay and high-failure 

potential. This decay occurs almost exclusively in hardwoods. The 

perennial conk is hoof-shaped with a concentrically zoned, smooth, and 

gray to gray-black upper surface. The underside is brown with small, 

regular-shaped pores. Early decay is brown and firm. Advanced decay is 

soft and spongy, yellow-white with dark to black zone lines. 

White trunk rot is caused by Phellinus hartigii and is found in living 

conifers and hardwoods (Table 7). Trees with one or more conks have 

medium-failure potential. The decay often occurs in a section of wood 

radiating in from the sapwood. Incipient decay is straw-colored to 

purple stain that is irregular in shape. Advanced decay has a bleached 

look with occasional light-brown areas or streaks. Trees with white trunk 

rot often fail within 20 feet of the ground. The conks are perennial and, 

if on the main stem, appear hoof-shaped with a dark-brown to black 

upper-surface and a brown and poroid lower surface. When formed on 

the lower surfaces of branches, the conks are flat against the branch and 

often occur where the branch joins the main stem; hence, the common 

name, “armpit fungus.” The conks are commonly associated with 

hemlock dwarf-mistletoe infections (p. 83). 

Yellow pitted rot is caused by Hericium abietis, the coral fungus, and 

occurs in some conifers (Table 7). Trees with one or more conks have 

medium-failure potential. The fruiting bodies are distinctive, soft, 

creamy-white, coral-like, annual conks. They occur at wounds on living 

trees. Incipient decay is a yellow to brown stain with scattered darker 

spots that give the wood a mottled appearance. Advanced decay is 
76

composed of elongated blunt-end pits, about 1⁄2 in. long; hence, the old 

common name, “long-pocket rot.” 

Sap Rots

Sap rots are decays that occur in the sapwood (Table 8). Most saprotting fungi cause rapid decay of dead sapwood only. When these fungi 

have decayed all of the available dead sapwood, then decay ceases and 

in most cases no heartwood is decayed. They compete poorly with other 

fungi that decay heartwood, and are seldom found past the heartwood/

sapwood interface. In living trees, sap rots occur on wood tissue killed 

by other agents, most often bark beetles and mechanical or weather 

damage. On dead trees, especially those killed by root diseases and/or 

bark beetles, sap rot is sure to occur, and the rate of sapwood decay can 

be rapid. On some true firs and hemlocks, sapwood is fully rotted within 

1 to 2 years of tree death. On other conifers, it may take as many as 3 to 

5 years for sap-rotting fungi to decay all of the available dead sapwood. 

Hardwoods are also subject to sap-rotting, and damage may be 

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

occurs in dead portions of living trees. On many Pacific Northwest 

hardwood species (poplars, maples, alders), sapwood decays very 

rapidly once it dies, and there may be few obvious external indicators. 

When external indicators of sap rot are lacking, testing may be required. 

Sap-rot depth can be determined by using a cordless drill, increment 

borer, or axe. Living hardwoods with sap rot in one or more stem 

quadrants have a medium-failure potential (Table 1).

Trees killed with a full complement of foliage, normally develop sap rot 

at a rapid rate. Trees killed by crowning fire or trees with broken tops, 

however, exhibit delayed sap rot development. In such trees, the level 

of xylem sap remains high, and it rather quickly ferments, turning sour. 

Table 8. Sap rots affecting trees on developed sites in Oregon and 

Washington.

Common name Scientific name of causal fungus Major hosts

Brown crumbly rot Fomitopsis pinicola Most tree species

Gray-brown sap rot Cryptoporus volvatus All conifers

Pitted sap rot Trichaptum abietinum All conifers and 

some hardwoods

Silver leaf disease Chondrostereum purpureum Mostly hardwoods
77

Bark beetles will rarely attack such 

trees, and the introduction of saprotting organisms will be delayed 

until bark splitting and sun 

checking or heart checking occurs. 

When bark beetles do attack 

such trees, breeding success is 

poor. In trees with soured sap, the 

succession of microorganisms and 

invertebrates is very different than 

that occurring in normal trees 

killed by bark beetles. With any of 

the following sap rots, dead trees 

have high-failure potential in 

developed sites.

Brown crumbly rot is caused by 

Fomitopsis pinicola, the red-belt 

fungus. This fungus causes a sap 

rot of dead trees but sometimes 

also a heart rot of living trees, 

especially those with trunk 

wounds. Live trees with >1 conks 

may have low- or medium-failure 

potential depending on the extent 

of dead sapwood (Table 1). Bark 

beetles transport propagules of 

the fungus to infested trees. Conks 

are leathery to woody, perennial, 

and bracket-shaped (Fig. 41). 

When young, the conks appear 

white and round. As they mature, 

the upper surfaces turn dark-gray 

to black, the lower pore surfaces 

remain white, and conspicuous reddish margins develop between the 

two surfaces; hence, the common name “red-belt conk.” Conks are often 

seen on dead and down trees. After tree or tissue death, decay develops 

rapidly in the sapwood and then progresses to the heartwood. Incipient 

decay is a faint yellow-brown to brown stain. Advanced decay is light 

reddish-brown and forms a crumbly mass of rough, small cubes with 

mycelial felts between the shrinkage cracks. 

Gray-brown sap rot is caused by Cryptoporus volvatus, the pouch 

fungus. It is one of the most easily recognized of the sap-rotting fungi. 

Fig. 41 – Red-belt conk of Fomitopsis 

pinicola, the most common decayer of dead 

wood in the Pacific Northwest.

Fig. 42 – Pouch-fungus conks of 

Cryptoporus volvatus often indicate 

considerable sap rot.
78

Table 9. Fungal cankers and stem rusts in Oregon and Washington; 

frequency of occurrence by host species where: 1=common, 

2=occasional, 3=infrequent, 4=rare, and blank means non-host or 

unknown occurrence.

Host species

Atropellis cankerCeratocystis cankerComandra blister rustCryptosphaeria cankerCytospora cankerHypoxylon cankerMadrone cankerMistletoe cankerNectria cankerPhytophthora canker of golden chinkapinRamorum cankerRedcedar pencil rotRed ring rot cankerSooty-bark cankerStalactiform rustSterile conk trunk rotWestern gall rustWhite pine blister rust

Alder 3 3 3 3

Aspen 2 3 2 3 2 2

Ash 3 3

Birch 3 3 2

Buckthorn 3

Cedar

 Alaska

 Incense 3

 Port-Orford

 Western red 3

Cherry 3 3

Chinkapin 2

Cottonwood 4 3 3 3 3 2 4

Dogwood 3 3

Douglas-fir 3

Hemlock

 Mountain 2

 Western 2

Juniper 3

Larch 3

Madrone 1 3

Maple 3 3

Myrtle 3 3

Oak 1 3 3
79

Host species

Atropellis cankerCeratocystis cankerComandra blister rustCryptosphaeria cankerCytospora cankerHypoxylon cankerMadrone cankerMistletoe cankerNectria cankerPhytophthora canker of golden chinkapinRamorum cankerRedcedar pencil rotRed ring rot cankerSooty-bark cankerStalactiform rustSterile conk trunk rotWestern gall rustWhite pine blister rust

Pine

 Jeffrey 4 3

 Knobcone 4 3 1

 Lodgepole 2 3 3 2 1

 Ponderosa 3 1 3 3 2

 Sugar 3 1

 Western white 3 1

 Whitebark 3 1

Redwood

Spruce

 Brewer

 Engelmann

 Sitka

Tanoak 1

True Fir

 Grand 3 2 2

 Noble 3 3 3

 Pacific silver 3 3 3

 Shasta red 3 3 3

 Subalpine 3 3 3

 White 3 2 1

Willow 3 3 3 3

Yew
80

The fungus is routinely introduced by tree killing bark beetles and wood 

borers. Conks are annual, leathery and produced on trees the first year 

after tree death. Fresh conks are small, round, initially soft and fleshy, 

yellow-brown to golden brown with pore surfaces covered by a hard 

membrane; hence, the common name, “pouch fungus” (Fig. 42). Conks 

bleach to a dirty white after one year. Early decay has gray areas that 

develop in the sapwood beneath the conks. Advanced decay appears 

the same and may completely destroy the sapwood. 

Pitted sap rot is caused by Trichaptum abietinum, the purple conk. 

The fungus infects its host via airborne spores through openings in the 

bark. Since this fungus is primarily a saprophyte, conks infrequently 

form on live trees but are numerous on dead trees and logs. Conks are 

small, annual, thin, and shelf-like. The upper surface is light gray, fuzzy, 

and zoned. Old conks become dark gray to black. The under surface is 

violet to purple when fresh that turns light brown with age. As conks 

age, the angular pores become elongated and separate into spines or 

ridges. Incipient decay is light yellow to tan and soft; advanced decay 

has small pits that become elongated in the direction of the grain, with 

a honeycombed look.

Silver leaf disease is caused by Chondrostereum purpureum. It occurs 

mostly on dead hardwoods but has been reported on living trees. The 

conks are annual, shelf-like, and often in groups. The upper surface 

is grayish-white to purple and zoned with a light margin. The lower 

surface is usually smooth, bright purple when young and brown-violet 

when old. Early decay is a reddish-brown stain; advanced decay is whitemottled to pale yellow.

Fungal Cankers and 

Stem Rusts

Fungal cankers and stem rusts are 

caused by many species of fungi that 

infect and kill portions of a tree bole. 

Cankers and rusts frequently occur on 

the stems and branches of pines and 

hardwoods. Canker fungi cause top-kill, 

branch death, or stem malformation. 

Stem malformations can be infected 

and subsequently decayed by other 

fungi, thus increasing the likelihood of 

Fig. 43 –Atropellis canker is a 

common disease of lodgepole pine 

that can result in stem breakage.
81

stem breakage. Cankered areas 

on true fir, hemlock, spruce, 

or hardwoods are more likely 

to be associated with failures 

than those on resinous species: 

Douglas-fir, pine, or larch and 

also decay-resistant cedar (Table 

1). Failure potential does not 

significantly increase until the face 

of the canker is deeply sunken, 

or the cross-section of the bole 

with sound wood is small (Fig. 

9). Failure potential increases as 

cankers develop.

Major cankers and stem rusts that 

result in tree hazards in developed 

sites in the Pacific Northwest 

include the following: 

Atropellis canker is caused by either Atropellis piniphila or A. pinicola 

(Table 9). It frequently occurs on the boles of pine species, especially 

lodgepole pine. 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 circumference at that 

point (Fig. 43). When the cankers result in <50% cross-section of the 

bole with sound wood, and the depressions are deep, failure potential 

is high (Table 1). This is most likely to occur in heavily infected stands 

where trees have multiple cankers and where individual trees have two 

or more cankers at the same height on the bole.

Ceratocystis canker, caused by the fungus Ceratocystis fimbriata, occurs 

on aspen and cottonwood (Table 9). Ceratocystis cankers are targetshaped with or without bark adhering to the surface of the canker. 

Infected wood behind the canker usually is stained. Macroscopic fruiting 

bodies may be produced on the cankers. Most of the cankers on aspen 

ultimately girdle the bole and kill the upper part of the tree. 

Comandra blister rust, caused by Cronartium comandrae, occurs 

on ponderosa pine and sometimes lodgepole pine in Oregon and 

Washington. Mortality can occur, especially in young, infected trees. 

Large infected pines exhibit dead tops that progressively die downward 

Fig. 44 – Dead tops of ponderosa pine, 

caused by Comandra blister rust, often are 

resin-impregnated, decay-resistant, and 

therefore of very low-failure potential. 
82

Fig. 45 –Dwarf mistletoe bole 

infections are especially common on 

grand and white fir, western hemlock, 

and western larch. 

Fig. 46 –True mistletoe bole and branch 

infections can cause cankers and subsequent 

decay in oaks.

(Fig. 44). Infected and dead tops are 

relatively decay resistant because of the 

copious resin associated with infection. 

These dead tops have very low-failure 

potential, even after several years, and 

rarely fail. 

Cryptosphaeria canker, caused by the 

fungus Cryptosphaeria populina, occurs 

on aspen and cottonwood. Cankers are 

elongated with some bleeding at the 

margins. Several, highly visible, black 

fruiting bodies form in the bark. Stain 

and decay may be extensive behind the 

cankers and determine the degree of 

failure potential.

Cytospora canker is caused by 

Cytospora chrysosperma on 

hardwoods and C. abietis on 

true firs. Cankers occur on boles, 

branches and twigs, forming long, 

dead areas with well defined 

borders. Several years after 

infection, dead bark lifts away 

from the bole and falls off. 

Hypoxylon canker, caused by 

Entoleuca (Hypoxylon) mammata, 

is found only on hardwoods, 

including alder, cottonwood, 

aspen, and willow. The canker first 

appears as sunken, yellow-orange areas on the bark that is centered 

around dead branch stubs or injuries. Older cankers have mottled bark 

with small, dead patches. Cankers can be 3 ft. in length. 

Madrone canker, caused by Fusicoccum arbuti and F. aesculi, occurs only 

on Pacific madrone. The causal fungus attacks weakened madrones, 

especially trees that are drought-stressed, have mechanical wounds, 

or are suddenly exposed to full sunlight. The fungus causes a stem and 

branch canker with branch, trunk, or complete tree dieback. Infected 

branches develop a purplish-black color, appear dry and cracked, and 

eventually die. Older stem cankers are sunken into the bark. Failures 
83

usually are infrequent until branches or stems have been dead for 

several years.

Mistletoe-bole and branch cankers are caused by dwarf mistletoe 

(Arceuthobium spp.) infection of the bole in conifers (Fig. 45), and true 

mistletoe (Phoradendron spp.) infection in the branches and boles 

of oaks (Fig. 46), incense-cedars, and junipers. Dwarf mistletoe bole 

infections are especially common on grand and white fir, western 

hemlock, and western larch. 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 not a serious issue. 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. Any of the fungi that 

function as wound parasites can be found decaying mistletoe-induced 

bole swellings. 

Nectria canker is caused by Nectria cinnabarina and occurs on many 

hardwood species. Sunken cankers are associated with wounds or 

develop at the base of dying branches. Cankers can girdle and kill stems, 

and when bark dies, it appears dry and cracked with age.

Phytophthora canker of golden chinquapin is caused by 

Phytophthora cambivora. The disease can cause tree mortality with leaf 

flagging being a common symptom of infected trees. In the inner bark, 

the girdling, basal cankers are reddish-orange and extend upward from 

infected, necrotic roots. The inner bark turns brown when the trees are 

dead; failure-potential then is high.

Ramorum canker is caused by 

Phytophthora ramorum, also the cause 

of sudden oak death. The causal agent, a 

fungus-like water mold, was introduced 

into southern Oregon in about 2000. 

This disease causes significant mortality 

of black and live oaks, tanoaks, and 

California bay in California. Ramorum 

canker is mentioned in the context 

of developed-site hazard 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. 

Although other tree species can serve Fig. 47 –Sooty-bark canker, as seen 

on this infected aspen, can result in 

tree failure.
84

as foliar hosts in the PNW: maple, madrone, myrtlewood, cascara, and 

Douglas-fir, none of these species have had bole cankers or have been 

killed, as yet, by the causal agent in Oregon or Washington. Infected 

trees are rapidly colonized by decay fungi, and trunk failures can occur 

even before trees are completely dead. Recently infected and dead oaks 

and tanoaks in developed sites have high-failure potential. 

Red ring rot canker is caused by Phellinus cancriformans in 

southwestern and west-central Oregon and occurs on true firs (Table 

9). The conks of the fungus are small and numerous with their upper 

surfaces being rough, dark, and furrowed (butterfly conks). They closely 

resemble P. pini conks (p. 72) but are smaller and occur in groups. 

The conks grow from a sunken area on the trunk with decayed wood 

beneath it (a canker). Substantial amounts of stem breakage can occur 

with this fungus.

Sooty-bark canker, caused by the fungus Encoella pruinosa, occurs 

on aspen and cottonwood. Sooty-bark cankers often have arcs of 

blackened bark tissue as a result of infection (Fig. 47). Fruiting bodies 

that form on the cankers are silver gray.

Stalactiform rust is caused by Cronartium coleosporioides and occurs 

primarily on lodgepole pine and less commonly on ponderosa and 

Jeffrey pine. Older infections form diamond-shaped cankers that can 

extend to 30 ft. long. Tree mortality may occur if boles are completely 

girdled. 

Fig. 48 –Lodgepole pine with western gall rust can break if stem cross-sectional 

area of sound wood is too low.
85

Sterile conk trunk rot is caused by 

Inonotus obliquus and affects some 

hardwoods (Table 9). Unless there is 

evidence of extensive decay (cracks or 

exposed rot), trees with ≥1 sterile conks 

have a medium-failure potential. The 

sterile conks are conspicuous, perennial, 

black masses of fungal tissue that erupt 

from stem cankers. The conk surface 

is rough and cracked; the interior is 

yellow- to rust-brown. The tree trunk is 

often thickened at the conk. Incipient 

decay is yellow-white in irregular zones. 

Advanced decay appears as alternating 

zones of white and light reddish-brown 

wood. White veins of mycelium are 

common near the cankers. 

Western gall rust is caused by 

Endocronartium harknessii and is common on lodgepole and knobcone 

pine. It frequently can be found on ponderosa pine, especially near 

water courses. The disease causes branch flagging, bole breakage, 

topkill, and mortality of young trees. The galls are small to large, round 

to pear-shaped swellings on branches and boles. “Hip cankers” are 

caused when the main stem flattens and broadens as it grows around 

bole infections (Fig. 48). 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.

White pine blister rust is caused by Cronartium ribicola and is found 

throughout the range of 5-needle pines in Oregon and Washington. The 

fungus causes branch flagging, top-kill, and death usually of pines <8 in. 

dbh (Fig. 49). Mountain pine beetles often attack older, infected trees. 

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. Cankers result in dead, 

roughened bark that has margins that appear greenish-yellow to 

orange. Heavy pitch flow often occurs with the bole cankers. Infected 

and dead tops are relatively decay resistant because of the copious resin 

associated with infection. Blister-rust-killed tops have very low-failure 

potential even after several years and rarely break and fall. 

Fig. 49 –Tops of trees killed by white 

pine blister rust are often resinsoaked with little decay and have 

very low-failure potential.
86

Fig. 50 –Frost cracks often indicate 

low-failure potential unless they are 

weeping, as shown here, then failure 

potential is medium to high.

Other Bole Defects

Cracks and splits in the main stem frequently occur and are often 

overlooked or regarded as insignificant. Cracks usually tell an important 

story and may reveal to the examiner that a closer inspection of the 

heartwood is warranted. Cracks and splits can be entry points for decaycausing micro-organisms or activate dormant spores of decay fungi, 

such as the Indian paint fungus (p. 74). 

Cracks and splits are produced in several ways: tension and compression 

failure associated with older injuries and internal decay, lightning 

strikes, wind shake, and frost action. Cracks can form by tension and 

compression failure when trees with extensive heart rot bend back and 

forth under the stress of high winds. The sound rind on the windward 

side of affected trees is under great tension when winds are strongest. 

The side of the tree to the lee of the wind becomes compressed by that 

same wind force. This difference in forces, when most exaggerated, 

creates a shearing action in the middle of the bole where the two forces 

meet, and the bole develops a vertical crack somewhere between 

the ground and where the extent of heart rot is the greatest. An open 

crack with independent movement of its sides indicates high-failure 

potential because the trees have already partially failed.

Lightning strikes cause cracks when electrical discharges are grounded 

through trees. When the discharge is insufficient to explode the tree 

or its parts, damage 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. Often huge chunks of 

wood may be blown out of the furrow 

contributing to its depth and impact 

on subsequent tree vigor and windfirmness. Occasionally, entire trees or 

portions will be shattered, severely 

cracked, or split. The failure potential 

of lightning-damaged trees increases 

with the length, width, and depth of 

cracks as well as with the extent of 

subsequent decay. On the other end 

of the spectrum, groups of trees may 

be synchronously killed by lightning 

without any apparent evidence of 

mechanical damage. 
87

Wind shake can cause cracks, especially on trees growing at higher 

elevations. High winds regularly impact conifer forests, and winds 

are often turbulent and twist trees in different directions. Under the 

influence of frequent high winds, trees often develop shake in the 

lowest section of the butt. The twisting action of the wind first causes 

separations to develop along the growth rings. Later, these develop 

“legs” which extend radially outward toward the bark. In time, this 

defect breaches the bark and can be observed from the outside. Shake 

cracks may occur on any side of the bole and “legs” may extend from 

a few feet to 20 or 30 feet above the ground. Extensive wind-shake 

defect indicates partial failure and may be associated with increasing 

butt rot. Wind-shake cracks also incite dormant Indian paint fungus (E. 

tinctorium) infections to develop active decay (p. 74). 

Extreme cold can cause bole cracks. Frost cracks, common at higher 

elevations and in cold-air drainages, appear on bark as raised nearly 

vertical callus lines that extend to the ground where the air is coldest 

(Fig. 50). This can be contrasted with wind-shake cracks which need 

not be vertical, often do not contact the ground, and may gradually 

spiral up the side of an affected tree. Frost cracks develop under the 

influence of freezing temperatures when the outer-sapwood growth 

rings become dehydrated by extracellular ice formation and produce a 

contraction on the circumference of the bole with no radial contraction. 

These cracks begin at the tree base, usually from an old wound, and 

seldom go higher than 15 feet up the bole. Defect is not commonly 

associated with true frost cracks, and they are seldom associated with 

high-failure potential unless they are weeping and have sound-rind 

thickness <20% of the stem diameter (Table 1). Older frost cracks 

develop “frost ribs,” a series of raised vertical ridges parallel to the frost 

cracks themselves. If frost cracks have exudates (weeping), they indicate 

Fig. 51 – Forked tops, such as this hardwood that is weeping and cracked (A) and this cedar 

with open cracks (B), have high-failure potential. The ponderosa pine with only embedded 

bark (C) has medium-failure potential.

•	 A •	 B •	 C
88

either high- or medium-failure potential depending on the soundrind thickness (Table 1).

Codominant stems, forked tops, or trees with multiple tops that are 

tightly V-shaped, can split and break from the green weight of foliage, 

heavy snow loads, or internal decay. Since a broad-angled-branch 

connection was not differentiated at the time the branch first formed, 

new radial growth at the point of branch convergence forces the acute 

angle further apart. Eventually, new radial growth will weaken the 

crotch to such a point that wind or snow load, or the added weight 

of new foliage causes a branch failure. This not only occurs in mature, 

forked conifers but also in conifers with severe ramicorn branching 

and hardwoods with large, spreading crowns. Tree crotches should be 

regularly examined with binoculars, because defect indicators such 

as open cracks, decay, mushrooms, or conks often suggest weakening 

and predisposition to failure (Fig. 51). Trees with these indicators have 

a high-failure potential (Table 1). Tree crotches with only embedded 

(included) bark (Fig. 51) without the above indicators have mediumfailure potential. V-shaped tops without defect indicators or U-shaped 

tops generally have low-failure potential (Table 1). Forked tops of 

ponderosa pine in central Oregon have a potential-failure-zone radius of 

1.5 times the length of the broken fork

Defective Branches

Hazards associated with defective branches are often exaggerated. 

The incidence of failure in this category is lowest of any listed in Table 

4. Table 4 does not indicate the magnitude of personal loss associated 

with branch failures, but personal injury and property damage are 

usually less serious than that associated with trees that fail at the roots, 

butt, or bole. Defective branches fall essentially straight down from the 

point of failure, and their impact area is considerably smaller than that 

of a tree failing at the roots, butt or bole. The potential-failure zone is 

the same radius as the length of the branch. While failure probability is 

medium for attached defective branches, free-hanging limbs should be 

removed immediately if they hang over a target. 

Hardwoods, especially poplars, cottonwoods, maples, and alders, are 

more susceptible to branch failure than most conifers because their 

crotches are structurally weaker, the lignin content of the wood is low 

by comparison, and their long branches are heavily weighted at the 

extremities with green foliage and fruit. As with conifers, crotches of 

major branches should be regularly examined for defect indicators 

such as open cracks, splits, or embedded (included) bark that suggest 

weakening and predisposition to failure or infection by decay fungi. 

Forked tops with open cracks have high-failure potential (Table 
89

1). Also, heart rots of hardwoods 

often extend into major branches 

creating higher potential for failure. 

Dead branches on resinous conifer 

species remain attached longer than 

on non-resinous species, and limbs of 

hardwoods fail sooner than those of 

most conifers. 

Black cottonwood branches have an 

increasingly high potential to break 

from the crown as the tree matures. 

Breakage will often occur at sound 

wood, although decay is also common 

and will increase failure potential. 

Breakage potential is greatest in the 

summer season when branches are 

weighed by foliage and cell structure is 

weakened by high transpiration. Black 

cottonwoods are a poor choice for longterm maintenance in developed sites, and location of targets should be 

well removed from large cottonwoods that will be retained. 

Each year, winter storms occur in developed sites and often cause 

failure of the most defective branches, tops, and trees. Severe storms 

have a sanitizing effect in an overstory that has many defective 

branches; few remain that are defective enough to fail during the next 

year under their own weight. This sanitation effect is especially common 

in the higher elevations. At lower elevations, severe storms may be less 

frequent or different in kind or abundance, and heavy snow/ice loads 

may be infrequent or may not occur at all. 

Large dwarf mistletoe brooms (>10 ft. in diameter), especially on 

Douglas-firs but sometimes on ponderosa pines, that are dead and 

hanging directly over stationary targets of value or over areas that are 

routinely exposed to heavy transitory traffic, should be removed by 

pruning (Fig. 52). In areas of normally high snow loading or violent 

winter storms, this hazard is often mitigated as brooms break off with 

snow and ice loading. Brooms with a high-failure probability will often 

fail in winter when sites are closed or visitor use is limited. Pruning of 

large, live brooms may improve the vigor of infected trees and may slow 

the spread of the parasite to the upper crown that eventually results in 

tree death or top-kill. Candidates for live-branch pruning are trees with 

dwarf-mistletoe brooms only in the lower one-third to one-half of the 

Fig. 52 –Douglas-fir dwarf mistletoe 

brooms that are dead and ≥10ft. in 

diameter have high-failure potential.
90

live crown, and trees with live-crown ratios that will still be >40% after 

pruning. With Douglas-firs consider using MCH pheromone around 

trees pruned in spring or summer to prevent lethal attack by bark 

beetles.

Treat hazardous defective branches by removal (Table 10). Candidates 

for this treatment are dead, broken, or free-hanging branches 

(completely loose and lodged), or large, dead, dwarf-mistletoebroomed branches that are above permanent targets or heavily used 

areas. Trees in need of treatment are climbed and pruned as needed. 

Some success has been reported using another pruning technique 

which eliminates climbing. A line is shot over the distal end of a 

defective branch via a crossbow or compound bow, and both ends of 

the line are pulled downward in a sharp movement, thereby breaking 

off and removing that portion most prone to failure. If the limb does not 

break readily with pulling, it is unlikely to fail within one season. 

Pruning of live branches should be done with care to avoid excessive 

bole wounding and decay. At the junction of the main stem and a 

branch, both coniferous and hardwood trees exhibit a folding of bark 

tissue called the branch collar. This collar is important in the production 

of a barrier zone of cells that wall-off tissues damaged by wounding 

and reduce the potential for decay. Pruning cuts should be made flush 

with the branch collar. A longer stub is a more suitable entrance court 

for decay fungi and it is less readily overgrown by callus tissues in the 

healing process. Wound dressings on pruning cuts or other wounds are 

not only unnecessary, but may even be detrimental. Dressings act as a 

moisture barrier and maintain for longer 

periods a suitable environment for 

decay fungi. Pruning is best done in the 

late fall and winter when trees are fully 

dormant. Also, possible insect attack by 

pitch moths or bark beetles is less likely 

in the fall and winter than in the spring 

and summer.

Dead or Broken Tops 

Dead tops on live trees eventually 

break out and fall to the ground (Fig. 

53). Before tops fail they often rot in 

place and are held by little or no sound 

wood. A gentle bumping or jarring of 

a top-killed tree may cause top failure. 

Fig. 53 –Failure potential of trees with 

dead tops depends on whether the tree 

species is resinous like Douglas-fir or 

non-resinous like white fir.
91

In developed sites, trees with dead, highly defective tops are often 

jarred by people or their vehicles. When dead tops are encountered in 

developed sites, hazard should be assessed immediately. Unacceptable 

hazards should be mitigated. 

The failure potential of dead tops of cedar, Douglas-fir, larch, and pines 

with rust-killed tops is normally very low (Table 1). Dead tops of true 

firs, hemlock, spruce, and hardwoods are highly susceptible to attack 

by decay fungi, and their failure potential is normally higher than that 

of other conifer species on the same sites. Large, heavy pieces of loose 

bark on dead tops also present a hazard. 

Trees with old, broken tops may have rot present below the break. This 

is especially true of non-resinous conifer species, although resinous 

species with top breaks are prone to brown top rot caused by Fomitopsis 

cajanderi (p. 67) or brown trunk rot caused by Fomitopsis officinalis (p. 

68). If the upper branches in the remaining top are thrifty and vigorous 

in their appearance, additional top failure is unlikely in the near future, 

though trees with tops broken out should be monitored regularly. The 

potential that new tops arising from upturned lateral branches will fail is 

also low unless indications of internal defect are evident. 

Burls

Burls are abnormal swellings on stems 

and branches (Fig. 54). Usually, burls are 

composed of undecayed wood and, as 

such, trees with burls have low-failure 

potential. Burls vary in size but can be 

several feet in diameter. Their cause is 

mostly unknown, but they are common 

among high-elevation tree species 

such as lodgepole pine and subalpine 

fir. When high in the tree or covered 

with moss or lichens, burls sometimes 

resemble conks and therefore require 

careful examination with binoculars. 

Fig. 54 – Burls are often large 

woody growths of unknown cause 

on conifers and hardwoods that 

resemble conks but indicate lowfailure potential.
92

Fire-Caused 

Damage

Fire-damaged tree boles or limbs 

may be so badly burned with 

associated wood consumption 

that they are structurally 

weakened which may cause the 

bole or limb to break and fail (Fig. 

55). Root systems may be partially 

consumed by fire, and the entire 

tree may fall. Before burning, the 

tree may have had conks or mushrooms that indicated severe decay. 

These may have burned off, eliminating their value as indicators of 

root disease or heart rot. Therefore, the tree may be less stable than 

the visible indicators suggest. Likelihood of failure is determined by 

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

remaining, and if the tree is dead (Table 1). Large pines, cedar, larch, 

or Douglas-fir with old, basal, fire scars may have compensated for 

any defect or decay by increasing their butt diameter; such trees have 

low-failure rates unless a subsequent burn causes additional loss of 

support. Fire-damaged trees may still have green crowns but dead 

cambium at their bases; essentially they are dead trees. Long lasting and 

smoldering fires at the bases of large pines usually kill the fine roots and 

may eventually contribute to death of the tree usually by predisposing 

it to bark beetles and wood borers. Fire-killed trees are rapidly infested 

by wood borers that introduce wood-decay fungi. Tunneling by larvae 

facilitates wood decay. 

Substantial damage, especially on ponderosa pine and Douglas-fir, can 

occur in trees that have old, resin-impregnated wounds that reburn. 

This seems to be especially true when fires are hot, burn after a long 

period without fires, and the trees involved have deep mounds of 

exfoliated bark and duff around their bases at the time of the fire. Trees 

with old catfaces or firescars should be examined carefully after a fire to 

determine how much damage to the cross-section of sound wood has 

been caused by reburning. For recent fire damage (<5-years old), use 

“fire-damaged trees” in Table 1; for older fire damage, use “bole wounds.”

Fig. 55 – Fire-damaged trees have failure 

potentials that depend on the amount of 

sound wood remaining.
93

High Height-to-Diameter Ratios

Live trees with a high height-to-diameter ratio (an index of slenderness) 

may fail depending on the ratio (Table 1). These trees can break or 

bend permanently usually from snow or ice loading in the winter. Tall, 

thin trees with dwarf-mistletoe brooms may be particularly prone to 

bending or breakage. To calculate height-to-diameter ratio, estimate 

the total tree height in feet and divide by the dbh measured in feet. For 

example, a tree 100 ft. tall and 1 ft (12 in.). dbh would have a heightto-diameter ratio of 100. Bending or breaking of tall, thin trees is most 

likely to occur after densely stocked stands or groups of trees are 

thinned.

Insect-Caused Damage

Forest insects can weaken roots, stems, tops, or branches and introduce 

fungal spores that result in wood decay and physical degradation. 

Insects interact with fungal pathogens to cause damage or directly 

kill trees or their parts. Bark beetles in the family Curculionidae are 

important in the Pacific Northwest in causing tree mortality. The most 

important beetles are the Douglas-fir beetle, fir engraver, spruce beetle, 

mountain pine beetle, western pine beetle, and pine engraver. Bark 

beetles frequently attack trees that are stressed from root disease, 

bole damage, defoliation, or drought. Symptoms of bark beetle attack 

include boring dust, pitch streams, galleries under the bark, fading 

or red crowns, dead tops, or group 

mortality (Fig. 56). 

Wood borers also are involved in killing 

trees but usually prefer weaker hosts 

than bark beetles. They also colonize 

recently killed trees. Wood borers 

can significantly lower the structural 

integrity of infested trees because they 

bore into the sapwood and even into 

the heartwood. In SW Oregon, the 

flatheaded fir borer actively kills lowelevation Douglas-fir. Wood borers and 

bark beetles introduce decay fungi as 

trees are being killed. Trees with woodborer holes in exposed wood need to be 

closely examined. 

Fig. 56 – Bark beetles often kill trees 

and form pitch tubes on attacked 

pines.
94

Carpenter ants and termites can colonize and further weaken trees that 

are already decayed. Defoliating insects such as the western spruce 

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

Dead tops of Douglas-fir can remain sound for several decades; dead 

tops of true firs, however, can fail relatively rapidly. Defoliator-killed 

trees or parts should be evaluated in the same fashion as other dead 

trees or parts.

Multiple Defects 

Trees are often encountered with two or more (multiple) defects. The 

potential for tree failure increases dramatically with the combined 

effects of multiple defects. In the case of multiple indicators, 

one condition (indicator) often worsens another; they interact 

synergistically. Some examples of multiple defects that indicate 

increased potential for failure are: 

1. Heart rot and cankers, stem injury, or saprot 

2. Root rot and lean 

3. Cracked forks and heart rot 

4. Wind shake and butt rot 

5. Leaning trees with hollow stems (Fig. 57) 

The sound-rind thickness 

guidelines (Table 3A and B) 

should be used with caution 

when other tree defects that 

worsen the condition are 

present. In this case, trees 

may fail with more than 

the minimum sound-rind 

thickness.

Fig. 57 – Multiple medium-failure indicators can 

imply high-failure potential such as this maple 

with hollow, leaning stems.
95

Chapter 4 - Hazard-Tree Management

Evaluations Prior to Site Development 

Ideally, hazard-tree management begins before there is a final decision 

on where to locate a proposed developed site. A thorough hazard 

evaluation of proposed sites prior to capital investment reveals the 

prudence and feasibility of establishing the site, and it alerts managers 

to problems prior to the investment of scarce resources. Examination 

of sites with old-growth trees prior to site development is particularly 

important because of the predictable decadence of many trees on these 

sites. Unfortunately, this has seldom occurred, as most current sites were 

established many years prior to the advent of vegetation management 

or hazard-tree management.

Old-growth stands, while more aesthetically appealing to many 

recreationists, are less well suited to developed site recreation. Not only 

is defect more abundant, but when old-growth stands are opened to 

establish access, parking, permanent camping spots, and structures, the 

probability of windthrow will usually increase, and continue increasing 

with each repeated salvage or hazard removal entry. Young, thrifty 

stands are more wind-firm, and they respond better and more rapidly to 

spacing entries. Trees in such stands readily re-establish wind-firmness, 

and they resist repeated attacks of insects, diseases, and the damage 

caused by visitors until they reach their pathological-rotation age. 

One possible approach is to conduct a two-phase evaluation. The first 

phase is a thorough evaluation of the stand on the candidate site to 

determine if the candidacy should be further considered. If root disease 

is found, the site should be eliminated from further consideration as 

a developed-recreation site. If the candidate site does not have root 

disease, the second phase is a detailed hazard evaluation of each tree. 

The best time to prepare a complete vegetation-management plan is 

after an informed decision is made to develop a site. This plan should 

include a stem map and information on the condition of each tree 

within striking distance of proposed stationary or moving targets. 

With this information in hand, the forest-resource manager can finalize 

designs, taking advantage of openings where hazardous trees will be 

removed. If it is desirable that the stand be opened in certain areas to 

introduce more light, or increase visibility, trees with varying degrees of 

hazard can be prioritized for removal, and treatment can occur during 

the construction phase. 
96

If a vegetation-management plan has not been developed prior to 

establishing a developed site, hazard management will be reactive 

rather than proactive. In these situations, creativity is important in 

treating hazardous trees. Tree removal may be the least desirable 

option. If the character value, scenic value, wildlife value, or historic 

value of a defective tree is high enough, moving a valuable target may 

be the preferred option. It is always wise to consult with appropriate 

forest-resource specialists to accurately determine the resource value of 

some hazard trees.

Management of Existing Sites

Some hazard trees can be treated without their removal. Others must be 

removed. Trees affected by root diseases and standing, dead trees fall 

into the latter category (see Table 10 for treatment options by category 

of damage). Since resistance to failure is related to the amount of sound 

wood remaining in the butt and stem, many trees with butt defects do 

not require immediate treatment but must be monitored if they are 

retained. Treatment likely will be required at some time in the future. 

Defective trees that present an acceptable amount of risk in the current 

year should be monitored at regular intervals to track intensification of 

the hazards. 

It is important to avoid creating new hazards while treating others. For 

example: 

•	 If large, defective trees are to be felled, care should be taken to 

prevent injury to surrounding trees. 

•	 In sites where stocking levels are high, care should be taken not 

to create canopy gaps that open the stand up for windthrow. 

•	 Prune defective limbs properly to avoid future stem decay. Prune 

branches flush with the branch collar, not flush with the stem. 

Stubs extending beyond the branch collar, both on living and 

dead branches, can allow decay fungi to enter. After pruning, 

do not paint cuts; wound dressings have been shown to 

increase decay in some cases.

•	 When removing true firs, hemlocks, and, on dry sites, ponderosa 

pine, consider treating the newly made stumps with an 

EPA-registered boron compound to reduce the potential for 

Heterobasidion spp. colonization and subsequent incidence of 

annosus root disease (p. 45). 

•	 During construction and rehabilitation activities, avoid damaging 

tree boles and roots to prevent future decay and associated 

hazards. 
97

Topping trees within striking distance of valuable targets is 

recommended only to remove dead tops. Topping live crowns is rarely 

recommended. Removal of live foliage reduces a tree’s ability to feed 

itself through photosynthesis. Topping also creates a large wound 

that can become an entry court for decay fungi. Topping live crowns 

may also attract bark beetles and other damaging insects. Topping 

may eventually lead to forked or multiple tops that may themselves 

subsequently fail. If topping of living crowns is done to create wildlife 

habitat, such trees should not be within striking distance of valuable 

targets.

Table 10. Tree damage and treatment options for developed sites in 

Oregon and Washington

Defect Pruning Topping

Cabling or 

Bracing1

Tree 

Removal

Root and butt rots X

Undermined, severed, 

 or broken roots

X X

Heart rots X X

Sap rots X

Cracked/split boles X X

Bole cankers X X

Bole flattening X X

Forked or multiple tops X

Dead or broken tops X X

Mistletoe brooms X

Defective branches X

Detached branches, tops, or bark remove 

piece

Leaning trees X X

Fire-damaged trees X X

Dead trees X2

1

Cabling or bracing only should be considered when retaining defective but highly valuable or historic 

trees.

2

Dead trees should always be removed when valuable targets are nearby. Developed sites are poor 

places to maintain snags for wildlife. 

In all cases, site closure, target removal or relocation, and/or exclusion of visitors 

from the impact zone are treatment options either alone or in combination, so 

they are not listed above.
98

References and Background Material 

Allen, E., D. Morrison, and G. Wallis. 1996. Common tree diseases of 

British Columbia. Natural Resources Canada/Canadian Forest Service, 

Victoria, B.C. 178p.

Anonymous. 2009. Tree protection on construction and developed sites: 

a best management practices guidebook for the Pacific Northwest. 

Oregon State University Extension Service, EM 8994, Corvallis. 17p.

Edmonds, R.L., J.K. Agee, and R.I. Gara. 2000. Forest health and 

protection. 1st ed., McGraw-Hill Co., Boston, MA. 630p.

Filip, G.M., and D.J. Goheen. 1982. Hazards of root disease in Pacific 

Northwest recreation sites. J. of For. 80(3):163-164.

Filip, G.M., D.J. Goheen, and J.W. Kimmey. 2009. Rust-red stringy 

rot caused by the Indian paint fungus. USDA Forest Service, Pacific 

Northwest Region, FS-R6-RO-FIDL#93, Portland, OR. 11p.

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.

Hagle, S.D. and G.M. Filip. 2010. Schweinitzii root and butt rot of western 

conifers. USDA Forest Service, Pacific Northwest Region, FS-R6-ROFIDL#177, Portland, OR. 8p.

Harvey, R.D. Jr. and P.F. Hessburg, Sr. 1992. Long-range planning for 

developed sites in the Pacific Northwest: the context of hazard tree 

management. USDA Forest Service, Pacific Northwest Region, FPMTP093-92, Portland, OR. 325p.

Mallams, K.M., K.L. Chadwick, and P.A. Angwin. 2010. Decays of white, 

grand, and red firs. USDA Forest Service, Pacific Northwest Region, FSR6-RO-FIDL#52, Portland, OR. 12p.

Mills, L.J. and K. Russell. 1981. Detection and correction of hazard trees 

in Washington’s recreation areas: a how-to guide for recreation site 

managers. DNR Rept. No. 42, Wash. Dept. of Natural Resources, Olympia, 

WA. 37p.
99

Paine, L.A. 1971. Accident hazard evaluation and control decisions on 

forested recreation sites. USDA Forest Service, PSW Research Paper PSW68, Berkeley, CA. 10p.

Smiley, E.T. and B.R. Fraedrich. 1992. Determining strength loss from 

decay. J. of Arboriculture 18(4):201-204. 

Shaw, D.C., P.T. Oester, and G.M. Filip, 2009. Managing insects and 

diseases of Oregon conifers. Oregon State University Extension Service, 

EM 8980, Corvallis, OR. 99p.

Thies, W.G. and R.N. Sturrock. 1995. Laminated root rot in western North 

America. USDA Forest Service/Canadian Forest Service, PNW Research 

Station/Pacific Forestry Centre, PNW-GTR-349, Portland, OR. 32p.

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. 64p.

Trummer, L. and P. Hennon. 2009. Hazard trees in Alaska: a guide to the 

identification and management of hazard trees in Alaska. USDA Forest 

Service, Alaska Region, R10-TP-142, Juneau, AK. 62p.

USDA. 2011. Publically managed recreation opportunities, Chapter 

2330, FSM 2300 Recreation, R6 Supplement No. 2300-2011-1, Pacific 

Northwest Region, USDA Forest Service, Portland, OR. 8 p. 

Wagener, W.W. 1963. Judging hazard from native trees in California 

recreation areas; a guide for professional foresters. USDA Forest Service 

Research Paper PSW-P1, Berkeley, CA. 29p.

Wallis, G.W., D.J. Morrison, and D.W. Ross. 1980. Tree hazards in 

recreation sites in British Columbia: management guidelines. BC 

Ministry of Lands, Parks, and Housing, Can. For. Serv., Joint Rept. No. 13, 

Victoria, BC. 52p.

For additional information and references about hazard trees, see http://

www.fs.fed.us/r10/spf/fhp/hazard/index.htm
100

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 

crumbling 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

Azimuth - a compass reading in degrees going from 00 (north) to 3590

Bark beetles – a group of often destructive forest insects whose adults 

and larvae make galleries in the cambial region of living or felled trees; 

a subfamily of the Curculionidae

Barrier zone of cells – Cells within a plant or tree that form around 

injured tissue as a response to wounding and microorganism invasion. 

These cells restrict the movement of the invading microorganisms

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

Branchlet stub - the remnant of a branchlet (small branch or twig) 

that breaks off near the main branch; often an entrance point for decay 

fungi, especially the Indian paint fungus

Branch whorl – a circle of branches developed from one node on a tree
101

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 

Butt rot - decay developing in and sometimes confined to the butt; 

originating at basal wounds or coming up through roots

Cabling or bracing – cabling is the installation of a cable within a tree 

between limbs or leaders to limit movement and provide supplemental 

support. Bracing is the installation of lag-threaded screws or threaded 

steel rods in limbs, leaders, or trunks to provide supplemental support. 

Both may be used to extend the time trees or their parts remain 

intact. Proper cabling and bracing require skill, hard work, and a keen 

understanding of tree construction. The treatment often wounds trees. 

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 

innermost 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

Catface – a partially healed or grown-over wound on a tree stem 

resulting from fire or equipment use; similar to a scar

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 

Climax stage - the last stage of natural forest succession; a latesuccessional stage usually containing shade-tolerant tree species

Codominant stems – two tree stems of equal size that are joined at the 

base or partway up the trunk
102

Compartmentalization – a process in living trees where woundinfecting microorganisms and subsequent decayed wood are confined 

to compartments within the tree. At least four interior walls restrict the 

movement of microorganisms and decay to adjacent compartments. 

Wall 4, the barrier zone, forms at the cambium after wounding and 

confines decay within a wood cylinder present at the time of wounding. 

Given enough time, all walls eventually will fail resulting in complete 

wood decay. Compartmentalization is repeated each time a tree is 

wounded 

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

Cull (tree) – a tree or tree part that is so highly defective as to be lacking 

in commercial value as a sawlog; a tree that is decayed through much of 

its length 

Cull rules – Values of defect and decay extent that are usually based 

on tree age, dbh, number of indicators (conks, punk knots), or distance 

of indicators above the ground. Cull rules sometimes provide a crude 

estimate of tree-failure potential. 

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

Defect - any feature, fault, or flaw that lowers the strength, integrity, or 

utility of an affected part
103

Delaminate - to separate into sheets as with the pages of a book; wood 

delaminates at the growth rings; characteristic of decay caused by 

Phellinus weirii and some other decay fungi

Developed forest sites – areas within the forest that contain 

human-developed structures, such as buildings, ski lifts, boat ramps, 

parking lots, picnic tables, or campsites that are used for recreation or 

administration

Disease – a prolonged disturbance of the normal form or function of a 

tree or its parts; usually caused by organisms such as fungi or mistletoes 

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 weirii; also called a mortality center or infection center

Distress (stress) cone crop – abundant, small cones that are often 

produced on root diseased trees

Drip line - the maximum radial extension of the tree crown projected to 

the ground

Duff – the partially decomposed organic material of the forest floor 

beneath the litter of freshly fallen twigs, needles, and leaves 

Dwarf mistletoe - a parasitic flowering plant with stems and seeds that 

develops extensive absorption systems in the xylem tissue 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 weirii 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
104

Frost ribs - parallel ridges of callus that form on either side of frost 

cracks which are repeatedly (often annually) aggravated by extreme 

cold

Fruiting body - conk, mushroom, or other fungal reproductive 

structure that produces spores

Fungal thallus - the entire assimilative phase of an individual fungus

Fungus (pl. fungi) - a non-vascular plant 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

Gill – blade-like formation on the underside of some fruiting bodies 

(mushrooms) that bears spores

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 that is within striking distance of 

a permanent or transitory target of value

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

Highly defective - trees or tree parts that possess such substantial 

decay or defect that they are extremely likely to fail

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
105

Inoculum - spores or tissue of a pathogen that serve to initiate disease

Larva (pl. larvae) – the immature stage between egg and pupa in 

insects such as bark beetles or wood borers; examples are maggots, 

caterpillars, or grubs

Lichens – a type of green plant composed of an alga and a fungus that 

grow in symbiotic association. Lichens often grow on tree boles and 

branches and can hide conks or cavities.

Live-crown ratio - the ratio of live-crown length to total tree height; 

usually expressed as a percentage

MCH-pheremone – a natural chemical used to protect down or 

standing high-value Douglas-fir trees from attack by the Douglas-fir 

beetle

Mesic - requiring a moderate amount of moisture 

Minor defect - damage that does not alter the structural integrity of a 

tree or tree part in any significant way

Moderate defect - damage that reduces the structural integrity of trees 

or tree parts but does not render them in immediate danger of failure; 

trees with moderate defect should be monitored. 

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 ostoyae, 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 

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

Parenchyma - the soft tissue of higher plants commonly used for food 

storage
106

Pathogen - a fungus, bacterium, virus, or other infective agent capable 

of causing disease in a particular host or range of hosts

Pathological rotation (age) - age of a forest stand when heart-rot 

fungi decay more wood than is produced; can also refer to loss of wood 

due to mortality induced by root diseases

Photosynthesis – the manufacture of organic compounds, particularly 

carbohydrates, in the chlorophyll cells of plants from carbon dioxide, 

water, and enzymes in the presence of light as the energy source

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

Plant association or community – a plant-group type based on landmanagement potential, successional patterns, and species composition 

Pore - a small hole in the undersurface of a fungal fruiting body from 

which spores emanate

Prophylactic treatment - action to reduce potential of infection or 

infestation 

Pruning – the removal, close to the branch collar, of side branches (live 

or dead) or multiple leaders from a standing tree

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

Ramicorn branch – a branch that protrudes at an acute angle 

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 
107

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 wood 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 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. 

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 or 

healing)

Second-growth (forest) - a relatively young forest that has been 

regenerated either naturally or artificially after some drastic disturbance 

such as extensive felling, wildfire, insect or disease attack, or blowdown; 

also called young-growth (forest)

Seral stage - the first stage of natural forest succession; an early 

successional stage

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 Phellinus pini
108

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, growth 

ring 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)

Silvics – study of the life history and general characteristics of forest 

trees and stands with particular reference to environmental factors

Snag - a standing dead tree often classified by different stages of decay

Spore - a microscopic reproductive propagule of fungi (and other 

cryptogams)

Sporophore - conk, mushroom, or other fungal reproductive structure 

that produces spores 

Springwood – that part of the annual ring of wood that is less dense 

and composed of large-diameter, thin-walled, secondary xylem cells laid 

down early in the growing season; also called earlywood 

Stem - the main trunk or central stalk of a plant; also called a bole in 

trees

Stocking (level) – an indication of growing-space occupancy relative 

to a pre-established standard; common indices of stocking are percent 

occupancy, stand density index, basal area, relative density, and crown 

competition factor 

Structural roots - major tree roots that significantly add to the support 

of a standing tree

Succession (forest) - a continuum of forest development where one 

community of plants is gradually replaced by another

Successional stage - a condition within forest succession; starts with 

the early seral stage and ends with the climax stage

Symptoms (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

Topping - removal of some of the upper crown of a tree; not 

recommended for live crowns
109

Undermined roots - roots that are no longer firmly anchored due to 

soil removal or loss, beneath and/or around them

Vascular (plant or system) - Specialized cells (phloem and xylem) 

within a plant that transport water and nutrients to and from roots and 

foliage

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

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 different strains of fungi or 

the host reaction.

Forked tree, Jubilee Lake campground, Umatilla National Forest
110

Hazard trees at Biglake Campground, Willamette National Forest
111

Cull rules used to identify the extent of red ring rot in Douglas-fir 

west of the Cascade Crest in Oregon and Washington.

Tree age (yrs.) Red ring rot extent

< 125 Trees with conks and defects warrant periodic evaluation

125 to 150 4 ft. above/below conks (punk knots); 2 ft. above/below swollen knots

151 to 200 10 ft. above/below conks (punk knots); 5 ft. above/below swollen knots

201 to 250 13 ft. above/below conks (punk knots); 7 ft. above/below swollen knots

251 to 300 18 ft. above/below conks (punk knots); 9 ft. above/below swollen knots

301 to 350 22 ft. above/below conks (punk knots); 11 ft. above/below swollen knots

Cull rules used to identify the extent of red ring rot in old-growth 

(>125 years) western hemlock and true firs west of the Cascade Crest 

in Oregon and Washington. 

Number of conks Red ring rot extent extent

Single conk 8 ft. above/below conk; 4-ft. above/below swollen knots when accompanying 

conks

Multiple conks 16 ft. above/below lowest and highest conk or punk knot); 

8 ft. above/below swollen knots

Cull rules used to identify the extent of red ring rot in Douglasfir, ponderosa pine, and western larch east of the Cascade Crest in 

Oregon and Washington. 

Tree age (yrs.) Red ring rot extent

< 125 4 ft. above/below conks (punk knots); 2 ft. above/below swollen knots

125 to 200 8 ft. above/below conks (punk knots); 4 ft. above/below swollen knots

201 to 250 12 ft. above/below conks (punk knots), 6 ft. above/below swollen knots

251 to 300 16 ft. above/below conks (punk knots); 8 ft. above/below swollen knots

301 to 350 20 ft. above/below conks (punk knots); 10 ft. above/below swollen knots

>350 24 ft. above/below conks (punk knots); 12 ft. above/below swollen knots

Cull rules used to identify the extent of red ring rot in true fir, 

hemlock, and spruce east of the Cascade Crest in Oregon and 

Washington. 

Tree age (yrs.) Red ring rot extent

<200 8 ft. above/below conks (punk knots); 4 ft. above/below swollen knots

>200 16 ft. above/below conks (punk knots); 8 ft. above/below swollen knots

Appendix
112

Cull rules for white and Shasta red fir in southwest Oregon used to 

estimate defect extent caused by the Indian paint fungus (Filip et 

al. 2009).

Conk age, number, and location: Rust-red stringy rot extent:

Conk is single, small, and young 8 ft. above and below conk

Lowest conk is 0 to 32 ft. from ground

Multiple conks are separated by <25 ft.

12 ft. below lowest conk; 21 ft. above

highest conk

Lowest conk is >32 ft. from ground

Multiple conks are separated by <25 ft.

20 ft. below lowest conk; 21 ft. above

highest conk

Conks are in bottom third of tree Decay in the middle and bottom third of

tree

Conks are in top third of tree Decay in top and middle third of tree

Multiple conks are separated by >25 ft Decay in the entire tree

Cull rules used to estimate defect extent caused by the Indian paint 

fungus for all species in Oregon and Washington.

Tree dbh (in.) Rust-red stringy rot extent:

<19 18 ft. above and below conks

19 to 26.9 18 ft. below lowest conk; 20 ft. above highest conk 

27 to 34.9 21 ft. below lowest conk; 20 ft. above highest conk 

> 34.9 22 ft. below lowest conk; 20 ft. above highest conk 

Cull rules used to identify the extent of red ring rot in western 

white pine and sugar pine east of the Cascade Crest in Oregon and 

Washington. 

Tree age (yrs.) Red ring rot extent

<200 4 ft. above/below conks (punk knots); 2 ft. above/below swollen knots

>200 8 ft. above/below conks (punk knots); 4 ft. above/below swollen knots
113

Signs and symptoms of damaging agents in developed sites in Oregon and Washington. X = the sign/symptom is routinely evident; O = the sign/symptom is occasionally evident

Sign or symptom AR CV ET FC FO FP GA HA HE IT LW OA PI PL PP PS PT PW SSReduced height growth X X O X X O X

Yellow foliage X O X X X

Slow crown decline X X O X O X

Distress cones X 0 X XRapid tree death X O X X O

Basal resinosis X X 0

Windthrown live trees X X X XLive-stem breakage X X X X X X X 0 X X X

Insect galleries under bark X X X X X X XMushrooms X 0 X

Mycelial fans under bark XMycelia in decay 0 X X O O X O 0

Rhizomorphs XPerennial conks X X X X X O X X X OAnnual conks X X X X X XSetal hyphae XRoot pustules XEctotrophic mycelium O O X

Damaging agents: AR=Armillaria spp., CV=Cryptoporus volvatus, ET=Echinodontium tinctorium, FC=Fomitopsis cajanderi, FO=Fomitopsis officinalis, FP=Fomitopsis pinicola, GA=Ganoderma spp., HA=Heterobasidion spp., HE=Hericium abietis, IT=Inonotus tomentosus, LW=Leptographium wageneri, OA=Oligoporus amarus, PI=Phellinus igniarius, PL=Phytophthora lateralis, PP=Phellinus pini, PS=Phaeolus schweinitzii, PT=Phellinus tremulae, PW=Phellinus weirii, SS=Stereum sanguinolentum
114

Sign or symptom AR CV ET FC FO FP GA HA HE IT LW OA PI PL PP PS PT PW SSDelamination pits - 1 side XDelamination pits - 2 sides XYellow stringy decay XWhite-spongy decay X X X

Rust-red-stringy decay XRed-brown-cubical decay X X X XWhite pocket rot X O X OHoneycomb decay X X XConk looks like cow pie XConk with spines XConk at branch stubs X X X O XConk is rose-colored XConk bottom is easily etched XConk is hoof-shaped X O X O 0

Conk looks like coral XConk looks like popcorn X 0

Conk has a red margin (belt) XConks turn red when bruised X

Damaging agents: AR=Armillaria spp., CV=Cryptoporus volvatus, ET=Echinodontium tinctorium, FC=Fomitopsis cajanderi, FO=Fomitopsis officinalis, FP=Fomitopsis pinicola, GA=Ganoderma spp., HA=Heterobasidion spp., HE=Hericium abietis, IT=Inonotus tomentosus, LW=Leptographium wageneri, OA=Oligoporus amarus, PI=Phellinus igniarius, PL=Phytophthora lateralis, PP=Phellinus pini, PS=Phaeolus schweinitzii, PT=Phellinus tremulae, PW=Phellinus weirii, SS=Stereum sanguinolentum

Signs and symptoms of damaging agents in developed sites in Oregon and Washington. X = the sign/symptom is routinely evident; O = the sign/symptom is occasionally evident
115

Equipment recommended for hazard-tree evaluations 

Equipment Intended Use

Pulaski Exposing roots and checking for decay, signs and 

symptoms

Axe or rubber mallet Sounding boles and inspecting stems for sap rot, 

heart rot, insect attack, or dead sapwood

Binoculars Examining stems for conks, punk knots, swollen 

knots and other indicators of stem decay, and for 

examining tree crowns for hazardous branches, 

dead or forked tops, and other defects

Diameter tape Measuring tree or branch diameter

Tape measure Measuring distances to targets or for stem 

mapping

Compass Recording azimuths for stem mapping and 

relationships to reference points

Laser measurer Measuring tree heights and distances

Cordless drill/ increment 

borer

Estimating the rind thickness of sound wood in 

the bole; detecting root and stem decay

Hand lens(10X) Examining advanced decay for setal hyphae and 

other indicators

Field guides Identifying tree species, diseases, insects, and 

defects by their indicators

Data forms Recording data and observations

Tree tags Providing a semi-permanent numbering system 

for trees that will be re-evaluated annually (tags 

are aluminum, numbered in series)

Aluminum nails Securing tags to trees; steel nails rust 

Tree paint or tree flagging Identify trees to be felled or treated; treatment 

should be immediate after marking

This equipment list can be modified to suit budgets and individual needs. These items 

have been routinely used to do a thorough job of recording a baseline evaluation to which 

subsequent annual evaluations and monitoring exams could be tiered. 
116

HAZARD-TREE DATA FORM Page___of___ 

Site name: ______________________ Unit No. or Location:___________________ 

Date: ______ Recorders:_________

Tree

no.

Tree

species

Tree

dbh

(in.)

Tree

height

(ft.)

Defect

height

(ft.)

Target

distance

(ft.)

Root/butt

disease

symptom1

Rind

(in.)2

Root/

butt

cause3

Stem

disease

defect4

Risk rating5 Recommended

treatment6

Treatment

FP DP date

1

Root/buttdisease symptom: DEAD=dead tree, REGR=reduced-height growth, DETO=dead top, DEBR=dead branches, THCR=thin 

crown, YECR=yellow crown, RESN=basal resinosis or weeping, CONK=conk(s) present, FANS=mycelial fans, ECTO=ectotrophic mycelium, 

WNDS=wound, CRACK=cracks

2

Sound-rind thickness in inches; average of four drillings at defect 3

Root/butt disease cause: PW=Phellinus weirii, AR=Armillaria spp., HE=Heterobasidion spp., PS= , IT=Inonotus 

tomentosus, X=unknown, etc. 4

Stem disease/defect: MECH=mechanical injury, FIRE=fire damage, STCR=stress crack, FRCR=frost crack, CANK=stem canker, FORK=forked or multiple top, HANG=detached branch, top, or bark, DMBR=dead mistletoe broom >10 ft. wide; for conks, 

ET=Echinodontium tinctorium, PP=Phellinus pini, CONK=unknown species, etc.); for dwarf mistletoe in live trees, use DMR5=dwarf 

mistletoe rating of 5, BB=bark beetle attack.

5

Risk rating: FP=failure potential (rating: 1 to 4) and DP=damage potential (rating 1 to 4) where 1=very low, 2=low, 3=medium, and 

4=high

6

Recommended treatment: TOPx=top tree where x is the remaining tree height, PRUN=prune branches, FELL=fell tree, BRAC=bracing 

or cabling of tree, MOTA=move target, EXPE=exclude people from target area, MONI=monitor tree
117

HAZARD-TREE EVALUATION

Facility: _______________________ Date: ___________ Evaluators: ____________

68 

Hazard Tree Evaluation

 Facility Date: Evaluators

Location: Top: Branches:

 Site ID Ref. Pt. Bear Dist. OK OK

Tree ID Species DBH Ht. Dying Dying

Dead Recent/ Old Dead

Stem: Detached

 OK Conks Ratings:

Cracks Old Recent Failure Pot. 

Open Length Forks Splitting Included bark Damage Pot.

Closed Ft2 % Lean Hazard Rating

Decayed Min rind Thickness Needed Dia. X 0.15 Photo

Reading Av. 

Roots: Targets 

OK

Exposed Wounded Decayed % Impaired

Comments 

Location: Top: Branches:

 Site ID Ref. Pt. Bear Dist. OK OK

Tree ID Species DBH Ht. Dying Dying

Dead Recent/ Old Dead

Stem: Detached

 OK Conks Ratings:

Cracks Old Recent Failure Pot. 

Open Length Forks Splitting Included bark Damage Pot.

Closed Ft2 % Lean Hazard Rating

Decayed Min rind Thickness Needed Dia. X 0.15 Photo

Reading Av. 

Roots: Targets 

OK

Exposed Wounded Decayed % Impaired

Comments 

Location: Top: Branches:

 Site ID Ref. Pt. Bear Dist. OK OK

Tree ID Species DBH Ht. Dying Dying

Dead Recent/ Old Dead

Stem: Detached

 OK Conks Ratings:

Cracks Old Recent Failure Pot. 

Open Length Forks Splitting Included bark Damage Pot.

Closed Ft2 % Lean Hazard Rating

Decayed Min rind Thickness Needed Dia. X 0.15 Photo

Reading Av. 

Roots: Targets 

OK

Exposed Wounded Decayed % Impaired

Comments 

Scar

Cavity

Canker

Scar

Cavity

Canker

Scar

Cavity

Canker
118

HAZARD-TREE DATA FORM PAGE ____ OF ____

SITE: ___________________________

DATE: ______ / ________ / ________

RECORDERS: ____________________

Tree # Species Location Memo Condition/Notes DBH Sound 

Rind DMR Stem Decay

Root 

Disease

Fail. 

Pot.

Dam. 

Pat.
119

HAZARD-TREE DATA FORM

HAZARD-TREE DATA FORM

SITE:___________________________ Date:______________

Examiner:_______________________ Page___of_____

Tree # Site ID: Ref. Pt. 

Distance: Azimuth:

Species DBH Height Dead Lean Top/branch defect

Stem 

defect/ 

decay

Butt 

rot 

Open

wound/

crack

Diameter 

inside 

bark

Sound

rind 

thickness

Root disease

PF + PD = RATING Recommended TREATMENT

Target(s):

Date & Treatment completed:

Remarks or drawing:

Tree # Site ID: Ref. Pt. 

Distance: Azimuth:

Species DBH Height Dead Lean Top/branch defect

Stem 

defect/ 

decay

Butt 

rot 

Open

wound/

crack

Diameter 

inside 

bark

Sound

rind 

thickness

Root disease

 PF + PD = RATING Recommended TREATMENT

Target(s):

Date & Treatment completed:

Remarks or drawing:
120

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

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

For assistance on State and Private Lands