United States

Department of

Agriculture

Forest Service

Pacific Northwest

Region

Forest Insects and

Diseases Group

R6–FI&D–TP–12–94

September 1994

Effects of the 1980s Western

Spruce Budworm Outbreak on the

Malheur National Forest in

Northeastern Oregon

David C. Powell
“The policy of the United States Department of Agriculture Forest Service prohibits discrimination on the basis of race, color, national origin, age, religion, sex, or disability, familial status, or

political affiliation. Persons believing they have been discriminated against in any Forest Service

related activity should write to: Chief, Forest Service, USDA, P.O. Box 96090, Washington, DC

20090–6090.”
Effects of the 1980s Western

Spruce Budworm Outbreak on

the Malheur National Forest in

Northeastern Oregon

David C. Powell

USDA Forest Service

Pacific Northwest Region

Natural Resources Staff

Forest Insects and Diseases Group

Portland, Oregon

Technical Publication R6–FI&D–TP–12–94

September 1994
Many people contributed to this project over the last 6 years. Tom

Gregg, Bruce Hostetler, Beth Willhite, and Tim McConnell (Pacific

Northwest Regional Office, Portland) provided advice, maps, and other

assistance. John Teply (Pacific Northwest Regional Office, Portland)

provided the original field cards and aerial photographs for each of the

forest inventory plots that were remeasured to obtain budworm-impact

information. Gene Paul (Forestry and Range Sciences Laboratory, La

Grande) arranged for the interpretation of 942 increment cores that

were used to analyze tree growth. George Taylor (Oregon State University, Corvallis) provided precipitation data and advice about its interpretation.

Wayne Long, retired Fire Management Officer for the Walla Walla

Ranger District of the Umatilla National Forest, prepared the silvicultural drawings used for figures 72–81, as well as several other illustrations in this report.

Unless noted otherwise in the figure captions, all photographs were

taken by the author or obtained from U.S. Forest Service photo files.

The report was significantly improved after reviews by Paul Flanagan,

John Hazard, Bruce Hostetler, and Boyd Wickman.

And last, but certainly not least, I express my appreciation and gratitude

for the patience and support provided by my wife Lori, and my family,

especially when a 3-year project ended up taking 6 years.

DAVID C. POWELL was a silviculturist in the Supervisor’s Office of

the Malheur National Forest in John Day, Oregon from November 1987

to October 1991. He is currently Forest Silviculturist for the Umatilla

National Forest in Pendleton, Oregon.

The photograph shows a western spruce budworm moth on the foliage

of a white fir in the Blue Mountains of northeastern Oregon.

The drawing shows a ruby-crowned kinglet feeding on a spruce budworm larva. At least 26 bird species have been documented as budworm predators, but it’s likely that more species than that play such a

role. Mountain chickadees and red-breasted nuthatches are particularly

important budworm predators in the Blue Mountains.

Acknowledgments

The Author

Cover Photo

Title Page

Drawing
TABLE OF CONTENTS v

Contents

MANAGEMENT SUMMARY .............................................................. XIII

INTRODUCTION................................................................................. 1

Evaluating Budworm Impacts .................................................................. 1

Special Project Objectives ........................................................................ 3

AN HISTORICAL PERSPECTIVE ON BUDWORM OUTBREAKS .................. 4

Insect Detection Surveys .......................................................................... 4

The Post–1980 Budworm Outbreak ......................................................... 4

The 1944–1958 Budworm Outbreak ........................................................ 7

Early Budworm Outbreaks ....................................................................... 7

Recent History of Defoliating Insects ....................................................... 7

Budworm Resurgence ............................................................................... 7

Douglas-fir Tussock Moth ........................................................................ 7

The 1963–1965 Tussock Moth Outbreak ................................................. 8

EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT ...................... 9

Distribution of Parklike Pine .................................................................... 9

Native American Burning ....................................................................... 10

Harvesting Food With Fire ..................................................................... 11

Piute Forestry .......................................................................................... 11

Declining Native American Use of Fire ................................................. 11

Interpreting Historical Accounts ............................................................. 11

Early Journal Accounts ........................................................................... 12

Captain Fremont Describes Blue Mountain Forests in 1843 .................. 13

How the Blue Mountains Got Their Name ............................................. 14

Early Forest Surveys ............................................................................... 14

1900-Era Forest Survey .......................................................................... 14

Oregon's Ponderosa Pine Forests in 1910–1911 ..................................... 15

Blue Mountains Ponderosa Pine in 1910–1911 ...................................... 15

Malheur NF Ponderosa Pine in 1906 ...................................................... 16

Fire’s Impact on Pine Forests ................................................................. 17

Fire As A Cause of Forest Damage ......................................................... 18

Malheur NF Fire History ........................................................................ 18

Fires During Euro-American Settlement ................................................ 18

Effect of Sheep Grazing on Fire Spread and Intensity............................ 19

Underburning in Danger of Extinction ................................................... 19

Changes in Forest Resiliency.................................................................. 19

Changes in Insect and Disease Susceptibility ......................................... 19

Plant Succession in Pine–Fir Forests ...................................................... 20

Changes in Forest Health ........................................................................ 21

Loss of Ponderosa Pine........................................................................... 21
vi EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Contents (cont.)

Changes in Ecological Sustainability ..................................................... 24

Fire As A Thinning Agent ....................................................................... 24

Effects of Fire Suppression..................................................................... 24

Changes in Fire Intensity ........................................................................ 25

Awareness of Fire-Caused Changes ....................................................... 25

Was Fire Suppression Justified? ............................................................. 26

EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT ........... 27

Early Timber Harvests in the Blues ........................................................ 27

Malheur NF Harvest History .................................................................. 28

Diameter Limit Cutting .......................................................................... 29

Why Was Diameter-Limit Cutting Used? ............................................... 30

Effects of Partial Cutting ........................................................................ 30

Vegetation Changes Recognized Early ................................................... 31

Budworm Feeding Ladders..................................................................... 31

Recent Harvest Trends By Species ......................................................... 31

THE ECOLOGICAL ROLE OF BUDWORM OUTBREAKS ......................... 34

Insects Provide Diversity ........................................................................ 34

Nutrient Cycling and Down Wood ......................................................... 34

Historical Range of Variation ................................................................. 34

Ecosystem Resilience ............................................................................. 36

Ecological Simplification ....................................................................... 37

Budworm Responds to Vegetation Changes ........................................... 37

Budworm Invigoration............................................................................ 38

Global Climate Change and Budworm Susceptibility ............................ 38

STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS ................ 39

This Study Was Not An Experiment ....................................................... 39

Limitations of Observational Studies ..................................................... 39

Using the Study Results .......................................................................... 39

Remeasuring Mixed-Conifer Inventory Plots ......................................... 39

Plot Selection Criterion .......................................................................... 40

Selected Plots.......................................................................................... 40

Survey Design ......................................................................................... 40

Sampling Methodology .......................................................................... 41

Information Collected ............................................................................. 42

Site Indices ............................................................................................. 42

Yield Capability Estimates ..................................................................... 43

Increment Core Collection...................................................................... 43

Increment Core Measurement................................................................. 43

Radial Increment and Age ...................................................................... 44
TABLE OF CONTENTS vii

Contents (cont.)

Increment Core Shrinkage ...................................................................... 44

Missing Growth Rings ............................................................................ 44

Analysis of Remeasurement Information ............................................... 44

Using Averages During Data Analysis.................................................... 44

Analysis of Geographic Information ...................................................... 44

Analysis of Budworm Impacts ............................................................... 45

IMPACTS OF THE BUDWORM OUTBREAK ........................................... 46

Defoliation .............................................................................................. 46

Topkilling................................................................................................ 46

Direct Mortality ...................................................................................... 46

Indirect Mortality .................................................................................... 46

Reduced Tree Growth ............................................................................. 46

Reduced Volume Production .................................................................. 46

Analysis of Budworm-Caused Impacts .................................................. 56

Budworm Impacts By Tree Species ........................................................ 57

Budworm Impacts By Tree Diameter ..................................................... 58

Budworm Impacts By Tree Height ......................................................... 59

Budworm Impacts By Tree Age.............................................................. 60

Budworm Impacts By Stand Density ...................................................... 61

Budworm Impacts By Live Crown Ratio ............................................... 62

Budworm Impacts By Crown Class........................................................ 62

Budworm Impacts By Site Productivity ................................................. 64

Budworm Impacts By Elevation ............................................................. 65

Budworm Impacts By Slope Gradient .................................................... 66

Budworm Impacts By Aspect ................................................................. 67

Budworm Impacts By Physiographic Position ....................................... 68

Budworm Impacts By Plant Association ................................................ 69

Budworm Impacts By Budworm Host Percentage ................................. 70

Budworm Impacts By Defoliation History ............................................. 71

Budworm Impacts By Defoliation Severity (1986–1989) ...................... 72

Budworm Impacts By Insecticide Treatment History ............................. 73

Future Timber Yields .............................................................................. 74

Computer Modeling Information............................................................ 74

Height Growth Modified For Topkill ..................................................... 74

Management Scenarios ........................................................................... 74

Modeling Results .................................................................................... 75

Consistency With Forest Plan ................................................................. 76

Forest Plan Yield Assumptions ............................................................... 76

MANAGING BUDWORM AND ITS IMPACTS ......................................... 80

Budworm Management Approaches....................................................... 80
viii EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Contents (cont.)

No Action Approach ............................................................................... 80

Direct Suppression Approach ................................................................. 80

Early Use of DDT for Budworm Control ............................................... 80

1980s Budworm Suppression Projects ................................................... 82

Suppression Project Objectives .............................................................. 82

Using Chemical Insecticides................................................................... 84

B.t. Becomes Primary Insecticide ........................................................... 84

B.t. Offers Environmental Benefits ........................................................ 84

Short-Term Stand Vigor Approaches ...................................................... 84

Tree Thinning ......................................................................................... 85

Thinning From Below ............................................................................ 85

Thinning Can Favor Budworm ............................................................... 85

Forest Fertilization.................................................................................. 86

Fertilization and Budworm Resistance ................................................... 86

Timing of Fertilization ............................................................................ 86

Other Benefits of Fertilization ................................................................ 87

Long-Term Silvicultural Approaches...................................................... 87

Stand Clearcutting .................................................................................. 87

Patch and Strip Clearcuts ........................................................................ 87

Seed-Tree Cutting ................................................................................... 87

Shelterwood Cutting ............................................................................... 87

Group Selection ...................................................................................... 92

Single-Tree Selection.............................................................................. 93

Uneven-Aged Management in Mixed Conifer Forests........................... 94

Overstory Removals ............................................................................... 95

Overstory Removals and Budworm........................................................ 95

Understory Removals ............................................................................. 96

Applying Understory Removals ............................................................. 96

Overstory and Understory Removals Compared .................................... 96

Tree Planting ........................................................................................... 97

Tree Pruning ........................................................................................... 97

Pruning for Fire Resistance .................................................................... 97

Prescribed Burning ................................................................................. 98

Prescribed Burning for Silviculture ........................................................ 98

Burning On A Regular Cycle .................................................................. 98

Fall Burns Are Ecologically Preferable .................................................. 99

Burning to Favor Nitrogen-Fixing Plants ............................................. 100

Salvage Logging of Budworm-Caused Tree Mortality ......................... 101

Retaining Some Dead Trees ................................................................. 101

Retaining Some Live Host Trees .......................................................... 102

Biological Legacies .............................................................................. 104

Maintaining Tree Species Diversity...................................................... 105

Natural Enemies of Budworm .............................................................. 105
TABLE OF CONTENTS ix

Contents (cont.)

Birds As Budworm Enemies................................................................. 105

Birds and Dwarf Mistletoe ................................................................... 105

Protecting Arthropods During Management ......................................... 105

FIRE EFFECTS INFORMATION FOR MIXED-CONIFER FORESTS ............ 109

Fire Effects and Project Planning ......................................................... 109

Fire Resistance Ratings ........................................................................ 109

Post-fire Response Ratings ................................................................... 110

Site Type Ratings .................................................................................. 110

ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM.... 137

REFERENCES ................................................................................ 152

APPENDIX 1: COMMON AND SCIENTIFIC NAMES ............................. 170

Bacteria ................................................................................................. 170

Birds...................................................................................................... 170

Herbs..................................................................................................... 170

Insects and Other Arthropods ............................................................... 170

Mammals .............................................................................................. 171

Pathogens .............................................................................................. 171

Trees and Shrubs................................................................................... 171

APPENDIX 2: SURVEY DESIGN AND RELIABILITY OF RESULTS .......... 172

The 1967–1968 Timber Inventory ........................................................ 172

The 1980 Timber Inventory .................................................................. 172

Plot Selection ........................................................................................ 173

The 1988–1989 Budworm Survey ........................................................ 173

Calculating Sample Means ................................................................... 174

Sample Sizes for Tree-Related Variables.............................................. 174

Figures

Figure 1—Distribution of climax forest types in the Blue Mountains ........... 1

Figure 2—Important forest insects of the Blue Mountains in northeastern

Oregon ........................................................................................................ 2

Figure 3—The Malheur NF is located in northeastern Oregon ...................... 3

Figure 4—Common trees of the mixed-conifer zone that are hosts of the

western spruce budworm............................................................................ 5

Figure 5—Common trees of the mixed-conifer zone that are not hosts of

western spruce budworm............................................................................ 6
x EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figures (cont.)

Figure 6—Area defoliated by western spruce budworm and Douglas-fir

tussock moth on the Malheur NF, 1947–1993 ........................................... 8

Figure 7—An open pine stand with a grassy undergrowth............................. 9

Figure 8—A low-intensity ground fire ......................................................... 10

Figure 9—Many ponderosa pines have basal scars caused by underburning, which was common before wildfire suppression efforts began ........ 17

Figure 10—Burned area (acres) on the Malheur NF .................................... 18

Figure 11—Decay in a conifer tree caused by Indian paint fungus .............. 20

Figure 12—Changes in forest cover types for the Malheur NF.................... 22

Figure 13—Change in species composition for selected mixed-conifer

inventory plots on the Malheur NF .......................................................... 22

Figure 14—The distribution of ponderosa pine around 1910–1911, and

mixed-conifer forests around 1980, in Oregon ........................................ 23

Figure 15—Insect and disease impacts vary with stand density................... 24

Figure 16—Fire intensity varies with stand density ..................................... 25

Figure 17—A high-intensity crown fire........................................................ 26

Figure 18—Trees that can tolerate shade are able to get established under

ponderosa pines ........................................................................................ 28

Figure 19—Timber volume harvested on the Malheur NF .......................... 29

Figure 20—Budworm feeding ladder effect in multi-storied stands ............ 32

Figure 21—Timber volume harvested on the Malheur NF in fiscal years

1970–1992................................................................................................ 33

Figure 22—Insects and pathogens are important for biodiversity ................ 35

Figure 23—Vegetation zones of central and southern Blue Mountains ....... 36

Figure 24—Aspen clone in the Blue Mountains .......................................... 37

Figure 25—Diagram of a forest inventory plot ............................................ 41

Figure 26—Budworm defoliation often causes severe growth reductions ... 43

Figure 27—Defoliation occurs as budworm larvae feed on host trees ......... 47

Figure 28—When budworm defoliation persists near the top of a host

tree’s crown, topkill is often the result ..................................................... 48

Figure 29—Occasionally, budworm kills a substantial number of the host

trees in an area.......................................................................................... 49

Figure 30—Proportions by tree class, and causes of mortality, for 130

mixed-conifer inventory plots measured in 1980 and 1988–1989 ........... 49

Figure 31—Defoliation, drought, root diseases, and other causes of stress

can increase a tree’s susceptibility to attack by bark beetles .................... 50

Figure 32—Tree mortality caused by bark beetles on the Malheur NF,

1988–1990................................................................................................ 51

Figure 33—Precipitation record for Austin and Seneca, Oregon ................. 51

Figure 34—Effect of dwarf mistletoe infection on budworm-induced tree

mortality ................................................................................................... 52

Figure 35—Radial growth for budworm host species, 1941 to 1989 ........... 52

Figure 36—Radial growth for nonhost species from 1941 to 1989 ............. 53
TABLE OF CONTENTS xi

Figures (cont.)

Figure 37—Radial growth for host and nonhost trees, and precipitation

for Austin, Oregon, for 1941–1989 .......................................................... 53

Figure 38—Radial growth for host and nonhost trees on inventory plots

affected by the 1944–1958 budworm outbreak ........................................ 54

Figure 39—Host and nonhost tree growth for 1941–1989, and average

growth for 1970–1979 .............................................................................. 54

Figure 40—Radial growth for host trees by defoliation percentage ............. 55

Figure 41—Comparison of live-tree damages in 1980 and 1988–1989 ....... 55

Figure 42—After budworm populations collapse and defoliation ceases,

there can still be long-term impacts from the outbreak............................ 56

Figure 43—Budworm impacts by host species ............................................ 57

Figure 44—Budworm impacts by tree diameter........................................... 58

Figure 45—Budworm impacts by tree height............................................... 59

Figure 46—Budworm impacts by tree age ................................................... 60

Figure 47—Budworm impacts by tree density ............................................. 61

Figure 48—Budworm impacts by live crown ratio ...................................... 62

Figure 49—Crown classes ............................................................................ 63

Figure 50—Budworm impacts by crown class ............................................. 63

Figure 51—Budworm impacts by site productivity...................................... 64

Figure 52—Budworm impacts by elevation ................................................. 65

Figure 53—Budworm impacts by slope gradient ......................................... 66

Figure 54—Budworm impacts by aspect...................................................... 67

Figure 55—Budworm impacts by physiographic position ........................... 68

Figure 56—Budworm impacts by plant association ..................................... 69

Figure 57—Budworm impacts by budworm host percentage ...................... 70

Figure 58—Budworm impacts by defoliation history .................................. 71

Figure 59—Budworm impacts by defoliation severity (1986–1989) ........... 72

Figure 60—Budworm impacts by insecticide treatment .............................. 73

Figure 61—Projected yields in 1990 for pre-outbreak and late-outbreak

conditions ................................................................................................. 76

Figure 62—Projected yields in 2130 for pre-outbreak and late-outbreak

conditions ................................................................................................. 77

Figure 63—Projected timber yields for pre-outbreak and late-outbreak

conditions under a low-density silvicultural regime ................................ 77

Figure 64—Projected timber yields for pre-outbreak and late-outbreak

conditions under a high-density silvicultural regime ............................... 78

Figure 65—Projected timber yields associated with pre-outbreak and

late-outbreak conditions for model component 502................................. 78

Figure 66—1992 mortality update................................................................ 79

Figure 67—Summary of defoliator suppression projects on the Malheur

National Forest ......................................................................................... 81

Figure 68—Trailing plumes of insecticide, an airplane applies DDT .......... 81

Figure 69—Budworm suppression projects completed during the 1980s

on the Malheur NF ................................................................................... 82
xii EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figures (cont.)

Figure 70—Tree thinning ............................................................................. 85

Figure 71—Fertilization of mixed-conifer stands ........................................ 86

Figure 72—Stand clearcutting ...................................................................... 88

Figure 73—Patch clearcutting ...................................................................... 89

Figure 74—Strip clearcutting ....................................................................... 90

Figure 75—Seed-tree cutting ........................................................................ 91

Figure 76—Shelterwood cutting................................................................... 92

Figure 77—Group selection ......................................................................... 93

Figure 78—Single-tree selection .................................................................. 93

Figure 79—Three common stand structures................................................. 94

Figure 80—Overstory removals ................................................................... 95

Figure 81—Understory removals ................................................................. 96

Figure 82—Tree planting.............................................................................. 97

Figure 83—Tree pruning .............................................................................. 98

Figure 84—Bark and lower-stem branching characteristics of a mature

white fir .................................................................................................... 99

Figure 85—Prescribed burning................................................................... 100

Figure 86—Mixed-conifer stand with an undergrowth dominated by

bracken fern............................................................................................ 100

Figure 87—Nitrogen-fixing plants ............................................................. 101

Figure 88—A mixed-conifer stand killed by budworm defoliation ........... 102

Figure 89—Natural resistance to budworm defoliation ............................. 103

Figure 90—A “cull” white fir ..................................................................... 104

Figure 91—Some natural enemies of western spruce budworm ................ 106

Figure 92—Douglas-fir infected with dwarf mistletoe .............................. 107

Figure 93—Thatch ant nest on a mixed-conifer site .................................. 108

Tables

Table 1—Shade tolerance, successional status, and budworm susceptibility

ratings for trees of mixed-conifer forests in the Blue Mountains ............ 21

Table 2—Bark thickness, crown length, and fire resistance rankings for

common trees of the mixed-conifer zone in the Blue Mountains ............ 31

Table 3—Change in selected stand attributes for ponderosa pine forests

near Austin, northeastern part of the Malheur NF, 1910–1980 ............... 35

Table 4—Treatment information for budworm suppression projects completed on the Malheur NF, 1982–1987 ..................................................... 83

Table 5—Fire effects information for plants of mixed-conifer forests ....... 111

Table 6—Distribution of inventory plots by measurement period and

model component ................................................................................... 175

Table 7—Data summary by analysis stratum ............................................. 175

Table 8—Model components that were field sampled ............................... 176
MANAGEMENT SUMMARY xiii

MANAGEMENT SUMMARY

T his report describes a study to determine the effects of westernspruce budworm defoliation on mixed-conifer forests in the

south-central Blue Mountains (Malheur National Forest). Budworm

populations reached outbreak levels in the early 1980s. The area defoliated by budworm feeding increased rapidly to a peak in 1986, and then

declined dramatically in 1987.

Late in 1987, the Forest initiated a special project to determine: 1) how

much tree damage occurred during the outbreak; 2) how budworm

impacts were related to certain tree, stand, and site characteristics; and

3) how future timber yields will be affected by budworm impacts sustained between 1980 and 1989. This report describes the results of that

project. It also provides a history of recent budworm outbreaks, and

describes two management practices that contributed to the extent of

the 1980s outbreak—fire suppression and selective harvesting.

During 1988 and 1989, remeasurements were completed for 130 inventory plots whose species composition in 1980 consisted of 50% or more

budworm host trees (white fir, subalpine fir, Douglas-fir, Engelmann

spruce, and western larch). In addition to typical inventory data, defoliation and topkill information was recorded for each host tree. Increment

cores were collected from 942 trees and analyzed at a dendrochronology laboratory to obtain growth and age information.

Information about defoliation, topkill, and tree mortality was analyzed

for these 17 factors: tree species, tree diameter, tree height, tree age,

stand density, live crown ratio, crown class, site productivity, elevation,

slope gradient, aspect, physiographic position, plant association, budworm host percentage, defoliation history, defoliation severity (1986–

1989), and insecticide treatment history.

In addition to instances where budworm killed host trees directly, indirect mortality from bark beetles, dwarf mistletoe, and other causes

was also examined. The effect of budworm defoliation on tree growth

was evaluated using information from the increment cores. The potential effects of budworm-caused tree damage on future volume production were analyzed using the Blue Mountain Prognosis model.

Some of the results of this study were:

• Between 1936 and 1980, the area of mixed-conifer forest more than

doubled, with a corresponding decline in the acreage of ponderosa

pine forest. On average, each acre of mixed-conifer forest supported

more budworm host trees in 1989 than it did in 1968, particularly for

white fir. Those changes in forest composition, resulting primarily
xiv EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

from wildfire suppression and historical harvesting practices, were

an important reason for the magnitude of budworm defoliation

between 1980 and 1990.

• The area of budworm-caused defoliation was about three times

greater at the height of the 1980s outbreak than at a comparable

point in the previous epidemic (1944–1958). Portions of the defoliated area were treated with insecticides during both outbreaks.

• Douglas-fir sustained more defoliation and mortality than white fir,

although white fir had the most topkill. Other hosts (Engelmann

spruce, subalpine fir, and western larch) comprised only 3.4% of the

sampled trees; they had very little defoliation or topkill, and no

budworm-induced mortality.

• Small trees, especially those in the overtopped and intermediate

crown classes, had the most defoliation, topkill, and mortality.

• In 1982, 1983, 1985, and 1987, portions of the Malheur National

Forest were treated with chemical or bacterial insecticides to suppress budworm populations. There were no significant differences

between treated and untreated areas in the amount of budwormcaused defoliation, topkill, and mortality.

• Between 1980 and 1988–1989, tree mortality on the inventory plots

increased from 6 to 21 percent, and much of the increase was due to

budworm defoliation. Even after accounting for the increased mortality, tree density was still quite high in 1989, when it averaged over

1,200 live trees per acre for the mixed-conifer plots.

• Douglas-firs infected with dwarf mistletoe were apparently killed by

spruce budworm more often than uninfected trees.

• Tree mortality caused by Douglas-fir beetles and fir engraver beetles

increased during the late 1980s; analysis of precipitation records

suggests that budworm-induced stress probably had a greater impact

on bark-beetle activity than a presumed drought.

• The budworm-related radial growth reduction for 1989 alone was

about 40%; cumulative growth reduction for the period of 1984–

1989 was about 27%.

• In 1990, volume reductions attributable to budworm impacts ranged

from 3.2 to 15.2 percent, varying by Forest Plan model component.

Reductions for the model component occupying the greatest acreage

(502) were a substantial 12.9 percent. Further analysis of computerized growth simulations showed that the 1980s budworm outbreak

resulted in a loss of about 9 years of growth.
INTRODUCTION 1

INTRODUCTION

M ixed-conifer forests are abundant in the Blue Mountains of

northeastern Oregon and southeastern Washington (fig. 1). They

provide wood products, forage, water, wildlife habitat, scenic beauty,

recreational opportunities, and many other natural resources. It is

uncertain if mixed-conifer forests can continue to supply those benefits

in the near future because of recent impacts from insects and pathogens,

particularly insects (fig. 2). Since 1980, nothing has affected the health

and vigor of mixed-conifer forests more than an insect called the

western spruce budworm (appendix 1 provides a list of scientific names

for all organisms mentioned in this report).

Figure 1—Distribution of climax forest types in the Blue Mountains. The

Blue Mountains are a large ecoregion encompassing northeastern Oregon and

adjacent parts of southeastern Washington and west-central Idaho (Omernik

and Gallant 1986). Mixed-conifer forest (shown here as the Douglas-fir/

grand fir series) is the most common vegetation type in the Blue Mountains.

In presettlement times, many mixed-conifer sites supported forests of pine

and larch because frequent fires prevented most of the grand firs and Douglas-firs from surviving. [Source: modified from Kuchler 1964.]

By the mid 1980s, budworm populations had reached unprecedented

levels on the Malheur National Forest (NF), which is located in the

south-central portion of the Blue Mountains (fig. 3). As it became

apparent that the budworm outbreak was causing significant impacts in

mixed-conifer forests, the Forest initiated a special project to determine

the extent and severity of budworm damage.

Evaluating

Budworm Impacts
2 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Western spruce budworm

feeds on Douglas-fir,

white fir, grand fir,

subalpine fir, Engelmann spruce, and, to a

limited extent, western

larch. Adults are small

grayish moths that lay

eggs on the underside

of conifer needles.

Larvae tunnel into

young needles and

new buds, leaving a

silken webbing behind. Outbreaks affected extensive areas on the Malheur NF, with more than

460,000 acres defoliated at the height of the 1944–

1958 outbreak, and over 1.3 million acres defoliated

in 1986 during the 1980s outbreak (see fig. 6).

Douglas-fir tussock moth

defoliates true firs and

Douglas-fir from the top

down, killing trees or

setting them up for future

attack by bark beetles.

Outbreaks are cyclic—the

Malheur NF was affected

in 1937–39, 1947–48,

1963–65 (Wickman and

others 1973), and 1992–

93. The 1963–65 outbreak affected about 66,000 acres before being

sprayed with DDT in June, 1965 (see fig. 6).

Douglas-fir beetle kills Douglas-firs by girdling them and

introducing a blue-stain fungus.

Trees weakened by fire, disease, drought, defoliation, or

other stresses are especially

vulnerable to attack. On the

Malheur NF, Douglas-fir beetle

caused considerable amounts of

tree mortality on the heels of

the 1980s budworm epidemic—

more than 115,000 acres were affected in 1989 (see

fig. 32).

Mountain pine beetle kills

lodgepole, ponderosa, whitebark, and western white pines.

It attacks by burrowing toward

the tree’s cambium. Healthy

trees repel an attack by producing enough resin to wash the

beetles out. In a successful

attack, the beetle penetrates to

the cambium within a few

hours, where it introduces a

blue-stain fungus that hitched its way there on the

beetle’s body. The blue-stain fungus eventually

spreads throughout the sapwood and helps kill the

tree. In the Blue Mountains, millions of overstocked

lodgepoles were killed by mountain pine beetle between 1972 and 1978. On the Malheur NF, more

than 110,000 acres were affected in 1989 (fig. 32).

Western pine beetle kills old

ponderosa pines, especially

those weakened by drought or

dwarf mistletoe. In recent years,

it has been attacking dense,

second-growth ponderosa pines

in the Blue Mountains. Like

mountain pine beetle, this insect

carries the blue-stain fungus.

Western pine beetle sometimes

reaches outbreak levels. A particularly severe

outbreak occurred in the southern Blues in 1932,

when entire stands up to 10 acres were killed, and

losses of 15% or more of the stand volume occurred

on extensive areas (Cowlin and others 1942, Weidman 1936). Outbreaks affected almost 10,000 acres

on the Forest in 1988.

Fir engraver attacks

white and subalpine firs

that have been weakened by defoliation,

drought, root disease, or

other factors causing

tree stress. These beetles

caused extensive tree mortality on the Malheur NF

in the late 1980s during a widespread budworm

outbreak—more than 120,000 acres were affected in

1989 (see fig. 32).

Figure 2—Important forest insects of the Blue Mountains in northeastern Oregon.
INTRODUCTION 3

Figure 3—The Malheur National Forest (shaded in black) is one of four

national forests located in the Blue and Ochoco Mountains of northeastern

Oregon.

The special project to evaluate budworm impacts had the following

objectives.

• Describe the history of budworm outbreaks on the Malheur NF, and

discuss how wildfire suppression and selective harvesting may have

contributed to the severity of the recent outbreak.

• Describe the natural role that budworm plays in the forested ecosystems of the Blue Mountains.

• Determine the types and amounts of budworm-related tree damage

that occurred during the recent outbreak (1980 to 1992).

• Describe how budworm impacts were related to certain tree, stand,

and site characteristics such as crown class, tree age, and aspect.

• Determine if future timber yields will be affected by budworm

impacts sustained between 1980 and 1989.

• Describe alternative approaches for avoiding or mitigating budworm

impacts.

• Provide land managers with some supplemental information such as

fire effects data for mixed-conifer forests, and summaries of important budworm literature.

Special Project

Objectives
4 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

AN HISTORICAL PERSPECTIVE ON BUDWORM OUTBREAKS

Those who cannot remember the past are condemned to

repeat it. George Santayana, American philosopher and poet

B udworm is usually an unobtrusive inhabitant of mixed-conifer

forests containing white fir or grand fir,* Douglas-fir, Engelmann

spruce, or subalpine fir (fig. 4). But occasionally, after weather and

other environmental conditions become ideal for its growth and survival, budworm populations explode in what is called an outbreak. When

conditions are not favorable for rapid population increases, budworm is

held in check by ants, birds, spiders, yellowjackets, and other natural

enemies (Torgersen and others 1990). Forests comprised mostly of

pines or western larch have little defoliation risk because those species

are not fed upon by spruce budworm (fig. 5).

* A note about white/grand fir: The Malheur NF lies in a transitional zone

between grand fir and white fir (Steinhoff 1978). Firs on the northern third of

the Forest are primarily grand fir, while those on the southern part are either

white fir, or a white fir/grand fir hybrid. Since most of the Forest has trees

with white fir characteristics, land managers have traditionally referred to all

low-elevation fir as white fir. I will do the same in this document.

The Pacific Northwest Region of the U.S. Forest Service began monitoring the impacts caused by important forest insects in 1947, when the

first aerial-detection survey was completed (Dolph 1980). An aerial

sketch mapping program was initiated to provide information about a

budworm outbreak that began in 1944. In 1947 and 1948, only the Blue

Mountains and other areas with active budworm defoliation were

surveyed. Beginning with the 1949 survey, all commercial forest land

in both Oregon and Washington was sketch mapped, and the effect of

insects other than budworm was also recorded (Whiteside 1956).

The present budworm outbreak apparently began in 1980, when the

Forest Service’s annual insect survey identified 13 areas of defoliation

in the Blue Mountains, one of which was located near the Middle Fork

of Canyon Creek on the Malheur NF (McConnell and others 1980). It’s

also possible that budworm feeding was first noticed four years before

then, when 380 acres of budworm defoliation were identified near

Dixie Mountain on Long Creek Ranger District (Dolph 1980). It is

unknown if the 1976 budworm mapping was ever verified on the

ground; if the mapping was correct, then the 1976 aerial sketch map

could have provided an “early warning” signal of an impending outbreak.

Insect Detection

Surveys

The Post-1980

Budworm Outbreak
AN HISTORICAL PERSPECTIVE ON BUDWORM OUTBREAKS 5

Douglas-fir is common

at lower elevations of

the mixed-conifer zone.

It has short needles on

small stalks (petioles);

shiny, pointed, reddishbrown buds; and twigs

with distinctive leaf

scars where older

needles used to be. Its

cones hang downward

and have three-pointed

or “rat-tail” bracts

poking out from

between the scales.

Douglas-fir has become

much more common

over the last 80 years as

a result of fire suppression. Mature Douglas-firs

resist fire due to their thick bark, but thin-barked

poles and saplings are easily damaged by burning.

Douglas-fir suffers considerable damage from

budworm feeding, but is not preferred as much as

white fir by that important defoliator.

Engelmann spruce is

uncommon in the lowelevation Blue Mountains. It has sharp,

inch-long needles that

are square in cross

section; thin, scaly,

orange or brown bark;

and medium-sized

cones with thin,

papery scales. Although it resists rots

and other diseases,

Engelmann spruce is

occasionally killed in

great numbers by

spruce beetles. Spruce

beetle outbreaks are often triggered by windthrow

that kills some of the larger trees in a stand. Although spruce suffers serious budworm damage in

other areas of the West, that was not the case for

remeasured inventory plots on the Malheur NF.

None of the spruce trees on remeasured plots were

killed by budworm, and few of them experienced

serious topkill or defoliation.

White fir, grand fir,

or a hybrid with

characteristics between the two, is the

most common tree

species in mixedconifer stands of the

Malheur NF. It has

flat or up-curved

needles with white

bands on both sides

of the needle (white

fir), or just the bottom side (grand fir).

Its gray bark is thin

and smooth on young

trees, and has large

blisters containing an aromatic, sticky resin called

balsam. White fir, the favorite food of spruce budworm, has flourished in the fir stands that have encroached on ponderosa pine sites over the last 80

years. By controlling natural underburns, land managers were inadvertently swapping ponderosa pines

and western larches for white firs and Douglas-firs.

Subalpine fir is

uncommon because

very little of the

Blue Mountains is

high enough to

support forests that

are characteristic of

the subalpine zone

(see fig. 23). It has

a slender, spirelike

crown that sheds

the heavy snows of

the high country

where it grows. Its

needles are graygreen and are produced from all

sides of the twig. The thin, gray bark also contains

resin blisters like those of white fir. Its purplish

cones are similar to those of other firs in that they

are produced upright, rather than hanging down like

most conifers. Although subalpine fir suffers

serious budworm damage in other areas of the

West, that was not true for remeasured inventory

plots on the Malheur NF.

Figure 4—Common trees of the mixed-conifer zone that are hosts of the western spruce budworm.
6 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Ponderosa pine is

one of the most

widely distributed

conifers of western

America. Its long,

green needles occur

in bundles (fascicles)

of two or three. The

woody, prickly cones

are green when immature, and purplish

or brown when mature. The bark is

black on young trees

(“blackjacks”), and

an attractive yellow,

orange, or cinnamon color on old trees (“yellowbarks”). Ponderosa pine depends on fire to clear

away accumulations of needles and twigs so its

seeds can find moist mineral soil, and to kill encroaching firs that prevent seedlings from getting

the unobstructed sunlight they need. This valuable

species grows especially well on warm, sunny

slopes, even those at relatively low elevations.

Lodgepole pine probably has

the widest range of any pine in

North America. It has two

short needles in each

bundle, and gray

or orange bark

occurring as

small, thin flakes.

Lodgepole pine

often regenerates

after standreplacing wildfires,

when it forms dense,

even-aged thickets. It

has adapted to fire by

producing small, knobby

cones that require heat to

open. The closed (serotinous) cones are not universal; their presence varies from area to area. This

slender, short-lived tree is well adapted to disturbed

sites, frost pockets, and other harsh environments.

Lodgepole pine seedlings establish easily on the

mineral soil seedbeds created by wildfire, prescribed burning, or timber harvesting.

Western white pine

is not as common in

the Blue Mountains

as in the heart of its

range—northern

Idaho. It has slender, delicate needles

produced in bundles

of five. The cones

are longer than

those of ponderosa

pine. Its bark is

blackish, purplish,

or cinnamon

colored, and

typically breaks up

in a platy, checkerboard pattern.

West-ern white pine is not plentiful today, chiefly

because of losses from white pine blister rust and

timber harvesting. It can be reestablished on suitable sites by planting rust-resistant stock.

Western larch

helps define the

lower Columbia

River basin, an

area encompassing western

Montana,

northern and

central Idaho,

eastern Washington, and

northeastern

Oregon. Its short

needles occur in

tufts of a dozen or

more. Unlike most other

conifers, this tree sheds

all of its needles each fall after they turn a bright,

lemon-yellow color. The small cones have short

bracts protruding from between the scales. Larch is

similar to ponderosa pine in that mature trees easily

survive low-intensity fires, mostly because of their

thick bark and high, sparse crowns. Although

budworm does feed on western larch (Fellin and

Schmidt 1973), it is not a preferred food source and

larch is seldom considered to be a host species.

Figure 5—Common trees of the mixed-conifer zone that are not hosts of western spruce budworm.
AN HISTORICAL PERSPECTIVE ON BUDWORM OUTBREAKS 7

The Blue Mountains have experienced two budworm outbreaks during

the last 50 years—the present one that began in 1980, and an earlier

outbreak which was discovered in its early stages on the Heppner

Ranger District of the Umatilla National Forest in 1944 (Whiteside

1956). By 1945, it is likely that budworm-caused defoliation was also

occurring on the Malheur and Wallowa–Whitman National Forests,

although maps displaying the location of budworm damage were not

available until 1947. On the Malheur NF, this previous outbreak was

eventually controlled by a combination of natural factors and application of a chemical insecticide (DDT) in 1955 and 1958.

Although detailed records are not available for periods before aerial

sketch mapping began in 1947, some information does exist about older

budworm outbreaks. Dolph (1980) noted that minor budworm defoliation was observed in central Oregon near Mitchell in 1931.

Wickman and others (1994) recently identified possible outbreaks by

analyzing the ring patterns of host and nonhost trees growing on the

same site. He inferred that a severe outbreak was present in the northern Blue Mountains between 1898 and 1909; other outbreaks apparently occurred during 1870–78, 1838–42, 1822–30, and 1775–1785. Outbreaks were also active during those same periods in northern New

Mexico (Swetnam and Lynch 1993), which indicates that budworm

fluctuations may have been synchronous over wide areas of the West.

Figure 6 summarizes the area affected by two important defoliators—

western spruce budworm and Douglas-fir tussock moth. It shows that

budworm was causing problems more than 30 years before the present

outbreak began in 1980, and that the 1980s budworm outbreak affected

considerably more area than the 1944–1958 epidemic.

The 1980s budworm outbreak has followed an unexpected pattern—it

grew rapidly to a major peak in 1986, dropped to low levels from 1987

to 1989, and then climbed again in 1990–91 (fig. 6). The 1990–91 increase is referred to as a budworm resurgence, which is somewhat uncommon but has been observed in Canada and other areas of western

North America (Blais 1962). Budworm defoliation dropped once again

in 1992, and disappeared entirely in 1993. Although it is not certain yet,

the precipitous decline in 1993 suggests that the budworm outbreak that

began in 1980 may have finally come to an end.

Cyclic outbreaks of Douglas-fir tussock moth are also common—

portions of the Malheur NF were affected in 1937–39, 1947–48, and

1963–65 (Wickman and others 1973). Pheromone-trap surveys completed from 1990 to 1992 showed that tussock-moth populations were

rising rapidly on some areas of the Forest (Willhite 1993), and new

outbreaks began in 1992. By 1993, tussock-moth defoliation occurred

on about 46,000 acres, primarily on the Burns Ranger District.

Recent History of

Defoliating Insects

Budworm

Resurgence

The 1944–1958

Budworm Outbreak

Early Budworm

Outbreaks

Douglas-fir Tussock

Moth
8 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 6—Area defoliated by western spruce budworm and Douglas-fir tussock moth on the Malheur NF, 1947–1993. The Blue Mountains have experienced two budworm outbreaks during the last 50 years—the present one that

began in 1980, and an earlier outbreak that began in 1944 (Whiteside 1956).

The 1980s budworm outbreak has followed an unexpected pattern—it grew

rapidly to a major peak in 1986, dropped to low levels from 1987 to 1989, and

then climbed again in 1990–91 during a period of budworm resurgence. Budworm defoliation dropped in 1992, and disappeared entirely in 1993. Although it’s not certain yet, the precipitous decline in 1993 suggests that the

recent budworm outbreak may have finally come to an end. Two tussock-moth

outbreaks occurred during this period: a major one in the mid 1960s, and the

present one that began in 1992. [Sources were Dolph (1980), and unpublished

acreage summaries for aerial-sketch maps from 1980 to 1993.]

A major tussock-moth outbreak occurred in the mid 1960s (see fig. 6)

on the southern half of the Malheur NF and a small portion of the

adjoining Ochoco National Forest. Mixed-conifer stands in the Silver

Springs (Snow Mountain), Gold Hill, King Mountain, Antelope Mountain and Vance Creek areas were defoliated between 1963 and 1965.

The outbreak collapsed after 65,945 acres were sprayed with DDT

between June 10 and July 1, 1965 (Perkins and Dolph 1967).

The 1963–1965

Tussock Moth

Outbreak

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

0

200

400

600

800

1,000

1,200

1,400

DEFOLIATION (THOUSAND ACRES)

DF TUSSOCK MOTH

SPRUCE BUDWORM
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 9

EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT

W hen early explorers, missionaries, and emigrants first crossed

the Blue Mountains in the middle part of the 1800s, they encountered a vegetation mosaic that reflected the long-term influence of

fire. Many areas were dominated by open, parklike forests of ponderosa

pine, often with a luxuriant undergrowth of tall grasses reaching as high

as their horse’s belly (fig. 7). Those attractive landscapes had been

created and maintained by low-intensity surface fires (fig. 8) occurring

at frequent intervals, usually every 8–20 years (Agee 1993, Anderson

and others 1987, Cooper 1961, Franklin and Dyrness 1973, Hall 1977,

Marouka 1993, Weaver 1947b).

Figure 7—An open pine stand with a grassy undergrowth. Pioneer journals

(Evans 1990), early forestry surveys (Gannett 1902, Munger 1917), and fire

history studies (Hall 1977) indicate that much of the Blue Mountains had

presettlement forests resembling the area shown in this photograph. By

suppressing underburns, land managers were inadvertently allowing many of

these areas of open pine (typically referred to as “parklike pine”) to be

replaced with white firs, Douglas-firs, and other budworm host trees.

The Blue Mountains did not have a monopoly on open, parklike pine; it

was present in almost every forested region of the western United States, including northeastern California (Laudenslayer and others 1989),

western Montana (Gruell and others 1982, Habeck 1990), central Idaho

(Brock and Brock 1993), Colorado’s Front Range (Marr 1967, Veblen

and Lorenz 1991), and Arizona and New Mexico (Woolsey 1911). Fire

was an important ecological process in areas with parklike pine; for

example, fires in California’s presettlement pine type occurred about

every 8 years between 1685 and 1889 (Show and Kotok 1924).

Distribution of

Parklike Pine
10 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 8—A low-intensity prescribed fire burning at night. Underburning

was an important ecological process for sustaining open, parklike stands of

ponderosa pine. Underburns were slowly-spreading fires with short flame

heights (less than 3 feet) that consumed dried grass, needles, twigs, downed

trees, and underbrush. They were often started by lightning, although native

American ignitions were important too. Underburns favored the thick-barked

ponderosa pines and western larches, while discriminating against the thinbarked white firs and Douglas-firs (Agee 1993, Hall 1977, Maruoka 1993). In

the early 1990s, Bob Mutch and other fire scientists recommended that prescribed fire use be increased tenfold as an option for addressing forest health

concerns in the Blue Mountains (Mutch and others 1993). But proposals to

greatly expand use of prescribed fire raised concerns about protection of

snags and down wood, causing mechanical treatments to also be considered.

Although some of the underburns were started by lightning storms in

mid or late summer (Plummer 1912), many others were ignited by

native Americans (Cooper 1961, Johnston 1970, Robbins and Wolf

1994). When analyzing early journals from the western U.S., Gruell

(1985) found that over 40 percent of the fires were described as being

started by native Americans.

Recent studies concluded that native Americans were far from passive

hunters and gatherers, as they were so often depicted in western novels

and movies. Their activities had a major influence on the structure and

composition of western vegetation. For example, they used hundreds of

plants and animals for food, fiber, shelter, forage, and medicine. Fire

was often their main tool for creating and maintaining the habitats

needed by those species (Martinez 1993).

Native American

Burning
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 11

Fire was used by native Americans to harvest food crops, to clear brush

for improved hunting access, and for entertainment. An example is that

Oregon Indians used smoke to harvest pandora moths infesting pine

forests—the caterpillars would drop from the trees to the ground and

were then gathered for food (Pyne 1982). [It is interesting that most of

the life stages of this insect were used for food—the Klamath and Modoc tribes dug up the pupae (called “bull quanch”), whereas the Piute

tribe gathered and dried the mature caterpillars and combined them

with vegetables in a stew-like dish called “peage” (Patterson 1929).]

The importance of native American burning was frequently noted in

early Forest Service reports about western forests; the following excerpt is a good example (Meinecke 1916).

...the assumption is that our forests today, having been untouched by

man and exposed to the same factors of their surroundings since

times immemorial, must represent more or less exactly the same

character they had 100 or 1,000 years ago. But we have practically no

genuinely virgin forests; in the great majority of commercial accessible stands, man has for centuries practiced some kind of primitive

forestry by setting fires. This “Piute forestry” has changed the aspect

of many stands so completely that the term “virgin forests” is far

from being correctly applied. At best, one can speak of scattered

virgin stands here and there.

It is possible that Blue Mountain forests may have been more “primeval” at the time of white settlement than they were previously. When

Columbus landed in 1492, it is estimated that North America (exclusive

of Mexico and central America) supported at least 3.8 million native

Americans. By 1800, their numbers had been reduced to a million or

less by measles, smallpox, cholera, influenza, and other European

diseases (Denevan 1992). Even though their populations were declining, native Americans may have expanded their use of fire in the early

1700s to promote forage for the horses that they had just acquired for

the first time (Mosgrove 1980).

The effects of fire were occasionally described in the journals of early

Euro-American explorers, missionaries, and emigrants. When reviewing their journal accounts, some of which are provided on the next three

pages, it is important to consider them in an appropriate context

(Forman and Russell 1983).

Many of the journals were written during a period with environmental

conditions particularly conducive to fires. For example, eastern Oregon

underwent a severe drought from 1839 to 1854 (Keen 1937), when

early Oregon Trail emigration occurred and many journals were written.

It is likely that fires were more prevalent during that dry period. By

1861, however, weather conditions had moderated and eastern Oregon

experienced a particularly wet year, resulting in extensive flooding.

Harvesting Food

With Fire

Piute Forestry

Interpreting

Historical Accounts

Declining Native

American Use of

Fire
12 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Portions of many early journals are contained in a recent book entitled

Powerful Rockey: The Blue Mountains and the Oregon Trail, 1811–

1883 (Evans 1990). Some passages from Powerful Rockey that describe

fire and vegetation are provided below; any misspellings or punctuation

errors from the original journals are retained in the excerpts.

...the grass has been lately consumed, and many of the trees blasted

by the ravaging fire of the Indians. These fires are yet smouldering,

and the smoke from them effectually prevents our viewing the surrounding country, and completely obscures the beams of the sun.

Journal of John Kirk Townsend, August 31, 1834.

Townsend’s journal was one of several that described the effect of fires

started by native Americans.

They [mountains] are mostly covered with high bunch grass, which at

this season is quite dry. This often gets on fire, burning for miles and

days together. One of these burnings is in sight of us today. It is on

the opposite side of the river from us, or I should feel alarmed. The

fire in the mountains last night was truly grand. It went to the tops of

them spreading far down their sides. We were obliged to go over after

our cattle at dark and bring them across the stream. The fire extended

for several miles, burning all night, throwing out great streamers of

red against the night sky. This morning there is none visible.

Journal of Esther Hanna, August 15-16, 1852.

Hanna’s comments illustrate how far-reaching the fires were, and how

fast they moved when burning through bunchgrass and other fine fuels.

After dinner, when we had ascended the first hill, we looked back

upon the country we had passed through. I can almost say I never saw

anything more beautiful, the river winding about through the ravines,

the forests so different from anything I have seen before. The country

all through is burnt over, so often there is not the least underbrush,

but the grass grows thick and beautiful. It is now ripe and yellow and

in the spaces between the groves (which are large and many) looks

like fields of grain ripened, ready for the harvest.

Journal of Rebecca Ketcham, September 6, 1853.

Ketcham’s journal eloquently describes the open, grassy, pine stands

that were apparently quite common during presettlement times (fig. 7).

Came to trees, at first quite thin & without underbrush having fine

grass. But as we arose we came to a densly timbered country, mostly

pine & fir. The most beautiful tall straight trees. Our traviling through

the timber was quite difficult as the path wound back and forth and

many logs lay across it.

Journal of Medorem Crawford, September 12, 1842.

Crawford’s observations demonstrate that the Blue Mountains supported more than just open pine stands.

Early Journal

Accounts
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 13

Captain John C. Fremont surveyed the Oregon Trail in the northern

Blue Mountains during fall of 1843. His journals provide detailed

information about Blue Mountains vegetation, although his tree names

are confusing. (His European larch was actually western larch; his

balsam pine was probably grand fir; and his white spruce was undoubtedly Engelmann spruce.) It is interesting that he found larch to be

abundant; the same statement would not be true today for most of the

Blue Mountains.

Fremont’s journals are also valuable because they provide quantified

information about tree dimensions—his journal entry for October 20th

mentioned that tree diameters averaged 38 to 46 inches, with pines

occasionally reaching 80 inches in diameter. Excerpts from his journal

for 3 days in October of 1843 are provided below.

...the mountains here are densely covered with tall and handsome

trees; and, mingled with the green of a variety of pines, is the yellow

of the European larch (pinus larix), which loses its leaves in the fall.

From its present color, we were enabled to see that it forms a large

proportion of the forests on the mountains, and is here a magnificent

tree, attaining sometimes the height of 200 feet, which I believe is

elsewhere unknown. [October 17, 1843.]

...we made an early start, continuing our route among the pines,

which were more dense than yesterday, and still retained their magnificent size. The larches cluster together in masses on the sides of

the mountains, and their yellow foliage contrasts handsomely with

the green of the balsam and other pines. After a few miles we ceased

to see any pines, and the timber consisted of several varieties of

spruce, larch, and balsam pine, which have a regular conical figure.

These trees appeared from 60 to nearly 200 feet in height; the usual

circumference being 10 to 12 feet, and in the pines sometimes 21

feet. In open places near the summit, these trees become less high and

more branching, the conical form having a greater base. [October 20,

1843.]

We continued to travel through the forest, in which the road was rendered difficult by fallen trunks, and obstructed by many small trees,

which it was necessary to cut down. Some of the white spruces which

I measured today were twelve feet in circumference, and one of the

larches ten; but eight feet was the average circumference of those

measured along the road. I held in my hand a tape line as I walked

along, in order to form some correct idea of the size of the timber.

Their height appeared to be from 100 to 180, and perhaps 200 feet,

and the trunks of the larches were sometimes 100 feet without a limb;

but the white spruces were generally covered with branches nearly to

the root. All these trees have their branches, particularly the lower

ones, declining. [October 21, 1843.]

Journal of Captain John Charles Fremont, October 17-21, 1843.

Captain Fremont

Describes Blue

Mountain Forests in

1843
14 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

It is widely believed that the Blue Mountains were named for the bluish

haze which enveloped them during late summer and fall, when fires

were burning (Mutch and others 1993). The two journal entries below

(Beckham 1991, Evans 1990) speculate that their name commemorates

the color imparted by extensive pine stands. In either case, fire was an

important reason for the name because it was not only responsible for

smoke, but also for the pine forests that would have been rare without

underburning.

It is probable that they have received their name of the Blue mountains from the dark-blue appearance given to them by the pines.

Journal of Captain John Charles Fremont, October 17, 1843.

I presume these mountains take their name from their dark blue appearance being densely timbered with pine timber, which being ever

green gives the forest a sombre appearance, besides the limbs of the

trees are all draped with long festoons of dark colored moss or

mistletoe.

Journal of John or David Dinwiddie, August 30, 1853.

Early surveys can provide valuable clues about presettlement conditions, although the surveys were not well quantified. General statements

such as “the forest floor is open, free from underbrush in any quantity,

so much so that it is possible to ride in almost any direction through the

forest without following trails” (Foster 1908) were common in early

surveys. Several early surveys are described next.

The Geological Survey examined Oregon’s forests almost a hundred

years ago. At the time of their survey, federal Forest Reserves were administered by the Department of Interior; the U.S. Forest Service had

not been created yet. The survey found Grant County to be 45% forested, with a total timber volume of 2.37 billion board feet and an average volume of 2,800 board feet per acre. Harney County was only 4%

forested, with a total timber volume of 336 million board feet and an

average volume of 1,300 board feet per acre. All of the timber volume

for both counties was shown as western yellow (ponderosa) pine. Fire’s

effect on vegetation was clearly recognized during the survey, as described in the following passage (Gannett 1902).

...the burns are greatest and most frequent in the most moist and most

heavily timbered parts of the State, and are smaller and fewer where

the rainfall is less and where the timber is lighter. This is owing to the

density and abundance of the undergrowth in the heavily forested

regions, which feeds the fire and vastly increases its heat. In the

comparatively sparsely timbered southern portions of the Coast

Range and the Cascades and in the Blue Mountains, where the forests

are largely or mainly of yellow pine in open growth, with very little

litter or underbrush, destructive fires have been few and small,

although throughout these regions there are few trees which are not

marked by fire, without, however, doing them any serious damage.

How the Blue

Mountains Got

Their Name

1900-Era Forest

Survey

Early Forest

Surveys
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 15

The first comprehensive study of Oregon’s ponderosa pine forests was

completed between 1910 and 1915 by the U.S. Forest Service (Munger

1917). The study found that more than 71 billion board feet of pine occurred on about 10 million acres of commercial forest land (see map in

top half of fig. 14). The total area of ponderosa pine in Oregon, including noncommercial stands, was about 14 million acres, almost a quarter

of the State and half of its forested land (Donk and others 1921).

Oregon’s largest concentration of ponderosa pine was in the Blue

Mountains; they had 42.7% of the commercial acreage and 43.9% of

the volume. Grant County ranked fourth of Oregon’s counties—about

8.2 billion board feet of pine was present on about 1.2 million acres.

Munger’s study also examined fire history, stand conditions, insect and

disease impacts, and a variety of other topics. The following excerpts

from his report describe stand conditions and fire effects in ponderosa

pine forests of the Blue Mountains (Munger 1917).

In most of the pure yellow-pine forests of the State the trees are

spaced rather widely, the ground is fairly free from underbrush and

debris, and travel through them on foot or horseback is interrupted

only by occasional patches of saplings and fallen trees. The forests

are usually not solid and continuous for great distances, except along

the eastern base of the Cascades, but are broken by treeless “scabrock ridges,” or natural meadows.

In the Blue Mountains the herbage is rather more luxuriant and varied

than on the eastern slopes of the Cascades and their outstanding ranges. In the early summer the open yellow-pine forests are as green

with fresh herbage as a lawn, except here and there where the green

is tinged with patches of yellow or purple flowers. Some of this

luxuriant herbage is pine grass (Calamagrostis sp.), a plant which is

not eaten by stock except very early in the season; but much of the

ground cover makes excellent range for cattle and sheep.

In the Blue Mountains western larch (Larix occidentalis) is its

[western yellow pine] usual companion and grows with it in an

intimate and harmonious mixture. In the moister situations white fir

(Abies concolor) is a common associate, as is also Douglas fir

(Pseudotsuga taxifolia) in most parts of the State. In the Blue Mountains it is common for the south slopes to be covered with a fine stand

of yellow pine, while the north slopes are covered almost entirely

with larch, white fir, and Douglas fir.

In the Blue Mountains the reproduction of yellow pine is very

abundant, both in the virgin forest and after cuttings. Perhaps it is

more prolific here than anywhere else. In this region where an area

has not been burned over by a surface fire for a number of years,

there is quite commonly a veritable thicket of little trees from a few

inches to several feet high. Actual counts have shown that there are

sometimes 14,000 seedlings on a single acre, the ages ranging from

13 to 21 years.

Blue Mountains

Ponderosa Pine in

1910–1911

Oregon’s Ponderosa

Pine Forests in

1910–1911
16 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

In pure, fully stocked stands in the Blue Mountains region there are

commonly from 20 to 30 yellow pines per acre over 12 inches in

diameter, of which but few are over 30 inches. Over large areas the

average number per acre is ordinarily less than 20. In mixed stands

the number of yellow pines of merchantable size is naturally less,

though the total number of trees of all species is as a rule larger, the

moist soil on which the mixed forest grows being able to carry a

denser stand.

Yellow pine grows commonly in many-aged stands; i.e., trees of all

ages from seedlings to 500-year-old veterans, with every age gradation between, are found in intimate mixture. Usually two or three or

more trees of a certain age are found in a small group by themselves,

the reason being that a group of many young trees usually starts in

the gap which a large one makes when it dies.

Light, slowly spreading fires that form a blaze not more than 2 or 3

feet high and that burn chiefly the dry grass, needles, and underbrush

start freely in yellow-pine forests, because for several months each

summer the surface litter is dry enough to burn readily. Practically

every acre of virgin yellow-pine timberland in central and eastern

Oregon has been run over by fire during the lifetime of the present

forest, and much of it has been repeatedly scourged. It is sometimes

supposed that these light surface fires, which have in the past run

through the yellow-pine forests periodically, do no damage to the

timber, but that they “protect” it from possible severe conflagrations

by burning up the surface debris before it accumulates. This is a mistake. These repeated fires, no matter how light, do in the aggregate an

enormous amount of damage to yellow-pine forests, not alone to the

young trees, but to the present mature merchantable timber.

A careful cruise of every tree on 154.5 sample acres in typical

yellow-pine stands in several localities in the Blue Mountains

showed that 42 out of every 100 trees were fire-scarred.

Ordinarily, a fire in yellow-pine woods is comparatively easy to

check. Its advance under usual conditions may be stopped by patrolmen on a fire line a foot or so wide, either with or without backfiring.

The open character of the woods makes the construction of fire lines

relatively easy, and in many places horses may be used to plow them.

The Malheur NF had extensive areas supporting open stands of ponderosa pine, possibly some of the finest pine stands in the western

United States (Erickson 1906):

The forest in the region south of the Strawberry range that bears

excellent yellow pine and tamarack covers approximately 800,000

acres. The yellow pine is more abundant and is found in more suitable situations on this reserve than I have seen its occurrence in any

other part of Oregon. It grows tall and straight, maintains a uniform

taper, and furnishes a large percentage of clear length. Trees thirty to

fifty inches in diameter, with height of 150 feet, are not uncommon.

Malheur NF

Ponderosa Pine in

1906
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 17

Two of the studies described earlier illustrate the differing perceptions

of fire’s role in ponderosa pine forests. Gannett (1902) surveyed the

federal forests before they were viewed as a source of commodities; he

found many trees with fire scars (fig. 9), although fire had not done

“them any serious damage.” Munger (1917) also found few stands

without some sign of fire’s influence, but he viewed fire as a scourge

which caused an “enormous amount of damage to yellow-pine forests.”

Munger’s comments reflect the commodity orientation of his era;

yellow pine forests were to be managed as a sustainable source of

valuable wood products, and fire was perceived as little more than an

obstacle to reaching that goal.

Figure 9—Many ponderosa pines have basal scars caused by underburning,

which was common before wildfire suppression efforts began around 1910.

Ponderosa pine is well adapted to handle the effects of low-intensity fire. At a

diameter of about 2 inches, it begins to develop a fire-resistant bark with a

dead outer layer that insulates the sensitive cambium tissues from heat.

Fire’s Impact on

Pine Forests
18 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Munger’s (1917) opinion of fire’s role in ponderosa pine forests was

shared by other investigators working in the western United States, as

demonstrated by the following passage from The Role of Fire in the

California Pine Forests (Show and Kotok 1924).

Physical conditions in the pine forests of California have led to the

frequent recurrence of fires for centuries, but the fact that magnificent forests still cover large areas and give the appearance of wellstocked, vigorous stands has blinded the public to the harm that fires

have done and are steadily working throughout the whole region.

Were it possible for the observer to visualize the entire area on which

pine has grown, and to behold it truly fully stocked, he would then

see by comparison that the present California pine forests represent

broken, patchy, understocked stands, worn down by the attrition of

repeated light fires.

Fire suppression efforts began immediately after creation of the Malheur NF in 1908. During the first decade of its existence, several large

burns occurred on the Forest (fig. 10). In 1910, a bad fire year throughout the western U.S., a total of 28,769 acres burned. Another 10,637

acres burned in 1915, followed by 30,828 acres in 1919. The next two

decades had few large fires. But in 1939, following a severe drought in

the mid 1930s, 10,734 acres burned (USDA Forest Service 1961).

Figure 10—Burned area on the Malheur NF, showing acreage burned by

wildfire between 1909 and 1960. [Source was USDA Forest Service 1961.]

Large fires were common during settlement of the Pacific Northwest.

Many fires were set by the emigrants, either accidentally or intentionally. Miners often set fires to clear away brush and forest debris, thereby

exposing rock outcrops for inspection by prospectors (Veblen and

Lorenz 1991). Correspondence from a northern California national

forest indicates that some early fires were started by livestock permittees to remove brush and promote grass growth (Harley 1918).

Fire As A Cause of

Forest Damage

Malheur NF Fire

History

Fires During EuroAmerican

Settlement

1909

1912

1915

1918

1921

1924

1927

1930

1933

1936

1939

1942

1945

1948

1951

1954

1957

1960

0

5

1 0

1 5

2 0

2 5

3 0

3 5

BURNED AREA (THOUSAND ACRES)
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 19

Even though emigrants caused some fires, they also contributed to conditions that limited fire intensity and spread. For instance, immense

bands of sheep grazed in the Blue Mountains during the latter part of

the nineteenth century, which caused enduring changes in the vegetative

composition (Coville 1898, Tucker 1940).

An early survey of sheep ranges found moist mountain meadows that

were entirely devoid of vegetation and experiencing severe soil erosion.

A complete collection of the plants growing in a heavily-grazed

meadow found not a single perennial species, and no annuals exceeding

2 inches in height. Few shrubs other than snowbrush ceanothus had not

been damaged by sheep browsing; even the small ponderosa pines were

fed upon (Griffiths 1903).

After sheep removed most of the herbaceous vegetation from beneath

forest stands, it was very difficult for fires to spread through them. That

was particularly true for open stands of ponderosa pine because herbaceous vegetation was an important fuel component.

Natural underburns are now endangered or extinct following a long

period of fire suppression. Land managers responded to wildfire with

an arsenal of slurry “bombers,” mountaintop fire lookouts, aerial

reconaissance flights, radar-assisted lightning detectors, and crews of

elite smokejumpers and specially-trained “hotshot” firefighters. In

many respects, fire suppression has been effective enough to be considered the most successful program in the U.S. Forest Service’s history.

Many land managers would agree that wildfire suppression was a policy with good intentions, but it was a policy that failed to consider the

ecological implications of a major shift in species composition. White

firs and Douglas-firs can get established under ponderosa pines in the

absence of underburning, but they may not have enough resiliency to

make it over the long run, let alone survive the next drought. This

means that many of the mixed-conifer stands that have replaced ponderosa pine are destined to become weak, and weak forests are susceptible to insect and disease outbreaks (Hessburg and others 1994).

By controlling natural underburns, land managers allowed fire-resistant

pines and larches to be replaced with shade-tolerant, late-successional

species. Many of the replacement species are susceptible to the effects

of western spruce budworm, Douglas-fir tussock moth, Indian paint

fungus, Armillaria root disease, and other insects and pathogens.

Indian paint fungus, a widespread pathogen of true firs in the Blue

Mountains (Seidel and Beebe 1983, Filip and Schmitt 1990), can cause

substantial amounts of tree decay (fig. 11). The budworm susceptibility

for major tree species of mixed-conifer forests is apparently related to

their shade tolerance and successional status (Table 1).

Effect of Sheep

Grazing on Fire

Spread and

Intensity

Underburning in

Danger of

Extinction

Changes in Forest

Resiliency

Changes in Insect

and Disease

Susceptibility
20 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 11—Decay in a conifer tree caused by Indian paint fungus. Indian

paint fungus is a common pathogen of older white fir trees in the Blue Mountains. The fungus usually enters the trunk after a long growth period in a

dying branch. When many branches die at about the same time, the fungus

may convert the entire central column of the trunk into a stringy, fibrous mass

of decayed material.

The successional roles of ponderosa pine and white fir were recognized

by early silvicultural researchers, as explained in the following comments about pine–fir forests of the Sierra Nevada mountains in central

California (Dunning 1923).

Where natural conditions of site favor white fir, this species is destined to succeed yellow pine unless the normal succession is disturbed by fire or other accidents. Fir seeds germinate more abundantly than pine under stands of yellow pine, whose litter and shade

exclude their own seedlings, and the young [fir] trees endure suppression longer. Moreover, height growth of fir is more rapid, and the

total height attained is greater than for yellow pine. In the past

occasional fires have been primarily responsible for sustaining

yellow pine on fir sites. Fir seedlings and young trees are far more

susceptible to fire damage than the pine because of their thinner bark

Plant Succession in

Pine–Fir Forests
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 21

with balsam cysts, more inflammable foliage, and small resinous

terminal buds which are far less resistant than those of yellow pine.

The fir is more often eliminated by fungi entering through fire scars

than is pine. Exposure of mineral soil and openings created by fire

favor yellow pine. Striking examples of the succession of white fir

with fire exclusion may be seen in many places, where the mature

stand is composed of practically pure yellow pine, while the reproduction beneath it is over 90 per cent white fir.

Table 1—Shade tolerance, successional status, and budworm susceptibility ratings for trees of mixed-conifer forests in the Blue Mountains.

SHADE SUCCESSIONAL BUDWORM

TOLERANCE STATUS SUSCEPTIBILITY

Subalpine Fir (most) Subalpine Fir (latest) White/Grand Fir (most)

White/Grand Fir White/Grand Fir Douglas-fir

Engelmann Spruce Engelmann Spruce Subalpine Fir

Douglas-fir Douglas-fir Engelmann Spruce

Western White Pine Western White Pine Western Larch (least)

Ponderosa Pine Ponderosa Pine Pines (nonhosts)

Lodgepole Pine Western Larch

Western Larch (least) Lodgepole Pine (earliest)

Sources: Daniel, Helms and Baker (1979) for shade tolerance; author’s

judgment for successional status; and results of this study for budworm

susceptibility. Species ratings are based on the predominant situation for

each trait. A trait can vary during the lifespan of an individual tree, and from

one individual to another in a population—ponderosa pine can tolerate some

shade when young, but requires almost full sunlight when mature.

Perhaps the recent deterioration of forest health is nature’s response to

vegetation changes that occurred after fire was prevented from playing

its natural role. How significant were the changes? Figure 12 shows

that the ponderosa pine type declined by more than half between 1936

and 1980, the mixed-conifer type almost tripled during that period,

whereas the lodgepole pine type remained relatively constant. Figure 13

shows that, on average, each acre of mixed-conifer forest supported

more budworm host trees in 1989 than in 1968, especially for white fir.

The species trends in figures 12 and 13 reflect a steady loss of ponderosa pine since the early 1900s (fig. 14). An early survey completed

around 1910 found that stands in a watershed at the head of one branch

of the John Day River contained 84% ponderosa pine, 9% western

larch, and 7% Douglas-fir, white fir, and lodgepole pine (Munger

1917). Another survey completed in the late 1930s found that the

ponderosa pine type “is remarkably pure, averaging 94 percent ponderosa pine in Oregon and 92 percent in Washington. Stands are characteristically uneven-aged and open, with little heavy underbrush. The

ground cover is chiefly grass or low shrubs” (Cowlin and others 1942).

Loss of Ponderosa

Pine

Changes in Forest

Health
22 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 12—Changes in forest cover types for the Malheur NF. The ponderosa pine forest type declined by more than half between 1936–37 and 1980,

the mixed-conifer type increased by an equivalent amount during the same

period, whereas the lodgepole pine type remained relatively constant. This

figure shows that prime budworm habitat (mixed-conifer forest) increased by

195% between 1936–37 and 1980, which was an important reason for the

magnitude of budworm defoliation between 1980 and 1992 (see fig. 6).

[Sources were Jones and others (1961), Lauridsen (1937), Moravets (1936),

Teply (1980), and USDA Forest Service (1970).]

Figure 13—Change in species composition for selected mixed-conifer inventory plots on the Malheur NF. The percentage of ponderosa pine, Douglas-fir,

and larch/other trees declined between 1968 and 1989, whereas lodgepole

pine had both increases and decreases during that period. But the most

obvious change was for white fir—it increased by 18% from 1968 to 1989.

This figure provides another reason for severe budworm defoliation in the

1980s—each acre of mixed-conifer forest supported a higher proportion of

budworm’s preferred food source (white fir) in 1989 than in 1968. [Based on

51 inventory plots measured in 1967–1968, 1980, and 1988–1989.]

PO NDERO SA PINE M IXED -CO NIFER LO DGEPO LE PINE

0

10

20

30

40

50

60

70

80

AREA (PERCENT)

1937

1959

1968

1980

LARCH/OTHER

PONDEROSA PINE

LODGEPOLE PINE

DOUGLAS-FIR

W HITE FIR

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

LIVE TREES (PERCENT)

1968

1980

1989
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 23

Figure 14—The distribution of ponderosa pine around 1910–1911 (above),

and mixed-conifer forests around 1980 (below), in Oregon. The upper map

shows that a high proportion of the Blue Mountains was covered with ponderosa pine forests during an early survey completed in 1910–1911 (modified

from Munger 1917). The lower map shows the distribution of mixed-conifer

forests by 1980 (modified from Seidel and Cochran 1981). It is obvious that

much of the Blue Mountains area supporting mixed-conifer forest in 1980

was previously dominated by ponderosa pine. Forest inventory statistics

corroborate the trend displayed on these maps (see fig. 12).
24 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Fire was traditionally viewed as an undesirable disturbance, but it was

an important ecological process in presettlement pine forests. In the

dryer ecosystems found east of the Cascade Mountains, natural decomposition of needles, twigs, and other forest litter occurs slowly. Lowintensity fire was important for periodically cycling the litter’s rich

supply of nutrients (Crane and Fischer 1986). Cool burns result in slight

increases in available nitrogen, whereas severe fires cause high levels

of nitrogen loss. High nitrogen losses often cause a decline in site

productivity (Harvey and others 1989, Harvey and others 1994).

Fire was also an important thinning agent (Weaver 1947a, 1957). Thinning was needed because ponderosa pine stagnates when growing in

dense, crowded stands. If dense stands were not thinned by fire, their

density was eventually reduced by bark beetles or pathogens (fig. 15).

Since fire’s influence was so pervasive, underburned pine stands were

stable, ecologically sustainable systems (fire-dependent communities).

Figure 15—Insect and disease impacts vary with stand density. Because open

stands have higher vigor levels than dense stands, they tend to be more resistant to insect and disease impacts. Maintaining a wide stand spacing results

in a condition where the trees are not competing with each other. Vigorous

trees can withstand attack from many different insects and pathogens.

After fires were suppressed, the effects were eventually dramatic. Multi-storied stands of budworm hosts got established, often at high densities. Thick layers of organic matter accumulated beneath the invading

fir trees, tying up nitrogen and other nutrients that are cycled slowly

without fire. Little natural mortality occurred, and the trees that died

were usually the small pines and larches that succumb to suppression

before the firs. Fuels accumulated at an alarming rate. Herbage production declined substantially, affecting both native and introduced ungulates. Stream flows were reduced by a third or more because dense tree

stands use more water than open ones (Covington and Moore 1994).

Changes in

Ecological

Sustainability

Fire As A Thinning

Agent

Effects of Fire

Suppression
EFFECTS OF FIRE SUPPRESSION ON BUDWORM HABITAT 25

Increased insect attacks are just one effect of fire suppression; perhaps a

more dramatic symptom was the catastrophic wildfires of 1989 and

1990 (Glacier, Corral Basin, Snowshoe, Sheep Mountain, and Whiting

Springs on the Malheur NF). Catastrophic fires occurred because fire

suppression allowed fuel loads to reach unnatural levels, and because

mixed-conifer forests tend to have dense, multi-layered canopies, which

provide “ladder” fuels allowing a ground fire to climb into the tree

crowns (fig. 16). Crown fires are intense and generally kill the whole

stand. Even though current technology allows low- and moderateintensity fires to be controlled, it is almost impossible to extinguish

high-intensity wildfires in heavy fuels—they burn until the fuel is gone

or until the weather changes (fig. 17).

Figure 16—Fire intensity varies with stand density. When a fire moves

through an open stand with widely-spaced trees, it stays on the ground as a

low-intensity burn. But when fire encounters a dense, closely-spaced stand, it

is much more likely to leave the ground and begin moving through the intermingled tree crowns, which usually kills the stand.

This section described how fire suppression contributed to dramatic

changes in forest composition. Were those changes recognized only

recently? Apparently, many of the changes caused by fire suppression

have been recognized for quite some time. The following passage

describes fire-related changes occurring shortly after establishment of

the Blue Mountains National Forests (Evans 1912).

There are patches of “scabland,” characterized by very shallow soil,

many rock fragments and a total absence of vegetation except in the

spring months. It is interesting to note that some of these areas are

being occupied by sagebrush where a few years ago, there was none.

A possible explanation is that the annual fires of the Indians kept it

killed out and now it has a chance to develop. Yellow pine is slowly

encroaching upon the sagebrush, the chief factor in its rate of advance being moisture, provided fire is kept out. The same statement

Changes in Fire

Intensity

Awareness of FireCaused Changes
26 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

will hold true in regard to the other open areas as well. As fast as the

reproduction has pushed out from under the protection of the parent

trees, the periodical fires have killed it back, thus keeping the timber

line practically stationary. In recent years, conditions have improved,

and it is noticeable that the pine is reaching out, although slowly. The

north slopes [are] being occupied by a thick stand of fir reproduction.

Even pine is gaining a foothold here, and is gradually creeping across

the ridge to the south slopes.

The following questions and observations were made by a prominent

fire researcher over fifty years ago (Weaver 1943).

It is obvious that the present policy of attempting complete protection

of ponderosa pine stands from fire raises several very important problems. How, for instance, will the composition of the reproduction be

controlled? If ponderosa pine is desired on vast areas how, unless fire

is employed, can other species such as white fir be prevented from

monopolizing the ground? On the other hand, if it is decided to permit such species as white fir to come in under mature ponderosa pine,

how much of the public’s money are foresters justified in spending in

trying to keep fire out? Even with unlimited funds, personnel, and

equipment, can they give reasonable assurance that they can continue

to keep such extremely hazardous stands from burning up? If they

feel reasonably sure of this, can they then give assurance that the

timber products of such stands will be more valuable than those that

might otherwise be derived from ponderosa pine and will in addition

justify the high protection costs?

Figure 17—A high-intensity crown fire. In dense forests with large amounts

of fuel, fires are very intense and travel rapidly from one tree crown to another. Crown fires were an important process for perpetuation of lodgepole pine

and western larch forests, although any particular area seldom experienced a

stand-replacing crown fire more often than once every 200 or 300 years.

Was Fire

Suppression

Justified?
EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT 27

EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT

F ire suppression allowed multi-storied stands to develop across

much of the Malheur NF (fig. 18). They typically had an overstory

of old-growth ponderosa pine and western larch, and an understory of

Douglas-fir, white fir, and occasionally lodgepole pine. When those

stands were harvested, much of the ponderosa pine was removed for

these reasons:

• The pine was usually old (often 200 years or more) and was adding

little or no timber volume because of its slow growth. Since old

pines often have low vigor and little resistance to insect attack, they

were harvested before being attacked and killed by western pine

beetle or mountain pine beetle. One reason for low vigor in oldgrowth pine trees was competition from a dense understory, an

understory that would not have been present if underburning had

been allowed to play its natural role.

• Old-growth ponderosa pine has historically had a much higher

selling value than associated species such as Douglas-fir, white fir,

western larch, and lodgepole pine. Because of its economic advantage, harvesting ponderosa pine provided an abundance of Knutson–

Vandenberg (K–V) receipts, which could then be used for tree

planting, thinnings, wildlife and range projects, and other land

management treatments within the timber sale area.

• As forestry intensified in the early 1950s to meet increasing lumber

demands after World War II (MacCleery 1992), mixed-conifer

stands began to be managed. Mature pines and larches were removed

from the overstory, followed by a thinning in the immature understory of Douglas-fir and white fir. That strategy seemed to make good

sense. It avoided the cost of tree planting, an expensive practice. It

avoided the undesirable appearance associated with clearcutting. It

maintained the semblance of a green, forested setting. And it capitalized on the previous growth of the understory trees, many of which

had been there for 60 years or more. The understory trees were a gift

of nature (i.e., not a result of human management). Why shouldn’t

they provide the next “crop” of timber products?

Some level of selective harvesting has been occurring ever since the

Blue Mountains were settled by European emigrants. The first commercial logging in the Northwestern pine region of eastern Oregon and

Washington began around 1890 (Weidman 1936), although limited

harvesting occurred during the preceding 25 years to meet the needs of

miners and early settlers. Some of the first roads reaching into the Blue

Mountains were wagon roads for hauling wood and rails out to farms

and ranches. Timber met a variety of needs, including logs for homes,

Early Timber

Harvests in the

Blues
28 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

posts and poles for corrals, and rails for fencing. The resinous, durable

woods of ponderosa pine and western larch were ideal for meeting

many homesteading needs (Robbins and Wolf 1994, Tucker 1940).

Timber removals accelerated after gold was discovered in Griffin

Gulch, located a few miles southwest of Baker City, in the fall of 1861.

Prospectors poured into the Blue Mountains shortly thereafter, quickly

establishing Auburn, Canyon City, Granite, Sumpter, Susanville, and

other mining settlements. By 1890, Baker, Union, and Grant counties

had a combined population of 23,900 (Lindgren 1901).

Figure 18—Trees that can tolerate shade are able to get established under

ponderosa pines, such as the white firs and Douglas-firs clustered around the

base of this pine. If the overstory pines and larches are eventually harvested, a

multi-layered stand of late-successional trees remains, and most of them are

highly susceptible to infestation by budworm and Douglas-fir tussock moth.

Controlled timber harvesting began on the Malheur NF soon after its

establishment in 1908. Prior to 1917, when the Oregon Lumber Company built a sawmill at Bates, the Forest provided small sales for local

consumption. Although few timber sales were offered in the early

years, the ones that were often included large volumes and covered

extensive acreages. For example, the Bates sawmill was established

following a 124 million board foot offering in 1916, which covered

Malheur NF

Harvest History
EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT 29

14,600 acres on the lower Middle Fork of the John Day River (then in

the Whitman NF). Logging continued at relatively low levels until

1928, when the Edward Hines Lumber Company was awarded a longterm contract for 890 million board feet in the Seneca area. Except for a

decline during the timber recession of the late 1970s and early 1980s,

timber harvests have increased steadily since then. An increase during

the early 1940s reflects high demand during World War II (fig. 19).

Figure 19—Timber volume harvested on the Malheur NF. Except for a decline during the timber recession of the late 1970s, and the current downturn

associated with timber sale appeals, the overall harvest trend has been steadily

upward. [Sources were USDA Forest Service (1961), and harvest records

available at the Malheur NF Supervisor’s Office.]

Due to market conditions, early partial cuttings were typically a “diameter-limit” harvest with the largest trees being removed. Diameter-limit

cutting gradually altered the forest composition by removing the marketable trees (large-diameter ponderosa pines, larches, and Douglasfirs), leaving behind a high proportion of unmerchantable firs and

Douglas-firs. The following passage describes how partial cutting was

applied in the early ponderosa pine forests of Oregon (Munger 1917).

The system of cutting which seems to be ideal for this type of forest is

a form of selection cutting. Periodic cuttings are made, in each of

which all the overmature and thoroughly ripe trees in the stand and all

the defective ones are removed; and the saplings, poles, and young,

thrifty trees are left standing to form the basis for the next crop. No

tree is removed until it has reached its majority, so to speak, and no

old, slow-growing tree is allowed to stand and occupy space which

should be devoted to young and rapid-growing trees. It is customary

to set an appropriate diameter limit of from 16 to 22 inches, the

majority of the trees above which limit are cut, and those below left.

Diameter Limit

Cutting

1909

1913

1917

1921

1925

1929

1933

1937

1941

1945

1949

1953

1957

1961

1965

1969

1973

1977

1981

1985

1989

1993

0

50

100

150

200

250

300

TIMBER HARVEST VOLUME (MMBF)
30 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Why Was DiameterLimit Cutting Used?

Why was diameter-limit cutting used if it favored firs instead of pine

and larch? Under the market conditions of that era, selective cutting

was viewed as a wise use of forest resources. It removed mature trees

that had some value, thereby initiating a rudimentary level of forest

management. Low-value trees were harvested to the extent that markets

would allow. Many low-value species were left in the hope that some of

them would become merchantable by the next entry in 40–60 years.

The following passage describes this situation for western white pine,

but it was also true for ponderosa pine forests (Haig and others 1941).

The low values are due to high susceptibility to heart rot of western

hemlock, grand fir, and some other species, and to the fact that the

selling price of lumber manufactured from these species is often insufficient to meet production costs even if nothing were paid for the

standing timber. Where trees of such species are not defective, the

Forest Service policy has been to leave them uncut in the hope that at

some future time they can be sold at a profit. But leaving these lowvalue species on areas that are cut over encourages their reproduction

and tends to decrease the proportion of western white pine in the reproduction—an undesirable result both silviculturally and economically.

In many respects, partial cutting was the opposite of how natural processes operated in mixed-conifer stands. Underburns discriminated

against the long-crowned, thin-barked invaders (grand fir and Douglasfir), while favoring the thick-barked trees with short, open crowns

(ponderosa pine and western larch)(Table 2). In contrast, partial cutting

removed fire-resistant pines and larches while retaining the late-successional species that are susceptible to a variety of insects and pathogens.

The late-successional species that were favored by partial cutting had

less value for timber products than ponderosa pine. Early Blue Mountains foresters recognized that partial cutting could have an undesirable

impact on species composition and timber values, as described below.

White fir, though of slower height growth, is far more tolerant than bull

pine, reproduces fairly freely, and under normal conditions would

naturally supplant the pine in time. This condition has been greatly

aggravated in the portions that have been lumbered by cutting the pine

and leaving the white fir. The fir, often already on the ground under the

pine, springs up, and pine reproduction is thus impossible (Kent 1904).

In all sales on this Forest, care should be exercised in marking the timber not to leave the cutting area in such condition that a valuable stand

be supplanted by inferior species. White fir, though occasionally used

for fuel when no better species are available, makes poor fuel wood,

while for saw timber it is all but valueless owing to the fact that nearly

all mature trees are badly rotted by a prevalent polyporus, and the wood

season-checks badly. Unless care is taken this species is prone to

supplant such species as yellow pine and tamarack since it is much

more tolerant of shade in early life (Foster 1907).

Effects of Partial

Cutting
EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT 31

Table 2—Bark thickness, crown length, and fire resistance rankings

for common trees of the mixed-conifer zone in the Blue Mountains.

BARK THICKNESS CROWN LENGTH FIRE RESISTANCE

Western Larch (thickest) Western Larch (shortest) Western Larch (highest)

Ponderosa Pine Western White Pine Ponderosa Pine

Douglas-fir Lodgepole Pine Douglas-fir

White/Grand Fir Ponderosa Pine Western White Pine

Western White Pine Douglas-fir White/Grand Fir

Engelmann Spruce White/Grand Fir Lodgepole Pine

Lodgepole Pine Engelmann Spruce Engelmann Spruce

Subalpine Fir (thinnest) Subalpine Fir (longest) Subalpine Fir (lowest)

Sources: Haig and others (1941), and Minore (1979). Species rankings are

based on the predominant situation for each trait. A species trait is not

absolute—it can vary during the lifespan of an individual tree, and from one

individual to another in a population. For example, white fir’s bark is thin

when young, but relatively thick when mature (see fig. 84).

The potential implications of selective harvesting and fire suppression

were clearly recognized during inventories completed by the Forest

Service’s forest survey unit. The following comments are from a report

summarizing the results of the 1950s forest inventories for eastern

Oregon counties (Gedney 1963).

If present trends continue, the proportion of ponderosa pine will be less

in the future than at present. In 29 percent of all the pine sawtimber

types, there is no understory of pine, only other species—Douglas-fir,

white fir, and lodgepole pine. In another 27 percent of the pine sawtimber stands, the understory is a mixture of young ponderosa pine and

other species. On more than half of this area, species other than pine

predominate. Unless something happens to change this relationship, or

unless more intensive forest management is undertaken, about 40

percent of the pine sawtimber type is likely to shift to some other type.

What were land managers left with after harvesting the old-growth

ponderosa pine from a mixed-conifer stand? Often, it was the multilayered stand structure that provides an ideal feeding ladder for dispersing budworm larvae (fig. 20). After dispersing on silken threads from

high in the forest canopy, some larvae are intercepted by smaller host

trees before falling to the forest floor, where they would have been

eaten by ants, small mammals, and other natural enemies of budworm.

How common was the practice of harvesting more ponderosa pine than

other species? Figure 21 shows that almost three-fourths of the timber

volume harvested on the Malheur NF between 1970 and 1992 was ponderosa pine. Since the ponderosa pine type occupies about half as much

acreage as the mixed-conifer type (see fig. 12), it is also evident that

much of the ponderosa pine volume was removed from mixed-conifer

stands.

Vegetation Changes

Recognized Early

Budworm Feeding

Ladders

Recent Harvest

Trends By Species
32 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 20—Budworm feeding ladder effect in multi-storied stands. In stands

comprised of two or more canopy layers, budworm impacts are usually concentrated on the smaller trees. Some budworm larvae disperse from taller

trees and are intercepted by understory stems before reaching the forest floor,

where they would have died from exposure or been preyed upon by ants, spiders, beetles, birds, small mammals, and other natural enemies of budworm.
EFFECTS OF SELECTIVE HARVESTING ON BUDWORM HABITAT 33

Figure 21—Timber volume harvested on the Malheur NF in fiscal years

1970–1992 (“associated species” include Douglas-fir, white fir, western larch,

and other species except ponderosa or lodgepole pines). During the 23-year

period included in this chart, 72% of the Forest’s harvested volume was

ponderosa pine. Since ponderosa pine stands occupied only 35% of the

Forest’s land base in 1980 (see fig. 12), this figure shows that much of the

pine volume was actually removed from the mixed-conifer type. The harvest

pattern shown here helped accelerate the replacement of ponderosa pine

stands with mixed-conifer forest, which contributed to significant increases in

the area of western spruce budworm habitat. [Chart was based on timber

harvest records available at the Malheur NF, Supervisor’s Office.]

“Many land managers would agree that wildfire suppression was a policy with good intentions, but it was a policy

that failed to consider the ecological implications of a

major shift in species composition. White firs and Douglas-firs can get established under ponderosa pines in the

absence of underburning, but they may not have enough

resiliency to make it over the long run, let alone survive

the next drought. This means that many of the mixedconifer stands that have replaced ponderosa pine are

destined to become weak, and weak forests are susceptible to insect and disease outbreaks.”

Effects of Fire Suppression on Budworm Habitat (page 19)

1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992

0

50

100

150

200

250

TIMBER HARVEST VOLUME (MMBF)

LODGEPOLE PINE

ASSOCIATED SPECIES

PONDEROSA PINE
34 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

THE ECOLOGICAL ROLE OF BUDWORM OUTBREAKS

E cological theory has traditionally held that ecosystems exist in astate of equilibrium, and that they return quickly to a condition of

stability or homeostasis following a disturbance. Recent ecological

research refutes that theory by showing that nature is in a continual

state of flux. Change and turmoil, rather than constancy and balance, is

the rule. We now know that the concept of a forest evolving to a stable

(climax) stage, which then becomes its naturally permanent condition,

is false (Stevens 1990). Wildfires, wind storms, insect outbreaks,

disease epidemics, and other natural processes are the harbingers of

change; they prevent most forests from ever reaching a climax stage.

Insects and pathogens are not only important agents of change, but

they also play a vital role in ecosystem function (Wickman 1992).

They cause tree mortality, which in turn affects natural succession and

the diversity of plant communities in an area. They create many of the

dead trees that provide important habitat for a wide variety of wildlife

species. In the Blue Mountains, standing dead trees (snags) are used

for nesting or shelter by 39 bird and 23 mammal species; downed,

dead trees are used by 179 wildlife species (Thomas 1979).

Nutrient cycling and production of down woody material are two important ecological processes influenced by insects and pathogens

(Wickman 1992). Both of those processes contribute to the long-term

productivity of forest ecosystems, particularly as they affect the habitat of soil-inhabiting fungi called mycorrhizae. In fact, when considering the variety of ecological benefits provided by these organisms, it is

questionable whether they should be viewed as pests (fig. 22).

Are extensive insect impacts an indicator of an unhealthy forest ecosystem? And what does a wide-ranging budworm outbreak mean in an

ecological sense? Since ecosystems are constantly undergoing change,

we need to evaluate their health in a similar context. Perhaps an appropriate yardstick of ecosystem health is natural variation: are the changes caused by budworm consistent with the historical range of variation

for similar ecosystems and vegetation conditions? For the mixedconifer forests of the southern Blue Mountains, the answer is probably

“no.” It seems that 80 years of fire suppression and 50 years of selective harvesting have resulted in vegetation conditions that differ

significantly from those of presettlement times (Table 3).

Recent ecological assessments of the Blue Mountains ecoregion found

that many river basins support vegetation whose composition and

structure are currently outside the historical range of variation (Caraher

and others 1992, O’Laughlin and others 1993).

Insects Provide

Diversity

Nutrient Cycling

and Down Wood

Historical Range of

Variation
THE ECOLOGICAL ROLE OF BUDWORM OUTBREAKS 35

Figure 22—Insects and pathogens are important components of biodiversity. Forests support an amazing diversity of life, ranging from soil microbes

to large, long-lived, woody plants. Insects and pathogens are an important

element of that diversity. Not only do they contribute to nutrient cycling, site

productivity, and other ecosystem processes, but they create wildlife habitat

(dead trees) and are a source of food for many wildlife species.

Table 3—Change in selected stand attributes for ponderosa pine forests near Austin, northeastern part of the Malheur NF, 1910–1980.

STAND ATTRIBUTE 1910–11 1980 Change

Live Trees Per Acre (1"+ DBH) 56.5 427.7 + 657%

 Ponderosa Pine Percentage 67.3 71.3 + 6%

Live Basal Area; Square Feet Per Acre (1"+) 94.6 88.4 – 7%

 Ponderosa Pine Percentage 83.6 57.6 – 31%

Quadratic Mean Diameter (Inches) 17.5 6.2 – 65%

Stand Density Index (trees/acre at 10" QMD) 138.6 196.8 + 42%

Live Trees Per Acre >21" DBH (Percent) 28.1 2.3 – 92%

Pine Trees Per Acre >21" DBH (Percent) 24.4 1.8 – 93%

Sources: 1910–1911 data is for ponderosa pine plots near Austin–Whitney

(Munger 1917, page 20); 1980 data is for two Malheur NF inventory plots

near Austin and at the same elevation (4500–4800 feet) as Munger’s plots.
36 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

How did fire suppression and partial cutting contribute to ecosystems

that are out of balance? Both of those practices contributed to a loss of

ecosystem resilience by reducing vegetation diversity and complexity,

especially at a landscape scale. The Blue Mountains supported a

variety of forest conditions in presettlement times, ranging from open

pine forests to dense stands of white fir, spruce/fir, western larch, or

lodgepole pine (fig. 23). Even nonforest communities with grasses or

shrubs were more common then than they are today. Fire suppression

and selective harvesting have perhaps had the single greatest impact on

landscape diversity in eastern Oregon (Hessburg and others 1994).

Figure 23—Vegetation zones of the central and southern Blue Mountains.

Vegetation types tend to occur in well-defined zones as you move up or

down a mountain slope. Since northerly exposures are cooler than southfacing aspects, the zones tend to occur at lower elevations on north slopes.

The plains zone occurs at low elevations; it contains grasslands and shrublands because moisture is too low to support forests except along waterways.

The foothills zone is usually dominated by western juniper, often with a

mixture of mountain-mahogany shrublands and grassy scablands. Located

just above the western juniper woodlands is the lower montane zone, which

contains forests of ponderosa pine. Lower montane sites are too dry to

support white fir or Douglas-fir forests except in riparian zones. The upper

montane zone is extensive in the Blue Mountains, where it provides ideal

environments for western spruce budworm. It includes mixed-conifer forests

of Douglas-fir, white fir, western larch, ponderosa pine, lodgepole pine and,

occasionally, western white pine. High elevations support a subalpine zone

with Engelmann spruce and subalpine fir, or an alpine zone near mountain

summits, where trees are absent. Neither subalpine nor alpine environments

are common in the relatively low-elevation Blue Mountains.

Ecosystem

Resilience
THE ECOLOGICAL ROLE OF BUDWORM OUTBREAKS 37

When European emigrants introduced livestock grazing, suppressed

underburns, and influenced other natural processes, the resulting

changes were akin to an ecological simplification. Aspen stands;

riverine forests of black cottonwood; riparian communities of thinleaf

alder, river birch, and willows; certain types of shrubland; and other

ecosystem components were reduced or lost altogether (fig. 24). One

of those changes was certainly predictable—resilient pine stands were

replaced with highly stressed forests comprised mostly of budwormhost trees. Forest diversity was reduced further when selective harvesting began removing the overstory pines and larches.

Figure 24—Aspen clone in the Blue Mountains. As a result of fire suppression, aspen is less common today than it used to be. Although aspen was

never abundant in the Blue Mountains, its distribution has suffered without

fire. Aspen regenerates primarily from root sprouts or suckers, which are

produced after most of the overstory trees have been killed by fire, pathogens, or timber harvest. When fire was curtailed as a landscape-level process, aspen was forced to seek ecological refuge along ephemeral streams,

around moist meadows, and on other semi-riparian sites. Allowing fire to

play its natural role in the Blue Mountains would not only benefit ponderosa

pine and western larch, but could also rejuvenate aspen on many sites.

As these vegetation shifts accelerated, the habitat for budworm and

other insects and pathogens continued to build, eventually reaching

levels that are apparently greater than ever before. When considered

from that perspective, conflagration fires and catastrophic budworm

impacts are an ecologically appropriate response to the vegetation

changes. Instead of minor budworm outbreaks affecting limited areas,

the Blue Mountains recently experienced an outbreak occurring over

wide areas. Perhaps the recent outbreak was a symptom of a problem

(an abundance of mixed-conifer forest), rather than the problem itself.

Ecological

Simplification

Budworm Responds

to Vegetation

Changes
38 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Several recent environmental controversies have been concerned with

human alteration of forested ecosystems and the resultant impacts on

one or more wildlife species (an example is the northern spotted owl in

western Oregon). Although public concern tends to focus on declining

species, particularly those which are threatened or endangered with

extinction, human activity has also led to the emergence of invigorated

species that are apparently doing better now than they ever have in the

past. Examples of invigorated species might include coyotes, raccoons,

house sparrows, red-winged blackbirds, bull thistles, and west-ern

junipers, to name just a few. Unfortunately, previous management

practices have probably contributed to an invigoration of western

spruce budworm, which defoliated much more area during the 1980s

outbreak than it did in the previous one (1944–1958; see fig. 6).

Recent studies indicate that man’s production of carbon dioxide could

be leading to a period of global warming. If global warming occurs, it

could have significant effects on western forests. Ponderosa pine and

other trees adapted to warm, dry environments would undoubtedly

suffer less damage than white fir and similar species that need relatively moist conditions. Open stands have little competition between trees

for nutrients and water; they would fare better in the harsher environments associated with global warming.

Reestablishing ponderosa pine and western larch on sites that are suitable for their survival and growth, and a thinning or prescribed fire

program to keep those stands open and vigorous, would probably do

much to address global warming concerns. Using a plan like that one

would not only restore much of the pine and larch that was removed by

partial cutting (see fig. 21), but it could also create healthy forests with

an increased resistance to a variety of insects and pathogens.

A note about global warming: It has not been conclusively proven that

global warming is already underway, or that its onset is imminent. It is

not possible to make accurate predictions about long-term climatic

trends. For example, scientists warned that the Earth was entering a

major period of global cooling in the mid 1970s, when we were heading “toward extensive northern hemisphere glaciation” (Hays and

others 1976). In less than two decades, a very short time period in a

climatic sense, scientific concern has shifted from global cooling to

global warming.

Budworm

Invigoration

Global Climate

Change and

Budworm

Susceptibility
STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS 39

STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS

T he study described here can best be termed an observational

study, case study, or descriptive survey. An observational study

differs from a controlled experiment in several important ways

(Snedecor and Cochran 1989). In an experiment, the investigator

controls the treatments to which the subjects are exposed and also

prevents their exposure to extraneous or confounding factors. Conversely, an observational study involves circumstances where an investigator lacks the power to create the groups to be compared; the choice

of observations or data to be collected and analyzed cannot be controlled in an experimental sense.

For this budworm study, it was not possible to assign the forest inventory plots to carefully controlled defoliation groups. The plots already

existed and were exposed to a wide variety of natural budworm defoliation that was essentially uncontrolled by humans, except for any influence exerted by the insecticide treatments. However, insecticides were

not applied to all of the defoliated area, the treatments were not completed in the same year or with the same insecticide, and the insecticide

applications did not eradicate budworm or its impact: they typically

suppressed budworm populations and associated tree impacts for a

period of three or four years at best.

Due to the limitations of an observational study, readers should be cautious when using the results contained in this report. Any apparent

correlations are merely clues to possible cause–effect relationships

(Schreuder and Thomas 1991). This study basically imposed a sampling

scheme on pre-existing inventory plots with the result that potential

relationships are being explored after the fact, rather than designing a

controlled experiment and accepting whatever results from it.

How the study results are used may depend on the level of uncertainty

that one is willing to accept. Because they were derived from an observational study, some of the results may have a relatively high degree of

uncertainty. On the other hand, the study was based on methodologies

and sampling units (long-term inventory plots) commonly used in

national forest management. The results may have less uncertainty for

typical national forest management situations.

By the mid 1980s, as it became apparent that budworm defoliation was

causing significant impacts, the Forest’s leadership team began considering options for acquiring information about budworm’s effect on

mixed-conifer forests. They decided that some of the Forest’s existing

inventory plots would be remeasured, a strategy offering the following

advantages:

Using the Study

Results

Remeasuring

Mixed-Conifer

Inventory Plots

This Study Was Not

An Experiment

Limitations of

Observational

Studies
40 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

• The plots were last measured in 1980, which also happened to be the

year that budworm populations began building to outbreak levels

(McConnell and others 1980). The 1980 measurements could then

provide a snapshot picture of host-type conditions as they existed

immediately before the onset of budworm-caused defoliation.

• The 1980 measurements could provide a known benchmark from

which to compare changes, many of which were presumably caused

by budworm defoliation. The availability of a baseline measurement

removes any need to estimate what pre-damage conditions were like.

In other studies of budworm impact, the investigators have used a

computer model to “backdate” measured conditions to pre-outbreak

levels (Beveridge and Cahill 1984), or they have attempted to correlate information from aerial sketch maps with budworm-related tree

damage (Harvey 1982). A potential problem with these back-dating

processes is the uncertainty about whether any observed differences

are due to the treatment or effect being analyzed, or due to the

backdating process itself or how the process was used.

• 51 of the 130 remeasured plots were initially established in 1967 or

1968. For those plots, the remeasurements in 1988–1989 represent

the third successive observation involving the same trees on the

same plot area. Measurements spanning more than 2 decades could

be used to assess mortality trends, for monitoring changes in species

composition, and to make other comparisons that benefit from using

the same set of trees on the same plot areas.

Since budworm defoliation is potentially most damaging in stands with

a high proportion of host trees, it was decided to remeasure inventory

plots whose composition consisted of 50% or more budworm host

species. For the purpose of selecting remeasurement plots, the following tree species were considered to be hosts of spruce budworm: white

fir, subalpine fir, Engelmann spruce, Douglas-fir, and western larch.

There were 402 inventory plots measured in 1980, of which 139 satisfied the “50% host species” criterion described above. Nine of the 139

candidates were located in wilderness areas established after the 1980

inventory; those plots were not considered for remeasurement because

wilderness areas are not representative of managed host type.

The 1980 forest inventory used a traditional stratified sample—strata

sizes were obtained from aerial photo delineations completed in 1979;

ground plots were measured in 1980 to characterize strata attributes.

Each of the 1980 inventory plots consisted of a 10-point plot cluster

designed to cover approximately one acre (fig. 25). Three of the sample

points (points 1–3) were considered “intensive” because a wide variety

of information was collected for each sample tree. The other seven

points were “extensive” because limited information was collected.

Plot Selection

Criterion

Selected Plots

Survey Design
STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS 41

Since tree height and other information for evaluating budworm impacts was unavailable on the extensive points, it was decided to

remeasure only the 3 intensive points on each inventory plot.

Figure 25—Diagram of a forest inventory plot. Plots used in the 1967–68

and 1980 inventories were a cluster of 10 sample points covering about an

acre. Each point was located at the apex of an equilateral triangle with 70-

foot sides. Measurements were collected on a variable-radius and a fixed-area

plot at each point. For this study, only the first three points (1–3) were remeasured because the other 7 points did not provide complete tree information.

The three intensive points for 130 forest inventory plots were remeasured during the 1988 and 1989 field seasons. Each point consisted of 2

subplots—a variable-radius plot (horizontal point sample) utilizing a

basal-area factor of 40, and a fixed-area plot covering 1/300 of an acre.

Sample trees 5 inches DBH and larger were selected with horizontal

point sampling, which uses probability proportional to the crosssectional area of a tree bole at 4.5 feet above the ground (basal area).

Sample trees less than 5 inches in diameter were selected on a circular,

fixed-area plot.

Sampling

Methodology
42 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Appendix 2, which was prepared by John W. Hazard, describes the

survey design used for the 1967–68 and 1980 inventories. It also describes the statistical analyses used for the budworm impact study, and

the reliability of results reported in this report.

A variety of site and tree information was collected on the remeasured

inventory plots, including the items described below.

Elevation (determined to nearest hundred feet).

Aspect (recorded as an azimuth, in degrees).

Slope Gradient (average of uphill and downhill readings).

Topographic Position (8 classes; stream bottom to ridgetop).

Undergrowth Plant Composition (canopy cover by species).

Tree Species.

Tree History (live, mortality, sound dead, nonsound dead, etc.).

Tree Diameter (taken at 4.5 feet above the ground, in inches).

Tree Height (total height, in feet).

Number of Stems (for grouping seedlings on the fixed plots).

Tree Growth (determined from increment cores).

Tree Age (determined from increment cores).

Crown Ratio (9 classes; 10 percent live crown ratio per class).

Crown Class (dominant, codominant, intermediate, etc.).

Damage/Death Causes (codes for 28 causes were used).

Dwarf Mistletoe Rating (used 6-class rating system).

Topkill (percent of tree height with topkill due to budworm).

Defoliation (foliage percentage missing due to budworm feeding).

Defoliation was measured by first splitting the host-tree crown into

thirds, and then obtaining an ocular estimate of missing foliage for each

crown third. Before completing any of the budworm-impact analyses, a

defoliation value was derived for each host tree by computing a

weighted mean of the crown thirds. The crown thirds were weighted

using the average proportion of foliar biomass present in each third; the

average biomass proportions were obtained from Crookston (1991).

To ensure that information was collected consistently—especially

defoliation and topkill percentages, the canopy coverage of undergrowth plants, and other items requiring an ocular estimate—all measurements were completed by the same person (author).

One or more of the trees on each inventory plot were used to calculate

site index, a productivity measure based on the height of dominant and

codominant trees at a specific reference age (generally 50 years). Sample trees of the following species were used to calculate site indices

(source of site index equations given in parentheses): white fir (Cochran 1979b), Douglas-fir (Cochran 1979a), western larch (Cochran

1985), Engelmann spruce (Brickell 1966), ponderosa pine (Barrett

1978), and lodgepole pine (Dahms 1975). It is seldom possible to comInformation

Collected

Site Indices
STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS 43

pare site indices from one tree species to another because of differences

in the site index relationships—reference ages vary by species, and

some site curves use breast-height age, while others use total age.

In order to compare productivity between tree species, mathematical

equations were used that relate site indices to a yield capability value.

Yield capability is the potential growth rate, in cubic feet per acre per

year, of a fully-stocked stand on an area with a given site index. Yield

capability equations were the same ones used in the Forest Service’s

stand examination program (USDA Forest Service 1987a).

Radial growth and age were not determined in the field because severe

budworm defoliation can reduce tree growth to the point where it is

very difficult to discern annual rings, even with the aid of a magnifying

glass. For that reason, 942 increment cores were collected during field

sampling for analysis at a dendrochronology laboratory. In the field,

cores were stored in plastic holders that allowed plot, point, and tree

identifications to be recorded for them.

After field sampling, the increment cores were sent to the Dendrochronology Center at the Forestry and Range Sciences Laboratory in La

Grande, Oregon, where they were removed from the plastic trays, glued

into grooved wooden blocks, and sanded to fully expose their annual

rings. Following this preparation phase, the cores were measured on a

Bannister incremental measuring machine connected to a computer for

recording and storage of the ring-width information (fig. 26). Annual

increment was measured to the nearest 0.01 millimeter.

Figure 26—Budworm defoliation often causes severe growth reductions. In

order to interpret the narrow growth rings of defoliated trees, cores were examined with a microscope at a dendrochronology laboratory.

Increment Core

Measurement

Yield Capability

Estimates

Increment Core

Collection
44 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Diameter growth was assumed to be complete by August 15th; if a core

had been collected before that date, radial increment was not measured

for the current year because the ring was assumed to be incomplete. For

cores from older trees, annual growth was measured for the last 90

years only; total age was determined for every core. Cores from four

extremely suppressed saplings could not be interpreted, even with full

microscopic magnification.

Since increment cores begin shrinking immediately after removal from

the tree, 76 cores collected during 1988 were marked in such a way that

their shrinkage could be determined later. Why was shrinkage important? One item of information to be acquired from each core was radial

increment, which involves measuring the distance (growth) between

each annual ring. Obviously, radial growth values would vary depending upon whether the core was measured in a fresh condition, or after

drying and shrinking had occurred. Shrinkage was minor—it averaged

only 3% for the 76-core sample, and varied little depending on whether

shrinkage was determined for the entire core (pith to cambium), or for

the moister sapwood portion only. Douglas-fir cores had more shrinkage (3.5%) than white fir (2.5%); cores from other species averaged

about 3%.

Constraints on time and funding did not allow the 938 usable cores to

be analyzed for missing rings (see Swetnam and others 1985). Forgoing

such an analysis was believed to pose little risk for misinterpreting core

data because recent research indicates that missing rings are uncommon, and that nonhost species such as ponderosa pine may have more

missing rings than budworm-host trees (Swetnam and Lynch 1989).

After completing the 1988–1989 remeasurements, plot information was

loaded into computerized databases or spreadsheets for editing and

analysis. Data from the 1980 measurements were also loaded for each

plot; in addition, earlier information was available for some of the plots

that had been established during the 1968 forest inventory. Incorporating those older measurements allowed growth trends and other historical comparisons to be made. The impact of budworm effects on future

timber volume was estimated using the Blue Mountain variant of the

Stand Prognosis model (see page 74).

The budworm-impact information in this report was developed using

weighted means. A mean value for budworm-caused defoliation,

topkill, and mortality was calculated for 125 of the 130 remeasured

inventory plots. Five plots were not used in the analysis because they

had been heavily logged between the 1980 and 1988–89 measurement

periods. Plot-based means were weighted using the trees/acre expansion factor associated with each sample tree. Plot weights were developed by dividing the strata areas by the number of plots in each stratum.

Refer to appendix 2 for further details.

Increment Core

Shrinkage

Radial Increment

and Age

Missing Growth

Rings

Analysis of

Remeasurement

Information

Using Averages

During Data

Analysis
STUDY DESIGN, AND SAMPLING AND ANALYSIS METHODS 45

Plot remeasurements provided most of the information that was needed

to evaluate budworm impacts. But some analyses required information

about the spatial distribution of budworm defoliation, or the location of

areas that had been treated during budworm-suppression projects. Most

of this information was available on digital or paper maps, and was

manipulated using a geographic information system called MOSS.

Some of the map-based information was unavailable on the Malheur

NF, and was obtained from the Forest Pest Management group in

Portland, Oregon (see acknowledgments).

Information about budworm impacts was summarized for 17 descriptive factors related to tree, stand, and site characteristics affecting budworm susceptibility and vulnerability. Many of the analysis factors had

been used for budworm studies in other areas of the western U.S. (Wulf

and Cates 1987). Analysis factors were selected that would help land

managers answer questions like these:

• How did budworm impacts (defoliation, topkill, and mortality) vary

by diameter, height, age, crown class, and for other tree characteristics?

• How did budworm impacts vary with changes in elevation, site productivity, physiographic position, aspect, and for other site and stand

factors?

• Did host trees in areas that were treated with an insecticide to suppress budworm populations have less damage than trees in untreated

areas?

Analysis of

Budworm Impacts

Analysis of

Geographic

Information
46 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

IMPACTS OF THE BUDWORM OUTBREAK

W hat happened during the 1980s budworm outbreak? Trees and

stands were affected in a variety of ways, many of which are

described below.

An adult western spruce budworm is a small, grayish moth. It causes

tree damage in the larval (caterpillar) stages of its life cycle. Damage

occurs when the larvae consume a tree’s foliage and buds in a process

called defoliation (fig. 27). Budworm-caused defoliation was assessed

on the Malheur NF in 1988 and 1989; the results of that assessment are

presented in this section of the report, beginning on page 56.

Topkilling occurs when budworm larvae consume the foliage and buds

near the top of a tree, thereby killing that part of its stem (fig. 28). Even

if defoliation is not severe enough to kill the top, height growth is

reduced or eliminated during each year that feeding occurs. Budwormcaused topkilling was assessed on the Malheur NF in 1988 and 1989;

the results of that assessment are presented in this section of the report,

beginning on page 56.

Direct mortality occurs when budworm defoliation occurs long enough

to kill trees directly (fig. 29). During the 1980s outbreak, budworm had

a pronounced effect on tree mortality in mixed-conifer forests of the

Blue Mountains (fig. 30). Budworm-induced mortality was assessed on

the Malheur NF in 1988 and 1989; the results of that assessment are

presented in this section of the report, beginning on page 56.

Indirect mortality occurs in two situations: 1) when defoliation stress

predisposes trees to be killed by bark beetles, drought, or other causes;

and 2) when trees which were stressed before defoliation began—such

as Douglas-firs infected with dwarf mistletoe, or any host tree weakened by suppression—died after being defoliated by budworm. Some

examples of indirect mortality are provided by figures 31–34.

Growth reductions occur after a tree has lost enough foliage to inhibit

photosynthesis, which is the biochemical process that trees use to create wood fiber. Radial growth usually starts declining during the year

that budworm feeding begins, and is progressively reduced with each

additional year of defoliation. After an outbreak collapses, defoliated

trees require several years to replace their missing foliage. During that

period, growth rates slowly recover to their pre-outbreak level. Tree

growth was analyzed and the results are provided by figures 35–40.

Fiber production declines as defoliated trees experience reduced diameter and height growth. Figure 41 shows that form defects increased

significantly between 1980 and 1989; much of that increase resulted

Defoliation

Topkilling

Direct Mortality

Indirect Mortality

Reduced Tree

Growth

Reduced Volume

Production
IMPACTS OF THE BUDWORM OUTBREAK 47

from the multiple leaders caused by topkill. Forks, crook, sweep, and

other form-related defect occurs after topkilling causes lateral branches

to turn upward and attempt to gain dominance as a tree’s new top (fig.

42). The effect of budworm impacts on future timber yields is also

assessed in this section of the report (see page 74).

Figure 27—Defoliation occurs as budworm larvae (caterpillars) feed on host

trees. This Douglas-fir seedling is missing at least half of its normal foliage

as a result of budworm defoliation. Although host trees in all size categories

were defoliated to some extent during the 1980s budworm outbreak, smaller

trees sustained significantly more damage (see fig. 44). Generally, seedlings

of this size had less missing foliage than saplings (trees with diameters of 1.0

to 4.9 inches). This seedling has short spaces between each set of branches

on the stem (the spaces are called internodes), which indicates that it is

suppressed. Suppressed and intermediate trees were much more likely to be

killed by budworm than taller, dominant trees (see fig. 50).
48 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 28—When budworm defoliation persists near the top of a host tree’s

crown, topkill is often the result. Many of the small Douglas-firs shown here

have dead tops caused by budworm defoliation. As budworm larvae feed in

the upper part of a tree, they also destroy most of the developing cones,

reducing seed production and natural regeneration capacity. Dead tops with a

basal diameter of three inches or more are likely to result in stem decay

(Ferrell and Scharpf 1982). Topkill is also responsible for stem deformity

(fork, crook, or sweep) affecting a tree’s merchantable volume (see figure

41). In addition to topkill, defoliation caused by herbivorous insects can

cause significant and sustained tree-growth reductions (fig. 35) and ultimately tree mortality (fig. 29); mortality tends to be a function of both the

magnitude and persistence of defoliation.
IMPACTS OF THE BUDWORM OUTBREAK 49

Figure 29—Occasionally, budworm kills a substantial number of the host

trees in an area. This photograph shows a distant view of Starr Ridge on Bear

Valley Ranger District. In the late 1970s, most of the old-growth ponderosa

pine in this area was harvested using helicopters. The residual stands were

comprised mostly of Douglas-firs, many of which were infected with dwarf

mistletoe. Note that budworm did not provide a uniform, evenly-distributed

thinning—trees were often killed in groups.

Figure 30—Proportions by tree class, and causes of mortality, for 130

mixed-conifer inventory plots measured in 1980 and 1988–1989. In 1980 (top

half of figure), only 6% of all trees had been recently killed (mortality), with

bark beetles and suppression being the two main causes. By 1988–1989

(bottom half of figure), mortality had increased substantially to 21% of all

trees; bud-worm was responsible for more than half of the mortality, but

logging and suppression also caused significant losses.
50 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 31—Defoliation, drought, root diseases, and other causes of stress

can increase a tree’s susceptibility to attack by bark beetles. The white firs in

the center of this photograph were killed by fir engraver beetles; fir engraver

and Douglas-fir beetle caused widespread damage on the Malheur NF during

the late 1980s and early 1990s (see figures 2 and 32). An important cause of

stress during the 1980s was spruce budworm defoliation—it not only contributed to fir engraver attacks, but was also responsible, in large part, for the

widespread mortality caused by Douglas-fir beetle. Trees defoliated by

budworm are also more likely to be killed during a tussock-moth outbreak;

several small tussock-moth outbreaks occurred on the Malheur NF in 1992

and 1993.
IMPACTS OF THE BUDWORM OUTBREAK 51

Figure 32—Tree mortality caused by bark beetles on the Malheur NF, 1988–

1990. The acreage of bark-beetle mortality shown here occurred because

stands had been weakened by budworm defoliation, and by reduced precipitation between 1986 and 1990. But which of those factors had the most influence? Figure 33 provides precipitation information for two stations located

near the Malheur NF, and it suggests that bark-beetle mortality was affected

more by budworm stress than by precipitation.

Figure 33—Precipitation record for Austin and Seneca, Oregon. These weather stations are located on the northern (Austin) and southern (Seneca) parts

of the Malheur NF. During the 1985–1992 “drought,” precipitation ranged

from 8% below (Austin) to .3% above (Seneca) the long-term means. Normal

precipitation (not unusually high or low) is defined as 80% of the variation

around the station’s long-term mean (the gray zone in the charts above); all of

the late 1980s precipitation values fall in the normal range.

1988 1989 1990

0

2 5

5 0

7 5

100

125

AFFECTED AREA (THOUSAND ACRES)

D O U G -FIR BEETLE

FIR EN G R AVER

M TN . PIN E B EETLE

W . PIN E BEETLE /IPS
52 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 34—Effect of dwarf mistletoe infection on budworm-induced tree

mortality. In 1980, 13% of the live Douglas-firs on 130 mixed-conifer inventory plots were infected with dwarf mistletoe (left chart). When those plots

were remeasured in 1988–1989, 19% of the Douglas-firs that were killed by

spruce budworm had dwarf mistletoe infections in 1980 (right chart). This

figure indicates that Douglas-firs infected with dwarf mistletoe were killed

by budworm more often than would be expected based on the infection

frequency for live trees. Presumably, infected Douglas-firs were killed more

often than uninfected trees because dwarf mistletoe causes physiological

stress, which would predispose those trees to budworm-induced mortality.

Research studies have not shown statistically significant interactions between

dwarf mistletoe and budworm in Douglas-fir stands (Filip 1993).

Figure 35—Radial growth for budworm host species, 1941 to 1989. Growth

of white fir, Douglas-fir, and other hosts (Engelmann spruce, subalpine fir,

and western larch) has generally followed a similar pattern during this 50-

year period. Beginning about 1960, radial growth for other hosts was considerably less than for white fir or Douglas-fir. Host-tree growth began declining

rapidly in 1983 or 1984, which is when budworm defoliation began to have

an effect on radial increment. As of 1989, growth was still heading down for

white fir and other hosts, whereas Douglas-fir increment had levelled out.

Since radial increment has not yet turned upward for any species, no more

than half of the budworm-induced growth losses are shown in this figure.

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

RADIAL GROWTH (mm)

W HITE FIR (359 TREES) DOUGLAS-FIR (359)

OTHER HOSTS (54) ALL HOSTS (772)
IMPACTS OF THE BUDWORM OUTBREAK 53

Figure 36—Radial growth for nonhost species from 1941 to 1989. Unlike the

situation for host trees (figure 35), the growth of ponderosa pine and lodgepole pine has not always followed the same pattern during this 50-year

period. Before the early 1950s, lodgepole pine growth was slower than

ponderosa pine growth; after about 1957, lodgepole pine increment was

usually higher than ponderosa pine’s by a substantial amount. Lodgepole pine

growth was not included for 1989 because of its small sample size—only 5 of

the 38 lodgepole pines had a 1989 growth value.

Figure 37—Radial growth for host and nonhost trees, and precipitation for

Austin, Oregon, for 1941–1989. Host-tree growth was always higher than

nonhost growth until about 1985, after which budworm defoliation caused

substantial reductions. The growth of both host and nonhost trees has generally followed a pattern similar to that of precipitation. Note that the spruce

budworm epidemic of 1944–1958 had no apparent effect on radial growth, or

at least no discernable effect when considering all 772 host trees. But when

growth is analyzed for certain plots known to have been affected by the

1944–1958 outbreak, an effect is apparent (figure 38).

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

0

0.2

0.4

0.6

0.8

1

1.2

1.4

RADIAL GROWTH (mm)

LODGEPOLE PINE (38) PONDEROSA PINE (128)

ALL NONHOSTS (166)

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0

10

20

30

40

50

60

70

80

RADIAL GROWTH (mm) PRECIPITATION (Inches)

ALL HO STS (772) ALL NO NHO STS (166) AUSTIN PRECIPITATIO N
54 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 38—Radial growth for host and nonhost trees on inventory plots affected by the 1944–1958 budworm outbreak. The Blue Mountains had two

outbreaks during the last 50 years—one from 1944 to 1958, and the present

one that began in 1980 (see fig. 5). Can any effect of the 1944–1958 outbreak

be seen in the radial increment of host trees? Figure 37 showed that if all 772

host trees are considered together, there is no apparent effect. This chart

shows radial increment for host and nonhost trees from plots that were

severely defoliated during the 1944–1958 outbreak. Not only is the earlier

outbreak clearly evident, but the 1980s epidemic is obvious too.

Figure 39—Host and nonhost tree growth for 1941–1989, and mean growth

for 1970–1979. In 1989, host trees were growing 62% less than their mean

for 1970–79, whereas nonhost trees were growing 22% below their 1970–79

mean. If nonhost growth reflects the effect of precipitation and factors other

than budworm, then the growth loss from defoliation would be about 40%

(62% – 22%). Host trees were growing below their 1970–79 mean from 1984

to 1989; during that period, cumulative growth loss amounted to 38%.

Cumulative growth loss for nonhost trees was only 11%, which indicates that

budworm-related losses for 1984–1989 were about 27% (38% – 11%).

1940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

0

0.2

0.4

0.6

0.8

1

1.2

1.4

RADIAL GROWTH (mm)

HOST TREES (18) NONHOST TREES (13)

Budworm

Outbreaks

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

RADIAL GROWTH (mm)

ALL HOSTS (772) ALL NONHOSTS (166)

HOST M EAN (1970-1979) NONHOST MEAN (1970-1979)
IMPACTS OF THE BUDWORM OUTBREAK 55

Figure 40—Radial growth for host trees by defoliation percentage. This

chart reinforces the relationship between crown class and defoliation (fig.

50): dominant trees had little defoliation and have always grown well,

whereas intermediate and overtopped trees had heavy defoliation and have

always grown slowly. Trees with no missing foliage in 1988–89 were growing 35% less than their 1970–79 mean in 1988. In 1989, trees with 1–39%

defoliation were growing 57% less than their 1970–79 mean; trees with 40–

79% defoliation were growing 71% less; and trees with defoliation of 80% or

more were growing 50% less. Growth in 1989 is not included for trees with

no defoliation due to a small sample size.

Figure 41—Comparison of live-tree damages in 1980 and 1988–1989. There

was little change between 1980 and 1989 for many damages, but the percentage of trees affected by defoliation increased significantly. The proportion of

trees with dead tops seems to have declined dramatically. That is actually not

the case because if a host tree had both topkill and defoliation, the most

serious of the two was coded as the primary damage. Since 89% of the

sampled host trees had topkill of 10% or less, defoliation was often coded as

the more serious damage.

1941

1943

1945

1947

1949

1951

1953

1955

1957

1959

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

RAD AI L GRO

WTH (m

m)

NONE 1-39% 40-79% 80% +

Anim al D am age

C rook and Sweep

D e a d To p s

D efoliators

D w arf M istletoe

Forks

Logging D am age

N atural M echanical

S uppression

O ther Dam age

0 5 10 15 20 25 30 35 40 45 5 0

AFFEC TED TREES (PER CENT)

1980

1989
56 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 42—After budworm populations collapse and defoliation ceases,

there can still be long-term repercussions from impacts associated with the

outbreak. One frequent consequence of budworm-induced topkill is form

defect, such as the large, deep fork in this Douglas-fir. A fork this low on the

bole can significantly reduce a tree’s merchantable volume. Research has

shown that form defects (forks, crooks, sweeps, etc.) seldom result in volume

losses exceeding 5% (Ferrell and Scharpf 1982), but board-foot reductions

can be much higher than that for a defect like the one shown here. Not only

are host trees with large topkills more susceptible to form defect, but they

also have a much higher risk of stem decay (Filip and Schmitt 1990).

Budworm impacts were analyzed using the 17 factors described below.

Each of the 17 factors was analyzed individually, as though all other

factors were held constant or otherwise accounted for. But in reality,

budworm reacts to its environment as a whole; the effect of any particular habitat component may be influenced by others. It is important to

realize that many of the site and stand variables are interrelated. For

those reasons, and because the sample data do not represent an unlimited range of site and stand conditions, any conclusions should not be

formed on the basis of a single analysis factor. Readers should look for

commonality among all of the variables, especially those that are

closely related, before arriving at any conclusions.

Analysis of

Budworm-Caused

Impacts
IMPACTS OF THE BUDWORM OUTBREAK 57

Budworm impacts were summarized for these host species or groupings

(fig. 43): white fir (74% of the remeasured plots had white firs), Douglas-fir (89% of the remeasured plots), and other hosts (western larch,

subalpine fir, and Engelmann spruce; 25% of the remeasured plots).

Since other hosts comprised such a small proportion of the sample—

only 3.4% of the trees sampled for budworm impacts—they were

ignored when analyzing the other factors.

Figure 43—Budworm impacts by host species. Douglas-fir sustained the

most defoliation, whereas white fir had the most topkill. Budworm-caused

mortality was significantly greater for Douglas-fir than for white fir, and

nonexistent for other hosts. The absence of budworm-induced mortality for

other hosts was not surprising when considering their low levels of defoliation and topkill. These results differ somewhat from those for the northern

Rocky Mountains, where defoliation is said to be greatest on grand fir

(Carlson and Wulf 1989). They also differ somewhat from the budworm

impacts observed during the 1944–1958 outbreak in the Blue Mountains.

When Williams (1966) assessed budworm effects in mixed-conifer stands on

the Wallowa National Forest in 1958–1959, he found that defoliation-related

damage was greatest and most variable on grand fir, and least for Douglas-fir.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all Douglas-fir and white fir trees (live and dead combined)

that were killed by budworm feeding. Error bars are the standard error of the

stratified mean estimate.

Budworm Impacts

By Tree Species

0

5

10

15

20

25

30

35

WHITE FIR DOUGLAS-FIR OTHER HOSTS

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
58 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for four classes of tree diameter

(fig. 44), as measured at breast height (DBH): seedlings (trees less than

1 inch DBH; 78% of the remeasured plots had host-tree seedlings), 1–

4.9 inches DBH (60% of the remeasured plots), 5–9.9 inches DBH

(70% of the remeasured plots), and 10 inches DBH and greater (94% of

the remeasured plots).

Figure 44—Budworm impacts by tree diameter. Defoliation was significantly greater for small trees (those less than 5" DBH) than for large ones.

Topkill amounts were relatively constant, although large trees (10" DBH and

greater) did have the lowest percentage. Budworm-induced mortality declined steadily as tree diameter increased, although the differences were not

statistically significant except for large trees (10"+ DBH). This figure suggests that small trees are much more likely to be killed by budworm than

large-diameter trees. Smaller trees had high mortality for two main reasons—

they had poor vigor and were least able to withstand the effects of budworm

feeding, and budworm larvae dispersing from taller trees tended to fall onto

them and continue feeding in what is referred to as a “feeding ladder” effect

(see fig. 20). Because small trees were killed most often, there were few

opportunities to salvage the budworm-caused mortality.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Tree Diameter

0

5

10

15

20

25

30

35

40

SEEDLING 1-4.9 5-9.9 10 +

TREE DIAMETER (Inches)

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 59

Budworm impacts were summarized for 4 classes of tree height (fig.

45): 6 inches–10 feet (81% of the remeasured plots had host trees in

that height category), 11–40 feet (66% of the remeasured plots), 41–80

feet (90% of the remeasured plots), and 81 feet and greater (49% of the

remeasured plots). Seedlings smaller than 6 inches were not sampled

during the plot remeasurements.

Figure 45—Budworm impacts by tree height. Trees less than 41 feet in

height had relatively high amounts of defoliation, topkill, and mortality when

compared to taller trees. This figure suggests that shorter trees are much more

likely to be affected by budworm feeding than taller trees. Shorter trees

sustained high mortality for two primary reasons—they had poor vigor and

were least able to withstand the effects of budworm feeding, and budworm

larvae dispersing from taller trees tended to fall onto them and continue

feeding in what is referred to as a “feeding ladder” effect (see fig. 20).

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Tree Height

0

5

10

15

20

25

30

35

0-10 11-40 41-80 81 +

TREE HEIGHT (Feet)

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
60 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 classes of tree age (fig. 46):

1–40 years (66% of the remeasured plots had host trees in that age

range), 41–80 years (80% of the remeasured plots), and 81 years and

greater (73% of the remeasured plots). Since age was available for live

trees only, budworm-induced mortality could not be assessed for this

factor.

For trees 3 inches or more in diameter, age was determined at 4.5 feet

above the ground; for seedlings and saplings smaller than 3 inches

DBH, it was determined between ground line and a height of 1 foot.

Age was deter-mined from the increment cores for all trees that were

large enough to provide a core; for smaller trees, age was determined by

counting branch whorls.

Figure 46—Budworm impacts by tree age. Some investigators believe that

budworm susceptibility increases as trees mature (Carlson and Wulf 1989).

Apparently, these results do not agree with that contention since the oldest

trees had the least amount of defoliation, although differences between age

classes were not always significant. Theoretically, old trees have high susceptibility because of low vigor, and because their larger size provides more

foliar biomass as budworm habitat. In this study, younger trees had high

susceptibility because they typically occurred in the overtopped and intermediate crown classes, both of which have low vigor, and because most budworm habitat was provided by small trees as a result of their abundance—

about 84% of the sampled trees were less than 20 feet tall.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Means were computed using the Douglas-fir and white fir sample trees only (other hosts were

excluded). Error bars are the standard error of the stratified mean estimate.

Budworm Impacts

By Tree Age

0

5

10

15

20

25

30

35

1-40 41-80 81 +

TREE AGE (Years)

PERCENT

DEFOLIATION

TOPKILL
IMPACTS OF THE BUDWORM OUTBREAK 61

Budworm impacts were summarized for 3 classes of stand density (fig.

47): a stand density index (SDI) of 0–150 (18% of the remeasured plots

had an SDI in that range), an SDI of 151–260 (41% of the remeasured

plots), and an SDI greater than 260 (42% of the remeasured plots).

Stand density index calculations included all trees (hosts and nonhosts)

that were alive in 1980, including those which subsequently died from

any cause, and trees that got established between the 1980 and 1989

measurements (ingrowth). (Note: stand density index is the number of

trees per acre that a stand would have at a quadratic mean diameter of

10 inches.)

The three categories analyzed for this factor were intended to encompass stand densities below the “management zone” (SDIs of 0–150),

densities within the management zone (SDIs of 151–260), and densities

above the management zone (SDIs greater than 260) for mixed-conifer

forests of the Blue Mountains (Cochran and others 1994).

Figure 47—Budworm impacts by tree density. Some investigators believe

that overstocked, dense forests are most susceptible to budworm damage

(Carlson and Wulf 1989). These results seldom support that assertion because

defoliation and topkill varied little with changes in density. Budworminduced mortality was greater for plots having a stand density index of 151 or

more when compared to plots with an index of 150 or less, although the

differences were not statistically significant.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Stand Density

0

5

10

15

20

25

30

35

40

0-150 151-260 261 +

STAND DENSITY INDEX

PERCENT

DEFOLIATION TOPKILL MORTALITY
62 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 classes of live-tree crown

ratios (fig. 48): 10–30 percent crown ratio (51% of the remeasured plots

had host trees in that category), 40–60 percent crown ratio (87% of the

remeasured plots), and 70 percent crown ratio or greater (92% of the

remeasured plots). Although budworm-caused mortality could not be

assessed for this factor because dead trees have no live crown, research

has shown that trees with small crown ratios have a high probability of

being killed by budworm defoliation (Ferguson 1988).

Figure 48—Budworm impacts by live crown ratio. This chart shows that

trees with the smallest, shortest crowns were missing the greatest proportion

of their foliage as a result of budworm defoliation; they also had the highest

amount of topkill. Defoliation and topkill percentages declined as live crown

ratio increased. The pattern of defoliation shown above is similar to the trend

by crown class (fig. 50), probably because many trees in the overtopped and

intermediate crown classes also had low crown ratios.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Means were computed using the Douglas-fir and white fir sample trees only (other hosts were

excluded). Error bars are the standard error of the stratified mean estimate.

Crown class is a measure of a tree’s position in the forest canopy (fig.

49). Budworm impacts were summarized for 3 crown classes (fig. 50):

suppressed or overtopped trees (78% of the remeasured plots had host

trees in those crown classes), intermediate trees (80% of the remeasured plots), and dominant and codominant trees (98% of the remeasured plots).

Budworm Impacts

By Live Crown

Ratio

Budworm Impacts

By Crown Class

0

10

20

30

40

50

60

10-30 40-60 70 +

LIVE CROWN RATIO (Percent)

PERCENT

DEFOLIATION

TOPKILL
IMPACTS OF THE BUDWORM OUTBREAK 63

Figure 49—Crown classes. Crown classes classify a tree’s position in the

forest canopy. Dominant trees (D) have crowns that rise above the general

canopy, where they enjoy full light from above and, to a certain degree, from

the sides. Codominant trees (C) are not quite as tall; their crowns are usually

hemmed in from the side. Intermediate trees (I) occupy a subordinate position; they have competition from the sides, but usually receive some overhead light through canopy holes. Suppressed trees (S) are overtopped entirely. Suppressed trees that can tolerate shade (such as true firs) may exist on

the filtered sunlight they receive for many decades; suppressed trees that

cannot tolerate shade (pines, etc.) will often die much more quickly than that.

Figure 50—Budworm impacts by crown class. Defoliation was significantly

less for upper-canopy trees (dominants and codominants) than for overtopped

or intermediate trees. Topkill was minor in any instance, and varied little with

changes in crown class. Mortality was strongly related to crown class—host

trees in the overtopped and intermediate crown classes had significantly

higher mortality than codominant and dominant trees. Defoliation means are

the percentage of a tree’s foliage that was missing as a result of budworm

feeding. Topkill means are the percentage of a tree’s height that consisted of

a dead top caused by budworm. Mortality means are the percentage of all

stems (live and dead combined) that were killed by budworm defoliation.

Means were computed using Douglas-firs/white firs only (other hosts were

excluded). Error bars are the standard error of the stratified mean estimate.

0

5

10

15

20

25

30

35

OVERTOPPED

(SUPPRESSED)

INTERMEDIATE DOMINANT AND

CODOMINANT

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
64 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 classes of potential growth

(fig. 51), in cubic feet per acre per year (cf/ac/yr): 20–39 cf/ac/yr (34%

of the remeasured plots had a productivity value in that range), 40–59

cf/ac/yr (46% of the remeasured plots), and 60 cf/ac/yr and greater

(21% of the remeasured plots). Productivity class was based on 444 site

trees that were measured on the 130 inventory plots (see “Site Indices”

and “Yield Capability Estimates” on pages 42–43). Productivity estimates may be conservative because 85% of the site trees were budworm hosts; underestimation of site index would be expected for host

trees because their height is more likely to have been affected by previous defoliator damage. (Most site index curves caution users against

selecting trees that may have sustained previous top damage.) From an

ecological perspective, site index was not underestimated unless it is

assumed that all future defoliator outbreaks will be suppressed, or that

host trees will be an insignificant component of the future stands.

Figure 51—Budworm impacts by site productivity. Defoliation, mortality,

and topkill impacts were greatest on sites with moderate or high productivity,

although the differences between productivity categories were not always

significant. Budworm-induced mortality was significantly greater for the

highly productive sites (60 +) when compared to the low or moderate productivity groups. These results for the high-productivity category (60 +) are similar to those for the low, sheltered physiographic positions (fig. 55), indicating

that the highly productive plots often occurred on those slope positions.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Site Productivity

0

5

10

15

20

25

30

35

40

45

50

20-39 40-59 60 +

SITE PRODUCTIVITY (CF/Ac/Yr)

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 65

Budworm impacts were summarized for 3 elevation classes (fig. 52):

less than 4,900 feet (23% of the remeasured plots occurred in that

elevational range), 5,000–5,900 feet (58% of the remeasured plots), and

6000 feet and greater (19% of the remeasured plots).

Figure 52—Budworm impacts by elevation. Defoliation and topkill did not

differ significantly by elevation, although mortality certainly did. Mortality

declined steadily with increasing elevation, although the differences between

categories were not always statistically significant. Some investigators believe that budworm damage is less severe at high elevations (Carlson and

Wulf 1989), and these results seem to support that assertion, particularly with

regard to mortality.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Elevation

0

5

10

15

20

25

30

35

40

0-4,900 5,000-5,900 6,000 +

ELEVATION (Feet)

PERCENT

DEFOLIATION TOPKILL MORTALITY
66 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 classes of slope steepness

(fig. 53): 0–15 percent (26% of the remeasured plots occurred on slopes

in that range), 16–30 percent (38% of the remeasured plots), and 31

percent and greater (36% of the remeasured plots).

Figure 53—Budworm impacts by slope gradient. Defoliation and topkill did

not differ significantly by slope gradient, although mortality certainly did.

Mortality increased steadily with increasing slope steepness, but the differences between categories were not always statistically significant.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Slope Gradient

0

5

10

15

20

25

30

35

40

0-15 16-30 31 +

SLOPE GRADIENT (Percent)

PERCENT

DEFOLIATION TOPKILL

MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 67

Budworm impacts were summarized for 4 aspects (fig. 54; aspect refers

to the direction in which a slope faces): north (40% of the remeasured

plots had a north-facing exposure), east (22% of the remeasured plots),

south (17% of the remeasured plots), and west (22% of the remeasured

plots).

Figure 54—Budworm impacts by aspect. Defoliation was greatest on southor east-facing exposures, whereas topkill percentages had little variation with

aspect. Budworm-caused mortality was greatest on westerly slopes. It is

possible that mortality was lowest on southerly exposures because those plots

tended to have lower stand densities, which means that sample trees would

have been under less competition-related stress than trees on crowded northfacing aspects.

It has been suggested that budworm impacts are most severe on warm, dry

sites, which were defined to be those with south and west exposures (Carlson

and Wulf 1989). Some of these results seem to support that assertion. In the

Pacific Northwest, however, east aspects may be drier than west-facing

slopes in some situations, primarily because west-facing slopes receive the

full impact of prevailing maritime storms moving eastward from the Pacific

ocean.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Aspect

0

10

20

30

40

50

60

NORTH EAST SOUTH WEST

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
68 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 physiographic classes (fig.

55): ridges (14% of the remeasured plots occurred on ridges), mountain

slopes (58% of the remeasured plots), and low, sheltered positions

(mid-slope benches, and bottoms or draws; 27% of the remeasured

plots).

Figure 55—Budworm impacts by physiographic position. Defoliation was

highest on ridges or low, sheltered positions, but really did not vary much

with changes in physiographic position. Topkill exhibited very little change

with physiography. Budworm-induced mortality was significantly greater on

low, sheltered positions when compared to the other two categories. These

results for the low, sheltered physiographic position category are similar to

those for high site productivity (the 60 + category; see fig. 51), indicating

that highly productive sites often occupied low, moist, sheltered slope

positions.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Physiographic

Position

0

5

10

15

20

25

30

35

40

45

LOW

POSITIONS

MOUNTAIN

SLOPES

RIDGES

PERCENT

DEFOLIATION TOPKILL

MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 69

Budworm impacts were summarized for 5 groups of plant associations

(fig. 56): Douglas-fir (DF)/sodgrass associations (PSME/CAGE and

PSME/CARU; 16% of the remeasured plots had those associations);

Douglas-fir (DF)/shrub associations (PSME/CELE, PSME/COST,

PSME/SYAL, and PSME/SYOR; 17% of the remeasured plots); white

fir (WF)/sodgrass associations (ABGR/ARCO, ABGR/BRVU, ABGR/

CAGE, and ABGR/CARU; 41% of the remeasured plots); white fir

(WF)/shrub associations (ABGR/SPBE, ABGR/VAME, and ABGR/

VASC; 17% of the remeasured plots); and white fir (WF)/forb associations (ABGR/CLUN and ABGR/LIBO2; 8% of the remeasured plots).

Two of the remeasured plots had subalpine fir associations and were

ignored for this analysis. During field sampling, species codes (using

Powell 1989) and canopy coverage values were recorded for every

vascular plant species on each sample point. Plant associations were

eventually determined after a revised vegetation classification was

produced for the Blue Mountains (Johnson and Clausnitzer 1992).

Figure 56—Budworm impacts by plant association. Defoliation was greatest

on the Douglas-fir/shrub and white fir/forb groups, which include some of

the moistest, most productive plant associations within those plant series.

Topkill amounts were low and showed little variation with changes in plant

association. Mortality was highest in the shrub-dominated plant associations,

regardless of whether they occurred in the Douglas-fir or white fir series. It

has been suggested that budworm does best on drier plant associations

(Carlson and Wulf 1989). These results seldom support that assertion because

moister groups had substantial budworm impacts. Defoliation means are the

percentage of a tree’s foliage that was missing as a result of budworm feeding. Topkill means are the percentage of a tree’s height that consisted of a

dead top caused by budworm. Mortality means are the percentage of all

stems (live and dead combined) killed by budworm defoliation. Means were

computed using the Douglas-firs and white firs only (other hosts were

excluded). Error bars are the standard error of the stratified mean estimate.

Budworm Impacts

By Plant

Association

0 10 20 30 40 50 60

WF/FORB

WF/SHRUB

WF/SODGRASS

DF/SHRUB

DF/SODGRASS

PERCENT

MORTALITY

TOPKILL

DEFOLIATION
70 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Budworm impacts were summarized for 3 classes of budworm-host

percentage (fig. 57): 0–60 percent host trees (22% of the remeasured

plots had a budworm host percentage in that range), 61–80 percent host

trees (18% of the remeasured plots), and 81–100 percent (59% of the

remeasured plots). The percentage of budworm host trees was calculated using all trees that were alive in 1980, including those which

subsequently died from any cause, and trees that became established

between the 1980 and 1989 measurements (ingrowth).

Figure 57—Budworm impacts by budworm host percentage. Defoliation was

greatest for plots with the lowest percentage of budworm host species (0–

60%), whereas topkill and mortality were highest on plots comprised almost

exclusively of host trees (81–100%). It has been suggested that susceptibility

to budworm damage increases as the proportion of host trees increases (Carlson and Wulf 1989, Campbell 1993), and some of the results shown here

seem to support that contention.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Budworm-Host

Percentage

0

5

10

15

20

25

30

35

40

45

50

0-60 61-80 81-100

BUDWORM HOST PERCENTAGE

PERCENT

DEFOLIATION TOPKILL MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 71

Budworm impacts were analyzed for 2 groups of defoliation history

(fig. 58): plots which had 0–4 years of mapped defoliation (45% of the

remeasured plots), and plots which had 5–8 years of mapped defoliation

(55% of the remeasured plots). Aerial sketch maps, which are prepared

annually by the Pacific Northwest Region, were used to estimate the

number of years that each plot had been defoliated between 1981 and

1989. During analysis of this factor and the next one (defoliation

severity), sketch-map information for the year in which a plot was

visited (1988 or 1989) was not used unless the plot had been measured

on August 15th or later. Measurements collected before August 15th are

not considered to be representative of defoliation conditions as they

existed when that year’s sketch map was prepared.

Figure 58—Budworm impacts by defoliation history. Surprisingly, defoliation was higher on plots that had been defoliated for 0–4 years than on plots

with 5 to 8 years of defoliation, although the difference was minor and not

statistically significant. It is certainly possible that defoliation was more

intense (severe) on the plots that had been defoliated for 0–4 years, even

though it was not sustained for as long as it was on the plots with 5–8 years

of budworm feeding. It is also possible that trees on plots with 5–8 years of

defoliation sustained their heaviest losses early in the outbreak, and were

then able to replace some foliage before the field data was collected in 1988–

1989. Topkill was highest on plots defoliated for 5–8 years, although the

difference was minor. Mortality was appreciably greater on plots with 5–8

years of defoliation, although the difference between those plots and the ones

with 0–4 years of defoliation was not statistically significant.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of tree height

that consisted of a dead top caused by budworm. Mortality means are the percentage of all stems (live and dead combined) killed by budworm defoliation.

Means were computed using Douglas-firs/white firs only (other hosts were

excluded). Error bars are the standard error of the stratified mean estimate.

Budworm Impacts

By Defoliation

History

0

5

10

15

20

25

30

35

0-4 YEARS OF

DEFOLIATION

5-8 YEARS OF

DEFOLIATION

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
72 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Beginning with the 1986 aerial sketch map, budworm defoliation was

recorded using four severity classes, ranging from barely-visible damage (severity of 1) to severe defoliation (severity of 4). Budworm impacts were summarized for 3 categories of defoliation severity (fig. 59):

very low (average defoliation severity of less than 1; 52% of the remeasured plots); low (average defoliation severity of 1 to 1.9; 32% of the

remeasured plots); and moderate/high (average defoliation severity of 2

or greater; 16% of the remeasured plots). A defoliation severity rating

was calculated for each plot by averaging the mapped severity values

from 1986 to the year in which it was remeasured (1988 or 1989). Years

in that range in which the plot was not shown as being defoliated were

assigned a value of zero and used in the severity calculations.

Figure 59—Budworm impacts by defoliation severity (1986–1989). Defoliation and topkill did not exhibit much variation with changes in defoliation

severity. Budworm-induced mortality increased steadily as defoliation

severity increased. The mortality means for the moderate/high and low

severity ratings were not statistically different because the moderate/high

value had a large standard error, which reflected the low sample size associated with that category.

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Defoliation

Severity (1986–

1989)

0

5

10

15

20

25

30

35

40

VERY LOW LOW MODERATE/HIGH

DEFOLIATION SEVERITY (1986-1989)

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
IMPACTS OF THE BUDWORM OUTBREAK 73

During the 1980s spruce budworm outbreak, portions of the Malheur

NF were sprayed four times with a chemical or biological insecticide to

suppress budworm populations (see figs. 67 and 69, and Table 4).

Budworm impacts were summarized for 3 treatment categories (fig.

60): untreated (54% of the remeasured plots); borderline (7% of the

remeasured plots); and treated (39% of the remeasured plots). The

borderline category includes those plots which fell within a quartermile of a spray project boundary, whether inside or outside. They were

included in a separate category because treatment maps do not have

enough resolution to indicate whether plots near the project-area

boundaries were actually treated.

Figure 60—Budworm impacts by insecticide treatment. This chart indicates

that there were no statistically significant differences in budworm-caused

defoliation, topkill, or mortality between treated and untreated plots. Does

that mean that the treatments were ineffective? Possibly, but it could also

indicate that treated areas had high defoliation levels before treatment, which

could have been one reason for their inclusion in an analysis area. It could

also indicate that budworm populations recovered completely within a few

years of treatment, or that more than one insecticide application would have

been required for long-term suppression of western spruce budworm populations. None of the remeasured inventory plots were treated with an insecticide more than once during the 1980s budworm outbreak. (However, there

were areas on the Malheur NF that were treated more than once during the

1980s budworm outbreak; see fig. 69.)

Defoliation means are the percentage of a tree’s foliage that was missing as a

result of budworm feeding. Topkill means are the percentage of a tree’s

height that consisted of a dead top caused by budworm. Mortality means are

the percentage of all stems (live and dead combined) that were killed by

budworm defoliation. Means were computed using the Douglas-fir and white

fir sample trees only (other hosts were excluded). Error bars are the standard

error of the stratified mean estimate.

Budworm Impacts

By Insecticide

Treatment History

0

10

20

30

40

50

60

UNTREATED BORDERLINE TREATED

TREATMENT HISTORY

PERCENT

DEFOLIATION

TOPKILL

MORTALITY
74 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

An objective of the special project was to determine if future timber

yields will be affected by budworm damages sustained from 1980 to

1989. That objective was accomplished by using these processes:

Inventory plots assigned to the same Forest Plan model component

were grouped together as a stratum. Eight of the 130 remeasured plots

had been harvested between the 1980 and 1988–1989 measurements

and were not included in the computer modeling process.

Two data sets were then created—one containing the 1980 measurements to provide an estimate of pre-outbreak conditions, and a second

one with the 1988–1989 information that portrayed conditions as they

existed late in the outbreak. The following model components, and the

number of tree records available for each, were used for the modeling:

101: ponderosa pine type, regeneration recommended (126 records

for 1980; 135 records for 1988-1989).

201: ponderosa pine type, commercial thinning recommended (165

records for 1980; 182 records for 1988-1989).

102: mixed-conifer type, regeneration recommended (318 records

for 1980; 380 records for 1988-1989).

202: mixed-conifer type, commercial thinning recommended (371

records for 1980; 438 records for 1988-1989).

502: mixed-conifer type, overstory removal recommended (428

records for 1980; 427 records for 1988-1989).

602: mixed-conifer type, no treatment recommended (237 records

for 1980; 243 records for 1988-1989).

An insufficient number of tree records were available for model components 501 and 601 (ponderosa pine types) and all of the lodgepole

pine components (103, 203, 503, and 603); therefore, they were not

included in the computer modeling process.

For the 1988–1989 data, older, taller trees with serious topkill had their

heights truncated so that no further height growth would occur. Host

trees with less serious topkill had their heights reduced to account for

the dead tops, but future height growth was allowed to occur.

Small Douglas-firs and white firs (trees 3 inches or less in diameter)

had their height growth reduced using formulas that correlate defoliation amounts with the proportion of expected height growth (Crookston

1991). Small trees had their height growth constrained until the year

2000, after which it was assumed that they would have regained their

pre-outbreak growth rates.

Three management scenarios were then simulated using the Blue

Mountain variant of the Stand Prognosis Model (Johnson 1990): an

unmanaged “base” run spanning as much as 150 years (to the year

Future Timber

Yields

Computer Modeling

Information

Height Growth

Modified For

Topkill

Management

Scenarios
IMPACTS OF THE BUDWORM OUTBREAK 75

2130); a low-density silvicultural regime involving an overstory removal and concurrent precommercial thinning to a relatively low

residual density, followed by one or more commercial thinnings; and a

high-density regime involving an overstory removal and concurrent

precommercial thinning to a relatively high residual density, followed

by one or more commercial thinnings.

Results of the computerized modeling are provided in figures 61 to 65.

Those figures describe the volume reductions resulting from budworm

impacts sustained between 1980 and 1989. The board-foot reductions

described in figures 61–65 are conservative and may represent the

minimum reduction that occurred, for these reasons:

• When budworm populations “crashed” in 1987 (see fig. 6), it was

believed that the outbreak was ending and that further defoliation

would cease in a year or two. That eventuality did not occur, and

budworm defoliation began increasing again in 1990. Field sampling

to measure budworm-related damage occurred in 1988 and 1989,

and no additional sampling was completed to determine the effects

of subsequent defoliation in 1990 or 1991. However, 32% of the

remeasured plots were visited again in 1992 by crews from the TriForest Inventory Group (headquartered in Pendleton, OR). Although

they did not record defoliation and topkill in a manner similar to that

used in 1988–89, they did assess mortality using comparable methods. The mortality increase between 1988–89 and 1992 was substantial but, surprisingly, the percentage of the mortality attributable to

budworm defoliation actually declined during that period (fig. 66).

• Computerized modeling was designed to analyze the effects of this

outbreak (1980-1989) only; no future outbreaks of either western

spruce budworm or Douglas-fir tussock moth were simulated. Why

was that assumption made? It would be difficult to determine the

volume reductions associated with the 1980s epidemic if the model

had been allowed to confound the situation by simulating further

outbreaks, whether by budworm or tussock moth. But formulating

computer simulations spanning 150 years that do not include future

budworm and tussock-moth outbreaks is not a reasonable representation of “real life” for mixed-conifer forests of the Blue Mountains.

For example, recent surveys indicate that tussock-moth populations

are rising again, and several small outbreaks occurred on the

Malheur NF in 1992 and 1993 (Willhite 1993).

• When the mixed-conifer inventory plots were remeasured in 1988

and 1989, the severity of a wide range of biotic and abiotic agents

was recorded for each sample tree (dwarf mistletoe ratings, etc.). For

that reason, the effects on tree growth from insects other than budworm and from diseases such as dwarf mistletoe and root rots, and

the effects of abiotic factors like drought and suppression, are inModeling Results
76 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

directly incorporated in the modeling results. If those non-budworm

factors remain relatively constant, the modeling has probably incorporated their effects adequately. But if they suddenly become worse,

such as accelerated impacts from annosus root disease in mixedconifer stands that have been partially cut, or a severe drought with

less rainfall than occurred during the late 1980s, it is likely that the

modeling does not reflect the total amount of potential reduction.

The situations described above explain why the volume losses portrayed in figures 61–65 may be conservative. But users of that information should also realize that nothing was done in the modeling to intentionally mitigate the effects of budworm. Each management scenario

was modeled using the same silvicultural assumptions that were used to

prepare managed-stand yield tables for the Forest’s Land and Resource

Management Plan (USDA Forest Service 1990).

The Plan’s yield tables assumed that existing understories would be

managed after the overstory had been removed, even though many of

those understories consist of white fir, Douglas-fir, and other species

susceptible to budworm impacts. Therefore, it’s possible that the volume losses described in figures 61–65 would not have occurred if the

existing understories, many of which were affected by budworm-caused

defoliation between 1980 and 1989, had been destroyed and replaced

with healthy trees—particularly if the replacement trees were ponderosa

pines and other seral species that aren’t hosts of budworm.

Figure 61—Projected yields in 1990 for pre-outbreak and late-outbreak conditions. The pre-outbreak volumes were derived by growing the unaffected

(1980) trees forward to 1990; late-outbreak values are the result of growing

the affected (1988–1989) trees forward to 1990. Volume reductions from

budworm varied, ranging from lows of 3.2% for model component 202 and

5.3% for component 602, to highs of 12.9% for component 502 and 15.2%

for component 101. Model components 201 and 102 had intermediate reductions, which were 5.8% and 7.9%, respectively.

Consistency With

Forest Plan

Forest Plan Yield

Assumptions

101 201 102 202 502 602

0

5

1 0

1 5

2 0

FOREST PLAN MODEL COMPONENT

MERCHANTABLE YIELD (MBF/ACRE)

PRE-OUTBREAK

LATE-OUTBREAK
IMPACTS OF THE BUDWORM OUTBREAK 77

Figure 62—Projected yields in 2130 for pre-outbreak and late-outbreak conditions. Figure 61 shows how budworm damage affected yields in 1990; this

figure compares yields about 150 years after the outbreak began in 1980.

Even though the volume difference between unaffected (pre-outbreak) and

affected (late-outbreak) conditions is greater for every component, in absolute terms, than it was in 1990, reductions by 2130 actually declined on a

percentage basis. Four of the six components had reductions of less than 5%

(201: 3.1%; 102: 3.7%; 202: 4.1%; 602: 4.8%), and only one component

(101) still had a substantial reduction (12.5%). Component 502, the largest

one on the Forest with over a half million acres, had a loss of 6.3% in 2130.

Figure 63—Projected timber yields for pre-outbreak and late-outbreak conditions under a low-density silvicultural regime. Total yield (standing volume

in 2130 plus harvest volumes from periodic overstory removals and commercial thinnings) is always higher for a low-density regime than it was for the

unmanaged scenario (fig. 62), but the volume reductions associated with lateoutbreak conditions varied widely. Five of the six components had relatively

minor reductions, ranging from 3% for component 201 to 6.9% for component 502. Component 101 had a substantial reduction; volumes for the lateoutbreak condition were 21.2% less than yields from the pre-outbreak plots.

101 201 102 202 502 602

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

FOREST PLAN MODEL COMPONENT

MERCHANTABLE YIELD (MBF/ACRE)

PRE-OUTBREAK

LATE-O UTBR EAK

101 201 102 202 502 602

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

FOREST PLAN MODEL COMPONENT

MERCHANTABLE YIELD (MBF/ACRE)

PRE-O UTBREAK

LATE-O U TBR EAK
78 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 64—Projected timber yields for pre-outbreak and late-outbreak conditions under a high-density silvicultural regime. Total yield (standing volume

in 2130 plus harvest volumes from periodic overstory removals and commercial thinnings) is generally higher for a high-density regime than it was for

either the unmanaged or low-density scenarios (figs. 62–63). The volume reductions attributable to late-outbreak budworm impacts (as of 1988–1989)

varied widely, ranging from none for model component 201 and an insignificant 1.5% for component 602, to more substantial declines of 9.9% for component 502 and 21.2% for component 101.

Figure 65—Projected timber yields associated with pre-outbreak and lateoutbreak conditions for model component 502. This figure shows cumulative

(standing) board-foot volumes for model component 502 only (unmanaged).

It demonstrates that volume reduction from budworm impacts tended to

remain rela-tively constant through time—the percentage reduction in 1990 is

similar (but not identical) to the percentage at each succeeding 10-year

interval. It also shows that the 1980s budworm outbreak caused a loss of

almost exactly 10 years of growth; the volume of affected (late-outbreak)

trees in 2040 is virtually identical to the volume attained by unaffected (preoutbreak) trees 10 years earlier (see arrows in the chart).

101 201 102 202 502 602

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

FOREST PLAN MODEL COMPONENT

MERCHANTABLE YIELD (MBF/ACRE)

PRE-O UTBREAK

LATE-O U TBR EAK

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090

0

1 0

2 0

3 0

4 0

5 0

6 0

RADIAL GROWTH (mm)

LATE-O UTBR EAK PRE-O UTBREAK
IMPACTS OF THE BUDWORM OUTBREAK 79

Figure 66—1992 mortality update. In 1992, 42 of the 130 inventory plots

used for this study were revisited by an inventory crew. Although defoliation

and topkill were not estimated in the same way as they were in 1988–89

(which means that changes cannot be compared for those budworm impacts),

the crew did assess tree mortality in a similar manner.

The top half of this chart summarizes tree composition and mortality causes

in 1988–1989 for the 42 remeasured plots; the bottom half summarizes the

same information for 1992. In the 3–4 year interval represented in the chart,

mortality increased substantially. However, the proportion of trees killed by

budworm actually declined in 1992, even though total mortality increased. It

is unclear whether the reduction in budworm-caused mortality is a real

change, or whether it occurred because the surveys were completed by

different individuals. It is possible that the change reflects differing interpretations about the causes of mortality in the 1988–1989 and 1992 surveys.
80 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

MANAGING BUDWORM AND ITS IMPACTS

Although this report was designed to describe recent impacts from

budworm defoliation, it was difficult to do so without discussing

how those impacts could have been mitigated or avoided. This section

of the report provides that discussion.

Managing budworm populations typically involves four approaches,

used independently or in concert. The approaches are described below.

• Taking no direct action; letting the outbreak run its natural course.

• Suppressing budworm populations by applying an insecticide.

• Reducing budworm impacts by improving tree and stand vigor.

• Avoiding budworm impacts by modifying the insect’s habitat with

silvicultural practices.

A no-action approach is appropriate when budworm damage is not

expected to prevent accomplishment of the management objectives for

an area, such as attainment of its desired future condition. Land managers have been considering a no-action approach more often than they

used to, especially as more information becomes available about the

important role that budworm and other insects play in the ecosystem.

But during the recent outbreak, many managers chose to implement the

direct suppression approach because the severity and extent of budworm impacts was greater than they could accept.

During the 1944–1958 budworm outbreak in the Blue Mountains,

almost 4.7 million acres were sprayed with an insecticide called DDT

(Dolph 1980). DDT became popular after two early successes—it was

used to control Douglas-fir tussock moth outbreaks in northern Idaho

(Carlson and others 1983) and the northern Blue Mountains (Wickman

and others 1973) in 1947, and for experimental suppression of spruce

budworm populations on part of the Heppner Ranger District (Umatilla

NF) and adjacent industrial lands (Kinzua) in 1948 (Eaton and others

1949). Several large DDT spray projects were completed on the

Malheur NF, including 233,764 acres in 1955 (Whiteside and others

1956) and 409,000 acres in 1958 (fig. 67).

DDT, a powerful chemical applied in a fuel oil diluent, could affect

many organisms besides budworm (Hunter 1990). Even though DDT

was commonly applied during the 1944–1958 outbreak in the Blue

Mountains (fig. 68), land managers eventually realized that it did not

provide any long-term budworm control because its use did not address

the underlying cause—proliferation of budworm habitat throughout the

western United States (Carolin and Coulter 1971, Fellin 1983). Because

of its environmental persistence and the broad spectrum of organisms

affected by it, DDT was eventually banned for all uses in 1972.

Budworm

Management

Approaches

No Action Approach

Direct Suppression

Approach

Early Use of DDT

for Budworm

Control
MANAGING BUDWORM AND ITS IMPACTS 81

Figure 67—Summary of defoliator suppression projects on the Malheur NF.

Several large projects using the insecticide DDT were completed against

budworm in 1955 and 1958. The 1965 DDT application was used to help

control an outbreak of the Douglas-fir tussock moth. When budworm reached

outbreak levels once again in the early 1980s, carbaryl was the primary

insecticide used to suppress budworm populations. In 1983, one relatively

small area was treated with mexacarbate, a chemical insecticide, and another

with B.t., a bacterial insecticide. By the mid 1980s, a bacterium called

Bacillus thuringiensis (B.t.) was being used for all of the national forest

treatment projects.

Figure 68—Trailing plumes of insecticide, an airplane applies DDT and a

diesel oil diluent to defoliated stands in the northern Blue Mountains in June

of 1951. On the Malheur NF, DDT was used as a budworm insecticide in

1955 and 1958, when more than 640,000 acres were treated.

1955 1958 1965 1982 1983 1985 1987

0

5 0

100

150

200

250

300

350

400

450

TREATED AREA (THOUSAND ACRES)

B.t.

CARBARYL

DDT
82 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

During the 1980s budworm outbreak direct suppression projects were

completed in 1982, 1983, 1985, and 1987. Those projects involved

application of a chemical or biological insecticide, on areas with varying sizes, to suppress budworm populations (fig. 69 and Table 4).

Figure 69—Budworm suppression projects completed during the 1980s on

the Malheur NF. During the 1980s outbreak, four different projects were

completed to suppress budworm populations, and three different insecticides

were used (Table 4). The “multiple” areas are those that were treated during

two different years.

The objective of the 1980s suppression projects was to reduce budworm populations to non-damaging levels for the remainder of the outbreak (USDA Forest Service 1982, 1983, 1985, and 1987b). For a variety of reasons, that objective was not achieved. One possible reason is

that insecticides were not applied to all of the area with visible defoliation, so that budworms in untreated areas could reinvade the treated

units. Another reason is that an insecticide application does not eradicate budworm or its impacts—it typically suppresses populations and

associated tree impacts for a period of three or four years at best.

1980s Budworm

Suppression

Projects

Suppression Project

Objectives
MANAGING BUDWORM AND ITS IMPACTS 83

Table 4—Treatment information for budworm suppression projects completed on

the Malheur NF, 1982–1987.

Acres Dosage Volume

Year Treatment Unit Treated Insecticide Per Acre* Diluent Per Acre

1982 Baldy 32,798 carbaryl 1 lb. AI diesel oil 64

Middle Fork 67,584 carbaryl 1 lb. AI diesel oil 64

Total (1982) 100,382

1983 Aldrich 127,748 carbaryl 1 lb. AI diesel oil 64

Logan North 10,520 carbaryl 1 lb. AI diesel oil 64

Logan South 1 62,741 carbaryl 1 lb. AI diesel oil 64

Logan South 2 39,897 carbaryl 1 lb. AI diesel oil 64

Snow 5,536 carbaryl 1 lb. AI diesel oil 64

Butte 6,743 carbaryl 1 lb. AI diesel oil 64

King 18,850 carbaryl 1 lb. AI diesel oil 64

Pogue Point 1 15,291 carbaryl 1 lb. AI diesel oil 64

Pogue Point 2 11,663 mexacarbate .1 lb. AI diesel oil 128

Pogue Point 3 12,309 B.t. 12 BIU water 96

P.A. 18,231 carbaryl 1 lb. AI diesel oil 64

Total (1983) 329,529

1985 Rail 9,598 B.t. 12 BIU undiluted 24

Scotty 10,070 B.t. 12 BIU undiluted 32

Burnt Cabin 7,815 B.t. 12 BIU water 48

Crooked 12,685 B.t. 12 BIU water 96

Lost Cabin 565 B.t. 15 BIU water 64

Total (1985) 40,733

1987 Dixie 18,445 B.t. 12 BIU water 96

Flat 46,223 B.t. 12 BIU water 96

Lost Cabin 23,774 B.t. 12 BIU water 96

Canyon 22,537 B.t. 12 BIU water 96

Starr 393 B.t. 12 BIU water 96

Total (1987) 111,372

Total (1982–87) 582,016

 * AI is active ingredient; BIU is Billion International Units.

Source: Unpublished project records provided by the Forest Insects and Diseases Group

of the Natural Resources Staff, located at the Regional Office for the Pacific Northwest

Region of the U.S. Forest Service in Portland, Oregon.
84 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

During the 1982 and 1983 treatments, chemical insecticides were applied in a diesel oil diluent. Diesel oil was used to improve the chemical’s adherence to foliage, and to minimize the risk of insecticide being

washed away by a rainstorm shortly after application (based on the

principle that oil and water don’t mix). A chemical called carbaryl was

applied in most of the general-forest situations; another chemical called

mexacarbate was used in one area having special environmental sensitivity. Beginning with an experimental application in 1983, the insecticide used for all subsequent projects on the Malheur NF (the 1985 and

1987 treatments) was a natural bacterium called Bacillus thuringiensis

(B.t.). B.t. was always applied in a water base, rather than the diesel oil

used with the predominant chemical insecticide—carbaryl.

By the mid 1980s, B.t. was the insecticide of choice because of its low

risk to the environment and human health. It directly affects a narrow

range of organisms—only butterflies and moths in the Lepidoptera

insect order are killed. B.t. is similar to the toxins contained in some

spider and snake venoms in that it is cytolytic—after ingestion, it

causes cells in the guts of susceptible insects to rupture and disintegrate

(Ware 1989). Following the success of B.t. and other natural insecticides, scientists are evaluating derivatives from marigolds and other

asters, soil microorganisms, the neem tree, and other natural sources in

their efforts to develop new insecticides for forestry applications

(Helson 1992). The need to develop biologically based pest management strategies is widely recognized (USDA Forest Service 1993).

Adoption of B.t. in the mid 1980s did not occur because the previous

insecticides (carbaryl, acephate, and mexacarbate) had been banned, as

was the case when DDT was abandoned in the early 1970s. A switch to

B.t. reflected an increasing awareness that chemical insecticides and

their diesel oil diluent may have had adverse environmental consequences. For example, using B.t. allowed land managers to maintain more of

the pretreatment arthropod diversity than was probable with carbaryl,

acephate, or mexacarbate. Some of that pretreatment diversity included

thatch ants, carpenter ants, jumping spiders, yellowjackets, and other

natural enemies of spruce budworm (see fig. 91).

In some situations, converting susceptible mixed-conifer stands to

resistant tree species, or adopting another long-term budworm approach, will not meet the short-term objectives for an area. In the past,

land managers reacted to those situations by implementing the direct

suppression approach (i.e., applying an insecticide). They now have

several other treatments to consider if adequate time (3 to 5 years) is

available before budworm defoliation reaches high levels. The objective of short-term treatments is to increase the vigor of host trees to the

point where most of them can survive a persistent budworm outbreak.

Using Chemical

Insecticides

B.t. Becomes

Primary Insecticide

B.t. Offers

Environmental

Benefits

Short-Term Stand

Vigor Approaches
MANAGING BUDWORM AND ITS IMPACTS 85

One stand-vigor approach is thinning (fig. 70), where some trees are

removed so that those which remain have access to additional growing

space, nutrients, and sunlight. Trees respond to a thinning by producing

more foliage; full-crowned trees typically experience less defoliation

damage (on a proportional basis) than short-crowned trees (see fig. 48).

Thinned, vigorous trees usually develop a higher level of root reserves,

which improves their ability to recover from prolonged defoliation.

Thinning from below is particularly beneficial because it creates the

open, single-storied stand structure that promotes mortality of dispersing budworm larvae (Carlson and Wulf 1989). Thinning also offers an

opportunity to remove some host trees and thereby favor nonhosts.

Budworm research conducted in western Montana showed beneficial

effects from thinning (Carlson and Wulf 1989), but thinned stands in

the Blue Mountains have seldom shown a similar response (Boyd

Wickman, personal communication; Wickman and others 1992).

Studies in the Blue Mountains found that thinning can actually favor

budworm. It allows more sun into the canopy, thereby creating warmer

budworm microhabitats. Warmer conditions allow budworm to develop

faster, eat more, and to possibly escape more natural predation while in

the larval stage (Boyd Wickman, personal communication).

Figure 70—Tree thinning. Thinning can offer at least three benefits for budworm management—vigor of the residual trees is increased, thereby increasing budworm resistance; a single-storied stand can be created by thinning

from below, which increases the mortality of dispersing larvae; and thinning

provides an opportunity to remove host trees and thereby favor nonhosts.

Tree Thinning

Thinning From

Below

Thinning Can

Favor Budworm
86 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Another promising stand-vigor approach is fertilization (fig. 71), a

treatment that allows host trees to produce more foliage than budworm

larvae can consume. In a study near King Mountain on Burns Ranger

District of the Malheur NF, fertilized trees had high foliage production,

rapid recovery from budworm-induced top damage, and dramatically

increased rates of diameter growth, as compared to the unfertilized

controls (Wickman and others 1992).

Figure 71—Fertilization of mixed-conifer stands. Recent research (Wickman

and others 1992) showed that fertilizer may help reduce budworm damage if

applied early in an outbreak. A study near Mt. Emily in the northern Blue

Mountains indicates that fertilization may not be effective if budworm

populations were high before treatment (photo courtesy of Art Tiedemann).

A recent study showed that budworm resistance may be related to the

nutritional qualities of foliage, and that susceptible trees had lower

levels of foliar nitrogen and sugars than resistant trees (Clancy and

others 1993). Fertilization may provide opportunities to modify foliar

chemistry and thereby improve a tree’s resistance to budworm defoliation. Fertilization would be particularly effective if it increased foliar

sucrose (sugar) without commensurate increases in the levels of foliar

nitrogen and other minerals (Clancy 1992).

A recent study in the northern Blue Mountains near Mt. Emily indicates

that fertilization may not be as effective when budworm populations are

very high (Boyd Wickman, personal communication). To achieve satisfactory results, fertilizer should apparently be applied early in an outbreak or, if possible, just before its onset. In areas with high susceptibility to budworm damage, it now appears that fertilization may be a

viable alternative to repetitive insecticide applications (Waring and

others 1992).

Forest Fertilization

Fertilization and

Budworm

Resistance

Timing of

Fertilization
MANAGING BUDWORM AND ITS IMPACTS 87

Fertilization may provide other benefits as related to insect and disease

management. It may help reduce stem decay for grand firs that have

been wounded during logging or by other agents (Filip and others

1992). By changing root chemistry, fertilization with nitrogen and

potassium apparently has beneficial effects on a tree’s resistance to

Armillaria root disease (Moore and others 1993).

Many silvicultural practices can reduce stand and forest susceptibility

to budworm, primarily by reducing the proportion of host trees in future

stands; by capitalizing on budworm-resistant genotypes; by regulating

stand density to optimize future vigor and associated budworm resistance; and by improving conditions for birds, ants, and other enemies of

budworm (Carlson and Wulf 1989). There is a pressing need to evaluate

how alternative silvicultural systems could address budworm outbreaks and other forest health concerns (USDA Forest Service 1993).

Some common silvicultural practices, and their effects on budworm

susceptibility, are described below.

Stand clearcutting (fig. 72) removes most of the trees from an area in a

single entry, with the objective of establishing a new, even-aged stand.

It can be an effective way to regenerate ponderosa pine, lodgepole pine,

western larch, and western white pine, all of which require open, sunny

environments for optimum regeneration and growth. Since those species are not budworm hosts, stand clearcutting can reduce budworm

susceptibility for the forests of the future. Stand clearcutting with

reserve trees (fig. 72) would be less effective at reducing budworm

susceptibility if host trees are selected as the reserves.

Small-patch and strip clearcuts (figs. 73 and 74) result in smaller harvest areas than with stand clearcutting. Although they are more visually

attractive than stand clearcuts, patch or strip clearcuts have greater

potential to create the shady post-harvest conditions conducive to

regeneration of budworm-host trees. But in areas with visual sensitivity,

both patch and strip clearcuts can provide regeneration opportunities

for nonhost species and still meet some aesthetic objectives.

Seed-tree cutting (fig. 75) is similar to clearcutting except that 6 or

more seed producing trees are left on each acre to promote natural

regeneration. When using this method, silviculturists can affect future

budworm resistance by their choice of seed trees, and by their decision

about whether to plant the harvest units. If future budworm resistance is

an objective, then retention of larches, pines, and other nonhost trees

should be considered when selecting the seed trees, unless harvested

areas will be planted to control their future species composition.

Shelterwood cutting (fig 76) differs from the seed-tree method in that

the number of residual trees is great enough to influence environmental

conditions over a large area, rather than next to each seed tree. A shelterwood seed cut retains at least 12 or more well-distributed trees on

Other Benefits of

Fertilization

Long-Term

Silvicultural

Approaches

Stand Clearcutting

Patch and Strip

Clearcuts

Seed-Tree Cutting

Shelterwood

Cutting
88 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

each acre. If future budworm resistance is an objective, and the harvest

area is not planted with nonhost species, then it would be important to

retain larches, pines, and other nonhost trees in the seed cut.

Figure 72—Stand clearcutting. Stand clearcutting can create single-storied,

even-aged stands with low budworm susceptibility, especially if nonhost

species like ponderosa pine and western larch are regenerated. In the past,

stand clearcutting resulted in all of the trees being removed from an area; now,

both dead trees (snags) and live reserve trees are retained. Although clearcutting can effectively create some of the environmental conditions conducive

to regeneration of seral, nonhost tree species, it is unlikely to be applied much

in the future because of public concern about its short-term impact on aesthetics and other values. In response to those concerns, the U.S. Forest Service

issued direction to reduce clearcutting on the national forests by 70% or more

from fiscal year 1988 levels (USDA Forest Service 1992).
MANAGING BUDWORM AND ITS IMPACTS 89

Figure 73—Patch clearcutting. Small-patch clearcuts are effective at reducing budworm susceptibility, although creation of small openings could result

in post-harvest conditions that are shady enough to favor regeneration of

budworm host trees. Although clearcutting can effectively create some of the

environmental conditions conducive to regeneration of seral, nonhost tree

species, it is unlikely to be applied much in the future because of public

concern about its short-term impact on aesthetics and other values. In response

to those concerns, the U.S. Forest Service issued direction to reduce clearcutting on the national forests by 70% or more from fiscal year 1988 levels

(USDA Forest Service 1992).
90 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 74—Strip clearcutting. Strip clearcuts are effective at reducing budworm susceptibility, although creation of narrow openings could result in

post-harvest conditions that are shady enough to favor regeneration of

budworm host trees. Although clearcutting can effectively create some of the

environmental conditions conducive to regeneration of seral, nonhost tree

species, it is unlikely to be applied much in the future because of public

concern about its short-term impact on aesthetics and other values. In response

to those concerns, the U.S. Forest Service issued direction to reduce clearcutting on the national forests by 70% or more from fiscal year 1988 levels

(USDA Forest Service 1992).
MANAGING BUDWORM AND ITS IMPACTS 91

Figure 75—Seed-tree cutting. Seed-tree cutting can reduce budworm susceptibility if host trees are removed in the seed cut, thereby favoring regeneration of non-host species. For both clearcutting and seed-tree cutting, planting

of the harvest units can help improve the proportion of nonhost species in the

future stand. Since it is likely that the seed trees will be retained for long

periods in the future (or never removed), so that they can serve as biological

legacies or to provide replacement snags for cavity-nesting birds, it is important to choose nonhost species as the seed trees.
92 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 76—Shelterwood cutting. Shelterwood cutting can reduce budworm

susceptibility if the host trees are removed in the seed cut. Since shelterwood

cutting results in more site shading than either clearcutting or seed-tree cutting, it can promote regeneration of host species. Planting the shelterwood

units can help improve the proportion of nonhost species in the future forest.

Group selection (fig. 77) is an uneven-aged cutting method where trees

are removed in small groups. The distance across an individual group is

usually no more than one or two times the height of the surrounding

trees, up to a maximum size of 2 acres. These openings permit more

sunlight to reach the forest floor than with single-tree selection; regeneration of some shade-intolerant trees is possible. However, the amount

of exposed ground is less than that produced by clearcutting, seed-tree

cutting, or other even-aged methods. If uneven-aged management is desired for an area with high budworm susceptibility, then group selection

cutting offers the most promise for regenerating some nonhost species.

Group Selection
MANAGING BUDWORM AND ITS IMPACTS 93

Figure 77—Group selection. Group selection cutting creates a series of small

openings in a stand. It offers some opportunities to provide suitable conditions

for regeneration of nonhost species. Since side shading from the uncut stand is

great in the small openings, group selection often promotes regeneration of

shade-tolerant host species.

Single-tree selection (fig. 78) is an uneven-aged cutting method where

individual trees are removed from certain size or age classes over an

entire treatment area. Removing single trees creates small openings

similar to those resulting from natural mortality. For that reason, singletree selection favors regeneration of species that can tolerate shade

(Powell 1987). In the mixed-conifer forests of the Blue Mountains, this

method is least acceptable for reducing budworm susceptibility, primarily because it favors regeneration of shade-tolerant host trees, and it

perpetuates a feeding ladder for budworm larvae (see fig. 20).

Figure 78—Single-tree selection. Single-tree selection is generally the least

acceptable cutting method for mixed-conifer forests of the Blue Mountains,

particularly if reducing budworm susceptibility is an important objective. This

cutting method can create ideal conditions for regeneration of white fir,

Douglas-fir, Engelmann spruce, and subalpine fir, all of which are hosts of

western spruce budworm.

Single-Tree

Selection
94 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

The effect of uneven-aged management depends on the successional

status of the species being managed. On dryer sites where ponderosa

pine is the climax species, it can be regenerated and sustained using

selection cutting. On slightly moister sites where Douglas-fir is climax,

it is possible to maintain a reasonable proportion of ponderosa pine or

western larch with uneven-aged management. On moist areas where

white fir or subalpine fir are the climax species, it is very difficult to

maintain an acceptable component of seral, nonhost trees when using

either single-tree or group selection cuttings. Uneven-aged management

can be expected to promote the multi-layered stand structure that is

particularly susceptible to budworm damage (fig. 79).

Figure 79—Three common stand structures. Single-storied stands (top third

of figure) are generally more resistant to budworm damage than other stand

structures. Two-storied stands (middle third) may have high budworm susceptibility because of the feeding ladder effect (see fig. 20). Uneven-aged stands

(lower third) have high budworm susceptibility because of the feeding ladder

effect, and because they promote establishment of shade-tolerant host species.

Uneven-Aged

Management in

Mixed-Conifer

Forests
MANAGING BUDWORM AND ITS IMPACTS 95

Overstory removals (fig. 80) are used in multi-storied stands with an

understory of healthy trees. On the Malheur NF, overstory removals

were originally intended to be used more than any other silvicultural

method when the Forest’s Land and Resource Management Plan was

developed (USDA Forest Service 1990). They were designed to take

advantage of the two-storied stands resulting from 80 or more years of

fire suppression. It was a strategy that seemed to make good sense—it

avoided the costly expense of tree planting and site preparation; it

avoided the undesirable appearance associated with clearcutting; it

maintained the semblance of a green, forested setting; and it capitalized

on at least 60 years of growth on the understory trees.

Figure 80—Overstory removals. Overstory removals are used in multi-storied

stands with healthy understory trees. In the past, all of the overstory trees were

typically removed; in the future, some of the overstory trees will be retained as

biological legacies, snag replacements, or for other purposes (as shown in this

figure). In areas with high budworm susceptibility, few of the reserve trees

should be host species to avoid creating a budworm feeding ladder.

Unfortunately, the potential benefits of overstory removals could not be

realized because many of the understory trees are hosts of spruce budworm. As budworm larvae rained down from the overstory trees in

what is referred to as a feeding ladder (see fig. 20), the understory trees

were damaged or killed. Research has shown that either all or none of

the overstory trees should be removed when using overstory removals—leaving half of the overstory trees resulted in the greatest understory mortality from budworm defoliation (Carlson and Schmidt 1989).

On the Malheur NF, it was also found that many of the understory trees

were affected by other insects and pathogens such as root diseases

promoted by previous partial cuttings, or latent infections of Indian

paint fungus. Many of the severely affected understories were destroyed, and the sites planted back to pines and other ecologically

sustainable species.

Overstory

Removals

Overstory

Removals and

Budworm
96 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Understory removals (fig. 81) are used in multi-storied stands with an

overstory of nonhost trees, and an understory of host species. The objective is to remove a high proportion of the understory host trees. Their

removal not only reduces overall budworm susceptibility, but also improves overstory vigor by reducing competition from the understory.

When the overstory trees are overmature ponderosa pines and western

larches, this treatment can be particularly effective for ensuring their

continued survival.

Figure 81—Understory removals. Understory removals are used in multistoried stands with an overstory of nonhost trees, and an understory of host

species. Since many of the overstory trees are overmature ponderosa pines and

western larches, this treatment can contribute to their continued survival.

Understory removals are implemented in at least two ways: on an area

basis, or around individual trees. In the first method, understory trees

are removed on large areas having a relatively uniform stand composition and structure. Area-wide understory removals can be especially

useful before initiating an underburning program. In areas lacking

uniform conditions, the understory is removed from around individual

overstory trees, primarily to prolong their survival by decreasing intertree competition and increasing their vigor.

The ecological differences between understory and overstory removals

are striking. Overstory removals harvest the mature pines and larches

that were historically maintained by fire, while favoring the small

Douglas-firs and white firs that invaded after fires were suppressed.

Understory removals harvest the small, shade-tolerant invaders, thereby

facilitating reintroduction of fire for the benefit of pines and larches. In

one instance (understory removals), the treatment is designed to mimic

an important ecosystem process; in the other (overstory removals), ecological conditions are moved even further away from the historical

range of variation.

Understory

Removals

Applying

Understory

Removals

Overstory and

Understory

Removals

Compared
MANAGING BUDWORM AND ITS IMPACTS 97

Planting (fig. 82) is a powerful tool for influencing the future composition of a forest. In areas with substantial budworm damage, planting

can help reestablish a high proportion (60–70%) of nonhost trees. At

lower elevations, Douglas-fir is the climax species and the choice of

nonhost species is limited, with ponderosa pine and western juniper

being the most obvious ones. At higher elevations and on cooler sites,

white fir or subalpine fir are climax and the selection of nonhost species is wider—lodgepole pine, western larch, ponderosa pine, western

white pine, or quaking aspen could be used depending on the ecological

conditions of the planting site.

Figure 82—Tree planting. Planting is a powerful way to influence the future

composition of a forest. In areas with substantial budworm damage, planting

can be used to establish a high proportion (60–70%) of nonhost trees.

Pruning (fig. 83) is typically used to produce clear, knot-free wood, but

it could also play a role in the management of budworm-susceptible

forests. In areas where budworm-host trees will continue to be a stand

component, pruning could provide several benefits. The first and most

obvious benefit is that by removing the lower crown portion of host

trees, pruning results in less food for the survival and growth of budworm larvae.

After pruning host trees that are large enough to have developed a fireresistant bark (fig. 84), it would be possible to underburn mixed stands

without “torching” the budworm hosts. Host trees with short, pruned

crowns would be less likely to serve as ladder fuels, thereby minimizing the risk of an underburn turning into a crown fire. Pruning host

trees must be carefully coordinated with the onset of an underburning

program; if trees were pruned too soon, epicormic sprouts could occur

on the stem and increase a tree’s risk of torching in an underburn.

Tree Planting

Pruning for Fire

Resistance

Tree Pruning
98 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 83—Tree pruning. Pruning could reduce budworm impacts by removing the lower crown portion of host trees, which results in less substrate (food)

being available for budworm larvae. Pruning can also be used to increase the

fire resistance of host trees (see fig. 84).

Prescribed burning (fig. 85) is a common practice that has been used to

reduce natural fuel loading, to treat logging residues, and to prepare a

site for planting or natural regeneration. In the future, it may play a

much greater role in the management of Blue Mountains ecosystems

(Mutch and others 1993), but only if smoke management concerns do

not unduly constrain its use. An example of how prescribed burning

could be used is described next.

A common silvicultural prescription for mixed-conifer forests is to regenerate them using the seed-tree or shelterwood systems. Ponderosa

pine, western larch, and western white pine (if available) are retained in

the seed cut. After harvest, the slash may be piled and burned, particularly on sites with high fuel loads, or treated by lopping it into small

pieces and scattering them across the site. At that point, a prescribed

fire may be used to cycle nutrients, reduce wildfire hazard, and expose

mineral soil for establishment of seral, nonhost species or to create

planting spots. Stimulation of perennial bunchgrasses, forbs, and a

variety of shrubs can also result from the burn.

After a new forest has gotten established, a regular cycle of prescribed

burning could then begin. Once the ponderosa pines and larches are 10

to 12 feet tall, the first burn could be completed, although a low-intensity fire would leave most of the 6- to 8-foot trees undamaged as well

(Wright 1978). From that point on, ground fires could be run through

the stand on a regular cycle, usually at intervals of 10 to 15 years.

Regular underburns would remove many of the budworm host trees that

had regenerated since the last burn, and could also provide an irregular

thinning of the pines and larches.

Prescribed Burning

Prescribed Burning

for Silviculture

Burning On A

Regular Cycle
MANAGING BUDWORM AND ITS IMPACTS 99

Figure 84—Bark and lower-stem branching characteristics of a mature white

fir. White fir has thin bark, a long crown, and other traits that result in low fire

resistance. However, those traits are most prominent when the trees are small.

As white firs mature, their bark thickens considerably, and when growing in

dense stands, their crowns become shorter as they self prune from areas of

deep shade upward. The main difference between the fire resistance of true

firs and ponderosa pine or western larch is that pine and larch develop a thick

bark and short crown much more quickly than the firs. Since underburns occurred frequently in many presettlement ecosystems (on an average of every

8–20 years at low elevations), it was difficult for firs to escape fire long

enough to develop the thick bark and short crown that ensured their survival.

Fall burns are preferable from an ecological standpoint because they

replicate the natural fire regime. Fall burning also results in fewer

losses of overmature pines to fire-induced stress or western pine beetle

attacks (Swezy and Agee 1991). Fire may not be beneficial on all

mixed-conifer sites (fig. 86); on moist areas, burns could favor dominance by bracken fern, western coneflower, and other allelopathic

plants that inhibit conifer regeneration (Adams and Ferguson 1990,

Ferguson 1991, Ferguson and Boyd 1988).

Fall Burns Are

Ecologically

Preferable
100 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 85—Prescribed burning. This common practice has been used to

reduce natural fuel loading, to treat logging residue, and to prepare a site for

planting or for regeneration of seral, nonhost species.

Figure 86—Mixed-conifer stand with an undergrowth dominated by bracken

fern. Some mixed-conifer stands have an undergrowth featuring bracken fern

or western coneflower, both of which can inhibit conifer regeneration by

producing chemicals that kill newly-germinated trees (Ferguson and Boyd

1988, Ferguson 1991). Both bracken and coneflower sprout from rhizomes

and can spread vigorously after fire. Heavy cutting or use of prescribed fire

should be carefully considered before treating sites where bracken is present.

Periodic burning can also be used to increase the nutrient capital of a

site by maintaining sparse stands of snowbrush ceanothus, tailcup

lupine, peavines, vetch, and other nitrogen-fixing plants (fig. 87).

Numerous studies have documented the slow decomposition rates

Burning to Favor

Nitrogen-Fixing

Plants
MANAGING BUDWORM AND ITS IMPACTS 101

associated with large, woody material in the interior West (Brock and

Brock 1993, Gary and Currie 1977, Gruell 1980, Gruell 1983, Gruell

and others 1982). Forests of the interior West may have depended more

on nitrogen-fixing plants to replenish soil nutrients than on the decomposition of woody debris. Providing adequate levels of site nutrition is

important for maintaining tree resistance to budworm and other insects

and pathogens (see fertilization discussion earlier in this section).

Figure 87—Nitrogen-fixing plants. Periodic burning was an important ecological process for maintaining snowbrush ceanothus, tailcup lupine, peavines,

vetch, and other nitrogen-fixing plants. Forests of the interior West may have

depended more on nitrogen-fixing plants to replenish soil nutrients than on

the decomposition of woody debris. The site shown here has a mixture of

snowbrush ceanothus and planted ponderosa pines.

In areas with substantial mortality from budworm defoliation (fig. 88),

some of the dead trees are usually salvaged. As is often the case with

land management practices, salvage logging can have both positive and

negative effects. Some important benefits of salvage are to harvest and

utilize wood fiber while it is still merchantable, to remove enough dead

trees to promote regeneration of sun-loving seral species, and to reduce

fuel loadings to the point where wildfire risk is acceptable and a prescribed burning program could be initiated.

But in order to avoid exacerbating an already unfortunate situation,

salvage logging should be done carefully. Enough dead trees should be

left to provide adequate habitat for cavity-dependent birds. Retaining

dead trees also provides habitat for ants and other invertebrates that

prey on budworm larvae. And standing dead trees eventually fall to the

ground, where they contribute to nutrient cycling, maintain long-term

site productivity, and provide mycorrhizal habitat.

Salvage Logging of

Budworm-Caused

Tree Mortality

Retaining Some

Dead Trees
102 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 88—A mixed-conifer stand killed by budworm defoliation. Stands

with the amount of mortality shown here are often logged to salvage some of

the dead trees. Without their removal, it may be difficult to create the open,

sunny conditions that are required for establishment of ponderosa pine,

western larch, and other seral species. Note the abundance of thistle in the

undergrowth of this stand. Typically, thistle invades following a hot prescribed

burn. But in situations like the one shown here, thistle can dominate in

unlogged, unburned stands because cattle grazing had created an ideal seedbed for its establishment.
MANAGING BUDWORM AND ITS IMPACTS 103

Managers can affect the future structure and composition of the forest

by how they handle the surviving host trees. The objective of salvage is

not to eradicate the budworm-host trees from an area. It makes good

sense to retain some of the host trees that survive an outbreak, especially if they demonstrate natural resistance to defoliation (fig. 89).

Figure 89—Natural resistance to budworm defoliation. This photograph

shows a dry-site, mixed-conifer stand dominated by Douglas-fir. Note that the

tree in the center has sustained much less defoliation than those just in front of

it, even though the crowns of the three trees are touching or intertwined. The

center tree seems to have some natural resistance to budworm feeding. Recent

research found that foliage from defoliated Douglas-firs had lower amounts of

terpenes (a defensive chemical) than nondefoliated trees, and that severelydefoliated trees broke bud 7 to 10 days earlier than nondefoliated trees

(Muzika and others 1993). Both of those characteristics could have application

in a genetics program to breed budworm-resistant trees.

Retaining Some

Live Host Trees
104 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Some of the surviving white firs and Douglas-firs could be ideal trees

to retain as biological legacies (fig. 90). Legacy trees can serve as a biological bridge between one generation of trees and the next. Some of

the legacies provided by remnant trees could include Indian paint fungus, mycorrhizae and associated soil flora and fauna, root diseases,

cavity-nesting bird habitat, black bear den sites, and many others.

Whether those legacies are “good” or “bad” depends on one's perspective, and whether the legacy affects a manager’s capability to achieve

the goals and objectives (desired future condition) for an area. For

example, overstory trees infected with Indian paint fungus may be a

desirable legacy from a wildlife standpoint because they provide cavitynesting bird habitat and black bear dens, but they may be undesirable

from a timber standpoint because of their reduced merchantability.

Figure 90—A “cull” white fir. In the past, large white firs such as the one

shown here would have been removed from a timber sale area and sold as

fiber (chips), or felled and left on site. It is infected with Indian paint fungus,

and has a lot of internal decay (see fig. 11). Now, these trees are often

retained as biological legacies, particularly for pileated woodpeckers and

other cavity-nesting birds that require large-diameter trees with internal rot.

Biological Legacies
MANAGING BUDWORM AND ITS IMPACTS 105

An important objective is to assure that salvage operations will not interfere with the ultimate goal of providing biologically diverse forests,

both now and in the future. To reach that goal, it will be important for

forest managers to promote mixed species stands. Even so, the proportion of budworm-host species should not be allowed to exceed 30 or 40

percent, at least for areas where a defoliator outbreak would jeopardize

being able to meet future objectives (desired future conditions).

Land managers may be able to influence the extent of future outbreaks

by how they affect the natural enemies of budworm and tussock moth

(fig. 91). Ants, birds, yellowjackets, and other budworm predators can

be affected by insecticide applications, prescribed fire, silvicultural

practices, insect and disease treatments, and logging methods.

Birds are important enemies of budworm (fig. 91). Budworm-feeding

birds can be promoted by using the following management practices

(Langelier and Garton 1986): provide stands with horizontal and vertical diversity; avoid large clearcuts; provide edges; avoid high-grading;

avoid homogeneous, plantation-like stands; leave some slash; reduce

herbicide use; control livestock grazing; provide habitat for cavitynesting birds; provide salt; and provide water.

Managers can also affect bird populations by how they handle insects or

pathogens other than budworm. For example, a recent study found bird

diversity and abundance to be greater in forests infected with dwarf

mistletoe (fig. 92). In fact, the number of bird species increased as the

dwarf mistletoe infection level increased. The study also found that

dwarf mistletoe was not being used as food—its berries are small and

hard—but the “witches brooms” it caused provided nesting and roosting sites, and served as habitat for butterflies, moths, and some of the

other insects that birds feed on (Mlot 1991).

Ants and ground-dwelling spiders can be affected by site preparation

activities, fuel or residue treatments, insecticide applications, and

logging practices. Retaining down woody material, particularly large

logs and standing dead trees (snags), is important for sustaining carpenter ants and other forest-floor arthropods. Recent recommendations for

retention of logs and snags for pileated woodpeckers and other vertebrates, long-term site productivity, fungi and bryophytes, nutrient

cycling, and for other purposes, would probably be adequate to meet

the needs of ants and forest-floor spiders.

During logging operations and other activities involving heavy equipment, thatch-ant nests should be avoided. Even if thatch ants are not

protected in recognition of their intrinsic value to the ecosystem, the

nests should be avoided because ants are important predators of spruce

budworm larvae (fig. 93).

Maintaining Tree

Species Diversity

Natural Enemies of

Budworm

Birds As Budworm

Enemies

Birds and Dwarf

Mistletoe

Protecting

Arthropods During

Management
106 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Birds are important budworm predators. At least 26

birds have been documented as budworm predators

(Garton 1987), but it’s likely that more species than

that may play such a role. The mountain chickadee,

shown here, and red-breasted nuthatches are particularly important budworm predators. Both of those

birds require dead wood (standing snags or tall

stumps) in which to nest.

Spiders outnumber all other arthropods on the

foliage of Douglas-fir and true firs. In the Blue

Mountains, hunting spiders are much more plentiful

than the web spinners (Mason 1992), although both

types prey on budworm. An especially effective

budworm predator is the jumping spider shown here.

Figure 91—Some natural enemies of western spruce budworm.

Ants are important predators of budworm. Thatch

ants, such as the one shown here, and carpenter ants

are effective at preying on budworm larvae that have

fallen to the forest floor. Some ants are arboreal

foragers; they can be very important by feeding on

budworm larvae that fall onto seedling- and saplingsized host trees.

Beetles and the true bugs (stink bugs, etc.) are just

two examples of insect groups which feed on budworm larvae that fall to the forest floor. Little information is available about the importance of these

insects as budworm predators. A carabid beetle

feeding on a budworm larva is shown here.

Many species of wasps and flies are known to

parasitize insect larvae. Parasitic insects find budworm larvae, pupae, or eggs, where they then lay

their own eggs. After their eggs hatch, the developing parasite feeds on the budworm host, eventually

killing it. The wasp shown here is a common Blue

Mountains species (Hyposoter masoni Torgersen).
MANAGING BUDWORM AND ITS IMPACTS 107

Figure 92—Douglas-fir infected with dwarf mistletoe. The Douglas-fir in this

photograph has several areas with dense, bunched branches (“witches

brooms”) caused by dwarf mistletoe. A recent study found bird diversity and

abundance to be greater in forests infected with dwarf mistletoe (Mlot 1991).

The study showed that dwarf mistletoe was not being used as food—its

berries are small and hard—but the “witches brooms” it caused provided

nesting and roosting sites, and served as habitat for butterflies, moths, and

some of the other insects that birds feed on. Since birds are important budworm predators, it may not be prudent to remove all of the mistletoe-infected

trees on areas with a high proportion of budworm host species.
108 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Figure 93—Large thatch ant nest on a mixed-conifer site. Ants, spiders, and

other forest-dwelling arthropods can be affected by timber harvest, site

preparation activities, fuel or residue treatments, insecticide applications, and

other management practices. During timber harvest operations and other

activities involving heavy equipment, thatch-ant nests should be avoided

because ants are important predators of spruce budworm larvae (photo courtesy of Torolf Torgersen). And perhaps not unsurprisingly, these nests also

function as hotspots for nutrient cycling because the ants' shredding treatment

of organic nest materials aids decomposition processes and nutrient release.
FIRE EFFECTS INFORMATION FOR MIXED-CONIFER FORESTS 109

FIRE EFFECTS INFORMATION FOR MIXED-CONIFER FORESTS

This report described an important reason for extensive budworm

defoliation during the 1980s—suppression of wildfires since about

1900, especially natural underburns (see “Effects of Fire Suppression

on Budworm Habitat,” page 9). Land managers who prefer to administer forests with low budworm susceptibility are ready, willing, and

eager to expand the use of prescribed fire in their management of Blue

Mountain ecosystems. More use of prescribed fire could help reestablish vegetation conditions similar to those of presettlement times,

including a higher proportion of ponderosa pine, western larch, and

other budworm-resistant species.

Project planning requires that fuels specialists, silviculturists, wildlife

biologists, and other members of an interdisciplinary team be able to

predict how plant species will respond to fire. Without that information,

it is difficult to evaluate the effect of alternative fire regimes on vegetation. The information in Table 5 was compiled to help meet the need

for fire effects information—it provides ratings of fire resistance and

post-fire response, and comments about regeneration characteristics

affecting a plant’s reaction to fire, for more than 70 species. Plants

included in Table 5 were the most common species on 130 mixedconifer inventory plots that were remeasured in 1988 and 1989.

Plants have varying degrees of fire resistance. A plant’s response to fire

depends on many factors, including the moisture content of soil and

duff at the time of burning, the physiological stage of the plant (immature, mature, etc.), and the fire’s severity, particularly with regard to the

amount of heat that permeates the litter, duff, and upper soil layers

(Crane and Fischer 1986). An important factor affecting a plant’s fire

resistance is whether it regenerates vegetatively (survivor plants) or

from off-site or buried seed (colonizer plants). Fire resistance ratings

(“Resistance” in Table 5) have the following interpretation (Volland

and Dell 1981):

• High—Greater than 65 percent chance that 50 percent of the species

population will survive or immediately reestablish after passage of a

fire with an average flame length of 12 inches.

• Medium—35 to 64 percent chance that 50 percent of the species

population will survive or immediately reestablish after passage of a

fire with an average flame length of 12 inches.

• Low—Less than 35 percent chance that 50 percent of the species

population will survive or immediately reestablish after passage of a

fire with an average flame length of 12 inches.

Fire Effects and

Project Planning

Fire Resistance

Ratings
110 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Post-fire response ratings (“Response” in Table 5) are an estimate of

how quickly a plant species will regain its prefire population level.

They have the following interpretation (Volland and Dell 1981):

• High—The species population will regain its preburn frequency or

cover in 5 years or less.

• Medium—The species will regain its preburn frequency or cover in

5 to 10 years.

• Low—The species will regain its preburn frequency or cover in more

than 10 years.

The site type ratings are somewhat subjective and were included in

Table 5 to describe the temperature and moisture relationships for sites

on which the species is abundant and widely distributed.

Post-fire Response

Ratings

Site Type Ratings
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 111

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS

Name: White/Grand Fir (Abies concolor/grandis). Code: ABCO.

Resistance: Medium. Response: Low. Site Type: Cool, Mesic.

Comments: White fir, or a natural hybrid with characteristics

intermediate between those of white fir and grand fir, is the most

common fir at lower elevations. White fir’s dense, low branching

habit and its flammable foliage, resinous bark, and high stand

density result in a moderate or high susceptibility to fire-induced

mortality. The thick bark of mature trees adds to their fire resistance

(fig. 84). Fire often causes high mortality on moist sites where the

trees have developed shallow lateral roots. Decay often enters

through, or is initiated by, fire scars. Because small white firs are

very sensitive to fire, low-intensity prescribed burns can be used to

intentionally kill them. White fir, the favorite food of spruce budworm, has flourished in the fir stands that have encroached on

ponderosa pine sites over the last 80 years.

Name: Subalpine Fir (Abies lasiocarpa). Code: ABLA2.

Resistance: Low. Response: Low. Site Type: Cold, Mesic.

Comments: Subalpine fir grows at high elevations where its slender, spire-like crown sheds the heavy snowfalls of subalpine winters.

Those snows often bend its lower branches to the ground, where

they root and eventually form independent trees in a process called

layering. This handsome tree produces inch-long needles from all

sides of the twig. It has thin, gray, smooth bark covered with resin

blisters; often, a single bark blister may hold up to half a teaspoon of

aromatic, sticky balsam. Purplish cones are produced upright on

branch tops high in the crown. It has very low fire resistance because of its thin bark; the presence of resin blisters on the bark; a

low, dense branching habit; a shallow root system; and a tendency to

occur in dense stands where neighboring trees are touching. Entire

stands of this high-elevation species are easily killed by fire.

Name: Western Yarrow (Achillea millefolium). Code: ACMI.

Resistance: Medium. Response: High. Site Type: Disturbed Areas.

Comments: Western yarrow is a strongly aromatic forb with

grayish, finely-divided leaves and flat-topped clusters of small,

white flowers. It is a weedy, widely-distributed plant that regenerates from short, shallow rhizomes, and from seed. Yarrow may

decline after severe fires, although reestablishment from off-site

seed usually occurs rapidly.
112 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Trailplant (Adenocaulon bicolor). Code: ADBI.

Resistance: Low. Response: Low. Site Type: Cool, Moist.

Comments: Trailplant is a low or mid-height forb with triangular,

bi-colored leaves that are green above, and white beneath. It grows

on shaded, highly-productive sites and regenerates from short

surface rhizomes and seed, generally surviving cool fires that don’t

consume all of the litter and duff layers or cause excessive soil

heating. The post-fire recovery of trail plant is usually slow.

Name: Serviceberry (Amelanchier alnifolia). Code: AMAL.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Serviceberry is a mid-height shrub that has dull-green

leaves with toothed tips, and attractive clusters of white, fragrant

flowers. It provides excellent big-game browse. This widespread

plant sprouts from the root crown, its stem bases, and from a large

rhizome, and usually survives severe fires if the soil is fairly moist

at the time of burning. Serviceberry sprouts immediately after fire

and often regains preburn levels within 2 or 3 years. Good fruit

production occurs every 3–5 years; its seeds are spread by birds and

bears that feed on the fruits.

Name: Rose Pussytoes (Antennaria rosea). Code: ANRO.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Rose pussytoes is a low, mat-forming forb with small,

pink, ball-shaped flowers produced on slender stalks. This diminutive plant reproduces by using trailing stolons, and from wind-blown

seed. It prefers sites with the light shading of a partial forest canopy.

Although fire effects information is scarce for rose pussytoes, it is

apt to increase slightly or remain unchanged following a low- or

moderate-intensity burn.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 113

Name: Red Columbine (Aquilegia formosa). Code: AQFO.

Resistance: Medium. Response: Medium. Site Type: Cool, Moist.

Comments: Red columbine is a slender, perennial forb with attractive, red-and-yellow flowers. This plant is commonly found on

moist, shaded sites, where it regenerates mostly from seed. Although

fire effects information is scarce for this species, it is likely that

moderate or hot fires which consume most of the litter and duff

layers are apt to have a detrimental effect on red columbine.

Name: Manzanita (Arctostaphylos nevadensis). Code: ARNE.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Pinemat manzanita is a creeping shrub with small,

thick, leathery leaves and white or pink, urn-shaped flowers. It

regenerates from the root crown, runners (stolons) or, most commonly, from seed. The seed is produced in bright red berries that are

a favorite food of birds and other wildlife. It survives cool fires if

the litter and duff layers were not completely consumed. Pinemat

manzanita often invades burned areas from unburned patches

nearby.

Name: Bigleaf Sandwort (Arenaria macrophylla). Code: ARMA3.

Resistance: Low. Response: Medium. Site Type: Cool, Mesic.

Comments: Bigleaf sandwort, a very common plant of the mixedconifer forest type, is a low forb with opposite, lance-shaped leaves

and small, white flowers borne on slender stalks. It regenerates from

shallow rhizomes and seed, and decreases slightly or remains

unchanged after fire, depending upon how much of the litter and

duff was consumed and how much soil heating occurred.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
114 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Heartleaf Arnica (Arnica cordifolia). Code: ARCO.

Resistance: Low. Response: High. Site Type: Cool, Mesic.

Comments: Heartleaf arnica is a shade-loving, early-blooming forb

with broad, heart-shaped, opposite leaves that have prominent veins

and are hairy and rough. Generally, each plant produces a single

large, showy, yellow flower. It often declines in clearcuts or other

openings. This species sprouts from surviving rhizomes, but is easily

killed by all except mild fires. However, heartleaf arnica readily

invades burned areas using windborne seed.

Name: Showy Aster (Aster conspicuus). Code: ASCO.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Showy aster is a moderately shade-tolerant forb with

alternate, sharply-toothed leaves that clasp the stem, and terminal

flowers with bluish or purplish rays. It regenerates by sprouting

from surviving rhizomes, and from seed. This plant typically survives cool or moderate fires that don’t cause excessive soil heating.

Occasionally, showy aster increases rapidly after burning because its

windborne seed disperses over long distances.

Name: Balsamroot (Balsamorhiza sagittata). Code: BASA.

Resistance: High. Response: High. Site Type: Warm, Dry.

Comments: Arrowleaf balsamroot, a common forb of dry, open

sites, has large, hairy, triangular leaves arising from a basal clump,

and attractive yellow flowers that look like small sunflowers. It

regenerates from a stout caudex (root crown) and from animaldisseminated seed, and generally survives even the severest fires—

plant densities are often greater than pre-burn levels by the second

growing season after burning. After trees get reestablished and site

shading increases, arrowleaf balsamroot populations can be expected to decline dramatically.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 115

Name: Creeping Hollygrape (Berberis repens). Code: BERE.

Resistance: Medium. Response: Medium. Site Type: Cool, Dry.

Comments: Creeping hollygrape is a low, prickly shrub with

compound, evergreen leaves. Each leaflet has wavy or shallowlylobed margins and spine-tipped teeth. Clusters of yellow flowers

appear early in spring and are followed by attractive, blue berries.

This plant sprouts from surviving rhizomes after fire. It survives all

but severe burns that cause high soil heating. Populations decrease

slightly or remain unchanged following low- or moderate-intensity

burns. Rarely does regeneration occur from the seeds contained in

its bright, blue berries.

Name: California Brome (Bromus carinatus). Code: BRCA.

Resistance: Medium. Response: Medium. Site Type: Warm, Dry.

Comments: California brome is a tall grass with narrow, upright

panicles of awned flowers. It regenerates from the root crown, and

from seed. Since it is a coarse-stemmed species with relatively

sparse foliage, California brome is more fire-resistant than fine,

leafy bunchgrasses. This plant is most susceptible to fire damage

when actively growing in spring and early summer.

Name: Columbia Brome (Bromus vulgaris). Code: BRVU.

Resistance: Medium. Response: Medium. Site Type: Cool, Moist.

Comments: Columbia brome is a medium or tall, non-rhizomatous

grass with open, drooping panicles of awned flowers. It regenerates

from seed, some of which may be stored in the soil. This species

declines following severe fires, although the moist sites on which it

grows are seldom easy to burn. Although Columbia brome persists

under a dense tree canopy, it often increases in the open environments provided by timber harvest and other disturbances.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
116 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Pinegrass (Calamagrostis rubescens). Code: CARU.

Resistance: Medium. Response: Medium. Site Type: Warm, Mesic.

Comments: Pinegrass, a creeping species, is one of the most common plants of mixed-conifer forests. It often increases in disturbed

areas or natural openings, especially on moist sites. Pinegrass

seldom flowers in the shade of a dense forest canopy, although

abundant seed is often produced during the year following a fire. It

regenerates from rhizomes and seed, and survives all but severe fires

that completely remove the litter and duff layers. Pinegrass can be a

formidable competitor with planted seedlings, especially if they are

not well established within 3 years of timber harvest. This plant is

not a preferred forage species for cattle, especially after it matures in

late summer (Hedrick and others 1968).

Name: Northwestern Sedge (Carex concinnoides). Code: CACO.

Resistance: Medium. Response: Medium. Site Type: Cool, Moist.

Comments: Northwestern sedge is a moist-site species with flat,

wide, shiny leaves and brownish leaf sheaths. It sprouts from

rhizomes located in the duff, or between the duff and mineral soil.

Those rhizomes allow this plant to form sparse, loose mats on mesic,

mixed-conifer sites. Since its creeping rhizomes are very shallow,

there is high risk that fires which consume most of the litter and duff

layer will have an adverse impact on this species.

Name: Elk Sedge (Carex geyeri). Code: CAGE.

Resistance: High. Response: High. Site Type: Warm, Mesic.

Comments: Elk sedge is a moderately shade-tolerant plant with flat,

leathery, rough-margined leaves and tight, narrow flower spikes. It

may be common in the undergrowth of mixed-conifer stands,

especially those on dryer sites. Following fire, it sprouts from

surviving rhizomes. Even though it decreases immediately after

burning, elk sedge then increases within a few years to form dense

stands. Although it is seldom abundant on mixed-conifer sites, elk

sedge is a preferred forage species for cattle (Hedrick and others

1968).

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 117

Name: Ross Sedge (Carex rossii). Code: CARO.

Resistance: High. Response: Medium. Site Type: Cool, Dry.

Comments: Ross sedge is a low-growing plant with thin, narrow

leaves and short spikes of small, brown flowers. Some of the flowers

are produced on stems longer than the foliage, while others occur

near the base of the plant and are hidden among the leaves. The leaf

bases usually have an obvious reddish color. It regenerates from

surviving rhizomes, and from seed stored in the duff and upper soil.

This species often increases after fires which don’t consume all of

the litter and duff layers or cause excessive soil heating. On dryer

sites, Ross sedge often becomes abundant after clearcutting and

scarification activities.

Name: Scarlet Paintbrush (Castilleja miniata). Code: CAMI2.

Resistance: Medium. Response: Medium. Site Type: Warm, Mesic.

Comments: Scarlet paintbrush is a mid-height forb with red or darkorange bracts and unbranched stems up to two feet tall. Its leaves are

lance-shaped and have entire margins. The reddish bracts are usually

lobed, although some are entire and have a sharp tip. This plant has

a tough, woody base. It regenerates from the crown of a deep

taproot, and from off-site seed. Its reestablishment in the post-fire

community is somewhat slow; usually, it does not even reappear

until the second or third year after burning.

Name: Snowbrush Ceanothus (Ceanothus velutinus). Code: CEVE.

Resistance: High. Response: High. Site Type: Warm, Mesic.

Comments: Snowbrush ceanothus is a clumpy, mid-height shrub

that can form dense stands after burning. If mature plants are present

before a fire, they resprout from their root crown. But most often, it

regenerates prolifically on sites where ceanothus plants weren’t

even present before the fire—they arise from seeds buried in the

soil, seeds that can remain viable for hundreds of years. Ceanothus

is a nitrogen-fixing shrub that grows best on south and west exposures. An intense fall burn is more likely to produce a dense stand of

ceanothus than a cooler spring fire. Using spring burns to intentionally produce a moderate stand of ceanothus, so it could then provide

nitrogen fixation, wildlife browse, vegetation diversity, and other

benefits, would not create a situation where the shrubs compete

seriously with tree regeneration.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
118 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Mountain Mahogany (Cercocarpus ledifolius). Code: CELE.

Resistance: Low. Response: Low. Site Type: Warm, Dry.

Comments: Mountain mahogany is an important wildlife species

with thick, leathery, in-rolled leaves, and distinctive fruits bearing

long, slightly-twisted plumes. It sprouts weakly after low-intensity

fires. Unfortunately, it is seriously damaged by all but the coolest of

burns. Following moderate or severe fires, this tall shrub must reestablish from off-site, wind-dispersed seed. Because of its low tolerance for fire, mountain mahogany is similar to bitterbrush in that it

has probably benefitted from the fire suppression programs initiated

in the early 1900s.

Name: Pipsissewa (Chimaphila umbellata). Code: CHUM.

Resistance: Low. Response: Medium. Site Type: Cool, Mesic.

Comments: Pipsissewa is a short, semi-woody forb with dark-green,

stiff, glossy leaves having toothed margins, and a single flower stalk

supporting a dozen or more round, pink blossoms. It sprouts from

shallow rhizomes following a fire, and usually survives cool or

moderate burns that don’t consume all of the litter and duff layers.

Pipsissewa is found on cool, moderately-moist, mixed-conifer sites

that often feature an abundance of mosses and lichens.

Name: Bull Thistle (Cirsium vulgare). Code: CIVU.

Resistance: Medium. Response: Medium. Site Type: Disturbances.

Comments: Bull thistle is a tall, biennial forb that regenerates from

root sprouts and seed. It often increases dramatically in clearcuts

after burning. Bull thistle is a moderate competitor with tree seedlings; competition is not intense during the first-year rosette stage,

but was found to inhibit ponderosa pine seedling growth during the

second-year adult stage (Randall and Rejmanek 1993). It has a short,

fleshy taproot, and weakly-developed lateral roots. In stands with a

high amount of budworm-caused mortality and active cattle grazing,

bull thistle can still dominate even if the dead trees are not salvaged

and no burning has occurred because cattle create good thistle

seedbeds (see fig. 88).

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 119

Name: Queencup Beadlily (Clintonia uniflora). Code: CLUN.

Resistance: Low. Response: Low. Site Type: Cool, Moist.

Comments: Queencup beadlily is a low, succulent forb with 2 or 3

basal, oblong leaves, and attractive white flowers. The flowers are

followed by shiny, blue berries. This species regenerates from

widely-spreading rhizomes, and from seed. Queencup beadlily

generally declines after fire, although the moist, shaded sites on

which it grows are seldom easy to burn.

Name: Blue Wildrye (Elymus glaucus). Code: ELGL.

Resistance: Medium. Response: Medium. Site Type: Warm, Mesic.

Comments: Blue wildrye is a tall bunchgrass with flat, rough leaves

less than a foot long and a dense, narrow spike of greenish flowers.

The flowers have an awn up to three-quarters of an inch long. This

grass regenerates from the root crown, rootstock sprouts, and from

seed. It is well adapted to sites disturbed by fire, overgrazing, or

logging. Most of its post-fire regeneration arises from seed that is

capable of surviving the surface temperatures associated with a

moderate-intensity burn. In fact, fire often creates an ideal seedbed

for the germination and establishment of this species. Blue wildrye

is a preferred forage species for cattle (Hedrick and others 1968).

Name: Longleaf Fleabane (Erigeron corymbosus). Code: ERCO3.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Longleaf fleabane is a mid-height forb with hairy,

strap-shaped leaves and purplish stem bases. The flowers contain

deep-blue or pinkish rays. It is typically found in dryer parts of the

Big Cow burn and on other areas with a fairly open tree canopy.

Since this species lacks rhizomes or stolons, it regenerates using offsite seed or by sprouting from a moderately well-developed rootcrown. Although fire effects information is scarce for longleaf

fleabane, it is apt to decrease slightly or remain unchanged following a low- or moderate-intensity burn.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
120 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Idaho Fescue (Festuca idahoensis). Code: FEID.

Resistance: Low. Response: Medium. Site Type: Warm, Dry.

Comments: Idaho fescue is a tough bunchgrass with narrow, bluish,

inrolled leaves and a narrow panicle of short-awned flowers. This

species regenerates from the surviving root crown, and from seed. It

can be badly harmed by hot summer fires, but resists spring or fall

burns fairly well. Since it grows as a dense, fine-leaved tuft, Idaho

fescue can be damaged by a smouldering fire long after the main

flame front has passed.

Name: Western Fescue (Festuca occidentalis). Code: FEOC.

Resistance: Low. Response: Low. Site Type: Cool, Mesic.

Comments: Western fescue is a short bunchgrass with basal tufts of

soft, inrolled leaves and an open panicle of awned flowers. This

species regenerates from the surviving root crown, and from off-site

seed. It almost always declines following fire, although the moist

sites on which it grows are seldom easy to burn. Western fescue

germinates well on bare, shaded soil. Unlike many other fescues that

prefer open, dry environments, this plant is found in the understory

of moist, mixed-conifer stands.

Name: Woods Strawberry (Fragaria vesca). Code: FRVE.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Woods strawberry is a low, creeping forb with greenish-yellow, hairy leaflets that have deep, prominent veins. The easily

recognized fruits have seeds attached on the outside, rather than in

deep pits. Also, its terminal leaflet tooth is not smaller than the

others and does not form a “gun sight” (see blueleaf strawberry

narrative). This common plant is generally found on moister sites

than its close relative—blueleaf strawberry. It regenerates from root

crown sprouts and runners (stolons), and from some seed stored in

the upper soil. Woods strawberry survives cool fires that don’t

consume all of the litter and duff layers.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 121

Name: Blueleaf Strawberry (Fragaria virginiana). Code: FRVI.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Blueleaf strawberry is a low, creeping forb with

smooth, blue-green leaves that have a distinctive “gun sight” notch

at the tip of their terminal leaflet. The small, 5-petalled, white

flowers are followed by the familiar sweet, red fruits with seeds

embedded in deep pits. It regenerates using root crown sprouts and

runners (stolons). Blueleaf strawberry survives cool fires that don’t

consume all of the litter and duff layers. It is generally found on

dryer sites than its close relative—woods strawberry.

Name: Northern Bedstraw (Galium boreale). Code: GABO.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Northern bedstraw is a low forb with whorled leaves

(four, three-veined leaves at each node) and a square (four-sided)

stem. The small, white flowers are fragrant and occur in bunched

clusters on the upper third of the plant. It regenerates from creeping,

underground stems called rhizomes, and from sticky seed. Northern

bedstraw is generally resistant to light underburns, but may decline

significantly following severe fires.

Name: Sweetscented Bedstraw (Galium triflorum). Code: GATR.

Resistance: Low. Response: Medium. Site Type: Cool, Moist.

Comments: Sweetscented bedstraw is a sprawling forb with

whorled leaves (six at each node) and small, inconspicuous, greenish flowers that occur in groups of three. It regenerates using rhizomes and seed. Sweetscented bedstraw decreases dramatically after

severe fires, but can increase following cool burns completed in

spring or late fall. Since this plant is typically found near streams,

springs, seeps, and on moist toeslopes and benches or other wellwatered landforms, the sites on which it grows are seldom easy to

burn.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
122 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Rattlesnake Plantain (Goodyera oblongifolia).Code: GOOB.

Resistance: Low. Response: Low. Site Type: Cool, Mesic.

Comments: Rattlesnake plantain is a common orchid that typically

grows as a small cluster of two or three, white-striped leaves on the

forest floor. Occasionally, it produces a single, straight stalk bearing

small, white flowers. It is found on cool, moderately-moist, mixedconifer sites that often feature an abundance of mosses and lichens.

This unobtrusive forb regenerates using rhizomes and seed. Rattlesnake plantain is easily killed by fire because its shallow rhizomes

are very sensitive to heat. Fires which consume most of the litter and

duff layers are likely to have a detrimental impact on this plant.

Name: Western Hawkweed (Hieracium albertinum). Code: HIAL2.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Western hawkweed is a hairy, upright forb with long,

woolly, strap-like leaves and yellow flowers. Flower color is a good

way to tell it apart from its close relative—white hawkweed. It lacks

rhizomes or another means of vegetative reproduction, but readily

invades burned areas using windborne seed. Since western hawkweed occurs on dry sites, it is most common in the undergrowth of

mixed-conifer forests established at lower elevations.

Name: White Hawkweed (Hieracium albiflorum). Code: HIAL.

Resistance: Low. Response: Medium. Site Type: Cool, Mesic.

Comments: White hawkweed is one of the most common plants of

the mixed-conifer forest type. This mid-height, white-flowered forb

has elliptic, wavy-edged leaves. It lacks rhizomes or another means

of vegetative reproduction, but readily invades burned areas using

windborne seed. White hawkweed grows on moister sites than the

closely-related western hawkweed and is found throughout the

mixed-conifer vegetation zone.
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 123

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Ocean Spray (Holodiscus discolor). Code: HODI.

Resistance: Medium. Response: High. Site Type: Warm, Dry.

Comments: Ocean spray is a mid-height shrub with lobed, toothed

leaves that are triangular in outline, and dense plumes of small,

creamy flowers. This plant regenerates from the surviving root

crown, and from seed stored in the soil. It may be enhanced by fire

because seedlings establish easily on the freshly-exposed mineral

soil created by burns that remove most of the litter and duff layers.

Name: Western Juniper (Juniperus occidentalis). Code: JUOC.

Resistance: Medium. Response: Low. Site Type: Warm, Dry.

Comments: Western juniper is a small tree found on dry, mixedconifer sites supporting mixed stands of ponderosa pine and Douglas-fir. It does not reproduce vegetatively, so all post-fire establishment occurs from seed, much of which is dispersed by animals

(rabbits, squirrels, etc.). Since small trees have thin bark and long

crowns, they are easily killed by fire. However, older stems are

moderately resistant to all but severe burns. Because of its low

tolerance for fire, western juniper is similar to bitterbrush in that it

has probably benefitted from the fire suppression programs initiated

in the early 1900s. This plant has had many cultural and ethnic

uses—Native Americans made beads from the seeds, and the berries

were used more recently to furnish the flavor compounds that give

gin (an alcoholic beveridge) its distinctive taste.

Name: Prairie Junegrass (Koeleria cristata). Code: KOCR.

Resistance: Medium. Response: Medium. Site Type: Warm, Dry.

Comments: Prairie junegrass is a cool-season, perennial bunchgrass

with basal leaves and a narrow seedhead up to five inches long. The

leaves are somewhat similar to those of bluegrasses because they

have boat-shaped tips. Its panicle may be relatively wide when

flowering in early spring; after seed is set, it becomes narrow and

tight. This common species regenerates from seed, and not from

rootstocks or rhizomes. It is susceptible to mortality from late-spring

burns, although its small clump size and coarse-textured foliage

make this plant one of our more fire-resistant bunchgrasses.
124 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Western Larch (Larix occidentalis). Code: LAOC.

Resistance: High. Response: High. Site Type: Cool, Mesic.

Comments: Western larch is plentiful in forests of the lower

Columbia River basin, an area encompassing western Montana,

northern and central Idaho, eastern Washington, and northeastern

Oregon. It has short, soft, tufted needles that are shed each fall after

turning a bright, lemon-yellow color, and small cones with short

bracts protruding out from between the cone scales. Western larch is

our most fire-resistant conifer because of its thick bark, short crown

length, and high tolerance to foliage loss. As a seral species, it is

well-adapted to colonization of mesic sites that have been disturbed

by fire or logging. Larch seedlings establish easily on mineral soil

seedbeds, and its diameter growth often increases after prescribed

fire. This important tree species can withstand a high proportion of

crown scorch.

Name: Thickleaf Peavine (Lathyrus lanzwertii). Code: LALA2.

Resistance: Medium. Response: High. Site Type: Warm, Dry.

Comments: Thickleaf peavine is a perennial legume with pinnatelycompound leaves bearing thick, narrow leaftlets, and clusters of

lavender or pinkish, pea-like flowers. It regenerates from rhizome

sprouts and seed. Although fire effects information is scarce for this

species, it apparently increases slightly or remains unchanged after

burning. Peavines are similar to other legumes in that they are

nitrogen fixers, which means they can help improve the nutrient

capital of a site.

Name: Cusick’s Peavine (Lathyrus nevadensis). Code: LANE.

Resistance: Medium. Response: High. Site Type: Warm, Mesic.

Comments: Cusick’s peavine is a shade-loving forb with pinnatelycompound leaves bearing 2–4 pairs of oval leaflets, and white or

pinkish flowers. This plant often declines in clearcuts or other

openings. It sprouts from surviving rhizomes, and generally increases slightly or remains unchanged after fire. Peavines are similar to

other legumes in that they are nitrogen fixers; they can help improve

the nutrient capital of a site. Peavines, preferred forage species for

cattle, help improve livestock utilization of pinegrass when the two

species occur together (Hedrick and others 1968).

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 125

Name: American Twinflower (Linnaea borealis). Code: LIBO2.

Resistance: Low. Response: Medium. Site Type: Cool, Moist.

Comments: American twinflower is a creeping sub-shrub that

produces short, leafless, forked flower stalks bearing twin pink

blossoms shaped like narrow bells. Its oval leaves are an inch or less

in length and have shallowly-toothed edges. This plant regenerates

from surviving root crowns and runners (stolons), and from seed. It

survives cool fires if the duff and litter layers were damp and not

totally consumed. Twinflower declines following fire, although the

moist sites on which it grows are seldom easy to burn. Often, its

runners quickly invade burned areas from adjacent, unburned

patches.

Name: Tailcup Lupine (Lupinus caudatus). Code: LUCA.

Resistance: High. Response: Medium. Site Type: Cool, Mesic.

Comments: Tailcup lupine is a common, mid-height forb with

hairy, silvery leaves and blue or violet flowers. This plant regenerates from the crown of a deep taproot, and from heavy seed. It

produces seed during the first year after a fire and then spreads

quickly. Since the seed can survive for long periods in the lower

duff and upper soil layers, it is not uncommon for this species to

dominate on sites where it was not plentiful before burning or

logging. In those situations, tailcup lupine may become more

abundant than another of the common colonizers, such as thistle,

mullein, or cheatgrass. Lupines are nitrogen fixers that can help

improve the nutrient capital of a site.

Name: False-Agoseris (Microseris troximoides). Code: MITR.

Resistance: Medium. Response: High. Site Type: Warm, Dry.

Comments: False-agoseris is a short, yellow-flowered forb with

long, narrow leaves that have shallowly-scalloped edges. This plant

regenerates from the crown of a deep taproot. It is typically found on

dry, mixed-conifer sites supporting mixed stands of ponderosa pine

and Douglas-fir. False agoseris increases or remains unchanged after

fires which don’t consume all of the litter and duff layers.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
126 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Sideflowered Mitella (Mitella stauropetala). Code: MIST2.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Sideflowered mitella is a shade-loving forb with heartshaped, scallop-edged leaves and small, greenish-white flowers in a

one-sided raceme. This plant regenerates from the root crown, and

from seed. It is found on cool, moderately-moist, mixed-conifer sites

that often feature an abundance of mosses and lichens. Fires which

consume most of the litter and duff layers are apt to have a detrimental impact on sideflowered mitella.

Name: Mountain Sweetroot (Osmorhiza chilensis). Code: OSCH.

Resistance: Medium. Response: Medium. Site Type: Cool, Moist.

Comments: Mountain sweetroot is a mid-height forb with compound, toothed leaves, tiny, inconspicuous flowers, and short, flat

fruits. This moist-site plant regenerates from a taproot or caudex

(root crown), and from seeds. Its barbed seeds are often disseminated by animals. Flowering usually increases after the tree canopy has

been opened by harvest or fire. Generally, mountain sweetroot is

unchanged or increases slightly after burning, although the moist

sites on which it grows are often difficult to burn.

Name: Myrtle Pachistima (Pachistima myrsinites). Code: PAMY.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Myrtle pachistima, a creeping, low-growing shrub, is

relished by elk and may be suppressed by big-game browsing in

areas with high elk populations. It has small, thick, oval leaves with

slightly-toothed edges and small, red flowers that appear in early

spring and are inconspicuous by being hidden in the foliage. This

plant regenerates from the crown of a deep taproot, or from stem

bud sprouts or stored seed. It may increase after cool or moderate

burns that don’t consume all of the litter and duff layers or cause

excessive soil heating.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 127

Name: Common Timothy (Phleum pratense). Code: PHPR.

Resistance: Medium. Response: High. Site Type: Disturbances.

Comments: Common timothy is a medium to tall bunchgrass with

slender, bristly seedheads. Its smooth, flat, or slightly-folded leaves

are prominently veined. It regenerates from the surviving root crown

or, more commonly, from seed that blows in from adjacent roadsides

and forest openings. Often, timothy seed arrives from closed roads,

skid trails, and other sites that have been seeded with a mix of nonnative grasses to prevent or control soil erosion.

Name: Engelmann Spruce (Picea engelmannii). Code: PIEN.

Resistance: Low. Response: Low. Site Type: Cold, Moist.

Comments: Engelmann spruce has sharp, inch-long needles that are

square in cross section; thin, scaly, orange or brown-colored bark;

and papery cones that hang or droop from the branch tips. The

young branches and leaf bases are hairy (pubescent). It is easily

killed by fire because of its long, full crown, thin bark, and a shallow root system. In the central and southern Blue Mountains,

Engelmann spruce tends to be a riparian species growing on sites

that may be difficult to burn. Despite its high damage risk, this

species is favored more by fire than a frequent associate on the highelevation sites where it commonly grows—subalpine fir.

Name: Lodgepole Pine (Pinus contorta). Code: PICO.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Lodgepole pine is a slender tree with one- to two-inch

long needles occurring in bundles of two or three; thin, scaly,

reddish or gray bark, and small, knobby cones. This widespread tree

can survive cool fires because of its fairly short, open crown. Its thin

bark results in low resistance to medium or hot burns. Lodgepole

pine often regenerates after stand-replacing wildfires, when it forms

dense, even-aged thickets. It has good post-fire response, especially

in stands where some of the trees have stored their seed in tightlyclosed cones (serotinous cones). The closed cones are not universal;

their presence varies from area to area. As a seral species that is well

adapted to colonization of disturbed sites, frost pockets, and other

harsh environments, its seedlings establish easily on mineral soil

seedbeds.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
128 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Ponderosa Pine (Pinus ponderosa). Code: PIPO.

Resistance: High. Response: High. Site Type: Warm, Mesic.

Comments: The thick bark, short crown lengths, and wide tree

spacing typically associated with ponderosa pine stands result in

high fire resistance for this species. At a diameter of about 2 inches,

ponderosa pine begins to develop fire-resistant bark with a dead

outer layer that insulates the sensitive cambium tissues from heat

damage. It also appears that decomposing ponderosa pine needles

produce a substance that inhibits pine growth; periodic burning

would prevent that substance from accumulating by periodically

removing the litter layer (Hall 1991). Seedling establishment is

favored by fires that expose mineral soil seedbeds. Ponderosa pine

experiences reduced diameter growth after high levels of crown

scorch. By controlling underburns, land managers were inadvertently swapping ponderosa pines for white firs and Douglas-firs.

Name: Wheeler Bluegrass (Poa nervosa). Code: PONE.

Resistance: Medium. Response: High. Site Type: Warm, Mesic.

Comments: Wheeler bluegrass is a creeping, mid-height grass with

narrow, sometimes-folded leaves and a sparse, open panicle of hairy,

unawned flowers. The flowers and stem bases tend to be a purplish

color. It regenerates from surviving rhizomes and seed. Like many

other rhizomatous grasses, Wheeler bluegrass is seldom damaged by

fire unless the litter and duff layers are consumed and excessive soil

heating has occurred.

Name: Kentucky Bluegrass (Poa pratensis). Code: POPR.

Resistance: High. Response: High. Site Type: Warm, Mesic.

Comments: Kentucky bluegrass is a creeping, sod-forming, midheight grass with stems from one to three feet tall and leaves that are

dark-green, flat or folded, and boat-shaped at their tip. Flowers are

produced in a loose, pyramidal panicle up to six inches long. This

aggressive, weedy species regenerates from basal stem buds and

slender rhizomes, and from seed. Kentucky bluegrass is seldom

damaged by fire, although population declines occasionally occur

following hot, spring burns.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 129

Name: Polemonium (Polemonium pulcherrimum). Code: POPU.

Resistance: Low. Response: Medium. Site Type: Cold, Moist.

Comments: Showy polemonium is a low, clumpy forb with compound leaves having two-ranked leaflets suggestive of a ladder. It

has dainty, wide-open, sky-blue flowers, and foliage that smells

“skunk-like” when crushed. This plant regenerates from the semiwoody crown of a large taproot, and from seed. Showy polemonium

usually declines following fire, although the cold, high-elevation

sites on which it grows are seldom easy to burn.

Name: Common Chokecherry (Prunus virginiana). Code: PRVI.

Resistance: Medium. Response: High. Site Type: Warm, Mesic.

Comments: Common chokecherry has reddish-brown bark, shiny,

toothed leaves, and attractive clusters of fragrant, white flowers.

After a fire, this medium to tall shrub sprouts prolifically from its

root crown. It decreases immediately after fire, but usually regains

preburn levels within 5 years. Occasionally, new chokecherry plants

are established after robins, waxwings and other birds, bears, and

mule deer spread the seeds by feeding on the fruit.

Name: Douglas-fir (Pseudotsuga menziesii). Code: PSME.

Resistance: High. Response: Medium. Site Type: Warm, Mesic.

Comments: Douglas-fir has short needles supported on small stalks;

long, pointed, shiny, brown buds; and hanging cones with unique,

three-pointed or “rat-tail” bracts protruding out from between their

scales. Its rough bark is gray when young, and thick, reddish-brown

and furrowed on older trees. Mature trees are fire resistant due to

their thick bark, but thin-barked poles and saplings are easily

damaged by burning. A long, dense crown and moderate stand

densities also add to Douglas-fir’s fire susceptibility in some instances. Because Douglas-fir saplings and poles are sensitive to fire,

low-intensity prescribed burns can be used to intentionally kill them.

Douglas-fir has become much more common over the last 80 years

as a result of fire suppression. By controlling natural underburns,

land managers were inadvertently swapping ponderosa pines and

western larches for white firs and Douglas-firs.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
130 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Name: Bracken Fern (Pteridium aquilinum). Code: PTAQ.

Resistance: High. Response: High. Site Type: Cool, Moist.

Comments: Bracken is a large, stout fern with triangular fronds up

to four feet tall. It is commonly found on moist toe-slopes or similar

topographic positions. Recent research found that bracken inhibits

conifer regeneration by producing chemicals that kill newly-germinated trees, a situation known as allelopathy (Ferguson and Boyd

1988). It may be a serious tree competitor on moist sites. Bracken

fern sprouts from surviving rhizomes and spreads vigorously after

fire. Native Americans used fire on Puget Sound's Whidbey Island

as a tool to maintain bracken (and camas) fields (Robbins and Wolf

1994).

Name: Sidebells Pyrola (Pyrola secunda). Code: PYSE.

Resistance: Low. Response: Low. Site Type: Cool, Mesic.

Comments: Sidebells pyrola is a low-growing forb with ovate

leaves and nodding, white or greenish flowers arranged along a

curved, four- to eight-inch stalk. The flowers all point in the same

direction, which accounts for another of its common names: onesided wintergreen. Although its leaves are evergreen, they do not

have the aromatic qualities of true wintergreens (Gaultheria). This

plant of shaded sites sprouts from rhizomes creeping along in the

lower duff, or established at the soil surface. Sidebells pyrola

commonly decreases after fire, but will survive when duff moisture

is high and excessive soil heating hasn’t occurred.

Name: Wax Currant (Ribes cereum). Code: RICE.

Resistance: Medium. Response: High. Site Type: Warm, Dry.

Comments: Wax currant is a spineless, mid-height shrub with

maple-like leaves having 3 or 5 shallow lobes, and bright red or

orange berries. The leaves are somewhat sticky and tend to have a

waxy upper surface. This plant regenerates from seed stored in the

litter and duff layers, and from basal stem sprouts. It often increases

after clearcutting on dryer sites, especially if the harvest units are

burned to reduce fuel accumulations or to prepare the site for

planting or natural regeneration. Wax currant is susceptible to fireinduced mortality, especially after severe burns. However, regeneration of wax currant is often favored by short-duration, low-intensity

fires.

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 131

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Prickly Currant (Ribes lacustre). Code: RILA.

Resistance: High. Response: High. Site Type: Cool, Moist.

Comments: Prickly currant is a prickly, mid-height shrub with

divided, maple-like leaves, and greenish or pinkish, saucer-shaped

flowers produced in drooping racemes. It grows near streams and on

other moist sites, where regeneration occurs from the root crown

and from seed. This plant, which harbors one of the life stages of

white pine blister rust, usually increases after burning, even if the

fire was a severe one. Cool or moderate-intensity fires favor establishment of prickly currant seedlings.

Name: Baldhip Rose (Rosa gymnocarpa). Code: ROGY.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Baldhip rose is a prickly, mid-height shrub with compound leaves bearing 5 to 7 oval, toothed leaflets, and small, pink

flowers produced singly, rather than in clusters. This common plant

regenerates from the root crown, stem bases, and from seed. It

responds vigorously to cool or moderate fires. New rose plants are

occasionally established after mice, coyotes, and birds spread the

seeds by feeding on the fruits (rose hips).

Name: Scouler Willow (Salix scouleriana). Code: SASC.

Resistance: High. Response: High. Site Type: Cool, Mesic.

Comments: Scouler willow, a tall shrub, differs from most other

willows because it is found on upland forest sites instead of along

streams or in other riparian habitats. Its hairy leaves are widest

above their middle (oblanceolate), which is another characteristic

that differs from most other willows. It regenerates by sprouting

from the root crown, or by using small, windborne seed produced in

small capsules that follow the showy catkins of early spring. In

many areas of the northern Rocky Mountains, Scouler willow

increases dramatically following a variety of burn intensities,

especially on relatively moist sites.
132 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Woolly Groundsel (Senecio integerrimus). Code: SEIN.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Woolly groundsel is an early-blooming forb with hairy,

lance-shaped leaves and an open cluster of small, yellow flowers.

The central flower is always older and shorter than others in the

cluster. It grows on dryer mixed-conifer sites. This hairy plant lacks

rhizomes, stolons, or a stout, persistent rootcrown, so regeneration

occurs mainly from off-site seed. Although fire effects information

is scarce for woolly groundsel, it is apt to decrease slightly or

remain unchanged following a low- or moderate-intensity burn.

Name: Bottlebrush Squirreltail (Sitanion hystrix). Code: SIHY.

Resistance: Medium. Response: High. Site Type: Warm, Dry.

Comments: Bottlebrush squirreltail is a low bunchgrass with

distinctive, bristly seedheads closely resembling a “bottlebrush.” Its

stems may reach two feet in height, but are most often a foot or so

tall. This weedy grass regenerates from the root crown, and from

seed. It has coarse, loosely-clustered stems and a minimum of leaf

matter, which means it burns quickly and that little heat is transferred downward to the underground tissues. Since it “cures” early,

bottlebrush squirreltail survives summer fires better than spring

ones.

Name: Feather Solomonplume (Smilacina racemosa).Code: SMRA.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Feather solomonplume is a mid-height forb with large,

oval leaves arranged alternately along the stem, and a 4- to 6-inch

long cluster of small, white flowers produced at the end of the stem.

The flowers are followed by lightly-striped, greenish to tan berries.

This common plant grows on moderately moist sites with heavy

shading. It regenerates from stout, creeping rhizomes, and is fairly

resistant to fire damage. Feather solomonplume usually maintains its

prefire frequency after burning, although it may be detrimentally

affected by fires that consume most of the litter and duff layers and

cause excessive heating of the upper soil.
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 133

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Starry Solomonplume (Smilacina stellata). Code: SMST.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Starry solomonplume is a low to medium forb with

long, narrow leaves; small, white flowers produced in a sparse, open

cluster; and yellowish-green berries. This common species sprouts

from creeping rhizomes. Starry solomonplume likes shade as much

as feather solomonplume does, although it typically occurs on

slightly drier sites than its close relative. It often decreases after fire,

especially severe burns that consume most of the litter and duff

layers and cause excessive heating of the upper soil.

Name: White Spiraea (Spiraea betulifolia). Code: SPBE.

Resistance: High. Response: High. Site Type: Cool, Mesic.

Comments: White spiraea is a low, spreading shrub with oval,

toothed leaves and dense, rounded clusters of small, white flowers.

It regenerates by sprouting from the root crown, and by use of deep

rhizomes located 2–5 inches beneath the soil surface. This common

plant usually increases after burning, even if the fire was a severe

one. White spiraea often flowers the year following a burn, although

the resultant seed has low viability and is probably unimportant for

post-fire recovery.

Name: Western Needlegrass (Stipa occidentalis). Code: STOC.

Resistance: Low. Response: Low. Site Type: Warm, Dry.

Comments: Western needlegrass is a mid-height bunchgrass with

narrow leaves less than a foot long, and a loose spike of small, hairy

flowers tipped with twisted awns up to an inch and a half long. This

high-elevation species regenerates from surviving root crowns, and

from seed. It is damaged most severely by early spring and late

summer fires. As a group, perennial needlegrasses are reported to

have some of the lowest fire resistance of the bunchgrasses.
134 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Common Snowberry (Symphoricarpos albus). Code: SYAL.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: Common snowberry is a low, spreading shrub with

opposite, elliptic leaves and small, white or pink flowers produced at

the end of the branches. This widely distributed plant is common in

mesic Douglas-fir and white fir plant associations. It increases after

site disturbance, but seldom competes aggressively with conifer

seedlings. Common snowberry regenerates from deep rhizomes and

basal stem buds, and from seed. Although favored by cool or

moderate fires, it usually survives severe ones too.

Name: Mtn. Snowberry (Symphoricarpos oreophilus).Code: SYOR.

Resistance: Low. Response: Medium. Site Type: Cool, Dry.

Comments: Mountain snowberry is a medium-sized shrub with

round or oval leaves and small, tubular, pink or white flowers. The

flowers are followed by white, porcelain-like berries that are relished by wild turkeys. When compared with common snowberry,

mountain snowberry is a taller plant, it occurs on dryer sites, and it

grows in clumps rather than from spreading rhizomes. It sprouts

weakly from its root crown, and from rhizomes. After cool or

moderate burns, it usually maintains its prefire cover and abundance.

Name: Common Dandelion (Taraxacum officinale). Code: TAOF.

Resistance: Medium. Response: Medium. Site Type: Disturbances.

Comments: Common dandelion is a low, weedy forb with lanceshaped, deeply-toothed leaves and attractive blossoms dominated by

narrow, yellow rays. It regenerates from the crown of a deep taproot,

and from light, windborne seed. Since a large amount of seed is

produced, common dandelion can quickly colonize burns located

adjacent to areas providing an ample seed source (road sides,

clearcuts, etc.).
FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS 135

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Huckleberry (Vaccinium membranaceum). Code: VAME.

Resistance: High. Response: Medium. Site Type: Cool, Mesic.

Comments: Big huckleberry is a low to mid-height shrub commonly

found in high-elevation snow zones. In the central and southern Blue

Mountains, it seldom competes with tree seedlings because of its

relatively low stature. Big huckleberry regenerates from rhizomes

and seed, although post-fire recovery may be slow. This shrub may

be difficult to underburn without some type of pretreatment. Fire

was used by native Americans to maintain huckleberry fields, both

to remove encroaching conifers and to regenerate declining plants

(Minore and others 1979). Big huckleberry is brittle and can be

easily damaged by machine piling or other mechanical site preparation treatments.

Name: Grouse Huckleberry (Vaccinium scoparium). Code: VASC.

Resistance: Medium. Response: Medium. Site Type: Cold, Mesic.

Comments: Grouse huckleberry is a creeping sub-shrub with small,

oval leaves and a tight, intricate branching pattern that often results

in a broom-like appearance. It has bright-green stems, pinkish, urnshaped flowers, and a bright red berry. This high-elevation species

regenerates from shallow rhizomes and seed. It usually survives cool

or moderate fires that don’t consume all of the litter and duff layers.

Grouse huckleberry typically grows on high, cold sites, but is sometimes found at lower elevations too, where it should then be considered an indicator of frost pocket conditions.

Name: American Vetch (Vicia americana). Code: VIAM.

Resistance: Medium. Response: High. Site Type: Cool, Mesic.

Comments: American vetch is a slender, climbing forb with reddish

or lavender “pea” flowers produced on slender stalks arising from

the leaf axils, and pinnately compound leaves with 8–12 small, oval

leaflets. It may resemble a vine because the long, twining tendrils

are used to climb on shrubs and small trees. This plant regenerates

by sprouting from rhizomes located in the upper soil layers. It is

seldom damaged by fire unless the litter and duff layers have been

consumed and excessive soil heating has occurred. Vetches are

similar to other legumes in that they are nitrogen fixers, which

means they can help improve the nutrient capital of a site.
136 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

TABLE 5–FIRE EFFECTS INFORMATION FOR PLANTS OF MIXED-CONIFER FORESTS (CONTINUED)

Name: Darkwoods Violet (Viola orbiculata). Code: VIOR2.

Resistance: Medium. Response: Medium. Site Type: Cool, Mesic.

Comments: Darkwoods violet is a perennial forb with round, wavyedged leaves and small, yellow flowers that have purplish veins. It

regenerates from short, slender rhizomes, and from seed stored in

the upper soil and litter or duff layers. Darkwoods violet usually

declines following fire, although the cool, moist sites on which it

grows are seldom easy to burn.

Sources: Common and scientific plant names generally follow the

nomenclature contained in “Flora of the Pacific Northwest” (Hitchcock and Cronquist 1973). Codes were taken from Powell (1989).

Fire resistance and post-fire response ratings were obtained from the

following sources: Bradley and others (1992), Crane and Fischer

(1986), Fischer and Bradley (1987), Fischer and Clayton (1983),

Flinn and Wein (1977), Geier-Hayes (1989), Hopkins and Rawlings

(1985), Leege and Godbolt (1985), McLean (1968), Noste and

Bushey (1987), Sampson (1917), Stickney (1986), and Volland and

Dell (1981). Valuable information was also obtained from the Fire

Effects Information System (FEIS) recently developed by the

Intermountain Fire Sciences Laboratory at Missoula, Montana

(Fischer 1990). For some plants, no literature sources were found

for one or both of the fire ratings, so an estimate was made using

information for species with similar morphological or reproductive

characteristics.

Note: Many of the drawings in this table were reproduced from the

5-volume Vascular Plants of the Pacific Northwest (Hitchcock and

others 1955, 1959, 1961, 1964, and 1969). They are copyrighted and

are reproduced here with permission from the University of Washington Press.
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 137

ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM

Many publications have been recently produced about the western

spruce budworm and its management, particularly during a 7-year research, development, and application program called CANUSA (Canada–United States Spruce Budworm Program). The goal of CANUSA

was to design and evaluate strategies for controlling or mitigating

spruce budworm impacts, and for managing budworm-susceptible forests to meet a variety of resource objectives. This section summarizes

some budworm publications that are useful for land managers of the

Malheur NF.

Aho, Paul E. 1984. Losses associated with Douglas-fir and true fir tops

killed by western spruce budworm in eastern Washington. Res. Pap.

PNW–318. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Experiment Station. 8

p.

A sample of 133 Douglas-firs and 69 true firs with dead tops caused by

budworm defoliation were felled, dissected, and examined for height

loss and decay incidence. Height loss was negligible for trees with only

the last year or two of their tops killed because lateral branches quickly

formed new tops. Infection of dead tops by decay fungi was low, probably because of their small basal diameters, the recency of topkilling,

and the low incidence of secondary attack by bark beetles.

Alfaro, R.I.; Thomson, A.J.; Van Sickle, G.A. 1985. Quantification

of Douglas-fir growth losses caused by western spruce budworm

defoliation using stem analysis. Canadian Journal of Forest Research. 15: 5–9.

Periodic growth and volume losses are described for a Douglas-fir

stand that was defoliated four times by western spruce budworm.

Losses were calculated by comparing periodic growth for the years of

reduced increment with potential growth, as estimated using a growth

and yield program. Cumulative tree volume losses, calculated by

adjusting growth during all loss periods to their potential values, were

estimated to be 44% of the potential volume the trees should have

reached by 1977 had they never been defoliated. The 1970s infestation

caused an estimated volume loss of 60 cubic meters per hectare (cm/ha)

in this stand, with 40 cm/ha from mortality, and 20 cm/ha from growth

losses.
138 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Alfaro, R.I.; Van Sickle, G.A.; Thomson, A.J.; Wegwitz, E. 1982.

Tree mortality and radial growth losses caused by the western spruce

budworm in a Douglas-fir stand in British Columbia. Canadian

Journal of Forest Research. 12: 780–787.

This study examined the effects of budworm defoliation on Douglas-fir

radial growth and tree mortality. Mortality reduced the number of stems

per hectare by 39.3%, and basal area per hectare by 11.6%, with most

of the losses occurring in the small-diameter trees (suppressed and

intermediate crown classes). Four budworm outbreaks occurred during

the life of the stand. The combined effect of the infestations amounted

to a loss of about 12% of the estimated potential diameter. The most

recent outbreak (1970–74) caused 10 years of subnormal growth,

including 5 years due to defoliation and 5 years of recovery.

Anderson, Leslie; Carlson, Clinton E.; Wakimoto, Ronald H. 1987.

Forest fire frequency and western spruce budworm outbreaks in

western Montana. Forest Ecology and Management. 22: 251–260.

Reduced fire frequency for the past 75 years has allowed extensive

areas with high budworm susceptibility to develop. Harvesting practices that removed the seral ponderosa pine and western larch aggravated

the problem. Budworm susceptibility can be reduced significantly by

using forest management practices that more closely resemble the pre1911 fire effects. Following timber harvest, site preparation practices

should be selected which encourage establishment and growth of seral,

nonhost conifers. Prescribed fire would do that job well in many instances. Seral species should also be favored when planting. Prescribed

fires in dense stands of Douglas-fir may reduce host-tree density and

remove the lower canopy layers; that practice may be particularly

effective in wilderness areas since timber harvests are prohibited, and

yet budworm susceptibility is often high. Mosaics of even-aged, seral

stands at a landscape level would be relatively resistant to budworm

damage; if those conditions are present at some future date, budworm

outbreaks may be less intense and of shorter duration.

Baskerville, G.L. 1975. Spruce budworm: super silviculturist. Forestry

Chronicle. 51: 138–140.

This paper provides a history of spruce budworm outbreaks (eastern

species) in New Brunswick, Canada. Periodic budworm outbreaks were

not viewed as a sign of instability because ecological stability in the

budworm–forest system must be measured on a time scale appropriate

to its function—periods of at least 50 to 100 years. To some extent,

management policy has been counterproductive; by spraying large areas

of mature host type that is not being immediately harvested, managers

are perpetuating an ideal food supply for the budworm. The forest

cannot be managed by harvesting small “bites” because that practice
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 139

maintains conditions that are conducive to an outbreak. The longer that

susceptible forests are protected in excess of what can be harvested, the

longer that high-risk areas are being exposed to an outbreak. Budworm

outbreaks were rarely mentioned before 1900 because many of the host

trees were not considered valuable; now that industry has decided that

balsam fir, red spruce, and white spruce are desirable, it is competing

with budworm for the opportunity to harvest those species.

Beveridge, Ron L.; Cahill, Donn B. 1984. Western spruce budworm

feeding effects on conifers located on the Boise and Payette National

Forests. Rep. No. 84–7. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Region, State and Private Fores-try,

Forest Pest Management. 25 p.

During 1981 and 1982, 85 stands comprised mostly of grand fir or

Douglas-fir were surveyed on the Boise and Payette National Forests to

evaluate spruce budworm damages sustained during the late 1970s.

Tree attributes were backdated to predefoliation levels and then projected through the defoliation period by using the Prognosis model. Differences between projected and measured increment provided an estimate

of radial-growth loss for true firs, and it ranged between 30 and 40

percent. Douglas-fir and spruce had a 15 percent reduction in radial

growth, while ponderosa pine and some lodgepole pine had a slight

increase in growth. Topkill, which was common on true firs, affected

10 to 20 percent of the sampled trees; host-tree mortality was infrequent.

Blais, J.R. 1962. Collection and analysis of radial-growth data from

trees for evidence of past spruce budworm outbreaks. Forestry

Chronicle. 38 (4): 474–484.

Studies of a spruce budworm outbreak showed that an average radialgrowth reduction of 50 percent was usually related to incipient mortality for highly vulnerable trees. Radial-growth suppression in white

spruce and balsam fir does not coincide with the onset of defoliation; at

breast height, it starts two to four years after the first severe year of defoliation and continues for some years after feeding has stopped.

Brookes, Martha H.; Campbell, Robert W.; Colbert, J.J.; Mitchell,

Russel G.; Stark, R.W., tech. coords. 1987. Western spruce budworm. Tech. Bull. 1694. Washington, DC: U.S. Department of

Agriculture, Forest Service, Coop. State Research Service. 198 p.

This comprehensive book summarizes current knowledge about the

western spruce budworm and its hosts. Chapter titles are: History;

Taxonomy of Spruce Budworms and Recognition of Associates; Life

History and Behavior; Description of Host Species; Host Responses;

Population Dynamics; Survival of Late Larvae and Early Pupae; Site
140 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

and Stand Characteristics; Modeling Budworm and Its Hosts; and

Recommendations.

Brookes, Martha H.; Colbert, J.J.; Mitchell, Russel J.; Stark, R.W.,

tech. coords. 1985. Managing trees and stands susceptible to western spruce budworm. Tech. Bull. 1695. Washington, DC: U.S.

Department of Agriculture, Forest Service, Cooperative State Research Service. 111 p.

This book is a guide for detecting and evaluating budworm effects on

susceptible forests, comparing budworm management strategies, and

providing support for budworm-related decisions. It focuses on budworm effects for both trees and stands, and describes detection, evaluation, and control operations. Chapter titles are: Historical Considerations; Western Budworm and Its Hosts; Effects of Infestations on Trees

and Stands; Site and Stand Characteristics; Surveys and Sampling

Methods for Population and Damage Assessment; Rating Stand Hazard

to Western Spruce Budworm; Tactics for Managing Trees and Stands;

and Selecting Management Tactics.

Brookes, Martha H.; Colbert, J.J.; Mitchell, Russel G.; Stark,

R.W., tech. coords. 1987. Western spruce budworm and forestmanagement planning. Tech. Bull. 1696. Washington, DC: U.S.

Department of Agriculture, Forest Service, Cooperative State Research Service. 88 p.

This book provides information for forest planners and policy makers

about protection of forests against outbreaks of the western spruce

budworm. Because its approach to forest protection—integrated pest

management (IPM)—is relatively new, it also describes the procedural,

structural, and legislative issues and constraints related to IPM. Chapter

titles are: Forest Conditions and the Western Spruce Budworm; Management Considerations in Integrated Pest Management; Damage and

Socioeconomic Impact; Management Strategies; Evaluating Management Options; and Institutional and Legal Factors Affecting Management of Western Spruce Budworm.

Brubaker, Linda B.; Greene, Shannon K. 1979. Differential effects

of Douglas-fir tussock moth and western spruce budworm defoliation on radial growth of grand fir and Douglas-fir. Canadian Journal

of Forest Research. 9: 95–105.

This study compared the effects of separate Douglas-fir tussock moth

and western spruce budworm infestations on the radial growth of two

host species: grand fir and Douglas-fir. Tussock-moth effects did not

differ statistically between the 2 species, but the impact of budworm

defoliation on grand fir was significantly greater than on Douglas-fir.

Differences occurred between the overall effects of tussock moth and
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 141

budworm, with tussock moth causing more rapid growth reductions and

greater growth losses than budworm.

Carlson, Clinton E.; Fellin, David G.; Schmidt, Wyman C. 1983.

The western spruce budworm in northern Rocky Mountain forests: a

review of ecology, insecticidal treatments and silvicultural practices.

In: O’Loughlin, J.; Pfister, R.D., eds. Management of SecondGrowth Forests: The State of Knowledge and Research Needs.

Missoula, MT: Montana Forest and Conservation Experiment

Station, School of Forestry, University of Montana: 76–103.

The western spruce budworm occupies a wide amplitude of ecological

niches in northern Rocky Mountain forests. Successful adaptation to

coniferous forest ecosystems has influenced several attributes of western spruce budworm in the northern Rockies, including 1) its extent and

persistence, 2) the periodicity of outbreaks, 3) its biology, behavior and

ecology on a variety of host trees growing on differing habitats, 4) the

factors that regulate it, and 5) the character of many forests and management decisions over the past three decades.

Carlson, C.E.; McCarthy, G.J. 1989. Dispersal of second-instar

western budworm above and below forest canopies in western

Montana. Res. Note INT–388. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station. 6 p.

Dispersal of second-instar western spruce budworm above and below

stand canopies was determined, using sticky traps, at two distinct

locations in western Montana. There was no significant difference

between catches above the canopy and 6 feet above ground. The presence of significant larvae numbers above forest canopies suggests that

budworm may be dispersed over long distances during vigorous frontal

systems and other periods with strong horizontal windflow.

Carlson, Clinton E.; McCaughey, Ward W. 1982. Indexing western

spruce budworm activity through radial increment analysis. Res.

Pap. INT–291. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station. 10 p.

Past spruce budworm activity in Douglas-fir forests of western Montana was assessed through radial increment analysis. A cumulative

growth function was graphically compared between a budworm host

(Douglas-fir) and a nonhost (ponderosa pine) species. Analysis showed

that Douglas-fir radial increment was very similar to that of ponderosa

pine in an area with no history of spruce budworm, and both growth

patterns appeared to be correlated with precipitation. During budworm

activity in mixed-species stands, acceleration of ponderosa pine radial

growth was observed.
142 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Carlson, Clinton E.; Schmidt, Wyman C. 1989. Influence of overstory removal and western spruce budworm defoliation on growth of

advance conifer regeneration in Montana. Res. Pap. INT–409.

Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 14 p.

The influence of four overstory removal levels on the height and diameter growth of advance regeneration was assessed in larch/Doug-las-fir

stands growing on subalpine fir habitat types of northwestern Montana.

Radial growth prior to treatment was the best indicator of post-treatment height and diameter growth for all species. Mortality was lowest

where either all or none of the overstory was removed, and was greatest

where about 50% of the overstory was removed. Following an overstory removal, growth response was mediocre and budworm susceptibility

increased. For those reasons, future volumes in stands of shade-tolerant

species may be substantially below volumes expected from stands of

seral trees on the same high-quality sites.

Carlson, Clinton E.; Wulf, N. William. 1989. Silvicultural strategies

to reduce stand and forest susceptibility to the western spruce budworm. Agric. Handbk. 676. Washington, DC: U.S. Department of

Agriculture, Forest Service, Coop. State Research Service. 31 p.

Silvicultural methods can be used to reduce forest and stand susceptibility to western spruce budworm and may be the most effective means

of dealing with budworm over the long run. Silvicultural methods

provide immediate protection for treated stands, and presumably will

provide long-term protection for large forested areas when enough area

has been treated. This publication describes a rating scheme for budworm susceptibility that is based on the following factors: regional

climate, site climate, species composition, stand density, stand heightclass structure, tree and stand vigor, maturity of trees and shrubs, and

adjacent host type.

Clancy, Karen M.; Itami, Joanne K.; Huebner, Daniel P. 1993.

Douglas-fir nutrients and terpenes: potential resistance factors to

western spruce budworm defoliation. Forest Science. 39 (1): 78–94.

Differences in the nutritional quality of Douglas-fir foliage may explain

why some individual trees are more resistant or susceptible than others

to damage from western spruce budworm. Susceptible trees also had

lower levels of nitrogen and sugars than resistant trees. Susceptible

trees had a greater proportion of total terpenes that were monoterpenes,

whereas resistant trees had a greater percentage of oxygenated monoterpenes. Resistant trees had delayed bud burst and shoot expansion as

compared to susceptible trees; they also had accumulated more radial

growth over the past 25 years, implying they were more vigorous than

susceptible trees.
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 143

Dolph, R. E., Jr. 1980. Budworm activity in Oregon and Washington,

1947–1979. Pub. R6–FIDM–033–1980. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region, State

and Private Forestry, Forest Pest Management. 54 p.

This paper summarizes western spruce budworm and Modoc budworm

activity, and projects undertaken to suppress them, in Oregon and

Washington between 1947 and 1979. Infestation acreages, and accompanying maps, are provided for each year from 1947 to 1979, and for

each national forest in Oregon and Washington.

Fellin, David G. 1983. Chemical insecticide vs the western spruce

budworm: after three decades, what’s the score? Western Wildlands.

9 (1): 8–12.

DDT spray programs treated more than eight million acres of budworm-infested forests in six Rocky Mountain states from the early

1950s to early 1960s. By the late 1950s, most managers in the northern

Rockies recognized that: 1) spraying was not a “one-shot” operation, 2)

budworm control was difficult where conditions favored the insect’s

development, and 3) the spruce budworm outbreak in the region had

not been controlled by spraying. The last time that DDT was used

against spruce budworm in the northern Rockies was in 1963, when the

President’s Science Advisory Committee recommended that governmental agencies curtail their use of persistent chemicals.

Fellin, David G.; Dewey, J.E. 1982. Western spruce budworm. Forest

Insect and Disease Leaflet 53. Washington, DC: U.S. Department of

Agriculture, Forest Service. 10 p.

This informative leaflet covers the following topics as related to western spruce budworm: description; life history; host trees; damage;

natural regulating factors; and management.

Fellin, David G.; Shearer, Raymond C.; Carlson, Clinton E. 1983.

Western spruce budworm in the northern Rocky Mountains: biology,

ecology and impacts. Western Wildlands. 9 (1): 2–7.

Despite tremendous ecological diversity, or perhaps because of it, most

Rocky Mountain forests appear to be susceptible to budworm outbreaks. Weather conditions may be the natural factor with the most

dramatic effect on spruce budworm populations. Radial increment

reduction from budworm defoliation was highest for dry Douglas-fir

habitat types located at low elevations and on steep slopes. In Douglasfir stands, budworm defoliation increased as crown closure increased.

Stands comprised of mixed species were less vulnerable to budworm

damage than pure stands of host species.
144 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Ferguson, Dennis E. 1988. Growth of regeneration defoliated by

spruce budworm in Idaho. Res. Pap. INT–393. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Research

Station. 13 p.

This paper describes budworm effects on four major aspects of regeneration development—dieback (topkill), height growth, crown ratio, and

mortality. Eleven percent of the host trees had dieback during the 5-

year measurement period. The probability of dieback increased with

increasing defoliation, increasing tree height, and decreasing crown

ratio. The amount of dieback varied from 0 to 67 percent of tree height.

Increasing defoliation was associated with decreasing height growth.

Only 3 percent of the sample trees died. Indications are that small

crown ratios or high defoliation levels increase the probability of smalltree mortality. Mathematical equations are provided to predict the

growth and development of regeneration for four conifer species defoliated by western spruce budworm in Idaho.

Ferrell, George T.; Scharpf, Robert F. 1982. Stem volume losses in

grand firs topkilled by western spruce budworm in Idaho. Res. Pap.

PSW–164. Berkeley, CA: U.S. Department of Agriculture, Forest

Service, Pacific Southwest Forest and Range Exp. Station. 10 p.

Two stands in the Little Salmon River drainage of west-central Idaho,

one cutover and one unmanaged, were affected by spruce budworm

outbreaks during the periods of 1922–30, 1952–55, and 1969–78. Forty

mature grand firs from the two stands were felled and dissected to

determine growth losses and decay associated with budworm-induced

topkilling. Stem decays, mainly from Indian paint fungus, caused most

of the volume loss. Almost all of the decay was associated with larger

tops killed during the 1922–30 outbreak. Little decay was present unless the top had been killed more than 30 years ago, and had a basal

diameter exceeding 3 inches. All but 2 of the 40 sample trees had been

topkilled at least once; one tree had been topkilled eight times. Decay

was associated with only 30% of the topkills. Topkills that were intact

(spikes), broken-off (stubs), or embedded all had associated decay.

Wetwood was almost always associated with topkilling in grand fir, but

it was not a reliable indicator that decay was present. Height growth of

topkilled firs in the cutover stand averaged 72.6% of predicted increment, while height growth in the uncut stand was 73.9% of the undamaged amount. Radial growth was apparently not related to topkill incidence. Volume losses associated with stem deformities (form defects)

never exceeded 5 percent of stem volume. In managed stands, grand

firs with dead tops having a basal diameter of 3 inches or more should

be harvested within 30 years to avoid extensive decay losses.
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 145

Gast, William R., Jr.; Scott, Donald W.; Schmitt, Craig; Clemens,

David; Howes, Steven; Johnson, Charles G., Jr.; Mason, Robert;

Mohr, Francis; Clapp, Robert A., Jr. 1991. Blue Mountains forest

health report: “new perspectives in forest health.” Portland, OR: US

Department of Agriculture; Forest Service; Pacific Northwest Region; Malheur, Umatilla, and Wallowa–Whitman National Forests.

This report summarizes the forest health situation for the Malheur,

Umatilla, and Wallowa–Whitman National Forests. It describes 12

issues related to forest health, and provides some strategies and recommendations for restoring forest health in the Blue Mountains of northeastern Oregon and southeastern Washington. Of particular interest is

Chapter II (Forest Insects and Diseases), which provides detailed descriptions of western spruce budworm and 7 other insects, as well as

informative discussions for 14 important tree diseases. Other chapter

titles are: Watershed Management and Forest Health; The Role of Fire

in the Blue Mountains; Long-Term Productivity; and Diversity.

Kemp, William P.; Everson, Dale O.; Wellington, W.G. 1985.

Regional climatic patterns and western spruce budworm outbreaks.

Tech. Bull. 1693. Washington, DC: U.S. Department of Agriculture,

Forest Service, Cooperative State Research Service. 31 p.

This study examined the hypothesis that if climatic characteristics are

important to budworm development and survival, then regional outbreak frequency should be related to regional weather conditions. The

authors found that generalized weather information, when combined

with stand level hazard-rating systems, could measurably improve our

present ability to forecast the onset of unacceptable budworm defoliation. Three classes of outbreak frequency were developed for the

forested areas of Idaho, Montana, Oregon, and Washington.

Langelier, Lisa A.; Garton, Edward O. 1986. Management guidelines for increasing populations of birds that feed on western spruce

budworm. Agric. Handbk. 653. Washington, DC: U.S. Department

of Agriculture, Forest Service, Coop. State Research Service. 19 p.

This manual is for managers who wish to enhance populations of predaceous birds in budworm-susceptible stands. Foraging behavior and

habitat preferences are summarized for the following birds that feed on

western spruce budworm (all 14 species occur on the Malheur NF):

American robin, Cassin’s finch, chipping sparrow, dark-eyed junco,

evening grosbeak, golden-crowned kinglet, Hammond’s flycatcher,

mountain chickadee, pine siskin, red-breasted nuthatch, Swainson’s

thrush, Townsend’s warbler, western tanager, and yellow-rumped

warbler. These are management recommendations for increasing

populations of budworm-feeding birds: plan for horizontal diversity;

plan for vertical diversity; avoid large clearcuts; provide edges; avoid
146 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

high-grading; avoid homogeneous, plantation-like stands; leave some

slash; reduce herbicide use; control grazing; provide for cavity-nesting

birds; provide salt; and provide water.

MacLean, David A. 1990. Impact of forest pests and fire on stand

growth and timber yield: implications for forest management planning. Canadian Journal of Forest Research. 20: 391–404.

The impact of forest pests and fire on stand growth and timber yield is

reviewed, with emphasis on spruce budworm impacts. Damaging

agents reduce tree growth, kill trees, destroy the commercial value of

stands, and sometimes reduce yield in subsequent rotations. Sustainable

harvest may be reduced up to 60% by a severe spruce budworm outbreak, and up to 40% by a 1% annual loss to fire. Serious overestimation of future timber supply can result from the failure to account for

catastrophic or continuous losses caused by fire or biotic agents. Current efforts to explicitly incorporate the effects of spruce budworm

defoliation into forest management planning are described, including

research studies about protection planning and delivery, damage detection, and defoliation-based growth forecasting. An improved understanding of the impact of insects, disease, and fire on stand yield, and

methods to incorporate this information into timber supply analyses, are

essential to reduce uncertainty about future timber supply.

MacLean, David A.; Ostaff, Donald P. 1983. Sample size-precision

relationships for use in estimating stand characteristics and spruce

budworm caused tree mortality. Canadian Journal of Forest Research. 13: 548–555.

Comparison of three plot types (prism point samples with BAF = 2.3;

circular, 0.01-hectare, fixed-area plots; and 0.05-hectare, fixed-area

plots) indicated that using larger numbers of small plots (either prism or

fixed-area) within each sampled stand would be the best method for

estimating tree mortality. Curves showing the required number of plots

to obtain a desired precision level were provided for estimating both

annual mortality and cumulative (total) mortality. As a rough approximation, sampling about 15 prism points in each stand should allow estimation of cumulative mortality to a precision of about plus or minus

10 percent.

Mason, Richard R.; Wickman, Boyd E.; Beckwith, Roy C.; Paul,

H. Gene. 1992. Thinning and nitrogen fertilization in a grand fir

stand infested with western spruce budworm. Part I: insect response.

Forest Science. 38 (2): 235–251.

Thinning and nitrogen fertilization were completed in a grand fir stand

near King Mountain on the southern part of the Malheur NF. In general,

defoliating insects seemed to benefit from both treatments, but es-
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 147

pecially from the fertilization. Overall budworm survival and prevailing

trends of the outbreak were unaffected by the treatments and seemed to

be determined mostly by other factors, probably natural enemies. This

means that the ultimate value of thinning and fertilization in budworminfested forests must be based on their effect on tree and stand vulnerability, rather than any direct impact on budworm populations.

McDonald, G. I. 1981. Differential defoliation of neighboring Douglas-fir trees by western spruce budworm. Res. Note INT–306.

Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 10 p.

Color photographs document the phenotypic variation of inland Douglas-fir populations in response to defoliation by western spruce budworm. Host-insect literature was reviewed, and tentative hypotheses to

explain the non-defoliated trees were suggested.

Montgomery, B.A.; Dimond, John B.; Witter, John A.; Simmons,

Gary A. 1984. Insecticides for control of the spruce budworm.

Agric. Handbk. 615. Washington, DC: U.S. Department of Agriculture, Forest Service, Cooperative State Research Service. 29 p.

This handbook is for forest entomologists, biologists, and extension

workers who are responsible for making recommendations about the

use of insecticides. It provides an application guide for common chemical and microbial insecticides registered for spruce budworm control

(eastern species) in the United States. Because application rates are

given as ranges, and because registrations change, actual pesticide

labels must be used as the final source of insecticidal information. The

differences between chemical insecticides and Bacillus thuringiensis

(B.t.), a bacterial insecticide, are also provided.

Murphy, C.F.; Croft, B.A. 1990. Forest ant composition and foraging

following aerial spraying of carbaryl to suppress western spruce

budworm. Canadian Entomologist. 122 (July/August): 595–606.

This study examined the effect of carbaryl treatment on foraging ants.

Four plots on the Malheur NF were used in the study—two treated plots

at Dan’s Creek and Murderer’s Creek, and two untreated plots at Starr

Ridge and Herberger Spring. After spraying, ant species diversity

declined in treated plots. Post-spray ant foraging decreased in all plots,

but the decrease was more rapid and pronounced in treated plots.

Among ground-foraging ants, budworm predators were obviously

affected by spraying. Ants that are arboreal foragers, nearly all of which

are also budworm predators, showed a significantly lower foraging rate

in the treated plots. Ant foraging continued at depressed levels for at

least 6 weeks after spraying, which was long enough for budworm to

reach the adult stage. This study concluded that carbaryl spraying may
148 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

inhibit some of the natural enemies that help keep budworm populations in check. Reduced ant predation on the sparse bud-worm populations present after spraying may contribute to budworm resurgence.

Muzika, Rose-Marie; Engle, Judith; Parks, Catherine; Wickman,

Boyd. 1993. Variation in phenology and monoterpene patterns of

defoliated and nondefoliated Douglas-fir (Pseudotsuga menziesii var.

glauca). Res. Pap. PNW–RP–459. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station. 10

p.

Foliage was collected from paired Douglas-fir trees characterized as

either “resistant” or “susceptible” to western spruce budworm attack.

Although there were no compositional differences in terpenes, foliage

from nondefoliated trees produced a greater amount of monoterpenes

than foliage from susceptible trees. Phenology patterns between the two

groups of trees differed greatly—severely-defoliated trees broke bud 7

to 10 days earlier than nondefoliated trees. The results of this study may

have implications for breeding Douglas-firs that are less susceptible to

budworm defoliation.

Nichols, Thomas J. 1988. The relationship between western spruce

budworm defoliation levels and growth of individual Douglas-fir and

grand fir trees. Forest Science. 34 (2): 496–504.

This study concluded that previous tree condition had a strong impact

on current-year growth. In budworm-infested stands, defoliation had a

major influence on tree condition. Proportional growth loss at a given

level of defoliation was the same regardless of growth rates prior to

defoliation. Variations in height and basal-area growth for defoliated

trees were best explained using models that predicted nondefoliated

growth, foliage level, and preceding-year tree condition.

Sanders, C.J.; Stark, R.W.; Mullins, E.J.; Murphy, J., eds. 1985.

Recent advances in spruce budworms research. Proceedings of the

CANUSA Spruce Budworms Research Symposium; 1984, September 16–20; Bangor, ME. Ottawa, Ontario, Canada: Canadian Forestry Service. 527 p.

This volume summarizes scientific advances achieved during the CANUSA program, the largest international cooperative forestry project ever

conducted. Information is provided in four major parts, whose titles are:

Part I: Spruce Budworms—Biology, Ecology, and Population Dynamics; Part II: Economic and Social Impacts of Spruce Budworms in

North American Forests; Part III: Tactics and Strategies for Prevention

and Suppression of Damage by Spruce Budworm; and Part IV: Integrated Forest and Pest Management.
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 149

Schmidt, Wyman C.; Fellin, David G.; Carlson, Clinton E. 1983.

Alternatives to chemical insecticides in budworm-susceptible forests. Western Wildlands. 9 (1): 13–19.

Silvicultural treatment, an approach given little consideration in the

past, now appears to be a promising option for reducing budworm impacts. As forest management becomes more intensive, most commercial forests will warrant some sort of silvicultural manipulation, whether spruce budworm remains a threat or not. Therefore, foresters have

only to select the silvicultural treatment most suited to the stand in

question, and least favorable to budworm. This requires that both

silviculturists and forest managers better understand the ecology of

western spruce budworm in the northern Rockies.

Swetnam, Thomas W.; Lynch, Ann M. 1989. A tree-ring reconstruction of western spruce budworm history in the southern Rocky

Mountains. Forest Science. 35 (4): 962–986.

Tree-ring chronologies from ten mixed-conifer stands in southern

Colorado’s Front Range and northern New Mexico’s Sangre de Cristo

Mountains were used to reconstruct the timing, duration, and radial

growth impacts of past budworm outbreaks. At least nine outbreaks

were identified in the stands between 1700 and 1983. The average

growth reduction period was 12.9 years; it ranged from 5 to 26 years.

There was a relatively long period of reduced budworm activity in the

first few decades of the twentieth century. Since that time, outbreaks

have been markedly more synchronous, probably because of changes in

age structure and species composition following partial cutting and fire

suppression in the twentieth century.

Thomson, A.J.; Alfaro, R.I. 1990. A method to calculate yield correction factors for the overstory component of budworm-attacked

Douglas fir. Forest Ecology and Management. 31: 255–267.

A method was developed to estimate yield reductions, at rotation age,

in overstory Douglas-fir trees after defoliation in a single budworm

outbreak. Budworm impact was expressed as correction factors which

could be applied to the expected volume at rotation. These factors

varied by site quality, stand age, and with the duration and severity of

defoliation. Yield loss was greater in stands attacked at young ages than

those attacked when older. Loss estimates were most sensitive to

changes in site quality, and defoliation duration and severity.
150 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Torgersen, Torolf R.; Mason, Richard R.; Campbell, Robert W.

1990. Predation by birds and ants on two forest insect pests in the

Pacific Northwest. Studies in Avian Biology. 13: 14–19.

A variety of techniques were used to identify bird and ant predation on

Douglas-fir tussock moth and western spruce budworm. Fourteen bird

species were observed to prey on tussock moth larvae. Both birds and

foliage-foraging ants were important predators of budworm larvae and

pupae. When crown enclosures and ant barriers were used to protect

larvae from predation, 2 to 15 times as many budworm survived to the

pupal stage. Predation was influenced by crown stratum: ants were

most effective in the lower crowns, while birds excelled at higher

levels. Populations of predatory ants and many of the insectivorous

birds are enhanced by the availability of dead wood and stumps.

Van Sickle, G.A.; Alfaro, R.I.; Thomson, A.J. 1983. Douglas-fir

height growth affected by western spruce budworm. Canadian

Journal of Forest Research. 13: 445–450.

Detailed dissections of Douglas-fir trees repeatedly defoliated by

western spruce budworm in two areas of British Columbia indicated

that budworm severely affected height growth. Dissected trees lost an

average of 7.3 internodes in each infestation, of which 4.2 were destroyed or failed to grow during the defoliation and recovery periods,

and 3.1 were existing internodes lost to dieback (topkill). Total height

was reduced by 32 percent and 19 percent in areas that sustained four

and two infestations, respectively. Height growth reductions were

attributed to 1) prevention of height growth during active defoliation

periods, 2) reduced height growth during recovery, and 3) dieback of

the existing stem from the terminal leader downward (topkill). It was

also found that budworm infestations resulted in an underestimation of

site index for Douglas-fir in the affected area.

Wickman, Boyd E. 1992. Forest health in the Blue Mountains: the

influence of insects and disease. Gen. Tech. Rep. PNW–GTR–295.

Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 15 p.

This summary report concluded that many of the current pest problems

in the Blue Mountains are related to human activities occurring over the

last 90 years. The virtual exclusion of low-intensity fires since 1900, in

combination with extensive logging of ponderosa pine, has resulted in

the establishment of fir on many thousands of acres that previously

supported pine. The fir forests are highly susceptible to insects and

diseases, and to catastrophic forest fires. Some long-term management

strategies are now needed to alleviate a variety of problems associated

with the change in forest composition.
ADDITIONAL INFORMATION ABOUT WESTERN SPRUCE BUDWORM 151

Wickman, Boyd E.; Mason, Richard R.; Paul, H. Gene. 1992.

Thinning and nitrogen fertilization in a grand fir stand infested with

western spruce budworm. Part II: tree growth response. Forest

Science. 38 (2): 252–264.

Thinning and nitrogen fertilization were completed in a grand fir stand

near King Mountain on the southern part of the Malheur NF. This study

found that fertilization of a defoliated stand provided the following

benefits, as compared to an untreated stand: defoliation was reduced,

height growth was greater, and radial growth was increased. Fertilized

trees apparently produced fewer buds per square meter of foliage, but

more foliage was produced on each shoot than could be consumed by

budworm. The study also found that the radial growth of trees on plots

that were thinned, but not fertilized, was significantly greater than the

untreated controls after 5 years.

Williams, Carroll B., Jr. 1967. Spruce budworm damage symptoms

related to radial growth of grand fir, Douglas-fir, and Engelmann

spruce. Forest Science. 13 (3): 274–285.

This study examined the effect of budworm damage during the 1944–

1956 outbreak on the radial increment of host trees. After the outbreak

subsided, measurements were collected from four stands on the Wallowa National Forest. Grand fir had the most variation in budwormcaused damage; growth losses ranged from 23.9 to 41.1 percent, and

topkilling caused 7.7 to 15 years of lost height growth, depending on

damage intensity. Douglas-fir had the least budworm damage, with

little growth loss and no topkilling observed. Engelmann spruce had

intermediate damage levels, ranging from 6.1 to 24.8 percent for radial

growth losses, and 6 to 7 years of height growth reduction.
152 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

REFERENCES

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mystery—the grand fir mosaic. Focus on Renewable Natural Resources. 15: 21–22.

Agee, James K. 1993. Fire ecology of Pacific Northwest forests.

Washington, DC: Island Press. 493 p.

Anderson, Leslie; Carlson, Clinton E.; Wakimoto, Ronald H. 1987.

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western Montana. Forest Ecology and Management. 22: 251–260.

Barrett, James W. 1978. Height growth and site index curves for

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Carolin, V.M.; Coulter, W.K. 1971. Trends of western spruce budworm and associated insects in Pacific Northwest forests sprayed

with DDT. Journal of Economic Entomology. 64 (1): 291–297.

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western spruce budworm defoliation. Forest Science. 39 (1): 78–94.

Cochran, P.H. 1979a. Site index and height growth curves for managed, even-aged stands of Douglas-fir east of the Cascades in Ore-
154 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

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Cochran, P.H. 1979b. Site index and height growth curves for managed, even-aged stands of white or grand fir east of the Cascades in

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Cochran, P.H. 1985. Site index, height growth, normal yields, and

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170 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

APPENDIX 1: COMMON AND SCIENTIFIC NAMES

Bacteria

Birds

Common Name Scientific Name

B.t. Bacillus thuringiensis

American Robin Turdus migratorius

Cassin’s Finch Carpodacus cassinii

Chipping Sparrow Spizella passerina

Dark-Eyed Junco Junco hyemalis

Evening Grosbeak Coccothraustes vespertinus

Golden-Crowned Kinglet Regulus satrapa

Hammond’s Flycatcher Empidonax hammondii

House Sparrow Passer domesticus

Mountain Chickadee Parus gambeli

Northern Spotted Owl Strix occidentalis caurina

Pileated Woodpecker Dryocopus pileatus

Pine Siskin Carduelis pinus

Red-Breasted Nuthatch Sitta canadensis

Red-Winged Blackbird Agelaius phoeniceus

Ruby-Crowned Kinglet Regulus calendula

Swainson’s Thrush Catharus ustulatus

Townsend’s Warbler Dendroica townsendi

Western Tanager Piranga ludoviciana

Yellow-Rumped Warbler Dendroica coronata

Bracken Fern Pteridium aquilinum

Bull Thistle Cirsium vulgare

Elk Sedge Carex geyeri

Marigold Calendula officinalis

Peavines Lathyrus spp.

Pinegrass Calamagrostis rubescens

Tailcup Lupine Lupinus caudatus

Vetch Vicia americana

Western Coneflower Rudbeckia occidentalis

Bark Beetles Dendroctonus spp. (primarily)

Carpenter Ants Camponotus spp.

Carabid Beetle Carabidae

Douglas-fir Beetle Dendroctonus pseudotsugae

Douglas-fir Tussock Moth Orgyia pseudotsugata

Fir Engraver Scolytus ventralis

Jumping Spider Metaphidippus aeneolus

Mountain Pine Beetle Dendroctonus ponderosae

Pandora Moth Coloradia pandora

Pine Engraver Beetles Ips spp.

Spruce Budworm (Eastern) Choristoneura fumiferana

Stink Bug Pentatomidae

Herbs

Insects and Other

Arthropods
APPENDIX 1: COMMON AND SCIENTIFIC NAMES 171

Common Name Scientific Name

Thatch Ants Formica spp.

Western Pine Beetle Dendroctonus brevicomis

Western Spruce Budworm Choristoneura occidentalis

Yellowjacket (Western) Vespula pennsylvanica

Black Bear Ursus americanus

Coyote Canus latrans

Raccoon Procyon lotor

Annosus Root Disease Heterobasidion annosum

Armillaria Root Disease Armillaria ostoyae

Douglas-fir Dwarf Mistletoe Arceuthobium douglasii

Dwarf Mistletoes Arceuthobium spp.

Indian Paint Fungus Echinodontium tinctorium

Black Cottonwood Populus trichocarpa

Bull Pine (See Ponderosa Pine)

Douglas-fir Pseudotsuga menziesii

Engelmann Spruce Picea engelmannii

Grand Fir Abies grandis

Lodgepole Pine Pinus contorta

Mountain Mahogany Cercocarpus ledifolius

Neem Tree Azadirachta indica

Ponderosa Pine Pinus ponderosa

Quaking Aspen Populus tremuloides

River Birch Betula occidentalis

Snowbrush Ceanothus Ceanothus velutinus

Subalpine Fir Abies lasiocarpa

Tamarack (See Western Larch)

Thinleaf Alder Alnus incana

Western Hemlock Tsuga heterophylla

Western Juniper Juniperus occidentalis

Western Larch Larix occidentalis

Western White Pine Pinus monticola

Western Yellow Pine (See Ponderosa Pine)

White Fir Abies concolor

Willows Salix spp.

Yellow Pine (See Ponderosa Pine)

Insects and Other

Arthropods (cont.)

Mammals

Pathogens

Trees and Shrubs
172 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

APPENDIX 2: SURVEY DESIGN AND RELIABILITY OF RESULTS

The budworm impact survey remeasured a subsample of permanent

plots established earlier for a different objective. Thus, to understand

the budworm design and estimation procedures, it is necessary to

understand the designs which produced the permanent plots that were

remeasured.

In 1967 and 1968, a timber management inventory was conducted on

the Malheur National Forest. This inventory was installed on “available” national forest lands to assess their current status, and to identify

trends in area and volume statistics. The primary use of the 1967–68

inventory was for management planning.

The 1967–68 survey design was a systematic grid sample uniformly

distributed over the entire Forest. The grid interval was 1.7 miles on a

side. This produced 766 grid locations distributed over 1,419,659 acres

of available forest land (AFL). Each grid location corresponded to a

field plot location, and each field plot represented 1853.34 acres. Estimates of subpopulation parameters for available forest land were made

by dividing the number of plots in the subclass of interest by the original 766 plots and multiplying by the known acres of AFL. For example,

the estimated acres of commercial forest land (CFL) was equal to:

CFL = {638 ÷ 766} x 1,419,659 acres = 1,182,432 acres.

Traditionally, the estimates of such systematic samples have been

treated as simple random samples for estimating sample variances. Systematic samples maximize the sample variance among plots; thus, in

most cases, they produce an estimated variance that is larger than the

variance which would have been obtained if simple random sampling

had been used. In other words, simple random sampling estimators produce conservative estimates of sample variances. Systematic sampling

does provide the best spatial coverage of an area being inventoried.

In 1980, a new timber management inventory was completed. The objectives of this new inventory differed from the 1967–68 inventory,

which resulted in a new survey design. In addition, the entire Forest

was mapped into model component polygons. Thus, the total area of

each model component was known within the accuracy limitations of

the mapping procedures. The objectives were still to assess the current

status and trends in area and volume statistics, but it was also desired to

control the precision estimates by model component. The precision

requirements were + 10% for ponderosa pine and mixed conifer strata,

and + 20% for lodgepole pine strata, both at the 68% probability level.

Prepared by Dr. John W. Hazard, Statistical Consulting Service

The 1967–1968

Timber Inventory

The 1980 Timber

Inventory
APPENDIX 2: SURVEY DESIGN AND RELIABILITY OF RESULTS 173

The 604 plots established in 1967–68 were transferred to the model

component map and the total number of 1967–68 plots were arrayed by

strata. Using variance estimates of board-foot volume from the 1967–

68 plot measurements by stratum, the number of plots necessary to

satisfy the specified levels of precision were computed. The computed

number of plots was compared to the number of 1967–68 plots for each

stratum. If the 1967–68 sample satisfied the specified precision, no new

plots were selected. If too few plots existed for a particular stratum,

then the number of additional plots necessary to satisfy the precision

requirement was determined.

For those strata that did not require new plots, the required number of

1967–68 plots was distributed uniformly among townships within ranger districts, attempting to get equal numbers of plots per township.

For those strata requiring additional plots, the number of new plots

equalled the required number of plots minus the existing number of

1967–68 plots. New plots were distributed to strata first by district, and

then by township. Within townships, new plots were distributed by

numbering polygons by strata and randomly selecting the required

number. Plot locations within polygons were determined by placing a

grid template over the polygon, and then randomly selecting a grid

point. The number of 1967–68 plots, new plots, and the total for each

stratum appear in Table 6.

Thus, the 1980 sample was a combination of remeasured 1967–68 plots

and supplemental plots installed in 1980. The strata areas were determined from the model component map. Estimates for the entire Forest

were made by assuming a stratified random sample. The sampling

intensities varied considerably among strata. Expansion factors for the

1980 combined sample appear in Table 6 (see “Acres/Plot” column).

The combined number of 1980 plots required to satisfy the specified

levels of precision for all strata was 400. Actually, 402 plots were

established in the field.

The 1988–89 spruce budworm survey, the basis for this report, used a

subset of the 1980 timber inventory plots. It was decided that only plots

which were determined to be budworm-host type would be visited in

the field. Thus, the 1988–89 spruce budworm survey was conditioned

on the selection rules used in the 1980 timber inventory survey, and had

the added condition that only host type plots within the various strata

would be visited and remeasured. Budworm host type was defined as

those plots containing 50% or more of their live trees in host species

(Engelmann spruce, white or subalpine fir, Douglas-fir, and western

larch). There were 130 of the 1980 plots selected for the 1988–89

budworm survey (Table 6). Note that there were 12 strata in the 1980

timber management inventory (Tables 6 and 8). The fact that only 130

Plot Selection

The 1988–1989

Budworm Survey
174 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

of the 402 plots were used in the budworm survey resulted in some

strata with few or no host type plots. To insure that estimates of host

types by strata contained an adequate sample, the 12 management strata

from 1980 were collapsed into 5 budworm-analysis strata (Table 7).

Strata with similar timber types were combined. For purposes of estimation in this report, the 1988–89 budworm survey was assumed to be

a stratified random sampling design.

There are two approaches that can be taken to estimate the average

amounts of topkill, defoliation, and mortality for the subpopulations of

interest. One way is to use the measured values for those plots in the

host type and zero for all the rest, and then form strata means according

to the strata delineations from the 1980 timber inventory. This method

is an exact one based on random sampling, but it produces means that

are averaged over all plots in each stratum. Thus, the means are diluted

by the zero values associated with the nonhost plots. Forest managers

don’t find this type of mean useful for management planning because it

includes situations where budworm damage will not occur (i.e., the

nonhost type). Instead, they prefer stratum estimates that include only

those plots on which damage could potentially occur (host type).

The second approach is to form means, as suggested, by using only the

host type plots included within strata defined for the 1980 timber

inventory. These means can be formed quite readily and weighted by

stratum areas to derive population estimates. The problem with this

estimation method is that the amount of host type by stratum is unknown. It can only be estimated by calculating the proportion of host

plots by strata, and then multiplying this proportion by the known strata

areas. When forming averages for strata with unknown strata areas or

sizes, sampling error is introduced for the estimates of host type areas.

An approximate method is to use the variability among host plots

within strata, since the estimated area of host type is not used for the

host strata means. Readers should keep in mind that if an exact method

existed for computing standard errors of average topkill, defoliation,

and mortality by host type, estimates of these parameters would be

larger than the approximations included in this report.

Confidence intervals are computed for a wide variety of subpopulations

of interest. In the bar graphs (figs. 43–60), error bars appear as 68%

confidence intervals. The estimated standard errors are computed as

stratified random sampling estimates, with effective degrees of freedom

(Cochran 1977). Note that for analysis factors pertaining to tree characteristics (species, diameter, height, age, crown ratio, and crown class),

the plot percentages for the categories associated with each factor will

sum to more than 100%. This occurred because each sample plot could

support trees that were assigned to different categories for a particular

analysis factor. For example, a plot may have supported Douglas-firs,

white firs, and other hosts (Engelmann spruce, subalpine fir, or western

Calculating Sample

Means

Sample Sizes for

Tree-Related

Variables
APPENDIX 2: SURVEY DESIGN AND RELIABILITY OF RESULTS 175

larch). In that instance, the plot supplied 3 values when assessing

budworm impacts by tree species—one mean for the Douglas-firs,

another mean for the white firs, and a third value for the other hosts.

The same situation was true for other tree-based analysis factors—a

plot could have both dominant and suppressed trees, old and young

trees, large- and small-diameter trees, tall and short trees, and so forth.

For the tree-related variables, the sample sizes provided in the report

include only those plots which contained trees that existed in the

subpopulation of interest.

Table 6—Distribution of inventory plots by measurement period and

model component.

Mod 1968 1980 Plots 1988–89 Plots Acreages Acres/

Com Plots Old New Tot Old New Tot Total Sample Plot

101 10 7 84 91 2 12 14 21037 3237 231.2

201 12 10 66 76 1 11 12 12154 1919 159.9

501 154 30 0 30 4 0 4 240378 32050 8012.6

601 25 14 7 21 1 1 2 60430 5755 2877.6

102 7 6 31 37 4 20 24 22217 14411 600.5

202 9 6 26 32 3 19 22 16716 11492 522.4

502 295 40 1 41 27 0 27 542400 357190 13229.3

602 15 15 14 29 9 7 16 54321 29970 1873.1

103 1 1 9 10 1 0 1 4545 455 454.4

203 8 5 10 15 1 2 3 15244 3049 1016.3

503 23 9 2 11 2 0 2 30451 5537 2768.3

603 6 5 4 9 1 2 3 12707 4236 1411.9

Total 565 148 254 402 56 74 130 1032600 469301

Notes: “Mod Com” is Model Component; “Tot” is Total. For the “acreages”

section, the “total” column is the total acreage associated with that model

component in the 1980 timber inventory. The “sample” column is the estimated acreage of budworm host type represented by plots that were remeasured for the 1988–89 budworm survey. For a description of model components, see Table 8. Source: forest inventory records available at the Malheur

NF, Supervisor's Office.

Table 7—Data summary by analysis stratum.

 Model Total Total Expansion:

Stratum Components Acreage Plots Acres/Plot

PPine 101/201 33191 167 198.75

Regen 102/103 26762 47 569.40

CThin 202/203 31960 47 680.00

OvRem 501/502/503 813229 82 9917.43

NoTmt 601/602/603 127458 59 2160.31

TOTAL 1032600 402
176 EFFECTS OF THE 1980S BUDWORM OUTBREAK—MALHEUR NF

Table 8—Model components that were field sampled.

Component Description

101 Ponderosa pine, regeneration treatment recommendation.

201 Ponderosa pine, commercial thinning recommendation.

501 Ponderosa pine, overstory removal recommendation.

601 Ponderosa pine, no treatment recommendation.

102 Mixed conifer, regeneration treatment recommendation.

202 Mixed conifer, commercial thinning recommendation.

502 Mixed conifer, overstory removal recommendation.

602 Mixed conifer, no treatment recommendation.

103 Lodgepole pine, regeneration treatment recommendation.

203 Lodgepole pine, commercial thinning recommendation.

503 Lodgepole pine, overstory removal recommendation.

603 Lodgepole pine, no treatment recommendation.

Notes: Model components are a combination of 2 factors—forest type

(referred to as a working group in inventory terminology), and a silvicultural

opportunity class or treatment recommendation. In the 1980 timber inventory,

there were 3 working groups (ponderosa pine, mixed conifer, and lodgepole

pine), and four treatment opportunity classes for which field plots were allocated (regeneration, commercial thinning, overstory removal, and no treatment). Since the 1980 inventory was based on timber volume, no field plots

were allocated to the reforestation and precommercial thinning opportunity

classes because there were no timber volumes associated with those strata.