United States

Department of

Agriculture

Forest Service

Northeastern

Research Station

General Technical

Report NE-308

David W. Williams

Richard A. Birdsey

Historical Patterns of Spruce Budworm

Defoliation and Bark Beetle Outbreaks

in North American Conifer Forests:

An Atlas and Description of Digital Maps
Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service

11 CAMPUS BLVD SUITE 200 Publications Distribution

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Delaware, OH 43015-8640

July 2003 Fax: (740)368-0152

Visit our homepage at: http://www.fs.fed.us/ne

Abstract

This atlas provides maps of historical defoliation by the eastern and western spruce

budworms and historical outbreaks of the mountain and southern pine beetles

during the past half century. The maps encompass various regions of the

conterminous United States and eastern Canada. The publication also serves as

documentation for an extended set of digital maps, which are available on our

website. The digital maps are useful for investigating spatial dynamics of insect

populations and for providing pest disturbance inputs to spatially explicit forest

simulation models.

The Authors

DAVID W. WILLIAMS is a research entomologist with the Northeastern Research

Station and RICHARD A. BIRDSEY is the program manager for the Northern Global

Change Research Program. Both authors are located at station headquarters in

Newtown Square, PA.
1

Introduction

Recent developments in geographic information system (GIS) software and the availability of

increasingly powerful hardware to run it have facilitated interests in the spatial aspects of forest

ecology (Liebhold and Barrett 1993). Moreover, the increasing availability of high-quality,

remotely sensed imagery has provided abundant data for mapping forests and the various

environmental factors affecting them (Zhu and Evans 1994, Gutman et al. 1997). Accurate

digital maps of forests have obvious utility for the routine management of resources. In

addition, they are useful for anticipating altered spatial distributions of forest species and stands

under global climate change (Iverson and Prasad 1998, Iverson et al. 1999).

Beyond the sheer acquisition, manipulation, and analysis of spatial data on forests, there are the

recent developments of spatially explicit vegetation models (Aber and Federer 1992, Neilson

1995). Such models facilitate the extrapolation of basic ecosystem processes to the landscape

and regional levels and permit the simulation of forest dynamics under changing environmental

conditions (Aber et al. 1993, 1997; Pan et al. 2003). Recently, vegetation models have

incorporated the effects of large-scale environmental disturbances, most notably fire (Bachelet et

al. 2001, Thonicke et al. 2001). But biotic disturbances, such as insect outbreaks, generally are

not yet considered in those modeling efforts (Williams et al. 2000). Because vegetation models

are evolving to include disturbance effects, the time is ripe to compile and make available

archived maps of insect outbreaks. Historical data are critical for the development of spatially

explicit models of disturbance for inclusion in vegetation models.

Here we describe maps of historical damage by four native species of forest insects that cause

extensive disturbances in North American forests. We present an atlas of previously

unpublished maps for the species and reference the more extensive set of digital coverages

available at www.fs.fed.us/ne/global/products. These pests of conifer forests include two

defoliators, the eastern spruce budworm (Choristoneura fumiferana) and the western spruce

budworm (Choristoneura occidentalis), and two bark beetles, the southern pine beetle

(Dendroctonus frontalis) and the mountain pine beetle (Dendroctonus ponderosae). The maps

have been used previously in studies of potential effects of climate change on the geographical

ranges of the species (Williams and Liebhold 1995, 1997, 2002; Williams et al. 2000) and of

the spatial dynamics of their populations at the regional level (Williams and Liebhold 2000a, b;

Peltonen et al. 2002). We make them available now for their obvious utility in simulating pest

disturbances in spatially explicit forest models. We describe the pest maps and their

development and explore ways in which they may be applied. A similar set of maps of historical

defoliation by gypsy moth (Lymantria dispar), a devastating exotic invasive insect attacking oak

forests in the eastern United States, is described in Liebhold et al. (1997) and available at

www.fs.fed.us/ne/morgantown/4557/gmoth.

Map Development

Maps of defoliation and damage were developed using the Idrisi (Eastman 1999) and GRASS

(U.S. Army Corps of Engineers 1993) GIS. Both systems are raster-based GIS, in which the

smallest map units (i.e., rasters) are square grid cells.

With the exception of the southern pine beetle maps, GIS coverages were created from paper

maps. The paper maps were assembled from individual state and province maps that, in turn,

were developed from aerial sketch maps of defoliation or tree mortality (McConnell et al.

2000). For the budworms, areas depicted as defoliated on sketch maps had defoliation visible

from the air, which was generally greater than 30 percent canopy loss (Webb et al. 1961). Bark

beetle damage was reported as “spots” that were observed in aerial surveys. A spot is a cluster of

attacked, fading trees (Coulson 1980). The minimum spot size is typically five to ten trees in

state monitoring programs (Price et al. 1998).
2

Damage areas indicated on the paper maps were traced onto transparent mylar film, along with

a variable number of georeference points located on well-defined political and natural

boundaries. The transparencies then were digitized using a digital scanner at 300 dots per inch

to produce binary tagged image format (TIF) files, which were converted to byte-binary format

files for use in the GIS.

The map layers for three of the four species, western spruce budworm, mountain pine beetle,

and southern pine beetle, were georeferenced to a vector line coverage of the conterminous

United States referenced to the Lambert Azimuthal Equal-Area projection. Those for the fourth

species, eastern spruce budworm, were georeferenced to a vector coverage of eastern North

America, including southern Canada and the northern United States, referenced to the Albers

Equal-Area Conic projection. Equal area projections were used because they equalize surface

areas across the geographical range of the coverage, facilitating analysis and modeling. Common

georeference points were identified on the various map layers and the reference map, and the

map layers were transformed to the resolution and projection of the reference map through

“rubber-sheeting.” Rubber-sheeting is a process by which one map is transformed

mathematically to fit a reference map given a set of common georeference points defined on

both maps (Antenucci et al. 1991). The rubber-sheeting of most maps used a second-order

polynomial transformation (U.S. Army Corps of Engineers 1993).

Resolutions of 2 km or 5 km were used because they represented the smallest resolution reliable

for the defoliation maps given various sources of mapping error. Errors may have occurred in

four processes of map production: aerial sketch mapping, replotting of sketch maps to produce

regional coverages, tracing, and scanning. The first two processes were beyond our control, so

we cannot estimate errors associated with them. However, potential errors in aerial sketch

mapping are well-documented (Van Sickle 1995). The coarse grid cell sizes that we used

probably minimized the effects of such errors. The paper maps that we traced came at a wide

variety of scales, as described below. Although we exercised great care in tracing, error was

possible because the pen width represented nearly 2 km on some of the maps traced. Scanning

error was likely to have been minimal because each scanned dot represented less than 1 km2

,

given the map scales and scanner resolution.

Sources of Map Sets

Eastern spruce budworm. Most of the defoliation maps were developed from maps published in

Hardy et al. (1986), which included annual maps of spruce budworm defoliation during 1938-

1980 in southeastern Canada and the northeastern United States at a scale of 1:11,000,000.

Because maps were unavailable for some states and provinces early in the series, we only used

maps from 1954 to 1980. Maps for the period 1981-1988 were assembled from defoliation

maps published in the series of annual insect and disease conditions reports of individual

provinces and states, including Manitoba at a scale of 1:10,000,000 (e.g., Cerezke and Emond

1989), Minnesota at 1:4,400,0001

, Ontario at 1:7,000,000 (e.g., Howse and Applejohn 1988),

Quebec at 1:6,000,000 (e.g., Bordeleau et al. 1989), Maine at 1:2,000,000 (e.g., Trial 1989),

the Maritime Provinces at 1:4,000,000 (e.g., Magasi 1989), and Newfoundland and Labrador

at 1:3,500,000 and 1:20,000,000, respectively (e.g., Clarke and Carew 1987). The resolution

for the eastern spruce budworm maps was set at 5 km.

Western spruce budworm and mountain pine beetle. Maps of defoliation by western spruce

budworm in the states of Washington and Oregon from 1947 to 1979 were developed from an

atlas by Dolph (1980), in which maps were at a scale of 1:3,500,000. Defoliation maps for

1980-1994 for the same states, as well as maps of mountain pine beetle outbreaks, were

1

Albers, J. Regional Forest Pest Specialist, Minnesota Department of Natural Resources, 1201 East

Highway 2, Grand Rapids, MN 55744. Personal communication.
3

converted to raster coverages from digital vector maps.2

 These recent maps were digitized from

aerial sketch maps at scales of 1:126,720 for Oregon and 1:100,000 for Washington (Sheehan

1996). They are available at www.fs.fed.us/r6/nr/fid/data.shtml. Maps of budworm defoliation

and mountain pine beetle outbreaks for the states of Idaho and Montana (including

Yellowstone National Park) for the years 1977-1996 and 1980-1995, respectively, were

developed from maps published in annual pest conditions reports at scales of 1:2,000,000 and

1:3,500,000, respectively (e.g., Beckman et al. 1996, McConnell 1996). The resolution for the

western spruce budworm defoliation maps in Washington, Oregon, Idaho, and Montana was

set at 5 km, and that for the mountain pine beetle outbreak maps across the same area was set at

2 km.

Southern pine beetle. Maps of southern pine beetle outbreaks in the southeastern United States

(i.e., Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South

Carolina, Tennessee, Texas, and Virginia) over the period 1960-1994 at a scale of about

1:12,000,000 have been published in an atlas by Price et al. (1998). These maps are now part of

the USDA Forest Service Southern Forest Health Atlas and may be viewed at fhpr8.srs.fs.fed.us/

atlas/spb/spb.html. The maps on our website were provided by the USDA Forest Service, Forest

Health Protection.3

 It must be noted that 1973 was the first year for which outbreak data were

available for all 11 states.

The southern pine beetle maps are very different from the others. They depict outbreaks at the

spatial scale of a county (i.e., as opposed to a grid cell). A county is defined to be in outbreak

status in a given year if it contains one spot (see definition above) or more per 1,000 acres (405

ha) of susceptible forest (Price et al. 1998). Beginning in 1978, a refined classification was

introduced that categorized counties into low, medium, and high outbreak states depending

upon numbers of spots per 1,000 acres. However, for the sake of simplicity, we decided to

retain the original outbreak definition and binary classification in the maps presented. That is,

for an individual year, a county is categorized as either in outbreak status (1) or not (0).

Insect Damage Maps

We include in this atlas only maps that have not been published previously. Maps of eastern

spruce budworm defoliation in eastern North America for the years 1981-1988 are shown in

Figure 1 a-h. Maps of mountain pine beetle damage in Washington, Oregon, Idaho, Montana,

and the northwestern corner of Wyoming for the years 1980-1995 are shown in Figure 2 a-p,

and maps of western spruce budworm defoliation over the same area for 1977-1993 are shown

in Figure 3 a-q. Figure 4 provides a summary map of the frequency of southern pine beetle

outbreaks in the southeastern United States from 1973 to 1994. It must be noted that all of the

digitized annual maps use a binomial classification, in which the presence of insect damage in a

grid cell or a county is denoted by a value of 1 and its absence is denoted by a value of 0. The

full set of digital maps is available at www.fs.fed.us/ne/global/products. The GIS coverages are

provided as ArcGrid files or ArcInfo shape files.

Applications of the Insect Damage Maps

Obvious uses of the maps include investigations of insect population dynamics or disturbance

inputs to forest simulation models. The basic annual time series of defoliation or damage may

be useful in some cases. However, interpretation of pest impact from the defoliation maps is

somewhat problematic because the annual maps show only presence of defoliation greater than

2

Johnson, J. GIS Coordinator, Forest Insects and Diseases Group, USDA Forest Service, Pacific

Northwest Region, P.O. Box 3623, Portland, OR 97208-3623. Personal communication.

3

Yockey, E. Forest Health Analyst, Forest Health Protection, USDA Forest Service, Southern Region,

200 Weaver Boulevard, Asheville, NC 28804. Personal communication.
4

30 percent without any information on its intensity. Moreover, a single year’s defoliation usually

does not lead to death or severe growth loss of a tree. By contrast, spots on the bark beetle maps

indicate areas where many trees are recently dead or moribund.

The summation of all annual maps for a species is used to produce a frequency map (Figs. 1i,

2q, 3r, and 4), which generally is useful to identify “hot spots” or infer areas of differing

vulnerability to the pest. Summary maps without frequency classes show areas where a pest was

present at least once. As such, they approximate the geographical ranges of outbreaks of the pest

species, and such maps are useful, among other things, for assessing the potential effects of

climate change (Williams and Liebhold 1995, 1997, 2002; Williams et al. 2000).

Another way of using the maps, particularly for investigating insect population dynamics, is to

create time series of relative abundance (Williams and Liebhold 2000a, b; Peltonen et al. 2002).

Estimates of relative abundance are produced by aggregating the pixels of the original annual

maps (i.e., having values of either 0 or 1) so as to produce larger pixels that are assigned

“population” values equal to the sums of the values of the smaller pixels. For example, a 4 × 4

aggregation of an annual defoliation map yields a map of larger pixels ranging in value from 0

to 16. Concatenating the aggregated annual maps produces a map with a time series of

defoliation in each large aggregate pixel. This technique produces satisfactory results for all but

the smallest levels of aggregation (i.e., 2 × 2 pixels, in which there is a range of only five possible

“population” sizes) (Williams and Liebhold 2000a).

Using the maps to quantify pest disturbances as inputs to forest simulation models requires

transformations of the basic damage maps or summarized frequency maps. The goal usually is

to estimate rates of tree mortality or growth loss given the number of years that damage is

sustained. Information for quantifying relationships between tree loss and time lengths of

disturbance impacts is available in the literature for a few common forest pests (e.g., Campbell

1979, MacLean 1980, Davidson et al. 1999, 2001). In this publication, we present a simple

model to illustrate a possible use of the data. As an example, we consider the effect of repeated

defoliation on mortality in forests susceptible to eastern spruce budworm.

MacLean (1980) reviewed the literature on the vulnerability of host stands to uncontrolled

spruce budworm outbreaks and presented a figure (his Fig. 1) relating cumulative percentage of

fir mortality to the number of years since the start of an outbreak for several budworm

outbreaks. In general, mortality was first observed after about four years and increased

approximately linearly, reaching 100 percent by about 10 years. Formulating this relationship

mathematically yields the following simple model:

0.0, 0 ≤ YRS DEFOL ≤ 4

% MORTALITY = 16.67*(YRS DEFOL) - 66.67, 4 < YRS DEFOL < 10 100.0, YRS DEFOL ≥ 10

It was not realistic to apply this model to the frequency map for the entire series of budworm

defoliation maps, which includes more than one major outbreak. Instead, we considered a

shorter span of defoliation from 1966, at the start of a major outbreak, through 1980, at its

peak. We summed the 15 annual maps to produce a frequency map and then applied the

mortality function to all pixels. The resulting map (Fig. 1j) is a hypothetical picture of the

forested areas in eastern North America that may have been most vulnerable to eastern spruce

budworm outbreaks during the 1970s. We stress that this is a simple illustration of a possible

use of the data; the results have not been validated on field data. More detailed and more

realistic algorithms using the time series of maps could be developed and validated depending

upon the needs of the individual modeler.

Clearly these historical series of insect defoliation and damage will be useful in a wide variety of

modeling applications.
5

Acknowledgments

We are grateful to the following individuals for

providing maps and publications: Edwin Yockey, USDA

Forest Service, Asheville, North Carolina; Katharine

Sheehan and Julie Johnson, USDA Forest Service,

Portland, Oregon; Kenneth Gibson, USDA Forest

Service, Missoula, Montana; R. Ladd Livingston, Idaho

Department of Lands, Coeur d’Alene, Idaho; Jana

Albers, Minnesota Department of Natural Resources,

Grand Rapids, Minnesota; and Henry Trial, Jr., Maine

Department of Conservation, Augusta, Maine. We thank

Valerie DeFelice, Gregory Bonynge, Eugene Luzader,

Heath Holt, and Jason Frederick for their technical

assistance in developing the digital coverages and Kevin

McCullough for his expertise with the web site. We are

grateful to Louis Iverson, Andrew Liebhold, and Ronald

Neilson for their thoughtful comments on the

manuscript. Development of the digital maps was

funded by the Northern Global Change Research

Program of the USDA Forest Service.

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8

Index to Figures

Figure 1a. .................................................................. 10

Area defoliated by eastern spruce budworm in 1981

Figure 1b. ..................................................................10

Area defoliated by eastern spruce budworm in 1982

Figure 1c. ...................................................................11

Area defoliated by eastern spruce budworm in 1983

Figure 1d. ..................................................................11

Area defoliated by eastern spruce budworm in 1984

Figure 1e. ...................................................................12

Area defoliated by eastern spruce budworm in 1985

Figure 1f. ...................................................................12

Area defoliated by eastern spruce budworm in 1986

Figure 1g....................................................................13

Area defoliated by eastern spruce budworm in 1987

Figure 1h. ..................................................................13

Area defoliated by eastern spruce budworm in 1988

Figure 1i. ...................................................................14

Frequency of defoliation by eastern spruce budworm

from 1954 to 1988

Figure 1j. ...................................................................14

Expected mortality of susceptible forest resulting from

eastern spruce budworm defoliation from 1966 to 1980

Figure 2a. ...................................................................15

Area damaged by mountain pine beetle in 1980

Figure 2b. ..................................................................15

Area damaged by mountain pine beetle in 1981

Figure 2c. ...................................................................16

Area damaged by mountain pine beetle in 1982

Figure 2d. ..................................................................16

Area damaged by mountain pine beetle in 1983

Figure 2e. ...................................................................17

Area damaged by mountain pine beetle in 1984

Figure 2f. ...................................................................17

Area damaged by mountain pine beetle in 1985

Figure 2g....................................................................18

Area damaged by mountain pine beetle in 1986

Figure 2h. ..................................................................18

Area damaged by mountain pine beetle in 1987

Figure 2i. ...................................................................19

Area damaged by mountain pine beetle in 1988

Figure 2j. ...................................................................19

Area damaged by mountain pine beetle in 1989

Figure 2k. ..................................................................20

Area damaged by mountain pine beetle in 1990

Figure 2l. ...................................................................20

Area damaged by mountain pine beetle in 1991

Figure 2m. .................................................................21

Area damaged by mountain pine beetle in 1992

Figure 2n. ..................................................................21

Area damaged by mountain pine beetle in 1993

Figure 2o. ..................................................................22

Area damaged by mountain pine beetle in 1994

Figure 2p. ..................................................................22

Area damaged by mountain pine beetle in 1995

Figure 2q. ..................................................................23

Frequency of outbreaks by mountain pine beetle

from 1980 to 1995

Figure 3a. ...................................................................24

Area defoliated by western spruce budworm in 1977

Figure 3b. ..................................................................24

Area defoliated by western spruce budworm in 1978

Figure 3c. ...................................................................25

Area defoliated by western spruce budworm in 1979

Figure 3d. ..................................................................25

Area defoliated by western spruce budworm in 1980

Figure 3e. ...................................................................26

Area defoliated by western spruce budworm in 1981

Figure 3f. ...................................................................26

Area defoliated by western spruce budworm in 1982

Figure 3g....................................................................27

Area defoliated by western spruce budworm in 1983

Figure 3h. ..................................................................27

Area defoliated by western spruce budworm in 1984

Figure 3i. ...................................................................28

Area defoliated by western spruce budworm in 1985

Figure 3j. ...................................................................28

Area defoliated by western spruce budworm in 1986

Figure 3k. ..................................................................29

Area defoliated by western spruce budworm in 1987

Figure 3l. ...................................................................29

Area defoliated by western spruce budworm in 1988

Figure 3m. .................................................................30

Area defoliated by western spruce budworm in 1989
9

Figure 3n. ..................................................................30

Area defoliated by western spruce budworm in 1990

Figure 3o. ..................................................................31

Area defoliated by western spruce budworm in 1991

Figure 3p. ..................................................................31

Area defoliated by western spruce budworm in 1992

Figure 3q. ..................................................................32

Area defoliated by western spruce budworm in 1993

Figure 3r. ...................................................................32

Frequency of defoliation by western spruce budworm

from 1977 to 1993

Figure 4. ....................................................................33

Frequency of outbreaks by southern pine beetle

from 1973 to 1994
10

Figure 1a.—Area defoliated by eastern spruce budworm in 1981.

500 km

500 km

Figure 1b.—Area defoliated by eastern spruce budworm in 1982.
11

Figure 1c.—Area defoliated by eastern spruce budworm in 1983.

500 km

500 km

Figure 1d.—Area defoliated by eastern spruce budworm in 1984.
12

500 km

500 km

Figure 1e.—Area defoliated by eastern spruce budworm in 1985.

Figure 1f.—Area defoliated by eastern spruce budworm in 1986.
13

500 km

500 km

Figure 1g.—Area defoliated by eastern spruce budworm in 1987.

Figure 1h.—Area defoliated by eastern spruce budworm in 1988.
14

500 km

500 km

Figure 1i.—Frequency of defoliation by eastern spruce budworm from 1954 to 1988.

Figure 1j.—Expected mortality of susceptible forest resulting from eastern spruce

budworm defoliation from 1966 to 1980.

No defoliation

1-3 years

4-7 years

8-12 years

13-29 years

No data

% mortality

0

17

33

50

67

83

100
15

200 km

200 km

Figure 2a.—Area damaged by mountain pine beetle in 1980.

Figure 2b.—Area damaged by mountain pine beetle in 1981.
16

200 km

200 km

Figure 2c.—Area damaged by mountain pine beetle in 1982.

Figure 2d.—Area damaged by mountain pine beetle in 1983.
17

200 km

200 km

Figure 2e.—Area damaged by mountain pine beetle in 1984.

Figure 2f.—Area damaged by mountain pine beetle in 1985.
18

200 km

200 km

Figure 2g.—Area damaged by mountain pine beetle in 1986.

Figure 2h.—Area damaged by mountain pine beetle in 1987.
19

200 km

200 km

Figure 2i.—Area damaged by mountain pine beetle in 1988.

Figure 2j.—Area damaged by mountain pine beetle in 1989.
20

200 km

200 km

Figure 2k.—Area damaged by mountain pine beetle in 1990.

Figure 2l.—Area damaged by mountain pine beetle in 1991.
21

200 km

200 km

Figure 2m.—Area damaged by mountain pine beetle in 1992.

Figure 2n.—Area damaged by mountain pine beetle in 1993.
22

200 km

200 km

Figure 2o.—Area damaged by mountain pine beetle in 1994.

Figure 2p.—Area damaged by mountain pine beetle in 1995.
23

200 km

Figure 2q.—Frequency of outbreaks by mountain pine beetle from 1980 to

1995.

No outbreaks

1 year

2 years

3 years

4+ years

No data
24

200 km

200 km

Figure 3a.—Area defoliated by western spruce budworm in 1977.

Figure 3b.—Area defoliated by western spruce budworm in 1978.
25

200 km

200 km

Figure 3c.—Area defoliated by western spruce budworm in 1979.

Figure 3d.—Area defoliated by western spruce budworm in 1980.
26

200 km

200 km

Figure 3e.—Area defoliated by western spruce budworm in 1981.

Figure 3f.—Area defoliated by western spruce budworm in 1982.
27

200 km

200 km

Figure 3g.—Area defoliated by western spruce budworm in 1983.

Figure 3h.—Area defoliated by western spruce budworm in 1984.
28

200 km

200 km

Figure 3i.—Area defoliated by western spruce budworm in 1985.

Figure 3j.—Area defoliated by western spruce budworm in 1986.
29

200 km

200 km

Figure 3k.—Area defoliated by western spruce budworm in 1987.

Figure 3l.—Area defoliated by western spruce budworm in 1988.
30

200 km

200 km

Figure 3m.—Area defoliated by western spruce budworm in 1989.

Figure 3n.—Area defoliated by western spruce budworm in 1990.
31

200 km

200 km

Figure 3o.—Area defoliated by western spruce budworm in 1991.

Figure 3p.—Area defoliated by western spruce budworm in 1992.
32

200 km

200 km

Figure 3q.—Area defoliated by western spruce budworm in 1993.

Figure 3r.—Frequency of defoliation by western spruce budworm from 1977

to 1993.

No defoliation

1 year

2-3 years

4-6 years

7+ years

No data
33

Figure 4.—Frequency of outbreaks by southern pine beetle from 1973 to 1994.

500 km

No outbreaks

1-2 year

3-5 years

6-10 years

11-16 years

No data
Printed on Recycled Paper

Williams, David W.; Birdsey, Richard A. 2003. Historical patterns of spruce

budworm defoliation and bark beetle outbreaks in North American conifer

forests: an atlas and description of digital maps. Gen. Tech. Rep. NE-308.

Newtown Square, PA: U.S. Department of Agriculture, Forest Service,

Northeastern Research Station. 33 p.

This atlas presents maps of historical defoliation by the eastern and western spruce

budworms and historical outbreaks of the mountain and southern pine beetles

during the past half century. The maps encompass various regions of the

conterminous United States and eastern Canada. This publication also serves as

documentation for an extended set of digital maps, which are available on our

website. The digital maps are useful for investigating spatial dynamics of insect

populations and for providing pest disturbance inputs to spatially explicit forest

simulation models.

Keywords: Choristoneura fumiferana, Choristoneura occidentalis, Dendroctonus

frontalis, Dendroctonus ponderosae, Lepidoptera, Tortricidae, Coleoptera,

Scolytidae, maps, spatial dynamics, disturbance, vegetation models, Canada
Headquarters of the Northeastern Research Station is in Newtown Square,

Pennsylvania. Field laboratories are maintained at:

Amherst, Massachusetts, in cooperation with the University of Massachusetts

Burlington, Vermont, in cooperation with the University of Vermont

Delaware, Ohio

Durham, New Hampshire, in cooperation with the University of New Hampshire

Hamden, Connecticut, in cooperation with Yale University

Morgantown, West Virginia, in cooperation with West Virginia University

Parsons, West Virginia

Princeton, West Virginia

Syracuse, New York, in cooperation with the State University of New York,

College of Environmental Sciences and Forestry at Syracuse University

Warren, Pennsylvania

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