United States

Department of 

Agriculture

Forest Service Forest Service

Northern

Research Station Research Station

State and Private

Forestry

General Technical 

Report NRS-73

October 2010

Susan M. Stein, Mary A. Carr, Ronald E. McRoberts, Susan M. Stein, Mary A. Carr, Ronald E. McRoberts, 

Lisa G. Mahal, and Sara J. Comas Lisa G. Mahal, and Sara J. Comas

Threats to At-Risk Species Threats to At-Risk Species 

in America’s Private Forests in America’s Private Forests

A Forests on the Edge Report
ABSTRACT

Stein, Susan M.; Carr, Mary A.; McRoberts, 

Ronald E.; Mahal, Lisa G.; Comas, Sara J. 

2010. Threats to at-risk species in America’s 

private forests: a Forests on the Edge report. 

Gen. Tech. Rep. NRS-73. Newtown Square, PA: 

U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 20 p.

More than 4,600 native animal and plant species 

associated with private forests in the United States 

are at risk of decline or extinction. This report 

identies areas across the conterminous United 

States where at-risk species habitats in rural private 

forests are most likely to decrease because of 

increases in housing density from 2000 to 2030. 

We also identify areas where the future of forested 

habitats for at-risk species could be compromised 

by additional pressures from wildre, insects, 

and disease. More than 90 percent of the 1,370 

watersheds that met our screening criteria support 

at least one at-risk species. Watersheds where 

increased housing density in rural private forests 

is likely to contribute to the decline of the largest 

numbers of forest-associated at-risk species are 

located primarily in the East but also in parts of the 

West and Southwest. Watersheds in which habitats 

for the greatest variety of at-risk species are likely 

to be affected by wildre are found in the Southeast, 

much of the Southwest, and along California’s Sierra 

Nevada range. Watersheds where private forests 

providing habitat for the greatest variety of at-risk 

species are most threatened by insects and disease 

are located throughout the East and also in the 

Southwest and in northern California. Conservation 

actions can reduce impacts on wildlife and plant 

species already at risk, while supporting compatible 

development of housing. This report updates 

methodology and ndings of a previous Forests on 

the Edge study of development impacts on at-risk 

species habitats. 

Key Words: private forests, development, 

wildre, insects and diseases, wildlife, threatened, 

endangered, imperiled

AUTHORS

Susan M. Stein is a private forest land studies 

coordinator and Sara J. Comas is a natural resource 

specialist, Cooperative Forestry Staff, U.S. Department 

of Agriculture, Forest Service, Washington, D.C. 

Mary A. Carr is a technical publications editor, 

Publishing Arts, U.S. Department of Agriculture, 

Forest Service, Olympia, WA. Ronald E. McRoberts

is a mathematical statistician, U.S. Department of 

Agriculture, Forest Service, Northern Research 

Station, St. Paul, MN. Lisa G. Mahal is a geographic 

information systems specialist, University of Nevada/

Las Vegas, St. Paul, MN.

About the Forests on the Edge Project

Sponsored by the Forest Service’s State and 

Private Forestry/Cooperative Forestry staff, in 

collaboration with Forest Service Research and 

Development and other partners, the Forests 

on the Edge project uses data prepared and 

analyzed by scientists across the country to 

increase understanding of the many public benefi ts 

derived from private forests and the pressures 

that might affect these benefi ts. Forests on the 

Edge researchers have presented fi ndings related 

to at-risk species in Frontiers in Ecology and the 

Environment, a publication of the Ecological Society 

of America (Robles et al. 2008); and the Journal of 

Forestry, a publication of the Society for American 

Foresters (Stein et al. 2010). Key points also were 

summarized in the Forests on the Edge publication, 

Private Forests, Public Benefi ts: Increased Housing 

Density and Other Pressures on Private Forest 

Contributions (Stein et al. 2009). 

iStockphoto.com © Jim Kruger

Gray wolf (Canis lupus)
1

USFWS

INTRODUCTION

A

merica’s private forests harbor thousands of 

species—from butter ies, bears, birds, and bats; to 

salmon, snails, and salamanders that inhabit streams 

and wetlands; to  owers, trees, and shrubs that feed and 

protect wildlife and enrich human lives. Many native 

animals and plants found in private forests nationwide 

are at risk of decline or extinction, in part because of 

impacts from increasing housing development. Plants 

and animals specically identied under the Endangered 

Species Act or by NatureServe1

 as being in jeopardy of 

extinction are characterized as at-risk species for this 

study. The effects of development on at-risk species in 

private forests are intensied by additional impacts from 

re, insects, and disease. 

Sixty percent of the at-risk species of plants and animals 

in the conterminous, or “lower 48,” United States are 

associated with private forests (Robles et al. 2008). 

More than 57 million acres of private forests across rural 

America are projected to experience substantial increases 

in housing density in coming decades (Stein et al. 2009). 

Most of the 100 watersheds predicted to experience the 

greatest increases in housing density on private forest 

land between 2000 and 2030 are in southeastern states 

and contain private forests with high densities of at-risk 

species (Robles et al. 2008).

This report updates the ndings of a previous 

analysis (Robles et al. 2008) sponsored by the U.S. 

Department of Agriculture, Forest Service, Forests 

on the Edge project. That analysis identied areas 

across the conterminous United States where at-risk 

species habitats in rural private forests are most likely 

to decrease because of increases in housing density 

from 2000 to 2030. This report uses updated data on 

at-risk species from NatureServe’s central databases 

(NatureServe 2008) and further identies areas where 

the future of forested habitats for at-risk species could 

be compromised by additional pressures from wildre 

and insects and diseases. We describe a range of 

implications, along with conservation actions that could 

help address the impacts on at-risk plant and animal 

species. 

Defining “At-Risk”

At-risk species, for purposes of this publication, are 

those classied under the U.S. Endangered Species 

Act (ESA) as threatened or endangered, or those with 

a global status of critically imperiled, imperiled, or 

vulnerable according to the NatureServe conservation 

status ranking system (Faber-Langendoen et al. 2009). 

The ESA denes an endangered species as one that is 

in danger of extinction throughout all or a signicant 

portion of its range; a threatened species is one that is 

likely to become endangered in the foreseeable future. 

Species that are designated as candidates or proposed for 

listing under the ESA are, for purposes of this study, also 

considered at-risk. NatureServe coordinates a nationwide 

network of Natural Heritage programs that maintain 

databases recording the status and locations of rare and 

endangered plants and animals in each state. Precise 

locational records are aggregated to provide integrated 

national and regional datasets.

Green pitcherplant (Sarracenia oreophila)

1 NatureServe, a nonprot conservation organization, provides data 

on at-risk species in the United States through a network of natural 

heritage conservation programs and data centers.
2

Who and Where 

Are Private Forests Owners? 

Seventy-fi ve percent of all forest lands in the 

East are privately owned, while lower percentages 

of forests in the West fall under this category: 

25 percent in the Rocky Mountain region and 

33 percent in the Pacifi c Coast region. America’s 

private forests are owned by about 11 million land 

owners, 92 percent of whom are “family forest” 

owners—families, individuals, trusts, estates, family 

partnerships, and other unincorporated groups of 

individuals (Butler 2008). Most of the remaining 

private forest lands are owned by corporations 

(Smith et al. 2009). Family forest owners—who 

hold 62 percent of all private forests (35 percent 

of all forest land)—value their forests for aesthetic 

values, family legacy, privacy, and nature protection 

among other reasons; they use their land for a 

variety of activities including recreation and wildlife 

habitat conservation (Butler 2008). 

Figure 1—Location of private and public forest, nonforest, and urban areas. About three-quarters of America’s private forests 

 are in the East.

Private Forests Are Key

More than half (423 million acres) of all U.S. forest land 

is privately owned (Smith et al. 2009) (Fig. 1). Privately 

owned lands support a disproportionate number of 

habitats that are critically important to numerous species 

of wildlife at some point in their life cycles; many rare 

or declining species require private lands for survival 

(Maestas 2007, Robles et al. 2008). Private lands are 

particularly important to wide-ranging animals, whose 

home ranges can encompass a network of public and

private lands. 

As reported in Robles et al. (2008), private forests 

support 60 percent of at-risk species found in the 

conterminous United States. In some watersheds, up to 

95 percent of forest-associated at-risk species occur only

in private forests. These forests are located across the 

country but particularly in the private forest matrix of the 

East, as well as along the prairie-forest border in Texas 

and Oklahoma and within riparian areas or isolated 

forests in the Midwest, Northeast, and western interior 

basins.
3

2 Because of insufcient data, we were not able to undertake a similar 

analysis for Alaska, Hawaii, or other areas afliated with the United 

States, although private forests in these areas also provide important 

wildlife habitat.

ASSESSING THREATS TO PRIVATE FOREST HABITATS 

FOR AT-RISK SPECIES

A

nalyses were conducted to answer the following 

questions concerning private forest habitats for atrisk wildlife species across the conterminous United 

States:2

• In which watersheds do privately owned forests 

support the greatest number of at-risk species?

• In which watersheds is increased housing density in 

rural private forests most likely to further jeopardize 

at-risk species?

• In which watersheds are wildre and insects and 

disease most likely to affect at-risk species on 

private forest lands? 

Although the methodology used is the same as that 

described in an earlier Forests on the Edge study (Robles 

et al. 2008), updated data on at-risk species, housing 

density projections, land ownership, and land cover 

3 Basal area is the cross-sectional area of a tree in square feet, 

commonly measured at breast height (4.5 feet in the United States). 

Stand- or plot-level basal area is the sum of basal areas for all trees 

growing in a stand or on a plot and is often used as an indicator of 

stand or plot attributes because it combines the number of trees and 

their sizes. 

have been used here; therefore, the results may differ 

somewhat.

We rst estimated the number of at-risk species 

associated with private forests in each watershed. Data 

came from several sources: 

• Fourth-level watershed boundaries as dened by 

Steeves and Nebert (1994) 

• Location of at-risk species recorded since 1970 

(NatureServe 2008)

• Land classication obtained from the National Land 

Cover Dataset (NLCD) of 2001 (Homer et al. 2004, 

2007) and the Protected Areas Database (PAD 4.6) 

(CBI 2007, DellaSala et al. 2001, Theobald 2007). 

To understand where, across the conterminous United 

States, at-risk species are most likely to be affected by 

future housing density increases in rural forests, we 

used geographic information system (GIS) techniques 

to combine (a) data on the number of at-risk species 

associated with private forests in each watershed with 

(b) estimates of the percentage of private forests in each 

watershed expected to experience increased housing 

density. These methods are reported in more detail 

in Stein et al. (2010). To be included in this analysis, 

watersheds had to be at least 10 percent forested and 

contain at least 10,000 acres of private forest. The size 

of the watersheds analyzed varied widely (coefcient of 

variation 0.76), from 53,000 acres to slightly more than 

14 million acres.

We also conducted two additional analyses that 

combined the data on the number of at-risk species on 

private forestland in each watershed with data on the 

level of wildland re potential for private forests in each 

watershed and with data on the threat (basal area3

 loss) 

from insects and diseases. Data on re were obtained 

from the Wildland Fire Potential Model produced by 

the Forest Service’s Fire Modeling Institute (http://

www.fs.fed.us/fmi/). Data on insect and disease threat 

were obtained from the Forest Service’s Forest Health 

Monitoring Program (Krist et al. 2007) and provide an 

estimate of the average loss of basal area due to insect 

pests and disease. Detailed descriptions of these data 

layers are provided in Stein et al. 2009.

Private lands in Florida account for half the habitat occupied by 

the endangered Florida panther (Felis concolor) (Robles et al. 

2008).

iStockphoto.com © DenGuy
4

KEY FINDINGS

At-Risk Species Associated With Private Forests

Most private forest land in the conterminous 

United States provides habitat for at least one of the 

4,613 at-risk plants and animals that use these forests 

for at least part of their life cycle. More than 90 percent 

of the 1,370 watersheds that met our screening criteria 

support at least one at-risk species. 

Most watersheds with the greatest total number of 

at-risk species associated with private forests are found 

in the East (Fig. 2). The highest percentile rankings in 

the East include a chain of watersheds extending along 

the Appalachian Mountains, from southern Pennsylvania 

into northern Georgia, and continuing through much 

of Mississippi and western Georgia. High-ranking 

watersheds also are found in Texas, Arkansas, Louisiana, 

most of Florida, at the southern tip of Lake Michigan, 

and in parts of New England. Further, high numbers 

of at-risk species are found in the West, especially in 

California, eastern Oregon, and parts of the Southwest.

Defi ning Increased Housing Density

As in previous Forests on the Edge studies, the 

terms housing development and increased housing 

density refer to an increase in the number of 

housing units per unit area on rural lands such that 

the housing density shifts from either the rural I 

or rural II categories to a higher density category 

(Stein et al. 2007, 2009; Theobald 2005), where:

Rural I is 16 or fewer housing units 

per square mile; 

Rural II is 17 to 64 housing units 

per square mile; and

Exurban-urban is 65 or more housing units 

per square mile. 

Sixteen housing units per square mile is equivalent 

to 1 unit per 40 acres, while 64 units per square 

mile is equivalent to 1 unit per 10 acres. A single 

family household is considered to be a unit, as is a 

single building with multiple households. Seasonal 

homes not occupied as primary residences are 

included in this analysis.

Figure 2—Number of at-risk species associated with private forest, by watershed. Most watersheds with the greatest total number 

 of forest-associated at-risk species are found in the East and in coastal California, but some also are located in the 

 South and West.

90th percentile or greater (22 - 79 species)

75th percentile or greater (13 - 21 species)

50th percentile or greater (6 - 12 species)

Less than 50th percentile (0 - 5 species)

Zero species recorded since 1970

No at-risk species data

Insufficient private forest for this analysis

Number of At-Risk Species
5

Watersheds with a high number of at-risk species in private forests are found in the East and in coastal California.

© Gelyngfjell, Dreamstime.com

iStockphoto.com © Loren Evans

At-Risk Species and Increased Housing Density 

in Private Forests

Watersheds in which increased housing density in rural 

private forests is likely to contribute to the decline of the 

largest numbers of forest-associated at-risk species are 

located primarily in the eastern United States—along 

coastal areas, in and around the southern Appalachians, 

along the shores of Lake Michigan, and throughout 

Florida (Fig. 3). Additional watersheds of concern are 

located in central California, Oregon, and parts of the 

Southwest. 

Additional Pressures from Wildfire 

and Insect Pests and Diseases

Wildres, native insects, extreme weather events, 

and timber harvest are among the ecological and 

socio-economic forces that keep forests dynamic and 

constantly changing (Stein et al. 2009). However, the 

extent and impacts of wildre and insect pests and 

disease can be exacerbated by the addition of houses 

to the landscape (Syphard et al. 2007, Meekins and 

McCarthy 2001). 

As indicated in Figure 4, watersheds in which wildres 

on private forests are most likely to affect at-risk species 

habitats are found in the southeastern United States, the 

Southwest, and along California’s Sierra Nevada range. 

In contrast, watersheds in which insects and diseases are 

most likely to affect at-risk species habitats provided by 

private forests are found in much of the eastern United 

States, especially along the Appalachian range, areas just 

inside the coastal Southeast, and the Great Lakes states 

(Fig. 5). Western areas of high overlap between private 

forest at-risk species habitat and insect and disease 

threats are found in the Southwest and in northern 

California.

IMPLICATIONS

Impacts from Housing Development 

Specic impacts of increased housing density on forestassociated at-risk species are likely to vary depending 

on the location, species, and level of development. The 

chief effects of housing development on native plant 

and animal populations—not only in the immediate 

vicinity of homes but also on nearby public and private 

Numbers of At-risk Species 

Occurring in or Associated with 

Private Forests

Vertebrate 

animals

564

Invertebrate

animals

1,349

Vascular 

plants

2,600

Nonvascular

plants

100
6

Figure 4—Wildfi re threat to at-risk species associated with private forests. Watersheds where at-risk species are most likely to be 

 affected by wildfi re are in the Southeast, the Southwest, and in California.

Figure 3—Threat to habitat for at-risk species associated with private forests as a result of increased housing density. Watersheds 

 in the East are particularly at risk of decline in forest-associated at-risk species due to increased housing density.

90th percentile

75th percentile

50th percentile

Less than 50th percentile

Zero species recorded since 1970

No at-risk species data

Insufficient private forest for this analysis

Increased Housing Density

Threat to At-Risk Species Habitat

90th percentile

75th percentile

50th percentile

Less than 50th percentile

Zero species recorded since 1970

No at-risk species data

Insufficient private forest for this analysis

Wildfire Threat

to At-Risk Species Habitat
7

Figure 5—Insect and disease threat to at-risk species associated with private forests. Watersheds where at-risk species are 

 most likely to be affected by insects and disease are in the East, with some vulnerable watersheds in the West

 and Southwest.

lands (Hansen et al. 2005, Houlahan et al. 2006, Maestas 

2007)—relate to a lowering of the quantity and quality 

of terrestrial and aquatic habitats. Such changes can 

result in numerous impacts on native species, including: 

• Increased predation and parasitism (Coleman and 

Temple 1993, Engels and Sexton 1994, Lepczyk 

et al. 2003, Sieving and Willson 1999) 

• Increased injuries and mortality from roads, fences, 

vehicle collisions, power lines, toxic substances, 

and other factors (Forman and Alexander 1998, 

Houlahan and Findlay 2003, Janss 2000, Maestas 

2007, Mumme et al. 2000, van Langevelde et al. 

2009) 

• Spread of invasive species (Houlahan et al. 2006, 

Meekins and McCarthy 2001) 

• Loss of pollinators or prey species (Harris and 

Johnson 2004, Lienert 2004) 

• Decreased ability to move and disperse (including 

plant seeds), nd food, and reproduce (Jacobson 

2006, Lampila et al. 2005) 

Further, some animals will alter their behaviors to avoid 

humans or to take advantage of human food and shelter, 

often to the detriment of both the animals and people 

(Maestas 2007, Miller et al. 2001, Sime 1999, Wisdom 

et al. 2000). The impacts may last for several decades 

following development (Hansen et al. 2005). 

Even low-density housing development in rural areas 

can have disproportionate impacts on wildlife, because 

places that are attractive to people for housing—such as 

near parks, rivers, and other natural areas—are also the 

places that are favored by native wildlife, particularly 

top carnivores and “wilderness” species (Hansen et 

al. 2005). Although many private forest landowners 

specically strive to protect and enhance wildlife habitat 

through careful and sustainable management (Butler 

2008), continuing loss and fragmentation of private 

forests could cause local populations of some forestassociated species to decline or disappear (Donovan and 

Flather 2002, Ewing and Kostyack 2005, Fahrig 2003, 

Lampila et al. 2005). 

At-risk species may be particularly vulnerable to 

these effects (Donavan and Flather 2002, Janss 2000); 

conversion of forests to developed landscapes has 

already contributed to the decline of approximately 35 

percent of threatened, endangered, or proposed species 

in the United States (Wilcove et al. 1998, 2000).

90th percentile

75th percentile

50th percentile

Less than 50th percentile

Zero species recorded since 1970

No at-risk species data

Insufficient private forest for this analysis

Insect and Disease Threat

to At-Risk Species Habitat
8

Beyond Habitat: Indirect Impacts 

Can Be Detrimental 

Increased housing development can have a 

negative impact on certain species even if 

direct loss or fragmentation of habitat has not 

occurred. In Texas, populations of endangered 

golden-cheeked warblers (Dendroica

chrysoparia) declined when populations of blue 

jays (Cyanocitta cristata) increased in nearby 

suburban developments. The blue jays preyed 

on warbler eggs and intimidated adult warblers 

so they failed to establish territories, echoing a 

widely observed effect in which human-adapted 

jays and crows predate on eggs and nestlings 

of other bird species (Engels and Sexton 1994, 

Sieving and Willson 1999).

AP

Some wildlife lose their fear of people, leading to ecological 

and public safety problems (Kloppers et al. 2005, Wisdom et al. 

2000, Yoder 2002) as well as increased costs for landowners 

from property or crop damage (Yoder 2002).

For every kilometer (0.62 mile) of highway construction, an 

estimated 644 hectares (1,591 acres) of land is converted 

from its original vegetative cover, resulting in signifi cant loss of 

habitat for wildlife (Ament et al. 2008).

© Stephen Vanhorn, Dreamstime.com

IMPACTS OF HOUSING DEVELOPMENT

© Scott Smith / Animals Animals - Earth Scenes

Ground-nesting species and birds that nest in the open in 

shrubs or trees are particularly vulnerable to predation from 

domestic cats (Coleman and Temple 1993, Lampila et al. 2005, 

Sieving and Willson 1999, Woods et al. 2003). In one study 

(Lepczyk et al. 2003), 800 to 3,000 outdoor cats in three 

rural-to-urban landscapes in southeastern Michigan killed 

between 16,000 and 47,000 birds of 23 species—including 

two of conservation concern—during one breeding season. 
9

AP

Development and road building often involve removal of 

large trees, snags, or down logs that are needed by cavitynesting birds and mammals. In boreal conifer forests, the bird 

species most sensitive to such forest change are resident 

cavity nesters that rely on older forests (Schmiegelow and 

Monkkonen 2002).

On the Edge

While the amount of habitat is considered to have 

the greatest impact on species population size, 

habitat fragmentation can also have a substantial 

effect in certain situations (Flather and Bevers 

2001). “Fragmentation” refers to the conversion 

of a large expanse of habitat into multiple smaller 

patches, which become isolated from each other 

and surrounded by different kinds of habitat 

(Fahrig 2003, Lampila et al. 2005). Over time the 

fragments get even smaller and more distant from 

each other, and their shapes may change. 

“Edges” are boundaries between different 

habitats such as forest and meadow (Kremsater 

and Bunnell 1999). Increases in edge resulting 

from forest fragmentation can result in increases 

in species that fi nd edges and small forest 

patches favorable—such as black-tailed deer, 

skunks, and raccoons (Kurki et al. 2000, Lepcyzk 

et al. 2003, Pedlar et al. 1997)—and declines in 

species that avoid edges or prefer forest interior 

habitat (Lienert 2004, Meekins and McCarthy 

2001, Wisdom et al. 2000), such as red squirrels 

(Mahan and Yahner 1999). 

—Illustration adapted from Wilcove et al. 1986, 

cited in Fahrig 2003.

Around 16 percent of the population of endangered key 

deer are killed on Florida roads every year (Forman and 

Alexander 1998). Physical contact with vehicles is the leading 

direct human cause of wildlife mortality on land, including 

extraordinary numbers of insects as well as frogs, toads, 

turtles, snakes, and birds that travel across or along roads 

(Forman and Alexander 1998, Wisdom et al. 2000). Collisions 

with large animals, such as deer and moose, also present 

hazards for humans (CDC 2006).

© Maresa Pryor / Animals Animals - Earth Scenes

IMPACTS OF HOUSING DEVELOPMENT

Some plants can persist in small populations for long periods of 

time, but many will decline if habitat loss adversely affects the 

animals needed for pollination or seed-dispersal (Harris and 

Johnson 2004, Lienert 2004).

© Sherry Anderson
10

Certain birds, such as the meadowlark, fl y away from roosting 

or nesting areas when dogs and pedestrians are present 

(Maestas 2007, Sime 1999).

© Thomas Woodruff, Dreamstime.com Susan Stein, USFS

A warning sign for key deer (Odocoileus virginianus clavium)

in the Florida Keys.

Amphibians are among the species that may be particularly 

vulnerable to declining water quality and increased exposure to 

toxic substances that often accompany an increase in habitat 

fragmentation and roads (Houlahan and Findlay 2003).

AP

Garlic mustard can invade both disturbed and undisturbed 

areas (Meekins and McCarthy 2001) and is currently displacing 

native understory species in the forests of northeastern United 

States and southern Canada. It is also a threat to species 

that depend on the native understory habitat, such as the 

endangered Virginia white butterfl y (Pieris virginiensis) and the 

native American butterfl y (Pieris napi aleracea).

AP

IMPACTS OF HOUSING DEVELOPMENT
11

Impacts From Insect Pests and Diseases

Whether native or exotic, insect pests and diseases can 

have important economic and ecological impacts on 

forest resources, ecosystems, and endangered species 

(Liebhold et al. 1995). Pimental et al. (2005) found that 

42 percent of federally listed threatened and endangered 

species were at risk primarily because of a nonnative 

invasive species. 

An example is the balsam woolly adelgid (Adelges

picea). Introduced from Europe around 1900, this insect 

pest has caused substantial damage and mortality to true 

r species (Abies spp.) (Ragenovich and Mitchell 2006). 

Particularly hard hit is one of its hosts, the Fraser r 

(Abies fraseri) in the southern Appalachian mountains. 

The balsam woolly adelgid (coupled with additional 

threats from increased recreation and pollution) has not 

only jeopardized the r trees (NatureServe 2009) but 

could also result in the extinction of several species 

closely associated with the Fraser r (Liebhold et al. 

1995). Among those species threatened are the spruce-r 

moss spider (Microhexura montivaga) (USFWS 2000b) 

and the rock gnome lichen (Gymnoderma lineare) 

(NatureServe 2009).

Impacts From Fire

Habitat destruction due to disruption of an area’s 

characteristic re pattern—either by re suppression or 

by controlled or uncontrolled res—constitutes one of 

the major threats to at-risk species (Wilcove et al. 1998). 

The season, frequency, extent, complexity, duration, 

intensity, and severity of a re will affect different 

species and their habitats differently (Anderson 2001, 

Smith 2000). For example, a patchy burn can add to 

wildlife habitat diversity in the short term by creating 

more “edge,” while a high intensity/high severity re 

can extensively alter habitat composition for extended 

periods of time (Anderson 2001). Some at-risk species 

such as the federally endangered Karner blue butter y 

(Plebejus melissa samuelis) depend on re to maintain 

their habitat (Mitchell and Carnes 1996), while others 

might be adversely affected by uncharacteristic re 

because of mortality, habitat loss, changes in stream 

temperature or nutrient loads, and other impacts (Smith 

2000, Ice et al. 2004). For plant species, factors such 

as fuels and moisture conditions can result in varied 

impacts among res or within different areas of one 

re, where some species may be eliminated or others 

may appear in areas not seen before the re (Miller and 

Findley 2001).

Some species already at risk can be further threatened by 

uncharacteristic wildfi re.

AP

Spruce-fi r moss spider (Microhexura montivaga)

Dr. Fred Coyle, USFWS

Karner blue butterfl y (Plebejus melissa samuelis)

© Jay Cossey/PhotographsFromNature.com
12

CASE STUDIES

© John J. Henderson, Dreamstime.com

One of the largest tree squirrels in the Western 

Hemisphere—at 30 inches and 3 pounds—the 

endangered Delmarva fox squirrel (Sciurus niger 

cinereus) is native to the mid-Atlantic region. The 

squirrel garners its name from the Delmarva Peninsula 

bordering the Chesapeake Bay; it was found historically 

throughout the peninsula in mature and mixed acornproducing hardwoods and mature loblolly pine stands. 

This fox squirrel’s original range was reduced to just 

10 percent primarily because of loss and fragmentation 

of habitat due to timber harvesting, conversion of forests 

to farmland, housing development, road construction, 

and commercial property developments (Kulynycz 2003, 

USFWS 1993). Consequently, the species was listed by 

the Fish and Wildlife Service as endangered in 1967. 

After reintroductions in Maryland, Delaware, Virginia, 

and Pennsylvania, and decades of conservation work by 

recovery partners, 11 of the 16 reintroduced populations 

are succeeding. Much of the habitat now occupied by 

Delmarva fox squirrels is on privately owned land.

 —Source: USFWS 2008 

Delmarva Fox Squirrel

Rob Schell, WRA Inc.

Described as large, stocky, and terrestrial, the California 

tiger salamander (Ambystoma californiense) is known 

to frequent grassland, oak savanna, and edges of mixed 

woodland and lower elevation coniferous forests. This 

salamander is recognized as endangered in two of the 

six known genetically distinct populations: the Sonoma 

and Santa Barbara populations of California. The species 

was listed as threatened range-wide in 2004 because 

its range and abundance continued to decline, most 

likely because of habitat loss and degradation. Most 

populations of this species are found on private land; 

only an estimated 5 percent of known populations occur 

on government-managed lands. In Santa Barbara County, 

the entire known and potential habitat for the California 

tiger salamander is largely on private land currently 

unprotected from development.

—Sources: USFWS 2000a, NatureServe 2009

California Tiger Salamander
13

Etonia rosemary (Conradina etonia) is a member 

of the mint family, found only in Putnam County 

in northeastern Florida. Discovered in 1990, the 

Etonia rosemary is restricted to limited areas of scrub 

vegetation with scrubby evergreen oaks (Quercus spp.) 

and sand pines (Pinus clausa). The only two sites where 

it is known, near Etonia Creek, are privately owned and 

were already subdivided for residential development or 

had been approved for development when the plant was 

discovered. Fire suppression also threatens the rosemary 

habitat. With its limited geographic distribution, small 

population size, and imminent threats to its habitat from 

residential development, Etonia rosemary was listed 

in 1994 by the U.S. Fish and Wildlife Service as an 

endangered species.

—Sources: NatureServe 2009, USFWS 1994

Etonia Rosemary

© Kay Maddox

CASE STUDIES

The black-capped vireo (Vireo atricapilla) is a small, 

insect-eating, migratory songbird found in mixed 

deciduous/evergreen shrublands in the south-central 

United States (Kansas, Louisiana, Oklahoma, and 

Texas). Habitat losses are occurring as a result of 

development, over-browsing, and nest parasitism, as 

well as suppression and alteration of natural disturbance 

regimes (re in particular). The U.S. Fish and Wildlife 

Service listed the species as endangered in 1987. The 

overall population of black-capped vireos is unknown 

because access to private property in Texas has been 

limited until recently. Of the known population, 

25 percent of documented occurrences have been 

on private lands. Incentive-based programs are now 

encouraging private landowners to manage their lands 

for sensitive species such as this rare bird. 

—Sources: USFWS 1991, 2007

Black-Capped Vireo

Anthony Mercieca, Photo Researchers Inc.
14

Several states in the range of the eastern massasauga 

rattlesnake (Sistrurus catenatus catenatus)—including 

Wisconsin, Michigan, Pennsylvania and New York—

consider it a critically imperiled species. This snake 

makes its home in a variety of habitats, from marshes 

to dry woodlands, preferring wetlands and the adjacent 

natural upland habitat. The primary threat to the eastern 

massasauga is the destruction, loss, or modication of 

its habitat due to human activities, including residential 

development. Szymanski (1998) cited articles where 

populations were isolated or fragmented by development 

or where a large residential development eliminated 

already critically degraded habitat. 

—Sources: NatureServe 2009, Szymanski 1998

Eastern Massasauga Rattlesnake

© James Deboer, Dreamstime.com

CASE STUDIES

A recently described species, the hops azure (Celastrina

humulus) is a highly range-restricted butter y that 

lives in the gulches and steep ravines of canyons on the 

Front Range of the Colorado Rockies. Extensive habitat 

alteration due to housing construction, recreation, and 

water development has placed pressure on this species. 

Threats to hops azure habitat will likely continue 

because of the proximity of its entire range to urban 

environments. NatureServe lists the hops azure as 

imperiled (global status G2G3).

—Source: NatureServe 2009

Hops Azure

© Paul Opler, Colorado State University
15

CONCLUSIONS

T

he alteration of habitat associated with increased 

housing density and the development of associated 

infrastructure can have numerous and varied 

impacts on at-risk species, including their further 

decline. As the human population continues to increase, 

more houses will be added to rural landscapes—both 

forested and nonforested—to the detriment of many 

rare plant and animal populations. With more attention 

focused on this issue, a host of conservation actions are 

being implemented to conserve wildlife and plan for 

sustainable development. 

Like previous Forests on the Edge reports and other 

national assessments, the ndings of this study 

are based on data available at a national level and 

may not precisely describe projections for specic 

locations or watersheds. Nonetheless, our ndings can 

provide a useful tool to individuals, communities, and 

organizations who wish to consider implications for 

threatened, endangered, and other imperiled  ora and 

fauna as a critical component of local and regional 

strategic planning efforts. 

Conservation Actions

Numerous actions can be taken to support the 

development of housing and associated infrastructure 

on the landscape while reducing impacts on wildlife and 

plant species already at risk. A few examples include: 

 Create tunnels across or under highways to help 

amphibians and other wildlife cross roads safely 

(Clevenger et al. 2003, Kobylarz 2003, Fahrig et al. 

1995, Litvaitis and Tash 2008).

 Modify road network congurations, trafc volumes, 

and vehicle speeds; and use fences to minimize 

dangers to animals on or near roads (Jaeger et al. 

2006, Seiler 2005). 

 Increase awareness about negative impacts of freeroaming cats and other pets (Lepczyk et al. 2003), 

and about moose and other large animals to help 

avoid vehicular collisions (CDC 2006).

 Pass zoning and other ordinances to protect nest 

trees and dens and to prevent picking of or damage 

to vulnerable plant populations. 

 Select pesticides, herbicides, and fungicides with a 

consideration for the sensitivity of pollinators such 

as bees and butter ies.

 Negotiate and implement conservation easements to 

keep private forest lands intact.

 Use federal, state, and local tax incentives to reduce 

costs of long-term private forest stewardship.

 Consider clustered housing developments that 

incorporate environmental considerations and help 

maintain open space.

 Expand forest certication programs such 

as Sustainable Forestry Initiative and Forest 

Stewardship Council.

 Encourage locally based comprehensive planning 

that considers forest benets such as wildlife 

and water quality. This may include informing 

landowners and planning boards of the relative 

ecological importance of at-risk species’ habitats that 

are, or will be, under consideration for development, 

and of any legal evaluation/analysis that must be 

made.

ACKNOWLEDGMENTS

T

he publication of this report would not have 

been possible without the help of many people. 

We thank Jason McNees of NatureServe for 

the careful and detailed analysis of at-risk species 

associated with private forests. We also wish to thank 

the following people for their helpful reviews: Leslie 

Honey, NatureServe; Mark Nelson, Forest Service 

Northern Research Station; Marc Bosch, Forest Service 

Washington Ofce; and J. Michael Foreman, Virginia 

Department of Conservation and Recreation. Curt 

Flather, Forest Service Rocky Mountain Research 

Station, has provided invaluable advice and guidance on 

wildlife data analysis throughout the Forests on the Edge 

project, including the preparation of this publication. 

We gratefully acknowledge David M. Theobald of 

Colorado State University for generously providing data 

on housing density projections. We also thank Susan 

Anderson, Greenlight 1-2-3, for professional assistance 

in researching and collecting many of the images that 

appear in this publication. Marcos Robles of The Nature 

Conservancy laid the framework for this report as senior 

author of the original Forests on the Edge study on the 

geography of private forests that support at-risk species; 

his invaluable contributions are greatly appreciated.
16

Metrics Table 

When you know: Multiply by: To fi nd:

Feet (ft) 0.305 Meters (m)

Acres (ac) 0.405 Hectares (ha)

Square feet (ft2

) .0929 Square meters (m2)

Square miles (mi2

) 2.59 Square kilometers (km2)

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© Anna Lisa Yoder, Dreamstime.com

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FORESTS ON THE EDGE 

Forests on the Edge is a project of the U.S. Department 

of Agriculture, Forest Service, State and Private 

Forestry, Cooperative Forestry staff, in conjunction 

with Forest Service Research and Development and 

other partners. The project aims to increase public 

understanding of the contributions of and pressures on 

America’s forests, and to create new tools for strategic 

planning. The fi rst report (Stein et al. 2005) identifi ed 

watersheds in the conterminous United States where 

private forests are most likely to experience housing 

development. Subsequent reports have provided more 

in-depth discussion and data on the locations and 

impacts of future housing development in rural areas, 

and the benefi ts and threats to urban forests. This report 

highlights threats to private forest habitats for at-risk 

species of plants and animals and identifi es watersheds 

nationwide where the future of at-risk species could be 

further complicated by additional pressures from wildlife, 

insects, and diseases.

Future Forests on the Edge work will include 

assessments of additional contributions and risks, and 

construction of an Internet-based system that permits 

users to view, combine, and depict results for selected 

contribution and threat layers.

For further information on Forests on the Edge, contact: 

Susan Stein, 

U.S. Forest Service, Cooperative Forestry staff

1400 Independence Avenue, SW, Mailstop 1123

Washington, DC 20250-1123 

(202) 205-0837 

sstein@fs.fed.us

http://www.fs.fed.us/openspace/fote/ 

Photo courtesy of Matt Jalbert, mattjalbert.com

Photos on front cover, from top then left to right: Jim Brandenburg/Minden Pictures; David Cappaert, Michigan State University,

Bugwood.org; Larry Korhnak; Larry Korhnak; and © Maresa Pryor/Animals Animals - Earth Scenes