U.S. Forest Ownership and Management: Background and Issues for Congress

November 24, 2021 R46976

U.S. Forest Ownership and Management:
November 24, 2021
Background and Issues for Congress
Katie Hoover
The 765 million acres of forests across the United States provide many social, economic, and
Specialist in Natural
ecological resources and uses. A forest’s health—generally, the status of its ecological integrity
Resources Policy
and functioning—influences its ability to provide resources and uses, including air and water

resources, fish and wildlife habitat, opportunities for recreation and cultural use, timber
Anne A. Riddle
resources, and more. As a result, Congress may be interested in the health and management of the
Analyst in Natural
nation’s forest resources. The potential scope of congressional involvement in U.S. forest
Resources Policy
resources varies, based primarily on ownership; Congress has a direct role in the management of

forests owned by the federal government but a more indirect role regarding forests in nonfederal
ownership.

As of 2017, the federal government managed 238 million acres (31%) of U.S. forests; the rest were in nonfederal (private,
state, or local) ownership. Private forest owners can be classified as corporate or noncorporate, and noncorporate forest
owners can be further classified as family, tribal, and other. Private noncorporate forests account for approximately 38% of
U.S. forest area (272 million acres), and corporate forests account for 20% (156 million acres). State and local governments
manage 84 million acres (11%) of U.S. forestland. The distribution of forest ownership varies regionally: most of the forests
in the eastern United States are privately owned, whereas most forests in the western regions are publicly owned.
Nationwide, more privately owned forests than publicly owned forests contain timberlands, a subset of forestland capable of
producing crops of industrial wood.
The resources and uses that a forest provides can be complementary or competing. As such, forest management and use are
perennially complex, often contentious issues. Forest owners may manage forests—intervene in their processes and
composition—to promote desired objectives, which vary; there is no single management objective across all U.S. forests or
ownerships. Private forest owners have nearly complete discretion over which management objectives to pursue. Conversely,
public forest management decisions are stipulated by laws and regulations, including requirements for transparency in the
decisionmaking process and opportunities for the public to comment on and challenge decisions. Most forest owners manage
their lands for multiple objectives, often with a primary objective. For example, some owners manage their forests principally
for timber production, undertaking specific management activities to promote productivity and timber growth. Most federal
forests are managed for a balance of multiple of uses, with no single or primary use as a principal management objective.
Because forests may be managed for different objectives, methods for measuring and assessing forest outcomes vary
considerably.
U.S. forest resources are heterogeneous, as are the biophysical conditions in forests and the management objectives,
constraints, and capabilities of forest owners. Biophysical characteristics (e.g., climate) determine a forest’s baseline potential
to support different tree species, growth, and productivity. Other factors, such as exposure to disturbances (e.g., hurricanes,
wildfires, pest infestations), can further affect forest conditions. Management choices can influence or mediate the effects of
some—but not all—biophysical factors and disturbances (e.g., by choosing which species to grow or whether to treat pest
infestations). The measurable outcomes for any given forest—such as timber production, forest health, or other metrics—
result from the merging of biophysical factors, disturbances, and management decisions. However, forest conditions may
produce resources and outcomes in ways that specific management activities, regardless of ownership, cannot mitigate or
overcome. For example, though forest management activities may focus on preventing, treating, or facilitating recovery from
various forest health stressors, the extent to which management practices can demonstrably improve health conditions is
difficult to assess. Although it is not possible to draw definitive conclusions regarding forest outcomes by ownership class,
some distinct ownership trends exist. For example, the South produces the most timber of any region; because most forests in
the South are privately owned, little of that timber production originates from public forests.
Congress’s interest in the nation’s forest resources is multifold. Across all ownerships, Congress may be interested in the
capacity of the nation’s forests to survive and recover from disturbance events and to adapt to changing climatic conditions.
Congress also may be interested in mitigating risks associated with adverse health conditions and otherwise ensuring forests
continue to provide benefits to surrounding communities. Issues for Congress may include whether and how to address those
interests and concerns, regardless of ownership. Congress also may have ownership-specific interests, such as federal forest
management or the federal government’s role in providing assistance for nonfederal forests. In addition, Congress has
expressed interest in understanding the extent, if any, to which nonfederal forests have better forest management and forest
health outcomes relative to federally managed forests.
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Introduction
One-third of U.S. land area is forested, and forests provide many public benefits. As such,
Congress is broadly interested in the health and management of the nation’s forest resources. The
potential scope of congressional involvement varies, in part based on ownership; Congress has a
direct role in the management of forests owned by the federal government but a more indirect role
regarding forests in nonfederal ownership. Congress also has expressed interest in the extent, if
any, to which nonfederal forests have better forest management—human intervention into forest
processes and composition—and forest outcomes relative to federal forests.
To inform congressional deliberations regarding U.S. forest resources, this report examines
nationwide and regional trends in forest ownership, health, and management.1 Forest management
outcomes generally, and forest health outcomes specifically, are difficult to measure, compare, or
attribute to any specific factor. As a result, it is not possible to definitively assess the specific
influence of individual forest attributes (e.g., forest ownership) on forest management outcomes.
Instead, this report analyzes forest outcomes that arise from the confluence of regional
biophysical, ownership, and management trends.
The report begins with an overview of the methodological approach for presenting the data and
analysis contained herein and an introduction to Congress’s roles with regard to the nation’s
forests. It then provides background on forestry concepts such as types, uses, health, and
management. The background section also introduces forest management principles specific to
timber production, a topic of congressional interest. The report then describes the extent,
distribution, uses, and management of federal and nonfederal forests and timber resources across
the United States, by ownership, and includes separate discussions of forest health and timber
production by ownership. Next, the report summarizes and highlights management and ownership
trends and their implications, to the extent possible, and discusses the challenges associated with
comparing forest management across ownership classes. The report concludes with a discussion
of some general, crosscutting issues related to U.S. forests that may be of interest to Congress.
Methods for Analyzing U.S. Forests
The nationwide overview of forests in this report generally examines forest characteristics across
four regions within the United States: North, South, Rocky Mountains (or Rockies), and Pacific
Coast (or Pacific). (See Figure 1.) These regions correspond to those in the Forest Resources of
the United States report (hereinafter, FRUS), a decennial assessment of forest resources prepared
by the U.S. Forest Service (FS, within the U.S. Department of Agriculture) pursuant to the Forest
and Rangeland Renewable Resources Planning Act.2 In a few cases, the report combines the four
regions or presents data at different regional scales. For example, some of the CRS analysis
compares forests in the eastern United States, which generally encompasses the North and South

1 This report primarily includes forest data and issues relevant to U.S. forests a whole. In-depth discussion of issues
specific to certain forests (e.g., federal forests) or concerns that may not be unique to forests (e.g., wildlife, outdoor
recreation, water) are beyond the scope of this report.
2 Forest and Rangeland Renewable Resources Planning Act, P.L. 93-378, 16 U.S.C. §1601. Sonja Oswalt et al., Forest
Resources of the United States, 2017: A Technical Document Supporting the Forest Service 2020 RPA Assessment,
Forest Service (FS), GTR-WO-97, 2019, at https://www.nrs.fs.fed.us/pubs/57903 (hereinafter cited as Oswalt et al.,
FRUS 2017). Unless specifically noted, the report and data herein reflect forest resources in the conterminous United
States, Alaska, and Hawaii but do not reflect forest resources in U.S. territories. Some of the figures in the report do not
include Alaska and Hawaii due to data availability issues.
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regions, with forests in the western United States, which generally encompasses the Rocky
Mountain and Pacific Coast regions. The national and regional trends discussed in this report are
general and may mask site-specific differences or deviations from such trends. Most data in this
report derive from the decennial FRUS reports.3
Figure 1. U.S. Forest Regions in the Forest Resources of the United States Report

Source: Congressional Research Service (CRS), adapted from Sonja Oswalt et al., Forest Resources of the United
States, 2017: A Technical Document Supporting the Forest Service 2020 RPA Assessment, Forest Service (FS), GTR-
WO-97, 2019 (hereinafter, Oswalt et al., FRUS 2017), Figure I-1.
Notes: U.S. territories are not included. The conterminous United States, Hawaii, and Alaska are represented at
different scales. The Rocky Mountain region is the largest region in terms of land area, consisting of 759 mil ion
acres, fol owed by the Pacific Coast region at 575 mil ion acres. The South region consists of 552 mil ion acres,
and the North region is the smallest, at 414 mil ion acres.
The report compares forest management across different ownership classes. At the broadest level,
forest ownership is classified as either public (e.g., governmental) or private.4 There is
considerable variation within both classes. Public ownership is further classified into federal and
other public (e.g., state and local) ownership, and private ownership is further classified into
private corporate and private noncorporate, consistent with FRUS classes. This classification
system does not fully represent the heterogeneity within the private corporate, private
noncorporate, and other public forest ownership classes. This report primarily focuses on
comparing federal and nonfederal (private and other public) forests, due to the different

3 Because of this report’s reliance on decennial Forest Resources of the United States (FRUS) data, it is not intended to
be updated until, at minimum, new FRUS data are published.
4 For purposes of this report, an owner of a public forest generally refers to the governmental agency charged with
managing the forest resources.
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congressional roles in relation to forests in these ownership classes. It includes other comparisons
(e.g., between public and private forests) when circumstances warrant.
Role of Congress
Congress’s role with regard to the nation’s forests varies based on numerous factors, including
forest ownership. Congress has a direct role in the management of forests owned by the federal
government, for example, but may have a more general interest in nonfederally owned forests.
Congress also supports forestry research, which applies across all ownerships.
The Property Clause of the U.S. Constitution (Article IV, §3, clause 2) authorizes Congress to
acquire, dispose of, and manage federal property. As such, Congress has the authority to enact
laws that address all aspects of managing federal forests and their resources. Much of Congress’s
legislative activity regarding federal forests primarily has focused on the four federal land
management agencies: the FS, in the U.S. Department of Agriculture (USDA), and the Bureau of
Land Management (BLM), National Park Service, and Fish and Wildlife Service in the
Department of the Interior (see “Federal Forests” for more information).5 Other federal agencies
also own land containing forest resources, however. To fulfill its role under the Property Clause,
Congress has passed numerous laws regarding federal forest management, from authorizing the
federal land management agencies’ general management missions to authorizing federal forests to
be managed and used for specific purposes.6 Congress also appropriates funding for managing
federal forests.7 Some of these laws directly relate to federal forest management, whereas others
relate indirectly to federal forests (e.g., laws concerning wildlife or air and water resources).8
Congress’s role in nonfederal forest management is less direct and generally relates to authorizing
(and appropriating funding for) federal programs to provide assistance for nonfederal forest
management, ownership, and use.9 Such programs may provide federal assistance in the form of
financial, technical, or other resources to a nonfederal entity, such as a state or individual. Often,
federal assistance is for a specified purpose, such as to promote forest health, prevent conversion
of forest to non-forest use, protect wildlife habitat, and meet other objectives. Congress has
authorized such programs in several USDA agencies, including the FS, Natural Resource
Conservation Service, and Farm Services Agency. Other federal agencies may administer
assistance programs focused on other topics—such as watersheds, energy, or wildlife—that also
may relate to nonfederal forest management.10 In addition, Congress has authorized assistance

5 For more information, see CRS In Focus IF10585, The Federal Land Management Agencies, coordinated by Katie
Hoover.
6 For example, Congress established general management missions for specified federal lands through the Multiple-Use
Sustained Yield Act of 1960 (national forests; Act of June 12, 1960; P.L. 86-517, 16 U.S.C. §§528-531), the Federal
Land Policy and Management Act of 1976 (BLM public lands; P.L. 94-579, 43 U.S.C. §§1701 et seq.), the National
Wildlife Refuge System (NWRS) Improvement Act of 1997 (NWRS, P.L. 105-57, 16 U.S.C. §§668dd et seq.), and the
National Park Service Organic Act of 1916 (National Park System, 39 Stat. 535).
7 For more information, see CRS Report R46557, Forest Service Appropriations: Ten-Year Data and Trends (FY2011-
FY2020), by Katie Hoover.
8 For example, Congress addressed federal forest health directly in the Healthy Forests Restoration Act (P.L. 108-148,
16 U.S.C. §§6501 et seq.). In contrast, the Endangered Species Act (P.L. 93-205, 16 U.S.C. §§1531 et seq.) may impact
federal forest management but does not address it directly.
9 For example, Congress authorized the USDA to provide nonfederal forest assistance through the Cooperative Forestry
Assistance Act (P.L. 95-313, 16 U.S.C. §§2101 et seq.). For more information, see CRS Report R45219, Forest Service
Assistance Programs, by Anne A. Riddle and Katie Hoover, and CRS Report R40763, Agricultural Conservation: A
Guide to Programs, by Megan Stubbs.
10 For example, federal assistance for Great Lakes water quality (P.L. 100-4, 33 U.S.C §1268) or federal outdoor
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programs to address forest issues internationally, largely in the FS and the U.S. Agency for
International Development.
Congress also authorizes and funds research related to forestry that can involve both federal and
nonfederal lands. In particular, Congress directed the FS to “conduct, support, and cooperate” in
forest and rangeland research, including basic and applied science, outreach, and cooperation
with nonfederal researchers.11 The FS also conducts and reports on the United States’
comprehensive forest inventory, the results of which form the basis of the FRUS (among other
products). Other agencies with research authorities also conduct research related to forests,
sometimes due to indirect relationships with other topics (e.g., energy, the environment).12 The
FS, other USDA agencies (e.g., the National Institutes of Food and Agriculture), and other federal
agencies (e.g., the National Aeronautics and Space Administration) also provide funding for
extramural research on forestry topics.
Background
The FRUS defines forests as lands dominated by trees.13 Forests also are ecosystems: groups of
living things (in this case, dominated by trees), the physical resources with which they interact,
and the resulting biotic and abiotic processes and cycles.14 Forests provide many ecological,
economic, and social resources (physical materials available in the environment) and uses
(human activities using forest resources or forest settings), many of which are listed below. A
forest’s health—generally, the status of its ecological integrity and ecosystem functioning—
influences its ability to provide these resources and uses. Forests are further influenced by forest
management—intentional, planned actions in forests to promote desired objectives.
This section discusses forest types, resources and uses, health, and management and introduces
concepts relevant to timber production. The forest health subsection includes a discussion on
wildfire but does not explore at length other factors influencing forest health (e.g., drought, insect
or diseases, weather events). Broad-scale regional variations are noted throughout these
background sections.
Forest Types
Forest ecosystems comprise physical characteristics (attributes of forest sites driven by nonliving
phenomena such as climate, latitude, and elevation) and biological characteristics (attributes of
the mix of species present on the site).15 This report focuses on an ecosystem’s physical
characteristics and the biological characteristics of a forest’s dominant tree species, although

recreation grants to states (P.L. 88-578, 54 U.S.C. §§200301 et seq.) may relate to nonfederal forests.
11 Forests and Rangelands Renewable Resources Research Act, P.L. 95-307, 16 U.S.C. §1642.
12 For example, see the National Aeronautics and Space Administration’s Global Ecosystem Dynamics Investigation
mission, at https://gedi.umd.edu/ or the U.S. Geological Survey’s Forest and Rangeland Ecosystem Science Center,
https://www.usgs.gov/centers/fresc.
13 Oswalt et al., FRUS 2017, defines forests or forestland as parcels of land at least 120 feet wide and at least 1 acre in
size, with at least 10% cover by live trees, including land that formerly had such trees where the trees will regrow (such
as land where timber was recently harvested). Forestland does not include urban land or agricultural land that is
covered with trees (such as an orchard). Lands with less than 10% cover by live trees are known as woodlands.
14 David Perry, Ram Oren, and Stephen Hart, Forest Ecosystems (Baltimore, MD: Johns Hopkins University Press,
2008). Hereinafter referred to as Perry, Oren, and Hart, Forest Ecosystems.
15 Perry, Oren, and Hart, Forest Ecosystems.
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other forest organisms also have biological characteristics. To describe a forest ecosystem as a
whole, physical and biological characteristics are jointly termed biophysical characteristics.
Physical characteristics vary according to both broad regional conditions and site-specific local
conditions and may influence which species can grow on a given site. On broad scales, regional
climate and latitude may determine factors such as average annual temperature, average annual
precipitation, and growing season length. These regional characteristics may vary further as they
interact with site-specific characteristics, such as elevation, soils, slope, and aspect; for example,
a site on top of a ridge is likely to be drier than one in a valley, although the two sites may receive
the same annual precipitation. Forests generally comprise species adapted to similar physical
conditions or similar frequencies of ecosystem phenomena that cause tree damage or death.
Although there are thousands of different tree species in the United States, trees can be divided
into two general types based on their biology. These biological differences influence their growth
characteristics and ranges:
 Softwoods are coniferous trees such as pine (Pinus sp.), fir (Abies sp.), Douglas
fir (Pseudotsuga menziesii), and spruce (Picea sp.). Softwood species grow
throughout the United States and dominate forests in the Rocky Mountain and
Pacific Coast regions and in some parts of the South.
 Hardwoods are non-coniferous, broadleaved trees such as oak (Quercus sp.),
maple (Acer sp.), walnut (Juglans sp.), and ash (Fraxinus sp.). Hardwood-
dominated forests grow almost exclusively in the North and South regions, with a
few commercially important species growing in California, Oregon, and
Washington.16
Hardwoods and softwoods may grow together in mixed forests, but one type grows exclusively in
many parts of the United States. (See Figure 2 for a map of forest types in the United States.)
Within the two types, forests come in groups of varying complexity, from forests dominated by
one or two species to forests with dozens of species. Trees’ biological characteristics also give
rise to different properties of growth—such as annual rates of growth or properties of strength or
stiffness—that influence their commercial desirability.

16 Michael Wiemann, “Characteristics and Availability of Commercially Important Wood,” in Wood Handbook: Wood
as an Engineering Material, FS, Forest Products Laboratory, FPL-GTR-282, 2021, p. 2-1.
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Figure 2. Forest Type Groups of the Contiguous United States, 2008

Source: CRS, using data from FS, “National Forest Type Dataset,” at https://data.fs.usda.gov/geodata/
rastergateway/forest_type/. This dataset does not include Alaska and Hawaii.
Forest Resources and Uses
Many factors influence the particular resources and uses a given forest provides. These factors
include the forest’s physical setting, its plant and animal species, and its ecological processes, as
well as the activities humans undertake in the forest. Forest resources and uses may be
complementary or in opposition to one another. As such, the management and use of forests are
perennially complex and often contentious issues. Some forest resources and uses include the
following:17
 Air. Through their growth processes, forests influence air, including carbon
dioxide, oxygen, and pollutants. Forests reduce air pollution, create oxygen
through photosynthesis, and consume carbon dioxide, ultimately sequestering
carbon in trees and soils. For example, in 2019, U.S. forests were a net sink of
greenhouse gases, meaning they sequestered more carbon from the atmosphere
than they released.18
 Animal Products. Due to the animal species that make up, reside in, and rely on
forests as part of their lifecycle, forests contribute to economically valuable
animal products, such as subsistence wildlife species or commercial anadromous
fish populations (e.g., salmon).

17 This report does not detail all of the possible ways forests are used and valued.
18 For more information, see CRS Report R46313, U.S. Forest Carbon Data: In Brief, by Katie Hoover and Anne A.
Riddle.
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 Biodiversity. For the purposes of this report, biodiversity refers to the mix of
plant and animal species present in the forest.19 These species—either as a mix or
as individuals—may contribute to other resources and uses, such as recreational
experiences (e.g., hunting, fishing, leaf peeping) or animal products. In addition,
the biodiversity of plants and animals may, in and of itself, be valued.
 Forest Products. The economically valuable tissues of trees and plants are a
prominent use of forests. Forests provide timber (unprocessed cut trees), a critical
material for construction, paper products, and many other uses. Forests also
produce fuelwood and non-timber forest products, such as food, fiber, medicines,
decorative products, and others.
 Recreational and Cultural Uses. Forests may be used for recreational,
educational, scientific, and spiritual purposes. Various forest resources—for
example, plant and animal resources, water, and physical setting—may combine
to determine each site’s desirability for such uses.
 Water. Water cycles through forests, which influences its flow and quality. As
such, forests play an important role in providing water, improving its quality, and
mediating the risk of water-related disasters (e.g., floods, landslides). About 80%
of the nation’s fresh water originates from forests.20
 Other Resources and Land Uses. Additional uses for forests include grazing,
energy and mineral development, and infrastructure and building siting.
Forests’ various uses and values may inform forest owners’ management choices or approaches.21
Owners may find a number of resources or uses to be significant or may be required or
constrained by law in how they treat certain forest resources or uses (or mixes of the two).
Forest Ecological Health
Forest health is not easily defined.22 One definition of forest health relates to a forest’s capacity to
provide ecological and economic goods; another definition generally refers to ecological integrity
and functioning, or a forest ecosystem’s ability to respond to forest health stressors, or
disturbances (e.g., wildfires, ice or wind storms, insect and disease infestations, timber
harvests).23 Forest ecosystems have inherent characteristics that enhance their capability to
survive such events (resistance) or facilitate recovery after disturbance (resilience). Some tree
species are adapted to specific disturbances occurring at regular intervals. Forest health stressors

19 Biodiversity can also refer to biological variation at other scales, such as the genetic or ecosystem scales.
20 James Sedell et al., Water and the Forest Service, FS-660, 2000.
21 For purposes of this report, an owner of a public forest generally refers to the governmental agency charged with
managing the forest resources.
22 For a discussion of forest health concepts, see T. E. Kolb, M. R. Wagner, and W. W. Covington, Forest Health from
Different Perspectives, FS, RMR-GTR-267, 1995, at https://www.fs.usda.gov/treesearch/pubs/23480; for a discussion
of ecosystem health generally, see Robert Costanza, “Toward an Operational Definition of Ecosystem Health,” in
Ecosystem Health: New Goals for Environmental Management, eds. Robert Costanza, Bryan Norton, and Benjamin
Haskell (Washington, DC: Island Press, 1992).
23 Disturbance is defined as “any relatively discrete event in time that disrupts ecosystems, community, or population
structure and changes resources, substrate availability, or the physical environment.” Steward T. A. Pickett and P. S.
White, The Ecology of Natural Disturbance and Patch Dynamics (Orlando: Academic Press, 1985). Disturbance events
may be unplanned (e.g., precipitation events) or planned (e.g., harvest, prescribed fire).
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may be biotic or abiotic, natural or anthropogenic, and may vary among biophysical regions and
local environments.
Forest health is also difficult to measure.24 Often, variables related to biophysical or ecological
characteristics are used to indicate measures of forest health, such as tree damage or mortality.
These indicator variables may be measured individually—or, more often, in combination—as a
proxy for measuring ecosystem function. In some cases, ecosystem function is assessed by the
degree of departure from a baseline or reference condition. For example, the FS uses watershed
function as one method of evaluating the condition of national forests; to do so, the FS uses a
combination of 12 different indicator variables to measure watershed function relative to a
baseline condition.25
The following sections discuss tree mortality and describe three interrelated forest health issues:
insect and disease infestations, adverse weather events, and wildfire-related issues.26
Tree Mortality
Some level of tree damage or mortality is expected in a forest, but high levels at large scales may
indicate declining or degraded forest health. Degraded forest ecosystems, for example, may take
longer to recover from or may be more susceptible to mortality in response to disturbances or
other health stressors. Different disturbances also may interact and exacerbate the effects of other
events in a feedback loop. For example, a prolonged drought may impair a tree’s resistance to an
insect or disease infestation or may make a tree more susceptible to damage during a wildfire.
Some research indicates that climate variability is reshaping forest landscapes by altering the
frequency, intensity, and timing of disturbance events in ways that may exceed many forests’
resistance and resilience capacities.27
Nationwide, FS reported that about 10 billion cubic feet of tree mortality was observed in 2016.28
In many cases, mortality can be attributed to multiple, sometimes interrelated, causes. This figure
includes mortality related to disturbances such as insect and disease infestations, adverse weather
events (e.g., drought; excessive moisture, wind, or ice), and wildfires. Each cause’s relative
contribution can be difficult to determine.
In the eastern United States (which most closely coincides with the North and South regions in
this report), tree mortality is low relative to tree growth, meaning new tree growth can replace
tree mortality relatively quickly.29 In many parts of the western United States (which most closely
coincides with the Rocky Mountain and Pacific Coast regions in this report), tree mortality can be

24 See, for example, D. J. Rapport, R. Costanza, and A. J. McMichael, “Assessing Ecosystem Health,” Trends in
Ecology and Evolution, vol. 13, no. 10 (October 1998), pp. 397-402.
25 For more information, see the FS, “Watershed Condition Framework,” at https://www.fs.fed.us/naturalresources/
watershed/condition_framework.shtml.
26 Other issues affecting forest health (e.g., potential impacts from climate change) are beyond the scope of this report.
27 James M. Vose, David L. Peterson, and Toral Patel-Weynard, Effects of Climate Variability and Change on Forest
Ecosystems: a Comprehensive Science Synthesis for the U.S., FS, PNW-GTR-870, 2012, at
http://www.treesearch.fs.fed.us/pubs/42610.
28 This figure reflects mortality as reported on U.S. timberlands. Oswalt et al., FRUS 2017, Appendix A, Table 33. For
more on timberlands, see “Forest Ownership Overview and Data.”
29 Kevin M. Potter and Barbara L. Conkling, Forest Health Monitoring: National Status, Trends, and Analysis 2020,
FS, GTR-SRS-261, July 2021, p. 27, at https://www.fs.usda.gov/treesearch/pubs/62839 (hereinafter cited as Potter and
Conkling, FHM 2020). The regions in the FHM 2020 report differ from the regions used in this report, which are
derived from regions in the FRUS. For a map of the FHM 2020 regions, see FS, “Forest Health Highlights,” at
https://www.fs.fed.us/foresthealth/protecting-forest/forest-health-monitoring/monitoring-forest-highlights.shtml.
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very high as a percentage of live volume or growth. In 2019, regions in the West experienced the
greatest extent of certain individual disturbances relative to the rest of the country, such as insect
and disease infestations, particularly in the Interior West (i.e., the Rockies).
Insect and Disease Infestations
According to some forest scientists, insects and diseases “represent the most serious threats to the
Nation’s forests” and have the potential for widespread ecological and economic impacts.30 Both
native and non-native invasive species present these threats. Insect and disease infestations vary
in their impact on forest ecosystems. Some insects are defoliators and damage trees by eating
their leaves and needles, disrupting the photosynthesis process (e.g., western spruce budworm).
Other insects, diseases, and pathogens damage trees internally (e.g., mountain pine beetles). Both
defoliation and internal damage can lead to tree mortality, though tree species vary in their
tolerance of different pests. For example, some hardwood species generally may be more resilient
to short-term defoliation events than some coniferous species, because they can refoliate in the
same year.
The FS’s Forest Health Monitoring (FHM) program annually reports the status of and trends in
forest insect and disease conditions nationally and regionally.31 The FHM program primarily
conducts these reports from a landscape perspective and not by ownership class, given the
regional extent of many infestations. In 2019, the FHM report included a retrospective on forest
health conditions from 1997 through 2016, by FRUS region.32 Across the 20-year period, insect-
and disease-related mortality was highest nationwide from 2002 to 2006 and highest in the
Rockies, relative to the other regions. These data reflect the significant impacts of the mountain
pine beetle in the Rockies, specifically from 2002 to 2011. Over the 20-year period, insects were
more widespread agents of mortality than diseases, and bark beetles were consistently the most
important mortality agent across regions and over time, especially in the West. During this period,
the North saw a larger proportion of tree mortality attributed to non-native invasive species than
the other regions. More recently, from 2012 to 2016, insect- and disease-related mortality was
highest in the Pacific Coast region.
Adverse Weather Events
Certain weather events adversely affect forest health. These events include discrete weather
events, such as hurricanes, and events that occur over longer periods, such as droughts.
Hurricanes, for example, can result in excessive precipitation and soil moisture, which deprive
tree roots of oxygen for a prolonged period. Hurricanes and other weather events also can include
high winds that break or uproot individual trees or groups of trees, an occurrence sometimes
referred to as windthrow or blowdown. Winter storms that result in large accumulations of ice on
tree branches also can result in damage or mortality to individual trees or groups of trees.
Drought occurs when there is a deficiency of moisture.33 Although a lack of precipitation is often
central to drought, high temperatures, high winds, lack of clouds, and low humidity also can
contribute. Droughts may be seasonal, multiyear, or multi-decadal in duration. Variable

30 Potter and Conkling, FHM 2020.
31 Potter and Conkling, FHM 2020.
32 Kevin M. Potter et al., Forest Health Monitoring: National Status, Trends, and Analysis 2019, FS, GTR-SRS-250,
2020, pp. 125-150, at https://www.srs.fs.usda.gov/pubs/60380.
33 Text in this paragraph is drawn from CRS Report R46911, Drought in the United States: Science, Policy, and
Selected Federal Authorities, coordinated by Charles V. Stern and Eva Lipiec.
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link to page 15 U.S. Forest Ownership and Management: Background and Issues for Congress

precipitation levels and rising temperatures are intensifying droughts, particularly in some
regions. Further, drought may affect certain regions of the United States on a short- or longer-
term basis, with varying intensity over time. For example, the North has rarely experienced
extreme or exceptional drought levels since 2000;34 in contrast, periods of extreme and
exceptional drought have been relatively common in the West since 2000.35
Trees absorb water from precipitation through their leaves or from the soil through their roots,
and they use that water to fuel growth and many other internal processes. Droughts can alter the
pattern, frequency, and total amount of water available to trees, which can disrupt those
processes. Drought-stressed trees are more susceptible to disease infections and insect invasions
than comparable trees not affected by drought. Because droughts reduce the overall moisture in a
tree, drought-stressed trees are also more susceptible to ignition during a wildfire event. In
addition, drought-stressed trees may take longer to recover from adverse events, such as impacts
from wildfires or insect infestations. Further, the detrimental impacts of drought may continue for
many years after the adverse event has concluded.
Wildfires
Wildfires are unplanned fires occurring in vegetated ecosystems. Wildfires are sometimes caused
by lightning strikes but are more frequently caused by human activities (deliberate or accidental),
such as sparks from equipment or campfires or loss of control over a prescribed burn. Weather
conditions (e.g., heat, humidity, and wind) and fuel conditions (e.g., the moisture content and
distribution of vegetation) affect wildfire spread and intensity. Wildfires can have some beneficial
impacts on an ecosystem, but they often threaten homes, communities, and other valuable
resources.
Different forest ecosystems have adapted to different wildfire frequencies and intensities,
sometimes referred to as fire regimes. Some ecosystems are adapted to relatively frequent, low-
intensity fires that burn the surface fuels (e.g., grasses, needles, leaves). Others are adapted to
periodic, high-intensity fires that spread across the forest canopy and kill much of the vegetation,
known as stand-replacing fires. Still other ecosystems are adapted to a mix of fire frequencies and
severities. (See Figure 3.)

34 Drought conditions impacting broad-scale areas are classified as ranging from abnormally dry to exceptionally dry,
according to a scale developed by the U.S. Drought Monitor, a federal and nonfederal partnership that researches,
monitors, and reports drought conditions. For more information on drought, see U.S. Drought Monitor, “Current Map,”
at https://droughtmonitor.unl.edu/ and CRS Report R46911, Drought in the United States: Science, Policy, and
Selected Federal Authorities, coordinated by Charles V. Stern and Eva Lipiec.
35 For example, most of the western United States experienced widespread drought conditions in 2021, and California
experienced severe droughts from 2012 to 2016.
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