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Forest Service

U.S. DEPARTMENT OF AGRICULTURE

Forest Service

U.S. DEPARTMENT OF AGRICULTURE

Bureau of Land Management

U.S. DEPARTMENT OF THE INTERIOR

FS-1242a | January 2024 

Introductory Report

Analysis of Threats to Mature and Old-Growth Forests on Lands

 Managed by the Forest Service and Bureau of Land Management

Fulfillment of Executive Order 14072, Section 2.c.ii

Overview 

Executive Order (EO) 14072–Strengthening the Nation’s 

Forests, Communities, and Local Economies–instructed 

the U.S. Department of the Interior, Bureau of Land 

Management (BLM) and U.S. Department of Agriculture 

(USDA), Forest Service to implement a set of actions 

focused on the health of the Nation’s forests. Section 

2.c.(ii) directed the agencies to analyze the threats 

to mature and old-growth forests on Federal lands, 

including from wildfires and climate change. To fulfill 

this direction, the agencies are creating a full report that 

will be available in early 2024. This introductory report 

summarizes initial key findings.

As recognized in section 1 of EO 14072, old-growth 

forests have decreased significantly from what existed 

historically. Understanding what threatens mature and 

old-growth forests is imperative to conserving and 

managing these forests and protecting their ecological, 

social, cultural, and economic value.

What Constitutes a Threat?

For this analysis, shaped by technical experts and 

feedback from the public, a threat is defined as a 

current or projected disturbance or stressor that may 

contribute to the enduring loss or degradation of the 

characteristic conditions, functions, or values of existing 

mature and old-growth forests. Disturbances resulting 

in a decline in the abundance of mature and old-growth 

forests, or enduring loss of conditions, functions, or 

values were considered negative outcomes, and are 

thus threats. Disturbances that resulted in neutral or 

beneficial outcomes, such as no change in abundance, 

or an increase in abundance of mature and old-growth 

forests, were not considered threats. 

Defining Mature and Old Growth

According to the Mature Forest Narrative Framework, 

mature forests are delineated ecologically as the stage 

of forest development immediately before old growth. 

The mature stage of stand development generally 

begins when a forest stand moves beyond self-thinning, 

starts to diversify in height and structure, and/or the 

understory begins to reinitiate. Structural characteristics 

that mark the transition from an immature to mature 

forest are unique to each forest type; they may include 

but are not limited to: abundance of large trees, large 

tree stem diameter, stem diameter diversity, horizontal 

canopy openings or patchiness, aboveground biomass 

accumulation, stand height, presence of standing and/or 

downed boles, vertical canopy layers, or a combination 

of these attributes.

Mature and old-growth forests come in all shapes and 

sizes and can often be abundant. Mature and old-growth 

forests offer biological diversity, carbon sequestration, 

wildlife and fisheries habitat, recreation, aesthetics, soil 

productivity, and clean water. These special forests also 

reflect diverse Tribal, social, and cultural values.

Key Findings

The initial threat analysis found that mature and oldgrowth forests have high exposure to a variety of 

threats and climate and disturbance projections show 

this exposure will likely increase. Currently, wildfire, 

exacerbated by climate change and fire exclusion, is 

the leading threat to mature and old-growth forests, 

followed by insects and disease. Tree cutting (any 

removal of trees) is currently a relatively minor threat 

despite having been a major disturbance historically. 

The analysis also found that two thirds of mature forests 
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and just over half of old-growth forests are vulnerable to 

these threats. Climate change has increased the level of 

these threats and is likely altering where, and what types 

of mature and old-growth forests can persist. Over the 

next five decades, the growth of younger and mature 

forests is projected to result in an increase of mature 

and old-growth forests despite increasing disturbances. 

However, gains lessen with each passing decade and 

the expanding wildland-urban interface complicates 

mitigation of threats.

Since 2000, wildfires resulted in a decrease of an 

estimated 2.57 million acres of mature and 712,000 

acres of old-growth forests on National Forest System 

(NFS) and BLM lands. Insects and disease caused a 

decrease of 1.86 million acres of mature and 182,000 

acres of old growth. Tree cutting by the BLM and Forest 

Service resulted in a decrease of 214,000 acres of mature 

forests and 9,000 acres of old growth. Where no forest 

disturbances have occurred, mature forests increased by 

2.21 million acres and old-growth forests by 1.20 million 

acres. Combined, there has been a 2.51-million-acre 

net decline of mature forests, with about a tenth of this 

becoming old growth (a 0.28-million-acre net increase in 

old growth). 

A total of 30,864 Forest Inventory and Analysis (FIA) plots, representing 81.5 million acres of mature and 31 million acres of old growth, were measured twice 

between 2000 and 2020. Net changes in mature and old-growth area (based on the definitions used in the mature and old-growth inventory) are shown 

above. Error bars represent 95 percent confidence intervals and asterisks indicate a statistically significant change.

Fire

Fire (wildfire, cultural burning, or other prescribed fire) is 

a disturbance that can have positive, neutral, or negative 

outcomes, with frequent, low-severity fire driving 

natural ecological processes in many forest types, often 

maintaining mature and old-growth characteristics. Some 

forests experience less frequent, but high-severity fire 

that removes mature and old-growth forest, reinitiating 

forest development. Adverse effects from fire depend 

on forest type, fire severity, fire extent, and the forest’s 

condition following the fire, including ecological, social, 

economic, and cultural impacts.

This century, wildfires have been increasing in frequency 

and extent, accounting for most of the losses of 

mature and old-growth forests on NFS and BLM lands. 

Historically, less than half of inventoried mature and 

old-growth forests had high exposure to mortality from 

fire. High exposure equates to about 0.1 to 0.3 percent of 

the area will experience moderate-to-high severity fire 

annually. Very high exposure is about 0.5 percent each 

year. Currently, 70-80 percent are considered at high 

exposure. Climate change projections predict greater than 

90 percent of inventoried mature and old-growth forests 

will be at very high exposure to wildfire-caused mortality 

by the end of the century. However, increasing exposure 

does not mean loss of mature and old-growth forests, 

but that an increasing proportion will experience fire, 

and, depending on conditions, may incur adverse effects. 

Forest Inventory and Analysis (FIA) plot remeasurements 

illustrate this point: a total of 7.1 million acres of mature 

and 1.7 million acres of old-growth forests have burned 

since 2000. Slightly over 60 percent of that still met mature 

and old-growth forest definitions.

The recent USDA Forest Service Resources Planning Act 

(RPA) assessment estimated that the largest increases 

in fire will occur disproportionately in the West among 

Douglas-fir, ponderosa pine, and piñon-juniper forests, 

as well as woodland hardwoods. In the East, fire-related 

mortality in the oak/hickory forest type group is projected 

to at least double (by volume) by 2070. However, an 

increase in fire may be beneficial to these oak/hickory 

forests if it signals more fire overall and an end to fire 

exclusion.
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This series of maps portrays exposure of mature and old growth to 

wildfire threats historically and through the end of the century based on 

past records and future climate predictions. 

Fire Exclusion

Fire exclusion began centuries ago, as European 

colonization disrupted frequent Tribal burning practices 

that maintained open forests and favored fire-tolerant 

trees. The wildfire suppression policies of the 20th 

century exacerbated fire exclusion. Removing fire from 

forest types that are adapted to relatively frequent fire 

can increase the probability of high-severity fire and 

stand replacement as stands become dense with smaller 

trees that facilitate canopy fire spread. Fire exclusion can 

also lead to adverse ecological outcomes such as highdensity, fire-sensitive, shade-tolerant understories that 

prefer moderate amounts of moisture. 

FIA plot remeasurements, published climate change 

projections, and fire exclusion history tell us that a third 

of mature and a quarter of old-growth forests have a 

fire deficit. Oak/hickory, ponderosa pine, and loblolly/

shortleaf pine forest type groups have the most mature 

and old-growth forests in fire deficit. The fire exclusion 

signature can also be seen through deeper analysis of 

FIA plots that meet old-growth inventory definitions—

when a plot is classified as old growth due to large 

tree densities, but also includes high densities of firesensitive small trees (such as red maple). 

Fireshed Registry1 project area map (about 25,000 acres each) of wildfire deficit. The bar chart highlights the top five forest type groups from largest area of mature 

and old-growth forests to lowest with the high amounts of fire deficit.

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 Firesheds are units of roughly 250,000 acres used to evaluate wildfire management and risks to local communities. For this effort and the 

maps displayed, firesheds have no wildfire context but are simply used as map units.
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Insects and Disease

Tree mortality from native insects and tree diseases 

sometimes results in substantial loss of mature and 

old-growth forest stands. In contrast, non-native 

insects and disease have caused extensive mortality of 

dominant overstory trees in several areas, sometimes 

moving mature and old-growth forests to earlier 

stages of forest development. Increased frequency of 

drought and more damaging wind or ice storms due 

to climate change may increase the vulnerability of 

forests to threats from both native and non-native 

forest insects and disease. Even when mature and oldgrowth forests remain after infestations, the changes 

to these forests may have substantial negative social, 

cultural, and economic impacts.

Evidence from FIA plot remeasurement suggests a net 

loss of 1.9 million acres (2.3 percent) of mature forest 

and 134,000 acres (0.4 percent) of old-growth forest to 

insect and disease. The overall severity of the effects 

of insect and disease was mostly low in 67 percent of 

mature and 73 percent of old-growth plots, resulting in 

no significant change in mature forests but a significant 

net gain in old-growth forest. This is likely due to 

increases in dead trees with elements of old growth 

definitions for some forest types. The current potential 

threat from insects and disease was highest in lodgepole 

pine (81 percent), fir/spruce/hemlock (63 percent), 

ponderosa pine (63 percent), Douglas-fir (61 percent), 

and piñon-juniper (56 percent).

Fireshed registry project area map (about 25,000 acres each) of current risk to forests from insects and disease. Bar chart highlights 

the top five forest type groups from largest area of mature and old growth to lowest with high exposure.

Tree cutting ranges from removal of individual trees 

for specialized use or safety to removal of many 

trees for structural lumber or habitat creation. From 

1950 through 1990, tree cutting was the number one 

disturbance, removing substantial areas of mature 

and old-growth forests; however, this is no longer the 

case as agency policy has since changed significantly. 

The economic, social, and ecological dimensions of 

tree cutting are complex, thus creating both potential 

threats and opportunities for mature and old-growth 

forest composition.

Tree Cutting

The latest remeasurement of FIA plots showed that 2.1 

million acres of mature forest and 400,000 acres of old 

growth experienced tree cutting effects. This comprised 

2.5 percent of mature forests and 1.3 percent of oldgrowth forests. In general, management improved or 

maintained these stands. In total, 200,000 acres (0.3 

percent) of mature forest and 9,000 acres (0.03 percent) 

of old growth were converted to other forest conditions 

by this tree cutting.
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Mill Infrastructure

Mills play a critical role in processing logs from activities 

aimed at reducing risk from fire, insects, and disease, but 

were also identified as a threat due to the relationship 

between mills and loss of mature and old growth due 

to timber harvest. The vast majority (81 percent) of 

mature and old-growth forests are in firesheds with 

low timber processing capacity. Capacity was highest 

in the Pacific Northwest and Southeast regions of the 

country. Almost half of inventoried mature and oldgrowth forests are in firesheds where wood processing 

capacity is low, but current threats, including severe 

fire, are high. This suggests these areas may struggle to 

practice active management to reduce such threats. 

This fireshed map combines mill capacity with threats to mature and old-growth forests. More than half of mature and old-growth 

forests are in firesheds where the threat of wildfire, insects/disease, and wildfire deficit are high, but mill capacity is low.

Climate Change

Climate change is a complex stressor with a variety of 

short and long-term outcomes, interacting with and 

exacerbating other stressors or threats (such as fire 

or insects). Consequences will take different forms in 

different regions and forest types. In virtually every 

scenario, the broad consequences of climate change 

mean that the ecosystem services and values with 

which various communities engage are likely to change 

too. Exposure to high temperatures and drought are 

two aspects of climate change that threaten mature 

and old-growth forests. 

The year 2023 marked the hottest year on record 

globally. For mature and old-growth forests, this 

climate metric means exposure to high temperatures 

can have direct, adverse effects on mature and oldgrowth forests. It also means secondary effects from 

other impacts of heat, such as drought, results in 

increased stress to trees.

Historically, about one-third of the mature and oldgrowth forests in the conterminous United States rarely 

exceeded 90 °F in any given year (less than one day 

per year; very low exposure). Depending on estimated 

climate change scenarios, roughly 15–32 percent of 

inventoried mature and 11–32 percent of old-growth 

forests may experience two or more months of extreme 

heat by the end of this century. Based on the current 

trajectory, less than 1 percent will not experience 

less than one day per year of extreme heat. Higher 

temperatures are expected to cause changes in the 

distribution and abundance of dominant forest species, 

with heat-tolerant species becoming more competitive. 

In forests located near streams and rivers, hotter 

temperatures will accelerate the drying of soils through 

evaporation as vegetation takes up water earlier and 

faster during the growing season. 
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According to the National Oceanic and Atmospheric 

Administration (NOAA), geographically extensive and 

long-duration drought conditions across the United 

States set several records in 2022. The time series 

maps, representing a three-decade climate normal, 

illustrate how climatic water deficit (a measure of 

drought) has already changed and may change into 

the future. Drought sensitivity varies by forest type 

and environmental factors such as elevation, latitude, 

and topography. The amount of mature forest area 

that historically had very low exposure to drought 

has already decreased by about half and old growth 

by about 43 percent (based on the RCP8.5 climate 

models). By the end of the century, less than 1 percent 

of inventoried mature and old-growth forests will have 

very low exposure. 

According to the most recent RPA assessment, recent 

exposure to drought was higher in the West than the 

East, and drought exposure for forests is expected 

to increase by 2070, with the largest increases in the 

Southwest. Climate change projections indicated 

levels of drought exposure will far exceed recent 

exposure for many forest type groups. By mid-century, 

over half of the piñon-juniper, woodland hardwoods, 

aspen/birch, and ponderosa pine type groups are 

projected to exceed the historical median exposure to 

severe or extreme drought.

This series of maps portrays exposure of mature and old growth to extreme heat 

and moisture stress historically and through the end of the century based on 

past records and future climate predictions. 

Challenges to Managing Mature and Old-Growth Forests

The wildland-urban interface, where housing meets 

forests, presents challenges to managing mature and 

old growth. According to census data, housing units 

have grown by 43 percent in mature and old-growth 

firesheds from 1990 to 2020. The social and ecological 

dynamics created by having housing in and around 

forested lands are complex, creating both potential 

threats and opportunities. 

The proximity of humans and housing to forests 

can increase the risk of wildfire ignitions, limit 

opportunities for prescribed fire use, and increase 

pressure to create fuel breaks, all of which could have 

negative impacts to mature and old-growth forests. 

Alternatively, increased investment through tools like 

Community Wildfire Defense Grants, could provide 

the opportunity for more targeted maintenance and 

restoration efforts, with positive impacts to mature 

and old-growth forests. 

Sunset view of the Salt Lake Valley (middle left) next to the Wasatch National Forest 

(mountains to the right), early October 2023. As people and businesses migrate into 

Utah, housing continues to expand into forested areas, as can be seen here by the 

Suncrest community nestled on top of the Traverse Mountains in Draper, Utah, part 

of the Wasatch Wildfire Crisis Strategy Landscape located between the Salt Lake 

and Utah valleys. USDA Forest Service photo by Nick Cieslak.
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This fireshed map combines housing growth with threats to mature and old-growth forests from wildfire deficits. More than half 

of mature and old-growth forests are in firesheds where housing growth is high and the threat from wildfire is also high.

The Future of Mature and Old-Growth Forests

Despite the threats highlighted in this analysis, the 

RPA assessment predicted an increasing trend in the 

amount of mature and old-growth forests on NFS 

and BLM lands until at least mid-century (2070), as 

the large amount of younger and mature forest age 

into older forests. This trend begins to decrease by 

mid-century under some shared socioeconomic and 

climate change scenarios.

Projections of increasing mature and old-growth 

forests are tempered by the reality that American 

forests are entering uncharted territory with climate 

change. As our understanding of the implications of 

climate change evolves, so will understanding the 

places and methods to best steward and conserve our 

Nation’s older forests. 

In the meantime, existing younger and mature forests 

provide the building blocks for future mature and 

old growth. A sound management approach will 

help ensure that older forest species composition 

and structure fits its environment (such as future fire 

patterns, climate, and locations least likely to burn). A 

deep understanding of ecological, social, and cultural 

dynamics must play a role. Most importantly, the 

environment of the predicted future, and not that of 

the past, should guide policy considerations related to 

mature and old-growth management. 

Modeled trends of mature and old-growth forests that account for 

forest disturbances under different future scenarios.
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Conclusion

This introductory threat analysis should be considered 

a first step towards understanding the myriad of 

interacting factors (biophysical and social) that threaten 

the persistence of older forests on public lands across the 

Nation, now and into the future. Monitoring the status 

and trend of these forests, coupled with monitoring forest 

disturbances, will inform understanding the causality for 

observed patterns and changes. 

Details related to this introductory report are also 

outlined in the mature and old growth section of the 

Forest Service’s online Climate Risk Viewer (CRV) tool, 

which illustrates a variety of map layers and climate 

assessment resources. 

See the Forest Service 2020 Resources Planning Act 

Assessment: Future of America’s Forests and Rangelands

for a summary about the status, trends, and projected 

future of the Nation’s forests and rangelands. The 2020 

RPA assessment specifically focuses on the effects of both 

socioeconomic and climatic change on the U.S. land base, 

disturbance, forests, forest product markets, rangelands, 

water, biodiversity, and outdoor recreation. 

See the Forest Inventory and Analysis: Fiscal Year 

2022 Business Report for authoritative data about 

forest carbon, forest products and services, biomass 

availability, economic development opportunities, 

land cover and land use change, incidence of nonnative 

invasive species, impacts of pests and diseases, and 

wildfire risk, and to support the sustainable management 

and conservation of forests, water resources, and 

biodiversity.

See a preliminary report, Mature and Old-Growth Forests: 

Definition, Identification, and Initial Inventory on Lands 

Managed by the Forest Service and Bureau of Land 

Management for additional information.

Old-growth forest, Mitkof Island, Tongass National Forest. 

USDA Forest Service photo by Karen L. Dillman.

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