Forest

Service

United States Department of Agriculture

General Technical Report 

RMRS-GTR-390

Rocky Mountain

Research Station April 2019

Guidelines for Aspen Restoration in Utah 

with Applicability to the Intermountain West 

Stanley G. Kitchen 

Patrick N. Behrens 

Sherel K. Goodrich 

Ashley Green 

John Guyon 

Mary O’Brien 

David Tart 
Kitchen, Stanley G.; Behrens, Patrick N.; Goodrich, Sherel K.; Green, Ashley; Guyon, John; 

O’Brien, Mary; Tart, David. 2019. Guidelines for aspen restoration in Utah with 

applicability to the Intermountain West. Gen. Tech. Rep. RMRS-GTR-390. Fort Collins CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 55 p.

Abstract 

As highly productive and biologically diverse communities, healthy quaking aspen (Populus 

tremuloides; hereafter aspen) forests provide a wide range of ecosystem services across western 

North America. Western aspen decline during the last century has been attributed to several 

causes and their interactions, including altered fire regimes, drought, excessive use by domestic 

and wild ungulates, and conifer encroachment. Today’s managers need science-based guidance 

to develop and implement strategies and practices to restore structure, processes, and resilience 

to the full range of aspen functional types across multiple spatial scales. In these guidelines, we 

detail a process for making step-by-step decisions about aspen restoration. The steps are: (1) 

assessment of aspen condition, (2) identification of problematic conditions, (3) determination of 

causal factors, (4) selection of appropriate response options, (5) monitoring for improvement, and 

(6) assessment and adaptation. We describe the need for reference areas in which the full range of 

natural environmental conditions and ecosystem processes associated with aspen can be observed 

and quantified, and provide a list of example sites for Utah. These guidelines provide a road map 

for decision makers to adaptively manage aspen in a time of increasing environmental stress and in 

anticipation of an uncertain future.

Keywords: Populus tremuloides, active restoration, passive restoration, aspen functional type, 

 decision chain, monitoring, ungulate browse pressure, climate change

Cover photo

Aspen with its fall foliage dominates the landscape at Chriss Lake, Boulder Mountain, Dixie 

National Forest (photo: Mary O’Brien, Grand Canyon Trust, used with permission). 

All Rocky Mountain Research Station publications are published by U.S. Forest Service employees and 

are in the public domain and available at no cost. Even though U.S. Forest Service publications are not 

copyrighted, they are formatted according to U.S. Department of Agriculture standards and research 

findings and formatting cannot be altered in reprints. Altering content or formatting, including the cover 

and title page, is strictly prohibited.
Authors

Stanley G. Kitchen is a Research Botanist with the USDA Forest Service, Rocky Mountain 

Research Station in Provo, Utah.

Patrick N. Behrens is a Regional Silviculturalist (retired) with the USDA Forest Service, 

Intermountain Region in Ogden, Utah.

Sherel K. Goodrich is a Forest Ecologist (retired) with the USDA Forest Service, Ashley National 

Forest in Vernal, Utah.

Ashley Green is the Habitat Section Chief for the Utah Division of Wildlife Resources in Salt Lake 

City, Utah.

John Guyon is a Forest Pathologist with the USDA Forest Service, Intermountain Region in 

Ogden, Utah.

Mary O’Brien is the Utah Forests Program Director for the Grand Canyon Trust in Castle Valley, 

Utah.

David Tart is a Regional Ecologist with the USDA Forest Service, Intermountain Region in Ogden, 

Utah.

Acknowledgments

We thank the Utah Forest Restoration Working Group member organizations and their 

designated representatives for a sustained commitment to provide improved management 

tools to government and nongovernment forest managers. We thank R. Justin DeRose, James 

N. Long, Karen E. Mock, and Douglas H. Page for technical review and insightful suggestions 

for improvement of an early version of this document. We also thank Adam Solt for technical 

assistance facilitating the revision process.

Scope and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Aspen Restoration in Utah: Ecological Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Aspen Functional Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

 Upland Persistent Aspen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

 Upland Seral Aspen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

 Riparian Aspen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Summary of Major Challenges to Aspen Restoration . . . . . . . . . . . . . . . . . . . . . . . . . 11

Reference Areas as Tools for Aspen Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Aspen Restoration Decision Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Step 1. Assess General Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

 Phase 1: Map Extent and Spatial Distribution of Aspen Functional Types

 in the Landscape or Other Area of Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

 Phase 2: Analyze Variability in Stand Composition, Structure, 

 and Successional Status Within Functional Types . . . . . . . . . . . . . . . . . . . . . . 16

Step 2. Identify Potential Problematic Conditions for Aspen . . . . . . . . . . . . . . . . . . . 17

 Low Levels of Aspen Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

 Low Levels of Aspen Recruitment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

 Evidence of Heavy Browsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

 Shading by, or Competition From, Dense Conifers . . . . . . . . . . . . . . . . . . . . . . . . 21

 Aspen Overstory Less Than 40 Percent Cover, or More Than 100 Years Old . . . 21

 Increasing Sagebrush Cover in a Declining Aspen Stand . . . . . . . . . . . . . . . . . . . 22

 Degraded Understory Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

 Insects and Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Step 3. Identify Probable Agents or Underlying Cause(s) 

 for Problematic Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

 Altered Disturbance Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

 Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

 Excessive Browsing by Wild or Domestic Ungulates . . . . . . . . . . . . . . . . . . . . . . . 25

 Recreation and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Step 4. Select Appropriate Response Option(s) 

 that Address the Causes of Problematic Conditions . . . . . . . . . . . . . . . . . . . . . . . 28

 Response Option Selection—General Recommendations . . . . . . . . . . . . . . . . . . 28

 A Menu of Possible Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Step 5. Implement Appropriate Monitoring to Establish Baseline Conditions

 and Detect Changes Related to Application of Selected Restoration Activities . . . 32

Step 6. Reassess and Adapt by Using Steps 1 Through 5 . . . . . . . . . . . . . . . . . . . . 33

Key Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Appendix A: Aspen Restoration Guidelines: Development and History . . . . . . . . . . . . . 43

Appendix B: Common Diseases and Insects of Aspen . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Appendix C: Comparison of Key Attributes of Forest Service Monitoring Methods 

 for Aspen Ecosystems, and a Method Used by Brigham Young University . . . . . . . . 49

Appendix D: Literature Relevant to Aspen in Utah and the Intermountain West . . . . . . . 53

Contents

U.S. Forest Service RMRS GTR-390. 2019. 1

Scope and Purpose

Healthy quaking aspen (Populus tremuloides; hereafter aspen) 

communities are characterized by high productivity and structural diversity 

(fig. 1). High-functioning, nonriparian aspen forests support a more diverse 

array of plant and animal species than any other upland forest type in the 

western United States (Chong et al. 2001; Mueggler 1985). In addition, 

aspen communities provide or enhance critical ecosystem services such as 

functioning as living firebreaks, beneficial soil water storage and discharge, 

and habitat for sensitive wildlife species; and are valued for recreational 

activities and aesthetic qualities.

Approximately 9 percent (5.1 million ac, or 2.1 million ha) of the land 

area in Utah is forested, excluding pinyon-juniper woodlands (10.7 million 

ac, or 4.3 million ha) (Werstak et al. 2016). Aspen is present, either as the 

dominant tree species (1.6 million ac, or 0.6 million ha) or as a subdominant 

(1.2 million ac, 0.5 million ha) on just over half (55 percent) of the forested 

lands in the State. The abundance of aspen is similar or less in other 

Intermountain States (Frescino et al. 2016; Witt et al. 2012).

Forested lands in Utah occur on lands administered by the Bureau of 

Land Management, U.S. Department of the Interior (39 percent); Forest 

Service, U.S. Department of Agriculture (34 percent); private interests 

Figure 1—A diverse understory is characteristic of a healthy aspen stand, such as 

this stand at the Mason Draw exclosure, La Sal Mountains, Manti-La Sal National 

Forest (photo credit: Faith Bernstein, Grand Canyon Trust, used with permission).
2 U.S. Forest Service RMRS GTR-390. 2019.

(15 percent), and State and other agencies (12 percent) (Werstak et al. 2016). 

Aspen is found across all ownership classifications, but is most prominent on 

lands administered by the Forest Service. 

Researchers disagree on aspen status and trend in the Intermountain 

West. Kay and Bartos (2000) report that aspen has decreased throughout 

the region during the 20th century, and that aspen-dominated acreage 

within the five national forests of Utah has declined by 50 percent or more. 

Other research based on Forest Service, Forest Inventory and Analysis 

data (Werstak et al. 2016) indicates that aspen in Utah has not decreased in 

area in the last 20 years, and that the rate of aspen decline may have been 

exaggerated. Differences in interpretation about status and trends in aspen 

may be related to the spatial and temporal scales on which inferences are 

based (Kulakowski et al. 2013). 

Any decline of aspen is cause for concern, as aspen in the West does 

not reliably reproduce from seed and thus the loss of an aspen stand may be 

considered to be permanent. Some recent aspen declines have been attributed 

to severe drought conditions interacting with multiple biotic stressors, 

especially in areas of marginally suitable habitat (Worrall et al. 2013) (fig. 2). 

Rehfeldt et al. (2009) predict climate change-driven losses in suitable aspen 

habitat of 40 to 94 percent in the western United States by the end of the 21st 

century. 

Figure 2—Three lone trees remain of this aspen stand on a marginal microsite on 

Monroe Mountain, Fishlake National Forest. Increased frequency and severity of 

drought interacting with other stressors lead to canopy decline and recruitment failure. 

In this near-terminal example, sagebrush steppe has almost completely replaced 

the aspen community (photo: Ellen Morris-Bishop, Grand Canyon Trust, used with 

permission). 
U.S. Forest Service RMRS GTR-390. 2019. 3

Aspen management decisions in Utah have substantial ecological, social, 

and economic implications. The aspen management strategies that are most 

likely to achieve desirable outcomes are those grounded in scientific research 

and careful observation. Land managers are urged to consider landscapescale conditions, as well as stand-specific factors, when making management 

decisions about the suitability of disturbance and protection options to restore 

aspen.

The term “restoration” can mean different things to different people, 

and definitions can range from broad concepts to narrow applications. Here, 

“aspen restoration” will refer primarily to actions that improve aspen health 

or resilience, or both, where the species is currently present and where 

environmental conditions are suitable for long-term persistence.

We intend the strategies and guidelines outlined herein as a road 

map for use by managers of public and private forested lands to identify, 

design, and implement projects to restore aspen forests. We recommend 

that managers follow a multistep pattern, namely: (1) assess the condition 

of aspen, (2) identify potential problematic conditions, (3) determine the 

causal factors that contribute to the identified problematic conditions, (4) 

select from a range of appropriate response options to address the causes of 

those conditions, (5) implement appropriate monitoring to establish baseline 

conditions and to detect changes related to treatments or management 

actions, and (6) reassess and adapt by using steps 1 through 5. Use of this 

approach will allow managers to learn more about aspen management in 

general, and to determine whether different treatments are warranted to 

achieve success. 

This set of guidelines is a revised and updated version of an earlier 

set prepared by the Utah Forest Restoration Working Group (2010) (see 

Appendix A). The principles and practices described in this working 

document will continue to be tested in aspen forests in Utah and elsewhere in 

the Intermountain West.
4 U.S. Forest Service RMRS GTR-390. 2019.

Aspen Restoration in Utah: Ecological Considerations

At the landscape scale, aspen condition varies due to variability in 

natural processes including fire, succession, extreme climatic events, and 

biotic agents; and due to human influences. For instance, much of the 

historical (20th-century) loss of aspen-dominated acreage is attributable to 

“encroachment” and overtopping by conifers (Kay 1997) (fig. 3). However, 

conifer presence with aspen does not by itself indicate unhealthy conditions 

or an inherent need for restoration. Aspen and conifers have commingled, 

and will continue to coexist, across a broad continuum of successional stages 

that are regulated by complex and variable fire regimes and other disturbance 

processes that vary across time and space (Heyerdahl et al. 2011). These 

patterns are in turn modified by oscillations and interactions of climate with 

wildlife and human activity. Restoration activities should have a landscapescale goal of creating conditions that support a balance of successional stages 

that collectively foster broad-scale sustainability and resilience to a wide 

range of disturbances. Even if we cannot precisely determine the natural 

range of variation in historical conditions, managing for resilience gives us 

the best chance for minimizing losses to future climate change.

Figure 3—The aspen in this stand on Gentry Mountain, Manti-La Sal National Forest, 

appears vigorous but is approaching an ecological threshold where shading by dense 

subalpine fir will lead to aspen decline. Without periodic disturbance, the conifer 

recruits into and eventually displaces aspen at some locations (photo: Stanley G. 

Kitchen, USDA Forest Service). 
U.S. Forest Service RMRS GTR-390. 2019. 5

Fire is a keystone disturbance process that shapes all but the wettest, 

driest, or most fire-protected plant communities of North America (Frost 

1998). Fire resets successional processes in upland aspen (see next subsection 

for description of aspen functional types), and favors shade-intolerant aspen 

by initiating pulses of root suckering and seedling establishment (fig. 4). 

Therefore, variations in fire regimes regulate the relative importance or 

dominance of aspen and conifers spatially and through time, often creating 

complex vegetation mosaics—legacies of past disturbance (Shinneman et al. 

2013; Tepley and Veblen 2015) (fig. 5). Reconstructed, multicentury fire and 

forest histories document a broad range of historical fire regimes associated 

Figure 4—(a) Vigorous aspen regeneration occurred during the first year after 

the Box Creek Fire at Monroe Mountain, Fishlake National Forest. Initial postfire 

suckering of aspen is often dense, especially when fire severity is high. (b) Recruiting 

young aspen within a burn perimeter contrasts with the mixed aspen-conifer stands 

that did not burn in a relatively recent fire at East Mountain, Manti-La Sal National 

Forest. Over time, postfire aspen suckers grow to maturity, thus resetting forest 

succession (photos: Stanley G. Kitchen, USDA Forest Service). 

a

b
6 U.S. Forest Service RMRS GTR-390. 2019.

with Utah aspen including frequent, low-severity surface fire; infrequent 

(possibly rare), high-severity fire; and mixed-frequency, mixed-severity fire 

that varied through time and across space (Heyerdahl et al. 2011).

Less is known about the role of fire and the nature of historical fire 

regimes in upland persistent aspen where conifers are largely absent 

(Shinneman et al. 2013). Though current thinking suggests that sustained 

crown fires are highly unlikely in this type (DeRose and Leffler 2014), the 

possibility of high canopy mortality caused by lower intensity burning of 

herbaceous, understory fuels—leading to pulsed regeneration—cannot be 

discounted. The necessary curing of what are typically burn-resistant fuels 

occurs most reliably in the fall when the probability of lightning ignitions 

from summer thunderstorms has diminished. This timing suggests that Native 

American ignitions may have been important where late-season fires in 

persistent aspen prevailed (Kitchen 2016). 

In many areas today, a high proportion of late-seral, conifer-dominated 

stands—including stands in which live aspen tree density is extremely low—

has been attributed to the absence of fire over the past 100 to 150 years (Kay 

1997). The effects of this change in fire regimes is especially notable for 

areas in which historical fire-free intervals were short to moderate in length. 

Late 19th-century disruption in natural fire regimes is well documented 

for western U.S. forests and has been attributed to the cumulative effects 

of livestock removal of fine fuels, disruption of Native American burning 

practices, and various levels of fire suppression (Covington and Moore 1994; 

Kitchen 2016). Early 20th-century climatic conditions were favorable for 

conifer establishment and very likely played an important and synergistic 

role with reduced fire in the regionwide shift to conifer dominance (Rogers 

et al. 2011). Forest stands which historically experienced long (100+ years) 

fire-free intervals are least impacted by 20th-century changes in fuels and fire 

management (Baker 2009).

Figure 5—This aspen-conifer dominated landscape on Monroe Mountain, Fishlake 

National Forest, contains vegetation patches in various stages of postdisturbance 

succession (photo: Aaron Rhodes, Brigham Young University, used with permission).
U.S. Forest Service RMRS GTR-390. 2019. 7

Expected warming and drying conditions in our region may promote 

disturbance patterns that are very different from what we have seen in the 

recent past (Littell et al. 2009; Westerling et al. 2006). Though we cannot 

predict the future with precision, we can encourage adaptive management 

strategies that enhance resilience and provide options for future generations. 

Taking a long-term view may mean, for example, adopting management 

practices that incorporate more frequent fire to promote aspen suckering or 

seedling establishment—as opposed to actively thinning conifer regrowth for 

short-term aspen advantage.

Population dynamics for ungulates and their predators changed 

dramatically in North America with Euro-American settlement, which in turn 

effected changes in browse pressure in wildland ecosystems. Variable levels 

of browsing and grazing within aspen communities by wild and domestic 

ungulates is another major consideration when planning aspen restoration 

(Weisberg and Bugmann 2003). Healthy aspen stands tend to sprout 

prolifically after rapid overstory mortality, but heavy browsing or grazing 

pressure by ungulates can greatly reduce chances of successful recruitment 

(Britton et al. 2016; Hessl and Graumlich 2002; Rogers and Mittanck 

2014) (fig. 6). Aspen seedlings that establish following fire are particularly 

vulnerable to ungulate herbivory.

Figure 6—Aspen is both heavily browsed and restricted to protected locations 1 year 

after the Box Creek Fire at Monroe Mountain, Fishlake National Forest. Excessive 

postdisturbance browse pressure is evident where suckers are heavily browsed 

or restricted to protected locations such as within shrubs or under logs. If pressure 

persists, postdisturbance recovery can fail and aspen will be lost (photo: Stanley G. 

Kitchen, USDA Forest Service). 
8 U.S. Forest Service RMRS GTR-390. 2019.

Variable intensity and timing of herbivory, in combination with changes 

in fire regimes, logging practices, and even high genetic variability among 

clones can alter expected outcomes (Britton et al. 2016; Kanaga et al. 2008). 

Thus, management decisions on different sites and at different spatial scales 

should attempt to account for these factors to the extent possible.

In sum, no guidelines for aspen management can anticipate all situations. 

The intent here is to promote holistic thinking in management decisions. 

When action precedes understanding—of either the larger ecological 

context or the agents operating on aspen in specific sites—the probability of 

irrevocable loss of aspen increases. Conversely, failure to act can also yield 

negative consequences. Predecision and postdecision monitoring is critical 

when management outcomes are uncertain. Documentation of restoration 

failures, as well as successes, is an important component of management. 

Aspen communities are typically classified based on the suitability 

for conifer establishment and growth, differences in ecological processes 

(i.e., succession), and the physical environment (fig. 7). Although distinct 

aspen types are defined for convenience, the environmental conditions and 

ecological processes that define these types vary incrementally, suggesting 

that the designation of discrete classes—although useful—is largely artificial 

in nature. With that caveat, we provide generalized definitions for three 

primary aspen functional types found in Utah: upland persistent aspen 

(commonly called stable or pure aspen), upland seral aspen, and riparian 

aspen.

Aspen 

Functional Types

Figure 7—Three aspen functional types are present on this landscape near 

Strawberry Peak, Ashley National Forest. Upland persistent aspen occupies broad 

ridge tops, upland seral aspen occurs with conifers on steep slopes, and riparian 

aspen follows drainage bottoms (photo: Stanley G. Kitchen, USDA Forest Service). 
U.S. Forest Service RMRS GTR-390. 2019. 9

Upland Persistent Aspen 

(Commonly Called Stable or Pure Aspen)

Aspen dominates the overstory in all stages of succession, and 

regeneration and recruitment are generally continuous or pulsed but may 

also be episodic. Conifers are absent, or, if they are present, numbers and 

importance remain sufficiently low through time such that they have minimal 

impact on aspen or understory species (fig. 8). Stands of upland persistent 

aspen range in size and connectivity from small isolated stands to large, more 

or less continuous stands.

Upland Seral Aspen

Upland seral aspen is found on sites favorable for conifer recruitment 

and growth and co-occurs with one or more conifer species. The relative 

abundance of aspen and conifers depends on the time since last disturbance—

aspen dominates early stages and conifers dominate late stages of succession 

(fig. 9). Aspen recruitment may be episodic in response to synchronized 

canopy mortality (aspen and conifers) related to discrete disturbance events 

(e.g., fire or other disturbance). But aspen also may respond to small gap 

formation in a more nuanced fashion, and thus is maintained across a wide 

range of spatial scales.

Riparian Aspen

Riparian aspen grows in soils that are affected by their proximity to 

surface water (fig. 10). Conifer abundance and importance and successional 

processes vary. 

Figure 8—Multiaged aspen stands on East Mountain, Manti-La Sal National Forest, 

are examples of the upland persistent aspen functional type (photo: Stanley G. 

Kitchen, USDA Forest Service). 
10 U.S. Forest Service RMRS GTR-390. 2019.

Figure 9—This aspen, pine, and spruce stand in the Tushar Mountains, Fishlake 

National Forest, typifies the upland seral aspen functional type (photo: Stanley G. 

Kitchen, USDA Forest Service). 

Figure 10—This stand 

on Monroe Mountain, 

Fishlake National 

Forest, is characteristic 

of the riparian aspen 

functional type (photo: 

Mary O’Brien, Grand 

Canyon Trust, used with 

permission). 
U.S. Forest Service RMRS GTR-390. 2019. 11

Other aspen stand types exist (e.g., lithic aspen or snow-pocket aspen), 

but these three types are by far the most spatially extensive, and hence the 

major ones for which management or restoration decisions are repeatedly 

made in Utah forests. These guidelines focus on upland persistent aspen and 

upland seral aspen. Because ecological processes for these vegetation types 

differ, management strategies may also need to differ to maximize resilience 

in these two general types of aspen forest. Guidelines for riparian aspen 

restoration will be developed independently for a separate publication.

Finally, these guidelines focus on restoration of aspen forests, 

specifically the trees; but the maintenance of healthy aspen communities—

including understory shrubs, grasses, and forbs—is of equal importance as 

a management focus. Given that aspen stands provide critical ecosystem 

services and support disproportionately high numbers of vascular plant, 

insect, bird, and mammalian species, an increase in aspen area may be 

expected to yield much greater increases in species diversity than would 

increases of other forest types (Chong et al. 2001).

• In many areas of Utah, conifer establishment and growth were favored in 

the early 20th century by a moist climate and lack of fire (Rogers et al. 

2011). Today, there is an overrepresentation of late-seral conditions, in 

which conifers are increasing in density and replacing aspen. 

• Aspen sucker abundance and growth following crown-killing disturbance 

may be reduced by domestic and wild ungulate browsing. In cases where 

pressure is high, browsing can result in complete recruitment failure and 

loss of aspen from a site in a matter of a few years (Britton et al. 2016; 

Hessl and Graumlich 2002). Small-scale pulsed recruitment associated 

with forest gap formation in mixed aspen-conifer stands and pulsed 

or continuous recruitment typical in upland persistent aspen stands 

are particularly sensitive to even moderate levels of chronic browse 

pressure, which may cause a loss of age cohorts and a reduction in clonal 

resilience (Rogers and Mittanck 2014). This loss of clonal resilience can 

lead to a downward spiral, resulting in loss of clones occupying the site 

(Worrall et al. 2013).

• Severe, prolonged drought due to a warming and drying climate has 

contributed to aspen decline in some areas, particularly stands at lower 

elevations (Worrall et al. 2013). 

• Budgetary, social, administrative, economic, technical, and ecological 

constraints may limit response options available to land managers 

charged with addressing these declines.

• Public understanding of the importance of aspen, the implications of 

aspen decline, and the rationale for selection of any given management 

response to decline varies from place to place. Consequently, there are 

varying levels of support for aspen treatment or management.

• Competing priorities may dilute support for restoration efforts in aspen. 

For example, wood fiber production, wildlife management, livestock 

grazing, human habitation, and fire suppression—in combination or 

separately—can complicate implementation of management actions 

deemed necessary for long-term aspen health.

Summary of Major 

Challenges to Aspen 

Restoration
12 U.S. Forest Service RMRS GTR-390. 2019.

Reference Areas as Tools for Aspen Restoration

Aspen restoration programs benefit when management targets are 

informed by quantifiable reference conditions. Reference areas help separate 

climate effects (e.g., drought) from management effects and provide 

indications of aspen community (overstory and understory) potential. 

Repeated documentation of conditions and changes within reference areas 

can provide understanding of aspen recruitment, disease, drought, understory 

development, and succession over long periods of time, shedding light on 

complex aspen ecosystem dynamics. As such, reference areas have the 

potential to provide multiple values beyond those associated with restoration. 

Reference areas should be selected to represent the full range of 

environmental conditions, thereby increasing opportunities to address a 

variety of issues (fig. 11). Areas large enough to capture a wide range of 

environmental variation, and to include ecological processes that operate 

across variable spatial scales, are preferred. Ideally, individual reference 

areas include a range of aspen types and are thus useful in addressing 

different questions. Areas that retain natural processes and composition 

are good candidates for reference areas. In contrast, aspen stands used for 

dispersed camping or livestock grazing, or those with high browse use by 

native ungulates, do not make good reference areas. 

Although long-term exclosures are helpful in disentangling cause-andeffect relationships (fig. 12), their value as reference areas is limited for 

several reasons. For example, full or high-fence exclosures do not allow 

the full complement of natural processes (i.e., ungulate herbivory), are 

expensive to maintain, and are typically small in size. Multi-unit exclosures 

may affect animal behavior in unplanned ways. For example, wild ungulates 

may be drawn to ungrazed patches caused by cattle-exclosure subunits when 

livestock grazing outside the exclosure is heavy. Exclosure maintenance is 

an ongoing requirement, particularly when livestock are drawn to ungrazed 

“green spots” in the landscape. Within these limitations, exclosures can 

be useful, especially when conditions are documented periodically. Biggame exclosures provide insight into the effects of wild ungulates, or the 

cumulative effects of wild and domestic ungulates on local vegetation. 

Similarly, monitoring data from a high-fence exclosure with an 18-in (46-cm) 

gap between soil and bottom edge of fence (to allow deer passage only), can 

provide some evidence of deer impacts separate from those of elk or cattle.

Because Utah’s aspen occurs across a wide range of physical and 

biological conditions, a network of suitable areas that include the full range 

of representative environments should be identified and maintained. Table 

1 provides a comparison of characteristics for a noncomprehensive list of 

example areas in Utah that qualify as aspen reference areas. 
U.S. Forest Service RMRS GTR-390. 2019. 13

Figure 11—(a) Twelve Hundred 

Dollar Ridge, Ashley National 

Forest, and (b) Cottonwood 

Allotment, Tushar Mountains, 

Fishlake National Forest, are aspen 

reference areas where understory 

vegetation is dominated by native 

perennial grasses; (c, d) in other 

reference areas, such as Walt 

Muegler-Butler Fork Research 

Natural Area, Uinta-WasatchCache National Forest, tall forbs 

with shrubs are often present in 

a subdominant to codominant 

role (photo a: Stanley G. Kitchen, 

USDA Forest Service; b: Mary 

O’Brien, Grand Canyon Trust, used 

with permission; c and d: Wayne 

Padgett, USDA Forest Service). 

Figure 12—The Grindstone Flat exclosure on the Tushar Mountains, Fishlake 

National Forest, was originally established in 1934 with two parts: a high fence to 

exclude all ungulates, and a low fence to exclude cattle only. A wildfire burned through 

the area in 1996 and the exclosure was rebuilt the next year. The exclosure is used 

to demonstrate the effects of long-term protection from herbivory on aspen. (photo: 

Stanley G. Kitchen, USDA Forest Service).

a b

c d
14 U.S. Forest Service RMRS GTR-390. 2019.

Reference areas 

with aspen present Size (ac) Size (ha) Location

Aspen 

type(s)

Time without 

livestock Description

Uinta-Wasatch-Cache National Forest

Walter F. MuegglerButler Fork Research 

Natural Area

1,270 510 Big Cottonwood 

Canyon

Persistent 

Seral 

Riparian

100+ years Established 

specifically for 

aspen; mixed 

conifer zone

Boxelder Peak 

(east side)

700 280 American Fork 

Canyon

Persistent 

Seral

25+ years 

(1990–present)

Mixed conifer zone

Mill Peak 4,000 1,600 American Fork 

Canyon

Persistent 

Seral

25+ years 

(1990–present)

Mixed conifer zone

Alpine Loop 1,200 500 American Fork and 

Provo Canyons 

along State Road 92

Persistent 25+ years 

(1990-present)

Mixed conifer zone

Timpooneke Road 350 140 North side of 

Mount Timpanogos 

Wilderness

Persistent 

Seral

25+ years 

(1990-present)

Mixed conifer and 

subalpine zones

Strawberry Valley 

Project Lands

64,000 

(~9,700 

ac 

aspen)

26,000 

(~4,000 

ha 

aspen)

Strawberry Valley Persistent 

Seral

25+ years 

(1990–present)

Mixed conifer zone

Ashley National Forest

Vernal Municipal 

Watershed

6,886 2,789 Ashley Creek 

drainage

Seral 

Persistent

42+ years 

(1973–present)

Mixed conifer zone

Twelve Hundred Dollar 

Ridge

60 24 4.5 mi (7.2 km) NE 

of Strawberry Peak

Persistent 

Seral

Unknown; isolated 

by steep terrain 

and distance to 

water

Native perennial 

grasses dominate 

understory; mixed 

conifer zone

Fishlake National Forest

Nielson Canyon 700 280 Monroe Mountain Persistent 

Seral

Unknown; remote Mixed conifer and 

subalpine zones

Cottonwood Allotment 46,516 

(~884 ac 

aspen) 

18,839 

(~358 ha 

aspen)

East side of Tushar 

Mountain Range

Persistent 

Seral 

35+ years Subalpine zone

Grindstone Flat 

Exclosure

0.1 0.04 Tushar Mountain 

Range

Seral 80+ years Published 

research; 

subalpine zone

Manti-La Sal National Forest

White Mesa Cultural 

Conservation Area

28,000 11,300 North Elk Ridge 

– Monticello

Persistent 

Seral

15+ years; fenced 

from trespass 

livestock in 2014

Treatments 

planned

Dixie National Forest

Timbered Cinder Cone 

Research Natural Area

640 260 Markagunt Plateau Seral Never had 

livestock

Subalpine zone; 

protected from 

livestock by lava 

flows

Table 1—Size, administrative unit (national forest), aspen functional types, livestock-free status, and general information for 

representative aspen reference sites in Utah.
U.S. Forest Service RMRS GTR-390. 2019. 15

Aspen Restoration Decision Chain

This section describes six primary steps for use in making decisions 

about aspen forest restoration. It provides the framework and logic for a 

step-by-step process to identify restoration needs and to select and validate 

appropriate practices to achieve restoration goals. Literature citations and 

brief descriptions support the application of the framework across the diverse 

environmental and cultural landscapes that exist in Utah. Our hope is that it 

will stimulate discussions within groups of resource specialists and others 

engaged in planning aspen restoration. Bartos (2007) and Shepperd (2001) 

describe approaches that parallel the process described in more detail here.

Step 1. Assess general conditions

Step 2. Identify potential problematic conditions 

Step 3. Identify probable agents or underlying cause(s) for problematic 

conditions

Step 4. Select appropriate response option(s) that address the probable agents 

or root causes and associated problematic conditions

Step 5. Implement appropriate monitoring to establish baseline conditions 

and detect changes related to application of selected restoration 

activities 

Step 6. Reassess and adapt by using steps 1 through 5

These guidelines are designed to be flexible across small to large (few to 

several thousand acres) spatial scales. Given apparent trends in aspen health, 

abundance, and recruitment across Utah, aspen restoration planning and 

implementation efforts must be scaled up to adequately address conditions 

manifested at broad spatial scales, and to effect meaningful change in aspen 

health trajectories across the landscape (Bartos 2007). For this reason, largescale aspen restoration projects (even if implemented incrementally) are 

preferred to truly benefit aspen forest communities over the long term.

Treatments, including simple management modifications (i.e., passive 

management) on relatively small areas can be useful for testing response 

options on specific locations, and should not be ruled out when they are used 

as part of an adaptive management approach. Small treatment areas may also 

be appropriate when aspen clones of interest are naturally small in size and 

scattered across the geophysical setting. To make the most positive change on 

the trajectory of aspen in a watershed, multiple small stands may need to be 

treated together.

Six Steps of the 

Aspen Restoration 

Decision Chain
16 U.S. Forest Service RMRS GTR-390. 2019.

Step 1. Assess 

General Conditions

The first step in the aspen restoration decision process is to compile an 

accurate picture of the status of aspen within and across ownerships and 

jurisdictions of the area of interest. We recommend a two-phase process; 

however, data collection and compilation efforts are complementary and may 

run concurrently. 

Phase 1 

In the first phase, extent and spatial distribution of aspen functional types 

(i.e., upland persistent and seral aspen and riparian aspen) on the landscape or 

other area of interest are mapped. Validation of map accuracy through ground 

or aerial surveys, or both, is highly recommended. Maps and supplemental 

spatial data that inform the decision process could include:

• Wildlife use and needs (e.g., big-game use patterns and habitat critical 

for species of management concern);

• Livestock use (e.g., water developments, allotment and pasture 

boundaries, grazing plans);

• Recreational use patterns (e.g., dispersed camping sites, trails for allterrain vehicles [ATVs]);

• Infrastructure (roads, buildings, developed campgrounds);

• Private inholdings;

• Special designations (e.g., wilderness, designated roadless areas, 

municipal watersheds, timber management areas); and

• Historical disturbance regimes (e.g., fire).

Phase 2 

In the second phase, the general condition of aspen within each 

functional type is assessed from data already available or collected for 

this purpose. Current successional trajectories should be assessed by 

assuming that no passive (changes in management) or active (treatments) 

restoration options are pursued. Key parameters may include estimates of 

stand composition and structure (e.g., variability in live-tree density, aspento-conifer ratio, age- and size-class structure), abundance of regeneration 

and recruits, and understory composition. If data are not already available, 

the nature of these data typically requires some level of boots-on-theground effort to ensure conditions are accurately assessed. Data for Step 

2 (identification of problematic conditions) may be collected as part of 

condition surveys to improve operational efficiency.

Once completed, the general assessment (Step 1) provides a foundation 

for determining (1) whether or not aspen restoration is needed, (2) the kinds 

of barriers and risks that will need to be addressed in the restoration strategy, 

and (3) a framework for setting realistic goals and metrics for determining 

when those goals have been met.

Although some indication of possible restoration response options can be 

made at this time, final decisions should wait until after potential problematic 

conditions (Step 2) and the probable agents responsible for those conditions 

(Step 3) are clearly identified.
U.S. Forest Service RMRS GTR-390. 2019. 17

Although the focus of Step 1 should be at the landscape level, it is 

important to recognize and map the presence of small isolated stands that 

may be biologically important and genetically unique. These stands may be 

particularly susceptible to climate change or current and future management 

practices and may merit special consideration when potential treatment or 

management options are evaluated.

While conducting aspen condition assessments, and opportunistically 

at other times, managers should document the presence or absence of 

factors known to be reliable indicators of risk to aspen ecosystems. These 

risk factors provide a basis for managers to prioritize stands for restoration 

consideration (table 2). 

Low Levels of Aspen Regeneration

Low levels of regeneration (suckers <6 ft tall) (table 3), especially for 

older, persistent aspen stands with open or declining canopies (aspen canopy 

Step 2. Identify 

Potential Problematic 

Conditions for Aspen

Risk indicator or potential problematic 

conditions

Persistent 

aspen

Seral 

aspen

Importance

Low levels of aspen regeneration Primary Secondary

Low levels of aspen recruitment Primary Secondary

Evidence of heavy browsing (i.e., hedged shoots) Primary Primary

Shading by or competition with dense conifers Not applicable Primary

Aspen overstory <40% cover 

 or trees >100 years old Primary Secondary

Increasing sagebrush cover in a declining 

 aspen stand Secondary Secondary

Degraded understory vegetation (shrubs, 

 grasses, forbs) Secondary Secondary

Insects and pathogens Secondary Secondary

Table 2—Common indicators of potential risk to aspen communities, and their 

importance in persistent and seral aspen stands.

Table 3—Levels of aspen regeneration and recruitment as indicators of capacity for 

stand self-replacement.

Aspen regeneration levels (suckers <6 ft [2 m] height)

>1,000/ac >2,500/ha self-replacing

500–1,000/ac 1,250–2,500/ha marginal

<500/ac <1,250/ha not self-replacing

Aspen recruitment levels (stems ≥6 ft and <canopy height)

<500/ac <1,250/ha not self-replacing, 

recommend investigation
18 U.S. Forest Service RMRS GTR-390. 2019.

cover <40 percent) (Bartos and Campbell 1998), may be an indication that 

stands are not self-replacing (Bartos and Campbell 1998; Britton et al. 2016; 

Campbell and Bartos 2001; Kurzel et al. 2007; Mueggler 1989; Rogers et al. 

2010) (fig. 13). However, regeneration for aspen stands with high densities 

of healthy trees and high canopy cover (typically, but not always, young 

to middle-aged stands) may be suppressed by apical dominance; hence, 

low densities of immature stems alone are not indicative of problematic 

conditions (fig. 14). Such stands often arise after disturbances (e.g., fire, 

disease, insects), and may thrive with low levels of regeneration for an 

extended period. 

Lack of aspen regeneration alone is an unreliable indicator of risk for 

seral aspen stands as well. Regeneration for healthy stands of this functional 

type is typically episodic and prolific with the timing of sucker initiation 

closely linked to synchronized death of overstory trees (e.g., after fire).

Low Levels of Aspen Recruitment

In persistent aspen communities, the presence of abundant regeneration 

alone is not sufficient to ensure that stands are self-replacing. In selfreplacing stands, evidence of adequate recruitment (subcanopy stems ≥6 ft 

tall) (table 3) may need to be present if a stand is to be considered healthy, 

especially for mature stands with open or declining canopies (Bartos and 

Campbell 1998; Britton et al. 2016; Campbell and Bartos 2001; Kurzel et 

al. 2007; Mueggler 1989; Rogers et al. 2010). A minimum density of 500 

Figure 13—Poor regeneration in aging persistent aspen will lead to loss of the 

stand if not corrected, Monroe Mountain, Fishlake National Forest (photo: Stanley G. 

Kitchen, USDA Forest Service).
U.S. Forest Service RMRS GTR-390. 2019. 19

Figure 14—Regeneration under persistent aspen may be limited due to apical dominance and competition by overstory 

trees. Sucker density for (a, b) this upland persistent aspen stand in the Ashley National Forest was estimated at 253 stems 

per ac (625 stems per ha) with all stems less than 6 ft (2 m) tall. Canopy tree density was measured at 664 stems per ac 

(1,641 stems per ha). A short distance away (c, d) in the same stand, sucker density was estimated at 6,956 stems per ac 

(17,188 stems per ha)—a 27-fold increase—with 35 percent of the shoots taller than 6 ft. In this portion of the stand, 

recent mortality had reduced live tree density in the overstory about 60 percent to 253 stems per ac (625 stems per ha) 

demonstrating that pulsed regeneration can occur when apical dominance and competition are reduced or lost with periodic 

overstory mortality (photos: Sherel K. Goodrich, USDA Forest Service).

recruits per ac (1,200 per ha) is recommended (Bartos and Campbell 1998) 

(fig. 15). This applies to small isolated stands as well as to larger, more 

continuous stands.

Lack of aspen recruitment is an unreliable indicator of risk for seral 

aspen stands. Recruitment for healthy stands of this functional type is 

typically episodic following disturbance-initiated, synchronized die-off of 

overstory trees. Successful aspen recruitment has been documented (DeRose 

and Long 2010; Kay and Bartos 2000) under the shaded conditions of high 

conifer canopy cover (60–70 percent) where ungulate browsing was not a 

factor. 

a b

c d
20 U.S. Forest Service RMRS GTR-390. 2019.

Figure 15—An estimated recruit (suckers ≥6 ft [2 m] tall) density of 1,000 stems 

per ac (2,500 stems per ha) for this stand in Ashley National Forest with declining 

overstory exceeds the 500 stems per ac (1,200 stems per ha) minimum threshold 

recommended for self-replacing stands (photo: Sherel K. Goodrich, USDA Forest 

Service). 

Evidence of Heavy Browsing 

Chronic repeated browsing will give aspen shoots a hedged or shrubby 

appearance, a condition that is easily detected from walking surveys 

(fig. 16). In extreme cases, live shoots may be restricted to the relative 

protection of shrub (e.g., sagebrush) canopies or log piles (fig. 17). Stems 

Figure 16—Chronic browsing produces aspen that has a shrubby or hedged 

appearance, and a low probability of ever recruiting into the canopy (photo: 

Faith Bernstein, Grand Canyon Trust, used with permission). 
U.S. Forest Service RMRS GTR-390. 2019. 21

Figure 17—A sagebrush plant protects hedged aspen (photo: Stanley G. Kitchen, 

USDA Forest Service). 

with heavily clipped apical meristems rarely recruit beyond the reach of 

browsing ungulates. 

Shading by, or Competition From, Dense Conifers 

Replacement by dense conifer forests through succession is a pervasive 

threat to seral aspen stands with long (>100 years) disturbance-free intervals 

(Bartos and Campbell 1998) (fig. 3). Conifer replacement is not a threat 

to persistent aspen stands. Increasing cover of subalpine fir shades aspen 

regeneration and alters soil chemistry in ways that negatively affect aspen 

growth (Calder et al. 2011). These soil changes reduce aspen height growth 

and biomass production and lower the production of defense compounds that 

may deter herbivory (Calder et al. 2011). Decreased light also greatly reduces 

mycorrhizal associations, decreasing aspen’s ability to take up soil nutrients 

(Clark and St. Clair 2011).

The presence of conifers in seral aspen or mixed aspen/conifer stands is 

not by itself an indication of problematic conditions. A dynamic interaction 

between conifer and aspen is characteristic of this functional type, and 

the relative abundance of either in any point in time may be indicative of 

successional stage and site-specific conditions that favor aspen or conifer 

species, or both. Use of historical range of natural variability of aspen and 

conifers at landscape scales is strongly recommended.

Aspen Overstory Less Than 40 Percent Cover 

or More Than 100 Years Old

An open, old, or declining aspen overstory in seral stands is often the 

result of competition from conifers. Persistent aspen stands with an open, 
22 U.S. Forest Service RMRS GTR-390. 2019.

declining overstory (<40 percent) (Bartos and Campbell 1998) are at risk if 

regeneration or recruitment is insufficient (fig. 13). Where both regeneration 

and recruitment are adequate, a declining overstory is less of a concern; we 

would expect the stand to be self-replacing (figs. 14, 15).

Increasing Sagebrush Cover in a Declining Aspen Stand 

Sagebrush species are shade intolerant but can survive in relatively 

open aspen stands. Mueggler (1988) describes an aspen/big sagebrush 

community type. This type may occur as an ecotone between aspen and 

sagebrush communities or in single-clone islands surrounded by sagebrushgrass steppe. In these settings, aspen stands with a declining overstory and 

insufficient regeneration and recruitment can be replaced by sagebrush 

(figs. 2, 13). Aspen stands with sagebrush cover greater than 10 percent may 

be at risk (Bartos and Campbell 1998). These stands may also be particularly 

vulnerable due to browsing or drought (Rogers and Mittank 2014).

Degraded Understory Vegetation 

In addition to the status of trees, understory species (forbs, grasses, or 

shrubs, or a combination thereof) are a major source of aspen community 

diversity and productivity (fig. 11) and may be depleted relative to potential 

(fig. 18). Indicators of understory degradation may include excessive bare 

soil exposure, increased dominance by shrubs, short stature of the herbaceous 

component, or dominance by grazing-tolerant, nonnative species such as 

smooth brome (Bromus inermis) or Kentucky bluegrass (Poa pratensis). 

Reduction of understory vegetation due to grazing and browsing may 

sufficiently reduce fine fuels to prevent the occurrence and spread of 

beneficial low-severity fire (DeRose and Leffler 2014).

Figure 18—(a) Dense cover by a diverse community of native tall forbs, shown here in Ephraim Canyon, Manti-La Sal 

National Forest, or perennial grasses (see figure 11) are characteristic of healthy aspen understory communities. (b) Bare 

ground, low productivity, and dominance by nonnative species are clear signs of understory degradation, shown here on 

Gentry Mountain, Manti-La Sal National Forest (photo a: Stanley G. Kitchen, USDA Forest Service; photo b: Mary O’Brien, 

Grand Canyon Trust, used with permission). 

a b
U.S. Forest Service RMRS GTR-390. 2019. 23

Insects and Pathogens

Aspen are host to a plethora of native insect and disease agents (Hinds 

1985) (fig. 19; see also Appendix B). Episodic disturbance due to these 

agents is a normal part of many aspen ecosystems, and otherwise healthy 

stands can recover from these events. Extreme climatic events such as 

drought and freeze-thaw cycles that are projected to intensify under future 

climate scenarios are expected to reduce aspen vigor through cavitation and 

defoliation events (Anderegg et al. 2012; Worrall et al. 2008). Competition 

with conifers and greater exposure to extreme climatic events can be 

expected to constrain physiological function, resulting in carbon depletion 

that will compromise aspen’s defense against defoliators and pathogens. 

Together these changes lead to decreases in aspen overstory growth rates 

(Shepperd 2001), and reduction in aspen regeneration vigor (Smith and 

Smith 2005).

Figure 19—(a) Bronze poplar borer is a common insect pest recognized by characteristic zigzag galleries under aspen bark. 

(b) Sooty bark canker is a common disease of aspen. These pests are two of the most common agents of aspen mortality 

in western North American landscapes (photo a: Brytten Steed, USDA Forest Service; photo b: John Guyon, USDA Forest 

Service).

a b
24 U.S. Forest Service RMRS GTR-390. 2019.

Problematic conditions provide symptomatic evidence that one or 

more aspects of the environment are no longer compatible with aspen 

sustainability. It is critical to correctly identify and characterize the agent 

or agents responsible for the development and perpetuation of problematic 

conditions manifested across the landscape. It is also essential to distinguish 

root causes of unfavorable conditions from the conditions themselves. For 

example, we have identified the development of dense stands of conifer 

within late successional seral aspen stands as a problematic condition. Thus, 

conifer “encroachment” is best thought of as a symptom rather than a cause 

in relation to aspen decline. 

An understanding of the possible causes of successional imbalance is 

needed to properly inform managers of best strategies for implementing 

corrective measures. In this case, changed fire regimes, climate anomalies, 

or reduced competition for seedlings due to chronic overgrazing of the 

herbaceous understory could each—alone or cumulatively—be contributing 

factors to increased conifer dominance. An understanding of the relative 

importance of each of these factors would in turn provide the basis for 

selecting the most appropriate response (including no response)—or suite of 

responses—to restore the aspen-conifer balance over the long term. 

We propose that there are relatively few root causes for aspen decline in 

Utah. Here we identify major factors, link them to problematic conditions, 

provide examples of how they interact, and make inferences about the likely 

effectiveness of mitigation efforts for each.

Altered Disturbance Regimes

We have established that some forms of disturbance (e.g., fire, conifer 

insect and disease outbreaks, avalanches, wind-throw) favor aspen over 

conifer by temporarily eliminating competition and by inducing pulses of 

aspen regeneration. Sprouting shrubs and herbaceous species that are present 

in the forest understory may also benefit from fire. Calder and St. Clair 

(2012) note that gaps in conifer overstory may be extremely important in 

creating high light conditions within late successional aspen-conifer stands 

that allow aspen to persist without larger disturbance. Shading or competition 

from conifer is often inaccurately blamed for a lack of aspen recruitment. The 

underlying causes described next are more likely to be the sources of the lack 

of recruitment. 

Changes in disturbance regimes (e.g., reduced fire frequency) can lead 

to aspen and understory decline relative to historical conditions, and can 

have cascading detrimental effects. Shaded aspen have reduced root system 

reserves and produce weaker regeneration responses and lower levels 

of secondary compounds that protect against herbivory (Donaldson and 

Lindroth 2007). These changes, in turn, make aspen stands more susceptible 

to even moderate browse pressure and drought. Reduced understory cover 

and vigor result in a reduced forage base for wild and domestic ungulates, 

increasing pressure on aspen suckers and the remaining herbaceous 

understory. 

Step 3. Identify 

Probable Agents or 

Underlying Cause(s) 

for Problematic 

Conditions
U.S. Forest Service RMRS GTR-390. 2019. 25

Response options such as prescribed fire, allowing lightning-ignited 

fires, and actions that remove or thin conifer are designed to correct the 

effects of lack of disturbance. Restoring disturbance regimes may, however, 

require a commitment to multiple actions over time rather than single 

treatment entries.

Climate Change 

The most conspicuous aspect of climate change comes in the form 

of increases in mean temperature over time. Precipitation patterns are 

projected with greater uncertainty, but we can expect changes in annual 

totals, seasonality, and class (i.e., rain versus snow). Although increases in 

atmospheric carbon dioxide (CO2) are not climatic in nature per se, they are 

linked to climate. Elevated CO2 levels have differential impacts on plant 

metabolism among species, and are expected to affect biotic relationships. 

Climate change is a present reality in Utah, as manifested by milder 

winters, increased drought severity, reduced snowpack, and longer fire 

seasons. Future changes are expected to be more extreme and are predicted to 

have major impacts on the distribution, composition, and function of natural 

ecosystems, including aspen communities (Rehfeldt et al. 2009). Stands that 

occur near the warmer and drier limits of aspen are most vulnerable (Rogers 

and Mittanck 2014; Worrall et al. 2013). Climate change is likely to interact 

with other drivers, such as disturbance regimes, to affect the extent and 

distribution of aspen in the future (Anderegg et al. 2012; Yang et al. 2015). 

Today, climate change may be inferred as a root cause of decline in stands 

that show problematic conditions (e.g., declining, weak overstory, weak 

regeneration, increased sagebrush cover in the understory) and where other 

possible root causes (e.g., excessive browse pressure) have been eliminated.

Restoration activities that increase genetic and age-class diversity, or 

reduce the impacts of other stressors, improve aspen resilience to climate 

change. Increased use of high-severity fire is one way to promote younger 

age classes through suckering and increased genetic diversity through 

establishment of seedlings. Susceptible stands may require higher levels of 

protection from browsers to accommodate longer regeneration timeframes 

dictated by more frequent and severe drought and insect or disease outbreaks. 

Treatments that reduce or eliminate competition from conifers are also 

expected to improve resilience to climate change.

Excessive Browsing by Wild or Domestic Ungulates

Browsing of aspen suckers is excessive when the timing or duration 

of domestic and wild ungulate foraging on aspen results in insufficient 

recruitment of aspen shoots into the canopy to ensure that stands are selfsustaining (Hessl and Graumlich 2002; Rogers and Mittanck 2014). Factors 

that affect whether browse thresholds are exceeded may be fairly constant 

(e.g., livestock stocking level or wildlife population size), under continual 

unidirectional change (e.g., reductions in forage base without disturbance), or 

variable from year to year (e.g., winter snowpack, summer monsoonal rains). 

Aspen stands that are near water, on gentle topography, or near livestock 
26 U.S. Forest Service RMRS GTR-390. 2019.

bedding grounds are particularly susceptible to ungulate herbivory (Kay 

2003). Heavy browse pressure on regeneration after aspen canopy removal 

(i.e., fire or clearcut) can result in depletion of root reserves and permanent 

loss of aspen in a matter of a few years (Britton et al. 2016) (fig. 20). Where 

browse pressure is high, ungulates are attracted disproportionately to small 

treatment areas where the flush of growth makes for an easy meal. In some 

cases, multi-unit exclosures can be used to assess the relative impacts of 

different classes of ungulates present at the site.

Figure 20—Aspen and conifers were removed in these clearcuts on the Fishlake 

National Forest on (a) Monroe Mountain and (b) a portion of the giant Pando 

clone with the expectation that the treatments would result in aspen regeneration. 

Subsequently, intense browse pressure prevented aspen recruitment and resulted 

in the complete loss of aspen from treatment areas. Young aspen trees in the 

background of panel b were also in a treated area but are within an exclosure 

protected by an 8-ft (2.4-m) tall fence (photo a: Aaron Rhodes, Brigham Young 

University, used with permission; photo b: Stanley G. Kitchen, USDA Forest Service).

a

b
U.S. Forest Service RMRS GTR-390. 2019. 27

The extent and severity of this driver of aspen instability are likely to 

expand in the future as average snowpack decreases (longer grazing season) 

and the frequency and severity of drought increase with changing climate. 

The greater challenge may be to develop public and institutional support 

for active and passive response options that are effective in proactively 

reducing the amount of browsing of aspen by wild and domestic ungulates to 

sustainable levels.

Recreation and Development 

Although negative effects of recreational activities on aspen are not 

generally observed at the same scales as those previously discussed, they can 

be consequential at local scales (fig. 21). Impacts such as physical damage 

to mature trees and suckers, crushing of herbaceous vegetation, and soil 

compaction and increased soil erosion are generally associated with dispersed 

camping, off-trail use of ATVs, and similar activities (Shepperd et al. 2006). 

The effectiveness of response options such as public education programs and 

development of improved campsites and trails will vary by site, depending 

on the nature of improvements and the degree of public support. 

Exurban development into forested settings is becoming increasingly 

widespread in Utah and throughout the West (fig. 22). Activities associated 

with this change in land use can have substantial detrimental impacts on 

forested communities, including aspen. Besides the obvious loss of habitat 

and damage from construction of infrastructure and buildings, increased 

human use can have impacts similar to those of recreational activities. 

Figure 21—Dispersed camping in aspen stands, Fishlake National Forest can cause 

negative impacts. (photo: Stanley G. Kitchen, USDA Forest Service).
28 U.S. Forest Service RMRS GTR-390. 2019.

Figure 22—Exurban development impacts aspen communities directly and limits 

future management options (photo: Stanley G. Kitchen, USDA Forest Service).

The phrase “response options” is used rather than “treatment options,” 

because some management actions are passive in nature and hence the term 

“treatment” does not apply. Response options that require treatments are 

classified under active restoration. One or more response options may be 

appropriate for any given combination of aspen functional type, problematic 

condition(s), and causes of those condition(s). Conversely, specific response 

options may be inappropriate when the goal is to protect particular resource 

values. 

One option will always be to continue with current management. If a 

publicly owned aspen forest or community exhibits problematic conditions, 

action is probably warranted. However, various circumstances can sometimes 

prohibit action. Where this is the case, managers should clearly document 

and communicate the reason(s) for no action, detailing the expected 

consequences of the decision.

Response Option Selection—General Recommendations

1. Select response options that address identified underlying cause(s) 

of problematic conditions. Some responses may be inappropriate for 

particular areas (e.g., roadless areas) or incapable of addressing the 

causes of the problematic conditions.

2. Rely on best available science and local experience to identify and select 

response opportunities that have the greatest probability of success in 

restoring and maintaining resilient aspen communities.

3. Establish quantifiable measures of restoration goals (overstory and 

understory) and develop baseline and post-implementation monitoring 

protocols as part of the restoration decision. Include monitoring costs in 

restoration project budgets. 

Step 4. Select 

Response Option(s) 

Relevant to the 

Particular Aspen 

Functional Type, 

Problematic 

Condition(s), 

Underlying Causes 

of the Problematic 

Condition(s), and 

Landscape Context
U.S. Forest Service RMRS GTR-390. 2019. 29

4. When strong disagreements prevent consensus on the causes of 

problematic conditions, preferred response options, or expected 

outcomes, trials with side-by-side treatment alternatives for comparison 

over time may be useful.

5. For areas designated as wilderness or with wilderness potential 

(including designated roadless), select restoration practices that have 

a reasonable probability of success and have minimal impact on 

wilderness or roadless values. A few likely scenarios in practice include 

prescribed burning over logging-related options and reliance on natural 

fuel breaks or substantially inconspicuous fuel break construction (e.g., 

use of masticator, flush-cut stems, and graduated or feathered edges of 

treatment areas), or a combination of these types of fuel breaks.

6. Document boundaries of pretreatment and desired posttreatment aspen 

extent. (Note: This is appropriate where there is concern that stand area 

may be reduced after treatment.)

A Menu of Possible Responses

Note: It is possible to combine several responses at the same time, or 

move to other options following monitoring. 

Many management activities, alone or in combination, have been 

considered and tested for restoring aspen (DeRose et al. 2014; Long and 

Mock 2012). Aspen stands vary considerably by functional type, stage of 

succession, and genotype. It is important to understand this variability and 

manage accordingly (Long and Mock 2012; Rogers and Mittanck 2014). 

Ultimately, the selected option(s) should be based on the likelihood of 

achieving well-defined, data-driven management objectives focused on 

reducing the risk of aspen loss.

Active restoration (active vegetation treatments)—

1. Prescriptively burn aspen and conifers.

2. Selectively cut overstory conifers or aspen, or both. The practice of 

leaving scattered large legacy trees (coppice with reserves) on the site 

does not seem to hinder sucker establishment, but the reserve trees are 

often subject to sunscald and insect and disease damage (Bartos et al. 

1994; Shepperd 2001). 

3. Cut subdominant conifers.

4. In conifer-dominated stands, create scattered canopy gaps in the conifer 

overstory to promote aspen suckering in the gaps (Long and Mock 

2012). This must be accompanied by close monitoring and actions 

(e.g., fencing, pasture rest, jackstrawing) to ensure that aspen sucker 

recruitment reaches the 6-ft+ height class in those cases where browse 

pressure appears to be contributing to recruitment problems.

For conifer-overtopped or late successional aspen-mixed conifer types 

found in potential wilderness or roadless areas, canopy gap creation 

or group selection (depending on tree number or gap size) may be 

recommended in lieu of a coppice and regeneration harvest prescription. 

In these cases, a number of associated mitigation measures are available 
30 U.S. Forest Service RMRS GTR-390. 2019.

to ensure consistency with WUI and potential wilderness or roadless 

values. These include jackstrawing tree boles to impede ungulate grazing 

in canopy gaps (and mitigate cost of fencing), flush-cutting smaller boles 

even with the forest floor, limiting stump heights on sawtimber-sized 

boles, and helicopter skidding.

5. Girdle conifers.

6. Cut aspen roots to stimulate suckering (“root separation”). Cutting roots 

has been used successfully to stimulate suckering in some settings (e.g., 

isolated clones) and may be useful when the objective is to expand the 

area covered by smaller clones (Shepperd et al. 2006). One value of 

root separation is that mature trees are left relatively undisturbed and 

remain a potential resource for further action in case the treatment does 

not reach the stated objective. At the same time, this treatment may have 

unacceptable impacts on site productivity.

7. Improve or increase the availability of native vegetation for wildlife 

nutritional opportunities outside of the aspen stands of concern.

8. Coppice (clearcut) aspen and conifers. Coppice has been commonly used 

in the past to promote even-aged aspen stand regeneration (Shepperd et 

al. 2015). There are ecological concerns that should be addressed when 

this option is used for aspen restoration, particularly if the cut trees are 

removed. These concerns include the following:

a. Some nutrients and opportunity for soil carbon enrichment are lost 

from the site when overstory tree biomass is removed from the site.

b. While many understory plants benefit from full sunlight, some may 

be impacted negatively by loss of shading.

c. Although the coppice option (cutting all trees) can introduce a new 

age class of aspen within cutting units, old standing (live and dead) 

trees that provide important ecological services (including potential 

seed trees and continued suckering) are eliminated from treatment 

units.

d. Recent practical experience (Shepperd et al. 2006) supports leaving 

large aspen trees inside a coppice treatment, as well as down 

jackstrawed trees to address the preceding issues and herbivory 

concerns.

e. Old-growth conifer trees which predate fire suppression activities 

and probably coexisted in or near the aspen stand during a 

more active fire regime are likely to resist fire when retained. 

Consideration should be given for retaining these legacy trees.

9. Plant aspen seedlings or rooted cuttings. Although further development 

of the techniques required for successful implementation of this response 

option is needed, this approach provides an opportunity to increase 

genetic diversity and expand restoration to locations where aspen has 

been completely eliminated.
U.S. Forest Service RMRS GTR-390. 2019. 31

Passive restoration (reduce or remove browsing and other pressures 

on aspen)—

1. Allow lightning-caused fires to burn. Lightning-ignited fires frequently 

burn at higher severity and with greater extent than do prescription fires, 

resulting in stronger suckering response, opportunities for aspen seedling 

establishment, and better dispersion of herbivores (Wan et al. 2014). 

2. Fence to exclude domestic or wild ungulates, or both, depending on 

prior determination of type of ungulate pressure. In situations where 

the relative impact of domestic livestock versus wildlife has not been 

determined, a livestock exclusion fence alone may be a reasonable first 

choice. The effectiveness of livestock exclusion on aspen recruitment 

should be documented using appropriate monitoring protocols. Large 

exclosures (especially high-fence exclosures) are expensive to build, 

difficult to maintain, and generally not practical. Rest, whether provided 

by fences or other management action, may be needed for 3 to 5 

(occasionally up to 15) years, or until aspen suckers reach a height that is 

relatively safe from browsing (≥6 ft tall).

3. Change livestock grazing management (e.g., length or timing of grazing, 

class or number of livestock, water development, placement of salt and 

nutritional supplements). For example, Jones (2010) found that the crude 

protein content of aspen suckers increases relative to other available 

forage in the later part of the grazing season. With this relative increase, 

livestock may site-specifically select for aspen suckers in the fall. The 

avoidance of fall grazing may therefore offer protection for suckers.

4. Establish and enforce annual browse utilization limits in grazing 

systems with the objective of ensuring that adequate densities of aspen 

regeneration reach the minimum recruitment height class (≥6 ft tall).

5. Rest livestock allotments or pastures where aspen stands are excessively 

browsed. Resting is an appropriate option when passive restoration 

options 3 and 4 are not sufficient or feasible, or when actions are needed 

across a landscape.

6. Explore evolving technologies and strategies to mitigate wild ungulate 

impacts on aspen regeneration and recruitment. Because wild ungulates 

can be wide-ranging and variable in their migratory habits, it can be 

difficult to achieve reduced browse impacts at the stand scale by using 

behavior modification or other non-fencing techniques while maintaining 

animal numbers over broader spatial scales (but see Weisberg and 

Bugmann 2003). 

7. Working within the existing framework for wildlife management, 

develop specific big-game herd objectives that are compatible with 

resource conditions within the area.

8. Prevent or reduce dispersed camping within aspen stands.

9. Post or sign dispersed camping restrictions in appropriate locations.
32 U.S. Forest Service RMRS GTR-390. 2019.

Other possible influences on selecting response options—

1. Interagency or public working groups (including a variety of stakeholders 

and interests) may be able to propose solutions for addressing 

complicated, site-specific problems using existing mechanisms and other 

creative options.

2. Local outreach and education efforts on the value of aspen forests and 

the need for aspen management may increase feasibility of particular 

response options.

3. Treatment options that increase fuel hazards on site may at times conflict 

with WUI management objectives. 

4. The coppice option (with or without reserves) may conflict with potential 

wilderness or roadless area values.

5. Jackstrawing trees in some cases has limited ungulate access, thus 

allowing suckers to grow into the 6-ft+ height class. However, 

jackstrawing is unsightly and increases dead woody fuels for some time.

6. Exploration of landscape-scale response options may help avoid ungulate 

browsing complications that may arise when the focus is on a single 

response option at a smaller geographic scale.

Do not treat monitoring as an afterthought, or optional activity. Baseline 

monitoring should be implemented before initiating response options, 

and monitoring should continue throughout the aspen restoration process. 

Consistency in protocols and data management is essential.

1. Clearly state project objectives and post-implementation desired 

conditions.

2. Monitor according to the schedule and methods for obtaining quantifiable 

desired conditions established prior to restoration implementation.

3. Develop, test, and document monitoring protocols (previously used 

methods should be documented in a central location for easy access, but 

may be modified for local conditions and issues).

a. Monitoring sites should be systematically or randomly based for 

objectivity and repeatability.

b. Monitor adjacent control sites for each action wherever possible.

4. Monitoring should be budgeted as part of the project.

5. Proper data management is a part of any monitoring program. Plans 

should include protocols for preserving and sharing the data.

6. Interpret monitoring data in reports.

7. Consider altering monitoring or restoration methods on the basis of 

monitoring results.

Refer to Appendix C for protocols that have been used to monitor the 

condition of aspen regeneration and recruitment following a variety of 

treatment or management changes.

Step 5. Implement 

Appropriate Monitoring 

to Establish Baseline 

Conditions and Detect 

Changes Related to 

Application of Selected 

Restoration Activities
U.S. Forest Service RMRS GTR-390. 2019. 33

Step 6. Reassess 

and Adapt by Using 

Steps 1 through 5

Aspen restoration programs should be flexible and incorporate learnas-you-go and adaptive strategies. Managers need to anticipate and plan for 

unexpected outcomes.

• Robust monitoring provides both a way of comparing realized versus 

expected outcomes and objective data needed either to validate the 

efficacy of restoration activities to date, or to justify consideration of a 

change of course. 

• A resetting of the decision process by periodically revisiting one or 

more of the prior steps—even when restoration efforts may appear to be 

on target to meet predetermined goals—can provide the platform for a 

transparent, healthy program reassessment. 

• Documentation of lessons learned (including successes and failures) 

should be peer-reviewed and shared to maximize learning among 

managers and to build a library of case histories to inform the decision 

processes of future managers.
34 U.S. Forest Service RMRS GTR-390. 2019.

Key Terminology

Aspen community: Aspen community types are communities containing 

aspen, as a foundational species, and its associated flora and fauna regardless 

of successional status. 

Best available science: Scientific data that are available at the time of 

a decision or action and that are determined to be the most accurate, 

reliable, and relevant for use in that decision or action. Reliable scientific 

information is objective and repeatable. Multiparty monitoring, collaborative 

or independent (or both) peer review of methods and interpretations can be 

useful means of assembling best available science.

Clone (genet): A genetic individual, potentially represented by many trees 

that have generated vegetatively and that originated from a single tree.

Coppice: Regeneration method in which “all trees in the previous stand are 

removed and the majority of regeneration is from sprouts or root suckers” 

(Helms 1998). In mixed aspen-conifer stands most of the regeneration will be 

aspen root suckers, but there may be some seedlings, both aspen and conifer, 

as well.

Coppice with reserves: Regeneration method in which “reserve trees are 

retained to attain goals other than regeneration” (Helms 1998). In mixed 

aspen-conifer stands, the reserve trees are typically mature aspen kept as 

insurance against excessive browsing of the root suckers. Some conifers may 

be kept as reserve trees to meet other management objectives such as wildlife 

mitigation or visual aesthetics, which may apply to both aspen and conifer 

reserve trees.

Exclosures: Exclosures are fenced areas designed to exclude one or more 

class of herbivore (usually ungulates but may also include small mammals 

such as rabbits, hares, or rodents). They are typically used to assess the 

effects of protection or exclusion on vegetation, such as aspen regeneration. 

Multi-unit exclosures (e.g., three- or four-way exclosures) are clusters of 

exclosures in which each subunit has fencing characteristics that restrict 

access to a different set of ungulates. For example, high fence subunits 

exclude all ungulates, low fence subunits exclude livestock while allowing 

deer and elk, and subunits that combine a high fence with bottom gap (18 in, 

or 48 cm) allow only deer or sheep. Exclosure size varies from a few feet on 

a side to several hundred acres. Benefits and drawbacks of exclosures vary 

with size, location, and monitoring or research question being asked.
U.S. Forest Service RMRS GTR-390. 2019. 35

Isolated persistent aspen stands: A description that refers to small or 

moderately small aspen stands (typically less than 50 ac [20 ha] in area) that 

are scattered across the landscape surrounded by nonforest vegetation types. 

Visually, these appear as individual units, but may represent fragments of 

larger, formerly connected stands. 

Jackstraw treatment: Using fallen trees to provide refugia from ungulate 

browsing (Ripple and Larsen 2001).

Ramet: Any individual stem of a larger aspen clone (whether juvenile or 

mature). A ramet has the same genetic makeup as all other stems from that 

clone.

Recruitment (of aspen): A process that refers to the addition of new 

individuals to a population of canopy trees. The term (or its shortened form, 

recruits) is sometimes used in reference to those individual aspen shoots 

that have reached sufficient height—at least 6 ft (2 m)—to indicate that 

recruitment is taking place but are not yet mature (distinctly shorter than 

canopy trees). Shoots taller than 6 ft are less vulnerable to browsing of 

terminal buds and are thus more likely to become future canopy trees. 

Regeneration (of aspen): Production of new aspen suckers or seedlings. The 

term (or its shortened form, regen) is sometimes used in reference to those 

individual shoots that are generally less than 6 ft tall, with terminal buds 

vulnerable to browsing. 

Restoration – active: Activities such as logging, burning, seeding, tree 

girdling, root ripping, or active reintroduction of a native species in order 

to restore conditions or processes considered ecologically essential, or to 

increase resilience. 

Restoration – passive: Allowing restoration of desirable ecological 

conditions through natural processes. May include removal or modification 

of management activities that delay or prevent attainment of restoration 

goals. Examples include allowing lightning-ignited fires to run their course 

(rather than suppressing these fires) and reducing or removing stress agents 

(e.g., changing management of grazing and browsing, or recreation) that have 

suppressed aspen recruitment.

Suckers: Vegetative shoots growing from lateral roots of a clone. Suckers 

have the same genotype as the root from which they are produced.

Wildland-urban interface (WUI): The wildland-urban interface is 

composed of the boundary or gradient where urban development and 

wildland vegetation meet and often intermix. Interface communities are areas 

with housing within 1.5 mi (2.4 km) of areas with greater than 50 percent 

wildland vegetation. Aspen may act as a firebreak within a WUI; generally, 

the higher the ratio of live aspen to conifers, the less flammable the landscape 

will be.
36 U.S. Forest Service RMRS GTR-390. 2019.
U.S. Forest Service RMRS GTR-390. 2019. 37

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Appendix A: Aspen Restoration Guidelines: 

Development and History

“Guidelines for Aspen Restoration on the National Forests in Utah” 

was the first major project of the Utah Forest Restoration Working Group 

(UFRWG). The UFRWG is a collaborative group formed for the purpose of 

reaching consensus while applying the best available science to critical forest 

issues primarily affecting national forest lands in Utah. As a consensusbased entity, UFRWG is composed of a wide variety of interest group 

representatives: the USDA Forest Service, State agricultural and natural 

resource agencies, county government, private citizens, and nongovernmental 

organizations (environmental, resource utilization, and industry). A complete 

list of 2018 UFRWG participants and members is shown below. 

In 2009, a UFRWG Ecology Committee was given approximately 

1 year to compile the first set of guidelines and recommendations for 

aspen management in a form agreeable to all parties. During this period 

the Ecology Committee gained input from managers around Utah working 

directly with aspen.

A December 2009 draft was circulated among a group of scientists who 

have both conducted aspen research and observed aspen conditions in Utah 

and the West, and the final report was published in 2010, and was reissued in 

April 2011, with minor corrections. 

In 2015, the UFRWG initiated a revision of the 2010–2011 guidelines 

to incorporate new scientific research and lessons learned during 5 years 

of use of the guidelines in various Utah sites. An Aspen Guidelines 

Revisions Committee was formed and the work of that group is found in this 

publication. 

We believe that these revised guidelines incorporate the most current 

aspen science with the intent to guide the diverse interests to move forward 

on a range of aspen-related restoration projects in Utah and throughout the 

Intermountain West. 

• Grand Canyon Trust

• Mule Deer Foundation

• Rocky Mountain Elk Foundation

• Six County Association of Governments 

• Society of American Foresters, Utah Chapter

• Trout Unlimited, Utah Council

• U.S. Department of Agriculture, Forest Service, Intermountain Region 

(Region 4)

Utah Forest 

Restoration Working 

Group Members 2018
44 U.S. Forest Service RMRS GTR-390. 2019.

• U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station

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

• U.S. Department of the Interior, National Park Service

• Utah Cattlemen’s Association

• Utah Department of Agriculture and Food 

• Utah Department of Environmental Quality

• Utah Division of Forestry, Fire and State Lands 

• Utah Division of Wildlife Resources 

• Utah Farm Bureau

• Utah Grazing Improvement Program

• Utah State University Extension

• Utah Woolgrower’s Association

• Western Aspen Alliance
U.S. Forest Service RMRS GTR-390. 2019. 45

Appendix B: Common Diseases and Insects of Aspen

The agents listed in table B1 include those most commonly observed in 

a survey of aspen insects and diseases conducted in 2007–2008 (Guyon and 

Hoffman 2011), and the personal experiences of the authors. Several of these 

agents cause significant damage only when their hosts are under stress. The 

most important stress agents include drought, grazing and browsing pressure, 

freezing damage, and competition from other plants. 

Guyon, J.; Hoffman, J.T. 2011. Survey of aspen dieback in the Intermountain 

Region. OFO-PR-11-01. Forest Health Protection. U.S. Department of 

Agriculture, Forest Service, Intermountain Region, State and Private 

Forestry. 19 p. 

Common name Genus and species Type of damage Aspen impact

Bronze poplar borer Agrilus liragus Cambial mining and wood boring Primary tree killer

Poplar borer Saperda calcarata Wood borer; weakens and 

causes physical damage

Usually found on stressed 

trees

Eastern poplar buprestid Poecilonota cyanipes Wood borer; weakens and 

causes physical damage

Attracted to damaged trees

Aspen bark beetles Trypophloeus populi and 

Procryphalus mucronatus

Bark beetles found in the outer 

bark; expedite cambial death

Attack trees under stress

Large aspen tortrix Choristoneura conflictana Foliar feeding insect; defoliates Occasional defoliator

Aspen twoleaf tier Enargia decolor Foliar feeding insect; defoliates Occasional defoliator

Sooty bark canker Encoelia pruinosa Canker disease; kills cambium Primary tree killer

Cytospora/Valsa canker Cytospora chryosperma Canker disease; kills cambium Damaging only on stems under 

stress; presence coincides with 

other damage agents

Ganoderma root rot Ganoderma applanatum Causes root system decay; 

causes windthrow

Present in many stands as 

cohorts age

White trunk rot Phellinus tremulae Causes stem decay; can lead to 

stem breakage

Increasingly prevalent in older 

ramets and cohorts

Marssonina leaf blight Marssonina spp. Foliar disease; defoliates Occasional defoliator; often 

associated with wet spring 

weather

Table B1—Common insects and diseases in aspen forests in Utah, the type of damage they cause and the impacts they have 

when present.

References
46 U.S. Forest Service RMRS GTR-390. 2019.

Figure B.1—

Zigzag galleries 

characteristic 

of the bronze 

poplar borer are 

found under the 

bark after ramet 

mortality (photo: 

Brytten Steed, 

USDA Forest 

Service).

Figure B.2—

Chunky frass 

falling from large 

bore holes is 

typical external 

evidence of attack 

by the poplar 

borer (photo: Tom 

Zegler, USDA 

Forest Service).

Figure B.3—The 

larvae of the 

eastern poplar 

buprestid, shown 

here as an adult, 

bore through the 

wood of living 

or dead aspen 

(photo: Tom 

Zegler, USDA 

Forest Service).

Figure B.4—

Galleries made 

by the aspen bark 

beetle are visible 

in the outer bark 

(photo: Brytten 

Steed, USDA 

Forest Service). 
U.S. Forest Service RMRS GTR-390. 2019. 47

Figure B.5—

Larvae of the 

large aspen tortrix 

commonly roll two 

to three leaves 

together (photo: 

Tom Zegler, USDA 

Forest Service).

Figure B.6—

Larvae of the 

aspen twoleaf 

tier tie two leaves 

together without 

rolling (photo: John 

Guyon, USDA 

Forest Service). 

Figure B.7—

Blackened 

cambium recently 

killed by sooty bark 

canker emerges 

through the outer 

bark (photo: Tom 

Zegler, USDA 

Forest Service).

Figure B.8—

Minute, whitetipped perithecia 

(spore-forming 

fruiting bodies) 

of the Cytospora 

canker become 

visible on the bark 

surface (photo: 

Tom Zegler, USDA 

Forest Service). 
48 U.S. Forest Service RMRS GTR-390. 2019.

Figure B.9—The 

fruiting body of 

the pathogen 

that causes 

Ganoderma root 

rot is attached to 

the base of the 

tree on the left. 

The tree on the 

right fell due to 

rotted roots (photo: 

Brytten Steed, 

USDA Forest 

Service).

Figure B.11—

Lesions on the leaf 

surface caused by 

Marssonina blight 

typically exhibit 

a brown center 

surrounded by a 

yellow halo (photo: 

Tom Zegler, USDA 

Forest Service).

Figure B.10—The 

characteristic 

fruiting body of 

the fungus that 

causes white 

trunk rot indicates 

substantial decay 

within the stem 

(photo: Brytten 

Steed, USDA 

Forest Service).
U.S. Forest Service RMRS GTR-390. 2019. 49

Appendix C: Comparison of Key Attributes of Forest Service 

Monitoring Methods for Aspen Ecosystems, and a Method Used 

by Brigham Young University 

Table C1—Comparison of four methods used for monitoring aspen trend.

Aspen assessment method

Attribute

USDA Forest 

Service Pacific 

Southwest Region 

(USDA FS 2004) Jones et al. (2005)

Campbell and 

Bartos (2001)

Monroe Mountain Working Group 

Aspen Regeneration/Recruitment 

Monitoring (Rhodes et al., n.d.)a

Flexibility of 

installation (can be 

adapted to specific 

situations)

Easy Involved Easy Easy

Permanence Temporary Permanent Temporary Permanent if staked; or temporary

Plot shape Roughly linear 

transect

Belt transect; 

shape can be 

modified

Typically circular Belt transect; shape can be modified

Plot size Indeterminate 

length; typically 

90 hits of sprouts or 

young aspen

600 ft2 (6 ft × 

100 ft) ≈ 60 m2

(2 m × 30 m); other 

sizes can be used

Typically 0.1 ac 

(0.04 ha)

1,280 ft2 (119 m2; two perpendicular 

2 m × 30 m transects)

Ease of 

implementation

Rapid assessment Robust, involved Rapid assessment Rapid assessment

Timing of 

monitoring relative 

to treatment

Typically after Before or after, 

or both

Typically before Before or after treatment, or used to 

monitor within-year or between-year 

variation

Elements 

monitored

• Percentage 

of stems with 

terminal leader’s 

current-year growth 

browsed. 

Method measures 

the primary stems 

of aspen sprouts 

and young trees ≤5 

ft (1.5 m) in height.

• Percentage of 

stems with terminal 

leader’s currentyear growth 

browsed 

• Trend for aspen 

regeneration 

density in four size 

classes 

• Percent conifer 

cover 

• Percent aspen 

cover 

• Percent sagebrush 

cover 

• Estimated age of 

dominant aspen 

• Number of aspen 

stems 5–15 ft 

(1.5–4.6 m) tall 

• Percent browse of apical meristems 

on leading (tallest) stems and 

subleaders within a 6-in (15-cm) 

sphere of the leading stem 

• Height distribution of suckers in 

3.9-in (10-cm) increments 

• Aspen sapling recruitment: number 

of aspen 6–12 ft (2–3.5 m) in height 

• Mid-canopy aspen >12 ft and below 

the dominant overstory 

• Density, composition, and basal 

area of overstory tree species 

(point-quarter method at 16-ft [5-m] 

increments along the center of the 

belt transect) 

• Percent defoliation (an ocular 

estimate of leaf removal at the site 

averaged across all aspen stems 

recorded in 5-percent increments)

(continued on next page)
50 U.S. Forest Service RMRS GTR-390. 2019.

Aspen assessment method

Attribute

USDA Forest 

Service Pacific 

Southwest Region 

(USDA FS 2004) Jones et al. (2005)

Campbell and 

Bartos (2001)

Monroe Mountain Working Group 

Aspen Regeneration/Recruitment 

Monitoring (Rhodes et al., n.d.)a

Quantities or 

thresholds 

for elements 

monitored

Yes Yes Yes Yes

Ease of conversion 

of results

Easy Moderate Easy Easy

Data analysis Tabular data sheet Tabular data sheet Tabular data sheet Tabular data sheet

Ease of 

interpretation

Easy Moderate Easy Easy

Complexity Simple Moderate Simple Simple

Provides response 

recommendations

No Yes Yes No

Table C1 (continued)—Comparison of four methods used for monitoring aspen trend.

a Rhodes, A.C.; St. Clair, S.B.; Maxwell, J. [n.d.] Monroe Mountain Working Group aspen regeneration/recruitment monitoring Unpublished 

data on file at: Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT.

Summary 

of the Methods

USDA Forest Service Pacific Southwest Region (USDA 2004)

Simple and quick method designed to determine the percentage of aspen 

sprouts and young stems that are less than or equal to 5 ft (1.5 m) tall, with 

the terminal leader browsed.

Jones et al. (2005)

Robust and involved method designed to measure percentage of 

regenerating aspen plants with terminal leaders utilized and the trend in 

density for four size classes. Can be used before and after treatments.

Campbell and Bartos (2001)

Walk-through rapid assessment of aspen stand health and condition. 

Quantitative data that would be meaningful before and after a project are 

typically not collected.

Monroe Mountain Working Group Aspen Regeneration/

Recruitment Monitoring (Rhodes et al. n.d.) 

Simple belt transect method focused on measuring height and browse on 

top leaders, combined with point quarter method for density of mature trees. 

Ocular estimates of recruitment and defoliation.
U.S. Forest Service RMRS GTR-390. 2019. 51

Campbell, R.B., Jr.; Bartos, D.L. 2001. Aspen ecosystems: Objectives 

for sustaining biodiversity. In: Shepperd, Wayne D.; Binkley, Dan; 

Bartos, Dale L.; [et al.], comps. Sustaining aspen in western landscapes: 

Symposium proceedings; 2000 June 3–15; Grand Junction, CO. 

Proceedings RMRS-P-18. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station: 299–307.

Jones, B.E.; Burton, D.; Tate, K.W. 2005. Effectiveness monitoring of 

aspen regeneration on managed rangelands. Unnumbered report. Vallejo, 

CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest 

Region. 19 p.

Rhodes, A.C.; St. Clair, S.B.; Maxwell, J. [n.d.] Monroe Mountain Working 

Group aspen regeneration/recruitment monitoring. Unpublished data on 

file with: Department of Plant and Wildlife Sciences, Brigham Young 

University, Provo, UT.

USDA Forest Service. 2004. Browsed plant method for young quaking 

aspen: An annual monitoring method for determining the incidence of use 

on sprouts and young plants during the growing season. U.S. Department 

of Agriculture, Forest Service, Pacific Southwest Region. 14 p.

References
52 U.S. Forest Service RMRS GTR-390. 2019.
U.S. Forest Service RMRS GTR-390. 2019. 53

Appendix D: Literature Relevant to Aspen in Utah 

and the Intermountain West

The following references include syntheses of information and important 

recent contributions regarding the ecology and management of aspen with 

specific emphasis on restoring resilient aspen communities in Utah. Some, 

but not all, were cited herein. For a more complete listing of aspen-related 

literature see the continually updated bibliography maintained by Utah State 

University, Western Aspen Alliance at: https://western-aspen-alliance.org. A 

searchable spatial bibliography developed in a joint effort by the Utah State 

University, Western Aspen Alliance, and the Plant and Wildlife Sciences 

Geospatial Lab at Brigham Young University is also available on the Western 

Aspen Alliance website. 

Bartos, D.L. 2007. Chapter 3: Aspen. In: Hood, S.M.; Miller, M., eds. Fire 

ecology and management of the major ecosystems of southern Utah. 

Gen. Tech. Rep. RMRS-GTR-202. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station: 39–55.

Brown, J.K.; Simmerman, D.G. 1986. Appraising fuels and flammability in 

western aspen: A prescribed fire guide. Gen. Tech. Rep. INT-205. Ogden, 

UT: U.S. Department of Agriculture, Forest Service, Intermountain 

Research Station. 48 p.

Calder, W.J.; St. Clair, S.B. 2012. Facilitation drives mortality patterns along 

succession gradients of aspen-conifer forests. Ecosphere. 3(6): 1–11.

Campbell, R.B., Jr.; Bartos, D.L. 2001. Aspen ecosystems: Objectives 

for sustaining biodiversity. In: Shepperd, Wayne D.; Binkley, Dan; 

Bartos, Dale L.; [et al.], comps. Sustaining aspen in western landscapes: 

Symposium proceedings; 2000 June 3–15; Grand Junction, CO. 

Gen. Tech. Rep. RMRS-P-18. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station: 299–307.

DeByle, N.V.; Winokur, R.P., eds. 1985. Aspen ecology and management in 

the western United States. Gen. Tech. Rep. RM-119. Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest 

and Range Experiment Station. 283 p.

Dudley, M.M.; Burns, K.S.; Jacobi, W.R. 2015. Aspen mortality in the 

Colorado and southern Wyoming Rocky Mountains: Extent, severity, and 

causal factors. Forest Ecology and Management. 353: 240–259.

Kulakowski, D.; Kaye, M.W.; Kashian, D.M. 2013. Long-term aspen cover 

change in the western US. Forest Ecology and Management. 299: 52–59.
54 U.S. Forest Service RMRS GTR-390. 2019.

Long, J.N.; Mock, K. 2012. Changing perspectives on regeneration ecology 

and genetic diversity in western quaking aspen: Implications for 

silviculture. Canadian Journal of Forest Research. 42(12): 2011–2021.

Mueggler, W.F. 1985. Vegetation associations. In: DeByle, N.V.; Winokur, 

R.P., eds. Aspen: Ecology and management in the western United 

States. Gen. Tech. Rep. RM-119. Fort Collins, CO: U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Forest and Range 

Experiment Station: 45–55.

Mueggler, W.F. 1988. Aspen community types of the Intermountain 

Region. Gen. Tech. Rep. GTR INT-250. Ogden, UT: U.S. Department of 

Agriculture, Forest Service, Intermountain Forest and Range Experiment 

Station. 135 p.

Mueggler, W.F. 1989. Age distribution and reproduction of Intermountain 

aspen stands. Western Journal of Applied Forestry. 4(2): 41–45.

Rogers, P.C. 2017. Guide to quaking aspen ecology and management: With 

emphasis on BLM lands in the western United States. Report No. BLMUT-G1017-001-8000. Washington, DC: U.S. Department of the Interior, 

Bureau of Land Management. 98 p.

Rogers, P.C.; Eisenberg, C.; St. Clair, S.B. 2013. Resilience in quaking aspen: 

Recent advances and future needs. Forest Ecology and Management. 

299(1): 1–5.

Rogers, P.C.; Landhäuser, S.M.; Pino, B.; [et al.]. 2014. A functional 

framework for improved management of western North American aspen 

(Populus tremuloides Michx.). Forest Science. 60(2): 345–359.

Rogers, P.C.; Mittanck, C. M. 2014. Herbivory strains resilience in 

drought-prone aspen landscapes of the western United States. Journal of 

Vegetation Science 25: 457–469.

Seager, S.T., Eisenberg, C.; St. Clair, S.B. 2013. Patterns and consequences 

of ungulate herbivory on aspen in western North America. Forest Ecology 

and Management. 299: 81–90.

Shepperd, Wayne D.; Binkley, Dan; Bartos, Dale L.; [et al.], comps. 2000. 

Sustaining aspen in western landscapes: Symposium proceedings; 2000 

June 3–15; Grand Junction, CO. Proceedings RMRS-P-18. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 460 p.

Shinneman, D.J.; Baker, W.L.; Rogers, P.C.; [et al.]. 2013. Fire regimes of 

quaking aspen in the Mountain West. Forest Ecology and Management. 

299(1): 22–34.

St. Clair, S.B.; Cavard, X.; Bergeron, Y. 2013. The role of facilitation and 

competition in the development and resilience of aspen forests. Forest 

Ecology and Management. 299(1): 91–99.
U.S. Forest Service RMRS GTR-390. 2019. 55

St. Clair, S.B.; Guyon, J.; Donaldson, J. 2010. Quaking aspen’s current and 

future status in western North America: The role of succession, climate, 

biotic agents and its clonal nature. In: Lüttge, U.; Beyschlag, W.; Büdel, 

B.; [et al.], eds. Progress in Botany 71. Berlin/Heidelberg: Springer: 

371–400.

St. Clair, S.B.; Mock, K.E.; LaMalfa, E.M; [et al.]. 2010. Genetic 

contributions to phenotypic variation in physiology, growth, and vigor of 

western aspen (Populus tremuloides) clones. Forest Science. 56: 222–230.

Worrall, J.J.; Rehfeldt, G.E.; Hamann, A.; [et al.]. 2013. Recent declines of 

Populus tremuloides in North America linked to climate. Forest Ecology 

and Management. 299: 35–51.

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