United States 

Department of Agriculture

Forest Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-806

May 2010

Aspen Biology, Community 

Classification, and Management 

in the Blue Mountains

David K. Swanson, Craig L. Schmitt, Diane M. Shirley, Vicky Erickson, 

Kenneth J. Schuetz, Michael L. Tatum, and David C. Powell
The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. 

Through forestry research, cooperation with the States and private forest owners, and management of the 

national forests and national grasslands, it strives—as directed by Congress—to provide increasingly greater 

service to a growing Nation.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the 

basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, 

parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part 

of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all 

programs.) Persons with disabilities who require alternative means for communication of program information 

(Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and 

TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, 1400 Independence 

Avenue, SW, Washington, DC 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is 

an equal opportunity provider and employer.

Author

David K. Swanson was an area ecologist, U.S. Department of Agriculture, Forest Service, 

P.O. Box 907, Baker City, OR 97814, is now an ecologist with the U.S. Department of the 

Interior, National Park Service, 4175 Geist Rd., Fairbanks, AK 99709. Craig L. Schmitt

is a zone pathologist, U.S. Department of Agriculture, Forest Service, 1401 Gekeler Lane, 

La Grande, OR 97850. Diane M. Shirley is a forestry technician, U.S. Department of 

Agriculture, Forest Service, Umatilla National Forest, P.O. Box 158, Ukiah, OR 97880. 

Vicky Erickson is the regional geneticist, and David C. Powell is a forest silviculturalist, 

U.S. Department of Agriculture, Forest Service, Umatilla National Forest, 2517 Hailey 

Avenue, Pendleton, OR 97801. Kenneth J. Schuetz (deceased) was a forest wildlife biologist, and Michael L. Tatum is a forest silviculturist, U.S. Department of Agriculture, 

Forest Service, Malheur National Forest, P.O. Box 909, John Day, OR 97845.

Cover photo: Aspen stand with buck-and-pole fence constructed of local thinning slash 

8 years prior to photo. Regeneration is lacking around the mature trees outside of the 

fenced area on the right. Blue Mountain Ranger District of the Malheur National Forest, in 

the vicinity of Camp Creek and Starr Ridge. Photo by Michael Tatum, Malheur National 

Forest.
i

Abstract

Swanson, David K.; Schmitt, Craig L.; Shirley, Diane M.; Erickson, Vicky; 

Schuetz, Kenneth J.; Tatum, Michael L.; Powell, David C. 2010. Aspen biology, 

community classification, and management in the Blue Mountains. Gen. Tech. Rep. 

PNW-GTR-806. Portland, OR: U.S. Department of Agriculture, Forest Service, 

Pacific Northwest Research Station. 117 p.

Quaking aspen (Populus tremuloides Michx.) is a valuable species that is declining in 

the Blue Mountains of northeastern Oregon. This publication is a compilation of over 

20 years of aspen management experience by USDA Forest Service workers in the 

Blue Mountains. It includes a summary of aspen biology and occurrence in the Blue 

Mountains, and a discussion of aspen conservation and management techniques such 

as fencing, conifer removal, and artificial propagation. Local data on bird use of aspen 

stands, insects and diseases in aspen, and genetic studies of aspen are also included. 

An aspen community classification developed from over 200 sample plots is presented, 

with plant species composition and cover, environment and soils, and management 

considerations.

Keywords: Populus tremuloides, forest management, forest ecology, plant community 

classification.

Preface

This publication is a collaboration that draws on the efforts of many people who have 

worked with aspen in the Blue Mountains. Primary authorship of the various sections 

is as follows:

• Aspen Biology and Ecology–David K. Swanson, Kenneth J. Schuetz (Bird use of 

aspen on the Malheur National Forest), David C. Powell, and Michael L. Tatum

• Genetic Diversity and Structure of Aspen Stands in the Blue Mountains–Vicky 

Erickson

• Insects and Diseases of Aspen in the Blue Mountains–Craig L. Schmitt

• Aspen Management in the Blue Mountains–David K. Swanson, Diane M. Shirley, 

Michael L. Tatum, and Vicky Ericson with contributions from most of the 

collaborators

• Aspen Community Classification in the Blue Mountains–David K. Swanson
ii
iii

Aspen Biology, Community 

Classification, and Management 

in the Blue Mountains

David K. Swanson, Craig L. Schmitt, Diane M. Shirley, Vicky Erickson, 

Kenneth J. Schuetz, Michael L. Tatum, and David C. Powell

With contributions from (listed alphabetically): Roderick R. Clausnitzer, Lynda Cobb, 

Bill J. Collar, Elizabeth A. Crowe, Terry Hicks, Jerold Hustafa, Charles G. Johnson, 

Jr., Betsy H. Kaiser, Cynthia L. Kranich, Mark A. Penniger, Roy Schwenke, Joseph M. 

Sciarrino, Paul W. Survis, and Martin Vavra.

United States Department of Agriculture, Forest Service, 

Pacific Northwest Research Station

General Technical Report PNW-GTR-806

May 2010
iv
v

Contents

1 Introduction

1 Aspen Biology and Ecology

1 Aspen Clones and Root System

1 Reproduction

4 Ecological Range

6 Competition and Succession

6 Fire Effects

7 Herbivores and Aspen

7 Aspen Occurrence in the Blue Mountains

9 Decline of Aspen in the Blue Mountains

10 Invasive Plants and Aspen

10 Bird Use of Aspen Habitats in the Blue Mountains

12 Genetic Diversity and Structure of Aspen Stands in the Blue Mountains

16 Genetic Variation at the Stand Level

16 Geographic Variation in Genetic Structure

17 Genetic Evidence for Decline of Aspen Clones

17 Management Implications

17 Insects and Diseases of Aspen in the Blue Mountains

18 Stem Decays

19 Trunk Butt and Root Rots

19 Canker Diseases

21 Foliage Diseases

22 Insect Pests of Aspen

25 Aspen Management in the Blue Mountains

25 Overview

28 Conifer Removal

30 Fencing

34 Fire

35 Aspen Felling and Girdling

35 Mechanical Site Preparation

36 Thinning

36 Establishment of Aspen Outside of Existing Stands

38 Vegetative Propagation

40 Propagation of Aspen From Seed

41 Restoring Understory Plant Diversity in Aspen Stands

42 Assessment of Aspen Regeneration

43 Aspen Stand Quick Assessment and Desired Future Condition

	 47	 Aspen Community Classification in the Blue Mountains

47 Study Area

48 Plant Association Concept
vi

48 Field Methods

49 Classification and Data Analysis Methods

50 Data Presentation

50 Keys to Aspen Communities of the Blue Mountains

51 Key to Riparian and Wetland Aspen Vegetation

52 Key to Upland Aspen Vegetation

53 Upland Grand Fir Series Aspen Type Key

54 Upland Ponderosa Pine and Douglas-Fir Series Aspen Type Key

55 Riparian and Wetland Aspen Plant Communities

55 Aspen-Engelmann Spruce Types

55 Aspen-Engelmann Spruce/Fowl Mannagrass-Bluejoint Reedgrass Plant 

 Community Type

56 Aspen-Tall Shrub Types

56 Aspen/Mountain Alder-Red-Osier Dogwood Plant Community Type

56 Aspen/Mountain Alder-Common Snowberry Plant Community Type

56 Aspen/Black Hawthorne Plant Community Type

57 Aspen/Tall Shrub Wetland Plant Communities on Slopes

58 Riparian Aspen/Common Snowberry Types

58 Grand Fir/Common Snowberry (Floodplain) Plant Community Type

58 Douglas-Fir/Common Snowberry (Floodplain) Plant Association

58 Ponderosa Pine/Common Snowberry (Floodplain) Plant Association

58 Aspen/Common Snowberry Plant Community Type

62 Herbaceous Aspen Meadow Types

62 Aspen/Aquatic Sedge Plant Community Type

62 Aspen/Woolly Sedge Plant Association

65 Aspen/Yellow Sedge Plant Community Type

66 Aspen/Bluejoint Reedgrass Plant Community Type

68 Aspen/Kentucky Bluegrass Plant Community Type

68 Aspen/Meadow Foxtail Plant Community Type

68 Aspen/Mesic Forb Plant Community Type

72 Upland Aspen Communities

72 Talus and Rock Outcrop Aspen Types

72 Aspen (Rubble, High) Plant Community Type

72 Aspen (Rubble, Low) Plant Community Type

75 Aspen Types of the Subalpine Fir Series

75 Aspen (Subalpine Fir)/Western Coneflower Plant Community Type

77 Aspen Types of the Grand Fir Series

77 Grand Fir/Twinflower Plant Association

78 Grand Fir/Big Huckleberry Plant Association

81 Grand Fir/Rocky Mountain Maple Plant Association

83 Aspen (Grand Fir)/Oceanspray Plant Community Type
vii

83 Aspen (Grand Fir)/Snowberry Plant Community Type

86 Other Grand Fir Series Aspen Communities

88 Aspen Types of the Ponderosa Pine and Douglas-Fir Series

88 Aspen/Chokecherry Plant Community Type

90 Aspen(Douglas-Fir)/Bitter Cherry Plant Community Type

92 Aspen (Ponderosa Pine–Douglas-Fir)/Snowberry Plant Community Type

95 Aspen/Pinegrass Plant Community Type

95 Aspen/Elk Sedge Plant Community Type

95 Aspen/Exotic Grass Plant Community Type

99 Other Douglas-Fir and Ponderosa Pine Series Aspen Communities

101 Acknowledgments

101 Metric Equivalents

102 References

109 Appendix A: Aspen Stands Sampled as Part of the Blue Mountains 

 Genetics Study

112 Appendix B: Plant Names Used in This Report

117 Appendix C: Current PLANTS Database Synonyms for the Names Used 

 in This Report

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 1

Introduction

Stands of quaking aspen (Populus tremuloides Michx.) 

are an uncommon and unique habitat type in the Blue 

Mountains (fig. 1). As one of very few broadleaf deciduous trees in a region dominated by conifers and semidesert grassland and scrub, aspen brings important diversity 

to the landscape. Aspen’s palatable twigs and foliage, and 

tendency to develop cavities, make it valuable habitat for 

wildlife such as deer (Odocoileus sp.), elk (Cervus elephas), 

woodpeckers, and songbirds. Aspen often grow in riparian 

areas, providing shade, streambank stability, and nutrients 

from leaf-fall to streams. Aspen are also appreciated for 

their scenic value, especially their golden colors in the fall.

With very few exceptions, aspen stands in the Blue 

Mountains have been declining in number, area, and 

stocking. This unfortunate situation has prompted action 

by managers of both public and private lands to protect, 

restore, and propagate aspen. United States Department of 

Agriculture (USDA) Forest Service land managers have 

gained considerable experience in aspen management over 

the past 25 years. The purpose of the present publication is 

to summarize the state of our knowledge about the biology, 

ecology, and management of aspen, especially as it pertains to the Blue Mountains area. The local experience with 

aspen described here was obtained mainly on lands of the 

Malheur, Umatilla, and Wallowa-Whitman National Forests 

of northeastern Oregon and adjacent Washington and Idaho 

(fig. 1). Our results will apply most closely to this ecological region, but they should also be pertinent to other parts of 

the semiarid Western United States.

Aspen Biology and Ecology

Aspen Clones and Root System

Aspen trees have the unique ability to spread laterally by 

roots and produce new stems (traditionally called suckers) 

that develop into trees. As a result, a grove of genetically 

identical aspen trees can develop from a single seedling that 

germinated some time in the past (Barnes 1966). Although 

individual aspen stems are relatively short-lived (roughly 

100 years), the clone itself may have existed for thousands 

of years. An aspen clone has existed for perhaps thousands 

of years in the Morsay Creek drainage of the North Fork 

John Day Ranger District (Shirley and Erickson 2001). 

One clone in Utah covers 107 acres, and its growth to this 

size must have taken thousands of years (Kemperman and 

Barnes 1976).

Many tree characteristics, such as leaf shape and size, 

bark color, branching habit, autumn leaf color, and disease 

resistance, are remarkably uniform within a clone but differ from one clone to another; in other words, clones are 

phenotypically diverse (Barnes 1975). Where clones grow 

together, variations in one or more of these characteristics 

can sometimes be used to identify different clones in the 

field without the cost of genetic testing.

Aspen roots can grow laterally far from their parent trees 

and produce suckers. Excavations of aspen root systems in 

the Great Lakes region revealed root growth rates of 2.5 ft/

year (Day 1944) to 4.5 ft/year (Buell and Buell 1959) in good 

soils without competing trees. Some managers believe that 

aspen clones grow preferentially in the south and southwesterly direction from the parent tree, presumably in response 

to increased light and higher soil temperatures. Root connections between developing trees persist even as some of 

the stems along a root die owing to natural self-thinning 

(DesRochers and Lieffers 2001a).

Although the large interconnected root system in aspen 

supports new suckers, the suckers also support the root 

system, both in laterally expanding clones and clones 

regenerating after disturbance. Root segments distal to a 

sucker (farther from the older trees) are enlarged for several 

feet (fig. 2) (Barnes 1966, Gifford 1966). In other words, 

the parent root has faster radial growth on the distal side 

of the sucker, suggesting that most of the photosynthates 

are directed toward the distal side of the parent root. Thus 

suckers contribute to the health and vigor of the root system 

and promote its continued spread. After the aboveground 

portion of an aspen clone is killed by disturbance (e.g., fire 

or clearcutting), an abundant crop of suckers can produce 

enough photosynthate to maintain much of the preexisting 

root system, such that only large roots at the bases of former 

trees may die (DesRochers and Lieffers 2001b). The regenerating stand can thus benefit from the nutrient- and watergathering ability of an extensive established root system.

Reproduction

Aspen are unique among the major western tree species in 

that they reproduce almost exclusively by vegetative means. 

The ability to regenerate vegetatively allows aspen to thrive 

after disturbance such as fire. Periodic disturbance is necessary to maintain clone vigor. Root suckers benefit from 

stored carbohydrate reserves and an established root system, 

allowing them to grow rapidly and initially outcompete other 

tree species that must regenerate from seed. Aspen’s ability 

to sprout from roots aids it in colonizing sites such as moist 

meadows with dense herbaceous vegetation where seedling 

establishment is difficult.

Sucker production in aspen is strongly influenced by the 

interplay of plant growth hormones. Suckering is suppressed 

by a plant growth hormone called auxin (Schier 1973). Auxin 

is produced by the aerial parts of the tree, including the 

stem, and moves downward along with carbohydrates in the 

phloem. The hormonal control exerted by a stem over the 

root system is called “apical dominance” (Schier et al. 1985a).
2 GENERAL TECHNICAL REPORT PNW-GTR-806

John Day • 

•

Portland

Pendleton •

• Baker City

Umatilla NF

Wallowa -

Whitman NF

Or Malheur NF egon

Washington

Idaho

• Boise

• Seattle

Blue Mountains Ecoregion

National forests (NF)

Figure 1–Blue Mountains aspen study area. Most of the data and experience that went into this publication was gained from the national forest lands 

within the Blue Mountains Ecoregion (boundaries from USEPA 2007).

Figure 2–A 20-ft-long root excavated from a 

sod-covered meadow. This root yielded several 

hundred plantable trees. The parent tree of this 

root was located to the left side of the photo, and 

the significant enlargement of the root can be seen 

particularly near the left hand of the person on the 

left and in front of the person second from right; in 

Alicia Ritner

both cases the swelling is distal to a sucker.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 3

When auxin movement into roots is halted or reduced by 

cutting, burning, girdling, killing, or defoliating the stems, 

auxin levels in the roots decline rapidly. Whereas auxin 

acts to suppress sucker production, another group of growth 

hormones–cytokinins–are produced by the root system 

and promote sucker initiation and development. Cytokinins 

and water move upward toward the crown through a tree’s 

xylem. High ratios of cytokinin to auxin favor sucker initiation, but low ratios inhibit it (Schier 1973, 1975; Schier et 

al. 1985a). Cytokinin production apparently may also be 

stimulated by increasing soil temperatures alone (Williams 

1972), for example, after removal of conifers shading a 

sparse aspen stand. However, if the aspen overstory layer is 

continuous, conifer removal is likely to stimulate overstory 

tree growth and suckering will continue to be suppressed.

It is common in the Blue Mountains to see two-storied 

aspen stands with an open cohort of mature and overmature 

aspen (often overtopped by conifers), and a relatively sparse 

cohort of aspen suckers or saplings. As overstory mortality 

causes reduced auxin production, limited amounts of aspen 

suckering occur. The age of a lower layer–if present at all–

typically coincides with the date at which fencing was constructed, allowing the aspen suckers to escape herbivory.

After a change in hormone balance triggers a new aspen 

cohort, carbohydrate reserves stored in the root system supply the energy needed for sucker initiation and early development. An elongating sucker is entirely dependent upon 

the parent root system until it emerges from the soil and 

can begin photosynthesizing on its own (Schier and Zasada 

1973, Tew 1970). Low carbohydrate reserves allow fewer 

root buds to initiate into suckers, or it results in some of the 

elongating suckers not being able to reach the soil surface, 

and either condition contributes to reduced aspen regeneration (Schier et al. 1985a).

A land manager can actively intervene to promote a new 

cohort of young aspen stems by killing the overstory aspen 

trees, thus reducing or eliminating auxin production and its 

inhibitory effect on sucker production. This tactic involves 

risk, however, because carbohydrates produced by overstory 

trees nourish the root system; if killing the overstory aspen 

trees does not result in suckering, both the root system and 

the clone might be lost.

A healthy aspen clone that has received strong hormonal 

stimulation by overstory removal will produce stem densities far in excess of what can be supported in a mature 

stand; densities as high as 30,000 stems/acre have been 

reported in the Rocky Mountain region (Schier et al. 1985a). 

In contrast to conifer stands, where very high seedling 

densities result in stunted growth owing to competition, 

dense stands of aspen suckers are thought to be beneficial 

to the future of the clone: high initial densities are able 

to maintain the clonal root biomass of the predisturbance 

stand so that it will be available in the future, and they limit 

competing vegetation (DesRochers and Lieffers 2001b, Frey 

et al. 2003). Sucker densities are highest where predisturbance aspen stocking is high. Removal of the aboveground 

stems in the dormant season results in more suckers than 

does stem removal in June or July, because carbohydrate 

reserves are low at the latter time and peak hormone production is past (Schier 1976, Schier et al. 1985b, Webber 

1990). In dense stands that form after fire or clearcutting, 

sucker numbers peak in the first or second growing season 

after the disturbance and decline rapidly by self-thinning in 

the first few years thereafter (Shepperd 1993). After conifer 

removal, the suckering response is more prolonged, and 

new suckers may appear for 4 or more years (Jones et al. 

2005).

Sucker growth rate and survival is strongly dependent 

on light availability (Farmer 1963, Sandberg and Schneider 

1953). Under well-stocked overstories, some aspen suckers 

appear but most die within a few years (Baker 1925). Under 

more open canopies, more suckers survive and they grow 

faster, which increases their chance of escaping herbivores. 

The suckers in a two-layer stand generally have low vigor as 

a result of ungulate browsing, shading by overstory aspen or 

encroaching conifers, and continuing influence from auxin 

produced by overstory aspen trees. However, satisfactory 

aspen regeneration can occur with a residual overstory basal 

area of about 50 ft2/ac on good sites in New Mexico and 

Colorado (Walters et al. 1982).

High soil temperatures are considered by many to be 

important in stimulating suckering and enhancing sucker 

growth rates (Maine and Horton 1966, Zasada and Schier 

1973). High temperatures are thought to favor suckering by 

affecting the cytokinin production as mentioned above, and 

by allowing faster physiological growth processes (Frey 

et al. 2003). Cold soils result in less leaf area for photosynthesis and reduced photosynthetic rates (Jackson 1993, 

Lawrence and Oechel 1983). Soil temperatures in the 70s 

and 80s °F appear to be optimal (Maine and Horton 1966). 

Soil temperatures under Douglas-fir (Pseudotsuga menziesii) (see app. B for plant names and authorities) were found 

to be distinctly lower than under aspen in northern New 

Mexico, especially on south-facing slopes (Gary 1968). 

Soil temperatures increase when the overstory is removed 

and more sunlight reaches the soil surface. The same is 

observed after fires, when the insulating litter is removed 

and the blackened soil surface absorbs sunlight (Hungerford 

1988). Large amounts of slash or chipped residue can retard 

suckering by reducing soil temperatures (Frey et al. 2003, 

Schier et al. 1985b), as can a dense herbaceous vegetation 

layer (Landhäusser and Lieffers 1998).

Existing aspen clones can also expand laterally by root 

growth and suckering beyond the existing perimeter of 
4 GENERAL TECHNICAL REPORT PNW-GTR-806

roots. Most suckers develop within about 30 ft of an existing stem, although in patches of severely hedged suckers, 

they can appear much farther from any normally developed 

stems. Suckers generally develop from horizontal roots that 

are 1 to 6 in below the surface and less than 2 inches in 

diameter (Schier and Campbell 1978).

Aspen are dioecious (male and female flowers are borne 

on separate plants). They produce numerous, small, windborne seeds. Seed reproduction by aspen is limited by 

short seed viability and exacting seedbed requirements 

(McDonough 1985). Aspen seed viability declines quickly 

under natural conditions to negligible levels within 2 

months, and seedlings require a moist mineral seedbed for 

germination and early growth. Seed production in our area 

may be limited by the scarcity of female clones growing in 

proximity to a male clone for pollination.

Although aspen reproduce predominantly by vegetative 

means, we have observed reproduction by seed after fires 

in the Blue Mountains. Our best-documented example is 

a group of aspen in a seed tree exclosure established after 

the 1989 Dooley Mountain Fire in T11S, R40E, section 

24, south of Baker City (fig. 3) (see also the genetics section below). There were no aspen stems in this area prior 

to the fire, and the nearest seed source is several miles 

away. As discussed further below, dry summers in the Blue 

Mountains make seedling establishment very difficult, and 

present herbivore levels in the Blue Mountains make survival of any seedlings unlikely.

Ecological Range

Quaking aspen is the most widespread tree in North 

America (Perala 1990). It grows in a wide variety of environments, such as temperate hardwood forests of eastern 

North America, as scattered groves in Great Plains grasslands, in riparian zones of semidesert shrub-steppes in 

the intermountain West, and in cold boreal forests of high 

elevation and in the far north near arctic treeline. It is shade 

intolerant and occurs as an early seral species in most 

environments. In the Blue Mountains, it is mostly restricted 

to riparian communities and moist areas, but occasionally 

Figure 3–Aspen established naturally from seed inside of a ponderosa pine seed tree exclosure after the 1989 Dooley Mountain wildfire. The photo was 

taken in 2003.

David Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 5

occurs in upland areas and talus slopes. More information 

on aspen communities is given in the aspen community 

classification chapter of this publication.

Temperature–

Aspen are highly tolerant of cold winter temperatures. 

Experiments with dormant twigs show that aspen can survive winter temperatures below -112 °F (-80 °C) (Sakai and 

Weiser 1973), which is considerably lower than any temperature ever recorded in the Blue Mountains. Among aspen’s 

conifer competitors, lodgepole pine (Pinus contorta), 

Engelmann spruce (Picea engelmannii), and subalpine 

fir (Abies lasiocarpa) are also resistant to extremely low 

temperatures when dormant, but grand fir (Abies grandis), 

ponderosa pine (Pinus ponderosa), Douglas-fir, and western 

larch (Larix occidentalis) show damage at temperatures 

in the -22 °F to -40 °F (-30 °C to -40 °C) range (Sakai and 

Weiser 1973). Only a few localities in the Blue Mountains 

(Seneca and Ukiah, Oregon) (Western Regional Climate 

Center 2007) have recorded temperatures below -40 °F, and 

the less cold-tolerant tree species are ubiquitous in the Blue 

Mountains. Thus the relatively mild winters in the Blue 

Mountains allow more competing conifers to grow here 

than in colder environments.

Summer frosts of 26.6 °F (-3 °C) do not harm aspen 

leaves, but most leaves are killed by temperatures of 21.2 °F 

(-6 °C) (Lamontagne et al. 1998). Aspen can escape spring 

frosts by leafing out late (Strain 1966), but this strategy 

may not be effective where lethal frosts occur throughout 

the summer. Climatic data for our area (Western Regional 

Climate Center 2007) show that some locations such as 

Austin, Seneca, and Ukiah, Oregon, have recorded temperatures in the low 20s °F in June, early July, and late August, 

which could prevent aspen growth. Meanwhile, ponderosa pine and lodgepole pine can tolerate summer freezes 

down to about 15 °F (-10 °C) (Cochran and Berntsen 1973, 

Korstian 1921, Parker 1955).

Soils–

Aspen grow on a wide variety of soil types. Aspen in 

the Blue Mountains have been documented growing on 

essentially the full range of soil textures that occur here. 

These are mostly clay loam, loam, and sandy loam; coarse 

fragments content ranges from none to so high that the 

loamy material occurs only in spaces between large rocks 

of a boulder field. Soils under stable (as opposed to seral) 

aspen communities in the Western United States are known 

for their thick, nutrient-rich surface A horizons that are 

produced by the rich litter of the aspen and associated 

herbaceous species (Jones and DeByle 1985c). In the Blue 

Mountains, riparian and meadow aspen usually occur on 

soils with thick A horizons, although there are factors in 

addition to the aspen themselves that act to increase soil fertility, including dense herbaceous vegetation, abundant soil 

moisture, and slow sedimentation by alluviation or slopewash. For more information on the morphology of soils in 

Blue Mountains aspen stands, see the aspen community 

classification section of this publication.

Aspen grow best in near-neutral soils. Aspen are sensitive 

to aluminum toxicity, and thus in acid soils, aspen growth 

rates increase with increasing soil pH (Chen et al. 1998, Lu 

and Sucoff 2003). Poor growth form of aspen saplings that 

could be attributed to soil pH limitations has been observed 

in the Blue Mountains on soils with pH readings of about 

5.6. Unpublished soils data from the Ecological Unit 

Inventory of the Blue Mountains (available from the USDANRCS National Soils Information System, http://soils.usda.

gov/technical/nasis [29 May 2009]) shows that soils with 

pH less than 6 formed in volcanic ash material are rather 

common in the grand and subalpine fir zones, and this could 

limit aspen occurrence there. Aspen regeneration after fires 

is probably enhanced by the release of bases from burned 

material that reduce soil acidity.

Soils with an alkaline, calcareous horizon within 2 ft 

of the surface have been reported to produce poor aspen 

growth (Jones and DeByle 1985c). Only one of 128 plots 

with pH data used in the community classification section 

of this publication had calcareous subsoil, in this case below 

14 in deep. Unpublished soils data from the Ecological Unit 

Inventory of the Blue Mountains show that calcareous soils 

with pH greater than 8 are quite rare on national forest lands 

in the Blue Mountains, but they are common at lower elevations in the area (e.g., Laird 1997).

Moisture–

Soil moisture is more important to aspen than soil texture 

per se, because aspen are not well adapted to extremes of 

either wetness or dryness (Jones and DeByle 1985c). Aspen 

occur on some of the wettest sites in our area, giving the 

impression that they require saturated soils. In fact, aspen’s 

coincidence with wetland habitats in the Blue Mountains 

is unusual from the perspective of aspen habitats across its 

whole range, where it is a typical mesic-site species. Aspen 

roots die in water-saturated, anaerobic soils (Bates et al. 

1998), and we must assume that the aspen we see in wetlands of the Blue Mountains are finding rooting space in the 

aerated soil above the water table. Aspen’s ability to sprout 

from roots is probably an important factor in its survival in 

wetlands in our area. An episode of high water table could 

kill most of the roots and tops of an aspen clone, but as long 

as some roots survive in a better-aerated part of the wetland, the clone can resprout and survive. Aspen can spread 

by root sprouts from these refugia in a subsequent dry climatic cycle and have a competitive advantage over conifers, 

which are also killed in anaerobic wet soils but must regenerate by seed in the dense sod of meadow vegetation.
6 GENERAL TECHNICAL REPORT PNW-GTR-806

Moist sites suitable for aspen may have been more widespread in the past when beavers (Castor canadensis) were 

common in the Blue Mountains. Beaver dams increase 

water storage in headwater streams, raise the water table in 

riparian zones, and increase the area of moist riparian habitat (Kay 1994). Aspen are well adapted to propagate around 

beaver ponds. Aspen can spread by root growth around and 

into lush meadows such as those that form along beaver 

ponds. The moist mud exposed after beaver dams breach 

is a good seed environment for willows (Salix sp.) and 

cottonwood (Populus trichocarpa) (Demmer and Beschta 

2008). The seed physiology and ecology of these plants are 

similar to aspen, and we can surmise that beavers increase 

the opportunity for aspen seedling establishment. Aspen 

is a preferred food of beaver, but beaver use tends to be 

episodic, allowing plants to resprout after cutting (Demmer 

and Beschta 2008).

Aspen are moderately drought-tolerant and occupy the 

grassland-forest ecotone in cold climates (Lieffers et al. 

2001). The leaf fluttering that gives quaking aspen its 

name is widely thought to be an adaptation that cools leaf 

temperatures and allows aspen to tolerate drought better 

than most other temperate-zone broadleaf deciduous trees. 

However, in our area, several other tree species (western 

juniper, ponderosa pine, and probably Douglas-fir) are more 

drought-tolerant than aspen. At low elevations in the Blue 

Mountains, where vegetation is mostly ponderosa pine 

forest, juniper woodland, sagebrush steppe, or grassland, 

aspen are limited by dryness to spatially very restricted 

sites with abundant soil moisture, such as wetlands and 

riparian areas. In environments with more precipitation–

those that support grand and subalpine fir–aspen have been 

documented in the Blue Mountains on a wide variety of 

upland habitats (see the community classification portion 

of this publication), although they are still uncommon and 

most frequent on relatively moist sites.

In the Intermountain Region, aspen are most common 

where mean annual precipitation is at least 20 in, although 

on moist sites they are common where precipitation is as 

low as 15 in (Jones and DeByle 1985a). The 20-in minimum for aspen to occur on upland sites is met over much 

of the Blue Mountains where grand fir is present, as shown 

by data for weather stations at Meacham, Granite, and 

Austin, Oregon (Western Regional Climate Center 2007), 

and USDA-NRCS SNOTEL precipitation monitoring stations (USDA NRCS 2007). However, nowhere in the portions of the West where aspen are prominent (i.e., Utah 

and Colorado) are routine summer droughts as severe as in 

the Blue Mountains. In the Blue Mountains, most stations 

with annual precipitation of 20 to 40 in (i.e., locations with 

annual precipitation totals adequate for aspen) average less 

than 2 in total for July and August. Summers are also dry 

in central Utah where aspen are widespread, but there most 

sites with aspen average at least 3 in total precipitation for 

July and August (Jones and DeByle 1985a, USDA NRCS 

2007).

Competition and Succession

Aspen is a shade-intolerant, early-seral species (Perala 

1990). Even our least shade-tolerant conifer, western juniper 

(Juniperus occidentalis) (Minore 1979), can outcompete 

aspen (Wall et al. 2001). Aspen’s ability to reproduce by 

root suckers and grow rapidly allow it to thrive as a seral 

species when conifers are removed by disturbance such as 

fire. Succession of aspen to conifers in our area is driven 

by both the greater shade tolerance of the conifers, and by 

competition for moisture. Conifers intercept more moisture 

than aspen, especially snow (DeByle 1985c). In the Blue 

Mountains, where most of the precipitation occurs as snow 

and summer moisture is very limited, this probably results 

in considerably less available soil moisture under conifers. 

As most of our conifers are more drought-tolerant than 

aspen, their presence probably provides a positive feedback 

mediated by soil moisture that promotes continued replacement of aspen by conifers.

Most aspen stands in the Blue Mountains are seral to 

conifers. Extensive stands of aspen forests that are stable 

or succeeding very slowly to conifers, such as those in the 

Intermountain Region (Mueggler 1988), are not present 

in the Blue Mountains. Only in rare microsites do aspen 

appear to be stable in our area. Aspen sometimes occur 

in narrow stands fringing wetlands that are not obviously 

succeeding to conifers. Here, aspen’s ability to tolerate 

fluctuating wetness conditions and reproduce by suckering 

in dense meadow sod may allow it to locally outcompete 

conifers. Aspen also occasionally occur in rubble or talus 

fields where conifer seedling establishment is rare but aspen 

can spread successfully by root suckering. These rubble 

and talus environments also serve as refugia from browsing 

ungulates, which typically avoid extremely rocky areas or 

talus slopes.

Fire Effects

Aspen is well known as a postfire seral species. After standreplacing fires, it regenerates abundantly by suckering and 

grows rapidly. Fire stimulates suckering by removal of the 

aspen overstory (which alters the hormone balance) and by 

postfire warming of the soil associated with reduced crown 

shading. Suckers thrive in the abundance of light and generally outgrow other trees species that regenerate by seed 

(Jones and DeByle 1985b). Aspen establishment by seed, 

although rare in comparison to vegetative regeneration, is 

more likely to occur on bare soil after fire than in a densely 

vegetated community. The reduced frequency of wildfires 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 7

starting around 1900 in the Blue Mountains (Heyerdahl et 

al. 2001) is widely believed to be an important factor in the 

decline of aspen here.

Aspen are highly fire-adapted, but aspen-dominated 

communities do not burn readily (Jones and Debyle 1985b). 

Aspen foliage is not highly flammable, and the moist herbaceous vegetation that typically forms the understory often 

will support only light ground fires or no fire at all. Severe 

fires in aspen are much more likely when there is a dense 

understory of shrubs or conifers (Jones and Debyle 1985b). 

Under the historical fire regime of the Blue Mountains, 

with its severe late-summer droughts that spawned frequent 

fires, invasion of aspen stands by conifers probably set the 

stage for stand-replacing fires that would kill the conifers 

and allow aspen to regenerate.

The numerous accounts in the literature of aspen fire 

ecology deal primarily with stand-replacing fires. Little has 

been written about the effect of low-severity fires in mixed 

aspen-conifer stands. This topic is especially pertinent 

because frequent low-severity underburns were the historical fire regime of most low-elevation forests in the Blue 

Mountains (Heyerdahl et al. 2001), and aspen occur here in 

small stands mixed with conifers. Prescribed fires in our 

area are also typically low-severity underburns, because the 

goal is usually to reduce fuels and thin small trees while 

retaining most large conifers. Several of aspen’s serious 

conifer competitors–ponderosa pine, Douglas-fir, western 

larch, and grand fir–are distinctly more tolerant of fires than 

aspen once they have achieved a diameter of 1 to 2 in. 

Thus, light fire in forests of aspen mixed with these species 

could kill most of the aspen while leaving intact a conifer 

overstory that will shade out and kill any aspen regeneration. Keyser et al. (2005) studied light and moderateseverity fires in small aspen clones with conifer invasion 

in the Black Hills of South Dakota. They found that with 

both types of fires, more aspen died than ponderosa pine; 

suckering was not significantly stimulated by light fires, 

and light fires hasten the succession of aspen to conifers by 

preferentially killing overstory aspen. The implication is 

that low-severity fires in stands of aspen mixed with mature 

fire-tolerant conifers will not favor aspen.

Herbivores and Aspen

Aspen communities provide important wildlife habitat in 

the Western United States used by a wide variety of ungulates, small mammals, and birds (DeByle 1985b). Aspen is 

a highly preferred forage species for domestic cattle (Bos 

taurus), deer, and elk in the Blue Mountains; this is a major 

factor contributing to poor aspen regeneration (Shirley and 

Erickson 2001). Most aspen in our area are either mature 

trees well beyond the reach of ungulate herbivores, or suckers with arrested-type growth form indicative of continuous intense browsing (Keigly and Frisina 1998, Keigley 

et al. 2002). An unbrowsed aspen sapling is a rare sight in 

the Blue Mountains outside of an exclosure. Moose (Alces 

alces), which have recently become established in the northern Umatilla National Forest, may add to aspen regeneration problems if they become common. Our observations 

suggest that wild and domestic ungulates impact aspen 

most in the late summer and fall when herbaceous vegetation has senesced and aspen leaves are still green. At this 

time, browsers strip leaves and trim fine green stems (fig. 

4). When elk and moose winter among aspen, they also consume larger twigs. Elk are well known for eating the bark 

off larger trees in the winter (DeByle 1985a). This provides 

entry for diseases and occasionally causes tree death by 

girdling (fig. 5).

Aspen’s relative scarcity in our area, combined with 

high palatability, make it highly vulnerable to browsing. 

Browsing pressure on aspen is greatest when sucker densities are low (Shepperd 1993) and where size classes of aspen 

susceptible to browsing occur in small patches of less than 

12 ac (Mueggler and Bartos 1977). Nearly all of the aspen 

stands in the Blue Mountains occur in small patches, and 

nearly all unfenced stands have low sucker density, making 

them particularly susceptible to browsing.

Aspen Occurrence in the Blue Mountains

Aspen is a widespread yet uncommon species in the Blue 

Mountains. Detailed inventories performed on some ranger 

districts have located hundreds of stands, broadly distributed over our entire area (fig. 6). Although these aspen 

stands are numerous, they are invariably small. An inventory of approximately 25 percent of the 1.7-million-ac 

Malheur National Forest has revealed 1,327 stands, with a 

median area of less than 1 ac; only 5 percent of the stands 

are greater than 10 ac. The Umatilla National Forest’s 

inventory (514 stands) also shows a median area of less than 

1 ac and only 1 percent of the stands larger than 10 ac. The 

total basal area of aspen is also quite low, less even than the 

very locally distributed species western white pine (Pinus 

monticola), mountain hemlock (Tsuga mertensiana), and 

black cottonwood, according to Current Vegetation Survey 

(CVS) data (Johnson 2001) from the three national forests in 

the Blue Mountains.

As described below, aspen are currently in decline in the 

Blue Mountains, but historical photography (Skovlin and 

Thomas 1992) and early accounts (Bright 1994) indicate 

that aspen forests were never as widespread here as in other 

parts of the West such as Colorado (Manier and Laven 

2002) and Utah (Mueggler 1988). The historical rarity of 

aspen in the Blue Mountains, even where mean annual precipitation is apparently adequate (over 20 in), is puzzling. 

Herbivory is obviously responsible for much of the decline 
8 GENERAL TECHNICAL REPORT PNW-GTR-806

in recent decades, but it alone cannot explain the historical 

low abundance of aspen here, because historically aspen 

were eaten by the same herbivores in the Blue Mountains as 

they were elsewhere in the West.

Our current working hypothesis is that, historically, 

climate and conifer competition interacted in the Blue 

Mountains to keep aspen abundance lower than in many 

other parts of the West; this low abundance has in turn 

made aspen more vulnerable here to modern negative factors such as increased herbivory and fire suppression. Eight 

species of coniferous trees are common across the Blue 

Mountains, and all are more shade tolerant than aspen. 

Two of the conifers (western larch and lodgepole pine) 

are fast-growing disturbance-adapted species like aspen, 

and two others (western juniper and ponderosa pine) are 

clearly more drought tolerant than aspen. The environmental factors that give conifers a competitive edge in the 

Blue Mountains were discussed above and are summarized 

as follows. First, the relatively mild winters of the Blue 

Mountains allow the growth of several temperate-zone 

conifer species that cannot survive over most of aspen’s 

range. Second, although winters in the Blue Mountains are 

relatively mild, summer frosts can be severe and are more 

lethal to aspen than at least some of the conifers. Third, 

extreme precipitation seasonality is a factor, perhaps the 

Figure 4–Example of aspen browsing by elk. Figure 5–Bark damage by elk tooth scraping has girdled and killed this 

tree.

Figure 6–Locations of inventoried aspen stands in the Malheur, Umatilla, 

and Wallowa-Whitman National Forests. Shaded administrative units 

have no data. Areas with many overlapping label points appear black. 

Sampling effort is uneven, which is responsible for some of the patchiness 

apparent in aspen occurrence.

Diane Shirley

Michael Tatum
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 9

most important. The severe summer droughts in the Blue 

Mountains present challenges for establishment of trees of 

any species, but especially for aspen with their tiny, shortlived seeds. Finally, soils with pH less than 6 formed in 

volcanic ash are fairly common in moist grand fir and subalpine fir forests of the Blue Mountains; this gives the more 

acid-tolerant conifers a competitive advantage even in areas 

where aspen are less limited by drought.

The hypothesis that conifer competition is the critical factor that has historically limited aspen’s overall abundance 

in our area is supported by aspen’s abundance on certain 

isolated mountains in eastern Oregon where the assortment 

of competing conifers is restricted. On Steens Mountain 

in east-central Oregon, where western juniper is the only 

widespread conifer, aspen form extensive pure stands in the 

7,000- to 7,500-ft elevation range above a zone dominated 

by juniper. In the Trout Creek Mountains of southeastern Oregon, even junipers are rare, and aspen forms large 

groves at about 7,500-ft elevation in a landscape otherwise dominated by sagebrush. On Big and Little Lookout 

Mountains in northeastern Oregon (Baker County), aspen 

is widespread in mixed stands with juniper and Douglasfir (fig. 7). Here lodgepole pine is absent, ponderosa pine is 

restricted to one small occurrence, and grand fir and larch 

occur only on restricted sites with favorable north aspects.

Decline of Aspen in the Blue Mountains

There is consensus among Forest Service land managers 

that aspen are seriously declining in the Blue Mountains 

(Shirley and Erickson 2001). A decline in the area occupied 

by aspen can be inferred from observations of dead aspen 

representing former groves with no survivors, the predominance of clones where many individuals are decadent 

or dead (fig. 8), and the rarity of unbrowsed aspen suckers or young age cohorts. The amount of decline in area of 

aspen since the arrival of Europeans is not known. The two 

main factors believed to be responsible for the decline of 

aspen in the Blue Mountains are herbivory and shading by 

conifers (Shirley and Erickson 2001). In most aspen stands, 

regeneration has been suppressed to some degree by both 

processes.

Herbivory–

Although many herbivores use aspen, those most often 

mentioned as responsible for aspen decline in the Blue 

Mountains are domestic cattle, elk, and deer (mainly mule 

deer, Odocoileus hemionus). Exclosures erected in the Blue 

Mountains to protect aspen have clearly demonstrated that 

these herbivores strongly suppress aspen regeneration in 

our area.

The most obvious reason for increased herbivore pressure 

on aspens in historical times is the introduction of domestic 

livestock (cattle, sheep, and horses). Livestock represent a 

negative effect that was entirely absent prior to the arrival 

of Europeans. Today cattle are the most important species 

of livestock, and they alone appear capable of preventing 

aspen regeneration in many areas. Livestock populations 

were much higher in the early 1900s than they are today, 

Figure 7–Aspen and Douglas-fir mosaic with steppe on Big Lookout 

Mountains, Baker County, Oregon. Shallow soils are steppe or steppe 

with scattered juniper (Juniperus occidentalis). Deeper soils have mixed 

aspen and Douglas-fir forest with shrub understory. This scene illustrates 

how aspen occupies a wide variety of upland sites when these two conifer 

species are its only competitors. Western larch (Larix occidentalis) is also 

present in the vicinity, but only on north-facing aspects not visible in this 

photograph.

David Swanson

Figure 8–This aspen clone near Crane Crossing on the Malheur National 

Forest suffered severe encroachment by ponderosa pine and is completely 

dead. The numerous white downed aspen trunks are evidence of a former 

dense aspen stand.

Michael Tatum
10 GENERAL TECHNICAL REPORT PNW-GTR-806

owing primarily to large numbers of sheep (Galbraith and 

Anderson 1971, Irwin et al. 1994, Powell 2008); this suggests that livestock have inhibited aspen regeneration here 

for over a century.

The population densities of native browsers in the Blue 

Mountains prior to European settlement remain unknown, 

although elk populations have increased substantially in 

the Blue Mountains since their near extirpation in the late 

1800s (Irwin et al. 1994). Several factors combine to make 

native herbivore browsing effects significant today, regardless of whether numbers are actually greater now than 

historically. First, there is probably lower overall diversity 

and quantity of browse plants available to herbivores today 

than in the past, which concentrates browsing pressure on 

remaining palatable plants such as aspen. We suspect that 

the abundance of many palatable species decreased during 

the peak of livestock numbers in the early 1900s. Continued 

heavy use today suggests a long-term decline of many palatable species, including western serviceberry (Amelanchier 

alnifolia), common chokecherry and bitter cherry (Prunus 

virginiana and P. emarginata), yew (Taxus brevifolia), curlleaf mountain mahogany (Cercocarpus ledifolius), bitterbrush (Purshia tridentata), Rocky Mountain maple (Acer 

glabrum), Cascade mountain ash (Sorbus scopulina), willow, cottonwood, and elderberry (Sambucus cerulea and S. 

racemosa). Exclosure studies in the Blue Mountains show 

that ungulates are indeed limiting shrub biomass at the 

present (Riggs et al. 2000). Because most of these browse 

plants are shade-intolerant early-seral species, fire suppression has also probably led to their decline. In addition, many 

low-elevation areas that once served as winter range for 

deer and elk are now occupied by farms and cities. Decline 

in all palatable browse species (including aspen), without a 

corresponding decline in herbivore numbers, concentrates 

continued use on remaining plants and is a positive feedback on their decline.

Finally, the behavior of native browsers has probably 

changed in the absence of their main historical predator–the 

gray wolf (Canis lupus). Studies in Yellowstone National 

Park have shown that aspen regeneration has improved 

since the reintroduction of wolves, and that both reduction 

in elk density and changes in elk behavior are responsible 

(Fortin et al. 2005, Halofsky and Ripple 2008, Ripple and 

Beschta 2007, Ripple et al. 2001). Damage of aspen by 

elk is particularly severe where elk are sedentary in aspen 

stands, a behavior that was presumably less common in 

our area when wolves were present. Also, postfire recruitment of aspen is probably more successful in the presence 

of wolves, because the thickets of aspen regeneration (which 

restrict visibility) and fire-killed dead-fallen trees (which 

are potential obstacles to elk escape) create a risky environment that elk may avoid (Halofsky et al. 2008).

Shading by conifers–

Loss of aspen owing to competition from more shadetolerant species is a natural process that on a landscape 

scale was historically balanced by disturbance, primarily 

by fire, and to a lesser degree by other processes such as 

windthrow, insect outbreaks, and snow avalanches. Fire 

frequency in the Blue Mountains decreased abruptly about 

1900 (Heyerdahl et al. 2001) owing to livestock grazing 

and fire suppression, and it is widely believed that this has 

allowed the more long-lived and shade-tolerant conifers to 

replace aspen.

Other factors–

The decline of aspen in the Blue Mountains may have 

also been furthered by reduction of soil moisture in 

some habitats. Soil moisture has been reduced by conifer 

encroachment (both in the aspen stands themselves and in 

the surrounding watersheds) and by lowered water tables 

resulting from downcutting of streams after extirpation of 

beavers (Finley 1937) and introduction of livestock. Beavers 

were historically present throughout the Blue Mountains 

before being extirpated by trappers in the early 1800s 

(Ontko 1993, Robbins 1997). They are still only locally 

present in our area and functioning dams are rare. As discussed above in connection with the effect of moisture on 

aspen, beavers increase the area of moist riparian habitat 

favorable to aspen, and the near extirpation of beavers over 

150 years ago was probably the first step in the long-term 

decline of aspen in the Blue Mountains.

Invasive Plants and Aspen

Our sample of 220 plots in aspen stands, which was taken 

for the aspen community classification section of this 

report and is described in detail there, includes five species currently listed on the Oregon State Noxious Weeds 

list (table 1). This sample is neither exhaustive nor statistically representative, but nonetheless provides a picture of 

the typical weed problems in aspen stands. Three of the 

weed species are rather common (were recorded on over 5 

percent of all plots), but canopy cover is low. The moist soils 

of aspen stands tend to produce a dense sod that inhibits the 

development of a high weed cover, although this sod often 

consists of nonnative species such as Kentucky bluegrass 

(Poa pratensis). Livestock grazing is often responsible for 

the surface disturbance that allows weed establishment and 

can also lead to the formation of a sod of introduced pasture 

grasses with low diversity of native forbs. More information 

on grazing effects on aspen communities is found in the 

aspen community classification section of this publication.

Bird Use of Aspen Habitats in the Blue Mountains

Scant information is available for avian species composition in aspen communities in the Blue Mountains. 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 11

Consequentially most avian information is extrapolated 

from studies that cover larger expanses of aspen’s range 

throughout the West, derived from studies unique to a 

single avian species, or locally observed but anecdotal in 

nature.

One of the most comprehensive compilations of information on aspen and wildlife in the interior Western United 

States is Debyle (1985b). Despite the omission of Oregon 

in its discussion on aspen range, much of the underlying 

avian information is applicable to the Blue Mountains. A 

wide variety of avian species are known to use aspen stands 

(Debyle 1985b). Aspen communities can provide nesting, foraging, and cover habitat. Some species appear tied 

almost exclusively to aspen habitats, whereas other species 

may use a variety of habitats. Bird species in aspen can be 

grouped by their nesting and feeding habits into a series of 

guilds (Debyle 1985b). Nesting guilds include canopy nesters, shrub or understory nesters, ground nesters, and cavity 

nesters. Feeding guilds include ground-insect, ground-seed, 

foliage-insect, air-perching, and air-soaring guilds. As examples, the tree swallow (Tachycineta bicolor) is a cavitynesting, air-soaring, insectivorous species; the warbling 

vireo (Vireo gilvus) is a canopy-nesting, foliage-insect 

feeder; and the dark-eyed junco (Junco hyemalis) is a 

ground-nesting, ground-seed eater.

Several studies throughout the West have concluded 

that bird species richness may be greater in more mature 

aspen stands versus younger stands and in aspen stands as 

a habitat type versus pure or mixed-conifer-aspen stands 

(Shepperd et al. 2006). In the Sierra Nevada Mountains, 

features of aspen stands that appear to increase bird species 

richness include a thick herbaceous layer for forage and 

cover; aspen’s susceptibility to heart rot, which provides 

habitat for primary and secondary cavity nesters; and the 

abundance and diversity of insects in aspen communities 

(Shepperd et al. 2006). In the Blue Mountains, these correlations may not be as strong given the drier climate and site 

conditions of local aspen habitats.

Richardson and Heath (2004) studied bird-habitat relationships within and across a range of aspen habitats in 

eastern Sierra Nevada Mountains of California and Nevada. 

Bird species richness and abundance were positively correlated with lower percentage of conifer cover, increased 

herbaceous cover, and lower shrub-class aspen cover. The 

results suggest that mature aspen stands with healthy herbaceous communities and limited or no conifer intrusion 

are optimal habitats for aspen-breeding birds in the eastern 

Sierra Nevada. These researchers suggest that to maximize bird species richness and bird abundance, management actions in aspen stands should concentrate on conifer 

removal, where conditions warrant, and the promotion of 

a healthy herbaceous layer. Again, given the wide ecological amplitude of quaking aspen, such correlations should 

be tested locally in the Blue Mountains before making 

similar conclusions about bird richness and abundance. 

Nevertheless, as discussed elsewhere in this publication, the 

removal of encroaching conifers can be justified for several 

reasons to ensure aspen persistence.

Two recent studies in the Blue Mountains have monitored 

avian species in aspen communities: Diurnal Breeding 

Birds in Aspen (Populus tremuloides) Communities on the 

Malheur National Forest, 1997 (Cobb 1997) and Restoring 

High Priority Habitats for Birds: Aspen and Pine in the 

Interior West (Sallabanks et al. 2005).

In the Malheur study, Lynda Cobb of the Grant County 

Bird Club monitored 34 aspen stands using point counts of 

10 minutes duration (table 2) (Cobb 1997). A total of 71 bird 

species were detected. The top five most frequently detected 

species were American robin (Turdus migratorius), warbling vireo, mountain chickadee (Poecile gambeli), northern flicker (Colaptes auratus), and western tanager (Piranga 

ludoviciana). A total of 101 active nests were located. 

Sixty-four cavity nests representing 10 species and 37 opencup nests representing 8 species made up the total. The top 

five cavity nesters were red-naped sapsucker (Sphyrapicus 

nuchalis), northern flicker, Williamson’s sapsucker 

(Sphyrapicus thyroideus), hairy woodpecker (Picoides 

villosus), and house wren (Troglodytes aedon). The top 

five open-cup nesters were American robin, Hammond’s 

flycatcher (Empidonax hammondii), western-wood pewee 

Table 1–Oregon state listed noxious weedsa recorded in plots on aspen stands

 Average cover 

Latin name Common name where present Constancyb

 ---------------Percent---------------

Agropyron repens Quackgrass 3 1

Cirsium arvense Canada thistle 1 6

Cirsium vulgare Bull thistle 1 18

Cynoglossum officinale Houndstongue 3 7

Hypericum perforatum St. Johnswort 1 2

a Oregon Department of Agriculture (2008).

b

 Constancy is the percentage of plots where the species was recorded (N = 220).
12 GENERAL TECHNICAL REPORT PNW-GTR-806

(Contopus sordidulus), warbling vireo, and dusky flycatcher 

(Empidonax oberholseri).

In the Wallowa Mountains, Sallabanks et al. (2005) are 

participating in a long-term habitat restoration study, which 

includes six aspen stands and six ponderosa pine stands. All 

six aspen stands are fenced to minimize or eliminate herbivory. Initial avian data were collected in 2000 and 2001. Bird 

count data detected 71 species in the aspen stands (table 3). 

Species closely associated with aspen included red-naped 

sapsucker, downy woodpecker (Picoides pubescens), dusky 

flycatcher, common raven (Corvus corax), red-winged 

blackbird (Agelaius phoeniceus), house wren, mountain 

bluebird (Sialia currucoides), western bluebird (Sialia 

mexicana), tree swallow, and Williamson’s sapsucker. In the 

aspen stands, a total of 637 nests representing 39 species 

were identified. Many of the species Sallabanks et al. (2005) 

found nesting in abundance match those observed by Cobb 

(1997). In addition, Sallabanks et al. identified chipping 

sparrow (Spizella passerina), dark-eyed junco, mountain 

chickadee, pygmy nuthatch (Sitta pygmaea), red-winged 

blackbird, tree swallow, western bluebird, and yellowrumped warbler (Dendroica coronata) as relatively abundant nesters in aspen. Multiple species were found nesting 

exclusively in the aspen stands, with few to no nests in the 

pine stands.

The Wallowa study (Sallabanks et al. 2005) suggested 

that aspen communities support a richer breeding bird community than ponderosa pine. This finding agrees with other 

bird richness studies discussed previously, but contrasts 

with Sallabanks et al. (2001) who analyzed species habitat 

associations in forests of eastern Oregon and Washington. 

In that review, 77 bird species were associated with upland 

aspen and 131 species were associated with ponderosa pine 

versus 71 species in aspen and 60 species in pine in the 

Wallowa study. Sallabanks et al. (2005) suggested that one 

possible reason for the relatively high number of species 

detected in the Wallowa study is that the aspen studied did 

not occur in pure stands of climax forest but rather as mixed 

seral forest including ponderosa pine, grand fir, lodgepole 

pine, and western larch. Increased habitat heterogeneity 

would presumably support a more diverse bird community. As a result, bird species that are not typically considered aspen associates were abundant in the aspen sites 

(e.g., chipping sparrow and pine siskin Carduelis pinus). 

Consequently, birds considered to be aspen specialists (e.g., 

red-naped and Williamson’s sapsuckers) may suffer negatively from increased competition with other species for 

resources.

The Oregon/Washington Partners in Flight Northern 

Rocky Mountains Conservation Plan (Altman 2000) identified aspen as a high-priority habitat for protection and restoration. The plan identifies red-naped sapsucker as the focal 

species for this habitat. Data from both the Malheur and 

Wallowa studies, as well as other bird-aspen habitat studies 

throughout the West, confirm the importance of aspen to 

birds and justify its classification by Partners in Flight as a 

high-priority habitat. Information in the studies reiterates 

the need for restoration efforts.

Genetic Diversity and Structure of Aspen 

Stands in the Blue Mountains

Information on genetic variability and clonal structure 

can aid in the development of efficient restoration strategies for aspen, and in prioritizing stands for treatment and 

protection. This information is also crucial for preserving 

aspen genetic resources, an important goal in conservation 

of “at-risk” species. If an aspen stand is a single clone, for 

example, protecting a small part of it will preserve existing 

diversity. If each stand contains many clones, more extensive efforts may be required to conserve genetic diversity. 

Genetic inventories also provide baseline information for 

monitoring regeneration and demographic trends, and for 

determining the effects of management practices and disturbances such as climate change on biodiversity.

In 1997, a genetic survey of aspen stands was initiated 

in the Blue Mountains. Leaf tissue from root suckers and 

young saplings was sampled from a total of 92 aspen stands 

in 7 geographic subregions (fig. 9). The purpose of the 

project was to (1) determine the number and uniqueness of 

clones in each stand, (2) determine whether stands are similar or genetically distinct from nearby stands, and (3) assess 

genetic diversity within and among individual stands and 

geographic areas within the Blue Mountains.

Samples were collected along transects made through the 

long axis of each stand. Characteristics such as bark and 

leaf color, angle between lateral branches and the main bole, 

degree of straightness of recent shoot extension growth, rust 

infection, and overall vigor were used to classify shoots as 

belonging to unique phenotypic groups (putative clones). 

Only one plant was sampled from each phenotypic group, 

except in stands comprising one or a very low number of 

overstory trees, where leaves were collected from at least 

two trees. Samples were taken at roughly even intervals 

along each transect, but each putative clone was sampled 

as well as isolated trees growing within the boundary or 

on the periphery of the main stand. Therefore, sampling 

was denser where two or more clones grew together and 

where tree spacing was uneven. The total number of plants 

sampled per stand ranged from 2 to 43 (app. A).

Sample/stand location maps were drawn for each site 

(fig. 10). Clone maps, as well as other study results, are 

available upon request from V. Erickson. Sampled leaf 

tissue was transported on ice to the National Forest 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 13

Table 2–Diurnal breeding birds in aspen communities on the Malheur National Foresta

English name Latin name Detections

Detection 

ranking

Nests 

found

Nest 

ranking

American robin Turdus migratorius 102 1 13 2

Warbling vireo Vireo gilvus 81 2 4 6

Mountain chickadee Poecile gambeli 81 2 4 6

Northern flicker Colaptes auratus 66 3 11 3

Western tanager Piranga ludoviciana 65 4

Hammond’s flycatcher Empidonax hammondii 60 5 9 4

Yellow-rumped warbler Dendroica coronata 58 6

Dark-eyed junco Junco hyemalis 52 7 1 8

Red-naped sapsucker Sphyrapicus nuchalis 50 8 15 1

Western wood-pewee Contopus sordidulus 41 9 4 6

Dusky flycatcher Empidonax oberholseri 41 9 4 6

Cassin’s finch Carpodacus cassinii 39 10

Williamson’s sapsucker Sphyrapicus thyroideus 37 11 11 3

Hairy woodpecker Picoides villosus 36 12 9 4

Red-breasted nuthatch Sitta canadensis 36 12

House wren Troglodytes aedon 33 13 5 5

Chipping sparrow Spizella passerina 32 14 1 8

Lincoln’s sparrow Melospiza lincolnii 30 15

Pine siskin Carduelis pinus 29 16

Brown-headed cowbird Molothrus ater 29 16

White-breasted nuthatch Sitta carolinensis 25 17 4 6

Steller’s jay Cyanocitta stelleri 17 18

Hermit thrush Catharus guttatus 15 19

Wilson’s snipe Gallinago delicata 13 20

Red-winged blackbird Agelaius phoeniceus 12 21

Downy woodpecker Picoides pubescens 12 21

Solitary vireo Vireo solitarius 12 21

Western bluebird Sialia mexicana 12 21 1 8

Red crossbill Loxia curvirostra 11 22

Western meadowlark Sturnella neglecta 11 22

Brewer’s blackbird Euphagus cyanocephalus 10 23 1 8

Macgillivray’s warbler Oporornis tolmiei 10 23

Ruby-crowned kinglet Regulus calendula 10 23

Common raven Corvus corax 7 24

Red-tailed hawk Buteo jamaicensis 7 24

Black-headed grosbeak Pheucticus melanocephalus 6 25

Brown creeper Certhia americana 6 25

Pileated woodpecker Dryocopus pileatus 5 26 2 7

Yellow warbler Dendroica petechia 5 26

Clark’s nutcracker Nucifraga columbiana 4 27

Hammond’s or dusky

flycatcher (unknown)

Empidonax hammondii 

or oberholseri

 4 27

Sandhill crane Grus canadensis 4 27

Townsend’s solitaire Myadestes townsendi 4 27

American crow Corvus brachyrhynchos 3 28

American kestrel Falco sparverius 3 28

Lazuli bunting Passerina amoena 3 28

European starling Sturnus vulgaris 2 29

Gray jay Perisoreus canadensis 2 29

Long-billed curlew Numenius americanus 2 29

Mountain bluebird Sialia currucoides 2 29

(continued)
14 GENERAL TECHNICAL REPORT PNW-GTR-806

Table 3–Breeding birds in aspen in the Wallowa Mountains, 2000 and 2001a

English name Latin name Detections

Detection 

ranking

Nests 

found

Nest 

ranking

House wren Troglodytes aedon 248 1 63 1

American robin Turdus migratorius 236 2 46 3

Warbling vireo Vireo gilvus 186 3 42 4

Dark-eyed junco Junco hyemalis 175 4 28 8

Chipping sparrow Spizella passerina 167 5 32 6

Dusky flycatcher Empidonax oberholseri 165 6 59 2

European starling Sturnus vulgaris 162 7 37 5 

Pine siskin Carduelis pinus 158 8 2 23

Mountain chickadee Poecile gambeli 140 9 30 7

Yellow-rumped warbler Dendroica coronata 137 10 13 16

Western wood-pewee Contopus sordidulus 123 11 24 10

Cassin’s finch Carpodacus cassinii 98 12 7 18

Western bluebird Sialia mexicana 91 13 46 3

Northern flicker Colaptes auratus 89 14 27 9

Red-breasted nuthatch Sitta canadensis 81 15 11 17

Ruby-crowned kinglet Regulus calendula 66 16 2 23

Red-winged blackbird Agelaius phoeniceus 65 17 23 11

Red crossbill Loxia curvirostra 62 18

Hairy woodpecker Picoides villosus 61 19 15 14

Western meadowlark Sturnella neglecta 58 20

Common raven Corvus corax 57 21

Brown-headed cowbird Molothrus ater 51 22

Tree swallow Tachycineta bicolor 50 23 20 12

Red-naped sapsucker Sphyrapicus nuchalis 47 24 24 10

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 14

English name Latin name Detections

Detection 

ranking

Nests 

found

Nest 

ranking

Mourning dove Zenaida macroura 2 29

Tree swallow Tachycineta bicolor 2 29 2 7

Vesper sparrow Pooecetes gramineus 2 29

White-headed woodpecker Picoides albolarvatus 2 29

Black-backed woodpecker Picoides arcticus 1 30

Broad-tailed hummingbird Selasphorus platycercus 1 30

Canada goose Branta canadensis 1 30

Common nighthawk Chordeiles minor 1 30

Evening grosbeak Coccothraustes vespertinus 1 30

Golden-crowned kinglet Regulus satrapa 1 30

Killdeer Charadrius vociferus 1 30

Orange-crowned warbler Vermivora celata 1 30

Olive-sided flycatcher Contopus cooperi 1 30

Spotted towhee Pipilo maculatus 1 30

Rufous hummingbird Selasphorus rufus 1 30

Song sparrow Melospiza melodia 1 30

Townsend’s warbler Dendroica townsendi 1 30

Vaux’s swift Chaetura vauxi 1 30

Willow flycatcher Empidonax traillii 1 30

a Sampling from 34 aspen stands in 1997. Stands range in size from 1 to 20 ac. Counts of individuals are from a single 10-minute point count at 

the center of each stand, or multiple points 200 m apart if the stands were large enough. Nest searches were conducted casually in all stands and 

systematically in seven stands. 

Source: Cobb 1997.

Table 2–Diurnal breeding birds in aspen communities on the Malheur National Foresta (continued)

(continued)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 15

English name Latin name Detections

Detection 

ranking

Nests 

found

Nest 

ranking

Macgillivray’s warbler Oporornis tolmiei 46 25 5 21

Pygmy nuthatch Sitta pygmaea 44 26 18 13

Western tanager Piranga ludoviciana 42 27 3 22

Lincoln’s sparrow Melospiza lincolnii 32 28 6 20

Orange-crowned warbler Vermivora celata 27 29

Hermit thrush Catharus guttatus 27 29

Mountain bluebird Sialia currucoides 26 30 14 15

White-breasted nuthatch Sitta carolinensis 21 31 8 18

Hammond’s flycatcher Empidonax hammondii 19 32 1

Downy woodpecker Picoides pubescens 17 33 7 19

Williamson’s sapsucker Sphyrapicus thyroideus 15 34 8 18

Brewer’s sparrow Spizella breweri 12 35

Golden-crowned kinglet Regulus satrapa 11 36

Steller’s jay Cyanocitta stelleri 11 36

Western meadowlark Sturnella neglecta 11 36

Calliope hummingbird Stellula calliope 9 37 1 24

Mountain quail Oreortyx pictus 8 38

Pileated woodpecker Dryocopus pileatus 8 38 2 23

Clark’s nutcracker Nucifraga columbiana 7 39

Gray jay Perisoreus canadensis 6 40

Red-tailed hawk Buteo jamaicensis 6 40

White-crowned sparrow Zonotrichia leucophrys 6 40

Cassin’s vireo Vireo cassinii 6 40

Rufous hummingbird Selasphorus rufus 5 41

Brown creeper Certhia americana 4 42 1 24

California quail Callipepla californica 4 42

Wilson’s warbler Wilsonia pusilla 4 42

Killdeer Charadrius vociferus 3 43

Lazuli bunting Passerina amoena 3 43

Spotted towhee Pipilo maculatus 3 43

Townsend’s warbler Dendroica townsendi 3 43

White-headed woodpecker Picoides albolarvatus 3 43 5 21

American goldfinch Carduelis tristis 2 44

Black-headed grosbeak Pheucticus melanocephalus 2 44

Brewer’s blackbird Euphagus cyanocephalus 2 44 1 24

Wilson’s snipe Gallinago delicata 2 44 1 24

Northern pygmy-owl Glaucidium gnoma 2 44

Olive-sided flycatcher Contopus cooperi 2 44

Yellow warbler Dendroica petechia 2 44

Cedar waxwing Bombycilla cedrorum 1 45

Common nighthawk Chordeiles minor 1 45

Prairie falcon Falco mexicanus 1 45

Ruffed grouse Bonasa umbellus 1 45

Sharp-shinned hawk Accipiter striatus 1 45

Song sparrow Melospiza melodia 1 45

Swainson’s thrush Catharus ustulatus 1 45

Townsend’s solitaire Myadestes townsendi 1 45

Vaux’s swift Chaetura vauxi 1 45

a Detections of individuals at 35 fixed-area (50-m-radius) plots in six aspen stands visited multiple times in May-June 2000 and 2001, for a total of 125 

point counts. Nest detections were made by comprehensive search of five of the stands, with an average plot area of 43 ac; 2 years of data are combined. 

Source: Sallabanks 2005.

Table 3–Breeding birds in aspen in the Wallowa Mountains, 2000 and 2001a (continued)
16 GENERAL TECHNICAL REPORT PNW-GTR-806

Genetic Electrophoresis Laboratory (NFGEL, Placerville, 

California) for analysis. A total of 19 allozyme loci were 

resolved using standard electrophoresis methodology.

Genetic Variation at the Stand Level

Over all sampled stands, the number of clones per stand 

ranged from 1 to 14 (mean = 2.5). Nearly half (41 of 92) 

of the stands were monoclonal, indicating that the genetic 

structure of aspen stands in the Blue Mountains is strongly 

influenced by clonal spread and persistence via root suckering. Exceptions to this overall pattern were observed 

in two young seedling stands growing in recent wildfire areas (Dooley Mountain, Baker Ranger District and 

Oriental Basin, North Fork John Day Ranger District). 

Here, nearly every sprout sampled represented a unique 

genotype. Similar effects of fire on aspen population 

structure have been reported in other geographic regions 

(Stevens et al. 1999, Tuskan et al. 1996). We suspect that 

the high diversity observed in the more established Target 

Springs stand (Wallowa Valley Ranger District) also reflects 

seedling establishment after fire (14 unique genotypes out 

of 14 samples).

Geographic Variation in Genetic Structure

The extent and diversity of clones varied within and among 

subregions owing to differences in stand size, the degree 

of spatial separation among stands, and possibly also fire 

history. For example, in the eastern portion of the North 

Fork John Day subregion (NFJD-E, fig. 9) where stands are 

extremely small and geographically isolated, 73 percent 

of the stands were monoclonal and no stand consisted of 

more than two clones. Stands in this subregion were also 

highly differentiated and had low genetic similarity. The 

data indicate that the stands are in a self-reinforcing cycle 

of rarity, being isolated and predominantly single sex, with 

limited opportunity for new recruitment or stand expansion via sexual reproduction. In contrast, stand structure 

and corresponding genetic patterns in the western portion 

of the subregion (NFJD-W, fig. 9) were very different, possibly owing to presettlement wildfire history. Aspen stands 

Figure 10–Sampling map of Elk Flat aspen stand 

(POTR0001, Walla Walla Ranger District). Nineteen aspen 

individuals were sampled for genetic analysis (1-19). Genetic 

analysis revealed four clones, as indicated by the red polygons. Maps of the additional 90 sampled stands are available 

upon request from V. Erickson.

Figure 9–Location of the 91 aspen stands sampled for genetic study in seven 

subregions of the Blue Mountains in northeastern Oregon. Subregions: BAK 

= Baker Ranger District, CTUIR = Confederated Tribes of the Umatilla Indian 

Reservation, HP = Heppner Ranger District, NFJD = North Fork John Day (east 

and west), WW = Walla Walla Ranger District, and WAV = Wallowa Valley 

Ranger District.

Vicky Erickson

120° 0’ 0” W 119° 0’ 0” W 118° 0’ 0” W 117° 0’ 0” W 116° 0’ 0” W

47° 0’ 0” N

46° 0’ 0” N

45° 0’ 0” N

44° 0’ 0” N

43° 0’ 0” N

120° 0’ 0” W 119° 0’ 0” W 118° 0’ 0” W 117° 0’ 0” W 116° 0’ 0” W

47° 0’ 0” N

46° 0’ 0” N

45° 0’ 0” N

44° 0’ 0” N

43° 0’ 0” N

125° 0’ 0” W 120° 0’ 0” W 115° 0’ 0” W 110° 0’ 0” W

125° 0’ 0” W 120° 0’ 0” W 115° 0’ 0” W

45° 0’ 0” N 45° 0’ 0” N
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 17

in this area are more abundant and expansive, with shorter 

distances between them. They exhibited exceptionally high 

within-stand diversity (as many as 14 clones per stand), and 

tended to form tight genetic clusters based on geographic 

proximity within a given drainage. Stands that showed 

strong genetic similarity may have seeded in during the 

same establishment event. Aspen in the NFJD-W subregion 

have much greater evolutionary potential as compared to 

those in the eastern portion of the district because they are 

generally multiclonal and likely contain more female clones. 

As a consequence, there are greater opportunities for sexual 

reproduction and increased seed availability when episodic 

disturbances (e.g., wildfires) create conditions conducive for 

seedling establishment.

Genetic Evidence for Decline of Aspen Clones

Among the surveyed stands, we found three clones that 

appear to represent the fragments of large relict stands 

(Jarboe Meadows, Walla Walla Ranger District; Morsay 

Creek, NFJD-W; and Taylor Creek, NFJD-W). Ramets of 

each of these three clones grow in what are now unconnected stands that are separated by over 770 ft (200 m). 

The Morsay clone was especially impressive, with some of 

the remnant segments separated by nearly 3,000 ft (M01 

and M02) (Shirley and Erickson 2001). Apparently a single 

aspen clone became established and spread along Morsay 

Creek, but died out in the middle section. The size of the 

original Morsay clone could rival that of the Fish Lake 

Basin aspen stand in Utah, which has been characterized as 

the most massive living organism on earth (Grant 1993).

Management Implications

Results from the genetic inventory can be used in conjunction with other survey information to help guide conservation and restoration activities and to identify priority 

stands for protection. Because most aspen stands contained 

clones with unique genotypes, we recommend that management strategies emphasize the protection and treatment of 

a large number of stands rather than many clones within 

each stand. From a genetic perspective, priority stands for 

restoration and protection include those that contain large 

amounts of genetic variation, are highly differentiated, or 

have rare or unusual genes. Individual stand clone maps 

(e.g., fig. 10) can assist in making more fine-scale management decisions, such as fence placement or the number and 

location of root collections to help ensure genetic diversity 

of planting stock.

Restoration activities that stimulate/protect vegetative 

regeneration and provide enhanced opportunities for sexual 

reproduction will play a vital role in preserving aspen 

genetic resources in the Blue Mountains. Without management actions such as fencing, removal of conifer encroachment, and planting, many aspen stands will continue to 

decline and will not replace themselves except through 

rare, episodic disturbance events such as wildfire. Isolated 

monoclonal stands with high herbivory pressure are at 

greatest risk of extirpation. When artificial regeneration is 

used to enhance genetic diversity or stand size, or to create 

new aspen stands, plantings should include both male and 

female individuals to help promote sexual reproduction in 

this dioecious species.

Insects and Diseases of Aspen in the Blue 

Mountains

Aspen is host to a relatively long list of insects and diseases 

that result in mortality and various types of damage and 

injury. Thin, living bark, characteristic of aspen, is easily 

damaged by man, animals, and birds. Feeding on bark is 

done by a variety of small and large mammals from voles to 

elk. Big game will often damage saplings and larger trees 

by rubbing their antlers against the stems. Even birds, sapsuckers for example, will scar trees when they drill holes. 

Wounding of the stem bark predisposes trees to attack or 

entry by damaging diseases and insects.

Aspen are damaged and killed by insects and diseases 

throughout their life history. Some blights and cankers will 

effectively kill small-diameter young stems, whereas those 

same agents on older larger trees are not lethal. However, 

the diversity of damaging agents and types and severity 

of damage generally increase as stems mature, and overmature aspen often decline and succumb to one or more 

disease or insect agents.

Because aspen has never been a commercial timber species in the Blue Mountains, the traditional goal of producing 

large straight and sound boles has never been an important 

management objective. Similarly, because of low economic 

value and minor utilization, documented history and even 

current information regarding insect and disease incidence 

and associated impacts are largely lacking for aspen in the 

Blue Mountains.

Ecological values, especially for wildlife, and its contributions to landscape diversity and aesthetic enjoyment, are 

generally considered the greatest importance of aspen in the 

Blue Mountains. Aspen health management strategies focus 

on restoring, maintaining, or expanding clone dimensions, 

and increasing stand vigor, reproduction, and resilience; 

however, these strategies do not strive to promote stands of 

insect- and disease-free trees. Defective trees, those with 

stem decay and dead tops and forks, especially the larger 

and older trees, create habitat and are valuable for a variety 

of wildlife.
18 GENERAL TECHNICAL REPORT PNW-GTR-806

Healthy stands of aspen can be characterized as being 

well represented by different age classes of stems, from 

sucker sprouts to large old trees. Often the oldest stems will 

be in poor condition, with breakage, decay, and cankering, which can result in dead branches, tops, or entire trees. 

However, healthy clones will have existing young and 

periodic recruitment of young stems to replace those that 

die. Healthy clones also maintain or fully occupy their community type, and especially where restorative action has 

occurred, may be expanding their colonized area. Healthy 

clones will be sufficiently large and with enough healthy 

stems and a vigorous root system that there is no danger 

of individual clones dying out in the short term because 

of disturbance, lack of disturbance, browsing and wounding by ungulates, competition by conifers, or pest-caused 

mortality. Healthy stands will retain the genetic diversity of 

existing different clones if they are present. Unfortunately, 

there are substantially fewer healthy aspen clones than those 

that are in poor condition, declining in size and number of 

stems.

Insects and diseases greatly increase diversity in stands of 

aspen, creating snags, downed stems, live trees with decay 

and broken tops, and generally resulting in the demise of 

overmature individuals. This provides habitat for a variety 

of birds and mammals.

The following descriptions are of insects and diseases of aspen confirmed or believed to occur in the Blue 

Mountains. With the exception of very recent mapping of 

defoliated aspen in the annual Aerial Insect and Disease 

Detection Survey (http://www.fs.fed.us/r6/nr/fid/data.

shtml), there are virtually no quantitative or distribution 

data on insects and diseases of aspen for this area; thus this 

information is observational.

Stem Decays

White trunk rot, also called aspen trunk rot–

The most common stem decay of aspen is white trunk rot, 

caused by Phellinus tremulae (fig. 11). This trunk rot is very 

common in aspen stands throughout the Blue Mountains. 

Only aspen is affected by P. tremulae, and some other 

species of hardwoods, exclusive of aspen, will host a very 

similar white trunk rot, caused by closely-related Phellinus 

igniarius, which is only distinguishable from P. tremulae

based on its host. Most Blue Mountain aspen communities 

have at least a minor amount of infection, as confirmed by 

conks or other indicators. Some clones have numerous decadent trees. No comprehensive survey has been done on the 

occurrence of white trunk rot, and in casual observations, 

no trends or patterns have been noticed. Susceptibility to 

infection is probably at least partially influenced by the 

genotype of the clone. Thrifty vigorous trees are less likely 

to have decay, and less thrifty and wounded trees are more 

likely to have white trunk rot.

Trees are infected by airborne spores of the causal fungus 

that colonize branch stubs and wounds. Following infection, decay develops and progresses in the stem, often 

affecting most of the length of the bole. One or more conks 

are produced on some infected and decadent trees. Conks 

are distinctive hoof-shaped perennial hard woody fungal 

fruiting bodies with a gray to black vertically cracked and 

roughened upper surface and a pored brown undersurface. 

In addition to conks, other indicators of decay include 

sterile conks, blind conks, or punk knots, which are swellings packed with fungal tissue generally at branch stubs. 

Unfortunately, many infected and decadent trees have no 

conks or other signs or indicators to aid recognition. In 

some cases, bird excavations and nesting holes expose heart 

rot and confirm infection in the absence of conks or other 

fungal signs.

Wood decay caused by P. tremulae is a white rot that is 

irregular in outline when viewed in cross section. Advanced 

decay is soft uniform yellow to white, bordered with distinct brown-black zone lines that outline the decayed wood. 

A reddish stain may surround the decay column. Cavityexcavating birds require trees with stem decay; they prefer 

to excavate trees with substantial advanced decay and will 

enter the decadent wood where the sapwood is thin. Sound 

sapwood is usually thinnest on the south sides of aspen 

with white trunk rot (Losin et al. 2006). Aspen stems that 

have been damaged by wounding and stands that have had 

fire damage are most likely to have a high incidence of 

white trunk rot. Open or thinned stands also have a higher 

incidence of decay (Callan 1998). Stands with wood borer 

infestation may also be predisposed to white trunk rot.

Live stems with decay that are used by birds and mammals are relatively valuable trees. These trees generally will 

remain standing and can serve as habitat for a number of 

Figure 11–Conk of Phellinus tremulae, cause of aspen trunk rot.

James S. Hadfield
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 19

years, whereas similar dead trees will not remain standing 

for long. White trunk rot will not cause tree mortality, that 

is, kill standing trees; however, trees with well-advanced 

decay may fail, especially at points where the sapwood is 

thin and bird excavation has weakened the bole.

Peniophora polygonia–

Decay and stain caused by Peniophora polygonia probably 

causes some level of damage to aspen in the Blue Mountains. 

However, incidence has not been confirmed and severity of 

infection is unknown. Hinds (1985) reported that Davidson 

et al. (1959) found P. polygonia to have a higher incidence in 

Colorado than white trunk rot caused by Phellinus tremulae.

Although incidence was high, total damage was substantially 

less, suggesting it slowly decays infected trees. Because a 

conk is not formed, this disease will not be recognized on 

live trees. Nearly all information regarding decay associated 

with disease is from saw-log defect and loss-of-merchantability studies (Davidson et al. 1959).

Infection may be recognized in the broken boles of trees. 

Infected younger trees usually have an incipient brown stain 

with a reddish-brown margin. In older trees, infection may 

have had time to develop into a yellow-stringy rot.

Trunk Butt and Root Rots

White mottled trunk and butt rot–

White mottled trunk and butt rot is caused by Ganoderma 

applanatum. The fruiting body of this fungus is commonly 

known as the “artist’s conk,” because the white, very fine 

pore surface is easily and permanently bruised brown when 

touched, allowing intricate designs to be drawn. These 

shelf-like woody, perennial conks are most commonly 

encountered on the roots or root collar of failed trees and at 

the ground line of dead standing trees. They have concentric ridges on the upper surface usually with a thick dusting 

of reddish brown spores. Conks rarely appear on trees while 

they are alive (Callan 1998), but the fungus actively causes 

decay in live trees.

White mottled trunk and butt rot affects a number 

of hosts in the Blue Mountains, but is most commonly 

observed on hardwoods including Populus, Betula, Prunus, 

and Salix. Of these, it is most frequently encountered on 

aspen and black cottonwood. It is also found on conifers. 

No comprehensive survey has been done to determine 

the distribution or prevalence of G. applanatum, or aspen 

stands that are infected in the Blue Mountains. It is occasionally observed and is not considered common. Reports 

in Colorado indicate that it is as common as Phellinus 

tremulae, which is not believed to be the case in the Blue 

Mountains.

With no apparent indicators except conks on dead material, nearly all G. applanatum-caused defect and damage 

to live trees is hidden. Moist sites and mature stands are 

most likely to host infection, decay, and occurrence of the 

recognizable conks (Ross 1976). Trees are infected through 

wounds and reportedly broken tops (Holsten et al. 2001). 

Infected trees will have decay that usually is most advanced 

in the roots and lower butt, and the decay column will 

extend well up the bole. Decay is white to cream-colored, 

soft and spongy, and a brown-colored zone of stain surrounds the decay column. Black zone lines commonly occur 

in the decayed wood. Infected trees may fail while alive and 

usually break at the root collar or lower butt. Once the tree 

is dead, decay will continue to spread in the bole.

Armillaria root disease–

Armillaria root disease of aspen is caused by one of at least 

two closely related species of Armillaria–A. sinipina and A. 

nabsnona–and possibly A. ostoyae (Callan 1998). These and 

several other species of Armillaria had been known collectively as Armillaria mellea until the 1970s and 1980s when 

enough differences were documented that taxonomists 

began breaking different species out of the Armillaria genus 

(Shaw and Kile 1991). Aspen and cottonwood have frequently been observed in the Blue Mountains with evidence 

of decay and root disease caused by one of the Armillaria

species. Prominence by species is not known.

In some regions of the West, Armillaria root disease 

in aspen is recognizable as mortality pockets in infected 

stands. Large aspen mortality pockets caused by Armillaria

are infrequently encountered in the Blue Mountains. When 

observed, most aspen Armillaria mortality is single trees 

or small groups of trees. Confirmation of infection is the 

prolific mushroom production in the fall, or abundant black 

“shoestring” rhizomorphs observed where the bark has 

sloughed off or on the exterior of exposed roots. Trees may 

be dead and down with exposed decay on the roots and in 

the lower butt. Decay will be a white or yellowish stringy 

rot often with numerous black zone lines. Other decays of 

aspen are similar, and decay is not diagnostic enough to 

identify cause of failure or mortality.

Canker Diseases

Stem cankers of aspen are very common throughout the 

range of aspen in the West, including the Blue Mountains. 

Aspen are especially susceptible to canker diseases owing 

to their thin soft living bark that is easily damaged. Wounds 

that penetrate the bark allow infection by spore-spread diseases, including canker diseases. There are several common 

canker diseases of aspen, and a number of less-common 

ones as well. Most Blue Mountain aspen stands have some 

incidence of cankers and some clones are especially susceptible to one or more of these diseases.
20 GENERAL TECHNICAL REPORT PNW-GTR-806

Canker diseases can girdle the stem, causing the crown 

above the canker to die, and if the canker is below the live 

crown, the stem will be killed. Some cankers will often be 

associated with decay that is behind the canker face, and 

stem breakage can occur, both in live trees and trees that 

have been killed.

Sooty-bark canker–

Sooty-bark canker is caused by Encoelia pruinosa, a common disease of aspen throughout the West (fig. 12). This 

canker is especially lethal, and infected trees will generally 

be killed within 3 to 10 years (Hinds 1985). Cankers extend 

rapidly in length, and can be as long as 12 ft within 4 years. 

Wounds are the common and the most frequent predisposing factor for infection by E. pruinosa.

Because the canker progresses so rapidly, callus tissue is not formed. Cankers may appear slightly sunken. 

The bark over the canker is dead, and after several years 

it sloughs off and the exposed inner bark is black. When 

well advanced, the bark is in long stringy strips. The term 

“sooty-bark” comes from the soot-like or powdery residue 

left on your hands when the dead bark is handled. Decay is 

usually not associated with this canker as wood tends to dry 

out and remain solid behind the canker face; however, stem 

breakage at the canker is not uncommon.

Sooty-bark canker is common in stands of aspen in the 

Blue Mountains based on observation. No local information 

is available for incidence, distribution, or severity of sootybark canker.

Black canker, target canker or Ceratocystis canker–

Black canker, also known as target canker and ceratocystis 

canker, is caused by Ceratocystis fimbriata (fig. 13). This 

canker is initiated most often at wounds. The canker face is 

characterized by a series of annually enlarging ragged callus ridges that take the appearance of a target, hence one of 

the common names. The wood and dead bark that adheres 

to the canker face are black, giving this canker its other 

common name. This canker enlarges faster vertically than 

horizontally, but growth is still relatively slow; slower than 

trees grow in circumference, so unless two or more cankers coalesce, girdling will not occur. Decay is usually not 

associated with this canker, and trees and stands can have 

a rather substantial amount of infection and not experience 

too much breakage or mortality. Impact to cankered trees is 

primarily stem deformity.

Black canker is common in Blue Mountain aspen, but 

no surveys have been done to document incidence and 

distribution.

Cryptosphaeria canker–

Cryptosphaeria canker, caused by Cryptosphaeria populina, is known to occur in the Blue Mountains; however, 

information involving distribution and prevalence is not 

available. It has been identified throughout the range of 

aspen from northern Mexico to Alaska. Cankers and 

wood decay are associated with this disease. Small trees 

or sprouts and saplings can be killed within 1 and 2 years, 

respectively. This can occur before they are completely 

girdled.

Trunk wounds most frequently predispose trees to infection. Cankers form that are long and narrow; usually only 2 

to 4 in wide, and 10 or more ft long (Hinds 1985). Infected 

bark beyond the vertical extent of the canker is stained light 

brown to orange. Annual callus tissue is formed, and dead 

black bark adheres to the canker face. Sapwood staining 

will occur beyond the vertical extent of the canker and is 

associated with decay development. The asexual stage of 

the causal fungus, Libertella, will often cause wood decay 

associated with cankers. Cankered trees with decay are predisposed to breakage.

Secondary infection by Cytospora chrysosperma is 

common on cryptosphaeria cankers and may complicate 

diagnosis.

Figure 12 (left)–Sooty-bark canker 

caused by Encoelia pruinosa on a 

dead aspen snag.

Figure 13 (right)–Bulls-eye targetlike form of black canker, caused by 

Craig L. SchmittCraig L. Schmitt

Ceratocystis fimbriata, on aspen stem.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 21

Cytospora canker–

Cytospora canker is caused by Cytospora chrysosperma,

also known by the sexual stage of the fungus, Valsa sordida. Aspen and other species of Populus and species of 

Salix, Alnus, and Prunus are common hosts to Cytospora 

canker, although evidence suggests hardwoods other than 

Populus are probably attacked by a different species of 

Cytospora. Cytospora canker is commonly found on aspen 

in the Blue Mountains, although distribution and prevalence 

have not been determined by survey.

Cytospora canker infects trees that have been wounded, 

weakened by drought, or damaged by frost, sunscald, or 

predisposed by other agents and is generally an opportunistic disease. Cankered trees may have topkill, or the entire 

crown may be killed by cankering that girdles the stem. 

Decay can also be associated with older cankers.

Infested trees will have bark on the canker face that 

initially discolors to an orange to orange-brown and in 

time will darken to black. Slightly sunken cankers may 

be diffuse or have concise boundaries. Several years after 

infection, the bark will start to slough off the canker face. 

Cankers are easily identified by the long orange conidial 

tendrils that are extruded during high humidity from pycnidia (small pimple-like fruiting bodies embedded in the 

bark). These will dry when the humidity drops but remnant 

orange threads may be found. Rain will partially dissolve 

conidial tendrils, which will dry into hard, orange hemispherical masses.

Foliage Diseases

Foliage of aspen may be damaged by several common and 

even more less-common diseases, which can infect the leaf 

tissue from the juvenile stage through senescence. Damage 

is characterized as development of spots, dying of portions 

or all of the leaf tissue, blackening, and shriveling, which 

usually results in premature defoliation. Symptoms generally become more pronounced as the season progresses.

Foliage diseases are generally annual, and infected tissues are confined to the leaf and petiole, being removed 

when the leaves fall. A few diseases can move from the 

foliage onto the shoot. Occurrence and severity of nearly 

all of these foliage diseases varies dramatically from year 

to year, depending primarily on favorable weather conditions coinciding with critical periods of fungi maturation 

and spore dispersal from fruiting bodies on older host 

tissue or fallen leaves on the ground and host bud flush in 

the spring. Two or more severe infection years in a row 

are much more likely to damage trees than single-year 

events. Susceptibility of aspen clones can differ, at least 

partially because timing of bud flush may differ between 

clones. Unusually mild wet spring weather will intensify 

foliage disease spread, development, and resultant effects 

during those years. Many aspen are in microsites that are 

high hazard for spore-spread diseases–those sites characterized as being sheltered, typically having high humidity 

and moderate temperatures. Such sites may have absent or 

minor occurrence of diseases during low incidence years, 

but are apt to have epidemics during years when conditions 

are favorable, and at levels higher than stands on lower risk 

sites.

At least three rust fungi cause foliage diseases of 

Populus, one of which is common on aspen. For successful 

completion of their life cycle, most rust fungi must alternate 

between different hosts. Conditions required for spread, 

infection, and development of foliar rust on aspen are likely 

to be different from other fungal foliage pathogens.

Ink spot–

Ink spot caused by Ciborinia whetzelii is a common leaf 

blight throughout most of the range of aspen in the West 

and is frequently observed in the Blue Mountains. No survey information is available that documents the frequency 

and severity of such infestations.

Following conditions early in the year that are favorable 

for infection, leaves turn brown in the spring, about a month 

after budburst. On trees with severe infestation, crowns 

will be mostly to almost entirely brown. When infestation 

is light to moderate, only a portion of foliage is browned. 

A diagnostic feature of this disease is that petioles on 

browned leaves remain mostly green. Circular to ellipsoid 

black sclerotia, which appear as “ink spots,” develop about 

a month after leaves turn brown and remain on the browned 

leaves until mid to late summer when they start to fall from 

the leaves, which are still attached to the tree. After the 

sclerotia fall, leaves have characteristic “shot-holes,” holes 

in the leaf where the sclerotia had been attached. Damaged 

leaves will start to prematurely drop from the tree starting midsummer. Foliage damage is highest close to the 

ground, small trees are affected more than larger trees, and 

the lower crowns of larger trees are more blighted than the 

upper crown.

Black leaf spot or marssonina leaf blight–

Black leaf spot of aspen is caused by Marssonina populi

and also reportedly by M. brunnea (Callan 1998). This is 

the most commonly occurring leaf disease of aspen in the 

Western United States. It is commonly observed in the Blue 

Mountains during years when it is in outbreak. Favorable 

weather conditions for spore dispersal coinciding with aspen 

bud burst is most apt to result in infection. In midsummer, brown spots start appearing on infected foliage. Spots 

later enlarge and turn black. These irregular-shaped black 

spots will have a distinctive yellow to golden-yellow border, 

and affected leaves will be smaller than similar uninfected 

leaves. Single-year damage is unlikely to cause appreciable 
22 GENERAL TECHNICAL REPORT PNW-GTR-806

damage, but consecutive years with severe defoliation have 

been documented as causing mortality (Walters 1984).

Aspen shoot and leaf blight or shepherds crook–

Aspen leaf and shoot blight is caused by Venturia macularis, which is likely a complex of at least several closely 

related species (Callan 1998). This is a common disease 

throughout the West, including the Blue Mountains. There 

is no information available regarding the distribution and 

levels of severity that have occurred in the past. Endemic 

damage has been observed in most years in some stands, 

especially those on sites where a high incidence of sporespread diseases can be expected.

These pathogens infect host material in the spring during 

bud break and as new leaves expand. Infection can occur 

both from spores released from mature fruiting bodies on 

fallen leaves, or from conidia produced on blighted twigs. 

Mild, wet weather in the spring is conducive for effective spread and development of extensive infection and a 

resulting epidemic. This can be a periodic event, and the 

disease may be nearly absent following poor conditions for 

infection.

After young succulent leaf tissue is infected, tissue wilts 

and turns black, and dead areas become coated with olivegreen fungal growth. Infected areas will enlarge, and infection may spread from the leaf down the petiole to the young 

shoot. In such cases, the shoot tip will wilt, die, and turn 

black. Later in the spring, secondary infections will develop 

rapidly on susceptible tissue. During outbreak years, most 

terminals will be affected and new sucker sprouts may be 

killed. Usually there is just terminal or tip dieback that 

results in loss of height growth in those years. Shoot tip 

dieback often is shaped like the crook in a shepherd’s staff, 

hence the common name “shepherd’s crook.”

Conifer-aspen rust, leaf rust of aspen–

Conifer-aspen rust, also called leaf rust of aspen, is caused 

by Melampsora medusae (fig. 14). This rust is very common 

in aspen throughout the Blue Mountains, and can be found 

in many clones at some level most years.

The causal fungus has a complex life cycle that requires 

spread between conifers and aspen. At least six conifer 

genera are known to host M. medusae. Spores are produced 

in the spring from dead infested aspen leaves that are on the 

ground. The fungus will spread to conifer needless that are 

rather close as these fragile spores do not remain viable for 

long. In the summer, relatively hardy aeciospores are produced on infected conifer needles, which can disperse and 

remain viable and infect aspen over rather long distances. 

Infection can intensify on aspen over the summer as urediospores produced on leaves will continue to spread the fungus within individuals and to additional aspen. Distinctive 

numerous small bright yellow tufts of fungal growth occur 

on the underside of aspen leaves. Later the fungi and leaf 

turn black. Colonized leaves will die and drop prematurely 

owing to this rust, but infection does not spread to perennial 

woody tissue. Effects from premature leaf mortality and 

drop are negligible, and this disease, although very common, is not considered serious.

Insect Pests of Aspen

There are a large number of insects that may feed on or 

infest aspen, causing various levels of damage. Nearly all 

insect pests of aspen that have been documented in the 

West are likely to be present in the Blue Mountains. Several 

insects have been observed locally commonly causing significant damage to aspen, and other insects may occasionally be damaging.

Defoliating insects and other foliage-damaging insects–

Defoliating insects that cause significant damage include 

leaf-feeding larvae of Lepidoptera. Defoliating beetles and 

their larvae may also occasionally cause damage. Leafrollers and leaf tiers are common; significant damage has 

not been noted, but may result during rarely occurring outbreaks. Healthy aspen may have another flush of foliage in 

the summer if defoliated in the spring. Summer-flushed foliage will be sparser and leaves smaller. Consecutive years of 

defoliation will weaken trees and may cause dieback, direct 

mortality, or contribute to predisposition to other insect 

or disease pests. Several defoliating insects probably are 

responsible for most of the defoliation during outbreaks in 

the Blue Mountains, including the forest tent caterpillar, 

satin moth, and large aspen tortrix. Other insects may also 

cause damage less frequently, for shorter duration, or on a 

smaller scale.

Figure 14–Yellow-colored uredinia of conifer-aspen rust (Melampsora 

medusae), on the underside surface of an aspen leaf.

Craig L. Schmitt
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 23

Forest tent caterpillar–

The forest tent caterpillar (Malacosoma disstria) has a wide 

host range, feeding on a variety of broadleaf hosts, although 

aspen is preferred. As with most insects, population levels 

cycle dramatically, and during outbreaks, heavy feeding 

occurs on a number of hosts, including aspen. The forest 

tent caterpillar has been observed defoliating aspen in the 

Blue Mountains, but distribution, periodicity, and severity 

of defoliation events have not been documented. Defoliation 

of aspen by the forest tent caterpillar has not been mapped 

in the annual Aerial Insect and Disease Detection Survey in 

the Blue Mountains.

The forest tent caterpillar overwinters as eggs. The young 

larvae begin to emerge prior to budburst and initially feed 

on expanding flower and leaf buds and then on leaves after 

budbreak. During outbreaks, trees may be completely defoliated by the end of June. Larvae mature in a month or more 

and pupate. They then soon emerge as moths in midsummer, mate, and the female lays eggs. The most effective 

means of spread is when weather fronts transport adults. 

Cold weather that occurs during larvae hatch is believed to 

be a significant factor in reducing populations. Parasites and 

predators also play a role, increasing in number along with 

their host or prey. In addition, a rather host-specific nucleopolyhedrosis virus may control caterpillar outbreaks. This 

virus builds during population outbreaks, spreading when 

densities of insects are high enough, and eventually causes 

populations to dramatically crash. As a result, outbreaks 

last several years and are then abruptly over.

Satin moth–

The satin moth (Leucoma salicis) is an exotic insect that 

was introduced to the west coast from Eurasia in the early 

1920s. The larvae of this insect feed on the foliage of aspen, 

as well as cottonwoods, other poplars, and willow. Damage 

is defoliation (fig. 15), and successive years of severe 

defoliation can cause branch dieback. Satin moths belong 

to the same family as tussock moths and the gypsy moth 

(Lymantriidae); of which the caterpillars are characterized 

as having elaborate and abundant setae (hair).

Defoliation by the satin moth is often striking and can 

be observed from the air. Satin moth defoliation has been 

sketchmapped only in recent years in the annual Aerial 

Insect and Disease Detection Survey. Substantial satin 

moth defoliation was sketchmapped in 2008, and in one 

polygon in 2000, in aspen communities in the Big Lookout 

Mountain area and vicinity southeast of Baker City. Lesser 

amounts were mapped elsewhere in 2008, including mapped 

polygons of defoliation in the Sugarbowl Creek area west of 

Ukiah, Oregon.

This insect overwinters as small larvae in silken cocoons, 

and they emerge when host buds burst and leaves elongate. 

Larvae feed through early summer, pupate and emerge as 

adults (fig. 16) in July. Females lay eggs in July, and, after 

hatching, the next generation of larvae skeletonize leaves 

until fall and the first frost when larvae prepare for hibernation. Damage is most noticeable about the end of June following feeding by mature larvae.

Lymantriidae tend to be generalist feeders, and have 

received most attention as a pest of ornamental and shade 

trees. In Blue Mountain forested communities, satin moths 

are most commonly observed on aspen. Severe defoliation of aspen has been noted at Elk Flats on the Umatilla 

National Forest, on the Malheur National Forest, and in 

large stands of aspen on Big Lookout Mountain southeast 

of Baker City. Other areas undoubtedly have been defoliated as well. Visible damage has been noted every few years 

during outbreaks. Low endemic populations of satin moths 

persist between outbreaks without causing noticeable damage. Birds are important predators, and a variety of parasitic and predatory insects, both native and introduced, help 

control this insect. Evidence in Wyoming suggests that epidemic outbreaks of satin moth are increasing in incidence 

and severity, and that situation may be occurring in the Blue 

Mountains as well.

Large aspen tortrix–

The large aspen tortrix (Choristoneura conflictana) is a leaf 

tier. It is considered the second most damaging defoliator 

Figure 15–Defoliation caused by the satin moth. Photo taken in 

early August. 

Craig L. Schmitt
24 GENERAL TECHNICAL REPORT PNW-GTR-806

of aspen in the West, behind the western forest caterpillar. 

The larvae overwinter as second instars in silken webs in 

the nooks and crannies of rough bark near the base of host 

trees. Upon emerging, larvae crawl up the tree and bore into 

swelling buds, which they then enter. As the leaves unfurl, 

the larvae webs several together and then feeds inside the 

resultant enclosure. By early June, the larvae are mature 

and most or all of webbed-together leaves have been consumed. Larvae pupate in silken cocoons attached to leaves 

and emerge as adults in late June, fly, and mate; the females 

then lay eggs on the upper surface of leaves. After hatching, the tiny larvae again web several leaves together and 

feed, which skeletonizes the leaves. By early August, they 

travel to the base of the tree in search of an overwintering 

site. Other insects can be associated with large aspen tortrix 

outbreaks, including the aspen leaftier (Pseudosciaphila 

duplex).

The large aspen tortrix is known to occur in the 

Blue Mountains, but no historical information is available on periodicity of epidemic defoliation or confirmed 

distribution.

Other leaf-damaging insects–

A number of other insects are commonly found on aspen 

leaves and probably infrequently or rarely cause appreciable damage at the stand level. These may include sawflies 

(Tenthredinidae), leafminers, leafhoppers (Cicadellidae), 

scales, Chrysomelid beetles, and a variety of true bugs 

(Hemiptera).

Boring insects–

The most important boring insects of aspen in the Blue 

Mountains belong to the Buprestidae (flatheaded borers) and perhaps the Cerambycidae (roundheaded borers). 

Wood-boring insects most often attack trees that have been 

weakened or damaged. In turn, boring facilitates colonization by various wood decay fungi, Phellinus tremulae, for 

example, as well as introducing other diseases and predisposing the tree to attacks by other insects.

The poplar borer–

The poplar borer, Saperda calcarata, is the most destructive insect pest of poplars, including aspen, in the Rocky 

Mountain region. Evidence of the poplar borer and associated damage is observed in numerous Blue Mountains 

aspen stands. Documented incidence, severity, and distribution are not available. Evidence of infestation on individual 

trees includes shellac-like exudate oozing from borer holes 

in the bark. Coarse-grained boring frass may be apparent being excavated from these boring holes. The larvae of 

these borers will remain in and mine the wood for several 

years.

Where borer damage occurs, stems that are 2 inches in 

diameter and larger can be attacked. Trees in fully stocked 

dense stands are less apt to be attacked than thinned stands 

or open-grown stands. It is likely that stands having recent 

conifer removal treatments may be susceptible to attack, 

especially if conifers are large. As the result of borer tunnels 

through the wood of branches and stems, trees are weakened 

and bole and branch breakage will occur. Affected trees 

will have evidence of boring in the boles, exude frass, and 

have wet stained areas resulting from sap leakage (fig. 17). 

Breakage will show evidence of mining through the wood. 

Infested trees are susceptible to attack by other insects and 

diseases as a result of reduced vigor and bore holes providing entrance for disease organisms and spores.

The bronze poplar borer–

Evidence of the bronze poplar borer (Agrilus granulatus 

liragus) has been frequently observed on dead and declining aspen in the Blue Mountains, and is believed to be the 

most common wood-boring insect affecting aspen in this 

area. This insect creates distinctive zig-zag winding galleries beneath the bark on large branches and the main stem 

(fig. 18). The gallery pattern can frequently be observed as 

“lumpy bark,” where the bark is still intact. Attacked trees 

may also have crown symptoms of abnormally small leaf 

size, and off-color foliage. This borer primarily attacks 

injured, weakened, or stressed trees. Stands with numerous Figure 16–Adult satin moth (female) in early August.

Craig L. Schmitt
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 25

wounded trees, often from big game disturbance, will have 

active borer activity. Breakage and trees killed by a combination of factors will often have bronze poplar galleries.

This insect generally has a 2-year life cycle. The larvae 

overwinter in one of several larval instars. Those that overwinter as the forth instar will begin feeding in the spring 

when sap begins to flow and, after a period, will pupate just 

under the bark. The adults will chew a “D”-shaped hole in 

the bark and emerge from about the end of June through 

the middle of August. Adult flying, mating, and egg-laying 

concludes about the end of August.

Aspen Management in the Blue Mountains

Overview

Efforts to save and restore dwindling aspen stands in the 

Blue Mountains have been underway for the past 25 years. 

The primary management objectives for aspen in the Blue 

Mountains are (1) to maintain genetic diversity through 

preservation of existing clones, (2) to restore a diversity of 

age structure among existing clones, and (3) to reverse the 

decline in aspen forest area. Our first priority is rescue of 

clones that are in danger of dying out entirely. Some believe 

that half or more of our remaining aspen clones on national 

forest lands could be lost in the next two decades if active 

measures are not taken. Managers are also working to 

facilitate a modest increase in aspen area, in an attempt to 

restore historical acreages. Aspen’s rarity and exceptional 

habitat value in the Blue Mountains essentially preclude 

any harvest for wood products. The issues and strategies 

for aspen management in the Blue Mountains are similar to 

those in the Sierra Nevada of California, and a recent publication about aspen in that area by Shepperd et al. (2006) 

contains much that is applicable to our area.

A decision model for aspen management (fig. 19) has 

been compiled by Mueggler (1989). Vigorous stands of 

mature aspen without codominant competing conifers need 

no treatment; however, if the overstory is breaking up, then 

regeneration is important. Breakup of the aspen overstory 

occurs as mature trees die owing to age, diseases, and 

insects, competition from conifers, or a combination of factors. In the Blue Mountains, there is very little aspen that 

could be considered self-sustaining; removal of competing conifers by natural disturbance or management action 

is required to perpetuate aspen. Although conifers are the 

main competitor in our area, aspen regeneration is occasionally affected by competition from deciduous tall shrub 

Figure 18–Distinctive zig-zag larval galleries of the bronze poplar borer, 

Agrilus granulatus liragus, on dead aspen stem. Note the Phellinus tremulae conk in the upper right.

Figure 17–Evidence of recent poplar borer attacks, including 

boring frass and exudate flow.

Craig L. SchmittCraig L. Schmitt
26 GENERAL TECHNICAL REPORT PNW-GTR-806

Remove 

conifers

Are conifers 

dominant in the 

overstory or 

becoming so? 

Is aspen stand 

healthy and not 

breaking up? 

End: Do 

nothing 

Is aspen 

reproduction 

adequate?

Is stand heavily 

grazed or 

browsed?

Protect with 

fence, wait two 

full growing 

seasons

Yes

Is soil too dry 

or wet? 

Is aspen 

reproduction 

adequate?

End: Maintain 

exclosure until 

reproduction is 

beyond

animals’ reach 

End: Alter soil 

wetness or plan 

for regeneration 

on more suitable 

site 

End: Wait a few 

years and reassess; or 

consider careful 

aspen burning or 

felling 

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

No

No

Are conifers or 

other plants 

suppressing 

regeneration? 

Yes

Remove 

competing

vegetation

Start: Assess 

aspen stand 

Figure 19–Aspen management 

decision flowchart for the Blue 

Mountains, modified from 

Mueggler (1989).
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 27

species, notably hawthorn (Crataegus spp.). Regeneration 

of aspen can be considered successful when vigorous young 

trees numerous enough to restock the stand reach a size that 

makes them resistant to browsers (fig. 20).

Successful vegetative regeneration of aspen requires 

simultaneous hormonal stimulation, proper growth environment, and protection from herbivores (Shepperd 2001). 

Inadequate aspen regeneration under a decadent aspen overstory in our area is most often due to (1) competition from 

conifers, (2) herbivores killing suckers, or (3) continuing 

suppression of suckering by apical dominance of the remaining mature aspen. Management actions that treat these basic 

factors limiting aspen regeneration have a very high success 

rate in the Blue Mountains. As discussed below, removal 

of as many conifers as possible from all size classes will 

benefit aspen regeneration. While mature aspen are healthy, 

conifers can colonize the understory without adversely 

affecting the mature aspen; but when the aspen overstory 

begins to break up, even sapling conifers should be removed 

to allow aspen regeneration. Herbivory will prevent aspen 

regeneration over most of our area, and thus fencing is usually needed. Browsing of aspen suckers is often so intense 

that suckers are difficult to find among other vegetation. 

Many will die, and those that survive after several years of 

intense browsing will develop into a low shrub or a single 

thick woody stub just a few inches high (fig. 21).

Management action is triggered when aspen regeneration is considered “inadequate.” How many aspen suckers are needed to regenerate a stand? The mortality rate of 

aspen suckers is very high in the first few years (Shepperd 

1993), and thus initially high density of suckers is considered beneficial. Several suckers are typically clustered at 

each root node, of which only one will usually survive to 

maturity. Mueggler (1989) considered stands with fewer 

than 500 suckers per acre to have regeneration problems, 

and stands with over 1,000 suckers per acre to have a good 

chance of replacing themselves. Thus management action 

(i.e., conifer removal and fencing) should be considered if 

a stand appears unable to bring 1,000 trees per acre (about 

6.5-ft spacing) to a size safe from herbivores. As discussed 

below, a safe size is diameter at breast height (d.b.h.) of 

about 4 in. The number of sucker clumps per acre may be a 

better guide to regeneration success than individual suckers, 

because only one sucker in a clump will survive to maturity. 

Schier (1975) considered clones with less than 300 sucker 

clumps per acre to be deteriorating, whereas healthy clones 

had 750 to 1,500 clumps per acre.

In our area, aspen are often in wetlands or riparian areas 

where major changes in soil wetness are possible and may 

affect aspen regeneration; for this reason we have added a 

decision diamond about soil wetness to Mueggler’s (1989) 

diagram (fig. 19). Aspen suckering among remnant trees on 

Figure 20–Successful aspen regeneration. The overstory is dying, but 

regeneration is present and large enough to withstand browsing pressure. 

Note the foliage trim line on young aspens from browsing. North Fork 

John Day Ranger District, Umatilla National Forest.

Figure 21–An aspen sucker subjected to many years of intense browsing 

pressure will develop into a thick woody stub.

Diane Shirley Michael Tatum
28 GENERAL TECHNICAL REPORT PNW-GTR-806

stream terraces may be weak after erosion and stream incision have reduced the available soil moisture. In such cases, 

we could attempt to raise the water table through stream 

restoration (e.g., sediment capture), or plan for aspen growth 

only on lower sites. We have also observed situations where 

locations that were formerly suitable for aspen became too 

wet as a result of a change in water-table depth and duration 

(fig. 22). In this situation, aspen regeneration may need to 

shift uphill from its original location for the clone to survive, 

and conifer removal and fencing should accommodate this.

Conifer Removal

Removal of competing conifers is considered essential for 

strong aspen regeneration (Jones et al. 2005). Even our least 

shade-tolerant conifer, western juniper (Minore 1979), can 

out-compete aspen (Wall et al. 2001). Mature competing 

conifers can suppress aspen overstory trees, and conifers 

of any size can suppress growth of aspen suckers. In addition, conifers compete strongly for soil moisture with aspen 

in an environment where moisture is often in short supply. Fortunately, our management experience has shown 

that even severely suppressed aspen will respond to conifer 

removal with new suckering, provided that live stems are 

present. A trenching study by Shepperd et al. (2001) found 

that a dense aspen root system persisted in mixed stands 

where half of the basal area consisted of conifers.

Managers in our area agree that all conifers should be 

removed in treated aspen stands, except for those that must 

be retained to meet other management objectives (e.g., 

large-tree conservation or stream shading). Conifer removal 

from a buffer zone around an aspen stand is also advised to 

permit more light and heat to reach the stand and thereby 

stimulate regeneration, and to allow for some clonal expansion. A buffer may extend 50 ft or more outside the existing live or dead aspen perimeter (see the discussion below). 

Girdling of conifers is also effective in removing conifer 

competition and preferred when harvest is not possible or 

snags are needed (fig. 23).

In situations where managers face opposition to conifer 

removal, they may be asked how much conifer overstory 

can be left while still allowing for adequate aspen regeneration. To our knowledge, all studies published to date 

have involved complete conifer removal. The consensus 

among aspen managers in the Blue Mountains is that aspen 

suckering and growth are inhibited to some degree by any 

amount of competing conifers. To test this position, we 

reviewed data from an unpublished survey of 155 aspen 

stands on the Malheur and Wallowa-Whitman National 

Forests and nearby Bureau of Land Management (BLM) 

lands in 1999 and 2000, by Lynda Cobb and Martin Vavra 

of Oregon State University. They recorded the number of 

aspen suckers in a 30-m (98-ft)-diameter circular plot (or 

two randomly selected quarters of a 15-m (49-ft)-circular 

plot where sprouts were very dense). The canopy cover of 

Figure 22–Effect of a change in soil moisture on the success of postfire aspen regeneration. On the left is ecology plot MW2991 in 1995, 1 year after a 

wildfire. Note mature aspen trees that existed before the fire. On the right is the same view in the year 2000, 6 years after the fire. The depression once 

occupied by an aspen grove is now a cattail marsh with no aspen regeneration. The increase in water supply to this wetland is presumably from loss of 

trees in the surrounding watershed.

Figure 23–Girdling of conifers to reduce competition in an aspen stand.

Roderick Clausnitzer, David Swanson

Cindy Kranich
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 29

conifers was also recorded at the center and margins of the 

30-m plots at the four cardinal directions, using a spherical 

densiometer. The data were collected on plots with livestock 

fencing (n = 6), deer-elk fencing (n = 35), and no fencing (n 

= 114). Plots with small cages were omitted from this analysis because their extent and effect was unknown. We pooled 

the fenced and unfenced stands here because the sample 

size for fenced stands is small and, although sucker density 

averages were higher in fenced stands, in fact, a wide range 

occurs in both fenced and unfenced stands.

A comparison of aspen suckers (count per acre) vs. 

associated conifer canopy cover shows that the maximum 

possible aspen sucker density decreases steadily with 

increasing conifer cover from about 7,000 per acre with no 

conifer overstory to zero at 60-percent conifer overstory 

canopy cover (fig. 24). The trend line in figure 24 represents 

the potential for aspen regeneration when conditions are 

optimal. (Numerous factors can inhibit aspen regeneration, 

even at low conifer cover, notably herbivory, competition 

from other plants, presence of a dense aspen overstory, low 

density or vigor of aspen parent trees, and poor soil conditions.) Just 5 percent of the stands had a relatively high 

sucker density of 3,500 per acre or more, and all of these 

had 20 percent or less conifer cover. The data in figure 24 

support the opinion of field managers that any amount of 

conifer cover inhibits aspen regeneration. Presumably conifer competition suppresses not only the number of suckers 

but also their growth rate, prolonging the time during which 

they are vulnerable to browsing.

Although removal of all conifers is most beneficial to 

aspen, retention of some widely spaced, large conifers for 

other resource needs is compatible with aspen regeneration. 

It is likely that aspen in the Blue Mountains historically 

coexisted with widely spaced large conifers in the parklike stands of old trees that are believed to have dominated 

here in the past. Where only some conifers can be removed, 

removal of those on the southeast to southwest portion of 

the aspen stand will promote soil warming and extra light 

reaching the soil surface. Retained conifers may also be 

pruned well up the stem to improve the amount of light 

reaching the ground.

Aspen regeneration is limited in areas with heavily compacted soils such as concentrated skid trails and 

landings (Frey et al. 2003, Schier et al. 1985b). The worst 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

0 20 40 60 80

Aspen suckers per acre

Conifer cover (percent)

Figure 24–A plot of aspen suckers (count per acre) vs. conifer canopy cover for 155 aspen stands on the Malheur and WallowaWhitman National Forests and nearby Bureau of Land Management lands in 1999 and 2000, sampled by Lynda Cobb and Martin 

Vavra of Oregon State University. The trend line traces the maximum sucker count observed for a given conifer canopy cover.
30 GENERAL TECHNICAL REPORT PNW-GTR-806

compaction occurs from traffic on wet, fine-grained soils. 

Unfortunately, soils are fine grained and moist to wet for 

much of the summer on most of our riparian and wetland 

aspen types (see the section on aspen community classification). Harvest should be timed to occur when soils are either 

frozen or dry.

Conifer slash disposal–

Two main approaches have been used successfully in the 

Blue Mountains for disposal of slash from conifer removal 

in aspen: burning in piles and scattering without burning. 

When slash is light, the latter is a good option. However, 

heavy aspen slash has been shown to inhibit suckering in 

some cases (Frey et al. 2003, Schier et al. 1985b), and it is 

reasonable to presume that heavy conifer slash would also 

have a similar effect. Slash can provide some amount of 

protection from browsing for aspen suckers, although managers in the Blue Mountains believe that browsing pressure 

is typically too intense here for this method to be effective. 

Whole-tree yarding of removed conifers may also be used 

to avoid slash in aspen stands.

Burning small hand piles of slash (approximately 4 ft 

high by 6 ft diameter) disposes of the slash and can stimulate suckering (fig. 25). Long, hot fires in large slash piles 

can kill aspen roots entirely under the piles and create invasion sites for weeds, and thus should be avoided (Jones et 

al. 2005). In most cases, slash piles should be placed a safe 

distance from residual mature aspen so the fire does not kill 

them, because our objective is usually to promote suckering 

in the openings created by conifer removal while preserving 

as many residual large aspen as possible.

Broadcast burning of slash is likely to kill residual mature 

aspen but can be very effective in stimulating suckering. 

Good regeneration has been obtained in our area by this 

method in conjunction with fencing (fig. 26).

Fencing

Managers agree that physical protection of suckers is critical for aspen regeneration and long-term survival in the 

Blue Mountains. Combined herbivory by deer, elk, and 

cattle makes young aspen with uninterrupted growth form 

(Keigley and Frisina 1998) a rare sight outside of fenced 

exclosures or talus slopes, where access by hoofed herbivores is restricted (see for example the POTR [RUBBLE, 

HIGH] aspen community type description in the section 

on aspen community classification). In many situations, 

fencing is the only treatment needed to promote successful 

sucker recruitment (fig. 27). In some places, herbivory is 

so intense that there appears to be no aspen suckering, but 

soon after placement of a fence, suckers become apparent. 

Fencing is needed to allow successful regeneration after 

conifer removal in most localities. Fencing should be in 

Figure 25–Hand pilling of slash for burning after conifer removal from 

an aspen stand. Slash was considered too much to leave in place and was 

piled outside of the aspen stand for burning.

Diane Shirley

Figure 26–Broadcast burning of conifer slash and aspen regeneration. Conifers were removed in 1997. On the left is a 1998 photo of decadent aspen over 

dense slash from conifer removal. The slash was broadcast burned in 1999 after fence construction, killing overstory aspen. On the right is a 2007 photo 

with a few remaining aspen snags and healthy aspen regeneration.

Michael TatumMichael Tatum
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 31

place before considering any treatments that involve killing 

overstory aspen to promote regeneration (such as felling or 

burning). Fencing alone may allow adequate regeneration 

and thus show further treatments to be unnecessary, and 

treatments that kill mature aspen without protecting the 

regeneration could result in loss of the clone.

Stands with abundant browsed suckers and a vigorous 

overstory (as indicated by a crown:bole ratio of at least 25 

percent) are most likely to respond strongly to fencing treatment, but even clones in very poor condition can often be 

regenerated with fencing alone (fig. 27).

Season of use and intensity of use by cattle, deer, and elk 

are unique to each time and place, although in many areas 

the heaviest pressure from all species is in late summer and 

early fall. Fences that exclude cattle alone are cheaper and 

have less effect on wildlife, but over much of our area they 

do not provide adequate protection. Experience in the Blue 

Mountains shows that cattle fencing is adequate locally 

where elk are not common or in elk summer range where 

human traffic prevents animals from lingering long in the 

aspen stands. Managers who suspect that cattle exclosures 

will be adequate in an area may want to test the effect of 

small cattle exclosures before investing in extensive fencing 

that may ultimately prove inadequate.

Most aspen exclosure fencing in the Blue Mountains 

consists of either 7- to 8-ft woven wire (fig. 28) or 6-ft 

Figure 28–Response of aspen to fencing on the Walla Walla Ranger 

District, Umatilla National Forest. The contrast between the aspen exclosure (left) and open area (right) is due to ungulate herbivores; there is no 

significant soil/site difference. Inside the exclosure, which had been in 

place for 10 years by the photo date, aspens were up to 15 ft tall. Outside, 

only a few heavily browsed suckers were located.

Figure 29–Buck-and-pole fencing to protect aspens.

David Swanson Diane Shirley

Figure 27–Response of aspen to fencing. (A) An aspen stand in 2001 on 

the Prairie City Ranger District, Malheur National Forest. Both trees had 

crowns that were marginally alive. By 2004, one of the standing trees 

had fallen and a careful search located about twenty 4- to 6-in-tall suckers 

in the vicinity. Fencing was placed in the summer of 2004. (B) The same 

aspen stand in July 2007. Suckers have increased steadily in number and 

height to over 6 ft.

A

B

Cindy Kranich
32 GENERAL TECHNICAL REPORT PNW-GTR-806

buck-and-pole fencing (fig. 29). The former is very effective 

but subject to snow damage, and thus should be restricted 

to lower elevation sites. Woven wire fences are usually 14 

gauge and can be constructed from single panels or two 

40-in panels joined with hog rings (Rolf 2001). Rolf (2001) 

also suggested placing two strands of high-tensile wire 

above the woven wire. Trees (typically conifers) make good 

corners if available. Some managers consider 5-ft woven 

wire fencing to be adequate except in the areas of highest 

elk browsing pressure. Managers agree that, in many situations, several smaller exclosures are easier to maintain than 

a single large exclosure, and the consequences of a breach 

less damaging.

Buck-and-pole fences are effective, withstand snow loading, can be constructed mostly with local materials, and 

are considered by many to have less visual impact than 

wire fences (fig. 30). Also, the spaces between the rails 

allow small mammals and grouse access to the stand. Local 

Construction Notes: Upright posts shall be 7 ft long x 

5- to 8-in diameter. Rails shall be 3- to 5-in diameter,

12 ft long, and 12 in apart. Back rail shall be 2- to 3-in

diameter, and placed between every other pair of

bucks. Secure rails with spikes long enough to ensure 

3 in nail penetration into the post.

Notch both posts to a depth of 

1/3 the diameter of the post, at

the point at which they cross.

Posts shall fit together snugly.

A-Frame Pattern consists of

one sheet of 3⁄4-in plywood with

2- by 4-in layout boards. Posts 

are placed on the boards,

overlapping each other and

70d spike 1 ft 6 in

overlapping each other, and

then the notches are cut. 

6'

12 in typical

60°

Angle

12 ft rails, 3- to 5-in diameter Back rail, 3- to 5-in

diameter, placed

between every

other set of

bucks. 60°

10 in

7 ft posts, 5- 8-in diameter

10 in

Bottom cross piece shall be 6 ft. 

long, 2- to 3-in diameter, 8 in off of 

g o nd Spike to posts ith 60d

60

Angle

2- by 4-in bracing.

ground. Spike to posts with 60d

spikes.

Construction Notes: For sliding gate, fasten 6 ft by 2- to 3-in 

holding poles to rails on adjacent bucks. Slide 12-ft long 

poles in between rails and holding poles. The gate

poles can easily be slid out and removed for access.

6-ft long pole, fastened to rails with nails.

Figure 30–

Construction 

diagram of buckand-pole fencing.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 33

lodgepole pine stands provide inexpensive materials, and 

may be used without peeling or treatment. Rails should be 

at least 3 inches in diameter. These buck-and-pole fences 

will remain effective with little maintenance for the 15-

year period needed for aspen regeneration and then can be 

allowed to deteriorate and fall in place. Wire fences require 

a labor-intensive cleanup because fallen wire presents a hazard to wildlife and livestock.

Welded-wire rod livestock panels (5 by 16 ft) have been 

used to protect hardwoods in the Blue Mountains (fig. 31). 

These panels are more expensive than rolled wire mesh 

fencing and are suited to protecting individual trees or small 

groups of trees. They are easy to install, resistant to snow 

loads and flooding, and can be disassembled and moved to 

a new location. Elk are able to reach over the panels and 

browse about 2 ft into the exclosure. Both square (fig. 31) 

and circular (fig. 32) layouts have been used. Two 16-ft 

panels shaped to a circular layout make an exclosure with a 

diameter of about 10 ft.

Gabion wire cages, 3 ft in diameter and 5 ft tall secured 

with two or three steel posts have been successful and 

proven to be cost-effective when 10 or fewer cages will 

protect a stand; typically this is a few suckers under a nearly 

dead aspen overstory (fig. 33). Gabion wire is heavy-duty 

mesh designed for construction of rock-filled erosioncontrol structures and the like. Fencing becomes a more 

cost-effective option when more than about 10 cages are 

needed. Small exclosures 10 to 20 ft in diameter can also be 

made quickly with gabion wire and used to protect isolated 

clumps of aspen or suckers around a few decadent parent trees. Use of light-gauge woven wire for building these 

cages has proven unsatisfactory, as large ungulates can 

crush the wire and access the contents of the cage.

Plastic mesh fences (7.5 ft tall) have been used successfully to exclude elk and moose in Montana (Kees 2004). 

Experience with such fencing in the Blue Mountains has 

shown that the plastic mesh holds up reasonably well, but 

steel posts are inadequate for corners, the plastic zip ties 

break in the cold weather, and the fencing tears loose from 

Figure 32–Circular aspen exclosure constructed from two 16-ft weldedwire rod fence panels.

Figure 31–Use of welded-wire rod fence panels to control browsing of 

hardwood tree plantings.

Figure 33–Gabion wire cages 5 years after installation (Prairie City 

Ranger District, Malheur National Forest). These cages were placed 

around the few surviving suckers near two decadent parent trees; at that 

time the suckers were hedged to less than 1 ft tall. Cost was about $25 

each in materials, and all were constructed in about an hour.

Betsy Kaiser

Vicky Erickson Michael Tatum
34 GENERAL TECHNICAL REPORT PNW-GTR-806

the posts. Existing trees provide more secure corners and 

can be used to create an exclosure of irregular shape; also, 

where winter browsing is minimal, snow damage can be 

minimized by letting the fencing down each winter (D. 

Bartos, 2008, personal communication, aspen ecologist, 

USDA Forestry Sciences Laboratory, Utah State University).

In regions with intense aspen use by wild and domestic ungulates such as the Blue Mountains, exclosures must 

be maintained well beyond the point where trees are tall 

enough for foliage to be out of reach. Antler rubbing, barking, and aggressive browsing that causes stem breakage can 

kill trees that are otherwise tall enough to be beyond the 

reach of browsers. Rolf (2001) found that elk in northern 

Arizona broke down and killed most aspen saplings less 

than 2 in d.b.h. and 12 to 15 ft tall. Barking of larger trees 

can lead to girdling or disease infection. Fencing is needed 

until trees reach about 4 in d.b.h., which typically requires 

10 to 15 years in the Blue Mountains area. Annual maintenance checks are needed to ensure the integrity of exclosures. Removing unsound or standing dead trees that might 

fall on the fence can reduce maintenance needs.

Felling trees to form a barrier around the perimeter of an 

aspen clone has been suggested as an alternative to fencing 

in South Dakota (Kota 2005). Based on observations of herbivores’ ability to jump over low fences and also find minor 

breaches in fences, managers in the Blue Mountains believe 

that this method may be effective in situations where browsing pressure is light and cattle are the main herbivore, but it 

would not be effective here in most situations.

Chemical repellents are a potential alternative to fencing for reducing browsing of aspen (Baker et al. 1999). 

Repellents allow some level of browsing, but this might be 

acceptable in a healthy regenerating aspen stand with many 

stems. Some repellents discourage cattle as well as deer and 

elk (Osko et al. 1993). Repellents are generally effective for 

at least a month after application, and are most effective if 

there is little rain. Broadcast application over large areas 

is cost prohibitive (Baker et al. 1999), but spot-spraying of 

isolated clones could prove to be more cost-effective than 

fencing in some situations. Managers in the Blue Mountains 

report that repellents have been used successfully on conifers, but aspen may prove to be more difficult to protect 

because of their high palatability and rapid growth rates: 

new growth after treatment may be browsed because it is 

unprotected. Several summer and fall treatments would be 

needed if elk are present for a long period. Repellents may 

be most promising where cattle are the main herbivore and 

they are present for a fairly short, well-defined interval.

Fire

Fire is generally beneficial to aspen because it removes 

competing conifers and stimulates suckering (Jones and 

DeByle 1985b). Thus prescribed fire is sometimes considered as a management tool to regenerate aspen stands. 

Prescribed fire has been used successfully to dispose 

of heavy conifer slash and stimulate suckering (fig. 26). 

Photo series for quantifying fuels are available for Rocky 

Mountain aspen (Ottmar et al. 2000). However, there are 

several important issues to consider before introducing prescribed fire into aspen in the Blue Mountains. First, aspen 

stands tend to be less flammable than other vegetation types 

in our area; hence when conditions are favorable for burning in aspen, they may be hazardous in surrounding areas. 

Slash from conifer removal in an aspen stand (fig. 26) can 

mitigate this problem by providing highly flammable fuel. 

Second, fire in aspen should be avoided if aspen suckering 

is already occurring, because fire in a stand of suckers can 

be followed by weaker suckering than in the original stand 

(Perala 1974). Third, postfire herbivory on aspen suckers is 

often intense and can prevent aspen regeneration (Shirley 

and Erickson 2001). Studies elsewhere in the West have 

shown that small patches of regenerating aspen–less than 12 

acres according to Mueggler and Bartos (1977), i.e., nearly 

all of our aspen stands–are likely to fail owing to herbivory. 

Coarse woody debris from the fire can be a deterrent, but it 

is generally not effective against elk (Forester et al. 2007), 

and we suspect it to be ineffective against deer also. Thus, 

fencing should be in place to protect new suckers in the 

first growing season after a fire. Fourth, the typical lowintensity prescribed fires used in fuel treatments in our area 

are designed to remove surface fuels and young conifers 

without killing large fire-resistant pines and Douglas-firs. 

These fires can kill mature aspen without removing conifers; as a result, suckers will grow weakly under the conifer 

overstory. Thus, competing conifers should be felled or 

girdled before the fire. Finally, severely weakened clones, 

consisting of just a few suppressed or decadent trees, may 

not have the carbohydrate reserves to regenerate vigorously 

after fire. Given the naturally high mortality rate of aspen 

suckers, the survival of a clone with just a few suckers is 

uncertain. A safer alternative in the case of a small weakened clone would be to first try to regenerate the clone by 

conifer removal and fencing or caging.

Wildfires present both opportunities and risks for aspen 

management. On the one hand, a wildfire can stimulate 

suckering and renewal of decadent aspen stands, plus it 

offers a rare opportunity for seed reproduction by aspen 

(all known examples of seed reproduction by aspen in our 

area have been after fires). On the other hand, after death of 

mature aspen in a fire, the survival of a clone is dependent 

on survival of suckers, which are vulnerable to browsing. 

Forage produced by other early-seral plants after a large 

fire may partly distract herbivores from aspen, but loss of 

aspen clones after fire from herbivory is still a concern. 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 35

Reproduction by seed after fires in our area is extremely 

rare, and seedlings, like suckers, are highly vulnerable 

to browsing. Steps that managers can take to favor aspen 

after wildfire include maintaining existing exclosures and 

constructing new exclosures if possible. Speed is crucial: 

after the overstory aspen are killed, the number of suckers 

will be highest in the first growing season and then decline 

annually in vigor and number under heavy browsing pressure as root reserves are depleted. A second step is reducing herbivory through grazing management. The latter 

approach is, of course, effective only where livestock are 

the main herbivores impacting aspen. Exclusion of livestock, at least during the period when they are especially 

attracted to aspen (late July, August, and September) can 

be very helpful. This management step should be continued 

until aspen are large enough to be safe from cattle browsing, which typically requires about 5 years. We know of a 

few cases where relatively large (10 ac), very vigorous aspen 

stands in the Blue Mountains burned in wildfires and produced regeneration dense enough to withstand herbivores. 

However, the increased frequency and severity of wildfires 

that has been observed in recent decades has not improved 

the overall situation for aspen in the Blue Mountains.

Aspen Felling and Girdling

Aspen are rarely felled in the Blue Mountains. Because 

aspen are not managed for wood products in the three 

national forests of the Blue Mountains, they are not normally harvested here. Harvest to produce stands of various 

ages for wildlife management (e.g., Gullion 1984) is also 

not practiced in the Blue Mountains: although the proportion of old aspen age classes is quite high here, the overall 

rarity of old aspen on the landscape relative to conifer types 

and their great wildlife value preclude harvest to improve 

wildlife habitat.

Girdling aspen is not recommended as a regeneration 

treatment because it stimulates little suckering (Schier and 

Smith 1979). Roots of girdled aspen are deprived of the 

photosynthate that they formerly received from the leaves; 

meanwhile, cytokinin can escape upward in the xylem of 

girdled stems, and thus suckering is not stimulated. In fact, 

girdling is only recommended as a treatment to eliminate

aspen from a site (Schier and Smith 1979).

Resource managers are faced with a difficult decision at 

the end of the flow chart in figure 19 when a deteriorating 

clone has not responded to conifer removal and fencing. 

If these measures have been in place for 2 or 3 years and 

no suckering response has occurred, then some managers 

recommend felling the remaining overstory trees to stimulate suckering (fig. 34). The drawback here is that we lose 

valuable mature trees, and there is some risk that the clone 

will fail to sucker and thus be eliminated by the treatment. 

However, felling may be needed to regenerate a decadent 

clone as described by Schier (1975): the root system of a 

clone may gradually die under diseased, declining overmature trees while these trees continue to suppress suckering. 

Unfortunately, less aggressive measures, such as felling 

only half of the remaining large trees in a deteriorating 

clone, result in weak suckering responses. If such a “last 

resort” felling of aspen is implemented, avoid felling soon 

after leaf flush, when carbohydrates have been translocated to the tops and root reserves are lowest (Schier 1976). 

Dormant-season felling is preferred (Schier et al. 1985b). 

And, of course, ensure that fencing is in place so that the 

suckers, which may be sparse under a severely weakened 

clone, are adequately protected.

Mechanical Site Preparation

Mechanical site preparation can stimulate suckering, but it 

can also lead to root damage that hinders sucker survival 

and future productivity (see reviews by Frey et al. 2003 

and Schier et al. 1985b). For example, disking severs roots, 

which disconnects them from overstory trees and releases 

them from apical dominance-related suppression of suckering; it can also increase soil temperatures and reduce competing vegetation. However, the small root segments created 

by disking have very limited water uptake and receive no 

energy inputs from neighboring trees. For these reasons, 

disking is generally not recommended (Schier et al. 1985b).

Separation of lateral roots from existing mature trees by 

deep soil ripping just outside the canopy limit has been recommended as a way to extend stand boundaries (Shepperd 

2001, Shepperd et al. 2006). Suckering from remote 

roots is stimulated by separation from overstory trees. 

Figure 34–Suckering response of degenerated aspen clone to felling. This 

clone responded weakly to conifer removal but regenerated well after felling the decadent overstory aspens, with fence protection.

Joe Sciarrino
36 GENERAL TECHNICAL REPORT PNW-GTR-806

Unfortunately this treatment is expensive and also cuts off 

any carbohydrates that the suckers would receive from the 

mature trees. In our experience, suckering from distal roots 

is usually adequate without ripping (e.g., fig. 35).

Thinning

Managers in the Blue Mountains are interested in thinning 

as a means to speed up the growth of aspen to a size class 

that is safe from herbivores. Thinning aspen often increases 

diameter growth rate, whereas height growth rate depends 

mainly on site quality (Jones and Shepperd 1985). Thus, 

thinning could shorten the time needed to create robust 

stands (e.g., trees 4 in d.b.h. or greater) resistant to antler 

rubbing, barking, and breaking by pushing and trampling.

Some arguments against thinning are as follows. Aspen 

effectively self-thin in dense postdisturbance stands, and 

thus artificial thinning is not necessary to the development 

of productive stands (Frey et al. 2003, Shepperd 1993). A 

high density of suckers provides some insurance against 

mortality losses to herbivores or other factors. Also, a dense 

stand of aspen suckers helps to maintain the root system 

that will be used by the clone in the future (DesRochers and 

Lieffers 2001b).

Fencing is crucial for any stands thinned in our area, 

because herbivore damage is greater in sparse stands 

(Shepperd 1993). Thinning of dense first-year stands can 

produce numerous new suckers that must be thinned again 

(Strothman and Heinselman 1957). Jones and Shepperd 

(1985) recommended thinning stands at 5 to 10 years of 

age, when the tallest trees are about 15 ft tall, to a spacing 

of about 5 by 5 ft (1,500 trees per acre). Thinnings in older 

stands are generally recommended for saw-log production 

and are not applicable to the Blue Mountains.

Establishment of Aspen Outside of Existing Stands

Establishment of new aspen stands is desirable to restore 

lost clones, increase connectivity between existing stands, 

increase genetic diversity, and improve the opportunity for 

A B

C D

Figure 35–Response of aspen to conifer removal and fencing, Geary Aspen Project, Blue Mountain Ranger District, Malheur National Forest. (A) March 

1994, prior to treatment. Note the conifer encroachment in the stand behind and stubs from browsed suckers in the foreground. (B) March 1994, after 

conifer removal. A fence was constructed soon after. (C) August 1995. The densest portions of the stand had approximately 10,000 stems/acre. (D) July 

2007. Regeneration was 6 to 10 ft high behind the fence; sparse browsed suckers were outside of the fence.

Michael Tatum
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 37

sexual reproduction by providing a mix of male and female 

plants (Shirley and Erickson 2001).

Expanding the boundaries of an existing aspen clone is 

often desirable, both to restore lost historical area and to 

increase the chances for long-term survival of the clone. 

For example, an aspen clone squeezed into a narrow zone 

between dense upland conifers and a wet sedge meadow 

is in a precarious position, vulnerable to elimination by 

a minor rise in the water table (figs. 22, 36). Many wetland margin aspen clones would be made safer by conifer 

removal that would allow them to expand into somewhat 

drier adjacent areas.

Aspen roots are often found well beyond the perimeter of 

existing trees. The range of the rooting for a clone can often 

be estimated by careful search for aborted suckers. Felling 

conifers and fencing to allow successful production of suckers from these existing roots often yields dramatic results 

and a rapid increase in the area occupied by aspen stems 

(fig. 35). As discussed in the “Aspen Biology and Ecology” 

section, aspen roots can grow laterally at a rate of perhaps 1 

yd per year under favorable conditions. Thus it makes sense 

to extend fencing and conifer treatment beyond any existing 

stems or aborted suckers if site conditions appear adequate. 

We have observed clonal expansion to be most successful 

on the south and southwest sides of existing aspen clones. 

This is presumably due to the greater light availability and 

higher soil temperatures to the south and southwest. Thus, 

a larger zone of conifer removal and fencing to the south 

or southwest side of a clone is advised. One of our ranger 

districts, as a rule of thumb, extends conifer removal and 

fencing 50 ft beyond the last live aspen on the north and 

east side of a stand and 100 ft to the south and west.

Planting artificially propagated aspen plants is more 

costly but necessary if the goal is to establish a new stand, 

rapidly expand a stand far beyond existing boundaries, or 

cross barriers to roots such as a stream channel (fig. 37). 

Planting stock should be derived from local sources, but 

not necessarily from the clone nearest the planting site; it 

is often desirable to intersperse material from various local 

clones to increase genetic diversity and to ensure a mix of 

male and female plants for sexual reproduction. For more 

information on propagation and planting see the “Vegetative 

Propagation” section below.

Choosing appropriate sites–

Clearly any area proposed for planting or expansion of an 

existing aspen clone must have suitable soil and site conditions, minimal competition from other vegetation, and the 

usual protection from herbivores. The latter two conditions 

do not differ from what is required for regenerating aspen 

clones within their present limit and was discussed previously. The answer to the former question–Where are soil/

site conditions correct for expansion of an aspen clone?–is 

not always obvious, yet must be answered before investment 

is made in fencing, conifer removal, or planting. Areas adjacent to a vigorous existing clone with similar landform and 

understory vegetation are good bets for successful expansion. The following guidelines are suggested if the objective 

is to plant or expand a clone into new areas unlike those 

currently occupied. They are based on our aspen community classification work.

1. In areas where the upland vegetation is dominated by 

the dry upland forest potential vegetation group (ponderosa 

pine or Douglas-fir series vegetation, or dry grand fir plant 

associations such as grand fir/pinegrass; see Powell et al. 

2007 for more information), aspen is usually restricted to 

riparian or wetland areas where supplemental moisture is 

available and soils are rich and loamy with a high available 

water capacity. Look for areas with a diversity of mesic 

forbs such as those listed for the aspen/mesic forb or aspen/

Figure 37–Aspen planted to enlarge a stand. Site conditions in the planted 

area are similar to the stand with vigorous regeneration in the background, but well beyond the extent of existing roots.

Diane Shirley

Figure 36–Aspens on meadow fringe. Aspens in the Blue Mountains 

often occur in a narrow zone between soils that are too wet and coniferous forest with too little light. If the water table in this meadow were to 

rise, the few remaining aspens could be killed.

David Swanson
38 GENERAL TECHNICAL REPORT PNW-GTR-806

common snowberry plant community types. Areas supporting a dense sod of introduced pasture grasses such as 

meadow foxtail (Alopecurus pratensis), Kentucky bluegrass 

(Poa pratensis), and timothy (Phleum pratense) will also 

usually support aspen (see the aspen/Kentucky bluegrass 

and aspen/meadow foxtail plant community types in the 

section on aspen community classification). Note that the 

presence of the introduced pasture grass, intermediate 

wheatgrass (Agropyron intermedium), alone is not a good 

indicator of suitability for aspen, because this grass can 

grow on sites too dry for aspen. Vegetation on proposed 

aspen sites should be distinctly more lush and diverse than 

in the adjacent dry upland forest. Areas dominated by 

wetland grasses and sedges such as aquatic sedge (Carex 

aquatilis) or bluejoint reedgrass (Calamagrostis canadensis) can sometimes support aspen, but are often too wet. For 

optimal aspen growth, the water table should recede at least 

2 ft below the surface for most of the growing season (Jones 

and Debyle 1985c).

2. In areas with upland vegetation dominated by moist 

upland forest or cold upland forest potential vegetation 

groups (moist grand fir or subalpine fir potential vegetation; 

Powell et al. 2007), aspen is still most common in wet areas, 

but moisture is also adequate for aspen to grow on a variety of upland sites. Thus established aspen clones can be 

enlarged from wetland margins onto adjacent drier soils, as 

long as the upland soils are not obviously shallow, droughty, 

or nutrient-poor. New plantings are most likely to succeed 

in moist mesic meadow areas such as those described above 

for the dry upland forest areas. If a new planting of aspen on 

an upland site is attempted, look for a relatively lush growth 

of the understory species listed for grand fir series aspen 

types (see the aspen community classification section), the 

most widespread of which is the aspen (grand fir)/snowberry plant community type. Mesic forbs such as mountain 

sweet-cicely (Osmorhiza chilensis), western meadowrue (Thalictrum occidentale), and nettleleaf horsemint 

(Agastache urticifolia) are good indicators of relatively rich, 

moist soil where aspen should flourish. As in the previous 

case, avoid areas with chronically saturated soils dominated 

by wetland grasses and sedges.

Vegetative Propagation

Stem cuttings of aspen root poorly, so a more elaborate 

procedure is required. A protocol developed in Denmark by 

Larsen (1943) has been modified and used with aspen in the 

Western United States, and is described in detail by Schier 

(1978) and Schier et al. (1985b). This method involves making root cuttings from an existing stand, developing suckers 

from the cuttings, then cutting and rooting these suckers. 

The following section is an account of local experience 

with this propagation method in the Blue Mountains. (See 

also propagation protocols assembled by the Native Plant 

Network at http://www.nativeplantnetwork.org/)

Root collection–

It is best to collect roots in the autumn, following leaf fall in 

mature trees, when the maximum amount of carbohydrates 

reside in the root system as opposed to in the apical shoots 

of stems (fig. 2). Autumn cuttings must be refrigerated for 

several months after collection, but then the entire subsequent growing season is available for rooted sucker production. Cuttings may also be made in early spring (Schier 

1978), although snow and frozen soil may interfere. Root 

cuttings should not be made during the spring leaf flush, 

because the high concentrations of auxins in the roots at 

this time suppress suckering (Scheir 1978).

A good rule of thumb is to collect roots that are, at a 

minimum, the size of your index finger in diameter. Roots 

larger than 3 inches in diameter are more cumbersome for 

the nursery to work with. Pulaskis, hoedads, and shovels 

have all been used successfully, as has washing roots from 

the ground using high-pressure water. A small hand trowel 

comes in handy for more delicate excavation of roots. Root 

suckers growing in a straight line are excellent indicators 

of where the mature root is located underground. Mature 

roots may be as close as 2 in beneath the ground surface but 

most often are found at a depth of 4 to 6 in. These surface 

roots take advantage of light rains that do not penetrate to 

the groundwater level and eventually will turn downward 

in search of more abundant moisture. It is important to use 

care when digging to prevent scraping the surface tissue of 

the roots. This tissue contains the primordia that become 

root suckers. Heavy-duty branch pruners are used to cut the 

roots into 8- to 12-in segments. Smaller pruners are useful 

to remove any suckers. You may leave the suckers intact and 

simply transplant it to another site; however, our success 

Figure 38–Aspen root cuttings after cleaning and before final wrapping. 

Roots should be kept moist and cold throughout this process.

Michael Tatum
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 39

rate for such transplants has been poor, probably owing to 

their weak root systems. Excavated roots are placed in large 

trash bags along with some sort of tag to identify the source 

of the collection site.

Upon returning to the office, one should futher trim roots 

and rinse off excess dirt (fig. 38). Rinsing also keeps the 

roots moist during shipping. We roll the roots up in burlap 

bags or polypropylene shop towels and then place these in 

clean plastic trash bags. A tag indicating stand location and 

elevation is placed in a sealable plastic bag inside the trash 

bag. This way more than one bag may be shipped in a box. 

Roots may first be mixed with sphagnum moss before wrapping, which will prevent the formation of mold when the 

roots are placed in cold storage over winter. Roots should be 

kept refrigerated until just before shipping. Overnight shipping of roots to the destination nursery reduces the potential 

for drying or overheating of roots.

Propagation of containerized aspen from collected 

roots–

Propagation, to date, has been carried out by the U.S. Forest 

Service J. Herbert Stone Nursery in Medford, Oregon, 

and the U.S. Forest Service Coeur d’Alene Nursery (Idaho 

Panhandle National Forest). Cost per plant was about $2.00 

from the latter source in 2008 for small quantities (several 

hundred), not including the cost of root collection, shipping, or outplanting. Root segments received in the fall were 

washed in a large tub containing a 10-percent alcohol solution, wrapped in polypropylene shop towels or burlap, and 

stored under refrigeration (Johann Visser, personal communication, culturist, J. Herbert Stone Nursery). In February or 

early March, root segments were placed in wooden containers measuring 2 by 3 by 6 in. Drainage holes were drilled 

into the base of the containers. The containers were then 

filled with a 1-in layer of pure perlite, followed by a 3- to 

4-in layer that was 40 percent peat, 40 percent vermiculite, 

and 20 percent perlite. Root segments were placed on top 

of the latter layer and covered with approximately a quarter inch of the same. The medium was moist but not wet to 

reduce disease. The containers were placed in a greenhouse 

maintained at 70 to 75 °F. Sprouting took place within 10 

days to 2 weeks. When root suckers reached 3 to 4 in tall, 

they were cut as close as possible to the old root section 

and the lower leaves removed, and then they were dipped 

in a commercial rooting hormone containing IBA (indole3-butyric acid) and placed in individual D-40 (40 in3) 

containers or in 1-gal pots filled with a mixture that was 40 

percent peat, 40 percent vermiculite, and 20 percent perlite. 

These were grown in a mist chamber under a 24-hour photoperiod at 90 percent relative humidity and 78 °F (during 

the day a layer of shade cloth was placed over the chamber 

to reduce sunlight by 50 percent). Roots emerged within a 

few weeks on about 70 percent of the cuttings. The plants 

were fertilized with a solution containing a 21-5-20 ratio 

of nitrogen, phosphorous, and potash and trace amounts of 

micronutrients. When the plants appeared to be growing 

vigorously, they were placed in a greenhouse and grown 

for 2 to 3 weeks, or until approximately 10 in tall. After the 

danger of hard frosts had passed, containers were moved 

outside to a shade house for the remainder of the growing 

season (fig. 39). The average height at the end of the growing 

Figure 39–Rooted aspens in 2.5-in diameter by 10-in deep (40 in3) plastic 

containers growing in a shade house.

Michael Tatum

Figure 40–A shade card improves the survival of planted aspen.

Diane Shirley
40 GENERAL TECHNICAL REPORT PNW-GTR-806

season was 16 in. Once plants had completely hardened off 

and entered dormancy in late fall, containers were moved 

into freezer storage until they were needed for outplanting 

the following spring.

Planting propagated aspen–

Propagating aspen is an expensive venture. It is imperative that planting procedures that will optimize survival are 

employed. Ensure that site conditions are appropriate, with 

adequate available soil moisture and removal of competing 

vegetation; see the previous section for more information. 

In addition, trees must be planted properly, in adequate 

densities, and protected from herbivores. Dormant containerized trees should be planted as early in the year as conditions allow.

Warm temperatures and severe drought are common 

in summer in the Blue Mountains, and preventing tree 

death from desiccation is a challenge, particularly on more 

coarse-grained soils along intermittent streams that run 

dry early in the summer. As temperatures rise to 90 °F and 

above, the heat load on the young aspen rises dramatically. 

This often results in dieback of the terminal shoot or death 

from desiccation. Placing a shade card approximately 2 to 

4 in from the planted tree, on the south-southwest side of 

the tree, blocks much of the afternoon sun, thereby reducing the heat load (fig. 40). It is important that the shade card 

is placed low enough to protect the root collar of the tree. 

Even if the aspen terminal dies back to the height of the 

shade card, the tree usually survives. Most often, a lateral 

shoot will assume dominance in the subsequent growing 

season. It is critical to keep the root system alive until the 

tap roots can grow down to the water table. If successful, 

the shoot can die back to ground level and the root system 

will send up a new shoot the following season.

Removing competing vegetation, such as sedges and 

grasses, will also reduce the competition for moisture. A 

scalp that is 24 in square is usually sufficient and provides a 

competition-free environment for the first growing season. Planting on sites that provide adequate soil moisture 

throughout the growing season, will of course, eliminate the 

need for the above measures.

Selecting an adequate planting density to ensure successful reforestation is dependant on the predicted survival 

rate for the site. One high-elevation site with plentiful soil 

moisture and relatively low heat load from the afternoon 

sun on the Umatilla National Forest had a survival rate of 

99 percent. Favorable predicted survival allows planting at 

much lower densities with the expectation that surviving 

trees will send up hundreds of root suckers in the future. 

This permits the manager to spread a limited number of 

aspen containers across several planting units.

Rigid, plastic tubing can provide short-term protection 

from herbivores for planted aspen on a new site. This relatively inexpensive measure will protect the young aspen; if 

survival is adequate, more expensive measures (e.g., fencing) can be justified. Tubes should be at least 24 in tall and 

are stapled to 1.5 in square, 30-in tall, wooden hubs. The 

hubs are pounded into the ground to a depth of 12 in. These 

hubs hold up much better in the snow than do bamboo 

stakes. Longer tubes (30 in) provide protection longer for 

the rapidly growing aspen, but we found that these larger 

tubes were more easily knocked over by cattle, probably 

because a proportionally longer segment of the wooden 

hub was exposed and acted as a lever to push the tube 

over. Once the aspen has outgrown the tube, the device has 

served its purpose and it is time to move on to a longer term 

solution: fencing.

Other vegetative propagation options–

Juvenile shoots of aspen hybrids (Populus tremuloides x P. 

tremula) grown from tissue culture have been successfully 

cut into short (two-node) cuttings and rooted with about 70 

percent success rate (Haapala et al. 2004). Multiple batches 

of greenwood cuttings were made from the same stock by 

cutting regrowth every 4 weeks. This technique could prove 

successful with suckers from root cuttings grown in the 

greenhouse as described above, allowing more plants to be 

obtained from each root cutting. Aspen have also been 

successfully propagated by tissue culture derived from 

seeds (Noh and Minocha 1986).

Propagation of Aspen from Seed

Propagation of aspen from seed is also possible, although 

abundant seed production events (fig. 41) appear to be rare 

in our area. Both bare root and containerized methods have 

been used (Day et al. 2003, Schier et al. 1985b; see also the 

Native Plant Network at http://www.nativeplantnetwork.

org/). Campbell (1984) believed that propagation from seed 

is faster and cheaper than vegetative propagation. Several 

issues should be kept in mind when propagating aspen from 

seeds. Aspen is dioecious, so female clones must be located 

for seed collection. Sex determination in aspen is not difficult, as the shape, color, and position of male and female 

floral structures are very distinctive (see photographs in 

Moench 2000). Although it is possible to determine sex 

from assessment of dormant buds in the fall, the task is 

easiest in late spring when trees are in full flower. Female 

flowers (catkins) emerge later in the season than males, and 

are most noticeable in May when they are green and fully 

extended (Moench 2000). The silhouette of a female aspen 

tree with a heavy seed crop is very striking.

Seed collection must be timed very carefully, because 

capsules can open quickly and release all seeds in windy 

weather. Conversely, seed that is collected prematurely will 

not ripen, and viability will be poor. Seed maturity is best 

determined by examination of seed color and appearance. 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 41

Immature seed is glossy and translucent, whereas mature 

seeds are pink or brown. The collection window typically 

ranges from late May to mid-June depending on elevation 

and local weather conditions (Moench 2000). At a given 

site, however, the range of appropriate collection time can 

be as narrow as 48 hours (Fung and Hamel 1993). The U.S. 

Forest Service Coeur d’Alene Nursery (Idaho Panhandle 

National Forest) recommends that female catkins be collected just before they disperse, and shipped immediately 

to the nursery for drydown and then sowing within 2 to 3 

days (Kent Eggleston, horticulturist, personal communication). Other methods include pruning branches with mature 

but closed catkins, followed by soaking branches in tubs of 

water for approximately 5 days until the catkins begin to 

release cotton. Capsules can be dislodged from the catkins 

with a vacuum, or gently stripped by hand into a container 

(Fung and Hamel 1993, Moench 2000).

Aspen seeds lack dormancy and can be sown immediately after collection. Seeds lose viability extremely rapidly 

(e.g., within 2 to 4 weeks; McDonough 1985) and must be 

dried and stored cold if not planted. Seeds and seedlings 

must be kept moist until well established. Under good growing conditions, 1-year-old plants are large enough to plant. 

Planting techniques are the same as those described above 

for vegetatively propagated aspen.

Restoring Understory Plant Diversity in Aspen 

Stands

Aspen stands in good condition support a diverse herbaceous understory. Heavy grazing not only prevents aspen 

regeneration, but also can suppress or eliminate native herbs 

from the understory. Prolonged heavy grazing in mesic 

aspen meadows will favor Kentucky bluegrass and other 

introduced sod-forming grasses; see for example the quaking aspen/Kentucky bluegrass plant community type in 

Crowe and Clausnitzer (1997) and in the aspen community 

classification section of this study. Plants that are commonly 

suppressed or eliminated from aspen stands include forbs 

such as heartleaf arnica (Arnica cordifolia), common camas 

(Camassia quamash), mountain sweet-cicely (Osmorhiza 

chilensis), straightbeak buttercup (Ranunculus orthorhynchus), starry false solomon’s seal (Smilacina stellata), sticky 

geranium (Geranium viscosissimum), and western meadowrue (Thalictrum occidentale). Natural recolonziation of 

degraded communities by these plants will be very slow 

owing to competition from the dense grass sod. However, 

the fencing that is in place to allow aspen regeneration will 

also protect herbaceous plantings, and conifer removal 

allows light to reach the forest floor, both of which present 

an ideal opportunity for restoration of native herbaceous 

plants.

A variety of shrubs occur in aspen stands, some of 

which are preferred browse species and have probably 

been reduced below their historical abundance by herbivores. These shrubs are potentially even more vulnerable 

to ungulate herbivory than aspen, because they may be 

shorter lived and are unable to grow tall enough to entirely 

escape the herbivores’ reach. It is probably no accident that 

in our area the most common understory shrubs in aspen 

stands are the less palatable browse species (e.g., snowberry 

Symphoricarpos spp., alder Alnus spp., and wax currant 

Ribes cereum) or are defended by thorns (roses Rosa spp. 

and hawthorn Crataegus spp.). We suspect that the highly 

palatable shrubs that occur sporadically in aspen communities in our area are less common than they were historically 

as a result of browsing, and thus they are good candidates 

for restoration efforts. On riparian and wetland aspen 

sites these include red-osier dogwood (Cornus stolonifera), chokecherry, and western serviceberry. On upland 

aspen sites they are chokecherry, bitter cherry (Prunus 

emarginata), Scouler willow (Salix scouleriana), Rocky 

Mountain maple (Acer glabrum), and western serviceberry. 

Riparian and wetland sites dominated by herbaceous species and lacking shrubs of any kind today are typically 

too wet and are not good candidates for shrub restoration. 

Figure 41–Seeds released by aspen on the Malheur National Forest, 19 

June, 2008.

Michael Tatum
42 GENERAL TECHNICAL REPORT PNW-GTR-806

However, riparian sites supporting some shrubs today (e.g., 

snowberry) are potential candidates for plantings to increase 

shrub diversity. The shrubs listed above for upland sites 

are quite drought tolerant (with the exception of maple), 

and could potentially occur over most of the environmental 

range of upland aspen. Thus, plantings of these species in 

typical aspen stands to increase understory diversity would 

be reasonable. The suitability of the driest aspen types 

(the aspen/pinegrass and aspen/elk sedge plant community 

types) for shrub restoration is questionable because they 

lack shrubs today. However, soil and environmental conditions of these types do not differ greatly from upland types 

with shrub understories, suggesting that shrub restoration 

may be possible here also.

Before beginning an understory restoration project, be 

sure that the hydrology of the site has not been altered such 

that typical aspen-grove species are no longer adapted. This 

commonly occurs when stream erosion and incision lowers 

the water table on a streamside terrace. The moist soil of 

many aspen groves with intact hydrology is ideal for plant 

propagation.

To select the species to plant, we recommend both searching the site for rare relict occurrences of native plants and 

classifying your site by this publication and examining the 

list of typical plants in the type description. Ideally seed 

will be gathered from the relict plants or from nearby less 

impacted areas. Planting containerized plants is more reliable than seeding. For many plants, this will require seed 

pretreatment plus growing in a greenhouse for the equivalent of a growing season. An excellent source for native 

plant propagation protocols is the Native Plant Network, at 

http://nativeplants.for.uidaho.edu/.

Competition from existing plants must be controlled to 

allow establishment of the new plants, especially herbaceous species. Tillage and herbicides are not recommended, 

because we do not want to endanger the aspen and other 

native plants. An effective but labor-intensive solution is to 

place each plant in the center of an area about 3 ft in diameter that has been scalped down to mineral soil. Also effective is to scalp and lay down woven weed-barrier fabric, 

then place the plants about 2 ft apart by slitting the fabric 

with an X (personal communication, Chris Hoag, USDA 

NRCS Plant Materials Center, Aberdeen, Idaho). Most 

aspen understory plants are moderately shade tolerant, but 

one should generally avoid patches of dense aspen regeneration or other competing woody vegetation.

Assessment of Aspen Regeneration

Management decisions in aspen stands are driven by stand 

structure and condition, including the density, size, and 

condition of aspen regeneration, overstory aspen, and competing conifers (fig. 19). Typically decisions can be based on 

a subjective assessment of an aspen stand. For example, the 

stand in figure 27 clearly had deficient regeneration and was 

in need of protection from herbivores, whereas the stand in 

figure 8 clearly would have benefitted from conifer removal. 

A quick classification of the predominant growth form of 

aspen regeneration by the system of Keigley and Frisina 

(1998) and Keigley et al. (2002) will usually determine 

whether browsing is intense and, hence, fencing or other 

herbivore-control measures are needed.

Once management actions have been taken, some sort of 

monitoring program is usually desired to track the success 

or failure of management actions and assess future needs. 

Repeat photography is a quick and usually adequate method 

to track the progress of aspen regeneration treatments. For 

best results, take photos from permanently marked locations (e.g., a fencepost) that are referenced by a written 

description and exact coordinates. When obtaining coordinates from the global positioning system (GPS), be sure to 

record the coordinate system (latitude-longitude, Universal 

Transverse Mercator, etc.), datum (North American Datum 

1983 is recommended), and estimated GPS error (if available) in addition to the coordinates themselves. Record the 

azimuth of each photograph and bring a copy of previous shots on revisits so the exact view can be matched. A 

scale reference such as a graduated pole placed a specified 

distance from the photographer is also helpful. For more 

information on setting up photographic monitoring points, 

see Hall (2001).

If quantitative information on stand response to management is needed, permanent monitoring plots may be 

installed and sampled according to the U.S. Forest Service 

Common Stand Exam protocols (USDA FS 2008). The 

following discussion is intended to guide the choice of 

protocol options to best fit the unique conditions of Blue 

Mountains aspen stands. Our aspen stands are typically too 

small for the standard layout of multiple plots in a systematic grid. In some cases, a single fixed-area plot may be 

established that encompasses most or all of an aspen stand. 

In other cases, the transect cross-section method is most 

appropriate, with the transect oriented along the long axis of 

the stand and plots placed at regular intervals. The transect 

may be conveniently located with ends at landmarks such as 

an exclosure fencepost or corner tree.

Aspen regeneration is usually sampled by counting suckers (i.e., by sampling stem density) in fixed-area plots (e.g., 

Schier 1975). Schier (1975) also counted sucker clumps 

(stems clustered together in an area no more than 8 inches 

in diameter), as only one stem per clump would usually 

survive to maturity. Given our typical sucker densities of 

a few thousand stems per acre or less, 1/100-ac (11.8-ft 

radius) plots would usually be appropriate. The number 

of plots will differ according to the size and density of the 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 43

stand. For example, in an oblong 1-ac aspen stand approximately 300 ft long, one might place five 1/100-ac plots at 

50-ft intervals. The total tree tally, given the typical aspen 

sucker densities in the Blue Mountains, would range from 

less than 30 to about 100 stems. Because survival to a 

height that is safe from herbivores is our main concern, we 

would normally record the height of all suckers less than 4.5 

ft high; both d.b.h. and height class for all larger stems up to 

some threshold value such as 4 in d.b.h.; and d.b.h. alone for 

larger trees.

Aspen Stand Quick Assessment and 

Desired Future Condition

The following quick assessment system was designed by 

M.L. Tatum for use in inventory of aspen stands on the 

Prairie City Ranger District of Malheur National Forest. 

The canopy layers of individual aspen stands are identified 

by letters (table 4) and the vigor of each layer is described 

with a number between 0 and 6 (table 5). The letters and 

numbers are then combined to produce a stand description 

code. For example, a stand with a nearly dead aspen understory, an aspen middle story with some good- and some 

poor-condition individuals, and an overstory in fair condition would be classified as “A4B3C2.”

The conifer competition in an aspen stand is described 

similarly, with letter codes for the conifer canopy layers 

(table 6) and a number for the conifer competition class of 

each layer; the latter describes the degree to which the conifer layer is suppressing aspen (table 7). The conifer competition description is particularly useful to identify stands in 

need of conifer removal.

The aspen layer and conifer competition systems can 

be combined into a composite aspen assessment code. 

Consider the following example aspen stand:

• Understory: aspen are nearly all dead and overtopped 

by a very thick and heavy carpet of grand fir regeneration; suckers/seedlings of aspen are not achieving any net 

annual height growth.

• Middlestory: aspen have some good- and some poor-condition individuals and a moderate conifer component that 

is only affecting some clumps of aspen.

• Overstory: aspen in fair condition with a light conifer 

overstory.

This stand would be classified as A4B3C2D6E3F1.

The structural classification of an aspen stand (tables 8 

and 9) can be derived from the assessment codes. The stand 

described above would thus be placed into HRV class 3, old 

forest multistrata.

Once the structural class and area of each aspen stand 

in a planning area is known, the total acreage of each class 

can be computed for all aspen stands. Then the proportion 

of area in each class can be compared to reference conditions to determine how the aspen stands meet the desired 

structural composition at a landscape scale. A proposed 

landscape composition of aspen stands is provided in table 

10. It suggests management for a dominance of young age 

classes in aspen stands; this is what we expect was historically present, based on our knowledge of the high historical 

fire frequency in the Blue Mountains (Heyerdahl et al. 2001). 

In addition, owing to aspen’s short lifespan and tendency for 

mature trees to become diseased, a high proportion of young 

age classes is needed to maintain aspen acreage on the landscape. Note that because aspen area as a whole is considered 

to be in deficit in our area, an increase in younger age classes 

of aspen should be obtained primarily through expansion of 

aspen area, not killing of existing old trees.

Table 4–Aspen layer classification

Code

Structural 

layer

Typical 

age Age class Size group

Years

A Understory 0-25 Suckers to juvenile Sucker to sapling

B Midstory 25-75 Immature to early mature Sapling/poles to large

C Overstory 75-125+ Late mature to overmatureLarge+
44 GENERAL TECHNICAL REPORT PNW-GTR-806

Table 5–Aspen layer vigor classification

Code Name Definition

0 Layer absent No individuals of this structure are present, common sense applies: if you have a clump of three 

large aspen and there are three suckers, then you shouldn’t use this code; if the same three 

suckers are contained within a 3-ac aspen stand, code them with this code as nonexistent.

1 Vigorous No evidence of permanent disease (conks); foliage disease may be present but not causing longterm damage; bark is healthy (not seriously damaged); evidence shows very good annual leader/

height growth; minor browsing/hedging.

2 Stable The layer appears to be free and clear to grow; only minor stem or leaf disease; browsing 

or hedging may be checking most of annual growth; other minor physical damage may have 

occurred; only occasional cavity excavation. Growth is good to fair.

3 Mixed condition A significant portion of the individuals in this structural layer meet condition 1 or 2, and a 

significant portion meet conditions 4 through 6.

4 Declining Shortening crown ratios, lack of or short annual growth, cavity excavators beginning frequent 

excavations, disease conks present, heavy browsing/hedging with reduced suckering, 

suppression or overtopping by other trees, or other physical damage causing serious injury. 

Occasional dead trees of this layer are present. Growth is poor.

5 Decadent Nearly dead; frost cracks; broken or split-out tops; major portion of tree dead; many cavities 

from bird use; typically at least 80 to 90 years old at minimum. Dead trees common of same age. 

Growth essentially stopped.

6 Dead

Table 6–Conifer layer classification

Code

Structural 

layer Typical age Age class Size group

Years

D Understory 0-25 Seedlings to juvenile Seedlings to sapling

E Midstory 25-150 Immature to early mature Poles to large

F Overstory 150+ Late mature to overmature Large+

Table 7–Conifer competition classification

Code Name Description

0 None No conifer present in this layer or nearly absent and not competing.

1 Light Scattered conifer competing lightly with aspen; no significant overtopping, crowding, or 

suppression.

2 Moderate Conifer beginning to have an apparent effect on aspen health and vigor across most of the 

site.

3 Mixed Some portions of the aspen stand or clumps within stands on aspen are being affected as in 

(2) moderate, some as in (4) suppressing. 

4 Suppressing Conifer in position to reduce aspen crowns, vigor, growing space and form. Aspen are 

showing the effects. Some aspen mortality or form deformation.

5 Near lethal Conifer exerting near lethal effects on aspen. Aspen suffering severe and significant 

suppression mortality. Significant mortality of middlestory and mature aspen; many are dead 

or near dead. Most dead aspen are still standing; some of the dead aspen are on the ground. 

If used to describe understory, aspen in the understory is overtopped with no growing space 

and showing poor architecture/breakage/abrasion damage.

6 Lethal Conifer totally dominating the site: overtopping, deforming, shading, crowding, and 

suppressing aspen, resulting in wholesale mortality. Very few mature aspen surviving. Most 

of the dead aspen are on the ground, some dead remain standing. If used to describe conifer 

effect on understory, the understory is stunted, has poor vigor, or consists of dead sprouts.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 45

Table 8–Aspen stand structural classification

Aspen canopy layers 

present or absent

HRV 

class

Number 

of layers

A

Understory

B

Midstory

C

OverstoryOldest 

age group

Structural 

classa Notes

Years

1 3 Present Present Present 80+ OFMS Rare except in stands treated 10 or more 

years ago.

2 2 Present Present Absent/

dead

40-80 SE, UR, 

YFMS

Overstory dead; a rare condition. May 

become more common as older burned or 

treated stands slowly recruit a middle story 

and regeneration continues.

3 2 Absent/

dead

Present Present 80+ OFMS Understory aspen absent or dead; a rare 

condition.

4 2 Present Absent/

dead

Present 80+ OFMS Understory and overstory present; common 

in treated stands with regeneration under old, 

decadent overstory. When the magnitude of 

the regeneration overwhelms the amount of 

remaining overstory, this will become class 5, 

and after several more years possibly class 2.

5 1 Present Absent/

dead

Absent/

dead

0-40 SI Understory only; a rare condition, usually 

happens after fire or treatment that kills 

overstory, or where the stand has expanded 

to several acres from original few parent trees 

and labeling the stand as class 7 doesn’t 

make sense because of widespread vigorous 

regeneration.

6 1 Absent/

dead

Present Absent/

dead

40-80 SE, UR, 

YFMS

Middle-story only; a rare condition. May be an 

older treated stand or older fire-created stand 

where recruitment of aspen occurred in the 

past but is not currently present.

7 1 Absent/

dead

Absent/

dead

Present 80+ OFSS Overstory only; the most common situation in 

our area. The overstory is usually decadent.

8 0 Absent/

dead

Absent/

dead

Absent/

dead

- - All aspen dead. Take care to ensure that no 

aspens are alive.

a For definitions of structural classes, see table 9.

Note: HRV = historical range of variation.
46 GENERAL TECHNICAL REPORT PNW-GTR-806

Table 9–Forest Structural Class Definitions

Code Name Description

SI Stand initiation Following a stand-replacing disturbance such as wildfire or timber harvest, growing space is occupied 

rapidly by vegetation that either survives the disturbance or colonizes the area. Survivors literally 

survive the disturbance above ground, or initiate growth from their underground roots or from seeds 

stored on site. A single-canopy stratum of tree seedlings and saplings is present in this class.

SE Stem exclusion open 

canopy or stem exclusion 

closed canopy

In this stage of development, vigorous, fast-growing trees that compete strongly for available light and 

moisture occupy the growing space. Because trees are tall and reduce sunlight, understory plants 

(including smaller trees) are shaded and grow more slowly. Species that need sunlight usually die; 

shrubs and herbs may become dormant. In this class, establishment of new trees is precluded by a lack 

of sunlight (stem exclusion closed canopy) or of moisture (stem exclusion open canopy).

UR Understory reinitiation As a forest develops, new age classes of trees (cohorts) establish as the overstory trees die or are 

thinned and no longer fully occupy growing space. Regrowth of understory vegetation then occurs, 

and trees begin to develop in vertical layers (canopy stratification). This class consists of a sparse to 

moderately dense overstory with small trees underneath.

YFMS Young forest multistrata In this stage of forest development, two or more tree layers are present as a result of canopy 

differentiation or because new cohorts of trees got established. This class consists of a broken or 

discontinuous overstory layer with a mix of tree sizes present (large trees are absent or scarce); it 

provides high vertical and horizontal diversity. This class is also referred to as “multistratum, without 

large trees” (USDA FS 1995).

OFMS Old forest multistrata Many age classes and vegetation layers mark this structural class and it usually contains large, old 

trees. Decaying fallen trees may also be present that leave a discontinuous overstory canopy. On cool 

moist sites without recurring underburns, multilayer stands with large trees in the uppermost stratum 

may be present.

OFSS Old forest single strata Many age classes but only a single fairly distinct overstory layer marks this structural class, and it 

usually contains large, old trees. Decaying fallen trees may also be present that leave a discontinuous 

overstory canopy.

Table 10–Desired age and structural composition of aspen standsa

Age Structural classb Proportion of aspen stand area

Years Percent

0-40 SI 45-50

40-80 SE, UR, YFMS 45-50

80+ OFMS, OFSS 5-10

a Based on historical range of variation (HRV) estimates by M.L. Tatum and K. Schuetz. 

Applies to aspen stand in areas dominated by the dry upland forest plant association group 

(Powell et al. 2007). Proportions of aspen stands are based only on acreages of live trees. 

Note: aspen area as a whole is considered to be in deficit in our area; thus the 0-40- and 

40-80-yr age classes should be restored through expansion of aspen area, not killing of 

existing aspen stands 80 yr and older.

b For definitions of structural classes, see table 9.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 47

Aspen Community Classification 

in the Blue Mountains

Study Area

Physiography and geology–

The study area (fig. 42) is dominantly an extensive lava 

plateau at elevations of 3,500 to 6,500 ft, dissected by some 

deep canyons with elevations as low as 2,000 ft. Several 

mountain ranges rise above the plateau to about 9,000 ft 

elevation. Bedrock is dominantly volcanic rocks that 

erupted during the Cenozoic Era: primarily basalt, but 

also andesite and rhyolite. Interbedded with these volcanic 

rocks are some relatively thin layers of tuffaceous sedimentary rocks. Locally in the southern half of the study 

area, the older sedimentary and metasedimentary rocks 

that occur beneath the volcanics are exposed. These consist 

mostly of graywacke, shale, and argillite deposited in a 

marine environment. One large area of granitic rock also 

occurs in the study area–the Bald Mountain batholith–

which is centered in the vicinity of Anthony Lakes, northwest of Baker City, Oregon (Orr and Orr 1999, Walker and 

McLeod 1991.)

A surface layer of wind-deposited loess or volcanic ash is 

locally present, particularly on flat or concave slopes where 

it has escaped erosion and often accumulated after erosion 

from surrounding slopes. This material is the parent material for the fine-grained soils occupied by many of our aspen 

stands.

Climate–

The climate of aspen communities in the Blue Mountain 

region is quite variable owing to their wide elevation range. 

At lower elevations (below 4,000 ft), the climate is temperate and semiarid, with annual precipitation of 10 to 20 

in and ephemeral snow cover in most winters (Western 

84

Sample plots

Oregon

Figure 42–Locations of 

plots used in the aspen 

community classification 

study.
48 GENERAL TECHNICAL REPORT PNW-GTR-806

Regional Climate Center 2007). At the higher elevations, 

annual precipitation ranges from 20 to 40 in, generally 

increasing with elevation and from south to north. Annual 

precipitation is locally 40 to 60 in at high elevations in the 

Wallowa Mountains and in the northeastern portion of the 

Umatilla National Forest (USDA NRCS 2007). Precipitation 

is highly seasonal, with most arriving between November 

and June; drought conditions are common in late summer. 

Temperatures generally decrease with increasing elevation, 

although low temperature extremes in all seasons tend to 

occur at moderate elevations on valley bottoms surrounded 

by higher terrain. Summer highs are typically in the high 

70s and 80s °F, and lows in the 40s. Winter highs average in 

the 30s °F and lows in the teens. Summer temperatures in 

the 90s °F are not unusual, and winter temperatures occasionally fall below 0 °F.

Soils–

Soils of aspen communities are highly variable thanks 

to aspen’s broad range of adaptation. Riparian and wetland aspen occur on fine-grained soils formed in loess and 

volcanic ash that has been reworked and deposited in low 

areas. These soils have a high organic matter content, high 

available water capacity, moderately acid to neutral reaction (pH 5.6 to 7.0), and are seasonally saturated with water 

within the upper 40 in. Most of these soils classify as Andic 

Argiudolls or Aquic Pachic Argiudolls (Soil Survey Staff 

1999). Aspen communities on upland sites occasionally 

occur in stoney colluvium or even rock rubble with loamy 

interstitial material, but in most cases a layer of mixed loess 

and volcanic ash more than 10 in thick overlies the stoney 

material. Where the surface loamy layer is more than 20 in 

thick, it usually becomes more clay-rich with depth. These 

soils have a rather thin organic-rich surface layer and moderately acid to neutral reaction (pH 5.6 to 7.2). Common 

soil classifications are Andic Haploxerepts and Andic 

Haploxeralfs.

Plant Association Concept

This publication uses the conventions for classifying 

vegetation that have been in use in the Pacific Northwest 

Region (Region 6) of the Forest Service for several decades. 

The plant association is the fundamental unit of classification. It is based on the potential natural vegetation of the 

site, the plant community that would become established 

if all successional sequences were completed under the 

present environmental and floristic conditions (Winthers 

et al. 2005). Plant associations are named by using both the 

dominant late-seral overstory species and other species that 

indicate environmental conditions such as moisture supply 

and temperature. Because aspen rarely occurs as a late-seral 

species, few plant associations have aspen as the named 

overstory species. A plant association includes the late-seral 

vegetation for which it is named and all the disturbed and 

early-seral vegetation that would succeed to that late-seral 

vegetation. This naming convention does not imply that 

the late-seral vegetation is or was ever dominant on the 

landscape.

The plant community type is an aggregation of plant 

communities with similar current composition and structure 

(Jacoby 1989). Thus plant community types are classes of 

existing as opposed to potential vegetation. In this study, 

aspen plant community types were created to join and 

describe communities at early seral stages that are difficult 

to place into a plant association and for which important 

management information can be assembled based on the 

current vegetation. Most of the vegetation classes described 

in this publication are plant community types; they have 

a Region 6 ecoclass code and in most cases are based on 

a sample size of two or more plots. The term type is used 

alone to refer to either plant associations or plant community types.

A series is an aggregation of plant associations (and 

therefore a unit of potential vegetation) based on the dominant overstory plants. For example, all of the aspen communities that have a grand fir overstory as their potential 

vegetation are placed in the grand fir series.

The term plant community is used here to refer to an 

assemblage of plants without reference to classification. In 

this publication we describe a few aspen plant communities as unique occurrences of aspen that are unlikely to be 

encountered elsewhere and are not given a Region 6 ecoclass code.

The keys and types are based on the concept of indicator plants. The indicator plants selected to define a plant 

community type or plant association are those plants that 

are thought to be the most diagnostic of a particular environment. They are plants common enough to be found 

on a useful number of plots, yet narrow enough in their 

range of adaptation that their presence tells us something 

unique about the environment. In the case of plant associations, the indicator plants are native plants diagnostic of the 

temperature and moisture conditions of the site. For plant 

community types, they may be either this or indicators of 

management disturbance such as Kentucky bluegrass in 

communities with a history of heavy grazing.

Field Methods

This study incorporates plots sampled by Elizabeth 

Crowe, Rod Clausnitzer, and Terry Hicks (from 1988 to 

1997) for riparian plant community classification (Crowe 

and Clausnitzer 1997); plots sampled by Charlie Johnson 

(in 2000) and the author (D. Swanson, in 2002-2005) for 

this study; and a few plots from other upland plant 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 49

classifications by Blue Mountains area ecologists (Clausnitzer 1993, Johnson 2004, Johnson and Simon 1987). 

A total of 219 plots were used, of which 153 were sampled 

by Swanson.

A 0.93-ac circular reconnaissance plot (72 ft in diameter) was established at each site, and canopy coverage was 

estimated for all vascular plant species. A plant canopy was 

defined as the outer perimeter of the plant, including small 

gaps. Cover was estimated to the nearest 5 percent, with 

additional cover classes of 3 percent, 1 percent, and trace 

(present at less than 1 percent cover). Trees were separated 

into overstory (more than 11 in d.b.h.) and understory (less 

than or equal to 11 in d.b.h.). Ground surface cover was 

estimated for bare soil, bedrock, rock, gravel, erosion pavement, mosses, lichens, litter, and submerged areas.

Environmental data gathered for each plot included elevation, slope aspect, slope steepness, slope shape, position on 

slope, landform, and a brief soil description (Soil Survey 

Division Staff 1993). Soil pH was determined in the field 

with indicator solutions. Photographs were taken from the 

plot center at two or more azimuths. To facilitate relocation 

of plots for future monitoring, each plot center was marked 

with a metal stake, a reference sign was placed on a tree 

nearby, GPS coordinates were recorded (after 2002), and 

narrative directions for locating the plot were recorded.

Classification and Data Analysis Methods

Many aspen communities described here fit into existing 

aspen-dominated riparian or wetland plant associations or 

community types (Crowe and Clausnitzer 1997), or they 

are seral communities of plant associations that have been 

defined in previous studies (Johnson and Clausnitzer 1992, 

Johnson and Simon 1987). Thus the keys and community 

definitions here follow closely the classes and indicator 

plants used in these earlier studies. As in the previous studies, the keys presented here generally progress from coldmoist to warm-dry environments.

Most of the 83 riparian and wetland aspen plots in this 

study fit readily into existing plant associations or plant 

community types defined by Crowe and Clausnitzer (1997). 

These types are described again here, in most cases with a 

larger sample size than in the original publication. Fifteen 

of the riparian and wetland aspen plots fit poorly into existing classes. Most of these (nine plots) are similar to the 

existing quaking aspen/Kentucky bluegrass plant community type of Crowe and Clausnitzer (1997) but are dominated by a mix of grasses rather than Kentucky bluegrass. 

These are placed in a new type, aspen/meadow foxtail. The 

remaining plots are unique and are either placed into their 

own new plant community types or are described as miscellaneous communities under “Aspen/Tall Shrub Wetland 

Communities on Slopes.”

Existing classifications are less complete for upland aspen 

communities, and hence more new upland types were created as a part of this study. Plots were first classified into 

series based on the potential conifer dominant, although in 

some cases this is not possible owing to lack of conifers or 

other reliable indicator plants.

Of 136 upland aspen plots, 10 fit readily into three existing grand-fir-series plant associations from Johnson and 

Clausnitzer (1992) or Johnson and Simon (1987) and are 

described here under those types, the grand fir/twinflower, 

grand fir/big huckleberry, and grand fir/Rocky Mountain 

maple plant associations. Aspen is a very minor seral 

component of these types and was not included in previous 

descriptions.

A large number of plots key into existing ponderosa pine/

snowberry and Douglas-fir/snowberry types in Johnson 

and Clausnitzer (1992) or Johnson and Simon (1987) (both 

common and mountain snowberry) or closely resemble 

these types despite lack of conifers. Ordination by nonmetric multidimensional scaling (NMS) (McCune and Grace 

2002) showed poor separation of these plots into series by 

community composition, so they are joined here into a new 

aspen (ponderosa pine–Douglas-fir)/snowberry plant community type.

Many aspen plots also key into existing ponderosa pine/

pinegrass, Douglas-fir/pinegrass, or grand fir/pinegrass 

communities, or resemble these types but lack conifers. 

Ordination by NMS again showed poor separation of these 

plots into series by community composition (and diagnostic 

conifers are often absent), so they were joined into a new 

aspen/pinegrass type. For the same reasons, aspen plots 

with elk sedge (with or without conifers) were joined into a 

new aspen/elk sedge type.

Remaining plots fit poorly into any existing plant associations or community types. Natural groupings in these plots 

were explored subjectively and by ordination using NMS to 

define new types.

For some types–the riparian aspen/common snowberry 

communities, the aspen/mesic forb plant community type, 

and the aspen (ponderosa pine–Douglas-fir)/snowberry 

plant community type–tabular data are presented to differentiate phases resulting from grazing-related degradation. 

The phases were developed as follows: (1) In the aspen/

common snowberry communities, two plots with exceptionally high grass cover and one with exceptionally high cover 

of unpalatable forbs are presented separately. These phases 

are known from previous studies to result from heavy grazing (Crowe and Clausnitzer 1997). (2) The aspen/mesic forb 

plant community type covers a range of plots with light to 

moderate grazing impacts (Crowe and Clausnitzer 1997). 

This type was divided into “less impacted” and “more 

impacted” phases based on the proportion of the plant cover 
50 GENERAL TECHNICAL REPORT PNW-GTR-806

in species known to be resistant to grazing based on previous publications (Crowe and Clausnitzer 1997, Johnson and 

Clausnitzer 1992, Johnson and Simon 1987). Species known 

to be grazing resistant include introduced sod-forming pasture grasses, most introduced forbs, and certain grazingresistant native forbs such as false hellebore (Veratrum

spp.). (3) For the aspen (ponderosa pine–Douglas-fir)/snowberry plant community type, the three phases presented in 

the table are simply the subjective rating of good, fair, or 

poor that was recorded in the field.

Soil available water capacity is computed for the upper 

40 in of soil by assuming a certain available water capacity 

for each soil texture, adjusted by the volumetric content of 

coarse fragments. The assumed water capacities are based 

on unpublished USDA Natural Resources Conservation 

Service (NRCS) guidelines and are as follows (in dimensionless units of water volume per soil volume): volcanic 

ash silt loam–0.34; silty clay loam–0.27; clay loam–0.24; 

silt loam, loam, or sandy clay loam–0.22; sandy loam–0.15; 

loamy sand–0.08; and sand–0.05.

Data Presentation

All scientific names follow Hitchcock and Cronquist (1973). 

All database codes follow the PLANTS National Database 

(USDA NRCS 2008). All plant species used in this report 

are listed in appendix B with scientific name, common 

name, and PLANTS database code. A cross reference to the 

currently recommended synonym (USDA NRCS 2008) is 

given in appendix C for cases where the recommended synonym differs from the name used here.

The tables of principal species with each type description present constancy (the percentage of plots on which the 

species was found) and mean cover computed using only 

the plots where the plant was present. To be included in the 

table, a plant must have a constancy of at least 50 percent 

when the average cover, where present, is 1 percent or less, 

or a constancy of at least 20 percent when the average cover 

is more than 1 percent. Average covers of less than 0.5 percent are written as “tr” (trace).

Keys to Aspen Communities of the Blue Mountains

The following keys are based on 219 plots located in the 

Blue Mountains. They may be used for any site where aspen 

are currently growing or grew in the past. Because the 

sample plots used to develop the classification are circular 

with a diameter of 36 ft, the keys will work best if an area 

with uniform vegetation approximately this size is chosen. 

To use the keys, compare the choices listed under “a” and 

“b” for each number, select the alternative that fits best, 

note the number given on the right margin and proceed to 

the lead with that number. Continue until a type name is 

reached. Turn to the page number indicated and check the 

type description to make sure that it fits.

Use the “Key to Riparian and Wetland Aspen Vegetation” 

(p. 51) for sites where a water table is found within 40 in 

of the surface during at least part of the growing season 

(wetlands), or for sites located on flood plains or alluvial 

terraces that have vegetation that is distinctly different 

from adjacent uplands thanks to flooding or enhanced soil 

moisture (riparian areas). Use the “Key to Upland Aspen 

Vegetation” (p. 52) for all other sites.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 51

VEGETATION KEY 

Key to Riparian and Wetland Aspen Vegetation

1a. Slopes ≤10 percent; riparian and lowland meadow communities.................................................................................................2

1b. Slope >10 percent; isolated tall-shrub dominated wetlands on slopes............................................................................................

....................................................................................................Aspen/Tall Shrub Wetlands Plant Communities on Slopes p. 57

2a. Engelmann spruce (Picea engelmannii) cover ≥10 percent, or site capable of such cover.........................................................

.......................................................................................................................................................POTR5-PIEN/GLST-CACA4 p. 55

2b. Engelmann spruce cover <10 percent and site not capable of supporting 10 percent Engelmann spruce cover..................3

3a. Mountain alder (Alnus incana) cover ≥25 percent...........................................................................................................................4

3b. Mountain alder cover <25 percent......................................................................................................................................................5

4a. Red-osier dogwood (Cornus stolonifera) cover ≥25 percent........................................................POTR5/ALIN2-COST4 p. 56 

4b. Red-osier dogwood cover <25 percent...............................................................................................POTR5/ALIN2-SYAL p. 56

5a. Black hawthorn (Crataegus douglasii) cover ≥25 percent........................................................................POTR5/CRDO2 p. 56

5b. Black hawthorn cover <25 percent......................................................................................................................................................6

6a. Common snowberry (Symphoricarpos albus) cover ≥25 percent..................................................................................................7

6b. Common snowberry cover <25 percent.............................................................................................................................................8

7a. Grand fir (Abies grandis) cover ≥10 percent or site capable of supporting such cover................................................................

...................................................................................................................................................ABGR/SYAL (FLOODPLAIN) p. 58

7b. Douglas-fir (Pseudotsuga menzesii) cover ≥10 percent or site capable of supporting such cover.............................................

....................................................................................................................................................PSME/SYAL (FLOODPLAIN) p. 58

7c. Ponderosa pine (Pinus ponderosa) cover ≥10 percent or site capable of supporting such cover................................................

......................................................................................................................................................PIPO/SYAL (FLOODPLAIN) p. 58 

7d. Conifer cover <10 percent and conifer potential unknown..........................................................................POTR5/SYAL p. 58

8a. Aquatic sedge (Carex aquatilis) cover ≥25 percent.......................................................................................POTR5/CAAQ p. 62

8b. Aquatic sedge cover <25 percent.........................................................................................................................................................9

9a. Woolly sedge (Carex lanuginosa) cover ≥10 percent................................................................................POTR5/CALA30 p. 62

9b. Woolly sedge cover <10 percent.........................................................................................................................................................10

10a. Yellow sedge (Carex flava) cover ≥25...........................................................................................................POTR5/CAFL4 p. 65

10b. Yellow sedge cover <25 percent.........................................................................................................................................................11

11a. Bluejoint reedgrass (Calamagrostis canadensis) cover ≥25 percent.......................................................POTR5/CACA4 p. 66

11b. Bluejoint reedgrass cover <25 percent..............................................................................................................................................12

12a. Kentucky bluegrass (Poa pratensis) cover ≥25 percent................................................................................POTR5/POPR p. 68

12b. Kentucky bluegrass cover <25 percent.............................................................................................................................................13

13a. Sum of cover by all grasses (Poaceae) ≥50 percent; introduced pasture grasses, especially meadow foxtail (Alopecurus 

pratensis) usually dominate..............................................................................................................................POTR5/ALPR3 p. 68

13b. Sum of cover by all grasses <50 percent...........................................................................................POTR5/MESIC FORB p. 68
Key to Upland Aspen Vegetation

1a. Over half of the ground surface is bedrock or rock rubble (rock fragments > 3 in diameter; rock may be partly covered 

with a thin layer of litter).......................................................................................................................................................................2

1b. Ground surface dominated by soil, gravel, and/or litter..................................................................................................................3

2a. Elevation above 6,000 ft.; subalpine fir (Abies lasiocarpa) often present...........................POTR5 (RUBBLE, HIGH) p. 72

2b. Elevation below 6,000 ft; wax currant (Ribes cereum), creeping Oregon grape (Berberis repens), common snowberry 

(Symphoricarpos albus), or hotrock penstemon (Penstemon deustus) usually present......POTR5 (RUBBLE, LOW) p. 72

3a. Subalpine fir with total cover ≥10 percent, or site capable of supporting such cover...................................................................

.......................................................................................................................................Aspen types of the subalpine fir series p. 75

3b. Subalpine fir cover <10 percent and site not capable of supporting 10 percent subalpine fir cover.........................................4

4a. Grand fir with total cover ≥10 percent, or site capable of supporting such cover..........................................................................

.......................................................................................................................................Upland grand fir series aspen type key p. 53

4b. Grand fir with total cover <10 percent and site not capable of supporting 10 percent grand fir cover....................................5

5a. Ponderosa pine or Douglas-fir with cover ≥10 percent, or site capable of supporting such cover.............................................

..............................................................................................Upland ponderosa pine and Douglas-fir series aspen type key p. 54

5b. Ponderosa pine or Douglas-fir with cover <10 percent and site not capable of supporting 10 percent ponderosa pine or 

Douglas-fir...........................................................................................................................................................Undefined aspen type

52 GENERAL TECHNICAL REPORT PNW-GTR-806

VEGETATION KEY
Upland Grand Fir Series Aspen Type Key

1a. Twinflower (Linnaea borealis) distributed throughout the stand with cover ≥1 percent .......................ABGR/LIBO3 p. 77

1b. Twinflower with cover <1 percent.......................................................................................................................................................2

2a. Big huckleberry cover (Vaccinium membranaceum) ≥5 percent...............................................................ABGR/VAME p. 78

2b. Big huckleberry cover <5 percent......................................................................................................................................................3

3a. Rocky Mountain maple (Acer glabrum) cover ≥5 percent.............................................................................ABGR/ACGL p. 81

3b. Rocky Mountain maple cover <5 percent..........................................................................................................................................4

4a. Oceanspray (Holodiscus discolor) cover ≥5 percent......................................................................POTR5(ABGR)/HODI p. 83 

4b. Oceanspray cover <5 percent...............................................................................................................................................................5

5a. Snowberry (common snowberry Symphoricarpos albus or mountain snowberry S. oreophilus) cover ≥5 percent.............

...............................................................................................................................................................POTR5(ABGR)/SYMPH p. 83

5b. Snowberry (common snowberry and mountain snowberry) cover <5 percent...........................................................................6

6a. Pinegrass (Calamagrostis rubescens) cover ≥5 percent..............................................................................POTR5/CARU p. 95 

6b. Pinegrass cover <5 percent...................................................................................................................................................................7

7a. Elk sedge (Carex geyeri) cover ≥5 percent...................................................................................................POTR5/CAGE2 p. 95

7b. Elk sedge cover <5 percent..................................................................................................................................................................8

8a. Cover by introduced grasses (intermediate wheatgrass Agropyron intermedium, orchardgrass Dactylis glomerata, etc.) 

≥5 percent..........................................................................................................................................POTR5/EXOTIC GRASS p. 95

8b. Cover by introduced grasses <5 percent..........................................................Other grand fir series aspen communities p. 86

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 53

VEGETATION KEY 
Upland Ponderosa Pine and Douglas-Fir Series Aspen Type Key

1a. Cover by cherry species (chokecherry Prunus virginiana or bitter cherry P. emarginata) ≥5 percent.................................2

1b. Cover by cherry species <5 percent....................................................................................................................................................3

2a. Chokecherry cover greater than bitter cherry cover.......................................................................................POTR5/PRVI p. 88

2b. Chokecherry cover less than less than bitter cherry......................................................................POTR5(PSME)/PREM p. 90

3a. Snowberry (common snowberry or mountain snowberry) cover ≥5 percent............POTR5(PIPO-PSME)/SYMPH p. 92

3b. Cover by snowberry <5 percent...........................................................................................................................................................4

4a. Pinegrass cover ≥5 percent................................................................................................................................POTR5/CARU p. 95 

4b. Pinegrass cover <5 percent...................................................................................................................................................................5

5a. Elk sedge cover ≥5 percent.............................................................................................................................POTR5/CAGE2 p. 95

5b. Elk sedge cover < 5 percent..................................................................................................................................................................6

6a. Cover by introduced grasses (intermediate wheatgrass, orchardgrass, etc.) ≥5 percent.............................................................

...........................................................................................................................................................POTR5/EXOTIC GRASS p. 95 

6b. Cover by introduced grasses <5 percent.................Other Douglas-fir and ponderosa pine series aspen communities p. 99

54 GENERAL TECHNICAL REPORT PNW-GTR-806

VEGETATION KEY
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 55

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Engelmann spruce is a common riparian and wetlandmargin species in the Blue Mountains. We sampled just 

one plot where aspen occurred with significant Engelmann 

spruce cover; it is in the Charlie Johnson Research Natural 

Area of the Wallowa-Whitman National Forest, at 5,480 ft 

elevation. The highly diverse understory is dominated by 

various wetland-adapted grasses, including mannagrass 

(Glyceria striata), bluejoint reedgrass (Calamagrostis 

canadensis), bentgrass (Agrostis stolonifera), and tufted 

hairgrass (Deschampsia cespitosa). The soil consists of layers of both loess or alluvial silt and volcanic ash, with colors 

indicating intermittent saturation below 3 ft depth. This site 

is highly productive and aspen is seral to spruce.

Aspen-Engelmann Spruce Types

Aspen-Engelmann Spruce/Fowl MannagrassBluejoint Reedgrass Plant Community Type

Populus tremuloides-Picea engelmannii/

Glyceria striata-Calamagrostis canadensis

POTR5-PIEN/GLST-CACA4 HQC113

55 GENERAL TECHNICAL REPORT PNW-GTR-806

WA016 D. Swanson

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 55
56 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

These two plant community types are represented by one 

plot each sampled by Crowe and Clausnitzer (1997). They 

occur on nearly level flood plains at 4,300 and 5,000 ft, 

respectively. Soils consist of silt loam over sand, gravel, 

and cobbles with a low to moderate available water capacity. Aspen form an open canopy over shrubs, primarily mountain alder (Alnus incana), common snowberry 

(Symphoricarpos albus), and, in POTR5/ALIN2-COST4, 

red-osier dogwood (Cornus stolonifera) and chokecherry 

(Prunus virginiana). Herbaceous plants include blue wildrye (Elymus glaucus), creeping bentgrass (Agrostis stolonifera), asters (Aster spp.) and a variety of other forbs at low 

cover.

These plant communities are a variant of the much more 

widespread flood-plain alder communities lacking aspen. 

Aspen occur in these alder communities thanks to their 

ability to colonize mesic disturbed sites. These ecosystems 

constantly change owing to flooding and sedimentation, 

stream channel migration, and succession. Thus long-term 

management of aspen in these communities would be difficult and unpredictable. Like other aspen communities, 

they provide valuable wildlife habitat and are vulnerable to 

browsing.

Aspen-Tall Shrub Types

Aspen/Mountain Alder–Red-Osier Dogwood 

Plant Community Type

Populus tremuloides/Alnus incanaCornus stolonifera

POTR5/ALIN2-COST4 HQS222 

(Crowe and Clausnitzer 1997)

Aspen/Mountain Alder-Common Snowberry 

Plant Community Type

Populus tremuloides/Alnus incanaSymphoricarpos albus

POTR5/ALIN2-SYAL HQS223 

(Crowe and Clausnitzer 1997)

MW1571 E. Crowe

One plot of this community type was sampled on a gentle 

slope at 4,160 ft elevation in Patterson Basin on the North 

Fork John Day Ranger District of the Umatilla National 

Forest. It is on a dark-colored, clay loamy soil with pH 

of 6.6 to 6.8. A stand of pole-sized aspen with few saplings and minor grand fir occurs over a dense stand of 

hawthorn (65 percent cover) and common snowberry 

(Symphoricarpos albus) (35 percent cover) with minor rose 

(Rosa sp.) and serviceberry (Amelanchier alnifolia). The 

most abundant herb is the introduced grass meadow foxtail (Alopecurus pratensis). Minor amounts of many forbs 

typical of aspen meadows are present, such as columbine 

(Aquilegia formosa), monkshood (Aconitum columbianum), and false Solomon’s seal (Smilacina racemosa). Sites 

of this type can probably support Douglas-fir or grand fir, 

and conifer encroachment could eliminate aspen over time. 

Both aspen and hawthorn can resprout after disturbance, 

and competition by hawthorn is likely to reduce the density 

of aspen regeneration after disturbance. Mechanical treatment of hawthorn may be needed in some cases to allow for 

aspen regeneration.

Aspen/Black Hawthorn Plant Community Type

Populus tremuloides/Crataegus douglasii

POTR5/CRDO2 HQS4

UA044 D. Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 57

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Aspen have been recorded growing in unusual shrubrich wetland communities located over seeps or springs 

on slopes. Three plots of this type were sampled between 

4,600 and 5,240 ft elevation on slopes of south or west 

aspect ranging from 15 to 55 percent. The three plots share 

no plants in common besides aspen; all have a rich shrub 

layer dominated by one or more of the following species: 

mountain alder (Alnus incana), black hawthorn (Crataegus 

douglasii), common chokecherry (Prunus virginiana), 

rose (Rosa), red elderberry (Sambucus racemosa), or 

common snowberry (Symphoricarpos albus). Sedges and 

forbs are also diverse and abundant, notably Dewey sedge 

(Carex deweyana), cleavers (Galium aparine), cowparsnip 

(Heracleum lanatum), and western coneflower (Rudbeckia 

occidentalis).

Aspen/Tall-Shrub Wetland Plant 

Communities on Slopes

Populus tremuloides/Tall Shrub

POTR5/Tall Shrub (wetland slope)

UA042 D. Swanson
58 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Aspen with an understory dominated by common snowberry occurs fairly frequently in riparian areas. The typical presence of more shade-tolerant conifers shows that 

aspen forest is a seral stage with a potential vegetation of 

coniferous trees. Ordination with nonmetric multidimensional scaling shows that our aspen plots in these communities separate poorly based on community composition. 

Furthermore, conifer species are sometimes absent in aspen 

communities, making differentiation based on trees unreliable. For this reason, the aspen communities in these four 

types are joined and described together here.

Environmental features—

Riparian aspen/common snowberry communities occur at 

moderate elevations, usually in swales or along intermittent 

stream courses.

Soils—

Soils are fine-grained and high in organic matter, with a 

neutral to slightly acid pH. The parent material is usually a 

mixture of weathered volcanic ash and loess, with layers of 

nearly pure ash in some profiles. A few profiles have some 

coarse fragments below 20 in depth, hinting at an underlying layer of gravelly alluvium. The surface texture is 

usually silt loam or silty clay loam, usually becoming more 

clay-rich with depth (except for fine sandy loam textures in 

some fresh ash layers). Colors are typically dark throughout 

the upper 2 or 3 ft of soil, indicating a high organic matter content, except in the ash layers, which tend to be light 

colored. Some profiles sampled in early June had a water 

table near the surface, whereas profiles sampled later in the 

summer were moist but free water was not present. The soil 

surface is well covered by litter.

Vegetation composition— 

Composition data here are divided into three groups: typical communities that presumably have been less impacted 

by grazing, communities with the herb layer dominated 

by Kentucky bluegrass (Poa pratensis), and a community 

dominated by unpalatable perennial forbs.

Coniferous trees (ponderosa pine, Douglas-fir, and grand 

fir) are usually present in the understory and sometimes in 

the overstory as codominants with aspen. A fairly dense 

shrub layer is present and dominated by common snowberry. A variety of grasses is present at low cover values. 

Kentucky bluegrass becomes the dominant herbaceous 

species on some plots that have been impacted greatly by 

grazing. A variety of native perennial forbs is present. Plots 

heavily impacted by grazing become dominated by certain unpalatable forbs, especially false hellebore (Veratrum

Riparian Aspen/Common Snowberry Types

Grand Fir/Common Snowberry (Floodplain) 

Plant Community Type

Abies grandis/Symphoricarpos albus

ABGR/SYAL (FLOODPLAIN) CWS314 

(Crowe and Clausnitzer 1997)

Douglas-Fir/Common Snowberry (Floodplain) 

Plant Association

Pseudotsuga menziesii/Symphoricarpos 

albus

PSME/SYAL (FLOODPLAIN) CDS628 

(Crowe and Clausnitzer 1997)

Ponderosa Pine/Common Snowberry 

(Floodplain) Plant Association

Pinus ponderosa/Symphoricarpos albus

PIPO/SYAL (FLOODPLAIN) CPS511 

(Crowe and Clausnitzer 1997)

Aspen/Common Snowberry Plant 

Community Type 

Populus tremuloides/Symphoricarpos albus

POTR5/SYAL HQS221 

(Crowe and Clausnitzer 1997)

UA002 D. Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 59

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

sp.). It appears that some palatable shrub species, such as 

western serviceberry (Amelanchier alnifolia) and red-osier 

dogwood (Cornus stolonifera), may also be eliminated in 

the more heavily grazing-impacted communities.

Successional relationships—

Succession is toward coniferous forest with snowberry 

understory. Moisture is probably adequate in most cases to 

support grand fir, although, as a result of the local seedsource environment, only ponderosa pine or Douglas-fir 

may be present.

The rate and degree to which grazing-sensitive perennial forbs can recover naturally after reduction of grazing 

pressure are unknown. The Kentucky bluegrass or unpalatable perennial forbs that dominate heavily impacted 

areas are likely to persist for some time even if grazing is 

discontinued.

Fire—

Fire frequency in these communities is strongly dependent on the fire frequency of surrounding uplands. Stands 

lacking conifers and downed woody debris are unlikely 

to carry ground fires, although heat from a crown fire in 

adjacent uplands may kill aspen in the small stands typical 

of our area. As mature aspen die and conifers become more 

abundant, the likelihood of fire in an aspen stand increases. 

Aspen typically resprout vigorously after stand-replacing 

fires. If, however, burn conditions are less severe (as would 

be typical of prescribed fires) and some large conifers are 

present that survive the fire, mature aspen will likely be 

killed and aspen regeneration will be compromised in the 

shade of the conifers.

Management considerations—

Conifer competition is intense in these communities, and 

removal of conifers may be required to allow aspen regeneration. If overstory conifers are present, light prescribed fires 

are likely to kill aspen without providing enough light for 

them to regenerate properly. Livestock grazing and wildlife 

browsing at levels typical of the Blue Mountains today will 

usually result in hedging of aspen saplings and no recruitment of new pole-sized aspen. Many aspen clones are at risk 

of dying out as older trees die of old age or shading by conifers. Heavy ungulate pressure also suppresses snowberry, 

but to a lesser degree than aspen. Heavy grazing can lead to 

replacement of grazing-sensitive native forbs by Kentucky 

bluegrass or unpalatable forbs such as false hellebore.

Environmental features

Site

Plots 14

Elevation, mean (range) (ft) 4,130 (3,140-4,900)

Slope, mean (range) (percent) 3 (0-10)

Aspect Any

Position Toeslope

Slope shape Concave or planar

Soil

Available water capacity (in) (n = 14) 6.5 to 10 (moderate to high)

pH (n = 11) 6.0 to 7.0
60 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Principal species

Latin name Common name Code

Typical

(N = 11)

Grassdominated

(N = 2)

Unpalatable 

forbdominated

(N = 1)

Cover (%)/constancy (%) Cover (%) Overstory trees:

Picea engelmannii Engelmann spruce PIEN 5

Pinus ponderosa Ponderosa pine PIPO 15/64

Populus tremuloides Quaking aspen POTR5 16/91 41/100 30

Pseudotsuga menziesii Douglas-fir PSME 12/36

Understory trees:

Abies grandis Grand fir ABGR 4/45

Pinus ponderosa Ponderosa pine PIPO 6/55

Populus tremuloides Quaking aspen POTR5 25/100 45/50 15

Pseudotsuga menziesii Douglas-fir PSME 3/45

Shrubs:

Amelanchier alnifolia Western serviceberry AMAL2 3/55

Cornus stolonifera Red-osier dogwood COST4 8/27

Crataegus douglasii Black hawthorn CRDO2 2/36

Potentilla fruticosa Shrubby cinquefoil POFR4 5/50

Ribes lacustre Prickly currant RILA 2/18 1

Rosa Rose ROSA5 2/55

Rosa nutkana Nootka rose RONU 5/9 8/50

Spiraea betulifolia Birchleaf spiraea SPBE2 3/27

Symphoricarpos albus Common snowberry SYAL 47/100 52/100 35

Grasses and grasslike:

Agrostis stolonifera Creeping bentgrass AGST2 20/50

Alopecurus pratensis Meadow foxtail ALPR3 2/18 1

Bromus carinatus Mountain brome BRCA5 2/27

Calamagrostis canadensis Bluejoint reedgrass CACA4 5

Calamagrostis rubescens Pinegrass CARU 2/27

Carex deweyana Dewey sedge CADE9 3/9 2/50

Carex geyeri Elk sedge CAGE2 9/18 3/50

Carex microptera Smallwinged sedge CAMI7 1

Dactylis glomerata Orchardgrass DAGL 3/36

Elymus glaucus Blue wildrye ELGL 2/45 5/50

Poa pratensis Kentucky bluegrass POPR 2/73 42/100 1

Forbs:

Achillea millefolium Common yarrow ACMI2 1/27 6/100

Aquilegia formosa Red columbine AQFO 2/27

Arnica cordifolia Heartleaf arnica ARCO9 2/36

Aster foliaceus Leafy aster ASFO 18/50

Aster modestus Few-flowered aster ASMO3 10/50

Camassia quamash Common camas CAQU2 2/27

Cerastium nutans Nodding chickweed CENU2 6/50

Cirsium Thistle CIRSI 5/50

Cirsium vulgare Bull thistle CIVU tr/27 2/50 (continued)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 61

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Forbs (continued):

Cynoglossum officinale Common houndstongue CYOF 20/50

Fragaria Strawberry FRAGA 2/73 8/100

Galium boreale Northern bedstraw GABO2 2/64 18/50 tr

Galium triflorum Fragrant bedstraw GATR3 1/9 2/50

Geranium viscosissimum Sticky geranium GEVI2 3/9 3/100

Geum macrophyllum Largeleaf avens GEMA4 2/18 4/100 tr

Iris missouriensis Rocky Mountain iris IRMI 1/45 2/50

Medicago lupulina Black medick MELU 3/50

Osmorhiza chilensis Mountain sweet-cicely OSCH 2/36 tr

Potentilla gracilis Slender cinquefoil POGR9 2/73

Ranunculus orthorhynchus Straightbeak buttercup RAOR3 4/27 20

Rudbeckia occidentalis Western coneflower RUOC2 10

Senecio crassulus Thickleaf groundsel SECR 13/18 35

Sidalcea oregana Oregon checker-mallow SIOR 4/64

Smilacina stellata Starry false Solomon’s seal SMST 2/64 1/50 1

Taraxacum officinale Common dandelion TAOF 1/64 8/50

Thalictrum occidentale Western meadowrue THOC 5/45 1/50 tr

Thermopsis montana Golden-pea THMO6 5/27 30

Urtica dioica Stinging nettle URDI 3/50

Veratrum False hellebore VERAT 11/36

Veratrum californicum California false hellebore VECA2 40

Viola Violet VIOLA 2/18 6/100

Ground surface features

Cover (%)

Bare ground Bedrock

Rock

Gravel

Moss, lichen

Litter

Principal species

Latin name Common name Code

Typical

(N = 11)

Grassdominated 

(N = 2)

Unpalatable 

forb-dominated 

(N = 1)

Cover (%)/constancy(%) Cover (%)

(continued)

 1

 0

 0

 0

 2

97
62 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

This is the wettest aspen plant community in the Blue 

Mountain region, and these sites are probably marginal for 

aspen survival because of wetness. Two plots were sampled, both near 4,100 ft elevation on nearly level concave 

topography. Soils are fine-grained (silt loam or sitly clay 

loam), dark-colored owing to high organic-matter content, 

and waterlogged within a foot of the surface for at least 

part of the summer. Our one soil pH sample is slightly acid. 

The soil surface is covered nearly completely by litter.

A few subalpine fir and Engelmann spruce trees occur 

in the understory, but the tree layer is dominated by aspen. 

Shrubs are nearly absent, and the herbaceous layer is 

dominated by aquatic sedge (Carex aquatilis) and bluejoint 

reedgrass (Calamagrostis canadensis). One of the plots 

also has abundant false hellebore (Veratrum californicum) 

and groundsel (Senecio crassulus).

Survival of aspen on these sites is tenuous owing to 

the high water table, because aspen roots require an aerated soil layer above the water table. However, wetness 

and water table fluctuations may give aspen a competitive 

advantage over conifers and allow it to persist for long periods. If a few aspen can survive a multiyear wet period, in 

subsequent drought years, they can expand by cloning into 

the dense sedge-grass vegetation where seedling establishment by conifers on this substrate is unlikely. Management 

actions (fencing, conifer removal) that allow aspen clones 

to expand to adjacent drier sites could improve their 

chances for survival over the long term.

Herbaceous Aspen Meadow Types

Aspen/Aquatic Sedge Plant Community Type

Populus tremuloides/Carex aquatilis

POTR5/CAAQ HQM212 

(Crowe and Clausnitzer 1997)

UA014 D. Swanson

Aspen/Woolly Sedge Plant Association

Populus tremuloides/Carex lanuginosa

POTR5/CALA30 HQM211 

(Crowe and Clausnitzer 1997)

MW1761 E. Crowe

The description below is based on five plots of this type 

that were sampled by Crowe and Clausnitzer (1997) and one 

additional plot sampled for the present study.

Environmental features—

This type occurs in wet basins or on flood plains.

Soils—

Soils consist of a thick layer (at least 2 ft) of silt loam, silty 

clay loam, or clay loam, probably derived from reworked 

volcanic ash and loess. Soils are dark-colored owing to high 

organic matter content. In early summer the soil profile is 

saturated with water, and a water table was present within 

30 in of the surface in all studied profiles.

Vegetation composition—

Aspen dominate the tree layer, and conifers are uncommon. 

Shrub cover is also low. The understory is dominated by 

herbaceous plants, especially woolly sedge, blue wildrye 

(Elymus glaucus), Kentucky bluegrass (Poa pratensis), and 

a variety of forbs dominated by starry false Solomon’s seal 

(Smilacina stellata).

Successional relationships—

Wetness limits succession to conifers on these sites. 

Conditions dry enough for conifers occur during dry episodes and on dry microsites, but dense sod limits site colonization by conifers.

Fire—

Fire is probably very rare in these communities because of 

the high moisture content of soils and vegetation through 

the summer. However, fire is possible during multiyear 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 63

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

droughts. In addition, these communities usually occur in 

small patches surrounded by forest where severe crown 

fires are possible, and heat from these fires may kill aspen. 

Resprouting of aspen after such fires is likely, although 

removal of trees from the watershed could result in greater 

yield of water to the depressions where the aspen/woolly 

sedge communities occur. In such cases, aspen may be 

unable to resprout in their former positions on the landscape, although they may survive by expanding upslope 

onto slightly drier habitats.

Management considerations—

Conifer competition is generally not an issue in aspen/

woolly sedge communities, although conifer removal may 

be necessary to allow aspen survival in cases where multiyear drought allows conifers to colonize these wetlands. 

Aspen are likely to expand uphill onto adjacent slightly 

drier sites if conifers are removed there; this would provide 

a more secure place for aspen in a future multiyear wet 

episode. Aspen regeneration is strongly inhibited by cattle 

grazing and browsing by deer and elk.

Environmental features

Site

Plots 6

Elevation, mean (range) (ft) 5,110 (4,780-5,510)

Slope, mean (range) (percent) 2 (0-5)

Aspect None

Position Toeslope or flat

Slope shape Concave, planar, or undulating

Soil

Plots 5

Available water capacity (in) 7 to 11 (moderate to high)
64 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Percent Overstory trees:

Populus tremuloides Quaking aspen POTR5 56/100

Abies grandis Grand fir ABGR 2/33

Understory trees:

Populus tremuloides Quaking aspen POTR5 11/100

Shrubs:

Symphoricarpos albus Common snowberry SYAL 2/33

Grasses and grasslike:

Carex lanuginosa Woolly sedge CALA30 36/100

Carex nebrascensis Nebraska sedge CANE2 2/33

Elymus glaucus Blue wildrye ELGL 25/50

Juncus balticus Baltic rush JUBA 2/33

Phleum pratense Common timothy PHPR3 2/33

Poa pratensis Kentucky bluegrass POPR 7/83

Trisetum canescens Tall trisetum TRCA21 3/33

Forbs:

Arnica chamissonis Chamisso arnica ARCH3 14/33

Aster Aster ASTER 5/50

Camassia quamash Common camas CAQU2 2/33

Fragaria Strawberry FRAGA 6/67

Galium boreale Northern bedstraw GABO2 2/50

Galium triflorum Fragrant bedstraw GATR3 4/33

Iris missouriensis Rocky Mountain iris IRMI 13/33

Mentha arvensis Field mint MEAR4 18/33

Smilacina stellata Starry false Solomon’s seal SMST 17/83

Taraxacum officinale Common dandelion TAOF 1/67

Thalictrum occidentale Western meadowrue THOC 8/50

Trifolium longipes Longstalk clover TRLO 10/50

Ground surface features

Cover (%)

Bare ground

Bedrock

Rock

Gravel

Moss, lichen

Litter

Submerged

 1

 0

 0

 0

 6

85

 8
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 65

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

An aspen grove in a wetland was sampled near Tipton 

Summit in the Wallowa-Whitman National Forest (5,110 ft 

elevation). This community is dominated by various grasslike wetland plants, including sedges (Carex flava and C. 

athrostachya), spikerush (Eleocharis acicularis), and rush 

(Juncus nevadensis). A few forb species are also present, 

notably greater creeping spearwort (Ranunculus flammula). 

The soil consists of light-colored silt loam volcanic ash over 

silty clay loam at 22-in depth. Soil colors indicate seasonal 

saturation, but no water table was within 2 ft of the surface 

in mid-July 2004. The pH is quite acid for an aspen site, 5.4 

to 5.8. Dried algae on the ground surface indicate standing 

water in the spring. This plot is an example of the diversity of wetland settings where aspen can occur in the Blue 

Mountains, and strongly fluctuating soil moisture conditions probably aid aspen by reducing conifer competition.

Aspen/Yellow Sedge Plant Community Type

Populus tremuloides/Carex flava 

POTR5/CAFL4 HQG113

WA031 D. Swanson
66 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Environmental features—

This type occurs on flat or slightly concave areas with 

rather wet soils at moderate elevations.

Soils—

Soils consist of a thick layer (at least 2 ft) of clay loam or 

silty clay loam, probably derived from reworked volcanic 

ash and loess; extremely gravelly material occurs below the 

clayey material in two profiles. Soils are dark-colored owing 

to high organic matter content. In early summer the soil 

profile is saturated with water, but by late summer it typically dries to a moist state. Soil pH is slightly to moderately 

acid.

Vegetation composition—

Aspen is the only common overstory tree; conifers are 

sometimes present in the understory, but fluctuating high 

water tables probably hinder the survival of larger conifers. 

Shrubs are rare or absent, and the herb layer is dominated 

by bluejoint reedgrass. A variety of forbs is also present, 

notably leafy aster (Aster foliaceus), buttercup (Ranunculus

spp.), thickleaf groundsel (Senecio crassulus), starry false 

Solomon’s seal (Smilacina stellata), and false hellebore 

(Veratrum spp.).

Successional relationship—

In general, succession is toward grand fir, subalpine fir, or 

Engelmann spruce forest. However, several factors act to 

maintain aspen on these sites. Fluctuations in the water 

table, specifically multiyear episodes where the water table 

remains near the surface for the entire summer, can cause 

widespread mortality of trees, particularly larger trees 

(including aspen). In a well-stocked aspen stand, a few 

aspen are likely to survive on drier microsites, and then 

expand vegetatively during a subsequent multiyear dry 

episode. Meanwhile, conifer seedling establishment is 

inhibited by the dense herbaceous vegetation and litter. 

The result is persistent presence of aspen with few conifers.

Fire—

Fire is probably very rare in these communities because of 

the high moisture content of soils and vegetation through 

the summer. However, fire is possible during multiyear 

droughts. In addition, these communities usually occur in 

small patches surrounded by dense fir forest where severe 

crown fires are possible, and heat from these fires may 

kill aspen. Resprouting of aspen after such fires is likely, 

although removal of trees from a watershed could result in 

greater yield of water to the depressions where the aspen/

bluejoint reedgrass communities occur. In such cases, aspen 

may be unable to resprout in their former positions on the 

landscape, although they may survive by sprouting on 

slightly drier habitats upslope.

Management considerations—

Conifer competition is generally not an issue in aspen/bluejoint reedgrass communities, although conifer removal 

may be necessary to allow aspen survival in special cases 

where multiyear drought allows conifers to colonize these 

wetlands. Aspen are likely to expand uphill onto adjacent 

slightly drier sites if conifers are removed there; this would 

provide a more secure place for aspen in a future multiyear 

wet episode. Aspen regeneration is strongly inhibited by 

cattle grazing and browsing by deer and elk.

Environmental features

Site

Plots 7

Elevation, mean (range) (ft) 4,490 (4,035-5,040)

Slope, mean (range) (percent) 1 (0-2)

Aspect None

Position Toeslope or flat

Slope shape Concave or planar

Soil

Available water capacity (in) (n = 4) 6.5 to 11 (moderate to high)

pH (n = 3) 5.6 to 6.4

Aspen/Bluejoint Reedgrass Plant 

Community Type

Populus tremuloides/Calamagrostis 

canadensis

POTR5/CACA4 HQM123 

(Crowe and Clausnitzer 1997)

UW1991 R. Clausnitzer
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 67

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Populus tremuloides Quaking aspen POTR5 41/100

Understory trees:

Abies grandis Grand fir ABGR 3/29

Abies lasiocarpa Subalpine fir ABLA 2/29

Pinus contorta Lodgepole pine PICO 3/29

Populus tremuloides Quaking aspen POTR5 36/100

Grasses and grasslike:

Alopecurus pratensis Meadow foxtail ALPR3 3/29

Calamagrostis canadensis Bluejoint reedgrass CACA4 57/100

Carex microptera Smallwinged sedge CAMI7 2/71

Deschampsia cespitosa Tufted hairgrass DECE 19/29

Forbs:

Aconitum columbianum Columbian monkshood ACCO4 2/29

Aster foliaceus Leafy aster ASFO 10/43

Ranunculus orthorhynchus Straightbeak buttercup RAOR3 4/43

Ranunculus uncinatus Little buttercup RAUN 3/43

Senecio crassulus Thickleaf groundsel SECR 31/57

Smilacina stellata Starry false Solomon’s seal SMST 15/71

Thermopsis montana Golden-pea THMO6 4/43

Veratrum californicum California false hellebore VECA2 14/57

Veratrum viride Green false hellebore VEVI 6/29

Viola Violet VIOLA 3/29

Ground surface features

Cover (%)

Bare ground

Bedrock

Rock

Gravel

Moss, lichen

Litter

10

 0

 0

 0

14

63
68 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

These three types are mesic (moderately moist) aspen 

meadows and together are the most widespread aspen communities in the Blue Mountains. They are drier than the 

preceding aspen-sedge community types. They have moist, 

nutrient-rich soils with nearly neutral pH, all properties that 

create an ideal environment for the growth of aspen. Three 

communities are treated together here because they appear 

to result mainly from differences in past history of grazing, 

browsing, and colonization by various exotic grasses. The 

aspen/mesic forb plant community type is the most pristine and the other two (POTR5/POPR and POTR5/ALPR3) 

are highly impacted. In the tables “Principal species” and 

“Ground surface features” below, the POTR5/MESIC 

Aspen/Kentucky Bluegrass Plant 

Community Type

Populus tremuloides/Poa pratensis

POTR5/POPR HQM122 

(Crowe and Clausnitzer 1997)

Aspen/Meadow Foxtail Plant Community Type

Populus tremuloides/Alopecurus pratensis

POTR5/ALPR3 HQM611

MA031 D. Swanson UA045 D. Swanson

Aspen/Mesic Forb Plant Community Type 

Populus tremuloides/Mesic Forb

POTR5/MESIC FORB HQM511 

(Crowe and Clausnitzer 1997)

MA008 D. Swanson

FORB communities are split into two groups according to 

level of grazing impacts. The “POTR5/MESIC FORB (less 

impacted)” plots have Kentucky bluegrass (Poa pratensis) 

cover of 10 percent or less, and cover by all exotic grasses 

and forbs plus grazing-tolerant native forbs is less than 25 

percent. (Grazing-tolerant mesic forbs include common 

dandelion Taraxacum officinale, false hellebore Veratrum

spp., longstalk clover Trifolium longipes, lupines Lupinus

spp., and yarrow Achillea millefolium). The “POTR5/

MESIC FORB (more impacted)” communities have 

Kentucky bluegrass cover of more than 10 percent or exotic 

grasses and forbs plus grazing-tolerant native forbs cover 

of 25 percent or more. They are transitional in composition 

to the POTR5/POPR and POTR5/ALPR3 types, which are 

dominated by exotic grasses.

Environmental features—

Mesic aspen meadows occur on gentle to nearly level slopes 

at midelevations. They are often situated in a swale or small 

valley that supports an intermittent stream. These aspen 

stands are often quite small (an acre or less), although in a 

exceptional cases they may occupy 5 to 10 ac.

Soils—

Soils are fine-grained and high in organic matter, with a 

neutral to slightly acid pH. The parent material is usually 

a mixture of weathered volcanic ash and loess, with layers 

of nearly pure ash in some profiles; coarse fragments are 

usually absent. The surface texture is usually silt loam or 

silty clay loam, often becoming more clay-rich with depth 

(except for fine sandy loam textures in some fresh ash layers). Colors are typically dark throughout the upper 2 or 3 ft 
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 69

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

of soil, indicating a high organic-matter content, except in 

the ash layers, which tend to be light colored. A water table 

is observed in some profiles below a depth of 24 in, usually 

in early summer (June). Later in the summer the soil is 

usually moist, but free water is not present. The soil surface is well covered by litter, even in the more grazingdisturbed stands, thanks to the vigorous rhizomatous 

grasses (Kentucky bluegrass, meadow foxtail, and others).

Vegetation composition—

Aspen generally dominate over an understory of forbs and 

grass. Coniferous trees are most common in the understory, 

but are occasionally codominant with aspen. Most of the 

coniferous tree species that inhabit the Blue Mountains can 

occur in mesic meadows together with aspen; ponderosa 

pine is most common. Shrub cover is low, with common 

snowberry (Symphoricarpos albus) the only common shrub. 

The understory in relatively pristine POTR5/MESIC FORB 

communities is dominated by a diverse assemblage of native 

forbs. Several of these forbs decline with grazing pressure, 

notably common camas (Camassia quamash), mountain 

sweet-cicely (Osmorhiza chilensis), straightbeak buttercup 

(Ranunculus orthorhynchus), starry false Solomon’s seal 

(Smilacina stellata), and western meadowrue (Thalictrum 

occidentale). Understories in POTR5/ALPR3 communities 

are dominated by large grasses, especially introduced pasture species such as meadow foxtail and timothy (Phleum 

pratense), but also some native species such as blue wildrye 

(Elymus glaucus). Kentucky bluegrass is also common. The 

community type is named after the most common large 

introduced pasture grass (meadow foxtail), but this species 

is not always present. Kentucky bluegrass dominates in the 

highly impacted POTR5/POPR communities. Weedy forbs 

such as houndstongue (Cynoglossum officinale) and Canada 

thistle (Cirsium arvense) are present on the more grazingimpacted sites, but the highly competitive sod-forming 

grasses prevent them from dominating.

Successional relationships—

Succession is toward conifer forest in almost all cases. High 

water tables may at times restrict the growth of conifers, but 

not to the degree that they do in the wetter aspen meadows 

described previously. Moisture is probably adequate to support grand fir, but in many environments the seed source 

is mainly ponderosa pine or occasionally lodgepole pine, 

so these are the most important competing conifers. These 

communities may succeed to the lodgepole pine/Kentucky 

bluegrass plant community type (CLM112), the ponderosa 

pine/Kentucky bluegrass (CPM112) plant community type, 

or some as yet undefined grand fir series plant community. 

Shading by these conifers will suppress and could eliminate aspen from a meadow, although aspen often are able to 

persist on the margins of openings with a fluctuating high 

water table where mature conifers may be killed by wetness 

and conifer seedlings have difficulty establishing.

The rate and ultimate outcome of understory plant recovery by succession if grazing disturbance is reduced is not 

well known. Kentucky bluegrass is highly competitive 

with the native forbs and once established may dominate 

for many years even after exclusion of grazing. If heavy 

grazing has produced a community dominated by bluegrass 

with some larger pasture grasses such as meadow foxtail or 

timothy, exclusion of grazing may allow the taller grasses to 

gradually replace Kentucky bluegrass by succession.

Fire—

Fire is probably rare in early seral mesic aspen meadows 

owing to the low flammability of fuels. As aspen die to produce surface woody fuels and conifers fill in, the likelihood 

of fire increases, as does fire severity. In addition, these 

communities usually occur in small patches surrounded 

by conifer forest where severe crown fires are possible, 

and heat from these fires may kill aspen. Fire frequency is 

highly dependent on the fire frequency of the neighboring 

upland forests. In the absence of fire, aspen is gradually 

eliminated by competing conifers.

Management considerations—

Mesic aspen meadows are highly productive and attractive to livestock and wild ungulates. Browsing pressure is 

intense in most parts of the study area; aspen are strongly 

hedged and regeneration is minimal outside of exclosures. 

Gradual death of old aspen trees and continuing hedging 

of regeneration could lead to complete loss of some aspen 

clones. Prolonged grazing pressure also tends to eliminate 

many native perennial forbs, which are replaced by the 

more grazing-tolerant grasses, especially Kentucky bluegrass. As mentioned above, we are uncertain about rate of 

recovery (or even the possibility of recovery) of a diverse 

native forb community where many species have been 

eliminated by grazing. Management should emphasize measures that prevent loss of vulnerable native forbs. Conifers 

are more shade tolerant and longer lived than aspen and 

compete strongly with aspen; thus conifer removal may be 

needed to ensure survival of aspen clones.

Environmental features

Site

Plots 46

Elevation, mean (range) (ft) 5,035 (3,930-6,240)

Slope, mean (range) (percent) 4 (0-20)

Aspect All

Position Footslope, toeslope

Slope shape Concave or planar

Soil

Available water capacity (in) (n = 43) 6.5 to 10.5 (moderate to high)

pH (n = 31) 6.2 to 7.0
70 GENERAL TECHNICAL REPORT PNW-GTR-806

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

Principal species

Latin name Common name Code

POTR5/ 

MESIC 

FORB (less 

impacted)

16 plots 

POTR5/ MESIC 

FORB (more 

impacted)

11 plots

POTR5/ALPR3

9 plots

POTR5/POPR

10 plots

 Cover (%)/constancy(%)

Overstory trees:

Pinus ponderosa Ponderosa pine PIPO 15/25 8/18 7/33 12/20

Populus tremuloides Quaking aspen POTR5 32/81 18/82 35/89 51/80

Understory trees:

Juniperus occidentalis Western juniper JUOC 1/31 6/45 1/22 6/30

Pinus contorta Lodgepole pine PICO 8/12 10/18 4/33 5/20

Pinus ponderosa Ponderosa pine PIPO 4/44 17/55 3/33 3/50

Populus tremuloides Quaking aspen POTR5 31/88 26/100 24/67 11/90

Pseudotsuga menziesii Douglas-fir PSME 2/25 2/27 tr/11 1/20

Shrubs:

Berberis repens Creeping Oregon grape BERE 2/25 tr/0

Ribes cereum Wax currant RICE 3/12 2/27 1/10

Rosa Rose ROSA5 2/31 4/27 15/11 2/10

Symphoricarpos albus Common snowberry SYAL 3/50 5/73 4/56 5/70

Grasses and grasslike:

Agrostis scabra Rough bentgrass AGSC5 tr/6 15/22

Agrostis stolonifera Creeping bentgrass AGST2 48/22

Alopecurus pratensis Meadow foxtail ALPR3 37/44

Bromus carinatus Mountain brome BRCA5 3/6 6/64 1/22 5/50

Calamagrostis rubescens Pinegrass CARU 4/25

Carex lanuginosa Woolly sedge CALA30 5/20

Carex microptera Smallwinged sedge CAMI7 1/31 9/44 7/30

Dactylis glomerata Orchardgrass DAGL 2/19 1/9 15/22 tr/30

Elymus glaucus Blue wildrye ELGL 3/31 4/73 32/33 4/20

Festuca occidentalis Western fescue FEOC 5/9 10/11 20/20

Juncus balticus Baltic rush JUBA tr/6 4/33 3/10

Phleum pratense Common timothy PHPR3 3/38 2/27 8/67 3/30

Poa pratensis Kentucky bluegrass POPR 5/62 13/82 8/89 52/100

Trisetum canescens Tall trisetum TRCA21 8/25 2/36 9/56 4/10

Forbs:

Achillea millefolium Common yarrow ACMI2 1/62 2/82 3/67 2/100

Actaea rubra Red baneberry ACRU2 2/20

Allium geyeri Geyer’s onion ALGE 12/38 12/27 tr/10

Aquilegia formosa Red columbine AQFO 7/19 7/55 tr/11 3/50

Arenaria macrophylla Bigleaf sandwort ARMA18 25/6 tr/18 2/20

Arnica cordifolia Heartleaf arnica ARCO9 3/38 2/18 1/11 2/30

Aster foliaceus Leafy aster ASFO 14/25 15/9 2/22 2/20

Camassia quamash Common camas CAQU2 6/50 2/36 8/22

Cirsium arvense Canada thistle CIAR4 tr/18 2/20

Cirsium vulgare Bull thistle CIVU 1/25 2/45 tr/33 1/40

Collinsia parviflora Small flowered blue- 

 eyed Mary

COPA3 tr/6 tr/18 2/30

(continued)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 71

RIPARIAN AND WETLAND ASPEN PLANT COMMUNITIES

 Cover (%)/constancy(%)

Collomia linearis Narrowleaf collomia COLI2 tr/9 2/20

Cynoglossum officinale Common houndstongue CYOF 6/36 1/30

Delphinium 

 depauperatum

Slim larkspur DEDE2 1/19 2/20

Epilobium Willowherb EPILO tr/6 2/22

Fragaria Strawberry FRAGA 2/81 6/73 4/67 6/90

Galium aparine Cleavers GAAP2 4/31 1/36 1/33 1/50

Galium boreale Northern bedstraw GABO2 4/56 8/82 1/44 5/60

Geranium viscosissimum Sticky geranium GEVI2 1/12 2/27 1/20

Geum macrophyllum Largeleaf avens GEMA4 1/19 2/44 2/40

Iris missouriensis Rocky Mountain iris IRMI 16/25 25/9 55/11 4/20

Lupinus Lupine LUPIN 1/6 3/20

Nemophila parviflora Smallflower nemophila NEPA 1/9 13/20

Osmorhiza chilensis Mountain sweet-cicely OSCH 8/44 4/27 1/44 1/50

Penstemon globosus Globe penstemon PEGL5 4/19 3/18 4/22

Penstemon procerus Small flowered 

 penstemon

PEPR2 3/6 3/9 1/11 3/20

Perideridia gairdneri Gairdner’s yampah PEGA3 5/19 tr/9 2/22 tr/10

Potentilla gracilis Slender cinquefoil POGR9 1/50 3/55 5/56 1/50

Prunella vulgaris Self-heal PRVU 4/22 2/20

Ranunculus 

 orthorhynchus

Straightbeak buttercup RAOR3 6/50 1/9 1/22 1/10

Ranunculus uncinatus Little buttercup RAUN 2/75 8/55 8/22 8/50

Senecio crassulus Thickleaf groundsel SECR 20/44 25/27 16/33 20/20

Sidalcea oregana Oregon checker-mallow SIOR 4/62 1/45 3/56 4/60

Smilacina stellata Starry false Solomon’s 

 seal

SMST 6/50 1/27 tr/22 1/50

Taraxacum officinale Common dandelion TAOF 3/69 6/82 2/67 3/70

Thalictrum occidentale Western meadowrue THOC 16/50 4/55 8/22 2/60

Trifolium longipes Longstalk clover TRLO 2/31 24/27 6/22 3/30

Veratrum False hellebore VERAT 1/6 1/22 14/20

Verbascum thapsus Common mullein VETH tr/18 2/20

Viola adunca Early blue violet VIAD 2/12 4/45 1/11 1/30

Viola nuttallii Nuttall’s violet VINU2 tr/11 2/20

Ground surface features

POTR5/MESIC 

FORB (less 

impacted)

16 plots

POTR5/MESIC 

FORB (more 

impacted)

11 plots

POTR5/ALPR3

 9 plots

POTR5/POPR 

10 plots

 Cover (%)

Bare ground 3 7 1 8

Bedrock 0 0 0 0

Rock 0 0 0 0

Gravel 0 0 0 0

Moss, lichen 3 2 2 1

Litter 96 91 97 91

Principal species

Latin name Common name Code

POTR5/ 

MESIC 

FORB (less 

impacted)

16 plots 

POTR5/ 

MESIC 

FORB (more 

impacted)

11 plots

POTR5/ALPR3

9 plots

POTR5/POPR

10 plots

(continued)
72 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Aspen are occasionally found growing out of crevices 

between large rocks in rubble fields, talus slopes, and 

fractured rock outcrops. Survival of aspen on these sites 

is favored by several factors. The poor footing for hoofed 

animals discourages browsing by deer, elk, and cattle. Rain 

and snowmelt are shed from the rock surfaces and concentrated in the crevices where the aspen root, providing 

a better moisture supply than would be available on a less 

rocky site. Once established, aspen can propagate by cloning as their roots follow the network of cracks and crevices 

between rocks.

Talus and Rock Outcrop Aspen Types

Aspen (Rubble, High) Plant Community Type

Populus tremuloides (Rubble, High)

POTR5 (RUBBLE, HIGH) HQR101

Aspen (Rubble, Low) Plant Community Type

Populus tremuloides (Rubble, Low)

POTR5 (RUBBLE, LOW) HQR102

Environmental features— 

The high and low variants of rubble aspen communities 

are well separated by elevation, with the former occurring above 6,000 ft and the latter below 6,000 ft elevation. 

Otherwise settings are similar: steep slopes of various 

aspects and soils dominated by coarse fragments.

Vegetation composition—

The plant cover on these communities is quite sparse 

owing to the lack of soil, and composition is highly variable. At high elevations, subalpine fir are often present but 

with low cover. Oregon boxwood (Pachistima myrsinites), 

western hawkweed (Hieracium albertinum), and a variety 

of other plants are sometimes present but have low cover. 

At lower elevations, common associated plants are ponderosa pine, wax currant (Ribes cereum), common snowberry (Symphoricarpos albus), elk sedge (Carex geyeri), 

fireweed (Epilobium angustifolium), and hotrock penstemon 

(Penstemon deustus). The ground surface is mostly bedrock or loose rock and gravel, with litter present in the gaps 

between rocks.

Successional relationships—

These communities are probably not transient seral stages: 

cover by other trees is kept low by the lack of soil, allowing 

aspen to persist indefinitely.

Fire effects—

Ground fires cannot move across the ground owing to lack 

of fuel. However, the rubble fields and rock outcrops in our 

area are often rather small, and trees on them are vulnerable 

to damage by heat from crown fires in surrounding forests. 

If trees are killed by such a fire, aspen should resprout readily, whereas conifers will reestablish with difficulty by seed.

Management considerations—

Rubble sites are valuable natural refugia for aspen. As a 

result of their natural protection from conifer encroachment 

and herbivory, these aspen stands are typically in better 

condition than aspen stands on sites without rock rubble. 

Aspen can propagate naturally from these refugia out onto 

adjacent areas by seed or root cloning where conditions are 

suitable.

UA046 D. Swanson QA076 C. Johnson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 73

UPLAND ASPEN COMMUNITIES

Environmental features

POTR5 (RUBBLE, HIGH) POTR5 (RUBBLE, LOW)

Plots 4 14

Elevation, mean (range) (ft) 6,758 (6,440-7,050) 5,040 (4,540-5,650)

Slope, mean (range) (percent) 32 (10-58) 57 (25-95)

Aspect All All

Position Shoulder, backslope Backslope, footslope

Slope shape Convex, planar Convex, planar, concave

Principal species

Latin name Common name Code

POTR5 (RUBBLE, HIGH) 

4 plots

POTR5 (RUBBLE, LOW) 

14 plots

 Cover (%)/constancy(%) Overstory trees:

Abies lasiocarpa Subalpine fir ABLA 5/25

Pinus ponderosa Ponderosa pine PIPO 11/29

Populus tremuloides Quaking aspen POTR5 13/50

Understory trees:

Abies grandis Grand fir ABGR 4/25 11/21

Abies lasiocarpa Subalpine fir ABLA 3/75

Pinus contorta Lodgepole pine PICO 8/25 6/43

Pinus ponderosa Ponderosa pine PIPO 2/43

Populus tremuloides Quaking aspen POTR5 44/100 29/79

Pseudotsuga menziesii Douglas-fir PSME 2/21

Shrubs:

Amelanchier alnifolia Western serviceberry AMAL2 tr/25 2/50

Arctostaphylos uva-ursi Kinnikinnick ARUV 7/29

Berberis repens Creeping Oregon grape BERE 3/64

Ceanothus velutinus Snowbrush ceanothus CEVE 40/25 tr /14

Cornus stolonifera Red-osier dogwood COST4 10/25

Pachistima myrsinites Oregon boxwood PAMY 9/50 6/29

Prunus virginiana Common chokecherry PRVI 8/36

Ribes cereum Wax currant RICE 12/57

Salix scouleriana Scouler willow SASC 3/25 11/29

Spiraea betulifolia Birchleaf spiraea SPBE2 1/25 4/29

Symphoricarpos albus Common snowberry SYAL 1/25 16/71

Symphoricarpos oreophilus Mountain snowberry SYOR2 7/21

Vaccinium scoparium Grouse huckleberry VASC 1/75 10/21

Grasses and grasslike:

Agropyron spicatum Bluebunch wheatgrass AGSP 8/21

Bromus carinatus Mountain brome BRCA5 2/75 1/14

Calamagrostis rubescens Pinegrass CARU 4/43

Carex Sedge CAREX 6/50

Carex geyeri Elk sedge CAGE2 1/25 6/86

Sitanion hystrix Bottlebrush squirreltail SIHY tr /25 2/21

Stipa occidentalis Western needlegrass STOC2 tr /75 1/7
74 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Forbs:

Achillea millefolium Common yarrow ACMI2 1/75 1/21

Apocynum androsaemifolium Spreading dogbane APAN2 3/21

Arnica cordifolia Heartleaf arnica ARCO9 3/25 2/14

Artemisia ludoviciana Western mugwort ARLU 15/25

Cymopterus terebinthinus 

 foeniculaceus

Turpentine cymopterus CYTEF 3/25

Epilobium angustifolium Fireweed EPAN2 2/64

Fragaria Strawberry FRAGA 4/43

Hackelia micrantha Blue stickseed HAMI 3/25

Helianthella uniflora Little sunflower HEUN 5/25

Heuchera cylindrica Roundleaf alumroot HECY2 16/21

Hieracium albertinum Western hawkweed HIAL 2/75 0/7

Lupinus sulphureus subsaccatus Sulphur lupine LUSUS3 5/25

Mertensia ciliata Ciliate bluebells MECI3 3/25

Paeonia brownii Brown’s peony PABR 3/25

Penstemon attenuatus Sulfur penstemon PEAT3 10/25

Penstemon deustus Hotrock penstemon PEDE4 2/50

Penstemon fruticosus Shrubby penstemon PEFR3 3/25 2/14

Phlox austromontana Mountain phlox PHAU3 5/25

Potentilla arguta convallaria Tall cinquefoil POARC 4/50 tr /14

Valeriana sitchensis Sitka valerian VASI 3/25

Ground surface features

POTR5 (RUBBLE,HIGH)

4 plots

POTR5 (RUBBLE,LOW)

14 plots

 Cover (%)

Bare ground 6 2

Bedrock 12 14

Rock 44 51

Gravel 16 1

Moss, lichen 0 4

Litter 21 30

Principal species

Latin name Common name Code

POTR5 (RUBBLE, HIGH) 

4 plots

POTR5 (RUBBLE, LOW) 

14 plots

 Cover (%)/constancy(%)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 75

UPLAND ASPEN COMMUNITIES

Aspen are present although rare in plant communities with 

subalpine fir potential in the Blue Mountains. Here the soil 

is more fine-grained than the rock rubble sites described 

previously. Two of the sample plots are in burned areas, one 

in a clearcut, the fourth on a mountain slope with fir parkland. Elsewhere in the Rocky Mountains, aspen is a common early seral species on sites with subalpine fir potential 

(Peet 2000), and it is likely that our sample does not portray 

the full range of subalpine fir sites that aspen could occupy 

in the Blue Mountains.

Environmental features—

The four plots sampled are on hillslopes.

Soils—

Soils formed in stoney colluvium or weathered bedrock. 

A loamy surface layer with few stones is present in some 

profiles, ranging in thickness up to 2 ft. Below is very to 

extremely gravelly or cobbly loamy soil. Available water 

holding capacity is low to moderate.

Vegetation composition—

Aspen are absent from one of the plots because they failed 

to regenerate after a fire, although snags from mature 

aspen are present. Subalpine fir is sometimes present in 

the understory. One plot has bitter cherry (Prunus emarginata) shrubs. The understory layer is dominated by 

grasses and the disturbance-adapted forb western coneflower (Rudbeckia occidentalis). Skunk-leaved polemonium 

(Polemonium pulcherrimum), a common associate of subalpine fir, is common. Some forb species typical of midelevation aspen stands (such as nettleleaf horsemint 

Agastache urticifolia and western meadowrue Thalictrum 

occidentale) are also present.

Successional relationships—

Succession should be toward subalpine fir forest in most 

cases, although poor site conditions may lead to open forest 

stands that allow aspen to persist for a long time.

Fire—

Fires in subalpine fir forests are infrequent but typically 

of high severity. Fires generally favor aspen, which can 

resprout afterward without conifer competition. However, 

the failure of aspen to resprout on one of these subalpine 

fir plots shows that small clones can on occasion be eliminated by fire, probably when severe fire kills a shallow root 

system.

Management considerations—

Aspen is probably capable of growing in many subalpine fir 

plant associations in the Blue Mountains as a seral species, 

but it is rare. The mixed- to stand-replacement fires typical of these communities should favor aspen, although fire 

suppression, browsing, competition by lodgepole pines, and 

lack of propagules (either seeds or preexisting aspen that 

could resprout) combine to make aspen quite uncommon.

Environmental features

Site

Plots 4

Elevation, mean (range) (ft) 6,245 (4,840-6,870)

Slope, mean (range) (percent) 32 (6-62)

Aspect All

Position Backslope

Slope shape Planar or concave

Soil

Available water capacity (in) (n = 3) 3.5 to 7.5 (low to moderate)

pH ( n = 3) 5.8 to 6.4

Aspen Types of the Subalpine Fir Series

Aspen(Subalpine Fir)/Western Coneflower 

Plant Community Type

Populus tremuloides (Abies lasiocarpa)/

Rudbeckia occidentalis

POTR5(ABLA)/RUOC2 HQC114

WA017 D. Swanson
76 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Abies grandis Grand fir ABGR 3/25

Abies lasiocarpa Subalpine fir ABLA 10/25

Pinus contorta Lodgepole pine PICO 5/25

Populus tremuloides Quaking aspen POTR5 17/75

Understory trees:

Abies grandis Grand fir ABGR 3/25

Populus tremuloides Quaking aspen POTR5 16/75

Shrubs:

Prunus emarginata Bitter cherry PREM 25/25

Sambucus Elderberry SAMBU 5/25

Symphoricarpos albus Common snowberry SYAL 3/50

Grasses and grasslike:

Bromus carinatus Mountain brome BRCA5 15/75

Bromus vulgaris Columbia brome BRVU 20/25

Carex microptera Smallwinged sedge CAMI7 3/25

Elymus glaucus Blue wildrye ELGL 15/50

Trisetum canescens Tall trisetum TRCA21 3/25

Forbs:

Achillea millefolium Common yarrow ACMI2 8/50

Agastache urticifolia Nettleleaf horsemint AGUR 2/100

Anaphalis margaritacea Common pearly-everlasting ANMA 2/75

Arenaria macrophylla Bigleaf sandwort ARMA18 3/25

Arnica cordifolia Heartleaf arnica ARCO9 3/25

Aster foliaceus Leafy aster ASFO 5/25

Aster modestus Few-flowered aster ASMO3 3/25

Collomia COLLO 5/50

Delphinium glaucum Sierra larkspur DEGL3 10/25

Epilobium angustifolium Fireweed EPAN2 3/25

Fragaria Strawberry FRAGA 10/25

Hackelia micrantha Blue stickseed HAMI 2/75

Heracleum lanatum Cowparsnip HELA4 3/50

Osmorhiza occidentalis Western sweetroot OSOC 2/50

Phacelia hastata Silverleaf phacelia PHHA 3/25

Phacelia heterophylla Varileaf phacelia PHHE2 3/25

Polemonium pulcherrimum Skunk-leaved polemonium POPU3 5/100

Rudbeckia occidentalis Western coneflower RUOC2 24/100

Sidalcea oregana Oregon checker-mallow SIOR 3/25

Thalictrum occidentale Western meadowrue THOC 1/100

Viola Violet VIOLA 2/50

Ground surface features

Cover (%)

Bare ground 15

Bedrock 5

Rock 7

Gravel 1

Moss, lichen 0

Litter 72
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 77

UPLAND ASPEN COMMUNITIES

One plot containing aspen was sampled from this plant 

association. It is located at 4,320 ft elevation on a gently 

sloping bench in the northern Blue Mountains. The soil 

consists of 20 in of fine-grained volcanic ash over gravelly 

sandy clay loam, with a pH of 6.2 to 6.6. A sparse overstory 

of Engelmann spruce, western larch, and Douglas-fir is 

present, with abundant understory aspen (35 percent cover) 

and grand fir seedlings and saplings (20 percent cover). The 

shrub and herb layer is dominated by twinflower (Linnaea 

borealis), false Solomon’s seal (Smilacina racemosa), 

prince’s pine (Chimaphila umbellata), and rose (Rosa gymnocarpa). This plant association of rather moist and rich 

sites is capable of supporting seral aspen, but aspen are 

rare here, probably owing to conifer competition and herbivory. The high cover of false Solomon’s seal (20 percent) 

is unusual for this plant association and may be an effect of 

enhanced nutrient cycling provided by aspen.

Aspen Types of the Grand Fir Series

Grand Fir/Twinflower Plant Association

Abies grandis/Linnaea borealis 

ABGR/LIBO3 

CWF311 (Johnson and Simon 1987)

CWF312 (Johnson and Clausnitzer 1992)

UA021 D. Swanson
78 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Aspen is a rare early-seral component in this widespread 

plant association.

Environmental features—

These communities occur in a variety of settings at moderate elevations on moderate slopes.

Soils—

Soils are well-drained and lack a water table or any other 

sign of wetness. Two of the soils studied formed in stoney 

colluvium or residuum from bedrock, with low available 

water capacity and slightly to moderately acid pH. Profiles 

consist of very gravelly or cobbly loamy material. The third 

study profile is more typical of the plant association and has 

over 2 ft of silty volcanic ash over very gravelly loam and a 

high available water capacity.

Vegetation composition—

Aspen share the tree layer with a variety of conifers, 

including Douglas-fir, grand fir, ponderosa pine, western larch, and lodgepole pine. The understory is rich in 

shrubs, especially big huckleberry (Vaccinium membranaceum), Scouler’s willow (Salix scouleriana), birchleaf 

spiraea (Spiraea betulifolia), and many others. Pinegrass 

(Calamagrostis rubescens), strawberry (Fragaria sp.), 

western meadowrue (Thalictrum occidentale), and other 

herbaceous plants form a rather sparse ground cover. These 

communities differ from typical early seral ABGR/VAME 

communities in that lodgepole pine is lacking or less abundant than aspen.

Successional relationships—

Aspen is a seral species that will be replaced by more 

shade-tolerant conifers unless disturbance interrupts succession. Ponderosa pine, Douglas-fir, and grand fir are 

all possible successors to aspen, and grand fir is likely to 

dominate over the long term in the absence of disturbance. 

Competion from the shade-intolerant but fast-growing conifers western larch and lodgepole pine can also limit aspen 

growth.

Fire—

Moist grand fir plant associations such as this are believed 

to have historically had a mixed fire regime. Occasional 

moderate- to high-severity fires removed the overstory and 

allowed aspen to resprout or regenerate by seed with minimal competition. Fire suppression has probably led to loss 

of seral aspen communities.

Management consideration—

Conifer competition is intense in these communities, and 

removal of overstory conifers is usually required to allow 

aspen regeneration. If overstory conifers are present, light 

prescribed fires are likely to kill aboveground parts of aspen 

without providing enough light for aspen suckers to thrive. 

Soil moisture should be adequate for aspen plantings in 

ABGR/VAME plant associations where aspen are lacking. These shrub-rich communities provide minimal forage 

for livestock and are rarely grazed by livestock. However, 

aspen are preferred wildlife browse and their growth is 

often suppressed by browsing; protection of aspen from 

browsing will often be needed to allow aspen regeneration to survive. The early-seral plot listed separately in the 

tables below probably established by seed into a clearcut. 

At sampling, the single aspen seedling in the plot had been 

browsed repeatedly and appeared unlikely to survive.

Environmental features

Site

Plots 5

Elevation, mean (range) (ft) 4,810 (3,980-5,450)

Slope, mean (range) (percent) 22 (15-30)

Aspect All

Position All

Slope shape All

Soil

Available water capacity (in) (n = 3) 2 to 9 (low to high)

pH (n = 3) 5.8 to 6.6

Grand Fir/Big Huckleberry Plant Association

Abies grandis/Vaccinium membranaceum

ABGR/VAME 

CWS211 (Johnson and Simon 1987)

CWS212 (Johnson and Clausnitzer 1992)

1089 C. Johnson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 79

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code

ABGR/VAME

4 plots

ABGR/VAME very 

early seral

1 plot

Cover (%)/constancy(%) Cover (%)

Overstory trees:

Larix occidentalis Western larch LAOC 35/25

Pinus contorta Lodgepole pine PICO 5/25

Pinus ponderosa Ponderosa pine PIPO 15/50

Populus tremuloides Quaking aspen POTR5 3/25

Pseudotsuga menziesii Douglas-fir PSME 3/25

Understory trees:

Abies grandis Grand fir ABGR 7/75

Larix occidentalis Western larch LAOC 10/50 3

Picea engelmannii Engelmann spruce PIEN 1/50 tr

Pinus contorta Lodgepole pine PICO 55/25 8

Pinus ponderosa Ponderosa pine PIPO 1/25 2

Populus tremuloides Quaking aspen POTR5 16/100 tr

Pseudotsuga menziesii Douglas-fir PSME 6/50

Shrubs:

Acer glabrum Rocky Mountain maple ACGL 3/25

Amelanchier alnifolia Western serviceberry AMAL2 10/50

Ceanothus velutinus Snowbrush ceanothus CEVE 4/50 5

Lonicera utahensis Utah honeysuckle LOUT2 6/50

Pachistima myrsinites Oregon boxwood PAMY 2/75

Prunus emarginata Bitter cherry PREM 10/25 1

Ribes lacustre Prickly currant RILA 3/25

Salix scouleriana Scouler’s willow SASC 9/100 3

Sorbus scopulina Cascade moutain-ash SOSC2 3/25

Spiraea betulifolia Birchleaf spiraea SPBE2 10/100

Symphoricarpos albus Common snowberry SYAL 30/25

Vaccinium membranaceum Big huckleberry VAME 30/100 1

Vaccinium scoparium Grouse huckleberry VASC 6/50 1

Grass and grasslike:

Agrostis scabra Rough bentgrass AGSC5 tr/25 1

Calamagrostis rubescens Pinegrass CARU 11/75

Carex geyeri Elk sedge CAGE2 4/50

Carex rossii Ross’ sedge CARO5 10/25 5

Festuca occidentalis Western fescue FEOC 1/25 tr

Forbs:

Achillea millefolium Common yarrow ACMI2 1/50 15

Anaphalis margaritacea Common pearly-everlasting ANMA 3

Antennaria microphylla Rosy pussytoes ANMI3 tr/25 1

Arnica cordifolia Heartleaf arnica ARCO9 2/50

Aster conspicuus Showy aster ASCO3 10/25

Epilobium angustifolium Fireweed EPAN2 1/50 tr

Fragaria Strawberry FRAGA 2/100 20

Gayophytum decipiens Deceptive groundsmoke GADE2 tr/25 3

Lupinus sericeus Silky lupine LUSE4 20/25

Solidago missouriensis Missouri goldenrod SOMI2 1

Thalictrum occidentale Western meadowrue THOC 5/50

Valeriana Valerian VALER 5/25

Vicia americana American vetch VIAM 1
80 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Ground surface features

ABGR/VAME

4 plots

ABGR/VAME, 

very early seral

1 plot

 Cover (%)

Bare ground 9 40 

Bedrock 0 0

Rock 2 0

Gravel 1 1

Moss, lichen 1 10

Litter 86 50
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 81

UPLAND ASPEN COMMUNITIES

Aspen occasionally occur in this plant association, usually 

on somewhat atypical sites where slope instability or snow 

avalanches have limited conifer competition.

Environmental features—

The communities occur on steep slopes at moderate

 elevations. Two of the plots are in distinct snow avalanche 

tracks, and a third is on a steep slope (48 percent) that was 

obviously unstable.

Soils—

Soils are formed in coarse-grained colluvial material with 

low available water capacity and slightly acid pH. Textures 

are very to extremely gravelly to bouldery loam or sandy 

loam.

Vegetation composition—

Overstory conifers are sparse owing to slope instability 

or avalanches. Overstory aspen may be present as bent, 

leaning, or gnarled forms. Understory grand fir and aspen 

are common. Shrubs are abundant, with Rocky Mountain 

maple dominant. A rich assemblage of grasses and forbs is 

also present, notably blue wildrye (Elymus glaucus), nettleleaf horsemint (Agastache urticifolia), strawberry (Fragaria 

sp.), and blue stickseed (Hackelia micrantha). The cover by 

herbaceous vegetation, especially grasses, is higher on these 

aspen plots than for other ABGR/ACGL plots that we have 

sampled, probably thanks to the light conifer overstory.

Successional relationships—

Seedling grand firs are usually present and suggest succession toward a grand fir forest with a few maples persisting 

in their shade. However, disturbance by avalanches or by 

soil instability will maintain some sites indefinitely in an 

early seral, shrub- and herb-dominated condition. 

Fire—

The typical vegetation dominated by deciduous shrubs and 

moist forbs is likely to carry fire only under extreme conditions, although these plants could be killed by intense heat 

of a fire in adjacent conifer stands. If extreme weather or 

conifer encroachment allow fire to burn through these communities, it is likely to be followed by resprouting of aspen 

and shrubs.

Management considerations— 

On sites where natural disturbance does not limit conifer growth, aspen would benefit from conifer removal. 

Establishment of aspen from seed for plantings is likely to 

be limited by shrub competition. Dense and tall shrubs may 

help to reduce browsing of aspen.

Environmental features

Site

Plots 4

Elevation, mean (range) (ft) 5,460 (5,240-5,720)

Slope, mean (range) (percent) 34 (23-48)

Aspect South and west

Position Backslope

Slope shape Planar

Soil

Available water capacity (in) (n = 2) 2 to 4.5 (low)

pH (n = 2) 6.0 to 6.6

Grand Fir/Rocky Mountain Maple Plant 

Association

Abies grandis/Acer glabrum

ABGR/ACGL

CWS912 (Johnson and Simon 1987)

CWS541 (Johnson and Clausnitzer 1992)

UA041 D. Swanson
82 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Abies grandis Grand fir ABGR 7/25

Populus tremuloides Quaking aspen POTR5 20/50

Pseudotsuga menziesii Douglas-fir PSME 5/25

Understory trees:

Abies grandis Grand fir ABGR 16/75

Picea engelmannii Engelmann spruce PIEN 3/25

Populus tremuloides Quaking aspen POTR5 12/75

Shrubs:

Acer glabrum Rocky Mountain maple ACGL 26/100

Berberis repens Creeping Oregon grape BERE 15/50

Prunus emarginata Bitter cherry PREM 4/50

Rubus parviflorus Thimbleberry RUPA 3/25

Salix scouleriana Scouler’s willow SASC 3/25

Sambucus cerulea Blue elderberry SACE3 3/25

Spiraea betulifolia Birchleaf spiraea SPBE2 15/25

Symphoricarpos albus Common snowberry SYAL 7/75

Symphoricarpos oreophilus Mountain snowberry SYOR2 5/25

Grasses and grasslike:

Bromus carinatus Mountain brome BRCA5 20/50

Calamagrostis rubescens Pinegrass CARU 18/50

Carex geyeri Elk sedge CAGE2 10/50

Carex hoodii Hood’s sedge CAHO5 10/50

Elymus glaucus Blue wildrye ELGL 17/100

Forbs:

Achillea millefolium Common yarrow ACMI2 4/50

Agastache urticifolia Nettleleaf horsemint AGUR 10/100

Aster conspicuus Showy aster ASCO3 10/25

Aster foliaceus Leafy aster ASFO 3/50

Delphinium occidentale Western larkspur DEOC 6/50

Fragaria Strawberry FRAGA 16/100

Hackelia micrantha Blue stickseed HAMI 13/75

Hieracium albiflorum White hawkweed HIAL2 2/75

Hydrophyllum fendleri Fendler’s waterleaf HYFE 5/25

Phacelia hastata Silverleaf phacelia PHHA 3/25

Polemonium pulcherrimum Skunk-leaved polemonium POPU3 3/25

Pteridium aquilinum Braken fern PTAQ 25/50

Rudbeckia occidentalis Western coneflower RUOC2 5/25

Senecio serra Tall butterweed SESE2 5/25

Thalictrum occidentale Western meadowrue THOC 1/75

Thlaspi fendleri Wild candytuft THFE3 5/25

Urtica dioica Stinging nettle URDI 5/25

Valeriana sitchensis Sitka valerian VASI 3/25

Viola Violet VIOLA 6/50

Ground surface features

Cover (%)

Bare ground 12

Bedrock 0

Rock 16

Gravel 2

Moss, lichen 4

Litter 66
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 83

UPLAND ASPEN COMMUNITIES

Two aspen plots were sampled with grand fir potential 

vegetation and an understory dominated by oceanspray 

(Holodiscus discolor). One plot is located at 4,680 ft on 

a shoulder slope on the east side of Bobsled Ridge, in the 

southwest part of the Walla Walla Ranger District, Umatilla 

National Forest. The soil is a dark-colored clay loam at least 

3 ft thick with pH of 6.6 to 7.0 and a high water-holding 

capacity. Overstory tree cover is less than 10 percent and 

consists of a mix of grand fir, western larch, and Douglasfir. Aspen saplings are abundant in a dense shrub understory of oceanspray, common snowberry (Symphoricarpos 

albus) and lesser amounts of western trumpet honeysuckle 

(Lonicera ciliosa), big huckleberry (Vaccinium membranaceum), mallow ninebark (Physocarpus malvaceus), 

Scouler’s willow (Salix scouleriana), and mountain ash 

(Sorbus scopulina), over diverse forbs. This rich and diverse 

community resembles communities of both the Douglasfir/oceanspray and grand fir/Rocky Mountain maple plant 

associations (Johnson and Clausnitzer 1992, Johnson and 

Simon 1987). Aspen are thriving and competing well with 

the tall shrubs. Once aspen are established in such a community, disturbance such as severe wildfire should favor 

them over conifers, because rapidly growing aspen suckers 

can compete with shrubs and conifer seed establishment is 

difficult among resprouting shrubs.

The second plot of this type is on a steep, rocky, southeast-facing slope at 4,440 ft elevation in the far western end 

of the Heppner Ranger District, Umatilla National Forest. 

The soil is stoney silt loam to a depth of 8 in, over very 

stoney silt loam, with pH of 6.6. The overstory is dominated 

by grand fir and Douglas-fir, with minor suppressed aspen. 

The understory is rather sparse and consists of aspen, 

oceanspray (Holodiscus discolor) and traces of other mesic 

shrubs, over sparse blue wildrye (Elymus glaucus) and 

forbs such as trailplant (Adenocaulon bicolor) and Sierran 

peavine (Lathyrus nevadensis). The plot is located below 

a talus aspen community that provides a refugium and 

propagule source for aspen to colonize nearby forests such 

as this.

Aspen occurs with snowberry understory in communities capable of supporting grand fir. Most key into existing 

grand fir/pinegrass, grand fir/hearleaf arnica, or grand fir/

elk sedge plant associations (Johnson and Clausnitzer 1992, 

Johnson and Simon 1987) and have environmental settings 

similar to these types. However, both aspen and significant 

shrub cover are unusual for these existing types, and thus 

this new type was created.

Environmental features—

Usually occurs on gentle to moderately steep hillslopes with 

southerly aspect and planar to concave shape.

Soils—

Soils are well drained and formed in a colluviated mixture 

of volcanic ash and loess over stoney colluvium or clay-rich 

subsoil. Surface textures are usually loam or silt loam at 

least 10 in thick. Very to extremely gravelly loamy material 

occurs within 3 ft of the surface in about half of the profiles. 

In other cases, the subsoil consists of clay loam or gravelly 

clay loam. Soil pH is moderately acid to neutral. Soil 

Aspen (Grand Fir)/Oceanspray Plant 

Community Type

Populus tremuloides (Abies grandis)/

Holodiscus discolor

POTR5(ABGR)/HODI HQC115

Aspen (Grand Fir)/Snowberry Plant 

Community Type

Populus tremuloides (Abies grandis)/ 

Symphoricarpos

POTR5(ABGR)/SYMPH HQC116

UA035 D. Swanson

UA036 D. Swanson
84 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

available water capacity ranges widely but is usually moderate to high.

Vegetation composition—

Ponderosa pine, Douglas-fir, and grand fir are all common associates of aspen, and are especially common as 

understory species. Shrub cover is substantial, and either 

species of snowberry (common Symphoricarpos albus or 

mountain S. oreophilus) may be present. The understory is 

dominated by grasses, most often pinegrass (Calamagrostis 

rubescens), and also elk sedge (Carex geyeri); forb cover is 

typically low, with heartleaf arnica (Arnica cordifolia) and 

strawberry (Fragaria sp.) the most abundant forbs.

Successional relationships—

Overstory shading by conifers and browsing by elk and deer 

should, over time, reduce or eliminate aspen and snowberry 

in most stands, thereby converting them into communities 

typical of the grand fir/pinegrass or grand fir/elk sedge plant 

associations.

Fire—

Dry mixed-conifer forests in the Blue Mountains historically had frequent low- or mixed-severity fires (Heyerdahl 

et al. 2001). This fire regime helped to maintain open stands 

of large pines or pines plus Douglas-firs, while keeping 

grand fir numbers low. This type of fire regime has ambiguous effects on aspen. On the one hand, canopy openings 

created by fires (especially in patches of mixed or highintensity fire) are good places for aspen to resprout or 

establish from seed. However, low-intensity fires that kill 

aboveground parts of aspen without killing overstory conifers force aspen to resprout under conifers where they are 

unlikely to thrive. Most understory species in these communities resprout strongly after light- to moderate-severity 

fires.

Management considerations—

Conifer competition is intense in these communities, and 

removal of conifers is usually required to allow aspen 

regeneration. If a conifer overstory is present, light prescribed fires are likely to kill aspen without providing 

enough light for them to grow after resprouting. Livestock 

grazing and wildlife browsing at levels typical of the Blue 

Mountains today will usually result in hedging of aspen 

saplings and no recruitment of new pole-sized aspen. Many 

aspen clones are at risk of dying out as older trees die of old 

age or shading by conifers. Heavy ungulate pressure also 

suppresses snowberry. Effects of heavy livestock grazing 

on understory herbaceous species are subtle, because this 

layer is dominated by shrubs and grazing-resistant pinegrass and elk sedge. The more grazing-sensitive species 

(especially native forbs) are always rather sparse owing to 

shading and competition. We would expect heavy grazing to reduce or eliminate some of the native forbs, such as 

mountain sweet-cicely (Osmorhiza chilensis) and western 

meadowrue (Thalictrum occidentale).

Environmental features

Site

Plots 22

Elevation, mean (range) (ft) 5,230 (3,110-6,265)

Slope, mean (range) (percent) 16 (0-38)

Aspect Usually south

Position All

Slope shape Usually planar or concave

Soil

Available water capacity (in) (n = 20) 3.0 to 10.5 (low to high)

pH (n = 18) 6.0 to 6.8
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 85

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Abies grandis Grand fir ABGR 12/27

Pinus ponderosa Ponderosa pine PIPO 14/32

Populus tremuloides Quaking aspen POTR5 22/77

Pseudotsuga menziesii Douglas-fir PSME 5/32

Understory trees:

Abies grandis Grand fir ABGR 9/68

Pinus ponderosa Ponderosa pine PIPO 9/45

Populus tremuloides Quaking aspen POTR5 27/86

Pseudotsuga menziesii Douglas-fir PSME 2/32

Shrubs:

Berberis repens Creeping Oregon grape BERE 4/36

Symphoricarpos albus Common snowberry SYAL 15/64

Symphoricarpos oreophilus Mountain snowberry SYOR2 22/36

Grasses and grasslike:

Bromus carinatus Mountain brome BRCA5 6/59

Calamagrostis rubescens Pinegrass CARU 24/50

Carex geyeri Elk sedge CAGE2 23/41

Elymus glaucus Blue wildrye ELGL 8/50

Poa pratensis Kentucky bluegrass POPR 5/45

Trisetum canescens Tall trisetum TRCA21 7/36

Forbs:

Achillea millefolium Common yarrow ACMI2 2/91

Antennaria microphylla Rosy pussytoes ANMI3 2/23

Arnica cordifolia Heartleaf arnica ARCO9 7/32

Collomia linearis Narrowleaf collomia COLI2 2/23

Fragaria Strawberry FRAGA 4/73

Geranium viscosissimum Sticky geranium GEVI2 2/23

Hackelia micrantha Blue stickseed HAMI 2/27

Osmorhiza chilensis Mountain sweet-cicely OSCH 2/41

Potentilla gracilis Slender cinquefoil POGR9 3/23

Sidalcea oregana Oregon checker-mallow SIOR 2/23

Thalictrum occidentale Western meadowrue THOC 2/41

Ground surface features

Cover (%) 

Bare ground 10

Bedrock 0

Rock 0

Gravel 0

Moss, lichen 0 

Litter 90
86 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

The Dooley Mountain seed tree exclosure aspen. This 

unique occurrence of aspen is in a fenced seed tree plantation of ponderosa pines east of Beaver Mountain in the 

Baker Ranger District of Wallowa Whitman National 

Forest. It is on a gentle slope at 5,495 ft elevation. Large 

ponderosa pines and smaller lodgepole pines were present 

here before the Dooley Mountain Fire of 1989. A potential 

vegetation of grand fir/pinegrass or related plant association is most likely. Today’s vegetation is sparse and dominated by a sedge (Carex concinnoides) and the grass Idaho 

fescue (Festuca idahoensis), with lesser amounts of yarrow 

(Achillea millefolium), fireweed (Epilobium angustifolium), 

and pinegrass (Calamagrostis rubescens). These aspen are a 

rare example of natural aspen seed establishment. The nearest seed source trees are probably at least 2 mi away. Aspen 

are scattered throughout the exclosure but are growing very 

poorly, with gnarled stems and dwarfed leaves suggestive of 

nutrient deficiency. The soil consists of gravelly loam with 

little organic matter and a pH of 5.6, near the lower limit for 

aspen growth. Acidification of the soil by previous conifer 

forest has made this site marginal for aspen. Of five stems 

sampled for DNA by V. Erickson (see the genetics sections 

of this report), four were genetically unique, indicating 

establishment of at least four different seeds (app. A).

Aspen–Engelmann spruce–grand fir/forb snowdrift community. This plot is on a shoulder slope on the lee side of a 

windswept ridgetop where a large snowdrift accumulates. 

It is at 5,000 ft near Black Mountain in the southwest part 

of the Walla Walla Ranger District, Umatilla National 

Forest. Aspen are gnarled and leaning, probably owing to 

downslope creep of the deep snowdrift. The overstory is 

dominated by Engelmann spruce and grand fir with suppressed aspen. Grand fir dominates the tree understory with 

aspen also present. Shrubs are absent and the herb layer 

is dominated by an unusual mix of forbs characteristic of 

moist (groundsel [Senecio crassulus]) and dry (stonecrop 

[Sedum stenopetalum]) sites, reflecting the ecotonal position 

of the plot along the transition from a dry, rocky ridge to a 

moist snowbed. Snowdrifts can favor aspen by providing 

supplemental moisture while suppressing conifers.

Other Grand Fir Series Aspen Communities

We sampled several other plots with aspen and grand fir 

potential. These are unique occurrences that demonstrate 

the ecological range of aspen, but appear unlikely to occur 

elsewhere.

WA003 D. SwansonUA034 D. Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 87

UPLAND ASPEN COMMUNITIES

Aspen/thimbleberry-bracken fern-starry false Solomon’s 

seal community. This plot is located at 5,900 ft in a moist 

concavity above the Imnaha River near where it leaves the 

Eagle Cap Wilderness area. The aspen grove has a dense 

understory of thimbleberry (Rubus parviflorus), brackenfern (Pteridium aquilinum), and starry false Solomon’s seal 

(Smilacina stellata). Potential vegetation here is likely to be 

grand fir.

Other Grand Fir Series Aspen Communities 

(continued)

6072 C. Johnson
88 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Aspen occurs locally in groves with an understory of chokecherry, a tall shrub. The plots described here have little in 

common beyond the rather warm and dry environment and 

the presence of aspen, chokecherry, and common snowberry (Symphoricarpos albus).

Environmental features—

The plots occur at moderate elevations on mostly steep, 

south-facing slopes.

Soils—

Soils range from very rocky and droughty on steep slopes to 

one plot in a swale on a hillslope with a deep loamy soil.

Vegetation composition—

The only plant species in common between all of the plots 

are aspen, chokecherry, and snowberry. Shrub cover is high 

and dominated by chokecherry, common snowberry, and 

the dwarf shrub, creeping Oregon grape (Berberis repens). 

Grasses have more cover than forbs, although droughty 

soils and competition from trees and shrubs limit both. The 

most abundant herbaceous plant is currently cheatgrass 

(Bromus tectorum), although originally the understory was 

probably dominated by elk sedge (Carex geyeri) and native 

sod-forming grasses such as blue wildrye (Elymus glaucus) 

or mountain brome (Bromus carinatus).

Successional relationships—

Colonization and increase of ponderosa pine, western juniper (Juniperus occidentalis), or Douglas-fir over time is 

likely.

Fire—

These communities typically occur in dry forest environments that historically had frequent low-intensity fires.

Management considerations—

Communities with aspen, chokecherry, and snowberry 

were probably more common in the past. A combination of 

conifer encroachment and herbivory have probably caused 

conversion of many communities to ponderosa pine or 

Douglas-fir over snowberry. The state of chokecherry in the 

Blue Mountains is much like aspen, declining because of 

shading by conifers and ungulate herbivory. Steps should 

be taken to preserve these communities where they still 

remain.

Environmental features

Site

Plots 4

Elevation, mean (range) (ft) 4,600 (3,480-6,015)

Slope, mean (range) (percent) 40 (20-75)

Aspect Mostly south

Position Backslope or footslope

Slope shape Planar or convex

Soil

Available water capacity (in) (n = 3) Variable

pH (n = 3) 6.8 to 7.6

Aspen Types of the Ponderosa Pine and 

Douglas-Fir Series

Aspen/Chokecherry Plant Community Type

Populus tremuloides/Prunus virginiana

POTR5/PRVI HQS5

WA011 D. Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 89

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Populus tremuloides Quaking aspen POTR5 10/25

Understory trees

Populus tremuloides Quaking aspen POTR5 44/100

Shrubs:

Amelanchier alnifolia Western serviceberry AMAL2 3/25

Artemisia tridentata Big sagebrush ARTR2 10/25

Berberis repens Creeping Oregon grape BERE 17/75

Chrysothamnus viscidiflorus Green rabbitbush CHVI8 5/25

Crataegus douglasii Black hawthorn CRDO2 3/25

Philadelphus lewisii Lewis’ mock-orange PHLE4 5/25

Prunus emarginata Bitter cherry PREM 5/25

Prunus virginiana Common chokecherry PRVI 34/100

Ribes aureum Golden currant RIAU 3/25

Rosa Rose ROSA5 10/25

Rosa woodsii Woods’ rose ROWO 16/50

Symphoricarpos albus Common snowberry SYAL 11/100

Grasses and grasslike:

Agropyron intermedium Intermediate wheatgrass AGIN2 5/25

Bromus carinatus Mountain brome BRCA5 20/25

Bromus tectorum Cheatgrass BRTE 10/50

Carex geyeri Elk sedge CAGE2 3/50

Elymus glaucus Blue wildrye ELGL 3/50

Poa juncifolia Alkali bluegrass POJU 3/25

Trisetum canescens Tall trisetum TRCA21 3/25

Forbs:

Agastache urticifolia Nettleleaf horsemint AGUR 5/25

Apocynum androsaemifolium Spreading dogbane APAN2 1/75

Clematis ligusticifolia Western clematis CLLI2 3/25

Madia glomerata Cluster tarweed MAGL2 5/25

Osmorhiza chilensis Mountain sweet-cicely OSCH 5/25

Penstemon deustus Hotrock penstemon PEDE4 3/25

Smilacina stellata Starry false Solomon’s seal SMST 3/25

Vicia americana American vetch VIAM 2/50

Ground surface features

Cover (%)

Bare ground 10 

Bedrock 0

Rock 6 

Gravel 4

Moss, lichen 6

Litter 74
90 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

This plant community type is particularly common on 

Lookout Mountain in Baker County (BLM administered 

lands), where three of our four plots are located. This 

unique area lacks pines (ponderosa or lodgepole), and grand 

fir and larch are narrowly restricted to moist sites. This 

leaves room for Douglas-fir and aspen to occupy a wider 

variety of sites than elsewhere in the Blue Mountains.

Environmental features—

Examples of this community type occur on rather steep, 

droughty south- and west-facing slopes at moderate 

elevations.

Soils—

The limited sample suggests rocky soils formed in colluvium from bedrock, with low available water capacity.

Aspen (Douglas-Fir)/ Bitter Cherry Plant 

Community Type

Populus tremuloides (Pseudotsuga 

menziesii)/Prunus emarginata

POTR5(PSME)/PREM HQC117

UA040 D. Swanson

Vegetation composition—

Douglas-fir is frequently present along with aspen and it 

probably represents the potential on most sites. Shrubs are 

abundant and dominated by bitter cherry, mountain snowberry (Symphoricarpos oreophilus), and creeping Oregon 

grape (Berberis repens). Blue wildrye (Elymus glaucus) is 

the only common grass. Forbs are diverse and lush in spite 

of the rather dry sites, with nettleleaf horsemint (Agastache 

urticifolia) the most common and mountain sweet-cicely 

(Osmorhiza chilensis) also important.

Successional relationships—

Succession should lead to Douglas-fir forest in the absence 

of disturbance.

Fire—

The aspen, deciduous shrubs, and forbs make this community less flammable than others in the dry forest zone. The 

natural fire regime is probably frequent light fires or mixed 

fires. It is dominated by species that resprout vigorously 

after fire.

Management considerations—

These unique communities are diverse and contain a variety 

of plants that are vulnerable to heavy grazing or wildlife 

browsing. They may have been more abundant in the past 

and have been converted to Douglas-fir/mountain snowberry communities.

Environmental features

Site

Plots 4

Elevation, mean (range) (ft) 5,310 (4,900-5,910)

Slope, mean (range) (percent) 30 (22-42)

Aspect South and west

Position Shoulder, backslope, or footslope

Slope shape All
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 91

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code Cover/constancy

Overstory trees: Percent

Populus tremuloides Quaking aspen POTR5 25/75

Pseudotsuga menziesii Douglas-fir PSME 22/50

Understory trees:

Abies lasiocarpa Subalpine fir ABLA 3/25

Juniperus occidentalis Western juniper JUOC 3/25

Populus tremuloides Quaking aspen POTR5 20/100

Shrubs:

Berberis repens Creeping Oregon grape BERE 28/50

Crataegus douglasii Black hawthorn CRDO2 40/25

Prunus emarginata Bitter cherry PREM 22/100

Prunus virginiana Common chokecherry PRVI 6/50

Symphoricarpos oreophilus Mountain snowberry SYOR2 18/75

Grasses and grasslike:

Elymus glaucus Blue wildrye ELGL 18/75

Forbs:

Achillea millefolium Common yarrow ACMI2 2/75

Agastache urticifolia Nettleleaf horsemint AGUR 16/100

Clarkia rhomboidea Common clarkia CLRH 5/25

Collinsia parviflora Small flowered blue-eyed Mary COPA3 3/50

Descurainia richardsonii Mountain tansymustard DERI2 9/50

Galium aparine Cleavers GAAP2 4/50

Hackelia micrantha Blue stickseed HAMI 3/25

Hydrophyllum fendleri Fendler’s waterleaf HYFE 5/25

Osmorhiza chilensis Mountain sweet-cicely OSCH 15/50

Osmorhiza occidentalis Western sweetroot OSOC 4/50

Phacelia Phacelia PHACE 6/50

Phacelia heterophylla Varileaf phacelia PHHE2 3/50

Rudbeckia occidentalis Western coneflower RUOC2 5/25

Senecio serra Tall butterweed SESE2 15/25

Sidalcea oregana Oregon checker-mallow SIOR 3/25

Smilacina racemosa Western false Solomon’s seal SMRA 3/25

Thalictrum occidentale Western meadowrue THOC 2/50

Urtica dioica Stinging nettle URDI 3/25

Vicia americana American vetch VIAM 5/25

Ground surface features

Cover (%)

Bare ground 6

Bedrock 0

Rock 1

Gravel 1

Moss, lichen 0

Litter 92
92 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Aspen occur occasionally in dry upland forests of ponderosa pine and Douglas-fir with an understory dominated by common (Symphoricarpos albus) or mountain (S. 

oreophilus) snowberry. These communities are seral stages 

in one of the following plant associations (Johnson and 

Clausnitzer 1992, Johnson and Simon 1987): Douglas-fir/

common snowberry (PSME/SYAL, CDS622 or CDS624); 

Douglas-fir/mountain snowberry (PSME/SYOR, CDS623 

or CDS625); ponderosa pine/common snowberry (PIPO/

SYAL, CPS522 or CPS524); or ponderosa pine/mountain 

snowberry (PIPO/SYOR, CPS525).

These are seral communities in which aspen will be 

replaced by ponderosa pine or Douglas-fir over time if there 

is no disturbance. According to Johnson and Clausnitzer 

(1992), the mountain snowberry plant associations are on 

slightly drier sites than their common snowberry counterparts. However, in the aspen data set there was complete 

overlap in plant community composition between common 

and mountain snowberry-dominated plots; thus they are 

treated together here. Also, owing to the similarity in plant 

communities between the two series, and frequent difficulty 

in determining which conifer is the potential in early seral 

stages, snowberry communities from both the ponderosa 

pine and Douglas-fir series are joined here.

The data are summarized in condition classes based on 

subjective field determination of past grazing pressure as 

follows: “poor” typically has severely hedged aspen with 

evidence of trampling and weedy understory plant species; 

“good” has a diverse understory composition and healthy 

aspen regeneration; “fair” is intermediate.

Environmental features—

These communities occur at moderate elevations and on 

gentle to moderately steep slopes of mostly south aspect.

Soils—

Soils are well drained and formed in colluvium derived 

from loess, volcanic ash, and weathered bedrock. Available 

water capacity in the upper 40 in ranges greatly, and pH 

ranges from moderately acid to neutral. Surface textures are 

silt loam or loam, becoming more gravel-rich and in some 

cases more clay-rich with depth. Very or extremely gravelly material occurs below 16 in depth in most profiles, but 

reaches the surface in a few.

Vegetation composition—

Ponderosa pine and Douglas-fir are common with aspen 

in the overstory and understory. A variety of shrubs may 

be present, with snowberry by far the most common. 

Snowberry and aspen regeneration cover are lower in plots 

judged to be in poor condition. The herbaceous layer is rich 

in grasses and elk sedge (Carex geyeri). Elk sedge declines 

on plots in poor condition, whereas Kentucky bluegrass 

(Poa pratensis) increases. Forb cover is fairly low, and 

the most abundant species on good sites (heartleaf arnica 

[Arnica cordifolia], strawberry [Fragaria sp.], mountain 

sweet-cicely [Osmorhiza chilensis], and western meadowrue [Thalictrum occidentale]) showed declines on the 

plots in poor condition. Other forb species (Sierran peavine 

[Lathyrus nevadensis] and starry false Solomon’s seal 

[Smilacina stellata]) were sometimes present on plots in 

good condition but conspicuously absent from plots in poor 

condition. Plots in poor condition also had more bare soil 

exposed.

Successional relationships—

Without disturbance, these communities will succeed to a 

conifer-dominated state. On sites with a Douglas-fir potential, both it and ponderosa pine will become dominant over 

aspen, with snowberry usually persisting in the understory. 

On sites not suitable for firs, aspen will be replaced by 

ponderosa pine, with snowberry usually persisting in the 

understory.

Fire—

Dry ponderosa pine and mixed-conifer forests historically 

had frequent low- or mixed-severity fires (Heyerdahl et 

Aspen (Ponderosa Pine–Douglas-Fir)/

Snowberry Plant Community Type

Populus tremuloides (Pinus ponderosaPseudotsuga menziesii)/Symphoricarpos

POTR5(PIPO-PSME)/SYMPH HQC118

QA300 C. Johnson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 93

UPLAND ASPEN COMMUNITIES

al. 2001). This fire regime helped to maintain open stands 

of large pines or pines and Douglas-firs. This type of fire 

regime has ambiguous effects on aspen. On the one hand, 

canopy openings created by fires (especially in patches of 

mixed- or high-intensity fire) are good places for aspen to 

resprout or establish from seed. However, low-intensity fires 

that kill aboveground parts of aspen without killing overstory conifers force aspen to resprout under conifers where 

they are unlikely to thrive. Most understory species in these 

communities resprout strongly after light- to moderateseverity fires.

Management considerations—

Conifer competition is intense in these communities, and 

removal of conifers may be required to allow aspen regeneration. If a conifer overstory is present, light prescribed 

fires are likely to kill aspen without providing enough light 

for them to thrive after resprouting. These sites are near 

the dry limit for survival of aspen in the Blue Mountains, 

so plantings of aspen may fail owing to drought. Livestock 

grazing and wildlife browsing at levels typical of the Blue 

Principal species

Latin name Common name Code

Good condition, 

15 plots

Fair condition, 

9 plots

Poor condition, 

5 plots

 Cover (%)/constancy(%) Overstory trees:

Pinus ponderosa Ponderosa pine PIPO 18/80 20/78 12/60

Populus tremuloides Quaking aspen POTR5 17/47 17/89 26/80

Pseudotsuga menziesii Douglas-fir PSME 23/20 12/22

Understory trees:

Juniperus occidentalis Western juniper JUOC 2/27 4/67 11/80

Pinus ponderosa Ponderosa pine PIPO 7/53 12/89 19/100

Populus tremuloides Quaking aspen POTR5 32/93 10/89 2/100

Pseudotsuga menziesii Douglas-fir PSME 13/40 8/33

Shrubs:

Amelanchier alnifolia Western serviceberry AMAL2 2/27 6/22 2/40

Berberis repens Creeping Oregon grape BERE 3/80 4/56 1/60 

Ribes cereum Wax currant RICE 2/33 4/78 3/60

Rosa Rose ROSA5 1/40 1/33 3/20

Salix scouleriana Scouler’s willow SASC 1/7 14/33

Spiraea betulifolia Birchleaf spiraea SPBE2 6/13 2/22 tr/20

Symphoricarpos albus Common snowberry SYAL 24/80 31/56 7/80

Symphoricarpos oreophilus Mountain snowberry SYOR2 43/20 21/44 15/20

Grasses and grasslike:

Bromus carinatus Mountain brome BRCA5 1/33 3/56 20/20

Calamagrostis rubescens Pinegrass CARU 15/27 20/44 5/20

Mountains today will usually result in hedging of aspen 

saplings and no recruitment of new pole-sized aspen. Many 

aspen clones are at risk of dying out as trees die of old 

age or shading by conifers. Heavy ungulate pressure also 

suppresses snowberry and other shrubs. Heavy livestock 

grazing also leads to the decline of elk sedge and grazingsensitive native forbs such as mountain sweet-cicely, 

sticky geranium (Geranium viscosissimum), and western 

meadowrue.

Environmental features

Site

Plots 29

Elevation, mean (range) (ft) 5,040 (3,440-6,920)

Slope, mean (range) (percent) 22 (4-58)

Aspect Mainly east and south

Position Backslope, footslope

Slope shape All

Soil

Available water capacity (in) (n = 22) 2.5 to 10 (low to high)

pH (n = 20) 6.0 to 7.0
94 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Carex geyeri Elk sedge CAGE2 29/73 24/67 3/20

Dactylis glomerata Orchardgrass DAGL tr/7 2/22 tr/40

Elymus glaucus Blue wildrye ELGL 2/40 7/56 12/40

Festuca occidentalis Western fescue FEOC 5/20 10/11 1/20

Koeleria cristata Prairie junegrass KOCR 3/20

Phleum pratense Common timothy PHPR3 2/13 tr/11 5/20

Poa juncifolia Alkali bluegrass POJU 5/20

Poa pratensis Kentucky bluegrass POPR 3/40 2/44 11/60

Sitanion hystrix Bottlebrush squirreltail SIHY 4/44 2/40

Stipa occidentalis Western needlegrass STOC2 9/40 7/33 1/20

Trisetum canescens Tall trisetum TRCA21 3/20 1/11

Forbs:

Achillea millefolium Common yarrow ACMI2 1/80 1/100 4/80

Arenaria macrophylla Bigleaf sandwort ARMA18 1/13 1/44 1/60

Arnica cordifolia Heartleaf arnica ARCO9 5/40 2/33

Collinsia parviflora Small flowered blue-eyed 

 Mary

COPA3 2/13 3/20

Epilobium angustifolium Fireweed EPAN2 2/27 5/11

Fragaria Strawberry FRAGA 7/67 2/67 3/40

Frasera speciosa Giant frasera FRSP 3/7 2/22

Galium bifolium Thinleaf bedstraw GABI 5/7 35/20

Galium boreale Northern bedstraw GABO2 4/47 3/11 1/20

Geranium viscosissimum Sticky geranium GEVI2 3/40 6/22 1/20

Hackelia micrantha Blue stickseed HAMI 5/20 1/20

Iris missouriensis Rocky Mountain iris IRMI 1/13 1/11 15/20

Lathyrus nevadensis Sierran peavine LANE3 6/27

Lupinus Lupine LUPIN tr/11 6/40

Osmorhiza chilensis Mountain sweet-cicely OSCH 6/67 4/78 3/60

Osmorhiza occidentalis Western sweetroot OSOC 3/20

Sidalcea oregana Oregon checker-mallow SIOR 2/27 tr/22 1/60

Smilacina stellata Starry false Solomon’s 

 seal

SMST 28/20 3/11 tr/20

Solidago missouriensis Missouri goldenrod SOMI2 3/27

Taraxacum officinale Common dandelion TAOF 1/40 4/44 2/40

Thalictrum occidentale Western meadowrue THOC 11/53 1/22

Ground surface features

Good condition, 

15 plots

Fair condition, 

9 plots

Poor condition, 

5 plots

 Cover (%)

Bare ground 2 5 12

Bedrock 0 0 0

Rock 2 1 0

Gravel

 0

 0 1

Moss, lichen 0 0

Litter 96 94 87

Principal species

Latin name Common name Code

Good condition, 

15 plots

Fair condition, 

9 plots

Poor condition, 

5 plots

 Cover (%)/constancy(%)

(continued)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 95

UPLAND ASPEN COMMUNITIES

Aspen occur as a seral species in a variety of warm, dry, 

upland forest plant associations with understory layers dominated by pinegrass (Calamagrostis rubescens), elk sedge 

(Carex geyeri), or introduced grasses that have replaced 

these species. The potential vegetation on these sites may 

be ponderosa pine (PIPO/CARU, CPG221 or PIPO/CAGE2, 

CPG222 plant associations), Douglas-fir (PSME/CARU, 

CDG112 and CDG121 or PSME/CAGE2, CDG111 plant 

associations), or grand fir (ABGR/CARU, CWG112 and 

CWG113 or ABGR/CAGE2, CWG111 plant associations). 

(These types are all defined in Johnson and Clausnitzer 

1992, Johnson and Simon 1987). However, the late-seral 

conifers needed to determine the potential vegetation are 

often not present. Fortunately the site characteristics and 

understory vegetation of aspen communities from the three 

pinegrass plant associations are quite similar to one another, 

so they are treated together here. The same is true for aspen 

communities of the three elk sedge plant associations, and 

they are also joined here under a broadened concept of the 

aspen/elk sedge plant community type originally defined by 

Johnson (2004).

Environmental features—

Aspen/pinegrass and aspen/elk sedge community types are 

found on sites with moderate elevations, slope steepness, 

and available soil moisture. Earlier studies (Johnson and 

Clausnitzer 1992, Johnson and Simon 1987) have determined that pinegrass requires slightly more warmth and 

moisture than elk sedge.

Soils—

Soils are well-drained and lack a water table or any other 

signs of wetness. They generally have a moderate available 

water capacity and slightly acid to neutral pH. They formed 

in a variety of materials, including volcanic ash, loess, colluvium, and alluvium. Soils have a surface layer of loam or 

silt loam at least 10 in thick and sometimes gravelly (up to 

35 percent gravel). In some profiles, this material continues beyond the depth of observation, whereas in others it is 

underlain by either more clay-rich material or very gravelly 

loamy material.

Vegetation composition—

Ponderosa pine, Douglas-fir, lodgepole pine, or grand fir 

may be present depending on the potential of the site, availability of seed, and stand history. Shrubs and forbs are 

typically sparse, and the understory is dominated by grass 

or sedge, usually pinegrass or elk sedge. Other common 

plants are mountain brome (Bromus carinatus), heartleaf 

arnica (Arnica cordifolia), and strawberry (Fragaria sp.). 

Where the community was disturbed and artificially seeded 

(POTR5/exotic grass in the table below), exotic species such 

as intermediate wheatgrass (Agropyron intermedium) may 

dominate.

Aspen/Pinegrass Plant Community Type

Populus tremuloides/Calamagrostis rubescens

POTR5/CARU HQG114

Aspen/Elk Sedge Plant Community Type

Populus tremuloides/Carex geyeri

POTR5/CAGE2 HQG112 (Johnson 2004)

Aspen/Exotic Grass Plant Community Type

Populus tremuloides/Poaceae

POTR5/EXOTIC GRASS HQC115

QA273 C. Johnson 7024 C. Johnson WA012 D. Swanson
96 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Successional relationships—

Aspen is a seral species that will be replaced by conifers 

unless disturbance interrupts succession. Ponderosa pine, 

Douglas-fir, and grand fir are all possible successors to 

aspen. Where moisture is limiting, succession is likely to 

end with ponderosa pine or mixed pine and Douglas-fir, and 

moister sites may be colonized by the more shade-tolerant 

grand fir.

Fire—

Warm dry upland forests with pinegrass or elk sedge understory are well known for their frequent, low-intensity fires 

(Heyerdahl et al. 2001). The three dominant conifers of 

these sites–ponderosa pine, Douglas-fir, and grand fir–have 

fire-resistant bark that allows mature trees to survive light 

fires. Light underburns are likely to kill some or all of the 

aspen while allowing overstory conifers to survive. Highseverity fires that remove the overstory and allow aspen to 

resprout (or, rarely, establish from seed) without competition are needed if aspen is to be maintained by fire.

Management considerations—

Conifer competition is intense in these communities, and 

removal of conifers may be required to allow aspen regeneration. If overstory conifers are present, light prescribed 

fires are likely to kill aspen without providing enough light 

for vigorous resprouting of aspen. These sites are near the 

dry limit for survival of aspen in the Blue Mountains, so 

plantings of aspen may fail owing to drought. Livestock 

grazing and wildlife browsing at levels typical of the Blue 

Mountains today will usually result in hedging of saplings 

and no recruitment of new pole-sized aspen. Many aspen 

clones are at risk of dying out as older trees die of old age or 

shading by conifers. Native understory vegetation is composed largely of grazing-tolerant grasses and sedges (pinegrass and elk sedge) and forbs with fairly low palatability; 

thus native understory vegetation can persist even as heavy 

grazing and browsing lead to the loss of aspen.

Environmental features

POTR5/CARU POTR5/CAGE2 POTR5/Exotic grass

Site

Plots 20 13 3

Elevation, mean (range) (ft) 5,550 (4,740-6,600) 5,460 (4,540-7,060) 5,460 (4,800-6,300)

Slope, mean (range) (percent) 14 (2-40) 19 (3-52) 25 (10-40)

Aspect All (more often S) All N

Position All All Backslope, footslope

Slope shape Convex, planar, concave Convex, planar, concave Concave, planar

Soil

Available water capacity (in) 4.5 to 7

(moderate) (n = 10)

3 to 10

(low to high) (n = 9)

2 to 8

(low to high) (n = 3)

pH 5.6 to 6.8 (n = 9) 6.0 to 7.0 (n = 9) 6.0 to 8.2 (n = 3)

Principal species

Latin name Common name Code

POTR5/ CARU

20 plots

POTR5/ CAGE2

13 plots

POTR5/exotic 

grass, 3 plots

 Cover (%)/constancy(%) Overstory trees:

Abies grandis Grand fir ABGR 12/10 20/15 5/33

Pinus contorta Lodgepole pine PICO 1/5 6/23 10/33

Pinus ponderosa Ponderosa pine PIPO 22/55 16/38

Populus tremuloides Quaking aspen POTR5 28/70 19/92 10/33

Pseudotsuga menziesii Douglas-fir PSME 28/25 24/31 20/33

Understory trees:

Abies grandis Grand fir ABGR 4/45 3/46 2/67

Pinus contorta Lodgepole pine PICO 17/30 7/31

Pinus ponderosa Ponderosa pine PIPO 6/65 11/69 6/67

Populus tremuloides Quaking aspen POTR5 13/95 12/92 75/100

Pseudotsuga menziesii Douglas-fir PSME 8/35 4/54 tr/33

(continued)
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 97

UPLAND ASPEN COMMUNITIES

Principal species

Latin name Common name Code

POTR5/ CARU

20 plots

POTR5/ CAGE2

13 plots

POTR5/exotic 

grass, 3 plots

 Cover (%)/constancy(%)

Shrubs:

Arctostaphylos uva-ursi Kinnikinnick ARUV 3/5 21/23

Artemisia tridentata Big sagebrush ARTR2 tr/5 1/67

Berberis repens Creeping Oregon grape BERE 1/35 2/38

Chrysothamnus viscidiflorus Green rabbitbush CHVI8 1/67

Ribes cereum Wax currant RICE 2/20 4/31

Spiraea betulifolia Birchleaf spiraea SPBE2 5/5 3/33

Symphoricarpos albus Common snowberry SYAL 2/30 2/69 3/67

Symphoricarpos oreophilus Mountain snowberry SYOR2 4/30 2/8

Grasses and grasslike:

Agropyron intermedium Intermediate wheatgrass AGIN2 tr/5 62/67

Agrostis scabra Rough bentgrass AGSC5 10/33

Bromus carinatus Mountain brome BRCA5 5/25 4/62 3/67

Calamagrostis rubescens Pinegrass CARU 29/100 2/31 1/33

Carex Sedge CAREX 5/5 1/8 3/33

Carex geyeri Elk sedge CAGE2 25/70 42/100

Dactylis glomerata Orchardgrass DAGL 1/10 3/8 3/67

Festuca idahoensis Idaho fescue FEID 4/23

Festuca rubra Red fescue FERU2 10/33

Melica subulata Alaska oniongrass MESU 4/23

Poa nervosa Wheeler’s bluegrass PONE2 4/23

Poa pratensis Kentucky bluegrass POPR 6/20 2/31

Stipa occidentalis Western needlegrass STOC2 4/20 2/46

Trisetum canescens Tall trisetum TRCA21 5/10 5/31 tr/33

Forbs:

Achillea millefolium Common yarrow ACMI2 1/85 2/92 1/100

Arenaria macrophylla Bigleaf sandwort ARMA18 3/15 2/31 tr/100

Arnica cordifolia Heartleaf arnica ARCO9 7/45 28/31 2/67

Cirsium arvense Canada thistle CIAR4 1/5 1/67

Collinsia parviflora Small flowered blue-eyed 

 Mary

COPA3 3/5 3/23

Epilobium angustifolium Fireweed EPAN2 2/25 1/23

Fragaria Strawberry FRAGA 6/95 9/92 1/67

Hieracium albertinum Western hawkweed HIAL 2/45 2/23 1/67

Hieracium albiflorum White hawkweed HIAL2 1/40 1/62 tr/33

Lupinus Lupine LUPIN 6/35

Lupinus caudatus Tailcup lupine LUCA 10/20 8/23

Medicago lupulina Black medick MELU 5/33

Osmorhiza chilensis Mountain sweet-cicely OSCH 5/40 2/77 1/33

Polemonium pulcherrimum Skunk-leaved polemonium POPU3 3/33

Sedum stenopetalum Wormleaf stonecrop SEST2 tr/5 2/23 10/33

Senecio serra Tall butterweed SESE2 2/67

Taraxacum officinale Common dandelion TAOF 1/20 2/62 tr/100

Thalictrum occidentale Western meadowrue THOC 2/25 8/38

Trifolium longipes Longstalk clover TRLO 13/15 15/33

Viola adunca Early blue violet VIAD 3/30 2/62 tr/33

(continued)
98 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Ground surface features

POTR5/CARU

20 plots

POTR5/CAGE2

13 plots

POTR5/exotic grass, 

3 plots

 Cover (%)

Bare ground 5 6 14

Bedrock 0 0 0

Rock 1 1 2

Gravel 1 2 3

Moss, lichen 3 0 0

Litter 90 91 81
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 99

UPLAND ASPEN COMMUNITIES

Aspen (Douglas-fir)/showy aster community. This plot 

is in a dense aspen thicket on the upper canyon slope of 

Needham Butte in the southeastern Wallowa Valley Ranger 

District of Wallowa-Whitman National Forest. It is on a 

steep north-facing slope at 5,220 ft elevation. Elsewhere in 

the Imnaha-Hells Canyon region, sites like this are usually occupied by Douglas-fir over ninebark (Physocarpus 

malvaceus), common snowberry (Symphoricarpos albus), 

and other shrubs, or thickets of these shrubs without trees. 

For reasons probably related more to site history than to 

environmental conditions, a vigorous aspen clone is present instead, with widely scattered Douglas-fir. Shrubs are 

absent and the understory is a rich assortment of forbs dominated by showy aster (Aster conspicuous) and Missouri 

goldenrod (Solidago missouriensis).

Aspen/blue wildrye community. This plot describes a 

strongly regenerating aspen clone 6 years after the 1994 

Little Malheur Fire. It is on a north-facing slope at 5,650 

ft elevation in the Prairie City Ranger District of Malheur 

National Forest. The grasses blue wildrye (Elymus glaucus, 60 percent cover) and bottlebrush squirreltail (Sitanion 

hystrix, 20 percent cover) are dominant. These two species 

are vigorous postfire resprouters like aspen. An aspen-grass 

community is likely to persist here for some time; the longterm trajectory is unknown.

Other Douglas-Fir and Ponderosa Pine Series 

Aspen Communities

WA040 D. SwansonQA205 C. Johnson
100 GENERAL TECHNICAL REPORT PNW-GTR-806

UPLAND ASPEN COMMUNITIES

Aspen/bluebunch wheatgrass community. Aspen were 

recorded cloning after fire up a slope vegetated mainly 

by bluebunch wheatgrass (Agropyron spicatum), western 

needlegrass (Stipa occidentalis), bottlebrush squirreltail 

(Sitanion hystrix), wax currant (Ribes cerum), and annual 

forbs. The plot is located on a north-facing footslope adjacent to a riparian zone at 5,090 ft on the Prairie City Ranger 

District of Malheur National Forest. Sites dominated by 

bunchgrasses are nearly always too dry to support aspen; 

this plot represents a rare exception to the rule that sites 

moist enough to support aspen will also support rhizomatous grasses and sedges rather than bunchgrass.

Slender cinquefoil-yarrow-timothy community. This 

unusual occurrence of aspen is at 5,370 ft elevation on a 

nearly treeless plateau near Marr Flat in the southern part 

of the Wallowa Valley Ranger District, Wallowa-Whitman 

National Forest. The plot is listed here, although it is not 

certain if ponderosa pine is truly the potential vegetation. 

The soil consists of about 2 ft of silty loess over gravelly 

clay loam that overlies basalt bedrock. Depressions on the 

flat are occupied by vernal pools. The vegetation consists 

of grazing-resistant unpalatable forbs (slender cinquefoil [Potentilla gracilis], yarrow [Achillea millefolium]) 

and introduced grasses (timothy [Phleum pratense] and 

Kentucky bluegrass [Poa pratensis]). This community 

results from historical overgrazing, and it is difficult to 

reconstruct the original vegetation, although a moist steppe 

community such as one of the Idaho fescue–prairie junegrass plant associations is likely. Small aspen sprouts inside 

cages are all that persist today, but large fallen aspen trunks 

show that mature trees can survive here too. The strongly 

contrasting soil water regime on sites like this is inhospitable to trees, and aspen survival is probably marginal.

Other Douglas-Fir and Ponderosa Pine Series 

Aspen Communities (continued)

QA101 C. JohnsonWA037 D. Swanson
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 101

Acknowledgments

Charles G. Johnson, Jr., former Area Ecologist for the Blue 

Mountains National Forests, provided the original impetus 

for this work. The authors gratefully acknowledge technical review comments by Dale Bartos (Aspen Ecologist, U.S. 

Forestry Sciences Laboratory, Logan, UT) Tom Demeo 

(Regional Ecologist, U.S. Forest Service Pacific Northwest 

Region), and Mary Manning (Regional Ecologist, U.S. 

Forest Service Northern Region), editorial review by Lynn 

Sullivan (U.S. Forest Service, Pacific Northwest Research 

Station), and publication layout by Adrianna Sutton. Thanks 

also to Marty Vavra and Edward DePuit (U.S. Forest 

Service, Pacific Northwest Research Station) for sponsoring 

this work as a Pacific Northwest Research Station publication. Primary funding for this publication was provided by 

the U.S. Forest Service Region 6 Ecology Program. The 

National Park Service, Alaska Region, contributed time for 

D.K. Swanson to complete this project after his departure 

from the U.S. Forest Service.

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 2.54 Centimeters 

Feet (ft) .3048 Meters

Yards (yd) .914 Meters

Miles (mi) 1.609 Kilometers

Square feet (ft2

) .093 Square meters

Acres (ac) .405 Hectares

Square feet per acre (ft2/ac) .229 Square meters per hectare

Cubic inches (in3) 16.4 Milliliters

Gallons (gal) 3.78 Liters

Degrees Fahrenheit (°F) Subtract 32 and then divide by 1.8 Celsius degrees 

Trees per acre 2.47 Trees per hectare
102 GENERAL TECHNICAL REPORT PNW-GTR-806

References

Altman, B. 2000. Conservation strategy for landbirds in 

the northern Rocky Mountains of eastern Oregon and 

Washington. Version 1.0. Oregon-Washington Partners 

in Flight. http://www.orwapif.org/consplan.html. (7 May 

2008).

Baker, F.S. 1925. Aspen in the central Rocky Mountain 

region. Bulletin 1291. Washington, DC: U.S. Department 

of Agriculture. 47 p.

Baker, D.L.; Andelt, W.F.; Burnham, K.P.; Shepperd, 

W.D. 1999. Effectiveness of Hot Sauce® and Deer 

Away® repellents for deterring elk browsing of aspen 

sprouts. Journal of Wildlife Management. 63(4): 1327–

1336.

Barnes B.V. 1966. The clonal growth habit of American 

aspens. Ecology. 47(3): 439–447.

Barnes, B.V. 1975. Phenotypic variation of trembling 

aspen in western North America. Forest Science. 21(3): 

319–328.

Bates, P.C.; Sucoff, E.; Blinn, S.R. 1998. Short-term 

flooding effects on root suckering of quaking aspen. 

Northern Journal of Applied Forestry. 15(4): 169–173. 

Bright, G.A. 1994. An extensive reconnaissance of the 

Wenaha National Forest in 1913. Powell, D.C., ed. Tech. 

Pub. F14-SO-08-94. Pendleton, OR: U.S. Department of 

Agriculture, Forest Service, Umatilla National Forest. 

56 p.

Buell, M.F.; Buell, H.F. 1959. Aspen invasion of prairie. 

Bulletin of the Torrey Botanical Club. 86(4): 264–269.

Callan, B.E. 1998. Diseases of Populus in British 

Columbia: a diagnostic manual. Victoria, BC: Natural 

Resources Canada, Canadian Forest Service. 157 p.

Campbell, R.B. 1984. Asexual vs. sexual propagation of 

quaking aspen. In: Murphy, P.M., ed. The challenge 

of producting native plants for the Intermountain area. 

Proceedings, Intermountain Nurseryman’s Association 

1983 conference. Gen. Tech. Rep. INT-GTR-168. Ogden, 

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

Intermountain Forest and Range Experiment Station: 

61–65.

Chen, H.Y.H.; Klinka, K.; Kabzems, R.D. 1998. Site 

index, site quality, and foliar nutrients of trembling 

aspen: relationships and predictions. Canadian Journal of 

Forest Research. 28: 1743–1755.

Clausnitzer, R.R. 1993. The grand fir series of 

northeastern Oregon and southeastern Washington: 

successional stages and management guide. R6-ECO-TP050-93. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Region. 193 p.

Cobb, L. 1997. Diurnal breeding birds in aspen (Populus 

tremuloides) communities on the Malheur National 

Forest, 1997. A summary report to the Malheur National 

Forest. Prairie City, OR: Grant County Bird Club. 22 p.

Cochran, P.H.; Berntsen, C.M. 1973. Tolerance of 

lodgepole and ponderosa pine seedlings to low night 

temperatures. Forest Science. 19(4): 272–280.

Crowe, E.A.; Clausnitzer, R.R. 1997. Mid-montane 

wetland plant associations of the Malheur, Umatilla, and 

Wallowa-Whitman National Forests. Tech. Pap. R6-NRECOL-TP-22-97. Baker City, OR: U.S. Department of 

Agriculture, Forest Service, Wallowa-Whitman National 

Forest. 299 p.

Davidson, R.W.; Hinds T.E.; Hawksworth, F.G. 1959.

Decay of aspen in Colorado. Station Paper 45. Fort 

Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Forest and Range Experiment 

Station. 14 p.

Day, M.W. 1944. The root system of aspen. American 

Midland Naturalist. 32(2): 502–509.

Day, R.A.; Walter, R.P.; Kozar, J.J.; Bricker, S.J.; 

Bowers, J.G. 2003. Propagation protocol for bareroot 

bigtooth and quaking aspen using seeds. Native Plants 

Journal. 4(2): 125–128.

Debyle, N.V. 1985a. Animal impacts. 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: 115–123.

Debyle, N.V. 1985b. Wildlife. 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: 135–152.

Debyle, N.V. 1985c. Water and watershed. 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: 153–160.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 103

Demmer, R.; Beschta, R.L. 2008. Recent history (1988-

2004) of beaver dams along Bridge Creek in central 

Oregon. Northwest Science. 82(4): 309–318.

DesRochers, A.; Lieffers, V.J. 2001a. The coarse-root 

system of mature Populus tremuloides in declining 

stands in Alberta, Canada. Journal of Vegetation 

Science. 12: 355–360.

DesRochers, A.; Lieffers, V.J. 2001b. Root biomass of 

regenerating aspen (Populus tremuloides) stands of 

different densities in Alberta. Canadian Journal of Forest 

Research. 31: 1012–1018.

Farmer, R.E. 1963. Effect of light intensity on growth of 

Populus tremuloides cuttings under two temperature 

regimes. Ecology. 44: 409–411.

Finley, W.L. 1937. The beaver–conserver of soil and water. 

Transactions North American Wildlife Conference. 2: 

295–297.

Forester, J.D.; Anderson, D.P.; Turner, M.G. 2007. Do 

high-density patches of coarse wood and regenerating 

saplings create browsing refugia for aspen (Populus 

tremuloides Michx.) in Yellowstone National Park 

(USA)? Forest Ecology and Management. 253: 211–219.

Fortin, D.; Beyer, H.L.; Boyce, M.S.; Smith, D.W.; 

Duchesne, T.; Mao, J.S. 2005. Wolves influence elk 

movements: behavior shapes a trophic cascade in 

Yellowstone National Park. Ecology. 86(5): 1320–1330.

Frey, B.R.; Lieffers, V.J.; Landhäusser, S.M.; Comeau, 

P.G.; Greenway, K.J. 2003. An analysis of sucker 

regeneration of trembling aspen. Canadian Journal of 

Forest Research. 33: 1169–1179.

Fung, M.Y.P.; Hamel, B.A. 1993. Aspen seed collection 

and extraction. Tree planters’ Notes. 44(3): 98–100.

Galbraith, W.A.; Anderson, E.W. 1971. Grazing history 

of the Northwest. Journal of Range Management. 24(1): 

6–12.

Gary, H.L. 1968. Soil temperatures under forest and 

grassland cover types in northern New Mexico. Res. 

Note RM-118. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Forest and 

Range Experiment Station. 11 p.

Gifford, G.F. 1966. Aspen root studies on three sites in 

northern Utah. American Midland Naturalist. 75(1): 

132–141.

Grant, M.C. 1993. The trembling giant. Discover. 14: 

83–89.

Gullion, G.W. 1984. Managing northern forests for 

wildlife. Coraopolis, PA: Ruffed Grouse Society. 72 p.

Haapala, T.; Pakkanen, A.; Pulkkinen, P. 2004. Variation 

in survival and growth of cuttings in two clonal 

propagation methods for hybrid aspen (Populus tremula

x P. tremuloides). Forest Ecology and Management. 193: 

345–354.

Halofsky, J.S.; Ripple, W.J. 2008. Fine-scale predation 

risk on elk after wolf reintroduction in Yellowstone 

National Park, USA. Oecologia. 155: 869–877.

Halofsky, J.S.; Ripple, W.J.; Beschta R.L. 2008.

Recoupling fire and aspen recruitment after wolf 

reintroduction in Yellowstone National Park, USA. 

Forest Ecology and Management. 256: 1004–1008.

Hall, F.C. 2001. Ground-based photographic monitoring. 

Gen. Tech. Rep. PNW-GTR-503. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific 

Northwest Research Station. 340 p.

Heyerdahl, E.K.; Brubaker, L.B.; Agee, J.K. 2001.

Spatial controls of historical fire regimes: a multiscale 

example for the interior West, USA. Ecology. 82(3): 

660–678.

Hinds, T.E. 1985. Diseases. 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: 87–106.

Hitchcock, C.L.; Cronquist, A.C. 1973. Flora of 

the Pacific Northwest. Seattle, WA: University of 

Washington. 730 p.

Holsten, E.; Hennon, P.; Trummer, L.; Schultz, M. 

2001. Insects and disease of Alaskan forests. R10-TP87. Juneau, AK: U.S. Department of Agriculture, Forest 

Service, Alaska Region. 242 p.

Hungerford, R.D. 1988. Soil temperatures and suckering 

in burned and unburned aspen stands in Idaho. Res. 

Note. INT-378. Ogden, UT: U.S. Department of 

Agriculture, Forest Service, Intermountain Research 

Station. 6 p.

Irwin, L.L.; Cook, J.G.; Riggs, R.A.; Skovlin, J.M. 

1994. Effects of long-term use by big game and livestock 

in the Blue Mountains forest ecosystems. Gen. Tech. 

Rep. PNW-GTR-325. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research 

Station. 49 p.
104 GENERAL TECHNICAL REPORT PNW-GTR-806

Jackson, M.B. 1993. Are plant hormones involved in root 

shoot communication? In: Callow, J.A., ed. Advances in 

botanical research. London: Academic Press: 104–187.

Jacoby, P.W., ed. 1989. A glossary of terms used in 

range management. Denver, CO: Society for Range 

Management. 20 p.

Johnson, C.G., Jr. 2004. Alpine and subalpine vegetation 

of the Wallowa, Seven Devils and Blue Mountains. R6-

NR-ECOL-TP-03-04. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Region. 

611 p. plus appendixes.

Johnson, C.G., Jr.; Clausnitzer, R.R. 1992. Plant 

associations of the Blue and Ochoco Mountains. R6-

ERW-TP-036-92. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Region. 

208 p.

Johnson, C.G., Jr.; Simon, S.A. 1987. Plant associations 

of the Wallowa-Snake Province. R6-ECOL-TP-255A86. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Region. 400 p. plus 

appendixes.

Johnson, M.D. 2001. Region 6 inventory and monitoring 

system: field procedures for the Current Vegetation 

Survey. Version 2.04. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Region. 

151 p. http://www.fs.fed.us/r6/survey/document.htm. 

(7 March 2008).

Jones, B.E.; Rickman, T.H.; Vazquez, A.; Sado, Y.; 

Tate, K.W. 2005. Removal of encroaching conifers to 

regenerate degraded aspen stands in the Sierra Nevada. 

Restoration Ecology. 13(2): 373–379.

Jones, J.R.; Debyle, N.V. 1985a. Climates. 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: 57–64.

Jones, J.R.; Debyle, N.V. 1985b. Fire. 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: 77–81.

Jones, J.R.; Debyle, N.V. 1985c. Soils. 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: 65–70.

Jones, J.R.; Shepperd, W.D. 1985. Intermediate 

treatments. 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: 

209–216.

Kay, C.E. 1994. The impact of native ungulates and beaver 

on riparian communities in the Intermountain West. 

Natural Resources and Environmental Issues. 1: 23–24.

Kees, G. 2004. Fencing out wildlife: plastic mesh fences 

and electric fences monitored by satellite telemetry. 

Tech. Rep. 0424-2838-MTDC. Missoula, MT: U.S. 

Department of Agriculture, Forest Service, Missoula 

Technology and Development Center. 18 p.

Keigley, R.B.; Frisina, M.R. 1998. Browse evaluation 

by analysis of growth form. Volume I. Methods for 

evaluating condition and trend. Helena, MT: Montana 

Fish Wildlife & Parks. 153 p.

Keigley, R.B.; Frisina, M.R.; Fager, C.W. 2002.

Assessing browse trend at the landscape level. Part 1: 

preliminary steps and field survey. Rangelands. 24(3): 

28–33.

Kemperman, J.A.; Barnes, B.V. 1976. Clone size in 

American aspens. Canadian Journal of Botany. 54: 

2603–2607.

Keyser, T.L.; Smith, F.W.; Shepperd, W.D. 2005. 

Trembling aspen response to a mixed-severity wildfire in 

the Black Hills, South Dakota, USA. Canadian Journal 

of Forest Research. 35: 2679–2685.

Korstian, C.F. 1921. Effect of late spring frost upon forest 

vegetation in the Wasatch Mountains of Utah. Ecology. 

2(1): 47–52.

Kota, A. 2005. Fences and on-site forest materials as 

ungulate barriers to promote aspen persistence in the 

Black Hills. Logan, UT: College of Natural Resources, 

Utah State University. 74 p. M.S. thesis

Laird, W.E. 1997. Soil survey of Baker Country area, 

Oregon. U.S. Department of Agriculture, Natural 

Resources Conservation Service. http://soils.usda.gov/

survey/printed_surveys/. (29 Jan 2009).

Lamontagne, M.; Margolis, H.; Bigras, F. 1998.

Photosynthesis of black spruce, jack pine, and trembling 

aspen after artificially induced frost during the growing 

season. Canadian Journal of Forest Research. 28: 1–12.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 105

Landhäusser, S.M.; Lieffers, V.J. 1998. Growth of 

Populus tremuloides in association with Calamagrostis 

canadensis. Canadian Journal of Forest Research. 28: 

396–401.

Larsen, C.M. 1943. Stiklinger af urteagtige skud paa 

rødder of bævreasp og graapoppil. [Cuttings from 

herbaceous shoots on the roots of aspen and gray poplar.] 

Dansk Skovforening Tidsskrift. 28: 96–113.

Lawrence, W.T.; Oechel, W.C. 1983. Effects of soil 

temperature on the carbon exchange of taiga seedlings. 

II. Photosynthesis, respiration, and conductance. 

Canadian Journal of Forest Research. 13: 850–859.

Lieffers, V.J.; Landhäusser, S.M.; Hogg, E.H. 2001.

Is the wide distribution of aspen a result of its stress 

tolerance? In: Shepperd, W.D.; Binkley, D.; Bartos, D.L.; 

Stohlgren, T.J.; Eskew, L.C., comps. Sustaining aspen 

in western landscapes. Proceedings RMRS-P-18. Fort 

Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station: 311–323.

Losin, N.; Floyd, C.H.; Schweitzer, T.E.; Keller, S.J. 

2006. Relationship between aspen heartwood rot and the 

location of cavity excavation by a primary cavity-nester, 

the red-naped sapsucker. The Condor. 108(3): 706–710.

Lu, E.-Y.; Sucoff, E.I. 2003. Responses of quaking aspen 

seedlings to solution calcium and aluminum. Journal of 

Plant Nutrition. 26: 97–123.

Maine, J.S.; Horton, K.W. 1966. Vegetative propagation 

of Populus spp. I. Influence of temperature on formation 

and initial growth of aspen suckers. Canadian Journal of 

Botany. 44(9): 1183–1189.

Manier, D.J.; Laven, R.D. 2002. Changes in landscape 

patterns associated with the persistence of aspen 

(Populus tremuloides Michx.) on the western slope of 

the Rocky Mountains, Colorado. Forest Ecology and 

Management. 167: 263–284.

McCune, B.; Grace, J.B. 2002. Analysis of ecological 

communities. Gleneden Beach, OR: MJM Software 

Design. 300 p.

McDonough, W.T. 1985. Sexual reproduction, seeds, 

and seedlings. 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: 25–28.

Minore, D. 1979. Comparative autoecological 

characteristics of northwestern tree species: a literature 

review. Gen. Tech. Rep. PNW-GTR-87. Portland, OR: 

U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Forest and Range Experiment Station. 72 p.

Moench, R.D. 2000. Aspen seed collection. Nursery 

Information Series. Fort Collins, CO: Colorado State 

Forest Service. 7 p. http://csfs.colostate.edu/pdfs/

aspenseed.pdf. (29 May 2009).

Mueggler, W.F. 1988. Aspen community types of the 

Intermountain Region. Gen. Tech. Rep. INT-GTR-250. 

Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Intermountain Research Station. 135 p.

Mueggler, W.F. 1989. Age distribution and reproduction of 

intermountain aspen stands. Western Journal of Applied 

Forestry. 4(2): 41–45.

Mueggler, W.F.; Bartos, D.L. 1977. Grindstone Flat 

and Big Flat exclosures–a 41-year record of changes in 

clearcut aspen communities. Res. Pap. INT-195. Ogden, 

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

Intermountain Research Station. 16 p.

Noh, E.-W.; Minocha, S.C. 1986. High efficiency shoot 

regeneration from callus of quaking aspen (Populus 

tremuloides Michx.). Plant Cell Reports. 5: 464–467.

Ontko, A.G. 1993. Thunder over the Ochoco. Vol I. The 

gathering storm. Bend, OR: Maverick Publications. 436 p.

Oregon Department of Agriculture. 2008. Oregon state 

noxious weed list. http://www.oregon.gov/ODA/PLANT/

WEEDS/statelist2.shtml. (1 April 2008).

Orr, E.L.; Orr, W.N. 1999. Geology of Oregon. Dubuque, 

IA: Kendall/Hunt. 254 p.

Osko, T.J.; Hardin, R.T.; Young, B.A. 1993. Research 

observation: chemical repellants to reduce grazing 

intensity on reclaimed sites. Journal of Range 

Management. 46: 383–386.

Ottmar, R.D.; Vihnanek, R.E.; Wright, C.S. 2000. Stereo 

photo series for quantifying natural fuels. Volume III: 

Lodgepole pine, quaking aspen, and gambel oak types 

in the Rocky Mountains. PMS 832. Boise, ID: National 

Wildfire Coordinating Group, National Interagency Fire 

Center. 85 p.

Parker, J. 1955. Annual trends in cold hardiness of 

ponderosa pine and grand fir. Ecology. 36(3): 378–380.

Peet, R.K. 2000. Forests and meadows of the Rocky 

Mountains. In: Barbour, M.G.; Billings, W.D., eds. North 

American terrestrial vegetation. Cambridge, United 

Kingdom: Cambridge University: 75–121.

Perala, D.A. 1974. Prescribed burning in an aspen-mixed 

hardwoods forest. Canadian Journal of Forest Research. 

4: 222–228.
106 GENERAL TECHNICAL REPORT PNW-GTR-806

Perala, D.A. 1990. Quaking aspen. In: Burns, R.M.; 

Honkala, B.H., tech. coords. Silvics of North America: 

2. Hardwoods. Agric. Handb. 654. Washington, DC: U.S. 

Department of Agriculture, Forest Service: 555–569.

Powell, D.C. 2008. Early livestock grazing in the Blue 

Mountains. http://www.fs.fed.us/r6/uma/publications/

centennial. (26 Feb 2009).

Powell, D.C.; Johnson, C.G., Jr.; Crowe, E.A.; Wells, 

A.; Swanson, D.K. 2007. Potential vegetation hierarchy 

for the Blue Mountains Section of northeastern Oregon, 

southeastern Washington, and west-central Idaho. 

Gen. Tech. Rep. PNW-GTR-709. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific 

Northwest Research Station. 87 p.

Richardson, T.W.; Heath, S.K. 2004. Effects of conifers 

on aspen-breeding bird communities in the Sierra 

Nevada. San Luis Obispo, CA: Transactions of the 

Western Section of the Wildlife Society. 40: 68–81.

Riggs, R.A.; Tiedemann, A.R.; Cook, J.G.; Ballard, 

T.M.; Edgerton, P.J.; Vavra, M.; Krueger, W.C.; 

Hall, F.C.; Bryant, L.D.; Irwin, L.L.; DelCurto, T. 

2000. Modification of mixed-conifer forests by ruminant 

herbivores in the Blue Mountains Ecological Province. 

Res. Pap. PNW-RP-527. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacific Northwest 

Research Station. 77 p.

Ripple, W.J.; Beschta, R.L. 2007. Restoring Yellowstone’s 

aspen with wolves. Biological Conservation. 138: 

514–518.

Ripple, W.J.; Larsen, E.J.; Renkin, R.A.; Smith, D.W. 

2001. Trophic cascades among wolves, elk and aspen on 

Yellowstone National Park’s northern range. Biological 

Conservation. 102(3): 227–234.

Robbins, W.G. 1997. Landscapes of promise: the Oregon 

story, 1800-1940. Seattle, WA: University of Washington 

Press. 392 p.

Rolf, J.M. 2001. Aspen fencing in northern Arizona: In: 

Shepperd, W.D.; Binkley, D.; Bartos, D.L.; Stohlgren, 

T.J.; Eskew, L.C., comps. Sustaining aspen in western 

landscapes. Proceedings RMRS-P-18. Fort Collins, CO: 

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

Mountain Research Station: 193–196.

Ross, W.D. 1976. Fungi associated with root diseases of 

aspen in Wyoming. Canadian Journal of Botany. 54: 

734–744.

Sakai, A.; Weiser, C.J. 1973. Freezing resistance of 

trees in North America with reference to tree regions. 

Ecology. 54(1): 118–126.

Sallabanks, R.; Christofferson, N.D.; Weatherford, 

W.W.; Anderson, R. 2005. Restoring high priority 

habitats for birds: aspen and pine in the interior West. 

Gen. Tech. Rep. PSW-GTR-191. Albany, CA: U.S. 

Department of Agriculture, Forest Service, Pacific 

Southwest Research Station: 391–403.

Sallabanks, R.; Marcot, B.G.; Riggs, R.A.; Arnett, E.B.; 

Mehl, C.A. 2001. Wildlife of eastside (interior) forests 

and woodlands. In: Johnson, D.H.; O’Neil, T.A., eds. 

Wildlife-habitat relationships in Oregon and Washington. 

Corvallis, OR: Oregon State University: 213–238.

Sandberg, D.; Schneider, A.E. 1953. The regeneration of 

aspen by suckering. Minnesota Forestry Notes 24. St. 

Paul, MN: School of Forestry, University of Minnesota. 

2 p.

Schier, G.A. 1973. Origin and development of aspen root 

suckers. Canadian Journal of Forest Research. 3(1): 

45–53.

Schier, G.A. 1975. Deterioration of aspen clones in the 

middle Rocky Mountains. Res. Pap. INT-170. Ogden, 

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

Intermountain Forest and Range Experiment Station. 14 p.

Schier, G.A. 1976. Physiological and environmental factors 

controlling vegetative regeneration of aspen. Gen. Tech. 

Rep. RM-29. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Forest and 

Range Experiment Station: 20–23.

Schier, G.A. 1978. Vegetative propagation of Rocky 

Mountain aspen. Gen. Tech. Rep. INT-44. Ogden, 

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

Intermountain Forest and Range Experiment Station. 13 p.

Schier, G.A.; Campbell, R.B. 1978. Aspen sucker 

regeneration following burning and clearcutting on two 

sites in the Rocky Mountains. Forest Science. 24(3): 

303–308.

Schier, G.A.; Jones, J.R.; Winokur, R.P. 1985a.

Vegetative regeneration. 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: 

29–33.

Schier, G.A.; Shepperd, W.D.; Jones, J.R. 1985b.

Regeneration. 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: 

197–208.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 107

Schier, G.A.; Smith, A.D. 1979. Sucker regeneration in 

a Utah aspen clone after clearcutting, partial cutting, 

scarification, and girdling. Res. Note INT-253. Ogden, 

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

Intermountain Forest and Range Experiment Station. 6 p.

Schier, G.A.; Zasada, J.C. 1973. Role of carbohydrate 

reserves in the development of root suckers in Populus 

tremuloides. Canadian Journal of Forest Research. 3: 

243–250.

Shaw, C.G., III; Kile, G.A. 1991. Armillaria root disease. 

Agric. Handb. 691. Washington, DC: U.S. Department of 

Agriculture, Forest Service. 233 p.

Shepperd, W.D. 1993. Initial growth, development, and 

clonal dynamics of regenerated aspen in the Rocky 

Mountains. Res. Pap. RM-312. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Forest and Range Experiment Station. 8 p.

Shepperd, W.D. 2001. Manipulations to regenerate aspen 

ecosystems. In: Shepperd, W.D.; Binkley, D.; Bartos, 

D.L.; Stohlgren, T.J.; Eskew, L.C., comps. Sustaining 

aspen in western landscapes. Proceedings RMRS-P-18. 

Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station: 355–365.

Shepperd, W.D.; Bartos, D.L.; Mata, S.A. 2001. Aboveand below-ground effects of aspen clonal regeneration 

and succession to conifers. Canadian Journal of Forest 

Research. 31(5): 739–745.

Shepperd, W.D.; Rogers, P.C.; Burton, D.; Bartos, 

D.L. 2006. Ecology, biodiversity, management, and 

restoration of aspen in the Sierra Nevada. Res. Pap. 

RMRS-178. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Forest and 

Range Experiment Station. 122 p.

Shirley, D.M.; Erickson, V. 2001. Aspen restoration in 

the Blue Mountains of northeast Oregon. In: Shepperd, 

W.D.; Binkley, D.; Bartos, D.L.; Stohlgren, T.J.; Eskew, 

L.C., comps. Sustaining aspen in western landscapes. 

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

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station: 101–115.

Skovlin, J.M.; Thomas J.W. 1992. Interpreting longterm trends in Blue Mountain ecosystems from repeat 

photography. Gen. Tech. Rep. PNW-GTR-315. Portland, 

OR: U.S. Department of Agriculture, Forest Service, 

Pacific Northwest Research Station. 102 p.

Soil Survey Division Staff. 1993. Soil survey manual. 

Agric. Handb. 18. Washington, DC: U.S. Department of 

Agriculture, Natural Resources Conservation Service.

Soil Survey Staff. 1999. Soil taxonomy: a basic system 

of soil classification for making and interpreting soil 

surveys. 2nd ed. Agric. Handb. 436. Washington, DC: 

U.S. Department of Agriculture, Natural Resources 

Conservation Service.

Stevens, M.T.; Turner, M.G.; Tuskan, G.A.; Romme, 

W.H.; Gunter, L.E.; Waller, D.M. 1999. Genetic 

variation in postfire aspen seedlings in Yellowstone 

National Park. Molecular Ecology. 8: 1769–1780.

Strain, R.R. 1966. The effect of a late spring frost on the 

raidal growth of variant quaking aspen biotypes. Forest 

Science. 12(3): 334–337.

Strothmann, R.O.; Heinselman, M.L. 1957. Five-year 

results in an aspen sucker density study. Res. Pap. LS-49. 

St. Paul, MN: U.S. Department of Agriculture, Forest 

Service, Lake States Forest Experiment Station. 2 p.

Tew, R.K. 1970. Root carbohydrate reserves in vegetative 

reproduction of aspen. Forest Science. 16(3): 318–320.

Tuskan, G.A.; Francis, K.E.; Russ, S.L.; Romme, W.H.; 

Turner, M.G. 1996. RAPD markers reveal diversity 

within and among clonal and seedling stands of aspen in 

Yellowstone National Park, U.S.A. Canadian Journal of 

Forest Research. 26: 2088–2098.

U.S. Department of Agriculture, Forest Service [USDA 

FS]. 2005. Forest inventory and analysis national core 

field guide. Volume I: field data collection procedures for 

phase 2 plots, Version 3.0. http://fia.fs.fed.us/library/fieldguides-methods-proc/. (30 July 2008).

U.S. Department of Agriculture, Forest Service [USDA 

FS]. 2008. Common stand exam users guide, March 

2008. http://www.fs.fed.us/emc/nris/products/fsveg/

index.shtml. (10 Dec 2008).

U.S. Department of Agriculture, Natural Resources 

Conservation Service [USDA NRCS]. 2007. Monthly 

precipitation averages—30-Year period. National Water 

and Climate Center. http://www.wcc.nrcs.usda.gov/snow/

30yrprec.html. (6 Nov 2007).

U.S. Department of Agriculture, Natural Resources 

Conservation Service [USDA NRCS]. 2008. The 

PLANTS Database [Database]. Baton Rouge, LA: 

National Plant Data Center, 70874-4490 USA. http://

plants.usda.gov. (16 April 2008).

U.S. Environmental Protection Agency [USEPA]. 2007.

Level III ecoregions of the conterminous United States. 

Western Ecology Division. http://www.epa.gov/wed/

pages/ecoregions/level_iii.htm. (29 Jan 2009).
108 GENERAL TECHNICAL REPORT PNW-GTR-806

Walker, G.W.; MacLeod, N.S. 1991. Geologic map of 

Oregon. [1:500,000]. Reston, VA: U.S. Geological 

Survey.

Wall, T.G.; Miller, R.F.; Svejcar, T.J. 2001. Juniper 

encroachment into aspen in the northwest Great Basin. 

Journal of Range Management. 54: 691–698.

Walters, J.W. 1984. An aid to identifying aspen diseases 

frequently encountered in the Rocky Mountains. 

Albuquerque, NM: U.S. Department of Agriculture, 

Forest Service, Southwestern Region, State and Private 

Forestry, Forest Pest Management. 20 p.

Walters, J.W.; Hinds, T.E.; Johnson, D.W.; Beatty, J. 

1982. Effects of partial cutting on diseases, mortality, 

and regeneration of Rocky Mountain aspen stands. Res. 

Pap. RM-240. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Forest and 

Range Experiment Station. 12 p.

Webber, M.G. 1990. Response of immature aspen 

ecosystems to cutting and burning in relation to vernal 

leaf-flush. Forest Ecology and Management. 31: 15–33.

Western Regional Climate Center. 2007. Western U.S. 

Climate Historical Summaries. http://www.wrcc.dri.edu/

Climsum.html. (5 Nov 2007).

Williams, K.R. 1972. The relationship of soil temperature 

and cytokinen production in aspen invasion. 

Albuquerque, NM: University of New Mexico. 39 p. 

M.S. Thesis.

Winthers, E.; Fallon, D.; Haglund, J.; DeMeo, T.; 

Nowacki, G.; Tart, D.; Ferwerda, M.; Robertson, 

G.; Gallegos, A.; Rorick, A.; Cleland, D.T.; Robbie, 

W. 2005. Terrestrial ecological unit inventory technical 

guide: landscape and land unit scales. Gen. Tech. 

Rep. WO-68. Washington, DC: U.S. Department of 

Agriculture, Forest Service, Ecosystem Management 

Coordination Staff. 245 p. 

Zasada, J.C.; Schier, G.A. 1973. Aspen root suckering in 

Alaska: effect of clone, collection date and temperature. 

Northwest Science. 47: 100–104.
ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 109

APPENDIX A 

Appendix A: Aspen Stands Sampled as Part of the Blue Mountains Genetics Study

Regiona Land statusb Drainage

Stand number

Standcode

Number of plants sampled

Number of clones Area

Latitude (north) 

Longitude (east) 

Hectares - - -- Decimal degrees ------

BAK WAW Dooley Mountain 1 DO 5 4 0.004 44.5924 -118.3520BAK WAW Mason Dam 1 MD 3 2 <0.001 44.6724 -117.9910BAK WAW Stage Gulch 1 SG1 7 2 0.004 44.7338 -118.2323BAK WAW Stage Gulch 2 SG2 4 2 0.004 44.7322 -118.2250CTUIR CTUIR Cabbage Hill 1 CH 3 1 0.025 45.6019 -118.6209CTUIR CTUIR Coyote Flat 1 CF 2 1 0.202 45.6584 -118.4888CTUIR CTUIR Halfmoon Allotment 1 HA 2 1 0.121 45.6081 -118.5551CTUIR CTUIR Kinine Ridge 1 KR 5 2 0.232 45.6284 -118.5025CTUIR CTUIR Minthorn Springs 1 MS 4 1 1.214 45.6742 -118.6067CTUIR CTUIR Pipeline POTR 1 PP 5 3 1.500 45.6164 -118.5195CTUIR CTUIR Sixth Spring 1 SS 7 2 0.081 45.6469 -118.4645CTUIR CTUIR Telephone Ridge 1 TELR1 5 1 0.167 45.6424 -118.4514CTUIR CTUIR Telephone Ridge 2 TELR2 3 1 0.641 45.6321 -118.4462HP UMA Long Prairie 1 383-50 5 1 0.534 44.9859 -119.8154HP UMA Long Prairie 2 382-49 5 3 4.532 44.9861 -119.8224HP UMA Long Prairie 3 385-46 4 2 0.475 44.9829 -119.8199HP UMA Long Prairie 4 384-48 6 2 0.102 44.9840 -119.8212HP UMA Wheeler Point 1 411-34 3 1 0.051 44.9370 -119.8716HP UMA Wheeler Point 2 409-35 6 1 0.128 44.9375 -119.8718HP UMA Wheeler Point 3 399-39 6 2 0.572 44.9545 -119.8499NFJD East UMA Blarney Creek 1 BLASP1 8 1 0.426 45.1566 -118.5977NFJD East UMA Bone Canyon 1 BCASP1 6 2 0.178 44.9830 -119.0125NFJD East UMA Bridge Creek 1 BRASP1 10 1 0.420 45.0630 -118.8549NFJD East UMA Bull Prairie 1 BPASP1 6 1 0.790 44.8666 -118.6918NFJD East UMA Bull Prairie 2 BPASP2 3 1 0.169 44.8657 -118.6879NFJD East UMA Bull Prairie 3 BPASP3 3 1 0.064 44.8649 -118.6868NFJD East UMA Bull Prairie 4 BPASP4 3 1 0.081 44.8640 -118.6864NFJD East UMA Camas Wallow 1 CAASP1 10 2 0.043 45.1713 -118.7121NFJD East UMA Desolation Creek 1 DEASP1 5 1 0.126 44.8302 -118.7059NFJD East UMA Desolation Creek 2 DEASP2 9 2 0.898 44.8144 -118.6660NFJD East UMA Granite Meadow 1 GRASP1 4 1 0.010 44.8323 -118.4145NFJD East UMA Howard Creek 1 HOASP1 18 2 0.544 44.8390 -118.7192NFJD East UMA Lane Creek 1 LCASP1 5 1 0.096 45.2715 -118.8118NFJD East UMA Oriental Springs 1 OSASP1 2 2 <0.001 unknown unknownNFJD East UMA Park Creek 1 PKASP1 11 1 0.999 44.9134 -118.7815
110 GENERAL TECHNICAL REPORT PNW-GTR-806

APPENDIX A

Regiona Land statusb Drainage

Stand number

Standcode

Number of plants sampled

Number of clones Area

Latitude (north) 

Longitude (east) 

Hectares - - -- Decimal degrees ------

NFJD East UMA Trough Creek 1 TCASP1 3 1 0.030 44.8540 -118.4540NFJD West UMA Turpentine Creek 1 WRASEC05 5 1 0.131 45.1600 -119.1647NFJD West UMA Deerlick Creek 1 DCASP1 8 1 0.077 45.1562 -119.0696NFJD West UMA Johnson Creek 1 WRASP40 7 1 0.452 45.2018 -119.1944NFJD West UMA Matlock Creek 1 WRASP135 4 1 0.149 45.1345 -119.1824NFJD West UMA Matlock Creek 2 WRASP129 8 2 0.251 45.1196 -119.1831NFJD West UMA Matlock Creek 3 WRASP124 7 2 0.251 45.1129 -119.1847NFJD West UMA Matlock Creek 4 WRASP121 11 6 0.017 45.1082 -119.1844NFJD West UMA Matlock Creek 5 WRASP78 9 2 0.369 45.0875 -119.1835NFJD West UMA Morsay Creek 1 WRASP185 20 1 0.646 45.1748 -119.1079NFJD West UMA Morsay Creek 2 WRASP44 14 1 0.756 45.1716 -119.1180NFJD West UMA Morsay Creek 3 WRASP24 20 3 0.907 45.1843 -119.1178NFJD West UMA Morsay Creek 4 WRASEC01 7 1 1.376 45.1996 -119.1415NFJD West UMA Morsay Creek 5 WRASP178 6 1 0.170 45.1771 -119.1138NFJD West UMA Rush Creek 1 WRASP66 23 3 0.503 45.0910 -119.1310NFJD West UMA Rush Creek 2 WRASP71 17 8 0.317 45.0770 -119.1351NFJD West UMA Rush Creek 3 WRASP67 6 1 0.195 45.0941 -119.1215NFJD West UMA Silver Creek 5212 WRASP53 9 2 0.196 45.1196 -119.1286NFJD West UMA Silver Creek 5252B WRASP52 5 1 0.238 45.1219 -119.1313NFJD West UMA Sugar Bowl 1 WRASP26A 18 4 0.860 45.1978 -119.1043NFJD West UMA Sugar Bowl 2 WRASP34 23 6 0.732 45.1933 -119.0880NFJD West UMA Sugar Bowl 3 WRASP37 12 6 0.413 45.1884 -119.0921NFJD West UMA Sugar Bowl 4 WRASEC02 18 7 6.954 45.1814 -119.0913NFJD West UMA Sugar Bowl 5 WRASP47 17 7 2.012 45.1693 -119.0929NFJD West UMA Sugar Bowl 6 WRASEC03 6 1 0.382 45.1671 -119.0952NFJD West UMA Sugar Bowl 7 WRASEC04 21 14 2.648 45.1665 -119.0996NFJD West UMA Sugar Bowl 3A WRASP35 18 6 2.779 45.1846 -119.0998NFJD West UMA Taylor Creek 1 WRASP143 7 2 0.261 45.1580 -119.2096NFJD West UMA Taylor Creek 2 WRASP137 27 5 1.260 45.1394 -119.1837NFJD West UMA Taylor Creek 3 WRASP150 3 2 0.027 45.1426 -119.1623NFJD West UMA Taylor Creek 4 WRASEC06 8 1 0.836 45.1389 -119.1551NFJD West UMA Taylor Creek 5 WRASP146 24 4 0.068 45.1392 -119.1521NFJD West UMA Taylor Creek 5212C WRASP49 12 1 0.971 45.1299 -119.1344

Appendix A: Aspen Stands Sampled as Part of the Blue Mountains Genetics Study (continued)
Regiona Land statusb Drainage

Stand number

Standcode

Number of plants sampled

Number of clones Area

Latitude (north) 

Longitude (east) 

Hectares - - -- Decimal degrees ------

NFJD West UMA Thompson Creek 1 WRASP83 8 3 0.514 45.0552 -119.1928NFJD West UMA Thompson Creek 2 WRASEC07 12 2 0.538 45.0513 -119.1914NFJD West UMA Thompson Creek 3 WRASP87 43 10 0.104 45.0397 -119.1916NFJD West UMA Thompson Creek 4 WRASP88A 2 1 0.194 45.0343 -119.1937WW UMA Elk Flat 1 POTR0001 19 4 0.113 45.9064 -117.7605WW UMA Jarboe Meadow 1 POTR0053 5 2 0.029 45.8066 -117.8536WW UMA Jarboe Meadow 2 POTR0054 3 1 0.030 45.8099 -117.8559WW UMA Jarboe Meadow 3 POTR0003 6 1 0.167 45.8016 -117.8561WW UMA Lower Brock Meadow 1 061/63 6 2 0.056 45.8110 -117.8690WW UMA Upper Brock Meadow 1 POTR0023 8 1 0.541 45.8163 -117.8626WW UMA Upper Brock Meadow 2 POTR0048 4 2 0.298 45.8143 -117.8617WW UMA Walla Walla RD 1 POTR0016 8 4 1.425 45.7979 -117.8635WW UMA Walla Walla RD 2 POTR0017 7 3 0.410 45.7956 -117.8625WW UMA Walla Walla RD 3 POTR0064 3 1 0.336 45.8052 -117.8699WW UMA Walla Walla RD 4 POTR0073 3 2 0.240 45.8068 -117.8710WAV BC Boise Cascade 1 BC 9 1 1.214 45.5179 -117.2750WAV WAW Cow Camp 1 2J109N99AR03 10 3 1.778 45.3246 -116.8921WAV WAW Harl Butte Lookout 1 2J109N99AR06 5 1 1.027 45.3324 -116.8782

WAV WAW Road Canyon Meadow 1 2J109S99ASP4 2 1 0.936 45.3013 -116.9199

WAV WAW Road Canyon Meadow 2 2J109S99ASP2 2 2 0.644 45.2997 -116.9192WAV WAW Road Canyon Meadow 3 2J109S99A044 5 3 0.427 45.2969 -116.9210WAV WAW Road Canyon Meadow 4 2J109S99A042 5 3 1.531 45.2986 -116.9255

WAV WAW Road Canyon Meadow 5 2J109S99A043 6 4 0.627 45.2992 -116.9269

WAV WAW Target Springs 1 2J109S99A055 14 14 2.405 45.2809 -116.9459

a Region: BAK = Baker Ranger District, CTUIR = Confederated Tribes of the Umatilla Indian Reservation, HP = Heppner Ranger District, NFJD = North Fork John Day Ranger District (east or west side), 

WW = Walla Walla Ranger District, WAV = Wallowa Valley Ranger District.

b 

Appendix A: Aspen Stands Sampled as Part of the Blue Mountains Genetics Study

Landstatus: BC = Boise Cascade Corporation, CTUIR = Confederated Tribes of the Umatilla Indian Reservation, UMA = Umatilla National Forest; WAW = Wallowa-Whitman National Forest.

 (continued)

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 111

APPENDIX A 
Appendix B: Plant Names Used in This Report

Common name Codea Latin name and authorb

Trees:

Black cottonwood POTR15 Populus trichocarpa Torr. & A. Gray ex Hook.

Douglas-fir PSME Pseudotsuga menziesii (Mirb.) Franco

Engelmann spruce PIEN Picea engelmannii Parry ex Engelm.

Grand fir ABGR Abies grandis (Douglas ex D. Don) Lindl.

Lodgepole pine PICO Pinus contorta Douglas ex Louden

Mountain hemlock TSME Tsuga mertensiana (Bong.) Carrière

Ponderosa pine PIPO Pinus ponderosa C. Lawson

Quaking aspen POTR5 Populus tremuloides Michx.

Subalpine fir ABLA Abies lasiocarpa (Hook.) Nutt.

Western juniper JUOC Juniperus occidentalis Hook.

Western larch LAOC Larix occidentalis Nutt.

Western white pine PIMO3 Pinus monticola Douglas ex D. Don

Yew TABR2 Taxus brevifolia Nutt.

Shrubs:

Baldhip rose ROGY Rosa gymnocarpa Nutt.

Big huckleberry VAME Vaccinium membranaceum Douglas ex Torr.

Big sagebrush ARTR2 Artemisia tridentata Nutt.

Birchleaf spiraea SPBE2 Spiraea betulifolia Pall.

Bitter cherry PREM Prunus emarginata (Douglas ex Hook.) D. Dietr.

Bitterbrush PUTR2 Purshia tridentata (Pursh) DC.

Black hawthorn CRDO2 Crataegus douglasii Lindl.

Blue elderberry SACE3 Sambucus cerulea Raf.

Cascade mountain ash SOSC2 Sorbus scopulina Greene

Common chokecherry PRVI Prunus virginiana L.

Common snowberry SYAL Symphoricarpos albus (L.) S.F. Blake

Creeping Oregon grape BERE Berberis repens Lindl.

Curl-leaf mountain mahogany CELE3 Cercocarpus ledifolius Nutt.

Elderberry SAMBU Sambucus L.

Golden currant RIAU Ribes aureum Pursh

Green rabbitbush CHVI8 Chrysothamnus viscidiflorus (Hook.) Nutt.

Grouse huckleberry VASC Vaccinium scoparium Leiberg ex Coville

Kinnikinnick ARUV Arctostaphylos uva-ursi (L.) Spreng.

Lewis’ mock-orange PHLE4 Philadelphus lewisii Pursh

Mallow ninebark PHMA5 Physocarpus malvaceus (Greene) Kuntze

Mountain alder ALIN2 Alnus incana (L.) Moench

Mountain snowberry SYOR2 Symphoricarpos oreophilus A. Gray

Nootka rose RONU Rosa nutkana C. Presl

Oceanspray HODI Holodiscus discolor (Pursh) Maxim.

Oregon boxwood PAMY Pachistima myrsinites (Pursh) Raf.

Prickly currant RILA Ribes lacustre (Pers.) Poir.

Prince’s pine CHUM Chimaphila umbellata (L.) W. Bartram

Red elderberry SARA2 Sambucus racemosa L.

Red-osier dogwood COST4 Cornus stolonifera Michx.

Rocky Mountain maple ACGL Acer glabrum Torr.

Rose ROSA5 Rosa L.

Scouler’s willow SASC Salix scouleriana Barratt ex Hook.

Shrubby cinquefoil POFR4 Potentilla fruticosa auct. non L.

Snowberry SYMPH Symphoricarpos Duham.

Snowbrush ceanothus CEVE Ceanothus velutinus Douglas ex Hook.

Thimbleberry RUPA Rubus parviflorus Nutt.

112 GENERAL TECHNICAL REPORT PNW-GTR-806

APPENDIX B
Common name Codea Latin name and authorb

Twinflower LIBO3 Linnaea borealis L.

Utah honeysuckle LOUT2 Lonicera utahensis S. Watson

Water birch BEOC2 Betula occidentalis Hook.

Wax currant RICE Ribes cereum Douglas

Western serviceberry AMAL2 Amelanchier alnifolia (Nutt.) Nutt. ex M. Roem.

Western trumpet honeysuckle LOCI3 Lonicera ciliosa (Pursh) Poir. ex DC.

Willow SALIX Salix L.

Woods’ rose ROWO Rosa woodsii Lindl.

Grasslike plants:

Baltic rush JUBA Juncus balticus Willd.

Dewey sedge CADE9 Carex deweyana Schwein.

Elk sedge CAGE2 Carex geyeri Boott

Hood’s sedge CAHO5 Carex hoodii Boott

Nebraska sedge CANE2 Carex nebrascensis Dewey

Needle spikerush ELAC Eleocharis acicularis (L.) Roem. & Schult.

Northwestern sedge CACO11 Carex concinnoides Mack.

Ross’ sedge CARO5 Carex rossii Boott

Sedge CAREX Carex L.

Sierra rush JUNE Juncus nevadensis S. Watson

Slenderbeak sedge CAAT3 Carex athrostachya Olney

Smallwinged sedge CAMI7 Carex microptera Mack.

Water sedge CAAQ Carex aquatilis Wahlenb.

Woolly sedge CALA30 Carex lanuginosa auct. non Michx.

Yellow sedge CAFL4 Carex flava L.

Grasses:

Alaska oniongrass MESU Melica subulata (Griseb.) Scribn.

Alkali bluegrass POJU Poa juncifolia Scribn.

Bentgrass AGROS2 Agrostis L.

Blue wildrye ELGL Elymus glaucus Buckley

Bluebunch wheatgrass AGSP Agropyron spicatum Pursh

Bluejoint reedgrass CACA4 Calamagrostis canadensis (Michx.) P. Beauv.

Bottlebrush squirreltail SIHY Sitanion hystrix (Nutt.) J.G. Sm.

Cheatgrass BRTE Bromus tectorum L.

Columbia brome BRVU Bromus vulgaris (Hook.) Shear

Common timothy PHPR3 Phleum pratense L.

Creeping bentgrass AGST2 Agrostis stolonifera L.

Fowl mannagrass GLST Glyceria striata (Lam.) Hitchc.

Idaho fescue FEID Festuca idahoensis Elmer

Intermediate wheatgrass AGIN2 Agropyron intermedium (Host) P. Beauv.

Kentucky bluegrass POPR Poa pratensis L.

Meadow foxtail ALPR3 Alopecurus pratensis L.

Mountain brome BRCA5 Bromus carinatus Hook. & Arn.

Orchardgrass DAGL Dactylis glomerata L.

Pinegrass CARU Calamagrostis rubescens Buckley

Prairie junegrass KOCR Koeleria cristata auct. non Pers. p.p.

Quackgrass AGRE2 Agropyron repens (L.) P. Beauv.

Red fescue FERU2 Festuca rubra L.

Rough bentgrass AGSC5 Agrostis scabra Willd.

Spike trisetum TRSP2 Trisetum spicatum (L.) K. Richt.

Tall mannagrass GLEL Glyceria elata (Nash ex Rydb.) M.E. Jones

Tall trisetum TRCA21 Trisetum canescens Buckley

Tufted hairgrass DECE Deschampsia cespitosa (L.) P. Beauv.

Western fescue FEOC Festuca occidentalis Hook.

Appendix B: Plant Names Used in This Report (continued)

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 113

APPENDIX B 
Common name Codea Latin name and authorb

Western needlegrass STOC2 Stipa occidentalis Thurb.

Wheeler’s bluegrass PONE2 Poa nervosa (Hook.) Vasey

Forbs:

American vetch VIAM Vicia americana Muhl. ex Willd.

Aster ASTER Aster L.

Bigleaf sandwort ARMA18 Arenaria macrophylla Hook.

Black medick MELU Medicago lupulina L.

Blue stickseed HAMI Hackelia micrantha (Eastw.) J.L. Gentry

Brakenfern PTAQ Pteridium aquilinum (L.) Kuhn

Brown’s peony PABR Paeonia brownie Douglas ex Hook.

Bull thistle CIVU Cirsium vulgare (Savi) Ten.

California false hellebore VECA2 Veratrum californicum Durand

Canada thistle CIAR4 Cirsium arvense (L.) Scop.

Chamisso arnica ARCH3 Arnica chamissonis Less.

Ciliate bluebells MECI3 Mertensia ciliata (James ex Torr.) G. Don

Cleavers GAAP2 Galium aparine L.

Cluster tarweed MAGL2 Madia glomerata Hook.

Columbian monkshood ACCO4 Aconitum columbianum Nutt.

Common camas CAQU2 Camassia quamash (Pursh) Greene

Common clarkia CLRH Clarkia rhomboidea Douglas ex Hook.

Common dandelion TAOF Taraxacum officinale F.H. Wigg.

Common houndstongue CYOF Cynoglossum officinale L.

Common mullein VETH Verbascum thapsus L.

Common pearly-everlasting ANMA Anaphalis margaritacea (L.) Benth.

Common yarrow ACMI2 Achillea millefolium L.

Cowparsnip HELA4 Heracleum lanatum Michx.

Deceptive groundsmoke GADE2 Gayophytum decipiens F.H. Lewis & Szweykowski

Early blue violet VIAD Viola adunca Sm.

False hellebore VERAT Veratrum L.

Fendler’s waterleaf HYFE Hydrophyllum fendleri (A. Gray) A. Heller

Few-flowered aster ASMO3 Aster modestus Lindl.

Field mint MEAR4 Mentha arvensis L.

Fireweed EPAN2 Epilobium angustifolium L.

Fragrant bedstraw GATR3 Galium triflorum Michx.

Gairdner’s yampah PEGA3 Perideridia gairdneri (Hook. & Arn.) Mathias

Geyer’s onion ALGE Allium geyeri S. Watson

Giant frasera FRSP Frasera speciosa Douglas ex Griseb.

Globe penstemon PEGL5 Penstemon globosus (Piper) Pennell & D.D. Keck

Golden-pea THMO6 Thermopsis montana Nutt.

Gooseberryleaf alumroot HEGR8 Heuchera grossulariifolia Rydb.

Greater creeping spearwort RAFL2 Ranunculus flammula L.

Green false hellebore VEVI Veratrum viride Aiton

Heartleaf arnica ARCO9 Arnica cordifolia Hook.

Hotrock penstemon PEDE4 Penstemon deustus Douglas ex Lindl.

Largeleaf avens GEMA4 Geum macrophyllum Willd.

Leafy aster ASFO Aster foliaceus Lindl. ex DC.

Little buttercup RAUN Ranunculus uncinatus D. Don ex G. Don

Little sunflower HEUN Helianthella uniflora (Nutt.) Torr. & A. Gray

Longstalk clover TRLO Trifolium longipes Nutt.

Lupine LUPIN Lupinus L.

Missouri goldenrod SOMI2 Solidago missouriensis Nutt.

Mountain phlox PHAU3 Phlox austromontana Coville

Mountain sweet-cicely OSCH Osmorhiza chilensis Hook. & Arn.

Appendix B: Plant Names Used in This Report (continued)

114 GENERAL TECHNICAL REPORT PNW-GTR-806

APPENDIX B
Common name Codea Latin name and authorb

Mountain tansymustard DERI2 Descurainia richardsonii O.E. Schulz

Narrowleaf collomia COLI2 Collomia linearis Nutt.

Nettleleaf horsemint AGUR Agastache urticifolia (Benth.) Kuntze

Nodding chickweed CENU2 Cerastium nutans Raf.

Northern bedstraw GABO2 Galium boreale L.

Nuttall’s violet VINU2 Viola nuttallii Pursh

Oregon checker-mallow SIOR Sidalcea oregana (Nutt. ex Torr. & A. Gray) A. Gray

Phacelia PHACE Phacelia Juss.

Red baneberry ACRU2 Actaea rubra (Aiton) Willd.

Red columbine AQFO Aquilegia formosa Fisch. ex DC.

Rocky Mountain iris IRMI Iris missouriensis Nutt.

Rosy pussytoes ANMI3 Antennaria microphylla Rydb.

Roundleaf alumroot HECY2 Heuchera cylindrical Douglas ex Hook.

Self-heal PRVU Prunella vulgaris L.

Showy aster ASCO3 Aster conspicuus Lindl.

Shrubby penstemon PEFR3 Penstemon fruticosus (Pursh) Greene

Sierra larkspur DEGL3 Delphinium glaucum S. Watson

Sierran peavine LANE3 Lathyrus nevadensis S. Watson

Silky lupine LUSE4 Lupinus sericeus Pursh

Silverleaf phacelia PHHA Phacelia hastata Douglas ex Lehm.

Sitka valerian VASI Valeriana sitchensis Bong.

Skunk-leaved polemonium POPU3 Polemonium pulcherrimum Hook.

Slender cinquefoil POGR9 Potentilla gracilis Douglas ex Hook.

Slim larkspur DEDE2 Delphinium depauperatum Nutt.

Small flowered blue-eyed Mary COPA3 Collinsia parviflora Lindl.

Small flowered penstemon PEPR2 Penstemon procerus Douglas ex Graham

Smallflower nemophila NEPA Nemophila parviflora Douglas ex Benth.

Spreading dogbane APAN2 Apocynum androsaemifolium L.

St. Johnswort HYPE Hypericum perforatum L.

Starry false Solomon’s seal SMST Smilacina stellata (L.) Desf.

Sticky geranium GEVI2 Geranium viscosissimum Fisch. & C.A. Mey. ex C.A. Mey.

Stinging nettle URDI Urtica dioica L.

Straightbeak buttercup RAOR3 Ranunculus orthorhynchus Hook.

Strawberry FRAGA Fragaria L.

Sulfur penstemon PEAT3 Penstemon attenuatus Douglas ex Lindl.

Sulphur lupine LUSUS3 Lupinus sulphureus Douglas ex Hook. ssp. subsaccatus (Suksd.) 

 L. Phillips

Tailcup lupine LUCA Lupinus caudatus Kellogg

Tall butterweed SESE2 Senecio serra Hook.

Tall cinquefoil POARC Potentilla arguta Pursh ssp. convallaria (Rydb.) D.D. Keck

Tall groundsel SEFO Senecio foetidus J.T. Howell

Thickleaf groundsel SECR Senecio crassulus A. Gray

Thinleaf bedstraw GABI Galium bifolium S. Watson

Thistle CIRSI Cirsium Mill.

Throughwort EUOC5 Eupatorium occidentale Hook.

Trailplant ADBI Adenocaulon bicolor Hook.

Trumpet COLLO Collomia Nutt.

Turpentine cymopterus CYTEF Cymopterus terebinthus (Hook.) Torr. & A. Gray var. foeniculatus 

 (Nutt. ex Torr. & A. Gray) Cronquist

Valerian VALER Valeriana L.

Varileaf phacelia PHHE2 Phacelia heterophylla Pursh

Violet VIOLA Viola L.

Western clematis CLLI2 Clematis ligusticifolia Nutt.

Appendix B: Plant Names Used in This Report (continued)

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 115

APPENDIX B 
Common name Codea Latin name and authorb

Western coneflower RUOC2 Rudbeckia occidentalis Nutt.

Western false Solomon’s seal SMRA Smilacina racemosa (L.) Desf.

Western hawkweed HIAL Hieracium albertinum Farr

Western larkspur DEOC Delphinium occidentale (S. Watson) S. Watson (pro sp.)

Western meadowrue THOC Thalictrum occidentale A. Gray

Western mugwort ARLU Artemisia ludoviciana Nutt.

Western sweetroot OSOC Osmorhiza occidentalis (Nutt. ex Torr. & A. Gray) Torr.

White hawkweed HIAL2 Hieracium albiflorum Hook.

Wild candytuft THFE3 Thlaspi fendleri A. Gray

Willowherb EPILO Epilobium L.

Woods strawberry FRVE Fragaria vesca L.

Wormleaf stonecrop SEST2 Sedum stenopetalum Pursh

a Code from the PLANTS database (USDA-NRCS 2008).

b Latin names follow Hitchcock and Cronquist (1973). For current synonyms see app. C.

Appendix B: Plant Names Used in this Report (continued)

116 GENERAL TECHNICAL REPORT PNW-GTR-806

APPENDIX B
Appendix C: Current PLANTS Database Synonyms for the Names Used in This Report

Hitchcock and Cronquist namea Current synonymb

Latin name Codec Common name Latin name Codec

Agropyron intermedium (Host) P. 

 Beauv.

AGIN2 Intermediate wheatgrass Thinopyrum intermedium (Host) Barkworth & D.R. Dewey THIN6

Agropyron repens (L.) P. Beauv. AGRE2 Quackgrass Elymus repens (L.) Gould ELRE4

Agropyron spicatum Pursh AGSP Bluebunch wheatgrass Pseudoroegneria spicata (Pursh) A. Löve ssp. spicata PSSPS

Arenaria macrophylla Hook. ARMA18 Bigleaf sandwort Moehringia macrophylla (Hook.) Fenzl MOMA3

Aster conspicuus Lindl. ASCO3 Showy aster Eurybia conspicua (Lindl.) G.L. Nesom EUCO36

Aster foliaceus Lindl. ex DC. ASFO Leafy aster Symphyotrichum foliaceum (Lindl. ex DC.) G.L. Nesom SYFO2

Aster modestus Lindl. ASMO3 Few-flowered aster Canadanthus modestus (Lindl.) G.L. Nesom CAMO32

Berberis repens Lindl. BERE Creeping Oregon grape Mahonia repens (Lindl.) G. Don MARE11

Carex lanuginosa auct. non 

 Michx.

CALA30 Woolly sedge Carex pellita Muhl. ex Willd. CAPE42

Cornus stolonifera Michx. COST4 Red-osier dogwood Cornus sericea L. ssp. sericea COSES

Epilobium angustifolium L. EPAN2 Fireweed Chamerion angustifolium (L.) Holub CHAN9

Eupatorium occidentale Hook. EUOC5 Throughwort Ageratina occidentalis (Hook.) King & H. Rob. AGOC2

Glyceria elata (Nash ex Rydb.) 

 M.E. Jones

GLEL Tall mannagrass Glyceria striata (Lam.) Hitchc. GLST

Heracleum lanatum Michx. HELA4 Cowparsnip Heracleum maximum Bartram HEMA80

Hieracium albertinum Farr HIAL Western hawkweed Hieracium scouleri Hook. var. albertinum (Farr) G.W. 

 Douglas & G.A. Allen

HISCA

Koeleria cristata auct. non 

 Pers. p.p.

KOCR Prairie junegrass Koeleria macrantha (Ledeb.) Schult. KOMA

Lupinus sulphureus Douglas ex 

 Hook. ssp. subsaccatus (Suksd.) 

 L. Phillips

LUSUS3 Sulphur lupine Lupinus bingenensis Suksd. var. subsaccatus Suksd. LUBIS

Osmorhiza chilensis Hook. & Arn. OSCH Mountain sweet-cicely Osmorhiza berteroi DC. OSBE

Poa juncifolia Scribn. POJU Alkali bluegrass Poa secunda J. Presl POSE

Populus trichocarpa Torr. & 

 A. Gray ex Hook.

POTR15 Black cottonwood Populus balsamifera L. ssp. trichocarpa (Torr. & A. Gray 

 ex Hook.) Brayshaw

POBAT

Potentilla fruticosa auct. non L. POFR4 Shrubby cinquefoil Dasiphora fruticosa (L.) Rydb. ssp. floribunda (Pursh) 

 Kartesz

DAFRF

Sambucus cerulea Raf. SACE3 Blue elderberry Sambucus nigra L. ssp. cerulea (Raf.) R. Bolli SANIC5

Senecio foetidus J.T. Howell SEFO Tall groundsel Senecio hydrophiloides Rydb. SEHY

Sitanion hystrix (Nutt.) J.G. Sm. SIHY Bottlebrush squirreltail Elymus elymoides (Raf.) Swezey ssp. elymoides ELELE

Smilacina racemosa (L.) Desf. SMRA Western false solomon’s 

 seal

Maianthemum racemosum (L.) Link ssp. amplexicaule

 (Nutt.) LaFrankie

MARAA

Smilacina stellata (L.) Desf. SMST Starry false solomon’s seal Maianthemum stellatum (L.) Link MAST4

Stipa occidentalis Thurb. STOC2 Western needlegrass Achnatherum occidentale (Thurb.) Barkworth ACOC3

a Names used in Hitchcock and Cronquist (1973) and this report.

b Recommended synonyms listed in the PLANTS database (USDA-NRCS 2008).

c Code from the PLANTS database (USDA-NRCS 2008).

ASPEN BIOLOGY, COMMUNITY CLASSIFICATION, AND MANAGEMENT IN THE BLUE MOUNTAINS 117

APPENDIX C



Pacific Northwest Research Station

Web site http://www.fs.fed.us/pnw

Telephone (503) 808-2592

Publication requests (503) 808-2138

FAX (503) 808-2130

E-mail pnw_pnwpubs@fs.fed.us

Mailing address Publications Distribution

 Pacific Northwest Research Station

 P.O. Box 3890

 Portland, OR 97208-3890
U.S. Department of Agriculture

Pacific Northwest Research Station

333 SW First Avenue

P.O. Box 3890

Portland, OR 97208-3890

Official Business

Penalty for Private Use, $300