USDA Forest Service RMRS-RN-26. 2005 1

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-26

August 2005

Introduction____________________

Aspen (Populus tremuloides Michx.) is a valuable part 

of many western landscapes, but is an especially desirable component of riparian areas where it contributes 

to the stability of streams, provides shade, nurtures a 

diverse and abundant understory community, and contributes a pleasing aesthetic component. Unfortunately, 

aspen has disappeared from some areas due to vegetative 

succession, overgrazing, and other factors (Bartos 2001). 

Regenerating these stands will require planting, because 

clonal root systems have died along with the aspen stems. 

However, attempts to plant aspen in upland sites such as 

campgrounds, mine reclamation, and highway projects has 

been largely unsuccessful, due to insufficient moisture to 

allow the transplanted seedlings to survive. Unlike natural aspen root suckers, planted seedlings do not have an 

extensive parental root system in place to supply moisture 

and nutrients. One study in interior Alaska (Zasada and 

others 1987) has reported success in planting aspen seedlings in a wildland environment, achieving survival rates 

of 40-80 percent after six years. The success of transplanting aspen for use as an ornamental in irrigated urban 

landscaping (Johnson and others 1985) and in irrigated 

nursery beds (Okafo and others 1978) indicates that aspen 

could be successfully transplanted in natural landscapes 

if sufficient moisture was available. Riparian areas may 

present one opportunity where moisture remains in the 

rooting zone long enough during the growing season to 

allow planted aspen seedlings to establish in the southern 

Rockies.

Naturally regenerated aspen sucker stands initially contain many thousands of stems per hectare. Stem densities 

of aspen forests do not remain stable or increase through 

Planting Aspen to Rehabilitate 

Riparian Areas: A Pilot Study

Wayne D. Shepperd1 and Stephen A. Mata

Abstract—We planted 742 greenhouse-grown containerized aspen seedlings 

in the riparian area of Hurd Creek on the Arapaho National Forest east of 

Tabernash, Colorado. Objectives were to (1) determine whether aspen seedlings can be planted in an operational setting and survive in sufficient numbers to successfully establish a mature aspen stand and (2) determine the effectiveness of fencing on aspen seedling survival. Five-year survival rates were 

18 percent in the fenced area and 23 percent in the unfenced area. Seedling 

heights were significantly taller in the fenced area than in the unfenced area.

1

 Research Forester and Research Technician, Rocky Mountain 

Research Station, Ft. Collins, CO.

time as in conifer forests, but follow a negative exponential 

decay curve as an aspen stand ages, decreasing through 

natural attrition to several hundred stems per hectare at 

maturity (Shepperd 1993). Because it is not feasible to 

plant thousands of aspen seedlings per hectare, protective fencing may be needed to slow the attrition process as 

much as possible.

The potential uncertainties associated with planting 

aspen in a natural setting prompted us to establish an operational test under a controlled experimental design to 

explore the feasibility of artificially re-establishing aspen 

in western landscapes. We felt that locating a test plantation in a riparian area where soil moisture is likely to 

remain favorable throughout the growing season and protecting the planted aspen from browsing animals would 

afford the best opportunity for success.

Objectives______________________

The objective of this study was to determine whether 

aspen seedlings can be planted in an operational setting 

and survive in sufficient numbers to successfully establish 

a mature aspen stand. The primary hypothesis to be tested 

was that containerized greenhouse-grown aspen seedlings 

could survive for at least five years and grow into trees 

(>2 m tall in a single-stem growth axis) if properly planted 

in a carefully selected riparian environment and protected 

from browsing animals.

Methods_______________________

For this study, we selected a site in the riparian area 

along Hurd Creek, on the Arapaho National Forest, east of 

Tabernash, Colorado (figure 1). The site was once stocked 

with mistletoe and beetle-infested lodgepole pine that 

was removed in the 1980s. The area selected for planting 
2 USDA Forest Service RMRS-RN-26. 2005

aspen consists of an alluvial outwash plain between Hurd 

Creek and the toe of the adjoining slope. The planting 

site is nearly flat but contained some low, wet spots that 

could not be planted (figure 2). Soils are poorly developed 

gravelly sands containing many large cobblestones and 

are derived from upslope granitic and metamorphic rock. 

Associate understory plants consist of rushes, willows, alder, and chokecherry in low areas near the stream with 

grasses, sedges, sage, buffaloberry, and other low perennials in slightly higher (<1 m) locations. This 2,600 m site 

receives about 50 cm of precipitation per year and is located 

within 2 km of the temperature-limited lower timberline in 

the Fraser River Valley, in one of the coldest mountain climates in Colorado. Although no aspen are present on this 

site, natural aspen stands are nearby. Parts of the planting 

area contain standing water during spring runoff and soils 

remain moist much of the three-month growing season.

During the summer of 1996, a 2.5 m-high hog-wire 

fenced enclosure was constructed around half of the planting area. Immediately following snowmelt in June of 1997 

the area was planted with 742 greenhouse-grown containerized aspen seedlings that were produced by the Colorado 

State Forest Service nursery in Ft. Collins, CO. Local 

Middle Park seed sources were germinated and grown using techniques similar to those discussed in Schier and 

others 1986. Three-hundred-seventy-three seedlings were 

planted in the unfenced area and 369 in the fenced area. 

Seedlings were grown in large Styrofoam block containers 

approximately 5 cm x 5 cm x 20 cm in size and were 20-50 

cm tall when planted. Planting spots were not on an evenly 

spaced grid but were selected to avoid rocky, dry, or excessively wet micro sites and were hand-scalped to mineral 

soil. Planting holes were dug using a chainsaw-powered 

auger. Seedlings were removed from the Styrofoam block 

Sterling

NEBRASKA

KANSAS

NEW MEXICO OKLAHOMA

ARIZONA

UTAH WYOMING

Study Site

Steamboat

Springs

Aspen

Alamosa

Trinidad

Eagle

Grand Junction

Telluride

Fort Collins

Boulder

Breckenridge

Greeley

Denver

Pueblo

Lamar

Figure 1—Location of 

plantation.

containers and immediately inserted into the prepared 

hole, backfilled with mineral soil and hand-packed. Each 

seedling was marked with a 9-guage wire stake containing 

a numbered metal tag. The location of each planted seedling was mapped with a transit so they could be relocated 

for survival checks (figure 2).

Results________________________

An initial survival check was completed in August 1997. 

Additional survival checks were completed annually for 

five years. Height and condition of each aspen seedling 

were recorded each year. Table 1 summarizes damages 

and seedling conditions that were noted. Browsing was the 

most prominent damage noted in the unfenced treatment, 

followed by branch stripping and rodent damage. Rodent 

damage was the predominant factor affecting seedlings 

in the fenced treatment, followed by poor growth form. A 

number of dead seedlings also re-sprouted from roots in 

subsequent years, which affected survival data (table 1).

Seedling survival over time for each treatment was estimated using the Kaplan-Meier product-limit estimator 

and compared using the log rank test (Lee 1992). Ending 

survival in 2001 was compared between treatments using 

Fisher’s exact test, and seedling height was compared between treatments for individual years using a t-test. SPSS 

(2002) procedure KM was used for the Kaplan-Meier analysis, CROSSTABS for the Fisher’s exact test, and T-TEST 

for t-test computations.

Seedling survival decreased more quickly in the fenced 

area than the unfenced area (log-rank test p = 0.006) with 

18.2 and 23.1 percent of seedlings remaining alive in 2001 
USDA Forest Service RMRS-RN-26. 2005 3

for fenced an unfenced treatments, respectively (table 

1, figure 3). However, ending survival was not different 

between treatments (fisher’s exact test p = 0.103). In 

contrast, seedlings were significantly taller in the fenced 

treatment compared to the unfenced treatment (p < 0.05) 

in 1999, 2000, and 2001 by 8.5 cm, 9.4 cm, and 11.6 cm 

respectively (figure 4). However, mean heights actually decreased between 1999 and 2001 in both fenced and unfenced 

treatments (figure 4), indicating that dieback of shoots was 

occurring. Although seedlings inside the enclosure were 

protected from deer and elk browsing, they were not protected from similar damage by rodents. Rodent damage 

to live seedlings was higher in the fenced treatment area 

than in the unfenced treatment area (table 1), which may 

indicate that rodents were protected from predators within 

the fenced enclosure.

Discussion_____________________

Although about a fifth of the original planted seedlings survived for five years, it is not likely that any of 

these trees will survive to maturity. Heights of surviving 

seedlings had increased only marginally since planting 

Hurd Ck

Unfenced Fenced

N

Figure 2—Map of plantation. Lines indicate numeric sequence of tagged trees to aid in relocation.

Table 1—Frequency distribution of damage condition codes of aspen sprouts planted at Hurd Creek.

Unfenced Fenced

Seedling conditions 1997 1998 1999 2000 2001 1997 1998 1999 2000 2001

OK 201 192 126 55 52 205 140 95 66 41

Browsing 1 16 7 26 8 0 0 0 

Branches stripped 9 3 

Poor form 1 2

Rodents 2 1 1 3 9 3 3 6

Cumulative mortality 171 165 238 272 287 161 220 271 294 302

Resprouted 10 22 5 18

Total planted 373 373 373 373 373 369 369 369 369 369

Surviving 202 208 135 101 86 208 149 98 75 67

and were much shorter than those observed in natural 

sucker populations (Shepperd 1993). Seedling heights 

were significantly taller inside the fence, but none of the 

seedlings were tall enough to be above competing vegetation or browsing animals and thus could not be considered 

to be established. Ironically, the fence appeared to have 

adversely affected seedling survival, most likely by exposing seedlings to rodents which had been protected from 

predation by the fenced enclosure.

The re-sprouting of new shoots from the roots of seedlings that had previously been declared dead was notable 

(table 1). This phenomenon demonstrates that root systems 

of the containerized seedlings were still viable after death 

of the original shoots and indicates that sufficient moisture 

was available in the riparian soils to keep the roots alive in 

spite of below average precipitation for some of the study 

period (figure 5).

In conclusion, the limited success of this study illustrates 

the difficulties of planting aspen in wildland environments. 

Use of containerized seedlings, fencing, and planting in a 

moist riparian area did not result in success in this case. 

Further investigation of other possible methods of planting 

aspen is needed to investigate how soil type, physiographic 

conditions, associate vegetation, type of planting stock, and 

other factors might affect success.
4 USDA Forest Service RMRS-RN-26. 2005

Figure 5—Annual precipitation 

for years 1996 to 2001 from 

Fraser Experimental Forest, 

headquarters weather station, 19 km southwest of the 

Hurd creek planting site, the 

closest weather station in 

similar terrain.

Figure 3—Proportion of planted aspen 

seedlings surviving in successive 

years by fencing treatment.

Figure 4—Average planted aspen 

seedling heights in successive 

years by fencing treatment (with 

95% SE bars).
USDA Forest Service RMRS-RN-26. 2005 5

Acknowledgment________________

The authors wish to thank the Daughters of the 

American Revolution, who provided funding to establish 

this plantation.

Literature Cited_________________

Bartos, Dale L. 2001. Landscape dynamics of aspen and conifer 

forests. In: Shepperd, Wayne D.; Binkley, Dan; Bartos, Dale 

L.; Stohlgren, Thomas J.; Eskew, Lane G., eds. Sustaining 

aspen in western landscapes: Symposium proceedings; 13-15 

June 2000; Grand Junction, CO. Proceedings RMRS-P-18. Fort 

Collins, CO: USDA Forest Service, Rocky Mountain Research 

Station. 5-14.

Lee, Elisa T. 1992. Statistical methods for survival data analysis. 

2nd ed. New York: Wiley 482 p.

Johnson, Craig W.; Brown, Thomas C.; Timmons, Michael L. 1985. 

Esthetics and landscaping. In: Norbert V. DeByle and Robert P. 

Winokur, eds. Aspen: ecology and management in the western 

United States. USDA Forest Service General Technical Report 

RM-119. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station. 185-188.

Okafo, Obinani A.; Hanover, James W. 1978. Two-year performance 

of barerooted and containerized trembling and bigtooth aspen 

seedlings. Tree Planter’s Notes. 29(2):24-28.

Schier, George A.; Shepperd, Wayne D.; Jones, John R. 1985. 

Regeneration. In: Norbert V. DeByle and Robert P. Winokur, 

eds. Aspen: ecology and management in the western United 

States. USDA Forest Service General Technical Report RM119. Fort Collins, CO: Rocky Mountain Forest and Range 

Experiment Station. 197-208.

Shepperd, Wayne 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.

SPSS Inc. 2002. SPSS for Windows Release 11.5. Chicago, IL: 

SPSS Inc.

Zasada, John C.; Norum, Rodney A.; Teutsch, Christian E.; 

Densmore, Roseann. 1987. Survival and growth of planted 

black spruce, alder, aspen, and willow after fire on black spruce/

feather moss sites in interior Alaska. Forestry Chronicle. 

63(2):84-88.
You may order additional copies of this publication by sending your 

mailing information in label form through one of the following 

media. Please specify the publication title and series number.

Fort Collins Service Center

Telephone (970) 498-1392

FAX (970) 498-1396

E-mail rschneider@fs.fed.us

Web site http://www.fs.fed.us/rm

Mailing address Publications Distribution

 Rocky Mountain Research Station

 240 West Prospect Road

 Fort Collins, CO 80526

Rocky Mountain Research Station

Natural Resources Research Center

2150 Centre Avenue, Building A

Fort Collins, CO 80526
The U.S. Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the basis of race, 

color, national origin, sex, religion, age, disability, political beliefs, 

sexual orientation, or marital or family status. (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, Room 326 W, Whitten Building, 1400 Independence 

Avenue, SW, Washington, D.C. 20250-9410 or call (202) 720-5964 

(voice and TDD). USDA is an equal opportunity provider and 

employer.

The Rocky Mountain Research Station develops scientific 

information and technology to improve management, 

protection, and use of the forests and rangelands. Research is 

designed to meet the needs of the National Forest managers, 

Federal and State agencies, public and private organizations, 

academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving 

ecosystems, range, forests, water, recreation, fire, resource 

inventory, land reclamation, community sustainability, 

forest engineering technology, multiple use economics, 

wildlife and fish habitat, and forest insects and diseases. 

Studies are conducted cooperatively, and applications may 

be found worldwide.

Research Locations

Flagstaff, Arizona Reno, Nevada

Fort Collins, Colorado* Albuquerque, New Mexico

Boise, Idaho Rapid City, South Dakota

Moscow, Idaho Logan, Utah

Bozeman, Montana Ogden, Utah

Missoula, Montana Provo, Utah

*Station Headquarters, Natural Resources Research Center, 

2150 Centre Avenue, Building A, Fort Collins, CO 80526.

RMRS

ROCKY MOUNTAIN RESEARCH STATION

Federal Recycling Program Printed on Recycled Paper