SPECIES CHARACTER
Description
Quaking aspen is a medium-sized, shade intolerant tree that attains heights of 40-70 feet
(12-21 meters), and diameters of 1-1.6 feet (0.3-0.5 meters). This tree has a short,
rounded crown, and trunks up to about 23 inches (60 cm) wide. Young trees have smooth
chalk-white to yellow-green bark. With age, the bark becomes thick, roughened by warty
bands, and divided into flattened ridges. Branches are slender and slightly drooping, with
hairless red-brown twigs during the first season. Leaves are alternate, deciduous, simple,
and broadest near the ovate to heart-shaped base. They are 0.8-3 inches (2-8 cm) long and
0.7-2.8 inches (1.8-7 cm) wide. A short pointed tip found on each leaf has 20-40 pairs of
fine teeth along the edges. Leaves are a dark shiny green above and a dull green beneath,
and turn golden in autumn. The tree obtained its name because the leaves flutter in the
slightest breeze due to long, flattened, slender leafstalks.
Similar Species
Quaking aspen is distinguished from other aspens, poplars and cottonwood by its finely
toothed, ovate leaves that lack a white felt of hairs on the under surface and by its
whitish bark. Big-tooth aspen has coarsley toothed, nearly circular leaves and bark that
is grayish-green. White poplar, an alien tree, has coarsely toothed, ovate leaves that are
covered by a white felt of hairs on the lower surface and has grayish-whitish bark.
Cottonwood has triangular leaves that are nearly flat across the bottom and gray bark.
Quaking aspen should be accurately identified before attempting any control measures. If
identification of the species is in doubt, the plant's identity should be confirmed by a
knowledgeable individual and/or by consulting appropriate books.
Distribution
Quaking aspen has one of the widest distributions of any tree in North America. This aspen
can be found from northern Alaska to Newfoundland, south to Pennsylvania, Missouri,
northern Mexico, and lower California. In Illinois, it is recorded from 38 counties and is
most common in the northern half of the state.
Habitat
This tree grows in many diverse soils, including shallow rocky soil, clay soil, rich soil,
or nutrient deficient sandy soil. Best growth occurs in rich, porous, limy soils.
Life History
This rapidly growing tree is one of the most aggressive of the pioneer species. It quickly
colonizes recently burned or bare areas and soon establishes dense stands of young trees.
Quaking aspens reproduce sexually by seeds and asexually by sending suckers from their
extensive lateral roots, forming stands that are clones. Apparently establishment of
quaking aspen by seed is uncommon. Establishment of stems by root suckering is much more
common. Quaking aspens begin to produce seed at 15-20 years of age and continue for about
50 years, although good seed crops are produced only every 4-5 years. Flowers or catkins
appear in April and May before the leaves, and fruits ripen 4-6 weeks later. Male and
female catkins grow on separate trees and reach lengths of 2.5-10 cm. Fruit is in elongated
clusters of drooping catkins with 0.2 inch (6 mm) long, light green capsules, each of which
contains numerous seeds with cottony hairs that allow the seeds to become airborne. Rarely,
trees live to be 150 years old.
Effects Upon Natural Areas
Aspen is a problem in some disturbed prairie areas where it forms large clones. It tends
to exclude prairie species and provides favorable conditions for other trees and shrubs to
become established.
CONTROL RECOMMENDATIONS
RECOMMENDED PRACTICES IN NATURAL COMMUNITIES OF HIGH QUALITY
Initial effort in areas of heavy infestation
Girdling is the preferred management technique if practical. Girdled trees die slowly over
the course of 1 to 2 years and girdling minimizes resprouting. Girdling is easiest in late
spring or early summer when the sap is flowing and the bark readily peels away from the
sapwood. Girdling also may be attempted at other times of the year, although one must be
more careful not to girdle too deeply into the sapwood. When girdling a tree, the bark and
phloem must be removed from a band around the tree trunk and the xylem must remain intact.
If girdled too deeply, the tree will respond as if it had been cut down and will resprout
from the roots.
Girdling can be done with an ax, saw, or chainsaw. Two parallel cuts 3-4 inches apart,
cutting through the bark slightly deeper than the cambium are needed. The bark is knocked
off using a blunt object like the head of an ax. The girdles should be checked every
several weeks at first to make sure bark does not develop over the cut area. When big
stems are girdled, it is important to cut any small stems present. This minimizes the
amount of resprouting. If the trees are too small to be girdled practically, cutting
twice in one year is sometimes effective.
A common mistake is to cut down large trees without any other treatment. This should not
be done, as it results in vigorous resprouting creating hundreds of small stems. However,
resprouting of cut trees can be controlled with herbicide application as discussed below.
Initial effort in areas of light infestation
Girdling or cutting twice in one year should be done as given above.
Maintenance control
A continuous burning program (with burns approximately every other year), will control
aspen within a few decades. Late spring (1-2 weeks after aspen flowering) seems to be an
especially effective time to burn. Successful burning requires a sufficient quantity of
leaf litter and/or grass to provide the fuel base to carry a fire thoroughly under aspen
groves. Cutting canopy trees to eliminate shade and produce fire fuels may be necessary
in conjunction with burning to achieve adequate control.
RECOMMENDED PRACTICES ON BUFFER AND SEVERELY DISTURBED SITES
Initial effort in areas of heavy infestation
Same as in high-quality areas except that managers may prefer to cut stems and treat the
stumps with herbicides if there is not enough labor to pursue the preferred mechanical
treatments listed above. Stems should be cut and the stumps treated with Roundup (a
formulation of glyphosate) within 2-3 hours after cutting. While the Roundup label
recommends a 50-100% concentration of Roundup for stump treatment, a 10-20% concentration
has proven effective. Roundup can be applied either by spraying individual stumps with a
low pressure hand-held sprayer or else by wiping each stump with a sponge applicator
sponge-type paint applicators can be used).
In addition, fosamine (tradeneme Krenite) is an effective herbicide for small saplings and
root suckers when applied as a foliar spray according to label directions. Thorough cover
with a soft water carrier is required and a nonionic surfactant will improve results.
Coverage of foliage should be complete. Krenite should be applied only in July-September.
No effects will be observed during the autumn season following application. Slight regrowth
may occur the following season but saplings will die during summer. Fosamine kills only
woody species and is non-volatile.
If either herbicide is used, care should be taken to prevent contacting nontarget plants
with the herbicide. The herbicide should be applied while backing away from treated areas
so as not to walk through the wet herbicide. By law, herbicides only may be applied
according to label instructions and by licensed herbicide applicators or operators when
working on public properties.
Initial effort in areas of light infestation
Same as in high-quality areas, although managers may prefer to use herbicides as described
above for buffer and severely disturbed sites.
Maintenance control
Prescribed burning as described above. Nearby seed sources should be removed if possible.
FAILED OR INEFFECTIVE PRACTICES
No effective biological controls that are feasible in natural areas are known.
ACKNOWLEDGEMENTS
Dr. Robert M. Mohlenbrock and the Southern Illinois University Press generously permitted use of illustrations from their Illustrated Flora of Illinois.
REFERENCES
Brown, Lauren. 1986. Audubon society nature guides: trees. Alfred A. Knopf, Inc., New York. 853 pp.
Converse, Carmen. 1987. Element stewardship abstract. The Nature Conservancy, Arlington, Virginia. 17 pp.
Fuller, G. and G. N. Jones. 1955. Vascular plants of Illinois. University of Illinois Press, Urbana. 549 pp.
Packard, Stephen. 1987. Complete control of aspen by shallow girdling (Illinois). Restoration and Management Notes 5(1):50.
Petrides, G. A. 1972. Field guide to trees and shrubs. Peterson Field Guide Series. Houghton Mifflin Co., Boston. 428 pp.
Rydberg, P. A. 1932. Flora of the prairies and plains of central North America. New York Botanical Garden, New York. 672 pp.
Swink, F. and G. Wilhelm. 1979. Plants of the Chicago region. Morton Arboretum, Lisle, Illinois. 922 pp.
The Nature Conservancy. Element stewardship abstract for Populus balsamifera, P. grandidentata, P. tremuloides. The Nature Conservancy. Minneapolis, Minnesota.
PERSONAL COMMUNICATION
Apfelbaum, Steve. 1988. Applied Ecological Services, Juda, Wisconsin.
Betz, Dr. Robert. 1988. Northwestern University of Illinois, Chicago, Illinois.
Harty, Fran. 1988. Division of Natural Heritage, Illinois Department of Conservation, Springfield, Illinois.
Martin, Mark. 1988. Wisconsin Department of Natural Resources, Madison, Wisconsin.
McFall, Don. 1988. Division of Natural Heritage, Department of Conservation, Springfield, Illinois.
Nyboer, Randy. 1988. Division of Natural Heritage, Illinois Department of Conservation, Springfield, Illinois.
Packard, Steve. 1989. The Nature Conservancy, Chicago, Illinois.
Pearson, John. 1988. Iowa Natural Heritage Survey, Des Moines, Iowa.
Schwegman, John E. 1988. Division of Natural Heritage, Illinois Department of Conservation, Springfield, Illinois.
Written for the Illinois Nature Preserves Commission by:
Jill Kennay and George Fell
Natural Land Institute
320 South Third Street
Rockford, Illinois 61108