Quaking Aspen
Physical information
The slightest breeze sets their leaves aflutter. The
Populus tremuloides, the Latin name for Quaking Aspen, is from the Willow family.
Bark is typically smooth, often furrowed at the
base. Young trees have smooth bark with warty horizontal lines, while old
trees may blacken and furrow near the base. The color varies from a greenish-white
to cream-grey, yellowish-white, or yellowish-brown. Bark on older trees is usually
1"-2" thick. The bark is often eaten by beavers, rabbits and other
mammals. Branches are generally spreading, forming a
narrow, rounded crown of slender branches. Bark is typically smooth, often furrowed at the
base. Young trees have smooth bark with warty horizontal lines, while old
trees may blacken and furrow near the base. The color varies from a greenish-white
to cream-grey, yellowish-white, or yellowish-brown. Bark on older trees is usually
1"-2" thick. The bark is often eaten by beavers, rabbits and other
mammals. Branches are generally spreading, forming a
narrow, rounded crown of slender branches.
Buds are 1-2" long, shiny, sharp
pointed lateral buds. Unlike other poplars, buds are essentially non resinous.
Dioecious, has flowers on dense, 1
1/2"-2 1/2", drooping catkins (A compact cluster of reduced, stalkless flowers).
Fruit is two-valved, light green to brown capsules
(A dry, thin-walled fruit containing two or more seeds and splitting along natural grooved
lines at maturity).Height is usually 20'-100' tall with a diameter of
4"-36".
Height is usually 20'-100' tall with a diameter
of 4"-36".
Leaves are simple, alternate. They are
broadly ovate to nearly round with a small pointed tip, 1"-3" in diameter.
The tops are dark green and shiny with the underside being pale green or silvery.
Small, rounded marginal teeth. Have long, slender, flattened leaf stem. The
Quaking Aspen is known for its brilliant fall colors when leaves turn bright yellow,
yellow-orange, gold or reddish after the first frosts.
Root system is extensive, and may cover
large areas, even when aboveground vegetation is relatively sparse. The lateral
roots have been known to extend more than 100' into surrounding areas. Lateral roots
occur in the top 2'-3' of soil. Roots are able to sucker and produce new stems after
fire or other disturbances.
Seeds are light and tufted for efficient wind
dispersal.
Twigs are smooth and slender, redish-brown becoming
grayish-brown to greyish-orange by the third year of growth. Not all, but some, are
self pruning with numerous small twigs dropping in the fall. This rids the tree of
excess foliage and it helps to replenish nutrients in the soil. The twigs are often
eaten by deer, elk, moose, sheep and goats.
Wood is much softer than most North American
hardwoods. It is light in color, fairly straight grained. Has a fine, uniform
texture and is odorless as well as tasteless. It is resistant to splitting when
nailed into, can be glued and painted. The wood is not very strong or shock
resistant, it warps easily and is susceptible to decay.
Horticultural information
Soil can very from shallow and rocky, to deep,
heavy clays. Quaking Aspens can grow in infertile dry sands, rich loams, waterlogged
mineral soils and peats. They generally grow best on rich, moist loams, or well
drained silt or clay loams with an abundant supply of calcium. They like sunlight
and often grow in groups. They are extremely intolerant of shade, more than any
other tree in the Lake States. Aspen leaves decay rapidly, returning nutrients to
the soil. A characteristic "Aspen soil" develops on sites which have
supported aspen for a number of generations, with a pH generally higher than on soils
where conifers dominate. A high water supply may be detrimental to growth. A
rapid growth occurs on soils where the water table is 18"-60" deep.
Disease is wide ranging due to the soft, thin
bark. In mature trees, the most common disease is the rot producing fungi that
enters through wounds. Diseases, such as Shoestring Root (Armillaria), spread
through the interconnected root system. Common stem and root rots are Aspen Trunk
Rot (Phellinus tremulae), Peniophora polygonia, Shoestring Root Disease (Armillaria
mellea, White Mottled Rot (Ganoderma applanatum, and Flammulina velutipes. Some
diseases known to possibly cause mortality are Cankers, such as, Black Canker
(Ceratocystis fimbriata), Sooty Bark Canker (Cenangium singulare) and Hypoxylon Canker.
Insects such as Poplar Borer, Western Tent
Caterpillar, leaf rollers, Leaf Miner Beetle, Roundheaded and Flathead Woolborer, attack
the Aspen.
Distribution
The Aspen is the most widely distributed tree in North
America. It spreads throughout much of the continent from Newfoundland to Alaska,
south to Virginia and in the Rocky Mountains, south to Arizona and New Mexico.
Aspens occur as the dominant tree species, often in pure stands, or as scattered
individuals in communities dominated by other trees with spruce, pine and birch.
They are tolerant of cold, but not of high temperatures. In parts of Minnesota, the
Aspen has rapid growth but is short lived, reaching 80' in the first four decades.
Deterioration typically begins by age sixty in the Lake States, some as early as
thirty-five to forty-five years.
The wood of the Aspen is much softer and lighter than most North American
hardwoods. It is light in color, fairly straight grained and of a fine, uniform
texture. It is also odorless as well as tasteless. This soft wood is resistant
to splitting when nailed into and can be glued or painted. Unfortunately, it has
relatively low strength, moderate shock resistance, warps easily and is susceptible to
decay. The most common uses of the wood are in pulp products such as books and
specialty papers, newsprint, insulation board, fiberboard, clipboard, flakeboard and
particle board. The wood is also used for furniture products, interior trim, crates,
pallets, lumber core stock and paneling. It used to be readily used for posts,
poles, bridge planks and mine timbers. Miscellaneous products such as, excelsior,
animal bedding, matchsticks, toys, beehives, tongue depressors, spoons and icecream
sticks, are made from the wood of Aspens. The commercial value of the Aspen has been
increasing over the past few years despite the low demand in past years.
Other important information
The slightest breeze sets their leaves aflutter, that is where the Quaking Aspen
got its name. The tree trunk is often used by lovers to carve a heart with initials
in it. Maybe even as a bears scratching post.
Vegetative regeneration usually occurs through suckering but sprouting
from root collars and stumps also takes place. This gives Aspen a mechanism to
survive and reproduce, even if faced with harsh and unfavorable environments. Most
suckers develop within 25' of the parent, but some may be as far away as 80'-100' or more.
Dioecious species, usually produce an abundance of viable seed.
However, the extremely restrictive conditions necessary for germination and establishment
have almost eliminated sexual reproduction , especially in the West.
Clonal species are capable of producing numerous individual, but
genetically identical stems from a single plant.
Sexual reproduction occurs when conditions are favorable for germination
and establishment will prevail. This form of reproduction can add greater genetic
diversity and allow for wider dispersal than can vegetative regeneration. At ten to
twenty years of age, the Aspen first flowers. The flowers are wind pollinated and
evidence suggests a greater abundance of male plants in a natural population. Every
2-3 or 4-5 years, a large seed crop occurs. An average mature tree can produce
approximately 1.6 million seeds annually, which are shed from early May through mid June.
Seeds are light, pear shaped, and tufted with a long silky seed hair
which helps facilitate wind dispersal. The Aspen seed may be carried more than
1,600' under typical prevailing winds or if high winds, up to several miles. The
seeds are somewhat resistant to water damage and can be dispersed by water if in a wet
habitat.
Seed viability of the Aspen is relatively short under natural
conditions. The viability of fresh seed is usually greater than 90% soon after
dispersal and if dried for three days before storage at cool temperatures, it retains good
viability for 1 1/2 years.
Germination and establishment requires a constant supply of moisture, a
favorable substrate such as exposed mineral soil and a suitable temperature.
Germination and subsequent growth may be limited by high temperatures, growth inhibitors
present in the seed hair, drought, disease, insects, heavy rains, extreme temperature or
unfavorable soil chemistry. Germination usually begins within a few hours to a few
days after moisture is received and can occur across a broad temperature range (32-92
degrees F). The best environment for germination is when the seed is at a very
shallow depth and burned sites are often good seedbeds. The Aspen is often replaced
by a variety of conifers of hardwoods.
Audubon Sociesty. (1980). The Audubon Society: A Field Guide to
North American Trees, Eastern Region. New York: Alfred A. Knopf, Inc.
Brockman, C. Frank. (1968). Trees of North America: A Field Guide to the
Major Native and Introduced Species North of Mexico. New York, N.Y.:
Golden Press.
Montgomery, F.H. (1970). Trees of the Northern United States and Canada.
New York: Frederick Warne & Co. Inc.
reader's Digest. (1984). ABC's of Nature: A Family Answer Book.
Pleasantville, New York: The Reader's Digest Association, Inc.
Smith, Norman F. (1952). Michigan Trees Worth Knowing. Hillsdale,
Michigan: Hillsdale Educational Publishers, Inc.
Vodopich, Moore Clark. (1998). Botany. United States of America:
WCB/McGraw-Hill.
This page written by Mandy for biology 141, Botany, Fall 1998.
  
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