Populus tremuloides
Encyclopedia
Populus tremuloides is a deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 tree native to cooler areas of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, commonly called quaking aspen, trembling aspen, American aspen, and Quakies,. The trees have tall trunks, up to 25 metres, with smooth pale bark, scarred with black. The glossy green leaves, dull beneath, become golden to yellow, rarely red, in autumn. The species often propagates through its roots to form large groves.

Name

The name references the quaking or trembling of the leaves that occurs in even a slight breeze due to the flattened petioles
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...

. The specific epithet, tremuloides, means similar to Populus tremula
Populus tremula
Populus tremula, commonly called aspen, common aspen, Eurasian aspen, European aspen, trembling poplar, or quaking aspen, is a species of poplar native to cool temperate regions of Europe and Asia, from the British Isles east to Kamchatka, north to inside the Arctic Circle in Scandinavia and...

, the European aspen.
Some species of Populus have petioles flattened partially along their length, while the aspens and some other poplars have them flattened from side to side along the entire length of the petiole.

One of several species to be referred to by the common name Aspen
Aspen
Populus section Populus, of the Populus genus, includes the aspen trees and the white poplar Populus alba. The five typical aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high altitudes in the mountains. The White Poplar, by...

, the names Mountain or Golden aspen, Trembling Poplar, Quakers, and Popple are also used.

Description

A tall, fast growing tree, usually 20–25 metres (66–82 ft) at maturity, with a trunk 20–80 centimetres (7.9–31 in) in diameter; records are 36.5 meters (120 ft) in height and 1.37 metres (4.5 ft) in diameter.

The bark is relatively smooth greenish-white to gray and is marked by thick black horizontal scars and prominent black knots.

The leaves on mature trees are nearly round, 4–8 centimetres (1.6–3.1 in) in diameter with small rounded teeth, and a 3–7 centimetres (1.2–2.8 in) long, flattened petiole. Young trees (including root sprouts) have much larger—10–20 centimetres (3.9–7.9 in) long—nearly triangular leaves.

The flowers are catkins 4–6 centimetres (1.6–2.4 in) long, produced in early spring before the leaves; it is dioecious, with male and female catkins on different trees. The fruit is a 10-centimetre (3.9 in) long pendulous string of 6-millimetre (0.24 in) capsules, each capsule containing about ten minute seeds embedded in cottony fluff, which aids wind dispersal of the seeds when they are mature in early summer.

Distribution

The northern limit is determined by its intolerance of permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

. It occurs across Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 in all provinces and territories, with the possible exception of Nunavut
Nunavut
Nunavut is the largest and newest federal territory of Canada; it was separated officially from the Northwest Territories on April 1, 1999, via the Nunavut Act and the Nunavut Land Claims Agreement Act, though the actual boundaries had been established in 1993...

. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, it can be found as far north as the southern slopes of the Brooks Range
Brooks Range
The Brooks Range is a mountain range in far northern North America. It stretches from west to east across northern Alaska and into Canada's Yukon Territory, a total distance of about 1100 km . The mountains top out at over 2,700 m . The range is believed to be approximately 126 million years old...

 in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, and it occurs at low elevations as far south as northern Nebraska
Nebraska
Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....

 and central Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...

. In the western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, this tree rarely survives at elevations lower than 1500 feet (457.2 m) due to the mild winters experienced below that elevation, and is generally found at 5000 –. It grows at high altitudes as far south as Guanajuato, Mexico
Guanajuato
Guanajuato officially Estado Libre y Soberano de Guanajuato is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 46 municipalities and its capital city is Guanajuato....



Shrub-like dwarf clones exist in marginal environments too cold and dry to be hospitable to full-size trees, for example at the species' upper elevation limits in the White Mountains
White Mountains (California)
The White Mountains of California are a triangular fault block mountain range facing the Sierra Nevada across the upper Owens Valley. They extend for approximately as a greatly elevated plateau about wide on the south, narrowing to a point at the north, with elevations generally increasing...

.

Ecology

It propagates itself primarily through root sprouts, and extensive clonal colonies
Clonal colony
A clonal colony or genet is a group of genetically identical individuals that have grown in a given location, all originating vegetatively from a single ancestor. In plants, an individual in such a population is referred to as a ramet...

 are common. Each colony is its own clone, and all trees in the clone have identical characteristics and share a single root structure. A clone may turn color earlier or later in the fall than its neighbouring aspen clones. Fall colors are usually bright tones of yellow; in some areas, red blushes may be occasionally seen. As all trees in a given clonal colony are considered part of the same organism, one clonal colony, named Pando
Pando (tree)
Pando is a clonal colony of a single male Quaking Aspen located in the U.S. state of Utah, all determined to be part of a single living organism by identical genetic markers and one massive underground root system, although whether it is a single tree is disputed...

, is considered the heaviest and oldest living organism at six million kilograms and approximately 80,000 years old. Aspens do produce seeds, but seldom grow from them. Pollination is inhibited by the fact that aspens are either male or female, and large stands are usually all clones of the same sex. Even if pollinated, the small seeds (three million per pound) are only viable a short time as they lack a stored food source or a protective coating.

Dieback

Beginning in 1996, individual North American scientists noticed an increase in dead or dying aspen trees. As this accelerated in 2004, word spread and a debate over causes began. No insect, disease, or environmental condition is yet specifically identified as a joint cause. Trees adjacent to one another are often stricken or not. In other instances entire groves have died.

Many areas of the Western US have experienced increased diebacks which are often attributed to ungulate grazing and wildfire suppression. At high altitudes where grasses can be rare, ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s can browse young aspen sprouts and prevent those young trees from reaching maturity. As a result, some aspen groves close to cattle or other grazing animals, such as deer or elk, have very few young trees and can be invaded by conifers, which are not typically browsed. Another possible deterrent to aspen regeneration is widespread wildfire suppression. Aspens are vigorous resprouter
Resprouter
Resprouters are plant species that are able to survive fire by the activation of dormant vegetative buds to produce regrowth.Plants may resprout by means of lignotubers at the base or epicormic buds on the trunk or major branches....

s and even though the above-ground portion of the organism may die in a wildfire, the roots, which are often protected from lethal temperatures during a fire, will sprout new trees soon after a fire. Disturbances such as fires seem to be a necessary ecological event in order for aspens to compete with conifers, which tend to replace aspen over long, disturbance-free intervals. The current dieback in the American West may have roots in the strict fire suppression policy in the United States.

Because of the vegetative regeneration method of reproduction used by the aspen, where an entire group of trees are essentially clones, there is a concern that something that hits one will eventually kill all of the trees, presuming they share the same vulnerability. A conference was held in Utah in September 2006 to share notes and consider investigative methodology.

Uses

Aspen bark contains a substance that was extracted by Native Americans and the pioneers of the American West as a quinine
Quinine
Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...

 substitute.

The leaves of the Quaking Aspen serve as food for caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...

s of various Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

. See List of Lepidoptera that feed on poplars.

In Canada, it is used mainly for pulp products such as books, newsprint, and fine printing paper. Aspen is especially good for panel products such as oriented strandboard and waferboard. Its lumber is light in weight and is used for furniture, boxes and crates, core stock in plywood, and wall panels.
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