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Derek, A - Quaking aspen

Page history last edited by Annie 12 years, 8 months ago

 

Quaking Aspen

Populus tremuloides 

Anne Derek

PBIO 209

 

 

    Known for its leaves, which have a tendency to "tremble" or "quake" in a slight breeze, Quaking Aspen is the most widely distributed tree species in North America. It is a 30-70 foot deciduous, perennial tree that is fast growing, but generally short lived and often replaced by conifers. The distribution of the Quaking Aspen is typically cooler regions of North America and higher elevations in the west, usually in a climate with cool, dry summers where annual precipitation is beyond the rate of evapotranspiration. It is cold tolerant and can be found in stream banks, moist low areas, moist upland woods, and disturbed areas, on a variety of soils. (Debyle and Winokur 1985) Because of the broad range of temperatures and climates Quaking Aspen can tolerate, it grows in multiple biomes. It can be found in temperate coniferous forests, boreal forests, temperate grasslands and parklands, temperate broadleaf and mixed forest and also in the tundra. (Conservation Science...updated 2008) It does especially well in areas that have a high occurrence of disturbance by fires, where they can grow quickly in the new soil and open sunlight. In the absence of fire, they are generally replaced by grass, shrubs, or conifers. (Burns and Honkala 1990)

 

Left: Distribution map of Populus tremuloides. (USDA 2008)

 

        I first became interested in Quaking Aspen after doing research about Pando, or The Trembling Giant, which is believed by some to be the world's oldest and largest living organism. Pando, found in the Wasatch Mountains of Utah, is a single male clonal Quaking Aspen containing 47,000 tree trunks and weighing over 13 million pounds! (Grant 1993) This is possible because aspens are capable of vegetative reproduction. This means they can reproduce by root sprouts, or suckers, which grow horizontally underground, eventually taking root and growing into a new, connected, genetically identical plant. Clones in aspens are usually formed following some kind of disturbance, such as fire, which destroys the genet. Although Quaking Aspens primarily grow by vegetative reproduction, they are also capable of sexual reproduction and are dioecious. The flowers are fluffy white catkins that usually appear in April or May, and the seeds are covered in long silky hairs which make it easily carried by the wind, although it can also be dispersed by water, too. Quaking Aspen can grow from seeds in Alaska, northern Canada, and eastern North America. However, in the west there are dry period that usually kill germinated seedlings before they have a chance to establish. (Burns and Honkala 1990)

 

 

        Quaking Aspen are a valuable resource for both wildlife and humans. They produce forage up to 6 times as rich as a conifer forest, and provide a habitat for hare, black bear, deer, elf, ruffed grouse, woodcock, and other small birds and animals. The ruffed grouse is one example of a mutualism between animal and tree, because they use young aspen for brooding and breeding, older stands for nests and feed extensively on aspen buds for winter food. If the aspen forest has a suitable density and structure, it makes a good grouse habitat. (Debyle and Winokur 1985)

       

        Like many trees, aspens provide a number of different wood products such as pulp, lumber, plywood, shingles, particleboard, and studs, as well as benches and playground structures. In fact, Quaking Aspens are one of the most important timber products in the east. Aspen chips can be processed and made into biomass fuels and animal feed as well. Aspens are also low in flammability and are sometimes used as firebreaks. (Burns and Honkala 1990) On top of all these uses, Quaking Aspen are very aesthetically pleasing and are used horticulturally across the nation. The bark is usually a light gray or white with a green tint and in the fall the leaves turn to a bright yellow or orange.

 

 

 

 

 

 

Left: Quaking Aspen leaves, responsible for its name. Long, flattened stocks flutter and "quake" in the wind. (Trees and Shrubs...[Updated 2006])

 

 

 

Right: Aspen grove and surrounding conifers along roadside. (Common Trees...[Updated 2006])

 

 

 

 

 

 

 

 

 

 


 

 

 

Quaking Aspen: Community and Threats

 

 

            The Quaking Aspen is extremely important to the ecology and community of North America, especially because it is so widely distributed and found in many different habitats. In fact, Quaking Aspen is the most widely distributed tree in North America and it grows in a variety of biomes. It is most commonly found in northern boreal forests and western montane forests, but also grows in temperate coniferous forests, temperate grasslands and parklands, temperate broadleaf and mixed forest and also in the tundra. (Conservation Science...updated 2008) Aspens are capable of such a broad distribution because of their tolerance to a wide range of climates.

 

            An Aspen community is generally very diverse and varies from region to region. Stands are usually the same age because of the tendency to reproduce quickly as clones after a disturbance, such as a fire. However, in the west, under certain conditions, aspens are capable of self perpetuating into uneven aged stands. (Debyle and Winokur 1985) Quaking Aspens are known for the abundant undergrowth which they are capable of supporting, especially when compared to the coniferous forests that typically surround them. This is because sufficient light is able to break through the canopy, creating multilayered undergrowth that usually consists of a mixture of grasses, forbs, and tall to medium shrubs and herbs. (Burns and Honkala 1990)

 

            Because aspens are generally found in groves surrounded by conifers, they are in constant competition. Aspens thrive in open areas where they can reproduce freely, however it is very intolerant of shade. Some aspen stands reach climax, but they are usually seral to conifers because of the great heights that conifers grow to. This replacement can be quick in mixed conifer forest, as quickly as a decade, but is usually a gradual event taking 100 – 200 years. (Burns and Honkala 1990) This competition is one reason that fires are so important to the Quaking Aspen’s existence. Fires will take out the conifers and the part of the aspens that are aboveground, but because aspens grow from a clonal root system, they survive underground and regenerate in a now conifer free area. As important as fires are to the natural survival of aspen forests, aspen trees are still very sensitive to fire damage. Very light fires can kill aspen because its bark is thin and green, and fire scars are often the cause of destructive rotting. Modern day fire suppression has created a decline of quaking aspens in the west. Allowing fires to burn would be one way to solve this problem, however this is not a good idea in populated areas because conifers are a more valuable timber resource than aspens. Moderately intense fires to occuring at infrequent intervals would be enough to kill the surrounding conifers but would allow most of the aspen stands to survive. However, more frequent fires would have an adverse effect and complete fire suppression would allow conifers to take over. (Dye 2000)

 

            Wildlife can also pose a threat to the growth of Quaking Aspen. Aspens provide a good habitat for the breeding, browsing, and foraging of a number of mammals and small birds. Elk, deer, and moose browse aspen all year round, which can be very damaging to young sprouts. Elk are especially harmful because they feed on bark, branches, and sprouts all year round in many places, and rub against the bark with their antlers. When they are in the early sapling stage, heavy browsing reduces growth, vigor, and number of trees. In the Rockies and some parts of the west, livestock browsing is causing damage to roots and a decline in mature stands that are adjacent to livestock concentrations. Other smaller animals, such as meadow mice and hare, can damage aspen by gnawing and stripping of the bark, which quaking aspen are especially susceptible to. Beaver feed on young bark and cut down trees found near their colonies, and porcupine are also known to damage young aspen stands by making them more susceptible to insects and disease. (Debyle and Winokur)

 

            The thin, soft, living bark makes Quaking Aspen especially vulnerable to disease and insect damage. In mature stands, rot producing fungi can enter through wounds, and other diseases can enter the root system underground. Some examples of these diseases are Shoestring Root, Aspen Trunk Rot, and White Mottled Rot. Cankers, such as the widely distributed Black Canker, can also affect aspens; however they are usually not severe enough to kill the tree. Some insects that pose a threat to quaking aspens are the poplar borer, which dig large tunnels and make the tree more susceptible to wind damage, and forest tent caterpillars. Forest tent caterpillars are very destructive, especially in the lake states and Canada, and cause mass defoliation as large as 259,000 km2. Aspens suffer growth loss during the infestation, and some trees never recover. The large aspen torix is another defoliator and growth reducer; however during the 2-3 year outbreak few trees are usually killed. (Burns and Honkala)

 

 


BIbliography
DeByle NV, Winokur RP, editors. 1985. Aspen: Ecology and Management in the Western United States. Fort Collins (CO): U.S. Department of Agriculture Forest Service. General Technical Report RM-119

 

Grant, MC. 1993. The Trembling Giant. DISCOVER magazine [Internet]. [cited 2008 Feb 14]. Available from: http://discovermagazine.com/1993/oct/thetremblinggian285/

 

 

Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2. [ cited 2008 Feb 14]. Available from

http://www.na.fs.fed.us/Spfo/pubs/silvics_manual/volume_2/populus/tremuloides.htm

 

 

USDA, NRCS. 2008. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA. [ cited 2008 Feb 17]. Available from: http://plants.usda.gov.

 

Dye, Lee. 2000 Sept 21. The Decline of the Quaking Aspen. ABC News [Internet]. [Cited Feb 28] Available from: http://abcnews.go.com/Technology/Story?id=119917&page=1
Common Trees [Internet]. [Updated 2006 Dec 13]. Wrangell-St. Elias: National Park Service, US Department of the Interior[Cited Feb 14]. Available from: http://www.nps.gov/wrst/naturescience/common-trees.htm
Trees and Shrubs with Alternate and Simple Leaves [Internet]. [Updated 2006 May 16]. Hiker's Guide to Trees and Shrubs, Glen State Park [Cited Feb 14] Available from: departments.bloomu.edu/.../P_tre_branch1tn.JPG
Conservation Science > Biomes and Biogeographical Realms [Internet]. [Updated 2008]. World Wildlife Fund [Cited February 17] Available from: http://www.worldwildlife.org/science/ecoregions/biomes.cfm

 

 

 

 

 

 

 

 

 

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