Section 1.2: Trembling Aspen 101

Outcomes

Students will:

  • Identify and describe characteristics of a trembling aspen tree, including root, trunk, canopy, catkins, and buds.

  • Acknowledge where trembling aspen grow and create a visual representation of the trembling aspen habitat across North America.

  • Investigate the reproductive tendencies of trembling aspen, including the factors that lead trembling aspen to populate in large numbers.

Key Terms

Catkins / Coniferous Tree / Clones / Deciduous Tree / Dioecious / Germination / Root Sprouting / Stands

See content or Module Glossary for definitions

Indigenous Groups Referenced in this Section

  • Anishinaabe (Ojibwe, Chippewa, or Saulteaux): ah-nish-ah-na-bay - The Eastern Woodlands, the Great Lakes, and westward across the Subarctic.

  • Denesųłiné: de-nay-suh-lin - The subarctic interior of present-day Alaska and northwestern Canada.

  • Innu (Montagnais): - The eastern portion of what is now known as the Quebec-Labrador Peninsula.

  • Kanien'kehá:ka (Mohawk): gan-yan-geh-ha-ga - Southeastern parts of present-day Ontario and Northern New York State.

  • Michif (Métis): - Extends across what is now Southeast Ontario, Manitoba, Saskatchewan, Alberta, Northeast British Columbia, and the southern part of the Northwest Territories.

  • Mi'kmaq (Micmac): mii-gê-maw - The Atlantic provinces now referred to as Nova Scotia, Prince Edward Island, New Brunswick, the Gaspe Peninsula of Quebec, and the Northeastern region of Maine in the United States.

  • Nakoda (Assiniboine): - Across the prairies of present-day Saskatchewan and Alberta.

  • Nehiyaw (Cree): nay-hee-ow - Across the prairie provinces and parts of what is now Ontario and Quebec.

  • Niitsitapi (Blackfoot): neet-sih-ta-pī - Parts of what is now southern Alberta, Saskatchewan, and northern Montana.

  • Secwepemc (Shuswap): suh-wep-muh - South-central interior of what is now British Columbia.

Trembling Aspen

Trembling aspen is one of the most widely distributed tree species native to North America, ranging from the tip of northern Canada through the United States and into Mexico. The scientific name for North America's trembling aspen is Populus tremuloides and they are a deciduous tree, meaning their leaves change colour and fall off in the autumn season. A single trembling aspen tree typically does not survive more than 150 years but it can live for more than 200 years and grow up to 20-25 m (65-80 ft). The diameter of the trunk is usually around 20 to 80 cm (8 inches to 2 feet 7 inches). The tallest trembling aspen recorded was 36.5 m (119 ft, 9 in) and 1.37 m (4 ft, 6 in) in diameter.

Trembling aspen are called as such due to their leaves. When you closely inspect a trembling aspen leaf, you should be able to notice how narrow the stem of the leaf is. When the wind blows, these leaves can easily be influenced to move and as such, you hear the trembling sound and see the leaves quivering in the wind. Aside from the trembling aspen title, they are also identified by many other names (see the table below). There is a closely related aspen species across the sea known as Populus tremula, whom European peoples have also referred to as quaking aspen because of the leaves’ tendency to quake or tremble.

Trembling Aspen Names

English name: Trembling Aspen

French name: Peuplier faux-tremble

Genus: Populus

Species: Populus tremuloides

Synonyms: Quaking Aspen, Quivering Aspen, Shivering Plant, Wagging Tongue, Golden Aspen, Mountain Aspen, Quakies, American Aspen, Trembling Poplar

TREE Video on identifying trembling aspen: http://bit.ly/TREE_Identifying

Other Poplar Species

The trembling aspen is not the only poplar species that can be found in Canada. Listed below are 5 other species that are related to Populus tremuloides. It is important to note that the common name, White Poplar, is sometimes used to refer to anyone of the species listed below. Someone on the east coast of Canada might identify one of these species of tree as white poplar while someone on the west coast or the prairies or up north will be referring to a completely different species when they use the name, white poplar. For this reason, the TREE program will avoid using this common name and use either trembling aspen, Populus tremuloides, or an Indigenous pronunciation when referring to the poplar tree this program focuses on.

  • Populus balsamifera: the balsam poplar

  • Populus deltoides: the eastern cottonwood or necklace poplar

  • Populus grandidentata: the large-tooth aspen or white poplar

  • Populus nigra: the cottonwood poplar, commonly referred to as black poplar

  • Populus trichocarpa: the black cottonwood or western balsam-poplar

Explore the Poplar/Populus Species

Learn more about the variety of species in the Populus family by clicking the link here: https://en.wikipedia.org/wiki/Populus

How to Say "Aspen" in Various Indigenous Languages

There are approximately 70 - 90 Indigenous languages spoken across what is now Canada. Each Indigenous language is a part of a distinct language family. The umbrella term for a language family, such as Algonquian, has a group of languages that derive from it. For example, Néhiyawéwin (Cree) and Innu (Montagnais) are two languages that are a part of the Algonquian language family. Languages that are related via the same language family may exhibit similarities in the names they use for nouns like aspen. Listed in the chart below are ten ways to say "Aspen"* in ten Indigenous languages across Canada**.

How to Say "Aspen" in Various Indigenous Languages

*Where possible, the word is hyperlinked to an audio recording of a language speaker saying "aspen" in that language. In other cases, the pronunciation is listed in parentheses. If no pronunciation could be found, the word stands alone.

**The ten languages included above are based on availability of resources (time and accessibility to information). In future editions of TREE, the aim is to expand this list to include more Indigenous languages. Please forward any websites or informative resources regarding Indigenous languages to education@lightsource.ca.

How to Identify Trembling Aspen

Trembling aspen are characterized by a large variety of traits found in their canopies, trunks, roots, growing habits, and seasonal changes. It is important to note that they have a close relative, the black poplar or Populus nigra, and it can be easy to mix up the two. Distinguishing characteristics of black poplar trees are that their bark is most often dark brown but can appear black and is thick. Sometimes it fades to white, the higher the tree grows. As well, black poplar leaves are similar to white poplar but have more of a spade shape and are usually larger. See Figure 7 for an image of a black poplar tree. The following lists describe characteristics of parts of the white poplar tree, which is the tree this program will focus on.

Figure 7 shows a black poplar. Notice the difference in the bark from this image to the one below. Image by harum.koh.
Figure 7 shows a black poplar. Notice the difference in the bark from this image to the one below. Image by harum.koh.

TREE Student Field Book

Information in this section will help students fill out the Student Field Book when collecting your samples.

Root

Trembling aspen roots are characterized as having:

  • A shallow growing depth.

  • A wide growth, up to 3 times wider than the tree's height.

  • A common root system among clones (explained in sections to follow).

Trunk

Trembling aspen trunks are characterized as having:

  • A long and smooth cylindrical base with little tapering (becoming narrower towards the end).

  • Little to no branches in the lower section closest to the ground.

  • Bark that appears smooth and waxy with a pale green to white colour (see Figure 8).

  • Dark horizontal lines that furrow (creates a groove) with age.

  • A diameter up to about 40 centimeters wide.


Figure 8 shows a stand of trembling aspen, with their distinct white bark. Image by Zion National Park.
Figure 8 shows a stand of trembling aspen, with their distinct white bark. Image by Zion National Park.
Figure 9 shows trembling aspen leaves. Image by James St. John.
Figure 9 shows trembling aspen leaves. Image by James St. John.

Canopy

Trembling aspen canopies are characterized as having:

  • A short-rounded shape.

  • A height up to 25 meters above ground.

  • Leaves roughly 3 to 7 centimeters long that are smoothly triangular in shape (heart-shaped), with a narrowed stem longer than the leaf (Figure 9).

  • Leaves that appear deep green from above, pale green from below, and turn yellow and occasionally red in autumn (Figure 10).

  • Leaves that tremble in the slightest breeze, giving the name trembling aspen.

Figure 10 shows a trembling aspen canopy in the autumn. Image by Fairsing.
Figure 10 shows a trembling aspen canopy in the autumn. Image by Fairsing.

Catkins

Trembling aspen are dioecious, meaning they have male and female reproductive organ, called catkins, on separate trees (see Figure 11). Catkins are characterized as having:

  • A cylindrical shape and a fuzzy appearance.

  • A length of 2 to 3 centimeters for males and 4 to 10 centimeters for females.

  • Tufts of hair covering thousands of seeds.

Buds

Trembling aspen grow their leaves and catkins from a bud (Figure 12). Buds are characterized as having:

  • A dark reddish-brown colour, with 6 to 7 shiny scales covered in resin.

  • A conical, pointed shape where the tips of the scales point inward.

  • A typical length of 6 to 7 millimeters, with catkin buds being longer than leaf buds.

Figure 11 shows a catkin covered in hairy seeds. Image by Kaz.
Figure 11 shows a catkin covered in hairy seeds. Image by Kaz.
Figure 12 shows the distinct dark red buds of a trembling aspen. Image by Matt Lavin.
Figure 12 shows the distinct dark red buds of a trembling aspen. Image by Matt Lavin.

How do Trembling Aspen Reproduce?

Trembling aspen reproduce through seeds or through root sprouting.

Seeds

Seeds develop on flowers called catkins (refer back to Figure 11) and the wind takes them to find the opposite reproductive organ. Reproduction through seeds produces trees with unique genetic makeup but is the least successful method due to the following reasons:

  • Pollen from male catkins must use the wind to find and fertilize female catkins.

  • Seeds from the fertilized female catkins use the wind to find soil with just the right conditions (water, elements, sunlight, etc.) to allow for germination (the growth of a plant from a seed).

  • Seeds lack protection or stored nutrients, so they are viable for a very short time.

Root Sprouting

The most common and successful way for trembling aspen to reproduce is by root sprouting. In this process, new aspen trees sprout from the roots of a mature aspen tree. These trees have a shared root system, which enables a process called root sprouting. Root sprouting produces numerous trees or clones with identical genetic information, leading to a colony of trembling aspen. Colonies can consist of a few to hundreds of identical trees.

Where do Trembling Aspen Grow?

Trembling aspen grow all across North America (see Figure 13). They are characterized as growing in a shade-less clearing, in sandy or gravelly soil that is rich in calcium, and in moist soils except in the wettest of soil sites. They are also an aggressive pioneer species, meaning they are the first tree species to colonize areas disturbed by fires, landslides, insect outbreaks, logging, and mining. For example, in the Central Rocky Mountains, the extensive group of aspen are usually attributed to repeated wildfires. They may dominate a site until replaced by less fire-enduring but more shade-tolerant coniferous tree, which are trees that have needles instead of leaves (such as pine trees).

Figure 13 shows the habitat of trembling aspen across North America, as shaded in (Green). Image by U.S. Geological Survey.
Figure 13 shows the habitat of trembling aspen across North America, as shaded in (Green). Image by U.S. Geological Survey.

What is a Stand?

In forestry, stands are areas within the forest that have been measured, mapped, outlined, and described as a distinct group of trees. Stands can be large or small, ranging from a few acres to hundreds. Trees within a stand will share similar characteristics such as age, size, condition, and species. Often, stands are defined by species dominance. For example, in an area with an abundance of trembling aspen trees, this becomes known as a trembling aspen stand.

A trembling aspen stand is what appears to be a group of individual trees, but are all connected via the same root system. Scientists have described trembling aspen stands as clones, or clonal stands, because of their reproductive tendency to sprout new stems from the same lateral roots, thus creating a shared root system with genetically identical trees (see Figure 15).

Trembling aspen stands can grow as a single-species stand or in a mixed-species stand. As stands with a single species age, more shade tolerant species may grow within that stand. This occurrence produces a mixed species stand that can include white spruce, black spruce, balsam fir, white birch, balsam poplar, and jack pine.

Figure 14 shows a mountainside covered in clonal colonies of trembling aspen. Each clone stand is identifiable by the difference in timing when turning to their autumn colours. Image by Beeblebox.
Figure 14 shows a mountainside covered in clonal colonies of trembling aspen. Each clone stand is identifiable by the difference in timing when turning to their autumn colours. Image by Beeblebox.
Figure 15 shows how a trembling aspen clone develops. Image by M. Grant & J. Mitton.
Figure 15 shows how a trembling aspen clone develops. Image by M. Grant & J. Mitton.

Additional Information about Clonal Aspen Stands

An aspen clone is a single tree that sends out individual stems from its roots (see Figure 15). If left undisturbed, these stems eventually grow into aspen trees. While the trees themselves are individuals, the root system is the same, meaning the trees connected to the same root system have identical DNA. Although the average lifespan of a single aspen tree is 150 - 200 years old, a clone can survive for thousands of years because of its ability to sprout new stems from its roots.

Aspen clones can cover a wide range of land from less than 1 acre to more than 100 acres. There can be a single clone in an area or there can be multiple (see Figure 14). When there are multiple clones in a single area, the stands are distinguished by various traits such as bark character, leaf shape and size, or resistance to disease. Autumn leaves offer the clearest indication of there being numerous clones in a single area. For instance, a clone may turn colour earlier or later or show a different fall colour than surrounding clones. In the spring, clones will produce leaves at different times and will pollinate at different times.

The Pando Clone

The Pando clone is one of the largest organisms on Earth and is located in Fishlake National Forest in southern Utah. In Latin, "pando" literally means "I spread." Also known as "The Trembling Giant," the Pando clone consists of 47,000 aspen trees spanning across roughly 100 acres. The total weight of the Pando clone is more than 13 million pounds! The general consensus on Pando's age is 80,000 years old, though some scientists argue it is closer to 1 million years in age. The typical age of aspen clones ranges between 5 years to 10, 000 years old while a single aspen tree averages a lifespan of 150-200 years old.

Figure 16 shows a small portion of the massive organism that is Pando. Image by J Zapell.
Figure 16 shows a small portion of the massive organism that is Pando. Image by J Zapell.

What Makes Up an Aspen Lesson

Identify trembling aspen characteristics and threats to this tree in this activity. Lessons can be downloaded and adapted from here: https://bit.ly/3DdJggV

Additional Resources & References for Section 1.2

Resources

References

Government of British Columbia. (2019). Trembling aspen: Populus tremuloides. Retrieved from https://www.for.gov.bc.ca/hfd/library/documents/treebook/tremblingaspen.htm

Native American Totems. (2012). Plant totem: Quaking aspen. Retrieved from http://native-american-totems.com/plant-and-mineral-totems/plant-totem-quaking-aspen/

Natural Resources Canada. (2015). Trembling aspen. Retrieved from https://tidcf.nrcan.gc.ca/en/trees/factsheet/58

U.S. Forest Service. (n.d.). How aspen grow. Retrieved from https://www.fs.fed.us/wildflowers/beauty/aspen/grow.shtml

Wikipedia. (2019). Populus tremuloides. Retrieved from https://en.wikipedia.org/wiki/Populus_tremuloides