Section 1.2: Trembling Aspen 101
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.
Catkins / Coniferous Tree / Clones / Deciduous Tree / Dioecious / Germination / Root Sprouting / Stands
See content or Module Glossary for definitions
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
Species: Populus tremuloides
Synonyms: Quaking Aspen, Quivering Aspen, Shivering Plant, Wagging Tongue, Golden Aspen, Mountain Aspen, Quakies, American Aspen, Trembling Poplar
Connect with Indigenous Groups
Indigenous groups in your area may have knowledge in trembling aspen. Check out our Indigenous Engagement Starting Points resource to learn how to connect: https://bit.ly/3eENsyn
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 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.
TREE Student Field Book
Information in this section will help students fill out the Student Field Book when collecting your samples. Click here to download a copy: https://bit.ly/3Bgxgw5
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).
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.
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.
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.
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.
Identifying Trembling Aspen Resource
Check out this resource which further highlights how to identify aspen: https://bit.ly/3zF86X3
How do Trembling Aspen Reproduce?
Trembling aspen reproduce through seeds or through root sprouting.
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.
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).
Connect with Indigenous Groups
Indigenous groups in your area may have knowledge where trembling aspen grow. Check out our Indigenous Engagement Starting Points resource to learn how to connect: https://bit.ly/3eENsyn
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.
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.
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 the link: https://bit.ly/3DdJggV
Additional Resources & References for Section 1.2
Case Study: The Glorious, Golden, and Gigantic Quaking Aspen: https://www.nature.com/scitable/knowledge/library/case-study-the-glorious-golden-and-gigantic-13261308/
An online article that discusses the general characteristics of quaking aspen, the reproduction processes of these trees, and how clone species develop.
Government of BC: General Trembling Aspen: https://www.for.gov.bc.ca/hfd/library/documents/treebook/tremblingaspen.htm
Website from the Government of BC that covers the general characteristics and uses of trembling aspen.
Natural Resources Canada: Trembling Aspen: https://tidcf.nrcan.gc.ca/en/trees/factsheet/58
Government of Canada website that covers general characteristics of trembling aspen, insects and diseases that impact these trees, and this website has a collection of aspen images.
US Department of Agriculture: How Aspens Grow: https://www.fs.fed.us/wildflowers/beauty/aspen/grow.shtml
United States Department of Agriculture, Forest Service website on how aspen grow, how they reproduce, and why they have the name of quaking or trembling aspen.
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