UPDATE on ERVCC’s Trembling Aspen Project…

ERVCC wanted to identify a clone of Aspen in the valley that we could then name just like the Pando clone in Utah. We had a community service learning student from the University of Alberta (Jack Mossey) who led us to relevant experts. However, after talking to the forestry genetics expert (Barb Thomas of U of A) and an expert in genetic testing (Susan Koziel of Innotech Alberta), we realized the project could be prohibitively expensive. We also learned from expert Raiany Dias de Andrade Silva, PhD, that the Trembling Aspen stands in Edmonton are complex, complicated, and very tricky. We came to understand that even after extensive testing, we might not have a full picture or a full story to tell regarding any particular stand of Aspen.

With the help of Raiany, we have shifted our project into an invitation—an invitation to find wonder in the complexity of one of our valley’s more common trees. Instead of genetic testing, we are now planning to host a field trip and didactic session. Stay tuned.

ERVCC thanks Raiany for helping us ensure the following narrative is scientifically accurate.

TREMBLING ASPEN (Populus tremuloides)

A tree that is often clonal in its reproductive nature can challenge our concept of a tree and make us fall further in love with the beauty of our kin, the river valley’s Trembling Aspen. What do we mean by “clonal”? Think of a tree that makes “babies” by sending up new shoots off an existing root system. Gardeners might call this form of reproduction “suckering.” Aspen also produces seeds. During dispersal, the cottony aspen seeds drifting through the air look like snow in the spring sunlight. Beauty aside, aspen seeds are tiny, and their successful establishment in nature is a rare event. That is why aspen is considered a clonal tree species. Aspen seeds have a higher chance of growing into seedlings if they fall in cleared areas, without competition from other plants, and with sufficient moisture.

Look at the picture below. Do you see a tree or a whole bunch of trees?

The people who named the tree stand above saw all of the vertical trunks as one large tree. It’s a stand sharing the same DNA: clones of one old Trembling Aspen. The tree stand was genetically tested and found to be exact copies of one DNA type that had spread out across the land to form 106 acres of what is effectively a single aspen “tree”. It is thought that some of the root system dies and is renewed underground. The above-ground shoots or “trees” also get “born” and die. The clonal trunks then end up being of different ages and sizes and not as old as the original root system,  but they all still share the original genes. This is why the locals saw this stand of clonal aspen as one “tree” and named it Pando. They understood the trembling aspen was not only a beautiful tree that dances in the wind, but a tree that can often be very old, very large and most likely, very wise.

Regardless of whether you see one tree or many trees, we hope you start looking at stands of Trembling Aspen in our river valley and appreciating them more deeply. ERVCC wants Trembling Aspen to be better seen, loved, and honoured. 

Trembling Aspen is native to our cool, Edmonton climate, but it is also the most widely distributed tree species in North America, ranging from the east to the west coasts and from Alaska all the way to Mexico. Aspen stands differ throughout North America; aspen clones in the western part of the continent are generally much smaller than the famous Pando. In Alberta, to be more specific, large aspen stands tend to have higher genetic diversity, which means that they have a few different clones within a stand. Some of these may be members of an aspen family, such as full siblings and half-siblings, while others may arise from old roots that have remained from long-lost trees that once grew in the landscape years and years ago.

Rainbow Sexual Expression

Aspen trees are also dioecious, meaning that generally only female reproductive parts exist on female trees and only male parts on male trees. However, bisexual trees, hermaphroditic flowers and even sex change can occasionally occur. You will have to look to another river valley tree, the Larch, to find an example of a tree that has both sexes on the same tree. Larch trees and other trees with both sexes found within the same tree are called monoecious.

The Trembling Aspen tree, as stated, mostly has reproductive parts from just one sex or the other. This singularity allows for the visual identification of aspen clones, as clones generally share the same sex. In most cases, rather than reproduce sexually with the help of the wind and other pollinators, aspen most often reproduce by budding off the root system to form a new tree. It is in this manner that it can produce a large stand of shoots all sharing the same genes (and sex), often with a shared root system, creating clonal stands like Pando, though in our river valley, the stands would likely be smaller.

Culturally Significant

First Nations of amiskwaciy-wâskahikan have a long relationship with aspen. The tree was and continues to be used for ceremony, food, medicine, and wood. Settler Gladys Reeves picked the aspen as one of the first trees to transplant onto Edmonton’s boulevards as part of a 1923 beautification movement. It is of interest that the “Populus” in Populus tremuloides comes from the Latin word for “people,” reflecting how commonly the tree was planted in public spaces like central squares. P. tremuloides may no longer dominate city boulevards, but it stands proudly and predominantly in our river valley.

Fascinating Genetics

With Pando, it is thought that the root system is as old as the oldest stem (tree), because the root system below ground receives as much renewal as the above-ground growth. The individual genotype of Pando, however, has likely been around since the last glaciation. So, Pando is not strictly a single organism, but has reproduced and renewed asexually from the same genetic origins. Regardless, aspens truly challenge our concept of what we mean when we say “tree.” For instance, more recently, genetic analyses have been used to determine clonal relationships in aspen trees within the same stand. Such analyses have shown that stands that appear different, based on aspects such as spring leaf out, bark texture, and fall colours, for example, may share similar genetic origins. And some genetically unrelated aspen trees may look similar, due to shared site characteristics (like soil moisture, drought, competition, insect defoliation, etc.)

Only genetic testing can confirm whether an aspen stand is made up of trees from the same clone or if it is a genetically diverse stand. Genetic testing is highly costly, and it still may not provide definitive answers, as scientists are still working to understand certain mechanisms in aspen, such as their sex expression.

What a mystery these trees are!

ERVCC is interested in having river valley enthusiasts report aspen they suspect to be clonal, or any stands that are interesting to you for other reasons. Maybe instead of a clone, you discover a mix of males, females, and bisexual trees, indicating a diverse stand. We would also love to receive photographs of your favourite stand.

ERVCC wonders what an appropriate ceremony for the aspen in our valley might be. It would be lovely to honour the tree yearly - perhaps we can ask an Elder to assist us with a naming ceremony for one Aspen stand. Another conservation group in Edmonton, The Long Tree Society, is asking how Edmonton can foster a culture that is prepared to steward trees that can live for over 1,000 years. ERVCC believes this kind of cultural work is essential to properly honour, steward, and learn from our river valley - and our river valley kin.

So, the next time you walk by a group of aspen trees in the spring, and you see they are all the same sex, they might be a clonal stand. If you believe you have spotted one, we’d love to hear from you.

Below are some tips for spotting a possible clone, but remember, looks can be deceiving. Aspen is are tricksters:

· They leaf out at the same time

· They are all the same sex

· They change colour at the same time in the fall

For identification help on how to discern if a Populus tremuloides is a girl or a boy, please go to the website of Plant Watch, run by ERVCC member Elisabeth Beaubien.

It would take quite a lot of observation and research to truly understand what we are seeing in Edmonton’s river valley when it comes to these beautiful aspen stands. Let’s at least try to understand their story and learn about them together!