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by David Lukas

The most widely distributed tree in North America is a mystery. Called quaking aspen for the trembling of its leaves, it is anything but timorous or fragile. It is unfathomably ancient and enduring, approaching what has been called "theoretical immortality." It is a lifeform persisting over time without offspring, in suspended animation, waiting patiently through the dark passage of millennia for something we can only guess at.

This is a species surviving in the apparent absence of sexual selection, living thousands, if not millions, of years between periods of successful reproduction. Would there be a theory of evolution if Darwin had picked as his object of study not the dazzling variety of forms found on tropical islands or in domestic pigeons, but the strange entity known as quaking aspen?

During the summer of 1996 a group of us at Art of the Wild, the annual Squaw Valley nature writing program, stopped on the morning nature walk in a spindly grove of aspens. It was hardly a stop designed to inspire awe. This tree, whose flaming autumn displays blanket millions of acres in the interior West, was here represented by a scattering of gnarly little suckers.

Because we were a group of writers and poets with an eye for nature, our interest meandered through both the linguistic and poetic possibilities of aspen terminology. After five summers of leading these walks in Squaw Valley, I savor the roll of "theoretical immortality" on my tongue and the effect this novel idea has on newcomers. Writers, and poets especially, are rapacious carnivores of playful language and the pens immediately come out to capture this morsel.

I think one's first inclination upon approaching a quaking aspen is to touch the bark. The tree looks and feels like it has been stripped naked or skinned alive. Do you avert your eyes out of reverence or stroke the exposed ivory skin in rapture? It is unbelievably smooth and delicate, easily cut and scarred. Fungi, gnawing rodents, burning sunbeams, and knife-wielding humans readily leave their mark. Old-time Basque sheepherders in the Great Basin discovered that carved messages last for decades in aspen bark and their homesick paeans still hang like whispers in remote mountain canyons.

One moves next to the dance of light, to the branches where shimmering leaves twist and clatter in the wind on their pliable petioles. Grasping a branch and pulling it in close, you could see how each leaf balances precariously on its curiously flattened stem. Does it wobble for a reason, to shed snow or to capture sunlight? The sound of quaking aspen leaves is one of the species's most distinctive features.

The generic name of aspen, Populus, is from a Latin word meaning "people, a great number," for the similarity between the continuous motion of a crowd and the trembling of leaves. The word "aspen" is itself an old word, encoded in some Indo-European languages for thousands of years. Originally the tree was known as "asp" with "aspen" being used as an adjectival form. Metaphorically, the adjective once referred to trembling, especially in fear or anger (as in Chaucer's, "That lyk an aspen leef he quook for ire").

The quaking aspen (Populus tremuloides) was named by the eminent French botanist Andre Michaux in his 1803 Flora Boreali-Americana. The scientific name tremuloides means "like tremula," commemorating its resemblance to the European form (Populus tremula). Subtle geographic variations have led some scientists to split aspens into multiple species, while other scientists have considered assigning all aspens to a single circumboreal superspecies. Given the difficulty of determining the age of individual aspens, the possibility of a close relationship to one ancestral form must be kept in mind.

In Squaw Valley we noticed that the trees in our scraggly patch had a similar crooked recumbent form, as if all had passed through the same environmental sieve. Where are the variations of form that characterize Darwin's struggle for survival? Aspens are in fact highly variable, ranging from stately Roman temple-like columns 100 feet high, to convoluted bonsai-like shrubs. These forms however, occur in discrete groves of uniform shapes much like the one in Squaw Valley.

Aspens call our whole concept of what we call a tree into question; only as a young seedling does the plant approximate a typical "tree" with a single trunk and simple root system. As the seedling (referred to as an ortet) grows, it sends out lateral roots that may extend over 100 feet in many directions. These roots possess an enormous potential for suckering, that is, sending up shoots much like a potato does. Suckers grow into woody stems that superficially resemble individual trees. One seedling eventually expands to as many as 47,000 genetically identical stems arising from a parent root system, and may cover over 100 acres. Suckering is the primary method of aspen propagation, as successful seedlings are extremely rare or unknown in many areas of the West.

The distinct stand of aspens in Squaw Valley captured the group's attention because each and every aspen, from one foot to twenty feet tall, had the exact same characteristics: twisting, knotting, and bending stems, creating an illusory stair step to the sky. Here was a perfect example of suckering. Each of these stems (each a sucker) was feeding off the same root system, hence each had the same genetic structure, and the health of each one depended on the health of the whole root system.

This parent root system is in essence the "tree," and the visible stems (known as ramets) are branches that turn upward into the sunlit world to feed. The root system is a very dynamic entity, able to transport water and nutrients from areas of excess to stems in need. In the spring it acts as a carbohydrate pantry, feeding new ramets until they grow enough to begin harvesting sunlight energy on their own. Grown ramets in turn export carbohydrates back to the root system for the next winter's supply.

The root system is also an adventitious and adventurous explorer, continually sending out roots ripe with possibility. As long as stems with viable leaves keep sending messages in the form of auxins the roots lie dormant, but a destructive event like fire, avalanche, or insect outbreak will cut off this signal and activate the roots which then grow upward as new stems into newly available sites. We could thus imagine a root system advancing into favorable areas and leaving less desirable ones behind, migrating as the climate changes over great periods of time.

A grove of genetically identical aspen stems, collectively called a clone, is readily recognized. This is especially easy in early spring or fall, when leaves are budding out or turning color according to the different schedules of each clone. Boundaries between clones are often abrupt and conspicuous. One can walk these boundaries looking for commonalities in leaf shape, bark texture, and stem characteristics, all unique to each clone. While stems themselves live no more than 200 years, clones apparently replicate indefinitely, giving an individual aspen "theoretical immortality." Large clones in the unglaciated wilds of Utah and Colorado are thought to be at least one million years old. Leaves of trees growing on the Columbia and Colorado Plateaus of western North America are nearly identical to those found in the fossil record, suggesting the passage of only a few generations over the course of fifteen million years.

A most remarkable aspect of aspen life history is that this immortal lifespan is coupled with a fervent and thoroughly mortal desire to reproduce. Year after year, for countless millennia, aspens have produced viable seeds in prolific quantities. Many of these seeds germinate, but rare are the seeds that becomes seedlings, so fickle are their needs for a continually moist seedbed during the dry summer season. Some botanists believe that not since the last ice age have conditions been right for seedling survival. If so, aspens are perhaps in an indefinite holding pattern, casting out seeds, waiting for the next ice age. How a species that ranges from Alaska to Mexico and coast to coast can persist without producing new seedlings is somewhat of a mystery. Old clones that die are not easily replaced, yet the species remains common. Some people are nevertheless concerned that human activities have led to a widespread loss of healthy stands. Grazing animals can cause substantial damage by eating young suckers, which eventually depletes the carbohydrate supplies of parent root systems. Timber cutting has led to the loss or damage of stands in many areas, while in other areas suckers are aggressively expanding into meadows and clearcuts.

Aspens rarely establish themselves as seedlings in new areas, so it is possible that their range could diminish over time. The vast majority of sucker stands are "trapped" in the location in which they first established themselves, unable to relocate or ensure their survival with seed dispersal. As the environment has changed over thousands of years, these clones have been unable to adapt, in a Darwinian sense, to new conditions. Whereas Darwin's theory of evolution is based on sexual reproduction and the passing on of genetically fit offspring, aspens survive despite being genetically frozen in time. If they are, in fact, adapting to the environment without altering their genetic makeup, they may offer a unique insight into the process of evolution.

Aspens challenge our imagination. The writers and poets stop taking notes and study the quivering leaves and chalky white bark. I wonder how long this particular stand will survive amongst the encroaching developments and changing landscape of Squaw Valley. "Theoretical immortality" is no safeguard against an uncertain future. We turn up the trail towards Shirley Canyon and wander into the ephemeral beauty of penstemons, Indian paintbrushes, and columbines.

David Lukas is a freelance naturalist and writer living in the Yuba Watershed of the Sierra Nevada. During the summer he is naturalist-in-residence at the Squaw Valley Community of Writers.

This essay was originally published in the Spring 1997 issue of Orion. To order a copy of this issue, please visit The Orion Society Marketplace, call (413) 528-4422, write The Orion Society, 195 Main Street, Great Barrington, MA 01230, or e-mail us at

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