Aspens: The Ever-Renewing Tree

I keep a variety of notebooks for journals, musings, what’s in bloom and which birds have arrived (in 2026: sandhill cranes on March 30, turkey vultures on March 31). Sometimes I wonder about the value of all this spiral-bound paper — I have boxes of old journals that I may never open again. Do I care when I picked the first snow peas in my garden in 1989?

This year, the weather has captured my attention, with a mix of joy at finding early wildflowers on a warm March afternoon and dread about the summer ahead with its threat of wildfires, heat waves, water shortages, and stress for fish, wildlife and people. On the last day of March, I woke to rain pecking at the window, and felt at least one layer of worry leave my chest. More raindrops have arrived in early April.

Before this rain, the air was filled with dust. A month before their usual time, the aspens have bloomed heavily, as conifers do under stress. Their staminate catkins are beautiful when they’re backlit by the morning sun as they dangle from the trees like silver-drop earrings, and they look a bit like prayer flags when the wind blows them horizontal.

Most years, the catkins fall just before the leaves appear, in early May. Before the end of March this year, the aspens in my yard shed most of their spent catkins and new leaves appeared. If they emerge too early, a hard frost can freeze their tender tissues. In years when this has happened, the aspens try again, often forming leaves that are larger and fewer than normal. The extra energy expended on leafing out more than once must be hard on them.

How the aspens will fare is among many concerns about the coming season. While many of the forests in Greater Yellowstone are dominated by conifer, aspens form long-lived and extensive plant communities in the Bridger-Teton and Caribou-Targhee national forests. Beyond sheer beauty, aspen is an important part of the community of life. Scientists report that aspen forests are far more diverse than any other vegetation type in our region.

Unique to aspens is their incomplete period of dormancy. They continue to produce chlorophyll all winter, a handy attribute for a tree that holds leaves for only a few months. Under their white outer bark is a photosynthetic layer that produces sugar. I often see tooth marks on aspen trunks left by elk and other wildlife, and have been told many times that this bark is eaten only when the elk are out of food and desperate. In fact, the bark is a favored delicacy, like having green grass instead of dried up hay. When I sit on a newly fallen log, I notice fresh grooves made by teeth, as if the elk were waiting around for an aspen to fall over so they could feast.

I also find numerous scars from bears climbing the aspens. My guess is that the do it for fun, and because the bark is softer than that of a spruce, the bears have an easier time of getting a claw in.

An aspen forest conserves water in the soil and helps keep that soil in place. It’s more fire-resistant than terpene-rich conifers, so it can slow or stop a wildfire.

For a natural history book I wrote, my research found that aspens in the Cache Creek drainage near Jackson serve many of what are now called “ecological services” for birds, insects, mammals, soil microorganisms, and other forms of wildlife. Though specific to this small area, the same applies regionwide.

Most of us have heard of, and perhaps visited, a famous aspen clone that grows in Central Utah: the Pando. (Pando comes from the Latin, which refers to its extensive geographic spread.) Like all clones, this 106-acre clone originated from one seed. Pando is often referred to as the largest organism on earth, and perhaps that’s true of terrestrial ones. There’s a seagrass clone off Australia that’s over 112 square miles and still growing. Like the Pando, its estimated age is in the thousands of years.

Aspen clones in the southern Greater Yellowstone area are considerably smaller than the Pando, perhaps because of establishment of many plants from single seeds in the same area after the Ice Age. Some of my favorites among them flow in waves of taller and shorter trees, clones that leaf out in May next to those that remain bare until the start of June; those that turn yellow in mid-September next to others that remain green. Each season displays a patchwork of aspens on a mountainside, and I can stand across a creek valley and pick out the various clones within the larger forest by their colors, branching patterns, and differences in timing of when leaves open or fall.

Wandering through one of these forests offers a close-up of the differences among clones. Some trunks are straight with branches spreading at the same angle. Others are twisted and fanciful in appearance. Some are susceptible to canker and shelf fungi, while others seem to resist them. And, as our warm days are about to show us, aspens in springtime are as spectacular as they are in fall, their bright lime-green glowing as though from a source within.

Regardless of the time of year, whenever I visit a wild stand of aspens, a sense of wonder fills me. I’m impressed by their hardiness, longevity, and resilience as much as their beauty. While we call aspens “trees,” what grows above ground are more aptly labeled “stems.” Established aspen stands are much older than their largest stems, which can exceed well over 100 years. The organism remains as the older stems fall and are replaced by new ones. As long as climate and moisture levels allow, and disturbances such as heavy browsing by elk or deer don’t weaken it, the lifespan of a single clone is nearly indefinite.

Contemplating the depth of time reflected in an aspen stand takes me out of myself and into a much more expansive point of view. It helps my vision of the world to expand beyond the narrow tunnel of the self.