On the hottest summer day when the air is still and so humid you can barely breathe, the slightest movement of air can stir the leaves of the quaking aspen. The whispering of the leaves provides a small measure of relief from the heat, even if it’s only psychological.
The Latin name for quaking aspen is Populus tremuloides and the reason that the leaves tremble as they do is structural. The petioles, the little stalks that connect the leaves to the stems, are flat and flexible so the leaves act like little fans trembling at the end of the petiole. The leaves are almost heart-shaped, but the top of the heart doesn’t quite dip downward. Leaf edges are very finely toothed.
In summer, the leaves are shiny green above and a dull green, almost sliver, below. They turn a beautiful bright gold in fall, and the bark is whitish in color, making quaking aspens probably the most photographed trees in North America. They are especially popular as September calendar photos.
Quaking aspen has a larger native range than any other tree in North America, crossing east-west over nine time zones and ranging north-south from Canada to Mexico. They are also the largest tree in North America. You might wonder how this can be when surely some of the stately oaks are bigger. Well, quaking aspens grow in colonies with a common root system. The largest single colony in the U.S. is in Utah’s Fishlake National Forest. It has over 47,000 stems, is estimated to weigh 13 million pounds, and covers 108 acres. That is one big tree!
Quaking aspens provide food and shelter for many animals, birds and butterflies. Deer, rabbits, porcupines and beavers eat the leaves and young stems. The flowers of quaking aspen appear in spring before the leaves emerge and are called catkins. These catkins provide food for an array of birds and insects. Beavers use the trunks and branches for dams and lodges. At the end of their lives, dead and rotting aspens provide shelter and food for wildlife and soil microorganisms.
A related tree, big-tooth aspen, is quite similar but has larger leaves edged with rounded teeth. Spring foliage of big-tooth aspen is almost white while the quaking aspen’s is a misty green.
Quaking aspen grows quickly, sometimes 30’ in its first ten years, and ultimately reaches up to 65’ tall. It thrives in both wet or dry soils. Because it grows so fast, its wood is not the strongest and because it tends to colonize it can become weedy, so it is best grown in naturalistic areas rather than as a landscape specimen. Quaking aspen is relatively short-lived as trees go, and 50 years is about all you can expect before they begin to decline. If you have the spot for quaking aspen in your landscape though, the fluttering of its leaves and its beauty will bring you much joy.