Quaking Aspen (Populus tremuloides)

Location: South east corner of Architecture Hall, just north of the walkway to the Population Health Building.

Summary: The Quaking Aspen is an immensely successful tree species, the most widely distributed species in North America, and fifth most widespread in the world. It inhabits landscapes from the tundra of Alaska to Nova Scotia, and from the midwestern woods to the mountains of the Southwest. Part of this geographic success has to do with the tree’s methods of reproduction. Aspens produce tiny cotton covered seeds like those of their cousins the Cottonwood tree; however, their main method of reproduction is clonal propagation. Aspen groves are populated mainly by trunks which have grown up from the roots of existing trees, thus whole forests of this species are often connected underground. Here at the UW, these sprouts are frequently cut back to adhere to the campus planting plan, but if this maintenance were ceased, we would very quickly have a lovely grove of aspens filling in the space between these specimens.

As a result of their ability to form vast clonal networks, wild Quaking Aspen can be immense, some of the largest living things on the planet. One grove in Utah, representing a single mass of connected trunks and roots, covers an area of about 107 acres. Thus, even though the individual trees may not appear extraordinary, they are but a small part of a grand whole. When an individual tree falls, the life of the aspen continues through all the genetically identical trunks remaining. Because these trees are constantly sending up new shoots even as old ones are dying back, there is speculation that Quaking Aspen may be one of the longest living organisms in the world. Some of these groves may have already survived for as much as 80,000 years, surviving fire, flood, ice ages, droughts, and more thanks to their incredible adaptations. 

Aspens in Washington are mainly concentrated in the eastern portion of the state in areas with adequate year-round water. Indigenous uses for the species include use as a medicine for treating pain and as a natural sunscreen (obtained from the bark). The tree also provides an excellent habitat for many animal species including deer, elk, moose, and beaver, all of which are prized as human food sources.

Historical Background: This species is the most widely distributed in all of North America, and worldwide only four other species have a broader range. A pioneer quick to return following disturbances such as fires, rockslides, and avalanches, this tree reproduces readily from broken stems and from roots, in fact they may reproduce clonally via root suckers as young as one year of age. The adult trees are generally dioecious, meaning there are both male and female individuals (as opposed to monoecious where one tree has both male and female reproductive bodies). While the trees do produce a good seed crop every 4-5 years, seedling survival in nature is limited due to a variety of factors, including competition from the trees growing as clones from the roots of other aspens. Although individual tree may only live from about 50-150 years, the interconnected root system between clones means that as a single organism aspens may live for thousands or even tens of thousands of years. One easy way to observe the size of a single interconnected clone group is to observe groves in fall color. Subtle or extreme differences in the unrivaled autumn display put on this tree can be an indicator of the identity of its whole being. In other words, if one slope of a mountain has aspens which are orange in fall and another has aspens which are red in fall, it is likely that the two separate groves are two separate organisms. Although a single grove may appear as dozens or hundreds of individual trees, it is possible that they are in reality one body connected by roots out of our sight. The twigs and foliage make a favorite forage for deer, elk, and moose, as well as other grazers, and the bark is targeted by beavers, rabbits, and other mammals. The buds in winter serve as still another food source, especially for birds including grouse and quail.

Native

Native Range: Across North America, as far south as Virginia in the east and New Mexico and Arizona in the west. Across the top of the continent they may be found from Alaska to the easternmost reaches of Newfoundland. They also occupy an immense vertical range depending on latitude, from sea level in the north up to greater than 10,000’ (3048m) in the south.

Identifying Features light: This tree is a special one. Known for occupying harsher climates than most species can withstand the opening of buds in spring heralds in a short growing season and adds a beautiful fresh green to the landscapes it occupies, sometimes the only significant vegetation to be seen. The trunks when young have beautiful smooth white bark, flecked with lateral black stripes, becoming deep gray and furrowed with age or environmental stress. Trunks of even the older specimens can be small and twisted, the product of deep snows in winter, a living sculpture, but they can also be arrow straight and immense, growing to heights of greater than 70’ (21m). In fall the nearly round leaves with the abrupt point change from a shiny green to autumn extravagance ranging from bright yellow to the deepest orange. They turn whole slopes into the warm color scheme of a Van Goph masterpiece, an effect especially spectacular if an early snow turns the backdrop to an unblemished white canvas leaving just the fire of the aspens to rage across the landscape. A relative of the black cottonwood, another native, one may draw comparisons between the two, noting that the margins of aspen leaves are wavy and that the long slender petiole of this species is almost flat, causing the whole tree to shake in the slightest breeze (hence the name Quaking aspen). This extremely pleasant effect may be used to identify this species even when its fall glory is not present. In summer one can watch the slopes for a dancing grove and follow that illusion straight to the beautiful and majestic Quaking Aspen.

Identifying Features In Depth:

1. Form: Narrow and rounded crown upon a straight trunk with short branches when conditions are optimal. In more stressed circumstances this species may appear as a bush or shrub, knocked about repeatedly by snow or rockslides, exhibiting twisted and bent trunks and branches.

2. Leaves: Almost round but for an abrupt short point. Venation is palmate, and the margins are finely sawtoothed. The base of each leaf is rounded and the tops are a shiny green, the bottoms a dull green. In autumn they turn a brilliant yellow-gold to orange color. Leafstalks/petioles are long and flattened, causing the leaves to quake in a breeze, possibly a mechanism to aid in transpiration.

3. Bark: White to gray and smooth, growing more rough and smokey gray with age, furrowed and thick at the base of older specimens.

4. Reproductive Bodies: This tree produces brownish catkins between 1-2.5” (2.5-6cm) long in the springtime before new leaves. The male and female catkins appear on separate trees. Fruits are .25” (6mm) in length, conical and light green in color. In late spring they split into two parts releasing many cotton-fluff seeds (although these are rarely seen in this species western range).