Aspen trees are also known as Quaking Aspen trees due to the fluttering of their leaves in the slightest breeze. They are found in Montane forests (from about 5,500 to 9,000 feet elevation) and Subalpine forests (cool wet areas from about 9,000 feet elevation to timberline) in the mountains.
The Aspen leaves flutter so easily because their stems (or “petioles”) are flattened, and attached perpendicular to the leaf, which allows the leaves to easily pivot on their stems.
Aspen trees are found in groves among the mountain conifers and are the primary deciduous trees in those elevations, losing their leaves after they turn gold in the fall. They are common where a gap in the conifers has opened up due to fire or avalanche and a large sunny spot is available for them to grow. At the edges of their growing range, they are frequently found along streams or other wet areas.
Aspen trees can be 18 to 45 feet tall with bright white smooth bark and leaves that are a rounded triangle shape.
The leaves are bright green in the spring and summer, contrasting with the dark needles of the conifers, and turn gold in the fall before falling off.
Scientific Name and Plant Family Information
The Scientific name is Populus tremuloides, referring to the trembling or quaking leaves in the breeze.
It is in the plant family Salicaceae (Willow), which also has Plains Cottonwood trees and poplars along with willow shrubs and trees. A couple of interesting things about this plant family are that the plants have male and female flowers on different plants (dioecious) and the bark has methyl salicylate, from which aspirin was originally derived.
Through the Seasons
In the spring, the female trees produce catkins, which are a dense spike of flowers, about 2-3 inches long.
In the fall, the leaves turn a brilliant gold, bringing out many people into the mountains to see the fall splendor.
In the winter, these tall, straight trees can be recognized by their white bark and bare branches in among the conifers.
Native or Non-Native?
The Quaking Aspen tree is native to this area and grows in the mountains, generally in groves. It can be found throughout central and western Colorado at elevations mostly from 8,000 to 10,000 feet, although it can grow as low as 6,000 feet on shady north-facing slopes and as high as 11,700 feet on protected south-facing slopes.
A Quaking Aspen grove of many trees is actually just one individual, with one network of roots. All the trees in the grove are clones, growing up from suckers from the roots. The roots can survive for thousands of years, waiting for an event to bring a patch of sunlight to the area so they can send up suckers. This is an important part of forest succession as they can grow quickly to become aspen trees once they have sensed the warming ground from the sunlight. When they have grown, their shade provides shelter for spruce and fur trees to grow beneath them and eventually become the dominant trees in the area as they shade-out the aspen trees.
Did You Know?
Many animals rely on Aspen to survive the harsh mountain conditions. Deer and elk eat aspen bark in the winter along with the leaves and new twigs in the other seasons. In Rocky Mountain Park, the Park Rangers have put up fenced enclosures around some Aspen groves to keep out the deer and elk so that the birds and other animals can have Aspen Trees that they need to survive.
Beavers also eat Aspen Trees and use them to build their dams and lodges. Birds such as nuthatches and flammulated owls nest in holes drilled into the bark.
- From Grassland to Glacier: The Natural History of Colorado and the Surrounding Region, by Cornelia Fleischer Mutel and John C. Emerick, 1992
- Botany in a Day: The Patterns Method of Plant Identification, by Thomas J. Elpel, 1967
- Flora of Colorado, by Jennifer Ackerfield, 2015
- Colorado Native Plant Database Data Portal, Colorado State University
- Explore Colorado, a Naturalist’s Notebook, by Frances Alley Kruger and Carron A. Meaney, published by Denver Museum of Natural History and Westcliffe Publishers, 1995
- The Naturalist’s Guide to the Southern Rockies, by Audrey DeLella Benedict, 2008