Scientific Name
Populus tremuloides ‘Aspen’
If Colorado’s state tree needed to be a deciduous species rather than a conifer, it would likely be the aspen, also commonly known as quaking aspen or trembling aspen. Roughly three quarters of the aspen’s native range lies in Canada, with the remainder extending through the northeastern United States and the Rocky Mountains, Cascade Range and Sierra Nevada.
Most visitors to the Regis Arboretum already recognize this tree. Aspen is easily identified by its smooth white bark with gray-green tints and the dark “eyes” left behind where old branches once grew. Its rounded leaves have pointed tips and flattened stems that allow them to flutter in even the slightest breeze. In fall, the leaves often turn a brilliant yellow.
Aspens usually grow in large groups called groves, which are often clones connected by a shared root system. The typical growth habit is a narrow oval form that may branch low in open settings, while trees growing in crowded groves usually develop tall, slender trunks without lower branches. Aspens commonly reach 50 to 60 feet tall, though much larger specimens exist in Colorado. Champion trees exceed 100 feet in height and have trunks more than 3 feet in diameter.
Individual trees can live more than 80 years, though the root system often produces replacement stems nearby before an older trunk dies. Because of this continual regeneration, it is not entirely accurate to think of the parent tree as dying in the traditional sense. This clonal process can continue for thousands of years. Some groves, such as the famous “Pando” grove in Utah, are considered among the world’s largest living organisms by weight, land area and number of stems, estimated at around 47,000. The organism is believed to have originated at least 10,000 years ago.
Aspen is not especially well suited to Front Range urban landscapes because of summer heat and sensitivity to drought stress. It can also spread aggressively through root suckers, particularly when the roots are disturbed. Foliage diseases and insect pests may further shorten its lifespan in urban settings, sometimes to as little as 20 years. However, aspens grow successfully in Colorado’s mountain towns, where summers are cooler, and they tolerate the low temperatures and short growing seasons found at high elevations remarkably well.