ASPENS AND ASPEN COLONIES

The aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high-altitude areas such as mountains or high plains. They are all medium-sized deciduous trees reaching 15–30 m (49–98 ft) tall. In North America, it is referred to as Quaking Aspen or Trembling Aspen because the leaves "quake" or tremble in the wind. This is due to their flattened petioles which reduces aerodynamic drag on the trunk and branches.

Aspens typically grow in environments that are otherwise dominated by coniferous tree species, and which are often lacking other large deciduous tree species. Aspens have evolved several adaptations that aid their survival in such environments. One is the flattened leaf petiole, which reduces aerodynamic drag during high winds and decreases the likelihood of trunk or branch damage. Dropping leaves in the winter (like most but not all other deciduous plants) also helps to prevent damage from heavy winter snow. Additionally, the bark is photosynthetic, meaning that growth is still possible after the leaves have been dropped. The bark also contains lenticels that serve as pores for gas exchange (similar to the stomata on leaves).
Aspens are also aided by the rhizomatic nature of their root systems. Most aspens grow in large clonal colonies, derived from a single seedling, and spread by means of root suckers; new stems in the colony may appear at up to 30–40 m (98–131 ft) from the parent tree. Each individual tree can live for 40–150 years above ground, but the root system of the colony is long-lived. In some cases, this is for thousands of years, sending up new trunks as the older trunks die off above ground. For this reason, it is considered to be an indicator of ancient woodlands. One such colony in Utah, given the nickname of "Pando", is estimated to be 80,000 years old,[3] making it possibly the oldest living colony of aspens. Some aspen colonies become very large with time, spreading about 1 m (3.3 ft) per year, eventually covering many hectares. They are able to survive forest fires, because the roots are below the heat of the fire, and new sprouts appear after the fire burns out. The high stem turnover rate combined with the clonal growth leads to proliferation in aspen colonies. The high stem turnover regime supports a diverse herbaceous understory.
Aspens do not thrive in the shade, and it is difficult for seedlings to grow in an already mature aspen stand. Fire indirectly benefits aspen trees, since it allows the saplings to flourish in open sunlight in the burned landscape, devoid of other competing tree species. Aspens have increased in popularity as a forestry cultivation species, mostly because of their fast growth rate and ability to regenerate from sprouts. This lowers the cost of reforestation after harvesting since no planting or sowing is required.
Recently, aspen populations have been declining in some areas. This may be due to several different factors, such as climate change, which exacerbates drought and modifies precipitation patterns. Recruitment failure from herbivory or grazing prevents new trees from coming up after old trees die. Additionally, successional replacement by conifers due to fire suppression alters forest diversity and creates conditions where aspen may be at less of an advantage. Sudden aspen death is also occurring more often as a result of drought stress.
In contrast with many trees, aspen bark is base-rich,[clarification needed] meaning aspens are important hosts for bryophytes[4] and act as food plants for the larvae of butterfly (Lepidoptera) species—see List of Lepidoptera that feed on poplars.
Young aspen bark is an important seasonal forage for the European hare and other animals in early spring. Aspen is also a preferred food of the European beaver. Elk, deer, and moose not only eat the leaves but also strip the bark with their front teeth.