Aspens and snow on the red cliffs of Redstone, Colorado

Aspen is a common name for trees of the Salicaceae family, most of those in a section, Populus sect. Populus, of the Populus (poplar) genus.

The five typical aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high altitudes in the mountains. The White Poplar, by contrast, is native to warmer regions, with hot, dry summers. These trees are all medium-sized deciduous trees ranging 15–30 metres tall.

All of the aspens (including the White Poplar) typically grow in large clonal colonies derived from a single seedling, and spreading by means ofroot suckers; new stems in the colony may appear at up to 30–40 metres 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 claimed to be 80,000 years old, making it possibly the oldest living colony of aspens. Some aspen colonies become very large with time, spreading about a metre per year, eventually covering many hectares. They are able to survive forest fires, since the roots are below the heat of the fire, with new sprouts growing after the fire burns out.

However, aspens do not thrive very well in the shade, and it is difficult for aspen 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. Lately, aspens have an increased popularity in forestry, mostly because of their fast growth rate and ability to regenerate from sprouts, making the reforestation after harvesting much cheaper, since no planting or sowing is required.

In contrast with many trees, aspen bark is base-rich, meaning that aspens are important hosts for bryophytes^[3] and act as food plants for thelarvae 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 tree of choice of theeuropean beaver.

Redstone is a census-designated place in Pitkin County, Colorado, United States. The population as of the 2010 Census was 130. The U.S. Post Office at Carbondale (ZIP Code 81623) now serves Redstone postal addresses. The village is listed on the National Register of Historic Places as an historic district and includes several properties that are also separately listed on the National Register.[