Montane, subalpine. Woodlands. Spring.
West Mancos Trail, October 9, 2008.

Aspens are the most widely distributed tree in North America, ranging from Newfoundland to Alaska, through the Sierras and Rockies to Mexico, and from the Pacific states across the northern and central tier of states in the United States to the Atlantic. See the map below.

The even-aged Aspen stand in the photograph at left probably sprouted from roots of trees logged 30-50 years ago.  Notice the tightly packed growth pattern, the lack of lower limbs, and the dark spots on the trunks where old limbs grew.  Lower limbs almost always do die (leaving a black inverted V-shaped scar) and the tree matures to a long, straight, single trunk, topped by a symmetrical crown of leaves. Trees can grow to three feet in diameter and 75 feet tall with the lower bark becoming gray and broadly cracked.  Aspens live only about 100 years.

Montane, subalpine. Woodlands. Spring.
Echo Basin Loop Road, June 7, 2004; Prairie Dog Knoll Trail, Abajo Mountains, Utah, June 15, 2020; Burro Bridge Trail, July 11, 2007; Calico Trail, October 10, 2012.

Aspen bark can be smooth, bright white, gray, warty, or all of the above on the same tree. As the tree grows toward maturity, thick bark forms at the base of the trunk.

Montane, subalpine. Woodlands. Spring.
Bear Creek Trail, October 4, 2012.

Thin Aspen bark is coated with a fine white powder, sloughed-off dried cells. On the trunk behind Robert Lang's finger tip, you can see the more gray-green bark that showed through after Robert wiped his finger down the trunk.

The outer cells of most trees form a thick bark; Aspen outer cells die, leaving a white powder behind. As Aspens age or when they are injured in some way, the outer cells do form a thick bark.

Elk-chew is acceptable, even exciting to see; human graffiti is neither.

Montane, subalpine. Woodlands. Spring.
Ryman Creek Trail, July 28, 2019; Sharkstooth Road, October 1, 2010; and West Mancos Trail, October 1, 2012.

It is common for new Aspen leaves to have a coppery-red hue.

Fall Aspen color is almost always yellow to golden yellow.

Montane, subalpine. Woodlands. Spring.
Trout Lake, September 13, 2000.

Patches of trees in the fall have marvelous maroons and reds.  Click to see Aspen gold.

Montane, subalpine. Woodlands. Spring.
Near Haviland Lake, April 31, 2008.

When you walk Aspen forests in the spring, use a hand lens and dive into the miniature beauty of the flowers.  Aspens, and other members of the Willow Family (Salicaceae), are dioecious, that is, they have male flowers (shown here) on one tree and female flowers on another.  In the photograph at left, hundreds of minute flowers are clustered in each catkin (a long spike chain).  Bracts are brown, finger-like, and surround creamy yellow flowers (the light creamy color in the photograph at left) with black-tipped stamens projecting.  

Montane, subalpine. Woodlands. Spring.
Near Haviland Lake, April 31, 2008.

An abundance of Aspen flowers emerge in early spring before Aspen leaves and provide quite a visual show, especially early in the morning when they glow in the low rays of the sun.   

More Populus tremuloides: 
Fall color page 1  
Fall color page 2

   Pure stands of Aspens (first photograph below) grow thickly in what was once an open very sunny area.  The Aspens are gradually invaded by conifers (second photograph) and as shade-loving conifer seedlings mature, new Aspen sprouts are shaded and kept from growing.  Eventually the forest will become pure conifers.

    Note, however, that in the foreground of the third photograph, small Aspens are sprouting and the field will soon become a pure Aspen forest  --  only to be replaced in a century or two by conifers.

A pure stand of

Populus tremuloides.

Young Picea Engelmannii (Engelmann Spruce) thrive in the shade of Populus tremuloides.

Eventually Populus tremuloides will not regenerate, for the conifers produce heavy shade and Aspens need strong sunlight to sprout new trees from their roots. 

In the top photograph at left, the sunny meadow in the foreground shows 3-5 foot tall Aspens sprouting from the roots of the Aspens that used to thrive in the background forest.

In the second photograph at left, you see a typical San Juan National Forest scene of a mixed Populus tremuloides and Picea engelmannii forest. Pure stands of Populus tremuloides are indeed gorgeous in the fall, but these mixed stands have a special dramatic beauty that appeals to many people.