Editor’s note: This is the first of two parts. Look for the second part in Sunday’s Vail Daily.
EAGLE COUNTY — The Colorado blue spruce is the state tree, but it is the quaking aspen that is the best known and most easily recognized tree in Colorado. The “gold rush” occurs every fall as millions of people are lured to the high country to view the beautiful colors of changing aspen trees. This member of the poplar family, which grows at elevations ranging from about 6,000 feet to almost 11,500 feet, can be found in all of Colorado’s national forests. Quaking aspen, Populus tremuloides, gets its scientific name from a characteristic of the leaf. The heart-shaped leaves have a fine-toothed margin, and the petiole — the stem that attaches the leaf to the tree — is flattened. The flat petiole causes the leaf to quake or tremble in the slightest breeze. Many legends revolve around the belief that the tree trembles in the presence of man.
There are two other trees that have a similar color change in the Colorado hills and from a distance may look like aspen. One is the lanceleaf cottonwood (Populus acuminata). These trees are common along river bottoms. Another similar poplar found in Colorado is the balsam poplar (Populus balsamifera) which has a notable fragrance. The bark of both trees is not as smooth and the leaves are long and thin.
The color change in the high country starts in the middle of September and lasts into October, depending on temperatures and weather conditions. On a clear, cool September day, the combination of blue-gray and pure white of snow-capped peaks, yellow to red-colored aspen and rich blue skies can easily cause a sensory overload.
What causes this incredible fall show? All the gold, yellow, and red colors seen in aspen trees in the fall are present in the leaf throughout the spring and summer, too, but the predominant green chlorophyll necessary for food production overshadows them. When the length of the day decreases and temperatures drop in the fall, chlorophyll production slows down and eventually stops. The trees then begin to absorb the chlorophyll and leave behind the other pigments: Carotenoid pigments, which produce yellow, orange, and brown colors like those in carrots and corn; and Anthocyanin pigments, which produce the reds found in cranberries and red apples. Eventually, the dying leaves flutter to the ground in a rain of gold.
No one has yet nailed down what temperature, amount of seasonal moisture and amount of rain and snow in the fall actually impacts the time, duration and intensity of the color changes. Adequate, but not excessive, summer moisture, cool nights without a freeze and an absence of fall rains and snows seem to produce the best fall shows. Here are some tips for finding the best fall colors:
• West-facing slopes tend to display more vibrant colors.
• Dry summers cause the leaves to dry out and fall more quickly off the trees.
• Wet summers tend to make the leaves darken to brown or black and become moldy.
• Trees at higher elevations, on north facing slopes and those in the northern part of the state tend to change earlier than other trees.
• Watch Front Range weather forecasts for viewing tips.
A general rule is that “spring comes one day later and fall comes one day earlier for every 100 feet of elevation gain.” In addition “spring comes one day later and fall comes one day earlier for every 10 miles of northern travel.” If you visit an area and the trees have yet to change or have already changed, then use these rules to change your drive.
Aspen trees grow in a unique way called “cloning.” What begins as one aspen becomes a whole grove when that tree’s root system sends up “suckers,” or shoots, which become new trees. This cloning produces huge areas of trees that all share the same root system. When you look at a grove of aspen trees, you are actually looking at one gigantic organism, all with the same genetic makeup connected to the same underground root structure. When fall begins, all the trees in the clone change colors at nearly the same time. This creates large expansive areas where all the trees are about the same color. This is even more obvious in the spring when all the trees in the stand leaf out at the same time.
Rick Spitzer is the author of “Colorado Mountain Passes,” published by Westcliffe Publishers and available at The Bookworm, City Market, Amazon and many stores across the state. The book provides photos and text about the history, lore, wildlife and scenery around the passes of Colorado.