Each year at the end of summer, Colorado hosts one of the most brilliant natural displays of color as the Aspen trees shed their leaves in anticipation of a cold winter. Oranges, yellows, reds and browns are lavishly splashed across the deep blue sky, as Colorado’s most prolific deciduous tree enters an energy-saving sleep that will carry it through to the next spring, as the Aspen leaves change color.
Why Do Aspen Leaves Change Color During Fall?
But what is it about the Aspen tree that makes this natural phenomenon such a visually appealing experience? Why don’t these leaves turn a solid hue of brown like most deciduous trees? Well, sometimes they do.
To fully understand the reason behind the color change, we first have to review the reason deciduous trees, like the Aspen, lose their leaves each winter. The days after the fall equinox will have much less sunlight, and this causes the deciduous tree to enter a dormant state.
Carbon Produces Sugars
During the summer months when there is abundant sunlight, trees use the carbon in the air, water in the earth and the solar energy to produce sugars. This is the process of photosynthesis, and an important compound called chlorophyll is what makes the whole thing work.
Chlorophyll is what is inside the leaf of any green plant; it is what makes a plant green by hiding the yellows, oranges or brown colors that are the real colors of the leaf. In order to continually produce chlorophyll and keep the tree a vibrant green, there must be sufficient sunlight.
Chlorophyll Production Declines
As the days grow shorter and summer ends, there is no longer enough sunlight to produce this chlorophyll and continue the process of photosynthesis. This is when the tree will withdraw its stores of sugars and enter the energy-saving dormant state that will allow the tree to survive the winter.
When a tree begins to gather its sugars and energy for storage, it signals the base of every leaf to form a special blockade called the abscission layer. This will stop any nutrients, waters or sugars from passing between the leaf and the rest of the tree. This also means no more chlorophyll will be produced in the leaf and it the leaves true colors of yellow and orange will become noticeable.
Trapped Sugars Produce Anthocyanins
Sugars that may have been trapped inside the leaf when the abscission layer went up will produce anthocyanins, causing the leaf to turn bright red. Higher concentrations of anthocyanins will produce deeper crimson hues. The colors will continue to change until the abscission layer is so thick that the leaf detaches from the tree and flutters to the ground.
In the case of the vibrantly colored Aspen tree this process is more dynamic. Each year the same family of Aspen trees can produce a different set of colors depending on specific conditions of their environment during the formation of the abscission layer.
The Perfect Storm For Colorful Aspens In The Fall
After the abscission layer forms, the sugars trapped in the leaves will produce many anthocyanins, if the days are warm and sunny and nights cool, but not too cold. This will be the perfect condition for a vibrant display in the Colorado Aspens.
The warm sun will quickly remove the chlorophyll from the Aspen leaves, revealing the color faster and the cool nights will inhibit the sugars and colorful anthocyanins from leaving the leaf through the forming abscission layer.
On the other hand, if there is an early frost or drop in temperature, the leaf can lose all ability to produce anthocyanins and the vibrant display could be lost. Other conditions, like a difficult year with little sunlight, can cause the abscission layer to form early and the colors can lose intensity.
In the end, every year will bring a unique set of factors that will create an individual display. But if you are hoping for an intense display with a dynamic set of colors, it will be warm days and cool nights in the fall that produce the proper conditions for red, orange and yellow across the Colorado landscapes as the Aspen leaves change.