Zornio: Sure, fall colors are gorgeous, but the science behind them is also impressive

Trish Zornio
Colorado Sun
The Colorado Sun

Few things are more magical than the arrival of a cool, crisp fall. This year, Colorado is projected to be especially brilliant in color, with the foliage changes happening as early as this week in some parts of the state.

But, when was the last time you set down your camera to marvel at aspen leaves not only for their golden yellow hues, but also for the science that makes it possible?

The visual artistry of Mother Nature is no doubt a powerful one. Yet, it’s only one way to experience this magical season. Whether it’s understanding how the leaves change or why, each year so many of us seem to miss out on the larger wonders of what is really going on around us. 

The annual scene has become all-too familiar. Eager tourists and locals, alike, drive up and down Colorado’s scenic highways to find the perfect spot. Upon spotting one, they quickly pull over, jump out of the car, walk a few hundred feet to snap a photo, and then rush back into the car to drive to the next spot.

The experience lasts only a handful of minutes at each stop, as if the primary goal is more about finding the perfect Instagram post rather than to fully immerse in the very beauty we seek.

But, taking the time to fully immerse ourselves into our natural environment can make the fall experience a richer, more fulfilling one. By setting aside our phones and the speedy pace of the daily grind, we can come to recognize the season for what it truly is: a time of change in preparation for a long, cold winter.

With this, we can enter the forest, learn to slow down with it, and take the time to learn about what is truly happening around us.

Take, for example, Colorado’s famous aspens. Most of us have hundreds of photographs of these beautiful trees changing colors. But, did you know that aspen leaves actually hold their yellow pigments all summer long — we simply can’t see them until the seasons change? 

Each spring, as new stems and buds begin to open, the increased sunlight and warmth triggers trees to produce chlorophyll, a chemical compound critical for photosynthesis. This chlorophyll colors the leaves a strong shade of green, a fact you might remember from grade school.

But, within each leaf, we often forget that other colorful chemical compounds still exist; they are simply overwhelmed by the green pigment. 

For most of the summer, it continues this way, with chlorophyll continuing to dominate as the primary chemical. Then, as the days begin to shorten, the tree starts to prepare for winter. It decreases food production and closes its veins. This prompts the breakdown of chlorophyll, and the green pigment slowly fades. It is at this time that other vibrant chemicals already in the leaf can finally reveal themselves. 

The resulting color of each leaf is based on the type of chemical compounds remaining. Leaves with a predominantly orange color tend to carry carotenoids, while trees with leaves of yellow are caused by the chemical compound xanthophyll.

Reds and purples are produced by anthocyanins, as more sugars become trapped in the leaves and cause chemical reactions, while brown leaves tend to be produced by tannins.

In each case, the strength of the leaf color is moderated by temperature, with warm days and cool, but not freezing, nights yielding the strongest chemical intensity. 

Of course, in the end, the tree drops its leaves entirely to conserve for winter. But, for a few magical weeks, we get to experience the impressive nature of the chemical spectrum as a glorious color display.

Learning about the chemical phenomena of fall foliage is only one way to more fully appreciate the majesty of autumn.

Whether it’s taking the time to understand how climate change is impacting the change of seasons or learning about how animals prepare for hibernation, there are endless ways to immerse in the knowledge of how our natural environment works — even if it can’t be captured by an iPhone or posted on Instagram.

Trish Zornio is a scientist, lecturer, and writer who has worked at some of the nation’s top universities and hospitals. She’s an avid rock climber and was a 2020 candidate for the U.S. Senate in Colorado. The Colorado Sun is a nonpartisan news organization:


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