As the season changes swiftly into Autumn, our nights become crisp and we trade chilled beverages for pumpkin spice and warm teas.

It is a time when, before the bustle of the holidays busies us with so many activities, we can indulge in a bit of reflection. We also are fortunate enough to be in an area of the world that can boast spectacular autumnal scenery as our views change from shades of green to golds and ambers. But what actually causes this spectacle?

The green we see in aspen leaves is caused by chlorophyll. Light energy is absorbed and chlorophyll converts this energy into sugars and starches, which allows the plant survive. As we move into the colder months, the aspens cease to produce chlorophyll. The green fades from the leaves as fast as our July tan lines and what is left are compounds like carotene. Carotene, which is also a photosynthetic compound and is the same compound that gives carrots their signature color, makes the leaves appear bright orange and yellow.  

Every once in a while, we are treated to aspens that produce a strong crimson color. This is created by a compound called anthocyanin. This compound is sensitive to the acidity of the tree sap. If the acidity of the sap is high, the leaves will appear bright red. The less acidic, the leaves will appear more purple.

Colorado is seeing an earlier peak this year among the high-altitude aspens. 2019 gave us a longer stretch of color, peaking in the third week of October. Our early frost in the beginning of September caused our golden season to be cut short, despite otherwise warm temperatures. When leaves have freeze damage, they turn brown rather than going through the change from green to gold. 

As with everything in nature, science may explain why something like the gilding of the forests happen. The lengthening of the night alerts the trees that it is time to prepare for change, just as it alerts us to dig out our fluffy slippers and cozy blankets. It does not though, take away from the beauty that surrounds us or the lovely anticipation of the sparkling snow and all the winter games that make our state such an amazing place to be. There is a comfort in knowing that, as the Northern Hemisphere falls into its winterly slumber, on the other side there will be budding trees, apple blossoms, and our neighbors to enjoy it with us. The difficulties we have faced individually and as a community this year reminds us that we should never take anything for granted. Even the turning of the leaves.