Fall is finally here! From bonfires to pumpkin patches, the OEP Team is ready for sweater season and all things spooky. And while we’re enjoying apple cider donuts and pumpkin coffee on our crisp autumn walks, we get to witness one of the coolest chemical processes in nature–the changing of the leaves! Read on to learn more about the science behind one of Ohio’s most scenic seasons.

Many of us recognize the beautiful colors of fall–red, orange, and yellow bursts begin to replace the tree canopies of lush green. Usually, this change is our first indicator that fall has arrived. But what is the trigger for this change?  Is it the cooler temperatures, less moisture, or the longer nights? Actually, all three factors have an effect.  

Weather can vary year to year, but our photoperiod is constant.  What is a photoperiod you wonder?  It is the length of the day.  In central Ohio, we have fifteen hours of daylight on the longest day of the year–the first day of summer.  On the other hand, the first day of winter will only have 9 hours and 20 minutes of daylight.  This phenomena does not change.  As we near winter and nights become longer, temperatures become cooler, and air holds less moisture, a complex chemical process takes place inside leaves.

If you were able to peer inside a leaf, you would find a chemical pigment called chlorophyll. This chemical allows the tree to capture the sun’s light energy. Transforming carbon dioxide and water into sugars, or carbohydrates, for energy, the tree also produces oxygen as a byproduct, which we enjoy each and every day. This win-win situation is known as photosynthesis, and it allows life, as we know it, to exist on this planet. 

Sunlight is basically white light, which means it is a combination of all colors (Dickman 1997).  Chlorophyll gives leaves their beautiful green color (Stuntz 2017) because it reflects shades of green and absorbs other colors. However, chlorophyll only absorbs blue and orange light. So why do our leaves appear green in the summer and not other hues? Nature does not waste anything, so other pigments in the leaf, known as carotenoids, absorb the other colors.  Think yellow, orange, and brown found in abundance in such things as carrots, corn, and buttercups. 

When days become shorter and sunlight becomes scarce, trees expend less energy by producing less chlorophyll (Donk 2019). Less chlorophyll means no more green leaves. With chlorophyll production slowing, the other pigments of the carotenoids begin to show (Palm), resulting in the beautiful hues we see each fall.

The most vibrant colors are the result of the sugars trees produce. Those stored sugars help the trees boost their production of anthocyanin, a pigment that provides a brilliant red leaf. That production, in turn, is bolstered by sunlight—so a sunny fall means, generally, a colorful fall. A less-sunny fall? You’ll get more yellows and browns, the results of consistently produced carotenoids and tannins in the leaves (Garber 2014). In addition, certain colors are more characteristic of particular species of trees. Oaks are likely red or brown. Sugar maples are typically orange-red while dogwoods reflect a purplish red. 

So this fall, get outside and take a look around. Not only is autumn one of the most beautiful seasons in Ohio, it’s also a treasure trove of science in action!

For more information on fall foliage in Ohio, check out:

https://ohiodnr.gov/wps/portal/gov/odnr/go-and-do/see-the-sights/fall-color/

For more information on the best Central Ohio fall color spots, check out:

Resources:

Dickman, A. (1997, August 25) Sustainability: What causes the leave on trees to change colors?  Retrieved September 26, 2020.  From http;//www.scientificamperical.com article/ive-heard-several-different-answers/

Donk, K. (2019, November 26). The Color of Autumn’s Changing Leaves Comes Down to Chemistry. Retrieved September 23, 2020, from https://www.discovery.com/science/Changing-Leaves-Chemistry

Garber, M. (2014, Septermber 23) Leaves Change Color Each Fall because of Dieting Trees. Retrieved September 26, 2020  https://www.theatlantic.com/technology/archive/2014/09/leaves-change-color-in-the-fall-because-trees-get-hungry

Palm, C. E., Jr. (n.d.). Around Your World. Retrieved September 23, 2020, from https://www.esf.edu/pubprog/brochure/leaves/leaves.htm

Stuntz, D. (2017, October 2). The Science Behind Fall Foliage. Retrieved September 23, 2020, from https://www.americanforests.org/blog/science-behind-fall-foliage/