Conservation Minnesota

Season of Change

Autumn is one of the best times of the year. You can enjoy being outside on the warm, sunny days catching up on everything you forgot to do instateofenergy the summer without the threat of melting, and you can enjoy the crisp, cool nights curled up with a blanket, a good book, and some type of pumpkin spiced beverage. The heat of summer is over and the bitterly depressing cold of winter is still a few months away. The best part of fall, in my opinion, is watching the leaves change colors. I am a self-admitted leafer. I love seeing all the trees changing from green to brilliant reds, yellows, and oranges.

I have always admired the breathtaking colors but had never stopped to think about what makes them change colors; I’m sure I’m not the only one. What better to blog about in the fall than the changing colors of the trees. So, why do leaves change colors?

There are three factors that influence color change: length of night, weather, and leaf pigment. As fall sets in, our nights get longer and colder. These conditions affect the three types of pigments found in leaves. First up is the familiar chlorophyll. Chlorophyll is what gives leaves their green color. If you have ever taken a biology course, you might remember that chlorophyll is what enables plants to use sunlight to manufacture sugar during photosynthesis. The second pigment is carotenoid which create the yellow, orange, and brown colors (it’s what gives corn, carrots, and bananas their color). Finally, there is anthocyanin which appear red, purple, or blue depending on the pH level (it gives cranberries, blueberries, and cherries their color). Chlorophyll and carotenoid are present throughout the growing season while anthocyanin is produced in the autumn in response to bright light and excess sugar.

Throughout the growing season, chlorophyll is continually produced and broken down. In the fall, with the length of nighttime increasing, the production of chlorophyll slows down and eventually all the pigment will stop being produced and the reserves will be used up. This simply means that the leaves will no longer be producing the green pigment in the leaves. The leftover pigments are then unmasked and show their colors.

The amount and brilliance of leaf color is related to weather conditions that occur before and during the time that chlorophyll production is slowing. To create the best colors you need a string of warm, sunny days with cool, crisp nights (although not freezing). These conditions produce large amounts of sugar during the day and during the night, the leaf veins close which prevents the sugars from leaving. Lots of sugar plus lots of sunlight means much more brilliant anthocyanin pigments. The years that we have these weather conditions are the best for colors. Since carotenoid is always present, the yellow and gold colors are constant every season; it is the fluctuation in the amount of anthocyanin produced that really determines if it’s a good leafing season or not.

Here are some tree types and the colors they turn in the autumn:

Tree Type:                              Color:

Oaks                                           Red, Brown, or Russet (brown with reddish-orange tint)

Hickories                                Golden Brown

Aspen/Yellow Poplar      Golden Yellow

Dogwood                                Purplish Red

Red Maple                             Brilliant Scarlet (bright red with orange tint)

Sugar Maple                         Orange-Red

If you are curious about where to find the best leaf colors in Minnesota, check out the DNR’s Leaf Color Finder. It is updated each day, shows you the percentage of trees at peak color in a particular area, and suggests the best state parks to visit for leaf viewing. Take an evening or weekend and go check out the leaf colors before it is too late. It’s a fun, free activity to do with friends, family, or even by yourself. The brilliant colors are sure to put a smile on your face.

About Whitney Thesing

Whitney Thesing
Whitney Thesing graduated in 2009 from the University of Minnesota - Morris with degrees in Economics and Environmental Studies.  After graduating, she has worked in many areas of natural resources including water quality, invasive species management, ecological experiments, phenology, and native ecosystem restoration. She volunteers her time as a member of St. Louis Park's Environment and Sustainability Commission, focusing on education and behavior change, and water resources, two causes near to her heart.
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