Why Do Those Leaves Change Color?
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Fall is here and that means fall festivals, cooler temperatures, and yes, the colorful leaf change from green to yellow, orange, and red. We have all heard the reasons why the fall leaf color is so brilliant or why the color is not so brilliant. “It has been a dry fall so the leaves are not going to be very pretty” or “It has been a hot fall so the leaves are not going to be pretty.” So what does make the leaf colors better some years than others? Well, both of the previous statements are true, to a point!
Oblige me for a minute to get a little technical. The leaves on certain species of trees have their fall color all summer; however, we cannot see this color because of the chlorophyll. Chlorophyll is the green pigment that enables the leaves to photosynthesize and create energy for the plant. Once the chlorophyll starts to fade, as the days get shorter and solar radiation decreases, the yellow (xanthophylls) and orange (carotene) pigments remain and become visible. The red pigment (anthocyanins) is produced during the fall in leaves of maples and other trees known for their red fall color. The yellow and orange pigments, though not seen during the summer do serve a purpose. They help disperse the light energy so the trees are not damaged. The red pigment keeps the leaves from sunburning much like sunscreen.
Ok, back to why do those leaves change color? According to Dr. Howard Neufeld, a professor of biology at Appalachian State University, temperature is the predominate factor. Neufeld says, as the temperature decreases chlorophyll degrades which allows the pigments xanthophylls and carotene to be seen. Decreased temperatures also cause sugar to build up in the leaves which causes the production of anthocyanins or red pigment. A warmer than normal fall does not mean less color, but it will delay the color. Cool temperatures are key, not freezing temperatures which will ruin the whole show. As for the rain, or lack thereof, and its effect on fall leaf color, too dry can cause leaves to drop prematurely, especially on species like Tulip Poplars and Birch, which are drought sensitive. Too much rain means cloudy weather, which in turn means less sugar production. Less sugar production means less anthocyanins and less red coloration on trees that normally turn red.
So there you have it. In order to have the perfect fall leaf color, you need to have a cool fall which is dry but not too dry. That sounds like the perfect fall to me.
This article was written with information taken from an article on the North Carolina ClimateOffice website by Corey Davis, The Leaves They Are a Changin’…But Why? posted on October 11, 2019.