The Inside Story on Fall Foliage

Just today we had our annual conversation, trying to remember what creates the colorful fall foliage. Here is the answer, first published in 2011, in a blog by Helen Petre, college biology instructor who was a volunteer at Hagerman National Wildlife Refuge at the time:

Every autumn, usually in November, nature puts on a brilliant show of color at Hagerman NWR. This is attributed to mild autumn days coupled with cold, but not freezing nights. Each autumn the amount of sunlight decreases as the days grow shorter. This is the signal for the leaves to stop making chlorophyll. When the leaves stop making chlorophyll, the other pigments become visible.

Autumn Color at HNWR by Laurie Sheppard

Leaves produce food by photosynthesis. They use the sun’s energy, water, and carbon dioxide to produce carbohydrates. Leaves produce carbohydrates for the tree or shrub all during the spring and summer. They do this so well, that by autumn, the tree or shrub has enough food stored in the trunk and roots that it can live through the whole long winter without making any more food.

The sun’s light is actually white light and consists of all the colors of the rainbow: red, orange, yellow, green, blue, indigo and violet. Most leaves have lots of chlorophyll and some carotenoids. Some leaves also have anthocyanin, tannin, and flavones. Chlorophyll absorbs all of the colors of light in sunlight except green. Green light is reflected, so a leaf that has mostly chlorophyll looks green.

Carotenoids are carotene and xanthophylls. Carotenes are similar to vitamin A and they look orange, like pumpkins, carrots, and sweet potatoes. Xanthophylls are the pigment in sunflowers, dandelions, corn and egg yolks.

Some leaves also have anthocyanin, which can be red or blue. If the plant is acidic, the color is red. If the plant is basic, the color is blue. Tannins are the brown color in tea, bark and blackjack oak leaves in the fall. Flavones are the yellow in horse chestnut and onions.

Autumn leaf color is due to newly made red pigments as well as yellow and orange carotenoids that were already present in the leaf and are rendered visible because the leaf is no longer making the dark green chlorophyll in autumn.  

Each species of deciduous tree and shrub has its own unique colors. Red oak and winged shining sumac leaves turn bright shades of red in autumn. This is because, as the amount of sunlight decreases, a layer of cells develops at the point where the leaf joins the stem. This blocks carbohydrates from moving out of the leaf and the increased amount of carbohydrate is used to make anthocyanin, the red color. 

Female shining sumac trees also produce red fruits that stay on the tree until frost. Anthocyanin production is inhibited by frost, so when it freezes the leaves can no longer make the red pigment and they turn brown from tannin. If the daytime temperatures are too warm, the colors will be less intense because the chlorophyll will still be masking the other colors.

Besides trees, poison ivy abounds at Hagerman NWR and it is one of the most beautiful plants in the fall. Be careful not to touch it. Many people mistake poison ivy for harmless foliage and gather it to use in decorations. The red, yellow and orange color is due to the anthocyanins.

Honey Locust trees at Hagerman turn yellow in autumn. They have no anthocyanin, but lots of carotenoids. Other fall plants at Hagerman that turn yellow are pecan, muscadine grapes, black walnuts, and cottonwood. Sycamores turn brownish yellow. Wild plums turn reddish yellow and rough leafed dogwoods turn purplish red. Persimmon turns yellow, orange and reddish purple.

When you come to Hagerman in the fall to view the migrating ducks and geese that come to feed in the fields and marshes for the winter, spend some time noticing the vibrant and beautiful colors of fall. The yellows and oranges were there all along, but they were not visible because of all the green of summer. Now is your chance. Enjoy.

For more photos of the Refuge as well as information on activities and events of the Friends of Hagerman, see www.friendsofhagerman.com.