Brilliant Fall Hues: Where they come from and where to see them

By Abby Henkel, Communications Director

This article originally appeared in the fall 2017 issue of The Twig, our 24-page member newsletter. To read more from this issue, click here. To become a member and receive The Twig in the mail, become a member.

Note: The print version of this article is especially beautiful, so I invite you to check it out!

We in southern Indiana are rightfully proud of this beautiful landscape, perhaps in the fall more than any other time. Entire hillsides and forests erupt in vivid colors every September, and the color tends to stay longer here than in some other parts of the country. Ever wonder how this happens? And where are some places off the beaten path to enjoy them?

Beanblossom Bottoms in the fall, by Danielle Lucas/Visit Bloomington

Changing daylight means changing colors

While the weather can affect the intensity of the colors, it’s the length of nighttime that causes leaves to start building up a corky (“abscission”) layer that eventually prevents nutrients from passing through the branch to the leaf.

Bye bye, chlorophyll

As the abscission layer builds up, chlorophyll production slows and eventually stops, and what’s left in the leaves is broken down into its component parts and pumped back into the tree to be used for next year’s new leaves. Since chlorophyll is what makes leaves green, and it breaks down when exposed to sunlight just like a photograph does, eventually the leaves lose their green color.

Before they’re brown, their bright and colorful

Hiding beneath the chlorophyll are carotenoids and xanthophylls, which produce those yellow and orange pigments. Red and purple come from anthocyanins, which are produced by sugars in the leaf. Then as these pigments all break down in the light, the only ones left are tannins, which are brown. Research has found that aphids and other insects that like to burrow in tree bark in cold weather are turned off by the brightest leaf colors, which send the signal that the tree is strong and will defend itself with extra toxins.

Why are they so vibrant here?

The more diverse the trees species in a forest or region, the greater chances of having an extended season of fall colors because the species go through this process at slightly different times. Because southern Indiana gets plenty of sunlight in the fall (unlike Europe), our forests aren’t usually dominated by a couple species (unlike New England), and our first frost isn’t until mid-October, Hoosiers can enjoy about a month of autumn’s colorful beauty. Factors like a rainy spring/early summer can signal brighter colors in the fall, because the leaves don’t seal those barriers too early. But rain later in the summer causes too much cloud cover as well as wind and rain, which can cause leaves to fall prematurely.

Our favorite Sycamore nature preserves for leaf-watching

You’ll see beautiful fall colors anywhere you go here, but these preserves offer some of my favorite views of the hills covered in bright autumn colors. Share your fall pictures on Instagram and tag @sycamorelandtrust!

Monroe County: Scarlet Oak Woods, Amy Weingartner Branigin Peninsula Preserve

Brown County: Laura Hare Nature Preserve at Downey Hill

Bartholomew County: Touch the Earth Natural Area

Greene County: Dilcher-Turner Canyon Preserve