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| Earth on Oct 03, 2012

Why do tree leaves turn red in fall?

Research shows red pigments in autumn leaves protect trees from damage by autumn sunlight. Autumn leaves may also help protect against insects.

In the fall, the leaves of some trees turn yellow, orange or red. The bright colors are wonderful to behold. But do they have some hidden purpose?

Autumn leaf in about mid-September 2012 from EarthSky Facebook friend Colin Chatfield in Saskatoon, Saskatchewan.

Bill Hoch is a plant physiologist at the University of Wisconsin. He’s especially interested in red leaves. He said:

Nature is very efficient, and doesn’t just do something for no reason. So we figured there had to be some purpose for the production of these pigments in autumn.

For much of the year, green leaves help convert sunlight into food. In the fall, trees break down the green pigments and nutrients stored in the leaves. As the leaves of the tree begin to change, nutrients are shuttled into the roots for reuse in the spring. Hoch suspected that some trees produce red pigments as a kind of sunscreen, protecting leaves from sunlight while the tree stores nutrients.

Autumn, early October 2012 in Hibbing, Minnesota. Photo by EarthSky Facebook friend Rosalbina Segura.

To find out, he conducted an experiment with plants that produce red pigments and other plants of the same species with a defective gene preventing them from making the color red.

He found that the plants without red pigments were more damaged by fall sunlight and couldn’t recover leaf nutrients as effectively.

Other researchers are doing experiments to see if the red pigments in autumn leaves have other benefits – such as protecting trees from insects.

Image Credit: treehouse1977

Image Credit: Ross Elliott

Bottom line: Why do leaves turn red in fall? Plant physiologist Bill Hoch at the University of Wisconsin reminded us that nature does everything for a purpose. He ran experiments to find out if some trees produce red pigments as a kind of sunscreen, protecting leaves from sunlight while the tree stores nutrients in its roots over the winter months. His experiments showed that without red pigments were more damaged by fall sunlight and couldn’t recover leaf nutrients as effectively. Meanwhile, other researchers suggest the fall colors of leaves might serve other purposes, such as protection from insects.