Ask the Expert: Why Leaves Change Color

Mr. Selner, beloved South Lakes HS environmental science teacher is our expert for this month.

This month, we’re excited to feature one of South Lakes High School’s environmental science teachers, Mr. Selner. Students love his science classes because he makes big topics like the environment, animals, and climate change easy to understand and exciting to learn about. He also takes them on nature walks!

Since it is almost fall, Mr. Selner is helping us to understand one of the season’s coolest mysteries: why leaves change colors.

1. Why do tree leaves change their color from the greens of summer to the reds, oranges, and yellows of fall?

Trees respond to the shorter days and cooler nights of fall by shutting down the sugar factories that are their bright green leaves. They need to save on energy and water and so the leaves die and then fall to the forest floor. As the leaves are dying a key green pigment named chlorophyll disappears and all the remaining pigments that reflect red, orange, tan and yellow wavelengths of light are revealed. The exact mix of colors depends on the tree species, so brilliant red for sugar maples and tans and yellows for chestnut oak trees! All these colors were there the whole time; you just couldn’t see them through all the green of summer!

2. What makes some trees turn colors before others?

A tree that has its leaves turn to the fall colors before other trees may be under stress from pests, poor soil nutrition or dry soil conditions. In Virginia, some types of trees change to fall colors earlier than the rest including black gum, yellow poplar and Virginia’s state tree, the flowering dogwood, Cornus florida.

Now go collect some leaves on your next nature walk!