Fall magic

Sep 15, 2016
We answer the question of why leaves change color. It might not be what you think.

Brilliant color along Lake Creek. Photo: Jay Mather.
Brilliant color along Lake Creek. Photo: Jay Mather.
Believe it or not, the leaves are beginning to turn at the Metolius Preserve! It seems early, but the vine maples are already starting to put on a show. This got us thinking; what is it that makes leaves begin to change color? Here's what we found out.

Winter is coming.

Leaves change color because of length of night and the pigments inherent in them. Sure, environmental factors like temperature, rainfall, food supply are part of the equation, but these factors are highly variable year after year and only play a part in the story. Length of night is the constant. As days grow shorter and nights grow longer and cooler, biochemical processes in the leaf begin the transformation.

It ain't easy being green, especially in autumn.
There are three types of pigments in leaves: chlorophyll, carotenoids and anthocyanins. Chlorophyll gives leaves their basic green color. Chlorophyll is not a very stable compound. It requires sunlight and warm temperatures. In fall, the chlorophyll gets sluggish as nights grow cooler and days are shorter. Once chlorophyll slows down, special layers in the leaf prohibit any water from reaching it. When this happens trees break down chlorophyll and the leaves’ true colors are exposed.

The carotenoids and anthocyanins that are present in the leaf are unmasked once chlorophyll production ceases. Carotenoids produce the yellow, orange and brown colors found in pumpkin, corn, carrots, and daffodils. Red and purple colors come from anthocyanins which are found in cranberries, red apples, plums and blueberries. Once the chlorophyll is gone, we see what is really there.

Timing is everything.
Leaves change color at different rates and times. This is genetically inherited. Even elevation does not affect this timing. It’s not the temperature that signals change, but temperatures and weather do play a part. The amount and brilliance of colors are related to weather conditions during the time the chlorophyll in the leaves is dwindling.

Layers of color at the Metolius Preserve. Photo: Jay Mather.
Layers of color at the Metolius Preserve. Photo: Jay Mather.

If the summer has ample moisture followed by a dry, cool and sunny autumn, with warm days, cool nights and no frost, leaves will be their most brilliant. Lack of wind and rain in the fall prolongs the colors. Wind and heavy rain cause leaves to drop before they reach their full potential. If we have a late spring and drought, there will be a delay of color. If the fall is too warm, there is less color intensity.

Shorter days are here and we're gearing up for a brilliant fall. Get out there and enjoy the color display! Check out our full schedule of fall hikes and join us at the Preserves.

Special thanks to Kelly Madden for the original blog post.

USDA Forest Service: Why Leaves Change Color
PBS.org: Why Do Leaves Change Color.