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Why leaves change color in the fall

Posted at 12:11 PM, Oct 21, 2018
and last updated 2018-10-21 14:11:08-04

Have you ever wondered why leaves change colors in the fall?

Leaves always have the potential for their fall colors, but one color prevents us from seeing the reds, oranges, and yellows all year round.

“The amount of chlorophyll, the green pigment that allows the plant to photosynthesize, is so abundant that it masks the color of the other three compounds,” said Clayton Marlow, Montana State Professor of Natural Resources and Range Land. “We have anthocyanin, which is the red color; carotene, which is the orange and some yellow; then xanthophyll, which is the yellow.”

But when fall comes around with cooler temps and less daylight, things change for the green in the leaves.

“It can’t produce enough carbohydrate to keep itself going, so it simply shuts off,” Marlow said.

Different trees turn different colors.

“Aspen tends to always be yellow. Cottonwoods are the same because of the high amount of xanthophyll in the leaves. On the other hand, some of the maples will turn more of an orange.” Marlow said.

With most of western Montana past peak fall foliage, the beautiful colors you saw on the trees are now on the ground, adding an extra outdoor chore. You can still see these colors but you need to go lower in elevation and further south.

“Into the southeastern United States, even the northeastern United States, now we’re starting to see this great burst of color. Their air temperature now matches what Cooke City had at Labor Day,” Marlow said.

Marlow added that because of the way the leaves are shaped on spruce, pine, and fir trees, they can stay green all year.

-Reported by Carson Vickroy/MTN News