Why do leaves change color in the fall?

Fall has arrived in the northern hemisphere, and leaves will soon be changing colors. We’ve all heard why they do this: the green color is created by chlorophyll, a substance key to photosynthesis, and when the chlorophyll is lost at the end of the summer, leaves reveal their true colors.

Now, some scientists think this story is wrong. They believe that, instead, trees actively work to create their brilliant fall colors.

Why would trees do this? One challenge plants face in life is being attacked by insects. To combat this, plants produce a variety of chemicals that deter insects from eating their leaves or burrowing in their bark.

Just as chlorophyll creates a green color in leaves, some of these insect-deterring chemicals create bright yellows, oranges, and reds. The more chemical a tree stores up, the more vibrant the colors.

In the same way that a male bird puts on showy colors in spring to prove that he is a healthy mate, trees display dramatic autumn hues to tell insects, “I’ve invested in defenses against you; don’t bother trying to attack me.”

Colorful fall leaves may therefore be not only a defensive strategy, but a method of communication – providing further evidence that plants are intelligent.

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Why do leaves change color in the fall?

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