Fall Colors Part 1: Why Do Leaves Change Color in the Fall?

Joshua VanBrakle Tuesday, 20 October 2015

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Fall may just be my favorite season. I’m not a fan of what follows it, but for those precious few weeks in September and October, fall is an amazing time to be in the woods. It’s cooler, which makes it easier to be active. Birds start their migrations south, so you can see a different variety of wildlife every day.

And then, of course, there’s the colorful show the woods put on. The uniform green of summer breaks apart into a vibrant mix of yellows, oranges, reds, and even the occasional purple

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Why does that change happen? What makes leaves change color in the fall?

The answer has to do with an odd green pigment called chlorophyll. Chlorophyll is the chemical leaves use to capture sunlight so they can turn it into food through the amazing process of photosynthesis.

What makes chlorophyll odd, though, is that even though its job is to capture light, it doesn’t handle exposure to light well. Bright sunlight breaks it down. To keep on growing, plants have to keep making more chlorophyll for their leaves.

In the fall, that process stops. The tree grows a barrier between the leaf and the rest of the plant so the leaf can eventually fall off. Why trees lose their leaves is a story for another time, but the point here is that once the barrier between leaf and plant forms, new chlorophyll can’t replace what breaks down in the leaf.

As the chlorophyll breaks down, it can no longer give its green color to the leaf. Instead, other pigments inside the leaf show through, giving us the many different colors of fall.
But why do different leaves turn different colors? And why do fall colors seem brighter some years than others? In my next post, I’ll talk more about exactly what makes fall colors tick. For now though, I think I’ll have a rest at this picnic table and enjoy my favorite season.

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