The Science of Changing Colors

In the fall, people in North America pile in their cars and get out into nature to “leaf peep.” Local forests are a symphony of color for a short few weeks in autumn—and as with everything that happens in nature, there’s fascinating science behind this annual display.

It all starts with photosynthesis

To understand why leaves change color, it’s important to talk about how trees get their nutrients. They do this through a process called photosynthesis, which means, literally, “putting together with light.”

Each green leaf is really a tiny solar-powered factory that is converting light into energy for the plant. Chloroplasts are small bodies that are present in leaves, and they contain chlorophyll, which is responsible for the green color of a leaf . When water and carbon dioxide come into contact with chlorophyll in the leaf, a chemical reaction takes place, and sugar (along with oxygen) is formed.

When it becomes cooler, it’s no longer efficient for the tree to produce food through photosynthesis, and it begins to prepare for the winter ahead. Chlorophyll starts to break down and other compounds in the leaf start to become visible. These compounds are responsible for leaf colors. Different tree varieties will release different compounds in their leaves, leading to a variety of colors in the forest in fall.

Bow River Watershed, Alberta (Photo by Kyle Meller)

Bow River Watershed, Alberta (Photo by Kyle Meller)

Change begins from carotenoids

The same compounds that are responsible for the orange color of carrots are the triggers for yellow, gold and orange leaf colors—carotenoids and xanthophylls.

Deciduous trees, poplars and birches, have carotenoid-rich leaves, and their leaves are predominantly golden in color as a result.

Bartholomew River Project, New Brunswick (Photo by Mike Dembeck)

Bartholomew River Project, New Brunswick (Photo by Mike Dembeck)

Anthocyanins responsible for darker hues

While brilliant golds dominate fall in some parts of the country, the breakout stars of the show are the leaves from trees that contain the most sugar, such as maples and oaks.

The leaves with the highest sugar content contain anthocyanins, which are byproducts of extra sugar formed late in the summer. They cause the leaves to turn glorious red and purple colors. Maples are especially prone to high sugar content in their leaves. These leaves contain carotenoids as well, and so will have some orange and yellow mixed in.

 

This post originally appeared in the Globe and Mail and on the Nature Conservancy of Canada’s blog Land Lines and were produced with the support of Randall Anthony Communications Inc.

Post photo: Green Mountains, Quebec (Photo by Mike Dembeck)

92 comments

Jeanne R
Jeanne Rogers7 months ago

Thank you for sharing.

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Jeanne R
Jeanne Rogers7 months ago

Thank you for sharing.

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Jeanne R
Jeanne Rogers7 months ago

Thank you for sharing.

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Jeanne R
Jeanne Rogers7 months ago

Thank you for sharing.

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Jeanne R
Jeanne Rogers7 months ago

Thank you for sharing.

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Julie Pham
Julie Pham1 years ago

Thanks

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Chen Boon Fook
Chen Boon Fook1 years ago

Thank you for sharing

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Jerome S
Jerome S1 years ago

thanks

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Jim Ven
Jim V1 years ago

thanks for sharing.

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Simon L
Simon L1 years ago

ty

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