Why do leaves change color in autumn?

Each autumn, in many parts of the world, forests transform from green into brilliant shades of yellow, orange, red, and brown. It is one of the most beautiful seasonal changes in nature. It can seem as if the trees are suddenly painting their leaves, but the truth is the opposite. The colors of autumn are not added to the leaves. They are revealed, as the leaves prepare for the coming winter.

During spring and summer, leaves are green because they are full of a pigment called chlorophyll. Chlorophyll is essential to the tree: it captures energy from sunlight and uses it to make sugars that feed the plant, a process called photosynthesis. There is so much chlorophyll in a healthy summer leaf that its strong green color dominates and hides the other pigments that are also present in the leaf. So all summer, the leaves stay a rich green.

Leaves actually contain other pigments besides chlorophyll all along. Yellow and orange pigments, called carotenoids, are present in the leaf even in summer, but they are masked by the overwhelming green. As autumn arrives, the days grow shorter and temperatures drop. The tree begins preparing for winter and slows down, then stops, its food-making process. As this happens, the chlorophyll breaks down and its green color fades away. With the green gone, the yellow and orange pigments that were hidden underneath finally become visible.

While yellows and oranges are revealed, the red and purple colors seen in some leaves work a little differently. These red pigments, called anthocyanins, are not simply uncovered. In many trees they are actively produced in the leaf during autumn itself. The exact mix of colors depends on the tree species and the weather, which is why some trees turn pure yellow while others blaze deep red. Eventually the tree seals off each leaf and lets it fall, having reclaimed the valuable nutrients it can save for next year.

This article was written using information from Wikipedia.