Why do leaves change color in autumn?
Leaves change color because trees stop making green chlorophyll in autumn. As the green fades, yellow and orange pigments show through, and some trees make new red ones.
During spring and summer, leaves are packed with chlorophyll, the green pigment that captures sunlight for photosynthesis. Chlorophyll breaks down constantly and the tree keeps replacing it. When days get shorter and nights cooler, trees prepare for winter and stop producing it.
Leaves also contain yellow and orange pigments called carotenoids, the same pigments that color carrots. They are there all summer but hidden by the green. Once the chlorophyll disappears, they finally show. Red and purple colors come from anthocyanins, which some trees, such as maples, make fresh in autumn from sugars trapped in the leaves.
Why some autumns are brighter
Sunny days and cool, but not freezing, nights produce the most vivid reds, because more sugar builds up in the leaves. A very warm autumn or an early hard frost can make the colors dull. Eventually a layer of cells forms where each leaf stem meets the branch, and the leaf falls.
Did You Know?
Evergreen trees such as pines keep their needles through winter. The needles have a thick waxy coating and a small surface area, which helps them survive cold and dry conditions.