In addition to green chlorophyll (used for photosynthesis), leaves also contain yellow-orange pigments called carotenoids. In summer, the far more abundant chlorophyll almost completely masks these colors â the leaves appear green.
As temperatures drop and days get shorter, the tree withdraws valuable components, including chlorophyll, from the leaves back into the trunk before shedding them. The chlorophyll breaks down, while the more stable carotenoids remain longer and now become visible.
In some trees, new red pigments called anthocyanins are additionally formed only in autumn, as a reaction to light and sugar accumulation in the leaf. The mix of leftover carotenoids and newly formed anthocyanins produces the typical autumn palette from yellow to red.