The science behind autumn's changing leaf colors

During spring and summer, chlorophyll masks the yellow and orange pigments already present in many leaves. In autumn, trees break down chlorophyll and move nutrients from leaves into roots for storage. As green fades, other pigments become visible, producing the season's yellows, oranges, reds, and browns.

Chlorophyll lets trees capture sunlight, and its abundance during the growing season conceals pigments that are already there. When autumn arrives, trees dismantle this green pigment and relocate stored nutrients into their roots, holding them for the following spring. Once chlorophyll disappears, the remaining pigments—or their absence, as with brown leaves—determine what we see.

Red is different: it is manufactured anew when bright days pair with chilly nights, a combination that favors sugar and red maples. DePauw researchers Bryan Hanson and Dana Dudle note that sunlight and cold exposure can even vary across a single tree, leaving some branches green while others flush. Sweetgum, ash, and ginkgo each display distinctive palettes.