Why are autumn leaves of different colours?

A new theory provided by Simcha Lev-Yadun, professor of biology at the University of Haifa-Oranim and Jarmo Holopainen of the University of Kuopio, Finland, propose taking a step 35 million years back, to solve the mystery.

The green of a tree's leaves is from the larger proportion of the chlorophyll pigment in the leaves.

The change in colour to red or yellow as autumn approaches is not the result of the leaves' dying, but of a series of processes -- which differ between the red and yellow autumn leaves.
When the green chlorophyll in leaves diminishes, the yellow pigments that already exist become dominant and give their colour to the leaves.

Red autumn leaves result from a different process: As the chlorophyll diminishes, a red pigment, anthocyanin, which was not previously present, is produced in the leaf.

These facts were only recently discovered and led to a surge of research studies that attempted to explain why trees expend resources on creating red pigments just as they are about to shed their leaves.

An evolutionary ecology approach infers that the strong autumn colours result from the long evolutionary war between the trees and the insects that use them as hosts.

These results were published in New Phytologist.