Show Details

Fall Color Differences

September 22, 2009

A new hypothesis explains why fall colors differ in the U.S. and northern Europe.


Explaining fall color contrasts. I’m Bob Hirshon and this is Science Update.

In Europe, fall leaves are mostly yellow, but American fall colors include reds and oranges. Now, researchers in Israel and Finland have proposed an explanation. Haifa University botanist Simcha Lev-Yadun explains that American trees have been battling insects uninterrupted for millions of years. During harsh glacial periods, the trees and their insect pests simply migrated southward. But in Europe, the Alps blocked any escape from these periodic deep freezes.

SIMCHA LEV-YADUN (University of Haifa):
And the insects that live on the trees, disappeared – died with them.

Without such interruptions, American trees developed more elaborate defenses against insects, including red pigments that advertise those defenses. Lev-Yadun says the red pigments are energetically costly, but they do ward off pests. I’m Bob Hirshon for AAAS, the Science Society.