Treetops near Song Mountain in Tully, N.Y., last week.CreditLauren Long/The Syracuse Newspapers, via Associated Press

We do not need to understand it to appreciate the beauty, but the science behind it is another wonder of its own:

Why Does Fall Foliage Turn So Red and Fiery? It Depends.

By JOANNA KLEIN

Leaves scream their final cries in color before dropping to the ground. Their shouts — in golden, crimson or scarlet — eventually fade to brown bellows, and their lifeless bodies dry up on the forest floor. It absorbs their crinkly corpses and that’s it — worm food. The fall of a leaf in autumn is an orchestrated death. A complex, brilliant, beautiful death.

Right now across the United States, fall foliage season is peaking, and everyone’s out to get a peep at the fiery show. Hiking trails are crowded. Mountain roads are packed, and leaf cams are getting lots of love. When you think of it as watching the death of leaves, it sounds morbid, but it’s captivating nonetheless. Does the way some turn red in the process serve any purpose?

Leaves actually start out yellow. Chlorophyll, the chemical responsible for giving leaves their green appearance and converting light to energy during photosynthesis, just overpowers it in the spring and summer. But when temperature, daylight and weather events like rain or drought cause leaves to die in the fall, chlorophyll breaks down and reveals the yellow or orange helper chemicals known as carotenes or carotenoids that were there all along.

Red is another story, because it’s made on purpose. As some leaves die, they produce chemicals called anthocyanins (also found in the skin of grapes and apples) from built up sugars. These chemicals produce a red pigment that can combine with green pigments left from chlorophyll and display different shades of red.

How bright this red is depends on what species the leaf belongs to, its inherent genetics and the environment around it — including the forest, the tree, and individual leaves, said John Silander, an ecologist and evolutionary biologist at The University of Connecticut.

But with the chemical explanation out of the way, the question still remains: Why do some leaves use precious energy to turn red right before dying? There are a handful of evolutionary explanations, Dr. Silander said, but many of them sound contradictory…

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