Autumn Leaves​—Why So Beautiful?

AGAINST the clear, blue autumn sky, the mountainsides are ablaze with brilliant colors​—red, violet, gold, yellow, orange, and brown. Indeed, the spectacular annual display of fall foliage in areas like the northeastern United States and eastern Canada is a masterpiece of the first rank.

What makes the leaves take on so many colors? Although some key factors still remain a mystery, scientists do know that the process is not so much a change as it is a disappearing act.

Chlorophyll​—the stuff that gives leaves their green color—​is normally bound to a protein. But the cool, dry autumn air triggers a series of changes in the tree, causing the protein to break down into amino acids. And like a frugal farmer getting ready for winter, the tree absorbs and stores the amino acids in the trunk or roots before shedding the leaves. With the protein removed, the chlorophyll starts to disintegrate, and the green color disappears, thus unveiling the natural colors of the leaf tissues​—yellow, orange, and brown—​that have been there all along.

But what about the flaming reds and scarlets of the sugar maple, sumac, and some other plants? That, according to researchers, involves another factor. The cool nights slow the flow of the sap in the tree, thus impeding the removal of sugar from the leaves. The bright autumn sun converts the residual sugar into a pigment called anthocyanin, which gives the leaves their bright red color.

So, in a way, this breathtaking display, associated with the brilliant sun and cool nights of autumn, is really the trees doing their annual housekeeping to get ready for the close of another growing season. It is all there for our enjoyment​—and to remind us of the great Artist and Designer behind it all.