By PAUL HETZLER

The signs are unmistakable: Kids back to school, shorter days and chilly nights, wood smoke in the air. Yep, it must be fall.

Our extremely dry summer caused many trees to begin turning colors early, which has given us an extended season in which to appreciate nature's vast and wondrous palette. Some of you may be wondering where those colors come from, although more likely you're wondering if the NHL lockout will end soon or if Mac really is better than PC.

The truth is, none of those questions has a definitive answer.

A common experiment in high school biology class involves leaching the chlorophyll out of a fresh leaf, thus revealing the yellow or possibly orange color that had been masked by green. This is what happens in the fall when cool temperatures and shorter days cause chlorophyll to break down.

That's pretty straightforward, though there are many different “brands” of colors. Yellow and orange leaf color comes from chemicals called xanthophylls and carotenoids, respectively. These pigments are combined in various ways to produce the range of yellows and oranges that we see.

Red, however, is a different story. Anthocyanin, the red pigment, is actually synthesized by the tree in the fall. Anyone who paints cars knows that red is the most expensive color. Well, it's not cheap for a tree to make anthocyanin. Why trees produce red at considerable expense at a time when they could be storing that energy for next year is still a mystery. If you can accurately predict when the hockey season will start this year, if it does at all, I'll try to find you a reasonable explanation for red leaves. Until then we'll just appreciate the colors.

Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.