The Science Of Autumn

It’s the season of hoodies and pumpkin-spiced everything. As much as I hate to admit that summer is over, I can’t ignore it any longer. Nature won’t let me.

Most obviously, the trees are putting on their annual fall fashion show. Many folks probably know it’s the chemical chlorophyll that makes leaves appear green. Chlorophyll helps the tree convert energy from light into food. When the trees sense the cues of shortening daylight and cooler temperatures, they stop producing food and begin to prepare for winter.

With no need for chlorophyll anymore, the trees stop making it. The chlorophyll that’s left in the leaves breaks down quickly in light and low temperatures, revealing the leaf’s true colors which were masked by the dominant green. Yellows are produced by chlorophyll’s sidekick, carotene, which helps absorb energy but is in less of a hurry to break down.

And, ah, the reds! The reds are coolest because their brightness and intensity depends on the pH inside the leaf’s cells. If it’s acidic, the leaf will turn bright red, while less acid yields deep purples. The reactions responsible for the red colors of leaves occur with high sugar concentrations and lots of light, so the best and brightest show will take place when conditions have been cool (but not below freezing) and dry (to increase the sugar concentrations in the leaves) and with bright sunlight (to break down the chlorophyll and catalyze the red reactions).

But the trees aren’t the only heralds of autumn. If you listen carefully, you might hear a spring peeper or two calling in a state of seasonal confusion which biologists like to refer to as autumnal recrudescence.

As the days get shorter and the temperatures drop, conditions resemble those occurring in the spring, and a few of the frogs will think it’s time to find a girlfriend. Birds sometimes do this too.

And the steelhead are beginning to run. Large rainbow trout from Lake Erie make their way into the same cold, clear streams where they were born in order to start a new generation.

As descendants of fish from Washington state, steelhead can tolerate both saltwater ocean, where they spend their adult life, and freshwater streams, where they return to spawn. This marine-to-freshwater migration is referred to as anadromy. These fish can weigh up to 55 pounds and measure 45 inches, and, if you hook one, you’re in for a fight. They’re kind of fun to catch. Like my fellow CWC Conservationist Dave Anderson said in his Chautauqua Watershed Notes article last week, trout need clean, cold water to live and reproduce. That’s part of why we do what we do.

The Chautauqua Watershed Conservancy is a local, private nonprofit organization with a mission to preserve and enhance the water quality, scenic beauty, and ecological health of the lakes, streams, wetlands and watersheds of the Chautauqua region. For more information on CWC, visit us at chautauquawatershed.org or facebook.com/chautauquawatershed or call 664-2166.