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Facts on Foliage
Natural History, Nov, 2000 by Robert (American businessperson and engineer) Anderson
Why do leaves change color? Ask most people this question, and you'll probably get a simple answer, such as "Because winter's coming." Of course, the story is much more complex than that, and at least two good Web sites tell us how nature produces so many vivid hues, seemingly out of thin air.
The first site (willow.ncfes.umn.edu /leaves/leaves.htm) is maintained by the U.S. Forest Service. It explains that the timing of the autumn display, although influenced by rainfall and temperature, is primarily triggered by the decreasing availability of light for photosynthesis as nights grow progressively longer. Also noted is the Forest Service's Fall Color Hotline (800-354-4595), which you can call for reports on peak foliage viewing around the country.
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The second good fall-color primer comes from Pacific Union College botanist Bryan Ness. In a feature found at About.com (botany.about.com/science /botany/library/weekly/aa120797.htm ?terms=fall+leaves), he goes into considerable detail about the chemistry underlying the fall show. I learned that as leaves die and change color, building materials are salvaged from them for winter storage. The most important of these is magnesium. The green chlorophyll must be broken down to recover this element, and what remains are the less dominant, so-called helper pigments, the carotenoids and anthocyanins, whose yellows, oranges, and reds give the dying leaf its color. Check out Ness's simple chemistry experiment, which reveals the pigments that lie hidden in any green leaf.
Robert Anderson is a freelance science writer based in Los Angeles.
COPYRIGHT 2000 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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