The Mysteries of Autumn Color

Autumn foliage at Sweet Spring

© Steven Foster

This year fall colors came in waves. First a wave of glorious yellows and reds from Sugar Maples (Acer saccharum) planted around Eureka Springs, Arkansas. I couldn’t help but notice that the Sugar Maples planted along the sidewalk in front of the Best Western Eureka Inn at the top of Planer Hill showed their colors and dropped their leaves before the wild Sugar Maples in the forest directly across the street even began to turn color. Same for the Sugar Maples along Spring Street. Those planted along the street have dropped their yellow-orange leaves, while those in the adjacent woods have a glorious color display of orange to burgundy leaves, dominating the current color trend. So what is the difference between the colors and timing of the planted Sugar Maples and wild Sugar Maples? I suspect it is some type of genetic clock trigger. Which begs the question, how are autumn tree colors formed?

There is no single, definitive answer to the question of why trees turn color. Much of our understanding is physiological. The major factor among a myriad of variables is the diminishing length of the autumn day, hence the amount of daylight. Production of chlorophyll ceases, and as the green chlorophyll degrades, sugars and anthocyanadins (the vast group of compounds responsible for color combinations of fruits, leaves and flowers) begin to dominate the leaves, aided by the variables of moisture and temperature changes. The recipe changes from year to year and species to species. This is convention wisdom.

In the last 20 years an entirely new field of study—plant-animal interactions— hints of broader mechanisms, beyond mere physiological changes in the leaves. Fall colors are integrated in nature, signaling to fruit-loving animals and insects that fruits are ready for harvest, thus aid in seed dispersal. In some trees, the colors may send a signal to insect herbivores that feeding is over. The new science of autumn tree color suggests the process is a mix of defensive, seed-dispersing, signaling, and physiological functions all working in a symphonic display of intricate beauty. Our role in the process is simply to enjoy it.

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Steven Foster

Describing her first visit with Steven Foster in 1977, Harvard University botanist, Dr. Shiu Ying Hu (1908-2012), wrote, “Our conversation reminded me of something that Confucius said two thousand years ago. ‘In any company of three persons, there must be one who can be my teacher’. . . I found in Steven Foster a teacher who could share a profound knowledge of economic botany, particularly in the cultivation and uses of herbs.” In 1974, at age 17, Steven Foster, began his career at the Sabbathday Lake, Maine, Shaker Community Herb Department —America's oldest herb business, dating to 1799. There he established three acres of production gardens and managed 1700 acres for the commercial harvest of botanicals. For forty-three years, Steven has photographed and researched herbs from the Amazon rainforest to the highlands of Vietnam. Foster has over 900 photo-illustrated articles published in a wide range of media. Steven also served as Chairman of the Board of Trustees of the American Botanical Council, and a Contributing Editor to the organization's journal, HerbalGram. Steven is the author, co-author and photographer of eighteen books, including the NEW 2014 Third Edition of A Peterson Field Guide to Medicinal Plants: Eastern and Central North America (with James A. Duke), along with National Geographic’s Complete Guide to Medicinal Herbs (2010), and A Desk Reference to Nature’s Medicine (2006, with Rebecca Johnson), awarded a 2007 New York Public Library “Best of Reference.” He is senior author of three other Peterson Field Guides, including A Field Guide to Medicinal Plants and Herbs (with Dr. James A. Duke), 1st & 2nd editions, 1990, 2000; A Field Guide to Western Medicinal Plants and Herbs with Dr. Christopher Hobbs, (2002); and A Field Guide to Venomous Animals and Poisonous Plants of North America (with Roger Caras, 1995). Other titles include Herbal Emissaries: Bringing Chinese Herbs to the West (with Prof. Yue Chongxi, 1992); Herbal Renaissance (1994); among others. Foster makes his home in Eureka Springs, Arkansas.

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