In Autumn, the receptors in our primate eyes revel in the red and gold of trees.

Our ability to perceive red color is an oddity, one shared by our cousins the Old World monkeys and apes, but not by most other mammals. Evolution endowed our ancestors with an extra type of light-sensing cone cell that helped them see fruit and edible young foliage against a background of mature dark green leaves.

Nowadays, we're still looking at tree leaves, but no longer as food. Instead, our gaze at forests is a source of both seasonal delight and awareness of local ecology. With the help of satellite technology, study of the changing colors of leaves reveals the rapidly changing ecology of our planet.

Our aesthetic affinity for leaf colors finds one expression in the phenomenon known in the United States as "leaf-peeping." Suburbanites and city-dwellers flock to forested areas to soak our eyes in the delights of the season. We clog rural roads and infuse tourist cash into local economies. Leaf-peeping is most well-known along the spine of the Appalachians, from New England to the Smoky Mountains. This is the native range of maple, sourwood, oak, and ash, the botanical fireworks of temperate forests. But the changing hues of leaves also hold our attention on city streets where colors of ginkgo and oak enliven asphalt's gray. In western mountains and the north woods, larch and aspen gild the evergreen.

These are the colors of home, the visual manifestation of the ecosystems in which we live. Yet our language is dismissive. Leaf-peeping? To peep is to cast a furtive glance. Peeping Toms violate the "other" being viewed. And although the "peep show" started in the 18th and 19th centuries as a family-friendly viewing of landscapes and city scenes through stereoscopes and boite d'optique, the term now refers to a commodified, dissociated sexual gaze.

Peep is not the right word for a celebration of forests.

Other cultures also have traditions of autumn leaf viewing, especially cultures in the range of the maple-rich temperate forests. In Japan, momijigari (紅葉狩), an "excursion for hunting of autumn leaves," is part of the annual cycle of awareness of the rhythms of life's community. This is a practice deeply woven into the fabric of culture. In my travels in Japan in autumn, even the fast-food lunch boxes at train stations had decorative maple leaves nestled into the rice.

On the sacred island of Miyajima, maples framed the view of torii gates and shrines, and visitors returned to the mainland with leaf-themed gifts for colleagues and family. The life of the forest is thus built into both religious and everyday connections among people. In South Korea, dan pung ku gyeong (단풍 구경) means a purposeful look at the changing colors of leaves. My friends there tell me that this is a time to connect with both landscape and traveling companions. Likewise, the autumnal temperate forests of northern China have inspired shangye (赏叶), the reward or appreciation of leaves, and some parks receive millions of shangye visitors every year.

The wide cultural range of leaf-viewing reflects common human response to the temperate forest's colors. Instead of leaf peeping, perhaps we Americans should speak of autumnal awe or leaf wonder. Awe and wonder lead us to meaning, not to diversion or titillation.

The most wonderful views of the forest are often from an elevated position, from overlooks and escarpments. With the help of space rockets, we now have the most elevated views of forests possible: from orbits around the Earth. LandSat, Sentinel, and other satellites scribe regular paths around our planet and, as they fly, scan the whole surface of the Earth with their lenses. Instruments on the satellites measure not only visible light, but also colors beyond what the unaided human eye can detect, especially "near infrared." Healthy plant leaves reflect a lot of near infrared, so measuring this color lets us assess plant growth and vitality from afar. This is the technological complement to our Earth-bound leaf wonder, a practice that yields both beautiful images and useful knowledge.

Awesome though the view from space is, the news from aloft is not good. In the first dozen years of this millennium, LandSat's unwavering visual examination of the Earth's colors shows that the Earth lost 2.3 million square kilometers of forest, but only 0.8 million regrew. The rhythm of the seasonal colors of the remaining forests are also awry. Color changes are happening later in autumn across the Northern Hemisphere: Between 1982 and 2011 about 70 percent of the land surface had delayed autumnal color changes. In Europe, the site of the longest continuous study of vegetation color, a delayed autumn is the main cause of an increase in the length of the growing season. Worldwide, seasonal patterns of colors have changed over 95 percent of the land surface.

Changing autumn colors in parts of New England and China reveal some of the effects of climate change, a late-season complement to the increasingly odd timing of Spring time. This local perspective does not tell the whole story, though. New England, Japan, South Korea, and urban parts of northern China — places where leaf wonder is highly developed — have reduced logging in many of their own forests and import wood from elsewhere, a process known as displacement. Now that we're in a globalized economy, our aesthetic responses to forests must be integrated with the dispassionate lofty stare of satellites. This combination of aesthetic awareness and scientific analysis puts us in direct, sensory relationship with the forest and gives us the ability to understand what we see.

An appreciation of the colors of the local environment was all our ancestors needed to assess their world and thus thrive. Now, human power and population is vastly increased, threatening forests and human wellbeing. Our leaf wonder must also now grow from peep, to leaf wonder, to awareness of changing forests beyond our immediate gaze.

David George Haskell is a professor of biology at The University of the South in Sewanee, Tennessee. His latest book, The Songs of Trees, uses the stories of a dozen trees around the world to explore how the lives of people and trees are interconnected. His first book, The Forest Unseen, was the winner of the National Academies' Best Book Award and a finalist for the Pulitzer Prize in nonfiction. You can connect with him on Twitter: @DGHaskell.

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