The heart-stopping scarlets and crimsons of some fall trees result from another process: The “abscission layer” at the base of the leafstalk traps sugars in the leaf. These last molecules of summer combine with other substances to produce a third type of pigment, called anthocyanin. The anthocyanins range in hue from bright red to deep blue. They often behave like the little slips of litmus paper familiar to high school chemistry classes: If the plant’s sap is acidic, the color will be red; if alkaline, blue. At other times of the year, anthocyanins give certain flowers and fruits their colors.
The vivid leaves mark the end of the growing season and the surrender of what were expensive, vital organs for the plant. All broad-leaved plants invest considerable energy into making leaves in the spring, only to lose their investment as the days shorten. It is one of the “little deaths” that many plants and animals endure.
Perhaps we pick up on this vibe. Fall festivals notwithstanding, at some level we understand that fall is a season of loss and decay. Autumn’s days are often marked with a sense of melancholy and even the sunniest hours can be bittersweet. As V’s of geese and swans traverse the sky, and our neighbor’s ponies grow shaggy coats, I find myself growing pensive, more reflective. Now on the shady side of 40, I ponder the inevitability of growing old, and am jarred by how quickly it happens. Everything seems transitory—leaves, seasons, life itself.
The end of summer, the loss of leaves, the expanding hours of darkness—we Midwesterners are forced to mark the passage of time. People in climates like ours live intimately with this annual heartbeat. Temporality pervades our art, our music, our literature, even our pop culture. “I wish it would rain!” Barbra Streisand’s character wails plaintively to Robert Redford in The Way We Were, as she pines for New York City’s seasons and its darker moods after life in (too) sunny California.
It’s not contemplation of death, per se, that inspires my mood, but rather an observation of my middle-age: Often the very old are aged only in body, not in essence. Somewhere amid the brittle bones and lined skin, there is a soul that still thinks about sex and good jokes, that still hasn’t figured everything out yet. This realization is both tragic and reassuring. When fall thrusts upon us each year the opportunity to dwell on transition, we are able to gradually accommodate ourselves to the unsettling fact that body, mind, and soul will not necessarily end up the same age.
Evolutionary biologists have a larger explanation for the phenomenon of autumnal color. To focus on the cessation of growth and the disintegration of plant pigments is to see the trees in the narrowest physiological sense. Leaves are vital organs, it’s true, but ones with a serious drawback. A leaf’s flat, broad surface leaks water like a sieve. That process, called transpiration, occurs on so grand a scale that it is a major part of the global water cycle. Leaves require continual replenishing from the tree’s roots in order to function.
But in winter, water freezes, and a tree can’t use it that way, so it faces a six-month drought. Trees could never replace the water lost by their leaves. The evolutionary solution is to cut them off and enter dormancy, rather than suffer the fate of death by dehydration.
It’s interesting to note that those trees with the very small, wax-layered leaves that we call “needles”—conifers—do not need to lose their leaves in the fall. Indeed, they continue to make sugars long after their broad-leaved cousins have settled into winter sleep. (Conifers do need to replace their leaves from time to time, but they shed in small amounts throughout the year.)
So here is another paradox to ponder. By enduring a “little death,” a tree can live a longer life. The shedding of leaves can be withstood for years into the future. The loss is not a death at all, but a necessary withdrawal from a condition which, given changing circumstances, has become a
n extravagance a tree cannot afford. The pensive melancholy that settles so naturally over October’s sunny days is less a mark of subtle mourning and more a tacit sense that loss and death are entwined forever with life.
The real marvel of autumn lies not in the changing leaves, but in the fact that we see them as beautiful. The attraction is spontaneous and genuine. For the tree, the stunning colors are nothing more than a chemical expression of how they make a living. They serve no further purpose. Carotinoids are more stable than chlorophyll; hence, they linger longer into the fall. But our human eyes take in the brilliance of the leaves and our brains process the information. It registers as something of great beauty. For that, there is no evolutionary explanation. Recognition of beauty will not get us through the winter. But it can certainly carry our fragile, not-quite-natural selves through life.