The entire forest seems to ask for quiet, a long shhh among the trees. Another great autumnal gust sweeps through the woods, shaking multicolored leaves in a susurration so all-encompassing it seems like a soft blanket of sound. Reds, yellows, oranges, and a vanishing hint of green wave and flutter, a few leaves carried off to tumble and twirl along the wind. Each one carries the last memory of summer as they lilt and eventually settle to carpet the forest floor as autumn makes itself comfortable in these ancient groves.
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In ways large and small, the forest is settling in for its slumber. The season of growth is long past. Birds aren’t belting their best to impress potential mates. Insects are sticking closer to their hiding spaces. For many species, the year’s offspring must now fend for themselves among the increasingly chilly nights. There’s no courting or nesting. Life seems to slow as the days grow shorter and shorter, some mornings bringing a rim of frost to puddles and ponds in this part of Pliocene Europe.
Some creatures have moved farther south, following the fading edge of warmth and the possibility of vegetation that does not slough off for months at a time. But some have lingered, feeling the seasonal turn. The great mastodon Anancus dozing to the soothing noise of the rustling leaves has seen this seasonal swing happen year after year, since she was a floppy-trunked youngster never far from the shadow of her mother.
With every snack she’s slowly been moving herself farther and farther south toward forests that keep leaves on offer longer.
The blaze of color she’s watched settle in each autumn takes its cue from the light. Trees have to live according to the rhythms of weather and climate, varying from one year to the next. One good year might be followed by a hard one, or several, trees slowing their growth and leaving a record within the rings that document their story just as geologic strata record the history of entire habitats.
But shorter days, longer nights, and the colder temperatures that come with them are practically constants dictated by Earth’s cooler and drier climate. The trees of this Eurasian forest have evolved to move with the changes, suppressing their activities so that they might see next spring. Earth isn’t basking in an endless, warm summer anymore. Through millions of years, a semitropical planet has turned to one with polar and temperate zones, places where organisms have to be flexible. Survival means swaying with the seasons.
It’s hard to thrive in the cold and the dark. Less sunlight each day means a cutback of photosynthesis, that most essential of plant activities. Trees could keep at it through the chillier half of the year, as evergreens do, but those gymnosperms have evolved to withstand extremes. Conifers have arrays of waxy needles that resist freezing and all the damage ice crystals can do. The comparatively soft and broad leaves of most angiosperms can’t do the same.
When the deep freezes set in and the ground is cold, such thin leaves would be damaged and torn even if the trees were to keep them. Without evolving new leaf shapes, the broad-leafed trees have done something else instead. Many angiosperm trees reclaim the materials they need from their own leaves, effectively going into a slumber when getting by on less may allow them to vibrantly leaf out again as warmer and longer days return.
The trees still spreading leaves above the head of Anancus are not intentionally changing their shades. The display is not an active effort to replace the summertime green with autumnal orange. During the spring and summer, leafy greens are created by an abundance of chlorophyll. They take in most every shade except for green, just as it’s been for hundreds of millions of years. But leaves also have other compounds within them, hidden by the abundance of chlorophyll. Many trees have carotenoids, pigments that appear as vibrantly yellow and orange when allowed to stand out. These hidden shades get their time to shine thanks to the process trees and shrubs use to shut down their leaves for the season, gradual and imperfect reabsorption causing leaves to change their colors.
Anancus will be back then, when all the reds, yellows, and browns have once again fed curtains, canopies, and carpets of green.
Some of the sugars created by the busily photosynthesizing leaves get shut off as the leaves are left to their end, as well, showcasing particular pigments—anthocyanins—that blaze bright red. As the long nights settle in and cooler air temperatures arrive, trees start shutting down the veins and vessels to their leaves as each stops creating new chlorophyll. The greens fade away, revealing shades determined by the carotenoids and anthocyanins that were there all along.
It’s a final splash of color before the tree begins to once again rid itself of what it doesn’t presently need. In this forest, the oval leaves of ash trees turn red, while shrubs called boxwoods, growing wherever the treetops allow enough light, shade to orange. Even though the bright hues make the gray hide of Anancus look a little on the drab side, the massive elephant now stands out among all the amazing colors because the subdued palette of winter settles in.
Anancus is a forest elephant. The massive molars in her mouth can handle entire branches as well as leaves and fruits. Her life is one of gradually pruning the forest, leaving bare patches from the ground to the tallest her trunk can reach. Over these past few weeks she’s been noshing her way southward until she reaches more comfortable temperatures. A season endlessly chewing on frostbitten bark alone will not be pleasant, and with every snack she’s slowly been moving herself farther and farther south toward forests that keep leaves on offer longer.
The decaying leaves in the forest she leaves behind are also a promise to the new plant growth that will come up from the soil. The leaves refresh the soil as they break down, returning some of the vital organic compounds to the loam. The ground is replenished every season, the leaves’ breakdown just as important to the plants that will come up in spring as the return of longer days. Anancus will be back then, when all the reds, yellows, and browns have once again fed curtains, canopies, and carpets of green.
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From the book When the Earth Was Green: Plants, Animals, and Evolution’s Greatest Romance by Riley Black. Copyright © 2025 by Riley Black. Published with the permission of St. Martin’s Press, an imprint of the St. Martin’s Publishing Group, a division of Macmillan.
