As trees go, the willow looks tired. Not so much weeping as it is sleeping—as if it might need a nap, like an old man slouched over, its burdens too great to continue to lift its limbs. Not so the pine, the birch, the palm, even the oak—these trees always seem to stand upright, solid, well-rested. But don’t let their posture fool you—even the birch needs to rest its branches after a long day standing in the hot sun.
This is what Eetu Puttonen from the Finnish Geospatial Research Institute in Masala, Finland, and his team of researchers recently discovered. As described in the journal Frontiers in Plant Science, Puttonen and his team used terrestrial laser scanning on a pair of silver birch trees—one in Finland and one in Austria—to measure the movements of their branches and foliage. While it has been known for a couple hundred years that plants experience daily leaf motion, this level of observation has never before been possible. Additionally, Puttonen’s study, unlike others, focused on just one day, rather than a season. What they confirmed and quantified in detail was that as the sun set, so did the trees; and as the sun began to rise, so did the trees. In everyday parlance, the trees fell asleep at night and awoke the next morning.
Do trees really need to rest? To sleep? To some degree this still needs to be determined. Puttonen explains that water balance within a tree or plant photoperiodism—a plant’s response to light or dark periods—could be the driving force behind the nightly slumber patterns. Yet there is increasing evidence, observational and genetic, that plants follow a circadian rhythm, much like animals. Circadian rhythm in plants is not simply an environmental response—like photoperiodism’s turning of a flower’s head toward the sun—but part of their physiological design. The “why” and “how” of this still needs to be discovered, notes C. Robertson McClung, writing in the journal The Plant Cell.
The idea that a tree sleeps sounds odd. We get that mammals sleep, and most animals, maybe even spiders and insects, but plants? Flowers, maybe. Trees we know by their height, their strength, their longevity. Trees we measure in terms of years, often hundreds of years, but not each day morning and night.
At the center of this is the circadian rhythm—the 24-hour cycle that biological processes follow. This rhythm originates within life, within its physical makeup, though external forces such as temperature and sunlight affect the rhythm. People have it, bacteria have it, trees have it; it is perhaps the most important “clock” for human existence. It affects how we learn and how we remember.
Given the importance of the circadian rhythm for human life, it should come as no surprise that this is the clock described in our creation narrative. When God started to work, this work was measured not by the age or the year but by the day. As the author of Genesis puts it: “There was evening, there was morning; one day.” When God ended his work, he blessed and sanctified that day. God seems to measure his creative works by the day.
The same is true when we read the Gospels. Take John: we are often reminded that this book covers a three-year period of Jesus’ public ministry. But it does not. At best, it covers a period of a few weeks—mostly a few notable days in the years of Jesus’ public ministry. The day there was a wedding in Cana, the day of a healing in Bethesda, the day Lazarus rose from the grave, the day Jesus sacrificed himself for the sake of others. Important days. John seems to measure the ministry of Jesus by the day.
We often don’t do this. When we read the Bible, we often start our clock at Genesis 3, not Genesis 1. We measure our world by the year, by the age, tracing an eschatological arc from the fall of people to the advent of Jesus to the consummation of the ages.
As biblical scholar and pastor Michael LeFebvre explains, “The massive, awe-inspiring scope of God’s creation is mapped across a simple, seven-day week in Genesis 1. The fourth commandment (Exod. 20:8–11) tells us why this is so. As the reflectors of God’s image, we are taught to keep a cadence of six days’ labor and one day to worship as we steward the creation toward its consummation.”
Tree lifespans range from the willow trees, which have relatively short lives—about the same lifespan as a human being—to centuries-old giants like redwoods and baobabs. Yet in the very biology of trees, in their circadian rhythm, they reflect the importance of the day in the cycle of creation. They awake with the sun and sleep with the dusk. Our attention and focus should be likewise—to make the day the primary measure of our lives.
Wake, sleeping willow, the sun is shining Up, sleeping willow, your branches twining Darkness is fleeing, lightness is being Reach, sleeping willow, glory divining!
Douglas Estes is assistant professor of New Testament & practical theology and DMin program director at South University–Columbia. He wrote about recent discoveries for issue 48 of The Behemoth.
