A friend of mine tells me that the latter days of summer always make her depressed. She feels this way because as the days get shorter she has less time for her favorite outdoor activities like hiking, fishing, canoeing, and exploring. I respond by telling her that the end of summer makes me joyous. The lengthening nights mean I have more time for observing the wonders of galaxies, nebulae, stars, planets, and moons.

What unites us is that we both acknowledge we are living on Earth at a time when the day-night cycle is optimal, not just for humans, but for many species of life that are crucial for sustaining our civilization and wellbeing. As I explain in my book, Improbable Planet,1 if the day-night cycle were slightly less than 24 hours, there would be less even precipitation distributed over Earth’s landmasses, a higher average surface temperature, and greater temperature extremes over the landmasses. On the other hand, if the day-night cycle were slightly more than 24 hours, the difference between day and night temperatures on many landmass regions would be too extreme for large animals that lack access to artificial cooling and heating. Either way, our current human population and level of civilization would not be possible.

Day-Night Cycle and Trees
A team of 12 environmentalists, biologists, and foresters, led by Roman Zweifel, recently published a paper in New Phytologist where they demonstrated how the day-night cycle also impacts the health and growth of trees.2 Zweifel’s team presented the first comprehensive study of the radial growth rate of tree trunks and stems with a temporal resolution (the precision of a measurement with respect to time) of 10 minutes. They conducted their study on seven different tree species in Switzerland over an eight-year period and analyzed a total of 57 million data points. The mean annual temperature and precipitation for the 50 tree sites that were part of the study ranged from 4.5 to 11.9°C (40 to 54°F) and 540 to 1700 mm (21 to 67 inches).

Zweifel’s team discovered that trees gain almost all their growth at night, with peak growth occurring during the hours after midnight. They also found that tree species able to grow significantly during the hours before midnight show the largest annual growth increase.

The team’s observations affirm a theory established a decade ago to explain tree trunk/stem growth.3 This theory connects soil water dynamics, tree hydraulics, and atmospheric water demand to determine the water potential in the cambium where new wood and bark cells form. The cambium is the tissue layer between the xylem and the phloem where plant growth occurs. It takes both carbon and water to facilitate new tree growth. Specifically, Zweifel’s team affirmed that it takes a high hydrostatic or turgor pressure in the cambium to draw up the needed carbon and water for rapid trunk/stem growth. Their observations established that this high hydrostatic pressure in the cambium is greatest at night and it peaks in the hours after midnight.

Optimal Time
Zweifel and his colleagues did not explicitly address—but it’s implied—that we are living at the optimal time in Earth’s history for tree growth. The team’s research findings showed that it takes time during the night for the hydrostatic pressure in the cambium to build up to where the maximum rate of trunk/stem growth can be initiated and sustained. These findings imply that the longer the day-night cycle, the greater the tree growth.

Given equivalent nutrient and water availability, a rotation rate of 24 hours per day is optimal for tree growth. We are living at a time when Earth’s rotation equals 24 hours per day.

The results come with one important caveat. Too long of a day-night cycle implies colder temperatures after midnight and warmer temperatures after noontime. There is a limit to how great a day-to-night temperature difference trees can tolerate before it impacts their growth rate. Deserts, for example, experience greater day-to-night temperature differences than do wetter, more humid land regions. It is well observed that trees in deserts grow at a much slower rate than trees in wetter regions, even where the deep soil water availability is comparable.

Day-Night Cycle Variation and Human Flourishing
Earth’s rotation rate has not always been 24 hours per day and will not be so in the future. When the planet Theia collided/merged with the proto-Earth to make a larger Earth and form the Moon, Earth’s rotation rate was less than 3 hours per day.4 Since then, tidal forces exerted by the Moon and Sun on Earth have gradually slowed down Earth’s rotation rate.

About 375 million years ago, Earth’s rotation had slowed down enough for significant tree growth to be possible. In less than 100 million years from now, the Earth will be rotating so slowly and the Sun shining so brightly that trees will no longer be able to exist. Thanks to many intricate designs in the Sun, Moon, Earth, and trees and to the timing of our own creation, we are able to reap the maximum possible benefits from trees during the human era.

Check out more from Reasons to Believe @Reasons.org


  1. Hugh Ross, Improbable PlanetHow Earth Became Humanity’s Home (Grand Rapids, MI: Baker Books, 2016): 58, 62–77.
  2. Roman Zweifel et al., “Why Trees Grow at Night,” New Phytologist (published online ahead of print June 12, 2021): doi:10.1111/nph.17552.
  3. David R. Woodruff and Frederick C. Meinzer, “Size-Dependent Changes in Biophysical Control of Tree Growth: The Role of Turgor,” in Size- and Age- Related Changes in Tree Structure and Function, eds. Frederick C. Meinzer, Barbara Lachenbruch, and Todd E. Dawson (Dordrecht, Netherlands: Springer, 2011): 363–384, doi:10.1007/978-94-007-1242-3_14.
  4. Matija Ćuk and Sarah T. Stewart, “Making the Moon from a Fast-Spinning Earth: A Giant Impact Followed by Resonant Despinning,” Science 338, no. 6110 (November 23, 2012): 1047–1052, doi:10.1126/science.1225542.

About The Author

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. I also am eager to equip Christians to engage, rather than withdraw from or attack, educated non-Christians. One of the approaches I’ve developed, with the help of my RTB colleagues, is a biblical creation model that is testable, falsifiable, and predictive. I enjoy constructively integrating all 66 books of the Bible with all the science disciplines as a way to discover and apply deeper truths. 1 Peter 3:15–16 sets my ministry goal, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience." Hugh Ross launched his career at age seven when he went to the library to find out why stars are hot. Physics and astronomy captured his curiosity and never let go. At age seventeen he became the youngest person ever to serve as director of observations for Vancouver's Royal Astronomical Society. With the help of a provincial scholarship and a National Research Council (NRC) of Canada fellowship, he completed his undergraduate degree in physics (University of British Columbia) and graduate degrees in astronomy (University of Toronto). The NRC also sent him to the United States for postdoctoral studies. At Caltech he researched quasi-stellar objects, or "quasars," some of the most distant and ancient objects in the universe. Not all of Hugh's discoveries involved astrophysics. Prompted by curiosity, he studied the world’s religions and "holy books" and found only one book that proved scientifically and historically accurate: the Bible. Hugh started at religious "ground zero" and through scientific and historical reality-testing became convinced that the Bible is truly the Word of God! When he went on to describe for others his journey to faith in Jesus Christ, he was surprised to discover how many people believed or disbelieved without checking the evidence. Hugh's unshakable confidence that God's revelations in Scripture and nature do not, will not, and cannot contradict became his unique message. Wholeheartedly encouraged by family and friends, communicating that message as broadly and clearly as possible became his mission. Thus, in 1986, he founded science-faith think tank Reasons to Believe (RTB). He and his colleagues at RTB keep tabs on the frontiers of research to share with scientists and nonscientists alike the thrilling news of what's being discovered and how it connects with biblical theology. In this realm, he has written many books, including: The Fingerprint of God, The Creator and the Cosmos, Beyond the Cosmos, A Matter of Days, Creation as Science, Why the Universe Is the Way It Is, and More Than a Theory. Between writing books and articles, recording podcasts, and taking interviews, Hugh travels the world challenging students and faculty, churches and professional groups, to consider what they believe and why. He presents a persuasive case for Christianity without applying pressure. Because he treats people's questions and comments with respect, he is in great demand as a speaker and as a talk-radio and television guest. Having grown up amid the splendor of Canada's mountains, wildlife, and waterways, Hugh loves the outdoors. Hiking, trail running, and photography are among his favorite recreational pursuits - in addition to stargazing. Hugh lives in Southern California with his wife, Kathy, and two sons.

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