You might think trees stand still and motionless throughout the night, barely alive compared to their daytime bustle. Yet groundbreaking laser scanning technology has revealed something remarkable about these silent giants. Trees actually “sleep” at night, their branches and leaves gradually drooping as darkness falls, only to return to their upright positions with the morning sun.
This nocturnal behavior isn’t just a curiosity. Scientists from Austria, Finland and Hungary have measured the sleep movement of fully grown trees using a time series of laser scanning point clouds consisting of millions of points each. Their findings challenge everything you thought you knew about how trees spend their nighttime hours.
The Discovery That Changed Everything
Imagine watching a time-lapse video of a silver birch tree through the night. The changes are not too large, only up to 10 cm for trees with a height of about 5 meters, but they were systematic and well within the accuracy of our instruments. This groundbreaking discovery emerged from researchers who used cutting-edge terrestrial laser scanning technology to monitor trees around the clock.
The research team focused on silver birch trees in two different countries to eliminate any environmental variables. A team of researchers from Austria, Finland and Hungary measured the sleep movement of fully grown trees using a time series of laser scanning point clouds consisting of millions of points each. The precision of their measurements revealed patterns that had never been documented before.
How Scientists Caught Trees Sleeping
For this study, the researchers used a terrestrial laser scanner to precisely map out a set of points on two separate silver birch trees – one in Austria, and one in Finland. By making a series of these maps between dusk and dawn, and measuring the displacement of each point, they were able to trace how the whole tree moved over the course of the night.
This wasn’t your typical nature observation. With a laser scanner, plant disturbance is minimal. The technology allowed scientists to document something that classical photography could never capture because visible light would interfere with the natural sleep patterns they were trying to observe.
The Dramatic Nighttime Transformation
The leaves and branches were shown to droop gradually, with the lowest position reached a couple of hours before sunrise. In the morning, the trees returned to their original position within a few hours. Think of it like watching a person slowly nod off to sleep, then wake up and stretch in the morning.
The timing couldn’t be more precise. The team determined that, close to sunrise, the branches of the trees were droopier than at twilight. Some of the branches displaced as much as 10cm from their position at dusk. This systematic movement excludes random effects from wind or other disturbances.
Water: The Hidden Force Behind Tree Sleep
The secret behind this nocturnal drooping lies in something called turgor pressure. It’s likely that the droop is caused by a decrease in turgor pressure, a type of internal water pressure that keeps plants upright. When photosynthesis stops at night, this crucial pressure system changes dramatically.
Leaves and branches replenish their water storage during the night, increasing their weight and causing them to droop down. Picture filling a balloon with water – it becomes heavier and sags under its own weight. It usually takes trees all night to replace the water lost during the day. During this time, the stomata are closed and the plant cells fill up with water.
The Ancient History of Plant Sleep Studies
You’d be surprised to learn this isn’t entirely new territory. Researchers have been studying the day and night cycle in plants for a long time: Linnaeus observed daily patterns in flower opening and closing, contributing to early understanding of plant rhythms, and Darwin recorded the overnight movement of plant leaves and stalks and called it “sleep”.
Ancient observations of plant rhythms date back centuries, with various historical accounts of daily plant movements. He observed that leaves of several tree species exhibit a horizontal position during the day and a more vertical position at night. However, until now, these studies focused only on small potted plants.
The Biological Clock Connection
It’s possible the droop is also related to circadian rhythms, which are encoded in almost every creature on earth. These internal biological clocks help organisms anticipate and prepare for daily environmental changes. A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment.
Some branches started to return to their daytime position before sunrise, hinting that perhaps the plants do follow an internal clock. This suggests trees don’t simply react to sunlight but actually anticipate dawn through their internal timing mechanisms.
The Mystery of Light Versus Internal Timing
It is not yet clear whether they were “woken up” by the sun or by their own internal rhythm. This remains one of the most intriguing questions in tree sleep research. Perhaps the most important open question is whether the observed branch movements take place under the influence of light from sunset and sunrise, or if they are independent from light and governed by the internal circadian clock of the plant.
The implications are fascinating. If trees wake up on their own internal schedule, it means they’re actively preparing for photosynthesis before the sun even rises. This would give them a competitive advantage in capturing the first precious moments of daylight.
Beyond Silver Birches: What Other Trees Might Sleep
Research scientists in Austria, Finland, and Hungary have used laser scanners to observe and record this “sleeping” behavior in silver birch thus it is natural to assume other tree species behave similarly. The research team is particularly interested in expanding their studies to include different species.
The researchers tell Coglan that they hope to repeat the experiment on other tree species, and are particularly interested in chestnuts and poplars, two trees in which genes associated with circadian rhythms have been found. Imagine discovering that entire forests are quietly sleeping and waking together each day.
Revolutionary Applications and Future Research
We believe that laser scanning point clouds will allow us to develop a deeper understanding of plant sleep patterns and to extend our measurement scope from individual plants to larger areas, like orchards or forest plots. This technology could transform how we understand forest ecosystems and agricultural management.
These findings also have practical applications. For example, laser scanning could be used to monitor plant water status in a greenhouse to automate watering regimes and save valuable resources. The potential for precision agriculture and water conservation is enormous.
Conclusion
The revelation that trees actually sleep at night transforms our understanding of these magnificent organisms. The changes are not too large, only up to 10 cm for trees with a height of about 5 meters, but they were systematic – proving that even the smallest movements in nature can reveal the most extraordinary secrets. From ancient Greek observations to modern laser technology, we’re finally glimpsing the hidden rhythms that govern forest life.
Next time you walk past a tree at dusk, remember that you’re witnessing the beginning of its nightly rest period. These sleeping giants are preparing for another day of photosynthesis, growth, and life. What do you think this discovery means for how we should care for our forests? Tell us in the comments.
