View of night sky and stars with silhouettes of pine trees.

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Do Trees Sleep? The Surprising Answer

· Article

Do Trees Sleep? The Surprising Answer

Dogs and cats do it. Chimps and insects do it.


Even trees may slumber.


In a study published in the journal Frontiers in Plant Science, scientists from Austria, Finland and Hungary observed trees drooping their leaves and branches at night — a possible equivalent to falling asleep in humans and animals.


“Our results show that the whole tree droops during night, which can be seen as position change in leaves and branches,” study co-author Eetu Puttonen, of the Finnish Geospatial Research Institute said in a statement. Though these changes were not too large — only up to 4 inches for branches in trees with a height of about 16 feet — they were systematic, Puttonen said.


To spy on trees’ sleeping habits, the researchers looked at two birches in Finland and Austria. Using laser scanners, the scientists examined how the trees’ leaves and branches drooped gradually at night, reaching their lowest position a couple of hours before sunrise. In the morning, the leaves and branches returned to their usual positions within just a few hours.


The researchers don’t know for sure if the trees changed their positions because they were “woken up” by the sun, or because they might have an internal clock that signals that it is time to wake up. But the fact that some branches began to return to their daytime position even before sunrise suggests that the latter might be the case, the researchers wrote in their study.


Trees are not the only plants that seem to adapt their behavior to the day-and-night cycle. If you have ever taken a late-night walk through a garden, you may have noticed that some flowers, like tulips, close up at night. The famous biologist Carl Linnaeus noted that flowers in a dark cellar continued to open and close, according to Scientific American. And the naturalist Charles Darwin, in his book The Power of Movement in Plants, recorded overnight movement of plant leaves and stalks, also calling it “sleep.”



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