Do Trees Sleep? Birch Trees Recorded Resting Branches At Night For The First Time

For the first time, scientists from Austria, Finland, and Hungary have observed physical changes in trees that correspond to the sleeping patterns in humans, leading to the question: do trees sleep?

Charles Darwin already discovered that smaller plants change overnight. Flowers open and close their petals at night, and trees have been known to close their leaves, but this is the first time researchers have seen the sleeping phenomena in large trees, according to News Discovery.

"It was a very clear effect and applied to the whole tree," Andras Zlinsky of Hungary's Centre for Ecological Research said. "No one has observed this effect before at the scale of whole trees, and I was surprised by the extent of the changes."

Researchers used laser scanners to scan two trees in different countries to scrutinize a cloud of millions of different points across their surface area. The testing was done on nights with no wind or condensation that could tamper with the results. Scientists learned that trees do in fact move overnight and droop in such a way that it seems they are sleeping, or at the very least relaxing.

"Our results show that the whole tree droops during [the] night, which can be seen as position change in leaves and branches," Eetu Puttonen, a researcher from the Finnish Geospatial Research Institute, said. "The changes are not too large, only up to 10 centimeters for trees with a height of about five meters, but they were systematic and well within the accuracy of our instruments."

Researches studied one tree in Finland and the other test was conducted on a tree in Austria. They measured the tree's sleeping movement by using a time series of lasers that would not interfere with the trees. The leaves and branches of both trees drooped gradually, with the lowest position recorded a couple of hours before sunrise. In the morning, as the sun rose, the trees regained their original rigidity within a few hours. Researches do not yet know whether they spring back into position because of the sun or because of an internal cycle.

"Plant movement is always closely connected with the water balance of individual cells, which is affected by the availability of light through photosynthesis...but changes in the shape of the plant are difficult to document even for small herbs as classical photography uses visible light that interferes with the sleep movement," said Zlinszky.

This is why the scientists used infrared lasers which reflect off the leaves. Using a laser scanner means disturbance to the plants natural rhythm and movement is minimal. Each point on a tree is illuminated for a fraction of a second. This technique allows a full-sized tree to be automatically mapped within minutes with sub-centimeter resolution according to New Scientist.

"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," said researcher Norbert Pfeifer.

The study to discover if trees sleep was on birch trees, and the team of scientists are now hoping to expand their research to see if other tree species have the same "sleep" patterns.

I'm confident it will apply to other trees," says Zlinszky.

The team offered two hypotheses for their findings, which were published in Frontiers in Plant Science. The first is that the drooping could be due to a loss of water, called turgor pressure, causing the branches and leaf stems to lose their rigidity. The second possible explanation is that trees do sleep and really are resting. It would mean that trees follow the same circadian rhythms of other flora and fauna according to The Washington Post.

"There have been some studies on circadian rhythms in trees, mostly studying gene expression, but this latest research is a beautiful way to watch it happen in individual trees," says C. Robertson McClung of Dartmouth College in Hanover, New Hampshire. "It shows things are happening in the real world."

[Photo via Dmitry Savin/Getty Images]