Space & Innovation

Do Trees Sleep?

Observations with laser scanners show that trees have a day-night rhythm too.

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The idea of an oak or a spruce tree taking a snooze seems a bit bizarre. But for the first time, scientists have observed physical changes in trees that correspond in some ways to sleep in humans and animals, or at least to our day-night rhythm.

Researchers from Austria, Finland and Hungary used laser scanners to scan two trees and scrutinize a cloud of millions of different points across their surface area. From that, they learned that trees actually move overnight, a phenomena that scientists dating back to Charles Darwin have observed in smaller plants.

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"Our results show that the whole tree droops during night which can be seen as position change in leaves and branches", Eetu Puttonen, a researcher from the Finnish Geospatial Research Institute, explained in a press release. "The changes are not too large, only up to 10 centimeters for trees with a height of about 5 meters, but they were systematic and well within the accuracy of our instruments."

To filter out effects from weather and location, the researchers studied one tree in Finland and another far away in Austria, under calm conditions with no wind. The leaves and branches drooped gradually, with the droopiest position achieved a couple of hours before sunrise. In the morning, the trees regained their original rigidity within a few hours.

But Another researcher, András Zlinszky of Hungary's Centre for Ecological Research, said that the drooping effect probably is caused by the loss of internal water pressure within the tree's cells, a phenomenon called turgor pressure.

Earth has Three Trillion Trees

"It means branches and leaf stems are less rigid, and more prone to drooping under their own weight," Zlinsky told the British publication New Scientist.

Turgor pressure is influenced by photosynthesis, which stops once the sun goes down, Zlinsky explained.

The study was published recently in Frontiers in Plant Science.

Photographer Beth Moon spent 14 years traveling across the world to find and photograph the world's oldest trees. She spent time in the United States as well as remote areas and reserves in Europe, Asia, the Middle East and Africa. Living up to 500 years, the Heart of the Dragon (pictured) is unique to Socotra island in Yemen. Growing in severe conditions, they have raised their branches upward over time in an effort to obtain moisture from the highland mists -- hence the distinctive appearance of their canopies, like an umbrella blown inside out.

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The legendary Bowthorpe Oak, with its rugged bole, gnarled branches, and great spreading crown, stands in a grassy meadow behind a stone farmhouse in Bourne, Lincolnshire. With a circumference of 40 feet, it competes for the title of largest-girthed living oak in Britain. It is also perhaps the oldest living oak tree, with an estimated age of 1,200 years (give or take a century).

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Above, a desert rose on the island of Socotra in Yemen, a UNESCO World Heritage Site. The trees store water in their trunks to survive the dry climate.

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This Spanish Chestnut on the grounds of Croft Castle in Herefordshire, England, is between four and five centuries old.

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Elegant in shape and form, these strange and magnificent baobabs,

Adansonia grandidieri

, seem to rise effortlessly to heights of 100 feet.

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At Wakehurst Place, set among 170 acres of beautifully manicured gardens, is a gloomy cliff of Ardingly sandstone. A few hundred English winters have eroded the soil, but the yews of these woods have adapted to their surroundings. Tangled, black and menacing, they send their naked roots cascading over the huge greenish-blue rocks of the cliff’s edge, in search of soil to sink into.

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There is something magical about these two stately yews, which act as pillars, framing the north door of the church in Stow-on-the-Wold, Gloucestershire. Not much is known about these trees. It is presumed that they were planted sometime in the 18th century and are the survivors of a formal avenue that led to the church. It has also been suggested that this church door was the inspiration for the Doors of Moria in The Lord of the Rings, as J.R.R. Tolkien is known to have passed through the area.

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Elegant in shape and form, these strange and magnificent baobabs seem to rise effortlessly to heights of 100 feet. They are found only on the island of Madagascar, where they are known as

renala

, Malagasy for ‘mother of the forest.’ These trees are a valuable source of food, fiber, dye, rope and fuel, among other things. The trees in this grove, known as the Avenue of the Baobabs, are approximately 800 years old. Sadly, these 20-25 baobabs are the only survivors of what was once a dense tropical forest. The avenue was granted temporary protected status in 2007, as a prelude to its promised future as Madagascar’s first natural monument.

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