It depends on how you define "sleep," it has been proven that trees do relax their branches at night, which might be a sign of snoozing, scientists said. To discover this researchers set up lasers that measured the movements of two silver birch trees (Betula pendula) at night. One tree was in Finland and the other in Austria, and both were monitored from dusk until morning on dry, windless nights in September for movements created by the environments to be the minimum possible. This was close to the solar equinox, when daylight and night time are about equal.The laser scanners used infrared light to illuminate different parts of the tree, each for fractions of a second. This provided enough detail to map each tree within minutes, the researchers said.
The silver birches' branches and leaves sagged at night; they reached their lowest position a few hours before sunrise, and then perked up again during the wee hours of the morning, the researchers found.
So if this is considered a form of sleep, trees after all might sleep after dark, according to precise laser measurements that detected the plants' branches drooping at night.
Eetu Puttonen said: "Our results show that the whole tree droops during night, which can be seen as position change in leaves and branches,", "The changes are not too large, only up to 10 centimeters [4 inches] for trees with a height of about 5 meters [16 feet]."
It's unclear if the sun "woke up" the trees or if they relied on their own internal circadian rhythm, the researchers said. But "the fact that some branches started returning to their daytime position already before sunrise would suggest this.The finding isn't too surprising, but oddly enough it hadn't been studied until now, the researchers said. Most living organisms have day and night circadian rhythms, and any gardener will notice that some plants open their flowers in the morning and that some trees close their leaves at night.
Supplied by Carol Mar. 3º Y