Wissenschaftler haben zum ersten mal den Tag/Nacht-Rythmus von Bäumen in freier Natur untersucht und sind zum (jetzt nicht sonderlich überraschenden) Ergebnis gekommen: Trees go to sleep too. Paper: Quantification of Overnight Movement of Birch (Betula pendula) Branches and Foliage with Short Interval Terrestrial Laser Scanning.
“Our results show that the whole tree droops during night which can be seen as position change in leaves and branches”, says Eetu Puttonen (Finnish Geospatial Research Institute), “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.”
To rule out effects of weather and location, the experiment was done twice with two different trees. The first tree was surveyed in Finland and the other in Austria. Both tests were done close to solar equinox, under calm conditions with no wind or condensation. 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. It is not yet clear whether they were “woken up” by the sun or by their own internal rhythm.