They don’t snore, but might creak during their slumbers. For the first time, trees have been shown to undergo physical changes at night that can be likened to sleep, or at least to day-night cycles that have been observed experimentally in smaller plants. Branches of birch trees have now been seen drooping by as much as 10 centimetres at the tips towards the end of the night. “It was a very clear effect, and applied to the whole tree,” says András Zlinszky of the Centre for Ecological Research in Tihany, Hungary. “No one has observed this effect before at the...