Trees and plants are more alive than most people might think, scientists in Europe are discovering.
They demonstrate varying patterns of movement at night, akin to sleep, and pump water like blood, new research shows.
It was widely thought vegetation follows a strict 24-hour pattern of photosynthesis, with trees and plants absorbing sunlight during the day as they process water and produce oxygen as a by-product - hence they're busiest in daylight hours.
But the new findings show some trees have shorter or longer "sleep" periods than 12 hours. And some trees appear to demonstrate sleep patterns, such as restless movement, lowering their branches by different margins.
The gradual branch movements take place at night and are difficult to identify with the naked eye. Scientists used laser scanning to discover trees lower their branches by up to 10 centimetres at night - and then back in the morning.
Researchers from Denmark and Hungary brought 22 tree and shrub species together and scanned them overnight in controlled conditions. All showed some movement of a few centimetres, with some trees having shorter or longer "sleep" periods.
"We detected a previously unknown periodic movement of up to one centimetre in cycles of two to six hours," said Aarhus University's András Zlinszky.
"The movement has to be connected to variations in water pressure within the plants, and this effectively means that the tree is pumping. Water transport is not just a steady-state flow, as we previously assumed."
Changes in water pressure within plant tissues cause short-term movements, which was generally assumed to be a steady process with no variations faster than the day-night cycle.
But now it seems that trees are more changeable than we believed - though whether they dream when they're "asleep" is yet to be uncovered.