Scientists look at the sleep cycles of trees to reveal stress and disease in crops

A study involving more than 20 different species of trees uncovered a mysterious cycle of canopy movement that takes place during the night. Furthermore, each species adhered to a different sleep cycle. An article in Science Daily states that changes to this overnight movement could be used to diagnose any anomalies in crops that are caused by stress or disease.

All plants draw water from the ground for transportation to their leaves, where they will be used in the photosynthetic process. It is a simple but important process that helps maintain life on Earth as we know it.

Water transportation continues to be a topic of hot debate. The general agreement is that the process is reliant on light and therefore takes places in 24-hour cycles.

The leaves of tree species from the legume family are known to move overnight. Recently, it was reported that certain other trees can lower their branches during the night and raise them up again during the morning. The latter behavior escaped notice for the longest time because the branches only move during the night and move very slowly, to boot.

The canopy movement was finally caught via terrestrial laser scanning. This survey method is used to create precise three-dimensional maps of buildings.

Researchers used the lasers to take accurate measurements of the positions of a tree’s branches and leaves throughout the night. It successfully showed the movements of birch trees in outdoor conditions. (Related: Start today: Plant these food-producing trees on your property now.)

New study says trees are much more active at night than previously thought

A joint Danish and Hungarian research team repeated the experiment. They collected more than 20 individual specimens of trees and shrubs from different species and scanned them all night long.

“We detected a previously unknown periodic movement of up to one centimeter in cycles of two to six hours. 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,” reported study author András Zlinszky from Aarhus University (Aarhus).

He reported that all of the trees moved their branches or leaves during the night. However, only seven species showed the expected “sleep” motion, where the leaves and/or branches moved back to their starting position within 12 hours.

Instead, some of the other trees demonstrated shorter sleep periods, while others enjoyed longer periods. Still, others showed slow and steady movements in one direction; these were theorized to be suffering from disease or old age.

Most importantly, all of the plants made tiny movements over small periods during the evening. The magnolia tree, in particular, went through three full cycles of branch or leaf movements during a single night.

Brief bursts of water transport in trees could be more common

Minute movements are caused by changing water pressure inside plant tissue. However, the commonly held view is that water transport in trees is an unchanging process that follows the speed of the day-and-night cycle.

The findings of the Aarhus study propose the reverse: Brief changes in water transport and tissue pressures is common among plants.

Earlier studies had dismissed tiny changes in the diameter of tree trunks as “noise.” The new study suggested this could be an unrecognized means of water transportation that changes the volume and water pressure in the trunk.

“We believe that detection of anomalies of overnight movement could become an efficient diagnostic tool to reveal stress or disease in crops. This would open up for early intervention, which is not only cost-efficient but also more environmentally friendly,” said Anders S. Barfod, the co-author of the study.

You can read more about newly discovered properties of trees at

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