Poplar trees straighten themselves by building opposing tension wood

Young poplar trees can straighten a curved stem by switching off tension wood on one side and forming it on the other, according to a study in New Phytologist. The work, led by Bruno Moulia and colleagues at INRAE, indicates that proprioception, the sense of one's own shape, directly controls where this force-generating wood develops. The authors describe the result as a sensorimotor loop in the woody parts of trees.

Isolating a sense that works alongside gravity and light

Plant proprioception was first demonstrated in 2012 by researchers working with INRAE. Plants were known to sense their own shape and adjust growth to stay as straight as possible, but the mechanism that converts this information into movement had remained unclear.

The difficulty is that stems also respond to gravity and to the direction of light, which makes the contribution of shape sensing hard to separate. The team therefore built a system that removed both cues. Trees stood on a horizontal platform that rotated around its axis, preventing a steady gravitational signal. The platform sat inside a sphere lit equally from all directions, which removed directional light information.

How tension wood acts like opposing muscles

The experiment began with young poplars placed horizontally. Their stems curved upwards as they grew, a response that relies on tension wood. This specialised tissue generates pulling forces as it forms. When it develops on the upper side of a stem, it pulls that side and bends the stem upwards.

After about ten days, once the stems were clearly curved, the trees were moved into the rotating, uniformly lit apparatus. Over the following weeks, the stems slowly became almost straight again.

Examination of the wood formed during this period explained the change. The original tension wood on the upper side stopped forming once the trees entered the apparatus. Identical tension wood began to form on the opposite side, pulling in the other direction. The opposing forces gradually brought the stem back to a straight form.

A wider role for tension wood

Tension wood was previously thought to form only on the upper side of leaning stems, a pattern often seen near the bases of trees on mountain slopes. The new findings show that it can form on either side of a stem and pull in different directions, much as opposing muscle groups hold an animal's posture.

The authors conclude that trees combine external information, such as light and gravity, with an internal awareness of their own shape. Together these signals regulate where tension wood develops. The cellular steps behind tension wood formation are complex, and the source does not detail how the shape signal reaches them.

Potential relevance for forestry and crops

The researchers point to several possible applications, which remain prospective rather than demonstrated:

• Resilience: restoring posture after storms or landslides may matter more as climate change brings more extreme conditions to forests.
• Breeding: identifying plants with particularly effective proprioception could allow selection of varieties that grow straighter and yield better wood.
• Timber quality: poorly coordinated activation of tension wood can create excessive internal stress, which may affect wood properties.
• Cereals: similar knowledge might help in breeding crops that resist lodging, the collapse of plants before harvest that can cause substantial yield losses.

Limits and next steps

The reported experiments used young poplar trees in an artificial setting designed to remove natural cues, so how closely the pattern applies to mature trees, other species or field conditions is not established by the source. Open questions include the molecular and cellular signalling that links shape sensing to the placement of tension wood, and whether variation in this control can be measured and exploited in breeding programmes. Moulia said the findings reshape applied research aimed at straighter, less internally stressed trees. His colleague Félix Hartmann stressed the value of combining expertise from different disciplines in the project.

The study is by Alexandre Caulus, Félix P. Hartmann, Éric Badel, Stéphane Ploquin, Nicole Brunel-Michac, Julien Ruelle, Mélanie Decourteix and Bruno Moulia (New Phytologist, 2026, DOI: 10.1111/nph.71238).

Source: Scientists discover the hidden “muscles” trees use to straighten themselves (ScienceDaily: top science, 1 November 2026).

Image: AI-generated illustration.