Trees can sense when their stems are bent and grow a specific type of wood to correct the problem, according to new research from France. A team from INRAE and the University Clermont Auvergne found that tension wood functions like a muscle, pulling a curved stem back toward a straight, upright position without relying on signals from gravity or light.
The findings, published in New Phytologist, build on earlier work that established plants have proprioception, the ability to sense the position and shape of their own body parts. That ability was long thought to belong only to animals. In 2012, a research team involving INRAE showed that plants also possess this sense, but the biological mechanism behind it remained unknown until now, as Phys.org reported.
To isolate proprioception from the other senses trees use to orient themselves, the researchers designed a specialized experimental setup. Young poplar trees with bent stems were placed on a horizontal rotating platform inside a sphere flooded with light from all directions. The rotation eliminated the trees' sense of gravity. The omnidirectional lighting eliminated their ability to follow a light source. The only sense left intact was their ability to perceive their own curvature.
The experiment worked in two stages. First, researchers placed young poplar trees horizontally. Over time, the trees curved upward, with tension wood forming on the upper side of the stem and pulling it toward a vertical position. This phase confirmed that tension wood can bend a stem.
After roughly 10 days, once the trees had developed a noticeable curve, they were moved into the rotating, omnidirectional light chamber. Over the following weeks, researchers observed the stems gradually straightening and returning to a rectilinear shape. They then examined the anatomy of the wood that formed during the straightening phase.
What they found was that the tension wood that had formed on the upper side of the stem during the bending phase stopped forming once the straightening process began. Instead, tension wood appeared on the lower side, now pulling the stem in the opposite direction. The process demonstrated that tension wood is not simply a mechanism for bending toward light or away from gravity. It responds directly to the shape of the stem itself.
The researchers say this ability has practical consequences for how trees survive in the wild. Storms, landslides, and other extreme events can push trees out of alignment. The capacity to detect and correct that misalignment, even in the absence of gravity or light cues, gives trees a biological tool for recovering from physical damage. The discovery adds a new layer of complexity to how scientists understand plant movement and resilience, and opens questions about what other mechanical sensing abilities plants may possess.
