Trees have a surprising ability to sense their own shape and adjust their posture using a special kind of wood called tension wood. This process is similar to how animals maintain balance and posture. Trees can grow straight and upright despite being knocked over by storms or landslides. Since the 1950s, scientists have known that trees have a type of wood that acts like a muscle, helping them to bend and correct their shape over time. Recent studies have shown that trees use a combination of senses to detect gravity, light, and their own curvature, allowing them to straighten themselves out. For a tree, growing straight and upward is not automatic. A strong wind or a landslide can tilt or even knock it down. However, the tree can gradually adjust its position so that its top returns to a vertical orientation. If a gap in the light appears after a neighboring tree falls, the tree tends to bend toward the light. These adjustments, in one direction or another, could lead to a twisted trunk. Yet, in large forests, trees often remain straight, even after experiencing disturbances. A straight and vertical form is crucial for trees. It allows them to reach sunlight quickly, which is vital in a competitive forest environment. It also reduces the risk of breaking under their own weight or in strong winds. This ability is increasingly important as extreme weather events become more common, and trees are exposed to stronger winds, unstable ground, or landslides during heavy rains. Over time, plants have developed the ability to sense gravity and light, as well as their own curvature. Specialized cells in their stems, called statoliths, help them detect the direction of gravity, similar to how the small stones in our inner ear help us sense balance. These statoliths are sensitive to the inclination of the stem, not sudden movements. Trees also use a process called proprioception—a way of sensing their own body position, though the exact mechanism is still being studied. In response to these perceptions, trees can actively bend their trunks. In broad-leaved species, this is done through tension wood, which forms on the upper side of inclined stems. As new fibers develop, they contract, helping the trunk to gradually straighten over weeks or years. This type of wood is problematic for loggers, as it can cause splintering when trees are felled or lead to deformations after cutting. Researchers tested whether tension wood acts like antagonist muscles in animals, working in opposition to each other to help maintain posture. To isolate the effect of proprioception, they used an experimental setup that canceled out other perceptions, such as light and gravity. They placed poplar trees in a rotating device called a clinostat, which prevents them from sensing gravity. This allowed researchers to observe how the trees adjusted their posture based solely on their own curvature. At the beginning of the experiment, the poplars were placed horizontally in a sphere. Without the clinostat, they bent upward, as expected, due to their perception of gravity. After a dozen days, the trees had developed a noticeable curve. Then, the clinostat was activated, eliminating the perception of gravity. Over the following weeks, the poplars gradually straightened their trunks. Cross-sections of the trunks showed that tension wood had formed on the upper side during the first phase of the experiment. Once the clinostat was active, new tension wood formed on the opposite side, confirming the hypothesis that it acts like an antagonist muscle. This experiment demonstrated that trees have a sensory-motor loop for posture control, similar to what is found in animals. In natural conditions, trees integrate various signals—light, gravity, and their own shape—to adjust their growth. In the past, the presence of tension wood was often seen as an anomaly, but it is now understood to be a key part of a tree’s ability to maintain an upright form. This ability is crucial for trees to access light and avoid breaking under their own weight. For humans, it also means that straight and strong wood is important for construction and furniture. Selecting trees that produce little tension wood was a mistake; instead, the ideal trees are those that can sense their posture and adjust it quickly and effectively.