Laser Scans Reveal Humidity‑Driven Motion in Dead Tree Branches

Researchers from Heidelberg University have documented that lifeless tree limbs are not immobile, but instead sway subtly as ambient humidity rises and falls, a phenomenon captured with high‑resolution laser scanning.

The team employed terrestrial LiDAR to record three‑dimensional point clouds of selected branches over the course of several days. By synchronising the scans with continuous humidity measurements, they were able to map minute expansions and contractions that corresponded directly to changes in atmospheric moisture.

Wood is a hygroscopic material; even after a tree has died, its cellular structure continues to absorb water from the air and release it as conditions shift. This absorption causes the fibers to swell, while drying leads to shrinkage. The researchers observed that these dimensional adjustments, though invisible to the naked eye, amount to measurable movement in the order of millimetres.

Understanding this hidden dynamism has practical implications. Forest engineers and ecologists rely on accurate models of branch stiffness and load‑bearing capacity to predict how trees respond to wind, snow, or other forces. If dead wood subtly changes shape throughout the day, current models may need refinement, especially in regions where humidity fluctuates sharply.

The study was conducted in partnership with the Finnish Geospatial Research Institute (FGI), combining expertise in geoinformatics and remote sensing. The cross‑institutional effort allowed the researchers to test their methodology in different climatic settings, reinforcing the robustness of the findings.

Looking ahead, the scientists plan to expand the monitoring to larger sections of forest canopies and to integrate the humidity‑induced motion data into broader ecological simulations. Such integration could improve predictions of forest stability under climate change scenarios, where altered humidity patterns may affect the mechanical behaviour of both living and dead vegetation.