Dead tree branches rise and fall with changing humidity, laser scans reveal

Dead tree branches are not stationary, but rather move throughout the day due to changing humidity levels, according to a study conducted by researchers at Heidelberg University in collaboration with the Finnish Geospatial Research Institute. By employing an autonomous laser scanning system, the scientists were able to map a specific forest plot at regular intervals and quantify the small branch movements driven by humidity fluctuations.

The study, published in Agricultural and Forest Meteorology, reveals that dead branches exhibit systematic daily movement patterns, with conifer branches moving downward during the day and upward at night, and birch branches moving in the opposite direction. The tips of the branches can shift up to 43 centimeters in height within a few days. This movement is closely tied to the wood equilibrium moisture content, which is influenced by relative humidity and air temperature.

The researchers found that the movement of dead branches is primarily attributed to the hygroscopic properties of the wood, which involve the absorption and release of moisture. By comparing the movement signatures of living and dead branches using a tracking algorithm and autonomous laser scanning system, it may become possible to identify dead branches without physical contact, enabling automated monitoring of tree health in forests and urban areas.