This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Dead tree branches are by no means static but move throughout the day. Geoinformatics researchers at Heidelberg University tracked these movements in a study conducted in cooperation with the Finnish Geospatial Research Institute (FGI).
With the help of an autonomously operating laser scanning system, the scientists mapped a specific forest plot at regular intervals. Using a specially developed tracking algorithm, they were able to quantify even small branch movements, which are driven by changes in humidity. Their approach opens up new opportunities for automated monitoring, which could make it possible to assess tree health based on characteristic movement patterns.
The work is published in the journal Agricultural and Forest Meteorology. Trees appear static at first sight but are constantly adapting to environmental influences and moving their branches in response. Systematic movement of dead tree branches had long been suspected but had not yet been quantitatively demonstrated under real forest conditions.
The 3D Geospatial Data Processing (3DGeo) research group at Heidelberg University's Institute of Geography, led by Dr. Bernhard Höfle, has now explored this question in international cooperation with the FGI. Using terrestrial laser scanning, the scientists succeeded in automatically measuring the suspected movement in detail every hour over several days and making it visible using the tracking algorithm.
To explain what drives these movements, the scientists modeled the anatomical and mechanical properties of tree branches. They found that relative humidity is one of the key factors: As it changes, the branch wood absorbs or releases moisture, causing the wood to expand or contract. "This change in length does not occur uniformly across the branch's cross section.
Depending on the tree species, the upper and lower parts expand at differing rates. As a result, even dead branches can move significantly up or down as humidity fluctuates during the day," explains Vanessa Guthier, a research assistant with the 3DGeo research group. The analyses show that all branches studied—from 16 conifers and a deciduous tree in a boreal forest in Hyytiälä, Finland—followed a clear, systematic pattern of daily movement.
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