Dead Tree Branches Shift With Humidity, Scans Show

Researchers at Heidelberg University and the Finnish Geospatial Research Institute have quantified a movement that is easy to miss in a forest: dead tree branches rise and fall as humidity changes.

The team used an autonomously operating terrestrial laser-scanning system to map a forest plot at regular intervals over several days. A tracking algorithm then measured small changes in individual branches, providing field-based quantitative evidence for movement that had previously been suspected but not demonstrated in detail under real forest conditions.

Wood still responds after a branch dies

The researchers found that relative humidity is a key driver. As humidity changes, branch wood absorbs or releases moisture and expands or contracts. Because that response is not uniform across a branch’s cross-section, the upper and lower portions can change length at different rates. The resulting imbalance bends a branch upward or downward.

The effect depends on the tree species and the branch’s anatomical and mechanical properties. The work therefore treats dead wood not as a fixed feature of a forest scene, but as material whose shape can continue to respond to the surrounding environment.

A route to automated forest monitoring

Laser scanning made it possible to monitor branch motion repeatedly without manually measuring every branch. The researchers combined those observations with modeling of branch structure and mechanics to connect the measured motion with changing humidity.

That approach could broaden the role of repeat 3D forest surveys. Characteristic movement patterns may eventually provide information relevant to assessing tree health, according to the researchers. The current study focuses on dead branches, but its measurement method offers a way to investigate how environmental conditions affect forest structure at fine scale.

Why the result matters

• It provides quantitative field measurements of humidity-driven movement in dead branches.
• It demonstrates regular, automated terrestrial laser scanning as a tool for tracking subtle forest motion.
• It links branch movement to moisture-related expansion and contraction in wood.
• It points toward monitoring approaches that could use movement patterns as part of forest assessment.

The study was published in Agricultural and Forest Meteorology. Its central finding is straightforward but consequential for remote sensing: even a seemingly static dead branch can carry a measurable record of changing atmospheric moisture.

This article is based on reporting by Phys.org. Read the original article.