Distributed Fibre Optic Sensing for Tree Dendrometry

Trees play a key role in climate-change mitigation and biodiversity conservation, but increasing drought and heat stress threaten their vitality. Monitoring tree water status and stem dynamics is therefore essential, particularly for early stress detection. However, conventional dendrometric approaches are often invasive or lack the spatial and temporal resolution required to resolve fine-scale structural and hydraulic dynamics along stems and branches.

Here, we evaluate Distributed Fibre Optic Sensing (DFOS) as a non-invasive method for continuous, high-resolution dendrometry and strain monitoring in trees. Using a LUNA ODiSI 7100 interrogator based on Rayleigh backscattering, we measure relative microstrain at a gage pitch (spacing of
adjacent gage centre points) of 0.65 mm under laboratory conditions. We test the hypothesis that water transport induces small but measurable changes in stem and branch geometry, producing strain signals that can be used to infer hydraulic and mechanical responses.

Initial experiments were conducted on hazel branch cuttings submerged in water and on a small beech tree under controlled conditions representative of active water transport. These tests provide a proof of concept for assessing signal sensitivity, stability, and the effective spatial resolution achievable in practice. The results are used to identify which strain patterns can be robustly recovered and to evaluate the suitability of DFOS for monitoring dynamic stem responses at scales not accessible with conventional point-based techniques.

We aim to establish the methodological basis for a field-deployable DFOS framework for tree monitoring. Beyond demonstrating feasibility, the approach offers potential for linking fine-scale stem mechanics with tree water transport and stress responses. In the longer term, DFOS could contribute to improved monitoring of tree functioning and resilience under increasingly frequent climate extremes.