BACKGROUND: The goal of the study was to determine circadian movements of silver birch
(Petula Bendula) branches and foliage detected with terrestrial laser scanning (TLS).
The study consisted of two geographically separate experiments conducted in Finland
and in Austria. Both experiments were carried out at the same time of the year and
under similar outdoor conditions. Experiments consisted of 14 (Finland) and 77 (Austria)
individual laser scans taken between sunset and sunrise. The resulting point clouds
were used in creating a time series of branch movements. In the Finnish data, the
vertical movement of the whole tree crown was monitored due to low volumetric point
density. In the Austrian data, movements of manually selected representative points
on branches were monitored. The movements were monitored from dusk until morning hours
in order to avoid daytime wind effects. The results indicated that height deciles
of the Finnish birch crown had vertical movements between -10.0 and 5.0 cm compared
to the situation at sunset. In the Austrian data, the maximum detected representative
point movement was 10.0 cm. The temporal development of the movements followed a highly
similar pattern in both experiments, with the maximum movements occurring about an
hour and a half before (Austria) or around (Finland) sunrise. The results demonstrate
the potential of terrestrial laser scanning measurements in support of chronobiology.
