– The whole tree droops during night which can be seen as position change in leaves and branches. The changes are not too large, only up to 10 centimetres for trees of about 5 metres in height, but they were systematic and well within the accuracy of our instruments, says Eetu Puttonen of the Finnish Geospatial Research Institute at the National Land Survey of Finland.
The leaves and branches were shown to droop gradually, with the lowest position reached a couple of hours before sunrise. In the morning, the trees returned to their original position within a few hours. The study does not say whether they were “woken up” by the sun or by their own internal rhythm.
More laser scanning of plants
Changes in the shape of plants are difficult to document as classical photography uses visible light that interferes with the sleep movement. With a laser scanner, plant disturbance is minimal. The scanners use infrared light, which is reflected well by the leaves. In addition, individual points on a plant are only illuminated for fractions of a second.
– We believe that laser scanning point clouds will allow us to monitor plant sleep pattern more generally and extend our measurement scope from individual plants to cover larger areas, like orchards or forest plots, says Norbert Pfeifer from TU Wien.
– We also aim to collect tree point clouds repeatedly with simultaneous water use measurements during the day and night. Simultaneous measurements will give us better understanding of daily tree water use and show how trees contribute in regulating the local or regional climate, says Eetu Puttonen.
This study was published in an open access article in the journal Frontiers in Plant Science:
Puttonen, E., Briese, C., Mandlburger, G., Wieser, M., Pfennigbauer, M., Zlinszky, A., Pfeifer N. (2016). “Quantification of Overnight Movement of Birch (Betula pendula) Branches and Foliage with Short Interval Terrestrial Laser Scanning”. Frontiers in Plant Science, 7:222. doi: 10.3389/fpls.2016.00222
The point cloud data collected in Finland is available free of charge.
Animation of how the whole tree droops during night
Senior Research Scientist Eetu Puttonen, 050 364 0555, firstname.lastname@example.org