Tree stems shrink during the day and expand again during the night. These daily stem radius fluctuations are a consequence of the current water saturation of the tree. The main influencing factors of water saturation are the transpiration of the leaves and the water uptake of the roots in the soil.
These water-related daily stem radius changes are overlaid with the growth of the tree rings and the bark. Hence, data measured over weeks and months show periods of radial stem growth.
Such measurement data are provided by point dendrometers. These devices continuously measure root radii with a resolution within a micrometer range. On each tree, one or more point dendrometers are mounted to the stem using carbon fiber frames and thread rods (Fig. 1).
Point dendrometer data are collected fully automatically on more than 300 trees at more than 30 locations throughout Switzerland as part of the international monitoring and research network TreeNet. The data will be used for the ongoing calculation of drought and growth indices, as well as for research on the water balance and carbon metabolism of trees.