An annually-resolved stem growth tool based on 3D laser scans and 2D tree-ring data

The combination of terrestrial laser scans and tree-ring data allows for a highly precise reconstruction of annual stem growth, and thus complex tree-growth analyses independent of species and site characteristics. Reliable carbon pools data are needed to quantify the carbon stored in ecosystems and for effective forest management. Terrestrial laser scanning allows researchers to quickly acquire data about forest structure and to derive tree parameters and volume data automatically. However, accurate models of the development of tree volume over time are still lacking. In contrast to terrestrial laser scanning, tree-ring data show the annual growth development of trees, but do not contain information about tree volume. The fusion of terrestrial laser scanning and tree-ring data may, therefore, lead to reliable stem development data, and thus annually resolved models of volume increment of trees. The aim of this study is to combine these data and apply a root-development model to the aboveground part of trees. Three spruce trees (Picea abies) and two firs (Abies alba) which were part of a long-term forest monitoring survey were scanned using a terrestrial 3D-laser-scanner. Combining these data with tree-ring measurements, we were able to reconstruct stem volume at an annual resolution. Results provide robust annually resolved volume data along with ring-width measurements at any point within the modeled tree stem, which present great potential for complex growth analyses. Stem volume, estimated with a bole volume function, deviated between - 1.65 and 1.9% from our model for four out of five trees. For the fifth tree deviations of 13% were observed. The agreement between the function and our model demonstrates the robustness of the presented approach.