Bettina Wagner's research while affiliated with Swiss Federal Institute for Forest, Snow and Landscape Research WSL and other places

Key message 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. Abstract 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.

Dynamic root-development models are indispensable for biomechanical and biomass allocation studies, and also play an important role in understanding slope stability. There are few root-development models in the literature, and there is a specific lack of dynamic models. Therefore, the aim of this study is to develop a 3D growth-development model for coarse roots, which is species independent, as long as annual rings are formed. In order to implement this model, the objectives are (I) to interpolate annual growth layers, and (II) to evaluate the interpolations and annual volume computations. The model developed is a combination of 3D laser scans and 2D tree-ring data. A FARO laser ScanArm is used to acquire the coarse-root structure. A MATLAB program then integrates the ring-width measurements into the 3D model. A weighted interpolation algorithm is used to compute cross sections at any point within the model to obtain growth layers. The algorithm considers both the root structure and the ring-width data. The model reconstructed ring profiles with a mean absolute error for mean ring chronologies of <9% and for single radii of <20%. The interpolation accuracy was dependent on the number of input sections and root curvature. Total volume computations deviated by 3.5–6.6% from the reference model. A new robust root-modelling tool was developed which allows for annual volume computations and sophisticated root-development analyses. KeywordsAllocation–Laser scanning–Root growth–Tree rings–Volume

In times of global change biomass calculations and the carbon cycle is gaining in importance. Forests act as carbon sinks and hence, play a crucial role in worlds and forests carbon budgets. Unfortunately, growth models and biomass calculations existing so far mainly concentrate on the above-ground part of trees. For this reason, the aim of the present study is to develop an annually resolved 3D growth model for tree roots, which allows for reliable biomass calculations and can later be combined with above-ground models. A FARO scan arm was used to measure the surface of a tree-root segment. In addition, ring-width measurements were performed manually on sampled cross sections using WinDENDRO. The main goal of this study is to model root growth on an annual scale by combining these data sets. In particular, a laser scan arm was tested as a device for the realistic reproduction of tree-root architecture, although the first evaluation has been performed for a root segment rather than for an entire root system. Deviations in volume calculations differed between 5% and 7% from the actual volume and varied depending on the used modeling technique. The model with the smallest deviations represented the structure of the root segment in a realistic way and distances and diameter of cross sections were acceptable approximations of the real values. However, the volume calculations varied depending on object complexity, modeling technique and order of modeling steps. In addition, it was possible to merge tree-ring borders as coordinates into the surface model and receive age information in connection with the spatial allocation. The scan arm was evaluated as an innovative and applicable device with high potential for root modeling. Nevertheless, there are still many problems connected with the scanning technique which have an influence on the accuracy of the model but are expected to improve with technical progress.

Details about the spatiotemporal development of root systems and their influence on ring-width variations in tree stems are still unknown. Furthermore, their size, spread and architecture play an important role in studying tree stability and their stabilizing effect on slopes. A major problem in this regard is the detailed 3D-data acquisition and modeling of its complex structure. The appli -cation of a laser scanner is a step towards the solution of this problem. Scanning the root system of a mature spruce tree facilitated creating a 3D scatter-plot of the root structure (resolution: 2 mm). The subsequent modeling of the structure allowed an automated replication of the coarse root structure down to a size of 0.5 cm of single roots. The resulting model of the root system facilitates cutting the roots for ring-width analysis while tagging the sample points in the model as a base for the further analysis of the root system's development.