Stefan Seifert

Structural crown properties of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in mixed versus pure stands revealed by terrestrial laser scanning

How tree morphology develops in mixed-species stands is essential for understanding and modelling mixed-stand dynamics. However, research so far focused on the morphological variation between tree species and neglected the variation within a species depending on intra- and interspecific competition. Our study, in contrast, addresses crown properties of nine mature Norway spruces (Picea abies [L.] Karst.) of a pure stand and compares them with ten spruces growing in mixture with European beech (Fagus sylvatica [L.]). The same was done with 11 pure stand beeches and 12 beeches growing in mixture with spruce. Through application of a terrestrial laser scanner and a new skeletonization approach, we deal with both species’-specific morphological traits such as branch angle, branch length, branch bending, crown volume and space occupation of branches within the crown, some of which were hardly accessible so far. Special attention is paid to distinct differences between trees growing in mixed and pure stands: for spruce, our study reveals significantly longer branches and greater crown volumes in the mixed stand when compared to the pure stand. In case of European beech, individuals growing in mixture show flatter branch angles, more distinct ramification, greater crown volumes and a lower share of a single branch’s space occupation in the total crown volume. The results show that the presented methods yield detailed information on the morphological traits analyzed in this study and that interspecific competition on its own may have a significant impact on crown structures. Implications for production ecology and stand dynamics of mixed-species forests are discussed.

Competition effects in an afrotemperate forest

BackgroundInformation about competition responses is mainly available for monospecific stands or mixed stands with a small number of species. Studies on complex multi-species and highly structured forest ecosystems are scarce. Accordingly, the objective of this study was to quantify competition effects and analyse competition responses in a species-diverse afrotemperate forest in South Africa, based on an observational study with mapped tree positions and long-term diameter increment records.MethodsThe sensitivity to competition was analysed for individual species and involved the calculation of the slope of the linear relation between the value of a competition index (CI) and diameter growth as a measure of sensitivity. In a next step different competition indices were combined and tree diameters were grouped in three classes as surrogates for canopy status and ontogenetic stage.ResultsFive competition indices were found to be effective in showing sensitivity to competition for a number of canopy and sub-canopy species. Significant linear regressions were fitted for 18 of a total of 25 species. Species reactions varied significantly in their sensitivity to the different CIs. The indices were classified as belonging to two groups, those that responded more to local crowding and those that are more sensitive to overtopping, which revealed species-specific sensitivities to both factors. The analysis based on diameter classes revealed that species clearly changed their sensitivity to crowding or overtopping depending on diameter. Canopy and sub-canopy species showed distinct differences in their reactions.ConclusionsThe application of multiple CIs brought novel insights relating to the dynamics of afrotemperate forests. The response patterns to different competition indices that focus on crowding and overtopping are varied and tree diameter dependent, indicating that oversimplified assumptions are not warranted in the interpretation of CI- growth relations.

Evaluation of a ray-tracing canopy light model based on terrestrial laser scans

The local light regime within the tree canopy is crucial information for modeling water, carbon and nutrient cycling, and vegetation–atmosphere interactions. We tested the performance of a new model to simulate the light environment in the canopy of a juvenile beech stand under controlled light conditions. The canopy architecture was determined using a terrestrial laser scanner to derive a three-dimensional voxel representation. Depending on whether a voxel represents stem biomass, leaf biomass, or air, different attributes of light are assigned to the voxel. The model combines a representation of the canopy as three-dimensional cells (voxels) with a fast ray tracing algorithm that calculates the absorbed fraction of incoming photosynthetic active radiation (PAR). The simulated light regime of the stand was compared with measurements of the PAR regime inside the canopy (model efficiency Nash–Sutcliffe efficiency (NSE) = 0.88, root mean square error (RMSE) = 124 µmol m−2 s−1) and at the soil surface (NSE = 0.65, RMSE = 22 µmol m−2 s−1). The model needs two input parameters, the edge length of the voxels and the light attenuation coefficient of the voxels. The best simulation results were achieved at a voxel size of 0.03 m. For model calibration, only measurements of the light fraction that reaches the soil surface are needed. The good agreement of the simulated and the measured light regime together with the fast computation by the ray tracing algorithm suggest that the model is also applicable to simulate the light regime of natural forests under variable light conditions.

Modelling and Simulation of Tree Biomass

A primary objective of sustainable bioenergy production is to quantify the available resource supply because all further planning of the value chain hinges on the available biomass that can be converted. Since biomass is costly to transport, the spatial quantification of the resource is also important. Thus, modern approaches to biomass supply chain management must embrace the resource quantity and location as a key element of the supply chain. Data on resource availability are usually obtained from different sources such as remote sensing and terrestrial inventories, as discussed in Chap. 2, which provide information on the spatial distribution of forests and trees and their dimensions but are, as such, not capable of estimating biomass directly with the necessary accuracy. Thus the main purpose of the application of modelling and simulation techniques in this context is the estimation of the biomass resource from broadly available tree and stand variables. This auxiliary information could be sourced from inventories and remote sensing or could be provided by model projections from growth models to estimate the biomass availability.

Methoden zur Visualisierung des Waldwachstums@@@Methods for visualisation of forest growth

ZusammenfassungDie dreidimensionale Visualisierung ergänzt die individuenbasierte Modellierung des Waldwachstums und eröffnet neue Möglichkeiten der Erkenntnisgewinnung und Informationsvermittlung. Mit Bestandesaufrisszeichnungen, Kronenkarten, Bestandesaufsichten, walkthrough und Landschaftsbildsimulation werden beispielhaft Methoden der wissenschaftlichen Visualisierung beschrieben, die der Illustration natürlicher Entwicklungen und menschlicher Operationen im Wald dienen. Sie können die forstwissenschaftliche Lehre und Forschung und die forstwirtschaftliche Praxis unterstützen, reichen aber u. a. auch in die Bereiche Landschaftsplanung und Naturschutz hinein. Unter wissenschaftlicher Visualisierung verstehen wir den Einsatz von Grafikprogrammen für die Aufbereitung und Erschließung von Wissen, das in Messungen und Simulationsergebnissen enthalten ist. Die Visualisierung von Makrostrukturen auf Einzelbaum-, Bestandes- und Landschaftsebene dient der Veranschaulichung und Analyse von Meßdaten, der modellhaften Nachbildung von Untersuchungsobjekten und der didaktischen Vermittlung forstwissenschaftlicher Forschungsergebnisse. Sie bringt den Paradigmenwechsel vom Bestandesdenken zum Einzelbaumansatz methodisch wirkungsvoll voran.SummaryThree-dimensional visualisation is a complement to single-tree modelling of forest growth and provides new possibilities for gaining insight into and spreading information on forest growth. Methods of scientific visualisation are described examplarily by means of stand profile drawings, crown maps, stand top views, walkthroughs and landscape image simulations all of which contribute towards illustrating natural developments and human operations in the forest. Not only do they support forest science instruction and research as well as forestry practice but they may also be useful in landscape planning and nature conservation. Scientific visualisation implies the use of graphics programmes for the processing and exploiting of knowledge contained in measuring and simulation results. The visualisation of macro structures at the individual tree, stand and landscape level assists in the illustration and analysis of measuring data, model preparation of investigation objects and the didactic transportation of research results into forest science. It represents an effective, methodological progress in the paradigm changeover from the stand concept to the single tree approach.