Comparison and benchmarking of functional-structural tree models at the example of GreenLab and LIGNUM, applied to Scots pine (Pinus sylvestris L.)
Plant Physiology
Final Report Abstract
Functional-structural plant models (FSPMs) are complex simulation models that intend to simulate the interactions between plant structure and ecophysiology. One aspect where the structure is of special importance is the complex calculation of light distribution in a plant which is in many models the basis for photosynthesis calculation. In this study, we investigated how the methods of mathematical modelling can be applied to quantify the impact of geometrical traits on light absorption. We used global sensitivity analysis, which allows to study the effect of multiple parameters simultaneously on the output of interest. Simulations were performed first for a single shoot model of Scots pine, then for a static tree of given age, as well as for a growing tree. For tree models, the LIGNUM FSPM for Scots pine was used. While all the simulations were executed on GroIMP, sensitivity analysis was performed in PYGMALION. A new interface was created to link both tools using a black-box approach and based on data exchange. The overall workflow was controlled by PYGMALION. Another challenging aspect in the context of FSPMs is their proper parameterisation, which is known to be a complex task. Sensitivity analysis can also help in the process of parameter estimation. It helps to identify model inputs or parameters that cause significant uncertainty in the output and should therefore attain special attention. Thanks to the new interface, first steps towards parameter estimation were done. A PYGMALION algorithm for parameter estimation was tested to estimate parameters related to photosynthesis calculation (based on light interception) in LIGNUM using a virtual experiment. The simulations showed that selected geometrical traits have an effect on light absorption and that the evolution of this effect might change with time. Additionally, the simulations showed that also the parameterisation of light models, i.e. of light sources (sky) or optical properties of tree segments and needles, affects the amount of absorbed light by tree elements, and should be carefully taken into account.
