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Abstract. For the modelling of the flood routing in the lower reaches of the Freiberger Mulde river and its tributaries the one-dimensional hydrodynamic modelling system HEC-RAS has been applied. Furthermore, this model was used to generate a database to train multilayer feedforward networks.To guarantee numerical stability for the hydrodynamic modelling of some 60 km of streamcourse an adequate resolution in space requires very small calculation time steps, which are some two orders of magnitude smaller than the input data resolution. This leads to quite high computation requirements seriously restricting the application -especially when dealing with real time operations such as online flood forecasting.In order to solve this problem we tested the application of Artificial Neural Networks (ANN). First studies show the ability of adequately trained multilayer feedforward networks (MLFN) to reproduce the model performance.

Key Message Morphological plasticity helps plants to cope to environmental conditions. Allometric responses of the mangrove Avicennia germinans to increasing salinity are easily detectable when focusing on the top height trees. Abstract Several studies show that mangrove trees possess high species-and site-related trait allometry, suggesting large morphological plasticity that might be related to environmental conditions, but the causes of such variation are not clearly understood and systematic quantification is still missing. Both aspects are essential for a mechanistic understanding of the development and functioning of forests. We analyzed the role of salinity in the allometric relations of the mangrove Avicennia germinans, using: (1) the top height trees (trees with the largest diameters at breast height, which reflect forest properties at the maximum use of resources); (2) the slenderness coefficient (which indicates competition and environmental conditions); and (3) the crown to DBH ratio. These standard tools for forest scientists dealing with terrestrial forests are suitable to analyze the plastic responses of mangroves to salinity. First, the top height trees help to recognize structural forest properties that are not detectable when studying the whole stand. Second, we found that at salinities above 55 %, trees are less slender and develop wider crowns in relation to DBH than when growing at lower salinities. Our results suggest a significant change in allometric traits in relation to salinity, and reflect the plastic responses of tree traits in response to environmental variation. Understanding the plastic responses of plants to their environment can help to better model, predict, and manage forests in changing environments.

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It is commonly accepted that vegetation patterns and water supply mutually define each other. In mangroves, soil water salinity and the corresponding osmotic potential are the main drivers of plant water supply. Below-ground processes thus may be key for the structure and dynamics of mangrove stands. Nevertheless, existing simulation models describing mangrove forest dynamics do not quantify the water uptake of the single plant from the soil and traditionally neglect any feedback of the vegetation on the water availability, but instead use empirical, statistical models for plant competition affecting growth. We provide a brief review on the state of the art of mangrove forest models with an emphasis on how below-ground processes are regarded. We follow mainly two directions: (1) phenomenological concepts for competition for below-ground resources and (2) assessing the impact of salinity and water supply on the vegetation and possible feedback mechanisms from the vegetation to the below-ground conditions. We hypothesise that a coupled vegetation-groundwater model would avail us to better understand the dynamics and properties of mangrove systems, their capability to persist or rehabilitate under stressful hydrological conditions, as well as their response to environmental changes related to the groundwater system and transport. The benefits of such a joint approach would (i) constitute an intrinsic below-ground competition description close to the governing processes and (ii) concurrently exploit secondary, constraining information from vegetation patterns to derive a new concept to acquire knowledge on subsurface heterogeneity and parametrisation. The aim of this paper is to lay the theoretical groundwork and guidelines for future modellers to follow in the creation of a more realistic mangrove model coupling above- and below-ground processes. The proposed modelling approach has the potential to be useful for a broad audience based particularly in forest sciences and plant ecology in general, but also for hydrodynamic modelling (e.g. subsurface flow and transport detected by vegetation patterns as above-ground proxy).