Process-based, spatially-explicit modelling of riparian forest dynamics in Central Europe : tool for decision-making in river restoration

During the last decades public awareness of the limitations of traditional engineering practices and the imperative to conserve nature have led to changes in river management; including river restoration measures. The enlargement of the fluvial corridor is one of the often considered management measures. However, the high-pressure on land-use, the conflict of interests, as well as the uncertainty of vegetation and landscape development scenarios after restoration, can make their implementation difficult. In actual decision-making processes of large river restoration projects, no dynamic long-term modelling approach of potential riparian woody species development exists mainly due to the complexity of interacting driving-processes creating lateral and longitudinal gradients. So far, forest succession models applied to riparian areas are not conceived for river areas found in Central Europe and do not address explicitly environmental influences like nitrogen scarcity or drought stress important for certain riparian systems, nor they cover integrally the vegetation-hydraulics interaction. To support and enhance the decision-making processes in river restoration projects and to provide a better understanding of riparian forest dynamics and its driving-processes, the present thesis develops a coupled model of ecological and hydraulic processes to simulate riparian forest dynamics for Central European conditions, particularly for the case of enlarged fluvial corridors. The developed model RIFOD ('RIparian FOrest Dynamics') – a distribution-based forest succession model (i.e. ecological model) coupled to a quasi-2D hydraulic model – simulates short or long-term riparian forest dynamics at a yearly time step. The model, applied on a 10 times 10 m mesh grid, is spatially-explicit concerning the interactions of the ecological and hydraulic processes and integrates 65 Central European tree and shrub species. The ecological model is based on developments of different upland forest succession models, which were improved, adapted and complemented in regard to the ecological processes in riparian areas, for example concerning regeneration, nitrogen dynamics, soil water availability or flooding stress. At the basis of the modelling of physiological flooding stress response of plants, we carried out an in-depth review of the actual knowledge of the flooding stress response of Central European tree and shrub species. The review could highlight the main biotic and abiotic factors that influence species response and revealed the broad but still vague knowledge about physiological mechanisms and species-specific data of plant response. Based on the above findings, the fuzzy set theory was chosen to model flooding stress response integrating the main abiotic factors (e.g. flooding duration, -depth). The Central European tree and shrub species were classified into flooding tolerance classes by use of clustering analysis based on proxy-data, which allowed us considering