Dynamic Feedbacks Between Vegetation and Hydrology in the Long Term

Abstract

The interaction between vegetation and hydrology is complex and varies dynamically at both spatial and temporal scales. A close-to-reality representation of this interaction requires models that are able to depict spatiotemporal dynamics between the vegetation (green) and the hydrology (blue) world in an integrated way. However, most current hydrological models simulate plants by either pre-defining their properties or by considering few plant species only. Vice-versa, most plant models simplify the hydrological conditions and ignore the temporal dynamics of spatially distributed hydraulic conditions. Simplifying or pre-defining hydrological or ecological components may limit the capability of models to fully investigate this dynamic interplay. In this thesis, an innovative modelling approach is presented, which is coupling an advanced 3-D hydrogeological model to an individual-based plant model. The modelling system consists of a fully integrated surface and subsurface flow model HydroGeoSphere (HGS) that is dynamically coupled with a highly flexible plant model (PLANTHeR). This coupled modelling framework is then used to explore the dynamic feedbacks between hydrology and plant communities on a long-term time scale. Three main research questions are being investigated: 1) What benefit and which additional insights are provided by using the PLANTHeR-HGS model instead of uncoupled models? 2) Under which climate condition is it most meaningful to use the PLANTHeR-HGS model? 3) Are high plant diversity communities able to buffer ecosystems against extreme climate events? The results show that the PLANTHeR-HGS model is superior to uncoupled HGS and PLANTHeR models in quantifying hydrological processes and plant community dynamics. For quantifying the transpiration, soil water dynamics, plant community richness and aboveground biomass in a drier climate, or analyzing the evaporation process and plant community diversity in a wetter climate, it is recommended to use the PLANTHeR-HGS model instead of uncoupled models. In addition, under dry climates, high diversity communities have been shown able to buffer ecosystems against extreme flood events and extreme drought and heavy rainfall events, through increasing their ecosystem stabilities. In summary, this dissertation demonstrates that using pre-defined plant properties in hydrological models flattered the climate change effects over plant growth. Vice-versa, simply the hydrological conditions in ecological models resulted in unrealistic plant distribution pattern, such as competing for water resources generated regular pattern. The PLANTHeR-HGS model developed in this study, is not only able to advance our understanding of both spatial and temporal water resource heterogeneity effects on plant community diversity and richness, but also can advance our understanding of multiple climate drivers impact on plant community performance and hydrological dynamics simultaneously.