Modelling mangrove forest structure and species composition over tidal inundation gradients: The feedback between plant water use and porewater salinity in an arid mangrove ecosystem

Abstract

Conceptual models have described mangrove forest structure in response to tidal inundation, porewater salinity and mangrove water use, however, the importance of feedbacks have not been assessed. We assessed the processes underlying the feedback between water availability and plant water use in mangrove ecosystems by applying the process- and individual-based mangrove model MANGA, evaluating individual tree growth behavior, emerging forest structure, and mangrove species composition. We compared simulation data with field data collected at a field site with a monospecific mangrove forest that showed a strong gradient in tree height and biomass across the intertidal zone. While tidal inundation and the resulting porewater salinity gradient caused variation in mangrove forest structure within the MANGA model, the inclusion of tree water use in the model led to high similarity between model results and field observations. We further show the importance of the feedback between tree water use and porewater salinity for emergence of species zonation patterns. In accordance with particular site observations, we simulated the response to a broad spectrum of modelled porewater salinity inputs of an artificial forest. The modelled forest consists of two distinct species differing in their water use efficiency and salt tolerance. The modelled feedback mechanism produced a strong correlation between mangrove species zonation along the intertidal gradient and porewater salinity inputs at the system boundaries. The results of this study describe and demonstrate the absolute and relative importance of the implemented interacting processes on mangrove vegetation patterns. A better understanding of the role of tidal inundation and the feedback loops between plant water use and porewater salinity in determining mangrove forest structure will help to predict and manage the fate of mangrove ecosystems in a changing climate.