The interplay between vegetation and water in mangroves: new perspectives for mangrove stand modelling and ecological research

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).