Ecogeomorphic relations between marsh surface elevation and vegetation properties in a temperate multi-species salt marsh

Salt marshes represent a fascinating example of an ecosystem whose dynamic response to climate change is chiefly governed by a two-way bio-physical coupling between marsh ecology and geomorphology. Relationships between vegetation biomass and marsh surface elevation, and between vegetation biomass and its physical properties that influence sedimentation rates, have been progressively formulated in the literature in order to provide mechanistic understandings and mathematical model descriptions of these ecogeomorphic feedbacks. In this study, a field survey was conducted in a temperate salt marsh grown by multiple halophyte species in order to quantify and validate these empirical relationships, yet in a location characterized by different climatic and ecological conditions from the locations where these relationships were initially derived. Regression analysis revealed that vegetation biomass can be expressed as a linearly increasing function of marsh elevation, providing therefore a direct empirical validation for such a relationship previously reported in the literature and implemented in some ecogeomorphic models. However, previously documented allometric relationships between total standing biomass and vegetation morphometrics – namely stem diameter, stem density and projected plant area per unit volume – were not confirmed by our results, which only showed an allometric scaling for stem height. These results suggest that previously documented formulations of mineral sediment trapping processes modulated by plants, which are partly derived on the basis of these allometric relationships, are not generally validated for multi-species salt marshes. Therefore, existing models that apply these process-based equations to study marsh evolution in a multi-species context may not capture in detail the vegetation-induced geomorphic work.