A Minimalist Model of Salt-Marsh Vegetation Dynamics Driven by Species Competition and Dispersal

Abstract

We present a new bidimensional, spatially-explicit ecological model describing the dynamics of halophytic vegetation in tidal saline wetlands. Existing vegetation models employ relatively simple deterministic or stochastic mechanisms, and are driven by local environmental conditions. In the proposed model, in contrast, vegetation dynamics depend not only on the marsh local habitat, but also on spatially-explicit mechanisms of dispersal and competition among multiple interacting species. The role of habitat quality, here determined by the local elevation relative to the mean sea level as a proxy for environmental conditions, is mathematically modeled by a logistic function that represents the fundamental (theoretical) niche of each halophytic species. Hence, the model does not artificially impose any constraints to the ability of a species to colonize elevated areas where it is usually not observed: such limitations naturally arise through competition with fitter species across marsh topographic gradients. We qualitatively test our model against field data based on a suitable assemblage of focus species, and perform a sensitivity analysis aimed at determining how dynamic equilibria in vegetation distributions are affected by changes in model input parameters. Results indicate that the model is robust and can predict realistic vegetation distributions and species-richness patterns. More importantly, the model is also able to effectively reproduce the outcomes of classical ecological experiments, wherein a species is transplanted to an area outside its realized niche. A direct comparison shows that previous models not accounting for dispersal and interspecific competitions are unable to reproduce such dynamics. Our model can be easily integrated into virtually any existing morphodynamic model, thereby strengthening our ability to simulate the coupled biotic and abiotic evolution of salt marshes under changing climate forcings.

Seaward expansion of salt marshes maintains morphological self-similarity of tidal channel networks

“…For example, sites where crab burrowing activity is more intense typically display higher 𝛿 due to the coupling of vegetation disappearance and reduction in local accretion, both aiding in reducing flow resistances and enhancing bottom shear stresses (Crotty et al, 2020;Escapa et al, 2007;Wilson et al, 2022). Besides, environmental changes, which can be significantly accelerated by human activities, can alternate vegetation distributions and biotic activities, thus possibly further modifying site-specific TCN morphological properties (Crotty et al, 2020;Finotello et al, 2022). Rinaldo et al (1999aRinaldo et al ( , 1999b are shown for each study case based on the exceedance probability 𝑃(𝐿 > ℓ).…”

The Sensitivity of Tidal Channel Systems to Initial Bed Conditions, Vegetation, and Tidal Asymmetry

“…The inundation stress may lead to smaller biomass production in the poorly drained lower landward areas (Figures 5h and 5l) because of the lower oxygen level (Fivash et al., 2020; Mossman et al., 2020). Furthermore, the modeling approach neglects the dispersal and competitive dynamics between different vegetation species affecting the encroachment of the intertidal platforms (e.g., Finotello et al., 2022), as well as bioturbation by critters. Finally, in the present model, a constant mean sea level is assumed.…”

Hydrodynamic Feedbacks of Salt‐Marsh Loss in the Shallow Microtidal Back‐Barrier Lagoon of Venice (Italy)

“…Moreover, biogeomorphological feedbacks, which are key drivers of marsh spatiotemporal evolution, are likely to vary geographically as a consequence of distinct ecological community assemblages and different climatic forcings. This further complicates predicting the morphodynamic effects of salt‐marsh loss, as well as the timescales over which such effects would manifest (Bertness & Ewanchuk, 2002; Finotello, D’Alpaos et al., 2022; Pennings & He, 2021; Wilson et al., 2022).…”