Mangrove-Saltmarsh ecotone patterns as indicators for critical impacts of sea level rise and climate change on coastal wetlands – MASCOT

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Background: (Sub)tropical coastal wetlands often consist of mangroves and salt marshes. While mangroves are mostly located in the regularly flooded zone, salt marshes dominate the upper drier, often hypersaline zone. The transition between the two habitat types is called "mangrove-saltmarsh ecotone" and is an indicator of the different effects of abiotic factors on mangrove and salt marsh vegetation. At the same time, plants change their local abiotic and biotic environment. These bidirectional feedbacks result in characteristic vegetation patterns that are reflected, for example, in the height structure of the vegetation and the sharpness of their transition, from abrupt to diffuse. Since changes in abiotic conditions lead to cascading effects within ecotones and their vegetation patterns, they might be excellent indicators of climate-induced changes and their consequences for coastal stability and ecosystem services. Following research on mountainous and boreal tree lineage shifts, we therefore hypothesise that the shape of mangrove-saltmarsh ecotones is the key to predicting their response to climate-induced change.Aim: With this project we want to contribute to the general understanding of the mechanisms underlying ecotone patterns and their dynamics. We want to understand how the flooding regime in combination with freshwater input shapes the plant community, how plants engineer their habitat, how these interactions lead to the observed zonation of habitat types, how their transition zone is formed and what trends can be expected under rising sea level and under altered rainfall regimes. This will allow us to use changes in patterns of mangrove-salt-marsh ecotones as indicators of critical impacts of observed and predicted changes in the hydrological regime of (sub)tropical coasts.Methods: We will extend the mechanistic simulation model approach MANGA for mangrove ecosystems by several components. These include the description of saltmarsh plants, the unsaturated soil layer required for saltmarshes, and the physiological plasticity of mangroves. The new Mascot model will describe the interactions between saltmarsh plants, mangrove shrubs, mangrove trees and soil water and thus allow the simulation of the entire mangrove-saltmarsh ecotone. Together with cooperation partners from South and Central America, Asia and Australia, we will systematically investigate the emergence, persistence and temporal shift of different ecotone patterns under changing hydrological conditions. Based on this, we will develop indicators by which the intensity and dynamics of environmental changes through spatio-temporal shifts in ecotone patterns can be detected at an early stage.